Solution and Photoproperties of N-(2-Hydroxypropyl)methacrylamide Copolymer−Meso-chlorin e6 Conjugates

Abstract

The solution properties of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers containing various numbers of meso-chlorin e6 monoethylenediamine (Mce6) molecules attached to the copolymer via either glycine (G) or tetrapeptide (GFLG) side chains were studied. Dynamic light scattering, spectroscopic, fluorescence quenching, and time-resolved fluorescence techniques were used. The photosensitizing efficiencies of the various derivatives were also examined. Reactions were measured in aqueous sodium phosphate buffer (SPB) and ethanol. The dynamic light scattering data indicate that the intermolecular aggregation of Mce6 species within the HPMA copolymer conjugates is not important at the conjugate concentration measured (5 × 10-4 g/mL). However, intramolecular aggregation of the hydrophobic Mce6 moieties does occur and was studied using absorption and fluorescence techniques. The degree of intramolecular aggregation was decreased by the addition of detergents or ethanol to the SPB solutions. The cationic detergent, CTAB, strongly enhanced the fluorescence of the copolymer conjugates due to its efficient electrostatic interactions with the negatively charged Mce6 species. It also significantly increased the relative quantum yield of oxygen uptake during the copolymer conjugate-sensitized photooxidation of furfuryl alcohol. The observed iodide quenching of copolymer conjugate fluorescence implies that hydrophobic domains of aggregated Mce6 moieties may exist in SPB solutions of the conjugates. The time-resolved fluorescence decay measurements showed that about 15% of the Mce6 species were aggregated in SPB solutions of those copolymer conjugates with the highest Mce6 content. There was a low degree of aggregation of free Mce6 molecules in SPB solutions at the concentrations used.