Estimation of the rotamerization constants of different conformations of N-acetylalanine: a theoretical and matrix-isolation FT-IR study.

Abstract The conformational landscape of N -acetylalanine has been investigated by a theoretical and matrix-isolation FT-IR study. Optimizations of N -acetylalanine structures has been conducted at successive higher levels of theory HF/3-21G, DFT(B3LYP)/6-31++G** and MP2/6-31++G**. This resulted in three stable conformations. Among these, one conformation contains an intramolecular H-bond. The vibrational properties of these conformations were calculated and used to identify the conformations in a cryogenic argon matrix. The intensities of some bands assigned to a particular conformation were used to estimate the rotamerization constants K r12 and K r13 for the equilibria NAA1 NAA2 and NAA1 NAA3, respectively. The obtained experimental values were in agreement with the theoretical predictions.