Probing the Structure and Dynamics of Peptides by Multiple Laser Pulses: Femtosecond Analogues of Multidimensional NMR

Shaul Mukamel , University of California

The response of complex molecules to sequences of infrared pulses provides multidimensional femtosecond snapshots of their structure and dynamical processes. The fundamental concepts underlying the design and interpretation of these experiments will be surveyed. New pulse sequences may be constructed for probing specific coherences and vibrational population dynamics, building upon the analogy with multidimensional NMR. Computational techniques for the necessary multipoint correlation functions based on a fluctuating exciton hamiltonian will be presented.

Two dimensional correlation plots of the signals show characteristic cross peak patterns which carry information about structures. The lineshapes provide information on conformational and solvent induced fluctuations. Distinct signatures of energy level fluctuations with arbitrary timescales and degree of correlation are identified. Resolution may be enhanced by applying novel polarization configurations of the optical fields which also provide chirality-specific information. Pulse shaping coherent control strategies and sensitivity analysis are used to simplify complex spectra and retrieve and enhance desired features. Applications will be made to ideal secondary structural motifs of peptides folding dynamics, and hydrogen bonding fluctuations.

"Multidimensional Femtosecond Correlation Spectroscopies of Electronic and Vibrational Excitations,'' S. Mukamel, Ann. Rev. Phys. Chem. 51, 691-729 (2000).

"Peptide Secondary Structure Determination by Three-Pulse Coherent Vibrational Spectroscopies; A Simulation Study", D. Abrahamavicius, W. Zhuang, S. Mukamel, J. Phys. Chem. B, 108,18034-18045 (2004).

"Disentangling Multidimensional Femtosecond Spectra of Excitons by Pulse Shapingwith Coherent Control", D. Abramavicius and S. Mukamel, J. Chem. Phys., 120, 8373-8378 (2004).

"Many-Body Approaches For Simulating Coherent Nonlinear Spectroscopies of Electronic and Vibrational Excitons " D. Abramavicius and S. Mukamel, Chem. Rev., 104, 2073-2098 (2004).

"Dissecting coherent vibrational spectra of small proteins into secondary structural elements by sensitivity analysis,'' W. Zhuang, D. Abramavicius , and S. Mukamel, PNAS 102, 7443-7448 (2005).

Fig. Top: Pulse sequence in four wave mixing. Middle right: a Feynmann diagram. Lower: two dimensional photon echo signal for an alpha helix (left) and a beta hairpin (right).

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