Molecular Containers Based on Amphiphilic PS-b-PMVE Dendrigraft Copolymers: Topology, Organization, and Aqueous Solution Properties

Metal Coordination Induces Phase Segregation in Amphipolar Arborescent Copolymers with a Core-Shell-Corona Architecture

Arborescent copolymers with a core-shell-corona (CSC) architecture were synthesized and the topology of the molecules was challenged (constrained) through intramolecular interactions, resulting in phase separation breaking the symmetry of radial density. The inner poly(2-vinylpyridine) shell of these arborescent polystyrene-g-[poly(2-vinylpyridine)-b-polystyrene] molecules can self-assemble by binding metallic salts and acids in apolar and intermediate-polarity solvents. Upon loading with HAuCl4, the characteristics of the polymer templates govern the "loading sites" of the metal within the molecules. Unique morphologies were observed for the metal-loaded G0-G4 arborescent copolymers investigated, namely, spherical, toroidal, raspberry-like, spherical nanocage, and a new worm-in-sphere morphology. The reason for the emergence of such morphologies is the interplay among intramolecular interactions of unlike polymer segments, solvent selectivity, the entropic elasticity of the arborescent substrate, and phase segregation induced by coordination with the charged metallic species. Meanwhile, the stability of the arborescent molecules against aggregation provides intramolecular phase segregation with imposed "confined" geometry and thus leads to nonconventional morphologies. Furthermore, the size of the arborescent molecules is much smaller than that of other known particles (droplets) serving as confined geometries. Computer simulations were used to model the mesostructure of the arborescent copolymers, to demonstrate the influence of solvent selectivity, together with HAuCl4 loading, on the evolution of the morphology of the macromolecules.

Core-shell nanoparticles: characterization and study of their use for the encapsulation of hydrophobic fluorescent dyes

Core-shell nanocapsules intended to be used as drug scavengers were prepared using a surfactant mixture containing octadecyltrimethoxysilane (OTMS) as a reactive amphiphile, to form spherical templates. A siloxane shell was grown on the surface of the templates by reacting tetramethoxysilane (TMOS) with the silanol groups obtained after the hydrolysis and condensation of OTMS. Dynamic light scattering (DLS) showed that particles with diameters in the range of 100-200 nm were obtained, with core and shell sizes controlled by varying component compositions. Atomic force microscopy (AFM) was used to study the effect of the silica coating of the templates on their robustness after deposition on a substrate. Subsequently, we present studies on the encapsulation of two hydrophobic fluorescent dyes, which are sensors of polarity and rigidity. Steady-state fluorescence spectroscopy was used to examine the fluorescence response of the dyes before and after shell growth. Changes in the emission of the encapsulated dyes were related to changes in the polarity and rigidity of the microenvironment where the dyes were located and correlated to the AFM results. Finally, dye-free core-shell particles were used to sequester the dyes from aqueous suspensions. Fluorescence of the sequestered species was compared to the dye-loaded particles to determine the final fate of the fluorophores in the nanoparticles.

Oxidation chemistry of poly(ethylene glycol)-supported carbonylruthenium(II) and dioxoruthenium(VI) meso-tetrakis(pentafluorophenyl)porphyrin

[Ru(II)(F(20)-tpp)(CO)] (1, F(20)-tpp=meso-tetrakis(pentafluorophenyl)porphyrinato dianion) was covalently attached to poly(ethylene glycol) (PEG) through the reaction of 1 with PEG and sodium hydride in DMF. The water-soluble PEG-supported ruthenium porphyrin (PEG-1) is an efficient catalyst for 2,6-Cl(2)pyNO oxidation and PhI==NTs aziridination/amidation of hydrocarbons, and intramolecular amidation of sulfamate esters with PhI(OAc)(2). Oxidation of PEG-1 by m-CPBA in CH(2)Cl(2), dioxane, or water afforded a water-soluble PEG-supported dioxoruthenium(VI) porphyrin (PEG-2), which could react with hydrocarbons to give oxidation products in up to 80 % yield. The behavior of the two PEG-supported ruthenium porphyrin complexes in water was probed by NMR spectroscopy and dynamic light-scattering measurements. PEG-2 is remarkably stable to water. The second-order rate constants (k(2)) for the oxidation of styrene and ethylbenzene by PEG-2 in dioxane-water increase with water content, and the k(2) values at a water content of 70 % or 80 % are up to 188 times that obtained in ClCH(2)CH(2)Cl.

Polymer Architecture and Drug Delivery

Polymers occupy a major portion of materials used for controlled release formulations and drug-targeting systems because this class of materials presents seemingly endless diversity in topology and chemistry. This is a crucial advantage over other classes of materials to meet the ever-increasing requirements of new designs of drug delivery formulations. The polymer architecture (topology) describes the shape of a single polymer molecule. Every natural, seminatural, and synthetic polymer falls into one of categorized architectures: linear, graft, branched, cross-linked, block, star-shaped, and dendron/dendrimer topology. Although this topic spans a truly broad area in polymer science, this review introduces polymer architectures along with brief synthetic approaches for pharmaceutical scientists who are not familiar with polymer science, summarizes the characteristic properties of each architecture useful for drug delivery applications, and covers recent advances in drug delivery relevant to polymer architecture.

Synthesis and Characterization of a Trifunctional Aminoamide Cellulose Derivative

As part of an effort to synthesize a dendronized cellulose, we have synthesized a trifunctional aminoamide derivative, which is the first generation of a dendron substituent. We anticipate that a dendronized cellulose would have applications in complexing metals and could be employed as an adjuvant for drugs. The trifunctional aminoamide substituent was introduced by coupling di-tert-butyl 4-[2-(tert-butoxycarbonyl)ethyl]-4-aminoheptanedicarboxylate, BA, directly to a (carboxymethyl)cellulose (CMC) backbone and converting the tert-butyl ester peripheral groups to aminoamide substituents by use of N,N-dimethyl-1,3-propanediamine. Confirmation of the proposed chemical structure of the intermediates as well as the water-soluble aminoamide derivative (CMCBADMPDA) was obtained by Fourier transform infrared (FT-IR) and NMR spectroscopy. The degree of substitution (DS) was determined to be 0.40 +/- 0.01 by thermogravimetric analysis. Typical weight average molecular weight (M(w)), molecular weight distribution (MWD), and molecular size of the dendronized polymers were found to be 97,000, 1.7, and 17.4 nm for derivatives of a CMC with corresponding M(w), MWD, and root-mean-square radius (RMS) of 230 000, 3.2, and 24 nm. A differential refractive index (dn/dc) for the aminoamide derivative measured in aqueous 0.40 N ammonium acetate-0.01 N NaOH was found to be 0.1473. The intrinsic viscosity of the dendronized cellulose decreased significantly when compared with that of CMC, that is, 0.40 dL/g relative to 5.60 dL/g. The hydrophobicity of the CMCBADMPDA microenvironment in aqueous solution was probed by evaluating the relative fluorescence intensities of the I(373)/I(384) pyrene bands; a slightly more hydrophobic environment was observed.