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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Electron paramagnetic resonance spectroscopic study of copper hopping in doped Bis(L-histidinato)cadmium dihydrate
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Electron paramagnetic resonance spectroscopic study of copper hopping in doped Bis(L-histidinato)cadmium dihydrate

机译：掺杂双（L-组氨酸）二水合镉中铜的电子顺磁共振谱研究

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摘要

Electron paramagnetic resonance (EPR) spectroscopy was used to study Cu(II) dynamic behavior in a doped biological model crystal, bis(l-histidinato)cadmium dihydrate, in order to gain better insight into copper site stability in metalloproteins. Temperature-dependent changes in the low temperature X-band EPR spectra became visible around 100 K and continued up to room temperature. The measured 298 K g-tensor (principal values: 2.17, 2.16, 2.07) and copper hyperfine coupling tensor (principal values: -260, -190, -37 MHz) were similar to the average of the 77 K tensor values pertaining to two neighboring histidine binding sites. The observed temperature dependence was interpreted using Anderson's theory of motional narrowing, where the magnetic parameters for the different states are averaged as the copper rapidly hops between sites. The EPR pattern was also found to undergo a sharp sigmoidal-shaped, temperature- dependent conversion between two species with a critical temperature T c ≈ 160 K. The species below Tc hops between the two low temperature site patterns, and the one above Tc represents an average of the molecular spin Hamiltonian coupling tensors of the two 77 K sites. In addition, the low and high temperature species hop between one another, contributing to the dynamic averaging. Spectral simulations using this 4-state model determined a hop rate between the two low temperature sites ν_(h4) = 4.5 × 10~8 s~(-1) and between the low and high temperature states ν_(h2) = 1.7 × 10~8 s~(-1) at 160 K. An Arrhenius relationship of hop rate and temperature gave energy barriers of ΔE_4 = 389 cm~(-1) and ΔE_2 = 656 cm~(-1) between the two low temperature sites and between the low and high temperature states, respectively.
机译：电子顺磁共振（EPR）光谱用于研究掺杂的生物模型晶体二水合双（1-组氨酸）镉中的铜（II）动态行为，以便更好地了解金属蛋白中的铜位稳定性。低温X波段EPR光谱中与温度有关的变化在100 K附近变得可见，并一直持续到室温。测得的298 K g张量（主值：2.17、2.16、2.07）和铜超细耦合张量（主值：-260，-190，-37 MHz）与77 K张量值的平均值相似，这两个值相邻的组氨酸结合位点。使用安德森运动变窄理论解释了观察到的温度依赖性，其中随着铜在站点之间快速跳变，将不同状态的磁参数平均。还发现EPR模式在两种具有临界温度T c≈160 K的物种之间经历了呈S形的，温度依赖性的急剧转换。Tc以下的物种在两个低温部位模式之间跳跃，而Tc之上的物种表示两个77 K位点的分子自旋哈密顿耦合张量的平均值。此外，低温和高温物质之间相互跳动，有助于动态平均。使用这种四态模型进行的光谱模拟确定了两个低温站点ν_（h4）= 4.5×10〜8 s〜（-1）之间以及低温状态和高温状态ν_（h2）= 1.7×10之间的跳跃率在160 K时〜8 s〜（-1）。跃点速率与温度的阿伦尼乌斯关系给出了两个低温点与温度之间的能垒ΔE_4= 389 cm〜（-1）和ΔE_2= 656 cm〜（-1）。分别处于低温和高温状态之间。

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