Application of chemometric method and computational analysis in the spectroscopic study of Azure A dimerization

Abstract

In this contribution we allied chemometric tools and theoretical calculus to comprehend the self-aggregation process of the phenothiazine Azure A (AA), a potential photosensitizer for Photodynamic Therapy. Firstly, due to the high spectral overlap between monomer and dimer, the MCR-ALS method successfully resolve AA's spectra, indicating the formation of a twisted sandwich-like dimer instead of pure H-type aggregate. This chemometric protocol helped not only in the resolution but also in more trustable values of KD. The difference between the KD values after the resolution of the curves was significant, which shows the importance of this procedure. The data extracted from experimental also converged with the informations retrieved from theoretical calculus. The optimization of the AA’s dimer showed the repulsion between the central nitrogen (and at the same time with the sulfur atoms) causes a slight distortion and displacement of one molecule in relation to the other, favoring dimAA-symTRANS, a twisted sandwich-like conformation.The studies also evaluated the impact of salts in the self-aggregation depicting that, besides the ionic strength, polarizable soft anions interact better with cationic species like AA. Thus, soft anions as iodide and bromine causes the most striking impact in self-aggregation. The present study shows the importance in resolve the spectra data set before calculate KD values, role succsesfull developed by MCR-ALS methodology. The approach used here can help in the investigation of others self-aggregation process of photosensitizers and active molecules.