Circular dichroism eigenspectra of polyproline II and β-strand conformers of trialanine in water: Singular value decomposition analysis.

Despite that a number of experimental and theoretical investigations have been carried out to determine the structure of trialanine in water, the reported populations of polyproline II (PPII) and β-strand conformers vary and were found to be dependent on which spectroscopic method was used. Such discrepancies are due to limitations of different spectroscopic methods used. Here, the temperature- and pH-dependent circular dichroism (CD) and NMR experiments have been carried out to develop a self-consistent singular value decomposition procedure.

Azido gauche effect on the backbone conformation of β-azidoalanine peptides.

To study the azido gauche effect on the backbone conformation of β-azidoalanine (Aza) dipeptide (AAD, Ac-Aza-NHMe) and tripeptide (AAT, Ac-Aza-Aza-NH(2)), we used spectroscopic methods in combination with quantum chemistry calculations and molecular dynamics (MD) simulations. From the (1)H NMR coupling constants and (1)H,(1)H NOESY experimental data, we found that AAD in water mainly adopts a seven-membered cyclic (C(7)) rather than polyproline II (P(II)) backbone conformation and prefers the gauche- (g(-)) side-chain conformer. From the amide I IR absorption and circular dichroism (CD) spectra, the backbone conformation of AAD in water is found to deviate from P(II) but is rather close to C(7).