Ilangovan Govindasamy, Zweier Jay L, Kuppusamy Periannan
Center for Biomedical EPR Spectroscopy and Imaging, Davis Heart and Lung Research Institute, The Ohio State University, 420 West 12th Avenue, Columbus, OH 43210, USA.
J Magn Reson. 2004 Sep;170(1):42-8. doi: 10.1016/j.jmr.2004.05.018.
EPR oximetry has been recognized as an important tool for determining oxygen concentration in biological tissues, in vivo. The method relies on the use of oxygen-sensitive paramagnetic probes whose linewidth varies predictably, mostly linear, with oxygen concentration. Lithium phthalocyanine (LiPc) radical has emerged as the probe of choice due to its superior EPR sensitivity, oxygen response, and biocompatibility. However, there are certain limitations in the preparation of this material in a pure and usable form. In our efforts to improve the synthesis of this material for reliable use in oximetry applications, we developed microcrystalline particulates that showed several advantages over other probes. Despite its advantages, the probe shows linear response to pO2 only in the range of 0-70 mmHg, beyond which a saturation behavior is observed. The goal of this study was to understand the mechanism of the interaction of oxygen with LiPc in order to interpret the experimentally observed linewidths. We propose a dual-spin model in which the freely diffusing spins of LiPc are converted to fixed spins by adsorption of molecular oxygen. The proposed mechanism was verified from the effect of oxygenation/deoxygenation processes on the linewidth of LiPc. In summary, we demonstrated that adsorption of oxygen molecules on LiPc contributes to a nonlinear line-broadening effect. This understanding is important for the future design of new EPR oximetry probes.
电子顺磁共振血氧测定法已被公认为是一种在体内测定生物组织中氧浓度的重要工具。该方法依赖于使用对氧敏感的顺磁探针，其线宽随氧浓度呈可预测的变化，大多呈线性关系。酞菁锂（LiPc）自由基因其卓越的电子顺磁共振灵敏度、氧响应和生物相容性，已成为首选探针。然而，以纯净且可用的形式制备这种材料存在一定局限性。在我们为改进这种材料的合成以使其能可靠用于血氧测定应用所做的努力中，我们开发了微晶颗粒，其显示出比其他探针具有若干优势。尽管有这些优势，但该探针仅在0 - 70 mmHg范围内对pO₂呈线性响应，超过此范围则观察到饱和行为。本研究的目的是了解氧与LiPc相互作用的机制，以便解释实验观察到的线宽。我们提出了一种双自旋模型，其中LiPc的自由扩散自旋通过分子氧的吸附转化为固定自旋。所提出的机制通过氧合/脱氧过程对LiPc线宽的影响得到了验证。总之，我们证明了氧分子在LiPc上的吸附会导致非线性线宽展宽效应。这种认识对于未来新型电子顺磁共振血氧测定探针的设计很重要。
