Phototriggered Secretion of Membrane Compartmentalized Bioactive Agents

A strategy for the light‐activated release of bioactive compounds (BODIPY, colchicine, paclitaxel, and methotrexate) from membrane‐enclosed depots is described. We have found that membrane‐permeable bioagents can be rendered membrane impermeable by covalent attachment to cobalamin (Cbl) through a photocleavable linker. These Cbl‐bioagent conjugates are imprisoned within lipid‐enclosed compartments in the dark, as exemplified by their retention in the interior of erythrocytes. Subsequent illumination drives the secretion of the bioactive species from red blood cells. Photorelease is triggered by wavelengths in the red, far‐red, and near‐IR regions, which can be pre‐assigned by affixing a fluorophore with the desired excitation wavelength to the Cbl‐bioagent conjugate. Pre‐assigned wavelengths allow different biologically active compounds to be specifically and unambiguously photoreleased from common carriers.     

DEPOLARIZATION OF MOUSE MYELOMA CELL MEMBRANES DURING PHOTODYNAMIC ACTION

The effect of photodynamic action on plasma membranes was examined using a fluorescent potentiometric indicator [di-SBA-C2(3)] to measure alterations in the plasma membrane potential of mouse myeloma cells treated with zinc phthalocyanine sulfonate and light. Plasma membrane depolarization was observed to be an early event in photodynamic action, showing both photosensitizer concentration and light dose dependence. Depolarization occurred while membrane integrity was retained and appears to be an early event preceding cell death.     

PHOTOPROPERTIES OF ALKOXY-SUBSTITUTED PHTHALOCYANINES WITH DEEP-RED OPTICAL ABSORBANCE

Triplet-state properties of 1,4,8,11,15,18,22,25-octa-n-butoxyphthalocyanine and its zinc derivative were determined for the first time. The T1 state of the metal-free phthalocyanine was characterized by a short lifetime (tau T = 17 microseconds) and low quantum yield (phi T = 0.095), and quenching of the triplet by O2 occurred with a bimolecular rate constant (kT sigma = 1.3 x 10(8) M-1 s-1) that is indicative of an endogonic reaction. The zinc complex (ZnPc(OBu)8) was markedly better as a triplet photosensitizer with respect to both tau T (60 microseconds) and phi T (0.5). Quenching by O2 produced singlet oxygen with nearly 100% efficiency, and kT sigma (1.7 x 10(9) M-1s-1) was close to the spin-statistical diffusion-controlled limit. Phosphorescence measurements showed the energy of the T1 state of ZnPc(OBu)8 to be 100 kJ/mol, which is 6 kJ/mol above the 1 delta g state of O2. These photoproperties, together with Q-band absorption maxima in the mid-700 nm range indicate that metal-centered 1,4,8,11,15,18,22,25-octaalkoxyphthalocyanines have excellent potential as sensitizers in photodynamic therapy.     

Cyclohexene oxide/CO2 copolymerization catalyzed by chromium(III) salen complexes and N-methylimidazole: effects of varying salen ligand substituents and relative cocatalyst loading

A detailed mechanistic study into the copolymerization of CO2 and cyclohexene oxide utilizing CrIII(salen)X complexes and N-methylimidazole, where H2salen = N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-ethylenediimine and other salen derivatives and X = Cl or N3, has been conducted. By studying salen ligands with various groups on the diimine backbone, we have observed that bulky groups oriented perpendicular to the salen plane reduce the activity of the catalyst significantly, while such groups oriented parallel to the salen plane do not retard copolymer formation. This is not surprising in that the mechanism for asymmetric ring opening of epoxides was found to occur in a bimetallic fashion, whereas these perpendicularly oriented groups along with the tert-butyl groups on the phenolate rings produce considerable steric requirements for the two metal centers to communicate and thus initiate the copolymerization process. It was also observed that altering the substituents on the phenolate rings of the salen ligand had a 2-fold effect, controlling both catalyst solubility as well as electron density around the metal center, producing significant effects on the rate of copolymer formation. This and other data discussed herein have led us to propose a more detailed mechanistic delineation, wherein the rate of copolymerization is dictated by two separate equilibria. The first equilibrium involves the initial second-order epoxide ring opening and is inhibited by excess amounts of cocatalyst. The second equilibrium involves the propagation step and is enhanced by excess cocatalyst. This gives the [cocatalyst] both a positive and negative effect on the overall rate of copolymerization.     

DMF As a Formate Anion Equivalent: Formolysis of Tosylates in Aqueous DMF1

Treatment of tosylates with aqueous dimethylformamide furnish mainly formates     

High efficiency, phase-locked operation of the harmonic-multiplyinginverted gyrotwystron oscillator

The inverted gyrotwystron (phigtron) is a millimeter wave frequency-doubling amplifier that has been demonstrated to produce over 300 kW peak power at twice the input frequency (centered at f_in =16.85 GHz and f_out=33.7 GHz) over a 0.5% bandwidth with a saturated gain of 30 dB and efficiency greater than 35%. The device has also been studied both theoretically and experimentally in a different operating regime where frequency-doubled, phase-locked oscillation is possible. A signal, injected via a fundamental gyro-traveling wave tube input section, modulated a 55 kV, 10 A electron beam. After transit through a drift section, the prebunched electron beam produced phase-locked, second harmonic oscillations in a TE₀₃ mode output cavity. RF output centered at either of two frequencies, 34.42 and 34.62 GHz, with a maximum output power of 180 kW, an efficiency of 32% and a locked signal gain of 35 dB was measured. A theoretical prediction of locking bandwidth, a design overview, and the experimental results are presented followed by a summary and discussion of the results     

Reactivities in olefin-difluorocarbene reactions

The relative rates of addition of difluorocarbene to a series of methyl-substituted olefins have been determined and correlated with similar data for dichlorocarbene, chlorofluorocarbene and ground-state oxygen atoms. The electrophilic nature and stabilization of difluorocarbene by the fluorine substituents is discussed. Relative activation energies for the difluorocyclopropane-forming reaction have been estimated and correlated with properties of the olefins as derived from molecular orbital theory.