EXAFS can be successfully applied to resolve local atomic structures of very low symmetry. We used this technique to get a better insight into the local environment of iron atoms in di-alanino acid derivative of protoporphyrin IX. Right now, these compounds undergo intensive clinical tests as potential photosensitizing candidates for photodiagnosis and photodynamic therapy (PDT). In PDT, the controlled photosensitization of reactive oxygen species (ROS), including singlet oxygen (¹∆_g), is believed to be responsible for triggering a cascade of subsequent biochemical processes resulting in eradication of tumor cells. In particular, di-amino acid derivatives of protoporphyrin IX attract a lot of attention since they reveal selective retention by malignant tissues and are also eficient ROS generators. Our preliminary electron spin resonance (ESR) study revealed the presence of high-spin, trivalent iron atoms (FeIII, S=5/2) in di-alanino acid derivative of protoporphyrin IX nominally iron-free compound. EXAFS measurements were performed at station BM26A at ESRF. The analysis of EXAFS spectra of Fe-K absorption edge indicated iron presence inside the protoporphyrin IX ring and revealed the bromine atom as one of the first neighbors. The comparison of the shift of Fe-K absorption edge for di-alanino acid derivative of protoporphyrin IX and the material of reference, Fe2O3, confirm the presence of the trivalent iron centers in this novel photosensitizer.

Most probably the location of iron and bromine depends on technological process of preparation the samples. Consequence of precise determination of place of bonding the heavy atoms will be finding the most efficient and no expensive purification procedure to obtain iron and bromine free photosensitizer and allowance to concentrate on most effective technology production process.

Acknowledgments :

This work was partially supported by grant N202 053 32/1197