Understanding the dielectric properties of liquid amides from a polarizable force field.

Printer-friendly versionPrinter-friendly versionPDF versionPDF version
TitleUnderstanding the dielectric properties of liquid amides from a polarizable force field.
Publication TypeJournal Article
Year of Publication2008
AuthorsHarder, E, Anisimov, VM, Whitfield, T, Mackerell, AD, Roux, B
JournalJ Phys Chem B
Volume112
Issue11
Pagination3509-21
Date Published2008 Mar 20
ISSN1520-6106
KeywordsAcetamides, Computer Simulation, Cryoprotective Agents, Electric Capacitance, Hydrogen Bonding, Molecular Conformation, Thermodynamics, Time Factors
Abstract

The role played by electronic polarization in the dielectric properties of liquid N-methyl acetamide (NMA) is examined using molecular dynamics simulations with a polarizable force field based on classical Drude oscillators. The model presented is the first force field shown to reproduce the anomalously large dielectric constant of liquid NMA. Details of the molecular polarizability are found to be important. For instance, all elements of the polarizability tensor, rather then just the trace, impact on the condensed phase properties. Two factors related to electronic polarizability are found to contribute to this large dielectric constant. First is the significant enhancement of the mean amide molecular dipole magnitude, which is 50% larger in the liquid than in the gas phase. Second is the consequent strong hydrogen bonding between molecular neighbors that enhances the orientational alignment of the molecular dipoles. Polarizable models of amide compounds that have two (acetamide) and zero (N,N-dimethyl acetamide) polar hydrogen-bond donor atoms are also investigated. Experimentally, the neat liquid dielectric constants at 373 K are 100 for NMA, 66 for acetamide and 26 for N,N-dimethyl acetamide. The polarizable models replicate this trend, predicting a dielectric constant of 92+/-5 for NMA, 66+/-3 for acetamide and 23+/-1 for N,N-dimethyl acetamide.

DOI10.1021/jp709729d
Alternate JournalJ Phys Chem B
PubMed ID18302362
PubMed Central IDPMC4754998
Grant ListR01 GM072558 / GM / NIGMS NIH HHS / United States
GM 072558 / GM / NIGMS NIH HHS / United States
GM 51501 / GM / NIGMS NIH HHS / United States
R01 GM051501 / GM / NIGMS NIH HHS / United States
R29 GM051501 / GM / NIGMS NIH HHS / United States