Study of the Mechanism of Thermal Chemical Processes in the Crystals of YAF Tripeptides by Means of Mass Spectrometry and Solid State NMR

Abstract

Thermal reactions in two Tyr-Ala-Phe (YAF) tripeptide crystals with different molecular packing (monoclinic and hexagonal), distinct stereochemistry of central amino acid (D or L alanine) and specific arrangement of molecules in the crystal lattice (head-to-tail) were investigated. Samples were heated up to 180 °C, while the melting point for YAF crystals is above the 220 °C. Below the melting temperature, in both cases the chemical reactions leading to formation of cyclic dipeptides (YA diketopiperazine) and leaving of phenylalanine were observed. Two possible mechanisms of chemical reaction in the crystal lattice assuming intra- and/or intermolecular pathways were considered. (13)C and (15)N enriched YAF samples were employed to study of mechanism of solid state reactivity using mass spectrometry and advanced solid state NMR techniques (2D DARR (Dipolar Assisted Rotational Resonance) and 2D Double CP (Cross-Polarization) correlations).

Tailoring the volatility and stability of oligopeptides

“…Upon evaporation of 1 at varying source temperatures up to T = 595 K, only molecular fragments were detected, both in EI‐QMS and VUV‐TOF‐MS. Three major fragments were observed that were tentatively assigned to the loss of the C‐terminal alanine (H 2 N‐CH(CH 3 )‐COOH) possibly resulting from thermal diketopiperazine formation (C 14 H 15 N 3 O 2 , 257 amu) as well as two common tryptophan fragments which were observed in all following mass spectra: the indole cation (C 8 H 6 N + , 116 amu) and the skatole cation (C 9 H 8 N + , 130 amu).…”