Organic thiols are highly reactive ligands and play an important role in the speciation of several metals and organic pollutants in the environment. Although small thiols can be isolated and their concentrations can be estimated using chromatographic and derivatization techniques, estimating concentrations of thiols associated with biomacromolecules and humic substances has been difficult. Here we present a fluorescence-spectroscopy-based method for estimating thiol concentrations in biomacromolecules and cell membranes using one of the soluble bromobimanes, monobromo(trimethylammonio)bimane (qBBr). The fluorescence of this molecule increases significantly when it binds to a thiol. The change in the sample fluorescence due to thiols reacting with qBBr is used to determine thiol concentration in a sample. Using this method, small thiols such as cysteine and glutathione can be detected in clean solutions down to ~50 nM without their separation and prior concentration. Thiols associated with dissolved organic matter (DOM) can be detected down to low micromolar concentration, depending on the DOM background fluorescence. The charge on qBBr prevents its rapid diffusion across cell membranes, so qBBr is ideal for estimating thiol concentration at the cell membrane-water interface. This method was successfully used to determine the thiol concentration on the cell envelope of intact Bacillus subtilis to nanomolar concentration without any special sample preparation. Among the chemical species tested for potential interferences (other reduced sulfides methionine and cystine, carboxylate, salt (MgCl(2))), carboxylates significantly influenced the absolute fluorescence signal of the thiol-qBBr complex. However, this does not affect the detection of thiols in heterogeneous mixtures using the presented method.
Understanding the global cycling of bioelements, such as carbon, requires linking their transport vectors and pools in atmospheric, aquatic, and terrestrial systems. Quantifying carbon movement through the oceanic system is critical for a complete picture of the global carbon budget. Given the variability in metabolic balance within and between marine and coastal aquatic ecosystems (Caffrey et al. 1998;del Giorgio and Duarte 2002;Gupta et al. 2009;Kemp et al. 1997;Raymond et al. 2000), lateral transport of carbon could be the key to reconciling gaps in carbon budgets. One possible transport vector that has not been thoroughly investigated is organic carbon transfer between surface waters and the atmosphere.There is currently no universally accepted method for quantifying the diffusive air-sea flux of OC. Previous studies have mainly measured only a few compounds and have used atmospheric gas phase OC (GOC) quantification techniques such as direct trapping followed by chromatographic analysis Chuck et al. 2005;Singh et al. 2003
AbstractA method for quantifying the diffusive air-sea exchange of gaseous organic carbon (OC) was developed. OC compounds were separated into two operational pools-those that were kinetically air limited in diffusion across the air-sea interface and those that were water limited-during simultaneous air/water sampling. The method separates OC compounds into low Henry's law constant (low-H) semivolatile OC (SOC) and high Henry's law constant (high-H) volatile OC (VOC) pools that can be categorized by relating diffusion kinetic parameters to Henry's Law constant. Air limited (low-H; H << ~0.1 L atm mol -1 ) compounds were collected in pure water traps and were quantified as dissolved OC, whereas water limited (high-H; H >> ~0.1 L atm mol -1 ) compounds were collected on solid sorbent tubes downstream from the water traps and were analyzed by gas chromatography-flame ionization detection (GC-FID). Separating OC based on H, rather than measuring OC as one bulk pool, allows improved estimates of OC concentration gradients and fluxes. A 10-month field study in the York River Estuary in Gloucester Point, VA revealed an average VOC flux of 138 µg C m -2 d -1 and an average SOC flux of 832 mg C m -2 d -1 (positive fluxes denote sea to air transfer).
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