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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Quasi-Equilibria and Polarization Transfer Between Adjacent and Remote Spins: H-1-C-13 CP MAS Kinetics in Glycine
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Quasi-Equilibria and Polarization Transfer Between Adjacent and Remote Spins: H-1-C-13 CP MAS Kinetics in Glycine

机译：相邻和远程旋转之间的准平衡和极化转移：甘氨酸中的H-1-C-13 CP MAS动力学

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摘要

The H-1-C-13 CP MAS kinetic curves were measured in glycine powder sample at the MAS rates of 7, 10, and 12 kHz. Each experimental curve contained up to 1000 equidistant points over the whole contact time range of 10 mu s - 10 ms. The CP kinetic data for CH(2 )group, i.e., for the system containing adjacent H-1-C-13 spin pairs with a definite dominant dipolar coupling can be described in the frame of the isotropic spin-diffusion approach. The local order parameter (S) approximate to 1.0, determined as the ratio of the measured dipolar H-1-C-13 coupling constant and the calculated static dipolar coupling constant, is very close to the values deduced in series of other amino acids. The strong narrow peaks observed in the spin coupling spectrum at multiples of the MAS frequency can be considered as the confirmation that the periodic quasi-equilibrium state can appear also in the powder samples. The anisotropic spin-diffusion approach improved by the introducing of the thermal equilibration in the proton bath is the most proper model to describe the CP kinetics in the system containing remote spins. Very realistic values of the spin-cluster size (N) have been obtained without any constraint on the flow of the nonlinear curve fitting. The finite values of N = 4 means that CP transfer is located within one glycine molecule.
机译：H-1-C-13 CP MAS动力学曲线在7,10和12kHz的MAS率下以甘氨酸粉末样品测量。每个实验曲线在整个接触时间范围内含有多达1000个等距点，在10 mu S-10 ms的情况下。用于CH（2）组的CP动力学数据，即包含具有明显显性偶极耦合的相邻H-1-C-13自旋对的系统，可以在各向同性自旋扩散方法的框架中描述。近似为1.0的本地订单参数，被确定为测量的偶极H-1-C-13耦合常数和计算的静态偶极耦合常数的比率非常接近于串联氨基酸中推导的值。在MAS频率的倍数下观察到的旋转耦合光谱中观察到的强窄峰可以被认为是粉末样品中也可以出现周期性准平衡状态的确认。通过介绍质子浴中的热平衡的各向异性自旋扩散方法是最适合的模型，用于描述含有远程旋转的系统中的CP动力学。已经获得了旋转簇大小（n）的非常现实的值，而没有对非线性曲线配件的流动的任何约束。 N＆LT; = 4的有限值表示CP转移位于一个甘氨酸分子内。

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