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Hybridization of Long Pyridine‐Dicarboxamide Oligomers into Multi‐Turn Double Helices: Slow Strand Association and Dissociation, Solvent Dependence, and Solid State Structures
Author(s) -
Baptiste Benoit,
Zhu Jiang,
Haldar Debasish,
Kauffmann Brice,
Léger JeanMichel,
Huc Ivan
Publication year - 2010
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.200900713
Subject(s) - oligomer , pyridine , chemistry , crystallography , kinetics , helix (gastropod) , stereochemistry , dissociation (chemistry) , solvent , polymer chemistry , organic chemistry , biology , ecology , physics , quantum mechanics , snail
Oligoamides of 2,6‐diaminopyridine and 2,6‐pyridinedicarboxylic acid comprised of 5, 7, 9, 11, or 13 units and bearing 4‐isobutoxychains on all pyridine rings and tert ‐butyl‐carbamate terminal groups have been synthesized stepwise, along with an 11 mer having benzyl‐carbamate terminal groups. The crystal structure of all five Boc‐terminated compounds has been obtained and shows a highly regular and conserved double helical hybridization motif of up to 3 complete turns for the 13 mer. Four pyridine units span one helical turn and define a helix pitch of ca 7 Å. Solution studies in CDCl 3 demonstrated that the Boc‐terminated oligomers strongly hybridize in this solvent, and that K dim values increase with oligomer length. The K dim values are 31000 and 7×10 5 L mol −1 for the 7 mer and the 9 mer, respectively, and are too high to be measured by NMR for the 11 mer and the 13 mer. Hybridization and dissociation kinetics at 2 m M proceed at decreasing rates upon increasing oligomer length. The rate was faster than minutes for the 7 mer, of the order of hours for the 9 mer, and days for the 11 mer and 13 mer. The same trend was observed in [D 5 ]pyridine but with considerably lower K dim values and faster kinetics. The benzylcarbamate 11 mer was also found to hybridize into a double helix but with reduced K dim values and faster kinetics compared to its Boc‐terminated analogue. Combined with previous studies, the results presented here frame a global understanding of the hybridization of these pyridinecarboxamide oligomers and provide useful guidelines for the design of other artificial double helices.