Bulk microphase segregation of an asymmetric organometallic-inorganic diblock copolymer: a remarkable example of concentric cylinders

We report that an asymmetric diblock copolymer, poly(ferrocenyldimethylsilane-b-dimethylsiloxane) (PFS90-b-PDMS900, PDI = 1.01, volume fraction PFS = 0.20), self-assembles in the bulk state to form a hexagonal periodic structure with a remarkable morphology. Part of the major component forms the core of concentric cylinders with a mean diameter of 35.5 nm surrounded by a 7 nm thick shell of PFS. The remaining PDMS fills the interstitial spaces. The morphology was elucidated by small-angle X-ray scattering, as well as by scanning and conventional transmission electron microscopy.     

Reactions of polyfunctional amines with 3-amino-4-(anilinothio-methylidene)-2-cyano-2-pentenedioic acid diethyl ester

3-Amino-4-(anilinothiomethylidene)-2-cyano-2-pentenedioic acid diethyl ester reacts with ethylenedi-amine, 1,3-propylenediamine and 1,4-butylenediamine affording bicyclic cyclocondensation products. The title compound reacts with diethylenetriamine and 2-(2-aminoethylamino)ethanol to give new seven membered ring tricyclic compounds. The mechanism for these reactions is discussed.     

Investigation of isothiocyanate addition to alkylidene derivatives of malononitrile and cyanoacetic acid esters

Addition of arylisothiocyanates to active methylene compounds leads to a variety of compounds depending on the structure of the starting material and conditions used to conduct the addition. Addition of arylisothiocyanate to 1c leads to a pyrido[2,3-d]pyrimidine resulting from addition of a second mole of cyanate to the initial adduct. Addition of arylisothiocyanate to 1b led to a mixture of pyridine and thiopyran adducts, while addition to 1a led to open chain structures.     

Pulsed field gradient NMR studies of polymer adsorption on colloidal CdSe quantum dots

Pulsed field gradient nuclear magnetic resonance (PFG NMR) experiments have been used to examine ligand exchange between poly(2-(N,N-dimethylamino)ethyl methacrylate) (PDMA) (Mn = 12,000, Mw/Mn = 1.20, Nn = 78) and trioctylphosphine oxide (TOPO) bound to the surface of CdSe/TOPO quantum dots (QDs). We show that PFG 1H NMR can quantify the displacement of TOPO by PDMA through its ability to differentiate signals due to TOPO bound to the QDs versus those from TOPO molecules free in solution. For CdSe QDs with a band edge absorption maximum at 558 nm (diameter 2.7 nm by transmission electron microscopy), we determined that, at saturation, 8 polymer chains on average displace greater than 90% of the surface TOPO groups. At partial saturation, with an average of 6 polymer chains/QD, each TOPO displaced requires 28 DMA repeat units. Assuming that one Me2N- group binds to a surface Cd2+ for each TOPO displaced, we infer that only about 3% of the DMA units are directly bound to the surface. The remaining groups are present as loops or tails that protrude into the solvent and increase the hydrodynamic diameter of the particles.     

Delivery platform for hydrophobic drugs: prodrug approach combined with self-assembled multilayers

We report the design of a platform for the delivery of hydrophobic drugs via a macromolecular prodrug approach combined with LbL-assembled polyelectrolyte multilayers. A hyaluronan ester prodrug of the chemotherapeutic drug paclitaxel has been synthesized. Conjugation of the drug to hyaluronan through a labile succinate ester did not inhibit its activity. Using quartz crystal microbalance, atomic force microscopy, and UV spectroscopy, we have shown that the presence of the hydrophobic paclitaxel moieties does not prohibit the layer-by-layer construction of the multilayers. Release of the drug from the paclitaxel-loaded multilayers upon hydrolysis of the ester linkage resulted in a drastic cell death. Application of this delivery platform to substrates such as colloids, biomedical implants, or vascular tissues may lead to new therapeutic strategies.     

Quenching of aromatic ketone phosphorescence by sterically hindered alkenes

The deactivation of the excited states of triplet ketones by sterically hindered alkenes results in lower rate constants (usually due to increased activation energies) than by relatively unhindered alkenes.     

Boron nitride nanotube-based amphiphilic hybrid nanomaterials for superior encapsulation of hydrophobic cargos

We report an organic-inorganic hybrid core-shell nanomaterial obtained by conjugation of an amphiphilic monomethoxy-poly(ethylene glycol)-b-poly(epsilon-caprolactone) diblock copolymer to hydroxylated boron nitride nanotubes (BNNTs). The extent of copolymer grafting reached 64% w/w, an exceptionally high value. The hybrid materials exhibit excellent physical stability in water and an outstanding loading capacity (31.3% w/w) for curcumin, a hydrophobic drug. Moreover, they present good compatibility with the Caco2 cell line, a model of intestinal epithelium. Our findings demonstrate the potential of multifunctional hybrid BNNTs to serve as a platform for complex amphiphilic nanoparticle architectures with improved features.     

Gas Phase Reactions OF 1,2:5,6-DI-O-Isopropylidene-α-D-Gluco- and Allofuranose with Electrophiles Derived From Acetone

ABSTRACT

In a quadrupole mass spectrometer, under chemical ionization conditions with acetone as the reagent gas, 1,2:5,6-di-O-isopropylidene-β-D-glucofuranose and 1,2:5,6-di-O-isopropylidene-β-D-allofuranose form M+1, M+43, and M+59 ions in the gas phase. In addition, the allo isomer produces M+41 ions. These ions and the corresponding ions derived from isotopomers in which the isopropylidene groups were differentiated by deuterium substitution were separately subjected to collisionally activated dissociation conditions. The different reactivities of these ions were attributed to the ability of the allo structure to hydrogen bond internally and the different sizes of the electrophilic groups which formed adducts with the neutral protected sugar molecules.     

Amphiphilic polyethylenes leading to surfactant-free thermoresponsive nanoparticles

Linear copolymers of ethylene and acrylic acid (PEAA) were prepared by catalytic polymerization of ethylene and tert-butyl acrylate followed by hydrolysis of the ester groups. The copolymers contained COOH groups inserted into the crystalline unit cell with formation of intramolecular hydrogen-bonds, as established on the basis of differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) studies. A solvent-exchange protocol, with no added surfactant, converted a solution in tetrahydrofuran of a PEAA sample containing 12 mol % of acrylic acid (AA) into a colloidally stable aqueous suspension of nanoparticles. Transmission electron microscopy (TEM), dynamic light scattering (DLS), and high sensitivity differential scanning calorimetry (HS-DSC) were used to characterize the nanoparticles. They are single crystals of elongated shape with a polar radius of 49 nm (σ = 15 nm) and an equatorial radius of 9 nm (σ = 3 nm) stabilized in aqueous media via carboxylate groups located preferentially on the particle/water interface. The PEAA (AA: 12 mol %) nanoparticles dispersed in aqueous media exhibited a remarkable reversible thermoresponsive behavior upon heating/cooling from 25 to 80 °C.     

Emulsion copolymerization of vinyl acetate and butyl acrylate in the presence of fluorescent dyes

This article describes our first experiments for preparing dye‐labeled latex particles by the emulsion copolymerization of a 4/1 (w/w) mixture of vinyl acetate‐butylacrylate (VAc‐BA). We discuss the synthesis of acrylate derivatives of phenanthrene, anthracene, and pyrene [9‐acryloxymethyl phenanthrene ( 7 ), 9‐acryloxymethyl‐10‐methyl anthracene ( 8 ), and 1‐acryloxymethyl pyrene ( 10 )] and an allyl ether derivative of anthracene [9‐allyoxymethyl‐10‐methyl anthracene ( 9 )]. Although the phenanthrene derivative 7 gave latex particles with high monomer conversion and good dye incorporation, the pyrene acrylate and both anthracene comonomers strongly inhibited the free‐radical reaction. To assist our search for a dye that would serve as a useful energy acceptor for phenanthrene and without suppressing VAc‐BA polymerization, we also examined batch emulsion polymerization in the presence of a variety of dye derivatives—substituted anthracenes, acridines, a coumarin, and two benzophenone derivatives. All of the anthracene derivatives, as well as acridine, strongly inhibited monomer polymerization. The coumarin dye 7‐hydroxy‐4‐methyl coumarin ( 22 ) that had only limited solubility allowed more than 90% monomer conversion. Most promising were 2‐hydroxy‐5‐methyl benzophenone ( 23 ) and 4‐N,N‐dimethylamino benzophenone ( 24 ) that at 1 mol % in the monomer mixture permitted virtually quantitative monomer conversion to latex. 4′‐Dimethylamino‐2‐acryloxy‐5‐methyl benzophenone ( 25 ) copolymerized well with the VAc‐BA mixture, yielding latex particles in high yield and with a narrow size distribution. These dyes appear to be useful acceptor dyes for energy‐transfer experiments with phenanthrene. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1594–1607, 2002