Solution-State (17)O Quadrupole Central-Transition NMR Spectroscopy in the Active Site of Tryptophan Synthase.

Oxygen is an essential participant in the acid-base chemistry that takes place within many enzyme active sites, yet has remained virtually silent as a probe in NMR spectroscopy. Here, we demonstrate the first use of solution-state (17)O quadrupole central-transition NMR spectroscopy to characterize enzymatic intermediates under conditions of active catalysis. In the 143 kDa pyridoxal-5'-phosphate-dependent enzyme tryptophan synthase, reactions of the α-aminoacrylate intermediate with the nucleophiles indoline and 2-aminophenol correlate with an upfield shift of the substrate carboxylate oxygen resonances.

Occurrence of halogenated transformation products of selected pharmaceuticals and personal care products in secondary and tertiary treated wastewaters from southern California.

Final effluent samples from 10 southern California (United States) wastewater treatment facilities, employing four distinct treatment schemes, were surveyed for selected pharmaceuticals, personal care products (PPCPs), alkylphenols, and 21 of their halogenated disinfection byproducts. Chlorinated and brominated standards and isotopically labeled internal standards were synthesized and purified to confirm and more accurately quantify selected disinfection byproducts of salicylic acid, bisphenol A, gemfibrozil, naproxen, diclofenac, technical 4-nonylphenol, and 4-tert-octylphenol using high-performance liquid chromatography and tandem mass spectrometry. Concentrations of parent compounds ranged from <10 to 3830 ng/L (gemfibrozil), and those of chloro/bromo byproducts ranged from <4 to 370 ng/L (dibromo nonylphenol).

Analytical and biological characterization of halogenated gemfibrozil produced through chlorination of wastewater.

The cholesterol-lowering pharmaceutical gemfibrozil is a relevant environmental contaminant because of its frequency of detection in U.S. wastewaters at concentrations which have been shown to disrupt endocrine function in aquatic species.

Determination of log D via automated microfluidic liquid-liquid extraction.

A method for log D (pH 7.4) measurement was developed using microfluidic liquid-liquid extraction. Values were determined for 26 compounds and compared to results obtained via shake-flask methods.