IR-LD spectroscopic characterization of l-Tryptophan containing dipeptides

IR-spectroscopic and stereo-structural analysis of aromatic l-Tryptophan containing dipeptides l-Tryptophan–l-Tryptophan (Trp–Trp), l-Tyrosine–l-Tryptophan (Tyr–Trp) and cyclo(Trp–Trp) have been carried out by means of solid-state linear-dichroic infrared (IR-LD) spectroscopy of oriented as suspension in nematic liquid crystal solids. The experimental data have been compared with analogous ones of the simple amino acids l-Tyrosnine (l-Tyr) and l-Tryptophan (l-Trp). In cyclo(Trp–Trp), the IR-spectral changes towards the IR-ones of acyclic Trp–Trp have been determined. A theoretical analysis of Tyr–Trp at Hartree–Fock level of theory and 6-31G** basis set is also applied.