title: Theoretical design of bioinspired macromolecular electrets based on anthranilamide derivatives.
abstract: Polypeptide helices possess considerable intrinsic dipole moments oriented along their axes. While for proline helices the dipoles originate solely from the ordered orientation of the amide bonds, for 3(10-) and alpha-helices the polarization resultant from the formation of hydrogen-bond network further increases the magnitude of the macromolecular dipoles. The enormous electric-field gradients, generated by the dipoles of alpha-helices (which amount to about 5 D per residue with 0.15 nm residue increments along the helix), play a crucial role in the selectivity and the transport properties of ion channels. The demonstration of dipole-induced rectification of vectorial charge transfer mediated by alpha-helices has opened a range of possibilities for applications of these macromolecules in molecular and biomolecular electronics. These biopolymers, however, possess relatively large bandgaps. As an alternative, we examined a series of synthetic macromolecules, aromatic oligo-ortho-amides, which form extended structures with amide bonds in ordered orientation, supported by a hydrogen-bond network. Unlike their biomolecular counterparts, the extended pi-conjugation of these macromolecules will produce bandgaps significantly smaller than the polypeptide bandgaps. Using ab initio density functional theory calculations, we modeled anthranilamide derivatives that are representative oligo-ortho-amide conjugates. Our calculations, indeed, showed intrinsic dipole moments oriented along the polymer axes and increasing with the increase in the length of the oligomers. Each anthranilamide residue contributed about 3 D to the vectorial macromolecular dipole. When we added electron donating (diethylamine) and electron withdrawing (nitro and trifluoromethyl) groups for n- and p-doping, respectively, we observed that: (1) proper positioning of the electron donating and withdrawing groups further polarized the aromatic residues, increasing the intrinsic dipole to about 4.5 D per residue; and (2) extension of the pi-conjugation over some of the doping groups narrowed the band gaps with as much as 1 eV. The investigated bioinspired systems offer alternatives for the development of broad range of organic electronic materials with nonlinear properties.
authors.affiliation: Department of Electrical Engineering, University of California, Riverside, CA 92521, USA. mashraf@ee.ucr.edu
authors.forename: M K
authors.initials: MK
authors.lastname: Ashraf
authors.forename: Brent
authors.initials: B
authors.lastname: Millare
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Gerasimenko
authors.forename: Duoduo
authors.initials: D
authors.lastname: Bao
authors.forename: Rajeev R
authors.initials: RR
authors.lastname: Pandey
authors.forename: Roger K
authors.initials: RK
authors.lastname: Lake
authors.forename: Valentine I
authors.initials: VI
authors.lastname: Vullev
mesh_terms: D001704:Biopolymers / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D062367:ortho-Aminobenzoates / Q000737:chemistry*
chemical_list: D001704:Biopolymers; D062367:ortho-Aminobenzoates; C000219:anthranilamide