School of Chemistry, Institute of Science, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand.
J Phys Chem B. 2010 Sep 23;114(37):12104-15. doi: 10.1021/jp102307s.
To gain more understanding into the mechanism that enables the dramatic resonant Raman enhancement of totally symmetric modes observed in hemozoin (malaria pigment) and other related heme supramolecular arrays when applying near-infrared excitation wavelengths, the iron(III) porphyrins Fe(TPP)Cl, Fe(TPP)O, Fe(OEP)Cl, and Fe(OEP)O along with β-hematin (synthetic hemozoin or malaria pigment) were analyzed in the solid state using resonance Raman spectroscopy. The critical finding was that from the model compounds investigated, all except Fe(OEP)O exhibited the enhancement of the totally symmetric mode ν(4) when exciting the molecules with 782 and 830 nm laser lines. Through a detailed comparison of X-ray crystallographic structures, it is proposed that intermolecular noncovalent interactions play an integral role in enabling excitonic interactions to occur in these heme supramolecular systems. Comparison of the solid- and solution-phase electronic spectra in the near-IR region indicated more absorbance in the solid state between 800 and 900 nm. The electronic spectrum of Fe(OEP)O shows minimal absorbance in this region compared to that of the other compounds. All heme derivatives investigated have similar structure with a five-coordinate high-spin iron(III) ion. The crystallographic data indicate no significant differences in porphyrin geometry between TPP and OEP derivatives studied. However, Fe(OEP)O contains less supramolecular interactions in comparison to the other species. The supramolecular bonding enhances the probability of through-space interactions between the transition dipoles from electronic transitions of extended π systems. Our results indicate that the intensity of ν(4) is in part strongly affected by C-H···X hydrogen bonding interactions when X is an electron-donating entity. Such information may have important implications in the design and monitoring of antimalarial drugs that specifically interfere with hemozoin formation.
为了更深入地了解在应用近红外激发波长时，血晶朊（疟色素）和其他相关血红素超分子阵列中观察到的完全对称模式的剧烈共振拉曼增强的机制，我们对铁（III）卟啉 Fe(TPP)Cl、[Fe(TPP)]2O、Fe(OEP)Cl 和 [Fe(OEP)]2O 以及 β-血晶朊（合成血晶朊或疟色素）进行了固态共振拉曼光谱分析。关键的发现是，在所研究的模型化合物中，除了 [Fe(OEP)]2O 之外，所有化合物在以 782 和 830nm 激光线激发分子时都表现出完全对称模式 ν(4)的增强。通过对 X 射线晶体结构的详细比较，提出分子间非共价相互作用在这些血红素超分子体系中发生激子相互作用中起着不可或缺的作用。在近红外区域比较固态和溶液相电子光谱表明，固态在 800nm 到 900nm 之间具有更多的吸收。与其他化合物相比，[Fe(OEP)]2O 的电子光谱在该区域的吸收最小。所研究的血红素衍生物具有相似的结构，具有五配位高自旋铁（III）离子。晶体学数据表明，在所研究的 TPP 和 OEP 衍生物之间，卟啉几何形状没有明显差异。然而，与其他物种相比，[Fe(OEP)]2O 中包含的超分子相互作用较少。超分子键合增强了扩展 π 系统的电子跃迁的跃迁偶极子之间的空间相互作用的可能性。我们的结果表明，当 X 是供电子实体时，ν(4)的强度部分强烈受到 C-H···X 氢键相互作用的影响。这些信息可能对设计和监测专门干扰血晶朊形成的抗疟药物具有重要意义。
