OXYGEN EFFECTS ON THE EPR SIGNALS FROM WOOD CHARCOALS: RESULTS AND NEW MODEL

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 活组织中pO 2的定量测量具有重要的临床和研究应用，EPR血氧测定法在这些测量中具有相当大的潜力。 该技术需要具有EPR可检测的顺磁中心的材料，并且涉及氧对EPR光谱性质的浓度依赖性扰动。一些分子自由基（如氮氧自由基，三苯甲基）和具有顺磁中心的材料，包括某些炭黑，煤和木炭和酞菁锂晶体（LiPc），已经研究了它们作为EPR血氧测定探针的潜力。溶解在水溶液中的氮氧化合物或三苯甲基化合物的EPR谱通常表现出溶解氧约0.5 mG/微摩尔的增宽。 然而，通过受控热解由热带硬木合成的某些木炭含有EPR可检测的物质，其可以通过溶解氧表现出50-100 mG/微摩尔的增宽，并且这种响应在气相中甚至更大。 体内EPR血氧测定法的成功应用需要开发具有优化性能的氧敏感顺磁材料。目前，LiPc和相关化合物被广泛使用，但存在几个探针标准（灵敏度、稳定性、可逆性、选择性等）。需要针对EPR血氧测定的不同应用进行优化。 特别地，需要对肿瘤中发现的低水平和脑中发现的较高水平的氧具有增加的敏感性的材料。然而，要合理开发这些材料，需要了解氧对焦炭顺磁中心影响的物理基础和机制。此外，这种理解可以通过将物理原理结合到光谱模型中来指导体内数据分析的改进。木炭具有与其与气体相互作用相关的某些物理性质。 它们是高度多孔的材料，其表面积与孔径成反比。 炭孔通常基于其直径分为三种尺寸，即大孔（>50 nm）、中孔（50-2 nm）和微孔（<2 nm）。 此外，它们是疏水材料，具有较差的水渗透性，特别是进入较小的孔隙。 最后，炭以其在其大表面积上吸附气体的能力而闻名。 本文研究了氧对木质炭EPR谱性质的影响。 这些包括量化自旋的浓度，并确定EPR谱的温度依赖性和频率依赖性。 用三个组分来拟合氧对煤焦的EPR谱，测量了三个组分的谱线宽度、强度和共振位置随氧浓度的变化关系。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The quantitative measurement of pO2 in living tissue has important clinical and research applications, and EPR oximetry has considerable potential for these measurements. This technique requires a material with EPR-detectable paramagnetic centers and involves concentration dependent perturbation of the EPR spectral properties by oxygen. A number of molecular radicals (e.g. nitroxides, trityls) and materials with paramagnetic centers, including certain carbon blacks, coals and charcoals and crystals of lithium phthalocyanine (LiPc), have been studied for their potential as probes for EPR oximetry. The EPR spectra of nitroxides or trityls, dissolved in aqueous solution typically exhibits ~0.5 mG/micromole broadening by dissolved oxygen. However, certain charcoals synthesized from tropical hardwoods by means of controlled pyrolysis contain EPR-detectable species that can exhibit 50-100 mG/micromole broadening by dissolved oxygen, and this response is even larger in the gas phase. Successful application of in vivo EPR oximetry requires the development of oxygen-sensitive paramagnetic materials with optimized properties. Currently, LiPc and related compounds are widely used, but there are several probe criteria (sensitivity, stability, reversibility, selectivity, etc.) that need to be optimized for different applications of EPR oximetry. In particular, there is a need for materials with increased sensitivity to oxygen at the low levels found in tumors and at the higher levels found in the brain. To rationally develop these materials, however, requires an understanding of the physical basis and mechanism of oxygen effects on the char paramagnetic centers. Further, this understanding may guide the improvement of in vivo data analysis by incorporating physical principles into the spectral model. Charcoals have certain physical properties that are relevant to their interaction with gases. They are highly porous materials with a surface area that is inversely proportional to the pore diameter. Charcoal pores are generally classified in three sizes based on their diameter, macropores (>50 nm), mesopores (50-2 nm) and micropores (<2 nm). In addition, they are hydrophobic materials with poor water penetration, particularly into smaller pores. Finally, chars are known for their ability to adsorb gases on their large surface area. We have studied the effect of oxygen on the EPR spectral properties of wood charcoals. These include quantifying the concentration of spins, and determining the temperature-dependence and frequency-dependence of the EPR spectrum. Three components are required to fit the O2-broadened EPR spectrum of the chars, and the oxygen dependence of the line width, intensity and resonance position of the three components have been measured.