# A Physical-Chemical Study of the Interference of Ceftriaxone Antibiotic with Copper Chloride Salt

Authors: Elsayed M. AbouElleef; Mowafak M. Mahrouka; Sherine E. Salem
Journal: Bioinorganic Chemistry and Applications
 (2021)

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## Abstract

The nano-CuCl2.2H2O salt was prepared by the ball milling method. The association parameters for bulk and nano-CuCl2 salts in H2O are estimated at different temperatures using the conductivity method by applying the Fuoss–Shedlovsky equation and it was higher for nano-CuCl2 than bulk CuCl2 salt. The interaction between the cation (Cu2+) and ligand (ceftriaxone) in H2O was determined also by the conductometric method. Two stoichiometric complexes 1/2 and 1/1 (M/L) are estimated and follow the order Kf (1/1) > Kf (1 : 2) and ∆Gf (1/1) > ∆Gf (1/2) for (M : L) (in negative values) indicate the favorable of formation of (1/1) complex compared to the (1 : 2) complex. The Gibbs free energies change was increased in negative signs with increasing the temperature. The antimicrobial activities of CFT, bulk Cu-CFT complex, and nano-Cu-CFT complex were studied on LB agar by the disc diffusion technique against clinical isolates of gram-negative bacteria (Klebsiella pneumonia and Pseudomonas aeruginosa) and Fungi (Candida albicans). It was observed that (CFT) has a higher zone of inhibition and antibacterial activity than that of bulk and nano-Cu-CFT complexes in Klebsiella pneumonia and Pseudomonas aeruginosa (gram-negative bacteria). The nano-Cu-CFT complex showed a higher clear zone of inhibition and antifungal activity against candida than bulk Cu-CFT complex while the absence of the inhibition zone in CFT, so nano-Cu-CFT complex, can be used as an antifungal drug.


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## Body

## 1. Introduction

Nanoparticles (NPs) are a wide class of materials that have a state between bulk and atomic or molecular structures in different shapes of 0D, 1D, 2D, or 3D and have a great scientific interest [1–5]. Bulk materials have constant physical properties, with size larger than one micrometer or micron. Nanoparticles can be used for various applications such as drug delivery purposes [6], diagnostics of cancer therapy, gene delivery purposes, chemical and biological sensing [7], gas sensing [8–10], CO2 capturing [11, 12], and other related applications [13–17]. Nanoparticles are often used to photocatalytically break down oil into biodegradable compounds, break down volatile organic pollutants in the air, and clean up carbon tetrachloride pollution in spring water [18, 19]. Nanoparticles (NPs) such as gold, silver, platinum, and palladium showed colors with the variation of shape and size and characteristic properties that can be utilized in bioimaging applications [20]. Another application of nanoparticles is the synthesis of photocatalysis S-doped TiO2 nanoparticles and the study of their photocatalytic, antimicrobial, and antioxidant activities under sunlight illumination [21].Ceftriaxone [22–25] is an antibiotic that belongs to a category of medicine referred to as cephalosporin antibiotics, and it treats a variety of bacterial infections by stopping the growth of bacteria variety of bacterial infections (e.g., middle ear, lower tract, skin, and urinary tract), meningitis, gonorrhea, pelvic disease, and joint infections.Thermodynamics parameters are an important tool for learning about the spontaneity of a given process at a particular temperature [26, 27]. Determination of the formation constant is fundamental for understanding the behavior of the metal cations in the presence of some chelating agent in a solution and is best explained using thermodynamics. A conductivity technique can be used to estimate the interaction between the metal cations and the chelating agent by estimating the thermodynamics parameters of metal-ligand complex formation [28–32].It is therefore necessary to study the effect of antibiotic ceftriaxone on the properties of copper chloride salt by determining thermodynamics parameters of interaction between them using conductometric techniques to find the extent of benefit of the antibiotic ceftriaxone.


## 2. Experimental

### 2.1. Materials and Solutions

The purities and sources of the materials used are presented in Table1. The structure of ceftriaxone is shown in Figure 1.Table 1
Sources and purity of the materials.
Chemical nameCAS reg. no.Mass fractionPurification methodSuppliersCeftriaxone104376-79-60.990Used as receivedSigma-AldrichEthanol64-17-50.995Used as receivedSigma-AldrichCuCl2·2H2O13464-92-10.980Used as receivedSigma-AldrichH2O7732-18-5k < 0.5 μS·cm−1DistillationOur labMass fraction purity was provided by the suppliers.Figure 1
Molecular structure of ceftriaxone antibiotic (CFT). Formula: C18H16N8Na2O7S3.3.5H2O. Molar mass: 598.54 g/mol.


### 2.2. Apparatus

The conductance measurements are carried out with a conductometer A JENCO, Vision plus-EC3175 conductance instrument, and connecting with Kottermann ultra-thermostat-4130 (a deviation ±0.01 K) with a cell constant equal unity. The conductivity bridge was calibrated using standard potassium chloride solutions [33].The BrukerD8 Advance X-ray diffractometer is a powder XRD instrument used to record X-ray diffraction (XRD) patterns of bulk and nanosamples. The Bruker diffractometer with CuKα anode radiation (λ = 0.1542 nm) as a source is operating at 40 kV and 30 mA. The scanning range of over an angular range was between 4° and 80°A at a temperature of 25°C, and the scan mode was applied with a step width of 0.02° per step and step time of 0.4 s.IR instrument of the type Thermo Scientific Nicolet iS10 FTIR spectrometer is operating in the spectral range of 7800 to 400 cm−1 with a resolution of 4 cm−1, midinfrared KBr beamsplitter 4000 to 400 cm−1.Solid samples can be prepared by grinding about 5 mg of sample mixed with 100 mg of spectroscopic grade KBr. This powder mixture is then compressed into a pellet using a mechanical press between 4 and 8 ton.cm−2 for 2 minutes in the form of 10 mm in diameter disks to form a translucent (http://en.wikipedia.org/wiki/Infrared_spectroscopy%20-%20cite_note-Har-2).


### 2.3. Procedure

#### 2.3.1. Preparation of Nanocopper Chloride

The nano-CuCl2.2H2O salt was prepared by the ball milling method by shaking CuCl2.2H2O salt in ball milling apparatus of the type Retsch MM 2000 swing mill at 20225 Hz at room temperature for one hour. The mill has 10 cm3 stainless steel double-walled tubes. Two balls made from stainless steel of 12 mm diameter were used.


#### 2.3.2. Preparation of Bulk Cu-CFT Complex and Nano-Cu-CFT Complex

Bulk Cu-CFT complex and nano-Cu-CFT were prepared according to a traditional method by refluxing 1 mmol of CFT under investigation with 1 mmol of bulk CuCl2.2H2O or nano-CuCl2.2H2O salts in an ethanolic solution for 2-3 h close to the boiling point of the solvent. The precipitate was filtered off, washed several times with absolute ethanol, and finally dried in vacuum desiccators over anhydrous calcium chloride.


#### 2.3.3. Conductance Measurements

To calculate the association parameters of CuCl2.2H2O solutions, a solution of metal cation (10−3 M, 20 mL) was placed in a double jacket glass conductance cell, and the conductance was measured after each addition of the solvent and stirring at a specific temperature.To calculate the formation constants between CuCl2.2H2O and a ligand (ceftriaxone) in the solvents, a solution of CuCl2.2H2O (10−3 M, 20 mL) was placed in a conductance cell, and the conductance was measured. The ligand (10−3 M) (ceftriaxone) was added step by step to the conductance cell using a micropipette and the conductance was measured after each addition.


#### 2.3.4. Biological Activity

The antimicrobial activities of CFT, bulk Cu-CFT complex, and nano-Cu-CFT complex were studied on LB agar by the disc diffusion technique against clinical isolates of gram-negative bacteria (Klebsiella pneumonia and Pseudomonas aeruginosa) and fungi (Candida albicans).Sterile filter paper discs (6 mm) were individually immersed in dimethyl sulfoxide (DMSO) extract of CFT, bulk Cu-CFT complex, and nano-Cu-CFT complex, and DMSO was used as control. All the discs were dried, placed on the surface of the test bacterial and fungal, and incubated for 18 to 24 h at 37°C. The standard antibiotic used is ceftazidime (30 mg) and finally, the zones of inhibition were examined.


## 2.1. Materials and Solutions

The purities and sources of the materials used are presented in Table1. The structure of ceftriaxone is shown in Figure 1.Table 1
Sources and purity of the materials.
Chemical nameCAS reg. no.Mass fractionPurification methodSuppliersCeftriaxone104376-79-60.990Used as receivedSigma-AldrichEthanol64-17-50.995Used as receivedSigma-AldrichCuCl2·2H2O13464-92-10.980Used as receivedSigma-AldrichH2O7732-18-5k < 0.5 μS·cm−1DistillationOur labMass fraction purity was provided by the suppliers.Figure 1
Molecular structure of ceftriaxone antibiotic (CFT). Formula: C18H16N8Na2O7S3.3.5H2O. Molar mass: 598.54 g/mol.


## 2.2. Apparatus

The conductance measurements are carried out with a conductometer A JENCO, Vision plus-EC3175 conductance instrument, and connecting with Kottermann ultra-thermostat-4130 (a deviation ±0.01 K) with a cell constant equal unity. The conductivity bridge was calibrated using standard potassium chloride solutions [33].The BrukerD8 Advance X-ray diffractometer is a powder XRD instrument used to record X-ray diffraction (XRD) patterns of bulk and nanosamples. The Bruker diffractometer with CuKα anode radiation (λ = 0.1542 nm) as a source is operating at 40 kV and 30 mA. The scanning range of over an angular range was between 4° and 80°A at a temperature of 25°C, and the scan mode was applied with a step width of 0.02° per step and step time of 0.4 s.IR instrument of the type Thermo Scientific Nicolet iS10 FTIR spectrometer is operating in the spectral range of 7800 to 400 cm−1 with a resolution of 4 cm−1, midinfrared KBr beamsplitter 4000 to 400 cm−1.Solid samples can be prepared by grinding about 5 mg of sample mixed with 100 mg of spectroscopic grade KBr. This powder mixture is then compressed into a pellet using a mechanical press between 4 and 8 ton.cm−2 for 2 minutes in the form of 10 mm in diameter disks to form a translucent (http://en.wikipedia.org/wiki/Infrared_spectroscopy%20-%20cite_note-Har-2).


## 2.3. Procedure

### 2.3.1. Preparation of Nanocopper Chloride

The nano-CuCl2.2H2O salt was prepared by the ball milling method by shaking CuCl2.2H2O salt in ball milling apparatus of the type Retsch MM 2000 swing mill at 20225 Hz at room temperature for one hour. The mill has 10 cm3 stainless steel double-walled tubes. Two balls made from stainless steel of 12 mm diameter were used.


### 2.3.2. Preparation of Bulk Cu-CFT Complex and Nano-Cu-CFT Complex

Bulk Cu-CFT complex and nano-Cu-CFT were prepared according to a traditional method by refluxing 1 mmol of CFT under investigation with 1 mmol of bulk CuCl2.2H2O or nano-CuCl2.2H2O salts in an ethanolic solution for 2-3 h close to the boiling point of the solvent. The precipitate was filtered off, washed several times with absolute ethanol, and finally dried in vacuum desiccators over anhydrous calcium chloride.


### 2.3.3. Conductance Measurements

To calculate the association parameters of CuCl2.2H2O solutions, a solution of metal cation (10−3 M, 20 mL) was placed in a double jacket glass conductance cell, and the conductance was measured after each addition of the solvent and stirring at a specific temperature.To calculate the formation constants between CuCl2.2H2O and a ligand (ceftriaxone) in the solvents, a solution of CuCl2.2H2O (10−3 M, 20 mL) was placed in a conductance cell, and the conductance was measured. The ligand (10−3 M) (ceftriaxone) was added step by step to the conductance cell using a micropipette and the conductance was measured after each addition.


### 2.3.4. Biological Activity

The antimicrobial activities of CFT, bulk Cu-CFT complex, and nano-Cu-CFT complex were studied on LB agar by the disc diffusion technique against clinical isolates of gram-negative bacteria (Klebsiella pneumonia and Pseudomonas aeruginosa) and fungi (Candida albicans).Sterile filter paper discs (6 mm) were individually immersed in dimethyl sulfoxide (DMSO) extract of CFT, bulk Cu-CFT complex, and nano-Cu-CFT complex, and DMSO was used as control. All the discs were dried, placed on the surface of the test bacterial and fungal, and incubated for 18 to 24 h at 37°C. The standard antibiotic used is ceftazidime (30 mg) and finally, the zones of inhibition were examined.


## 2.3.1. Preparation of Nanocopper Chloride

The nano-CuCl2.2H2O salt was prepared by the ball milling method by shaking CuCl2.2H2O salt in ball milling apparatus of the type Retsch MM 2000 swing mill at 20225 Hz at room temperature for one hour. The mill has 10 cm3 stainless steel double-walled tubes. Two balls made from stainless steel of 12 mm diameter were used.


## 2.3.2. Preparation of Bulk Cu-CFT Complex and Nano-Cu-CFT Complex

Bulk Cu-CFT complex and nano-Cu-CFT were prepared according to a traditional method by refluxing 1 mmol of CFT under investigation with 1 mmol of bulk CuCl2.2H2O or nano-CuCl2.2H2O salts in an ethanolic solution for 2-3 h close to the boiling point of the solvent. The precipitate was filtered off, washed several times with absolute ethanol, and finally dried in vacuum desiccators over anhydrous calcium chloride.


## 2.3.3. Conductance Measurements

To calculate the association parameters of CuCl2.2H2O solutions, a solution of metal cation (10−3 M, 20 mL) was placed in a double jacket glass conductance cell, and the conductance was measured after each addition of the solvent and stirring at a specific temperature.To calculate the formation constants between CuCl2.2H2O and a ligand (ceftriaxone) in the solvents, a solution of CuCl2.2H2O (10−3 M, 20 mL) was placed in a conductance cell, and the conductance was measured. The ligand (10−3 M) (ceftriaxone) was added step by step to the conductance cell using a micropipette and the conductance was measured after each addition.


## 2.3.4. Biological Activity

The antimicrobial activities of CFT, bulk Cu-CFT complex, and nano-Cu-CFT complex were studied on LB agar by the disc diffusion technique against clinical isolates of gram-negative bacteria (Klebsiella pneumonia and Pseudomonas aeruginosa) and fungi (Candida albicans).Sterile filter paper discs (6 mm) were individually immersed in dimethyl sulfoxide (DMSO) extract of CFT, bulk Cu-CFT complex, and nano-Cu-CFT complex, and DMSO was used as control. All the discs were dried, placed on the surface of the test bacterial and fungal, and incubated for 18 to 24 h at 37°C. The standard antibiotic used is ceftazidime (30 mg) and finally, the zones of inhibition were examined.


## 3. Results and Discussion

### 3.1. X-Ray Diffraction (XRD)

The X-ray diffraction (XRD) pattern for the bulk and nano-CuCl2.2H2O salt is shown in Figure 2. The positions of the main peaks and their relative intensities as measured by powder diffraction are listed in Table 2.Figure 2
X-Ray diffraction of bulk and nano-CuCl2·2H2O salt.Table 2
Intensity (%) and crystal size (nm) of bulk and nano-CuCl2.2H2O salt.
Bulk CuCl200B72H2O saltNano-CuCl2·2H2O saltAngle (2-theta °)d value (angstrom)Intensity (count)Intensity %Crystal size (nm)Angle (2-theta °)d value (angstrom)Intensity (count)Intensity %Crystal size (nm)16.3755.40883241100158.216.1715.4765428.576.816.17122.0974.019578033.258.421.9374.0484120.45521.93726.763.3287629.912.4101.528.8253.0947624.565.928.82528.9383.0829521.28.858.433.9542.6381437.110033.95432.9162.7189140.817111.334.7272.5811413.335.934.72735.4912.5273319.88.252.135.3492.5371513.335.835.34938.192.3546618.97.898.140.7932.2102517.246.340.79344.9332.0157230.712.767.443.0182.1009411.230.143.01849.2541.8485265.227.1132.344.7262.0245713.335.944.72650.1991.8159313.55.6134.645.2342.0030313.636.545.23454.5581.6806915.86.6356.0881.638410.829.156.08857.5721.5996714.66.1107.957.3431.605516.143.457.34363.9151.4553515.46.4140.763.2081.469919.7226.263.20868.7881.3636441.617.3The mean size of nanocrystals was determined from the diffraction peaks corresponding to the most intensive reflections according to the Joint Committee on Powder Diffraction Standards database. Scherrer’s equation was used to determine the average crystallite size for nanoparticles from the XRD diffraction pattern measured [34, 35]:(1)d=Kλβcosθ,where K is Scherrer’s constant (about 0.9), λ is the wavelength (λ = 0.154 nm), β is the line broadening at half the maximum intensity in radians, θ is the Bragg angle, and d is the averaged dimension of crystallites in nanometers. Groth assigned CuCl2·2H2O to the bipyramidal class of the orthorhombic crystalline system with the axial ratios a : b :  c = 0.9179 : 1: 0.4627. Layer line measurements give the identity distances a0 = 7.38 Å, b0 = 8.04 Å, c0 = 3.72 Å. These lead to the ratios a : b : c = 0.918 : 1: 0.462, in good agreement with the crystallographic data [36]. The mean crystal size (nm) of bulk and nano-CuCl2·2H2O salts obtained by XRD are mentioned in Table 2 [37].A little difference was observed between bulk and nanosalts in peaks other than their intensities. Also, it was found that the salt remains in the crystalline form by converting it to nanoparticles. The main difference between the bulk and nanosalt was in the crystal size, as shown in Table3.Table 3
Mean crystal size (nm) of bulk and nano-CuCl2·2H2O salts.
SampleCrystal sizedXRD (nm)Bulk CuCl2.2H2O94.146Nano-CuCl2.2H2O43.98


### 3.2. Infrared Analysis (IR)

Infrared spectra (IR) were used to identify the structure of ceftriaxone (CFT), as shown in Figure3, and its complexes with bulk and nano-CuCl2.2H2O salts as their functional groups give rise to characteristic bands in terms of both intensity and position (frequency), as shown in Figures 4 and 5.Figure 3
IR spectra of ceftriaxone (CFT).Figure 4
IR spectra of bulk Cu-CFT complex.Figure 5
IR spectra of nano-Cu-CFT complex.It was observed from the IR spectra of ceftriaxone (CFT) ligand that amidic N-H stretching vibrations mean strong intensity bands occurring at 3440 and 3261 cm−1 are due to N-H asymmetric and symmetric stretching, respectively [38]. Amidic C=O stretching vibrations mean a strong intensity band identified at 1649 cm−1 is due to C=O stretching vibrations [38]. Amidic N-H deformation and C-N stretching mean the strong bands observed at 1608, 1537, and 1500 cm−1 are due to amide N-H deformation vibrations [38, 39]. C-H stretching vibrations mean the weak bands occurring at 2891 cm−1 are assigned to CH3 symmetric stretching. The bands appearing at 2934 cm−1 in the IR spectra are due to CH3 asymmetric stretching vibrations [40]. C-H deformation vibrations mean the weak bands observed at 822, 804, and 730 cm−1 are allotted as C-H out-of-plane deformation vibrations and medium-to-weak intensity bands present at 1104 and 1033 cm−1 are allotted as C-H in plane deformation vibrations. A strong band occurring at 1399 cm−1 is due to the -CH2- deformation vibration. Weak bands present at 1243 and 760 cm−1 are due to CH2 wagging and CH2 rocking vibrations, respectively [40]. Lactam C=O stretching vibrations mean a strong band observed at 1741 cm−1 in the IR spectrum of ceftriaxone is allotted to be due to C=O stretching vibration [41]. C-O-C stretching vibrations mean strong bands present at 1033 and 1243 cm−1 are assigned as C-O-C symmetric and asymmetric stretching vibrations, respectively [41]. C-S stretching vibrations mean weak bands observed at 646 and 616 cm−1 are due to C-S stretching vibrations [42]. C-N stretching vibrations mean the medium band present at 1285 cm−1, weak band at 1243 cm−1, and medium band present at 1185 cm−1 are due to C-N stretching vibrations. C=C and C=N stretching vibrations mean very strong intensity bands present at 1608, 1537, and 1500 cm−1 are assigned to C=C and C=N stretching vibrations [43]. O-H stretching vibrations mean strong intensity bands identified at 3440 and 3261 cm−1 are allotted as O-H stretching vibrations [44]. C-C and C-C-C bending vibrations mean a very weak band occurring at 507 cm−1 in is due to C-C out-of-plane bending vibrations. The weak bands occurring at 646 and 606 cm−1 are due to C-C-C in plane and out of plane deformation vibrations, respectively [45].In the IR spectra of bulk Cu-CFT complex, as shown in Figure4, after ceftriaxone coordination to copper ion, the frequencies of the (C=O) lactam shifted from 1741 cm−1 to higher wavenumber 1775 cm−1, one amidic (C=O) shifted from 1649 to lower wavenumber 1624 cm−1, and also another amidic (C=O) triazine shifted from 1608 to lower wavenumber 1553 cm−1. There are three functional groups participating in the formation of a complex. The increase in the vibrational frequencies of carbonyl groups can be explained by oxygen of lactam and triazine coordinating to Cu(II) indicates the formation of a chelate complex [46, 47]. These intramolecular interactions between oxygen and copper ion result in a more rigid molecular structure around the oxygen and shift of carbonyl (C=O) vibrational frequencies to higher wavenumbers. The frequency of the symmetric stretching mode νs(COO−) shifts from 1391 to 1398 cm−1. These shifts indicate that the carboxylate group (COO), the lactam carbonyl group (C=O), and the oxo group of the triazine ring are involved in the formation of [Cu(CFT)]·3H2O. This analysis is in agreement with previous studies where ceftriaxone is described as a polydentate chelating ligand [46, 47]. The broadband in the [Cu(CFT)]·3H2O spectrum at 1624 cm−1 has a high intensity and a low resolution due to the overlap of several vibrational modes, including ν(C=O)-amide, ν(C=O)-triazine, νas(COO–), ν(C=C), and ν(C=N). A new band appearing at the frequency 468 cm−1 in the complex that is absent in the free ligand is due to ν (Cu-N) stretching vibration also giving strong evidence for the coordination of tertiary nitrogen atom with copper ion [47].Also, the IR spectra of nano-Cu-CFT complex asym.(NH2) shifted from 3440 to lower wavenumber 3427 cm−1, carboxylic (-OH) group appeared at wavenumber 2924 cm−1, carboxylic (C=O) appeared at wavenumber 1742 cm−1, one amidic (C=O) shifted from 1649 to lower wavenumber 1638 cm−1 and also another amidic (C=O) shifted from 1608 to lower wavenumber 1553 cm−1, as in Figure 5. This indicates the formation of a complex between CuCl2.2H2O salt and CFT antibiotic.


### 3.3. Conductometric Measurements

#### 3.3.1. Calculation of Association Parameters for Bulk and Nano-CuCl2·2H2O Salts in Distillate H2O

The specific conductance values (Ks) of different concentrations of bulk and nano-CuCl2·2H2O salt in distillate H2O were measured experimentally in absence of (CFT) at different temperatures (288.15, 293.15, 298.15, and 303.15 K). The molar conductance (Λm) values were calculated [48–50] using (2)Λm=Ks−Ksolv×1000C,where Ks and Ksolv are the specific conductance of the solution and the solvent (distillate H2O), respectively, and C is the concentration of the bulk and nano-CuCl2·2H2O solutions.The experimental data for conductance measurements were analyzed using Fuoss–Shedlovsky extrapolation techniques [51–53] which follow equations (3)–(12):(3)1ΛSZ=1Λo+KAΛo2CΛγ±2SZ.The results obey the Fuoss–Shedlovsky equation and can be applied to obtain the value of limiting molar conductivity (Λo) and association constant (KA) by plotting a graph between 1/ΛS(z) and CΛSzγ±2, which is presented in Figure 6, giving straight line with intercept (1/Λo) and slope (KA/Λo2):(4)SZ=1+Z+Z22+Z32+…,(5)Z=SΛC1/2Λ03/2,(6)S=aΛ0+b,(7)a=8.2×105εT3/2,b=82.4ηεT1/2,(8)α=ΛSZΛ0,(9)logγ±=−AαC1/21+BroαC1/2,(10)A=1.824×106εT−3/2,B=50.29×108εT−1/2,(11)KA=CMXn⋅γMXnCMn+⋅γMn+⋅CX−n⋅γX−n,where (S) is the Onsager slope; (ε) is the dielectric constant of the solvent, ; (ηo) is the viscosity of the solvent; (T) is the temperature; (α) is the degree of dissociation; (γ±) is the mean activity coefficients; (z−, z+) are the charges of ions in solutions; (A, B) are the Debye–Hückel constant; (ro) is the solvated radius; and (KA) is the association constant.Figure 6
Variation of the molar conductance, l/ΛS(z) with CΛγ±2Sz for (a) bulk CuCl2·2H2O and (b) nano-CuCl2·2H2O in distillate H2O at (288.15, 293.15, 298.15, and 303.15) K.
(a)(b)The dissociation constant (KD) is calculated by the following equation:(12)KD=1KA.The Walden product (Λoηo) values were calculated from the values of limiting molar conductance (Λo) [54]:(13)Walden product=Λoηo.The triple ion association constantK3 can be calculated from (14)ΛC1/21−Λ/Λo1/2=ΛoKA1/2+λ3oCK3KA1/21−ΛΛo.The values of free energy of association (∆GA) of bulk and nano-CuCl2.2H2O salt in H2O at different temperatures of 288.15, 293.15, 298.15, and 303.15 K were calculated from the association constant KA values [55] by using (15)ΔGA=−2.303RTlogKA.The activation energy of the transfer process can be estimated depending on the relation between conductance of ion, ion mobility, and temperature degree, as in the Arrhenius equation:(16)Λo=Ae−Ea/RT,where A is the frequency factor and Ea Arrhenius activation energy of the transport process.(17)logΛo=logΑ−Ea2.303RT.By plotting log Λo versus l/T, as shown in Figure 7, the activation energy of transfer processes values can be calculated from the slope [56].Figure 7
Variation of log Λo with l/T (K−1) of for bulk and nano-CuCl2·2H2O in H2O.The calculated values of Λo,S(Z), α, γ±, KA, KD, and K3 for the solutions of bulk and nano-CuCl2·2H2O salt with distillate H2O at different temperatures of 288.15, 293.15, 298.15, and 303.15 K are calculated and reported in Tables 4 and 5.Table 4
Different association parameters (limiting molar conductance (Λo), Fuoss–Shedlovsky parameter S(z), degree of dissociation (α), activity coefficient (γ±), association constant (KA), dissociation constant (KD), triple ion association constant (K3)) for bulk CuCl2·2H2O in distillate H2O at 288.15, 293.15, 298.15, and 303.15 K in absence of CFT.
T (K)ΛoS·cm2·mol−1Λoη S·cm2·MPa·s·mol−1αγ±KA dm3·mol−110−3KD mol·dm−3105K3 (dm3·mol−1)2288.15270.00307.430.98060.902299.740.01001.322293.15281.69282.140.96680.901393.390.01071.273298.15284.90254.160.97550.900582.790.01201.190303.15292.39233.090.99120.899578.320.01271.154Table 5
Different association parameters (limiting molar conductance (Λ0), Fuoss–Shedlovsky parameter S(z), degree of dissociation (α), activity coefficient (Ɣ±), association constant (KA), dissociation constant (KD), triple ion association constant (K3)) for nano-CuCl2·2H2O in distillate H2O at 288.15, 293.15, 298.15, and 303.15 K in the absence of CFT.
T (K)Λo S·cm2·mol−1Λoη S·cm2·MPa ·s·mol−1αγ±KA dm3·mol−110−3KD mol dm−3105K3 (dm3·mol−1)2288.15266.21302.580.97540.902260.600.01650.9949293.15271.73282.140.90130.901356.350.01770.9546298.15277.00247.110.98730.900546.160.02160.8499303.15282.48225.190.98740.899534.470.02900.0714Table4 shows that the limiting molar conductivity (Λo) increases with increasing temperature due to the increase in mobility of ions and increasing kinetic energy which increases the separation among the oppositely charged ions while the Walden product (Λoη) decreases with increasing the temperature due to the decrease in viscosity; also, the association constant (KA) decreases with increasing the temperature due to the decrease in the association of ions and the increase in mobility of ions; and similarly, the triple ion association constant (K3) decreases with increasing the temperature due to the decrease for the same reason.Table5 shows the same trend, that is, the limiting molar conductivity (Λo) increases with increasing the temperature while the Walden product (Λoη) decreases with increasing the temperature; also association constant (KA) decreases with increasing the temperature; and similarly, the triple ion association constant (K3) decreases with increasing the temperature.The enthalpy (ΔHA) for bulk and nano-CuCl2·2H2O salts with distillate H2O at different temperatures were calculated by using Van ’t Hoff equation:(18)logK=−ΔH2.303R1T+constant.By drawing the relation between logKA and 1/T, ΔHA can be calculated from the slope of each line which equals (-ΔHA/2.303 R), as shown in Figure 8. The entropy (ΔSA) for bulk and nano-CuCl2·2H2O salts were calculated by using (19)ΔGA=ΔHA−TΔSA,where (S) is the entropy of the system. The calculated values of (ΔHA) and (ΔSA) for bulk and nano-CuCl2·2H2O salts are presented in Table 6. It is obvious that the limiting molar conductance (Λo) increased as the temperature increased while the dissociation degree decreased as the temperature increased indicating a higher solvation process. The values of the association constant (KA) and the triple ion association constant (K3) were decreased by increasing the temperature. Gibbs free energies change of association (∆GA) was decreased with negative signs by increasing the temperature indicating that association is favored with lowering of dielectric constant of solvent mixture. The decrease in the values of activity coefficient, limiting molar conductance, association constant, Gibbs free energy change of association, and Walden product for nano-CuCl2·2H2O in comparison to bulk CuCl2·2H2O indicates that the association of nano-CuCl2·2H2O is greater than bulk CuCl2·2H2O salt, due to the high surface to volume ratio of nanoparticles which leads to a greater ability for ion-pair formation.Figure 8
Variation of logKa with l/T (K−1) of for bulk and nano-CuCl2.2H2O in distillate H2O at 288.15, 293.15, 298.15, and 303.15 K.Table 6
Gibbs free energy of association (ΔGA), enthalpy change (ΔHA), and entropy change (ΔSA) for bulk and nano-CuCl2·2H2O in distillate H2O at different temperatures.
T (K)ΔGA (kJ mol−1)ΔHA (kJ mol−1)EA (kJ mol−1)ΔSA (kJ mol−1K−1)BulkNanoBulkNanoBulkNanoBulkNano288.15−11.028−9.322−0.0496−0.0904293.15−11.059−9.828−12.928−22.9183.603.72−0.0487−0.0842298.15−10.949−9.501−0.0477−0.0824303.15−10.993−8.924−0.0468−0.0807


#### 3.3.2. Calculation of Formation Constants for Bulk and Nano-Cu-CFT Complexes in H2O at Different Temperatures

Different lines were obtained with breaks indicating the formation of (1 : 2) and (1 : 1) (M : L) stoichiometric complexes [57] on drawing the molar conductance (Λm) for bulk and nano-Cu-CFT complexes at different temperatures versus the molar ratio of metal to ligand [M]/[L] concentrations, as shown in Figure 9.Figure 9
The relation between Λm and the [M]/[L] molar ratio for (a) bulk Cu-CFT complex and (b) nano-Cu-CFT complex in distillate H2O at different temperatures.
(a)(b)The formation constants (Kf) for bulk and nano-Cu-CFT complexes were calculated for each type of complexes (1 : 2) and (1 : 1) (M : L) by using (20)M2++L↔ML2+,Kf=ML2+M2+L=ΛM−ΛobsΛobs−ΛMLL,(21)L=Lt–MtΛM−ΛobsΛM−ΛML,where Λm is the limiting molar conductance of the bulk and nano-CuCl2.2H2O alone, Λobs is the molar conductance of solution during titration, ΛML is the molar conductance of the complex, and [L] is the CFT concentration.The Gibbs free energies changes of formation (ΔGf) for each stoichiometric complex were calculated [4] by using (22)ΔGf=−2.303RTlogKf.The obtained values (Kf) for bulk and nano-Cu-CFT complexes and their calculated ΔGf values are presented in Tables 7 and 8.Table 7
Limiting molar conductance (Λo) and formation constant (Kf) for bulk Cu-CFT complex in distillate H2O at different temperatures.
T (K)[M] : [L]ΛoS cm2·mol−1ΛobsS cm2·mol−1logKf dm3·mol−1288.151 : 2912.11433.624.2111 : 1554.03440.054.424293.151 : 2958.50473.224.1861 : 1584.60331.164.375298.151 : 2966.40465.304.1791 : 1594.50322.254.342303.151 : 2985.30481.144.1741 : 1593.40347.494.275Table 8
Limiting molar conductance (Λo) and formation constant (Kf) for nano-Cu-CFT complex in distillate H2O at different temperatures.
T (K)[M] : [L]ΛoS cm2·mol−1ΛobsS cm2·mol−1LogKf dm3·mol−1288.151 : 2912.00439.564.1911 : 1555.00290.004.426293.151 : 2966.00473.224.1771 : 1593.00331.164.349298.151 : 2958.00485.104.1801 : 1584.00335.614.323303.151 : 2985.30481.144.1711 : 1593.00348.984.263By drawing the relation between logKf and 1/T, different lines were obtained indicating the formation of (1 : 2) and (1 : 1) (M : L) stoichiometric complexes, as shown in Figure 10.Figure 10
Variation of logKf with l/T for (a) bulk Cu-CFT complex and (b) nano-Cu-CFT complex in distillate H2O.
(a)(b)From the relation between logKf and 1/T, ΔHf can be calculated for each type of complexes, from the slope of each line which equals (−ΔHf/2.303 R). The entropy (ΔSf) for bulk and nano-Cu-CFT complexes was calculated for each type of complexes (1 : 2) and (1 : 1) (M : L) by using (23)ΔGf=ΔHf−TΔSf.The calculated values of (ΔHf) and (ΔSf) for bulk and nano-Cu-CFT complexes are presented in Tables 9 and 10.Table 9
Different formation parameters (Gibbs free energy of formation (ΔGf), enthalpy change (ΔHf), and entropy change (ΔSf)) for bulk Cu-CFT complex in distillate H2O at different temperatures.
T (K)Complex ratio (M : L)ΔGf (kJ mol−1)ΔHf (kJ mol−1)ΔSf (kJ mol−1K−1)288.15(1 : 2)−23.23−3.970.0252293.15−23.500.0257298.15−23.860.0265303.15−24.230.0273288.15(1 : 1)−24.41−15.960.0847293.15−24.560.0838298.15−24.790.0831303.15−24.820.0819Table 10
Different formation parameters (Gibbs free energy of formation (ΔGf), enthalpy change (ΔHf), and entropy change (ΔSf)) for nano-Cu-CFT complex in distillate H2O at different temperatures.
T (K)Complex ratio (M : L)ΔGf (kJ mol−1)ΔHf (kJ mol−1)ΔSf (kJ mol−1K−1)288.15(1 : 2)−23.12−1.820.0208293.15−23.440.0215298.15−23.860.0226303.15−24.210.0234288.15(1 : 1)−24.42−17.130.0847293.15−24.410.0833298.1524.680.0828303.15−24.750.0816It was observed that inflections at (1 : 2) M/L proportion and (1 : 1)M/L indicating the formation of both stoichiometric complexes in the solutions. These types of stoichiometric complexes are formed as a result of the interaction of bulk or nano-CuCl2 with CFT in distillate H2O at different temperatures. The complex formation parameters for (1 : 1) complexes are greater than those of (1 : 2) complexes indicating more favorable complexes. Also, the complex formation parameters (Kf, ΔGf) increased by increasing temperatures due to an increase in the kinetic energies. This trend was supported by entropies data which are greater for (1 : 1) M/L complexes than (1 : 2) M/L complexes.


## 3.1. X-Ray Diffraction (XRD)

The X-ray diffraction (XRD) pattern for the bulk and nano-CuCl2.2H2O salt is shown in Figure 2. The positions of the main peaks and their relative intensities as measured by powder diffraction are listed in Table 2.Figure 2
X-Ray diffraction of bulk and nano-CuCl2·2H2O salt.Table 2
Intensity (%) and crystal size (nm) of bulk and nano-CuCl2.2H2O salt.
Bulk CuCl200B72H2O saltNano-CuCl2·2H2O saltAngle (2-theta °)d value (angstrom)Intensity (count)Intensity %Crystal size (nm)Angle (2-theta °)d value (angstrom)Intensity (count)Intensity %Crystal size (nm)16.3755.40883241100158.216.1715.4765428.576.816.17122.0974.019578033.258.421.9374.0484120.45521.93726.763.3287629.912.4101.528.8253.0947624.565.928.82528.9383.0829521.28.858.433.9542.6381437.110033.95432.9162.7189140.817111.334.7272.5811413.335.934.72735.4912.5273319.88.252.135.3492.5371513.335.835.34938.192.3546618.97.898.140.7932.2102517.246.340.79344.9332.0157230.712.767.443.0182.1009411.230.143.01849.2541.8485265.227.1132.344.7262.0245713.335.944.72650.1991.8159313.55.6134.645.2342.0030313.636.545.23454.5581.6806915.86.6356.0881.638410.829.156.08857.5721.5996714.66.1107.957.3431.605516.143.457.34363.9151.4553515.46.4140.763.2081.469919.7226.263.20868.7881.3636441.617.3The mean size of nanocrystals was determined from the diffraction peaks corresponding to the most intensive reflections according to the Joint Committee on Powder Diffraction Standards database. Scherrer’s equation was used to determine the average crystallite size for nanoparticles from the XRD diffraction pattern measured [34, 35]:(1)d=Kλβcosθ,where K is Scherrer’s constant (about 0.9), λ is the wavelength (λ = 0.154 nm), β is the line broadening at half the maximum intensity in radians, θ is the Bragg angle, and d is the averaged dimension of crystallites in nanometers. Groth assigned CuCl2·2H2O to the bipyramidal class of the orthorhombic crystalline system with the axial ratios a : b :  c = 0.9179 : 1: 0.4627. Layer line measurements give the identity distances a0 = 7.38 Å, b0 = 8.04 Å, c0 = 3.72 Å. These lead to the ratios a : b : c = 0.918 : 1: 0.462, in good agreement with the crystallographic data [36]. The mean crystal size (nm) of bulk and nano-CuCl2·2H2O salts obtained by XRD are mentioned in Table 2 [37].A little difference was observed between bulk and nanosalts in peaks other than their intensities. Also, it was found that the salt remains in the crystalline form by converting it to nanoparticles. The main difference between the bulk and nanosalt was in the crystal size, as shown in Table3.Table 3
Mean crystal size (nm) of bulk and nano-CuCl2·2H2O salts.
SampleCrystal sizedXRD (nm)Bulk CuCl2.2H2O94.146Nano-CuCl2.2H2O43.98


## 3.2. Infrared Analysis (IR)

Infrared spectra (IR) were used to identify the structure of ceftriaxone (CFT), as shown in Figure3, and its complexes with bulk and nano-CuCl2.2H2O salts as their functional groups give rise to characteristic bands in terms of both intensity and position (frequency), as shown in Figures 4 and 5.Figure 3
IR spectra of ceftriaxone (CFT).Figure 4
IR spectra of bulk Cu-CFT complex.Figure 5
IR spectra of nano-Cu-CFT complex.It was observed from the IR spectra of ceftriaxone (CFT) ligand that amidic N-H stretching vibrations mean strong intensity bands occurring at 3440 and 3261 cm−1 are due to N-H asymmetric and symmetric stretching, respectively [38]. Amidic C=O stretching vibrations mean a strong intensity band identified at 1649 cm−1 is due to C=O stretching vibrations [38]. Amidic N-H deformation and C-N stretching mean the strong bands observed at 1608, 1537, and 1500 cm−1 are due to amide N-H deformation vibrations [38, 39]. C-H stretching vibrations mean the weak bands occurring at 2891 cm−1 are assigned to CH3 symmetric stretching. The bands appearing at 2934 cm−1 in the IR spectra are due to CH3 asymmetric stretching vibrations [40]. C-H deformation vibrations mean the weak bands observed at 822, 804, and 730 cm−1 are allotted as C-H out-of-plane deformation vibrations and medium-to-weak intensity bands present at 1104 and 1033 cm−1 are allotted as C-H in plane deformation vibrations. A strong band occurring at 1399 cm−1 is due to the -CH2- deformation vibration. Weak bands present at 1243 and 760 cm−1 are due to CH2 wagging and CH2 rocking vibrations, respectively [40]. Lactam C=O stretching vibrations mean a strong band observed at 1741 cm−1 in the IR spectrum of ceftriaxone is allotted to be due to C=O stretching vibration [41]. C-O-C stretching vibrations mean strong bands present at 1033 and 1243 cm−1 are assigned as C-O-C symmetric and asymmetric stretching vibrations, respectively [41]. C-S stretching vibrations mean weak bands observed at 646 and 616 cm−1 are due to C-S stretching vibrations [42]. C-N stretching vibrations mean the medium band present at 1285 cm−1, weak band at 1243 cm−1, and medium band present at 1185 cm−1 are due to C-N stretching vibrations. C=C and C=N stretching vibrations mean very strong intensity bands present at 1608, 1537, and 1500 cm−1 are assigned to C=C and C=N stretching vibrations [43]. O-H stretching vibrations mean strong intensity bands identified at 3440 and 3261 cm−1 are allotted as O-H stretching vibrations [44]. C-C and C-C-C bending vibrations mean a very weak band occurring at 507 cm−1 in is due to C-C out-of-plane bending vibrations. The weak bands occurring at 646 and 606 cm−1 are due to C-C-C in plane and out of plane deformation vibrations, respectively [45].In the IR spectra of bulk Cu-CFT complex, as shown in Figure4, after ceftriaxone coordination to copper ion, the frequencies of the (C=O) lactam shifted from 1741 cm−1 to higher wavenumber 1775 cm−1, one amidic (C=O) shifted from 1649 to lower wavenumber 1624 cm−1, and also another amidic (C=O) triazine shifted from 1608 to lower wavenumber 1553 cm−1. There are three functional groups participating in the formation of a complex. The increase in the vibrational frequencies of carbonyl groups can be explained by oxygen of lactam and triazine coordinating to Cu(II) indicates the formation of a chelate complex [46, 47]. These intramolecular interactions between oxygen and copper ion result in a more rigid molecular structure around the oxygen and shift of carbonyl (C=O) vibrational frequencies to higher wavenumbers. The frequency of the symmetric stretching mode νs(COO−) shifts from 1391 to 1398 cm−1. These shifts indicate that the carboxylate group (COO), the lactam carbonyl group (C=O), and the oxo group of the triazine ring are involved in the formation of [Cu(CFT)]·3H2O. This analysis is in agreement with previous studies where ceftriaxone is described as a polydentate chelating ligand [46, 47]. The broadband in the [Cu(CFT)]·3H2O spectrum at 1624 cm−1 has a high intensity and a low resolution due to the overlap of several vibrational modes, including ν(C=O)-amide, ν(C=O)-triazine, νas(COO–), ν(C=C), and ν(C=N). A new band appearing at the frequency 468 cm−1 in the complex that is absent in the free ligand is due to ν (Cu-N) stretching vibration also giving strong evidence for the coordination of tertiary nitrogen atom with copper ion [47].Also, the IR spectra of nano-Cu-CFT complex asym.(NH2) shifted from 3440 to lower wavenumber 3427 cm−1, carboxylic (-OH) group appeared at wavenumber 2924 cm−1, carboxylic (C=O) appeared at wavenumber 1742 cm−1, one amidic (C=O) shifted from 1649 to lower wavenumber 1638 cm−1 and also another amidic (C=O) shifted from 1608 to lower wavenumber 1553 cm−1, as in Figure 5. This indicates the formation of a complex between CuCl2.2H2O salt and CFT antibiotic.


## 3.3. Conductometric Measurements

### 3.3.1. Calculation of Association Parameters for Bulk and Nano-CuCl2·2H2O Salts in Distillate H2O

The specific conductance values (Ks) of different concentrations of bulk and nano-CuCl2·2H2O salt in distillate H2O were measured experimentally in absence of (CFT) at different temperatures (288.15, 293.15, 298.15, and 303.15 K). The molar conductance (Λm) values were calculated [48–50] using (2)Λm=Ks−Ksolv×1000C,where Ks and Ksolv are the specific conductance of the solution and the solvent (distillate H2O), respectively, and C is the concentration of the bulk and nano-CuCl2·2H2O solutions.The experimental data for conductance measurements were analyzed using Fuoss–Shedlovsky extrapolation techniques [51–53] which follow equations (3)–(12):(3)1ΛSZ=1Λo+KAΛo2CΛγ±2SZ.The results obey the Fuoss–Shedlovsky equation and can be applied to obtain the value of limiting molar conductivity (Λo) and association constant (KA) by plotting a graph between 1/ΛS(z) and CΛSzγ±2, which is presented in Figure 6, giving straight line with intercept (1/Λo) and slope (KA/Λo2):(4)SZ=1+Z+Z22+Z32+…,(5)Z=SΛC1/2Λ03/2,(6)S=aΛ0+b,(7)a=8.2×105εT3/2,b=82.4ηεT1/2,(8)α=ΛSZΛ0,(9)logγ±=−AαC1/21+BroαC1/2,(10)A=1.824×106εT−3/2,B=50.29×108εT−1/2,(11)KA=CMXn⋅γMXnCMn+⋅γMn+⋅CX−n⋅γX−n,where (S) is the Onsager slope; (ε) is the dielectric constant of the solvent, ; (ηo) is the viscosity of the solvent; (T) is the temperature; (α) is the degree of dissociation; (γ±) is the mean activity coefficients; (z−, z+) are the charges of ions in solutions; (A, B) are the Debye–Hückel constant; (ro) is the solvated radius; and (KA) is the association constant.Figure 6
Variation of the molar conductance, l/ΛS(z) with CΛγ±2Sz for (a) bulk CuCl2·2H2O and (b) nano-CuCl2·2H2O in distillate H2O at (288.15, 293.15, 298.15, and 303.15) K.
(a)(b)The dissociation constant (KD) is calculated by the following equation:(12)KD=1KA.The Walden product (Λoηo) values were calculated from the values of limiting molar conductance (Λo) [54]:(13)Walden product=Λoηo.The triple ion association constantK3 can be calculated from (14)ΛC1/21−Λ/Λo1/2=ΛoKA1/2+λ3oCK3KA1/21−ΛΛo.The values of free energy of association (∆GA) of bulk and nano-CuCl2.2H2O salt in H2O at different temperatures of 288.15, 293.15, 298.15, and 303.15 K were calculated from the association constant KA values [55] by using (15)ΔGA=−2.303RTlogKA.The activation energy of the transfer process can be estimated depending on the relation between conductance of ion, ion mobility, and temperature degree, as in the Arrhenius equation:(16)Λo=Ae−Ea/RT,where A is the frequency factor and Ea Arrhenius activation energy of the transport process.(17)logΛo=logΑ−Ea2.303RT.By plotting log Λo versus l/T, as shown in Figure 7, the activation energy of transfer processes values can be calculated from the slope [56].Figure 7
Variation of log Λo with l/T (K−1) of for bulk and nano-CuCl2·2H2O in H2O.The calculated values of Λo,S(Z), α, γ±, KA, KD, and K3 for the solutions of bulk and nano-CuCl2·2H2O salt with distillate H2O at different temperatures of 288.15, 293.15, 298.15, and 303.15 K are calculated and reported in Tables 4 and 5.Table 4
Different association parameters (limiting molar conductance (Λo), Fuoss–Shedlovsky parameter S(z), degree of dissociation (α), activity coefficient (γ±), association constant (KA), dissociation constant (KD), triple ion association constant (K3)) for bulk CuCl2·2H2O in distillate H2O at 288.15, 293.15, 298.15, and 303.15 K in absence of CFT.
T (K)ΛoS·cm2·mol−1Λoη S·cm2·MPa·s·mol−1αγ±KA dm3·mol−110−3KD mol·dm−3105K3 (dm3·mol−1)2288.15270.00307.430.98060.902299.740.01001.322293.15281.69282.140.96680.901393.390.01071.273298.15284.90254.160.97550.900582.790.01201.190303.15292.39233.090.99120.899578.320.01271.154Table 5
Different association parameters (limiting molar conductance (Λ0), Fuoss–Shedlovsky parameter S(z), degree of dissociation (α), activity coefficient (Ɣ±), association constant (KA), dissociation constant (KD), triple ion association constant (K3)) for nano-CuCl2·2H2O in distillate H2O at 288.15, 293.15, 298.15, and 303.15 K in the absence of CFT.
T (K)Λo S·cm2·mol−1Λoη S·cm2·MPa ·s·mol−1αγ±KA dm3·mol−110−3KD mol dm−3105K3 (dm3·mol−1)2288.15266.21302.580.97540.902260.600.01650.9949293.15271.73282.140.90130.901356.350.01770.9546298.15277.00247.110.98730.900546.160.02160.8499303.15282.48225.190.98740.899534.470.02900.0714Table4 shows that the limiting molar conductivity (Λo) increases with increasing temperature due to the increase in mobility of ions and increasing kinetic energy which increases the separation among the oppositely charged ions while the Walden product (Λoη) decreases with increasing the temperature due to the decrease in viscosity; also, the association constant (KA) decreases with increasing the temperature due to the decrease in the association of ions and the increase in mobility of ions; and similarly, the triple ion association constant (K3) decreases with increasing the temperature due to the decrease for the same reason.Table5 shows the same trend, that is, the limiting molar conductivity (Λo) increases with increasing the temperature while the Walden product (Λoη) decreases with increasing the temperature; also association constant (KA) decreases with increasing the temperature; and similarly, the triple ion association constant (K3) decreases with increasing the temperature.The enthalpy (ΔHA) for bulk and nano-CuCl2·2H2O salts with distillate H2O at different temperatures were calculated by using Van ’t Hoff equation:(18)logK=−ΔH2.303R1T+constant.By drawing the relation between logKA and 1/T, ΔHA can be calculated from the slope of each line which equals (-ΔHA/2.303 R), as shown in Figure 8. The entropy (ΔSA) for bulk and nano-CuCl2·2H2O salts were calculated by using (19)ΔGA=ΔHA−TΔSA,where (S) is the entropy of the system. The calculated values of (ΔHA) and (ΔSA) for bulk and nano-CuCl2·2H2O salts are presented in Table 6. It is obvious that the limiting molar conductance (Λo) increased as the temperature increased while the dissociation degree decreased as the temperature increased indicating a higher solvation process. The values of the association constant (KA) and the triple ion association constant (K3) were decreased by increasing the temperature. Gibbs free energies change of association (∆GA) was decreased with negative signs by increasing the temperature indicating that association is favored with lowering of dielectric constant of solvent mixture. The decrease in the values of activity coefficient, limiting molar conductance, association constant, Gibbs free energy change of association, and Walden product for nano-CuCl2·2H2O in comparison to bulk CuCl2·2H2O indicates that the association of nano-CuCl2·2H2O is greater than bulk CuCl2·2H2O salt, due to the high surface to volume ratio of nanoparticles which leads to a greater ability for ion-pair formation.Figure 8
Variation of logKa with l/T (K−1) of for bulk and nano-CuCl2.2H2O in distillate H2O at 288.15, 293.15, 298.15, and 303.15 K.Table 6
Gibbs free energy of association (ΔGA), enthalpy change (ΔHA), and entropy change (ΔSA) for bulk and nano-CuCl2·2H2O in distillate H2O at different temperatures.
T (K)ΔGA (kJ mol−1)ΔHA (kJ mol−1)EA (kJ mol−1)ΔSA (kJ mol−1K−1)BulkNanoBulkNanoBulkNanoBulkNano288.15−11.028−9.322−0.0496−0.0904293.15−11.059−9.828−12.928−22.9183.603.72−0.0487−0.0842298.15−10.949−9.501−0.0477−0.0824303.15−10.993−8.924−0.0468−0.0807


### 3.3.2. Calculation of Formation Constants for Bulk and Nano-Cu-CFT Complexes in H2O at Different Temperatures

Different lines were obtained with breaks indicating the formation of (1 : 2) and (1 : 1) (M : L) stoichiometric complexes [57] on drawing the molar conductance (Λm) for bulk and nano-Cu-CFT complexes at different temperatures versus the molar ratio of metal to ligand [M]/[L] concentrations, as shown in Figure 9.Figure 9
The relation between Λm and the [M]/[L] molar ratio for (a) bulk Cu-CFT complex and (b) nano-Cu-CFT complex in distillate H2O at different temperatures.
(a)(b)The formation constants (Kf) for bulk and nano-Cu-CFT complexes were calculated for each type of complexes (1 : 2) and (1 : 1) (M : L) by using (20)M2++L↔ML2+,Kf=ML2+M2+L=ΛM−ΛobsΛobs−ΛMLL,(21)L=Lt–MtΛM−ΛobsΛM−ΛML,where Λm is the limiting molar conductance of the bulk and nano-CuCl2.2H2O alone, Λobs is the molar conductance of solution during titration, ΛML is the molar conductance of the complex, and [L] is the CFT concentration.The Gibbs free energies changes of formation (ΔGf) for each stoichiometric complex were calculated [4] by using (22)ΔGf=−2.303RTlogKf.The obtained values (Kf) for bulk and nano-Cu-CFT complexes and their calculated ΔGf values are presented in Tables 7 and 8.Table 7
Limiting molar conductance (Λo) and formation constant (Kf) for bulk Cu-CFT complex in distillate H2O at different temperatures.
T (K)[M] : [L]ΛoS cm2·mol−1ΛobsS cm2·mol−1logKf dm3·mol−1288.151 : 2912.11433.624.2111 : 1554.03440.054.424293.151 : 2958.50473.224.1861 : 1584.60331.164.375298.151 : 2966.40465.304.1791 : 1594.50322.254.342303.151 : 2985.30481.144.1741 : 1593.40347.494.275Table 8
Limiting molar conductance (Λo) and formation constant (Kf) for nano-Cu-CFT complex in distillate H2O at different temperatures.
T (K)[M] : [L]ΛoS cm2·mol−1ΛobsS cm2·mol−1LogKf dm3·mol−1288.151 : 2912.00439.564.1911 : 1555.00290.004.426293.151 : 2966.00473.224.1771 : 1593.00331.164.349298.151 : 2958.00485.104.1801 : 1584.00335.614.323303.151 : 2985.30481.144.1711 : 1593.00348.984.263By drawing the relation between logKf and 1/T, different lines were obtained indicating the formation of (1 : 2) and (1 : 1) (M : L) stoichiometric complexes, as shown in Figure 10.Figure 10
Variation of logKf with l/T for (a) bulk Cu-CFT complex and (b) nano-Cu-CFT complex in distillate H2O.
(a)(b)From the relation between logKf and 1/T, ΔHf can be calculated for each type of complexes, from the slope of each line which equals (−ΔHf/2.303 R). The entropy (ΔSf) for bulk and nano-Cu-CFT complexes was calculated for each type of complexes (1 : 2) and (1 : 1) (M : L) by using (23)ΔGf=ΔHf−TΔSf.The calculated values of (ΔHf) and (ΔSf) for bulk and nano-Cu-CFT complexes are presented in Tables 9 and 10.Table 9
Different formation parameters (Gibbs free energy of formation (ΔGf), enthalpy change (ΔHf), and entropy change (ΔSf)) for bulk Cu-CFT complex in distillate H2O at different temperatures.
T (K)Complex ratio (M : L)ΔGf (kJ mol−1)ΔHf (kJ mol−1)ΔSf (kJ mol−1K−1)288.15(1 : 2)−23.23−3.970.0252293.15−23.500.0257298.15−23.860.0265303.15−24.230.0273288.15(1 : 1)−24.41−15.960.0847293.15−24.560.0838298.15−24.790.0831303.15−24.820.0819Table 10
Different formation parameters (Gibbs free energy of formation (ΔGf), enthalpy change (ΔHf), and entropy change (ΔSf)) for nano-Cu-CFT complex in distillate H2O at different temperatures.
T (K)Complex ratio (M : L)ΔGf (kJ mol−1)ΔHf (kJ mol−1)ΔSf (kJ mol−1K−1)288.15(1 : 2)−23.12−1.820.0208293.15−23.440.0215298.15−23.860.0226303.15−24.210.0234288.15(1 : 1)−24.42−17.130.0847293.15−24.410.0833298.1524.680.0828303.15−24.750.0816It was observed that inflections at (1 : 2) M/L proportion and (1 : 1)M/L indicating the formation of both stoichiometric complexes in the solutions. These types of stoichiometric complexes are formed as a result of the interaction of bulk or nano-CuCl2 with CFT in distillate H2O at different temperatures. The complex formation parameters for (1 : 1) complexes are greater than those of (1 : 2) complexes indicating more favorable complexes. Also, the complex formation parameters (Kf, ΔGf) increased by increasing temperatures due to an increase in the kinetic energies. This trend was supported by entropies data which are greater for (1 : 1) M/L complexes than (1 : 2) M/L complexes.


## 3.3.1. Calculation of Association Parameters for Bulk and Nano-CuCl2·2H2O Salts in Distillate H2O

The specific conductance values (Ks) of different concentrations of bulk and nano-CuCl2·2H2O salt in distillate H2O were measured experimentally in absence of (CFT) at different temperatures (288.15, 293.15, 298.15, and 303.15 K). The molar conductance (Λm) values were calculated [48–50] using (2)Λm=Ks−Ksolv×1000C,where Ks and Ksolv are the specific conductance of the solution and the solvent (distillate H2O), respectively, and C is the concentration of the bulk and nano-CuCl2·2H2O solutions.The experimental data for conductance measurements were analyzed using Fuoss–Shedlovsky extrapolation techniques [51–53] which follow equations (3)–(12):(3)1ΛSZ=1Λo+KAΛo2CΛγ±2SZ.The results obey the Fuoss–Shedlovsky equation and can be applied to obtain the value of limiting molar conductivity (Λo) and association constant (KA) by plotting a graph between 1/ΛS(z) and CΛSzγ±2, which is presented in Figure 6, giving straight line with intercept (1/Λo) and slope (KA/Λo2):(4)SZ=1+Z+Z22+Z32+…,(5)Z=SΛC1/2Λ03/2,(6)S=aΛ0+b,(7)a=8.2×105εT3/2,b=82.4ηεT1/2,(8)α=ΛSZΛ0,(9)logγ±=−AαC1/21+BroαC1/2,(10)A=1.824×106εT−3/2,B=50.29×108εT−1/2,(11)KA=CMXn⋅γMXnCMn+⋅γMn+⋅CX−n⋅γX−n,where (S) is the Onsager slope; (ε) is the dielectric constant of the solvent, ; (ηo) is the viscosity of the solvent; (T) is the temperature; (α) is the degree of dissociation; (γ±) is the mean activity coefficients; (z−, z+) are the charges of ions in solutions; (A, B) are the Debye–Hückel constant; (ro) is the solvated radius; and (KA) is the association constant.Figure 6
Variation of the molar conductance, l/ΛS(z) with CΛγ±2Sz for (a) bulk CuCl2·2H2O and (b) nano-CuCl2·2H2O in distillate H2O at (288.15, 293.15, 298.15, and 303.15) K.
(a)(b)The dissociation constant (KD) is calculated by the following equation:(12)KD=1KA.The Walden product (Λoηo) values were calculated from the values of limiting molar conductance (Λo) [54]:(13)Walden product=Λoηo.The triple ion association constantK3 can be calculated from (14)ΛC1/21−Λ/Λo1/2=ΛoKA1/2+λ3oCK3KA1/21−ΛΛo.The values of free energy of association (∆GA) of bulk and nano-CuCl2.2H2O salt in H2O at different temperatures of 288.15, 293.15, 298.15, and 303.15 K were calculated from the association constant KA values [55] by using (15)ΔGA=−2.303RTlogKA.The activation energy of the transfer process can be estimated depending on the relation between conductance of ion, ion mobility, and temperature degree, as in the Arrhenius equation:(16)Λo=Ae−Ea/RT,where A is the frequency factor and Ea Arrhenius activation energy of the transport process.(17)logΛo=logΑ−Ea2.303RT.By plotting log Λo versus l/T, as shown in Figure 7, the activation energy of transfer processes values can be calculated from the slope [56].Figure 7
Variation of log Λo with l/T (K−1) of for bulk and nano-CuCl2·2H2O in H2O.The calculated values of Λo,S(Z), α, γ±, KA, KD, and K3 for the solutions of bulk and nano-CuCl2·2H2O salt with distillate H2O at different temperatures of 288.15, 293.15, 298.15, and 303.15 K are calculated and reported in Tables 4 and 5.Table 4
Different association parameters (limiting molar conductance (Λo), Fuoss–Shedlovsky parameter S(z), degree of dissociation (α), activity coefficient (γ±), association constant (KA), dissociation constant (KD), triple ion association constant (K3)) for bulk CuCl2·2H2O in distillate H2O at 288.15, 293.15, 298.15, and 303.15 K in absence of CFT.
T (K)ΛoS·cm2·mol−1Λoη S·cm2·MPa·s·mol−1αγ±KA dm3·mol−110−3KD mol·dm−3105K3 (dm3·mol−1)2288.15270.00307.430.98060.902299.740.01001.322293.15281.69282.140.96680.901393.390.01071.273298.15284.90254.160.97550.900582.790.01201.190303.15292.39233.090.99120.899578.320.01271.154Table 5
Different association parameters (limiting molar conductance (Λ0), Fuoss–Shedlovsky parameter S(z), degree of dissociation (α), activity coefficient (Ɣ±), association constant (KA), dissociation constant (KD), triple ion association constant (K3)) for nano-CuCl2·2H2O in distillate H2O at 288.15, 293.15, 298.15, and 303.15 K in the absence of CFT.
T (K)Λo S·cm2·mol−1Λoη S·cm2·MPa ·s·mol−1αγ±KA dm3·mol−110−3KD mol dm−3105K3 (dm3·mol−1)2288.15266.21302.580.97540.902260.600.01650.9949293.15271.73282.140.90130.901356.350.01770.9546298.15277.00247.110.98730.900546.160.02160.8499303.15282.48225.190.98740.899534.470.02900.0714Table4 shows that the limiting molar conductivity (Λo) increases with increasing temperature due to the increase in mobility of ions and increasing kinetic energy which increases the separation among the oppositely charged ions while the Walden product (Λoη) decreases with increasing the temperature due to the decrease in viscosity; also, the association constant (KA) decreases with increasing the temperature due to the decrease in the association of ions and the increase in mobility of ions; and similarly, the triple ion association constant (K3) decreases with increasing the temperature due to the decrease for the same reason.Table5 shows the same trend, that is, the limiting molar conductivity (Λo) increases with increasing the temperature while the Walden product (Λoη) decreases with increasing the temperature; also association constant (KA) decreases with increasing the temperature; and similarly, the triple ion association constant (K3) decreases with increasing the temperature.The enthalpy (ΔHA) for bulk and nano-CuCl2·2H2O salts with distillate H2O at different temperatures were calculated by using Van ’t Hoff equation:(18)logK=−ΔH2.303R1T+constant.By drawing the relation between logKA and 1/T, ΔHA can be calculated from the slope of each line which equals (-ΔHA/2.303 R), as shown in Figure 8. The entropy (ΔSA) for bulk and nano-CuCl2·2H2O salts were calculated by using (19)ΔGA=ΔHA−TΔSA,where (S) is the entropy of the system. The calculated values of (ΔHA) and (ΔSA) for bulk and nano-CuCl2·2H2O salts are presented in Table 6. It is obvious that the limiting molar conductance (Λo) increased as the temperature increased while the dissociation degree decreased as the temperature increased indicating a higher solvation process. The values of the association constant (KA) and the triple ion association constant (K3) were decreased by increasing the temperature. Gibbs free energies change of association (∆GA) was decreased with negative signs by increasing the temperature indicating that association is favored with lowering of dielectric constant of solvent mixture. The decrease in the values of activity coefficient, limiting molar conductance, association constant, Gibbs free energy change of association, and Walden product for nano-CuCl2·2H2O in comparison to bulk CuCl2·2H2O indicates that the association of nano-CuCl2·2H2O is greater than bulk CuCl2·2H2O salt, due to the high surface to volume ratio of nanoparticles which leads to a greater ability for ion-pair formation.Figure 8
Variation of logKa with l/T (K−1) of for bulk and nano-CuCl2.2H2O in distillate H2O at 288.15, 293.15, 298.15, and 303.15 K.Table 6
Gibbs free energy of association (ΔGA), enthalpy change (ΔHA), and entropy change (ΔSA) for bulk and nano-CuCl2·2H2O in distillate H2O at different temperatures.
T (K)ΔGA (kJ mol−1)ΔHA (kJ mol−1)EA (kJ mol−1)ΔSA (kJ mol−1K−1)BulkNanoBulkNanoBulkNanoBulkNano288.15−11.028−9.322−0.0496−0.0904293.15−11.059−9.828−12.928−22.9183.603.72−0.0487−0.0842298.15−10.949−9.501−0.0477−0.0824303.15−10.993−8.924−0.0468−0.0807


## 3.3.2. Calculation of Formation Constants for Bulk and Nano-Cu-CFT Complexes in H2O at Different Temperatures

Different lines were obtained with breaks indicating the formation of (1 : 2) and (1 : 1) (M : L) stoichiometric complexes [57] on drawing the molar conductance (Λm) for bulk and nano-Cu-CFT complexes at different temperatures versus the molar ratio of metal to ligand [M]/[L] concentrations, as shown in Figure 9.Figure 9
The relation between Λm and the [M]/[L] molar ratio for (a) bulk Cu-CFT complex and (b) nano-Cu-CFT complex in distillate H2O at different temperatures.
(a)(b)The formation constants (Kf) for bulk and nano-Cu-CFT complexes were calculated for each type of complexes (1 : 2) and (1 : 1) (M : L) by using (20)M2++L↔ML2+,Kf=ML2+M2+L=ΛM−ΛobsΛobs−ΛMLL,(21)L=Lt–MtΛM−ΛobsΛM−ΛML,where Λm is the limiting molar conductance of the bulk and nano-CuCl2.2H2O alone, Λobs is the molar conductance of solution during titration, ΛML is the molar conductance of the complex, and [L] is the CFT concentration.The Gibbs free energies changes of formation (ΔGf) for each stoichiometric complex were calculated [4] by using (22)ΔGf=−2.303RTlogKf.The obtained values (Kf) for bulk and nano-Cu-CFT complexes and their calculated ΔGf values are presented in Tables 7 and 8.Table 7
Limiting molar conductance (Λo) and formation constant (Kf) for bulk Cu-CFT complex in distillate H2O at different temperatures.
T (K)[M] : [L]ΛoS cm2·mol−1ΛobsS cm2·mol−1logKf dm3·mol−1288.151 : 2912.11433.624.2111 : 1554.03440.054.424293.151 : 2958.50473.224.1861 : 1584.60331.164.375298.151 : 2966.40465.304.1791 : 1594.50322.254.342303.151 : 2985.30481.144.1741 : 1593.40347.494.275Table 8
Limiting molar conductance (Λo) and formation constant (Kf) for nano-Cu-CFT complex in distillate H2O at different temperatures.
T (K)[M] : [L]ΛoS cm2·mol−1ΛobsS cm2·mol−1LogKf dm3·mol−1288.151 : 2912.00439.564.1911 : 1555.00290.004.426293.151 : 2966.00473.224.1771 : 1593.00331.164.349298.151 : 2958.00485.104.1801 : 1584.00335.614.323303.151 : 2985.30481.144.1711 : 1593.00348.984.263By drawing the relation between logKf and 1/T, different lines were obtained indicating the formation of (1 : 2) and (1 : 1) (M : L) stoichiometric complexes, as shown in Figure 10.Figure 10
Variation of logKf with l/T for (a) bulk Cu-CFT complex and (b) nano-Cu-CFT complex in distillate H2O.
(a)(b)From the relation between logKf and 1/T, ΔHf can be calculated for each type of complexes, from the slope of each line which equals (−ΔHf/2.303 R). The entropy (ΔSf) for bulk and nano-Cu-CFT complexes was calculated for each type of complexes (1 : 2) and (1 : 1) (M : L) by using (23)ΔGf=ΔHf−TΔSf.The calculated values of (ΔHf) and (ΔSf) for bulk and nano-Cu-CFT complexes are presented in Tables 9 and 10.Table 9
Different formation parameters (Gibbs free energy of formation (ΔGf), enthalpy change (ΔHf), and entropy change (ΔSf)) for bulk Cu-CFT complex in distillate H2O at different temperatures.
T (K)Complex ratio (M : L)ΔGf (kJ mol−1)ΔHf (kJ mol−1)ΔSf (kJ mol−1K−1)288.15(1 : 2)−23.23−3.970.0252293.15−23.500.0257298.15−23.860.0265303.15−24.230.0273288.15(1 : 1)−24.41−15.960.0847293.15−24.560.0838298.15−24.790.0831303.15−24.820.0819Table 10
Different formation parameters (Gibbs free energy of formation (ΔGf), enthalpy change (ΔHf), and entropy change (ΔSf)) for nano-Cu-CFT complex in distillate H2O at different temperatures.
T (K)Complex ratio (M : L)ΔGf (kJ mol−1)ΔHf (kJ mol−1)ΔSf (kJ mol−1K−1)288.15(1 : 2)−23.12−1.820.0208293.15−23.440.0215298.15−23.860.0226303.15−24.210.0234288.15(1 : 1)−24.42−17.130.0847293.15−24.410.0833298.1524.680.0828303.15−24.750.0816It was observed that inflections at (1 : 2) M/L proportion and (1 : 1)M/L indicating the formation of both stoichiometric complexes in the solutions. These types of stoichiometric complexes are formed as a result of the interaction of bulk or nano-CuCl2 with CFT in distillate H2O at different temperatures. The complex formation parameters for (1 : 1) complexes are greater than those of (1 : 2) complexes indicating more favorable complexes. Also, the complex formation parameters (Kf, ΔGf) increased by increasing temperatures due to an increase in the kinetic energies. This trend was supported by entropies data which are greater for (1 : 1) M/L complexes than (1 : 2) M/L complexes.


## 4. Biological Activity

Many transition metals show arresting biological activity, working as active centers within important bioactive molecules in living systems. Copper (II) plays a significant function in cell metabolism and has proved beneficial in numerous diseases [58–60]. Ceftriaxone-metal complexes have both pharmacological and toxicological properties [61]. The interaction between metal ions and ceftriaxone can lead to precipitation resulting in serious adverse drug events [62]. Ceftriaxone complexes have antibacterial properties that can decrease or increase relative to pure ceftriaxone [61]. The antimicrobial activity was estimated based on the size of the inhibition zone formed around discs of bulk CuCl2·2H2O, nano-CuCl2·2H2O, CFT, and its bulk and nano-Cu complexes on a petri dish with Luria Bertani agar (LB-agar) plates as it measures the compound’s efficacy.


### 4.1. Antibacterial Activity

The antibacterial activities of bulk CuCl2.2H2O, nano-CuCl2·2H2O, bulk and nano-Cu-CFT complexes were compared with the activity of CFT and as presented in Table 11. Bulk CuCl2·2H2O provides an excellent antimicrobial activity, and such property is greatly improved when using nano-CuCl2.2H2O. It was observed also that CFT has a higher zone of inhibition than bulk and nano-Cu-CFT complexes in Klebsiella pneumonia and Pseudomonas aeruginosa (gram-negative bacteria), Figure 11.Table 11
Inhibition zones for antibacterial activity (gram-negative bacteria) and antifungal activity (Candida albicans).
CompoundInhibition zone (mm)Types of gram-negative bacteriaType of fungiKlebsiella pneumoniaStaphylococcus aureusCandida albicansBulk CuCl2·2H2O191712Nano-CuCl2·2H2O232214Ceftriaxone (CFT)34330Bulk Cu-CFT complex24218Nano-Cu-CFT complex25169Figure 11
Inhibition zone around the discs (6 mm) containing (1) CFT, (2) bulk Cu-CFT complex, and (3) nano-Cu-CFT complex placed on the surface of an LB-agar plate with (a)Klebsiella pneumonia and (b) Pseudomonas aeruginosa.
(a)(b)The antibacterial activity of Cu-CFT complexes depends on the bacterial species. The complexes and antibiotics presented inhibition zones of diameters larger than 20 mm showing that they have good activity as bactericides [63]. The antibacterial effect againstStaphylococcus aureus is present at the bulk and nano-Cu-CFT complexes (the inhibition zones are 21 and 16 mm, respectively). These values are lower than the corresponding values for bulk CuCl2·2H2O and nano-CuCl2·2H2O and ceftriaxone. The data indicate that ceftriaxone ligand is more active than their metal complexes; this may be because the chelating ligands containing N and O donor atoms show wide biological activity through bonding to metal ions [64, 65]. However, the synergetic effects of ceftriaxone and Cu ion may play an important function in the inhibition of bacterial growth after the complex decomposition. These effects are due to the different mechanisms of the action of antibiotics and heavy ions on the bacteria metabolism [66, 67].


### 4.2. Antifungal Activity

The experimental antifungal activity data are presented in Table11 which indicates that the nano-Cu-CFT complex showed a higher clear zone of inhibition against Candida albicans compared to the bulk Cu-CFT complex while there was an absence of the inhibition zone in CFT. So, the nano-Cu-CFT complex can be used as an antifungal drug, as shown in Figure 12. The zone of inhibition after treatment with bulk and nano-Cu-CFT complex was 8 and 9 mm, respectively. According to the standard criteria for evaluation of the drugs, the antifungal action such as a small zone of inhibition indicates that Candida albicans is stable with respect to CFT. The inhibition zones were completely absent, indicating the resistance of these fungi to CFT as well.Figure 12
Inhibition zone around the discs (6 mm) containing (1) CFT, (2) bulk Cu-CFT complex, and (3) nano-Cu-CFT complex placed on the surface of an LB-agar plate withCandida albicans.


## 4.1. Antibacterial Activity

The antibacterial activities of bulk CuCl2.2H2O, nano-CuCl2·2H2O, bulk and nano-Cu-CFT complexes were compared with the activity of CFT and as presented in Table 11. Bulk CuCl2·2H2O provides an excellent antimicrobial activity, and such property is greatly improved when using nano-CuCl2.2H2O. It was observed also that CFT has a higher zone of inhibition than bulk and nano-Cu-CFT complexes in Klebsiella pneumonia and Pseudomonas aeruginosa (gram-negative bacteria), Figure 11.Table 11
Inhibition zones for antibacterial activity (gram-negative bacteria) and antifungal activity (Candida albicans).
CompoundInhibition zone (mm)Types of gram-negative bacteriaType of fungiKlebsiella pneumoniaStaphylococcus aureusCandida albicansBulk CuCl2·2H2O191712Nano-CuCl2·2H2O232214Ceftriaxone (CFT)34330Bulk Cu-CFT complex24218Nano-Cu-CFT complex25169Figure 11
Inhibition zone around the discs (6 mm) containing (1) CFT, (2) bulk Cu-CFT complex, and (3) nano-Cu-CFT complex placed on the surface of an LB-agar plate with (a)Klebsiella pneumonia and (b) Pseudomonas aeruginosa.
(a)(b)The antibacterial activity of Cu-CFT complexes depends on the bacterial species. The complexes and antibiotics presented inhibition zones of diameters larger than 20 mm showing that they have good activity as bactericides [63]. The antibacterial effect againstStaphylococcus aureus is present at the bulk and nano-Cu-CFT complexes (the inhibition zones are 21 and 16 mm, respectively). These values are lower than the corresponding values for bulk CuCl2·2H2O and nano-CuCl2·2H2O and ceftriaxone. The data indicate that ceftriaxone ligand is more active than their metal complexes; this may be because the chelating ligands containing N and O donor atoms show wide biological activity through bonding to metal ions [64, 65]. However, the synergetic effects of ceftriaxone and Cu ion may play an important function in the inhibition of bacterial growth after the complex decomposition. These effects are due to the different mechanisms of the action of antibiotics and heavy ions on the bacteria metabolism [66, 67].


## 4.2. Antifungal Activity

The experimental antifungal activity data are presented in Table11 which indicates that the nano-Cu-CFT complex showed a higher clear zone of inhibition against Candida albicans compared to the bulk Cu-CFT complex while there was an absence of the inhibition zone in CFT. So, the nano-Cu-CFT complex can be used as an antifungal drug, as shown in Figure 12. The zone of inhibition after treatment with bulk and nano-Cu-CFT complex was 8 and 9 mm, respectively. According to the standard criteria for evaluation of the drugs, the antifungal action such as a small zone of inhibition indicates that Candida albicans is stable with respect to CFT. The inhibition zones were completely absent, indicating the resistance of these fungi to CFT as well.Figure 12
Inhibition zone around the discs (6 mm) containing (1) CFT, (2) bulk Cu-CFT complex, and (3) nano-Cu-CFT complex placed on the surface of an LB-agar plate withCandida albicans.


## 5. Conclusion

The nano-CuCl2·2H2O salt was prepared by ball milling method. The thermodynamic association parameters of both bulk and nano-CuCl2·2H2O salts in H2O were calculated using the conductometric method by applying the Fuoss–Shedlovsky method at different temperatures. It shows that the association parameters of nano-CuCl2·2H2O are greater than bulk CuCl2·2H2O salt due to the high surface-to-volume ratio of the nanoparticles which leads to a greater ability for ion-pair formation.The thermodynamic parameters of complexation between bulk and nano-CuCl2·2H2O salts and ceftriaxone antibiotic in H2O were calculated from conductance measurement. It was found that the formation of Gibbs free energies change (∆Gf) was decreased in negative signs with increasing temperatures. Two stoichiometric complexes, 1/2 and 1/1 (M/L), are formed with the formation constant and Gibbs free energy of the formed complexes following the order Kf (1 : 1) > Kf (1 : 2) for (M : L) and ∆Gf (1 : 1) > ∆Gf (1 : 2) for (M : L) (in negative values) indicates the favorable of formation of (1 : 1) complex compared to (1 : 2) complex. Also, there is a decrease in values of Kf and ∆Gf in case of using nano-CuCl2·2H2O compared to using bulk CuCl2·2H2O but in small difference due to the more solvation effect in case of using nanoparticles.It was observed that CFT has a higher zone of inhibition and antibacterial activity than that of bulk and nano-Cu-CFT complexes inKlebsiella pneumonia and Pseudomonas aeruginosa (gram-negative bacteria). The nano-Cu-CFT complex showed a higher clear zone of inhibition and antifungal activity against candida compared to the bulk Cu-CFT complex while there was an absence of the inhibition zone in CFT, so the nano-Cu-CFT complex can be used as an antifungal drug.



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