Temperature- and pressure-responsive properties of <Emphasis Type="SmallCaps">l</Emphasis>- and<Emphasis Type="SmallCaps"> dl</Emphasis>-forms of poly(<Emphasis Type="Italic">N</Emphasis>-(1-hydroxymethyl)propylmethacrylamide) in aqueous solutions

The structural transition of the l- and dl forms of poly(N-(1- hydroxymethyl)propylmethacrylamide (PHMPMA) in aqueous solution was studied by measuring the pressure dependence of the apparent scattering intensity, differential scanning calorimetry (DSC), and circular dichroism (CD). The thermodynamic implications of the results are discussed in relation to the chiral structure of the side chain, and differences in the thermal and barometric transitions. T-P diagrams of the transition showed characteristic ellipsoid features. Antagonism of the temperature and pressure effects was observed only for P(dl-HMPMA). For P(l-HMPMA), the transition temperature (T _tr) decreased with increasing pressure, and the highest T _tr was observed at atmospheric pressure (0.1 MPa). For both polymers, the highest P _trs were observed at the lowest temperatures. The l polymer showed a specific negative peak in its CD spectrum at around 220 nm in the lower temperature region and the temperature dependence was reproduced by a single-step transition, with the midpoint corresponding to the T _tr obtained from the scattering measurements. Coupled with the results from the DSC, the different behavior between the P(l-HMPMA) and P(dl-HMPMA) could be explained in terms of the chain states before and after the transition. The cooperative factors derived from the DSC measurement revealed that about 4 to 5 polymers of the present size were necessary to perform a thermal transition for P(l-HMPMA), and that P(dl-HMPMA) underwent its transition as an almost single molecular event.This revised version was published online in June 2005 with correction to the article category.     

QM/MM study on catalytic mechanism of aspartate racemase from <Emphasis Type="Italic">Pyrococcus horikoshii</Emphasis> OT3

The enzyme aspartate racemase from Pyrococcus horikoshii OT3 catalyzes the interconversion between l- and d-Asp. In this work, we employed the hybrid QM/MM approach with the self-consistent charge-density functional tight binding (SCC-DFTB) model to study the catalytic mechanism for the conversion of l-Asp into d-Asp. The molecular dynamics simulation showed that the substrate l-Asp forms an extensive network of interactions with the active-site residues of the aspartate racemase through its side chain carboxylate, ammonium group, and α-carboxylate. The potential of mean force calculations confirmed that the racemization reaction involves two proton transfers (from the α-carbon to Cys194 and from Cys82 to the α-carbon), which occurs in a concerted way, although highly asynchronous. The calculated free energy of activation is 17.5 kcal/mol, which is consistent with the reaction rate measured from experiment. An electrostatic interaction analysis was performed to estimate the key role played by individual residues in stabilizing the transition state. The docking study on the binding of l-Asp and d-Asp to aspartate racemase indicates that this enzyme employs a “two-base” mechanism not a “one-base” mechanism.     

Complexation of Cu(II) with <Emphasis Type="SmallCaps">L</Emphasis>- and <Emphasis Type="SmallCaps">DL</Emphasis>-threonine: An ESR study

Complexation of Cu(II) ions with L- and DL-threonine in aqueous solution was studied. Treatment of the ESR spectra of solutions containing Cu(II) and threonine in various ratios and having various pH, involving total line shape analysis, revealed formation of geometric isomers of the complex ions [Cu(thrH_–1)₂]^2– differing in the mutual arrangement of the N and O atoms in the equatorial plane; the complexation and isomerization equilibrium constants were determined.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 8, 2004, pp. 1388–1391.Original Russian Text Copyright © 2004 by Statsenko, Bolotin, Panyushkin.This revised version was published online in April 2005 with a corrected cover date.     

A kinetic study of the oxidation of <Emphasis Type="SmallCaps">l</Emphasis>-methionine by water soluble colloidal MnO<Subscript>2</Subscript>

Aqueous solution of water soluble colloidal MnO₂ was prepared by Perez-Benito method. Kinetics of l-methionine oxidation by colloidal MnO₂ in perchloric acid (0.93 × 10⁻⁴ to 3.72 × 10⁻⁴ mol dm⁻³) has been studied spectrophotometrically. The reaction follows first-order kinetics with respect to [H⁺]. The first-order kinetics with respect to l-methionine at low concentration shifts to zero order at higher concentration. The effects of [Mn(II)] and [F⁻] on the reaction rate were also determined. Manganese (II) has sigmoidal effect on the rate reaction and act as auto catalyst. The exact dependence on [Mn(II)] cannot be explained due to its oxidation by colloidal MnO₂. Methionine sulfoxide was formed as the oxidation product of l-methionine. Ammonia and carbon dioxide have not been identified as the reaction products. The mechanism with the observed kinetics has been proposed and discussed.     

Non-isothermal dehydration and decomposition of <Emphasis Type="Italic">dl</Emphasis>-lactates of transition metals and alkaline earth metals

A comparative study of the non-isothermal decomposition of the dl-lactate hydrates of magnesium, calcium and strontium has been made with that of the dl-lactate hydrates chromium(III), manganese(II), iron(II), cobalt(II), nickel(II), copper(II) and zinc(II) keeping dry air as the purge gas and the heating rate maintained at 10 K min^-1. While the dl-lactates of manganese(II), cobalt(II) and copper(II) followed single step decomposition scheme suggesting that dehydration and decomposition steps overlapped, the dehydration steps of the other compounds were distinct. &agr;-T plots of none of the dehydration steps showed any induction period, indicating no physical desorption, nucleation or branching. Neither the &agr; _max-values nor the onset temperatures of the dehydration steps did show any pattern. The TG data of the dehydration steps have also been analyzed using the Freeman-Carroll, Horowitz-Metzger, Coats-Redfern, Zsak&oacute;, Fuoss-Salyer-Wilson and Karkhanavala-Dharwadkar methods. Values of order of reaction, activation energy and Arrhenius factor have been approximated and compared. There are similarities in the activation energy values for the dehydration steps (&lt; 60 kJ mol^-1 in general). It is higher with group 2 metals and lower in transition metals (maximum in magnesium and lowest in chromium and iron lactates). In cases of overlapping of dehydration and decomposition steps, the activation energy values are on the lower side with the same trend (lower in cobalt and copper cases).     

<Emphasis Type="SmallCaps">d</Emphasis>-Amino Acids in Animal Peptides

Summary. Secreted peptides from diverse sources have been found to contain a d-amino acid. From the sequence of cloned mRNAs coding for the precursors of such peptides it could be deduced that in all cases tested so far the d-amino acid in the final product is derived from the corresponding l-amino acid present in the primary product of translation. Enzymes catalyzing such an l- to d-isomerization in peptide linkage have been isolated from the venom of a spider and the skin secretions of frogs. Even though these are completely different proteins, the reaction mechanism is the same, namely a de-protonation/re-protonation of the α-carbon of an amino acid with concomitant inversion of the chirality. Sequences potentially coding for homologues of the frog enzyme are present in the genome of different vertebrate species.     

Synthesis of <Emphasis Type="Italic">N</Emphasis><Superscript>2</Superscript>-Arylisocytidines and <Emphasis Type="Italic">N</Emphasis><Superscript>2</Superscript>-Aryl-2′-deoxyisocytidines

Summary. 2-(Arylamino)pyrimidin-4-ones were synthesized, silylated, and condensed with l,2,3,5-tetra-O-acetyl-β- d-ribofuranoside to afford the corresponding N ²-aryl protected isocytidines. Deprotection of the acetylated isocytidines using saturated NH₃ in MeOH solution gave 1-(β-d-ribofuranosyl)-2-(arylamino)-4-pyrimidinones. Methyl 2-deoxy-3,5-di-O-toluyl-α/β-d-ribofuranoside was prepared and condensed with the previously silylated bases to afford the anomeric mixture of protected nucleosides. The pure β-anomers were synthesized with better yield by treating the sodium salts of N ²-arylisocytosine derivatives with 2-deoxy-3,5-di-O-toluyl-α-d-ribofuranosyl chloride. Deprotection of the latter anomers afforded the corresponding free hydroxyl derivatives. The synthesized free nucleosides are under antiviral and oligonucleotide investigations.     

Structural and spectroscopic analysis of dipeptide <Emphasis Type="SmallCaps">l</Emphasis>-methionyl-glycine and its hydrochloride

Dipeptide l-methionyl-glycine (Met-Gly) hydrochloride was characterized structurally by means of solid-state linear polarized IR (IR-LD) spectroscopy of oriented samples as colloidal suspension in nematic liquid crystal. Quantum chemical ab initio calculations and vibrational analysis support the experimental data. ¹H and ¹³C nuclear magnetic resonance (NMR) data, mass spectrometry (ESI-MS and FAB-MS) techniques, thermogravimetry (TGV), and differential scanning calorimetry (DSC) method were employed as well. The experimental and theoretical data of hydrochloride salt were compared with analogous data of the neutral dipeptide with the aim to explain the role of intermolecular hydrogen bonding on the conformational behavior and spectroscopic properties of the compound studied.     

Detection of additional impurities in the UV-chromatogram of <Emphasis Type="SmallCaps">l</Emphasis>-[<Emphasis Type="Italic">S</Emphasis>-methyl-<Superscript>11</Superscript>C]methionine

Samples of l-[S-methyl-¹¹C]methionine prepared by on-column [¹¹C]methylation on a C18 cartridge were analyzed by HPLC under different conditions in order to explain some anomalies observed in the UV-chromatograms. By so doing, two new unlabelled impurities were found and identified as iodide and homocystine. Their amounts are still compatible with the safe human use of the radiotracer solution. Nevertheless, if needed, iodide can be totally removed by elution through an anion-exchange resin, while homocystine can be reduced by either decreasing the amount of precursor used in the synthesis or preventing its air oxidation.     

Bioconversion of <Emphasis Type="SmallCaps">d</Emphasis>-glucose into <Emphasis Type="SmallCaps">d</Emphasis>-glucosone by Glucose 2-oxidase from <Emphasis Type="Italic">Coriolus versicolor</Emphasis> at Moderate Pressures

Glucose 2-oxidase (pyranose oxidase, pyranose:oxygen-2-oxidoreductase, EC 1.1.3.10) from Coriolus versicolor catalyses the oxidation of d-glucose at carbon 2 in the presence of molecular O₂ producing d-glucosone (2-keto-glucose and d-arabino-2-hexosulose) and H₂O₂. It was used to convert d-glucose into d-glucosone at moderate pressures (i.e. up to 150 bar) with compressed air in a modified commercial batch reactor. Several parameters affecting biocatalysis at moderate pressures were investigated as follows: pressure, [enzyme], [glucose], pH, temperature, nature of fluid and the presence of catalase. Glucose 2-oxidase was purified by immobilized metal affinity chromatography on epoxy-activated Sepharose 6B-IDA-Cu(II) column at pH 6.0. The rate of bioconversion of d-glucose increased with the pressure since an increase in the pressure with compressed air resulted in higher rates of conversion. On the other hand, the presence of catalase increased the rate of reaction which strongly suggests that H₂O₂ acted as inhibitor for this reaction. The rate of bioconversion of d-glucose by glucose 2-oxidase in the presence of either nitrogen or supercritical CO₂ at 110 bar was very low compared with the use of compressed air at the same pressure. The optimum temperature (55°C) and pH (5.0) of d-glucose bioconversion as well as kinetic parameters for this enzyme were determined under moderate pressure. The activation energy (E _a) was 32.08 kJ mol⁻¹ and kinetic parameters (V _max, K _m, K _cat and K _cat/K _m) for this bioconversion were 8.8 U mg⁻¹ protein, 2.95 mM, 30.81 s⁻¹ and 10,444.06 s⁻¹ M⁻¹, respectively. The biomass of C. versicolor as well as the cell-free extract containing glucose 2-oxidase activity were also useful for bioconversion of d-glucose at moderate pressures. The enzyme was apparently stable at moderate pressures since such pressures did not affect significantly the enzyme activity.     

Synthesis of LiCoO<Subscript>2</Subscript> by <Emphasis Type="SmallCaps">l</Emphasis>-apple acid assisted sol–gel method and its electrochemical behavior in aqueous lithium-ion battery

The synthesis process of LiCoO₂ prepared by l-apple acid (l-HOOCCH(OH)CH₂COOH) assisted sol–gel method is studied by using Fourier transforms infrared spectroscopy, mass spectroscopy, simultaneous thermogravimetric and differential thermal analysis, X-ray diffraction analysis, and elemental analysis. The results show that lithium and cobalt ions are trapped homogeneously on an atomic scale throughout the precursor. Lithium carbonate and Co₃O₄ are intermediate products during heat treatment of the precursor. Moreover, the kinetics for formation of LiCoO₂ by l-apple acid assisted sol–gel method is faster than the case of the conventional solid-state reaction between lithium carbonate and Co₃O₄. In comparison with the solid-state reaction, the sol–gel method significantly shortens the required reaction time for synthesizing LiCoO₂, and also reduces the particle size. In the electrochemical test, it is found that the specific discharge/charge capacities as well as the coulomb efficiency substantially increase with increasing the calcination temperature. It is considered that LiCoO₂ with a good-layered structure facilitates the insertion and de-insertion of lithium ions in aqueous electrolyte. As a result, the combination of the sol–gel method with proper calcination processes is highly successful in producing LiCoO₂ powders with large specific capacity and good cycle performance in aqueous lithium-ion battery.     

Production of <Emphasis Type="SmallCaps">d</Emphasis>-tagatose,a Functional Sweetener,Utilizing Alginate Immobilized <Emphasis Type="Italic">Lactobacillus fermentum</Emphasis> CGMCC2921 Cells

d-tagatose is a ketohexose that can be used as a novel functional sweetener in foods, beverages, and dietary supplements. This study was aimed at developing a high-yielding d-tagatose production process using alginate immobilized Lactobacillus fermentum CGMCC2921 cells. For the isomerization from d-galactose into d-tagatose, the immobilized cells showed optimum temperature and pH at 65 °C and 6.5, respectively. The alginate beads exhibited a good stability after glutaraldehyde treatment and retained 90% of the enzyme activity after eight cycles (192 h at 65 °C) of batch conversion. The addition of borate with a molar ratio of 1.0 to d-galactose led to a significant enhancement in the d-tagatose yield. Using commercial β-galactosidase and immobilized L. fermentum cells, d-tagatose was successfully obtained from lactose after a two-step biotransformation. The relatively high conversion rate and productivity from d-galactose to d-tagatose of 60% and 11.1 g l⁻¹ h⁻¹ were achieved in a packed-bed bioreactor. Moreover, lactobacilli have been approved as generally recognized as safe organisms, which makes this L. fermentum strain an attracting substitute for recombinant Escherichia coli cells among d-tagatose production progresses.     

Europium(<Emphasis Type="SmallCaps">iii</Emphasis>) phthalocyanine complexes with 8-oxyquinoline

Europium(iii) phthalocyanine complexes containing 8-oxyquinoline fragments were synthesized. The complexes were identified and structurally characterized by IR and UV-Vis absorption spectroscopy and mass spectrometry.     

Optical enzyme sensor for determining <Emphasis Type="SmallCaps">l</Emphasis>-lysine content using <Emphasis Type="SmallCaps">l</Emphasis>-lysine oxidase from the rockfish <Emphasis Type="BoldItalic">Sebastes schlegeli</Emphasis>

l-Lysine (l-Lys) in living bodies is critical for metabolism; therefore, determination of its levels in food is important. Most enzymatic methods for l-Lys analysis are performed using l-lysine oxidase (LyOx), but commercially manufactured LyOx is generally not highly selective for l-Lys among amino acids. We previously isolated LyOx as an antibacterial protein secreted from the skin of the rockfish Sebastes schlegeli. In the present study, we developed an optical enzyme sensor system for rapid and continuous determination of l-Lys using this LyOx. The system comprised an immobilized LyOx membrane, an optical oxygen probe, a flow system, and a personal computer. The amount of l-Lys was detected as a decrease in the oxygen concentration due to the LyOx reaction. The specificity of the sensor was examined against various amino acids. The sensor response was specific for l-Lys. Good reproducibility was obtained in 58 assays. The response of the sensor using commercially prepared LyOx was unstable compared with the response using LyOx isolated in our laboratory. Our sensor system could be used for 5 weeks without our having to change the enzyme membrane. The calibration curve for a standard l-Lys solution was linear from 0.1 to 3.0 mmol L⁻¹. One assay could be completed within 2 min. The sensor was applied to determine the l-Lys content in food samples such as bonito cooking water and scallop hepatopancreas. The values obtained using the sensor and conventional high-performance liquid chromatography methods were well correlated.     

Synthesis and characterization of some new cobalt(II) and nickel(II) ternary complexes of <Emphasis Type="Italic">N</Emphasis>-acetyl, <Emphasis Type="Italic">N</Emphasis>-benzoyl and <Emphasis Type="Italic">N</Emphasis>-tosyl derivatives of amino acids

A series of some new cobalt(II) and nickel(II) ternary complexes of N-(acetyl)phenylalaninate (acphe), N-(acetyl)tyrosinate (actyr), N-(benzoyl)leucinate (bzleu), N-(benzoyl)phenylalaninate (bzphe), N-(tosyl)glutamic acid (tsglu), N-(tosyl)arginine (tsarg) with certain N-heterocyclic ligands such as imidazole (imi), methylimidazole (mimi), 2,2′-bipyridyl (bipy) 1,10-phenanthroline (phen) have been synthesized and characterized by elemental analyses, IR and electronic spectra. as well as thermogravimetry. The structure of the cobalt(II) N-phthaloylglycinate complex was also characterized by X-ray single crystal. It was found that the cobalt atom coordinates a 1,10-phenanthroline molecule and four water oxygen atoms, forming a distorted octahedral conformation. A molecule of N-phthaloylglycinate is connected by van der Waals contact and H-bonds.     

Determination of serum <Emphasis Type="SmallCaps">d</Emphasis>-lactic and <Emphasis Type="SmallCaps">l</Emphasis>-lactic acids in normal subjects and diabetic patients by column-switching HPLC with pre-column fluorescence derivatization

d-Lactic and l-lactic acids were simultaneously determined by means of a column-switching high-performance liquid chromatography (HPLC) with fluorescence detection. As a fluorescence reagent, 4-nitro-7-piperazino-2,1,3-benzoxadiazole (NBD-PZ) was employed for the fluorescence derivatization of lactic acid. The proposed HPLC system adopted both octylsilica (Cadenza CD-C8) and amylose-based chiral columns (CHIRALPAK AD-RH), which proved to give a sufficient enantiomeric separation of the lactic acid derivatives with a separation factor () of 1.32 and a resolution (R_s) of 1.98. Moreover, the features of the first elution of d-lactic acid peak in the proposed HPLC were convenient for the determination of trace amount of serum d-lactic acid, which is known to increase under diabetes. Intra-day and inter-day accuracies were in the range of 90.5–101.2 and 89.0–100.7%, and the intra-day and inter-day precisions were 0.3–1.2 and 0.4–4.8%, respectively. The proposed method was applied to determine d-lactic and l-lactic acids in human serum of normal subjects and diabetic patients, showing that both d-lactic and l-lactic acid concentrations were significantly increased in the serum of diabetic patients (n=31) as compared with normal subjects (n=21). This fact was found for the first time owing to the development of the proposed HPLC method which is able to determine d-lactic and l-lactic acid simultaneously. Finally, serum d-lactic acid concentrations determined by the proposed HPLC method were compared with those from a reported enzymatic assay, and the smaller p value between normal subjects and diabetic patients was shown by the proposed HPLC method.     

<Emphasis Type="Italic">N</Emphasis>-Bromoacetyl-β-<Emphasis Type="SmallCaps">D</Emphasis>-glycopyranosylamines in the synthesis of glycoconjugates of nitrogen-containing physiologically active compounds

A series of nitrogen-containing physiologically active compounds underwent smooth N-monoalkylation with N-bromoacetyl-β-glycopyranosylamines derived from N-acetyl-D-glucosamine and lactose. This reaction was demonstrated to be promising for the introduction of carbohydrate residues into heterocyclic compounds, viz., pyridine, imidazole, pyrimidinetrione, carboline, and piperazine derivatives, and into an amino acid, 5-hydroxy-L-tryptophan, which is unstable in alkaline media. Dedicated to Academician N. K. Kochetkov on the occasion of his 90th birthday. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1256–1259, May, 2005.     

Metastable complexes of some <Emphasis Type="Italic">d</Emphasis>- and <Emphasis Type="Italic">f</Emphasis>-block metals with mesogenic cyanobiphenyls

Formation of metastable complexes with different metal to mesogenic ligand ratio (M/L = 1/2 and 1/1) has been shown by IR–, UV–Vis, ESR-spectroscopic techniques for low temperature co-condensation of some d- and f-block transition metals (Ag, Cu, Eu, Sm) and mesogenic derivatives of cyanobiphenyls. The Quantum chemistry calculations have been carried out to study equilibrium structures of complexes. Biligand complex models with one and two metal atoms and antiparallel disposition of two ligand molecules are considered. Relative spectral shifts and relative thermal stability of complexes are discussed.     

Mass spectrometric study of the overheated vapor over nickel(II), Copper(II), and Zinc(II) <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>′-Ethylenebis(salicylaldiminato) complexes

A mass spectrometric study of the overheated vapor over the nickel(II), copper(II), and zinc(II) N,N′-ethylenebis(salicylaldiminato) complexes between 300 and 865°C has been carried out. Throughout this temperature range, the overheated vapor over all of the complexes contains no ions heavier than the molecular ion [MO₂N₂C₁₆H₁₄]⁺. At ∼600°C, Cu(salen) and Zn(salen) interact with the structural material of the double-chamber two-temperature effusion cell (Kh18N10T steel). The complexes are thermally very stable. The fragmentation pattern of the chelates under electron-impact ionization is metal-dependent.     

Poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactide) networks with tailored water sorption

A poly(l-lactide) diol was obtained through ring opening polymerization of l-lactide, using 1,6 hexanediol and tin(II) 2 ethylhexanoate as a catalyst. In the second step, the poly(l-lactide) macromer (mLA) was obtained by the reaction of poly(l-lactide) diol with methacrylic anhydride. The effective incorporation of the polymerizable end groups was assessed by Fourier transform infrared spectroscopy and nuclear magnetic resonance (¹H NMR). Besides, poly(l-lactide) networks (pmLA) were prepared by photopolymerization of mLA. Further, the macromer was copolymerized with 2-hydroxyethyl acrylate seeking to tailor the hydrophilicity of the system. A set of hydrophilic copolymer networks were obtained. The phase microstructure of the new system and the network architecture was investigated by differential scanning calorimetry, infrared spectroscopy, dynamic mechanical spectroscopy, thermogravimetry, and water sorption studies.