867 resultados para BITTER ACIDS
Resumo:
To assess the correlation between macular pigment optical density and plasma levels of lutein, zeaxanthin, and fatty acids, especially omega-3 polyunsaturated fatty acids (PUFAs).
Inhibition of Pseudomonas aeruginosa biofilms with a glycopeptide dendrimer containing D-amino acids
Resumo:
Low mol. wt. (LMW) org. acids are important and ubiquitous chem. constituents in the atm. A comprehensive study of the chem. compn. of pptn. was carried out from June 2007 to June 2008 at a rural site in Anshun, in the west of Guizhou Province, China. During this period, 118 rainwater samples were collected and the main LMW carboxylic acids were detd. using ion chromatog. The av. pH of rainwater was 4.89 which is a typical acidic value. The most abundant carboxylic acids were formic acid (vol. wt. mean concn.: 8.77 μmol L-1) and acetic acid (6.90 μmol L-1), followed by oxalic acid (2.05 μmol L-1). The seasonal variation of concns. and wet deposition fluxes of org. acids indicated that direct vegetation emissions were the main sources of the org. acids. Highest concns. were obsd. in winter and were ascribed to the low winter rainfall and the contribution of other air pollution sources northeast of the study area. The ratio of formic and acetic acids in the pptn. ([F/A]T) was proposed as an indicator of pollution source. This suggested that the pollution resulted from direct emissions from natural or anthropogenic sources. Comparison with acid pptn. in other urban and rural areas in Guizhou showed that there was a decreasing contribution of LMW org. acids to free acidity and all anions in rainwater from urban to remote rural areas. Consequently, it is necessary to control emissions of org. acids to reduce the frequency of acid rain, esp. in rural and remote areas. [on SciFinder(R)]
Resumo:
A high dietary protein intake has been shown to blunt the deposition of intrahepatic lipids in high-fat- and high-carbohydrate-fed rodents and humans.
Resumo:
The purpose of this thesis was to synthesize biodegradable polyesters from a wide array of functionalized ¿-hydroxy acids. The initial strategy was to use amido-functionalized ¿-hydroxy acids and 2-bromopropanoyl bromide to form amido-functionalized cyclic diesters. Then, the resulting cyclic diesters would be used in ring opening polymerization to create biodegradable polyesters. However, the spontaneous rapid degradation of the secondary amido-functionalized cyclic diester structure, as seen with 2-benzamido-hydroxyacetic acid, limited ring formation to tertiary amido-functionalized ¿-hydroxy acids. Also, the hydrophilic nature of most ¿-hydroxy acids allowed water into the crystal structure of the ¿-hydroxy acid. Then, when the ¿-hydroxy acid was used in ring forming reactions, the associated water deactivated reactive reagents and limited cyclic diester synthesis. These issues led to the synthesis of hydrophobic and tertiary amido- and imido-functionalized ¿-hydroxy acids, 2-phthalimido-2-hydroxyacetic acid and 2-(1-oxoisoindolin-2-yl) hydroxyacetic acid. The new ¿-hydroxy acids were used in two new polymerization techniques, melt polycondensation and solution polymerization, instead of ring open polymerization. Melt polycondensation and solution polymerization had shown previous success in forming oligomers of amido-functionalized ¿-hydroxy acids. Melt polycondensation was conducted by heating the monomer past its melting temperature under reduced pressure. The uncatalyzed melt polycondensation of 2-(1-oxoisoindolin-2-yl) hydroxyacetic acid created polyesters (¿ 960 g/mol). The scandium(III) trifluoromethanesulfonate enhanced melt polycondensation polymerization created slightly larger oligomers (¿ 1340 g/mol). However, 2-phthalimido-2-hydroxyacetic acid was not compatible with melt polycondensation because thermal degradation occurred. Thus, solution polymerization was conducted via Steglich esterification. Only oligomeric functionalized polyesters were formed (¿ 1060 g/mol). Future work should focus on optimization of the catalyst and the reaction conditions to obtain higher molecular weight polyesters. Also, 2-(1-oxoisoindolin-2-yl) hydroxyacetic acid should be utilized in the cyclic diester synthesis technique.
Determination of stable carbon isotopes of organic acids and carbonaceous aerosols in the atmosphere
Resumo:
The sequences of rat testis carbonyl reductase (rCR1) and rat ovary carbonyl reductase (rCR2) are 98% identical, differing only at amino acids 140, 141, 143, 235 and 238. Despite such strong sequence identity, we find that rCR1 and rCR2 have different catalytic constants for metabolism of menadione and 4-benzoyl-pyridine. Compared to rCR1, rCR2 has a 20-fold lower K(m) and 5-fold lower k(cat) towards menadione and a 7-fold lower K(m) and 7-fold lower k(cat) towards 4-benzoyl-pyridine. We constructed hybrids of rCR1 and rCR2 that were changed at either residues 140, 141 and 143 or residues 235 and 238. rCR1 with residues 140, 141 and 143 of rCR2 has similar catalytic efficiency for menadione and 4-benzoyl-pyridine as rCR1. rCR1 with Thr-235 and Glu-238 of rCR2 has the catalytic constants of rCR2, indicating that it is this part of rCR2 that contributes to its lower K(m) for menadione and 4-benzoyl-pyridine. Comparisons of three-dimensional models of rCR1 and rCR2 show how Thr-235 and Glu-238 stabilize rCR2 binding of NADPH and menadione.