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...     

Solid–liquid equilibria in the acetic acid–propanoic acid and propanoic acid–trifluoroacetic acid systems

Solid–liquid equilibria in the binary systems, propanoic acid–acetic acid and propanoic acid–trifluoroacetic acid, were measured by a synthetic method. A solid compound (1:1) was found in the propanoic acid–trifluoroacetic acid system. The obtained activity coefficients were successfully fitted by the Wilson equation.     

Synergy between Brønsted acid sites and Lewis acid sites

Synergy between Br?nsted acid sites and Lewis acid sites in mesoporous Al-Zr-TUD-1 was demonstrated to exist in Br?nsted acid catalysed reactions, but not in Lewis acid catalysed reactions.     

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.     

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.     

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.     

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.     

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

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Lethaclado acid A and B from Lethariella cladonioides

Two new compounds,lethaclado acid A(1) and B(2),were isolated from the acetone extract of Lethariella cladonioides.Their structures were elucidated on the basis of 1D and 2D NMR as well as ESI-MS spectral data.     

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 reactivity of 3-(trichlorogermyl)propanoic acid and 3-(triphenylgermyl) propanoic acid

3-(Trichlorogermyl)propanoic acid (la) reacts with phenylmagnesium bromide in malar ratio 1:4 to give 3-(triphenylgermyl)propanoic acid (2a).In the compounds la and 2a theβ-carboxylic functional group shows some unusual properties when they react with excess of phenylmagnesium bromide.The compound la reacts with phenylmagnesium bromide in molar ratio 1:5 to give phenyl 2-(triphenylgermyl)ethylketone (3a) and in molar ratio 1:6 to give l,l-diphenyl-3-(triphenylgermyl)propanol (4a).The compound 2a reacts with phenylmagnesium bromide in molar ratio 1:2 to give 3a and in molar ratio 1:3 to give 4a also.Dehydration of the compound 4a with dilute hydrochloric acid seems especially easy.Moreover,the compound la reacted with phenylmagnsium bromide in molar ratio 1:6,then the mixture was treated with dilute hydrochloric acid to give 1,1-diphenyl-3-(triphenylgermyl)-1-propene (5a) in one pot reaction.Alkyl Ge-C bond in the compound 5a can be cleaved selectively by lithium aluminium hydride ( LiAlH4) in good yiel     

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.     

A path integral molecular dynamics study on intermolecular hydrogen bond of acetic acid–arsenic acid anion and acetic acid–phosphoric acid anion clusters

We apply ab initio path integral molecular dynamics simulation employing ωB97XD as the quantum chemical calculation method to acetic acid–arsenic acid anion and acetic acid–phosphoric acid anion clusters to investigate the difference of the hydrogen bond structure and its fluctuation such as proton transfer. We found that the nuclear quantum effect enhanced the fluctuation of the hydrogen bond structure and proton transfer, which shows treatment of the nuclear quantum effect was essential to investigate these systems. The hydrogen bond in acetic acid–arsenic acid anion cluster showed characters related to low-barrier hydrogen bonds, while acetic acid–phosphoric acid anion cluster did not. We found non-negligible distinction between these two systems, which could not be found in conventional calculations. We suggest that the difference in amount of atomic charge of the atoms consisting the hydrogen bond is the origin of the difference between acetic acid–arsenic acid and acetic acid–phosphoric acid anion cluster. © 2018 Wiley Periodicals, Inc.     

Preparation,characterization and determination of acid dissociation and stability constants of some acid divalent-metal 1 : 2 nitrilotriacetate complexes

H₂[M^II(HNTA)₂]·xH₂O complexes of eleven divalent metals were prepared. These complexes were characterized via elemental analysis, IR spectra, TGA, DTA and ¹H NMR. pKa₁ and pKa₂ of these acids were determined together with their log?β ₁ and log?β ₂ as metal complexes.     

Electrodeposition of hyaluronic acid and hyaluronic acid–bovine serum albumin films from aqueous solutions

Hyaluronic acid (HYH) films were prepared from aqueous sodium hyaluronate (HYNa) solutions by anodic electrodeposition. The film thickness was varied in the range of 0–20 μm by the variation of the deposition time and HYNa concentration. The deposition rate was low at HYNa concentration below 1 g L⁻¹ and increased significantly in the range of 3–5 g L⁻¹. The addition of bovine serum albumin (BSA) to the HYNa solutions resulted in increased deposition yield, which was attributed to the formation of composite HYH–BSA films. The thickness of the HYH–BSA films deposited by anodic electrodeposition was varied in the range of 0–80 μm. The HYH and composite HYH–BSA films were studied by scanning electron microscopy, thermogravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy and circular dichroism spectroscopy. The deposition mechanism and kinetics of deposition are discussed.     

Simultaneous determination of uric acid and ascorbic acid at a ferrocenium–thioglycollate modified electrode

Self-assembled monolayers (SAMS) of chemisorbed thioglycollate on a gold electrode surface have been used as a base interface for the electrostatic adsorption of ferrocenium ion. Electrochemical impedance spectra (EIS) and cyclic voltammetry (CV) were used to evaluate the electrochemical properties of the supramolecular film. The bare gold electrode failed to distinguish the oxidation peaks of ascorbic acid (AA) and uric acid (UA) in phosphate buffer solution (PBS, pH 7.0), while the ferricinium–thioglycollate modified electrode could separate them efficiently. In differiential pulse voltammetric measurements, the prepared gold electrode could separate AA and UA signals, allowing the simultaneous determination of AA and UA. Under optimal conditions and within the linear range of 1.0 × 10⁻⁶ to 5.0 × 10⁻⁴ M, the detection limits of AA and UA achieved were 2.0 × 10⁻⁷ and 1.0 × 10⁻⁷ M, respectively. The applicability of the prepared electrode was demonstrated by measuring AA and UA in human urine without any pretreatment. Figure Fabrication process for the modified electrode     

Reaction of α-cyanoacrylic acid and cyanoacrylates with dialkyl and diaryl phosphites

-Cyanoacrylic acid and -cyanoacrylates add dialkyl and diaryl phosphites and diethyl thiophosphite at the C=C double bond in the absence of catalyst. This is an anti-Markovnikov reaction, which yields the corresponding phosphonates and thiophosphonates.A. N. Nesmeyanov Institute of Organometallic Compounds, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1913–1915, August, 1992.     

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.