Structural and IR-Spectroscopic Elucidation of Dipeptide L-Threonyl-LMethionine in Solid State

Abstract

Dipeptide (L)-threonyl-(L)-methionine (Thr-Met) is characterized structurally by means of a solid-state linear polarized IR- spectroscopy (IR-LD) of oriented samples as a colloidal suspension in nematic liquid crystal and quantum chemical ab initio calculations. Vibrational analysis supports the experimental data as well. The role of intermolecular hydrogen bonding on conformational behavior and spectroscopic properties of the compound, studied in solid state is determined.

Dipeptide L -Seryl- L -Methionine—Linear Dichroic IR and Theoretical Characterization

“…Conclusions about the geometry and IR characteristic bands of the dipeptide were obtained. In contrast to Thr-Met, where a transconfiguration of the C¼O-NH amide fragment is preferable, [30] in Ser-Met, a cisoide-configuration is predicted (with a dihedral angle of 163.2(1) ).…”

“…The multiple 3100-2300 cm À1 peak corresponds to the asymmetric and symmetric stretches n as and 1475 cm À1 , [21][22][23][24]26,29] while in glycine, the n as COOÀ and n s COOÀ modes are at 1575 cm À1 and 1417 cm À1 . In contrast to L-threonyl-L-methionine dipeptides [30] the d NH is observed in the low-frequency region, which is typical for cis-or cisoide-configurated O¼C-NH amide fragments. [31] A direct experimental confirmation of this assumption is seen in the difference IR-LD spectrum (Fig.…”