bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fluorescence quenching of β‐carboline alkaloids in micellar media. A study to select the adequate surfactant to use in analytical techniques
Authors: Martín Laura , Olives Ana I. , del Castillo Benito , Martín M. Antonia 
Published: May 2005

AbstractThe study of fluorescence quenching of the fluorophores allows the localization of the alkaloids (harmane and harmine) in the micelles (SDS, CTAB, Brij‐35) to be established. In aqueous micellar solutions (SDS and Brij‐35) at pH 13.0, emission corresponding to the neutral or zwitterionic forms can be observed. In the presence of CTAB (pH = 13.0) it was possible to observe the emission of anionic form. These species are not present in buffered aqueous solutions at these pH values. Bromide ion was added to the different surfactant solutions and the quenching effect was studied according to the Stern–Volmer equation. In the presence of SDS the quenching effect is considerably reduced compared to the aqueous solutions without surfactants, while for Brij‐35 micelles were similar to those observed in homogeneous aqueous solution. For CTAB micelles a notable fluorescence quenching was observed for the different pH values studied. The fluorescence quenching studies show that the neutral species are associated inside the micelles, instead of the ionic species (cationic, zwitterionic or anionic) remaining on the surface of the micelles. The anionic surface of SDS micelles prevents the quenching effect by anionic quenchers for both neutral and charged species. Copyright © 2005 John Wiley & Sons, Ltd.
Detection of synthetic corticosteroids in bovine urine by chemiluminescence high‐performance liquid chromatography
Authors: Vázquez B. I. , Feás X. , Lolo M. , Fente C. A. , Franco C. M. , Cepeda A. 
Published: May 2005

AbstractThe development of a black market of chemical cocktails for illegal growth promotion in food‐producing animals includes substances that are potentially dangerous for human health, such as synthetic corticosteroids. The potential presence of these residues in food makes it necessary to develop rapid and sensitive analytical methodologies to detect such substances, preferably in live animals before they arrive at the market. A chemiluminescence (CL) detection method for the determination of four synthetic corticosteroids (prednisolone, betamethasone, dexamethasone and flumethasone) in bovine urine has been developed. The proposed system, which does not need any derivatization procedure, offers an easy method well suited for routine research. Urine samples were homogenized with methanol:water (50:50, v[sol ]v) and centrifuged. The upper layer was collected and Strata™ X cartridges were used for cleaning up. The purified residues were evaporated to dryness and then redissolved in the mobile phase. Analysis of the extracts was performed using high‐performance liquid chromatography with chemiluminescence detection, employing luminol as the CL reagent. The recovery curves, obtained at four spiking levels (different for each corticosteroid), showed that recoveries of at least 70% could be obtained for urine. The chemiluminescence detection procedure afforded satisfactory results with respect to sensitivity and the LOD and LOQ, taken as the first point of the regression curve, ranged from 4 ppb to 65 ppb. The maximum mean RSD was below 13% and below 15% for intra‐ and inter‐day assay, respectively, in all cases. Copyright © 2005 John Wiley & Sons, Ltd.
Characteristics of endogenous flavin fluorescence of Photobacterium leiognathi luciferase and Vibrio fischeri NAD(P)H:FMN‐oxidoreductase
Authors: Vetrova E. V. , Kudryasheva N. S. , Visser A. J. W. G. , van Hoek A. 
Published: May 2005

AbstractThe bioluminescent bacterial enzyme system NAD(P)H:FMN‐oxidoreductase–luciferase has been used as a test system for ecological monitoring. One of the modes to quench bioluminescence is the interaction of xenobiotics with the enzymes, which inhibit their activity. The use of endogenous flavin fluorescence for investigation of the interactions of non‐fluorescent compounds with the bacterial luciferase from Photobacterium leiognathi and NAD(P)H:FMN‐oxidoreductase from Vibrio fischeri has been proposed. Fluorescence spectroscopy methods have been used to study characteristics of endogenous flavin fluorescence (fluorophore lifetime, the rotational correlation time). The fluorescence anisotropy behaviour of FMN has been analysed and compared to that of the enzyme‐bound flavin. The fluorescence characteristics of endogenous flavin of luciferase and NAD(P)H:FMN‐oxidoreductase have been shown to be applicable in studying enzymes' interactions with non‐fluorescent compounds. Copyright © 2005 John Wiley & Sons, Ltd.
Fluorescence analysis of photoinduced degradation of ecotoxicants in the presence of humic acids
Authors: Tchaikovskaya O. N. , Sokolova I. V. , Yudina N. V. 
Published: May 2005

AbstractThe photolysis of humic acids and phenols in water containing humic acids was investigated. Humic acids extracted from peat (Vasuygan Bog, Tomsk Region, Russian Federation) induce the phototransformation of 4‐chlorophenol at 365 and 222 nm. Humic acids were characterized by UV‐, fluorescence‐, IR‐ and EPR‐spectroscopy and laser‐induced fluorescence. The influence of humic acids on the phototransformation of phenols in different irradiation conditions was investigated. Comparison of the data on mercury lamp irradiation showed that the most effective phenols degradation was observed under exposure to KrCl* exilamp light (λ = 222 nm) in the presence of humic acids. Copyright © 2005 John Wiley & Sons, Ltd.
Bioluminescence determination of enzyme activity of firefly luciferase in the presence of pesticides
Authors: Trajkovska Snezana , Tosheska Katerina , Aaron Jean Jacques , Spirovski Filip , Zdravkovski Zoran 
Published: May 2005

AbstractFirefly luciferase (EC 1.13.12.5) (FL) is the key enzyme in the firefly bioluminescence method (FB), which is widely used to determine the viability of living cells. The FB method can also be applied to monitoring the influence of different pollutants, such as pesticides. Firefly luciferase is a hydrophobic enzyme and its activity depends on the type of solvent, pH and substances present in the reaction mixture. The influence of three aromatic pesticides, including fenoxaprop‐p‐ethyl (I), diclofop‐methyl (II) and metsulfuron methyl (III), on the enzyme activity was indirectly evaluated through the measurement of emitted light in the bioluminescence reaction, expressed in relative luminescence units (RLU). The reaction mixture used in the bioluminescence measurements consisted of: Tris buffer (pH 7.75), adenosine triphosphate (ATP) and ATP monitoring reagent, where FL is present. Ethanol–water solutions of each pesticide were then added at concentrations of 2.4 × 10−4–2.4 × 10−8 mol[sol ]L. The FL activity inhibition factors (FL In%) were determined. The FL activity was maximally inhibited in the presence of all pesticides under study at a concentration of 2.4 × 10−4 mol[sol ]L and was lowered by about 15–26% for pesticide I at concentrations of 2.4 × 10−5–2.4 × 10−8 mol[sol ]L, whereas pesticides II and III, applied in the same concentration range, showed smaller FL inhibition values (5.3–20%). The pesticide degradation products (obtained after a 1 month period), measured in the same experimental conditions, in most cases exhibited a much less inhibitory effect on the enzyme activity than the corresponding initial pesticide. Copyright © 2005 John Wiley & Sons, Ltd.
Nanosized γ‐Al2O3 + Nd2O3‐based cataluminescence sensor for ethylene dichloride
Authors: Cao Xiaoan , Feng Guiming , Gao Haihua , Luo Xiaoqing , Lu Hailiang 
Published: May 2005

AbstractA gas‐sensor utilizing cataluminescence (CTL) on nanosized γ‐Al2O3 + Nd2O3 for measuring low concentrations of gaseous ethylene dichloride (EDC) was developed. The results showed that γ‐Al2O3 nanoparticles as a catalyst offered high sensitivity and selectivity in the detection of EDC. The addition of a small quantity of Nd2O3 increased the intensity of CTL more than two‐fold. Quantitative analysis was performed at a wavelength of 400 nm and at an optimal temperature of 279°C, and the optimal flow rate of carrier gas was 320 mL[sol ]min. Under the optimized conditions, the linear range of CTL intensity vs. concentration is 6–5000 ppm (R = 0.9996; n = 7), with a detection limit of 2 ppm. The response time is <5 s. No interference or only very low levels of significant interference were observed when substances such as formaldehyde, n‐hexane, methyl benzene, carbon tetrachloride, chloroform and benzene were passed through the sensor. Copyright © 2005 John Wiley & Sons, Ltd.
Flow cytometric analysis of fine particles in a eutrophic lake
Authors: Guo Pei‐yong , Zhu Yin‐mei , Zhang Zhi‐jian 
Published: May 2005

AbstractFine particles play an important role, not only in aquatic biogeochemical processing but also in the distribution, transfer and transformation of pollutants in the aquatic environment. Flow cytometry, widely used in biomedical research, allows fast counting and optical analysis of individual particles. Organic autotrophic particles contain naturally fluorescing pigments, such as chlorophyll and phycoerythrin. Different populations have different sizes and pigments. They also have different ratios of pigments. In general, side angle scatter (SSC) is related to the size, shape and refractive index of particles. When a 488 nm wavelength was used to excite chlorophyll and phycoerythrin fluorescence, the pigments of organic autotrophic particles emitted red and orange light. Fine particles were detected by flow cytometry (FCM) in the southern part of a eutrophic lake in winter. We found that organic autotrophic particles belonged to three populations, which represented only 15.89% of total fine particles. Organic non‐living particles and inorganic particles represented the greater part (84.11%) of total fine particles. This study also demonstrated that flow cytometry is well suited to the dynamic monitoring and analysis of natural water aquatic particles that were difficult to study with traditional methods. Copyright © 2005 John Wiley & Sons, Ltd.
Proton relaxation in aqueous DNA solutions
Authors: Sprinz Helmut , Döllstädt Rosemarie , Hübner Gerhard 
Published: May 2005

AbstractBy use of D2O we found that the shortening of the longitudinal proton relaxation time which occurs in the investigated aqueous yeast DNA solutions (≦ 2.4% with 2% protein) was not based on a hydration effect, but was caused by magnetic impurities only. An estimate shows that the mobility of the hydrated water molecules is reduced by less than two orders of magnitude in comparison with the free water molecules.
Kinetics of denaturation of DNA
Authors: Massie Harold R. , Zimm Bruno H. 
Published: May 2005

AbstractThe kinetics of denaturation of DNA have been studied by relaxation techniques. Examination of the terminal relaxation times for a variety of DNA's under a variety of conditions has shown that DNA denaturation is principally a hydrodynamically limited process. Measurements within the helix–coil transition have demonstrated that the experimentally measured terminal relaxation times are a function of the following: (1) position in the helix–coil transition; (2) ionic strength of the solvent; (3) solvent viscosity; (4) DNA concentration; (5) molecular weight; (6) number and position of single‐strand breaks. The dependence of the terminal relaxation time on the above mentioned factors can be attributed to hydrodynamic effects. Thus a hydrodynamic model for DNA unwinding is required. The model which best fits the data involves the assumption of a rotational frictional coefficient independent of molecular weight. This assumption is suggested by the fact that the relaxation time is proportional to the first power of the molecular weight.
Counterion binding in partially neutralized poly(D‐glutamic acid) and poly(DL‐glutamic acid)
Authors: Sugai Shintaro , Nitta Katsutoshi 
Published: May 2005

AbstractSodium counterion association with partially neutralized poly(D‐glutamic acid) or poly(DL‐glutamic acid) was measured by use of Wall's transference method with radioactive sodium. In the region where both polyacids are in completely random coil form, fractions of association were considerably less than that with poly(acrylic acid) in the same region of degree of neutralization. Even in the region where poly (D‐glutamic acid) is in the helical form, the fraction of association was less than that with poly(acrylic acid) in the same region. No pronounced characteristics attributable to counterion association corresponding to the helix–coil transition could be found. The association phenomena were discussed on the basis of a rodlike model of polyelectrolyte.
Flow birefringence and intrinsic viscosity of a T2 bacteriophage DNA–methylated bovine serum albumin complex
Authors: Harrington Rodney E. , Martin Kathleen V. 
Published: May 2005

AbstractThe flow birefringence, extinction angles, and intrinsic viscosity have been determined at low velocity gradients for a complex of T2 bacteriophage DNA and methylated serum albumin prepared in dilute solution to a stoichiometry of approximately 90 proteins per DNA molecule. Comparative data upon equivalent solutions of pure uncomplexed T2 DNA are also presented, and these data are completely in accord with the results of previous study. The experimental data are interpreted in terms of current dynamical theory and indicate that the complex has an essentially linear chain structure, consisting of approximately two DNA molecules, which is hydrodynamically indistinguishable from the pure DNA and that extensive internal or intramolecular binding in the complex does not occur. Although interpretation of the results is hampered by an apparent moderate degree of polydispersity in the complex preparations and by relatively large shear extrapolations, the data for both DNA and the complex are substantially in accord with dynamical theory for a nondraining bead subchain model having high kinetic segmental rigidity.
Single crystals of poly(L‐glutamic acid)
Authors: Keith H. D. , Giannoni G. , Padden F. J. 
Published: May 2005

AbstractLamellar single crystals of alkaline earth salts of poly(L‐glutamic acid) have been grown by precipitation from dilute aqueous solution and studied by optical and electron microscopy and by x‐ray and electron diffraction. The calcium, strontium and barium salts were crystallized in the β form above room temperature and could be converted to crystals of β‐poly(L‐glutamic acid) by washing in dilute hydrochloric acid. The magnesium salt, on the other hand, was crystallized in the α form at or below room temperature but could not be converted into crystals of α‐poly(L‐glutamic acid) by washing in hydrochloric acid. The crystalline lamellae are very thin (thicknesses range from 25 to 60 Å in β crystals and are about 100 Å in α crystals) and the polypeptide chains are oriented normal to the planes of the lamellae. It is clear from the disparity between crystal thickness and molecular length that the molecules crystallize by folding at the upper and lower surfaces of the crystals. Conformations of the molecules at these folds are discussed briefly.
Single crystals of poly‐L‐lysine
Authors: Padden F. J. , Keith H. D. , Giannoni G. 
Published: May 2005

AbstractCrystals of poly‐L‐lysine have been grown from aqueous solution in the presence of divalent anions. The most stable of these incorporate the HPO ion and are precipitated by the addition of sodium monohydrogen phosphate to solutions of poly‐L‐lysine HBr. Precipitation at or slightly above room temperature gives rise to single crystals of α‐poly‐L‐lysine HPO4 in the form of hexagonal lamellae about 150 Å thick. The axes of the helical polypeptide molecules are oriented normal to the planes of the lamellae, and since molecular length is about 1100 Å in the α‐helical conformation, these helices must be folded. The a parameter of the hexagonal unit cell is 19.55 Å for crystals immersed in mother liquor, and the lysine side chains are almost fully extended. Precipitation brought about by heating the same solutions to about 75°C produces micro‐crystals of β‐poly‐L‐lysine HPO4. A mode of packing of the anions in these crystals is proposed tentatively on the basis of an intersheet spacing determined from x‐ray powder diffraction patterns. In general, α crystals are transformed to β structures on drying; conditions under which the transition can either be forestalled or reversed are discussed.
Infrared spectrum of a DNA–RNA hybrid
Authors: Higuchi Shigesada , Tsuboi Masamichi , Iitaka Yoichi 
Published: May 2005

AbstractThe infrared absorption spectrum in the 4000–400 cm− region of an oriented film of a DNA–RNA hybrid in its undeuterated and deuterated states was observed with the polarized radiation. Most of the stronger bands found in the double‐helical DNA's and double‐helical RNA's are identified in the spectrum of the hybrid. The absorption band at 1225 cm−1 shows a perpendicular dichroism and that at 1085 cm−1 shows almost no dichroism. These facts indicate that the orientation of the group with respect to the helix axis in the hybrid structure is not entirely the same as that in the double‐helical Na DNA at, 75% RH., although the x‐ray diffraction pattern of the hybrid is quite similar to that of the DNA A form. The PO2− orientation is not the same as that in the double‐helical RNA either. The observed dichroism is explained, however, by considering that the PO2− group in the RNA moiety takes nearly the same orientation as that in the double‐helical RNA, and the PO2− group in the DNA moiety takes nearly the same as that in the double‐helical DNA.
Polymerization of amino acid derivatives by polymer catalysts. I. Polymerization by poly‐2‐vinylpyridine
Authors: Suzuoki Kazuhiro , Imanishi Yukio , Higa‐Shimura Toshinobu , Okamura Seizo 
Published: May 2005

AbstractPolymerizations of D,L‐β‐phenylalanine, p‐nitro‐D,L‐β‐ phenylalanine, and o,p‐dinitro‐D,L‐β‐phenylalanine NCA's were carried out with the use of α‐picoline or poly‐2‐vinyl‐pyridine as initiator. Polymerizations induced by the polymer catalyst were always faster than those with α‐picoline in the same base concentrations. Furthermore, the polymer effect was more marked when the number of nitro groups in the NCA's increased. It was considered that the polymer catalyst interacts with the NCA's primarily by hydrogen bonding and increases the effective concentration of NCA along the chain. The increase of the NCA concentration in the vicinity of the polymer catalyst wits also achieved through charge‐transfer complexes between nitrophenyl groups in the NCA's and pyridine groups in the polymer catalyst. As the polymer chain is flexible, a collision between an adsorbed NCA and a pyridine unit in the same polymer chain is favored, thus increasing the polymerization rate.
Dielectric properties of hemoglobin and myoglobin. I. Influence of solvent and particle size on the dielectric dispersion
Authors: Schlecht P. , Mayer A. , Hettner G. , Vogel H. 
Published: May 2005

AbstractDielectric dispersion measurements with aqueous solutions of hemoglobin and myoglobin have been performed in the frequency range from 100 kcps to 15 Mcps. The influence of preparation, particle size, and solvent conditions was studied. The results are analyzed in terms of an orientational polarization mechanism.
Sedimentation, diffusion, and osmotic pressure of sodium DNA in salt‐free solution
Authors: Auer Henry E. , Alexandrowicz Z. 
Published: May 2005

AbstractThe osmotic, sedimentation, and diffusion coefficients of sonicated sodium DNA in aqueous solutions which were rendered rigorously free of salts have been obtained in order to study the polyelectrolyte effect on these parameters. Both native and heat denatured DNA's were studied. All three parameters were found to be independent of concentration between 2 and 10 mmole/1. The osmotic coefficient gives the fraction of counterions not immobilized by the polyelectrolyte potential, under conditions of equilibrium. The value (ca. 0.18) obtained for this fraction agrees very well with that predicted by a theory of rodlike polyelectrolytes. A simplified model that permits the computation of fractions of mobile ions from sedimentation and diffusion coefficients, when applied to the experimental data, showed that under these conditions of flow between 0.5 to 0.9 of counterions are not immobilized. The experimental data also showed that for native DNA the translation frictional coefficient seems to have different values in sedimentation and diffusion, which agrees with a finding reported for another saltfree polyelectrolyte. For denatured DNA, however, the values were found to be equal: no satisfactory explanation could be found for this difference of behavior.
Raman spectra of polyglycines
Authors: Smith M. , Walton A. G. , Koenig J. L. 
Published: May 2005

AbstractThe laser‐excited Raman spectrum of helical polyglycine II has been obtained. Oligomers of polyglycine are in the planar zigzag conformation and their Raman spectra are indicative of the spectrum of polyglycine I. The Raman spectra of polyglycines have bands complementary to the infrared which are sensitive to the conformation of the chain. The spectra of the oligomers have bands sensitive to the length of the polyglycine. The Raman spectra of di‐ and triglycine in aqueous solution suggest the conformation is neither planar nor helical.
Etude, par spectroscopie infra‐rouge, de la conformation de quelques composés peptidiques modèles
Authors: Avignon M. , Huong P. V. , Lascombe J. , Marraud M. , Neel J. 
Published: May 2005

AbstractSome experimental data are given on the infrared spectra between 3300 and 3500 cm−1 of dilute solutions in carbon tetrachloride of three types of model compounds: CH3−CONH‐CH(R1)‐CONH(R2), (I); CH3‐CON(CH3)‐CH(R1)‐CONH(R2), (II) and CH3‐CONH‐CH(R1)‐CON(R2)2, (III). In studying the N‐H stretching bands, it was found that there are two types of intramolecular hydrogen bonds in these molecules; these result in two different cyclized conformations, C5 and C7, which contain respectively, five and seven atoms in the ring. By using model substances I, II, and III, in which the nitrogen atoms are unequally substituted, it is possible to identify the N‐H stretching bands which are to be ascribed to the N‐H oscillators included in the two different chelated conformations. It is found also that the stretching frequency of a free N‐H oscillator depends upon the substituent on the nitrogen atom. Thus, it is possible to observe, with some of the model compounds I, four different absorption bands located at 3340, 3420, 3440, and 3460 cm−1. The first two are ascribed to the N‐H oscillators included in the Hbonds which lock the C7 and C5 conformations; the last two correspond to free N‐H which differ with the substituent on the nitrogen atom.
Low‐frequency infrared bands and chain conformations of polypeptides
Authors: Masuda Yukio , Fukushima Kunio , Fujii Toyoko , Miyazawa Tatsuo 
Published: May 2005

AbstractInfrared spectra of polypeptides were measured in the region of 1800–400 cm−1. For the α‐helical form, disordered form, and antiparallel‐chain β‐form, amide V band‐ arising from N‐H out‐of‐plane bending models were observed at 610–620, around 650, and 700–705 cm−1, respectively, and amide V′ bands arising from N‐D out‐of‐plane bending modes were observed at 455–465, around 510, and a 515–530 cm−1, respectively. These correlations are useful for conformation diagnoses, particularly for copolyamino‐acids or proteins which are not oriented. The nature of low‐frequency amide bands are discussed with reference to potential energy distributions calculated for the α‐helical form and β form.