Poly (L-Lysine Citramide), a Water-Soluble Bioresorbable Carrier for Drug Delivery: Aqueous Solution Properties of Hydrophobized Derivatives

Poly(L-lysine citramide) (PLCA), a novel biocompatible and bioresorbable water-soluble polymer, was designed as a macromolecular prodrug carrier coupling drugs to hydrophilic carriers generally leads to hydrophobization of the precursor macromolecules which then form micelle-like water-dispersed aggregates or are completely insoluble. To study these phenomena, hydrophobization of PLCA was investigated. Alkyl groups (C7 and C12) were covalently attached to the lysine of the polymer which was prepared by either step-growth polymerization or selective hydrolysis of alkylated derivatives. Hydrophobized macromolecules formed nanosized multimolecular aggregates in aqueous media. The size of these aggregates was influenced by concentration, ionic strength, degree of ionization, alkyl substitution and alkyl group length.

Influence of pH on aggregation and photoproperties of n-(2-hydroxypropyl)methacrylamide copolymer-meso-chlorin e6 conjugates

The influence of pH on the aggregation and photoproperties of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers containing meso-chlorin e(6) monoethylenediamine (Mce(6)) attached to the copolymer via either nonbiodegradable G or biodegradable GFLG side chains was studied. Dynamic light scattering, UVIVIS and fluorescence spectroscopy, time-resolved fluorescence spectroscopy, and fluorescence quenching techniques were used. The photosensitizing efficiencies of these conjugates were also determined. The dynamic light-scattering data indicate that the intermolecular aggregation of Mce(6) species within the copolymer conjugates is not significant and is not affected by pH or loading of Mce(6) to copolymer at 5 x 10(-4) g/mL of copolymer conjugate concentration. However, intramolecular aggregation of the Mce(6) species within the copolymer conjugates does occur in aqueous buffers, as demonstrated by absorption and fluorescence measurements in ethanol-buffer mixtures. The fluorescence lifetime of excited Mce(6) was influenced by aggregation, mainly attributed to the pH and copolymer side-chain hydrophobicity. The Stern-Volmer collisional quenching constant, K(sv) iodide anion with Mce(6) species was found to be a function of pH, reflecting both the electrostatic repulsion between negatively charged Mce(6) species and iodide anions and the intramolecular aggregation of Mce(6) moieties. The extent of aggregation was found to be a function of solvent pH, loading of Mce(6) to copolymer, and side-chain hydrophobicity. The photosensitizing efficiency of the copolymer bound Mce(6), as determined through the photooxidation of furfuryl alcohol, was dominated by Mce(6) loading to copolymer and side-chain hydrophobicity, but was only slightly pH dependent. Evidently, the Mce(6) aggregation only weakly influenced the charge transfer in the process of oxygen generation.

Effect of hydrophobic interactions on properties and stability of DNA-polyelectrolyte complexes

Polyplexes are polyelectrolyte complexes of DNA and polycations, designed for potential gene delivery. We investigated the properties of new polyplexes formed from cholesterol-modified polycations and DNA. Three complexes were tested; their cholesterol contents were 1.4, 6.3, and 8.7 mol %. UV spectroscopy and fluorescence assay using ethidium bromide proved the formation of polyplexes. The kinetics of turbidity of polyplexes solutions in physiological solution showed that the colloid stability of polyplexes increases with increasing content of cholesterol in polycations. Dynamic, static, and electrophoretic light scattering, small-angle X-ray scattering, and atomic force microscopy were used for characterization of polyplexes. The observed hydrodynamic radii of polyplexes were in the range of 30-60 nm; they were related to the polycation/DNA ratio and hydrophobicity of the used polycations (the cholesterol content). The properties of polyplex particles depend, in addition to polycation structure, on the rate of polycation addition to DNA solutions.