Vibrational Spectroscopic Determination of Local Solvent Electric Field, Solute鈥揝olvent Electrostatic Interaction Energy, and Their Fluctuation Amplitudes
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- 作者：Hochan Lee ; Gayeon Lee ; Jonggu Jeon ; Minhaeng Cho
- 刊名：The Journal of Physical Chemistry A
- 出版年：2012
- 出版时间：January 12, 2012
- 年：2012
- 卷：116
- 期：1
- 页码：347-357
- 全文大小：999K
- 年卷期：v.116,no.1(January 12, 2012)
- ISSN：1520-5215
文摘
IR probes have been extensively used to monitor local electrostatic and solvation dynamics. Particularly, their vibrational frequencies are highly sensitive to local solvent electric field around an IR probe. Here, we show that the experimentally measured vibrational frequency shifts can be inversely used to determine local electric potential distribution and solute鈥搒olvent electrostatic interaction energy. In addition, the upper limits of their fluctuation amplitudes are estimated by using the vibrational bandwidths. Applying this method to fully deuterated N-methylacetamide (NMA) in D2O and examining the solvatochromic effects on the amide I鈥?and II鈥?mode frequencies, we found that the solvent electric potential difference between O(鈺怌) and D(鈭扤) atoms of the peptide bond is about 5.4 V, and thus, the approximate solvent electric field produced by surrounding water molecules on the NMA is 172 MV/cm on average if the molecular geometry is taken into account. The solute鈥搒olvent electrostatic interaction energy is estimated to be 鈭?37 kJ/mol, by considering electric dipole鈥揺lectric field interaction. Furthermore, their root-mean-square fluctuation amplitudes are as large as 1.6 V, 52 MV/cm, and 41 kJ/mol, respectively. We found that the water electric potential on a peptide bond is spatially nonhomogeneous and that the fluctuation in the electrostatic peptide鈥搘ater interaction energy is about 10 times larger than the thermal energy at room temperature. This indicates that the peptide鈥搒olvent interactions are indeed important for the activation of chemical reactions in aqueous solution.