The Influence of Effect of Polysaccharides and Polyvinylpyrrolidone on the Photocatalytic Activity of Chlorin e6 in Tryptophan Oxidation

The effect amphiphic polymer poly-N-vinylpyrrolidone (PVP) and polysaccharides (PSs), sodium alginate (SA) and hyaluronic acid (HA), have on the photosensitizing activity of chlorin e6 (Ce6) in the reaction of tryptophan oxidation is established. This reaction is considered a model in searching for the most efficient pharmaceutical formulations of photosensitizers for antimicrobial photodynamic therapy. It is shown that the initial photosensitizing activity of Ce6, characterized by effective rate constant keff of tryptophan oxidation, grows as binary (Ce6–PVP and Ce6–SA(HA)) and (to a greater extent) ternary systems (Ce6–PVP–SA and Ce6–PVP–SA(HA)) form in aqueous solutions. This rise in activity is found to be related to disaggregation of the associates of photosensitizer (PhS) molecules initially present in aqueous solutions, resulting from the formation of complex bonds between PhS molecules and fragments of polymers added to the solution. This conclusion is confirmed for the considered binary and ternary systems by the accumulated data of electronic absorption spectra and fluorescence spectra of chlorin e6 in the absence of polymers (PVP, SA, and HA) and after they are added to the reaction system, and by 1H NMR data. In light of the most recent findings (according to which each polymeric component (PVP, SA, and HA) affects the activity of PhS, while almost no direct interaction between PVP and PS is detected in the 1H NMR spectra), ternary photosensitizing systems form in aqueous media during the formation of intertwining PVP–PS polymeric chains upon exposure to local hydrodynamic flows, followed by complex bonding between PhS molecules and fragments of both polymers.