Permanent Electric Dipole Moments of Carboxyamides in Condensed Media: What Are the Limitations of Theory and Experiment?

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• 作者：Srigokul Upadhyayula ; Duoduo Bao ; Brent Millare ; Somaia S. Sylvia ; K. M. Masum Habib ; Khalid Ashraf ; Amy Ferreira ; Stephen Bishop ; Robert Bonderer ; Samih Baqai ; Xiaoye Jing ; Miroslav Penchev ; Mihrimah Ozkan ; Cengiz S. Ozkan ; Roger K. Lake ; Valentine I. Vullev
• 刊名：Journal of Physical Chemistry B
• 出版年：2011
• 出版时间：August 4, 2011
• 年：2011
• 卷：115
• 期：30
• 页码：9473-9490
• 全文大小：1340K
• 年卷期：v.115,no.30(August 4, 2011)
• ISSN：1520-5207

文摘

Electrostatic properties of proteins are crucial for their functionality. Carboxyamides are small polar groups that, as peptide bonds, are principal structural components of proteins that govern their electrostatic properties. We investigated the medium dependence of the molar polarization and of the permanent dipole moments of amides with different state of alkylation. The experimentally measured and theoretically calculated dipole moments manifested a solvent dependence that increased with the increase in the media polarity. We ascribed the observed enhancement of the amide polarization to the reaction fields in the solvated cavities. Chloroform, for example, caused about a 25% increase in the amide dipole moments determined for vacuum, as the experimental and theoretical results demonstrated. Another chlorinated solvent, 1,1,2,2-tetrachloroethane, however, caused an 鈥渁bnormal鈥?increase in the experimentally measured amide dipoles, which the theoretical approaches we used could not readily quantify. We showed and discussed alternatives for addressing such discrepancies between theory and experiment.