Deuterium Nuclear Spin-Lattice Relaxation Times and Quadrupolar Coupling Constants in Isotopically Labeled Saccharides

Abstract

13C and 2H spin-lattice relaxation times have been determined by inversion recovery in a range of site-specific 13C- and 2H-labeled saccharides under identical solution conditions, and the data were used to calculate deuterium nuclear quadrupolar coupling constants (2H NQCC) at specific sites within cyclic and acyclic forms in solution. 13C T1 values ranged from ∼0.6 to 8.2 s, and 2H T1 values ranged from ∼79 to 450 ms, depending on molecular structure (0.4 M sugar in 5 mMEDTA (disodium salt) in 2H2O-depleted H2O, pH 4.8,30°C). In addition to providing new information on 13C and 2H relaxation behavior of saccharides in solution, the resulting 2H1 NQCC values reveal a dependency on anomeric configuration within aldopyranose rings, whereas 2H NQCC values at other ring sites appear less sensitive to configuration at Cl. In contrast, 2H NQCC values at both anomeric and nonanomeric sites within aldofuranose rings appear to be influenced by anomeric configuration. These experimental observations were confirmed by density functional theory (DFT) calculations of 2H NQCC values in model aldopyranosyl and aldofuranosyl rings. © 2000 Academic Press.