Stimuli responsive poly(1-[11-acryloylundecyl]-3-methyl-imidazolium bromide): dewetting and nanoparticle condensation phenomena

A stimuli-responsive homopolymer poly(ILBr) is fabricated via a "two-phase" atom transfer radical polymerization (ATRP) process, where ILBr stands for the reactive ionic liquid surfactant, 1-[11-acryloylundecyl]-3-methyl-imidazolium bromide. An extraordinarily wide molecular weight distribution (PDI = 6.0) was obtained by introducing the initiator (4-bromomethyl methyl benzoate) in a heterogeneous two-phase process. The molecular weight distribution of poly(ILBr) was characterized by size-exclusion chromatography (SEC). The resulting homopolymer was found to be surface active and stimuli responsive. Poly(ILBr) films coated on quartz exhibit stimuli-responsive dewetting after ion exchange of Br(-) by PF(6)(-). This dewetting phenomenon can be understood in chain segmental terms as a stimuli-induced structural relaxation and appears to be the first such reported stimuli-responsive polymeric dewetting. Titrating aqueous poly(ILBr) with aqueous bis(2-ethylhexyl)sulfosuccinate induces nanophase separation and results in the condensation of nanoparticles 30-60 nm in diameter.     

The action of bentonitic earth on natural product epoxides

The ring opening of the epoxide group in the epoxiguaianolides by commercially available bentonitic earth produces specifically the trans diol in good yield under mild conditions.     

Excitation of polymer-shelled contrast agents with high-frequency ultrasound

Few experimental and complementary theoretical studies have investigated high-frequency (>20 MHz) nonlinear responses from polymer-shelled ultrasound contrast agents. Three polymer agents with different shell properties were examined for their single-bubble backscatter when excited with a 40 MHz tone burst. Higher-order harmonic responses were observed for the three agents; however, their occurrence was at least partly due to nonlinear propagation. Only one of the agents (1.1 microm mean diameter) showed a subharmonic response for longer excitations (approximately 10-15 cycles) and midlevel pressure excitations ( 2.5 MPa). Theoretical calculations of the backscattered spectrum revealed behavior similar to the experimental results in specific parameter regimes.     

Ethylene polymerization and copolymerization with a polar monomer using an α‐iminocarboxamide nickel complex activated by trimethylaluminum

An α‐iminocarboxamide nickel complex was activated by trimethylaluminum (TMA) and used in the polymerization of ethylene and its copolymerization with 10‐undecen‐1‐ol. The best activity was observed upon activation with 9 equiv of TMA at a temperature of 26 °C. NMR spectroscopic studies did not show 10‐undecen‐1‐ol incorporation. However, FTIR analyses suggest the incorporation of a very small amount of comonomer, which affects the glass transition temperature, the degree of branching, and the mechanical properties of the materials. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 54–59, 2008     

A new tantalum dinitrogen complex and a parahydrogen-induced polarization study of its reaction with hydrogen

Reduction of Cp*(2)TaCl(2) with sodium amalgam in THF under a nitrogen atmosphere results in the formation of the novel complex (Cp*(2)TaCl)(2)(micro-N(2)). This dinuclear complex containing a micro-eta(1):eta(1) dinitrogen bridge has been characterized by NMR and X-ray crystallography. The complex possesses a C(2)-symmetric structure with each Ta bound to diastereotopic Cp* rings and chloride in addition to the micro-N(2) bridge. The Ta-N and N-N distances of 1.885(10) and 1.23(1) A, respectively, suggest modest reduction of the dinitrogen moiety. The two Cp* resonances on each Ta center remain inequivalent in solution, even up to 80 degrees C. Addition of hydrogen results in the formation of two isomers of the dihydride complex Cp*(2)TaH(2)Cl. Under parahydrogen, polarized resonances are observed for the unsymmetrical isomer with adjacent hydrides as the product of H(2) oxidative addition. The symmetric isomer of Cp*(2)TaH(2)Cl also forms, most likely by isomerization of the unsymmetrical kinetic isomer. The reactivity of (Cp*(2)TaCl)(2)(micro-N(2)) was compared to that of the related monomer, Cp*(2)TaCl(THF). The THF adduct yields the same hydrogen addition products, but the reaction is much more facile than for the nitrogen dimer, indicative of the structural integrity of the micro-N(2) complex.     

Sensitivity of whole human teeth to fast neutrons and gamma-rays estimated by L-band EPR spectroscopy

This paper reports the first attempt to use L-band spectroscopy for estimating the sensitivity of whole teeth to fast neutrons and gamma-rays. Three teeth were successively irradiated first with fast neutrons with a wide energy spectrum (mean energy around 30 MeV) up to 160 Gy and then with gamma-rays up to 14 Gy. After each irradiation, L-band (1 GHz) EPR spectra of each whole tooth surrounded by the surface–coil resonator were recorded, yielding a single composite line principally due to CO₂⁻ and native radicals. The sensitivities are estimated by the slopes of the linear dose response curves of the dosimetric CO₂⁻ radicals. The ratios of the gamma/neutron sensitivities were found to be in the range 8–9 (±2) for the three teeth.     

PHOTODYNAMIC ACTIVITIES and SKIN PHOTOSENSITIVITY OF THE bis(DIMETHYLTHEXYLSILOXY)SILICON 2,3-NAPHTHALOCYANINE IN MICE

The photodynamic therapy (PDT) activity of the bis(dimethylthexylsiloxy)silicon 2,3-na-phthalocyanine (SiNc 8 ) was evaluated against the EMT-6 tumor implanted intradermally in BALB/c mice. The SiNc 8 was formulated in aqueous emulsions based on Cremophor EL or Solutol HS 15. The formulation was shown to affect plasma clearance and overall pharmacokinetics. Compared to Cremophor, Solutol promoted rapid plasma clearance and high liver retention of the dye, combined with a slight increase of dye tumor concentrations. The PDT action spectrum for tumor response of SiNc 8 in Cremophor (190 mW cm², 200 J cm², 24 h postinjection [p.i.] of 1 (jimol kg¹) showed a maximum at 780 nm, which corresponds to the absorption maximum of the monomelic dye as well as the in vivo maximum change in the “diffuse optical density” produced by the dye. The extent of tumor necrosis increased with augmented dye and light doses. Regardless of the formulation, at 1 h p.i. of 0.1 μmol kg^?! SiNc 8 , PDT efficiency (190 mW cm'², 400 J cm²) was high but accompanied by severe damage to normal tissues, at 24 h PDT resulted in complete tumor regression in 80% of the animals without adverse effects to adjacent tissues, while at 72 h p.i. PDT induced no tumor response with Cremophor and only a partial response with Solutol. At the latter time point, plasma dye clearance was nearly complete while tumor tissue levels remained high, suggesting that tumor response correlates with plasma rather than tumor dye levels. Skin sensitivity of SKhl mice to solar-simulated radiation was lower with SiNc 8 as compared to Photofrin®. Our data suggest the potential of SiNc 8 as a far-red absorbing photosensitizer in clinical PDT.