Analysis of resolved ESR spectra of neutral nitroxide radicals in ethanol and pyridine: the dynamic behavior in fast motion conditions
Analysis of resolved ESR spectra of neutral nitroxide radicals in ethanol and pyridine: the dynamic behavior in fast motion conditions
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乙醇和吡啶中中性硝基氧自由基的解析 ESR 光谱分析：快速运动条件下的动态行为
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发表时间：
1987
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影响因子：
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通讯作者：
M. Ottaviani
中科院分区：
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作者：
M. Ottaviani
通过对4-羟基-2,2,6,6-四甲基吡啶-1-氧基（Tempol）和3-氨基甲酰-2,2,5,5-四甲基吡啶-1-氧基（Tempyo）自旋探针在乙醇和吡啶溶液中的ESR光谱分析，获得了溶液中自由基的动力学行为信息。为了评估真实线宽，我们分析了质子和碳-13超细耦合常数对温度和溶剂极性的依赖关系，并将其作为a/sub / N/的函数。Tempol和Tempyo的a/sub H/对a/sub N/的依赖性相反。此外，溶剂极性的变化对Tempol结构的影响大于Tempyo。根据线宽计算运动的相关次数。Tempol和Tempyo与乙醇形成弱氢键。然而，只有乙醇中的Tempol产生了各向异性旋转重定向运动，绕x轴旋转速度最快。除吡啶中的Tempol外，所有样品都显示偏离德拜光谱密度。流体动力旋转半径比有效几何球面半径小约3倍。然而，Tempyo在其旋转运动中施加的扭矩略大于Tempol。在最高温度下（T > 298 K），根据自由体积摩尔»模型，动态行为与预期一致，而在较低温度下，自由基和乙醇分子之间的h键强度增加。«少
The ESR spectra of ethanol and pyridine solutions of the spin probes 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (Tempol) and 3-carbamoyl-2,2,5,5-tetramethylpyrroline-1-oxyl (Tempyo) were analyzed to obtain information on the dynamic behavior of the radicals in solution. In order to evaluate the true line widths, the dependence of the proton and carbon-13 hyperfine coupling constants on temperature and on solvent polarity were analyzed as a function of a/sub N/. Tempol and Tempyo showed an opposite dependence of a/sub H/ on a/sub N/. Furthermore the structure of Tempol was affected more than that of Tempyo by variations of solvent polarity. From the line widths the correlation times for motion were evaluated. A weak hydrogen bond was formed by Tempol and Tempyo with ethanol. However, only Tempol in ethanol gave rise to an anisotropic rotational reorientational motion, with the fastest rotation about the x axis. All samples, except for Tempol in pyridine, showed a deviation from the Debye spectral densities. The hydrodynamic rotational radii were about 3 times lower than the effective geometric spherical radii. However, Tempyo exerted slightly greater torques than Tempol during its rotational motion. At the highest temperatures (T > 298 K), the dynamic behavior was as expected on the basis of the free volumemore » model, whereas at lower temperatures an increase in the H-bonding strength was found between radical and ethanol molecules.« less