Oxyanions Raman spectroscopy

Mass spectrometry has been used to identily complexes formed in the gas phase by reaction of oxyanions and carbanions with 1,3,5-triazine. Spectroscopic studies and DFT calculations on the species formed by reaction of ethylamine with 2,4-dinitrotoluene in DMSO indicate that transfer of a methyl proton rather than nucleophilic attack is the major interaction. Two methods for the detection of 2,4,6-trinitrotoluene (TNT) using fluorescence techniques rely on the formation of its complexes with amines. Also cobalt-doped zinc sulfide quantum dots have been used to interact with complexes formed from TNT and L-cysteine allowing detection of the nitro compound. A complex between 2,4-dinitroanisole and L-cysteine methyl ester has been identified by surface-enhanced Raman spectroscopy. ... 

Qualitative methods for the identification are given in Table 15. Quantitative methods are well documented. Sulfur compounds are readily studied by vibrational spectroscopy, both IR and Raman. The oxides and oxyanions have characteristic spectra in the IR while the sulfanes and cyc/o-sulfur compounds give strong Raman spectra as a result of their high polarizability. The only potentially useful NMR nucleus is S, which is quadrupolar and low in abundance (Table 2). In general, measurements of NMR... 

While in the trypsins the oxyanion hole is comprised of main chain N-H groups, in subtilisin-BPN one N-H is donated by the side chain of Asn-155. Whiting and Peticolas (1994) investigated the nature of the binding of an acyl moiety to the oxyanion hole in subtilisin by Raman difference spectroscopy. On the basis of the results, they postulate that a tetrahedrally distorted carbonyl exists in the intermediate acyl-enzyme and that this distortion is essential for strong oxyanion hole hydrogen bonding. 

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