Solvation of N,C-Protected Valine: Interactions with DMSO and a Chiral Solvating Agent

Small protected amino acids find applications in many fields of chemistry. Their solvation, however, is often only studied in aqueous solution. In this contribution, the solvent-dependent conformational preferences of N,C-protected Boc-Val-NH-C3H7 are investigated by a combined VCD spectroscopic and theoretical approach. Replica exchange molecular dynamics simulations at the PM6 level and DFT calculations are both found to predict the conformational preferences in chloroform very well, which is confirmed by comparison of experimental and calculated IR and VCD spectra. In the case of DMSO, we find that solute-solvent interactions have to be taken into account explicitly in the simulation of the spectra. Furthermore, we show that the experimental spectra are better resembled by considering the conformational distribution obtained from the REMD simulations than from DFT. Finally, we also show that the weak interaction of Boc-Val-NH-C3H7 with a chiral solvating agent also induces a small VCD spectral signature.