This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Infrared markers, such as nitriles and azides, have become useful as vibrational probes of biomolecules. In particular, ultrafast measurements of the stretching mode of the nitrile group in biological systems have provided local site-specific vibrational dynamics. Several studies, including peptide membrane interactions and drug?enzyme interactions, havetaken advantage of the relatively sharp spectral features of nitriles that occur in a spectrally transparent region of most biological molecules while having sensitivity to the local environment. However, the relatively small absorption cross section of the nitrile vibrational transition compromises its utility for nonlinear IR work and necessitates the use of higher concentrations than desirable for biological systems in both linear and nonlinear IR experiments;furthermore the absorption signal overlaps some water absorption bands. Thus, new vibrational probes are needed that are suitable to be used as biological probes. One promising candidate for nonlinear spectroscopy is the azido-, N3, group. The absorption cross section of azides is about one order of magnitude greater than nitriles allowing for much lower concentrations to be utilized. Also, the N3 transition, like CN, is sensitive to changes in the local environment. The aliphatic azides are stable under most conditions. The potential utility of the azido group as an infrared probe of local environment has been demonstrated in peptides and proteins. This utility has been further extended to nucleosides as infrared and NMR experiments. The azido-group has a relatively simple vibrational signature in the 2100 cm-1 region where one sharp transition is observed. The goal of this project is to investigate the potenital use of azides as environmental probes in 2D IR spectroscopy.
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