A multitechnique approach on adsorption, self-assembly and quercetin solubilization by Tetronics® micelles in aqueous solutions modulated by glycine

Fate of Photoinduced Electron Transfer Reactions with Temperature- and pH-Induced Assembly/Disassembly of Star Block Copolymer Micelles

The assembly/disassembly of star block copolymers induced by changes in temperature or pH of the medium is anticipated to have interesting implications for hosting/releasing drugs and tuning chemical reactions. This study investigates the possibility of employing the dually sensitive self-assembly of an ethylene oxide-propylene oxide star block copolymer, Tetronic T904, to influence photoinduced electron transfer (ET) reactions, on switching from the assembled state (micelle) when temperature is above the critical micelle temperature (CMT) and pH of the medium is above the pK_a of T904 to the dissociated (unimer) state when either the temperature is below the CMT or the polymer is protonated. Steady-state and time-resolved fluorescence techniques have been used to characterize the microenvironments of the reactants in T904 solutions under different temperature and pH conditions and to determine ET rate constants. Interestingly, the bimolecular ET rate constants in both assembled and disassembled states of T904 depict a bell-shaped correlation with the driving force of the reaction, in accordance with Marcus inversion behavior instead of the usual Rehm-Weller behavior seen in conventional solvents. The assembly/disassembly of T904 stimulated by temperature or pH affects the micropolarity in the reactant environment, the magnitude of ET rate constants, and the position of inversion on the exergonicity scale.

Pharmaceutical excipient salts effect on micellization and drug solubilization of PEO-PPO-ph-PPO-PEO block copolymer

Hydrophobic modification PEO-PPO copolymer BP123 was synthesized, with two aromatic rings in the centre linked to PEO-PPO blocks, and the identical PEO and PPO block numbers were possessed with commercial copolymer P123. The influence of three common pharmaceutical excipient salts sodium chloride (NaCl), sodium citrate (NaCA) and sodium benzoate (NaBZ) on self-assembly behaviors of BP123 and P123 was investigated via cloud point, surface tension, pyrene fluorescence and dynamic light scattering. Solubilization for hydrophobic drug simvastatin (SV) and in vitro drug release behavior were assessed accordingly. In the presence of NaCl or NaCA, cloud point and critical micellization concentration (CMC) decreased, micelles became more hydrophobic, micellar size and drug solubilization increased, drug release rate slowed, and the impact of NaCA was more significant than NaCl. Oppositely, cloud point and CMC increased with the addition of NaBZ. NaBZ could participate in the formation of micelles by hydrophobic aromatic ring, which greatly raised solubilization of SV. Moreover, a different performance occurred when NaBZ was added to BP123 or P123, due to the hydrophobic benzene rings in BP123, which prominently enhanced the interaction with hydrophobic drug, leading to obvious delay of drug release for BP123. This work is conducive to turning copolymer property in diverse pharmaceutical applications and in drug delivery systems as drug carriers.

Effect of Ionic Liquids as Cosurfactants on Photoinduced Electron Transfer in Tetronic Micelles

This study investigates the role of varying alkyl chain lengths of a series of surface-active 1-alkyl-3-methylimidazolium tetrafluoroborate ([C _nMIm][BF₄], n = 4, 6, and 10) ionic liquids (ILs) as cosurfactants in modifying the micellar characteristics of a tetronic star-block copolymer, T1304, and the consequent effects on bimolecular photoinduced electron transfer (PET) reactions carried out in these T1304-IL mixed micellar systems. Using coumarin 153 as the probe dye and following ground-state absorption, steady-state fluorescence, and time-resolved emission measurements, the micropolarity, microviscosity, and solvent relaxation dynamics in the micellar palisade layer have been revealed both in pure T1304 and in T1304-IL systems. With increasing alkyl chain length of the ILs, the palisade layer of the micelles gradually becomes more polar and less viscous, suggesting better incorporation of the longer alkyl chain length ILs as cosurfactants into the T1304 micelles. The bimolecular PET reactions, involving 7-aminocoumarins as acceptors and N, N-dimethylaniline as the donor, are considerably modulated in T1304 micelles by the presence of the ILs, the effect being more prominent for ILs with longer alkyl chain lengths. In all of the micellar systems, correlations of the electron transfer (ET) kinetics with the reaction exergonicity (-Δ G⁰) show clear Marcus inversion (MI) behavior where onsets of MI invariably appear at significantly lower exergonicities, suggesting the involvement of a two-dimensional ET mechanism. Interestingly, the Marcus correlations display significant variations, namely, enhanced reaction rates and gradual shift in the onset of MI toward higher exergonicity, as longer alkyl chain length ILs are sequentially introduced as cosurfactants. From the observed results, it is convincingly realized that 1-alkyl-3-methylimidazolium-based ILs can be used satisfactorily as cosurfactants in tetronic star-block copolymer solutions to modulate PET reactions very significantly for their better utilizations in suitable applied areas.

Pegylated poly(anhydride) nanoparticles for oral delivery of docetaxel

The aim of this work was to investigate the potential of pegylated poly(anhydride) nanoparticles to enhance the oral bioavailability of docetaxel (DTX). Nanoparticles were prepared after the incubation between the copolymer of methyl vinyl ether and maleic anhydride (Gantrez® AN), poly(ethylene glycol) (PEG2000 or PEG6000) and docetaxel (DTX). The oral administration of a single dose of pegylated nanoparticles to mice provided sustained and prolonged therapeutic plasma levels of docetaxel for up 48-72 h. In addition, the relative oral bioavailability of docetaxel was around 32%. The organ distribution studies revealed that docetaxel underwent a similar distribution when orally administered encapsulated in nanoparticles as when intravenously as Taxotere®. This observation, with the fact that the clearance of docetaxel when loaded into the oral pegylated nanoparticles was found to be similar to that of intravenous formulation, suggests that docetaxel would be released at the epithelium surface and then absorbed to the circulation.

Effect of Novel Quercetin Titanium Dioxide-Decorated Multi-Walled Carbon Nanotubes Nanocomposite on Bacillus subtilis Biofilm Development

The present work was targeted to design a surface against cell seeding and adhering of bacteria, Bacillus subtilis. A multi-walled carbon nanotube/titanium dioxide nano-power was produced via simple mixing of carbon nanotube and titanium dioxide nanoparticles during the sol-gel process followed by heat treatment. Successfully, quercetin was immobilized on the nanocomposite via physical adsorption to form a quercetin/multi-walled carbon nanotube/titanium dioxide nanocomposite. The adhesion of bacteria on the coated-slides was verified after 24 h using confocal laser-scanning microscopy. Results indicated that the quercetin/multi-walled carbon nanotube/titanium dioxide nanocomposite had more negativity and higher recovery by glass surfaces than its counterpart. Moreover, coating surfaces with the quercetin-modified nanocomposite lowered both hydrophilicity and surface-attached bacteria compared to surfaces coated with the multi-walled carbon nanotubes/titanium dioxide nanocomposite.

A Comparative Study on Micellar and Solubilizing Behavior of Three EO-PO Based Star Block Copolymers Varying in Hydrophobicity and Their Application for the In Vitro Release of Anticancer Drugs

The temperature and pH dependent self-assembly of three star shaped ethylene oxide-propylene oxide (EO-PO) block copolymers (Tetronics^® 304, 904 and 908) with widely different hydrophobicity was examined in aqueous solutions. Physico-chemical methods viz. viscosity, cloud point, solubilization along with thermal, scattering and spectral techniques shows strongly temperature and salt dependent solution behavior. T304 possessing low molecular weight did not form micelles; moderately hydrophilic T904 remained as micelles at ambient temperature and showed micellar growth while very hydrophilic T908 formed micelles at elevated temperatures. The surface activity/micellization/solubilization power was favored in the presence of salt. The copolymers turn more hydrophilic in acidic pH due to protonation of central ethylene diamine moiety that hinders micelle formation. The solubilization of a model insoluble azo dye 1-(o-Tolylazo)-2-naphthol (Orange OT) and hydrophobic drugs (quercetin and curcumin) for copolymer solutions in aqueous and salt solutions are also reported. Among the three copolymers, T904 showed maximum solubility of dye and drugs, hence the in vitro release of drugs from T904 micelles was estimated and the effect on cytotoxicity of loading the drugs in T904 micelles was compared with the cytotoxicity of free drugs on the CHO-K1 cells. The results from the present work provide a better insight in selection of Tetronics^® for their application in different therapeutic applications.