Spectrophotometric Evidence for the Formation of a Mixed Bismuth-Phosphorus Heteropoly Acid

Abstract

Spectrophotometric evidence is presented to show that bismuth interacts with phosphate and molybdate in acid solution to form a mixed bismuth-phosphorus heteropoly acid. The complex is similar to 12-molybdophosphoric acid by virtue of its degree of dissociation in both concentrated and dilute acid solutions. The complex is more stable than 12-molybdophosphoric acid because it is formed when bismuth is added to a solution of 12-molybdophosphoric acid. The proposed bismuth-phosphorus compound is reduced much more readily to a heteropoly blue than is 12-molybdophosphoric acid, a fact that has contributed to a false belief that the bismuth may have been acting catalytically in the reduction of 12-molybdophosphoric acid.     

Photostability of Ferulic Acid and Its Antioxidant Activity Against Linoleic Acid Peroxidation

Ferulic acid (4‐hydroxy‐3‐methoxycinnamic acid), a phenyl‐propenoid derivative of cinnamic acid, can undergo photolysis upon UV irradiation. The photodegradation kinetics of ferulic acid were thus investigated in different systems. The micellar solutions did not protect the acid from photodegradation. On the contrary, they catalyzed its degradation at a variable extent depending on the surfactant structure. The photodegradation of ferulic acid in microemulsions was slower than in micelles and near to that in water. TiO₂, habitually employed as a physical sunscreen, showed photocatalytic action toward ferulic acid degradation especially at higher initial concentration of ferulic acid. The action of ferulic acid on the peroxidation of linoleic acid in micelles and microemulsions also was evaluated. When the ferulic acid is absent the peroxidation is continuous while when it is present an induction time of 40 minutes or higher was observed. Accordingly, it is likely that linoleic acid acts as photosensitizer for ferulic acid, and that in turn ferulic acid acts as an antioxidant for linoleic acid, reducing the rate of peroxidation.     

Proton hopping in phosphoric acid solvated nafion membrane: a molecular simulation study

Molecular simulation studies of the microstructure and of the proton transport properties of phosphoric acid solvated Nafion membrane are carried out. The ab initio calculations show that the phosphoric acid is a good solvent to promote the proton ionization of the sulfonic acid group, and only two phosphoric acid molecules are necessary for the dissociation of one sulfonic acid group. A mechanism of proton hopping between phosphoric acid and protonated phosphoric acid cation in the hydrophilic subphase is also elucidated by ab initio calculations. The molecular dynamics simulations, conducted at a phosphoric acid concentration of 25.4% (wt) which is slightly lower than that of phosphoric acid swollen Nafion, show that the phosphoric acid exists in subphases and that it cannot develop into a continuous subphase. Thus, proton-hopping pathways are interrupted, and the conductivity is expected to be lower than that for pure phosphoric acid. The molecular dynamics simulations, conducted at a phosphoric acid concentration of 45.1% (wt) which corresponds to an unstable state, show that the hydrophobic poly(tetrafluoroethylene) backbones trend to gather together forming hydrophobic clusters and that the phosphoric acid forms a continuous subphase with the sulfonic acid groups located at the hydrophobic/hydrophilic interface. Thus, proton-hopping pathways can develop uninterruptedly like the pure phosphoric acid, and high conductivity is expected. The molecular dynamics study also shows that the hydrogen-bonding characteristics of phosphoric acid and sulfonate anion are similar regardless of the factor that the former can move freely while the latter is attached to Nafion backbone.     

三乙醇胺交联聚硅氧烷树脂对羧酸吸附性能研究

本文研究了甲酸、乙酸、丙酸和戊酸在三乙醇胺交联聚硅氧烷树脂上的吸附行为。通过其吸附速度、吸附等温线的研究,得出甲酸和乙酸在该树脂上以单分子吸附为主,丙酸和戊酸以多分子吸附为主,而且吸附的强弱与羧酸的解离有关,解离越强吸附越弱,反之,吸附越强。     

二元羧酸半酯与环氧化合物反应动力学研究

用于印制电路板 ( PCB)的传统的热固化或光固化阻焊油墨是利用屏印的方法把图案印刷在覆铜板上 ,然后固化 .通过这种方法得到的图案不够精细 ,应用上也受到一定限制 .为此 ,近年来国际上研制出一类新型的阻焊油墨——碱液显影型阻焊油墨 [1～ 3] .它是通过曝光、显影及后固化等步骤形成精确的图案 ,可用于制备高密度的电路板 .通常 ,碱水显影型阻焊油墨由碱溶性光敏树脂 (组分 A)、环氧化合物 (组分 B)、光引发剂、热固化剂和稀释剂组成 .组分 A由二元羧酸与含有光聚合性双键的线性酚醛型环氧化合物通过半酯化反应得到 ,羧基的引入使其具…     

Use of Trifluoromethanesulfonic Acid in Fischer Glycosylations

Abstract

The Fischer glycosylation₁ is one of the standard reactions in carbohydrate chemistry, in which a reducing sugar is reacted under acid catalysis with a simple alcohol to give a glycoside. Hydrochloric acid is the classical catalyst, but other proton, Lewis acid, or acid form ion echange resins have also been used. Now, the use of trifluoromethanesulfonic acid (triflic acid) as a catalyst is communicated.     

The Interaction of Zinc(II) and Hydroxamic Acids and a Metal‐Triggered Lossen Rearrangement

The structure and reactivity of a complex of zinc(II), water, acetic acid, and acetohydroxamic acid, in which one of the acids is deprotonated, is investigated by means of mass spectrometry, labeling studies, and density functional calculations to unravel the exceptional binding properties of hydroxamic acids towards zinc‐containing enzymes at the molecular level. It is shown that acetohydroxamic acid is deprotonated in the complex, whereas acetic acid is present in its neutral form. The binding energies of the ligands towards zinc increase in the following order: water<acetic acid<acetohydroxamic acid. The structure of the complex and its fragmentation provide experimental evidence for the proposed mode of operation of drugs based on hydroxamic acids. Furthermore, coordinatively unsaturated complexes of zinc and acetohydroxamic acid undergo a zinc‐assisted Lossen rearrangement followed by elimination of water if acetohydroxamic acid is present as a neutral ligand, or by loss of methylisocyanate if acetohydroxamic acid is deprotonated.     

(1-PYRENYL)METHYL CARBAMATES FOR FLUORESCENT "CAGED" AMINO ACIDS AND PEPTIDES

A highly fluorescent 1-pyrenylmethyloxycarbonyl amino acid (Pmoc-amino acid) is obtained in moderate yield by the reaction of (1-pyrenylmethyl)-4-nitrophenylcarbonate with an amino acid in the presence of sodium carbonate. The condensation of Pmoc-amino acid with an amino acid gives Pmoc-peptide in the presence of 1-ethyl-3-(3-dimethylaminepropyl)carbodiimide and 1-hydroxyben-zotriazole. The amino acid is recovered from an H₂O-dioxane (2:3) solution of Pmoc-amino acid by irradiation through a Pyrex filter with a medium pressure Hg lamp or at 340 nm. Although the quantum yield of the photolysis is rather low (ca 0.01), the photolysis proceeds fast and efficiently due to the large absorption coefficient of Pmoc-amino acid at around 340 nm. Thus, the use of Pmoc-amino acid as a “caged” amino acid is promising.     

The formation and structure of phenylcamphoric acid and related compounds

The complete structure and stereochemistry of (+)-phenylcamphoric acid has been determined. The acid obtained from the Friedel-Crafts reaction of benzene with isolauronolic acid is identified as (±)-phenylcamphoric acid, α-Campholytic acid is shown to be a likely precursor of phenylcamphoric acid in these reactions. The Friedel-Crafts reaction of 3-cyano-1,2,2-trimethylcyclopentanecarbonyl chloride or 3-cyano-2,2-dimethyl-1-methylenecyclopentane with benzene provides a mixture of phenylcamphornitrile and an isomer. Isofenchocamphoric anhydride similarly provides a mixture of the epimeric 4-phenyl-2,2,4-trimethylcyclopentanecarboxylic acids.     

High-speed liquid chromatographic determination of phenylpyruvic acid.

A high-speed liquid chromatographic method has been developed for the determination of urinary phenylpyruvic acid. This acid is converted by treatment with naphthalene-2,3-diamine into 3-benzyl-2-hydroxybenzoquinoxaline, which is extracted into carbon tetrachloride for separation. 2-Mercaptoethanol is a useful stabilizer, and 2-chlorothioxanthone is a suitable internal standard. The method is specific, and the results are not affected by the presence of such 2-oxo-acids as pyruvic acid, 2-oxobutyric acid, 2-oxoglutaric acid, and 4-hydroxphenylpyruvic acid.     

Spectrophotometric determination of bismuth in copper and cartridge brass by the iodide method

An improved spectrophotometric method is proposed for the determination with iodide of trace amounts of bismuth in copper and cartridge brass. The sample is dissolved in nitric acid and the bismuth is separated from the copper by an ammoniacal precipitation in the presence of iron(III) hydroxide as a gathering agent. The hydroxide precipitate is dissolved in hydrochloric acid, sulfuric acid is added, the solution is evaporated to a few ml, hydrobromic acid is added to volatilize the antimony and tin, and the solution is evaporated to fumes of sulfuric acid. The bismuth iodide color is then developed with a composite potassium iodide—sodium hypophosphite reagent. Factors affecting the bismuth iodide color are investigated.     

Verteilung von Säure,Wasser, Methanol, Äthanol und Aceton Zwischen Gemischt Wässrig-Organischen Salpetersäurelösungen und Lösungen von Trilaurylammoniumnitrat in Cyclohexan

The distribution of acid, water, methanol, ethanol and acetone between mixed aqueous-organic nitric acid solutions and solutions of trilaurylammoniumnitrate in cyclohexane has been investigated. The distribution of acid rises with increasing concentrations of nitric acid, methanol, ethanol and acetone in the mixed aqueous-organic phase. The effect of the organic additives in increasing the distribution of the acid is methanol<ethanol<acetone. The concentration of nitric acid in the organic phase can be calculated by a formula similar to that describing the extraction from pure aqueous solutions. The distribution curves of water, methanol and ethanol resemble each other, all of them showing a minimum, when the distribution ration is plotted versus the nitric acid concentration in the mixed aqueous-organic phase. The acetone distribution decreases steadily with increasing nitric acid concentration. The shape of the curves is briefly discussed.      

The dimethyldioxirane-mediated oxidation of phenylethyne

The product pattern found for the dimethyldioxirane-mediated oxidation of phenylethyne strongly depends on the reaction conditions. Dimethyldioxirane generated in situ from caroate (HSO(5)(-)) and acetone in acetonitrile-water furnishes phenylacetic acid as the main product. With solutions of dimethyldioxirane in acetone, mandelic acid and phenylacetic acid are mainly formed. The relative abundances of the two acids depend on the residual water present in the dimethyldioxirane-acetone solution. Application of thoroughly dried solutions of the reagent effects increased formation of mandelic acid. When phenylethyne is oxidized by dimethyldioxirane transferred into tetrachloromethane, to minimize traces of water even further, oligomeric mandelic acid is obtained. The results are rationalized by the initial formation of phenyloxirene, which is known to equilibrate with phenylformylcarbene and benzoylcarbene. Subsequent Wolff rearrangement produces intermediate phenylketene, which can be trapped by water as phenylacetic acid or suffer from further oxidation to the alpha-lactone of mandelic acid. The alpha-lactone can either react with water to yield mandelic acid or, under anhydrous conditions, to yield oligomeric mandelic acid. In addition to mandelic acid and phenylacetic acid phenylglyoxylic acid, benzoic acid and benzaldehyde are observed as reaction products. The formation of phenylglyoxylic acid by transfer of two oxygen atoms to the unrearranged carbon skeleton of phenylethyne followed by oxygen insertion into the aldehydic C-H bond of the intermediately formed phenylglyoxal is discussed. In a second pathway this acid is formed by partial oxidation of mandelic acid. Benzaldehyde and benzoic acid are explained as products of the oxidative degradation of the alpha-lactone by dimethyldioxirane. Under in situ conditions benzoic acid is also formed by caroate initiated oxidative decarboxylation of phenylglyoxylic acid and/or intermediate phenylglyoxal.     

A Combined Effect of Thermal and Enzymatic Racemization for d‐Aspartic Acid to l‐Aspartic Acid by High‐Performance Liquid Chromatography Assay

The racemization of d ‐aspartic acid to l ‐aspartic acid has been successfully performed with a coupled enzyme system at 90 °C and a pH of about 4.0 by the assay of high‐performance liquid chromatography. This coupled enzymatic racemization is a successive two‐step reaction first induced by d ‐amino acid oxidase and a subsequent coupled reaction by an aminotransferase clonezyme with the help of coenzyme pyridoxal 5′‐phosphate and cosubstrate l ‐glutamate. Due to the very high temperature, part of the l ‐aspartic acid is produced by the thermal effect. In fact the thermal racemization for aspartic acid can proceed from either d ‐ or l ‐aspartic acid via an intermediate fumaric acid and leads to the formation of d ,l ‐malic acid. The formation of α‐oxalacetic acid formed irreversibly from d ‐aspartic acid with d ‐amino acid oxidase can induce a side reaction to l ‐alanine. The thermal effect may also be responsible for the production of d ‐, and l ‐alanine.     

Über Rosmarin und Rosmarinsäure

Rosmarinic acid, a tan from Lamiaceae, is found in rosemary and many other plants such as thyme, painted nettle, savory, sage, oregano, or lemon balm, from which it has been isolated here. It is a caffeic acid ester and a chiral, aromatic natural product. Rosmarinic acid tastes bitter, which may be attractive for rosemary as spice. Due to the catechol subunit the acid is an antioxidant. Using rosmarinic acid as a cure is possible due to manyfold physiological effects which are still under investigation. The rosmarinic acid biosynthesis pathway was completely elucidated at the painted nettle. This led to attempts to produce the acid biotechnologically by plant cell cultures in high yields. The preparation of a spectroscopically pure sample is challenging. All analytical spectra were recorded and are reproduced and interpreted either in the main part or in the supporting information.     

SINGLE AND BINARY ADSORPTION PERFORMANCE OF SALICYLIC ACID AND 5-SULFOSALICYLIC ACID ONTO HYPERCROSSLINKED POLYMERIC ADSORBENTS

Single and binary adsorption behaviors of salicylic acid and 5-sulfosalicylic acid onto hypercrosslinked polymeric adsorbents, i.e. NDA-101 and NDA-99 were investigated. The Freundlich model can successfully describe all the adsorption isotherms tested, which indicates a favorable and exothermic adsorption process. The adsorption of salicylic acid relies on π-π interaction, while the electrostatic interaction further influences the adsorption of 5-sulfosalicylic acid onto NDA-99. The adsorptive capacity of salicylic acid on NDA-99 decreases but increases on NDA-101 with 5-sulfosalicylic acid as the background component in a binary solute system. The amount of 5-sulfosalicylic acid adsorbed was decreased with the increase in initial concentration of salicylic acid on both adsorbents. The competition for the adsorption sites is considered to be predominant in the solid-to-liquid interaction process. The adsorption selectivity of salicylic acid onto NDA-101 is higher than onto NDA-99 by more than an order of magnitude. Thus, combination technique involving NDA-101 followed by NDA-99 can be effectively applied to separate and recover salicylic acid and 5-sulfosalicylic acid from wastewater.     

Radiation-Induced Reactions with Cellulose. XV. Effect of Mineral and Organic Acids on Grafting of Monomers Using Ionizing Radiation

The effect of a range of inorganic and organic acids on the radiation-induced grafting of styrene in methanol to cellulose is discussed using the simultaneous method. Sulfuric acid is the most effective acid for increasing the grafting yield, hydrochloric being the next most efficient. Acetic acid retards the copolymerization. Under the most favorable radiation conditions, inclusion of sulfuric acid (up to 1.1 M) produces a twentyfold increase in graft. The presence of mineral acid also 1) enhances the intensity of a Trommsdorff peak if already present in the grafting solution and 2) induces a peak if none were previously present without acid. A mechanism for the enhanced acid effects in these grafting reactions is proposed involving charge-transfer intermediates.     

High-performance liquid chromatographic determination of humic acid in environmental samples at the nanogram level using fluorescence detection

A high-performance liquid chromatographic method for the determination of humic acid in environmental samples is presented. The humic acid is chromatographed as its sodium or calcium complex, eluting as a single, sharp peak. Coral skeletal matter, sea water, river water, soils and plant matter were successfully analysed. The detection limit is 15 ng. The relative standard deviation for a coral skeletal sample is 1.9%. Unusual chromatographic properties such as the occurrence of peak broadening with increased concentration appear to be due to a slow change in the equilibrium composition of humic acid. In solution, fulvic acid showed similar properties to humic acid.     

Ultraviolet photodegradation of folic acid

The vitamin folate is vital for all living creatures. Scientists have suggested that ultraviolet degradation of folate in vivo played a role in the evolution of mankind. In order to better understand the photodegradation of folate, we have provided a spectroscopic study of the ultraviolet photodegradation of aqueous folic acid under aerobic conditions. We found strong indications that the folic acid molecule is cleaved into p-aminobenzoyl-L-glutamic acid and 6-formyl pterin when exposed to ultraviolet radiation. When the irradiation continues, 6-formyl pterin is degraded to pterin-6-carboxylic acid. The photodegradation of folic acid is divided into three phases. In the first phase, the formation of photoproducts follows a zero order rate law. In the second phase the presence of photoproducts sensitizes the degradation of folic acid and the degradation process is accelerated. In the third phase the degradation of 6-formyl pterin to pterin-6-carboxylic acid is the dominating process. This reaction follows a first order rate law. We show that both 6-formyl pterin and pterin-6-carboxylic acid sensitize the photodegradation of folic acid. However, experiments performed in heavy water indicate that generation of singlet oxygen is probably not the explanation for the photosensitizing of folic acid.     

Ion-exclusion chromatography determination of organic acid in uridine 5'-monophosphate fermentation broth

Simultaneous determination of organic acids using ion-exclusion liquid chromatography and ultraviolet detection is described. The chromatographic conditions are optimized when an Aminex HPX-87H column (300 × 7.8 mm) is employed, with a solution of 3 mmol/L sulfuric acid as eluent, a flow rate of 0.4 mL/min and a column temperature of 60°C. Eight organic acids (including orotic acid, α-ketoglutaric acid, citric acid, pyruvic acid, malic acid, succinic acid, lactic acid and acetic acid) and one nucleotide are successfully quantified. The calibration curves for these analytes are linear, with correlation coefficients exceeding 0.999. The average recovery of organic acids is in the range of 97.6% ～ 103.1%, and the relative standard deviation is in the range of 0.037% ～ 0.38%. The method is subsequently applied to obtain organic acid profiles of uridine 5'-monophosphate culture broth fermented from orotic acid by Saccharomyces cerevisiae. These data demonstrate the quantitative accuracy for nucleotide fermentation mixtures, and suggest that the method may also be applicable to other biological samples.