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Originally published in Science Express on 23 May 2002
Science 28 June 2002:
Vol. 296. no. 5577, pp. 2369 - 2373
DOI: 10.1126/science.1071563
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Reports

Conformational Dynamics in a Dipeptide After Single-Mode Vibrational Excitation

Brian C. Dian, Asier Longarte, Timothy S. Zwier*

The dynamics of conformational isomerization are explored in a methyl-capped dipeptide, N-acetyl-tryptophan methyl amide (NATMA), using infrared-ultraviolet (IR-UV) hole-filling and IR-induced population transfer spectroscopies. IR radiation selectively excites individual NH stretch vibrational fundamentals of single conformations of the molecule in the early portions of a gas-phase expansion, and then this excited population is collisionally recooled into its conformational minima for subsequent conformation-specific detection. Efficient isomerization is induced by the IR excitation that redistributes population between the same conformations that have population in the absence of IR excitation. The quantum yields for transfer of the population into the various conformational minima depend uniquely on which conformation is excited and on which NH stretch vibration is excited within a given conformation.

Department of Chemistry, Purdue University, West Lafayette, IN 47907-1393, USA.
*   To whom correspondence should be addressed. E-mail: zwier{at}purdue.edu

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