Synergistic n → π* and nN → π*Ar interactions in C-terminal modified prolines: effect on Xaa-Pro cis/trans
Jugal Kishore Rai Deka1, Debashree Borah1, Paramesh Das1
1New Chemistry Unit, Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Jakkur, Bangalore 560064, India. bksarma@jncasr.ac.in.
Abstract:
Carbonyl-carbonyl (CO⋯CO) n → π* interaction often coexists with a hydrogen bond (HB) or another n → π* interaction. Although the interplay between HB and n → π* interaction was previously studied, there is no systematic investigation that shows a synergistic relationship of n → π* with another noncovalent interaction. Herein, we have studied a set of proline-diacylhydrazine (Pro-DAH) molecules and observed that increase in the strength of the nN → π*Ar interaction on their DAH side strengthened the n → π* interaction on the Pro side, which was experimentally determined by measuring the K of the Xaa-Pro amide bond. Overall, we describe a simple C-terminal modification strategy to stabilize the trans-Pro geometry that could be useful to stabilize PPII helices and collagen triple helices that require Pro to adopt the trans amide geometry.
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