1 research outputs found
Structural Stability in Dimer and Tetramer Clusters of l‑Alanine in the Gas Phase and the Feasibility of Peptide Bond Formation
Stability in low-energy
structures of the dimer and tetramer clusters
of l-alanine in the gas phase is studied by accurate quantum
chemical computations at the DLPNO2013-CCSDÂ(T) level. It is found
that the dispersion interaction energies in the dimer (−0.3
to −0.6 kcal/mol) and in the tetramer (−1.3 to −2.5
kcal/mol) have a small role in the stability of the clusters as compared
to the hydrogen bond (HB) energies −4.1 to −14.2 and
−32.2 to −40.1 kcal/mol, respectively. The HB energy
in the alanine cluster is obtained from the binding energy (BE) of
DLPNO2013-CCSDÂ(T)//B2PLYP/def2-TZVP by subtracting the dispersion
interaction energy. Local HB energies deduced from the dimer structures
are found to be suitable to estimate total HB energies in similar
environments. The BEs of OH···NH and OH···OC
bonds are −9.5 and −7.1 kcal/mol, respectively. This
suggests that the higher clusters are formed through OH···NH
bonds as they confer more stability. Analysis of bonding in the tetramer
shows that the low-energy tetramer and higher clusters are formed
through the OH···NH mode of hydrogen bonding, unlike
the dimer which is formed through the OH···OC bond.
Feasibility of the amino acid cluster to function as a precursor for
polypeptide formation is examined because the orientation of the OH···NH
mode of hydrogen bonding is suitable for chemical condensation. The
propensity of forming coiled structures in higher clusters and thus
in the polypeptides is examined based on the conformational stability
in the tetramer of alanine