Alpha-ketocarboxylic Acid Research Articles

Characterization of alkali treated Nelumbo nucifera fiber and properties of its reinforced composite

ABSTRACT Natural fibers are being extensively used in recent technological and structural applications due to the need for biodegradable materials. This paper deals with extraction of new cellulosic fiber from the stem of Nelumbo nucifera (Nn) (lotus) and the investigations via physical, structural and thermal properties on the alkali-treated fiber were carried out. The XRD analysis of the Nn fiber provides the crystallinity index of about 52.53% that implies its high crystalline structure and own associated strength. The FTIR analysis proves the presence of alcoholic and alpha keto carboxylic acid in Nn fiber. Thermal stability of Nn composite is found around 210°C and the TGA results prove that the extracted as well as alkali-treated fibers provide a good reinforcement to the matrix, which can be well synthesized mechanically improved biocomposites. Test samples of three different weight % of Nn fiber with the epoxy basement are designated as L10, L15 and L20 to measure the tensile and flexural strength. Test sample with L20 as weight % exhibits better Young’s and flexural modulus. Alkali treated Nn composite is an important candidate for the natural fiber reinforcement and such a category can serve as a good material for household applications.

Primary photodissociation mechanisms of pyruvic acid on S1: observation of methylhydroxycarbene and its chemical reaction in the gas phase.

Pyruvic acid, a representative alpha-keto carboxylic acid, is one of the few organic molecules destroyed in the troposphere by solar radiation rather than by reactions with free radicals. To date, only its stable final products were identified, often with contribution from secondary chemistry, making it difficult to elucidate photodissociation mechanisms following excitation to the lowest singlet excited-state (S1) and the role of the internal hydrogen bond in the most-stable Tc conformer. Using multiplexed photoionization mass spectrometry we report the first direct experimental evidence, via the observation of singlet methylhydroxycarbene (MHC) following 351 nm excitation, supporting the decarboxylation mechanism previously proposed. Decarboxylation to MHC + CO2 represents 97-100% of product branching at 351 nm. We observe vinyl alcohol and acetaldehyde, which we attribute to isomerization of MHC. We also observe a 3 ± 2% yield of the Norrish Type I photoproducts CH3CO + DOCO, but only from d1-pyruvic acid. At 4 Torr pressure, we measure a photodissociation quantum yield of 1.0+0-0.4, consistent with IUPAC recommendations. However, our measured product branching fractions disagree with IUPAC. In light of previous calculations, these results support a mechanism in which hydrogen transfer on the S1 excited state occurs at least partially by tunneling, in competition with intersystem crossing to the T1 state. We present the first evidence of a bimolecular reaction of MHC in the gas phase, where MHC reacts with pyruvic acid to produce a C4H8O2 product. This observation implies that some MHC produced from pyruvic acid in Earth's troposphere will be stabilized and participate in chemical reactions with O2 and H2O, and should be considered in atmospheric modeling.

Stereocontrolled Synthesis of Functionalized cis-Cyclopentapyrazolidines by 1,3-Dipolar Cycloaddition Reactions of Azomethine Imines

The reaction of alkene-tethered alpha-ketocarboxylic acid derivatives with monosubstituted hydrazines allows highly substituted cis-cyclopentapyrazolidine ring systems to be constructed rapidly. Successful cyclocondensations are realized under thermal reaction conditions; in some cases, protic or Lewis acids accelerate these reactions. alpha-Methoxy-alpha,beta-unsaturated esters are suitable alkene components, as are alkenes having either electron-withdrawing or electron-donating substituents at the terminal alkene carbon. alpha-Ketoesters, alpha-ketoamides, and alpha-ketothioesters can be employed. Various hydrazines substituted with N-acyl, N-carboalkoxy, or N-carbamothioyl protecting groups are tolerated in these transformations. The rate of intramolecular cycloaddition is found to reflect not only the reactivity and equilibrium concentration of the azomethine imine intermediate, but, also in some cases, the rate at which hydrazone stereoisomers interconvert under the reaction conditions.

Divalent and trivalent alpha-ketocarboxylic acids as inhibitors of protein tyrosine phosphatases.

Protein tyrosine phosphatases (PTPases) are important targets for the treatment of insulin resistance in patients with type II diabetes and as antibacterial agents. As a result, there is a growing interest in the development of potent and specific inhibitors for these enzymes. This paper describes a series of inhibitors that contain two or three alpha-ketocarboxylic acid groups that are designed to form multiple contacts with residues inside or near the active site of phosphatases. The inhibitors have been assayed against three PTPases: the Yersinia PTPase, PTP1B, and LAR. The best of the inhibitors has IC(50) values against the Yersinia PTPase and PTP1B of 0.7 and 2.7 microM, respectively. These divalent and trivalent compounds are significantly more potent than their corresponding monovalent analogues. In addition, they show good selectivity for PTP1B and the Yersinia PTPase as compared to LAR.

A histochemical study of the apparent deamination of proteins by sodium hypochlorite.

The possible chemical mechanisms by which neutral solutions of sodium hypochlorite containing a high concentration of sodium chloride abolish the acidophilia of proteins in sections of fixed tissue are reviewed. The most probable one is the chlorination of the protein terminal amino groups, followed by the breakdown of the N-chloramine so formed into alpha-ketocarboxylic acid, nitrile or aldehyde groups. Hypochlorite solutions certainly do not deaminate tissue sections as was previously thought. Experimental evidence for the formation of relatively stable N-chloramine groups in situ and their limited conversion to aldehydes is reported. For example, the acidophilia of hypochlorite-treated sections was found to be restored after flooding them with hydriodic acid followed by the extraction of the liberated iodine with an alcohol. The significance of these experimental findings is discussed.