DMSO, under ambient conditions. The one-dimensional 1H
NMR (500 MHz) spectra of 1e, in H2O : D2O, (90 : 10, v/v),
and DMSO-d6 were highly dispersed and showed a single set of
well-resolved signals, suggesting the existence of a single conformer
in these solvents. The observed nOe pattern in two-dimensional
nuclear Overhauser spectroscopy (2D NOESY, Fig. 3) of 1e
(detailed data in ESI{) in both the solvents strongly suggested
the prevalence of its solid-state extended conformation (of the
individual molecule) in solution-state as well. Interestingly, the nOe
patterns in both the solvents had a close resemblance to one
another, implying that 1e displays similar conformational features
in both DMSO and H2O.
self-assembly, even under a non-propitious environment, forming
robust sheet structures that are reminiscent of protein b-sheets.5
The findings, supported unambiguously by single crystal X-ray
diffraction (see crystal data{) and 2D NOESY studies, would fuel
intense research interests in delineating the exact correlation
between poly-N-acrylamide tacticity, conformation, and hydrogen
bonding propensities. In addition, this finding also provides new
insights that can be used to guide future attempts to engineer oligo-
N-acrylamide-based novel protein secondary structural mimics
that exclusively employ side chain amide groups for their
secondary structure stabilization.5 Interestingly, a prominent
question pops up eventually: what would have been the
conformation and consequently the hydrogen-bonding arrange-
ment if the oligo-N-alkyl acrylamide carbon backbone had the
amide side chains in an 1–3 anti (syndiotactic) configuration? In
order to answer such a question unambiguously, it is essential to
generate N-alkyl acrylamide oligomers having the amide side
chains in an 1,3 anti configuration; a work that we are rigorously
pursuing at present.
In summary, the result reported herein constitutes the first
unequivocal evidence of the ability of isotactic N-alkyl acrylamide
oligomers to undergo hydrogen-bond-mediated supramolecular
AK thanks CSIR, New Delhi for a research fellowship.
Notes and references
{ CCDC 273802 (1a) and 273803 (1e). For crystallographic data in CIF or
other electronic format see DOI: 10.1039/b601317a
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Fig. 3 Partial 2D NOESY spectra (500 MHz) of 1e in H2O : D2O (90 :
10). For aiding spectral interpretation, the crystal structure of 1e with
selected labelled atoms is also shown. (a) Single crystal X-ray structure. (b)
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2758 | Chem. Commun., 2006, 2756–2758
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