The 35Cl NQR spectra and structure of pentafluorophenyltetrachlorophosphorane C6F5PCl4

The low temperature structure of C₆F₅PCl₄ was confirmed by ³⁵Cl NQR measurements as ψ-trigonal bipyramidal, with the C₆F₅ group axial. Discrepancies were found with previously reported data, possible causes of these are discussed.     

LIGHT DAMAGE IN THE RAT RETINA: EFFECT OF A RADIOPROTECTIVE AGENT (WR-77913) ON ACUTE ROD OUTER SEGMENT DISK DISRUPTIONS

Primary events in the course of light induced retinal lesions are still not fully elucidated. Under chronic conditions, lipid peroxidation in the retina and death of photoreceptor cells are observed. The radioprotective agent WR-77913 scavenges singlet oxygen, hydrated electrons and free radicals. WR-77913 was used to protect against acute light induced photoreceptor outer segment membrane disruptions in the rat retina. There was a partial but not complete protection at higher illuminance levels (800 lx for 30 min), whereas threshold lesions (400 lx for 30 min) were almost completely prevented. These observations indicate an involvement of photodynamic reactions in causing acute photoreceptor lesions.     

Transmission spectra of light to the mammalian retina

A simple method has been developed to determine the optical properties of the anterior segment of the intact eye. This consists of a probe that is inserted into the posterior sclera and detects light passing through the anterior segment. The probe is connected to a charge-coupled device spectrophotometer via a fiber optic bundle. It was determined that the young rat anterior segment transmits light down to 300 nm, whereas calf and rabbit eyes transmit no UVB and only part of the UVA to the posterior segment. The absorbing species in these animals is most likely NAD(P)H, which has an absorption maximum at approximately 345 nm and is associated with zeta-crystallin. A young primate anterior segment transmits almost no UV with a steep increase in transmission at CA 400 nm. Because some experiments employed a light tube that is used to illuminate the retina during vitrectomies, this method can be used to determine the transmission spectra of the anterior segment of humans in vivo.     

IN VITRO AND IN VIVO PROTECTION AGAINST PHOTOTOXIC SIDE EFFECTS OF PHOTODYNAMIC THERAPY BY RADIOPROTECTIVE AGENTSWR–2721 ANDWR–77913

Abstract— The experimental radioprotective agentsS–2-(3-aminopropylamino) ethyl phosphorothioate(WR–2721) and 3-amino-2-hydroxypropyl phosphorothioate(WR–77913) are also protective against photosensitized oxidation. They reduce porphyrin-induced photopolymerization of lens cytosol proteins in vitro, and phototoxic damage to mouse skin in vivo. The phototoxic dose modification factor (DMF) was 1.5 which is similar to that found in ionizing radiation. Part of the mechanism by which sulfhydryls afford this protection is by accelerating photobleaching of the porphyrins.     

Polymerization and copolymerization of α-methacrylophenone

Under a variety of conditions it has not been possible to induce the free-radical-initiated homopolymerization of α-methacrylophenone (α-MAP). The only product isolated from such efforts was the Diels-Alder dimer of the monomer. A Mayo-Lewis plot of the free-radical copolymerization of α-MAP and styrene shows considerable scatter but the copolymer composition indicates that an α-MAP unit can add to itself. These results have been ascribed to a penultimate effect. α-MAP is homopolymerized by dimsylsodium or n-butyllithium. Attempted copolymerization of α-map and styrene with n-butyllithium produces >95% α-MAP. Unexpectedly, α-MAP does not homopolymerize with lithium dispersion, but does react in the presence of styrene to give product containing a relatively small amount of α-MAP.     

Experimental Gibbs free energy considerations in the nucleation and growth of single-walled carbon nanotubes

Gas feed composition and reaction temperature were varied to identify the thermodynamic threshold conditions for the nucleation and growth of SWNT from methane on supported Fe/Mo catalyst. These reaction conditions closely approximate the pseudoequilibrium conditions that lead to the nucleation and growth of SWNT. These measurements also serve to determine an upper limit of the Gibbs free energy of formation for SWNT. The Gibbs free energy of formation relative to graphite is in good agreement with literature values predicted from simulations for SWNT nuclei containing approximately 80 atoms, while considerably larger than that predicted for bulk (5,5) SWNT. Our estimate over the range 700 to 1000 degrees C of 16.1 to 13.9 kJ mol(-1) falls between the results of these simulations and literature values for diamond.     

THE PHOTOLYSIS OF TRYPTOPHAN WITH 337.1 nm LASER RADIATION

Abstract— Aqueous solutions of L-tryptophan were photolyzed by exposure to 337.1 nm radiation from a pulsed nitrogen laser. These data were compared with results for the 290 nm conventional-source photolysis of tryptophan. The progress of photolysis was monitored by fluorescence analysis of tryptophan. UV absorption spectroscopy, HPLC, TLC, and proton NMR spectroscopy. The loss of Trp was observed to be first order for 290 nm photolysis but of mixed order for 337.1 nm photolysis. Five photolysis products were detected by TLC analysis, including: N-formylkynurenine. kynurenine, tryptamine (detected after 290 nm photolysis but not 337.1 nm photolysis) and two unknown products. The tryptophan-containing peptides N-acetyl-tryptophanamide (NATA) and tryptophylglycine (Trp-Gly) were also observed to photolyze upon 337.1 nm laser radiation demonstrating that this phenomenon is not restricted to free tryptophan monomer.
Since Trp is not ordinarily thought to absorb U V radiation at wavelengths as long as 337.1 nm. a number of experiments were performed in an effort to determine the mechanism of photolysis at this wavelength. Evidence is presented which indicates that the 337.1 nm laser photolysis of Trp does not result from two photon absorption, dielectric breakdown, or other laser-specific processes. Instead. it is concluded that this photolysis results either from a very weak absorption tail extending to 337.1 nm in tryptophan itself or from a reaction involving an impurity sensitizer which absorbs the 337.1 nm radiation. The sensitizing impurity. if present, could not. however, be removed by preparative HPLC and could not be detected by TLC or fluorescence analysis.     

THE PHOTOCHEMISTRY OF HUMAN RETINAL LIPOFUSCIN AS STUDIED BY EPR

Fluorescent material generated in the human retina accumulates within lipofuscin (HLF) granules of the retinal pigment epithelium (RPE) during aging. We have been investigating the possible light-induced contribution of these fluorophores to various diseases including age-related macular degeneration. Our studies have shown that some of the fluorescent components of HLF are products of the reaction of retinaldehyde with ethanolamine and that synthetic mixtures of this reaction can serve as a useful model for photophysical studies. Previous research by us has demonstrated that irradiation of either natural or synthetic lipofuscin resulted in the formation of a triplet state and possibly a free radical. Here EPR studies were performed to verify the formation of that radical. The UV irradiation of either synthetic or natural human retinal lipofuscin extracts in oxygen-free methanol led to the formation of a 5,5-dimethylpyrroline-N-oxide (DMPO) spin-trapped carbon-centered radical resulting from either hydrogen atom or electron abstraction from solvent molecules. In the presence of oxygen superoxide was formed, which was observed as a DMPO adduct. It is concluded that certain components of the chloroform-soluble fluorophores of human RPE lipofuscin granules and the fluorescent reaction products of retinaldehyde and ethanolamine are photophysically similar but not the same. Electron or hydrogen abstraction from a substrate by these fluorophores in vivo and the resulting radical products may contribute to the age-related decline of RPE function and blue light damage in the retina.     

Identification of Photooxidation Sites in Bovine α-Crystallin

Abstract— Because UV irradiation of proteins can produce reactive oxygen species and exposure to UV light has been implicated in cataractogenesis, the sites of photooxidation of bovine α-crystallin, a major lens protein with molecular chaperone activity, were identified using tandem mass spectrometry (MS/MS). Bovine α-crystallin was irradiated with UV light (293 nm) for 1, 4 and 8 h, digested with trypsin and analyzed by matrix-assisted laser de-sorption ionization, time-of-flight mass spectrometry (MALDI) to identify the oxidized sequences. Tryptic peptides were purified by reverse-phase HPLC and oxidized peptides were sequenced by MS/MS to determine the sites of oxidation. Tryptophan fluorescence decreased exponentially with increasing time of UV exposure and peptides containing residues 1-11 of α-crystallin and 1-11, 12-22 and 57-69 of α-crystallin were determined to be oxidized by shifts of 16 D or multiples of 16 Da above the mass of the unmodified peptide. The MALDI analysis revealed single oxidation of all four sequences, which increased with increasing time of UV exposure and possible double oxidation of α 12-22. The specific sites of photooxidation indicate that the N-terminal regions of α-and β-crystallin are exposed to an aqueous environment and are in the vicinity of tryptophan residues from neighboring subunits.