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The Source of Helicity in Perfluorinated N-Alkanes

Jang, Seung Soon and Blanco, Mario and Goddard, William A., III and Caldwell, Gregg and Ross, Richard B. (2003) The Source of Helicity in Perfluorinated N-Alkanes. Macromolecules, 36 (14). pp. 5331-5341. ISSN 0024-9297. doi:10.1021/ma025645t.

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The well-known helical conformations of double stranded DNA and poly(alanine) are stabilized by inter- and intramolecular hydrogen bonds, respectively. Perfluorinated n-alkanes also exhibit stable helical conformations, with ordered chiralities at low temperatures. In the absence of hydrogen bonds, one may ask what forces stabilize perfluorinated n-alkane helices. We combine ab initio and empirical data to study the likely classical source of this helical behavior. Past studies point to bad sterics (van der Waals interactions) between neighboring fluorine atoms as the source of helicity in perfluorinated linear alkanes. In these early studies electrostatics were ignored. We undertook a detailed force field parameter optimization strategy, using experimental and ab initio data, to obtain transferable, uncorrelated estimates of the separate classical energy components. We find that the dominant energy term, the source of helicity, is electrostatics. The coulomb repulsion, from a classical fixed-charge model, reproduces reasonably well the position of the energy minima and the energy barrier between the helical and the all-trans conformations. Polarization effects, changes in atomic charges as a result of conformational changes, are not significant. Dihedral interactions and van der Waals terms adjust the exact position of the minima only slightly. In the absence of electrostatic contributions, van der Waals and dihedral interactions predict the incorrect stable conformations.

Item Type:Article
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URLURL TypeDescription Information
Jang, Seung Soon0000-0002-1920-421X
Goddard, William A., III0000-0003-0097-5716
Additional Information:© 2003 American Chemical Society. Received 5 September 2002. Published online 20 June 2003. Published in print 1 July 2003. This work was supported by the 3M Company. The facilities of the MSC were partly funded by NSF MRI and ARO/DURIP and are also supported by grants from DOE-ASCI, ARO/MURI, Chevron, NIH, ONR, Seiko-Epson, Avery-Dennison, Kellogg's, General Motors, Beckman Institute, Asahi Chemical, and Nippon Steel.
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Army Research Office (ARO)UNSPECIFIED
Department of Energy (DOE)UNSPECIFIED
Office of Naval Research (ONR)UNSPECIFIED
Caltech Beckman InstituteUNSPECIFIED
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Issue or Number:14
Record Number:CaltechAUTHORS:20170721-152727949
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Official Citation:The Source of Helicity in Perfluorinated N-Alkanes Seung Soon Jang, Mario Blanco, William A. Goddard III, Gregg Caldwell, and Richard B. Ross Macromolecules 2003 36 (14), 5331-5341 DOI: 10.1021/ma025645t
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:79275
Deposited By: Ruth Sustaita
Deposited On:21 Jul 2017 22:41
Last Modified:15 Nov 2021 17:46

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