Effect of micelles on the acid hydrolysis of N-phenylbenzohydroxamic acid

The effect of cationic (cetylpyridinium bromide and cetylpyridinium chloride) anionic (sodium dodecyl sulfate and lithium dodecyl sulfate) and non-ionic (Brij-35 and Triton-X-100) micelles on the acid-catalyzed hydrolysis of N-phenylbenzohydroxamic acid in 20 vol.% dioxane medium has been investigated. The kinetic results are explained by both pseudo-phase and Piszkiewicz cooperativity models.     

Synthesis of α-bromoisovaleric acid in the poliphosphoric acid medium

Bromination of isovaleric acid with bromine in the polyphosphoric acid mediumis was studied, regularities of the process including influence of the polyphosphoric acid composition were revealed, the process was shown technologically attractive for the organization of industrial manufacturing of α-bromoisovaleric acid.     

Nature of the transformations of oleanolic acid in an acid medium

3-Trifluoroacetoxyoleanolic acid and 3-trifluoroacetoxyolean-13(18)-en-28-oic acid have been isolated from the mixture of the products of the transformation of oleanolic acid in a trifluoroacetic acid medium, and their structures have been established with the aid of IR, PMR and mass spectra. The formation of these products indicates an unambiguous route of the stabilization of the intermediate carbocation with the charge on the C-13 atom. The hydroxy group at C-3 is esterified by the trifluoroacetic acid.All-Union Scientific-Research Institute of Medicinal Plants, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 320–323, May–June, 1986.     

Bimetallic nanocatalysts for the conversion of muconic acid to adipic acid

Adipic acid (2) production currently entails use and generation of environmentally harmful materials: an efficient catalyst, consisting of nanoparticles of Ru10Pt2 anchored within the pores of mesoporous silica, facilitates the production of (2) by hydrogenating muconic acid, that may be derived biocatalytically from D-glucose.     

Theoretical studies of the quinolinic acid to nicotinic acid mononucleotide transformation

Quinolinate phosphoribosyl transferase (QPRTase) is an essential enzyme that catalyzes the transformation of quinolinic acid (QA) to nicotinic acid mononucleotide (NAMN), a key step on the de novo pathway for nicotinamide adenine dinucleotide (NAD) biosynthesis. We describe herein a theoretical study of the intrinsic energetics associated with the possible mechanistic pathways by which QA forms NAMN. Our main interest is in probing the decarboxylation step, which is intriguing since the product is a vinylic anion, not unlike the reaction catalyzed by orotidine 5'-monophosphate (OMP) decarboxylase, an enzyme whose mechanism is under fierce debate. Our calculations indicate that a path involving a quinolinic acid mononucleotide (QAMN) intermediate is the most energetically attractive, favoring decarboxylation. We also find that the monocarboxylate form of QAMN will decarboxylate much more favorably energetically than will the dicarboxylate form of QAMN. Furthermore, our calculations indicate that decarboxylation is not a likely first step; the substrate in such a mechanism would prefer to decarboxylate at the C3 position, not the desired C2 position. We also discuss our results in the context of existing experimental data.     

Synthesis of the dibenzyl ester of tert-butoxycarbonyl-L-alanyl-D-glutamic acid from racemic glutamic acid

M. V. Frunze Simferopol' State University. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 865–866, November–December, 1991.     

Origins of the solvent effect on the propagation kinetics of acrylic acid and methacrylic acid

In this study, the relative rate of polymerization of acrylic acid (AA) versus methacrylic acid (MAA) and the effect of water on the polymerization kinetics are investigated within a combined static and molecular dynamics set of computational tools. Experimentally the relative rate of propagation of AA versus MAA is around 35 in bulk and 31 in water. Classical Molecular Dynamics calculations have been carried out to determine the location of the solvent molecules in the proximity of the dimeric poly(AA) and poly(MAA) units. A combined implicit/explicit solvent model was used for the evaluation of the kinetics of the dimeric polymer chains. We show that the rate acceleration of both polymers in water is mainly due to entropic rather than electrostatic effects and is in agreement with experimental findings. Moreover the slower propagation rate of MAA versus AA is ascribed to additional steric effects present in MAA due to the methyl group at the α position of the monomer. Among the functionals used, the M06‐2X/6‐311+G(3df,2p)//B3LYP/6‐31+G(d) methodology reproduces the experimental rate constants quantitatively the best. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

New method for the spectrophotometric determinations of ascorbic acid and dehydroascorbic acid

Summary The condensation of dehydroascorbic acid with o-phenylene diamine or its 4,5-dimethyl derivative yields quinoxaline derivatives which can be measured by photometry. Ascorbic acid can be determined after preliminary oxidation with mercury(II) chloride in the same way. This highly specific method has been employed for determinations in pharmaceutical formulations (coefficient of variation ± 1–1.5%).

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Neue spektrophotometrische Methode zur Bestimmung von Ascorbinsäure und Dehydroascorbinsäure

Zusammenfassung Die Kondensation von Dehydroascorbinsäure mit o-Phenylendiamin oder 4,5-Dimethyl-o-phenylendiamin führt zur Bildung von spektrophotometrisch auswertbaren Chinoxalinderivaten. Ascorbinsäure kann nach vorangehender Oxidation mit Quecksilberchlorid auf die gleiche Weise bestimmt werden. Die Methode wurde zu Bestimmungen in pharmazeutischen Präparaten verwendet (Variationskoeffizient ± 1–1,5%).

The author thanks Mrs. S.V. Ramakrishnan and Miss K. Mihályfi for their technical assistance.     

Controlled release of 4-hydroperoxycyclophosphamide from the fatty acid dimer-sebacic acid copolymer

Controlled polymeric release of chemotherapeutic agents has shown promise in the management of malignant gliomas. 4-Hydroperoxycyclophosphamide (4HC), loaded on the fatty acid dimer–sebacic acid copolymer (FAD:SA, 1:1), significantly prolonged survival in rats implanted with F98 and 9L gliomas. Here, we studied the in vitro and in vivo release kinetics in phosphate-buffered saline and rat brain of 20% 4HC/FAD:SA (wt:wt), the optimal dose for treatment of rat gliomas. In vitro release under infinite sink conditions was steady over the initial 12 hr to a peak of 20–35% of impregnated drug, consistent with early phase control via surface erosion. Release over the next 3 weeks was minimal, consistent with barrier formation around the polymer by an oily fatty acid dimer degradation product and consequent slowing of release. However, the polymer started to disintegrate by day 4, and there were minimal visible remnants by 3 weeks. Thus, a considerable amount of polymer-carried drug was probably lost in the disintegrating fragments. Also, drug loss is expected from its inherent hydrolytic instability. In vivo release into brain revealed two peak levels of drug at 0–1 hr and 5–20 days. With loaded polymer implanted intraperitoneally or cyclophosphamide injected systemically, peak brain drug levels were measured in 2–8 hr, with substantial decrease by 48 hr without a second peak. Brain levels were substantially higher than blood levels at all time periods. We conclude that FAD:SA (1:1) adequately protects the otherwise labile 4HC, allowing effective and substained drug release in vivo. Furthermore, it should be possible to modify the polymer to adjust the time of peak release for more beneficial therapeutic effects.     

水杨酸荧光增强法测定酵母核糖核酸

核酸是生物体内重要的生物大分子,定量测定核酸是研究核酸的基础,由于核酸内源荧光很弱,直接利用荧光技术来研究核酸的结构和性质受到限制.     

Polarography of thiodiglycolic acid and thiodipropionic acid at the dropping mercury electrode

The polarographic behaviour of thiodiglycolic acid (R?S?R) and thiodipropionic acid (R?CH₂?S?CH₂R) at the DME, has been investigated in presence of 0.1 M KCl and 0.01% thymol with respect to the effects of changes in pH, concentration, drop time, and temperature on the wave characteristics. Well-defined irreversible cathodic waves were obtained in the pH range 2.40 to 4.76 for R?S?R and 2.3 to 4.98 for R?CH₂?S?CH₂R. At lower (<2.0) and higher (>5) pH values, ill-defined waves were obtained. The mechanism of the electrode process in aqueous solutions has also been elucidated.     

On the fractionation of natural radioactivity in the production of phosphoric acid by the wet acid method

The fractionation of different natural radionuclides (U-isotopes,²²⁶Ra and²¹⁰Po) in the process used for the production of phosphoric acid in some factories located in the southwest of Spain is analyzed. As a consequence, different ways of natural radionuclide liberation to the environment can be evaluated due to these industrial activities.