Kitchin Simon J, Tutoveanu Gianina, Steele Matthew R, Porter Elaine L, Harris Kenneth D M
School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, England.
J Phys Chem B. 2005 Dec 8;109(48):22808-13. doi: 10.1021/jp0532418.
Solid state dynamic properties have been investigated for the racemic (DL) and enantiomerically pure (L) crystalline forms of the amino acid serine [HO x CH2 x CH(NH3(+)) x CO2(-)] using 2H NMR line shape analysis and 2H NMR spin-lattice relaxation time measurements for samples of DL-serine and L-serine deuterated in the NH3(+) and OH groups. 2H NMR line shape analysis indicates that, for both L-serine and DL-serine, the ND3(+) group undergoes a 3-site 120 degrees jump motion, with jump frequencies in the intermediate motion regime (10(3) s(-1) to 10(8) s(-1)) in the temperature range 153-313 K. However, at a given temperature, the jump frequency is substantially higher for L-serine (e.g., at 233 K, the jump frequency is 5.0 x 10(6) s(-1) for L-serine and 6.0 x 10(4) s(-1) for DL-serine). The OD group is not dynamic on the 2H NMR time scale within the temperature range studied. The results from both 2H NMR line shape analysis (LA) and 2H NMR spin-lattice relaxation time measurements (SLR) indicate that the activation energy for the 3-site 120 degree jump motion of the ND3(+) group is significantly higher for DL-serine [38.0 +/- 1.0 kJ mol(-1) (LA); 39.7 +/- 0.8 kJ mol(-1) (SLR)] than for L-serine [23.4 +/- 0.8 kJ mol(-1) (LA); 23.8 +/- 0.3 kJ mol(-1) (SLR)]. The difference in activation energies between DL-serine and L-serine is substantially greater than any reported previously for an amino acid in different crystal forms.
利用2H NMR线形分析以及对NH3(+)和OH基团氘代的DL-丝氨酸和L-丝氨酸样品进行2H NMR自旋晶格弛豫时间测量，研究了氨基酸丝氨酸[HO x CH2 x CH(NH3(+)) x CO2(-)]的外消旋（DL）和对映体纯（L）晶型的固态动力学性质。2H NMR线形分析表明，对于L-丝氨酸和DL-丝氨酸，ND3(+)基团都经历了一种三位点120度跳跃运动，在153 - 313 K的温度范围内，其跳跃频率处于中间运动区域（10(3) s(-1)至10(8) s(-1)）。然而，在给定温度下，L-丝氨酸的跳跃频率显著更高（例如，在233 K时，L-丝氨酸的跳跃频率为5.0 x 10(6) s(-1)，DL-丝氨酸的跳跃频率为6.0 x 10(4) s(-1)）。在所研究的温度范围内，OD基团在2H NMR时间尺度上不具有动力学活性。2H NMR线形分析（LA）和2H NMR自旋晶格弛豫时间测量（SLR）的结果均表明，DL-丝氨酸[38.0 +/- 1.0 kJ mol(-1)（LA）；39.7 +/- 0.8 kJ mol(-1)（SLR）]中ND3(+)基团三位点120度跳跃运动的活化能显著高于L-丝氨酸[23.4 +/- 0.8 kJ mol(-1)（LA）；23.8 +/- 0.3 kJ mol(-1)（SLR）]。DL-丝氨酸和L-丝氨酸之间活化能的差异显著大于此前报道的任何一种氨基酸不同晶型之间的差异。
