13 Matching Results

Search Results

Advanced search parameters have been applied.

Photoinduced charge separation in linked donor-chromophore-acceptor systems. Progress report, September 1, 1993--May 31, 1993

Description: Focus has been mainly on preparation and characterization of triply bridged dinuclear complexes containing a tris-2-2`- bipyridineruthenium chromophore and a second tris-bipyridine metal complex which is to serve as electron donor or acceptor, and of linked RuL{sub 3}-containing D-C-A complexes where D is a phenothiazine donor and A is a diquat type acceptor. (DLC)
Date: June 1, 1993
Creator: Elliott, C. M.
Partner: UNT Libraries Government Documents Department

Charge Separation in Photoredox Reactions. Final Report

Description: The structural aspects controlling charge separation in molecular photoionization reactions in organized molecular assemblies involving micelles, reverse micelles and vesicles are being studied by optical and electron magnetic resonance techniques including the time domain technique of deuterium electron spin echo modulation (ESEM) and matrix proton electron nuclear double resonance (ENDOR) to measure weak electron-nuclear dipolar interactions. ESEM and matrix ENDOR are particularly well adapted to the study of disordered systems as exemplified by micelles and vesicles. The photoionization yields of alkylphenothiazines in micelles and vesicles have been shown to depend on the alkyl chain length and to correlate with relative distances from the surfactant assembly interface measured by deuterium ESEM and matrix proton ENDOR. The photoionization of alkylmethylviologens versus alkyl chain length has also been studied in vesicles, micelles and reverse micelles. Nitroxide spin probes have been used to study the degree of water penetration into mixed ionic/nonionic poly(ethylene oxide) and cationic/anionic micelles by using ESEM methods and selectively deuterated surfactants. The effect of urea interaction at micellar interfaces on the interface hydration has also been evaluated by studying nitroxide probes with ESEM.
Date: July 15, 1993
Creator: Kevan, L.
Partner: UNT Libraries Government Documents Department

Mechanisms of immunosuppression and cellular mechanisms of secondary disease. Final report, September 1, 1971--August 31, 1973

Description: The development of antibody-producing cells was studied in vivo and in vitro using radiation, anti-tumor drugs, and antibiotics. The mechanism of action of phenothiazines was studied at the cellular level using a cell separation technique. The effects of puromycin and purine antimetabolites on the various development stages of cells were studied. (HLW)
Date: January 1, 1973
Creator: Uyeki, E M
Partner: UNT Libraries Government Documents Department

Photoinduced charge separation in linked donor-chromophore-acceptor systems

Description: Focus has been mainly on preparation and characterization of triply bridged dinuclear complexes containing a tris-2-2'- bipyridineruthenium chromophore and a second tris-bipyridine metal complex which is to serve as electron donor or acceptor, and of linked RuL[sub 3]-containing D-C-A complexes where D is a phenothiazine donor and A is a diquat type acceptor. (DLC)
Date: June 1, 1993
Creator: Elliott, C.M.
Partner: UNT Libraries Government Documents Department

Electron transfer reactions of excited dyes with metal complexes. Progress report, March 1, 1978-February 28, 1979. [Iron-methylene blue]

Description: An intense absorption band of /sup 3/MBH/sup 2 +/ at 700nm was characterized in several media and its pK/sub A/ was measured to be 7.17 +- .1 in water. Flash photolysis show that semiethylene blue, MBH/sup +/, formed by quenching /sup 3/MBH/sup 2 +/ with Fe/sub II/(H/sub 2/O)/sub 6//sup 2 +/, decays by disproportionation at a diffusion-controlled rate. Rates of decay of the photostationary state of solutions of MB/sup +/ and Fe/sup II/(H/sub 2/O)/sub 6//sup 2 +/ in acidic media were measured using crossed beams to yield specific rates of oxidation of leucomethylene blue (MBH/sub 3//sup 2 +/) by MB/sup +/ (synproportionation) and by Fe(III). Laser flash-photolysis shows that quenching of MB/sup +/(S/sub 1/) by Fe(H/sub 2/O)/sub 6//sup 2 +/ can result in electron transfer to give MBH/sup +/. Profound differences between processes initiated by quenching triplet methylene blue with Fe(H/sub 2/O)/sub 6//sup 2 +/ and with stable coordination complexes of Fe(II) were found. Quenchers included (Fe/sup II/(CN)/sub 6/)/sup 4 -/, (Fe/sup II/(CN)/sub 4/(bpy)/sub 2/)/sup 2 -/, (Fe/sup II/(CN)/sub 2/(bpy))/sup 0/, and (Fe/sup II/(bpy)/sub 3/)/sup 2 +/. Measurements were made in aqueous and aqueous-alcoholic solutions at pH 2, 4.4, and 8.2. Quenching of /sup 3/MBH/sup 2 +/ or /sup 3/MB/sup +/ by a stable complex of Fe(II) is diffusion-controlled and 10/sup 2/ to 10/sup 3/ times the rate at which Fe(H/sub 2/O)/sub 6//sup 2 +/ quenches /sup 3/MBH/sup 2 +/. Net electron transfer accounts for less than 1/3 of total quenching by complexed Fe(II). In contrast, quenching by Fe(H/sub 2/O)/sub 6//sup 2 +/ goes essentially entirely with net electron transfer. It is concluded that quenching of triplet methylene blue by complexes proceeds via electron transfer which is reversible in the encounter complex. The MBH/sup +/ which results from net electron transfer from complexes of Fe(II) decays essentially entirely to MB/sup ...
Date: March 15, 1979
Creator: Lichtin, N.N.
Partner: UNT Libraries Government Documents Department

Previously unreported intense absorption band and the pK/sub A/ of protonated triplet methylene blue

Description: Excitation by a Q-switched giant ruby laser (1.2 joule output at 694 nm, approx. 50 nsec flash) of 2-10 ..mu..M solutions of methylene blue in water, 30% ethanol in water or 50 v/v% water - CH/sub 3/CN at pH values in the range 2.0 - 9.3 converted the dye essentially completely to its T/sub 1/ state. The absorption spectrum of T/sub 1/ dye was measured in different media at pH 2.0 and 8.2 by kinetic spectrophotometry. Previously reported T-T absorption in the violet in acidic and alkaline solutions and in the near infrared in alkaline solution was confirmed. Values found for these absorptions in the present work with 30% ethanol in water as solvent are lambda/sub max/ approx. 370 nm, epsilon/sub max/ approx. 13,200 M/sup -1/ cm/sup -1/ at pH 2 and lambda/sub max/ approx. 420 nm, epsilon/sub max/ approx. 9,000 M/sup -1/ cm/sup -1/, lambda/sub max/ approx. 840 nm, epsilon/sub max/ approx. 20,000 M/sup -1/ cm/sup -1/ at pH 8.2. Long-wavelength T-T absorption in acidic solution is reported here for the first time: lambda/sub max/ approx. 680 nm, epsilon/sub max/ approx. 19,000 M/sup -1/ cm/sup -1/ in 30% ethanol in water at pH 2. Observation of a pH-independent isobestic point approx. 720 nm confirms that the long-wavelength absorptions are due to different protonated states of the same species, MB/sup +/(T/sub 1/) and MBH/sup 2 +/(T/sub 1/). The pK/sub A/ of MBH/sup 2 +/(T/sub 1/) in water was determined from the dependence on pH of absorption at 700 and 825 nm to be 7.1/sub 4/ +- .1 and from the kinetics of decay of triplet absorption to be 7.2. The specific rate of protonation of MB/sup +/(T/sub 1/) by H/sub 2/PO/sub 4//sup -/ in water at pH 4.4 was found to be 4.5 +- .4 x 10/sup 8/ M/sup -1/ ...
Date: January 1, 1979
Creator: Ohno, T.; Osif, T.L. & Lichtin, N.N.
Partner: UNT Libraries Government Documents Department

Charge separation in photoredox reactions

Description: This report deals with the photoreduction of alkylmethylviologens in vesicles in which the combined effect of the alkylmethylviologen chain length and the addition of cholesterol to the vesicle system has been assessed. Although the alkyl chain length effect predominately controls the photoreduction yield it is shown that cholesterol addition can tune the magnitude of this effect. A series of neutral alkylphenothiazines has been synthesized and the effect of alkyl chain length in variously charged vesicles on the photoionization efficiency has been evaluated. 9 refs.
Date: October 1, 1991
Creator: Kevan, L.
Partner: UNT Libraries Government Documents Department

The degradation of organic dyes by corona discharge

Description: Several dyes in water were individually exposed to corona discharge. Light absorbance decreased for all organic dyes with time. Absorbance losses with methylene blue, malachite green, and new coccine were studied. The loss of color was followed using an in situ colorimeter and the effects of varying the current, voltage, gas phase, stirring rates, salinity, and electrode spacing were investigated. The highest reaction rates were observed using the highest current, highest voltage (up to 10kV), highest stirring rate, lowest salinity, smallest electrode spacing, and an environment containing enhanced levels of oxygen. Current was higher in the presence of nitrogen than in the presence of oxygen (for the same voltage), but the reaction of methylene blue did not proceed unless oxygen was present. These results help identify conditions using corona discharge in which dyes, and potentially other organics, can be destroyed. 22 refs., 5 figs.
Date: February 1, 1992
Creator: Goheen, S.C.; McCulloch, M.; Durham, D.E. & Heath, W.O.
Partner: UNT Libraries Government Documents Department

Development of unique catalysts for hydrodenitrogenation of coal-derived liquids. Annual report, September 15, 1979-September 15, 1980

Description: Hydrodenitrogenation of quinoline and decahydroquinoline has been studied employing several catalysts: Bronsted and Lewis acid catalysts without metal, and silica-alumina, ..gamma..-alumina and magnesia impregnated with molybdenum, tungsten, nickel or cobalt. Our results show that nitrogen removal rate was highest for molybdenum on alumina and tungsten on silica-alumina or alumina catalysts. Nitrogen abstraction using ..gamma..-alumina support is considerably faster than with magnesia support. Several catalysts have been prepared and tested, with the emphasis on understanding the role of acidity in the carbon-nitrogen bond scission reaction. Hydrodenitrogenation of quinoline has been studied by using Ni,Mo/chlorided or fluorided alumina catalysts, with various halide concentrations. Preliminary results from this study indicate that halogenation of ..gamma..-alumina catalysts slightly enhanced the hydrogenolysis activity but showed little effect on the hydrogenation activity. Initial results from phenothiazine hydroprocessing show that carbon-sulfur bonds in the reactant are broken much faster than the carbon-nitrogen bonds. Data relevant to this reaction are being evaluated, utilizing kinetic analysis to give quantitative rates of C-N and C-S bond scission and the extents and rates of hydrogenation. Note: this report contains 5th, 6th, 7th and 8th quarterly reports.
Date: December 15, 1980
Creator: Katzer, J.R.; Stiles, A.B. & Kwart, H.
Partner: UNT Libraries Government Documents Department

Investigation of molecular mechanisms in photodynamic action and radiobiology with nanosecond flash photolysis and pulse radiolysis. Progress report, October 1, 1980-September 30, 1981

Description: Laser flash photolysis experiments have led to a new mechanism for the ultraviolet photolysis of aqueous tryptophan (Trp), indole (Ind) and certain indole derivatives. Excitation at 265 nm leads to photoionization via a pre-fluorescent state with thermal activation. A new formula is proposed for predicting enzyme inactivation quantum yields. The predictions are in good agreement with measurements on six important enzymes at 254 nm and 280 nm. Kinetics models have been developed and tested for important stages in the photosensitization of DNA to near-ultraviolet radiation by furocoumarin compounds currently used for PUVA therapy (psoralen plus UV-A) of psoriasis and other human skin diseases. Experiments on photobinding of psoralen (Ps) and 8-methoxypsoralen (8-MOP) to calf thymus DNA are consistent with the assumption that equilibrium dark complexing of the furocoumarin to the DNA is a precondition for the formation of covalent monoadducts and cross-links. Singlet oxygen generation by furocoumarins has been investigated with liposomes and human erythrocytes (rbc). Results obtained with 3-carbethoxypsoralen (3-CPs), an experimental alternate PUVA sensitizer claimed to be non-tumorigenic, show that 3-CPs interacts with liposome and rbc membranes in the dark. Studies on photosensitization of egg lecithin liposomes by methylene blue (MB) incorporated in the membrane have led to the new result that membrane lysis is a two-stage process. The first stage induced by red light irradiation leads to membrane damage initiated by O/sub 2/*. Membrane lysis takes place in the dark, second stage under the action of mild hydrodynamic stress, such as slow gas bubbling.
Date: June 1, 1981
Creator: Grossweiner, L I
Partner: UNT Libraries Government Documents Department

On-line assessment of mixing in an acid waste neutralization system

Description: The acid was neutralization system at Sandia National Laboratories treats process waste water from the Microelectronics Development Laboratory (MDL). The system consists of two 9,500 liter stirred tank reactors in series with an approximate feed rate of 3.17 L/s. The tanks are equipped with 320 W mixers with single impellers. pH sensors in each tank control acid and caustic delivery pumps. Sporadic excursions outside the required range of pH 5 to 11 were observed. Tracer experiments using methylene blue dye were performed during normal MDL operations to assess mixing in the individual reactors and the system. Tracers were injected as instantaneous pulses into the reactors and time dependent concentrations were measured in the effluent. Dimensionless exit age distributions were obtained which were similar to distributions for continuous stirred tank reactors (CSTR). These age distributions were extended to predict fluoride concentrations. The data indicate a separate fluoride collection system will be required to meet local environmental safety and health (ES H) regulations. Results from these tracer experiments have lead to cost effective design improvements in our neutralization system. 4 refs., 8 figs., 1 tab.
Date: January 1, 1990
Creator: Brown, N.E.; Resnick, P.J. & Bickel, T.C.
Partner: UNT Libraries Government Documents Department

Dosimetric implications of new compounds for neutron capture therapy (NCT)

Description: Systemic application of radiolabeled or cytotoxic agents should allow targeting of primary and metastatic neoplasms on a cellular level. In fact, drug uptake in non-target cell pools often exceeds toxic levels before sufficient amounts are delivered to tumor. In addition, at the large concentration of molecules necessary for therapy, effects of saturation are often found. Application of NCT can circumvent problems associated with high uptake in competing non-target cell pools, as the /sup 10/B(n,..cap alpha..)/sup 7/Li reaction is activated only within the radiation field. A comparison with other modes of particle therapy indicated that NCT provides significant advantages. It is however, difficult to obtain vehicles for boron transport which demonstrate both the tumor specificity and concentration requisite for NCT. A number of biomolecules have been investigated which show both the necessary concentration and specificity. These include chlorpromazine, thiouracil, porphyrins, amino acids, and nucleosides. However, these analogs have yet to be made available for NCT. Dosimetric implications of binding sites are considered, as well as alternate neutron sources. (ERB)
Date: January 1, 1982
Creator: Fairchild, R.G.
Partner: UNT Libraries Government Documents Department

New compounds for neutron capture therapy (NCT) and their significance

Description: Clearly the most effective tumor therapy would be obtained by the selective targeting of cytotoxic agents to tumor cells. Although many biomolecules are known to be taken up in tumors, the targeting of cytotoxic agents to tumors is limited by the fact that other essential cell pools compete with equal or even greater effectiveness. The approach of delivering stable non-toxic isotopes to tumor, with activation by means of an external radiation beam, is advantageous for two reasons: (1) it obviates problems associated with high uptake of isotopes in normal tissues, as these cell pools can be excluded from the radiation field, and (2) the general tumor area can be included in the activating beam field; thus, the possibility exists that all microscopic tumor extensions can be irradiated. As long as range of reaction products is short, dose will be restricted to the tumor, with a resultant high therapeutic ratio. This method can be accomplished with either photon activation therapy (PAT) or Neutron Capture Therapy (NCT), the latter will be emphasized here. The range of the high LET, low OER particles from the /sup 10/B(n,..cap alpha..)/sup 7/Li reaction is approx. 10 ..mu..m, or one cell diameter; hence this reaction is optimal for cell killing. A number of biomolecules have been investigated as possible vehicles for transport of boron to tumors, including phenothiazines, thiouracils, porphyrins, nucleosides, and amino acids. Biodistributions of these compounds show selective concentration in tumor adequate for therapy. The biological halflives are in the order of days, allowing the possibility of fractionated or protracted irradiations. The radiobiological and physical implication of these parameters on NCT are discussed. The possibility of using an approximately-monoenergetic, scandium-filtered beam of about 2 keV, to reduce the dose from background radiations by about 85%, is also discussed. (ERB)
Date: January 1, 1982
Creator: Fairchild, R.G. & Bond, V.P.
Partner: UNT Libraries Government Documents Department