Pyridazines. LXV. Reactions of some I-phenacylazolopyridazinium halides with 2,3-diphenylcyclopropenone, -thione,or hydrazine

I-Phenacylazolopyridazinium bromides reacted with 2,3-diphenylcyclopropenone or -thione in the presence of triethylaminc to give 3,4,6-triphenyl-2-pyrone or -2-thiopyrone and the corresponding azolopyridazine. Quaternized azolopyridazines reacted with hydrazine to give either 3,6-diphenylpyridazine and the corresponding azoloazine or hy ring opening of the azine part to give 1-methyl-2-(pyrazolyl-5′)imidazole.     

Role of vibrationally excited NO in promoting electron emission when colliding with a metal surface: a nonadiabatic dynamic model

A nonadiabatic quantum dynamic model has been developed to study the process of electron emission from a low-work-function metal surface. The process is initiated by scattering a highly vibrationally excited NO molecule from a surface composed of a Cs layer covering a Ru crystal. The model addresses the increasing quantum yield of the electron emission as a function of the molecular vibrational excitation and incident kinetic energy. The reaction mechanism is identified as a long-range harpooning electron transfer to a molecular ion which is then accelerated toward the surface. Upon impact, the molecular ion emits its excess electron.     

Novel methyl helianthrones as photosensitizers: synthesis and biological evaluation

A combination of light, oxygen and a photosensitizer is used to induce death of cancer cells by photodynamic therapy. In this study, we have synthesized several new methyl helianthrone derivatives and compared their phototoxicity with that of hypericin. In contrast to hypericin, methyl helianthrones are soluble in aqueous solutions and have a broad range of light absorbance, which allows the use of polychromatic light. Structural modifications of methyl helianthrone demonstrated that substitution of hydrogen atoms of methyl helianthrone at Positions 2 and 5 with Br atoms or methylation of its phenolic hydroxyls, significantly increases the corresponding singlet oxygen quantum yield and their phototoxicity toward alphaT3-1, M2R and LNCaP cells. The phototoxicity of some of these compounds was similar to that of hypericin. Methyl helianthrones, like hypericin, accumulated mainly in the perinuclear region as evident by confocal microscopy. Irradiation of cells pretreated with methyl helianthrone derivatives generates intracellular reactive oxygen species and lipid free radicals, as shown by a fluorescentic probe and electron paramagnetic resonance methods, respectively. The phototoxicity of these methyl helianthrones as well as their ability to oxidize membrane lipids were significantly decreased on addition of specific Type-II inhibitors, suggesting the involvement of singlet oxygen as the main oxidant.     

Effect of Substituents and of Wavelength of Irradiation on the Photo-Fries-Rearrangement of Enol-Esters Preliminary Communication

Enol-esters 1a-1e undergo clean Photo-Fries-rearrangements without side reactions. With anthroyl derivatives the reaction is observed only at 254 nm, not at 366 nm.     

Gas phase unimolecular decomposition and chemiluminescence of tetramethyldioxetane initiated by a tea CO2 laser

Time resolved chemiluminescence spectra of pure tetramethyldioxetane are obtained for the first time using pulsed infrared laser excitation. The only major product, acetone, is shown to be formed by at least two pathways: a unimolecular, collision free, decomposition and a collision induced mechanism. Spectral and temporal behaviour indicate that neither singlet nor triplet acetone are the primary products. Other possibilities are discussed.     

The importance of ground-state vibronic mixing in molecular Raman scattering

We consider Albrecht's theory for Raman scattering of fundamentals in the far and pre-resonance regions. Destructive interferences inherent to the A and B terms augment the conventionally suppressed C term dramatically. Raman excitation profiles for the ν₁(a_1g) and ν₆(e_2g fundamentals in benzene can be well fitted with theoretical C-term profiles involving the ¹E_1u(π-π^*) state at 1800 A.     

Quantitative electrochemical formation of phosphotungstate heteropolyanion blues

The optical and ESR spectra of electrochemically reduced phosphotungstate and polyphosphotungstate anions in phosphoric acid were examined as quantitative functions of W⁵⁺ concentration. The optical spectra obey Beer-Lambert laws and are similar to the spectra of reduced silicotungstate anions, indicating the secondary nature of the central cluster in the keggin structure with regard to interactions with the reduction electron. ESR spectra indicate an equivalent correspondence for the W⁵⁺ concentration and unpaired spins for the reduced polyphosphotungstate anion but for the reduced phosphotungstate anion monomer the unpaired spin concentration estimated by ESR was much lower than the W⁵⁺ concentration. Reacting reduced phosphotungstate anions with oxygen showed a I-electron reduction of the oxygen molecule with concomitant oxidation of W⁵⁺ to W⁶⁺ and possibly production of high-molecular-weight, polyanion clusters.