α-Picolinic acid and quinaldinic acid in the separation and volumetric determination of palladium

Analytical and Bioanalytical Chemistry - Palladium can be determined volumetrically after separation with α-picolinic or quinaldinic acid by dissolving the complex in an excess of standard...     

Synthesis and antitumor activity of derivatives of 23-hydroxybetulinic acid

A series of natural product 23-hydroxybetulinic acid derivatives were prepared.In the preparation of mono-O-benzoyl ester derivative,it was observed that benzoyl group migrated from 3-O-to 23-O-position during the detritylation.     

Polarity and structure of α-nitrocinnamic acid esters

Polarity and structure of ethyl α-nitrocinnamates have been studied by means of dipole moments method and quantum-chemical calculations. These compounds exist in the form of Z-isomers in solution, that is, nitro group and benzene ring are cis-positioned.     

Quantum DFT and DF–DFT study of vibrational spectra of sulfuric acid,sulfuric acid monohydrate,formic acid and its cyclic dimer

Rigorous theoretical treatment of vibrational frequencies is critically important for the interpretation of unassigned experimental vibrational spectra and accurate determination of thermodynamic properties of molecular clusters. IR spectra of trans monomers of sulfuric and acetic acids, sulfuric acid monohydrate and cyclic dimer of the formic acid have been studied using DFT and DF–DFT methods using BLYP, B3LYP and PW91 with 12 different Pople and Dunning basis sets. New data for above-mentioned structures have been reported, scaling factors have been calculated and a comprehensive analysis of the performance of BLYP, B3LYP and PW91 methods has been performed. Comparison of the obtained results with experiments shows that results of pure PW91 and BLYP are better than predictions of well-established hybrid B3LYP method. Our analysis shows on the existence of the considerable difference in scaling factors weighted to high and low frequencies. In the case of formic acid dimer, the deviation the predicted low frequencies from the experimental data is considerable that leads to quite large (∼6–7 kcal mol⁻¹) uncertainties in the absolute values of the cluster Gibbs free energy. In order to determine an efficient computational strategy that comprises accuracy and reasonable computational costs, the effect of density fitting (DF) and basis set superposition error (BSSE) on the vibration frequencies has been investigated. We found that application of the DF that substantially (2.5–3.5 times) increases the performance of pure PW91 and BLYP methods gives excellent results, which are very close to those of conventional DFT. This suggests that DF–DFT is a viable low-cost alternative to conventional DFT in predicting vibrational spectra. It has been found that while vibrational spectra obtained using the counterpoise correction (CP) for the BSSE do not deviate much from uncorrected ones, the difference in absorption intensities between corrected and uncorrected spectra obtained using small and medium-sized basis sets is considerable. This suggests that application of DF–DFT uncorrected for the BSSE with large basis sets is a more efficient strategy of predicting vibrational spectra than the application of conventional DFT with small basis sets.     

Synthesis and properties of fibers prepared from lactic acid–glycolic acid copolymer

A method for preparing laboratory samples of fibers from glycolide-co-D,L-lactide to produce bioresorbing suture filaments with a controlled complex of properties is developed. The morphology of fibers obtained through melt spinning is studied. The peculiarities of the mechanical properties of fibers are investigated.     

Formation of hyaluronic acid–ellagic acid microfiber hybrid hydrogels and their applications

Microfiber assemblies prepared from ellagic acid (EA) were functionalized with histidine (His) and dispersed in hyaluronic acid (HA) hydrogel microstructures. Swelling studies indicated that the hybrids had a relatively lower water uptake compared to HA and was pH dependent. The percentage swelling ratio for EA–His–HA hybrids was 48 % when 0.04 mg/mL of HA was incorporated and increased to 70 % when 1.2 mg/mL HA was integrated. Release studies using the dye crystal violet (CV) as a model drug showed that the rates were concentration-dependent. Further the hybrids were found to be thermally stable compared to HA. Cellular toxicity assays performed with normal rat kidney (NRK) cells indicated biocompatibility and adherence of the hybrids to the cells. Thus, we have developed a new family of hybrid hydrogels which readily formed on the EA–His functionalized microfibers and may have potential applications in drug delivery or tissue regeneration applications.     

Kinetic and mechanism of reactions of L-α-Glutamic acid and L-Glutamine with pyridoxal

The kinetics and mechanisms of condensation of pyridoxal with L-α-glutamic acid and L-glutamine were studied by UV spectroscopy and polarimetry. L-α-Glutamic acid reacts with pyridoxal to form a Schiff base whose subsequent hydrolysis gives rise to pyridoxamine and α-ketoglutaric acid. The reaction of Lglutamine with pyridoxal involves the Γ-NH₂ group and affords a Schiff base whose subsequent hydrolysis gives rise to pyridoxamine and L-α-glutamic acid.     

Thermodynamics of mixture of boric acid with lithium borate and chloride

The first thermodynamic dissociation constants of boric acid in aqueous solution of lithium chloride with borate at five different temperatures from 278.15 to 318.15 K were evaluated from emf values of the cell without liquid junction potential with the improved extrapolation and polynomial approximation on the basis of Pitzer's theory. Values obtained from both methods are in good agreement with each other. Pitzer's parameters β(0) and β(1) of LiB(OH)4 and other thermodynamic quantities of dissociation process of boric acid are obtained. Results have been discussed.     

Preparation and antibacterial activity of aromatic derivatives of β-aminopropionic and γ-aminobutyric acid

Ten aromatic derivatives of β-aminopropionic acid and γ-aminobutyric acid were prepared.Their compositions and structures were identified by elemental analysis,IR,and 1H NMR.They have been examined for their antibacterial action against Staphylococcua aurens and Escherichia coli.These compounds showed higher activity than the aromatic derivatives of ct-amino acid which were reported previously.The general conclusion to be drawn is that the distance between amino and carboxylic group in these molecules could affect their antibacterial activity.Furthermore,those compounds with p-methyl substituent in phenyl ring exhibit higher activity than the others,and all the compounds exhibit higher activity against Escherichia coli and against Staphylococcua aureus.     

Visual chiral recognition of mandelic acid and α-amino acid derivatives by enantioselective gel formation and precipitation

Novel chiral receptors based on l-phenylalanine and l-valine have been synthesized and their chiral recognition properties toward mandelic acid and N-tosyl α-amino acids are studied. The phenylalanine-based receptor undergoes enantioselective gel formation with R-mandelic acid and N-tosyl-d-valine, whereas the valine-linked receptor in their presence results in the formation of precipitates.     

Inclusion complex of α-lipoic acid and modified cyclodextrins

The solubility of α-lipoic acid (LA) with the addition of modified cyclodextrins was investigated using the solubility method. The solubility of LA in the presence of β-cyclodextrin (β-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD), mono-6-O-glucopyranosyl-β-cyclodextrin (mono-G₁-β-CD), methyl-β-cyclodextrin (Me-β-CD), 2,6-di-O-methyl-β-cyclodextrin (DM-β-CD), and sulfobutylether-β-cyclodextrin (SBE-β-CD) was higher than that of LA itself. In particular, the solubility of LA in the presence of SBE-β-CD was 20 times higher than that of LA alone. The structure of the inclusion complex of SBE-β-CD and LA in aqueous solution was examined by ¹H-¹H ROESY NMR spectroscopy. The 1,2-dithiolane moiety of LA was included from the secondary hydroxyl face of SBE-β-CD. The solid complexes of LA and SBE-β-CD were prepared by the kneading and freeze-drying methods. Formation of the solid complexes was confirmed by X-ray diffraction patterns (XRD), differential scanning calorimetry (DSC), and infrared spectroscopy (IR). The kneading and freeze-drying methods were successful for obtaining the solid inclusion complexes with improved thermal stability.     

Structure and kinetics of lipid–nucleic acid complexes

The structure and function of lipid-based complexes (lipoplexes) have been widely investigated as cellular delivery vehicles for nucleic acids—DNA and siRNA. Transfection efficiency in applications such as gene therapy and gene silencing has been clearly linked to the local, nano-scale organization of the nucleic acid in the vehicle, as well as to the global properties (e.g. size) of the carriers. This review focuses on both the structure of DNA and siRNA complexes with cationic lipids, and the kinetics of structure evolution during complex formation.     

The synthesis of (−)-cis- and (−)-trans-crobarbatic acid

The synthesis of both cis- and trans-crobarbatic acid is reported. The five-step sequence proceeds in high yield and with control of both relative and absolute stereochemistry. The key step in the synthesis is the Birch reductive alkylation of a chiral furoic acid which sets the absolute stereochemistry of the products. The stereochemistry of the compounds described was proven unambiguously by X-ray crystallography on one synthetic intermediate and on trans-crobarbatic acid.     

Deracemization of unnatural amino acid: homoalanine using D-amino acid oxidase and ω-transaminase

A deracemization method was developed to generate optically pure L-homoalanine from racemic homoalanine using D-amino acid oxidase and ω-transaminase. A whole cell reaction using a biphasic system converted 500 mM racemic homoalanine to 485 mM L-homoalanine (>99% ee).     

Synthesis and characterization of novel β-amino acid derivatives

In the work discussed in this paper, novel β-amino acid derivatives were prepared by Michael addition between 3-substituted-2-propenic acid and hydrazine hydrate. The optimum reaction conditions were determined by analyzing the effects of the ratio of the starting materials, temperature, and reaction time. The conclusions were: reaction temperature 80 °C, reaction time 8 h, n (3-substituted-2-propenic acid)/n (hydrazine hydrate) = 1:15. Products were characterized by measurement of melting point, elemental analysis, and IR and ¹H NMR spectroscopy.     

Kinetics of thermal decomposition of γ-irradiated and unirradiated complexes of mandelhydroxamic acid

The thermal decomposition of -irradiated and unirradiated complexes of mandel-hydroxamic acid (HMA), Co(HMA)₂.1/2H₂O, Mn(HMA)₂.2H₂O, Ba(HMA)₂.2H₂O and Cd(HMA)₂.2H₂O have been studied thermogravimetrically (under isothermal conditions). The thermal dehydration of each complex occurred in one step, while the decomposition of dehydrated complexes occurred in two steps. The kinetic parameters for dehydration were computed by different models. The thermal dehydration is regulated by random nucleation A₃ for Co-, Mn-, and Cd-complexes and by phase-boundary (R₃) for Ba-complex. The effect of -irradiation on the kinetic parameters of thermal decomposition is discussed. Radiation did not modify the mechanism of the reaction but accelarated the dehydration steps in the case of Mn- and Co-complexes.     

Synthesis of new β- and γ-benzyloxy-S-glutamic acid derivatives and evaluation of their activity as inhibitors of excitatory amino acid transporters

An efficient stereoselective preparation of the two enantiomerically pure diasteroisomers of γ-benzyloxy-S-glutamic acid was performed using trans-4-hydroxy-l-proline as a source of chirality, while the erythro and threo isomers of β-benzyloxy-S-glutamic acid were prepared starting from (R)-Garner's aldehyde. All new derivatives were tested for their inhibitory activity against excitatory amino acid transporters in a rat synaptosomal preparation and their IC₅₀ values were compared to that of TBOA, a one carbon lower homologue commonly used as the reference blocker of glutamate transporters.     

Phase equilibria of supercritical CO_2-ethanol-stearic acid ternary system and hydrogen bonding between ethanol and stearic acid

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