bluuebunny/crossref_metadata_2025_split huggingface dataset:
Viscometric Behavior of Some Symmetrical Tetraalkylammonium Bromides in Acetonitrile + Water Mixtures at 303.15 K
Authors: Nikam Pandharinath S , Sawant Arun B 
Published: June 2006

Abstract
The viscosity measurements for some symmetrical tetraalkyl ammonium bromide (R4NBr, R = CH3 to C5H11) KCl, and KBr solutions in acetonitrile (ACN) + water mixtures containing 0, 10, 30, 50, 70, 90, and 100 mass% of ACN at 303.15 K have been performed. The Jones–Dole equation was used for the analysis of viscosity data of these salts. The viscosity B-coefficients in the entire range of ACN+water mixtures were obtained from the computerized least-squares method. The experimental criterion B(K+) = B(Cl−) = (1/2)B(KCl) was applied in order to obtain the ionic B-coefficients. The B± coefficients are interpreted in terms of solvent structure and ion-solvent interactions in the solvents.
Heat Treatment of Hydrogen Molybdenum Bronze in an Oxygen-Free Atmosphere. Formation of a Defect Structure and Attempt to Carry Out a Catalytic Reaction
Authors: Nakamura Kentaro , Eda Kazuo , Sotani Noriyuki 
Published: June 2006

Abstract
Hydrogen molybdenum bronze, HxMoO3 (x = 0.25), was treated in vacuo, which was changed by four steps to form MoO3 and MoO2 through the Type-I and the MoO3-like structure with defects, such as an oxygen vacancy. The structural changes were studied by TG-DTA, XRD, ESR, and XANES. Type-I with a defect structure was effective for the isomerization of 1-butene.
Second-Order Perturbational Effect on the Interlayer Interactions in Graphite and Graphite Intercalation Compounds
Authors: Yoshizawa Kazunari , Kato Takashi , Yamabe Tokio 
Published: June 2006

Abstract
The role of second-order perturbations in interlayer interactions of two-dimensional electronic systems is examined from simple two-layer models. The preferred nuclear motions are discussed specifically for the preferred stacking of layers in graphite on the basis of transition-density analyses for extended systems. The well-known ABAB stacking of layers in neutral graphite and the AAAA stacking of layers in graphite intercalation compounds (GICs) such as C6Li and C8K complexes are proposed to be consequences of orbital interactions (near the Fermi level) between nearest neighbor layers. This paper raises doubts about a widely accepted belief that the interlayer interaction between graphite layers is of the van der Waals type.
X-Ray Analyses of Complexes Formed between Surfactants and Aromatic Compounds. I. A Common Structural Pattern of the Complexes
Authors: Sawada Keiju , Kitamura Tatsuo , Ohashi Yuji , Iimura Nahoko , Hirata Hirotaka 
Published: June 2006

Abstract
The cationic surfactants such as hexadecyl-, tetradecyl-, dodecyl-, and decyltrimethylammonium bromides form complexes with a variety of aromatic compounds in aqueous solutions. Well-defined crystals were obtained if the aromatic compounds had hydrogen donor moieties. The structures of ten kinds of the complex crystals were analyzed by X-rays. All the crystal structures had a common pattern of complex formation, in which the aromatic compounds are sandwiched by the two alkyl chains of the surfactant molecules. There are two modes of stacking when the complexes with the common pattern are piled up to form the crystalline lattice. The common pattern of complex formation is responsible for the high viscoelasticity of the aqueous solutions containing cationic surfactants and aromatic compounds.
Extraction and Stripping of Copper(I) as a Neocuproine Complex in a Surfactant System and Determination of Copper in Steel
Authors: Tagashira Shoji , Murakami Yoshiko , Yano Mituya , Sasaki Yoshiaki 
Published: June 2006

Abstract
An aqueous solution containing surfactants exhibits the property of being separated into two phases due to a temperature change or an addition of salts. The extraction and stripping of copper(I) as a neocuproine complex were investigated between the anionic surfactant of sodium dodecylsulfate (SDS) and aqueous phases. When the surfactant was separated by the addition of NaCl, the copper complex was extracted into the SDS phase. The stripping of copper(I) into the aqueous phase was maintained by phase separation, which was achieved by cooling the solution. Since neocuproine is a highly specific chromogen for copper(I), iron(II) could not form a complex with neocuproine, and was scarcely extracted into the SDS phase. This selective extraction was applied to the separation of copper from iron and the determination of copper in steel samples by a spectrophotometric method and/or an atomic-absorption spectrometric method (AAS).
Synthesis and Structural Characterization of Thiolato-Bridged Zinc(II) Complexes with NNS-Tridentate Thiolic Ligands
Authors: Mikuriya Masahiro , Jian Xiao , Ikemi Shin-ichiro , Kawahashi Takako , Tsutsumi Hideyuki 
Published: June 2006

Abstract
Zinc(II) complexes with 2-[(2-aminoethyl)amino]ethanethiol (HL1), 2-[(3-aminopropyl)amino]ethanethiol (HL2), 2-[(2-pyridylmethyl)amino]ethanethiol (HL3), and 2-{[2-(2-pyridyl)ethyl]amino}ethanethiol (HL4), [Zn(L1)](ClO4) (1), [Zn{Zn(L1)2}2](ClO4)2 (2), [Zn(L2)](ClO4) (3), [Zn{Zn(L3)2}2](ClO4)2 (4), and [Zn3(L4)3](ClO4)3 (5), have been synthesized and characterized by measurements of the infrared and electronic spectra. The molecular structures of these complexes were determined by the single-crystal X-ray structure analysis. Complex 1 has a thiolato-bridged polymeric chain structure, in which each metal atom is essentially four-coordinated in a distorted tetrahedron. Complexes 2 and 4 have a thiolato-bridged trinuclear complex with a linear arrangement of three metal atoms. Complex 5 is a thiolato-bridged trinuclear complex displaying a six-membered ring of Zn3S3.
Experimental and Theoretical Studies of the Possible and Preferred Site of Protonation in Polyfunctional N1,N1-Dimethyl-N2-benzoylformamidine in the Gas Phase
Authors: Raczynska Ewa D , Mishima Masaaki , Mustanir  
Published: June 2006

Abstract
Proton-transfer reactions for N1,N1-dimethyl-N2-benzoylformamidine containing three basic sites, the carbonyl-O, imino-N, and amino-N atoms, have been studied by experimental (FT-ICR) and theoretical (ab initio) methods. The ICR study gave a GB of 225.5 kcal mol−1 for this compound. The empirical structure-basicity relationships predicted GB values of 224.8 and 212.8 kcal mol−1 for protonation at the imino-N and carbonyl-O atoms, respectively. The observed GB values is close to the value for the imino-N atom. Theoretical calculations (B3LYP/6-311+G(2d,p)//HF/6-31G(d)) also showed that protonation at the imino-N atom is preferred by 7 kcal mol−1 compared to protonation at the carbonyl-O atom.
Conformational Effect (Induced-Fit) on Catalytic Activity of α-Chymotrypsin
Authors: Kawai Yasushi , Matsuo Takashi , Ohno Atsuyoshi 
Published: June 2006

Abstract
The kinetics for the hydrolyses of p-nitrophenyl esters of acetic acid and certain amino acid derivatives mediated by α-chymotrypsin have been studied. The kinetics are a function of the medium viscosity, which indicate that the enzyme must change its conformation during the reaction. Detailed analysis of the dependence of kinetic rate constants on the medium viscosity has revealed that (1) the reaction is associated with the induced-fit conformational adjustment of the enzyme: When the enzyme-substrate (ES) complex is converted into the corresponding acyl enzyme, the conformation of the enzyme is changed in order to accommodate the acyl group in the pocket of the enzyme at an appropriate position. (2) The conformationally distorted α-chymotrypsin recovers its conformation when it releases the acid part of the substrate ester. (3) The formation of an ES complex is independent of any induced-fit movement. The induced-fit conformational adjustment of the enzyme plays a crucial role in its catalytic activity.
Single-Stranded DNA Recognition of a 24-mer Peptide Derived from RecA Protein
Authors: Nakano Shu-ichi , Sugimoto Naoki 
Published: June 2006

Abstract
A 24-mer peptide with L2 and helix G amino acids of E. coli RecA protein (Ac–Ile–Arg–Met–Lys–Ile–Gly–Val–Met–Phe–Gly–Asn–Pro–Glu–Thr–Thr–Thr–Gly–Gly–Asn–Ala–Leu–Lys–Phe–Tyr–NH2) showed a single-stranded DNA (ssDNA) binding property with a more than 1000 times affinity difference than for a double-stranded DNA. However, a truncated 15-mer peptide (sequence) showed no ssDNA binding activity. In the ssDNA binding, the 24-mer peptide changed its conformation with the perturbation of an α-helix structure. The ssDNA binding and the DNA discrimination property of this peptide were due to almost all L2 and helix G amino acids, respectively. This result useful to design synthetic peptides as functional materials for DNA recognition.
Reaction of Benzanthrone (7H-Benz[d,e]anthracen-7-one) with Nitrogen Dioxide Alone or in Admixture with Ozone. Implications for the Atmospheric Formation of Genotoxic 3-Nitrobenzanthrone
Authors: Enya Takeji , Suzuki Hitomi , Hisamatsu Yoshiharu 
Published: June 2006

Abstract
The reaction of benzanthrone (7H-benz[d,e]anthracen-7-one, 1) with nitrogen dioxide alone or in admixture with ozonized oxygen has been investigated in polar and nonpolar organic solvents at different temperatures. A remarkable change of product distribution was observed depending on the solvent employed; 3-nitrobenzanthrone (4) was the main product from the reaction in dichloromethane, while 2-nitrobenzanthrone was obtained as the major product in tetrachloromethane. Addition of protonic acid or inorganic solid support was found to promote the reaction, favoring the formation of the former nitro compound at the expense of the latter. All major products were identified. The variation of isomer distribution depending on the conditions employed has been discussed in terms of the competition between the homolytic and heterolytic mechanisms involved in the nitration of ketone 1. On the basis of the results obtained, the atmospheric formation of the genotoxic nitro ketone 4 has been briefly discussed.
Synthesis and Properties of Europium Complexes with β-Diketone Ligands for Organic Electroluminescent Devices
Authors: Uekawa Masahiro , Miyamoto Yasuo , Ikeda Hitoshi , Kaifu Katsuaki , Nakaya Tadao 
Published: June 2006

Abstract
Europium complexes with new β-diketone ligands with fluorene for organic electroluminescent (EL) devices have been synthesized and their properties examined. The absorption spectra of the complexes were varied by changing the conjugated system of the β-diketone; also, the energy transfer from the host material to the europium complexes and the intramolecular energy transfer have been improved. Concerning the volatility, the thermal properties of the europium complexes were improved by using phenanthroline derivatives. We fabricated organic EL devices using the synthesized complexes, and investigated the luminance of the devices.
Thermodynamic Study on Dioxygen Binding of Diiron(II) and Dicobalt(II) Complexes Containing Various Dinucleating Ligands
Authors: Sugimoto Hideki , Nagayama Toshihiko , Maruyama Sachihito , Fujinami Shuhei , Yasuda Yuichi , Suzuki Masatatsu , Uehara Akira 
Published: June 2006

Abstract
A new dinucleating ligand containing a sterically bulky imidazolyl group, Ph-Htidp (N,N,N′,N′-tetrakis[(1-methyl-4,5-diphenyl-2-imidazolyl)methyl]-1,3-diamino-2-propanol), and its μ-alkoxo-diiron(II) complexes [Fe2(Ph-tidp)(RCO2)](ClO4)2, (RCO2 = C6H5CO2 (1), C6F5CO2 (2), CF3CO2 (3), and C2H5CO2 (4)), were synthesized. The structure of complex 1 was determined by X-ray crystallography. Complex 1 crystallizes in the monoclinic space group P21/c with a = 13.464(2), b = 19.223(4), c = 31.358(4) Å, β = 92.84(2)°, and Z = 4. The complex has a doubly-bridged structure with μ-alkoxo of Ph-tidp and μ-benzoate; the two iron centers have a distorted five-coordinate structure with N3O2 donor set. All the complexes showed fairly good reversible oxygenation below −30 °C in CH2Cl2, which was monitored by UV-vis and NMR spectroscopies, and dioxygen up-take measurements. Introduction of 4,5-diphenyl substituents into 2-imidazolyl group stabilized the μ-peroxo diiron species against irreversible oxidation, just as introduction of 6-methyl substituent into 2-pyridyl group did. Phenyl substituents appear to weaken the electron donor ability of a dinucleating ligand to stabilize divalent oxidation state of iron and to form a hydrophobic cavity for a O2 binding site, which would suppress the irreversible oxidation and facilitate the reversible oxygenation. Dioxygen affinities of the Ph-tidp and Me4-tpdp diiron(II), and the tpdp and bpmp dicobalt(II) complexes were measured, [Fe2(Me4-tpdp)(RCO2)]2+ (RCO2 = C6H5CO2 and RCO2 = CF3CO2) and [Co2(L)(RCO2)]2+ (L = tpdp, RCO2 = CH3CO2, and L = bpmp, RCO2 = C6F5CO2, and CF3CO2), where Me4-tpdp, tpdp, and bpmp are N,N,N′,N′-tetrakis[(6-methyl-2-pyridyl)methyl]-1,3-diamino-2-propanolate, N,N,N′,N′-tetrakis(2-pyridylmethyl)-1,3-diamino-2-propanolate, and 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-methylphenolate, respectively. Within a series of the Ph-tidp diiron(II) complexes, dioxygen affinity is well correlated with electron donor ability of bridging carboxylates (1 (C6H5CO2) &gt; 2 (C6F5CO2) &gt; 3 (CF3CO2)). In contrast to the above trend, dioxygen affinities of the Ph-tidp complexes are lower than those of the Me4-tpdp complexes, although electron donor abilities of the Me4-tpdp complexes are weaker than those of the Ph-tidp complexes. Significant enhancement of dioxygen affinity was observed for both iron and cobalt complexes with 2,6-bis(aminomethyl)phenolate bridging skeleton compared to the complexes with a 1,3-diamino-2-propanolate bridging one. Thermodynamic study suggested that the observed enhancement is mainly attributable to a favorable entropy effect along with a steric effect.
Cooperative Ligand Binding to Globular Protein(I). Binding of Monoanionic Azo Dyes to Hen Egg White Lysozyme
Authors: Murakami Kiyofumi 
Published: June 2006

Abstract
Binding of sodium 4-(2- or 4-hydroxy-1-naphthylazo)benzenesulfonate and sodium 4-[4-(amino or dialkylamino)phenylazo]benzenesulfonate (alkyl: methyl, ethyl, or butyl) to hen egg white lysozyme has been studied by an equilibrium dialysis method at pH = 7.0 (0.1 mol dm−3 phosphate buffer) and 25 °C. In the case of the (2- or 4-hydroxy-1-naphthylazo)benzenesulfonate system, a single cooperative binding stage has been observed with a maximum binding number of 10. In the case of the 4-[4-(dialkylamino)phenylazo]benzenesulfonate systems, two cooperative binding stages have been observed for the dyes having alkyl groups longer than a methyl group. The maximum binding numbers of the first stage are 14 and 13 for 4-[4-(diethylamino)phenylazo]benzenesulfonate and 4-[4-(dibutylamino)phenylazo]benzenesulfonate, respectively, and those of the second stage were the same as those for the first one. The binding isotherms have been well interpreted by the stepwise binding model, which takes account of the free energy decrease due to interactions between bound ligands and of its reduction as the binding step proceeds, and binding constants have been evaluated. On the basis of the binding constants and the free energy changes of binding, the detailed binding mechanism is discussed.
Molecular Recognition in Ternary Complexes of γ-Cyclodextrin with Naphthalenedicarboxylate Ions and a Space-Regulator Ion
Authors: Tan Wei Hua , Ishikura Takahiro , Maruta Aya , Yamamoto Tatsuyuki , Matsui Yoshihisa 
Published: June 2006

Abstract
Complexation of γ-cyclodextrin (γ-CD) with the 2,6-naphthalenedicarboxylate ion (2,6-NDC) in alkaline D2O was greatly enhanced by the addition of 2,6-bis(1-pyridiniomethyl)naphthalene dibromide (2,6-PMN) as a space-regulator. Formation of a ternary 1 : 1 : 1 complex between γ-CD, 2,6-NDC, and 2,6-PMN was confirmed by means of 1H NMR spectroscopy, together with the measurements of induced circular dichroism spectra and UV absorption spectra. Changes in chemical shifts (δ) of the γ-CD protons in the presence of an excess amount of 2,6-PMN with the addition of NDC regioisomers were analyzed by a curve-fitting procedure to give binding constants (K6) for complexation of NDC’s with a γ-CD–2,6-PMN binary complex. The K6 values increased in the order of 1,5-NDC &lt; 1,4-NDC &lt; 1,8-NDC &lt; 1,3-NDC &lt; 1,6-NDC &lt; 2,3-NDC &lt; 2,7-NDC &lt; 2,6-NDC, indicating that a binary complex of γ-CD with 2,6-PMN is able to recognize the molecular structures of NDC’s. The open space between the γ-CD cavity and 2,6-PMN will be favorable for the accommodation of a slender molecule such as 2,6-NDC, but unfavorable for the accommodation of a bulky molecule such as 1,5-NDC.
Chemistry of o-Mercaptophenolate: Syntheses, Structures, and Characterization of Titanium(IV) Complexes
Authors: Wen Ting-Bin , Kang Bei-Sheng , Su Cheng-Yong , Wu Da-Xu , Wang Li-Ge , Liao Sen , Liu Han-Qin 
Published: June 2006

Abstract
The reaction of Cp2TiCl2 with o-mercaptophenolate in the presence of a base (Et3N or NaOMe) afforded the complex (BnMe3N)2[Ti(o-SC6H4O)3] or (Et4N)2[Ti2(o-SC6H4O)4(OMe)2]·2H2O under slightly varied conditions. Single-crystal X-ray diffraction studies showed that the Ti(IV) geometry in both complexes is a severely distorted octahedron with average trans-angles of 162.2° and 159.1(2)°, respectively. Crystallographic data for (BnMe3N)2[Ti(o-SC6H4O)3]: a = 9.884(3), b = 16.501(7), c = 23.028(7) Å; β = 99.89(3)°, V = 3700.2(22) Å3, Z = 4, final R = 0.050 for 3134 observed reflections; for (Et4N)2[Ti2(o-SC6H4O)4(OMe)2]·2H2O: a = 8.953(4), b = 10.148(3), c = 14.527(3) Å; α = 73.16(2)°, β = 73.00(3)°, γ = 83.56(4)°, V = 1207.4(9) Å3, Z = 1, final R = 0.082 for 2233 observed reflections. The isolation of (BnMe3N)2[Ti(o-SC6H4O)3] provides strong evidence for the synthon character of [Ti(mp)3]2−, which was previously predicted to be present in the complex (Et4N)2[Ti(mp)3Na(MeOH)2]2. Both electronic and 1H NMR spectra showed a similar rigidity of the mp chelate rings to Ti(IV) in the complexes.
Kinetics and Mechanism of the Copper(II)-Catalyzed Oxidation of the Iodide Ion to Iodine by the Vanadium(V) Ion in an Aqueous Solution
Authors: Kimura Masaru , Shiga Yuko , Tsukahara Keiichi 
Published: June 2006

Abstract
The vanadium(V) ion, which is described as VV herein, could hardly oxidize the iodide ion to iodine at pH ≥ 2.8; however, the oxidation reaction occurred catalytically upon adding traces of copper(II) ion. When a copper(II) solution of 10−8—10−5 M (M = mol dm−3) was mixed with an iodide solution, after a rapid formation of iodine, the iodine concentration remained constant. After such iodine formation had occurred, if a VV solution was added into the reacting mixture, the iodine began to form again in accordance with a rate law of 2(d[I2]/dt) = −d[VV]/dt = k[CuI][VV], in which [CuI] is a steady-states’ concentration in a chain cycle CuI+/CuI. The reaction rate was independent of the time to add the VV ion, and the formation of iodine I2 (or triiodide ion I3−) stopped at the time when all of the VV was consumed, indicating the stoichiometry to be 2I− + 2VV → I2 + 2VIV. The initial rate (Vi) after VV addition was proportional to the concentrations of not only the added VV over the range 10−6—10−5 M, but also the added copper(II) ion. Although a self-inhibiting effect did not appear over the pH range 2.8—3.6, it occurred at pH &gt; 3.6. It was found that such a retarding effect was caused by the vanadium(IV) ion (denoted as VIV herein), which was the reduced product of VV; the VIV inhibiting effect was extremely dependent on the pH in the reacting solution. The mechanisms for the retardation reaction as well as iodine formation are discussed in terms of accounting for the obtained results.
Difference in the Reactions of N-Methylhydroxylamine and N-Phenylhydroxylamine with Nitrosobenzene
Authors: Magro Jacir Dal , Yunes Rosendo Augusto 
Published: June 2006

Abstract
The reaction of nitrosobenzene with N-methylhydroxylamine was studied. The pH-rate profile exhibits a negative break at between pH 0.5 and 3.0, which is considered to be caused by a change in the rate-determining step of the reaction from an attack of the amine on nitrosobenzene at low pH, to the dehydration of an addition intermediate previously formed between the reagents at higher pH. This behavior is different from that of the reaction between N-phenylhydroxylamine and nitrosobenzene where, over the entire pH range, the only rate-determining step is dehydration of the addition intermediate. This fact confirms the special behavior of phenylhydroxylamine as a nucleophile, as was observed in its reactions with aromatic aldehydes.
An Easy Direct Conversion of Pyridine- and Pyrimidine-Thiones into Multi-Fused Heterocyclic Compounds
Authors: Erian Ayman Wahba , Abu-Shanab Fathi Ali 
Published: June 2006

Abstract
The reaction of azine-thiones with ethyl chlorofluoroacetate afforded 2-fluorothienoazines. The latter underwent self-condensation and gave multi-fused heterocyclic compounds. A wide range of unique heterocycles could be obtained on treatment of 2-fluorothienoazines with nitrogen nucleophilic reagents. The reactivity of the pyrimidine-thiones towards a variety of electrophilic reagents was studied. Chemical and spectroscopic evidence of the newly synthesized compounds are described.
A Facile Preparation and Cyclopropanation of 1-Alkenylsilanols
Authors: Hirabayashi Kazunori , Takahisa Eisuke , Nishihara Yasushi , Mori Atsunori , Hiyama Tamejiro 
Published: June 2006

Abstract
Alkenylsilanols are prepared by the reaction of hexamethyltrisiloxane (D3) with alkenyllithiums or alternatively by the reaction of cyclic siloxanes substituted by an alkenyl group with organolithiums and transformed to the corresponding cyclopropylsilanols using diiodomethane and diethylzinc. Lithium alkenylsilanolates, primary products of the preparation, also undergo cyclopropanation. As in the case of allylic alcohols, the silanol functionality is found to enhance the rate of cyclopropanation compared with that of alkenyltrialkylsilane or alkoxydialkylsilane. The obtained cyclopropylsilanols are further converted into the corresponding cyclopropanols by the Tamao oxidation.
Specific Deuterium Labeling of Archaeal 36-Membered Macrocyclic Diether Lipid
Authors: Arakawa Kenji , Eguchi Tadashi , Kakinuma Katsumi 
Published: June 2006

Abstract
Described in this paper is a practical synthesis of the specifically deuterated 36-membered macrocyclic diether lipid 4 and its acyclic deuterated counterpart 5, both of which are essential to the detailed biophysical studies of the conformational order of phospholipids in vesicles. The synthesis of 4 was principally composed of the preparation of deuterated diether 15, subsequent macrocyclization of the crucial dialdehyde 21 by McMurry coupling, and final transformation into the phosphocholine derivative. The acyclic deuterated counterpart 5 was also synthesized from the common intermediary tosylate 16.
Theoretical Study on Carbocation Formation Reactions. Resonance Demands and Transition Structures
Authors: Mishima Masaaki , Yamataka Hiroshi 
Published: June 2006

Abstract
Ab initio molecular-orbital calculations were carried out for two carbocation-generating reactions, the SN1 reaction of protonated 1-phenylethyl alcohol (H2O leaving group) and the acid-catalyzed hydration of styrene. Separated reactants, reactant complexes, transition states (TSs), product complex, and separated products were optimized at MP2/6-31G* and the vibrational frequencies were analyzed. The SN1 TS lies halfway between the reactant and the product with respect to the bond lengths, charge distribution, and secondary deuterium isotope effects. The degree of the π-orbital overlap between the benzylic carbon and the phenyl ring is almost the same in the SN1 TS and the 1-phenylethyl cation. The proton-transfer TS of the hydration, on the other hand, reaches earlier, and the π-orbital overlap in the TS is less effective. These differences are responsible for the difference in the experimental substituent effect reported in the literature for the two reactions.