Acceleration of carbon-13 spin-lattice relaxation times in amino acids by electrolytes.
Measurements of the enhancement, by various electrolytes, of the spin-lattice relaxation time of carbon-13 at different locations in a number of amino acids are reported. Spin-lattice relaxation times T1 of all the carbons in amino acids generally tend to decrease with increase in the concentration of electrolytes, the largest effects often being observed for the charged carboxylate groups of the amino acids. Carboxylic carbons in amino acids are the sensitive 'acceptor' of the 13C spin-lattice relaxation accelerating effects offered by electrolytes, and the 13C spin-lattice relaxation accelerating ability of electrolytes decreases in the order Mg(ClO4)2 > MgCl2 > CaCl2 > NaCl > KCl > LiClO4 > NaOH. The mechanisms of the observed phenomena are discussed in terms of intermolecular interaction, paramagnetic impurities in electrolytes and other mechanisms; large contributions of intermolecular interactions with electrolytes are present on complex formation between amino acids and metal ions and the incoming 'unsaturation' of the primary solvation shell of cations with the increase in electrolyte concentration.
Tian
Jinping
J
Department of Chemistry, Tsinghua University, Beijing 100084, China.
Yin
Yingwu
Y
D000596:Amino Acids / Q000032:analysis / Q000737:chemistry*; D002247:Carbon Isotopes / Q000737:chemistry*; D004573:Electrolytes / Q000032:analysis / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D013113:Spin Labels
D000596:Amino Acids; D002247:Carbon Isotopes; D004573:Electrolytes; D013113:Spin Labels