Magnetic relaxation dispersion of lithium ion in solutions of DNA.
Magnetic relaxation dispersion of lithium ion in solutions of DNA.
复制标题
DNA 溶液中锂离子的磁弛豫色散。
DOI：
10.1002/mrc.1382
复制
发表时间：
2004
期刊：
影响因子：
--
通讯作者：
Bryant,RobertG
中科院分区：
文献类型：
--
作者：
Victor,KenG;Teng,Ching-Ling;Dinesen,TRD;Korb,Jean-Pierre;Bryant,RobertG
核自旋-晶格弛豫速率常数的磁场依赖性定义了磁弛豫色散（MRD），并提供了导致系统中磁耦合波动的分子动力学的直接表征，也可以指示运动的尺寸约束。围绕线性多电解质离子（如溶液中的DNA）的反离子云为离子约束提供了一个有趣的机会，有助于理解多电解质与其他溶质之间相互作用的热力学和动力学。在天然小牛胸腺DNA的稀水溶液中记录了锂离子和四甲基铵离子的MRD谱图，它提供了一个长而带电的杆状结构，其定向缓慢。7li离子通过核电四极耦合和质子-锂偶极-偶极耦合弛豫；四甲基铵离子的质子通过偶极-偶极耦合而松弛。7li +离子的MRD谱主要由与DNA的瞬态相互作用决定，这使得自旋晶格弛豫速率常数与拉莫尔频率的对数呈线性关系。这种磁场依赖性与扩散离子运动是一致的，扩散离子运动调制了两个空间坐标，这些坐标表征了多极化附近的弛豫耦合。在棒周围的运动和离子距离的波动与锂的这些限制是一致的。四甲基铵离子质子弛豫速率常数的磁场依赖性较弱，但也近似为拉莫尔频率对数的线性函数，这意味着磁场依赖性部分是由DNA溶液中的局部顺序引起的。版权所有©2004 John Wiley & Sons， Ltd
The magnetic field dependence of the nuclear spin–lattice relaxation rate constant defines the magnetic relaxation dispersion (MRD) and provides a direct characterization of the molecular dynamics that cause fluctuations in the magnetic couplings in the system and may also indicate the dimensional constraints on the motion. The counterion cloud surrounding a linear polyelectrolyte ion, such as DNA in solution, provides an interesting opportunity for ion confinement that helps in understanding the thermodynamics and the dynamics of the interactions between the polyion and other solutes. The MRD profiles of lithium ion and tetramethylammonium ion were recorded in dilute aqueous solutions of native calf thymus DNA, which provides a long, charged rod that reorients slowly. The7Li ion relaxes through the nuclear electric quadrupole coupling and the proton–lithium dipole–dipole coupling; the protons of the tetramethylammonium ion relax by dipole–dipole coupling. MRD profiles of the7Li+ion are dominated by transient interactions with the DNA that yield a linear dependence of the spin–lattice relaxation rate constant on the logarithm of the Larmor frequency. This magnetic field dependence is consistent with diffusive ion motions that modulate two spatial coordinates that characterize the relaxation couplings in the vicinity of the polyion. Motions around the rod and fluctuations in the ion distance from the rod are consistent with these constraints for lithium. The magnetic field dependence of the tetramethylammonium ion proton relaxation rate constant is weak, but also approximately a linear function of the logarithm of the Larmor frequency, which implies that the field dependence is caused in part by local order in the DNA solution. Copyright © 2004 John Wiley & Sons, Ltd.