Proton NMR relaxation studies of solid tyrosine derivatives and their mixtures with l-leucinamide

Abstract

Proton NMR relaxation time measurements were carried out on solid tyrosine derivatives: acetyl- l-tyrosine ethyl ester (Ac-Tyroet), N-carbobenzyloxy- l-tyrosine ethyl ester (CBZ-Tyroet), N-trifluoroacetyl- l-tyrosine ethyl ester (TFAc-Tyroet) and their mixtures with l-leucinamide. It was found that spin-lattice relaxation was driven mainly by methyl group rotation at low temperature for the pure solids and the mixtures. Benzene ring flipping motion and a third motion (possibly whole molecule tumbling) were found to be responsible for relaxing Ac-Tyroet and CBZ-Tyroet at high temperature. However, these motions were highly hindered in TFAc-Tyroet. Molecular tumbling motion was detected in the supercooled liquid mixtures of l-leuNH/CBZ-Tyroet and l-leuNH/Ac-Tyroet, while this motion is absent in the mixture l-leuNH/TFAc-Tyroet. The hindered motion in TFAc-Tyroet may be one of the factors affecting its ability to form a supercooled liquid with l-leucinamide.