聚氨大环-氰基合钴超分子的转动相关时间及59Co核四极耦合常数的测定——动态激光光散射的应用

对于自旋I>1/2的核，其运动的相关时间τ_c以及核四极耦合常数NQCC是表征分子局部和微观动力学结构的重要参数. 然而，在溶液中，这些参数均难以测定. 该工作以聚氨大环-氰基合钴超分子体系为例，利用在高分子体系中广泛使用的激光光散射技术成功地测量了溶液中超分子络合物［12］aneN₄［Co(CN)₆］, ［18］aneN₆［Co(CN)₆］, ［24］aneN₈［Co(CN)₆］,［16］aneN₄［Co(CN)₆］, ［24］aneN₆［Co(CN)₆］ 和 ［32］aneN₈［Co(CN)₆］ 的水合半径，从而根
据Stokes-Einstein-Debye理论计算出了分子转动的相关时间τ_c. 这些超分子的水合半径在0.4～0.6 nm之间. 对应的转动相关时间τ_c在3.8～9.5×10^-11 s之间. 这一时间范围对于分子量在300～500的分子，有相当的合理性. 进而，通过测量超分子在稀溶液中的纵向弛豫时间T₁，结合计算出的相关时间τ_c，我们得到了该超分子体系中⁵⁹Co的四极耦合常数，其范围在0.5～2.2 MHz之间. 我们发现，这些超分子在溶液中的四极耦合常数明显小于在固体状态时的值（5～7 MHz）. 导致这一现象很可能的原因是在固体状态下⁵⁹Co核周围的电场梯度是各向异性的，从而有较大的四极耦合常数值. 而在溶液中，由于分子的快速运动，各向异性被平均，因而有较小的四极耦合常数.

DETERMINATION OF ROTATIONALREORIENTATION CORRELATION TIME AND 59 Co NUCLEAR QUADRUPOLAR COUPLINGCONSTANT OF POLYAMMONIUM MACROCYCLIC COBALTICYANIDE SUPERCOMPLEXES IN DILUTE AQUEOUS SOLUTIONS--An Application of Dynamic Laser Light Scattering Method

The correlation time, τc, and the nuclear quadrupolar coupling constant (NQCC) of I>1/2 nuclei are important parameters for characterizing local and microdynamic structures of molecules. However, it is often difficult to determine those constants in solution. In this study,τc and NQCC of the 59Co nuclei were determined for a series of supercomplexes［12］aneN4［Co(CN)6］, 18］an eN 6Co(CN) 6］,［24］aneN8［Co(CN)6］,［16］aneN4［Co(CN)6］,［24］aneN6［Co(CN)6］and［32］aneN8［Co(CN)6］in dilute solution. The Dynamic Laser Lig ht Scattering (DLLS) method, which is now widely used in macromolecule research, was first applied to determine the hydrodynamic radii (0.4～0.6 nm) of these molecules. Based on the Stokes Einstein Debye equation and the measured hydrodynamic radii, the rotational reorientation correlation times τc were calculated.τc obtained in this study had a range of 3.8～9.5×10-11s, which are fairly reasonable for molecules with molecular weights of WT]GK2]about 300～500. Finally, NQCC of the59Co nuclei in the supercomplexes were determined by combining the τc values calculated and the experimentally measured longitudinal relaxation times, T1, of the 59Co nuclei. The NQCC values obtained ranged from 0.5 to 2.2 MHz, which are considerably lower than those extracted from solid tatic NMR lineshape (5 to 7 MHz). The difference is probably due to the structural effects originating from the anisotropy of local electric gradient around 59Co nucleus in solid.