Anharmonic vibrational probe for N-methylacetamide in different micro-environments |
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| Institution: | 1. Minneapolis Heart Institute, Abbott Northwestern Hospital Minneapolis, Minnesota;2. Palo Alto Cooperative Studies Program Coordinating Center, Palo Alto, California;3. VA North Texas Health Care System and University of Texas Southwestern Medical Center, Dallas, Texas;4. Harvard Medical School, Boston, Massachusetts;5. Sarver Heart Center, Tucson, Arizona;6. Mayo Clinic School of Graduate Medical Education, Rochester, Minnesota;7. Durham Veteran Affairs Medical Center, Durham, North Carolina;8. San Francisco Veteran Affairs Medical Center, San Francisco, California;9. Atlanta Veteran Affairs Medical Center, Decatur, Georgia;10. Memphis Veteran Affairs Medical Center, Memphis, Tennessee;11. North Florida/South Georgia Veterans Health System, Gainesville, Florida;12. Minneapolis Veteran Affairs Medical Center, Minneapolis, Minnesota;13. Desert Cardiology of Tucson, Tucson, Arizona;14. John L. McClellan Memorial Veteran Affairs Medical Center, Little Rock, Arkansas;15. Oklahoma City VA Medical Center, Oklahoma City, Oklahoma;p. Denver VA Medical Center, Denver, Colorado;q. Louis Stokes Cleveland Veteran Affairs Medical Center, Cleveland, Ohio;r. Michael E. DeBakey Department of Veterans Affairs Medical Center, Houston, Texas;s. Hines/North Chicago Veteran Affairs Medical Center, Hines, Illinois;t. Harry S. Truman Memorial VA Medical Center, Columbia, Missouri;u. Veteran Affairs Cooperative Studies Program Clinical Research Pharmacy, Albuquerque, New Mexico;v. Health Economics Resource Center, VA Palo Alto, California;w. Division of Invasive Cardiology, Second Department of Internal Medicine and Cardiology Center, University of Szeged, Szeged, Hungary;x. Department of Health Research and Policy, Stanford University, Stanford, California |
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| Abstract: | In the present study, anharmonic vibrational properties of the amide modes in N-methylacetamide (NMA), a model molecule for peptide vibrational spectroscopy, are examined by DFT calculations. The 3N-6 normal mode frequencies, diagonal and off-diagonal anharmonicities are evaluated by means of the second order vibrational perturbation theory (VPT2). Good performance of B3LYP/6-31+G** is found for predicting vibrational frequencies in comparison with gas phase experimental data. The amide vibrational modes are assigned through potential energy distribution analysis (PED). The solvation effect on the amide vibrational modes is modeled within the PCM method. From gas phase to polar solvents, red shifts are observed for both harmonic and anharmonic vibrational frequency of amide I mode while the C O bond length increases upon the solvent polarity. Cubic and quartic force constants are further calculated to evaluate the origin of the anharmonicity for the amide I mode of NMA in different micro-environments. |
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