The effect of N-methylation on the conformational landscape of alanine: the case of N-methyl-l-alanine

Abstract

The non-proteinogenic amino acid N-methyl-L-alanine has been brought into the gas phase using laser ablation techniques and studied by high resolution chirped pulse and molecular-beam Fourier transform microwave spectroscopies coupled to supersonic expansion. Four conformers showing the three types of hydrogen bond interactions I (NH⋯OC), II (OH⋯N) and III (N–H⋯O–H) have been unambiguously identified, based on the comparison of the experimental rotational and ¹⁴N nuclear quadrupole constants with the calculated ab initio values. The observation of a type III conformer evidences the role of methyl groups in both sides to impose the steric hindrance, precluding the relaxation from type III to type I conformers and explains the responsibility for the unique conformational landscape observed in the case of NMA.