How water links to cis and trans peptidic groups: the rotational spectrum of N-methylformamide–water

We investigated the Fourier transform microwave spectra of the hydrated forms of the N-methylformamide (NMF) in a supersonic expansion and assigned the rotational spectra of two mono-hydrated species. The conformation of each molecular complex was reliably determined on the basis of the values of the rotational constants, of the relative intensities of a- and b-type transitions, and of the features of the 14N quadrupole hyperfine structure of the rotational transitions. In both complexes water acts as a proton donor and NMF has a trans configuration of the peptidic group. In the most stable of these conformers, water is also weakly bound to the methyl group.