Buszko M L, Andrew E R
Department of Physics, University of Florida, Gainesville, 32611.
Solid State Nucl Magn Reson. 1992 Jul;1(3):115-9. doi: 10.1016/0926-2040(92)90011-w.
Polycrystalline D-lactic acid lithium salt [(R)-2-hydroxypropanoic acid lithium salt, lithium D-lactate] has been investigated by pulsed proton magnetic resonance methods between 77 and 300 K at 25 MHz. The main relaxation mechanism is methyl rotation; the motion is characterized by an activation energy Ea = 14.5 +/- 0.5 kJ/mol and time factor tau 0 = (1.5 +/- 0.5) x 10(-13) s. The activation energy is higher than the potential barrier obtained by ESR and ENDOR techniques for methyl rotation in the lactate radical. The methyl rotation is also responsible for a reduction of the dipolar second moment. Below 100 K the reduction of the dipolar second moment is ascribed to quantum-mechanical tunneling; an excitation energy of 6.1 +/- 1 kJ/mol is derived from a contribution to the spin-lattice relaxation times from the tunneling.
采用脉冲质子磁共振方法，在77至300K温度范围、25MHz频率下对多晶D-乳酸锂盐[（R）-2-羟基丙酸锂盐，D-乳酸锂]进行了研究。主要弛豫机制为甲基旋转；该运动的特征是活化能Ea = 14.5±0.5 kJ/mol，时间因子tau 0 =（1.5±0.5）×10^(-13) s。该活化能高于通过电子自旋共振（ESR）和电子核双共振（ENDOR）技术获得的乳酸根自由基中甲基旋转的势垒。甲基旋转还导致偶极二次矩减小。在100K以下，偶极二次矩的减小归因于量子力学隧穿；从隧穿对自旋晶格弛豫时间的贡献得出激发能为6.1±1 kJ/mol。
