Effect of Solvent Polarity on the Vibrational Dephasing Dynamics of the Nitrosyl Stretch in an FeII Complex Revealed by 2D IR Spectroscopy

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• 作者：Jennifer F. Brookes ; Karla M. Slenkamp ; Michael S. Lynch ; Munira Khalil
• 刊名：The Journal of Physical Chemistry A
• 出版年：2013
• 出版时间：July 25, 2013
• 年：2013
• 卷：117
• 期：29
• 页码：6234-6243
• 全文大小：920K
• 年卷期：v.117,no.29(July 25, 2013)
• ISSN：1520-5215

文摘

The vibrational dephasing dynamics of the nitrosyl stretching vibration (谓_NO) in sodium nitroprusside (SNP, Na₂[Fe(CN)₅NO]路2H₂O) are investigated using two-dimensional infrared (2D IR) spectroscopy. The 谓_NO in SNP acts as a model system for the nitrosyl ligand found in metalloproteins which play an important role in the transportation and detection of nitric oxide (NO) in biological systems. We perform a 2D IR line shape study of the 谓_NO in the following solvents: water, deuterium oxide, methanol, ethanol, ethylene glycol, formamide, and dimethyl sulfoxide. The frequency of the 谓_NO exhibits a large vibrational solvatochromic shift of 52 cm^鈥?, ranging from 1884 cm^鈥? in dimethyl sulfoxide to 1936 cm^鈥? in water. The vibrational anharmonicity of the 谓_NO varies from 21 to 28 cm^鈥? in the solvents used in this study. The frequency鈥揻requency correlation functions (FFCFs) of the 谓_NO in SNP in each of the seven solvents are obtained by fitting the experimentally obtained 2D IR spectra using nonlinear response theory. The fits to the 2D IR line shape reveal that the spectral diffusion time scale of the 谓_NO in SNP varies from 0.8 to 4 ps and is negatively correlated with the empirical solvent polarity scales. We compare our results with the experimentally determined FFCFs of other charged vibrational probes in polar solvents and in the active sites of heme proteins. Our results suggest that the vibrational dephasing dynamics of the 谓_NO in SNP reflect the fluctuations of the nonhomogeneous electric field created by the polar solvents around the nitrosyl and cyanide ligands. The solute solvent interactions occurring at the trans-CN ligand are sensed through the 蟺-back-bonding network along the Fe鈥揘O bond in SNP.