Effect of temperature on partial molar volumes and viscosities of aqueous solutions of α-dl-Aminobutyric acid,dl-Norvaline and dl-Norleucine

In this work, we present experimental results for partial molar volumes and viscosities of aqueous solutions of α-dl-aminobutyric acid, dl-norvaline and dl-norleucine at 288.15, 293.15, 298.15 and 303.15?K. The thermodynamic behavior of aqueous amino acid solutions is compared with that reported for glycine and α-alanine in water and is discussed in terms of group additivity and electrostriction.

The temperature dependence of the infinite dilution partial molar volumes and the B viscosity coefficients are interpreted in terms of amino acid hydration. According to the usual hydrophobicity criteria, the amino acids considered do not have a hydrophobic character and their behavior is dominated by the polar groups.     

Formation constants and coordination thermodynamics for binary complexes of Cu(II) and some α-amino acids in aqueous solution

In this study, the formation constants of 1?:?1 binary complexes of Cu(II) with L-glutamic acid, L-aspartic acid, glycine, L-alanine, L-valine, and L-leucine and 1?:?2 binary complexes of L-glutamic acid, glycine and the protonation macro- and microconstants of all these amino acids were determined potentiometrically in aqueous solutions at 5.0, 20.0, and 35.0°C at a constant ionic strength of I?=?0.10?mol?L^?1 (NaClO₄). The thermodynamic parameters ΔG _f°, ΔH _f°, and ΔS _f° were determined for the protonation of all amino acids used in this study and for the complex formation reactions of them with Cu(II). The results were analysed by means of Principle of hard and soft [Lewis] acids and bases. Additionally, in order to confirm the complex formation and determine the stability constants of complexes, UV-Vis spectroscopic studies were carried out. The stability constants obtained by spectrophotometrically are confirmed by those determined potentiometrically.     

Synthesis,characterization and crystal structures of two binary acid complexes based on L-glutamate and L-aspartate

Two amino acid complexes, [Cd(L-glu)(H₂O)] _n ?·?nH₂O (1) and [Co(L-asp)(phen)(N₃)]?·?2H₂O (2) (L-glu?=?L-glutamate, L-asp?=?L-aspartate, phen?=?1,10-phenanthroline), have been synthesized and characterized by elemental analyses, IR spectra and TG-DSC analysis. Single crystal X-ray structure analyses revealed that each L-glutamate acts as a pentadentate ligand binding to three octahedral Cd(II) atoms through the amino group and two carboxyl groups to form a neutral helical network. Complex 2 is a mononuclear compound in which Co(III) is octahedrally coordinated by tridentate L-aspartate, monodentate azide and chelating phen ligand. Thermal stability and fluorescence of 1 have been investigated. The complex shows strong blue fluorescence in the solid state.     

Volumetric,Acoustic and Transport Properties of Metformin Hydrochloride Drug in Aqueous <Emphasis Type="SmallCaps">d</Emphasis>-Glucose Solutions at <Emphasis Type="Italic">T</Emphasis> = (298.15–318.15) K

Apparent molar volumes, apparent molar adiabatic compressibilities and viscosity B-coefficients for metformin hydrochloride in aqueous d-glucose solutions were determined from solution densities, sound velocities and viscosities measured at T = (298.15–318.15) K and at pressure p = 101 kPa as a function of the metformin hydrochloride concentrations. The standard partial molar volumes (\( \phi_{V}^{0} \)) and slopes (\( S_{V}^{*} \)) obtained from the Masson equation were interpreted in terms of solute–solvent and solute–solute interactions, respectively. Solution viscosities were analyzed using the Jones–Dole equation and the viscosity A and B coefficients discussed in terms of solute–solute and solute–solvent interactions, respectively. Adiabatic compressibility (\( \beta_{s} \)) and apparent molar adiabatic compressibility (\( \phi_{\kappa }^{{}} \)), limiting apparent molar adiabatic compressibility (\( \phi_{\kappa }^{0} \)) and experimental slopes (\( S_{\kappa }^{*} \)) were determined from sound velocity data. The standard volume of transfer (\( \Delta_{t} \phi_{V}^{0} \)), viscosity B-coefficients of transfer (\( \Delta_{t} B \)) and limiting apparent molar adiabatic compressibility of transfer (\( \Delta_{t} \phi_{\kappa }^{0} \)) of metformin hydrochloride from water to aqueous glucose solutions were derived to understand various interactions in the ternary solutions. The activation parameters of viscous flow for the studied solutions were calculated using transition state theory. Hepler’s coefficient \( (d\phi /dT)_{p} \) indicated the structure making ability of metformin hydrochloride in the ternary solutions.     

Primary Amine‐Initiated Polymerizations of α–Amino Acid N‐Thiocarbonic Acid Anhydrosulfide

The N‐thiocarbonic acid anhydrosulfides NTAs of D,L‐leucine, D,L‐phenylalanine and sarcosine were polymerized in dioxane by addition of n‐hexylamine as initiator. Despite variation of the monomer‐initiator ratio (M/I) only low yields of oligopeptides were obtained from D,L‐Leu‐ and D,L‐Phe‐NTA. Both yields and molecular weights were almost twice as high for polymerizations of Sar‐NTA. MALDI‐TOF mass spectra confirmed that the isolated oligo‐and polypeptides possess the expected structure with one reactive amino end group. Therefore, it is surprising that the polymerizations stopped at low conversions. Two hypotheses explaining this phenomenon are discussed.     

Thermal Arndt–Eistert Reactions of N‐Tosyl Cyclic α‐Amino Acids

Thermal Arndt–Eistert reactions of N‐tosyl cyclic α‐amino acids were studied to explore the preparation of α,β‐unsaturated esters bearing a terminal tosylamino group. For L‐N‐tosyl‐aziridine 2‐carboxylic acid and L‐N‐tosyl‐azetidine 2‐carboxylic acid, the corresponding (E)‐α,β‐unsaturated esters were obtained stereospecifically.     

Regioselective Monoacetylation of Methyl Pyranosides of Pentoses and 6‐Deoxyhexoses by Acetic Anhydride in the Presence of MoCl5

Convenient regioselective syntheses of 3‐acetates of methyl pyranosides of α‐L‐rhamnose, α‐ and β‐L‐arabinose, α‐D‐fucose, α‐D‐lyxose, and β‐D‐ribose with good yields have been attained using MoCl₅ as catalyst. Methyl β‐L‐rhamnopyranoside under this conditions gave 2‐acetate.     

Synthesis of Ribavirin Analogues Containing Amino‐Acid Residues

Abstract

A convenient procedure for coupling 1,2,3,5‐tetra‐O‐acetyl‐β‐D‐ribofuranose and 4‐nitroimidazole was developed to obtain β‐anomer as the major product. A novel category of nucleoside analogues with the introduction of natural L‐amino acids to the base moiety were designed and synthesized to develop selective and effective antiviral agents.     

Synthesis,characterization and bioactivity of Schiff base copper(II) complexes derived from L-glutamine and L-asparagine

To investigate the structure–activity relationship of L-glutamine and L-asparagine Schiff base copper complexes in applications, L-glutamine and L-asparagine Schiff bases (GV and AV) and their copper complexes [Cu₃(GV)₂(CH₃COO)₂(H₂O)] · 2H₂O (GVC) and [CuAV(H₂O)₃] (AVC) have been synthesized and characterized by molar conductance, elemental analysis, UV-Vis, IR, ¹H-NMR, and TG-DTG. We examined the geometries of GV, AV, GVC, and AVC through Hartree–Fock method and electronic absorption spectra. We also tested their antibacterial activity against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Bacillus subtilis bacteria and antiproliferation activity on human breast cancer MDA-MB-231 cells. The side chain difference between L-glutamine and L-asparagine results in different geometry of GV and AV, which leads to different geometry of GVC and AVC. GVC, a trinuclear Cu(II) complex, shows the highest antibacterial activity and the highest growth inhibition activity on MDA-MB-231 cells. Our results suggest that GVC has potential as an antibacterial and anticancer agent.     

Conformational Analysis of Thiosugars: Theoretical NMR Chemical Shifts and 3 J H,H Coupling Constants of 5‐Thio‐Pyranose Monosaccharides

The conformational space of D and L, deoxy and nondeoxy, 5‐thio‐pyranoses with biological properties as enzymatic inhibitors was explored using MM and B3LYP/6–31+G* methods in gas phase and solution. The preferred ring conformation for α and β anomers of 5‐thio‐L‐fucopyranose was the ¹C₄ form (about 99%), and for 5‐thio‐D‐glucopyranose and 5‐thio‐D‐mannopyranose, the ⁴C₁ one. The experimental conformational order (⁴C₁>¹C₄>²S_S) for L‐ido derivatives was reproduced only considering the solvent, though for 3‐O‐methyl‐5‐thio‐α‐L‐idopyranose, the inclusion of methyl in C₃ changed the ²S_S form to the B_1,4 one.     

Magnetic hybrid imprinted polymers with three-templates modified by DESs for the rapid purification of monosaccharide from seaweed

Fe₃O₄@hybrid-molecular-imprinted polymers (Fe₃O₄@HMIPs) with three monosaccharide templates (D-(+)-galactose, L-(?)-fucose, and D-(+)-mannose), and hybrid materials were modified by deep eutectic solvents (DESs). The materials obtained were combined with solid-phase extraction (SPE) to purify of D-(+)-galactose, L-(?)-fucose, and D-(+)-mannose from seaweed, and the SPE procedure was optimized further. Compared to Fe₃O₄@HMIPs, DESs-Fe₃O₄@HMIPs were developed to achieve stronger recognition and higher recoveries of D-(+)-galactose, L-(?)-fucose, and D-(+)-mannose from seaweed. The optimal practical recoveries of the three monosaccharides, D-(+)-galactose, L-(?)-fucose, and D-(+)-mannose, purified by DESs-4-Fe₃O₄@HMIPs from seaweed were 90.12, 92.82, and 91.94%, respectively. When acetone was used as the washing solution, the actual amounts extracted were 6.87, 4.17, and 5.29?mg?·?g^?1, respectively.     

Thermo-sensitive random poly(L-alanine-co-L-lactic acid) with no cytotoxicity by the structure-controlled synthesis for a nano-drug carrier

A random poly(L-alanine-co-L-lactic acid) (PAL) with excellent thermo-sensitivity and no cytotoxicity was synthesized by the structure-controlled polycondensation from natural L-alanine and L-lactic acid. Only those PALs in which the contents of L-alanine structural unit are rigidly controlled in the smaller range of 53–65% show a reversible lower critical solution temperature of 35–60°C. The change of secondary structure in poly(L-alanine) segments by the introduction of L-lactic acid structural unit plays a decisive role in regulating the thermo-sensitivity of PAL. The viability of HeLa cells exposed to PAL reaches up to 91–116% after incubation of 24 and 72?h, indicating no cytotoxicity. Furthermore, PAL can easily form curcumin-loaded nano-carriers through its thermo-sensitivity and self-assembly. The curcumin-loaded PAL nano-particles are observed to clearly internalize into the cells by confocal laser-scanning microscopy, and thus can be used as a potential nano-drug-carrier.     

Pentaric Acids and Derivatives from Nitric Acid–Oxidized Pentoses

This report describes the preparation of the four stereoisomeric pentaric acids by nitric acid oxidation of d-xylose, d-arabinose, l-arabinose, and d-ribose, with xylaric, d-arabinaric, and l-arabinaric acids being made in a reactor under computer control. The pentaric acids were converted to their crystalline N,N′-dimethylpentaramides, derivatives that proved useful for isolation of the arabinaric acids from their respective oxidation mixtures. The N,N′-dimethylpentaramides were readily convertible to the corresponding pentaric acid disodium salts in aqueous sodium chloride. The 2,3,4-O-triacetyl-N,N′-dimethylpentaramides of xylaric, l-arabinaric, and ribaric acid were also prepared. Ribaric acid was isolated as crystalline 1,4(5,2)-ribarolactone and further characterized by x-ray crystallography.     

Resolution of racemic Vigabatrin using tartaric acid

An efficient and simple resolution methodology for the preparation of (S)- and (R)-Vigabatrin has been developed. In addition, a method of preparation for the novel compounds Vigabatrin-l-tartarate and Vigabatrin-d-tartarate is also described. The title compounds have been synthesized via resolution of Vigabatrin using commercially available l-(+)- and d-(?)-tartaric acids respectively.     

Enantioselective Recognition of Proline Enantiomers Using Sulfhydryl-modified Self-assembled Gold Electrodes

Penicillamine, cysteine, and N-isobutyryl-cysteine enantiomers self-assembled gold electrodes were used for the enantioselective recognition of proline in the presence of copper(II). High stereoselectivity for proline was obtained for the D-form of the sulfhydryl compounds, particularly on the D-penicillamine-modified gold electrode. Cyclic voltammetry and electrochemical impedance spectroscopy were used to confirm the chiral discrimination of proline enantiomers on the D-penicillamine modified gold electrode in the presence of copper(II). The largest electrochemical response was obtained for D-proline for the recognition of its enantiomers, whereas small responses were obtained for the L- and D-forms of phenylalanine, tyrosine, serine, and glutamic acid. The influences of incubation time and pH for chiral ligand exchange were evaluated. This study complements and enhances applications for the recognition of amino acid enantiomers based on ligand exchange by electrochemical analysis.     

SYNTHESIS OF 3-O-ARABINOSYLATED (1→6)-β-D-GALACTAN EPITOPES

Two tetrameric arabinogalactans, β-D-galactopyranosyl-(1→6)-β-D-galactopyranosyl-(1→6)-[α-L-arabinofuranosyl-(1→3)]-D-galactopyranose (14) and α-L-arabinofuranosyl-(1→3)-β-D-galactopyranosyl-(1→6)-β-D-galactopyranosyl-(1→6)-D-galactopyranose (25), which are good candidates for CCRC-M7 epitope characterization, were synthesized efficiently using a convergent strategy. Migration of an acceptor acetyl group proved to be an obstacle to synthesis, but regioselective glycosylation or 4-O-benzyl protection of the acceptor circumvented this problem allowing efficient synthesis of the 1→6 linked target compounds.     

Synthesis of 3‐Methoxyoxetane δ‐Amino Acids with D‐lyxo,D‐ribo,and D‐arabino Configurations

Starting from 1,2‐isopropylidene‐d‐xylose (1), 3‐methoxyoxetane δ‐amino acids with d‐lyxo, d‐ribo, and d‐arabino configurations were synthesized. The early introduction of an azide function at C‐5 of 1 shortened the synthetic pathway. Ring contraction of the intermediate d‐xylono‐1,4‐lactone 6 via triflation and treatment with base led to the corresponding 3‐methoxyoxetane δ‐amino ester with d‐lyxo configuration 7. The analogous procedure for d‐ribono‐1,4‐lactone 16 furnished a mixture of d‐ribo and d‐arabino esters 17 and 18. Hydrolysis of the methyl esters 7, 17, and 18 to their corresponding δ‐amino acids was successful with LiOH in THF, in contrast to that of their 3‐hydroxy analog 11.