Conformational states of N-acylglycine dithioesters in solution: resonance Raman studies of isotopically substituted models for enzyme-substrate complexes.

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Resonance Raman (RR) and FTIR spectroscopic studies, taken with X-ray crystallographic data, are used to define the three major conformational states of N-acylglycine dithioesters in solution and to set up spectra-structure correlations. Importantly, each conformer has a characteristic RR signature, and thus the RR spectrum can be used to follow conformational events within dithioester enzyme-substrate intermediates. The signatures are further defined in the present work by the synthesis and spectroscopic characterization of 13C and 15N derivatives of N-benzoylglycine ethyl dithioester and N-(beta-phenylpropionyl)glycine ethyl dithioester. The observed isotope shifts offer insight into the normal mode character of the RR bands and provide standards with which to compare the shifts in the corresponding enzyme-substrate intermediates.