Surface enhanced Raman spectroscopic (SERS) behavior of phenylpyruvates used in heterogeneous catalytic asymmetric cascade reaction.

The strength and geometry of adsorption of substituted phenylpyruvates on silver surface was studied by means of surface enhanced Raman spectroscopy (SERS) using silver sol. 2'-nitrophenylpyruvates were used as starting materials in a newly developed heterogeneous catalytic asymmetric cascade reaction to produce substituted quinoline derivatives. Substituents on the aromatic ring of the starting materials had significant influence on the yield of the desired quinoline derivatives. Product selectivity of the transformation of nitrophenylpyruvates were enhanced by the acid added. The geometry and the strength of the adsorption are assumed to play an important role in the outcome of this reaction, so we have tried to find correlation between the structure of adsorbed phenylpyruvates and their catalytic performance. Based on the results of our spectroscopic measurements, the enol form is predominant in the series of phenylpyruvates in solid form and methanol solutions. Stronger adsorption of phenylpyruvates in acidic media through oxygen atoms was indicated by the increased enhancement in the SERS spectrum. The nitro group of 2'-nitrophenylpyruvates has no direct role in the adsorption on Ag surface. This observation has explained why the hydrogenation of the keto group (presumably via the enol form) occurs preferentially and why the formation of the undesired indole derivatives requiring reduction of the nitro group is suppressed. The SERS behavior has helped to get a closer look on the first step of adsorption of starting materials contributing to a better understanding of the cascade reaction studied, thus providing a better flexibility in catalyst design.

Bacillus safensis JG-B5T affects the fate of selenium by extracellular production of colloidally less stable selenium nanoparticles.

Understanding the impact of microorganisms on the mobility of selenium (Se) is important for predicting the fate of toxic Se in the environment and improving wastewater treatment technologies. The bacteria strain Bacillus safensis JG-B5T, isolated from soil in a uranium mining waste pile, can influence the Se speciation in the environment and engineered systems. However, the mechanism and conditions of this process remain unknown. This study found that the B. safensis JG-B5T is an obligate aerobic microorganism with an ability to reduce 70% of 2.5 mM selenite to produce red spherical biogenic elemental selenium nanoparticles (BioSeNPs). Only extracellular production of BioSeNPs was observed using transmission electron microscopy. The two-chamber reactor experiments, genome analysis and corona proteins identified on BioSeNPs suggested that the selenite reduction process was primarily mediated through membrane-associated proteins, like succinate dehydrogenase. Extracellular presence and low colloidal stability of BioSeNPs as indicated by ζ-potential measurements, render B. safensis JG-B5T an attractive candidate in wastewater treatment as it provides easy way of recovering Se while maintaining low Se discharge. As this microorganism decreases Se mobility, it will affect Se bioavailability in the environment and decreases its toxicity.

Quantification of low drug concentration in model formulations with multivariate analysis using surface enhanced Raman chemical imaging.

This paper reports the application of surface enhanced Raman chemical imaging (SER-CI) as a potentially non-destructive quantitative analytical method for the investigation of model pharmaceutical formulations containing the active pharmaceutical ingredient (API) in low concentrations (0.5-2%). The application of chemometric techniques for processing the spectra enables the determination of API distribution in products of different concentrations. In addition, the applied multivariate curve resolution can be proper method to identify unexpected contaminants in illicit drugs. The drastic Raman signal enhancement in the presence of silver nanoparticles provides significantly improved calibration accuracy and, at the same time, radically decreased image acquisition time compared to conventional Raman chemical imaging.

Specific behavior of the p-aminothiophenol--silver sol system in their Ultra-Violet-Visible (UV-Visible) and Surface Enhanced Raman (SERS) spectra.

The UV-Visible and Surface Enhanced Raman Spectroscopy (SERS) behavior of silver sol (a typical SERS agent) were studied in the presence of different bifunctional thiols such as p-aminothiophenol, p-mercaptobenzoic acid, p-nitrothiophenol, p-aminothiophenol hydrochloride, and 2-mercaptoethylamine hydrochloride in diluted aqueous solution. Our results confirm that the p-aminothiophenol induced aggregation of citrate stabilized silver colloid originates from its electrostatic nature, as well as the azo-bridge formation cannot be the reason of the observed time dependent UV-Visible spectra. Based on our parallel SERS and electrospray ionization mass spectrometry measurements, we have concluded that certain amount of oxidized form of the probe molecule has to be present for the so-called b2-mode enhancement in the SERS spectrum of p-aminothiophenol. Our findings seem to support the idea that the azo-bridge formation is responsible for the b2-mode enhancement in the SERS spectrum of p-aminothiophenol.

Investigation of drug distribution in tablets using surface enhanced Raman chemical imaging.

This paper reports the first application of surface enhanced Raman chemical imaging on pharmaceutical tablets containing the active ingredient (API) in very low concentrations. Taking advantage of the extremely intensive Raman signals in the presence of silver colloids, image aquisition time was radically decreased. Moreover, the investigation of drug distribution below the detection limit of regular micro-Raman spectrometry was made feasible. The characteristics of different manufacturing technologies could be revealed at very low API concentrations by using chemometric methods for processing and evaluating the large number of varying spectra provided with this imaging method.