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Solvent Polarity Controls the Helical Conformation of Short Peptides Rich in C α ‐Tetrasubstituted Amino Acids
Author(s) -
Bellanda Massimo,
Mammi Stefano,
Geremia Silvano,
Demitri Nicola,
Randaccio Lucio,
Broxterman Quirinus B.,
Kaptein Bernard,
Pengo Paolo,
Pasquato Lucia,
Scrimin Paolo
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200600719
Subject(s) - chemistry , circular dichroism , polarity (international relations) , helix (gastropod) , solvent , crystallography , polar , methanol , stereochemistry , proton nmr , amino acid , solvent polarity , organic chemistry , biochemistry , ecology , physics , astronomy , biology , snail , cell
The two peptides, rich in C α ‐tetrasubstituted amino acids, Ac‐[Aib‐ L ‐(αMe)Val‐Aib] 2 ‐ L ‐His‐NH 2 ( 1 ) and Ac‐[Aib‐ L ‐(αMe)Val‐Aib] 2 ‐O‐ t Bu ( 2 a ) are prevalently helical. They present the unique property of changing their conformation from the α‐ to the 3 10 ‐helix as a function of the polarity of the solvent: α in more polar solvents, 3 10 in less polar ones. Conclusive evidence of this reversible change of conformation is reported on the basis of the circular dichroism (CD) spectra and a detailed two‐dimensional NMR analysis in two solvents (trifluoroethanol and methanol) refined with molecular dynamics calculations. The X‐ray diffractometric analysis of the crystals of both peptides reveals that they assume a prevalent 3 10 ‐helix conformation in the solid state. This conformation is practically superimposable on that obtained from the NMR analysis of 1 in methanol. The NMR results further validate the reported CD signature of the 3 10 ‐helix and the use of the CD technique for its assessment.