自聚集在纳米金粒上的烷基硫醇单分子层的NMR驰豫时间研究

通过质子的自旋-晶格驰豫时间（T_1）、自旋-自旋驰豫时间（T_2）研究烷基 巯基X(CH_2)_nS-]单分子层保护的纳米金粒中配体分子的运动。本研究涉及两种 典型配体：CH_3(CH_2)_7SH和Py(CH_2)_(12)SH及该两配体的不同配比的测合配体 。实验监测了配体中不同位置的质子的NMR驰豫时间随空间距离及配体比例改变的 变化情况。不同位置的质子，因主要影响因素的不同，表现出各自特殊的运动特征 。配体与金粒配位后，2，3位T_1，T_2值减少，1，4位T_1，T_2值增加。混合配体 中Py(CH_2)_(12)SH含量增加，1，2，3位T_1，T_2值都会减小；而4位T_1值减小， T_2值却增加；不同位置T_1，T_2值变化快慢有别。2位因其特殊位置，在配体配比 PY:C_8 = 1:1PY代表Py(CH_2)_(12)SH，C_8代表CH_3(CH_2)_7SH]时，分子运动最 自由。实验结果显示T_1总是大于T_2，这说明配体处于低频运动区。

NMR Relaxation Times of Alkanethiol Monolayer Self-assembling on Nano-scale Gold Particles

The motion of alkanethiol ligand molecules self-assembling on nano- scale gold particles was studied by measuring the spin-lattice relaxation time (T_1) and spin-spin relaxation time (T_2). Two types of ligands, Py(CH_2)_(12)SH and CH_3(CH_2)_7SH as well as their mixtures of different ratio are employed in this work. NMR relaxation times of four protons at different positions versus steric effect and mixing proportion in ligand mixtures were monitored. Due to different influences of various factors, each of these protons show different motion characteristics. For the ligands connected with Au particle, NMR T_1 and T_2 at position 2 and 3 decrease whereas those at position 1 and 4 increase. For the mixed ligands, with increasing of Py(CH_2)_ (12)SH content, T_1 and T_2 at position 1, 2, 3 and T_1 at position 4 decrease, while NMR T_2 at position 4 increases. However, protons at different positions have different T_1 and T_2 variation speeds. The proton at position 2, due to its special location, has the largest flexibility in the motion with ligands mixing ratio PY:C_8 = 1:1 PY represents Py(CH_2)_(12)SH; C_8 represents CH_3(CH_2)_7SH]. The experimental results also show that T_1 is always greater than the corresponding T_2, which indicates that ligands is in low frequency motion region in the system investigated.