kinetic studies were made of the reactions between triphenylphosphine 1, dialkyl acetylenedicarboxylates 2 in the presence of nh-acid, such as maleimid (as a protic/nucleophilic reagent) 3. to determine the kinetic parameters of the reactions, they were monitored by uv spectrophotometery. the second order fits were automatically drawn and the values of the second order rate constant (k2) were a...

: 1h nmr spectra of a series of enaminones r-co-ch=c(nhch2ph)-r  [1, r=ch3; 2, r=c6h5; 3, r=cf3; 4, r=ch2ch2ch2; 5, r=ch2c(ch3)2ch2], were obtained in the presence of trifluoroacetic acid in cdcl3 or dmso-d6 at 28 °c. steric, solvent, electronic and hydrogen bonding effects on the rates of acid-catalyzed nh proton exchanges were investigated. rate constants were calculated by 1h nmr line shape ...

We present new findings in our drug discovery effort to develop an anticomplement therapeutic. We have designed several active analogues of compstatin by altering its amino acid composition at positions 4 and 9. The most effective analogues have tryptophan or fused-ring non-natural amino acids at position 4 and alanine or an unbranched single-methyl amino acid at position 9. Twenty-one of these...

This study was undertaken to determine the mechanism by which ammonium chloride (NH(4)Cl) inhibits stimulated acid secretion in the bullfrog gastric mucosa. To this end, four possible pathways of inhibition were studied: 1) blockade of basolateral K(+) channel, 2) blockade of ion transport activity, 3) neutralization of secreted H(+) in the luminal solution, or 4) ATP depletion. Addition of nut...

Nitrogen-limited cells of Selenastrum minutum (Naeg.) Collins are able to assimilate NH(4) (+) in the dark under anaerobic conditions. Addition of NH(4) (+) to anaerobic cells results in a threefold increase in tricarboxylic acid cycle (TCAC) CO(2) efflux and an eightfold increase in the rate of anaplerotic carbon fixation via phosphoenolpyruvate carboxylase. Both of these observations are cons...

1. The degradative pathway of melamine (1,3,5-triazine-2,4,6-triamine) was examined in Pseudomonas sp. strain A. 2. The bacterium grew with melamine, ammeline, ammelide, cyanuric acid or NH+4 as sole source of nitrogen, and each substrate was entirely metabolized. Utilization of ammeline, ammelide, cyanuric acid or NH+4 was concomitant with growth. But with melamine as substrate, a transient in...

The covalent linkage of graphene acid (GA) with amine-functionalized UiO-66-NH 2 via an amide bond. resultant hybrid GA@UiO-66-NH acts as a chemiresistive CO sensor wth significant efficiency owing to its unique structural features.

The rate of hydrolysis of trans -[Cr(NH ) F ] was obtained as a function of acid concentsation in perchloric, sulfuric and nitric acid at 3Q°C. The results have been analyzed by the treatment of Bunnett and Olsen. Values of the parameter ?in Olsen equation are consistent with the participation of water as a proton-wansfer agent in the rate-determining step. The Arrhenius plot for perchlori...

NH(4)(+) transport by the distal nephron and NH(4)(+) detoxification by the liver are critical for achieving regulation of acid-base balance and to avoid hyperammonemic hepatic encephalopathy, respectively. Therefore, it has been proposed that rhesus type B glycoprotein (Rhbg), a member of the Mep/Amt/Rh NH(3) channel superfamily, may be involved in some forms of distal tubular acidosis and con...

Understanding the microscopic mechanisms of new particle formation under acid-rich conditions is significance in atmospheric science. Using quantum chemistry calculations, we investigated mechanism methanesulfonic acid (MSA)–methylamine (MA)–ammonia (NH 3 ) clusters. We focused on binary (MSA) 2n -(MA) n and ternary 3n -(NH , ( = 1–4) systems which contain more than base molecules. found that l...