title: Permanent electric dipole moments of carboxyamides in condensed media: what are the limitations of theory and experiment?
abstract: 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 "abnormal" 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.
authors.affiliation: Department of Bioengineering, University of California, Riverside, California 92521, United States.
authors.forename: Srigokul
authors.initials: S
authors.lastname: Upadhyayula
authors.forename: Duoduo
authors.initials: D
authors.lastname: Bao
authors.forename: Brent
authors.initials: B
authors.lastname: Millare
authors.forename: Somaia S
authors.initials: SS
authors.lastname: Sylvia
authors.forename: K M Masum
authors.initials: KM
authors.lastname: Habib
authors.forename: Khalid
authors.initials: K
authors.lastname: Ashraf
authors.forename: Amy
authors.initials: A
authors.lastname: Ferreira
authors.forename: Stephen
authors.initials: S
authors.lastname: Bishop
authors.forename: Robert
authors.initials: R
authors.lastname: Bonderer
authors.forename: Samih
authors.initials: S
authors.lastname: Baqai
authors.forename: Xiaoye
authors.initials: X
authors.lastname: Jing
authors.forename: Miroslav
authors.initials: M
authors.lastname: Penchev
authors.forename: Mihrimah
authors.initials: M
authors.lastname: Ozkan
authors.forename: Cengiz S
authors.initials: CS
authors.lastname: Ozkan
authors.forename: Roger K
authors.initials: RK
authors.lastname: Lake
authors.forename: Valentine I
authors.initials: VI
authors.lastname: Vullev
mesh_terms: D000577:Amides / Q000737:chemistry*; D004980:Ethane / Q000031:analogs & derivatives / Q000737:chemistry; D006843:Hydrocarbons, Chlorinated / Q000737:chemistry; D008962:Models, Theoretical; D011506:Proteins / Q000737:chemistry*; D055672:Static Electricity
chemical_list: D000577:Amides; D006843:Hydrocarbons, Chlorinated; D011506:Proteins; C015530:1,1,2,2-tetrachloroethane; D004980:Ethane