567 Matching Results

Search Results

Advanced search parameters have been applied.

in subjects: "Photochemical Reactions"

open access

Photoinitiated electron transfer in multichromophoric species: Synthetic tetrads and pentads featuring diquinone moieties

This project involves the design, synthesis and photophysical study of complex molecular systems engineered to achieve long lived charge separated states by a biomimetic, photoinitiated multistep electron transfer process. The use of these artificial systems to investigate different electron and energy transfer strategies will allow the evolution of more efficient molecular devices for the gathering of light energy and its transformation into chemical potential energy. The three major aspects o… more

Date: April 30, 1992

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Photochemistry and enzymology of photosynthesis

In the first task, a specially designed mass spectrometer system monitors the gas exchange occurring in response to single short flashes of light. This apparatus will be primarily used to study photosystem II donor reactions, such as the photooxidation of hydroxylamine, hydrazine, and hydrogen peroxide. This technique will also be used to study the light-induced exchange of O/sub 2/ and CO/sub 2/ in algae. The second task, biochemical studies, will focus on the role of chloroplast copper in pho… more

Date: July 30, 1979

Creator: Radmer, R.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Photochemical activation and reactivity of polynuclear transition metal complex molecules. Progress report, June 1979-May 31, 1980

During this contract year several new ligands and binuclear metal complexes have been prepared including many that can be expected to exhibit long-lived excited states. The metal ions represented are Cu(II), Ni(II), Co(II), Mn(II), Cr(III), Ti(IV), V(IV), U(VI), and Pd(II). In addition, many mononuclear complexes that are precursors in the formation of heterobinuclear complexes were prepared. These include complexes of Cu(II), Ni(II), Pd(II), and Ru(II). Many of these compounds will be used in … more

Date: February 1, 1980

Creator: Endicott, J.F. & Lintvedt, R.L.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Experimental investigation of the chemistry of excited states of rare gases. Second quarterly progress report, January 15, 1978-April 15, 1979

The reactions of Kr(/sup 3/P/sub 1/) and Xe(/sup 3/P/sub 1/) with halogen compounds, producing rare gas halides, was studied. Abstracts of two papers on excited rare gas states are included. (DLC)

Date: May 1979

Creator: Setser, D. W.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Magnetic relaxation--coal swelling, extraction, pore size

The grant activities during this period fall into four categories: (1) Completion of preparatory work, (2) Procedure refinement and actual preparation of whole coal, coal residue, coal extract and swelled coal samples for NMR studies, (3) Related studies of coal photolysis that employ materials from preliminary extractions and that examine the u.v.-visible and mass spectra of the extracts and (4) Continued investigations of the pulsed EPR characteristics of the whole coal samples that were prep… more

Date: January 1, 1991

Creator: Doetschman, D.C.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Yields, photosynthetic efficiencies, and proximate chemical composition of dense cultures of marine microalgae. A subcontract report

The yields, photosynthetic efficiencies, and proximate composition of several microalgae were compared in dense cultures grown at light intensities up to 70% sunlight. Yields ranged from 3.4 to 21.7 g dry weight/m/sup 2/ day. The highest yield was obtained with Phaeodactylum; the lowest in Botryococcus cultures. The same species had the highest and lowest efficiencies of utilization of photosynthetically active radiation. In nitrogen-sufficient cells of all but one species, most of the dry weig… more

Date: July 1, 1983

Creator: Thomas, W. H.; Seibert, D. L. R.; Alden, M.; Eldridge, P. & Neori, A.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Experimental investigation of the chemistry of exccited states of rare gases. Fourth quarterly (and annual) progress report, July 15, 1978-October 15, 1978. [Reaction of Ar(/sup 3/P/sub 2/) or Xe(/sup 3/P/sub 2/) with XeO/sub 4/]

A brief account is given of work on the quenching of XeF(B) and other excited rare-gas systems. A more detailed report is given of the studies of the vacuum uv photolysis of XeO/sub 4/ and reactions of Xe(/sup 3/P/sub 2/) and Ar(/sup 3/P/sub 2/) with XeO/sub 4/. (DLC)

Date: December 1978

Creator: Setser, D. W.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Gas Phase Radiolysis and Vacuum Ultraviolet Photolysis of Heterocyclic Organic Compounds. Progress Report, Feburary 1, 1979-February 1, 1980

The long-range objective of our research group is to gain a better understanding of the processes by which complex organic molecules react when they absorb large amounts of energy. This progress report describes the results of our recent work in three areas: diradicals derived from heterocyclic compounds; trimethylene diradicals from various sources; and ion-molecule reactions.

Date: January 1, 1980

Creator: Scala, A. A.; Nguyen, D.; Rourke, W. & Caputo, M.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Spectroscopy, reaction, and photodissociation in highly vibrationally excited molecules

Highly vibrationally excited molecules often control the course of chemical reactions in the atmosphere, combustion, plasmas, and many other environments. The research described in this Progress Report uses laser excitation and interrogation techniques to study and control the dynamics of highly vibrationally excited molecules. In particular, they show that it is possible to unravel the details and influence the course of photodissociation and bimolecular reaction. The experiments use laser exc… more

Date: January 1, 1991

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

A computer modeling study of isotopically selective, laser photodissociation of OCS in cryogenic solutions

Computer model calculations are presented for enrichments of carbon, oxygen, and sulfur isotopes by two-step, IR/UV, laser photodissociation of OCS in rare gas liquid solutions. The model calculations are based on previously measured fundamental physical properties, including spectroscopic parameters of the IR absorption bands of OCS in cryogenic solution, UV photodissociation cross sections for specific vibrational levels of OCS, and rates for vibrational relaxation of OCS by cryogenic solvent… more

Date: December 23, 1991

Creator: Zittel, P.F.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

ABSOLUTE ASYMMETRIC SYNTHESIS. I. ON THE MECHANISM OF THEPHOTOCHEMICAL ABSOLUTE ASYMMETRIC SYNTHESIS OF HELICENES WITH CIRCULARLYPOLARIZED LIGHT. . WAVELENGTH DEPENDENCE OF THE OPTICAL YIELD OFOCTAHELICENE.

The synthesis of nonracemic yields of hexa-, hepta-, octa-, and nonhelicene with circular light was observed, and the structural and wavelength dependence of the induced optical yields was examined. The results obtained, together with a detailed consideration of the mechanism of helicene synthesis from the parent diarylolefins, indicate that the induced optical activity is due to selective reaction of enantiomeric conformations of the parent cis diarylolefins by circular light.

Date: May 1, 1971

Creator: Bernstein, William J.; Calvin, Melvin & Buchardt, Ole.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

PHOTOCHEMICAL COUPLING OF BENZO [a]PYRENE WITH 1-METHYL-CYTOSINE;PHOTO-ENHANCEMENT OF CARCINOGENICITY

Irradiation of the carcinogenic benzo[a]pyrene (I) with 1-methylcytosine hydrochloride IIa (molar ratio 1:10) at 3500 {angstrom} in methanol-acetone produces the 6-(1-methylcytos-5-yl)-benzo[a]pyrene (III). The structure of the product shows the hydrocarbon bound through the most active 6-carbon atom to the nucleophilic 5-position of the base. In the second part, the possibility of observing carcinogenic effects on the mouse skin from non-carcinogenic hydrocarbons under the action of UV light i… more

Date: January 1, 1971

Creator: Cavalieri, E. & Calvin, Melvin.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

ORBITAL SYMMETRY CONTROL IN THE NITRONE-OXAZIRIDINE SYSTEM.NITRONE PHOTOSTATIONARY STATES

Recent the orbital symmetry rules have been shown to apply to hetero-atom systems such as nitrone thermal cycloaddition reactions and the thermal and photochemical aziridine ring cleavage at the C-C bond. The concerted photocyclization is disrotatory and the reverse thermal cleavage is conrotatory in these molecules with four {pi} electrons. In contrast to the azomethine ylide-aziridine system, the stereochemistry of the nitrone photocyclization to oxaziridine can only be observed on carbon and… more

Date: June 1, 1971

Creator: Splitter, Janet S.; Su, Tah-mun; Ono, Howard & Calvin, Melvin.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Path of Carbon in Photosynthesis III

Although the overall reaction of photosynthesis can be specified with some degree of certainty (CO{sub 2} + H{sub 2}O + light {yields} sugars + possibly other reduced substances), the intermediates through which the carbon passes during the course of this reduction have, until now, been largely a matter of conjecture. The availability of isotopic carbon, that is, a method of labeling the carbon dioxide, provides the possibility of some very direct experiments designed to recognize these interme… more

Date: June 1, 1948

Creator: Benson, A. A. & Calvin, M.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

PHOTOCHEMICAL COUPLING OF BENZO [a]PYEENE WITH 1-METHYLCYTOSINE.POSSIBLE MECHANISM OF THE LINKAGE IN VIVO

Irradiation of benzo[a]pyrene 1 with 1-methylcytosine hydrochloride 2a (molar ratio 1:10) at 3500 {angstrom} in methanol-acetone produces the 6-(1-methylcytos-5-yl)-benzo[pa]pyrene 3. The structure of the photoproduct shows the hydrocarbon bound through the most active 6-carbon atom to the nucleophilic 5-position of the base. The specific substitution of both moieties combined with other data allows them to understand the carcinogenic activity of the hydrocarbon and thereby to propose a possibl… more

Date: August 1, 1970

Creator: Cavalieri, E. & Calvin, M

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Summary of the LLNL one-dimensional transport-kinetics model of the troposphere and stratosphere: 1981

Since the LLNL one-dimensional coupled transport and chemical kinetics model of the troposphere and stratosphere was originally developed in 1972 (Chang et al., 1974), there have been many changes to the model's representation of atmospheric physical and chemical processes. A brief description is given of the current LLNL one-dimensional coupled transport and chemical kinetics model of the troposphere and stratosphere.

Date: September 1, 1981

Creator: Wuebbles, D.J.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

The active site of ribulose-bisphosphate carboxylase/oxygenase

The active site of ribulose-bisphosphate carboxylase/oxygenase requires interacting domains of adjacent, identical subunits. Most active-site residues are located within the loop regions of an eight-stranded {beta}/{alpha}-barrel which constitutes the larger C-terminal domain; additional key residues are located within a segment of the smaller N-terminal domain which partially covers the mouth of the barrel. Site-directed mutagenesis of the gene encoding the enzyme from Rhodospirillum rubrum ha… more

Date: January 1, 1991

Creator: Hartman, F. C.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Studies relevant to the catalytic activation of carbon monoxide

Research activity has included continued mechanistic investigations of the nucleophilic activation of carbon monoxide such as homogeneous catalysis of the water gas shift and key steps in the relevant catalytic cycles. Other investigations of related processes included the application of fast reaction techniques to prepare and to investigate quantitatively reactive organometallic intermediates relevant to the activation of hydrocarbons toward carbonylation and other functionalizations. 8 refs.

Date: September 4, 1991

Creator: Ford, P.C.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

A molecular genetic analysis of carotenoid biosynthesis and the effects of carotenoid mutations on other photosynthetic genes in Rhodobacter capsulatus

The nine known R. capsulatus carotenoid genes are contained within the 46 kilobase (kb) photosynthesis gene cluster. An 11 kb subcluster containing eight of these genes has been cloned and its nucleotide sequence determined. A new gene, crtK, has been located in the middle of the subcluster. The carotenoid gene cluster contains sequences homologous to Escherichia coli ..omega../sup 70/ promoters, rho-independent transcription terminators, and prokaryotic transcriptional factor binding sites. Th… more

Date: April 1, 1989

Creator: Armstrong, Gregory Aleksandr

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Intramolecular energy transfer reactions in polymetallic

This report is concerned with intramolecular, energy-transfer reactions. The concept of preparing synthetically a complex molecular species, capable of absorbing a photon at one metal center (antenna fragment), transferring that energy to a second metal center (reactive fragment) via a bridging ligand was first reported by our group in 1979. It is now apparent that a major emphasis in inorganic chemistry in the future will involve these types of molecular ensembles. Complexes discussed include … more

Date: November 1, 1990

Creator: Petersen, J.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Toxic organic compounds from energy production

The US Department of Energy's Office of Health and Environmental Research (OHER) has supported work in our laboratory since 1977. The general theme of this program has been the identification of potentially toxic organic compounds associated with various combustion effluents, following the fates of these compounds in the environment, and improving the analytical methodology for making these measurements. The projects currently investigation include: an improved sampler for semi-volatile compoun… more

Date: September 20, 1991

Creator: Hites, R.A.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Proceedings of the Fourteenth DOE solar photochemistry research conference

The central themes of this year's Solar Photochemistry Research Conference encompassed initial charge separation in photosynthesis, photoinduced charge separation in other organized assemblies, electron transfer, organic and inorganic photochemistry, and photoelectrochemistry. This volume contains a copy of the program the abstracts of 29 formal presentations and 47 posters, a record of the discussion following each presentation, and an address list for the 96 attendees. Individual projects are… more

Date: January 1, 1989

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Space nuclear power requirements for ozone layer modification

This work estimates the power requirements for using photochemical processes driven by space nuclear power to counteract the Earth's ozone layer depletion. The total quantity of ozone (O{sub 3}) in the Earth's atmosphere is estimated to be about 4.7 {times} 10{sup 37} molecules. The ozone production and destruction rates in the stratosphere are both on the order of 4.9 {times} 10{sup 31} molecules/s, differing by a small fraction so that the net depletion rate is about 0.16 to 0.26% per year. T… more

Date: October 15, 1991

Creator: Dolan, T.J.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Photofragment imaging: The photo-dissociation of bromomethane, bromoethane, and bromoethanol

Bromomethane, bromoethane and bromoethanol are photolyzed with 205-nm light and the velocity of the bromine atoms is recorded by the technique of photofragment imaging. The velocity distribution of the bromine atoms is a direct reflection of the internal-state distribution of the methyl, ethyl, and hydroxy-ethyl radicals and the orientation of the transition moment in the parent molecule. 8 refs., 2 figs., 1 tab.

Date: September 1, 1990

Creator: Chandler, D.W. (Sandia National Labs., Albuquerque, NM (United States)); Thoman, J.W. Jr. (Williams Coll., Williamstown, MA (United States). Dept. of Chemistry) & Hess, W.P. (Battelle Pacific Northwest Lab., Richland, WA (United States))

Item Type: Article

Partner: UNT Libraries Government Documents Department