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ESEEM Measurements of Local Water Concentration in D2O-Containing Spin-Labeled Systems

机译：ESEEM测量包含D2O的自旋标签系统中的局部水浓度

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To calibrate electron spin echo envelope modulation (ESEEM) amplitudes with respect to the deuterium water content in spin-labeled biological systems, ESEEM of nitroxide TEMPO has been studied in frozen glassy D2O-dimethylsulfoxide mixtures of different composition. The interaction between the unpaired electron of nitroxide and the deuterium nuclei manifests itself in a cosine Fourier transform spectrum as the sum of a narrow line with the doublet quadrupole splitting and of a broad one. The narrow line arises form interaction with nearby nuclei belonging to nitroxide-water molecule complexes. The dependence on water concentration was found to be nonlinear for the intensity of the narrow line and close to linear for the intensity of the quadrupole doublet. Therefore, the intensity of the quadrupole doublet is suggested as a measure of concentration of free water around a spin label in biological objects. Fourier transform line shape was theoretically simulated for different model distributions of water molecules around the spin label. Simulations confirm the linear dependence of the quadrupole doublet intensity on water concentration seen in the experiment. The suggest approach was applied to analyze data for spin-labeled dipalmitoylphosphatidylcholine (DPPC) and DPPC-cholesterol D2O-hydrated model membranes. The concentration of free water near the spin-labeled fourth carbon atom along the lipid chain was estimated as 5.2 and 7.2 M for DPPC and DPPC-cholesterol membranes, respectively.
机译：为了在自旋标记生物系统中相对于氘水含量校准电子自旋回波包络调制（ESEEM）幅度，已经在不同成分的冷冻玻璃状D2O-二甲基亚砜混合物中研究了氮氧化物TEMPO的ESEEM。一氧化二氮和氘核的不成对电子之间的相互作用以余弦傅立叶变换谱的形式表现出来，该谱为具有双峰四极分裂的窄线和宽双峰的总和。窄线是与附近的核相互作用而形成的，该核属于一氧化氮-水分子复合物。发现对水浓度的依赖性对于窄线的强度是非线性的，而对于四极子双峰的强度则接近线性。因此，建议使用四极双峰的强度作为生物对象中自旋标记周围自由水浓度的量度。理论上模拟了自旋标记周围水分子的不同模型分布的傅里叶变换线形。仿真结果证实了四极子二重峰强度对实验中水浓度的线性依赖性。该建议的方法用于分析自旋标记的二棕榈酰磷脂酰胆碱（DPPC）和DPPC-胆固醇D2O水合模型膜的数据。对于DPPC和DPPC-胆固醇膜，沿着脂质链旋转标记的第四碳原子附近的游离水浓度估计分别为5.2 M和7.2M。

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