Photochemical transformation of phenylurea herbicides in surface waters: a model assessment of persistence, and implications for the possible generation of hazardous intermediates.

PubMed

Fabbri, Debora; Minella, Marco; Maurino, Valter; Minero, Claudio; Vione, Davide

2015-01-01

This work models the phototransformation kinetics in surface waters of five phenylurea herbicides (diuron, fenuron, isoproturon, metoxuron and chlortoluron), for which important photochemical parameters are available in the literature (direct photolysis quantum yields and reaction rate constants with ·OH, CO3(-·) and the triplet states of chromophoric dissolved organic matter, (3)CDOM*). Model calculations suggest that isoproturon and metoxuron would be the least photochemically persistent and diuron the most persistent compound. Reactions with ·OH and (3)CDOM* would be the main phototransformation pathways for all compounds in the majority of environmental conditions. Reaction with CO3(-) could be important in waters with low dissolved organic carbon (DOC), while direct photolysis would be negligible for fenuron, quite important for chlortoluron, and somewhat significant for the other compounds. The direct photolysis of metoxuron and diuron is known to increase toxicity, and such a photoreaction pathway would be enhanced at intermediate DOC values (1-4 mg C L(1)). The reaction between phenylureas and ·OH is known to produce toxic intermediates, differently from (3)CDOM*. Therefore, the shift of reactivity from ·OH to (3)CDOM* with increasing DOC could reduce the environmental impact of photochemical transformation. Copyright © 2014 Elsevier Ltd. All rights reserved.

Photochemical activity of a key donor-acceptor complex can drive stereoselective catalytic α-alkylation of aldehydes.

PubMed

Arceo, Elena; Jurberg, Igor D; Alvarez-Fernández, Ana; Melchiorre, Paolo

2013-09-01

Asymmetric catalytic variants of sunlight-driven photochemical processes hold extraordinary potential for the sustainable preparation of chiral molecules. However, the involvement of short-lived electronically excited states inherent to any photochemical reaction makes it challenging for a chiral catalyst to dictate the stereochemistry of the products. Here, we report that readily available chiral organic catalysts, with well-known utility in thermal asymmetric processes, can also confer a high level of stereocontrol in synthetically relevant intermolecular carbon-carbon bond-forming reactions driven by visible light. A unique mechanism of catalysis is proposed, wherein the catalyst is involved actively in both the photochemical activation of the substrates (by inducing the transient formation of chiral electron donor-acceptor complexes) and the stereoselectivity-defining event. We use this approach to enable transformations that are extremely difficult under thermal conditions, such as the asymmetric α-alkylation of aldehydes with alkyl halides, the formation of all-carbon quaternary stereocentres and the control of remote stereochemistry.

Photochemical Reactions of (n(5)-Pentamethylcyclpentadienyl)-Dicarbonyliron-Alkyl and -Silyl Complexes: Reversible Ethylene Insertion into an Iron-Silicon Bond and Implications for the Mechanism of Transition Metal-Catalyzed Hydrosilation of Alkenes.

DTIC Science & Technology

1985-12-11

RD-R162 462 PHOTOCHEMICAL REACTIONS OF(N(S)-P NTANETNYLCVCLPENTADIENYL)-DICARRONVLIR.. (U) MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF CHEMISTRY...34 Photochemical Reactions of (n5-Pentamethylcyclpentadienyl)- Dicarbonyliron-Alkyl and -Silyl Complexes: Reversible Ethylene Insertion into an Iron-Silicon Bond...Chemical Society) PHOTOCHEMICAL REACTIONS OF (n5-PENTAMETHYLCYCLOPENTADIENYL)- DICARBONYLIRON-ALKYL AND -SILYL COMPLEXES: REVERSIBLE ETHYLENE INSERTION INTO

Simulation of photoreactive transients and of photochemical transformation of organic pollutants in sunlit boreal lakes across 14 degrees of latitude: A photochemical mapping of Sweden.

PubMed

Koehler, Birgit; Barsotti, Francesco; Minella, Marco; Landelius, Tomas; Minero, Claudio; Tranvik, Lars J; Vione, Davide

2018-02-01

Lake water constituents, such as chromophoric dissolved organic matter (CDOM) and nitrate, absorb sunlight which induces an array of photochemical reactions. Although these reactions are a substantial driver of pollutant degradation in lakes they are insufficiently understood, in particular on large scales. Here, we provide for the first time comprehensive photochemical maps covering a large geographic region. Using photochemical kinetics modeling for 1048 lakes across Sweden we simulated the steady-state concentrations of four photoreactive transient species, which are continuously produced and consumed in sunlit lake waters. We then simulated the transient-induced photochemical transformation of organic pollutants, to gain insight into the relevance of the different photoreaction pathways. We found that boreal lakes were often unfavorable environments for photoreactions mediated by hydroxyl radicals (OH) and carbonate radical anions (CO 3 - ), while photoreactions mediated by CDOM triplet states ( 3 CDOM*) and, to a lesser extent, singlet oxygen ( 1 O 2 ) were the most prevalent. These conditions promote the photodegradation of phenols, which are used as plastic, medical drug and herbicide precursors. When CDOM concentrations increase, as is currently commonly the case in boreal areas such as Sweden, 3 CDOM* will also increase, promoting its importance in photochemical pathways even more. Copyright © 2017 Elsevier Ltd. All rights reserved.

Analysis of photochemical pollution in summer and winter using a photochemical box model in the center of Tokyo, Japan.

PubMed

Huang, H; Akustu, Y; Arai, M; Tamura, M

2001-07-01

In order to give an effective and rapid analysis of the photochemical pollution and information for emission control strategies, a photochemical box model (PBM) was applied to one moderate summer episode, 11 July 1996, and one typical winter episode, 3 December 1996, in the center of Tokyo, Japan. The box model gave a good prediction of the photochemical pollution with minimal investment. As expected, the peak ozone in summer is higher than in winter. The NOx concentrations in winter are higher than those in summer. In summer, NO and NO2 have one peak in the morning. In winter, NO and NO2 show two peaks during the day. Three model runs including no reactions, a zero ozone boundary condition and dark reactions were conducted to understand the photochemical processes. The effects of emission reduction on the formation of the photochemical pollution in the center of Tokyo have been studied. The results show that the reduction of NMHC emission can decrease the ozone, however, the reduction of NOx emission can increase the ozone. It can be concluded that if the NOx emission are reduced, the reduction of NMHC should be more emphasized in order to decrease the ozone concentration in the center of Tokyo, Japan, especially the reduction of the NMHC from stationary source emission.

Photochemical synthesis of biomolecules under anoxic conditions

NASA Technical Reports Server (NTRS)

Folsome, C.; Brittain, A.; Zelko, M.

1983-01-01

The long-wavelength UV anoxic photosynthesis of uracil, various sugars (including deoxyribose and glycoaldehyde), amino acids, and other organic photoproducts is reported. The reactions were conducted in a mixture of water, calcium carbonate, hydrazine, and formaldehyde which were subjected to 24 hr or 72 hr radiation. Product yields were greatest when the hydrazine/formaldehyde ratio was one, and when the reactant concentrations were low. These data suggest that organic products can be formed in variety from those amounts of formaldehyde and hydazine precursors which are themselves formed under anoxic UV photochemical conditions.

Loss of Functional Photosystem II Reaction Centres in Zooxanthellae of Corals Exposed to Bleaching Conditions: Using Fluorescence Rise Kinetics.

PubMed

Hill, R; Larkum, A W D; Frankart, C; Kühl, M; Ralph, P J

2004-01-01

Mass coral bleaching is linked to elevated sea surface temperatures, 1-2 degrees C above average, during periods of intense light. These conditions induce the expulsion of zooxanthellae from the coral host in response to photosynthetic damage in the algal symbionts. The mechanism that triggers this release has not been clearly established and to further our knowledge of this process, fluorescence rise kinetics have been studied for the first time. Corals that were exposed to elevated temperature (33 degrees C) and light (280 mumol photons m(-2) s(-1)), showed distinct changes in the fast polyphasic induction of chlorophyll-a fluorescence, indicating biophysical changes in the photochemical processes. The fluorescence rise over the first 2000ms was monitored in three species of corals for up to 8 h, with a PEA fluorometer and an imaging-PAM. Pocillopora damicornis showed the least impact on photosynthetic apparatus, while Acropora nobilis was the most sensitive, with Cyphastrea serailia intermediate between the other two species. A. nobilis showed a remarkable capacity for recovery from bleaching conditions. For all three species, a steady decline in the slope of the initial rise and the height of the J-transient was observed, indicating the loss of functional Photosystem II (PS II) centres under elevated-temperature conditions. A significant loss of PS II centres was confirmed by a decline in photochemical quenching when exposed to bleaching stress. Non-photochemical quenching was identified as a significant mechanism for dissipating excess energy as heat under the bleaching conditions. Photophosphorylation could explain this decline in PS II activity. State transitions, a component of non-photochemical quenching, was a probable cause of the high non-photochemical quenching during bleaching and this mechanism is associated with the phosphorylation-induced dissociation of the light harvesting complexes from the PS II reaction centres. This reversible process may account for the coral recovery, particularly in A. nobilis.

Aqueous-Phase Photochemical Production of Oxidants in Atmospheric Waters.

NASA Astrophysics Data System (ADS)

Allen, John Morrison

1992-01-01

The photochemical formation and subsequent reactions of oxidants plays an important role in the overall chemistry of the atmosphere. Much of the interest in atmospheric oxidation reactions has been fueled by the environmental consequences of the oxidation of sulfur dioxide (SO _2) forming sulfuric acid (H_2 SO_4). Oxidation reactions also play a crucial role in other atmospheric chemical transformations such as: (1) the destruction of tropospheric ozone, (2) redox cycling of transition metals, and (3) oxidation of organic compounds. Much of the research pertaining to atmospheric oxidant formation and the reactions that these oxidants undergo has centered upon gas-phase photochemical oxidant formation and: (1) subsequent reactions in the gas phase, or (2) partitioning of oxidants into cloud and fog drops and subsequent reactions in the aqueous phase. Only a very limited amount of data is available concerning aqueous -phase photochemical sources of oxidants in cloud and fog drops. The focus of one aspect of the work presented in this dissertation is upon the aqueous-phase sunlight photochemical formation of oxidants in authentic cloud and fog water samples from across the United States and Canada. It will be demonstrated that atmospheric waters typically absorb solar ultraviolet radiation at wavelengths ranging from 290 to 340 nm. This absorption is due to the presence of chemical constituents in the cloud and fog waters that contain chromophoric functional groups that give rise to the formation of: (1) singlet molecular oxygen O_2(^1Delta_ {rm g}), (2) peroxyl radicals (HO _2cdot and RO_2 cdot), (3) peroxides (HOOH, ROOH, and ROOR '), and (4) hydroxyl radical ( cdotOH). This work will demonstrate that aqueous-phase photochemical reactions are a significant and in some cases dominant source of these oxidants in cloud and fog drops. The transition metal catalyzed oxidation of SO _2 to H_2SO _4 by molecular oxygen has been extensively studied. This reaction is thought to be an important pathway by which a strong acid is produced within cloud drops under certain conditions. Experiments performed in distilled, deionized water presented in this dissertation will demonstrate that the oxidation of SO_2 in the presence of Fe(III) is much slower in sunlight than in the dark.

Photochemical reactions of aromatic compounds and the concept of the photon as a traceless reagent.

PubMed

Hoffmann, Norbert

2012-11-01

Electronic excitation significantly changes the reactivity of chemical compounds. Compared to ground state reactions, photochemical reactions considerably enlarge the application spectrum of a particular functional group in organic synthesis. Multistep syntheses may be simplified and perspectives for target oriented synthesis (TOS) and diversity oriented synthesis (DOS) are developed. New compound families become available or may be obtained more easily. In contrast to common chemical reagents, photons don't generate side products resulting from the transformation of a chemical reagent. Therefore, they are considered as a traceless reagent. Consequently, photochemical reactions play a central role in the methodology of sustainable chemistry. This aspect has been recognized since the beginning of the 20th century. As with many other photochemical transformations, photochemical reactions of aromatic, benzene-like compounds illustrate well the advantages in this context. Photochemical cycloadditions of aromatic compounds have been investigated for a long time. Currently, they are applied in various fields of organic synthesis. They are also studied in supramolecular structures. The phenomena of reactivity and stereoselectivity are investigated. During recent years, photochemical electron transfer mediated reactions are particularly focused. Such transformations have likewise been performed with aromatic compounds. Reactivity and selectivity as well as application to organic synthesis are studied.

Pauson-Khand reactions in a photochemical flow microreactor.

PubMed

Asano, Keisuke; Uesugi, Yuki; Yoshida, Jun-ichi

2013-05-17

Pauson-Khand reactions were achieved at ambient temperature without any additive using a photochemical flow microreactor. The efficiency of the reaction was better than that in a conventional batch reactor, and the reaction could be operated continuously for 1 h.

Photochemical degradation of triazine herbicides - comparison of homogeneous and heterogeneous photocatalysis.

PubMed

Klementova, Sarka; Zlamal, Martin

2013-04-01

Photochemical degradation of atrazine under different conditions was studied and compared, namely degradation via photocatalysis on TiO2, UV C photolysis, and homogeneous photocatalysis in the presence of added ferric ions. The reaction rate constants in heterogeneous photocatalytic reactions on TiO2 and of photolytic degradation by means of UV C light are similar, 0.018 min(-1) and 0.020 min(-1), respectively. The reaction rate constants in homogeneous photocatalytic reactions with Fe(III) added depend strongly on the Fe(III) concentration, 0.0017 min(-1) for 1.6 × 10(-6) mol l(-1) Fe(III) to 0.105 min(-1) for 3.3 × 10(-4) mol l(-1) Fe(III). In all types of reactions, dechlorination was observed; in homogeneous photocatalytic reactions and in UV C (250-300 nm) photolysis, dechlorination proceeds with a 1 : 1 stoichiometry to atrazine degradation, in photocatalytic reactions on TiO2, dechlorination measured as chloride ion release reaches only 1/5 of the substrate degradation. In photocatalytic reactions on TiO2, mineralisation of 40% carbon was observed.

Photochemical Dimerization of Dibenzylideneacetone: A Convenient Exercise in [2+2] Cycloaddition Using Chemical Ionization Mass Spectrometry

ERIC Educational Resources Information Center

Rao, G. Nageswara; Janardhana, Chelli; Ramanathan, V.; Rajesh, T.; Kumar, P. Harish

2006-01-01

Chemical reactions induced by light have been utilized for synthesizing highly strained, thermodynamically unstable compounds, which are inaccessible through non-photochemical methods. Photochemical cycloaddition reactions, especially those leading to the formation of four-membered rings, constitute a convenient route to compounds that are…

Photoinduced catalytic synthesis of biologically important metabolites from formaldehyde and ammonia under plausible "prebiotic" conditions

NASA Astrophysics Data System (ADS)

Delidovich, I. V.; Taran, O. P.; Simonov, A. N.; Matvienko, L. G.; Parmon, V. N.

2011-08-01

The article analyzes new and previously reported data on several catalytic and photochemical processes yielding biologically important molecules. UV-irradiation of formaldehyde aqueous solution yields acetaldehyde, glyoxal, glycolaldehyde and glyceraldehyde, which can serve as precursors of more complex biochemically relevant compounds. Photolysis of aqueous solution of acetaldehyde and ammonium nitrate results in formation of alanine and pyruvic acid. Dehydration of glyceraldehyde catalyzed by zeolite HZSM-5-17 yields pyruvaldehyde. Monosaccharides are formed in the course of the phosphate-catalyzed aldol condensation reactions of glycolaldehyde, glyceraldehyde and formaldehyde. The possibility of the direct synthesis of tetroses, keto- and aldo-pentoses from pure formaldehyde due to the combination of the photochemical production of glycolahyde and phosphate-catalyzed carbohydrate chain growth is demonstrated. Erythrulose and 3-pentulose are the main products of such combined synthesis with selectivity up to 10%. Biologically relevant aldotetroses, aldo- and ketopentoses are more resistant to the photochemical destruction owing to the stabilization in hemiacetal cyclic forms. They are formed as products of isomerization of erythrulose and 3-pentulose. The conjugation of the concerned reactions results in a plausible route to the formation of sugars, amino and organic acids from formaldehyde and ammonia under presumed 'prebiotic' conditions.

The Dynamics of the Photofragmentation of Ketene 3-Cyclopentenone, 3,5-Cycloheptadienone, and Tropone.

DTIC Science & Technology

1985-01-01

suggested that the concerted reaction should be allowed photochemically and the conrotatory mode should be favored. The data were in accord with this...crossing), or (4) reaction to form products, e.g., isomers or fragments, directly from the excited state. Further radiative, non-radiative, and photochemical ...processes can occur from intermediate excited states. Typical photochemical reactions observed in simple ketones in the gas phase are: (1) Norrish

The elusive abnormal CO2 insertion enabled by metal-ligand cooperative photochemical selectivity inversion.

PubMed

Schneck, Felix; Ahrens, Jennifer; Finger, Markus; Stückl, A Claudia; Würtele, Christian; Schwarzer, Dirk; Schneider, Sven

2018-03-21

Direct hydrogenation of CO 2 to CO, the reverse water-gas shift reaction, is an attractive route to CO 2 utilization. However, the use of molecular catalysts is impeded by the general reactivity of metal hydrides with CO 2 . Insertion into M-H bonds results in formates (MO(O)CH), whereas the abnormal insertion to the hydroxycarbonyl isomer (MC(O)OH), which is the key intermediate for CO-selective catalysis, has never been directly observed. We here report that the selectivity of CO 2 insertion into a Ni-H bond can be inverted from normal to abnormal insertion upon switching from thermal to photochemical conditions. Mechanistic examination for abnormal insertion indicates photochemical N-H reductive elimination as the pivotal step that leads to an umpolung of the hydride ligand. This study conceptually introduces metal-ligand cooperation for selectivity control in photochemical transformations.

Water catalysis and anticatalysis in photochemical reactions: observation of a delayed threshold effect in the reaction quantum yield.

PubMed

Kramer, Zeb C; Takahashi, Kaito; Skodje, Rex T

2010-11-03

The possible catalysis of photochemical reactions by water molecules is considered. Using theoretical simulations, we investigate the HF-elimination reaction of fluoromethanol in small water clusters initiated by the overtone excitation of the hydroxyl group. The reaction occurs in competition with the process of water evaporation that dissipates the excitation and quenches the reaction. Although the transition state barrier is stabilized by over 20 kcal/mol through hydrogen bonding with water, the quantum yield versus energy shows a pronounced delayed threshold that effectively eliminates the catalytic effect. It is concluded that the quantum chemistry calculations of barrier lowering are not sufficient to infer water catalysis in some photochemical reactions, which instead require dynamical modeling.

Degradation of artificial sweeteners via direct and indirect photochemical reactions.

PubMed

Perkola, Noora; Vaalgamaa, Sanna; Jernberg, Joonas; Vähätalo, Anssi V

2016-07-01

We studied the direct and indirect photochemical reactivity of artificial sweeteners acesulfame, saccharin, cyclamic acid and sucralose in environm entally relevant dilute aqueous solutions. Aqueous solutions of sweeteners were irradiated with simulated solar radiation (>290 nm; 96 and 168 h) or ultraviolet radiation (UVR; up to 24 h) for assessing photochemical reactions in surface waters or in water treatment, respectively. The sweeteners were dissolved in deionised water for examination of direct photochemical reactions. Direct photochemical reactions degraded all sweeteners under UVR but only acesulfame under simulated solar radiation. Acesulfame was degraded over three orders of magnitude faster than the other sweeteners. For examining indirect photochemical reactions, the sweeteners were dissolved in surface waters with indigenous dissolved organic matter or irradiated with aqueous solutions of nitrate (1 mg N/L) and ferric iron (2.8 mg Fe/L) introduced as sensitizers. Iron enhanced the photodegradation rates but nitrate and dissolved organic matter did not. UVR transformed acesulfame into at least three products: iso-acesulfame, hydroxylated acesulfame and hydroxypropanyl sulfate. Photolytic half-life was one year for acesulfame and more than several years for the other sweeteners in surface waters under solar radiation. Our study shows that the photochemical reactivity of commonly used artificial sweeteners is variable: acesulfame may be sensitive to photodegradation in surface waters, while saccharin, cyclamic acid and sucralose degrade very slowly even under the energetic UVR commonly used in water treatment.

Temporal mapping of photochemical reactions and molecular excited states with carbon specificity

NASA Astrophysics Data System (ADS)

Wang, K.; Murahari, P.; Yokoyama, K.; Lord, J. S.; Pratt, F. L.; He, J.; Schulz, L.; Willis, M.; Anthony, J. E.; Morley, N. A.; Nuccio, L.; Misquitta, A.; Dunstan, D. J.; Shimomura, K.; Watanabe, I.; Zhang, S.; Heathcote, P.; Drew, A. J.

2017-04-01

Photochemical reactions are essential to a large number of important industrial and biological processes. A method for monitoring photochemical reaction kinetics and the dynamics of molecular excitations with spatial resolution within the active molecule would allow a rigorous exploration of the pathway and mechanism of photophysical and photochemical processes. Here we demonstrate that laser-excited muon pump-probe spin spectroscopy (photo-μSR) can temporally and spatially map these processes with a spatial resolution at the single-carbon level in a molecule with a pentacene backbone. The observed time-dependent light-induced changes of an avoided level crossing resonance demonstrate that the photochemical reactivity of a specific carbon atom is modified as a result of the presence of the excited state wavefunction. This demonstrates the sensitivity and potential of this technique in probing molecular excitations and photochemistry.

Suppression of new particle formation from monoterpene oxidation by NOx

NASA Astrophysics Data System (ADS)

Wildt, J.; Mentel, T. F.; Kiendler-Scharr, A.; Hoffmann, T.; Andres, S.; Ehn, M.; Kleist, E.; Müsgen, P.; Rohrer, F.; Rudich, Y.; Springer, M.; Tillmann, R.; Wahner, A.

2013-10-01

The impact of nitrogen oxides (NOx = NO + NO2) on new particle formation (NPF) and on photochemical ozone production from real plant volatile organic compound (BVOC) emissions was studied in a laboratory set up. At high NOx conditions (BVOC/NOx < 7, NOx > 23 ppb) no new particles were formed. Instead photochemical ozone formation was observed resulting in higher hydroxyl radical (OH) and lower nitrogen monoxide (NO) concentrations. As soon as [NO] was reduced to below 1 ppb by OH reactions, NPF was observed. Adding high amounts of NOx caused NPF orders of magnitude slower than in analogous experiments at low NOx conditions (NOx ~ 300 ppt), although OH concentrations were higher. Varying NO2 photolysis enabled showing that NO was responsible for suppression of NPF suggesting that peroxy radicals are involved in NPF. The rates of NPF and photochemical ozone production were related by power law dependence with an exponent of approximately -2. This exponent indicated that the overall peroxy radical concentration must have been the same whenever NPF appeared. Thus permutation reactions of first generation peroxy radicals cannot be the rate limiting step in NPF from monoterpene oxidation. It was concluded that permutation reactions of higher generation peroxy radical like molecules limit the rate of new particle formation. In contrast to the strong effects on the particle numbers, the formation of particle mass was less sensitive to NOx concentrations, if at all. Only at very high NOx concentrations yields were reduced by about an order of magnitude.

Suppression of new particle formation from monoterpene oxidation by NOx

NASA Astrophysics Data System (ADS)

Wildt, J.; Mentel, T. F.; Kiendler-Scharr, A.; Hoffmann, T.; Andres, S.; Ehn, M.; Kleist, E.; Müsgen, P.; Rohrer, F.; Rudich, Y.; Springer, M.; Tillmann, R.; Wahner, A.

2014-03-01

The impact of nitrogen oxides (NOx = NO + NO2) on new particle formation (NPF) and on photochemical ozone production from real plant volatile organic compound (BVOC) emissions was studied in a laboratory setup. At high NOx conditions ([BVOC] / [NOx] < 7, [NOx] > 23 ppb) new particle formation was suppressed. Instead, photochemical ozone formation was observed resulting in higher hydroxyl radical (OH) and lower nitrogen monoxide (NO) concentrations. When [NO] was reduced back to levels below 1 ppb by OH reactions, NPF was observed. Adding high amounts of NOx caused NPF to be slowed by orders of magnitude compared to analogous experiments at low NOx conditions ([NOx] ~300 ppt), although OH concentrations were higher. Varying NO2 photolysis enabled showing that NO was responsible for suppression of NPF. This suggests that peroxy radicals are involved in NPF. The rates of NPF and photochemical ozone production were related by power law dependence with an exponent approaching -2. This exponent indicated that the overall peroxy radical concentration must have been similar when NPF occurred. Thus, permutation reactions of first-generation peroxy radicals cannot be the rate limiting step in NPF from monoterpene oxidation. It was concluded that permutation reactions of higher generation peroxy-radical-like intermediates limit the rate of new particle formation. In contrast to the strong effects on the particle numbers, the formation of particle mass was substantially less sensitive to NOx concentrations. If at all, yields were reduced by about an order of magnitude only at very high NOx concentrations.

Enantioselective catalysis of photochemical reactions.

PubMed

Brimioulle, Richard; Lenhart, Dominik; Maturi, Mark M; Bach, Thorsten

2015-03-23

The nature of the excited state renders the development of chiral catalysts for enantioselective photochemical reactions a considerable challenge. The absorption of a 400 nm photon corresponds to an energy uptake of approximately 300 kJ mol(-1) . Given the large distance to the ground state, innovative concepts are required to open reaction pathways that selectively lead to a single enantiomer of the desired product. This Review outlines the two major concepts of homogenously catalyzed enantioselective processes. The first part deals with chiral photocatalysts, which intervene in the photochemical key step and induce an asymmetric induction in this step. In the second part, reactions are presented in which the photochemical excitation is mediated by an achiral photocatalyst and the transfer of chirality is ensured by a second chiral catalyst (dual catalysis). © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Photochemical Reactions of Particulate Organic Matter: Deciphering the Role of Direct and Indirect Processes

NASA Astrophysics Data System (ADS)

Carrasquillo, A. J.; Gelfond, C. E.; Kocar, B. D.

2016-12-01

Photochemical reactions of natural organic matter (NOM) represent potentially important pathways for biologically recalcitrant material to be chemically altered in aquatic systems. Irradiation can alter the physical state of organic matter by facilitating the cycling between the particulate (POM) and dissolved (DOM) pools, however, a molecular level understanding of this chemically dynamic system is currently lacking. Photochemical reactions of a target molecule proceed by the direct absorption of a photon, or through reaction with a second photolytically generated species (i.e. the hydroxyl radical, singlet oxygen, excited triplet state NOM, hydrogen peroxide, etc.). Here, we isolate the major direct and indirect photochemical reactions of a lignocellulose-rich POM material (Phragmites australis) to determine their relative importance in changing the the chemical structure of the parent POM, and in the production of DOM. We measured POM molecular structure using a combination of NMR and FTIR for bulk analyses and scanning transmission x-ray microscopy (STXM) for spatially resolved chemistry, while the chemical composition of photo-produced DOM was measured using ultra-high resolution mass spectrometry. Results are discussed in the context of the differences in chemical composition of both NOM pools resulting from the isolated photochemical pathways. All treatments result in an increase in DOM with reaction time, indicating that the larger POM matrix is likely fragmenting into smaller more soluble species. Spectroscopic measurements, on the other hand, point to functionalization reactions which increase the abundance of alcohol, acid, and carbonyl moieties in both carbon pools. This unique dataset provides new insight into how photochemical reactions alter the chemical composition of NOM while highlighting the relative importance of indirect pathways.

Photochemically Switching Diamidocarbene Spin States Leads to Reversible Büchner Ring Expansions.

PubMed

Perera, Tharushi A; Reinheimer, Eric W; Hudnall, Todd W

2017-10-18

The discovery of thermal and photochemical control by Woodward and Hoffmann revolutionized how we understand chemical reactivity. Similarly, we now describe the first example of a carbene that exhibits differing thermal and photochemical reactivity. When a singlet ground-state N,N'-diamidocarbene 1 was photolyzed at 380 nm, excitation to a triplet state was observed. The triplet-state electronic structure was characteristic of the expected biradical σ 1 p π 1 spin configuration according to a combination of spectroscopic and computational methods. Surprisingly, the triplet state of 1 was found to engage a series of arenes in thermally reversible Büchner ring expansion reactions, marking the first examples where both cyclopropanation and ring expansion of arenes were rendered reversible. Not only are these photochemical reactions different from the known thermal chemistry of 1, but the reversibility enabled us to perform the first examples of photochemically induced arene exchange/expansion reactions at a single carbon center.

Photochemical Effects of Sunlight

PubMed Central

Daniels, Farrington

1972-01-01

The importance of sunlight in bringing about not only photosynthesis in plants, but also other photochemical effects, is reviewed. More effort should be devoted to photochemical storage of the sun's energy without the living plant. There is no theoretical reason to believe that such reactions are impossible. Ground rules for searching for suitable solar photochemical reactions are given, and a few attempts are described, but nothing successful has yet been found. Future possibilities are suggested. Photogalvanic cells which convert sunlight into electricity deserve further research. Eugene Rabinowitch has been an active pioneer in these fields. PMID:5037333

Photochemical effects of sunlight.

PubMed

Daniels, F

1972-07-01

The importance of sunlight in bringing about not only photosynthesis in plants, but also other photochemical effects, is reviewed. More effort should be devoted to photochemical storage of the sun's energy without the living plant. There is no theoretical reason to believe that such reactions are impossible. Ground rules for searching for suitable solar photochemical reactions are given, and a few attempts are described, but nothing successful has yet been found. Future possibilities are suggested. Photogalvanic cells which convert sunlight into electricity deserve further research. Eugene Rabinowitch has been an active pioneer in these fields.

Nonsymmetrical 3,4-dithienylmaleimides by cross-coupling reactions with indium organometallics: synthesis and photochemical studies.

PubMed

Mosquera, Angeles; Férnandez, M Isabel; Canle Lopez, Moisés; Pérez Sestelo, José; Sarandeses, Luis A

2014-10-27

The synthesis and photochemical study of novel nonsymmetrical 1,2-dithienylethenes (DTEs) with a maleimide bridge have been carried out. The synthetic approach to the DTEs was based on successive selective palladium-catalyzed cross-coupling reactions of 5-susbtituted-2-methyl-3-thiophenyl indium reagents with 3,4-dichloromaleimides. The required organoindium reagents were prepared from 2-methyl-3,5-dibromothiophene by a selective (C-5) coupling reaction with triorganoindium compounds (R3 In) and subsequent metal-halogen exchange. The coupling reactions usually gave good yields and have a high atom economy with substoichiometric amounts of R3 In. The results of photochemical studies show that these novel dithienylmaleimides undergo a photocyclization reaction upon irradiation in the UV region and a photocycloreversion after excitation in the visible region, thus they can be used as photochemical switches. ON-OFF operations can be repeated in successive cycles without appreciable loss of effectiveness in the process. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Photochemical Creation of Fluorescent Quantum Defects in Semiconducting Carbon Nanotube Hosts.

PubMed

Wu, Xiaojian; Kim, Mijin; Kwon, Hyejin; Wang, YuHuang

2018-01-15

Quantum defects are an emerging class of synthetic single-photon emitters that hold vast potential for near-infrared imaging, chemical sensing, materials engineering, and quantum information processing. Herein, we show that it is possible to optically direct the synthetic creation of molecularly tunable fluorescent quantum defects in semiconducting single-walled carbon nanotube hosts through photochemical reactions. By exciting the host semiconductor with light that resonates with its electronic transition, we find that halide-containing aryl groups can covalently bond to the sp 2 carbon lattice. The introduced quantum defects generate bright photoluminescence that allows tracking of the reaction progress in situ. We show that the reaction is independent of temperature but correlates strongly with the photon energy used to drive the reaction, suggesting a photochemical mechanism rather than photothermal effects. This type of photochemical reactions opens the possibility to control the synthesis of fluorescent quantum defects using light and may enable lithographic patterning of quantum emitters with electronic and molecular precision. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Photochemical parameters of atmospheric source gases: accurate determination of OH reaction rate constants over atmospheric temperatures, UV and IR absorption spectra

NASA Astrophysics Data System (ADS)

Orkin, V. L.; Khamaganov, V. G.; Martynova, L. E.; Kurylo, M. J.

2012-12-01

The emissions of halogenated (Cl, Br containing) organics of both natural and anthropogenic origin contribute to the balance of and changes in the stratospheric ozone concentration. The associated chemical cycles are initiated by the photochemical decomposition of the portion of source gases that reaches the stratosphere. Reactions with hydroxyl radicals and photolysis are the main processes dictating the compound lifetime in the troposphere and release of active halogen in the stratosphere for a majority of halogen source gases. Therefore, the accuracy of photochemical data is of primary importance for the purpose of comprehensive atmospheric modeling and for simplified kinetic estimations of global impacts on the atmosphere, such as in ozone depletion (i.e., the Ozone Depletion Potential, ODP) and climate change (i.e., the Global Warming Potential, GWP). The sources of critically evaluated photochemical data for atmospheric modeling, NASA/JPL Publications and IUPAC Publications, recommend uncertainties within 10%-60% for the majority of OH reaction rate constants with only a few cases where uncertainties lie at the low end of this range. These uncertainties can be somewhat conservative because evaluations are based on the data from various laboratories obtained during the last few decades. Nevertheless, even the authors of the original experimental works rarely estimate the total combined uncertainties of the published OH reaction rate constants to be less than ca. 10%. Thus, uncertainties in the photochemical properties of potential and current atmospheric trace gases obtained under controlled laboratory conditions still may constitute a major source of uncertainty in estimating the compound's environmental impact. One of the purposes of the presentation is to illustrate the potential for obtaining accurate laboratory measurements of the OH reaction rate constant over the temperature range of atmospheric interest. A detailed inventory of accountable sources of instrumental uncertainties related to our FP-RF experiment proves a total uncertainty of the OH reaction rate constant to be as small as ca. 2-3%. The high precision of kinetic measurements allows reliable determination of weak temperature dependences of the rate constants and clear resolution of the curvature of the Arrhenius plots for the OH reaction rate constants of various compounds. The results of OH reaction rate constant determinations between 220 K and 370 K will be presented. Similarly, the accuracy of UV and IR absorption measurements will be highlighted to provide an improved basis for atmospheric modeling.

Secondary Organic Aerosol Formation from Glyoxal: photochemical versus dark uptake and reversible versus irreversible SOA formation

NASA Astrophysics Data System (ADS)

Waxman, E.; Slowik, J. G.; Kampf, C. J.; Timkovsky, J.; Noziere, B.; Praplan, A. P.; Pfaffenberger, L.; Holzinger, R.; Hoffmann, T.; Dommen, J.; Prevot, A. S.; Baltensperger, U.; Volkamer, R.

2011-12-01

Glyoxal forms secondary organic aerosol (SOA) by partitioning to the aerosol aqueous phase according to Henry's law. The subsequent processing by heterogeneous and multiphase reactions shifts the partitioning towards aerosols. Currently it is not well understood whether these reactions result in reversible or irreversible SOA formation, and what parameters influence the rate limiting step of multiphase processing. We conducted a series of simulation chamber experiments at PSI in April and May 2011 to investigate processing under dark conditions, UV and/or visible light irradiated conditions, and in the presence and absence of OH radicals. Experiments used ammonium sulfate or ammonium sulfate/fulvic acid mixtures as seed aerosols, and were conducted between 50% and 85% relative humidity at approximately constant RH over the course of any given experiment. Glyoxal was produced photochemically from acetylene, using HONO photolysis as the OH radical source. Gas-phase glyoxal was measured by the CU LED-Cavity Enhanced-DOAS. The Thermal-Desorption Proton-Transfer-Reaction Mass Spectrometer (TD-PTR-MS) and Ion Chromatography Mass Spectrometer (IC-MS) monitored both gas and aerosol-phase organic reaction products. Particle composition was monitored by High-Resolution Time-of-Flight Aerosol Mass Spectrometry (HR-ToF-AMS), and HPLC-ESI MS/MS and LC-MS analysis of filter samples.

Secondary Organic Aerosol Formation from Glyoxal: photochemical versus dark uptake and reversible versus irreversible SOA formation

NASA Astrophysics Data System (ADS)

Waxman, E.; Slowik, J.; Kampf, C.; Timkovsky, J.; Noziere, B.; Praplan, A.; Pffafenberger, L.; Holzinger, R.; Hoffmann, T.; Dommen, J.; Prevot, A.; Baltensperger, U.; Volkamer, R.

2012-04-01

Glyoxal forms secondary organic aerosol (SOA) by partitioning to the aerosol aqueous phase according to Henry's law. The subsequent processing by heterogeneous and multiphase reactions shifts the partitioning towards aerosols. Currently it is not well understood whether these reactions result in reversible or irreversible SOA formation, and what parameters influence the rate limiting step of multiphase processing. We conducted a series of simulation chamber experiments at PSI in April and May 2011 to investigate processing under dark conditions, UV and/or visible light irradiated conditions, and in the presence and absence of OH radicals. Experiments used ammonium sulfate or ammonium sulfate/fulvic acid mixtures as seed aerosols, and were conducted between 50% and 85% relative humidity at approximately constant RH over the course of any given experiment. Glyoxal was produced photochemically from acetylene, using HONO photolysis as the OH radical source. Gas-phase glyoxal was measured by the CU LED-Cavity Enhanced-DOAS. The Thermal-Desorption Proton-Transfer-Reaction Mass Spectrometer (TD-PTR-MS) and Ion Chromatography Mass Spectrometer (IC-MS) monitored both gas and aerosol-phase organic reaction products. Particle composition was monitored by High-Resolution Time-of-Flight Aerosol Mass Spectrometry (HR-ToF-AMS), and HPLC-ESI MS/MS and LC-MS analysis of filter samples.

Gas-Phase Formation Rates of Nitric Acid and Its Isomers Under Urban Conditions

NASA Technical Reports Server (NTRS)

Okumura, M.; Mollner, A. K.; Fry, J. L.; Feng, L.

2005-01-01

Ozone formation in urban smog is controlled by a complex set of reactions which includes radical production from photochemical processes, catalytic cycles which convert NO to NO2, and termination steps that tie up reactive intermediates in long-lived reservoirs. The reaction OH + NO2 + M -4 HONO2 + M (la) is a key termination step because it transforms two short-lived reactive intermediates, OH and NO2, into relatively long-lived nitric acid. Under certain conditions (low VOC/NOx), ozone production in polluted urban airsheds can be highly sensitive to this reaction, but the rate parameters are not well constrained. This report summarizes the results of new laboratory studies of the OH + NO2 + M reaction including direct determination of the overall rate constant and branching ratio for the two reaction channels under atmospherically relevant conditions.

Products of BVOC oxidation: ozone and organic aerosols

NASA Astrophysics Data System (ADS)

Wildt, Jürgen; Andres, Stefanie; Carriero, Giulia; Ehn, Mikael; Fares, Silvano; Hoffmann, Thorsten; Hacker, Lina; Kiendler-Scharr, Astrid; Kleist, Einhard; Paoletti, Elena; Pullinen, Iida; Rohrer, Franz; Rudich, Yinon; Springer, Monika; Tillmann, Ralf; Wahner, Andreas; Wu, Cheng; Mentel, Thomas

2015-04-01

Biogenic Volatile Organic Compounds (BVOC) are important precursors in photochemical O3 and secondary organic aerosol (SOA) formation. We conducted a series of laboratory experiments with OH-induced oxidation of monoterpenes to elucidate pathways and efficiencies of O3 and SOA formation. At high NOx conditions ([BVOC] / [NOx] < 7 ppbC / ppb) photochemical ozone formation was observed. For -pinene as individual BVOC as well as for the monoterpene mixes emitted from different plant species we observed increasing ozone formation with increasing [NOX]. Between 2 and 3 O3-molecules were formed from 1 monoterpene when ozone formation was BVOC limited. Under such high NOX conditions, new particle formation was suppressed. Increasing [BVOC] / [NOX] ratios caused increasing efficiency of new particle formation indicating that peroxy radicals are the key intermediates in both, photochemical ozone- and new particle formation. The classical chemistry of peroxy radicals is well established (e.g. Master Chemical Mechanism). Peroxy radicals are produced by addition of molecular oxygen to the alkyl radical formed after OH attack at the BVOC. They either react with NO which leads to ozone formation or they react with other peroxy radicals and form chemically stable products (hydroperoxides, alkoholes and ketones). Much less knowledge exists on such reactions for Highly Oxidized Peroxy Radicals, (HOPR). Such HOPR were observed during ozonolysis of several volatiles and, in case of monoterpenes as precursors, they can contain more than 12 Oxygen atoms (Mentel et al., 2015). Although the OH-initiated formation of HOPR is yet not fully understood, their basic gas phase reactions seem to follow classical photochemical rules. In reactions with NO they can act as precursor for O3 and in reactions with other HOPR or with classical less oxidized peroxy radicals they can form highly oxidized stable products and alkoxy radicals. In addition, HOPR-HOPR reactions lead to the formation of dimers that, in case of monoterpenes as reactants, consist of a skeleton with 20 carbon atoms. These dimers seem to play a major role in new particle formation and their existence may explain the observations of Wildt et al. (2014) who found power law dependence with an exponent approaching -2 between new particle formation and ozone formation. The monomer products of HOPR-HOPR reactions play a dominant role in SOA mass formation because their vapour pressures are low enough to allow condensation on pre-existing particulate matter (Ehn et al., 2014). Furthermore, the minor impacts of NOX on particle mass formation (Wildt et al., 2014) are explainable by similar yields of alkoxy radicals in HOPR-HOPR and HOPR-NO reactions, respectively.

A model assessment of the ability of lake water in Terra Nova Bay, Antarctica, to induce the photochemical degradation of emerging contaminants.

PubMed

Minella, Marco; Maurino, Valter; Minero, Claudio; Vione, Davide

2016-11-01

The shallow lakes located in Terra Nova Bay, Antarctica, are free from ice for only up to a couple of months (mid December to early/mid February) during the austral summer. In the rest of the year, the ice cover shields the light and inhibits the photochemical processes in the water columns. Previous work has shown that chromophoric dissolved organic matter (CDOM) in these lakes is very reactive photochemically. A model assessment is here provided of lake-water photoreactivity in field conditions, based on experimental data of lake water absorption spectra, chemistry and photochemistry obtained previously, taking into account the water depth and the irradiation conditions of the Antarctic summer. The chosen sample contaminants were the solar filter benzophenone-3 and the antimicrobial agent triclosan, which have very well known photoreactivity and have been found in a variety of environmental matrices in the Antarctic continent. The two compounds would have a half-life time of just a few days or less in the lake water during the Antarctic summertime, largely due to reaction with CDOM triplet states ((3)CDOM*). In general, pollutants that occur in the ice and could be released to lake water upon ice melting (around or soon after the December solstice) would be quickly photodegraded if they undergo fast reaction with (3)CDOM*. With some compounds, the important (3)CDOM* reactions might favour the production of harmful secondary pollutants, such as 2,8-dichlorodibenzodioxin from the basic (anionic) form of triclosan. Copyright © 2016 Elsevier Ltd. All rights reserved.

PHOTOCHEMICAL REACTIONS AMONG FORMALDEHYDE, CHLORINE, AND NITROGEN DIOXIDE IN AIR

EPA Science Inventory

Photochemical reactions among chlorine, nitrogen dioxide, and formaldehyde were studied, using parts-per-million concentrations in 1 atm of air. The reactant mixtures were irradiated by ultraviolet fluorescent lamps and simultaneously analyzed by the Fourier transform infrared te...

Impact of Diurnal Variations of Precursors on the Prediction of Ozone

NASA Astrophysics Data System (ADS)

Hamer, P. D.; Bowman, K. W.; Henze, D. K.; Singh, K.

2009-12-01

Using a photochemical box model and its adjoint, constructed using the Kinetic Pre-Processor, we investigate the impacts of changing observational capacity, observation frequency and quality upon the ability to both understand and predict the nature of peak ozone events within a variety of polluted environments. The model consists of a chemical mechanism based on the Master Chemical Mechanism utilising 171 chemical species and 524 chemical reactions interacting with emissions, dry deposition and mixing schemes. The model was run under a variety of conditions designed to simulate a range of summertime polluted environments spanning a range of NOx and volatile organic compound regimes (VOCs). Using the forward model we were able to generate simulated atmospheric conditions representative of a particular polluted environment, which could in turn be used to generate a set of pseudo observations of key photochemical constituents. The model was then run under somewhat less polluted conditions to generate a background and then perturbed back towards the polluted trajectory using sequential data assimilation and the pseudo observations. Using a combination of the adjoint sensitivity analysis and the sequential data assimilation described here we assess the optimal time of observation and the diversity of observed chemical species required to provide acceptable forecast estimates of ozone concentrations. As the photochemical regime changes depending on NOx and VOC concentrations different observing strategies become favourable. The impact of using remote sensing based observations of the free tropospheric photochemical state are investigated to demonstrate the advantage of gaining knowledge of atmospheric trace gases away from the immediate photochemical environment.

Reaction Gradients Viewed Inside Single Photoactive Particles

NASA Astrophysics Data System (ADS)

Alpert, P.; Corral Arroyo, P.; Dou, J.; Kreiger, U.; Luo, B.; Peter, T.; Ammann, M.

2017-12-01

In terms of chemical selectivity and spatial resolution, a technique known as scanning transmission X-ray microscopy coupled to near-edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS) is unmatched and will remain so for years into the future. We present a recent development coupling STXM/NEXAFS to a custom-built photochemical environmental reactor in which aerosol particles reside allowing for in situ chemical imaging. A laboratory investigation of metal-organic complex photochemistry was conducted. Transition metals are of great importance to atmospheric chemistry and aerosol photochemical aging due to their ability to catalyze oxidation reactions. Aerosol particles composed of mixtures of citric acid and iron citrate were probed for their organic carbon composition and iron oxidation state under atmospherically relevant conditions. At 40% relative humidity, oxygen diffusion and reaction was severely limited. Fe was reoxidized in the first 200 nm of the particle surface leaving reduced iron in the core. Similar gradients were observed at 60% RH, however waiting approximately 2 hours in the dark resulted in a recovery of the initial Fe(III) concentration. We draw two main conclusions from our findings. Frist, the oxidation gradients must have been the result of anoxic conditions at the interior of aerosol particles. This was predicted using a newly developed model for molecular diffusion through multiple layers with a reaction framework describing the photochemical processing of the metal organic matrix. Second, the lifetime of organic radicals in an anoxic diffusion limited organic matrix must be considerably long ( hours) to completely reoxidize iron as they wait for molecular oxygen. Long radical lifetimes in viscous organic aerosol in turn, could create high radical concentrations or favor radical-radical reactions in particles typically not considered when oxygen is plentiful. Our results impact predictions of aerosol physiochemical properties, e.g. aerosol toxicity, hygroscopicity, lifetime and light scattering properties over time which may be limited and evolve at different rates at the surface or core of particles.

A Simple Parallel Photochemical Reactor for Photodecomposition Studies

ERIC Educational Resources Information Center

Xiaobo Chen; Halasz, Sarah M.; Giles, Eric C.; Mankus, Jessica V.; Johnson, Joseph C.; Burda, Clemens

2006-01-01

A simple and useful parallel photochemical reactor intended to study the photodecomposition of dyes using semiconductor photocatalysis is presented. The photochemical reactions are followed through time-dependent changes in the ground-state absorption spectra of the dyes.

Surface retention and photochemical reactivity of the diphenylether herbicide oxyfluorfen.

PubMed

Scrano, Laura; Bufo, Sabino A; Cataldi, Tommaso R I; Albanis, Triantafyllos A

2004-01-01

The photochemical behavior of oxyfluorfen [2-chloro-1-(3-etoxy-4-nitrophenoxy)-4-(trifluoromethyl) benzene] on two Greek soils was investigated. Soils were sampled from Nea Malgara and Preveza regions, characterized by a different organic matter content. Soils were spiked with the diphenyl-ether herbicide and irradiation experiments were performed either in the laboratory with a solar simulator (xenon lamp) or outside, under natural sunlight irradiation; other soil samples were kept in the dark to control the retention reaction. Kinetic parameters of both retention and photochemical reactions were calculated using zero-, first- and second- (Langmuir-Hinshelwood) order equations, and best fit was checked through statistical analysis. The soil behaviors were qualitatively similar but quantitatively different, with the soil sampled from the Nea Malgara region much more sorbent as compared with Preveza soil. All studied reactions followed second-order kinetics and photochemical reactions were influenced by retaining capability of the soils. The contributions of the photochemical processes to the global dissipation rates were also calculated. Two main metabolites were identified as 2-chloro-1-(3-ethoxy-4-hydroxyphenoxy)-4-(trifluoromethyl)benzene and 2-chloro-1- (3-hydroxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene.

Light-Induced C-H Arylation of (Hetero)arenes by In Situ Generated Diazo Anhydrides.

PubMed

Cantillo, David; Mateos, Carlos; Rincon, Juan A; de Frutos, Oscar; Kappe, C Oliver

2015-09-07

Diazo anhydrides (Ar-N=N-O-N=N-Ar) have been known since 1896 but have rarely been used in synthesis. This communication describes the development of a photochemical catalyst-free C-H arylation methodology for the preparation of bi(hetero)aryls by the one-pot reaction of anilines with tert-butyl nitrite and (hetero)arenes under neutral conditions. The key step in this procedure is the in situ formation and subsequent photochemical (>300 nm) homolytic cleavage of a transient diazo anhydride intermediate. The generated aryl radical then efficiently reacts with a (hetero)arene to form the desired bi(hetero)aryls producing only nitrogen, water, and tert-butanol as byproducts. The scope of the reaction for several substituted anilines and (hetero)arenes was investigated. A continuous-flow protocol increasing selectivity and safety has been developed enabling the experimentally straightforward preparation of a variety of substituted bi(hetero)aryls within 45 min of reaction time. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Investigation of the Reactions and Distribution of Polycyclic Aromatic Hydrocarbons and Fullerenes in Extraterrestrial Material

NASA Technical Reports Server (NTRS)

Zare, Richard N.

2005-01-01

The work funded by this research grant includes four specific projects: (1) Mapping the spatial distribution of polycyclic aromatic hydrocarbons (PAHs) in a variety of meteoritic samples and comparing this distribution with mineralogical features of the meteorite to determine whether a correlation exists between the two. (2) Developing a method for detection of fullerenes in extraterrestrial samples using microprobe laser-desorption laser-ionization mass spectrometry ( pL2MS) and utilizing this technique to investigate fullerene presence, while exploring the possibility of spatially mapping the fullerene distribution in these samples through in situ detection. (3) Investigating a possible formation pathway for meteoritic and ancient terrestrial kerogen involving the photochemical reactions of PAHs with alkanes under prebiotic and astrophysically relevant conditions. (4) Studying reaction pathways and identifying the photoproducts generated during the photochemical evolution of PAH-containing interstellar ice analogs as part of an ongoing collaboration with researchers at the Astrochemistry Lab at NASA Ames.

Photochemical processes on Titan: Irradiation of mixtures of gases that simulate Titan's atmosphere

NASA Astrophysics Data System (ADS)

Tran, Buu N.; Joseph, Jeffrey C.; Force, Michael; Briggs, Robert G.; Vuitton, Veronique; Ferris, James P.

2005-09-01

Photochemical reaction pathways in Titan's atmosphere were investigated by irradiation of the individual components and the mixture containing nitrogen, methane, hydrogen, acetylene, ethylene, and cyanoacetylene. The quantum yields for the loss of the reactants and the formation of products were determined. Photolysis of ethylene yields mainly saturated compounds (ethane, propane, and butane) while photolysis of acetylene yields the same saturated compounds as well as ethylene and diacetylene. Irradiation of cyanoacetylene yields mainly hydrogen cyanide and small amounts of acetonitrile. When an amount of methane corresponding to its mixing ratio on Titan was added to these mixtures the quantum yields for the loss of reactants decreased and the quantum yields for hydrocarbon formation increased indicative of a hydrogen atom abstraction from methane by the photochemically generated radicals. GC/MS analysis of the products formed by irradiation of mixtures of all these gases generated over 120 compounds which were mainly aliphatic hydrocarbons containing double and triple bonds along with much smaller amounts of aromatic compounds like benzene, toluene and phenylacetylene. The reaction pathways were investigated by the use of 13C acetylene in these gas mixtures. No polycyclic aromatic compounds were detected. Vapor pressures of these compounds under conditions present in Titan's atmosphere were calculated. The low molecular weight compounds likely to be present in the atmosphere and aerosols of Titan as a result of photochemical processes are proposed.

The chitosan - Porphyrazine hybrid materials and their photochemical properties.

PubMed

Chełminiak-Dudkiewicz, Dorota; Ziegler-Borowska, Marta; Stolarska, Magdalena; Sobotta, Lukasz; Falkowski, Michal; Mielcarek, Jadwiga; Goslinski, Tomasz; Kowalonek, Jolanta; Węgrzynowska-Drzymalska, Katarzyna; Kaczmarek, Halina

2018-04-01

Three magnesium sulfanyl porphyrazines differing in the size of peripheral substituents (3,5-dimethoxybenzylsulfanyl, (3,5-dimethoxybenzyloxy)benzylsulfanyl, 3,5-bis[(3,5-bis[(3,5-dimethoxybenzyloxy)benzyloxy]benzylsulfanyl) were exposed to visible and ultraviolet radiation (UV A + B + C) in order to determine their photochemical properties. The course of photochemical reactions in dimethylformamide solutions and the ability of the systems to generate singlet oxygen were studied by UV-Vis spectroscopy, which additionally gave information on aggregation processes. The porphyrazines were found to be stable upon visible light irradiation conditions, but when exposed to high energy UV radiation, the efficient photodegradation of these macrocycles was observed. Therefore, these three magnesium sulfanyl porphyrazines were incorporated into chitosan matrix. The obtained thin films of chitosan doped with porphyrazines were subjected to polychromatic UV-radiation and studied by spectroscopic methods (UV-Vis, FTIR), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Application of chitosan as a polymer matrix for porphyrazines was found to be successful method that effectively stopped the unwelcome degradation of macrocycles, thus worth considering for their photoprotection. In addition, the surface properties of the hybrid material were determined by contact angle measurements and calculation of surface free energy. Intermolecular interactions between these novel porphyrazines and chitosan were detected. The mechanism of photochemical reactions occurring in studied systems has been discussed. Copyright © 2018 Elsevier B.V. All rights reserved.

Modelling the photochemical attenuation pathways of the fibrate drug gemfibrozil in surface waters.

PubMed

Fabbri, Debora; Maurino, Valter; Minella, Marco; Minero, Claudio; Vione, Davide

2017-03-01

Gemfibrozil (GFZ) is a relatively persistent pollutant in surface-water environments and it is rather recalcitrant to biological degradation. The GFZ photochemical lifetimes are relatively short in shallow waters with low levels of dissolved organic carbon (DOC), but they can reach the month-year range in deep and high-DOC waters. The main reason is that GFZ undergoes negligible reaction with singlet oxygen or degradation sensitised by the triplet states of chromophoric dissolved organic matter, which are the usually prevalent photochemical pathways in deep and high-DOC sunlit waters. Nitrate and nitrite scarcely affect the overall GFZ lifetimes, but they can shift photodegradation from direct photolysis to the OH process. These two pathways are the main GFZ phototransformation routes, with the direct photolysis prevailing in shallow environments during summer. Under these conditions the GFZ photochemical lifetimes are also shorter and the environmental significance of photodegradation correspondingly higher. The direct photolysis of GFZ under UVB irradiation yielded several transformation intermediates deriving from oxidation or cleavage of the aliphatic lateral chain. A quinone derivative (2,5-dimethyl-1,4-benzoquinone), a likely oxidation product of the transformation intermediate 2,5-dimethylphenol, is expected to be the most acutely and chronically toxic compound arising from GFZ direct photolysis. Interestingly, literature evidence suggests that the same toxic intermediate would be formed upon OH reaction. Copyright © 2016 Elsevier Ltd. All rights reserved.

The reactions of O(ID) and OH with CH3OH, oxidation of the HCO radial, and the photochemical oxidation of formaldehyde. [photochemical reactions in stratosphere

NASA Technical Reports Server (NTRS)

Osif, T. L.

1976-01-01

An experimental, laboratory study of the various photochemical reactions that can occur in the mesosphere and stratosphere is presented. N2O was photolyzed at 2139 A in the presence of CH3OH and CO. The O(id) produced in the photolysis reacted with CH3OH to produce OH radicals, and thus the reactions of both O(id) and OH were able to be studied. Also considered was the oxidation of the HCO radical. Mixtures of Cl2, O2, H2CO, and sometimes N2 or He were irradiated at 3660 A at several temperatures to photodecompose the Cl2. The photochemical oxidation of formaldehyde was studied as follows: formaldehyde in the presence of N2 and/or O2 (usually dry air) was photolyzed with a medium pressure Hg lamp used in conjunction with various filters which transmit different relative amounts of Hg lines from 2894 A to 3660 A. Results are presented and discussed, along with a description of experimental procedures and apparatus, and chemical reaction kinetics.

Ultrafast Adiabatic Photodehydration of 2-Hydroxymethylphenol and the Formation of Quinone Methide.

PubMed

Škalamera, Đani; Antol, Ivana; Mlinarić-Majerski, Kata; Vančik, Hrvoj; Phillips, David Lee; Ma, Jiani; Basarić, Nikola

2018-04-20

The photochemical reactivity of 2-hydroxymethylphenol (1) was investigated experimentally by photochemistry under cryogenic conditions, by detecting reactive intermediates by IR spectroscopy, and by using nanosecond and femtosecond transient absorption spectroscopic methods in solution at room temperature. In addition, theoretical studies were performed to facilitate the interpretation of the experimental results and also to simulate the reaction pathway to obtain a better understanding of the reaction mechanism. The main finding of this work is that photodehydration of 1 takes place in an ultrafast adiabatic photochemical reaction without any clear intermediate, delivering quinone methide (QM) in the excited state. Upon photoexcitation to a higher vibrational level of the singlet excited state, 1 undergoes vibrational relaxation leading to two photochemical pathways, one by which synchronous elimination of H 2 O gives QM 2 in its S 1 state and the other by which homolytic cleavage of the phenolic O-H bond produces a phenoxyl radical (S 0 ). Both are ultrafast processes that occur within a picosecond. The excited state of QM 2 (S 1 ) probably deactivates to S 0 through a conical intersection to give QM 2 (S 0 ), which subsequently delivers benzoxete 4. Elucidation of the reaction mechanisms for the photodehydration of phenols by which QMs are formed is important to tune the reactivity of QMs with DNA and proteins for the potential application of QMs in medicine as therapeutic agents. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Thermodynamics and mechanics of photochemcially reacting polymers

NASA Astrophysics Data System (ADS)

Long, Rong; Qi, H. Jerry; Dunn, Martin L.

2013-11-01

We develop a thermodynamics and mechanics theory for polymers that when irradiated with light, undergo photochemical reactions that alter their macromolecular structure, e.g., by bond breaking and/or reformation, and in turn affect their mechanical and physical behavior. This emerging class of highly-engineered active materials shows great promise for myriad applications and is a subset of a broader class of polymers with covalent bonds that can be dynamically tuned with various environmental stimuli. We formulate a general thermodynamic and kinetic framework to model the complex photochemical-thermal-mechanical coupling in these materials. Our theory considers the behavior of a polymer that is subjected to the combination of mechanical and thermal loading while simultaneously irradiated by light with multiple frequency components and directions. We introduce an approach to model the photochemical reactions that can change the network topology, resulting chemical species transport, heat conduction and finite deformation. We describe the interaction of the material with light via a radiometric description and show how it can be linked to a full electromagnetic treatment when appropriate and if desired. Our approach is sufficiently general to permit the modeling of various materials that operate via different photochemical reaction mechanisms. After formulating the general theory, we specialize it to a polymer that when irradiated with light undergoes a series of photochemical reactions that cause chain scission and reformation which continuously rearrange the polymer network into a stress-free configuration. Based on the operant physical mechanisms we develop a constitutive model using a polymer chain decomposition and evolution approach to track the molecular structure changes during simultaneous irradiation and mechanical loading. In the special case of isothermal conditions with monochromatic and unidirectional irradiation, we recover a previous model based on intuitive ad-hoc assumptions and thus put it on strong thermodynamic footing. Finally we use our model to simulate the behavior of a polymer that is biaxially stretched and then irradiated with light from one side. We simulate the process and emphasize the spontaneous bending that occurs due to inhomogeneous photoinduced stress relaxation. From our theory, we obtain an analytical expression of a characteristic time for photo-induced stress relaxation in terms of the dominating system parameters.

Evaluation of Data Used for Modelling the Stratosphere of Saturn

NASA Astrophysics Data System (ADS)

Armstrong, Eleanor Sophie; Irwin, Patrick G. J.; Moses, Julianne I.

2015-11-01

Planetary atmospheres are modeled through the use of a photochemical and kinetic reaction scheme constructed from experimentally and theoretically determined rate coefficients, photoabsorption cross sections and branching ratios for the molecules described within them. The KINETICS architecture has previously been developed to model planetary atmospheres and is applied here to Saturn’s stratosphere. We consider the pathways that comprise the reaction scheme of a current model, and update the reaction scheme according the to findings in a literature investigation. We evaluate contemporary photochemical literature, studying recent data sets of cross-sections and branching ratios for a number of hydrocarbons used in the photochemical scheme of Model C of KINETICS. In particular evaluation of new photodissociation branching ratios for CH4, C2H2, C2H4, C3H3, C3H5 and C4H2, and new cross-sectional data for C2H2, C2H4, C2H6, C3H3, C4H2, C6H2 and C8H2 are considered. By evaluating the techniques used and data sets obtained, a new reaction scheme selection was drawn up. These data are then used within the preferred reaction scheme of the thesis and applied to the KINETICS atmospheric model to produce a model of the stratosphere of Saturn in a steady state. A total output of the preferred reaction scheme is presented, and the data is compared both with the previous reaction scheme and with data from the Cassini spacecraft in orbit around Saturn.One of the key findings of this work is that there is significant change in the model’s output as a result of temperature dependent data determination. Although only shown within the changes to the photochemical portion of the preferred reaction scheme, it is suggested that an equally important temperature dependence will be exhibited in the kinetic section of the reaction scheme. The photochemical model output is shown to be highly dependent on the preferred reaction scheme used within it by this thesis. The importance of correct and temperature-appropriate photochemical and kinetic data for the atmosphere under examination is emphasised as a consequence.

Spectroscopy and reactions of molecules important in chemical evolution

NASA Technical Reports Server (NTRS)

Becker, R. S.

1974-01-01

The research includes: (1) hot hydrogen atom reactions in terms of the nature of products produced, mechanism of the reactions and the implication and application of such reactions for molecules existing in interstellar clouds, in planetary atmospheres, and in chemical evolution; (2) photochemical reactions that can lead to molecules important in chemical evolution, interstellar clouds and as constituents in planetary atmospheres; and (3) spectroscopic and theoretical properties of biomolecules and their precursors and where possible, use these to understand their photochemical behavior.

Upper atmosphere research: Reaction rate and optical measurements

NASA Technical Reports Server (NTRS)

Stief, L. J.; Allen, J. E., Jr.; Nava, D. F.; Payne, W. A., Jr.

1990-01-01

The objective is to provide photochemical, kinetic, and spectroscopic information necessary for photochemical models of the Earth's upper atmosphere and to examine reactions or reactants not presently in the models to either confirm the correctness of their exclusion or provide evidence to justify future inclusion in the models. New initiatives are being taken in technique development (many of them laser based) and in the application of established techniques to address gaps in the photochemical/kinetic data base, as well as to provide increasingly reliable information.

The determination and role of peroxyacetil nitrate in photochemical processes in atmosphere

PubMed Central

2012-01-01

Peroxyacetilnitrates (PAN) is the most characteristic photoxidant of a range of secondary pollutants formed by the photochemical reaction of hydrocarbons with nitrogen oxides in the atmosphere: it is phytotoxic and shows an increasing role in human health effects due to ambient air exposure, especially in presence of high ozone concentrations. Because of the similarity of the conditions required for their photochemical production PAN is observed in conjunction with elevated ozone concentrations. PAN has very low natural background concentrations so it is the very specific indicator of anthropogenic photochemical air pollution. In this paper we report PAN concentrations determined in Rome urban area during winter- and summer-period. PAN measurements were carried out by means of a gas-chromatograph equipped with an Electron Capture Detector (ECD) detector. For identifying the acute episodes of atmospheric photochemical pollutants the relationship between PAN and the variable Ox (=NO2+O3) which describes the oxidation process evolution is investigated. The role of Volatile Organic Compounds and PAN in the ozone formation is investigated as well the issue of taking in account the autovehicular emissions for checking the NOx fraction in fuel. PMID:22594443

Polycyclic aromatic hydrocarbons - Primitive pigment systems in the prebiotic environment

NASA Technical Reports Server (NTRS)

Deamer, D. W.

1992-01-01

The chemical evolution of meteoritic organics in the primitive earth is examined experimentally with attention given to the photochemical effects of hydrocarbon/water mixtures. Also addressed are the generation of amphiphilic products by photochemical reactions and the transduction of light energy into potentially useful forms. Polycyclic aromatic hydrocarbons (PAHs) absorb light and exist in carbonaceous chondrites; PAHs are therefore examined as primitive pigments by means of salt solutions with pyrene, fluoranthene, and pyrene derivatives with hexadecane. The hexadecane undergoes photochemical oxidation and yields long-chain amphiphiles with oxygen supplied by water, and acid pH shifts also occur. PAHs are also tested in lipid bilayer membranes to examine light-energy transduction. Protons are found to accumulate within the membrane-bounded volume to form proton gradients, and this reaction is theorized to be a good model of primitive photochemical reactions that related to the transduction of light energy into useable forms.

The crystal and molecular structure of sodium 4-(2,4,6-triisopropylbenzoyl)benzoate in terms of the photochemical behaviour of the anion.

PubMed

Konieczny, Krzysztof; Bąkowicz, Julia; Turowska-Tyrk, Ilona

2015-05-01

Contrary to the known 4-(2,4,6-triisopropylbenzoyl)benzoate salts, di-μ-aqua-bis[tetraaquasodium(I)] bis[4-(2,4,6-triisopropylbenzoyl)benzoate] dihydrate, [Na2(H2O)10](C23H27O3)2·2H2O, (1), does not undergo a photochemical Norrish-Yang reaction in the crystalline state. In order to explain this photochemical inactivity, the intermolecular interactions were analyzed by means of the Hirshfeld surface and intramolecular geometrical parameters describing the possibility of a Norrish-Yang reaction were calculated. The reasons for the behaviour of the title salt are similar crystalline environments for both the o-isopropyl groups in the anion, resulting in similar geometrical parameters and orientations, and that these interaction distances differ significantly from those found in salts where the photochemical reaction occurs.

Growth of fluorescence gold clusters using photo-chemically activated ligands

NASA Astrophysics Data System (ADS)

Mishra, Dinesh; Aldeek, Fadi; Michael, Serge; Palui, Goutam; Mattoussi, Hedi

2016-03-01

Ligands made of lipoic acid (LA) appended with a polyethylene glycol (PEG) chain have been used in the aqueous phase growth of luminescent gold clusters with distinct emission from yellow to near-IR, using two different routes. In the first route, the gold-ligand complex was chemically reduced using sodium borohydride in alkaline medium, which gave near- IR luminescent gold clusters with maximum emission around 745 nm. In the second method, LA-PEG ligand was photochemically modified to a mixture of thiols, oligomers and oxygenated species under UV-irradiation, which was then used as both reducing agent and stabilizing ligand. By adjusting the pH, temperature, and time of the reaction, we were able to obtain clusters with two distinct emission properties. Refluxing the gold-ligand complex in alkaline medium in the presence of excess ligand gave yellow emission within the first two hours and the emission shifted to red after overnight reaction. Mass spectrometry and chemical assay were used to understand the photo-chemical transformation of Lipoic Acid (LA). Mass spectroscopic studies showed the photo-irradiated product contains thiols, oligomers (dimers, trimers and tetramers) as well as oxygenated species. The amount of thiol formed under different conditions of irradiation was estimated using Ellman's assay.

Photooxidation of 3-substituted pyrroles:  a postcolumn reaction detection system for singlet molecular oxygen in HPLC.

PubMed

Denham, K; Milofsky, R E

1998-10-01

A postcolumn photochemical reaction detection scheme, based on the reaction of 3-substituted pyrroles with singlet molecular oxygen ((1)O(2)), has been developed. The method is selective and sensitive for the determination of a class of organic compounds called (1)O(2)-sensitizers and is readily coupled to HPLC. Following separation by HPLC, analytes ((1)O(2)-sensitizers) are excited by a Hg pen-ray lamp. Analytes that are efficient (1)O(2)-sensitizers promote ground-state O(2) ((3)Σ(g)(-)) to an excited state ((1)Σ(g)(+) or (1)Δ(g)), which reacts rapidly with tert-butyl-3,4,5-trimethylpyrrolecarboxylate (BTMPC) or N-benzyl-3-methoxypyrrole-2-tert-carboxylate (BMPC), which is added to the mobile phase. Detection is based on the loss of pyrrole (BTMPC or BMPC). The reaction is catalytic in nature since one analyte molecule may absorb light many times, producing large amounts of (1)O(2). Detection limits for several (1)O(2)-sensitizers were improved by 1-2 orders of magnitude over optimized UV-absorbance detection. This paper discusses the optimization of the reaction conditions for this photochemical reaction detection scheme and its application to the detection of PCBs, nitrogen heterocycles, nitro and chloro aromatics, and other substituted aromatic compounds.

Photophysical and photochemical insights into the photodegradation of sulfapyridine in water: A joint experimental and theoretical study.

PubMed

Zhang, Heming; Wei, Xiaoxuan; Song, Xuedan; Shah, Shaheen; Chen, Jingwen; Liu, Jianhui; Hao, Ce; Chen, Zhongfang

2018-01-01

For organic pollutants, photodegradation, as a major abiotic elimination process and of great importance to the environmental fate and risk, involves rather complicated physical and chemical processes of excited molecules. Herein, we systematically studied the photophysical and photochemical processes of a widely used antibiotic, namely sulfapyridine. By means of density functional theory (DFT) computations, we examined the rate constants and the competition of both photophysical and photochemical processes, elucidated the photochemical reaction mechanism, calculated reaction quantum yield (Φ) based on both photophysical and photochemical processes, and subsequently estimated the photodegradation rate constant. We further conducted photolysis experiments to measure the photodegradation rate constant of sulfapyridine. Our computations showed that sulfapyridine at the lowest excited singlet state (S 1 ) mainly undergoes internal conversion to its ground state, and is difficult to transfer to the lowest excited triplet states (T 1 ) via intersystem crossing (ISC) and emit fluorescence. In T 1 state, compared with phosphorescence emission and ISC, chemical reaction is much easier to initiate. Encouragingly, the theoretically predicted photodegradation rate constant is close to the experimentally observed value, indicating that quantum chemistry computation is powerful enough to study photodegradation involving ultra-fast photophysical and photochemical processes. Copyright © 2017 Elsevier Ltd. All rights reserved.

Simulations of photochemical smog formation in complex urban areas

NASA Astrophysics Data System (ADS)

Muilwijk, C.; Schrijvers, P. J. C.; Wuerz, S.; Kenjereš, S.

2016-12-01

In the present study we numerically investigated the dispersion of photochemical reactive pollutants in complex urban areas by applying an integrated Computational Fluid Dynamics (CFD) and Computational Reaction Dynamics (CRD) approach. To model chemical reactions involved in smog generation, the Generic Reaction Set (GRS) approach is used. The GRS model was selected since it does not require detailed modeling of a large set of reactive components. Smog formation is modeled first in the case of an intensive traffic emission, subjected to low to moderate wind conditions in an idealized two-dimensional street canyon with a building aspect ratio (height/width) of one. It is found that Reactive Organic Components (ROC) play an important role in the chemistry of smog formation. In contrast to the NOx/O3 photochemical steady state model that predicts a depletion of the (ground level) ozone, the GRS model predicts generation of ozone. Secondly, the effect of direct sunlight and shadow within the street canyon on the chemical reaction dynamics is investigated for three characteristic solar angles (morning, midday and afternoon). Large differences of up to one order of magnitude are found in the ozone production for different solar angles. As a proof of concept for real urban areas, the integrated CFD/CRD approach is applied for a real scale (1 × 1 km2) complex urban area (a district of the city of Rotterdam, The Netherlands) with high traffic emissions. The predicted pollutant concentration levels give realistic values that correspond to moderate to heavy smog. It is concluded that the integrated CFD/CRD method with the GRS model of chemical reactions is both accurate and numerically robust, and can be used for modeling of smog formation in complex urban areas.

Fundamental insights into interfacial catalysis.

PubMed

Gong, Jinlong; Bao, Xinhe

2017-04-03

Surface and interfacial catalysis plays a vital role in chemical industries, electrochemistry and photochemical reactions. The challenges of modern chemistry are to optimize the chemical reaction processes and understand the detailed mechanism of chemical reactions. Since the early 1960s, the foundation of surface science systems has allowed the study of surface and interfacial phenomena on atomic/molecular level, and thus brought a number of significant developments to fundamental and technological processes, such as catalysis, material science and biochemistry, just to name a few. This themed issue describes the recent advances and developments in the fundamental understanding of surface and interfacial catalysis, encompassing areas of knowledge from metal to metal oxide, carbide, graphene, hexagonal boron nitride, and transition metal dichalcogenides under ultrahigh vacuum conditions, as well as under realistic reaction conditions.

Photochemical insertion of alkynes into Cp sub 2 Fe sub 2 (CO) sub 2 (. mu. -CO) sub 2 : A mechanistic study by laser flash photolysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bursten, B.E.; McKee, S.D.; Platz, M.S.

1989-04-26

Cp{sub 2}Fe{sub 2}(CO){sub 2}({mu}-CO){sub 2} (1: Cp = {eta}{sup 5}-C{sub 5}H{sub 5}) has a rich and diverse photochemistry, as evidenced by the plethora of synthetic and mechanistic studies of it in the literature. Early photochemical studies of 1 have demonstrated homolysis to the radical Cp(CO){sub 2}Fe{sup {sm bullet}} (2). Recent work on metal dimers indicates that a dinuclear species is formed concomitantly. Tyler, Schmidt, and Gray (TSG) first proposed that irradiation of 1 leads to the dinuclear species 3, which they suggested was the intermediate responsible for phosphine substitution. Research by other individuals has indicated that the substitutionally active speciesmore » is the CO-loss photoproduct CpFe({mu}-CO){sub 3}FeCp (4). The authors interest in the photochemistry of 1 stemmed from their theoretical studies on piano-stool dimers. One reaction of particular concern is the photochemical insertion of alkynes into 1 to yield dimetallacyclopentenone 5. On the basis of MO calculations, the authors proposed a possible LUMO-controlled mechanism for this reaction that involved alkyne addition to the TSG transition state 3, followed by CO loss. In this contribution, they report initial experimental studies which demonstrate that 4 is the photochemical intermediate responsible for this reaction. They consider this reaction to be a paradigm for photochemical substitution and insertion reaction in such systems.« less

Comparison of Direct and Indirect Photolysis in Imazosulfuron Photodegradation.

PubMed

Rering, Caitlin; Williams, Katryn; Hengel, Matt; Tjeerdema, Ronald

2017-04-19

Imazosulfuron, a sulfonylurea herbicide used in rice cultivation, has been shown to undergo photodegradation in water, but neither the photochemical mechanism nor the role of indirect photolysis is known. The purpose of this study was to investigate the underlying processes that operate on imazosulfuron during aqueous photodegradation. Our data indicate that in the presence of oxygen, most photochemical degradation proceeds through a direct singlet-excited state pathway, whereas triplet-excited state imazosulfuron enhanced decay rates under low dissolved oxygen conditions. Oxidation by hydroxyl radical and singlet oxygen were not significant. At dissolved organic matter (DOM) concentrations representative of rice field conditions, fulvic acid solutions exhibited faster degradation than rice field water containing both humic and fulvic acid fractions. Both enhancement, via reaction with triplet-state DOM, and inhibition, via competition for photons, of degradation was observed in DOM solutions.

Photochemical Synthesis and Ligand Exchange Reactions of Ru(CO)[subscript 4] (Eta[superscript 2]-Alkene) Compounds

ERIC Educational Resources Information Center

Cooke, Jason; Berry, David E.; Fawkes, Kelli L.

2007-01-01

The photochemical synthesis and subsequent ligand exchange reactions of Ru(CO)[subscript 4] (eta[superscript2]-alkene) compounds has provided a novel experiment for upper-level inorganic chemistry laboratory courses. The experiment is designed to provide a system in which the changing electronic properties of the alkene ligands could be easily…

Fabrication of refractive index distributions in polymer using a photochemical reaction

NASA Astrophysics Data System (ADS)

Kada, Takeshi; Obara, Atsushi; Watanabe, Toshiyuki; Miyata, Seizo; Liang, Chuan Xin; Machida, Hideaki; Kiso, Koichi

2000-01-01

We demonstrate that a photochemical reaction can create various distributions of refractive index in polymer. When the polymer containing a photochemically active material is irradiated by UV light, the photochemical reaction which breaks the π-conjugated system in the material and decreases its linear polarizability can reduce refractive index of the polymer. We prepared a PMMA film added DMAPN ((4-N,N-dimethylaminophenyl)-N'-phenylnitrone) with a rate of 23 wt % by use of spin coating. Electronic structural change of DMAPN and refractive indices of the film before and after UV irradiation were evaluated by UV absorption spectra and m-line method, respectively. The UV irradiation decreased λmax at 380 nm in the absorption spectra, which is attributed to nitrone, and the refractive indices exponentially with irradiation time. The change of refractive indices reached 0.028. The refractive index profile upon depth of the film was investigated by measuring refractive indices of stacked DMAPN/PMMA films. When UV with a power of 10.7 mW/cm2 irradiated upon three stacked DMAPN/PMMA films for 35 s, variation of the refractive index change showed a quadratic profile. The refractive index profile with various irradiation time can be accounted with the combination of the chemical kinetics with the steady state approximation and Lambert-Beer's law. Thus, the photochemical reaction can be used to control the refractive index distribution in polymer.

Near-field photochemical and radiation-induced chemical fabrication of nanopatterns of a self-assembled silane monolayer

PubMed Central

Hentschel, Carsten; Fontein, Florian; Stegemann, Linda; Hoeppener, Christiane; Fuchs, Harald; Hoeppener, Stefanie

2014-01-01

Summary A general concept for parallel near-field photochemical and radiation-induced chemical processes for the fabrication of nanopatterns of a self-assembled monolayer (SAM) of (3-aminopropyl)triethoxysilane (APTES) is explored with three different processes: 1) a near-field photochemical process by photochemical bleaching of a monomolecular layer of dye molecules chemically bound to an APTES SAM, 2) a chemical process induced by oxygen plasma etching as well as 3) a combined near-field UV-photochemical and ozone-induced chemical process, which is applied directly to an APTES SAM. All approaches employ a sandwich configuration of the surface-supported SAM, and a lithographic mask in form of gold nanostructures fabricated through colloidal sphere lithography (CL), which is either exposed to visible light, oxygen plasma or an UV–ozone atmosphere. The gold mask has the function to inhibit the photochemical reactions by highly localized near-field interactions between metal mask and SAM and to inhibit the radiation-induced chemical reactions by casting a highly localized shadow. The removal of the gold mask reveals the SAM nanopattern. PMID:25247126

Influence of the Diadinoxanthin Pool Size on Photoprotection in the Marine Planktonic Diatom Phaeodactylum tricornutum1

PubMed Central

Lavaud, Johann; Rousseau, Bernard; van Gorkom, Hans J.; Etienne, Anne-Lise

2002-01-01

The pool size of the xanthophyll cycle pigment diadinoxanthin (DD) in the diatom Phaeodactylum tricornutum depends on illumination conditions during culture. Intermittent light caused a doubling of the DD pool without significant change in other pigment contents and photosynthetic parameters, including the photosystem II (PSII) antenna size. On exposure to high-light intensity, extensive de-epoxidation of DD to diatoxanthin (DT) rapidly caused a very strong quenching of the maximum chlorophyll fluorescence yield (Fm, PSII reaction centers closed), which was fully reversed in the dark. The non-photochemical quenching of the minimum fluorescence yield (Fo, PSII centers open) decreased the quantum efficiency of PSII proportionally. For both Fm and Fo, the non-photochemical quenching expressed as F/F′ − 1 (with F′ the quenched level) was proportional to the DT concentration. However, the quenching of Fo relative to that of Fm was much stronger than random quenching in a homogeneous antenna could explain, showing that the rate of photochemical excitation trapping was limited by energy transfer to the reaction center rather than by charge separation. The cells can increase not only the amount of DT they can produce, but also its efficiency in competing with the PSII reaction center for excitation. The combined effect allowed intermittent light grown cells to down-regulate PSII by 90% and virtually eliminated photoinhibition by saturating light. The unusually rapid and effective photoprotection by the xanthophyll cycle in diatoms may help to explain their dominance in turbulent waters. PMID:12114593

Impact of Enhanced Ozone Deposition and Halogen Chemistry on Tropospheric Ozone over the Northern Hemisphere.

PubMed

Sarwar, Golam; Gantt, Brett; Schwede, Donna; Foley, Kristen; Mathur, Rohit; Saiz-Lopez, Alfonso

2015-08-04

Fate of ozone in marine environments has been receiving increased attention due to the tightening of ambient air quality standards. The role of deposition and halogen chemistry is examined through incorporation of an enhanced ozone deposition algorithm and inclusion of halogen chemistry in a comprehensive atmospheric modeling system. The enhanced ozone deposition treatment accounts for the interaction of iodide in seawater with ozone and increases deposition velocities by 1 order of magnitude. Halogen chemistry includes detailed chemical reactions of organic and inorganic bromine and iodine species. Two different simulations are completed with the halogen chemistry: without and with photochemical reactions of higher iodine oxides. Enhanced deposition reduces mean summer-time surface ozone by ∼3% over marine regions in the Northern Hemisphere. Halogen chemistry without the photochemical reactions of higher iodine oxides reduces surface ozone by ∼15% whereas simulations with the photochemical reactions of higher iodine oxides indicate ozone reductions of ∼48%. The model without these processes overpredicts ozone compared to observations whereas the inclusion of these processes improves predictions. The inclusion of photochemical reactions for higher iodine oxides leads to ozone predictions that are lower than observations, underscoring the need for further refinement of the halogen emissions and chemistry scheme in the model.

Effects of inorganic seeds on secondary organic aerosol formation from photochemical oxidation of acetone in a chamber

NASA Astrophysics Data System (ADS)

Ge, Shuangshuang; Xu, Yongfu; Jia, Long

2017-12-01

Photochemical oxidations of acetone were studied under different inorganic seed (NaCl, (NH4)2SO4 and NaNO3) conditions in a self-made chamber. The results show that no secondary organic aerosol (SOA) can be formed in the experiments either in the absence of artificially added seed particles or in the presence of solid status of the added particles. Liquid water content is the key factor for the formation of SOA in the experiments with seeds. The amount of SOA was only about 4-7 μg m-3 in the experiments with the initial acetone of ∼15 ppm under different seed conditions. The analysis of SOA compositions by Exactive-Orbitrap mass spectrometer equipped with electro-spray interface (ESI-MS) shows that chlorine-containing and sulfur-containing compounds were detected in SOA formed from the experiments with NaCl and (NH4)2SO4 seeds, respectively, which were not identified in SOA from those with NaNO3. The compositions of SOA were mainly esters, organonitrates, hydroperoxides, etc. It is concluded that inorganic seed particles participated into the formation of SOA. Acetone SOA was mainly formed in the aqueous phase in which dissolved SOA precursors underwent further oxidation reactions, esterification reactions and/or radical-radical reactions. Our experiments further demonstrate that low-molecular-weight VOCs, such as acetone, can form SOA under certain conditions in the atmosphere, although their contributions to SOA may not be large.

Effect of chemical kinetics uncertainties on calculated constituents in a tropospheric photochemical model

NASA Technical Reports Server (NTRS)

Thompson, Anne M.; Stewart, Richard W.

1991-01-01

Random photochemical reaction rates are employed in a 1D photochemical model to examine uncertainties in tropospheric concentrations and thereby determine critical kinetic processes and significant correlations. Monte Carlo computations are used to simulate different chemical environments and their related imprecisions. The most critical processes are the primary photodissociation of O3 (which initiates ozone destruction) and NO2 (which initiates ozone formation), and the OH/methane reaction is significant. Several correlations and anticorrelations between species are discussed, and the ozone/transient OH correlation is examined in detail. One important result of the modeling is that estimates of global OH are generally about 25 percent uncertain, limiting the precision of photochemical models. Techniques for reducing the imprecision are discussed which emphasize the use of species and radical species measurements.

Laser-enhanced chemical reactions and the liquid state. II. Possible applications to nuclear fuel reprocessing

DOE Office of Scientific and Technical Information (OSTI.GOV)

DePoorter, G.L.; Rofer-DePoorter, C.K.

1976-01-01

Laser photochemistry is surveyed as a possible improvement upon the Purex process for reprocessing spent nuclear fuel. Most of the components of spent nuclear fuel are photochemically active, and lasers can be used to selectively excite individual chemical species. The great variety of chemical species present and the degree of separation that must be achieved present difficulties in reprocessing. Lasers may be able to improve the necessary separations by photochemical reaction or effects on rates and equilibria of reactions. (auth)

Actinometric measurement of solar ultraviolet and development of a weighted solar UV integral. [photochemical reaction rate determination

NASA Technical Reports Server (NTRS)

Gupta, A.; Coulbert, C.

1978-01-01

An actinometer has been developed to measure outdoor irradiance in the range 295-400 nm. Actinometric measurements of radiation are based on determination of photochemical reaction rates for reactions of known quantum efficiency. Actinometers have the advantage of providing irradiance data over surfaces of difficult accessibility; in addition, actinometrically determined irradiance data are wavelength weighted and therefore provide a useful means of assessing the degradation rates of polymers employed in solar energy systems.

Time-resolved EPR study on the photochemical reactions of benzil

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mukai, Masahiro; Yamnauchi, Seigo; Hirota, Noboru

1992-04-16

TREPR and optical studies on the photochemical reactions of benzil in 2-propanol and benzene-TEA conclude that emissive signals are due to the reaction from T{sub n} produced via the S{sub n} pointing right T{sub n} intersystem crossing process. The free-pair radical-pair mechanism can account for the main features of the slow rise component of the chemically induced dynamic electron polarization signal of the ketyl radical in 2-propanol. 27 refs., 10 figs., 2 tabs.

VALIDATION TESTING OF NEW MECHANISMS WITH OUTDOOR CHAMBER DATA, VOLUME 3: CALCULATION OF PHOTOCHEMICAL REACTION PHOTOLYSIS RATES IN THE UNC OUTDOOR CHAMBER

EPA Science Inventory

A new model is described for computing in-chamber actinic flux using site specific conditions that include time of day, air pressure, total column ozone, total column water vapor, relative humidity, aerosol type, aerosol optical density at 500 nm, and the spectral albedo of the g...

Economic photoprotection in photosystem II that retains a complete light-harvesting system with slow energy traps

NASA Astrophysics Data System (ADS)

Belgio, Erica; Kapitonova, Ekaterina; Chmeliov, Jevgenij; Duffy, Christopher D. P.; Ungerer, Petra; Valkunas, Leonas; Ruban, Alexander V.

2014-07-01

The light-harvesting antenna of higher plant photosystem II has an intrinsic capability for self-defence against intense sunlight. The thermal dissipation of excess energy can be measured as the non-photochemical quenching of chlorophyll fluorescence. It has recently been proposed that the transition between the light-harvesting and self-defensive modes is associated with a reorganization of light-harvesting complexes. Here we show that despite structural changes, the photosystem II cross-section does not decrease. Our study reveals that the efficiency of energy trapping by the non-photochemical quencher(s) is lower than the efficiency of energy capture by the reaction centres. Consequently, the photoprotective mechanism works effectively for closed rather than open centres. This type of defence preserves the exceptional efficiency of electron transport in a broad range of light intensities, simultaneously ensuring high photosynthetic productivity and, under hazardous light conditions, sufficient photoprotection for both the reaction centre and the light-harvesting pigments of the antenna.

Mechanism for the Coupled Photochemistry of Ammonia and Acetylene: Implications for Giant Planets, Comets and Interstellar Organic Synthesis

NASA Astrophysics Data System (ADS)

Keane, Thomas C.

2017-09-01

Laboratory studies provide a fundamental understanding of photochemical processes in planetary atmospheres. Photochemical reactions taking place on giant planets like Jupiter and possibly comets and the interstellar medium are the subject of this research. Reaction pathways are proposed for the coupled photochemistry of NH3 (ammonia) and C2H2 (acetylene) within the context Jupiter's atmosphere. We then extend the discussion to the Great Red Spot, Extra-Solar Giant Planets, Comets and Interstellar Organic Synthesis. Reaction rates in the form of quantum yields were measured for the decomposition of reactants and the formation of products and stable intermediates: HCN (hydrogen cyanide), CH3CN (acetonitrile), CH3CH = N-N = CHCH3 (acetaldazine), CH3CH = N-NH2 (acetaldehyde hydrazone), C2H5NH2 (ethylamine), CH3NH2 (methylamine) and C2H4 (ethene) in the photolysis of NH3/C2H2 mixtures. Some of these compounds, formed in our investigation of pathways for HCN synthesis, were not encountered previously in observational, theoretical or laboratory photochemical studies. The quantum yields obtained allowed for the formulation of a reaction mechanism that attempts to explain the observed results under varying experimental conditions. In general, the results of this work are consistent with the initial observations of Ferris and Ishikawa (1988). However, their proposed reaction pathway which centers on the photolysis of CH3CH = N-N = CHCH3 does not explain all of the results obtained in this study. The formation of CH3CH = N-N = CHCH3 by a radical combination reaction of CH3CH = N• was shown in this work to be inconsistent with other experiments where the CH3CH = N• radical is thought to form but where no CH3CH = N-N = CHCH3 was detected. The importance of the role of H atom abstraction reactions was demonstrated and an alternative pathway for CH3CH = N-N = CHCH3 formation involving nucleophilic reaction between N2H4 and CH3CH = NH is advanced.

Mechanism for the Coupled Photochemistry of Ammonia and Acetylene: Implications for Giant Planets, Comets and Interstellar Organic Synthesis.

PubMed

Keane, Thomas C

2017-09-01

Laboratory studies provide a fundamental understanding of photochemical processes in planetary atmospheres. Photochemical reactions taking place on giant planets like Jupiter and possibly comets and the interstellar medium are the subject of this research. Reaction pathways are proposed for the coupled photochemistry of NH 3 (ammonia) and C 2 H 2 (acetylene) within the context Jupiter's atmosphere. We then extend the discussion to the Great Red Spot, Extra-Solar Giant Planets, Comets and Interstellar Organic Synthesis. Reaction rates in the form of quantum yields were measured for the decomposition of reactants and the formation of products and stable intermediates: HCN (hydrogen cyanide), CH 3 CN (acetonitrile), CH 3 CH = N-N = CHCH 3 (acetaldazine), CH 3 CH = N-NH 2 (acetaldehyde hydrazone), C 2 H 5 NH 2 (ethylamine), CH 3 NH 2 (methylamine) and C 2 H 4 (ethene) in the photolysis of NH 3 /C 2 H 2 mixtures. Some of these compounds, formed in our investigation of pathways for HCN synthesis, were not encountered previously in observational, theoretical or laboratory photochemical studies. The quantum yields obtained allowed for the formulation of a reaction mechanism that attempts to explain the observed results under varying experimental conditions. In general, the results of this work are consistent with the initial observations of Ferris and Ishikawa (1988). However, their proposed reaction pathway which centers on the photolysis of CH 3 CH = N-N = CHCH 3 does not explain all of the results obtained in this study. The formation of CH 3 CH = N-N = CHCH 3 by a radical combination reaction of CH 3 CH = N• was shown in this work to be inconsistent with other experiments where the CH 3 CH = N• radical is thought to form but where no CH 3 CH = N-N = CHCH 3 was detected. The importance of the role of H atom abstraction reactions was demonstrated and an alternative pathway for CH 3 CH = N-N = CHCH 3 formation involving nucleophilic reaction between N 2 H 4 and CH 3 CH = NH is advanced.

Forging Fluorine‐Containing Quaternary Stereocenters by a Light‐Driven Organocatalytic Aldol Desymmetrization Process

PubMed Central

Cuadros, Sara; Dell'Amico, Luca

2017-01-01

Abstract Reported herein is a light‐triggered organocatalytic strategy for the desymmetrization of achiral 2‐fluoro‐substituted cyclopentane‐1,3‐diketones. The chemistry is based on an intermolecular aldol reaction of photochemically generated hydroxy‐o‐quinodimethanes and simultaneously forges two adjacent fully substituted carbon stereocenters, with one bearing a stereogenic carbon–fluorine unit. The method uses readily available substrates, a simple chiral organocatalyst, and mild reaction conditions to afford an array of highly functionalized chiral 2‐fluoro‐3‐hydroxycyclopentanones. PMID:28746742

Seasonal Photochemical Transformations of Nitrogen Species in a Forest Stream and Lake

PubMed Central

Porcal, Petr; Kopáček, Jiří; Tomková, Iva

2014-01-01

The photochemical release of inorganic nitrogen from dissolved organic matter is an important source of bio-available nitrogen (N) in N-limited aquatic ecosystems. We conducted photochemical experiments and used mathematical models based on pseudo-first-order reaction kinetics to quantify the photochemical transformations of individual N species and their seasonal effects on N cycling in a mountain forest stream and lake (Plešné Lake, Czech Republic). Results from laboratory experiments on photochemical changes in N speciation were compared to measured lake N budgets. Concentrations of organic nitrogen (Norg; 40–58 µmol L−1) decreased from 3 to 26% during 48-hour laboratory irradiation (an equivalent of 4–5 days of natural solar insolation) due to photochemical mineralization to ammonium (NH4 +) and other N forms (Nx; possibly N oxides and N2). In addition to Norg mineralization, Nx also originated from photochemical nitrate (NO3 −) reduction. Laboratory exposure of a first-order forest stream water samples showed a high amount of seasonality, with the maximum rates of Norg mineralization and NH4 + production in winter and spring, and the maximum NO3 − reduction occurring in summer. These photochemical changes could have an ecologically significant effect on NH4 + concentrations in streams (doubling their terrestrial fluxes from soils) and on concentrations of dissolved Norg in the lake. In contrast, photochemical reactions reduced NO3 − fluxes by a negligible (<1%) amount and had a negligible effect on the aquatic cycle of this N form. PMID:25551441

PHOTOCHEMICAL HEATING OF DENSE MOLECULAR GAS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Glassgold, A. E.; Najita, J. R.

2015-09-10

Photochemical heating is analyzed with an emphasis on the heating generated by chemical reactions initiated by the products of photodissociation and photoionization. The immediate products are slowed down by collisions with the ambient gas and then heat the gas. In addition to this direct process, heating is also produced by the subsequent chemical reactions initiated by these products. Some of this chemical heating comes from the kinetic energy of the reaction products and the rest from collisional de-excitation of the product atoms and molecules. In considering dense gas dominated by molecular hydrogen, we find that the chemical heating is sometimesmore » as large, if not much larger than, the direct heating. In very dense gas, the total photochemical heating approaches 10 eV per photodissociation (or photoionization), competitive with other ways of heating molecular gas.« less

Quantum Mechanics/Molecular Mechanics Free Energy Maps and Nonadiabatic Simulations for a Photochemical Reaction in DNA: Cyclobutane Thymine Dimer.

PubMed

Mendieta-Moreno, Jesús I; Trabada, Daniel G; Mendieta, Jesús; Lewis, James P; Gómez-Puertas, Paulino; Ortega, José

2016-11-03

The absorption of ultraviolet radiation by DNA may result in harmful genetic lesions that affect DNA replication and transcription, ultimately causing mutations, cancer, and/or cell death. We analyze the most abundant photochemical reaction in DNA, the cyclobutane thymine dimer, using hybrid quantum mechanics/molecular mechanics (QM/MM) techniques and QM/MM nonadiabatic molecular dynamics. We find that, due to its double helix structure, DNA presents a free energy barrier between nonreactive and reactive conformations leading to the photolesion. Moreover, our nonadiabatic simulations show that most of the photoexcited reactive conformations return to standard B-DNA conformations after an ultrafast nonradiative decay to the ground state. This work highlights the importance of dynamical effects (free energy, excited-state dynamics) for the study of photochemical reactions in biological systems.

Potential Chemical Systems for Intramolecular Cycloaddition Cures

DTIC Science & Technology

1979-05-01

allowed electrocyclic photochemical ring closure of stilbene to dihydrophenanthrene is well known (Reference 12). The presence of an oxidant , e.g...CH (c) R 3 0 00 > 0 I I (42) The keto-diynes 36 follow a uniform reaction pathway with chlorotris- ( triphenylphosphine )rhodium[I] to yield the...Irradiation of 36b similarly gives 49. The mechanism proposed for the photochemical reaction involves an initial formation of the reactive cyclobutadiene by

JPRS Report, Science & Technology, USSR: Chemistry

DTIC Science & Technology

1990-11-08

desorption cycle. The photochemical activity of the oxides was determined by irradiating them with UV light at 353 K during the oxidation reactions of...No 1, Jan 90] 8 Acid-Base Properties Photochemically Active Titanium Oxide Surfaces [N D. Konovalova, V. I. Stepanenko, etal; UKRAINSKIY...Figures 4; references 13: 10 Russian, 3 Western. UDC 541.183 Acid-Base Properties Photochemically Active Titanium Oxide Surfaces 907M0149B Kiev

Photochemical isotope separation

DOEpatents

Robinson, C. Paul; Jensen, Reed J.; Cotter, Theodore P.; Greiner, Norman R.; Boyer, Keith

1987-01-01

A process for separating isotopes by selective excitation of isotopic species of a volatile compound by tuned laser light. A highly cooled gas of the volatile compound is produced in which the isotopic shift is sharpened and defined. Before substantial condensation occurs, the cooled gas is irradiated with laser light precisely tuned to a desired wavelength to selectively excite a particular isotopic species in the cooled gas. The laser light may impart sufficient energy to the excited species to cause it to undergo photochemical reaction or even to photoionize. Alternatively, a two-photon irradiation may be applied to the cooled gas to induce photochemical reaction or photoionization. The process is particularly applicable to the separation of isotopes of uranium and plutonium.

Singlet oxygen in the coupled photochemical and biochemical oxidation of dissolved organic matter.

PubMed

Cory, Rose M; McNeill, Kristopher; Cotner, James P; Amado, Andre; Purcell, Jeremiah M; Marshall, Alan G

2010-05-15

Dissolved organic matter (DOM) is a significant (>700 Pg) global C pool. Transport of terrestrial DOM to the inland waters and coastal zones represents the largest flux of reduced C from land to water (215 Tg yr(-1)) (Meybeck, M. Am. J. Sci. 1983, 282, 401-450). Oxidation of DOM by interdependent photochemical and biochemical processes largely controls the fate of DOM entering surface waters. Reactive oxygen species (ROS) have been hypothesized to play a significant role in the photooxidation of DOM, because they may oxidize the fraction of DOM that is inaccessible to direct photochemical degradation by sunlight. We followed the effects of photochemically produced singlet oxygen ((1)O(2)) on DOM by mass spectrometry with (18)O-labeled oxygen, to understand how (1)O(2)-mediated transformations of DOM may lead to altered DOM bioavailability. The photochemical oxygen uptake by DOM attributed to (1)O(2) increased with DOM concentration, yet it remained a minority contributor to photochemical oxygen uptake even at very high DOM concentrations. When DOM samples were exposed to (1)O(2)-generating conditions (Rose Bengal and visible light), increases were observed in DOM constituents with higher oxygen content and release of H(2)O(2) was detected. Differential effects of H(2)O(2) and (1)O(2)-treated DOM showed that (1)O(2)-treated DOM led to slower bacterial growth rates relative to unmodified DOM. Results of this study suggested that the net effect of the reactions between singlet oxygen and DOM may be production of partially oxidized substrates with correspondingly lower potential biological energy yield.

Photochemical Reaction Altered Cardiac Toxicity of Diesel Exhaust Inhalation

EPA Science Inventory

Rationale: Epidemiological studies have indicated an association between urban air pollution exposure and cardiovascular morbidity and mortality. The present study was designed to evaluate the cardiac effects of inhaled diesel exhaust and compared with photochemically altered d...

Batch and Flow Photochemical Benzannulations Based on the Reaction of Ynamides and Diazo Ketones. Application to the Synthesis of Polycyclic Aromatic and Heteroaromatic Compounds

PubMed Central

Willumstad, Thomas P.; Haze, Olesya; Mak, Xiao Yin; Lam, Tin Yiu; Wang, Yu-Pu; Danheiser*, Rick L.

2013-01-01

Highly substituted polycyclic aromatic and heteroaromatic compounds are produced via a two-stage tandem benzannulation/cyclization strategy. The initial benzannulation step proceeds via a pericyclic cascade mechanism triggered by thermal or photochemical Wolff rearrangement of a diazo ketone. The photochemical process can be performed using a continuous flow reactor which facilitates carrying out reactions on a large scale and minimizes the time required for photolysis. Carbomethoxy ynamides as well as more ketenophilic bissilyl ynamines and N-sulfonyl and N-phosphoryl ynamides serve as the reaction partner in the benzannulation step. In the second stage of the strategy, RCM generates benzofused nitrogen heterocycles, and various heterocyclization processes furnish highly substituted and polycyclic indoles of types that were not available by using the previous cyclobutenone-based version of the tandem strategy. PMID:24116731

The effect of photochemical models on calculated equilibria and cooling rates in the stratosphere

NASA Technical Reports Server (NTRS)

Blake, D.; Lindzen, R. S.

1973-01-01

Simplified models were developed for radiative heating and cooling and for ozone photochemistry in the region 22-60 km. The latter permit the inclusion of nitrogen and hydrogen reactions in addition to simple oxygen reactions. The simplicity of the scheme facilitates the use of a wide variety of cooling and reaction rates. It is shown that joint radiative-photochemical equilibrium is appropriate to the mean state of the atmosphere between 35 and 60 km. The relaxation of perturbations from joint radiative-photochemical equilibrium was also investigated. In all cases the coupling between temperature dependent ozone photochemistry and radiation lead to a reduction of the thermal relaxation time from its purely radiative value. The latter, which amounts to about 10 days, is reduced to 2-4 days at heights of 31-35 km. This greatly enhances the dissipation of waves traveling through the stratosphere.

Photochemical conversion of tin-oxo cage compounds studied using hard x-ray photoelectron spectroscopy

NASA Astrophysics Data System (ADS)

Zhang, Yu; Haitjema, Jarich; Liu, Xiaomeng; Johansson, Fredrik; Lindblad, Andreas; Castellanos, Sonia; Ottosson, Niklas; Brouwer, Albert M.

2017-03-01

Several metal-containing molecular inorganic materials are currently considered as photoresists for extreme ultraviolet lithography (EUVL). This is primarily due to their high EUV absorption cross section and small building block size, properties which potentially allow both high sensitivity and resolution as well as low line-edge roughness. The photochemical reaction mechanisms that allow these kinds of materials to function as photoresists, however, are still poorly understood. As a step in this direction, we here discuss photochemical reactions upon deep UV (DUV) irradiation of a model negative-tone EUV photoresist material, namely the well-defined molecular tin-oxo cage compound [(SnR)12O14(OH)6]X2 (R = organic group; X = anion) which is spin coated to thin layers of 20 nm. The core electronic structure (Sn 3d, O 1s and C 1s) of fresh and DUV exposed films were then investigated using synchrotron radiationbased hard X-ray photoelectron spectroscopy (HAXPES). This method provides information about the structure and chemical state of the respective atoms in the material. We performed a comparative HAXPES study of the composition of the tin-oxo cage compound [(SnR)12O14(OH)6](OH)2, either fresh directly after spin-coated vs. DUV-exposed materials under either ambient condition or under a dry N2 atmosphere. Different chemical oxidation states and concentrations of atoms and atom types in the fresh and exposed films were found. We further found that the chemistry resulting from exposure in air and N2 is strikingly different, clearly illustrating the influence of film-gas interactions on the (photo)chemical processes that eventually determine the photoresist. Finally, a mechanistic hypothesis for the basic DUV photoreactions in molecular tin-oxo cages is proposed.

Forging Fluorine-Containing Quaternary Stereocenters by a Light-Driven Organocatalytic Aldol Desymmetrization Process.

PubMed

Cuadros, Sara; Dell'Amico, Luca; Melchiorre, Paolo

2017-09-18

Reported herein is a light-triggered organocatalytic strategy for the desymmetrization of achiral 2-fluoro-substituted cyclopentane-1,3-diketones. The chemistry is based on an intermolecular aldol reaction of photochemically generated hydroxy-o-quinodimethanes and simultaneously forges two adjacent fully substituted carbon stereocenters, with one bearing a stereogenic carbon-fluorine unit. The method uses readily available substrates, a simple chiral organocatalyst, and mild reaction conditions to afford an array of highly functionalized chiral 2-fluoro-3-hydroxycyclopentanones. © 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Photochemical studies on aromatic γ,δ-epoxy ketones: efficient synthesis of benzocyclobutanones and indanones.

PubMed

Shao, Yutian; Yang, Chao; Gui, Weijun; Liu, Yang; Xia, Wujiong

2012-04-11

Irradiation of terminal aromatic γ,δ-epoxy ketones with a 450 W UV lamp led to Norrish type II cyclization/semi-pinacol rearrangement cascade reaction which formed the benzocyclobutanones containing a full-carbon quaternary center, whereas irradiation of substituted aromatic γ,δ-epoxy ketones led to the indanones through a photochemical epoxy rearrangement and 1,5-biradicals cyclization tandem reaction. This journal is © The Royal Society of Chemistry 2012

Variable photosynthetic units, energy transfer and light-induced evolution of hydrogen in algae and bacteria.

NASA Technical Reports Server (NTRS)

Gaffron, H.

1971-01-01

The present state of knowledge regarding the truly photochemical reactions in photosynthesis is considered. Nine-tenths of the available knowledge is of a biochemical nature. Questions regarding the activities of the chlorophyll system are examined. The simplest photochemical response observed in living hydrogen-adapted algal cells is the release of molecular hydrogen, which continues even after all other known natural reactions have been eliminated either by heating or the action of poisons.

PHOTOCHEMICAL MINERALIZATION OF DISSOLVED ORGANIC NITROGEN TO AMMONIUM IN THE BALTIC SEA

EPA Science Inventory

Solar radiation-induced photochemistry can be considered as a new source of nutrients when photochemical reactions release bioavailable nitrogen from biologically non-reactive dissolved organic nitrogen (DON). Pretreatments of Baltic Sea waters in the dark indicated that >72% of ...

Photochemical isotope separation

DOEpatents

Robinson, C.P.; Jensen, R.J.; Cotter, T.P.; Greiner, N.R.; Boyer, K.

1987-04-28

A process is described for separating isotopes by selective excitation of isotopic species of a volatile compound by tuned laser light. A highly cooled gas of the volatile compound is produced in which the isotopic shift is sharpened and defined. Before substantial condensation occurs, the cooled gas is irradiated with laser light precisely tuned to a desired wavelength to selectively excite a particular isotopic species in the cooled gas. The laser light may impart sufficient energy to the excited species to cause it to undergo photochemical reaction or even to photoionize. Alternatively, a two-photon irradiation may be applied to the cooled gas to induce photochemical reaction or photoionization. The process is particularly applicable to the separation of isotopes of uranium and plutonium. 8 figs.

Laser photochemical lead isotopes separation for harmless nuclear power engineering

NASA Astrophysics Data System (ADS)

Bokhan, P. A.; Fateev, N. V.; Kim, V. A.; Zakrevsky, D. E.

2016-09-01

The collisional quenching of the metastable 3 P 1,2 and 1 D 2 lead atoms is studied experimentally in the gas flow of the lead atoms, reagent-molecules and a carrier gas Ar. The experimental parameters were similar to the conditions that are required in the operation of the experimental setup for photochemical isotope separation. Excited atoms are generated under electron impact conditions created by a gas glow discharge through the mixture of gases and monitored photoelectrically by attenuation of atomic resonance radiation from hollow cathode 208Pb lamp. The decay of the excited atoms has been studied in the presence various molecules and total cross section data are reported. The flow tube measurements has allowed to separate the physical and chemical quenching channels and measure the rates of the chemical reaction excited lead with N2O, CH2Cl2, SF6 and CuBr molecules. These results are discussed in the prospects of the obtaining isotopically modified lead as a promising coolant in the reactors on the fast-neutron.

A Model for Negative Ion Chemistry in Titan’s Ionosphere

NASA Astrophysics Data System (ADS)

Mukundan, Vrinda; Bhardwaj, Anil

2018-04-01

We developed a one-dimensional photochemical model for the dayside ionosphere of Titan for calculating the density profiles of negative ions under steady-state photochemical equilibrium condition. We concentrated on the T40 flyby of the Cassini orbiter and used the in situ measurements from instruments on board Cassini as input to the model. Using the latest available reaction rate coefficients and dissociative electron attachment cross sections, the densities of 10 anions are calculated. Our study shows CN‑ as the dominant anion, followed by C3N‑, which agrees with the results of previous calculations. We suggest that H‑ could be an important anion in Titan’s ionosphere and is the second most abundant anion at altitudes greater than 1200 km. The main production channel of the major ion CN‑ is the reaction of H‑ with HCN. The H‑ also play a major role in the production of anions C2H‑, C6H‑, and OH‑. We present a comparison of the calculated ion density profiles with the relative density profiles derived using recently reported Cassini CAPS/ELS observations.

Photochemical transformation of azoxystrobin in aqueous solutions.

PubMed

Boudina, A; Emmelin, C; Baaliouamer, A; Païssé, O; Chovelon, J M

2007-07-01

The photochemical behaviour of azoxystrobin fungicide (AZX) in water was studied under laboratory conditions. Photodegradation was initiated using a solar simulator (xenon arc lamp) or a jacketed Pyrex reaction cell equipped with a 125 W, high-pressure mercury lamp. HPLC/MS analysis (APCI and ESI in positive and negative modes) was used to identify AZX photoproducts. The calculated polychromatic quantum efficiencies (phi) of AZX at pH 4.5, 7 and 9 were 5.42 x 10(-3), 3.47 x 10(-3) and 3.06 x 10(-3) (degraded molecules per absorbed photon), respectively. The relatively narrow range of values indicates the stability of AZX with respect to photodegradation in the studied pH range. Results from the HPLC/MS analysis suggest that the phototransformation of AZX proceeds via multiple, parallel reaction pathways including: (1) photo-isomerization (E-->Z), (2) photo-hydrolysis of the methyl ester and of the nitrile group, (3) cleavage of the acrylate double bond, (4) photohydrolytic ether cleavage between the aromatic ring giving phenol, and (5) oxidative cleavage of the acrylate double bond.

Photochemical reaction between triclosan and nitrous acid in the atmospheric aqueous environment

NASA Astrophysics Data System (ADS)

Ma, Jianzhong; Zhu, Chengzhu; Lu, Jun; Lei, Yu; Wang, Jizhong; Chen, Tianhu

2017-05-01

Nitrous acid (HONO) is an important tropospheric pollutant and a major source of hydroxyl radical in the atmospheric gas phase. However, studies on the role of HONO in atmospheric aqueous phase chemistry processes are relatively few. The present work investigated the photochemical reaction of HONO with triclosan (TCS), which is an emerging contaminant, using a combination of laser flash photolysis spectrometry and gas chromatography mass spectrometry. With these techniques, the reaction pathway of HONO with TCS was proposed by directly monitoring the transient species and detecting the stable products. ·OH was generated from the photodissociation of the HONO aqueous solution and attacked TCS molecules on different sites to produce the TCS-OH adducts with a second-order rate constant of 1.11 × 109 L mol-1 s-1. The ·OH added a C atom adjacent to the ether bond in the aromatic ring of TCS and self-decayed when the ether bond broke. The intermediates generated from the addition of ·OH to the benzene ring of the TCS molecular structure were immediately nitrated by HONO, which played a key role in the formation process of nitrocompounds. An atmospheric model suggests that the aqueous oxidation of TCS by ·OH is a major reaction at high liquid water concentrations, and the photolysis of TCS dominates under low-humidity conditions.

Enhanced photochemical conversion of NO2 to HONO on humic acids in the presence of benzophenone.

PubMed

Han, Chong; Yang, Wangjin; Yang, He; Xue, Xiangxin

2017-12-01

The photochemical conversion of NO 2 to HONO on humic acids (HA) in the presence of benzophenone (BP) was investigated using a flow tube reactor coupled to a NO x analyzer at ambient pressure. BP significantly enhanced the reduction of NO 2 to HONO on HA under simulated sunlight, as shown by the increase of NO 2 uptake coefficient (γ) and HONO yield with the mass ratio of BP to HA. The γ and HONO yield on the mixtures of HA and BP obviously depended on the environmental conditions. Both γ and HONO yield increased with the increase of irradiation intensity and temperature, whereas they decreased with pH. The γ exhibited a negative dependence on the NO 2 concentration, which had slight influences on the HONO yield. There were maximum values for the γ and HONO yield at relative humidity (RH) of 22%. Finally, atmospheric implications about the photochemical reaction of NO 2 and HA in the presence of photosensitive species were discussed. Copyright © 2017 Elsevier Ltd. All rights reserved.

Modulated photochemical reactivities of O-acetylated (3',5'-dimethoxyphenyl)heteroaryl acyloin derivatives under direct irradiation and photo-induced electron transfer conditions.

PubMed

Bisht, Rajesh; Singh, Saumya; Krishnamoorthy, Kothandam; Nithyanandhan, Jayaraj

2018-05-25

3',5'-Dimethoxybenzoin esters are important photoremovable protecting groups which form 2-phenylbenzofuran derivatives upon photo-release. We utilized a similar concept to test a photochemical method of installing a benzofuran moiety to the conjugated backbone by subjecting O-acetylated (3',5'-dimethylphenyl)heteroaryl acyloin derivatives through direct photo irradiation and a photo-induced electron transfer reaction. These photochemical methods were explored for a variety of heteroaromatic substrates appended on the ketone part of the O-acetylated cross-acyloin derivatives. The furan, thiophene and bithiophene derivatives led to the expected cyclized (benzofuran capped) products but the derivatives with extended conjugation decomposed under direct irradiation. However, under irradiation in the presence of an electron donor such as triethylamine, the extended acyloin derivatives afforded both cyclized and deacetoxylated products. The semiconducting nature of the extended cyclized products was also explored and tested for solution-processed organic field effect transistors, providing a maximum hole mobility of 1.3 × 10-6 cm2 V-1 s-1.

Energy Transduction Inside of Amphiphilic Vesicles: Encapsulation of Photochemically Active Semiconducting Particles

NASA Astrophysics Data System (ADS)

Summers, David P.; Noveron, Juan; Basa, Ranor C. B.

2009-04-01

Amphiphilic bilayer membrane structures (vesicles) have been postulated to have been abiotically formed and spontaneously assemble on the prebiotic Earth, providing compartmentalization for the origin of life. These vesicles are similar to modern cellular membranes and can serve to contain water-soluble species, concentrate species, and have the potential to catalyze reactions. The origin of the use of photochemical energy in metabolism (i.e. energy transduction) is one of the central issues in the origin of life. This includes such questions as how energy transduction may have occurred before complex enzymatic systems, such as required by contemporary photosynthesis, had developed and how simple a photochemical system is possible. It has been postulated that vesicle structures developed the ability to capture and transduce light, providing energy for reactions. It has also been shown that pH gradients across the membrane surface can be photochemically created, but coupling these to drive chemical reactions has been difficult. Colloidal semiconducting mineral particles are known to photochemically drive redox chemistry. We propose that encapsulation of these particles has the potential to provide a source of energy transduction inside vesicles, and thereby drive protocellular chemistry, and represents a model system for early photosynthesis. In our experiments we show that TiO2 particles, in the ~20 nm size range, can be incorporated into vesicles and retain their photoactivity through the dehydration/rehydration cycles that have been shown to concentrate species inside a vesicle.

Energy transduction inside of amphiphilic vesicles: encapsulation of photochemically active semiconducting particles.

PubMed

Summers, David P; Noveron, Juan; Basa, Ranor C B

2009-04-01

Amphiphilic bilayer membrane structures (vesicles) have been postulated to have been abiotically formed and spontaneously assemble on the prebiotic Earth, providing compartmentalization for the origin of life. These vesicles are similar to modern cellular membranes and can serve to contain water-soluble species, concentrate species, and have the potential to catalyze reactions. The origin of the use of photochemical energy in metabolism (i.e. energy transduction) is one of the central issues in the origin of life. This includes such questions as how energy transduction may have occurred before complex enzymatic systems, such as required by contemporary photosynthesis, had developed and how simple a photochemical system is possible. It has been postulated that vesicle structures developed the ability to capture and transduce light, providing energy for reactions. It has also been shown that pH gradients across the membrane surface can be photochemically created, but coupling these to drive chemical reactions has been difficult. Colloidal semiconducting mineral particles are known to photochemically drive redox chemistry. We propose that encapsulation of these particles has the potential to provide a source of energy transduction inside vesicles, and thereby drive protocellular chemistry, and represents a model system for early photosynthesis. In our experiments we show that TiO2 particles, in the approximately 20 nm size range, can be incorporated into vesicles and retain their photoactivity through the dehydration/rehydration cycles that have been shown to concentrate species inside a vesicle.

Feedbacks between microphysics and photochemical aging in viscous aerosol

NASA Astrophysics Data System (ADS)

Dou, Jing; Corral Arroyo, Pablo; Alpert, Peter A.; Ammann, Markus; Peter, Thomas; Krieger, Ulrich K.

2017-04-01

Fe(III)-citrate complex photochemistry, which plays an important role in aerosol aging, especially in lower troposphere, has been widely recognized in both solution and solid states. It can get excited by light below about 500 nm, inducing the oxidation of carboxylate ligands and the production of peroxides (e.g., OH•, HO2•), which have a significant impact on the climate, air quality and health. Recently, there is literature reporting that aqueous aerosol particles may attain highly viscous, semi-solid or even glassy physical states under a wide range of atmospheric conditions. However, systematic studies on the effect of high viscosity on photochemical processes are scarce. In this research, mass and size changes of a single, aqueous Fe(III)-citrate/citric acid particle levitated in an electrodynamic balance (EDB) are tracked during photochemical processing. We observe an overall mass loss during photochemical processing due to evaporation of volatile (e.g., CO2) and semi-volatile (e.g., ketones) compounds. It is known that relative humidity and temperature strongly effects the viscosity of citric acid. Hence, under light intensities large enough not limiting photochemical processing (at a wavelength of either 375 nm or 473 nm), the quasi-steady state evaporation rate in our experiments depends on relative humidity and temperature. The same holds true for the characteristic time scale for reaching thermodynamic equilibrium after switching off the light source. We are focusing on the high viscosity case (i.e., reduced molecular mobility and low water content), which slows down the transport of products but can also affect chemical reaction rates (e.g., initial absorption process, charge and energy transfer). Data are compared to kinetic modeling and diffusivities for semi-volatile compounds are estimated aiming at a more detailed understanding of the feedbacks between microphysics and photochemical aging.

Chemical degradation of proteins in the solid state with a focus on photochemical reactions.

PubMed

Mozziconacci, Olivier; Schöneich, Christian

2015-10-01

Protein pharmaceuticals comprise an increasing fraction of marketed products but the limited solution stability of proteins requires considerable research effort to prepare stable formulations. An alternative is solid formulation, as proteins in the solid state are thermodynamically less susceptible to degradation. Nevertheless, within the time of storage a large panel of kinetically controlled degradation reactions can occur such as, e.g., hydrolysis reactions, the formation of diketopiperazine, condensation and aggregation reactions. These mechanisms of degradation in protein solids are relatively well covered by the literature. Considerably less is known about oxidative and photochemical reactions of solid proteins. This review will provide an overview over photolytic and non-photolytic degradation reactions, and specially emphasize mechanistic details on how solid structure may affect the interaction of protein solids with light. Copyright © 2014 Elsevier B.V. All rights reserved.

The Hammett relationship and reactions in the excited electronic state: hemithioindigo Z/E-photoisomerization.

PubMed

Cordes, Thorben; Schadendorf, Torsten; Priewisch, Beate; Rück-Braun, Karola; Zinth, Wolfgang

2008-01-31

The photochemical reaction dynamics of a set of photochromic compounds based on thioindigo and stilbene molecular parts (hemithioindigos, HTI) are presented. Photochemical Z/E isomerization around the central double bond occurs with time constants of 216 ps (Z --> E) and 10 ps (E --> Z) for a 5-methyl-hemithioindigo. Chemical substitution on the stilbene moiety causes unusually strong changes in the reaction rate. Electron-donating substituents in the position para to the central double bond (e.g., para-methoxy) strongly accelerate the reaction, while the reaction is drastically slowed by electron-withdrawing groups in this position (e.g., para-nitrile). We correlate the experimental data of seven HTI-compounds in a quantitative manner using the Hammett equation and present a qualitative explanation for the application of ground-state Hammett constants to describe the photoisomerization reaction.

Continuous Photo-Oxidation in a Vortex Reactor: Efficient Operations Using Air Drawn from the Laboratory

PubMed Central

2017-01-01

We report the construction and use of a vortex reactor which uses a rapidly rotating cylinder to generate Taylor vortices for continuous flow thermal and photochemical reactions. The reactor is designed to operate under conditions required for vortex generation. The flow pattern of the vortices has been represented using computational fluid dynamics, and the presence of the vortices can be easily visualized by observing streams of bubbles within the reactor. This approach presents certain advantages for reactions with added gases. For reactions with oxygen, the reactor offers an alternative to traditional setups as it efficiently draws in air from the lab without the need specifically to pressurize with oxygen. The rapid mixing generated by the vortices enables rapid mass transfer between the gas and the liquid phases allowing for a high efficiency dissolution of gases. The reactor has been applied to several photochemical reactions involving singlet oxygen (1O2) including the photo-oxidations of α-terpinene and furfuryl alcohol and the photodeborylation of phenyl boronic acid. The rotation speed of the cylinder proved to be key for reaction efficiency, and in the operation we found that the uptake of air was highest at 4000 rpm. The reactor has also been successfully applied to the synthesis of artemisinin, a potent antimalarial compound; and this three-step synthesis involving a Schenk-ene reaction with 1O2, Hock cleavage with H+, and an oxidative cyclization cascade with triplet oxygen (3O2), from dihydroartemisinic acid was carried out as a single process in the vortex reactor. PMID:28781513

Ladderenes: The mechanochemistry and the photochemistry of an exciting class of substances

NASA Astrophysics Data System (ADS)

Frank, Irmgard

2018-06-01

Recently, Chen et al. presented a fascinating paper about the synthesis and mechanochemical transformation of ladderenes. These compounds are sufficiently stable to undergo controlled transformation to polyacetylene if exposed to mechanical load caused, for example, by ultrasound. The present paper adds a closer analysis of the behaviour of the electronic structure under these conditions as well as a study of the photochemical behaviour. The influence of potential side reactions is discussed.

Kinetics of the heterogeneous photo oxidation of the pesticide bupirimate by OH-radicals and ozone under atmospheric conditions.

PubMed

Bouya, H; Errami, M; Chakir, A; Roth, E

2015-09-01

This article is concerned with the study of the photochemical degradation of bupirimate adsorbed on a quartz surface by atmospheric oxidants, namely ozone and OH radicals. OH oxidation experiments were conducted relative to two reference compounds, terbuthylazine and (4-chlorophenyl)(3,4-dimethoxyphenyl) methanone. Meanwhile, ozone oxidation experiments were performed in the absolute mode and were interpreted by both, the Surface Layer Reaction and the Gas Surface Reaction models of heterogeneous reactions. The obtained results show that the rate constants for the reactions between bupirimate and OH radicals and ozone are (cm(3)molecule(-1)s(-1)): (1.06 ± 0.87) × 10(-12) and (5.4 ± 0.3) × 10(-20), respectively. As a consequence, for the experimental conditions used in this study, the lifetime of bupirimate at quartz like surface/atmosphere interfaces is several months against ozone and a tenth of days against OH-radical. Copyright © 2015 Elsevier Ltd. All rights reserved.

Seasonal budgets of ozone and oxidant precursors in an industrial coastal area of northern Italy

NASA Technical Reports Server (NTRS)

Georgiadis, T.; Alberti, L.; Bonasoni, P.; Fortezza, F.; Giovanelli, G.; Strocchi, V.

1994-01-01

The seasonal budgets and evolution of photochemical oxidants reported for greater Ravenna's urban-industrial area in the present study were calculated using the combined data from on-site systematic surveys (1978-1989) and from the monitoring network of the local environmental authorities. The notable differences in the concentrations of ozone and nitrogen oxides depended on season, and meteorological variables showed a marked correlation to the seasonal budget of trace constituents. The weak local circulation, the land-sea breeze system, and high solar radiation in summer, which may persist at length because of the anticyclonic conditions, can produce episodes of intense photochemical reactions. In winter, by contrast, low solar radiation and the absence of the breeze system results in very different evolutions of both pollutant concentrations and their seasonal budget.

A model approach to assess the long-term trends of indirect photochemistry in lake water. The case of Lake Maggiore (NW Italy).

PubMed

Minella, Marco; Rogora, Michela; Vione, Davide; Maurino, Valter; Minero, Claudio

2011-08-15

A model-based approach is here developed and applied to predict the long-term trends of indirect photochemical processes in the surface layer (5m water depth) of Lake Maggiore, NW Italy. For this lake, time series of the main parameters of photochemical importance that cover almost two decades are available. As a way to assess the relevant photochemical reactions, the modelled steady-state concentrations of important photogenerated transients ((•)OH, ³CDOM* and CO₃(-•)) were taken into account. A multivariate analysis approach was adopted to have an overview of the system, to emphasise relationships among chemical, photochemical and seasonal variables, and to highlight annual and long-term trends. Over the considered time period, because of the decrease of the dissolved organic carbon (DOC) content of water and of the increase of alkalinity, a significant increase is predicted for the steady-state concentrations of the radicals (•)OH and CO₃(-•). Therefore, the photochemical degradation processes that involve the two radical species would be enhanced. Another issue of potential photochemical importance is related to the winter maxima of nitrate (a photochemical (•)OH source) and the summer maxima of DOC ((•)OH sink and ³CDOM* source) in the lake water under consideration. From the combination of sunlight irradiance and chemical composition data, one predicts that the processes involving (•)OH and CO₃(-•) would be most important in spring, while the reactions involving ³CDOM* would be most important in summer. Copyright © 2011 Elsevier B.V. All rights reserved.

Photochemical Upconversion: A Physical or Inorganic Chemistry Experiment for Undergraduates Using a Conventional Fluorimeter

ERIC Educational Resources Information Center

Wilke, Bryn M.; Castellano, Felix N.

2013-01-01

Photochemical upconversion is a regenerative process that transforms lower-energy photons into higher-energy light through two sequential bimolecular reactions, triplet sensitization of an appropriate acceptor followed by singlet fluorescence producing triplet-triplet annihilation derived from two energized acceptors. This laboratory directly…

Photocatalytic Degradation Property of NANO-TiO2/DIATOMITE for Rodamine B Dye Wastewater

NASA Astrophysics Data System (ADS)

Liu, Yue; Zheng, Shuilin; Du, Gaoxiang; Shu, Feng; Chen, Juntao

The Nano-TiO2/Diatomite compound photocatalyst is used to degrade rhodamine B dye wastewater in photochemical reactor. The test result indicates that the rate of photodegradation of rhodamine B is influenced by reactive conditions. The best technical conditions are concentration of rhodamine B solution 10mg/L, ultraviolet light 300W, the compound photocatalyst amount used 1g/L, the pH 5.8, reaction time 20min. Under these conditions the rate of photodegradation of rhodamine B may reach as high as 97.80%. And the efficiency of photodegradation of catalyst only has a little changed in recycling.

Photochemical Stereocontrol Using Tandem Photoredox–Chiral Lewis Acid Catalysis

PubMed Central

2016-01-01

Conspectus The physical, biological, and materials properties of organic compounds are determined by their three-dimensional molecular shape. The development of methods to dictate the stereochemistry of organic reactions has consequently emerged as one of the central themes of contemporary synthetic chemistry. Over the past several decades, chiral catalysts have been developed to control the enantioselectivity of almost every class of synthetically useful transformation. Photochemical reactions, however, are a conspicuous exception. Relatively few examples of highly enantioselective catalytic photoreactions have been reported to date, despite almost a century of research in this field. The development of robust strategies for photochemical enantiocontrol has thus proven to be a long-standing and surprisingly difficult challenge. For the past decade, our laboratory has been studying the application of transition metal photocatalysts to a variety of problems in synthetic organic chemistry. These efforts have recently culminated in the discovery of an effective system in which the activity of a visible light absorbing transition metal photoredox catalyst is combined with a second stereocontrolling chiral Lewis acid catalyst. This dual catalyst strategy has been applied to a diverse range of photochemical reactions; these have included highly enantioselective photocatalytic [2 + 2] cycloadditions, [3 + 2] cycloadditions, and radical conjugate addition reactions. This Account describes the development of the tandem Lewis acid photoredox catalysis strategy utilized in our laboratory. It provides an analysis of the factors that we believe to be particularly important to the success of this seemingly robust approach to photocatalytic stereocontrol. (1) The photocatalysts utilized in our systems are activated by wavelengths of visible light where the organic substrates are transparent, which minimizes the possibility of competitive racemic background photoreactions. (2) The high degree of tolerance that Ru(bpy)32+ and similar octahedral metal polypyridine complexes exhibit toward Lewis acids affords great flexibility in tuning the structure of the stereocontrolling chiral catalyst without perturbing the photoredox properties of the photocatalyst. (3) Synthetic chemists have amassed a substantial understanding of the features that are common in highly successful chiral Lewis acid catalyzed reactions, and these deep, well-validated insights are readily applied to the reactions of a variety of photogenerated intermediates. We hope that the recent success of this and similar dual catalytic systems will provide a useful foundation for the further development of powerful, stereocontrolled photochemical reactions. PMID:27505691

Photochemical Stereocontrol Using Tandem Photoredox-Chiral Lewis Acid Catalysis.

PubMed

Yoon, Tehshik P

2016-10-18

The physical, biological, and materials properties of organic compounds are determined by their three-dimensional molecular shape. The development of methods to dictate the stereochemistry of organic reactions has consequently emerged as one of the central themes of contemporary synthetic chemistry. Over the past several decades, chiral catalysts have been developed to control the enantioselectivity of almost every class of synthetically useful transformation. Photochemical reactions, however, are a conspicuous exception. Relatively few examples of highly enantioselective catalytic photoreactions have been reported to date, despite almost a century of research in this field. The development of robust strategies for photochemical enantiocontrol has thus proven to be a long-standing and surprisingly difficult challenge. For the past decade, our laboratory has been studying the application of transition metal photocatalysts to a variety of problems in synthetic organic chemistry. These efforts have recently culminated in the discovery of an effective system in which the activity of a visible light absorbing transition metal photoredox catalyst is combined with a second stereocontrolling chiral Lewis acid catalyst. This dual catalyst strategy has been applied to a diverse range of photochemical reactions; these have included highly enantioselective photocatalytic [2 + 2] cycloadditions, [3 + 2] cycloadditions, and radical conjugate addition reactions. This Account describes the development of the tandem Lewis acid photoredox catalysis strategy utilized in our laboratory. It provides an analysis of the factors that we believe to be particularly important to the success of this seemingly robust approach to photocatalytic stereocontrol. (1) The photocatalysts utilized in our systems are activated by wavelengths of visible light where the organic substrates are transparent, which minimizes the possibility of competitive racemic background photoreactions. (2) The high degree of tolerance that Ru(bpy) 3 2+ and similar octahedral metal polypyridine complexes exhibit toward Lewis acids affords great flexibility in tuning the structure of the stereocontrolling chiral catalyst without perturbing the photoredox properties of the photocatalyst. (3) Synthetic chemists have amassed a substantial understanding of the features that are common in highly successful chiral Lewis acid catalyzed reactions, and these deep, well-validated insights are readily applied to the reactions of a variety of photogenerated intermediates. We hope that the recent success of this and similar dual catalytic systems will provide a useful foundation for the further development of powerful, stereocontrolled photochemical reactions.

Rapid Covalent Immobilization of Proteins by Phenol-Based Photochemical Cross-Linking.

PubMed

Ren, Jun; Tian, Kaikai; Jia, Lingyun; Han, Xiuyou; Zhao, Mingshan

2016-10-19

A strategy for photoinduced covalent immobilization of proteins on phenol-functionalized surfaces is described. Under visible light irradiation, the reaction can be completed within seconds at ambient temperature, with high yields in aqueous solution of physiological conditions. Protein immobilization is based on a ruthenium-catalyzed radical cross-linking reaction between proteins and phenol-modified surfaces, and the process has proven mild enough for lipase, Staphylococcus aureus protein A, and streptavidin to preserve their bioactivity. This strategy was successfully applied to antibody immobilization on different material platforms, including agarose beads, cellulose membranes, and glass wafers, thus providing a generic procedure for rapid biomodification of surfaces.

Effects of 1,3-Butadiene, Isoprene, and Their Photochemical Degradation Products on Human Lung Cells

PubMed Central

Doyle, Melanie; Sexton, Kenneth G.; Jeffries, Harvey; Bridge, Kevin; Jaspers, Ilona

2004-01-01

Because of potential exposure both in the workplace and from ambient air, the known carcinogen 1,3-butadiene (BD) is considered a priority hazardous air pollutant. BD and its 2-methyl analog, isoprene (ISO), are chemically similar but have very different toxicities, with ISO showing no significant carcinogenesis. Once released into the atmosphere, reactions with species induced by sunlight and nitrogen oxides convert BD and ISO into several photochemical reaction products. In this study, we determined the relative toxicity and inflammatory gene expression induced by exposure of A549 cells to BD, ISO, and their photochemical degradation products in the presence of nitric oxide. Gas chromatography and mass spectrometry analyses indicate the initial and major photochemical products produced during these experiments for BD are acrolein, acetaldehyde, and formaldehyde, and products for ISO are methacrolein, methyl vinyl ketone, and formaldehyde; both formed < 200 ppb of ozone. After exposure the cells were examined for cytotoxicity and interleukin-8 (IL-8) gene expression, as a marker for inflammation. These results indicate that although BD and ISO alone caused similar cytotoxicity and IL-8 responses compared with the air control, their photochemical products significantly enhanced cytotoxicity and IL-8 gene expression. This suggests that once ISO and BD are released into the environment, reactions occurring in the atmosphere transform these hydrocarbons into products that induce potentially greater adverse health effects than the emitted hydrocarbons by themselves. In addition, the data suggest that based on the carbon concentration or per carbon basis, biogenic ISO transforms into products with proinflammatory potential similar to that of BD products. PMID:15531432

The efficiency of non-photochemical fluorescence quenching by cation radicals in photosystem II reaction centers.

PubMed

Paschenko, V Z; Churin, A A; Gorokhov, V V; Grishanova, N P; Korvatovskii, B N; Maksimov, E G; Mamedov, M D

2016-12-01

In a direct experiment, the rate constants of photochemical k p and non-photochemical k p + quenching of the chlorophyll fluorescence have been determined in spinach photosystem II (PS II) membrane fragments, oxygen-evolving PS II core, as well as manganese-depleted PS II particles using pulse fluorimetry. In the dark-adapted reaction center(s) (RC), the fluorescence decay kinetics of the antenna were measured at low-intensity picosecond pulsed excitation. To create a "closed" P680 + Q A - state, RCs were illuminated by high-intensity actinic flash 8 ns prior to the measuring flash. The obtained data were approximated by the sum of two decaying exponents. It was found that the antennae fluorescence quenching efficiency by the oxidized photoactive pigment of RC P680 + was about 1.5 times higher than that of the neutral P680 state. These results were confirmed by a single-photon counting technique, which allowed to resolve the additional slow component of the fluorescence decay. Slow component was assigned to the charge recombination of P680 + Pheo - in PS II RC. Thus, for the first time, the ratio k p + /k p  ≅ 1.5 was found directly. The mechanism of the higher efficiency of non-photochemical quenching comparing to photochemical quenching is discussed.

Photochemical pathways of the dimeric, mixed dimer, and monomeric sulfophthalocyanines of cobalt(III) and iron(II)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ferraudi, G.

1979-04-01

The photochemical reactivity of the dimeric, mixed dimer, and monomeric sulfophthalocyanines of cobalt (III) and iron (II) was investigated by steady-state and flash irradiations. The dimeric species photodissociated into sulfophthalocyanine radicals which were coordinated to either Co(III) or Fe(II) metal centers. Reactions of such intermediates were investigated by interception with alcohols and O/sub 2/. Also, photoredox reactions were detected with monomeric acidocobalt(III) sulfophtahlocyanines. These processes produce the oxidation of the acido ligands (Cl/sup -/, Br/sup -/, N/sub 3//sup -/, I/sup -/) and the reduction of the metal center. The photoredox dissociation was also investigated by using mixed dimers of themore » cobalt sulfophthalocyanines with Cr(bpy)/sub 3//sup 3 +/ and Ru(bpy)/sub 3//sup 2 +/. The photogeneration of sulfophthalocyanine radicals was observed as a general reaction which was produced by excitation of either the Cr(bby)/sub 3//sup 3 +/ or Ru(bpy)/sub 3//sup 2 +/ units in the mixed dimer. The nature of the reactive excited states involved in the various photochemical reactions of the sulfophthalocyanines of Co(II), Co(III), Cu(II), and Fe(II) is discussed.« less

Facile one-pot preparation of thermally and photochemically convertible soluble precursors of copper phthalocyanine and naphthalocyanine.

PubMed

Kikukawa, Yuu; Fukuda, Takamitsu; Fuyuhiro, Akira; Ishikawa, Naoto; Kobayashi, Nagao

2011-08-14

Soluble copper phthalocyanine (CuPc) and naphthalocyanine (CuNc) precursors which can be converted thermally and photochemically into insoluble CuPc and CuNc, respectively, have been synthesized by a one-step reaction using commercially available chemicals. This journal is © The Royal Society of Chemistry 2011

Laboratory measurements. [chemical and photochemical data relative to stratospheric modeling

NASA Technical Reports Server (NTRS)

1977-01-01

A compilation of chemical and photochemical data that are relevant to stratospheric modeling is presented. There are three broad categories of data: (1) rate constants for chemical reactions, including temperature and pressure dependencies along with product distributions; (2) absorption cross sections, photodissociation quantum yield, and photolysis; (3) heterogeneous chemical processes.

The photochemical formation and gas-particle partitioning of oxidation products of decamethyl cyclopentasiloxane and decamethyl tetrasiloxane in the atmosphere

NASA Astrophysics Data System (ADS)

Chandramouli, Bharadwaj; Kamens, Richard M.

Decamethyl cyclopentasiloxane (D 5) and decamethyl tetrasiloxane (MD 2M) were injected into a smog chamber containing fine Arizona road dust particles (95% surface area <2.6 μM) and an urban smog atmosphere in the daytime. A photochemical reaction - gas-particle partitioning reaction scheme, was implemented to simulate the formation and gas-particle partitioning of hydroxyl oxidation products of D 5 and MD 2M. This scheme incorporated the reactions of D 5 and MD 2M into an existing urban smog chemical mechanism carbon bond IV and partitioned the products between gas and particle phase by treating gas-particle partitioning as a kinetic process and specifying an uptake and off-gassing rate. A photochemical model PKSS was used to simulate this set of reactions. A Langmuirian partitioning model was used to convert the measured and estimated mass-based partitioning coefficients ( KP) to a molar or volume-based form. The model simulations indicated that >99% of all product silanol formed in the gas-phase partition immediately to particle phase and the experimental data agreed with model predictions. One product, D 4TOH was observed and confirmed for the D 5 reaction and this system was modeled successfully. Experimental data was inadequate for MD 2M reaction products and it is likely that more than one product formed. The model set up a framework into which more reaction and partitioning steps can be easily added.

Transition metal ion-assisted photochemical generation of alkyl halides and hydrocarbons from carboxylic acids.

PubMed

Carraher, Jack M; Pestovsky, Oleg; Bakac, Andreja

2012-05-21

Near-UV photolysis of aqueous solutions of propionic acid and aqueous Fe(3+) in the absence of oxygen generates a mixture of hydrocarbons (ethane, ethylene and butane), carbon dioxide, and Fe(2+). The reaction becomes mildly catalytic (about five turnovers) in the presence of oxygen which converts a portion of alkyl radicals to oxidizing intermediates that reoxidize Fe(2+). The photochemistry in the presence of halide ions (X(-) = Cl(-), Br(-)) generates ethyl halides via halogen atom abstraction from FeX(n)(3-n) by ethyl radicals. Near-quantitative yields of C(2)H(5)X are obtained at ≥0.05 M X(-). Competition experiments with Co(NH(3))(5)Br(2+) provided kinetic data for the reaction of ethyl radicals with FeCl(2+) (k = (4.0 ± 0.5) × 10(6) M(-1) s(-1)) and with FeBr(2+) (k = (3.0 ± 0.5) × 10(7) M(-1) s(-1)). Photochemical decarboxylation of propionic acid in the presence of Cu(2+) generates ethylene and Cu(+). Longer-chain acids also yield alpha olefins as exclusive products. These reactions become catalytic under constant purge with oxygen which plays a dual role. It reoxidizes Cu(+) to Cu(2+), and removes gaseous olefins to prevent accumulation of Cu(+)(olefin) complexes and depletion of Cu(2+). The results underscore the profound effect that the choice of metal ions, the medium, and reaction conditions exert on the photochemistry of carboxylic acids.

1,2-diketones promoted degradation of poly(epsilon-caprolactone)

NASA Astrophysics Data System (ADS)

Danko, Martin; Borska, Katarina; Ragab, Sherif Shaban; Janigova, Ivica; Mosnacek, Jaroslav

2012-07-01

Photochemical reactions of Benzil and Camphorquinone were used for modification of poly(ɛ-caprolactone) polymer films. Photochemistry of dopants was followed by infrared spectroscopy, changes on polymer chains of matrix were followed by gel permeation chromatography. Benzoyl peroxide was efficiently photochemically generated from benzyl in solid polymer matrix in the presence of air. Following decomposition of benzoyl peroxide led to degradation of matrix. Photochemical transformation of benzil in vacuum led to hydrogen abstraction from the polymer chains in higher extent, which resulted to chains recombination and formation of gel. Photochemical transformation of camphorquinone to corresponding camphoric peroxide was not observed. Only decrease of molecular weight of polymer matrix doped with camphorquinone was observed during the irradiation.

[Effects of plastic film mulching and rain harvesting modes on chlorophyll fluorescence characteristics, yield and water use efficiency of dryland maize].

PubMed

Li, Shang-Zhong; Fan, Ting-Lu; Wang, Yong; Zhao, Gang; Wang, Lei; Tang, Xiao-Ming; Dang, Yi; Zhao, Hui

2014-02-01

The differences on chlorophyll fluorescence parameters, yield and water use efficiency of dryland maize were compared among full plastic film mulching on double ridges and planting in catchment furrows (FFDRF), half plastic film mulching on double ridges and planting in catchment furrows (HFDRF), plastic film mulching on ridge and planting in film-side (FS), and flat planting with no plastic film mulching (NM) under field conditions in dry highland of Loess Plateau in 2007-2012. The results showed that fluorescence yield (Fo), the maximum fluorescence yield (Fm), light-adapted fluorescence yield when PS II reaction centers were totally open (F), light-adapted fluorescence yield when PS II reaction centers closed (Fm'), the maximal photochemical efficiency of PS II (Fv/Fm), the actual photochemical efficiency of PS II in the light (Phi PS II), the relative electron transport rate (ETR), photochemical quenching (qP) and non-photochemical quenching (qN) in maize leaves of FFDRF were higher than that of control (NM), and the value of 1-qP was lower than that of control, at 13:00, chlorophyll fluorescence parameters values of FFDRF was significantly higher than control, which were increased by 5.3%, 56.8%, 10.7%, 36.3%, 23.6%, 56.7%, 64.4%, 45.5%, 23.6% and -55.6%, respectively, compared with the control. Yield and water use efficiency of FFDRF were the highest in every year no matter dry year, normal year, humid year and hail disaster year. Average yield and water use efficiency of FFDRF were 12,650 kg x hm(-2) and 40.4 kg x mm(-1) x hm(-2) during 2007-2012, increased by 57.8% and 61.6% compared with the control, respectively, and also significantly higher compared with HFDRF and PS. Therefore, it was concluded that FFDRF had significantly increased the efficiency of light energy conversion and improved the production capacity of dryland maize.

Atmospheric Production of Perchlorate on Earth and Mars

NASA Astrophysics Data System (ADS)

Claire, M.; Catling, D. C.; Zahnle, K. J.

2009-12-01

Natural production and preservation of perchlorate on Earth occurs only in arid environments. Isotopic evidence suggests a strong role for atmospheric oxidation of chlorine species via pathways including ozone or its photochemical derivatives. As the Martian atmosphere is both oxidizing and drier than the driest places on Earth, we propose an atmospheric origin for the Martian perchlorates measured by NASA's Phoenix Lander. A variety of hypothetical formation pathways can be proposed including atmospheric photochemical reactions, electrostatic discharge, and gas-solid reactions. Here, we investigate gas phase formation pathways using a 1-D photochemical model (Catling et al. 2009, accepted by JGR). Because perchlorate-rich deposits in the Atacama desert are closest in abundance to perchlorate measured at NASA's Phoenix Lander site, we start with a study of the means to produce Atacama perchlorate. We found that perchlorate can be produced in sufficient quantities to explain the abundance of perchlorate in the Atacama from a proposed gas phase oxidation of chlorine volatiles to perchloric acid. These results are sensitive to estimated reaction rates for ClO3 species. The feasibility of gas phase production for the Atacama provides justification for further investigations of gas phase photochemistry as a possible source for Martian perchlorate. In addition to the Atacama results, we will present a preliminary study incorporating chlorine chemistry into an existing Martian photochemical model (Zahnle et al. JGR 2008).

Light-induced changes in bottled white wine and underlying photochemical mechanisms.

PubMed

Grant-Preece, Paris; Barril, Celia; Schmidtke, Leigh M; Scollary, Geoffrey R; Clark, Andrew C

2017-03-04

Bottled white wine may be exposed to UV-visible light for considerable periods of time before it is consumed. Light exposure may induce an off-flavor known as "sunlight" flavor, bleach the color of the wine, and/or increase browning and deplete sulfur dioxide. The changes that occur in bottled white wine exposed to light depend on the wine composition, the irradiation conditions, and the light exposure time. The light-induced changes in the aroma, volatile composition, color, and concentrations of oxygen and sulfur dioxide in bottled white wine are reviewed. In addition, the photochemical reactions thought to have a role in these changes are described. These include the riboflavin-sensitized oxidation of methionine, resulting in the formation of methanethiol and dimethyl disulfide, and the photodegradation of iron(III) tartrate, which gives rise to glyoxylic acid, an aldehyde known to react with flavan-3-ols to form yellow xanthylium cation pigments.

Photochemical oxidant processes in the presence of dust: An evaluation of the impact of dust on particulate nitrate and ozone formation

NASA Technical Reports Server (NTRS)

Zhang, Yang; Sunwoo, Young; Kotamarthi, Veerabhadra; Carmichael, Gregory R.

1994-01-01

The influence of dust on the tropospheric photochemical oxidant cycle is studied through the use of a detailed coupled aerosol and gas-phase chemistry model. Dust is a significant component of the troposphere throughout Asia and provides a surface for a variety of heterogeneous reactions. Dust is found to be an important surface for particulate nitrate formation. For dust loading and ambient concentrations representative of conditions in East Asia, particulate nitrate levels of 1.5-11.5 micrograms/cubic meter are predicted, consistent with measured levels in this region. Dust is also found to reduce NO(x) levels by up to 50%, HO2 concentrations by 20%-80%, and ozone production rates by up to 25%. The magnitude of the influence of dust is sensitive to mass concentration of the aerosol, relative humidity, and the value of the accommodation coefficient.

NMR Studies on the Aqueous Phase Photochemical Degradation of TNT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thorn, Kevin A.; Cox, Larry G.

2008-04-06

Aqueous phase photochemical degradation of 2,4,6-trinitrotoluene (TNT) is an important pathway in several environments, including washout lagoon soils, impact craters from partially detonated munitions that fill with rain or groundwater, and shallow marine environments containing unexploded munitions that have corroded. Knowledge of the degradation products is necessary for compliance issues on military firing ranges and formerly used defense sites. Previous laboratory studies have indicated that UV irradiation of aqueous TNT solutions results in a multicomponent product mixture, including polymerization compounds, that has been only partially resolved by mass spectrometric analyses. This study illustrates how a combination of solid and liquidmore » state 1H, 13C, and 15N NMR spectroscopy, including two dimensional analyses, provides complementary information on the total product mixture from aqueous photolysis of TNT, and the effect of reaction conditions. Among the degradation products detected were amine, amide, azoxy, azo, and carboxylic acid compounds.« less

Photochemical dissolution of Turkish lignites in tetralin at different irradiation power and reaction times

DOE Office of Scientific and Technical Information (OSTI.GOV)

F. Karacan; T. Torul

2007-08-15

The effect of the power of ultraviolet (UV) irradiation on the tetrahydrofuran (THF) solubles yield (the total soluble product) and the soluble product distribution of the dissolution of Turkish lignites (Beypazari and Tuncbilek lignite) in tetralin at ambient temperatures has been investigated. The lignite samples were exposed to UV irradiation for 1, 2, 3, 5, and 10 days in the power of irradiation ranging from 0 to 180 W at 60 W intervals. The yields of THF solubles and oils increased with increasing irradiation power and time. The optimum irradiation power depends on the irradiation time to obtain the highestmore » degradation products. However, the yield of degradation products depends also on the lignite type. The largest fraction obtained from lignites by photochemical energy is oil. While the yields of THF solubles and oils sharply increased with irradiation power at longer reaction times, the yields of asphaltenes (AS) slightly decreased. Increasing oil yields is relatively larger when AS yields tend to decrease. These trends of AS and oil yields are ascribable to conversion of AS to oils at higher power. Small changes were observed in the PAS yields under all conditions. 27 refs., 5 figs., 1 tab.« less

Spectroscopic Evidence Against Nitric Acid Trihydrate in Polar Stratospheric Clouds

NASA Technical Reports Server (NTRS)

Toon, Owen B.; Tolbert, Margaret A.

1995-01-01

Heterogeneous reactions on polar stratospheric clouds (PSC's) play a key role in the photochemical mechanism thought to be responsible for ozone depletion in the Antarctic and Arctic. Reactions of PSC particles activate chlorine to forms that are capable of photochemical ozone destruction, and sequester nitrogen oxides (NOx) that would otherwise deactivate the chlorine. Although the heterogeneous chemistry is now well established, the composition of the clouds themselves is uncertain. It is commonly thought that they are composed of nitric acid trihydrate, although observations have left this question unresolved. Here we reanalyse infrared spectra of type 1 PSCs obtained in Antarctica in September 1987, using recently measured optical constants of the various compounds that might be present in PSCs. We find these PSCs were not composed of nitric acid trihydrate but instead had a more complex compositon, perhaps that of a ternary solution. Because cloud formation is sensitive to their composition, this finding will alter our understanding of the locations and conditions in which PSCs form. In addition, the extent of ozone loss depends on the ability of the PSCs to remove NOx permanently through sedimentation, The sedimentation rates depend on PSC particle size which in turn is controlled by the composition and formation mechanism.

The composition dependence of the photochemical reactivity of strontium barium titanate

NASA Astrophysics Data System (ADS)

Bhardwaj, Abhilasha

The efficiency of particulate water photolysis catalysts is impractically low due to the recombination of intermediate species and charge carriers. The back reaction can occur easily if the oxidation and reduction sites on the surface of the catalyst are not far enough apart. It is hypothesized that it will be possible to increase the separation of the sites of the two half reactions and reduce the recombination of photogenerated charge carriers by using a ferroelectric material with permanent internal dipolar fields. This separation of the reaction sites may significantly increase the efficiency of the process. The present work compares the photochemical reactivities of ferroelectric and nonferroelectric materials (SrxBa1-xTiO 3, 0.0≤ x ≤1.0) with similar composition and structure. The reactivities are compared by measuring the color change of methylene blue dye after the aqueous dye solution reacts on the surface of ceramic sample pellets as a result of exposure to UV light. The reactivities are also compared by measuring the amount of silver that is formed when an aqueous AgNO3 solution photochemically reacts on the surface. The change in the color of the dye is measured by diffuse reflectance spectroscopy and absorbance measurements. The amount of silver is measured by atomic force microscopy. The photochemical reactivity of SrxBa1-xTiO3 shows a local maximum at the composition of the ferroelectric to non-ferroelectric transition. Also, the reactivities decrease as BaTiO3 and SrTiO3 become less pure. The dominant factors causing this trend in reactivities of SrxBa1-xTiO3 are the dielectric constant and alloy scattering. It is found that higher values of the dielectric constant increase the photochemical reactivity by enlarging the space charge region. The increase in alloy scattering in SrxBa1-xTiO 3 solid solutions as x increases from zero or decreases from 1, has adverse effect on reactivity. There are other factors such as ferroelectric polarization, relative band edge positions and pH of the solution that can influence the reactivity. However, these factors are not significant in determining the composition dependence of the photochemical reactivity of SrxBa 1-xTiO3. The comparison of the surfaces of SrxBa 1-xTiO3 samples imaged by AFM after reaction (with silver nitrate) also showed that the mode of reaction gradually changes from spatially selective reactivity for BaTiO3 to spatially uniform reactivity for SrTiO3. The spatially selective reactivity disappears completely when x in SrxBa1-xTiO3 is greater than or equal to 0.28. The mechanism of the photochemical reaction of methylene blue dye on SrxBa1-xTiO3 was also studied. It is found that the dye reacts by a mechanism similar to that of silver. The methylene blue dye and silver reduce on the surfaces of positively charged domains and the reduced reaction products remain at the reduction reaction site. Extensions of this research would be to experimentally determine the band edges and defect concentrations in SrxBa1-xTiO 3 to get a better understanding of their influence on photochemical reactivity. Since the long term goal of this research is to find a efficient particulate catalyst for photocatalysis of water, the next step in this research is to carry out the photocatalysis of water using SrxBa1-x TiO3 powders. The effect of catalyst particle size should also be analyzed.

Sources and Potential Photochemical Roles of Formaldehyde in an Urban Atmosphere in South China

NASA Astrophysics Data System (ADS)

Wang, Chuan; Huang, Xiao-Feng; Han, Yu; Zhu, Bo; He, Ling-Yan

2017-11-01

Formaldehyde (HCHO) is an important intermediate in tropospheric photochemistry. However, study of its evolution characteristics under heavy pollution conditions in China is limited, especially for high temporal resolutions, making it difficult to analyze its sources and environmental impacts. In this study, ambient levels of HCHO were monitored using a proton-transfer reaction mass spectrometer at an urban site in the Pearl River Delta of China. Continuous monitoring campaigns were conducted in the spring, summer, fall, and winter in 2016. The highest averaged HCHO concentrations were observed in autumn (5.1 ± 3.1 ppbv) and summer (5.0 ± 4.4 ppbv), followed by winter (4.2 ± 2.2 ppbv) and spring (3.4 ± 1.6 ppbv). The daily maximum of HCHO occurs in the early afternoon and shows good correlations with O3 and the secondary organic aerosol tracer during the day, revealing close relationships between ambient HCHO and secondary formations in Shenzhen, especially in summer and autumn. The daytime HCHO is estimated to be the major contributor to O3 formation and OH radical production, indicating that HCHO plays a key role in the urban atmospheric photochemical reactions. Anthropogenic secondary formation was calculated to be the dominant source of HCHO using a photochemical age-based parameterization method, with an average proportion of 39%. The contributions of biogenic sources in summer (41%) and autumn (39%) are much higher than those in spring (26%) and winter (28%), while the contributions of anthropogenic primary sources in spring (20%) and winter (18%) are twice those in summer (9%) and autumn (9%).

Mercury Isotopes in Earth and Environmental Sciences

NASA Astrophysics Data System (ADS)

Blum, Joel D.; Sherman, Laura S.; Johnson, Marcus W.

2014-05-01

Virtually all biotic, dark abiotic, and photochemical transformations of mercury (Hg) produce Hg isotope fractionation, which can be either mass dependent (MDF) or mass independent (MIF). The largest range in MDF is observed among geological materials and rainfall impacted by anthropogenic sources. The largest positive MIF of Hg isotopes (odd-mass excess) is caused by photochemical degradation of methylmercury in water. This signature is retained through the food web and measured in all freshwater and marine fish. The largest negative MIF of Hg isotopes (odd-mass deficit) is caused by photochemical reduction of inorganic Hg and has been observed in Arctic snow and plant foliage. Ratios of MDF to MIF and ratios of 199Hg MIF to 201Hg MIF are often diagnostic of biogeochemical reaction pathways. More than a decade of research demonstrates that Hg isotopes can be used to trace sources, biogeochemical cycling, and reactions involving Hg in the environment.

Photochemical reactions of cyanoacetylene and dicyanoacetylene: Possible processes in Titan's atmosphere

NASA Technical Reports Server (NTRS)

Ferris, J. P.; Guillemin, J. C.

1991-01-01

Titan has an atmosphere which is subject to dramatic chemical evolution due mainly to the dramatic effect of the UV flux from the Sun. The energetic solar photons and other particles are converting the methane-nitrogen atmosphere into the unsaturated carbon compounds observed by the Voyager probes. These same solar photons are also converting some of these unsaturated reaction products into the aerosols observed in the atmosphere which obscure the view of the surface of Titan. In particular, the photochemical reactions of cyanoacetylene, dicyanoacetylene, acetylene and ethylene may result in the formation of the higher hydrocarbons and polymers which result in the aerosols observed in Titan's atmosphere. Polymers are the principal reaction products formed by irradiation of cyanoacetylene and dicyanoacetylene. Irradiation of cyanoacetylene with 185 nm of light also yields 1,3,5-tricyanobenzene while irradiation at 254 nm yields 1,2,4-tricyanobenzene and tetracyano cyclooctatetraenes. Photolyses of mixtures of cyanoacetylene and acetylene yields mono- and di- cyanobenzenes. The 1-Cyanocyclobutene is formed from the photochemical addition of cyanoacetylene with ethylene. The photolysis of dicyanoacetylene with acetylene yields 2,3-dicyano-1,3-butadiene and 1,2-dicyanobenzene. Tetracyano cyclooctatetraene products were also observed in the photolysis of mixtures of dicyanoacetylene and acetylene with 254 nm light. The 1,2-Dicyano cyclobutene is obtained from the photolysis dicyanoacetylene and ethylene. Reaction mechanisms will be proposed to explain the observed photoproducts.

Photochemical Reactions of Tris (Oxalato) Iron (III): A First-Year Chemistry Experiment.

ERIC Educational Resources Information Center

Baker, A. D.; And Others

1980-01-01

Describes a first-year chemistry experiment that illustrates the fundamental concepts of a photoinduced reaction. Qualitative and quantitative parts of the photoreduction of potassium ferrioxalate are detailed. (CS)

Photochemical transformations of diazocarbonyl compounds: expected and novel reactions

NASA Astrophysics Data System (ADS)

Galkina, O. S.; Rodina, L. L.

2016-05-01

Photochemical reactions of diazocarbonyl compounds are well positioned in synthetic practice as an efficient method for ring contraction and homologation of carboxylic acids and as a carbene generation method. However, interpretation of the observed transformations of diazo compounds in electronically excited states is incomplete and requires a careful study of the fine mechanisms of these processes specific to different excited states of diazo compounds resorting to modern methods of investigation, including laser technology. The review is devoted to analysis of new data in the chemistry of excited states of diazocarbonyl compounds. The bibliography includes 155 references.

Kinetics of the Br2-CH3CHO Photochemical Chain Reaction

NASA Technical Reports Server (NTRS)

Nicovich, J. M.; Shackelford, C. J.; Wine, P. H.

1997-01-01

Time-resolved resonance fluorescence spectroscopy was employed in conjunction with laser flash photolysis of Br2 to study the kinetics of the two elementary steps in the photochemical chain reaction nBr2 + nCH3CHO + hv yields nCH3CBrO + nHBr. In the temperature range 255-400 K, the rate coefficient for the reaction Br((sup 2)P(sub 3/2)) + CH3CHO yields CH3CO + HBr is given by the Arrhenius expression k(sub 6)(T) = (1.51 +/- 0.20) x 10(exp -11) exp(-(364 +/- 41)/T)cu cm/(molecule.s). At 298 K, the reaction CH3CO + Br2 yields CH3CBrO + Br proceeds at a near gas kinetic rate, k(sub 7)(298 K) = (1.08 +/- 0.38) x 10(exp -10)cu cm/(molecule.s).

Recent Advances in the Synthesis of Cyclobutanes by Olefin [2 + 2] Photocycloaddition Reactions

PubMed Central

2016-01-01

The [2 + 2] photocycloaddition is undisputedly the most important and most frequently used photochemical reaction. In this review, it is attempted to cover all recent aspects of [2 + 2] photocycloaddition chemistry with an emphasis on synthetically relevant, regio-, and stereoselective reactions. The review aims to comprehensively discuss relevant work, which was done in the field in the last 20 years (i.e., from 1995 to 2015). Organization of the data follows a subdivision according to mechanism and substrate classes. Cu(I) and PET (photoinduced electron transfer) catalysis are treated separately in sections 2 and 4, whereas the vast majority of photocycloaddition reactions which occur by direct excitation or sensitization are divided within section 3 into individual subsections according to the photochemically excited olefin. PMID:27018601

Anaerobiosis Induced State Transition: A Non Photochemical Reduction of PQ Pool Mediated by NDH in Arabidopsis thaliana

PubMed Central

Tirupathi, Malavath; Subramanyam, Rajagopal

2012-01-01

Background Non photochemical reduction of PQ pool and mobilization of LHCII between PSII and PSI are found to be linked under abiotic stress conditions. The interaction of non photochemical reduction of PQ pool and state transitions associated physiological changes are critically important under anaerobic condition in higher plants. Methodology/Findings The present study focused on the effect of anaerobiosis on non-photochemical reduction of PQ pool which trigger state II transition in Arabidopsis thaliana. Upon exposure to dark-anaerobic condition the shape of the OJIP transient rise is completely altered where as in aerobic treated leaves the rise is unaltered. Rise in F o and F J was due to the loss of oxidized PQ pool as the PQ pool becomes more reduced. The increase in Fo′ was due to the non photochemical reduction of PQ pool which activated STN7 kinase and induced LHCII phosphorylation under anaerobic condition. Further, it was observed that the phosphorylated LHCII is migrated and associated with PSI supercomplex increasing its absorption cross-section. Furthermore, evidences from crr2-2 (NDH mutant) and pgr5 mutants (deficient in non NDH pathway of cyclic electron transport) have indicated that NDH is responsible for non photochemical reduction of the PQ pool. We propose that dark anaerobic condition accelerates production of reducing equivalents (such as NADPH by various metabolic pathways) which reduce PQ pool and is mediated by NDH leading to state II transition. Conclusions/Significance Anaerobic condition triggers non photochemical reduction of PQ pool mediated by NDH complex. The reduced PQ pool activates STN7 kinase leading to state II transition in A. thaliana. PMID:23185453

1,2-diketones promoted degradation of poly(epsilon-caprolactone)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Danko, Martin; Borska, Katarina; Ragab, Sherif Shaban

2012-07-11

Photochemical reactions of Benzil and Camphorquinone were used for modification of poly({epsilon}-caprolactone) polymer films. Photochemistry of dopants was followed by infrared spectroscopy, changes on polymer chains of matrix were followed by gel permeation chromatography. Benzoyl peroxide was efficiently photochemically generated from benzyl in solid polymer matrix in the presence of air. Following decomposition of benzoyl peroxide led to degradation of matrix. Photochemical transformation of benzil in vacuum led to hydrogen abstraction from the polymer chains in higher extent, which resulted to chains recombination and formation of gel. Photochemical transformation of camphorquinone to corresponding camphoric peroxide was not observed. Only decreasemore » of molecular weight of polymer matrix doped with camphorquinone was observed during the irradiation.« less

Laboratory Studies of Chemical and Photochemical Processes Relevant to Stratospheric Ozone

NASA Technical Reports Server (NTRS)

Zahniser, Mark S.; Nelson, David D.; Worsnop, Douglas R.; Kolb, Charles E.

1996-01-01

The purpose of this project is to reduce the uncertainty in several key gas-phase kinetic processes which impact our understanding of stratospheric ozone. The main emphasis of this work is on measuring rate coefficients and product channels for reactions of HOx and NOx species in the temperature range 200 K to 240 K relevant to the lower stratosphere. Other areas of study have included infrared spectroscopic studies of the HO radical, measurements of OH radical reactions with alternative fluorocarbons, and determination of the vapor pressures of nitric acid hydrates under stratospheric conditions. The results of these studies will improve models of stratospheric ozone chemistry and predictions of perturbations due to human influences.

Light limitation plays a central role in regulating DOM reactions in temperate watersheds

NASA Astrophysics Data System (ADS)

Yoon, B.; Hosen, J. D.; Kyzivat, E.; Fair, J. H.; Weber, L.; Aho, K. S.; Stubbins, A.; Lowenthal, R. S.; Raymond, P. A.

2017-12-01

Biological uptake and photochemical oxidation determine how much dissolved organic matter (DOM) can be removed and exported from inland waters. It is thus critical to understand the control on the biological and photochemical oxidation of DOM, and identify potential synergy between these two DOM removal processes. Yet, the variability of biological and photochemical lability, and the prevalence of priming effects between the two removal mechanisms are poorly understood at larger spatiotemporal scale. To address this knowledge gap, we analyzed the lability of 900 samples collected throughout the Connecticut River across two years (n = 510 for biolability, n=394 for photolability). Furthermore, we measured the effect of photochemical priming for biological removal and of biological priming for photochemical removal (n= 151, n=146, respectively). Our results show that photolability is on average 5 times greater than biolability, and that the mass of photolabile DOM can be predicted from UV absorbance at 254 nm. Photochemical DOM removal also led to additional "unlocking" of previously bio-recalcitrant DOM in 80% of the samples, and increased the biological lability by threefold on average. Scaling further, we extrapolate our model to estimate that the DOM fluxes leaving the Connecticut River and the Mississippi River are 49% and 45% photolabile, respectively. The significant photoreactivity observed across the samples and the subsequent increase in biolability demonstrate that sunlight is a more potent agent of DOM removal than the biological reactions. Yet, the photolability of DOM fluxes leaving the Connecticut River and Mississippi River indicates that the full photo-oxidation potential is not achieved due to light limitation.

Photochemical modeling of the Antarctic stratosphere: Observational constraints from the airborne Antarctic ozone experiment and implications for ozone behavior

NASA Technical Reports Server (NTRS)

Rodriguez, Jose M.; Sze, Nien-Dak; Ko, Malcolm K. W.

1988-01-01

The rapid decrease in O3 column densities observed during Antarctic spring has been attributed to several chemical mechanisms involving nitrogen, bromine, or chlorine species, to dynamical mechanisms, or to a combination of the above. Chlorine-related theories, in particular, predict greatly elevated concentrations of ClO and OClO and suppressed abundances of NO2 below 22 km. The heterogeneous reactions and phase transitions proposed by these theories could also impact the concentrations of HCl, ClNO3 and HNO3 in this region. Observations of the above species have been carried out from the ground by the National Ozone Expedition (NOZE-I, 1986, and NOZE-II, 1987), and from aircrafts by the Airborne Antarctic Ozone Experiment (AAOE) during the austral spring of 1987. Observations of aerosol concentrations, size distribution and backscattering ratio from AAOE, and of aerosol extinction coefficients from the SAM-II satellite can also be used to deduce the altitude and temporal behavior of surfaces which catalyze heterogeneous mechanisms. All these observations provide important constraints on the photochemical processes suggested for the spring Antarctic stratosphere. Results are presented for the concentrations and time development of key trace gases in the Antarctic stratosphere, utilizing the AER photochemical model. This model includes complete gas-phase photochemistry, as well as heterogeneous reactions. Heterogeneous chemistry is parameterized in terms of surface concentrations of aerosols, collision frequencies between gas molecules and aerosol surfaces, concentrations of HCl/H2O in the frozen particles, and probability of reaction per collision (gamma). Values of gamma are taken from the latest laboratory measurements. The heterogeneous chemistry and phase transitions are assumed to occur between 12 and 22 km. The behavior of trace species at higher altitudes is calculated by the AER 2-D model without heterogeneous chemistry. Calculations are performed for solar illumination conditions typical of 60, 70, and 80 S, from July 15 to October 31.

Materials and Mechanisms of Photo-Assisted Chemical Reactions under Light and Dark Conditions: Can Day-Night Photocatalysis Be Achieved?

PubMed

Sakar, M; Nguyen, Chinh-Chien; Vu, Manh-Hiep; Do, Trong-On

2018-03-09

The photoassisted catalytic reaction, conventionally known as photocatalysis, is expanding into the field of energy and environmental applications. It is widely known that the discovery of TiO 2 -assisted photochemical reactions has led to several unique applications, such as degradation of pollutants in water and air, hydrogen production through water splitting, fuel conversion, cancer treatment, antibacterial activity, self-cleaning glasses, and concrete. These multifaceted applications of this phenomenon can be enriched and expanded further if this process is equipped with more tools and functions. The term "photoassisted" catalytic reactions clearly emphasizes that photons are required to activate the catalyst; this can be transcended even into the dark if electrons are stored in the material for the later use to continue the catalytic reactions in the absence of light. This can be achieved by equipping the photocatalyst with an electron-storage material to overcome current limitations in photoassisted catalytic reactions. In this context, this article sheds lights on the materials and mechanisms of photocatalytic reactions under light and dark conditions. The manifestation of such systems could be an unparalleled technology in the near future that could influence all spheres of the catalytic sciences. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Holographic interferometry imaging monitoring of photodynamic (PDT) reactions in gelatin biophantom

NASA Astrophysics Data System (ADS)

Davidenko, N.; Mahdi, H.; Zheng, X.; Davidenko, I.; Pavlov, V.; Kuranda, N.; Chuprina, N.; Studzinsky, S.; Pandya, A.; Karia, H.; Tajouri, S.; Dervenis, M.; Gergely, C.; Douplik, A.

2018-01-01

Heat and photochemical reactions with human hemoglobin and photosensitizer were monitored by holography interference method in gelatin phantom. The method has successfully facilitated monitoring the reactions as a highresolution refraction index mapping in real time video regime. Methylene Blue was exploited as a photosensitizer.

Mechanism of the photochemical ligand substitution reactions of fac-[Re(bpy)(CO)(3)(PR(3))](+) complexes and the properties of their triplet ligand-field excited states.

PubMed

Koike, Kazuhide; Okoshi, Nobuaki; Hori, Hisao; Takeuchi, Koji; Ishitani, Osamu; Tsubaki, Hideaki; Clark, Ian P; George, Michael W; Johnson, Frank P A; Turner, James J

2002-09-25

We report herein the mechanism of the photochemical ligand substitution reactions of a series of fac-[Re(X(2)bpy)(CO)(3)(PR(3))](+) complexes (1) and the properties of their triplet ligand-field ((3)LF) excited states. The reason for the photostability of the rhenium complexes [Re(X(2)bpy)(CO)(3)(py)](+) (3) and [Re(X(2)bpy)(CO)(3)Cl] (4) was also investigated. Irradiation of an acetonitrile solution of 1 selectively gave the biscarbonyl complexes cis,trans-[Re(X(2)bpy)(CO)(2)(PR(3))(CH(3)CN)](+) (2). Isotope experiments clearly showed that the CO ligand trans to the PR(3) ligand was selectively substituted. The photochemical reactions proceeded via a dissociative mechanism from the (3)LF excited state. The thermodynamical data for the (3)LF excited states of complexes 1 and the corrective nonradiative decay rate constants for the triplet metal-to-ligand charge-transfer ((3)MLCT) states were obtained from temperature-dependence data for the emission lifetimes and for the quantum yields of the photochemical reactions and the emission. Comparison of 1 with [Re(X(2)bpy)(CO)(3)(py)](+) (3) and [Re(X(2)bpy)(CO)(3)Cl] (4) indicated that the (3)LF states of some 3- and 4-type complexes are probably accessible from the (3)MLCT state even at ambient temperature, but these complexes were stable to irradiation at 365 nm. The photostability of 3 and 4, in contrast to 1, can be explained by differences in the trans effects of the PR(3), py, and Cl(-) ligands.

From Mars Meteorites to Laboratory Investigations: Understanding Heterogeneous Photochemical Transformations Using Oxygen Triple Isotope Anomalies of Carbonates

NASA Astrophysics Data System (ADS)

Shaheen, R.; Smirnova, V.; Jackson, T. L.; Mang, L.; Thiemens, M. H.

2016-12-01

The planet Mars is unique in our solar system with a positive O-isotope anomaly observed in its bulk silicate and carbonates minerals ranging from 0.3 to 0.6 ‰. The carbonate isotopic signature can be used to reveal its origin, past history and atmosphere-hydrosphere-geosphere-interactions. Ozone is a powerful natural tracer of photochemical processes in Earth's atmosphere. It possess the highest enrichment in heavy isotopes δ17O ≈ δ18O (70-150‰) and oxygen isotopic anomaly (Δ17O = 30-40‰). The oxygen isotopic anomaly from ozone is transferred to other oxygen carrying molecules in the atmosphere through different mechanisms. Laboratory experiments were conducted with the JSC-Mars Simulant and iron oxide to investigate how this anomaly can be transferred to water and minerals under conditions similar to present day Mars. Three sets of laboratory experiments (O3-H2O-UV-minerals; O2-H2O-UV-minerals; O3-H2O-minerals) were performed. The oxygen triple isotopic analysis of product mineral carbonates formed from adsorbed CO2 reaction showed an oxygen isotopic anomaly (Δ17O = 0.4-3‰). The oxygen triple isotopic composition of water at photochemical equilibrium shifted towards ozone with Δ17O = 9‰ indicating reaction of ozone with water vapor via electronically excited oxygen atoms and transfer of the anomaly via hydroxyl radicals. HOx (HO, HO2) are extremely reactive and have very short life time (< μs), however, our data indicate that its signature is preserved through surficial interactions with adsorbed CO2 on mineral surfaces. Hydroxyl radicals may have played a significant role in heterogeneous photochemical transformations on mineral dust in the atmosphere of Mars and transfer of ozone anomaly to water and other oxygen bearing minerals through surficial reactions. Series of experiments were performed to constrain the amount of H2O required to preserve the oxygen isotope anomaly observed in carbonate minerals in the Martian meteorites. These observation will help refine Mars photochemistry models and also to constrain the past hydrological cycle and its coupling with the regolith. The observed inverse correlation between ozone and water vapor also suggests a dynamic role of hydroxyl radical chemistry in the atmosphere of Mars.

A Universal Protocol for Photochemical Covalent Immobilization of Intact Carbohydrates for the Preparation of Carbohydrate Microarrays

PubMed Central

Wang, Huibin; Zhang, Yiming; Yuan, Xun; Chen, Yi; Yan, Mingdi

2010-01-01

A universal photochemical method has been established for the immobilization of intact carbohydrates and their analogues, and for the fabrication of carbohydrate microarrays. The method features the use of perfluorophenyl azide (PFPA)-modified substrates and the photochemical reaction of surface azido groups with printed carbohydrates. Various aldoses, ketoses, non-reducing sugars such as alditols and their derivatives can be directly arrayed on the PFPA-modified chips. The lectin-recognition ability of arrayed mannose, glucose and their oligo- and polysaccharides were confirmed using surface plasmon resonance imaging and laser-induced fluorescence imaging. PMID:21138274

A universal protocol for photochemical covalent immobilization of intact carbohydrates for the preparation of carbohydrate microarrays.

PubMed

Wang, Huibin; Zhang, Yiming; Yuan, Xun; Chen, Yi; Yan, Mingdi

2011-01-19

A universal photochemical method has been established for the immobilization of intact carbohydrates and their analogues, and for the fabrication of carbohydrate microarrays. The method features the use of perfluorophenyl azide (PFPA)-modified substrates and the photochemical reaction of surface azido groups with printed carbohydrates. Various aldoses, ketoses, nonreducing sugars such as alditols, and their derivatives can be directly arrayed on the PFPA-modified chips. The lectin-recognition ability of arrayed mannose, glucose, and their oligo- and polysaccharides were confirmed using surface plasmon resonance imaging and laser-induced fluorescence imaging.

Photoinduced ethane formation from reaction of ethene with matrix-isolated Ti, V, or Nb atoms.

PubMed

Thompson, Matthew G K; Parnis, J Mark

2005-10-27

The reactions of matrix-isolated Ti, V, or Nb atoms with ethene (C(2)H(4)) have been studied by FTIR absorption spectroscopy. Under conditions where the ethene dimer forms, metal atoms react with the ethene dimer to yield matrix-isolated ethane (C(2)H(6)) and methane. Under lower ethene concentration conditions ( approximately 1:70 ethene/Ar), hydridic intermediates of the types HMC(2)H(3) and H(2)MC(2)H(2) are also observed, and the relative yield of hydrocarbons is diminished. Reactions of these metals with perdeuterioethene, and equimolar mixtures of C(2)H(4) and C(2)D(4), yield products that are consistent with the production of ethane via a metal atom reaction involving at least two C(2)H(4) molecules. The absence of any other observed products suggests the mechanism also involves production of small, highly symmetric species such as molecular hydrogen and metal carbides. Evidence is presented suggesting that ethane production from the ethene dimer is a general photochemical process for the reaction of excited-state transition-metal atoms with ethene at high concentrations of ethene.

Photochemical mechanisms of ocular photic injury (Abstract Only)

NASA Astrophysics Data System (ADS)

Stuck, Bruce E.; Lund, David J.; Zuclich, Joseph A.

2000-03-01

Mechanisms of photic injury to the eye can be categorized as photochemical, photothermal or photodistruptive. Exposure wavelength, exposure duration, ocular tissue characteristics and response criteria are key factors in the delineation of the ocular injury mechanisms. Depending on the exposure condition, one or all of the laser-tissue interaction mechanisms can be involved. Although photic injury to the eye was initially assumed to involve thermal mechanisms, more recent research has demonstrated that ocular effects can be produced by light exposure without a significant retinal temperature rise. Photochemical mechanisms are also implicated in UV photic injury to the cornea and lens. Exposure of the retina to short visible wavelengths for prolonged durations results in photochemical retinal damage with negligible localized retinal temperature elevation. For exposure conditions where photochemical mechanisms are dominate, the reciprocity of irradiance and exposure duration is apparent. The latency until observation of a photochemical lesion is often 24-48 hours whereas a thermal lesion is observed immediately or within a few hours after the exposure. Action spectra for photochemical injury to the eye are discussed in the context of ocular injury thresholds and current permissible exposure limits.

Evaluated kinetic and photochemical data for atmospheric chemistry

NASA Technical Reports Server (NTRS)

Baulch, D. L.; Cox, R. A.; Hampson, R. F., Jr.; Kerr, J. A.; Troe, J.; Watson, R. T.

1980-01-01

This paper contains a critical evaluation of the kinetics and photochemistry of gas phase chemical reactions of neutral species involved in middle atmosphere chemistry (10-55 km altitude). Data sheets have been prepared for 148 thermal and photochemical reactions, containing summaries of the available experimental data with notes giving details of the experimental procedures. For each reaction a preferred value of the rate coefficient at 298 K is given together with a temperature dependency where possible. The selection of the preferred value is discussed, and estimates of the accuracies of the rate coefficients and temperature coefficients have been made for each reaction. The data sheets are intended to provide the basic physical chemical data needed as input for calculations which model atmospheric chemistry. A table summarizing the preferred rate data is provided, together with an appendix listing the available data on enthalpies of formation of the reactant and product species.

Accelerated gas-liquid visible light photoredox catalysis with continuous-flow photochemical microreactors.

PubMed

Straathof, Natan J W; Su, Yuanhai; Hessel, Volker; Noël, Timothy

2016-01-01

In this protocol, we describe the construction and use of an operationally simple photochemical microreactor for gas-liquid photoredox catalysis using visible light. The general procedure includes details on how to set up the microreactor appropriately with inlets for gaseous reagents and organic starting materials, and it includes examples of how to use it to achieve continuous-flow preparation of disulfides or trifluoromethylated heterocycles and thiols. The reported photomicroreactors are modular, inexpensive and can be prepared rapidly from commercially available parts within 1 h even by nonspecialists. Interestingly, typical reaction times of gas-liquid visible light photocatalytic reactions performed in microflow are lower (in the minute range) than comparable reactions performed as a batch process (in the hour range). This can be attributed to the improved irradiation efficiency of the reaction mixture and the enhanced gas-liquid mass transfer in the segmented gas-liquid flow regime.

Experimental study of heterogeneous organic chemistry induced by far ultraviolet light: Implications for growth of organic aerosols by CH3 addition in the atmospheres of Titan and early Earth

NASA Astrophysics Data System (ADS)

Hong, Peng; Sekine, Yasuhito; Sasamori, Tsutoni; Sugita, Seiji

2018-06-01

Formation of organic aerosols driven by photochemical reactions has been observed and suggested in CH4-containing atmospheres, including Titan and early Earth. However, the detailed production and growth mechanisms of organic aerosols driven by solar far ultraviolet (FUV) light remain poorly constrained. We conducted laboratory experiments simulating photochemical reactions in a CH4sbnd CO2 atmosphere driven by the FUV radiations dominated by the Lyman-α line. In the experiments, we analyzed time variations in thickness and infrared spectra of solid organic film formed on an optical window in a reaction cell. Gas species formed by FUV irradiation were also analyzed and compared with photochemical model calculations. Our experimental results show that the growth rate of the organic film decreases as the CH4/CO2 ratio of reactant gas mixture decreases, and that the decrease becomes very steep for CH4/CO2 < 1. Comparison with photochemical model calculations suggests that polymerizations of gas-phase hydrocarbons, such as polyynes and aromatics, cannot account for the growth rate of the organic film but that the addition reaction of CH3 radicals onto the organic film with the reaction probability around 10-2 can explain the growth rate. At CH4/CO2 < 1, etching by O atom formed by CO2 photolysis would reduce or inhibit the growth of the organic film. Our results suggest that organic aerosols would grow through CH3 addition onto the surface during the precipitation of aerosol particles in the middle atmosphere of Titan and early Earth. On Titan, effective CH3 addition would reduce C2H6 production in the atmosphere. On early Earth, growth of aerosol particles would be less efficient than those on Titan, possibly resulting in small-sized monomers and influencing UV shielding.

A dual-catalysis approach to enantioselective [2 + 2] photocycloadditions using visible light.

PubMed

Du, Juana; Skubi, Kazimer L; Schultz, Danielle M; Yoon, Tehshik P

2014-04-25

In contrast to the wealth of catalytic systems that are available to control the stereochemistry of thermally promoted cycloadditions, few similarly effective methods exist for the stereocontrol of photochemical cycloadditions. A major unsolved challenge in the design of enantioselective catalytic photocycloaddition reactions has been the difficulty of controlling racemic background reactions that occur by direct photoexcitation of substrates while unbound to catalyst. Here, we describe a strategy for eliminating the racemic background reaction in asymmetric [2 + 2] photocycloadditions of α,β-unsaturated ketones to the corresponding cyclobutanes by using a dual-catalyst system consisting of a visible light-absorbing transition-metal photocatalyst and a stereocontrolling Lewis acid cocatalyst. The independence of these two catalysts enables broader scope, greater stereochemical flexibility, and better efficiency than previously reported methods for enantioselective photochemical cycloadditions.

Direct evidence of photochemical α-cleavage of benzoin in fluid solutions

NASA Astrophysics Data System (ADS)

Koyanagi, Motohiko; Futami, Hiroshi; Mukai, Masahiro; Yamauchi, Seigo

1989-02-01

By means of optical absorption, 1 NMR, and transient EPR techniques, the fate of diluted benzoin upon light irradiation to its S 1 (nπ*) state has been investigated in methylcyclohexane and benzene solutions at room temperature. The CIDEP spectrum of benzoin is observed for the first time, and the intermediate radicals involved are assigned. The overall results show that the main scheme of the photochemical reactions is the α-cleavage occurring in the excited triplet state of benzoin, as proved in the almost net emission pattern of the CIDEP spectra. A stoichiometric reaction leading to effective benzaldehyde formation is established for the benzoin solutions.

Photochemical reduction of cytochrome c by a 1,4,5,8-naphthalenediimide radical anion.

PubMed

Campos, Ivana B; Nantes, Iseli L; Politi, Mario J; Brochsztain, Sergio

2004-01-01

Steady-state UV irradiation of aqueous solutions containing cytochrome c (cyt c) and N,N'-bis(2-phosphonoethyl)-1,4,5,8-naphthalenediimide (BPNDI), a water-soluble aromatic imide, resulted in the reduction of the heme iron from the Fe(III) to the Fe(II) oxidation state. The reaction kinetics were followed by the increase of the ferrocytochrome c absorbance band at 549 nm. The rate of the photochemical reaction was pH dependent, reaching its maximum values over the pH range 4-7. Addition of electrolyte (NaCl) at pH 5 resulted in a decrease in the reaction rate, as expected for reactions between oppositely charged species. Flash photolysis studies revealed that the actual reductant in the reaction was a photogenerated BPNDI radical anion, which transferred an electron to the cyt c heme iron. The participation of imide radicals in the process was confirmed by the ready reduction of cyt c by BPNDI radicals chemically generated with sodium dithionite.

A box model study on photochemical interactions between VOCs and reactive halogen species in the marine boundary layer

NASA Astrophysics Data System (ADS)

Toyota, K.; Kanaya, Y.; Takahashi, M.; Akimoto, H.

2004-09-01

A new chemical scheme is developed for the multiphase photochemical box model SEAMAC (size-SEgregated Aerosol model for Marine Air Chemistry) to investigate photochemical interactions between volatile organic compounds (VOCs) and reactive halogen species in the marine boundary layer (MBL). Based primarily on critically evaluated kinetic and photochemical rate parameters as well as a protocol for chemical mechanism development, the new scheme has achieved a near-explicit description of oxidative degradation of up to C3-hydrocarbons (CH4, C2H6, C3H8, C2H4, C3H6, and C2H2) initiated by reactions with OH radicals, Cl- and Br-atoms, and O3. Rate constants and product yields for reactions involving halogen species are taken from the literature where available, but the majority of them need to be estimated. In particular, addition reactions of halogen atoms with alkenes will result in forming halogenated organic intermediates, whose photochemical loss rates are carefully evaluated in the present work. Model calculations with the new chemical scheme reveal that the oceanic emissions of acetaldehyde (CH3CHO) and alkenes (especially C3H6) are important factors for regulating reactive halogen chemistry in the MBL by promoting the conversion of Br atoms into HBr or more stable brominated intermediates in the organic form. The latter include brominated hydroperoxides, bromoacetaldehyde, and bromoacetone, which sequester bromine from a reactive inorganic pool. The total mixing ratio of brominated organic species thus produced is likely to reach 10-20% or more of that of inorganic gaseous bromine species over wide regions over the ocean. The reaction between Br atoms and C2H2 is shown to be unimportant for determining the degree of bromine activation in the remote MBL. These results imply that reactive halogen chemistry can mediate a link between the oceanic emissions of VOCs and the behaviors of compounds that are sensitive to halogen chemistry such as dimethyl sulfide, NOx, and O3 in the MBL.

High-temperature photochemical destruction of toxic organic wastes using concentrated solar radiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dellinger, B.; Graham, J.L.; Berman, J.M.

1994-05-01

Application of concentrated solar energy has been proposed to be a viable waste disposal option. Specifically, this concept of solar induced high-temperature photochemistry is based on the synergistic contribution of concentrated infrared (IR) radiation, which acts as an intense heating source, and near ultraviolet and visible (UV-VIS) radiation, which can induce destructive photochemical processes. Some significant advances have been made in the theoretical framework of high-temperature photochemical processes (Section 2) and development of experimental techniques for their study (Section 3). Basic thermal/photolytic studies have addressed the effect of temperature on the photochemical destruction of pure compounds (Section 4). Detailed studiesmore » of the destruction of reaction by-products have been conducted on selected waste molecules (Section 5). Some very limited results are available on the destruction of mixtures (Section 6). Fundamental spectroscopic studies have been recently initiated (Section 7). The results to date have been used to conduct some relatively simple scale-up studies of the solar detoxification process. More recent work has focused on destruction of compounds that do not directly absorb solar radiation. Research efforts have focused on homogeneous as well as heterogeneous methods of initiating destructive reaction pathways (Section 9). Although many conclusions at this point must be considered tentative due to lack of basic research, a clearer picture of the overall process is emerging (Section 10). However, much research remains to be performed and most follow several veins, including photochemical, spectroscopic, combustion kinetic, and engineering scale-up (Section 11).« less

Investigation of the Photochemical Method for Uranium Isotope Separation

DOE R&D Accomplishments Database

Urey, H. C.

1943-07-10

To find a process for successful photochemical separation of isotopes several conditions have to be fulfilled. First, the different isotopes have to show some differences in the spectrum. Secondly, and equally important, this difference must be capable of being exploited in a photochemical process. Parts A and B outline the physical and chemical conditions, and the extent to which one might expect to find them fulfilled. Part C deals with the applicability of the process.

Sunlight-induced Transformations of Graphene-based Nanomaterials in Aquatic Environments

EPA Science Inventory

Graphene-based nanomaterials and other related carbon nanomaterials (CNMs) can be released from products during their life cycles. Upon entry into aquatic environments, they are potentially transformed by photochemical reactions, oxidation reactions and biological processes, all ...

Likelihood of achieving air quality targets under model uncertainties.

PubMed

Digar, Antara; Cohan, Daniel S; Cox, Dennis D; Kim, Byeong-Uk; Boylan, James W

2011-01-01

Regulatory attainment demonstrations in the United States typically apply a bright-line test to predict whether a control strategy is sufficient to attain an air quality standard. Photochemical models are the best tools available to project future pollutant levels and are a critical part of regulatory attainment demonstrations. However, because photochemical models are uncertain and future meteorology is unknowable, future pollutant levels cannot be predicted perfectly and attainment cannot be guaranteed. This paper introduces a computationally efficient methodology for estimating the likelihood that an emission control strategy will achieve an air quality objective in light of uncertainties in photochemical model input parameters (e.g., uncertain emission and reaction rates, deposition velocities, and boundary conditions). The method incorporates Monte Carlo simulations of a reduced form model representing pollutant-precursor response under parametric uncertainty to probabilistically predict the improvement in air quality due to emission control. The method is applied to recent 8-h ozone attainment modeling for Atlanta, Georgia, to assess the likelihood that additional controls would achieve fixed (well-defined) or flexible (due to meteorological variability and uncertain emission trends) targets of air pollution reduction. The results show that in certain instances ranking of the predicted effectiveness of control strategies may differ between probabilistic and deterministic analyses.

Thermal and Photochemical Reactions of NO2 on a Chromium (III) Oxide Surface

NASA Astrophysics Data System (ADS)

Nishino, N.; Finlayson-Pitts, B. J.

2011-12-01

Chromium oxide (Cr2O3) is a major component of the oxide layer on stainless steel surfaces. It is also widely used as pigment in paints and roofs and as a protective coating on various surfaces. While many studies have focused on the catalytic activity of Cr2O3 surfaces for selective catalytic reduction (SCR), less attention has been paid to its surface chemistry involving atmospherically important species such as NO2 under atmospheric conditions. In this study, we have investigated thermal and photochemical reactions of NO2 in the presence and the absence of water vapor, using a thin layer of Cr2O3 as a model for the surface of stainless steel as well as other similarly coated surfaces in the boundary layer. A 30 nm thick Cr2O3 film was deposited on a germanium attenuated total reflectance (ATR) crystal, and the changes in the surface species were monitored by Fourier Transform Infrared (FTIR) spectroscopy. Upon NO2 adsorption, nitrate (NO3-) ions appeared likely coordinated to Cr3+ ion(s). The NO3- peaks reversibly shifted when water vapor was added, suggesting that NO3- become solvated. Irradiation at 311 nm led to a decrease in NO3- ions under both dry and humid conditions. The major gas-phase species formed by the irradiation was NO under dry conditions, while NO2 was mainly formed in the presence of H2O. Possible mechanisms and the implications for heterogeneous NO2 chemistry in the boundary layer will be discussed. The results will also be compared to similar chemistry on other surfaces.

Primary photochemical processes in fac-ClRe(CO){sub 3}L{sub 2} (L = 4-phenylpyridine and 4-cyanopyridine): A steady-state and flash photochemical study of reaction products and intermediates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feliz, M.; Ferraudi, G.; Altmiller, H.

1992-01-09

The photochemistry of fac-ClRe(CO){sub 3}L{sub 2}, L = 4-phenylpyridine and 4-cyanopyridine, has been investigated by monochromatic steady-state and flash photolyses between 400 and 229 nm. Two parallel photoprocesses, the photogeneration of the emissive MLCT state and the photoredox dissociation in (ClRe(CO){sub 3}L{sup +}, L{sup {sm_bullet}{minus}}) products, have been observed with both compounds. A third photoprocess, namely, the photogeneration of a Re(I)-ligand biradical, has been observed only in photolyses of the 4-phenylpyridine complex. While this Re(I)-ligand biradical reduces Cu{sup II}(TIM){sup 2+} to the corresponding Cu(I) species, no such reaction is undergone by the MLCT state. Differences between the electronic structures ofmore » these complexes, shown by extended Hueckel MO calculations, were related to their intrinsic photochemical behavior. 54 refs., 9 figs., 1 tab.« less

Photogeochemical reactions of manganese under anoxic conditions

NASA Astrophysics Data System (ADS)

Liu, W.; Yee, N.; Piotrowiak, P.; Falkowski, P. G.

2017-12-01

Photogeochemistry describes reactions involving light and naturally occurring chemical species. These reactions often involve a photo-induced electron transfer that does not occur in the absence of light. Although photogeochemical reactions have been known for decades, they are often ignored in geochemical models. In particular, reactions caused by UV radiation during an ozone free early Earth could have influenced the available oxidation states of manganese. Manganese is one of the most abundant transition metals in the crust and is important in both biology and geology. For example, the presence of manganese (VI) oxides in the geologic record has been used as a proxy for oxygenic photosynthesis; however, we suggest that the high oxidation state of Mn can be produced abiotically by photochemical reactions. Aqueous solutions of manganese (II) as well as suspensions of rhodochrosite (MnCO3) were irradiated under anoxic condition using a 450 W mercury lamp and custom built quartz reaction vessels. The photoreaction of the homogeneous solution of Mn(II) produced H2 gas and akhtenskite (ɛ-MnO2) as the solid product . This product is different than the previously identified birnessite. The irradiation of rhodochrosite suspensions also produced H2 gas and resulted in both a spectral shift as well as morphology changes of the mineral particles in the SEM images. These reactions offer alternative, abiotic pathways for the formation of manganese oxides.

Characterizing non-photochemical quenching in leaves through fluorescence lifetime snapshots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sylak-Glassman, Emily J.; Zaks, Julia; Amarnath, Kapil

2015-03-12

A technique is described to measure the fluorescence decay profiles of intact leaves during adaptation to high light and subsequent relaxation to dark conditions. We illustrate how to ensure that photosystem II reaction centers are closed and compare data for wild type Arabidopsis thaliana with conventional pulse-amplitude modulated (PAM) fluorescence measurements. Unlike PAM measurements, the lifetime measurements are not sensitive to photobleaching or chloroplast shielding, and the form of the fluorescence decay provides additional information to test quantitative models of excitation dynamics in intact leaves.

Photochemical transformations accelerated in continuous-flow reactors: basic concepts and applications.

PubMed

Su, Yuanhai; Straathof, Natan J W; Hessel, Volker; Noël, Timothy

2014-08-18

Continuous-flow photochemistry is used increasingly by researchers in academia and industry to facilitate photochemical processes and their subsequent scale-up. However, without detailed knowledge concerning the engineering aspects of photochemistry, it can be quite challenging to develop a suitable photochemical microreactor for a given reaction. In this review, we provide an up-to-date overview of both technological and chemical aspects associated with photochemical processes in microreactors. Important design considerations, such as light sources, material selection, and solvent constraints are discussed. In addition, a detailed description of photon and mass-transfer phenomena in microreactors is made and fundamental principles are deduced for making a judicious choice for a suitable photomicroreactor. The advantages of microreactor technology for photochemistry are described for UV and visible-light driven photochemical processes and are compared with their batch counterparts. In addition, different scale-up strategies and limitations of continuous-flow microreactors are discussed. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Spectroscopic Evidence Against Nitric Acid Trihydrate in Polar Stratospheric Clouds

NASA Technical Reports Server (NTRS)

Toon, Owen B.; Tolbert, Margaret A.

1995-01-01

Heterogeneous reactions on polar stratospheric clouds (PSC's) play a key role in the photochemical mechanisms thought to be responsible for ozone depletion in the Antarctic and the Arctic. Reactions on PSC particles activate chlorine to forms that are capable of photochemical ozone destruction, and sequester nitrogen oxides (NOx) that would otherwise deactivate the chlorine. Although the heterogeneous chemistry is now well established, the composition of the clouds themselves is uncertain. It is commonly thought that they are composed of nitric acid trihydrate, although observations have left this question unresolved. Here we reanalyse infrared spectra of type I PCS's obtained in Antarctica in September 1987, using recently measured optical constraints of the various compounds that might be present in PSC's. We find that these PSC's were not composed of nitric acid trihydrate but instead had a more complex composition perhaps that of a ternary solution. Because cloud formation is sensitive to their composition, this finding will alter our understanding of the locations and conditions in which PSCs form. In addition, the extent of ozone loss depends on the ability of the PSC's to remove NOx permanently through sedimentation. The sedimentation rates depend on PSC particle size which in turn is controlled by the composition and formation mechanism.

Photochemistry of biogenic emissions over the Amazon forest

NASA Technical Reports Server (NTRS)

Jacob, Daniel J.; Wofsy, Steven C.

1988-01-01

The boundary layer chemistry over the Amazon forest during the dry season is simulated with a photochemical model. Results are in good agreement with measurements of isoprene, NO, ozone, and organic acids. Photochemical reactions of biogenic isoprene and NOx can supply most of the ozone observed in the boundary layer. Production of ozone is very sensitive to the availability of NOx, but is insensitive to the isoprene source strength. High concentrations of total odd nitrogen (NOy) are predicted for the planetary boundary layer, about 1 ppb in the mixed layer and 0.75 ppb in the convective cloud layer. Most of the odd nitrogen is present as PAN-type species, which are removed by dry deposition to the forest. The observed daytime variations of isoprene are explained by a strong dependence of the isoprene emission flux on sun angle. Nighttime losses of isoprene exceed rates of reaction with NO3 and O3 and appear to reflect dry-deposition processes. The 24-hour averaged isoprene emission flux is calculated to be 38 mg/sq m per day. Photooxidation of isoprene could account for a large fraction of the CO enrichment observed in the boundary layer under unpolluted conditions and could constitute an important atmospheric source of formic acid, methacrylic acid, and pyruvic acid.

On the detection of carbon monoxide as an anti-biosignature in exoplanetary atmospheres

NASA Astrophysics Data System (ADS)

Wang, Yuwei; Tian, Feng; Li, Tong; Hu, Yongyun

2016-03-01

Recent works suggest that oxygen can be maintained on lifeless exoplanets in the habitable zones of M dwarfs as the results of photochemical reactions. However, the same photochemical models also predict high concentrations of carbon monoxide (CO) in the corresponding atmospheres. Here we use a line-by-line radiative transfer model to investigate the observation requirements of O2 and CO in such atmospheres. The results show that photochemically produced CO can be readily detected at 1.58, 2.34, and 4.67 μm. We suggest that future missions aiming at characterization of exoplanetary atmospheres consider detections of CO as an anti-biosignature.

SOA FROM ISOPRENE OXIDATION PRODUCTS: MODEL SIMULATION OF CLOUD CHEMISTRY

EPA Science Inventory

Recent laboratory evidence supports the hypothesis that secondary organic aerosol (SOA) is formed in the atmosphere through aqueous-phase reactions in clouds. The results of batch photochemical reactions of glyoxal, methylglyoxal and hydrogen peroxide are presented. These labor...

Acrylic Tanks for Stunning Chemical Demonstrations

ERIC Educational Resources Information Center

Mirholm, Alexander; Ellervik, Ulf

2009-01-01

We describe the use of acrylic tanks (400 x 450 x 27 mm) for visualization of chemical demonstrations in aqueous solutions. Examples of well-suited demonstrations are oscillating reactions, pH indicators, photochemical reduction of Lauth's violet, and chemoluminiscent reactions. (Contains 1 figure.)

Photochemical reduction of UO(2)(2+) in the presence of alcohol studied by density functional theory calculations.

PubMed

Tsushima, Satoru

2009-06-01

A well-known photochemical process of U(VI)O(2)(2+) reduction to U(V)O(2)(+) in the presence of alcohols was studied by density functional theory (DFT) calculations. It was found that the first process which takes place is a photoexcitation of the ground-state UO(2)(2+) to the triplet excited state (*UO(2)(2+)) followed by a significant shortening of the *UO(2)(2+)-to-alcohol O(ax)-H distance. A charge transfer from *UO(2)(2+) to alcohol and hydrogen abstraction takes place in the following step. Consequently, U(VI)O(2)(2+) gets reduced to U(V)O(OH)(2+). The photochemical byproduct RCHOH acts further as a reducing agent toward UO(2)(2+) to yield UO(2)(+) and RCHO (aldehyde). Only a combination of these two reactions can explain a high quantum yield of this reaction. In the absence of alcohol, the lowest-lying triplet state exhibits a different character, and photoreduction is unlikely to take place via the same mechanism. The present results agree well with recent experimental finding [J. Am. Chem. Soc. 2006, 128, 14024] and supports the idea that the O(ax)-H linkage between UO(2)(2+) and the solvent molecule is the key to the photochemical reduction process.

Diels-Alder Trapping of Photochemically Generated o-Quinodimethane Intermediates: An Alternative Route to Photocured Polymer Film Development

NASA Technical Reports Server (NTRS)

Tyson, Daniel S.; Ilhan, Faysal; Meador, Mary Ann B.; Smith, Dee Dee; Scheiman, Daniel A.; Meador, Michael A.

2004-01-01

Photolysis of o-methylphenyl ketones generates bis-o-quinodimethane intermediates that can be trapped in situ by dienophiles through Diels-Alder cycloadditions. This well-known photochemical process is applied to a series of six new photoreactive monomers containing bis-(o-methylphenyl ketone) functionalities combined with diacrylate and triacrylate ester monomers for the development of acrylic ester copolymer blends. Irradiation of cyclohexanone solutions of the bis-(o-methylphenyl ketone)s and acrylate esters produce thin polymer films. Solid state 13C NMR data indicated 47- 100% reaction of the bis-(o-methylphenyl ketone)s, depending on experimental conditions, to yield the desired products. DSC and TGA analyses were performed to determine the glass transition temperature, T,, and onset of decomposition, Td, of the resulting polymer films. A statistical Design of Experiments approach was used to obtain a systematic understanding of the effects of experimental variables on the extent of polymerization and the final polymer properties.

Modeling of a solar-pumped iodine laser

NASA Technical Reports Server (NTRS)

Wilson, J. W.; Lee, J. H.

1980-01-01

The direct conversion in space of solar radiation into laser radiation for power transmission to earth, satellites, or deep space probes shows promise as a reasonably simple technology and may have cost advantage in deployment and greater reliability compared to other methods of space power generation and transmission. The main candidates for solar pumping are the gas dynamic, photochemical, and direct photoexcited lasers. Here consideration is given to the photochemical reaction of alkyliodides which predominantly excite the I(2P1/2) state which then lases at 1.315 microns. The iodine ground state is eventually lost to reconstituting the gas or in the formation of molecular iodine. The rates at which the gas is required to be recycled through the laser system are modest. The side exposure at 100-fold solar concentration of a 100-m long tube with a 1 sq m cross section is estimated to provide 20 kW of continuous laser output. Scaling laws and optimum operating conditions of this system are discussed.

Introductory study of the chemical behavior of jet emissions in photochemical smog. [computerized simulation

NASA Technical Reports Server (NTRS)

Whitten, G. Z.; Hogo, H.

1976-01-01

Jet aircraft emissions data from the literature were used as initial conditions for a series of computer simulations of photochemical smog formation in static air. The chemical kinetics mechanism used in these simulations was an updated version which contains certain parameters designed to account for hydrocarbon reactivity. These parameters were varied to simulate the reaction rate constants and average carbon numbers associated with the jet emissions. The roles of surface effects, variable light sources, NO/NO2 ratio, continuous emissions, and untested mechanistic parameters were also assessed. The results of these calculations indicate that the present jet emissions are capable of producing oxidant by themselves. The hydrocarbon/nitrous oxides ratio of present jet aircraft emissions is much higher than that of automobiles. These two ratios appear to bracket the hydrocarbon/nitrous oxides ratio that maximizes ozone production. Hence an enhanced effect is seen in the simulation when jet exhaust emissions are mixed with automobile emissions.

Method and apparatus for removing and preventing window deposition during photochemical vapor deposition (photo-CVD) processes

DOEpatents

Tsuo, S.; Langford, A.A.

1989-03-28

Unwanted build-up of the film deposited on the transparent light-transmitting window of a photochemical vacuum deposition (photo-CVD) chamber is eliminated by flowing an etchant into the part of the photolysis region in the chamber immediately adjacent the window and remote from the substrate and from the process gas inlet. The respective flows of the etchant and the process gas are balanced to confine the etchant reaction to the part of the photolysis region proximate to the window and remote from the substrate. The etchant is preferably one that etches film deposit on the window, does not etch or affect the window itself, and does not produce reaction by-products that are deleterious to either the desired film deposited on the substrate or to the photolysis reaction adjacent the substrate. 3 figs.

Method and apparatus for removing and preventing window deposition during photochemical vapor deposition (photo-CVD) processes

DOEpatents

Tsuo, Simon; Langford, Alison A.

1989-01-01

Unwanted build-up of the film deposited on the transparent light-transmitting window of a photochemical vacuum deposition (photo-CVD) chamber is eliminated by flowing an etchant into the part of the photolysis region in the chamber immediately adjacent the window and remote from the substrate and from the process gas inlet. The respective flows of the etchant and the process gas are balanced to confine the etchant reaction to the part of the photolysis region proximate to the window and remote from the substrate. The etchant is preferably one that etches film deposit on the window, does not etch or affect the window itself, and does not produce reaction by-products that are deleterious to either the desired film deposited on the substrate or to the photolysis reaction adjacent the substrate.

A Dual-Catalysis Approach to Enantioselective [2+2] Photocycloadditions Using Visible Light

PubMed Central

Du, Juana; Skubi, Kazimer L.; Schultz, Danielle M.; Yoon, Tehshik P.

2015-01-01

In contrast to the wealth of catalytic systems that are available to control the stereochemistry of thermally promoted cycloadditions, few similarly effective methods exist for the stereocontrol of photochemical cycloadditions. A major unsolved challenge in the design of enantioselective catalytic photocycloaddition reactions has been the difficulty of controlling racemic background reactions that occur by direct photoexcitation of substrates while unbound to catalyst. Here we describe a strategy for eliminating the racemic background reaction in asymmetric [2+2] photocycloadditions of α,β-unsaturated ketones to the corresponding cyclobutanes by employing a dual-catalyst system consisting of a visible light-absorbing transition metal photocatalyst and a stereocontrolling Lewis acid co-catalyst. The independence of these two catalysts enables broader scope, greater stereochemical flexibility, and better efficiency than previously reported methods for enantioselective photochemical cycloadditions. PMID:24763585

Laser isotope separation

DOEpatents

Robinson, C. Paul; Jensen, Reed J.; Cotter, Theodore P.; Boyer, Keith; Greiner, Norman R.

1988-01-01

A process and apparatus for separating isotopes by selective excitation of isotopic species of a volatile compound by tuned laser light. A highly cooled gas of the volatile compound is produced in which the isotopic shift is sharpened and defined. Before substantial condensation occurs, the cooled gas is irradiated with laser light precisely tuned to a desired wavelength to selectively excite a particular isotopic species in the cooled gas. The laser light may impart sufficient energy to the excited species to cause it to undergo photolysis, photochemical reaction or even to photoionize. Alternatively, a two-photon irradiation may be applied to the cooled gas to induce photolysis, photochemical reaction or photoionization. The process is particularly applicable to the separation of isotopes of uranium.

Isotope separation by laser means

DOEpatents

Robinson, C. Paul; Jensen, Reed J.; Cotter, Theodore P.; Greiner, Norman R.; Boyer, Keith

1982-06-15

A process for separating isotopes by selective excitation of isotopic species of a volatile compound by tuned laser light. A highly cooled gas of the volatile compound is produced in which the isotopic shift is sharpened and defined. Before substantial condensation occurs, the cooled gas is irradiated with laser light precisely tuned to a desired wavelength to selectively excite a particular isotopic species in the cooled gas. The laser light may impart sufficient energy to the excited species to cause it to undergo photochemical reaction or even to photoionize. Alternatively, a two-photon irradiation may be applied to the cooled gas to induce photochemical reaction or photoionization. The process is particularly applicable to the separation of isotopes of uranium and plutonium.

Diagnostic analysis of two-dimensional monthly average ozone balance with Chapman chemistry

NASA Technical Reports Server (NTRS)

Stolarski, Richard S.; Jackman, Charles H.; Kaye, Jack A.

1986-01-01

Chapman chemistry has been used in a two-dimensional model to simulate ozone balance phenomenology. The similarity between regions of ozone production and loss calculated using Chapman chemistry and those computed using LIMS and SAMS data with a photochemical equilibrium model indicate that such simplified chemistry is useful in studying gross features in stratospheric ozone balance. Net ozone production or loss rates are brought about by departures from the photochemical equilibrium (PCE) condition. If transport drives ozone above its PCE condition, then photochemical loss dominates production. If transport drives ozone below its PCE condition, then photochemical production dominates loss. Gross features of ozone loss/production (L/P) inferred for the real atmosphere from data are also simulated using only eddy diffusion. This indicates that one must be careful in assigning a transport scheme for a two-dimensional model that mimics only behavior of the observed ozone L/P.

Infrared matrix-isolation and theoretical studies of the reactions of ferrocene with ozone.

PubMed

Kugel, Roger W; Pinelo, Laura F; Ault, Bruce S

2015-03-19

The reactions between ferrocene (Cp2Fe) (2a) and ozone (O3) were studied using low-temperature matrix-isolation techniques coupled with theoretical density functional theory (DFT) calculations. Co-deposition of Ar/Cp2Fe and Ar/O3 gas mixtures onto a cryogenically cooled CsI window produced a dark-green charge-transfer complex, Cp2Fe-O3, that photodecomposed upon red (λ ≥ 600 nm) and infrared (λ ≥ 1000 nm) irradiation but was stable to green or blue irradiation. Products of photodecomposition were characterized by FT-IR, oxygen-18 labeling, and DFT calculations using the B3LYP functionals and the 6-311G++(d,2p) basis set. Likely, photochemical products included four structures having the molecular formula C10H10FeO, identified by DFT calculations based on their calculated infrared spectra and (18)O isotope shifts. Each of these calculated molecules had one intact and fully coordinated η(5)-C5H5 cyclopentadienyl (Cp) ring and (1) an η(5)-C5H5O cyclic ether (pyran ring) (2b), (2) an η(4)-C5H5O linear aldehyde (2c), (3) a bidentate cyclic aldehyde with a seven-membered ring including the iron atom (2d), or (4) an Fe-O bond and an η(2)-C5H5 (Cp) ring (2e). No conclusive evidence for a gas-phase thermal reaction between ferrocene and ozone was observed under the conditions of these experiments. However, strong evidence for a surface-catalyzed thermal reaction was observed in merged-jet experiments wherein the gases were premixed before deposition. Surface-catalyzed ferrocene-ozone reaction products included a thin film of Fe2O3 observed on the walls of the merged tube as well as cyclopentadiene (C5H6), cyclopentadienone (C5H4O), and further oxidation products observed in the matrix. Possible mechanisms for both the photochemical and the thermal reactions are discussed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hinks, Mallory L.; Brady, Monica V.; Lignell, Hanna

This work explores the effect of environmental conditions on the photodegradation rates of atmospherically relevant, photolabilie, organic molecules embedded in a film of secondary organic material (SOM). Three types of SOM were studied: a-pinene/O3 SOM (PSOM), limonene/O3 SOM (LSOM), and aged limonene/O3 obtained by exposure of LSOM to ammonia (brown LSOM). PSOM and LSOM were impregnated with 2,4-dinitrophenol (2,4-DNP), an atmospherically relevant molecule that photodegrades faster than either PSOM or LSOM alone, to serve as a probe of SOM matrix effects on photochemistry. Brown LSOM contains an unidentified chromophore that absorbs strongly at 510 nm and photobleaches upon irradiation. Thismore » chromophore served as a probe molecule for the brown LSOM experiments. In all experiments, the temperature and relative humidity (RH) surrounding the SOM films were varied. The extent of photochemical reaction in the samples was monitored using UV-Vis absorption spectroscopy. For all three model systems examined, the observed photodegradation rates were slower at lower temperatures and lower RH, under conditions that make SOM more viscous. Additionally, the activation energies for photodegradation of each system were positively correlated with the viscosity of the SOM matrix as measured in poke-flow experiments. These activation energies were calculated to be 50, 24, and 17 kJ/mol for 2,4-DNP in PSOM, 2,4-DNP in LSOM, and brown LSOM, respectively and PSOM was found to be the most viscous of the three. These results suggest that the increased viscosity is hindering the motion of the molecules in SOM and is slowing down photochemical reactions in which they participate.« less

Overall kinetics of heterogeneous elemental mercury reactions on TiO2 sorbent particles with UV radiation

EPA Science Inventory

A system consisting of a photochemical reaction was used to evaluate the kinetic parameters, such as reaction order and rate constant for the elemental mercury uptake by TiO2 in the presence of uv irradiation. TiO2 particles generated by an aerosol route were used in a fixed bed...

77 FR 37610 - Air Quality: Revision to Definition of Volatile Organic Compounds-Exclusion of trans-1,3,3,3...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-06-22

... through atmospheric photochemical reactions. Different VOCs have different levels of reactivity--that is...: (i) The reaction rate constant (known as k OH ) with the hydroxyl radical (OH); (ii) the maximum... per mole basis. Differences between these three metrics are discussed below. The k OH is the reaction...

Photodecomposition of Mo(CO)/sub 6/ adsorbed on Si(100)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Creighton, J.R.

1985-01-01

The photochemical decomposition of Mo(CO)/sub 6/ layers physisorbed on Si(100) was investigated to determine the feasibility of molybdenum deposition and also to examine the photochemical reaction mechanism and efficiency. Temperature programmed desorption (TPD) was used to investigate the interaction of Mo(CO)/sub 6/ with the silicon surface before and after irradiation. Auger spectroscopy was used to determine surface elemental composition before Mo(CO)/sub 6/ adsorption and after photodecomposition.

A DIRECT ROUTE TO ACYLHYDROQUINONES FROM ALPHA-KETO ACIDS AND ALPHA-CARBOXAMIDO ACIDS. (R825330)

EPA Science Inventory

Abstract

The reaction of quinones with in situ generated acyl- or carboxamido radicals provides a direct route to the synthesis of acylhydroquinones not accessible by the photochemical reaction of quinones with aldehydes.

Organic chemistry on Titan

NASA Technical Reports Server (NTRS)

Chang, S.; Scattergood, T.; Aronowitz, S.; Flores, J.

1978-01-01

Observations of nonequilibrium phenomena on the Saturn satellite Titan indicate the occurrence of organic chemical evolution. Greenhouse and thermal inversion models of Titan's atmosphere provide environmental constraints within which various pathways for organic chemical synthesis are assessed. Experimental results and theoretical modeling studies suggest that the organic chemistry of the satellite may be dominated by two atmospheric processes: energetic-particle bombardment and photochemistry. Reactions initiated in various levels of the atmosphere by cosmic ray, Saturn wind, and solar wind particle bombardment of a CH4 - N2 atmospheric mixture can account for the C2-hydrocarbons, the UV-visible-absorbing stratospheric haze, and the reddish color of the satellite. Photochemical reactions of CH4 can also account for the presence of C2-hydrocarbons. In the lower Titan atmosphere, photochemical processes will be important if surface temperatures are sufficiently high for gaseous NH3 to exist. Hot H-atom reactions initiated by photo-dissociation of NH3 can couple the chemical reactions of NH3 and CH4 and produce organic matter.

Investigating the pathway for the photochemical formation of VOCs in presence of an organic monolayer at the air/water interface.

NASA Astrophysics Data System (ADS)

Tinel, Liselotte; Rossignol, Stéphanie; Ciuraru, Raluca; George, Christian

2015-04-01

Investigating the pathway for the photochemical formation of VOCs in presence of an organic monolayer at the air/water interface. Liselotte Tinel, Stéphanie Rossignol, Raluca Ciuraru and Christian George Université de Lyon, Université Lyon 1, CNRS, UMR5256, IRCELYON, Institut de recherches sur la catalyse et l'environnement de Lyon, Villeurbanne, F-69626, France Recently the surface microlayer (SML) has received growing attention for its role in the deposition and emission of trace gases. This SML is presumably a highly efficient environment for photochemical reactions thanks to its physical and chemical properties, showing enrichment in chromophores [1]. Still, little is known about the possible photochemical processes that could influence the emission and deposition of volatile organic compounds (VOCs) in the SML. A recent study underlines the particularity of the presence of an organic microlayer, showing enhanced formation of peptide bonds at the air-water interface, although this reaction is thermodynamically disfavoured in bulk water [2]. Also, emissions of small gas phase carbonyl compounds formed photochemically by dissolved organic matter have been measured above natural water and glyoxal, for example, measured above the open ocean is thought to be photochemically produced [3, 4]. This study presents the results of a set of laboratory studies set up in order to better understand the role of the SML in the photochemical production of VOCs. Recently, our group has shown the formation of VOCs by light driven reactions in a small quartz reactor (14mL) containing aqueous solutions of humic acids (HA) in the presence of an organic (artificial or natural) microlayer [5]. The main VOCs produced were oxidized species, such as aldehydes, ketones and alcohols, as classically can be expected by the oxidation of the organics present at the interface initiated by triplet excited chromophores present in the HA. But also alkenes, dienes, including isoprene and unsaturated aldehydes were detected and a reaction pathway, initiated by a H-abstraction of the surfactant by the excited HA*, has been proposed. This mechanism infers that the presence of the surface microlayer will enhance protonation and self-reactions, leading to the formation of dimers as suggested in [6]. These products could explain the formation of the unsaturated products observed. To confirm the hypothesis of an initiative step of H-abstraction, the system was simplified using OH radicals, generated by the photolysis of H2O2, in presence of an artificial organic layer of nonanoic acid. The VOCs produced, monitored by PTR/SRI-TOF-MS in NO+ and H3O+ ionization mode, were less abundant compared to the system with HA, but the same classes of products could be observed, including oxidation products such as aldehydes but also unsatured products like dienes. The underlying water was sampled before and after the experiment and analysed by HR-ESI-MS, showing mostly enrichment of oxidative products, such as hydroxy- and keto-acids immediately derived from the photochemical oxidation of the nonanoic acid layer. These products, showing lower volatility and higher polarity, partition preferentially to the bulk water. The results of this simplified system confirm the reaction mechanism proposed and the role an organic layer can play in the photochemical formation of VOCs, which could influence the marine boundary layer chemistry. 1. Peter S. Liss, R.A.D., ed. Sea Surface and Global Change. 1997, Cambridge University Press: Cambridge. 509. 2. Griffith, E.C. and V. Vaida, In situ observation of peptide bond formation at the water-air interface. Proceedings of the National Academy of Sciences, 2012. 109(39): p. 15697-15701. 3. Sinreich, R., et al., Ship-based detection of glyoxal over the remote tropical Pacific Ocean. Atmospheric Chemistry and Physics, 2010. 10(23): p. 11359-11371. 4. Kieber, R.J., X.L. Zhou, and K. Mopper, Formation of carbonyl-compounds from uv-induced photodegradation of humic substances in natural-waters - fate of riverine carbon in the sea. Limnology and Oceanography, 1990. 35(7): p. 1503-1515. 5. R. Ciuraru, L. Fine, M. van Pinxteren, B. D'Anna, H. Herrmann, C. George, Unravelling new processes at interfaces: chemical isoprene production at the sea surface. submitted. 6. Griffith, E.C., et al., Photoinitiated Synthesis of Self-Assembled Vesicles. Journal of the American Chemical Society, 2014. 136(10): p. 3784-3787.

Fluorogenic, catalytic, photochemical reaction for amplified detection of nucleic acids.

PubMed

Dutta, Subrata; Fülöp, Annabelle; Mokhir, Andriy

2013-09-18

Photochemical, nucleic acid-induced reactions, which are controlled by nontoxic red light, are well-suited for detection of nucleic acids in live cells, since they do not require any additives and can be spatially and temporally regulated. We have recently described the first reaction of this type, in which a phenylselenyl derivative of thymidine (5'-PhSeT-ODNa) is cleaved in the presence of singlet oxygen (Fülöp, A., Peng, X., Greenberg, M. M., Mokhir, A. (2010) A nucleic acid directed, red light-induced chemical reaction. Chem. Commun. 46, 5659-5661). The latter reagent is produced upon exposure of a photosensitizer 3'-PS-ODNb (PS = Indium(III)-pyropheophorbide-a-chloride: InPPa) to >630 nm light. In 2012 we reported on a fluorogenic version of this reaction (Dutta, S., Flottmann, B., Heilemann, M., Mokhir, A. (2012) Hybridization and reaction-based, fluorogenic nucleic acid probes. Chem. Commun. 47, 9664-9666), which is potentially applicable for the detection of nucleic acids in cells. Unfortunately, its yield does not exceed 25% and no catalytic turnover could be observed in the presence of substrate excess. This problem occurs due to the efficient, competing oxidation of the substrate containing an electron rich carbon-carbon double bonds (SCH═CHS) in the presence of singlet oxygen with formation of a noncleavable product (SCH═CHSO). Herein we describe a related, but substantially improved photochemical, catalytic transformation of a fluorogenic, organic substrate, which consists of 9,10-dialkoxyanthracene linked to fluorescein, with formation of a bright fluorescent dye. In highly dilute solution this reaction occurs only in the presence of a nucleic acid template. We developed three types of such a reaction and demonstrated that they are high yielding and generate over 7.7 catalytic turnovers, are sensitive to single mismatches in nucleic acid targets, and can be applied for determination of both the amount of nucleic acids and potentially their localization.

Photochemistry of Iron and Ruthenium Carbonyl Complexes: Evidence for Light-Induced Loss of Carbon Monoxide and Reductive Elimination of Triethylsilane from cis-mer-HM(SiEt3)(CO)3(PPh3).

DTIC Science & Technology

1983-05-21

JEOL FX9OQ Fourier transform or Bruker 250 or 270 MHz Fourier transform spectrometer. Irradiations. Photochemical reactions were carried out using a...Ph 3 ) 3nd -t-Etin V,- a 313 nm quantum yield of -0.6. The process is photochemically everse if the cis-mer-HM(SiPh 3 )(CO) 3 (PPh 3) is irradiated...process is photochemically reversed if the cis-mer-HM(SiPh 3 )(CO)3 (PPh 3 ) is irradiated in t.e presence of excess Et3SiH. Irradiation of cis-mer-HM

STUDY USING A THREE-DIMENSIONAL PHOTOCHEMICAL SMOG FORMATION MODEL UNDER CONDITIONS OF COMPLEX FLOW: APPLICATION OF THE URBAN AIRSHED MODEL TO THE TOKYO METROPOLITAN AREA

EPA Science Inventory

The purpose of this study is to evaluate the Urban Airshed Model (UAM), a three-dimensional photochemical urban air quality simulation model, using field observations from the Tokyo Metropolitan Area. mphasis was placed on the photochemical smog formation mechanism under stagnant...

Quantitative assessment on the contribution of direct photolysis and radical oxidation in photochemical degradation of 4-chlorophenol and oxytetracycline.

PubMed

Liu, Yiqing; He, Xuexiang; Fu, Yongsheng; Dionysiou, Dionysios D

2016-07-01

In UV-254 nm/H2O2 advanced oxidation process (AOP), the potential degradation pathways for organic pollutants include (1) hydrolysis, (2) direct H2O2 oxidation, (3) UV direct photolysis, and (4) hydroxyl radical (HO(•)) reaction. In this study, the contribution of these pathways was quantitatively assessed in the photochemical destruction of 4-chlorophenol (4-CP), demonstrating pathways (3) and (4) to be predominantly responsible for the removal of 4-CP by UV/H2O2 in 50 mM phosphate buffer solution. Increasing reaction pH could significantly enhance the contribution of direct photolysis in UV/H2O2 process. The contribution of HO(•) oxidation was improved with increasing initial H2O2 concentration probably due to the increased formation of HO(•). Presence of sodium carbonate (Na2CO3) as in UV/H2O2/Na2CO3 system promoted the degradation of 4-CP, with carbonate radical (CO3 (•-)) reaction and direct photolysis identified to be the main contributing pathways. The trends in the contribution of each factor were further evaluated and validated on the degradation of the antibiotic compound oxytetracycline (OTC). This study provides valuable information on the relative importance of different reaction pathways on the photochemical degradation of organic contaminants such as 4-CP and OTC in the presence and absence of a CO3 (•-) precursor.

RESEARCH ACTIVITIES IN THE FIELD OF MATERIALS SCIENCE.

DTIC Science & Technology

MAGNETIC RESONANCE, COMPLEX COMPOUNDS, CRYSTAL STRUCTURE, ELECTROCHEMISTRY, CHEMILUMINESCENCE, PHOTOCHEMICAL REACTIONS, PHOSPHORUS HETEROCYCLIC COMPOUNDS...RADIATION CHEMISTRY, POLYMERS, ROCK, SUPERCONDUCTORS, POSITRONS , DAMAGE, RADIATION EFFECTS, HALIDES

A box model study on photochemical interactions between VOCs and reactive halogen species in the marine boundary layer

NASA Astrophysics Data System (ADS)

Toyota, K.; Kanaya, Y.; Takahashi, M.; Akimoto, H.

2003-09-01

A new chemical scheme is developed for the multiphase photochemical box model SEAMAC (size-SEgregated Aerosol model for Marine Air Chemistry) to investigate photochemical interactions between volatile organic compounds (VOCs) and reactive halogen species in the marine boundary layer (MBL). Based primarily on critically evaluated kinetic and photochemical rate parameters as well as a protocol for chemical mechanism development, the new scheme has achieved a near-explicit treatment of oxidative degradation of up to C3-hydrocarbons CH4, C2H6, C3H8, C2H4, C3H6, and C2H2) initiated by reactions with OH radicals, Cl- and Br-atoms, and O3. Rate constants and product yields for reactions involving halogen species are taken from the literature where available, but the majority of them need to be estimated. In particular, addition reactions of halogen atoms with alkenes will result in the formation of halogenated organic intermediates, whose photochemical loss rates are carefully evaluated in the present work. Model calculations with the new chemical scheme reveal that the oceanic emissions of acetaldehyde (CH3CHO) and alkenes (especially C3H6) are important factors for regulating reactive halogen chemistry in the MBL by promoting the conversion of Br atoms into HBr or more stable brominated intermediates in the organic form. The latter include brominated hydroperoxides, bromoacetaldehyde, and bromoacetone, which sequester bromine from reactive inorganic pool. The total mixing ratio of brominated organic species thus produced is likely to reach 10-20% or more of that of inorganic gaseous bromine species over wide regions over the ocean. On the other hand, the reaction between Br atoms and C2H2 is unimportant for determining the degree of bromine activation in the remote MBL. It is suggested that peroxyacetic acid formed via CH3CHO oxidation is one of the important chemical agents for triggering autocatalytic halogen release from sea-salt aerosols. These results imply that reactive halogen chemistry can mediate a link between the oceanic emissions of VOCs and the behaviors of compounds that are sensitive to halogen chemistry such as dimethyl sulfide, NOx, and O3 in the MBL.

Atmospheric origins of perchlorate on Mars and in the Atacama

NASA Astrophysics Data System (ADS)

Catling, D. C.; Claire, M. W.; Zahnle, K. J.; Quinn, R. C.; Clark, B. C.; Hecht, M. H.; Kounaves, S.

2010-01-01

Isotopic studies indicate that natural perchlorate is produced on Earth in arid environments by the oxidation of chlorine species through pathways involving ozone or its photochemical products. With this analogy, we propose that the arid environment on Mars may have given rise to perchlorate through the action of atmospheric oxidants. A variety of hypothetical pathways can be proposed including photochemical reactions, electrostatic discharge, and gas-solid reactions. Because perchlorate-rich deposits in the Atacama desert are closest in abundance to perchlorate measured at NASA's Phoenix Lander site, we made a preliminary study of the means to produce Atacama perchlorate to help shed light on the origin of Martian perchlorate. We investigated gas phase pathways using a 1-D photochemical model. We found that perchlorate can be produced in sufficient quantities to explain the abundance of perchlorate in the Atacama from a proposed gas phase oxidation of chlorine volatiles to perchloric acid. The feasibility of gas phase production for the Atacama provides justification for future investigations of gas phase photochemistry as a possible source for Martian perchlorate.

Photochemical reactions between mercury (Hg) and dissolved organic matter decrease Hg bioavailability and methylation

DOE PAGES

Luo, Hong-Wei; Yin, Xiangping; Jubb, Aaron M.; ...

2016-11-09

Atmospheric deposition of mercury (Hg) to surface water is one of the dominant sources of Hg in aquatic environments and ultimately drives methylmercury (MeHg) toxin accumulation in fish. It is known that freshly deposited Hg is more readily methylated by microorganisms than aged or preexisting Hg; however the underlying mechanism of this process is unclear. Here we report that Hg bioavailability is decreased by photochemical reactions between Hg and dissolved organic matter (DOM) in water. Photo-irradiation of Hg-DOM complexes results in loss of Sn(II)-reducible (i.e. reactive) Hg and up to an 80% decrease in MeHg production by the methylating bacteriummore » Geobacter sulfurreducens PCA. Loss of reactive Hg proceeded at a faster rate with a decrease in the Hg to DOM ratio and is attributed to the possible formation of mercury sulfide (HgS). Lastly, these results suggest a new pathway of abiotic photochemical formation of HgS in surface water and provide a mechanism whereby freshly deposited Hg is readily methylated but, over time, progressively becomes less available for microbial uptake and methylation.« less

Photochemical reactions between mercury (Hg) and dissolved organic matter decrease Hg bioavailability and methylation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luo, Hong-Wei; Yin, Xiangping; Jubb, Aaron M.

Atmospheric deposition of mercury (Hg) to surface water is one of the dominant sources of Hg in aquatic environments and ultimately drives methylmercury (MeHg) toxin accumulation in fish. It is known that freshly deposited Hg is more readily methylated by microorganisms than aged or preexisting Hg; however the underlying mechanism of this process is unclear. Here we report that Hg bioavailability is decreased by photochemical reactions between Hg and dissolved organic matter (DOM) in water. Photo-irradiation of Hg-DOM complexes results in loss of Sn(II)-reducible (i.e. reactive) Hg and up to an 80% decrease in MeHg production by the methylating bacteriummore » Geobacter sulfurreducens PCA. Loss of reactive Hg proceeded at a faster rate with a decrease in the Hg to DOM ratio and is attributed to the possible formation of mercury sulfide (HgS). Lastly, these results suggest a new pathway of abiotic photochemical formation of HgS in surface water and provide a mechanism whereby freshly deposited Hg is readily methylated but, over time, progressively becomes less available for microbial uptake and methylation.« less

Solar Photochemical Synthesis: From the Beginnings of Organic Photochemistry to the Solar Manufacturing of Commodity Chemicals.

PubMed

Oelgemöller, Michael

2016-09-14

Natural sunlight offers a cost-efficient and sustainable energy source for photochemical reactions. In contrast to the lengthy and small-scale "flask in the sun" procedures of the past, modern solar concentrator systems nowadays significantly shorten reaction times and enable technical-scale operations. After a brief historical introduction, this review presents the most important solar reactor types and their successful application in preparative solar syntheses. The examples demonstrate that solar manufacturing of fine chemicals is technically feasible and environmentally sustainable. After over 100 years, Ciamician's prophetic vision of "the photochemistry of the future" as a clean and green manufacturing methodology has yet to be realized. At the same time, his warning "for nature is not in a hurry but mankind is" is still valid today. It is hoped that this review will lead to a renewed interest in this truly enlightening technology, that it will stimulate photochemists and photochemical engineers to "go back to the roots onto the roofs" and that it will ultimately result in industrial applications in the foreseeable future.

Photochemically induced focal cochlear lesions in the guinea pig: II. A transmission electron microscope study.

PubMed

Miyashita, H; Iwasaki, S; Hoshino, T

1998-05-15

Photochemically induced focal lesions in guinea pig cochleas were studied by light microscopy and transmission electron microscopy. The lesions were induced in the second cochlear turns of 35 adult guinea pigs by illumination for 10 minutes with a focused green light immediately after a rose bengal solution was injected into the jugular vein. The cochlear lateral wall and organ of Corti were examined 5, 10, 20, 30, and 90 minutes, 12 and 24 hours, and 3, 7, and 30 days after the procedure. Aggregations of platelets and red blood cells were found in strial capillaries at 5 minutes after illumination. After 30 minutes, marginal cell surfaces protruded into the endolymphatic space; surface membranes were ruptured and the cytoplasm was expelled into the space. In outer hair cells, disruption of the cellular membrane was found near the cuticular plate 12 hours after the procedure. All cellular elements of the lateral wall and organ of Corti were markedly degenerated in the 30-day specimens. Histological changes found in the stria vascularis were consistent with cell damage caused by active oxygen species. It is likely that the stria vascularis is more sensitive to the photochemical reaction than other parts of the cochlea. Cell damage in other parts of the cochlea seemed to have been caused by local microvascular ischemia in addition to the action of active oxygen species induced by the photochemical reaction.

Theory of time-resolved x-ray photoelectron diffraction from transient conformational molecules

NASA Astrophysics Data System (ADS)

Tsuru, Shota; Sako, Tokuei; Fujikawa, Takashi; Yagishita, Akira

2017-04-01

We formulate x-ray photoelectron diffraction (XPD) from molecules undergoing photochemical reactions induced by optical laser pulses, and then apply the formula to the simulation of time-dependent XPD profiles from both dissociating I2 molecules and bending C S2 molecules. The dependence of nuclear wave-packet motions on the intensity and shape of the optical laser pulses is examined. As a result, the XPD simulations based on such nuclear wave-packet calculations are observed to exhibit characteristic features, which are compared with the XPD profiles due to classical trajectories of nuclear motions. The present study provides a methodology toward creating "molecular movies" of ultrafast photochemical reactions by means of femtosecond XPD with x-ray free-electron lasers.

Laser isotope separation

DOEpatents

Robinson, C.P.; Reed, J.J.; Cotter, T.P.; Boyer, K.; Greiner, N.R.

1975-11-26

A process and apparatus for separating isotopes by selective excitation of isotopic species of a volatile compound by tuned laser light is described. A highly cooled gas of the volatile compound is produced in which the isotopic shift is sharpened and defined. Before substantial condensation occurs, the cooled gas is irradiated with laser light precisely tuned to a desired wavelength to selectively excite a particular isotopic species in the cooled gas. The laser light may impart sufficient energy to the excited species to cause it to undergo photolysis, photochemical reaction or even to photoionize. Alternatively, a two-photon irradiation may be applied to the cooled gas to induce photolysis, photochemical reaction or photoionization. The process is particularly applicable to the separation of isotopes of uranium.

Photogenerated radical intermediates of vitamin K 1: a time-resolved resonance Raman study

NASA Astrophysics Data System (ADS)

Balakrishnan, G.; Umapathy, S.

1999-01-01

Quinones play a vital role in the process of electron transfer in bacterial photosynthetic reaction centers. It is of interest to investigate the photochemical reactions involving quinones with a view to elucidating the structure-function relationships in the biological processes. Resonance Raman spectra of radical anions and the time-resolved resonance Raman spectra of vitamin K 1 (model compound for Q A in Rhodopseudomonas viridis, a bacterial photosynthetic reception center) are presented. The photochemical intermediates of vitamin K 1, viz. radical anion, ketyl radical and o-quinone methide have been identified. The vibrational assignments of all these intermediates are made on the basis of comparison with our earlier TR3 studies on radical anions of naphthoquinone and menaquinone.

Photophysical and Photochemical Properties of Some Fluorescent Derivatives of Vitamin B1

NASA Astrophysics Data System (ADS)

Marciniak, B.

1987-05-01

Absorption and emission spectra, depopulation kinetics of the lowest excited singlet and triplet states and acid-base equilibria of two fluorescent vitamin B, derivatives, the products I and II of the reaction of N-methylated vitamine B, with cytidine and adenosine, respectively, were investigated. Analysis of the lifetime and quantum yield data indicate that at 77 K emissions are the main processes of deactivation of the S1 and T1 states for the free ion and protonated forms. The pKa values indicate a much higher acidity in the excited singlet and triplet states than in the ground state. I and II undergo very slow photochemical reactions in solution in the presence of oxygen (Φ ~ 10-4).

A mass spectrometry and electron paramagnetic resonance study of photochemical and thermal aging of triterpenoid varnishes.

PubMed

Dietemann, P; Kälin, M; Zumbühl, S; Knochenmuss, R; Wülfert, S; Zenobi, R

2001-05-01

Photochemical and thermal aging of triterpenoid dammar and mastic resins used as varnishes on paintings were studied using graphite-assisted laser desorption/ionization mass spectrometry. This extends an earlier study on similar materials (Zumbühl et al., Anal. Chem. 1998, 70, 707-715) that focused on photoaging. Progressive aging results in development of groups of signals spaced by 14 and 16 Da, indicating incorporation of oxygen as well as simultaneous loss of hydrogen. Oligomers up to tetramers are formed, while cleavage reactions lead to increased signal intensities in the mass ranges between the oligomers and below the monomers. No major differences were found between the mass spectra of samples aged in light or darkness, except that deterioration was faster in light. Electron paramagnetic resonance spectroscopy revealed similar and significant amounts of radicals in films of dammar stored either in light or in darkness. It is concluded that oxidative radical reactions also take place in darkness and that differences in light and dark aging pathways are minor, although rates may differ. These findings lead to a unified explanation for yellowing of natural resin varnishes, one of the major degenerative changes in the appearance of paintings. It is also shown that the commercially available, nominally fresh resins are already in an advanced stage of oxidation and degradation. Energy-rich substances are formed upon irradiation with sunlight and are believed to restart the autoxidative chain reactions, regardless of storage conditions. As a result, varnishes are oxidized quite quickly (months) even when kept in darkness.

Photobiomolecular deposition of metallic particles and films

DOEpatents

Hu, Zhong-Cheng

2005-02-08

The method of the invention is based on the unique electron-carrying function of a photocatalytic unit such as the photosynthesis system I (PSI) reaction center of the protein-chlorophyll complex isolated from chloroplasts. The method employs a photo-biomolecular metal deposition technique for precisely controlled nucleation and growth of metallic clusters/particles, e.g., platinum, palladium, and their alloys, etc., as well as for thin-film formation above the surface of a solid substrate. The photochemically mediated technique offers numerous advantages over traditional deposition methods including quantitative atom deposition control, high energy efficiency, and mild operating condition requirements.

Photobiomolecular metallic particles and films

DOEpatents

Hu, Zhong-Cheng

2003-05-06

The method of the invention is based on the unique electron-carrying function of a photocatalytic unit such as the photosynthesis system I (PSI) reaction center of the protein-chlorophyll complex isolated from chloroplasts. The method employs a photo-biomolecular metal deposition technique for precisely controlled nucleation and growth of metallic clusters/particles, e.g., platinum, palladium, and their alloys, etc., as well as for thin-film formation above the surface of a solid substrate. The photochemically mediated technique offers numerous advantages over traditional deposition methods including quantitative atom deposition control, high energy efficiency, and mild operating condition requirements.

Photo-oxidation degradation mechanisms in P3HT for organic solar cells: Insights from first-principles simulations

NASA Astrophysics Data System (ADS)

Leung, Kevin; Sai, Na; Zador, Judit; Henkelman, Graeme

2014-03-01

Photo-oxidation is one of the leading chemical degradation mechanisms in polymer solar cells. In this work, using hybrid density functional theory and periodic boundary condition, we investigate reaction pathways that may lead to the sulfur oxidation in poly(3-hexylthiophene)(P3HT) as a step toward breaking the macromolecule backbone. We calculate energy barriers for reactions of P3HT backbone with oxidizing radicals suggested by infrared spectroscopy (IR) and XPS studies. Our results strongly suggest that an attack of hydroxyl radical on sulfur as proposed in the literature is unlikely to be thermodynamically favored. On the other hand, a reaction between the alkylperoxyl radical and the polymer backbone may provide low barrier reaction pathways to photo-oxidation of conjugated polymers with side chains. Our work paves way for future studies using ab-initio calculations in a condensed phase setting to model complex chemical reactions relevant to photochemical stability of novel polymers. Supported by the Energy Frontier Research Center funded by the U.S. DOE Office of Basic Energy Sciences under Award #DE-SC0001091.

Impact of Anthropogenic Emissions on Isoprene Photochemical Oxidation Pathways in Central Amazonia

NASA Astrophysics Data System (ADS)

Thayer, M. P.; Dorris, M. R.; Keutsch, F. N.; Goldstein, A. H.; Guenther, A. B.; Isaacman-VanWertz, G. A.; Jimenez, J. L.; Kim, S.; Liu, Y.; Martin, S. T.; Palm, B. B.; Park, J. H.; Seco, R.; Sjostedt, S. J.; Springston, S. R.; Wernis, R. A.; Yee, L.

2016-12-01

The atmosphere over the Amazon rainforest is characterized by high concentrations of biogenic volatile organic compounds (BVOCs) - most notably isoprene, which is the most abundant non-methane VOC both locally and globally. These BVOCs are photochemically oxidized, forming oVOCs, especially via reaction with the hydroxyl radical (OH). This photochemical processing can result in formation of secondary pollutants such as ozone (O3) and secondary organic aerosol (SOA). During the Green Ocean Amazon campaign (GoAmazon2014/5), we obtained formaldehyde and glyoxal measurements together with OH, peroxy radicals (RO2+HO2), nitrogen oxides (NOx), CO, CO2, O3, (o)VOCs, and aerosol particle size distribution. Here we present data collected during 2014 at the T3 field site, 60 km to the west of Manaus, Brazil (3°12'47.82"S, 60°35'55.32"W). The T3 GoAmazon site varies between sampling strictly pristine (biogenic) emissions and influence from anthropogenic emissions from Manaus, depending on meteorological conditions. The day-to-day oscillation provides an ideal setting for evaluating the impact of pollution from biomass burning and urban emissions on VOC oxidation and resultant secondary pollutant production. Anthropogenic plumes contain not only additional VOC precursors, but also enhanced NOx, which drastically alters the relative importance of various isoprene oxidation pathways. We utilize a 0-D photochemical box model to examine how these factors impact reactivity and pollutant formation. Due to ongoing expansion of human influence and emissions in previously-pristine areas, understanding the sensitivity of biogenic oxidation to anthropogenic influence has significant impacts for tropospheric air quality, both in the rapidly-developing Amazon Basin and other BVOC-dominated regions.

INTERACTIONS OF LIGHT AND CHEMICAL REACTIONS IN THE AQUATIC ENVIRONMENT: KINETIC AND MECHANISTIC ASPECTS

EPA Science Inventory

Changes in the ozone layer over the past two decades have resulted in increases in solar ultraviolet (UV) radiation that reaches the surface of aquatic environments. Recent studies have demonstrated that these UV increases cause changes in photochemical reactions that affect the...

Light-driven dinitrogen reduction catalyzed by a CdS:nitrogenase MoFe protein biohybrid.

PubMed

Brown, Katherine A; Harris, Derek F; Wilker, Molly B; Rasmussen, Andrew; Khadka, Nimesh; Hamby, Hayden; Keable, Stephen; Dukovic, Gordana; Peters, John W; Seefeldt, Lance C; King, Paul W

2016-04-22

The splitting of dinitrogen (N2) and reduction to ammonia (NH3) is a kinetically complex and energetically challenging multistep reaction. In the Haber-Bosch process, N2 reduction is accomplished at high temperature and pressure, whereas N2 fixation by the enzyme nitrogenase occurs under ambient conditions using chemical energy from adenosine 5'-triphosphate (ATP) hydrolysis. We show that cadmium sulfide (CdS) nanocrystals can be used to photosensitize the nitrogenase molybdenum-iron (MoFe) protein, where light harvesting replaces ATP hydrolysis to drive the enzymatic reduction of N2 into NH3 The turnover rate was 75 per minute, 63% of the ATP-coupled reaction rate for the nitrogenase complex under optimal conditions. Inhibitors of nitrogenase (i.e., acetylene, carbon monoxide, and dihydrogen) suppressed N2 reduction. The CdS:MoFe protein biohybrids provide a photochemical model for achieving light-driven N2 reduction to NH3. Copyright © 2016, American Association for the Advancement of Science.

Light-driven dinitrogen reduction catalyzed by a CdS:nitrogenase MoFe protein biohybrid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brown, K. A.; Harris, D. F.; Wilker, M. B.

The splitting of dinitrogen (N2) and reduction to ammonia (NH3) is a kinetically complex and energetically challenging multistep reaction. In the Haber-Bosch process, N2 reduction is accomplished at high temperature and pressure, whereas N2 fixation by the enzyme nitrogenase occurs under ambient conditions using chemical energy from adenosine 5'-triphosphate (ATP) hydrolysis. We show that cadmium sulfide (CdS) nanocrystals can be used to photosensitize the nitrogenase molybdenum-iron (MoFe) protein, where light harvesting replaces ATP hydrolysis to drive the enzymatic reduction of N2 into NH3. The turnover rate was 75 per minute, 63% of the ATP-coupled reaction rate for the nitrogenase complexmore » under optimal conditions. Inhibitors of nitrogenase (i.e., acetylene, carbon monoxide, and dihydrogen) suppressed N2 reduction. The CdS:MoFe protein biohybrids provide a photochemical model for achieving light-driven N2 reduction to NH3.« less

Role of effluent organic matter in the photochemical degradation of compounds of wastewater origin.

PubMed

Bodhipaksha, Laleen C; Sharpless, Charles M; Chin, Yu-Ping; MacKay, Allison A

2017-03-01

The photoreactivity of treated wastewater effluent organic matter differs from that of natural organic matter, and the indirect phototransformation rates of micropollutants originating in wastewater are expected to depend on the fractional contribution of wastewater to total stream flow. Photodegradation rates of four common compounds of wastewater origin (sulfamethoxazole, sulfadimethoxine, cimetidine and caffeine) were measured in river water, treated municipal wastewater effluent and mixtures of both to simulate various effluent-stream water mixing conditions that could occur in environmental systems. Compounds were chosen for their unique photodegradation pathways with the photochemically produced reactive intermediates, triplet-state excited organic matter ( 3 OM*), singlet oxygen ( 1 O 2 ), and hydroxyl radicals (OH). For all compounds, higher rates of photodegradation were observed in effluent relative to upstream river water. Sulfamethoxazole degraded primarily via direct photolysis, with some contribution from OH and possibly from carbonate radicals and other unidentified reactive intermediates in effluent-containing samples. Sulfadimethoxine also degraded mainly by direct photolysis, and natural organic matter appeared to inhibit this process to a greater extent than predicted by light screening. In the presence of effluent organic matter, sulfadimethoxine showed additional reactions with OH and 1 O 2 . In all water samples, cimetidine degraded by reaction with 1 O 2 (>95%) and caffeine by reaction with OH (>95%). In river water mixtures, photodegradation rate constants for all compounds increased with increasing fractions of effluent. A conservative mixing model was able to predict reaction rate constants in the case of hydroxyl radical reactions, but it overestimated rate constants in the case of 3 OM* and 1 O 2 pathways. Finally, compound degradation rate constants normalized to the rate of light absorption by water correlated with E 2 /E 3 ratios (sample absorbance at 254 nm divided by sample absorbance at 365 nm), suggesting that organic matter optical properties may hold promise to predict indirect compound photodegradation rates for various effluent mixing ratios. Copyright © 2016 Elsevier Ltd. All rights reserved.

Reaction Profiles and Molecular Dynamics Simulations of Cyanide Radical Reactions Relevant to Titan's Atmosphere

NASA Astrophysics Data System (ADS)

Trinidad Pérez-Rivera, Danilo; Romani, Paul N.; Lopez-Encarnacion, Juan Manuel

2016-10-01

Titan's atmosphere is arguably the atmosphere of greatest interest that we have an abundance of data for from both ground based and spacecraft observations. As we have learned more about Titan's atmospheric composition, the presence of pre-biotic molecules in its atmosphere has generated more and more fascination about the photochemical process and pathways it its atmosphere. Our computational laboratory has been extensively working throughout the past year characterizing nitrile synthesis reactions, making significant progress on the energetics and dynamics of the reactions of .CN with the hydrocarbons acetylene (C2H2), propylene (CH3CCH), and benzene (C6H6), developing a clear picture of the mechanistic aspects through which these three reactions proceed. Specifically, first principles calculations of the reaction profiles and molecular dynamics studies for gas-phase reactions of .CN and C2H2, .CN and CH3CCH, and .CN and C6H6 have been carried out. A very accurate determination of potential energy surfaces of these reactions will allow us to compute the reaction rates which are indispensable for photochemical modeling of Titan's atmosphere.The work at University of Puerto Rico at Cayey was supported by Puerto Rico NASA EPSCoR IDEAS-ER program (2015-2016) and DTPR was sponsored by the Puerto Rico NASA Space Grant Consortium Fellowship. *E-mail: juan.lopez15@upr.edu

Photochemically Induced Intramolecular Radical Cyclization Reactions with Imines.

PubMed

Lefebvre, Corentin; Michelin, Clément; Martzel, Thomas; Djou'ou Mvondo, Vaneck; Bulach, Véronique; Abe, Manabu; Hoffmann, Norbert

2018-02-16

The photochemically induced intramolecular hydrogen abstraction or hydrogen atom transfer in cyclic imines 8a,b followed by a cyclization is investigated. Two types of products are observed, one resulting from the formation of a C-C bond, the other from the formation of a C-N bond. A computational study reveals that hydrogen is exclusively transferred to the imine nitrogen leading to a triplet diradical intermediate. After intersystem crossing, the resulting zwitterionic intermediate undergoes cyclization leading to the final product.

Photochemical dimerization and functionalization of alkanes, ethers, primary alcohols and silanes

DOEpatents

Crabtree, Robert H.; Brown, Stephen H.

1988-01-01

The space-time yield and/or the selectivity of the photochemical dimerization of alkanes, ethers, primary alcohols and tertiary silanes with Hg and U.V. light is enhanced by refluxing the substrate in the irradiated reaction zone at a temperature at which the dimer product condenses and remains condensed promptly upon its formation. Cross-dimerization of the alkanes, ethers and silanes with primary alcohols is disclosed, as is the functionalization to aldehydes of the alkanes with carbon monoxide.

Photochemical dimerization and functionalization of alkanes, ethers, primary alcohols and silanes

DOEpatents

Crabtree, R.H.; Brown, S.H.

1988-02-16

The space-time yield and/or the selectivity of the photochemical dimerization of alkanes, ethers, primary alcohols and tertiary silanes with Hg and U.V. light is enhanced by refluxing the substrate in the irradiated reaction zone at a temperature at which the dimer product condenses and remains condensed promptly upon its formation. Cross-dimerization of the alkanes, ethers and silanes with primary alcohols is disclosed, as is the functionalization to aldehydes of the alkanes with carbon monoxide.

Relationship Between Photochemical Quenching and Non-Photochemical Quenching in Six Species of Cyanobacteria Reveals Species Difference in Redox State and Species Commonality in Energy Dissipation.

PubMed

Misumi, Masahiro; Katoh, Hiroshi; Tomo, Tatsuya; Sonoike, Kintake

2016-07-01

Although the photosynthetic reaction center is well conserved among different cyanobacterial species, the modes of metabolism, e.g. respiratory, nitrogen and carbon metabolism and their mutual interaction, are quite diverse. To explore such uniformity and diversity among cyanobacteria, here we compare the influence of the light environment on the condition of photosynthetic electron transport through Chl fluorescence measurement of six cyanobacterial species grown under the same photon flux densities and at the same temperature. In the dark or under weak light, up to growth light, a large difference in the plastoquinone (PQ) redox condition was observed among different cyanobacterial species. The observed difference indicates that the degree of interaction between respiratory electron transfer and photosynthetic electron transfer differs among different cyanobacterial species. The variation could not be ascribed to the phylogenetic differences but possibly to the light environment of the original habitat. On the other hand, changes in the redox condition of PQ were essentially identical among different species at photon flux densities higher than the growth light. We further analyzed the response to high light by using a typical energy allocation model and found that 'non-regulated' thermal dissipation was increased under high-light conditions in all cyanobacterial species tested. We assume that such 'non-regulated' thermal dissipation may be an important 'regulatory' mechanism in the acclimation of cyanobacterial cells to high-light conditions. © The Author 2015. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists.

Enzymology below 200 K: The kinetics and thermodynamics of the photochemistry catalyzed by protochlorophyllide oxidoreductase

PubMed Central

Heyes, Derren J.; Ruban, Alexander V.; Wilks, Helen M.; Hunter, C. Neil

2002-01-01

The chlorophyll biosynthesis enzyme protochlorophyllide reductase (POR) catalyzes the light-dependent reduction of protochlorophyllide (Pchlide) into chlorophyllide in the presence of NADPH. As POR is light-dependent, catalysis can be initiated by illumination of the enzyme-substrate complex at low temperatures, making it an attractive model for studying aspects of biological proton and hydride transfers. The early stages in the photoreduction, involving Pchlide binding and an initial photochemical reaction, have been studied in vitro by using low-temperature fluorescence and absorbance measurements. Formation of the ternary POR-NADPH-Pchlide complex produces red shifts in the fluorescence and absorbance maxima of Pchlide, allowing the dissociation constant for Pchlide binding to be measured. We demonstrate that the product of an initial photochemical reaction, which can occur below 200 K, is a nonfluorescent intermediate with a broad absorbance band at 696 nm (A696) that is suggested to represent an ion radical complex. The temperature dependence of the rate of A696 formation has allowed the activation energy for the photochemical step to be calculated and has shown that POR catalysis can proceed at much lower temperatures than previously thought. Calculations of differences in free energy between various reaction intermediates have been calculated; these, together with the quantum efficiency for Pchlide conversion, suggest a quantitative model for the thermodynamics of the light-driven step of Pchlide reduction. PMID:12177453

Fe Isotope Fractionation During Fe(III) Reduction to Fe(II)

NASA Astrophysics Data System (ADS)

Baker, E. A.; Greene, S.; Hardin, E. E.; Hodierne, C. E.; Rosenberg, A.; John, S.

2014-12-01

The redox chemistry of Fe(III) and Fe(II) is tied to a variety of earth processes, including biological, chemical, or photochemical reduction of Fe(III) to Fe(II). Each process may fractionate Fe isotopes, but the magnitudes of the kinetic isotope effects have not been greatly explored in laboratory conditions. Here, we present the isotopic fractionation of Fe during reduction experiments under a variety of experimental conditions including photochemical reduction of Fe(III) bound to EDTA or glucaric acid, and chemical reduction of Fe-EDTA by sodium dithionite, hydroxylamine hydrochloride, Mn(II), and ascorbic acid. A variety of temperatures and pHs were tested. In all experiments, Fe(III) bound to an organic ligand was reduced in the presence of ferrozine. Ferrozine binds with Fe(II), forming a purple complex which allows us to measure the extent of reaction. The absorbance of the experimental solutions was measured over time to determine the Fe(II)-ferrozine concentration and thus the reduction rate. After about 5% of the Fe(III) was reduced, Fe(III)-EDTA and Fe(II)-ferrozine were separated using a C-18 column to which Fe(II)-ferrozine binds. The Fe(II) was eluted and purified through anion exchange chromatography for analysis of δ56Fe by MC-ICPMS. Preliminary results show that temperature and pH both affect reduction rate. All chemical reductants tested reduce Fe(III) at a greater rate as temperature increases. The photochemical reductant EDTA reduces Fe(III) at a greater rate under more acidic conditions. Comparison of the two photochemical reductants shows that glucaric acid reduces Fe(III) significantly faster than EDTA. For chemical reduction, the magnitude of isotopic fractionation depends on the reductant used. Temperature and pH also affect the isotopic fractionation of Fe. Experiments using chemical reductants show that an increase in temperature at low temperatures produces lighter 56Fe ratios, while at high temperatures some reductants produce heavier 56Fe ratios. The magnitude of isotope fractionation is not related to the reduction rate generalized over all reductants. The measured isotopic fractionations produce δ56Fe from -3.82 to +3.05 across all of the reductants tested, highlighting the large impact that redox chemistry may have on fractionating Fe isotopes in the environment.

Evaluation of different photosensitizers for use in photochemical gene transfection.

PubMed

Prasmickaite, L; Høgset, A; Berg, K

2001-04-01

Many potentially therapeutic macromolecules, e.g. transgenes used in gene therapy, are taken into the cells by endocytosis, and have to be liberated from endocytic vesicles in order to express a therapeutic function. To achieve this we have developed a new technology, named photochemical internalization (PCI), based on photochemical reactions inducing rupture of endocytic vesicles. The aim of this study was to clarify which properties of photosensitizers are important for obtaining the PCI effect improving gene transfection. The photochemical effect on transfection of human melanoma THX cells has been studied employing photosensitizers with different physicochemical properties and using two gene delivery vectors: the cationic polypeptide polylysine and the cationic lipid 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP). Photochemical treatment by photosensitizers that do not localize in endocytic vesicles (tetra[3-hydroxyphenyl]porphyrin and 5-aminolevulinic acid-induced protoporphyrin IX) do not stimulate transfection, irrespective of the gene delivery vector. In contrast, photosensitizers localized in endocytic vesicles stimulate polylysine-mediated transfection, and amphiphilic photosensitizers (disulfonated aluminium phthalocyanine [AlPcS2a] and meso-tetraphenylporphynes) show the strongest positive effect, inducing approximately 10-fold increase in transfection efficiency. In contrast, DOTAP-mediated transfection is inhibited by all photochemical treatments irrespective of the photosensitizer used. Neither AlPcS2a nor Photofrin affects the uptake of the transfecting DNA over the plasma membrane, therefore photochemical permeabilization of endocytic vesicles seems to be the most likely mechanism responsible for the positive PCI effect on gene transfection.

What is missing between model and Aura MLS observations in mesospheric OH?

NASA Astrophysics Data System (ADS)

Wang, S.; Li, K. F.; Zeng, Z.; Sander, S. P.; Shia, R. L.; Yung, Y. L.

2017-12-01

Recent Aura Microwave Limb Souder observations show higher mesospheric OH levels than earlier versions and previous satellite observations. The current photochemical model with standard chemistry is not able to accurately simulate MLS OH in the mesosphere. In particular, the model significantly underestimates OH over the altitude range of 60-80km. In the standard middle atmospheric chemistry, HOx over this altitude range is controled mainly through the reactions of H2O + hv (< 205 nm) → H + OH; H + O2 + M → HO2 + M; and OH + HO2 → H2O + O2. In an attempt to resolve the model-observation discrepancy, we adjust the rate coefficients of these reactions within recommended uncertainty ranges using an objective Bayesian approach. However, reasonable perturbations to these reactions are not capable of resolving the mesospheric discrepancy without introducing disagreements in other regions of the atmosphere. We explore possible new reactions in the Earth's atmosphere that are not included in current standard models. Some candidate reactions and their potential impacts on mesospheric HOx chemistry will be discussed. Our results urge new laboratory studies of these candidate reactions, whose rate coefficients have never been measured for the atmospheric conditions.

Softoxometalate [{K6.5Cu(OH)8.5(H2O)7.5}0.5@{K3PW12O40}]n (n = 1348-2024) as an Efficient Inorganic Material for CO2 Reduction with Concomitant Water Oxidation.

PubMed

Das, Santu; Kumar, Saurabh; Garai, Somenath; Pochamoni, Ramudu; Paul, Shounik; Roy, Soumyajit

2017-10-11

An immediate challenge for chemists is to devise different methods to trap chemical energy using light by reduction of carbon dioxide to a transportable fuel. To reach this goal the major obstacle lies in finding a suitable material that is abundant and possesses catalytic power to effect such reduction reaction and perform this reduction reaction without using any external photosensitizer. Here we report for the first time a softoxometalate based on a {[K 6.5 Cu(OH) 8.5 (H 2 O) 7.5 ] 0.5 [K 3 PW 12 O 40 ]} metal oxide framework which is stable in reaction conditions that effectively performs photochemical CO 2 reduction reaction in water with a very high turnover number of 613 and TOF of 47.15 h -1 . We observe that during this reaction water gets oxidized to oxygen, while the electrons released directly go to CO 2 reducing it to formic acid. A detailed account of the characterization of the catalyst along with that of products of this reaction is reported.

Reactive oxygen species explicit dosimetry (ROSED) of a type 1 photosensitizer

NASA Astrophysics Data System (ADS)

Ong, Yi Hong; Kim, Michele M.; Huang, Zheng; Zhu, Timothy C.

2018-02-01

Type I photodynamic therapy (PDT) is based on the use of photochemical reactions mediated through an interaction between a tumor-selective photosensitizer, photoexcitation with a specific wavelength of light, and production of reactive oxygen species (ROS). The goal of this study is to develop a model to calculate reactive oxygen species concentration ([ROS]rx) after Tookad®-mediated vascular PDT. Mice with radiation-induced fibrosarcoma (RIF) tumors were treated with different light fluence and fluence rate conditions. Explicit measurements of photosensitizer drug concentration were made via diffuse reflective absorption spectrum using a contact probe before and after PDT. Blood flow and tissue oxygen concentration over time were measured during PDT as a mean to validate the photochemical parameters for the ROSED calculation. Cure index was computed from the rate of tumor regrowth after treatment and was compared against three calculated dose metrics: total light fluence, PDT dose, reacted [ROS]rx. The tumor growth study demonstrates that [ROS]rx serves as a better dosimetric quantity for predicting treatment outcome, as a clinically relevant tumor growth endpoint.

High-resolution biophysical analysis of the dynamics of nucleosome formation

PubMed Central

Hatakeyama, Akiko; Hartmann, Brigitte; Travers, Andrew; Nogues, Claude; Buckle, Malcolm

2016-01-01

We describe a biophysical approach that enables changes in the structure of DNA to be followed during nucleosome formation in in vitro reconstitution with either the canonical “Widom” sequence or a judiciously mutated sequence. The rapid non-perturbing photochemical analysis presented here provides ‘snapshots’ of the DNA configuration at any given moment in time during nucleosome formation under a very broad range of reaction conditions. Changes in DNA photochemical reactivity upon protein binding are interpreted as being mainly induced by alterations in individual base pair roll angles. The results strengthen the importance of the role of an initial (H3/H4)2 histone tetramer-DNA interaction and highlight the modulation of this early event by the DNA sequence. (H3/H4)2 binding precedes and dictates subsequent H2A/H2B-DNA interactions, which are less affected by the DNA sequence, leading to the final octameric nucleosome. Overall, our results provide a novel, exciting way to investigate those biophysical properties of DNA that constitute a crucial component in nucleosome formation and stabilization. PMID:27263658

Mutagenicity in Salmonella of a Simulated Urban-Smog Atmosphere Generated Using a Mobile Reaction Chamber

EPA Science Inventory

The EPA Mobile Reaction Chamber (MRC) is a 24-foot trailer containing a 14.3-m3 Teflon lined photochemical chamber used to generate simulated urban atmospheres. Photochemistry in the MRC is catalyzed by 120 fluorescent bulbs evenly mixed with black light bulbs and UV bulbs (300 &...

A Molecular Reaction Cycle with a Solvatochromic Merocyanine Dye: An Experiment in Photochemistry, Kinetics, and Catalysis.

ERIC Educational Resources Information Center

Abdel-Kader, M. H.; Steiner, U.

1983-01-01

Three experiments using merocyanine M suitable as an integrated laboratory experience for undergraduates are described. Experiments demonstrate: complete molecular cycle composed of photochemical, thermal, and protolytic reaction steps; kinetics of cis-trans isomerization of the dye; and mechanism of base catalysis for thermal isomerization of the…

Synthesis of perfluorinated polyethers. [for sealers

NASA Technical Reports Server (NTRS)

Depasquale, R. J.; Padgett, C. D.; Patton, J. R.; Psarras, T.

1982-01-01

A series of highly fluorinated acetylenes was prepared and their cyclization reactions were studied. A series of perfluoropolytriazines with -CF2I pendent groups were prepared. These materials can be cured thermally or photochemically to an elastomeric gum. Perfluoropolytriazines with -CN pendent groups were prepared. These materials can be crosslinked by reaction with terephthalonitrile oxide.

Highly oriented photosynthetic reaction centers generate a proton gradient in synthetic protocells

PubMed Central

Altamura, Emiliano; Milano, Francesco; Tangorra, Roberto R.; Trotta, Massimo; Omar, Omar Hassan; Stano, Pasquale

2017-01-01

Photosynthesis is responsible for the photochemical conversion of light into the chemical energy that fuels the planet Earth. The photochemical core of this process in all photosynthetic organisms is a transmembrane protein called the reaction center. In purple photosynthetic bacteria a simple version of this photoenzyme catalyzes the reduction of a quinone molecule, accompanied by the uptake of two protons from the cytoplasm. This results in the establishment of a proton concentration gradient across the lipid membrane, which can be ultimately harnessed to synthesize ATP. Herein we show that synthetic protocells, based on giant lipid vesicles embedding an oriented population of reaction centers, are capable of generating a photoinduced proton gradient across the membrane. Under continuous illumination, the protocells generate a gradient of 0.061 pH units per min, equivalent to a proton motive force of 3.6 mV⋅min−1. Remarkably, the facile reconstitution of the photosynthetic reaction center in the artificial lipid membrane, obtained by the droplet transfer method, paves the way for the construction of novel and more functional protocells for synthetic biology. PMID:28320948

Shape-dependence of the thermal and photochemical reactions of methanol on nanocrystalline anatase TiO2

NASA Astrophysics Data System (ADS)

Bennett, David A.; Cargnello, Matteo; Diroll, Benjamin T.; Murray, Christopher B.; Vohs, John M.

2016-12-01

Structure-activity relationships and the influence of particle size and shape on the partial- and photo-oxidation of methanol on nanocrystalline anatase TiO2 were investigated using temperature-programmed desorption. The study employed two distinct nanoparticle morphologies: truncated bipyramids exposing primarily {101} facets, and flatter platelets exposing primarily {001} surfaces, whose nominal sizes ranged from 10 to 25 nm. The platelets were found to be more active for thermally-driven reactions, such as coupling of methoxide groups to produce dimethyl ether, and deoxygenation to produce methane. A dependence of the reactivity of {001} facets for the coupling of methoxide groups to produce dimethyl ether on facet size was also observed. In contrast to the thermally-driven reactions, the bipyramidal nanoparticles were observed to be more active for a range of photochemical reactions, including oxidation and coupling to produce methyl formate, and photo-decomposition of surface methoxide species. This study also shows how well-defined nanocrystals can be used to help bridge the materials gap between studies of single crystal model catalysts and their high surface area industrial analogs.

Experimental study of the interaction of HO2 radicals with soot surface.

PubMed

Bedjanian, Yuri; Lelièvre, Stéphane; Le Bras, Georges

2005-01-21

The reaction of HO2 with toluene and kerosene flame soot was studied over the temperature range 240-350 K and at P = 0.5-5 Torr of helium using a discharge flow reactor coupled to a modulated molecular beam mass spectrometer. A flat-flame burner was used for the preparation and deposition of soot samples from premixed flames of liquid fuels under well controlled and adjustable combustion conditions. The independent of temperature in the range 240-350 K value of gamma = (7.5 +/- 1.5) x 10(-2) (calculated with geometric surface area) was found for the uptake coefficient of HO2 on kerosene and toluene soot. No significant deactivation of soot surface during its reaction with HO2 was observed. Experiments on soot ageing under ambient conditions showed that the reactivity of aged soot is similar to that of freshly prepared soot samples. The results show that the HO2 + soot reaction could be a significant loss process for HOx in the urban atmosphere with a potential impact on photochemical ozone formation. In contrast this process will be negligible in the upper troposphere even in flight corridors.

Improving Joint Function Using Photochemical Hydrogels for Articular Surface Repair

DTIC Science & Technology

2013-10-01

riboflavin and blue light in hypoxic conditions. Control gels were not photochemically crosslinked . New cartilage matrix was formed in vivo in mice after 4...Sections were probed with AlexaFluor 568- conjugated secondary antibodies and counterstained with DAPI for cell nuclei. All samples were processed at...calcium deposits demonstrated with von Kossa stains; 2) A degradable form of photochemically crosslinked PEG norbomene gel was formulated and growth

Dopant type and/or concentration selective dry photochemical etching of semiconductor materials

DOEpatents

Ashby, Carol I. H.; Dishman, James L.

1987-01-01

A method of selectively photochemically dry etching a first semiconductor material of a given composition in the presence of a second semiconductor material which is of a composition different from said first material, said second material substantially not being etched during said method, comprises subjecting both materials to the same photon flux of an energy greater than their respective direct bandgaps and to the same gaseous chemical etchant under conditions where said etchant would be ineffective for chemical etching of either material were the photons not present, said conditions also being such that the resultant electronic structure of the first semiconductor material under said photon flux is sufficient for the first material to undergo substantial photochemical etching under said conditions and being such that the resultant electronic structure of the second semiconductor material under said photon flux is not sufficient for the second material to undergo substantial photochemical etching under said conditions. In a preferred mode, the materials are subjected to a bias voltage which suppresses etching in n- or p- type material but not in p- or n-type material, respectively; or suppresses etching in the more heavily doped of two n-type or two p-type materials.

Dopant type and/or concentration selective dry photochemical etching of semiconductor materials

DOEpatents

Ashby, C.R.H.; Dishman, J.L.

1985-10-11

Disclosed is a method of selectively photochemically dry etching a first semiconductor material of a given composition in the presence of a second semiconductor material which is of a composition different from said first material, said second material substantially not being etched during said method. The method comprises subjecting both materials to the same photon flux of an energy greater than their respective direct bandgaps and to the same gaseous chemical etchant under conditions where said etchant would be ineffective for chemical etching of either material were the photons not present, said conditions also being such that the resultant electronic structure of the first semiconductor material under said photon flux is sufficient for the first material to undergo substantial photochemical etching under said conditions and being such that the resultant electronic structure of the second semiconductor material under said photon flux is not sufficient for the second material to undergo substantial photochemical etching under said conditions. In a preferred mode, the materials are subjected to a bias voltage which suppresses etching in n- or p-type material but not in p- or n-type material, respectively; or suppresses etching in the more heavily doped of two n-type or two p-type materials.

Thermal and photochemical reactions of NO2 on chromium(III) oxide surfaces at atmospheric pressure.

PubMed

Nishino, Noriko; Finlayson-Pitts, Barbara J

2012-12-05

While many studies of heterogeneous chemistry on Cr(2)O(3) surfaces have focused on its catalytic activity, less is known about chemistry on this surface under atmospheric conditions. We report here studies of the thermal and photochemical reactions of NO(2) on Cr(2)O(3) at one atm in air. In order to follow surface species, the interaction of 16-120 ppm NO(2) with a 15 nm Cr(2)O(3) thin film deposited on a germanium crystal was monitored in a flow system using attenuated total reflectance (ATR) coupled to a Fourier transform infrared (FTIR) spectrometer. Gas phase products were monitored in the effluent of an ~285 ppm NO(2)-air mixture that had passed over Cr(2)O(3) powder in a flow system. A chemiluminescence NO(y) analyzer, a photometric O(3) analyzer and a long-path FTIR spectrometer were used to probe the gaseous products. In the absence of added water vapor, NO(2) formed nitrate (NO(3)(-)) ions coordinated to Cr(3+). These surface coordinated NO(3)(-) were reversibly solvated by water under humid conditions. In both dry and humid cases, nitrate ions decreased during irradiation of the surface at 302 nm, and NO and NO(2) were generated in the gas phase. Under dry conditions, NO was the major gaseous product while NO(2) was the dominant species in the presence of water vapor. Heating of the surface after exposure to NO(2) led to the generation of both NO(2) and NO under dry conditions, but only NO(2) in the presence of water vapor. Elemental chromium incorporated into metal alloys such as stainless steel is readily oxidized in contact with ambient air, forming a chromium-rich metal oxide surface layer. The results of these studies suggest that active photo- and thermal chemistry will occur when boundary layer materials containing chromium(III) or chromium oxide such as stainless steel, roofs, automobile bumpers etc. are exposed to NO(2) under tropospheric conditions.

Surey of Alternate Stored Chemical Energy Reactions.

DTIC Science & Technology

1985-12-01

Fr., Report No. CEA-N-1293, 36 p. Pilipovich. D.; Rogers, H. H. and Wilson, R. D., 1972, Chlorine trifluoride oxide. II. Photochemical synthesis...some fluorine and chlorine compounds: Zh. Fiz. Khim., V. 43, No. 2, p. 386-9. Rogers, H. H. and Pilipovich, D., 1973, Oxychlorine trifluoride (Patent...chemical energy reactions has been made for purposes of comparison with the lithium- aluminum /water, lithium/sulfur hexafluoride, and other reaction schemes

Stratospheric Ozone Loss Over the US in Summer: Recent Advances in Observations of Temperatures, Convective Injection of Condensed Phase Water, and Analyses of Volcanic Injections That are Used to Inform Model Calculations of Catalytic Mechanisms that Control the Response of O3.

NASA Astrophysics Data System (ADS)

Anderson, J. G.

2016-12-01

In the context of changes to the structure of the Earth's climate, consequences to stratospheric ozone over the US in summer are considered. Key advances in observations directly related to the catalytic loss of ozone in the lower stratosphere include: Analysis of high resolution temperature observations over the central US in July and August from both SEAC4RS in situ observations and radio occultation (RO) observations, Inclusion of gravity wave observations from both SEAC4RS and RO measurements, Climatology of NEXRAD weather radar mapping of the 3D convective injection of condensed phase water over the central US in summer, Analysis of the impact on ozone in the lower stratosphere over the US in summer using the AER 2D model calculations of the key rate limiting radicals and rate limiting catalytic loss rates as a function of water vapor, temperature and sulfate loading in the lower stratosphere, Analysis of the impact on ozone in summer over the US under conditions of volcanic injection, overt sulfate addition for solar radiation management, and/or convective injection of water vapor, Emphasis in the analysis is placed specifically on the geographic region over the Great Plains of the US in summer because of the confluence of temperatures and water vapor concentrations that initiate the heterogeneous catalytic conversion of inorganic chlorine, primarily HCl and ClONO2, to free radical form, ClO. The ClO radical in turn engages gas phase catalytic cycles that remove ozone via the photochemical reaction mechanisms virtually identical to the catalytic photochemical processes that remove ozone over the Arctic each year in late spring. In situ observations, in the lower stratosphere of the Arctic, of the principal reaction networks that establish the relationship between observed ozone loss and the threshold in temperature, water vapor and sulfate loading is used to establish the photochemical coordinate system required to analyze ozone loss in the lower stratosphere globally. Analysis is also presented of observed ozone loss resulting from the eruption of Mt. Pinatubo that tests the photochemical structure of large ozone loss at mid-latitude for the range in sulfate loading that accompanies a volcanic eruption.

Quantum Chemical Investigation on Photochemical Reactions of Nonanoic Acids at Air-Water Interface.

PubMed

Xiao, Pin; Wang, Qian; Fang, Wei-Hai; Cui, Ganglong

2017-06-08

Photoinduced chemical reactions of organic compounds at the marine boundary layer have recently attracted significant experimental attention because this kind of photoreactions has been proposed to have substantial impact on local new particle formation and their photoproducts could be a source of secondary organic aerosols. In this work, we have employed first-principles density functional theory method combined with cluster models to systematically explore photochemical reaction pathways of nonanoic acids (NAs) to form volatile saturated and unsaturated C 9 and C 8 aldehydes at air-water interfaces. On the basis of the results, we have found that the formation of C 9 aldehydes is not initiated by intermolecular Norrish type II reaction between two NAs but by intramolecular T 1 C-O bond fission of NA generating acyl and hydroxyl radicals. Subsequently, saturated C 9 aldehydes are formed through hydrogenation reaction of acyl radical by another intact NA. Following two dehydrogenation reactions, unsaturated C 9 aldehydes are generated. In parallel, the pathway to C 8 aldehydes is initiated by T 1 C-C bond fission of NA, which generates octyl and carboxyl radicals; then, an octanol is formed through recombination reaction of octyl with hydroxyl radical. In the following, two dehydrogenation reactions result into an enol intermediate from which saturated C 8 aldehydes are produced via NA-assisted intermolecular hydrogen transfer. Finally, two dehydrogenation reactions generate unsaturated C 8 aldehydes. In these reactions, water and NA molecules are found to play important roles. They significantly reduce relevant reaction barriers. Our work has also explored oxygenation reactions of NA with molecular oxygen and radical-radical dimerization reactions.

A monolithic and flexible fluoropolymer film microreactor for organic synthesis applications.

PubMed

Kim, Jin-Oh; Kim, Heejin; Ko, Dong-Hyeon; Min, Kyoung-Ik; Im, Do Jin; Park, Soo-Young; Kim, Dong-Pyo

2014-11-07

A photocurable and viscous fluoropolymer with chemical stability is a highly desirable material for fabrication of microchemical devices. Lack of a reliable fabrication method, however, limits actual applications for organic reactions. Herein, we report fabrication of a monolithic and flexible fluoropolymer film microreactor and its use as a new microfluidic platform. The fabrication involves facile soft lithography techniques that enable partial curing of thin laminates, which can be readily bonded by conformal contact without any external forces. We demonstrate fabrication of various functional channels (~300 μm thick) such as those embedded with either a herringbone micromixer pattern or a droplet generator. Organic reactions under strongly acidic and basic conditions can be carried out in this film microreactor even at elevated temperature with excellent reproducibility. In particular, the transparent film microreactor with good deformability could be wrapped around a light-emitting lamp for close contact with the light source for efficient photochemical reactions with visible light, which demonstrates easy integration with optical components for functional miniaturized systems.

Interactive effects of cadmium and acid rain on photosynthetic light reaction in soybean seedlings.

PubMed

Sun, Zhaoguo; Wang, Lihong; Chen, Minmin; Wang, Lei; Liang, Chanjuan; Zhou, Qing; Huang, Xiaohua

2012-05-01

Interactive effects of cadmium (Cd(2+)) and acid rain on photosynthetic light reaction in soybean seedlings were investigated under hydroponic conditions. Single treatment with Cd(2+) or acid rain and the combined treatment decreased the content of chlorophyll, Hill reaction rate, the activity of Mg(2+)-ATPase, maximal photochemical efficiency and maximal quantum yield, increased initial fluorescence and damaged the chloroplast structure in soybean seedlings. In the combined treatment, the change in the photosynthetic parameters and the damage of chloroplast structure were stronger than those of any single pollution. Meanwhile, Cd(2+) and acid rain had the interactive effects on the test indices in soybean seedlings. The results indicated that the combined pollution of Cd(2+) and acid rain aggravated the toxic effect of the single pollution of Cd(2+) or acid rain on the photosynthetic parameters due to the serious damage to the chloroplast structure. Copyright © 2011 Elsevier Inc. All rights reserved.

Enhanced Indirect Photochemical Transformation of Histidine and Histamine through Association with Chromophoric Dissolved Organic Matter.

PubMed

Chu, Chiheng; Lundeen, Rachel A; Remucal, Christina K; Sander, Michael; McNeill, Kristopher

2015-05-05

Photochemical transformations greatly affect the stability and fate of amino acids (AAs) in sunlit aquatic ecosystems. Whereas the direct phototransformation of dissolved AAs is well investigated, their indirect photolysis in the presence of chromophoric dissolved organic matter (CDOM) is poorly understood. In aquatic systems, CDOM may act both as sorbent for AAs and as photosensitizer, creating microenvironments with high concentrations of photochemically produced reactive intermediates, such as singlet oxygen (1O2). This study provides a systematic investigation of the indirect photochemical transformation of histidine (His) and histamine by 1O2 in solutions containing CDOM as a function of solution pH. Both His and histamine showed pH-dependent enhanced phototransformation in the CDOM systems as compared to systems in which model, low-molecular-weight 1O2 sensitizers were used. Enhanced reactivity resulted from sorption of His and histamine to CDOM and thus exposure to elevated 1O2 concentrations in the CDOM microenvironment. The extent of reactivity enhancement depended on solution pH via its effects on the protonation state of His, histamine, and CDOM. Sorption-enhanced reactivity was independently supported by depressed rate enhancements in the presence of a cosorbate that competitively displaced His and histamine from CDOM. Incorporating sorption and photochemical transformation processes into a reaction rate prediction model improved the description of the abiotic photochemical transformation rates of His in the presence of CDOM.

Regioselectivity of enzymatic and photochemical single electron transfer promoted carbon-carbon bond fragmentation reactions of tetrameric lignin model compounds.

PubMed

Cho, Dae Won; Latham, John A; Park, Hea Jung; Yoon, Ung Chan; Langan, Paul; Dunaway-Mariano, Debra; Mariano, Patrick S

2011-04-15

New types of tetrameric lignin model compounds, which contain the common β-O-4 and β-1 structural subunits found in natural lignins, have been prepared and carbon-carbon bond fragmentation reactions of their cation radicals, formed by photochemical (9,10-dicyanoanthracene) and enzymatic (lignin peroxidase) SET-promoted methods, have been explored. The results show that cation radical intermediates generated from the tetrameric model compounds undergo highly regioselective C-C bond cleavage in their β-1 subunits. The outcomes of these processes suggest that, independent of positive charge and odd-electron distributions, cation radicals of lignins formed by SET to excited states of sensitizers or heme-iron centers in enzymes degrade selectively through bond cleavage reactions in β-1 vs β-O-4 moieties. In addition, the findings made in the enzymatic studies demonstrate that the sterically large tetrameric lignin model compounds undergo lignin peroxidase-catalyzed cleavage via a mechanism involving preliminary formation of an enzyme-substrate complex.

Effect of high pressure on the photochemical reaction center from Rhodobacter sphaeroides R26.1.

PubMed Central

Gall, A; Ellervee, A; Bellissent-Funel, M C; Robert, B; Freiberg, A

2001-01-01

High-pressure studies on the photochemical reaction center from the photosynthetic bacterium Rhodobacter sphaeroides, strain R26.1, shows that, up to 0.6 GPa, this carotenoid-less membrane protein does not loose its three-dimensional structure at room temperature. However, as evidenced by Fourier-transform preresonance Raman and electronic absorption spectra, between the atmospheric pressure and 0.2 GPa, the structure of the bacterial reaction center experiences a number of local reorganizations in the binding site of the primary electron donor. Above that value, the apparent compressibility of this membrane protein is inhomogeneous, being most noticeable in proximity to the bacteriopheophytin molecules. In this elevated pressure range, no more structural reorganization of the primary electron donor binding site can be observed. However, its electronic structure becomes dramatically perturbed, and the oscillator strength of its Q(y) electronic transition drops by nearly one order of magnitude. This effect is likely due to very small, pressure-induced changes in its dimeric structure. PMID:11222309

Excimer laser induced surface chemical modification of polytetrafluoroethylene

NASA Astrophysics Data System (ADS)

Révész, K.; Hopp, B.; Bor, Z.

1997-02-01

Polytetrafluoroethylene has a notoriously non adhesive and non reactive character. Its successful surface photochemical modification was performed by irradiating the polytetrafluoroethylene/liquid triethylamine interface with an ArF excimer laser (λ=193 nm). Due to the photochemical treatment the polytetrafluoroethylene surface became more hydrophilic. The water receding contact angle decreased from 94° to 43°. The reaction cross section was determined from the decrease of the contact angles. It was found to be as high as 6.4×10-18 cm2. XPS measurements evidenced the removal of fluorine from the polytetrafluoroethylene, incorporation of alkyl carbon and nitrogen. Photochemical dissociation path of the triethylamine makes probable that it bonded to the fluoropolymer backbone via the α-carbon atom of an ethyl group. A radical, or a photoinduced electron transfer mechanism was suggested to describe this reaction. A selective area electroless plating of silver was performed after pretreating the sample with patterned photomodification. The increased adhesion of the sample was proved by gluing with epoxy resin. As a result of the surface modification the tensile strength of gluing increased by 210× and reached 24% of the value characteristic for the bulk material.

Lagrangian photochemical modeling studies of the 1987 Antarctic spring vortex. II - Seasonal trends in ozone

NASA Technical Reports Server (NTRS)

Austin, J.; Jones, R. L.; Mckenna, D. S.; Buckland, A. T.; Anderson, J. G.; Fahey, D. W.; Farmer, C. B.; Heidt, L. E.; Proffitt, M. H.; Vedder, J. F.

1989-01-01

A photochemical model consisting of 40 species and 107 reactions is integrated along 80-day air parcel trajectories calculated in the lower stratosphere for the springtime Antarctic. For the trajectory starting at 58 deg S, which may be regarded as outside the circumpolar vortex, only a small change in O3 occurs in the model. In contrast, for the air parcel starting in the vortex at 74 deg S, the O3 concentration is reduced by 93 percent during the 80 days from the beginning of August to late October. The model results for several species are compared with measurements from the Airborne Antarctic Ozone Experiment and, in general, good agreement is obtained. In the model, the dentrification of the air parcels in polar stratospheric clouds increases the amount of chlorine present in active form. Heterogeneous reactions maintain high active chlorine which destroys O3 via the formation of the ClO dimer. Results of calculations with reduced concentrations of inorganic chlorine show considerably reduced O3 destruction rates and compare favorably with the behavior of total O3 since the late 1970s. The remaining major uncertainties in the photochemical aspects of the Antarctic ozone hole are highlighted.

Modeling the formation and aging of secondary organic aerosols during CalNex 2010

NASA Astrophysics Data System (ADS)

Hayes, P. L.; Ortega, A. M.; Ahmadov, R.; McKeen, S. A.; Washenfelder, R. A.; Alvarez, S.; Rappenglueck, B.; Holloway, J. S.; Gilman, J. B.; Kuster, W. C.; De Gouw, J. A.; Zotter, P.; Prevot, A. S.; Kleindienst, T. E.; Offenberg, J. H.; Jimenez, J. L.

2012-12-01

Several traditional and recently proposed models are applied to predict the concentrations and properties of secondary organic aerosols (SOA) and organic gases at the Pasadena ground site during the CalNex campaign. The models are constrained with and compared against results from available observations. The CalNex campaign and specifically the Pasadena ground site featured a large and sophisticated suite of aerosol and gas phase instrumentation, and thus, it provides a unique opportunity to test SOA models under conditions of strong urban emissions at a range of low photochemical ages. The oxidation of volatile organic compounds (VOCs) using an updated traditional model cannot explain the observed ambient SOA, and under-predicts the measurements by a factor of ~40. Similarly, after accounting for the multi-generation oxidation of VOCs using a volatility basis set (VBS) approach as described by Tsimpidi et al. (2010), SOA is still under-predicted by a factor of ~8. For SOA formed from VOCs (V-SOA) the dominant precursors are aromatics (xylenes, toluene, and trimethylbenzenes). The model SOA formed from the oxidation of primary semivolatile and intermediate volatility organic compounds (P-S/IVOCs, producing SI-SOA) is also predicted using the parameterizations of Robinson et al. (2007) and Grieshop et al. (2009), and the properties of V-SOA + SI-SOA are compared against the measured O:C and volatility. We also compare the results of the different models against fossil/non-fossil carbon measurements as well as tracers of different SOA precursors. Potential Aerosol Mass (PAM) measurements of the SOA forming potential of the Pasadena air masses are also compared against that predicted by the models. The PAM analysis allows for model/measurement comparisons of SOA properties over a range of photochemical ages spanning almost two weeks. Using the V-SOA model, at low photochemical ages (< 1 day) the modeled PAM V-SOA is less than the measured PAM SOA, similar to the ambient results. In contrast, at high photochemical ages (i.e., more than about three days) the modeled PAM V-SOA is substantially greater than that measured, which is likely due fragmentation reactions that are not included in that model. We derive a parameterization of the measured PAM SOA as a function of the input photochemical age and the PAM photochemical age that serves as a comparison with other SOA models.

A cloud-ozone data product from Aura OMI and MLS satellite measurements

NASA Astrophysics Data System (ADS)

Ziemke, Jerald R.; Strode, Sarah A.; Douglass, Anne R.; Joiner, Joanna; Vasilkov, Alexander; Oman, Luke D.; Liu, Junhua; Strahan, Susan E.; Bhartia, Pawan K.; Haffner, David P.

2017-11-01

Ozone within deep convective clouds is controlled by several factors involving photochemical reactions and transport. Gas-phase photochemical reactions and heterogeneous surface chemical reactions involving ice, water particles, and aerosols inside the clouds all contribute to the distribution and net production and loss of ozone. Ozone in clouds is also dependent on convective transport that carries low-troposphere/boundary-layer ozone and ozone precursors upward into the clouds. Characterizing ozone in thick clouds is an important step for quantifying relationships of ozone with tropospheric H2O, OH production, and cloud microphysics/transport properties. Although measuring ozone in deep convective clouds from either aircraft or balloon ozonesondes is largely impossible due to extreme meteorological conditions associated with these clouds, it is possible to estimate ozone in thick clouds using backscattered solar UV radiation measured by satellite instruments. Our study combines Aura Ozone Monitoring Instrument (OMI) and Microwave Limb Sounder (MLS) satellite measurements to generate a new research product of monthly-mean ozone concentrations in deep convective clouds between 30° S and 30° N for October 2004-April 2016. These measurements represent mean ozone concentration primarily in the upper levels of thick clouds and reveal key features of cloud ozone including: persistent low ozone concentrations in the tropical Pacific of ˜ 10 ppbv or less; concentrations of up to 60 pphv or greater over landmass regions of South America, southern Africa, Australia, and India/east Asia; connections with tropical ENSO events; and intraseasonal/Madden-Julian oscillation variability. Analysis of OMI aerosol measurements suggests a cause and effect relation between boundary-layer pollution and elevated ozone inside thick clouds over landmass regions including southern Africa and India/east Asia.

Rapid In Situ Profiling of Lipid C═C Location Isomers in Tissue Using Ambient Mass Spectrometry with Photochemical Reactions.

PubMed

Tang, Fei; Guo, Chengan; Ma, Xiaoxiao; Zhang, Jian; Su, Yuan; Tian, Ran; Shi, Riyi; Xia, Yu; Wang, Xiaohao; Ouyang, Zheng

2018-05-01

Rapid and in situ profiling of lipids using ambient mass spectrometry (AMS) techniques has great potential for clinical diagnosis, biological studies, and biomarker discovery. In this study, the online photochemical reaction involving carbon-carbon double bonds was coupled with a surface sampling technique to develop a direct tissue-analysis method with specificity to lipid C═C isomers. This method enabled the in situ analysis of lipids from the surface of various tissues or tissue sections, which allowed the structural characterization of lipid isomers within 2 min. Under optimized reaction conditions, we have established a method for the relative quantitation of lipid C═C location isomers by comparing the abundances of the diagnostic ions arising from each isomer, which has been proven effective through the established linear relationship ( R 2 = 0.999) between molar ratio and diagnostic ion ratio of the FA 18:1 C═C location isomers. This method was then used for the rapid profiling of unsaturated lipid C═C isomers in the sections of rat brain, lung, liver, spleen, and kidney, as well as in normal and diseased rat tissues. Quantitative information on FA 18:1 and PC 16:0-18:1 C═C isomers was obtained, and significant differences were observed between different samples. To the best of our knowledge, this is the first study to report the direct analysis of lipid C═C isomers in tissues using AMS. Our results demonstrated that this method can serve as a rapid analytical approach for the profiling of unsaturated lipid C═C isomers in biological tissues and should contribute to functional lipidomics and clinical diagnosis.

A Cloud-Ozone Data Product from Aura OMI and MLS Satellite Measurements.

PubMed

Ziemke, Jerald R; Strode, Sarah A; Douglass, Anne R; Joiner, Joanna; Vasilkov, Alexander; Oman, Luke D; Liu, Junhua; Strahan, Susan E; Bhartia, Pawan K; Haffner, David P

2017-01-01

Ozone within deep convective clouds is controlled by several factors involving photochemical reactions and transport. Gas-phase photochemical reactions and heterogeneous surface chemical reactions involving ice, water particles, and aerosols inside the clouds all contribute to the distribution and net production and loss of ozone. Ozone in clouds is also dependent on convective transport that carries low troposphere/boundary layer ozone and ozone precursors upward into the clouds. Characterizing ozone in thick clouds is an important step for quantifying relationships of ozone with tropospheric H 2 O, OH production, and cloud microphysics/transport properties. Although measuring ozone in deep convective clouds from either aircraft or balloon ozonesondes is largely impossible due to extreme meteorological conditions associated with these clouds, it is possible to estimate ozone in thick clouds using backscattered solar UV radiation measured by satellite instruments. Our study combines Aura Ozone Monitoring Instrument (OMI) and Microwave Limb Sounder (MLS) satellite measurements to generate a new research product of monthly-mean ozone concentrations in deep convective clouds between 30°S to 30°N for October 2004 - April 2016. These measurements represent mean ozone concentration primarily in the upper levels of thick clouds and reveal key features of cloud ozone including: persistent low ozone concentrations in the tropical Pacific of ~10 ppbv or less; concentrations of up to 60 pphv or greater over landmass regions of South America, southern Africa, Australia, and India/east Asia; connections with tropical ENSO events; and intra-seasonal/Madden-Julian Oscillation variability. Analysis of OMI aerosol measurements suggests a cause and effect relation between boundary layer pollution and elevated ozone inside thick clouds over land-mass regions including southern Africa and India/east Asia.

Time resolved thermal lens in edible oils

NASA Astrophysics Data System (ADS)

Albuquerque, T. A. S.; Pedreira, P. R. B.; Medina, A. N.; Pereira, J. R. D.; Bento, A. C.; Baesso, M. L.

2003-01-01

In this work time resolved thermal lens spectrometry is applied to investigate the optical properties of the following edible oils: soya, sunflower, canola, and corn oils. The experiments were performed at room temperature using the mode mismatched thermal lens configuration. The results showed that when the time resolved procedure is adopted the technique can be applied to investigate the photosensitivity of edible oils. Soya oil presented a stronger photochemical reaction as compared to the other investigated samples. This observation may be relevant for future studies evaluating edible oils storage conditions and also may contribute to a better understanding of the physical and chemical properties of this important foodstuff.

Flow Tube Studies of Gas Phase Chemical Processes of Atmospheric Importance

NASA Technical Reports Server (NTRS)

Molina, Mario J.

1998-01-01

The objective of this project is to conduct measurements of elementary reaction rate constants and photochemical parameters for processes of importance in the atmosphere. These measurements are being carried out under temperature and pressure conditions covering those applicable to the stratosphere and upper troposphere, using the chemical ionization mass spectrometry turbulent flow technique developed in our laboratory. The next section summarizes our research activities during the first year of the project, and the section that follows consists of the statement of work for the third year. Additional details concerning the projects listed in the statement of work were described in our original proposal.

Tested Demonstrations.

ERIC Educational Resources Information Center

Gilbert, George L., Ed.

1981-01-01

Provides procedures for demonstrations: (1) the ferrioxalate actinometer, which demonstrates a photochemical reaction; and (2) the silver mirror, which demonstrates the reduction of a metal salt to the metal and/or the reducing power of sugars. (CS)

Catalysts for low-energy aldehyde processes

NASA Technical Reports Server (NTRS)

Gupta, A.; Rembaum, A.; Frazier, C.; Gray, H. B.

1977-01-01

Photochemical reaction of dicobalt octacarbonyl with polymeric support systems results in formation of polymer bonded metal catalyst. Catalyst is used in hydroformylation (addition of carbon dioxide and hydrogen) of olefins to yield aldehydes.

Extensions of a Basic Laboratory Experiment: [4+2] and [2+2] Cycloadditions

ERIC Educational Resources Information Center

Amarne, Hazem Y.; Bain, Alex D.; Neumann, Karen; Zelisko, Paul M.

2008-01-01

We describe an extended third-year undergraduate chemistry laboratory exercise in which a number of techniques and concepts are applied to the same set of chemical reactions. The reactions are the photochemical and thermal cycloadditions of [beta]-nitrostyrene and 2,3-dimethylbutadiene. This can be viewed as a single long lab or a series of…

Photochemical charge separation in zeolites: Electron transfer dynamics, nanocrystals and zeolitic membranes. Final technical report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dutta, Prabir K.

2001-09-30

Aluminosilicate zeolites provide an excellent host for photochemical charge separation. Because of the constraints provided by the zeolite, the back electron transfer from the reduced acceptor to the oxidized sensitizer is slowed down. This provides the opportunity to separate the charge and use it in a subsequent reaction for water oxidation and reduction. Zeolite-based ruthenium oxide catalysts have been found to be efficient for the water splitting process. This project has demonstrated the usefulness of zeolite hosts for photolytic splitting of water.

Chemical Kinetics and Photochemical Data for Use in Atmospheric Studies Evaluation Number 16. Supplement to Evaluation 15: Update of Key Reactions

NASA Technical Reports Server (NTRS)

Sander, S. P.; Friedl, R. R.; Barker, J. R.; Golden, D. M.; Kurylo, M. J.; Wine, P. H.; Abbatt, J.; Burkholder, J. B.; Kolb, C. E.; Moortgat, G. K.;

Construction of a photochemical reactor combining a CCD spectrophotometer and a LED radiation source.

PubMed

Gombár, Melinda; Józsa, Éva; Braun, Mihály; Ősz, Katalin

2012-10-01

An inexpensive photoreactor using LED light sources and a fibre-optic CCD spectrophotometer as a detector was built by designing a special cell holder for standard 1.000 cm cuvettes. The use of this device was demonstrated by studying the aqueous photochemical reaction of 2,5-dichloro-1,4-benzoquinone. The developed method combines the highly quantitative data collection of CCD spectrophotometers with the possibility of illuminating the sample independently of the detecting light beam, which is a substantial improvement of the method using diode array spectrophotometers as photoreactors.

Patterned Functionalization of Gold and Single Crystal Silicon via Photochemical Reaction of Surface-Confined Derivatives of (Eta5-C5H5)MN(CO)3

DTIC Science & Technology

1990-11-01

output at -355 nm) until significant conversion of the tricarbonyl to the dicarbonyl phosphine was achieved, as determined by IR. The disubstitited product...forms rapidly once the dicarbonyl phosphine is present in solution so care was taken to stop the irradiation prior to extensive formation of...photochemical behavior and yields photoproducts analogous to those formed upon irradiation of (T5 -C 5 H4 )Mn(CO) 3 in the presence of phosphines . 7 UV

Photochemical dimerization and functionalization of alkanes, ethers, primary and secondary alcohols, phosphine oxides and silanes

DOEpatents

Crabtree, Robert H.; Brown, Stephen H.

1989-01-01

The space-time yield and/or the selectivity of the photochemical dimerization of alkanes, ethers, primary and secondary alcohols, phosphine oxides and primary, secondary and tertiary silanes with Hg and U.V. light is enhanced by refluxing the substrate in the irradiated reaction zone at a temperature at which the dimer product condenses and remains condensed promptly upon its formation. Cross-dimerization of the alkanes, ethers and silanes with primary alcohols is disclosed, as is the functionalization to aldehydes of the alkanes with carbon monoxide.

Photochemical dimerization and functionalization of alkanes, ethers, primary and secondary alcohols, phosphine oxides and silanes

DOEpatents

Crabtree, R.H.; Brown, S.H.

1989-10-17

The space-time yield and/or the selectivity of the photochemical dimerization of alkanes, ethers, primary and secondary alcohols, phosphine oxides and primary, secondary and tertiary silanes with Hg and U.V. light is enhanced by refluxing the substrate in the irradiated reaction zone at a temperature at which the dimer product condenses and remains condensed promptly upon its formation. Cross-dimerization of the alkanes, ethers and silanes with primary alcohols is disclosed, as is the functionalization to aldehydes of the alkanes with carbon monoxide.

A versatile method for the determination of photochemical quantum yields via online UV-Vis spectroscopy.

PubMed

Stadler, Eduard; Eibel, Anna; Fast, David; Freißmuth, Hilde; Holly, Christian; Wiech, Mathias; Moszner, Norbert; Gescheidt, Georg

2018-05-16

We have developed a simple method for determining the quantum yields of photo-induced reactions. Our setup features a fibre coupled UV-Vis spectrometer, LED irradiation sources, and a calibrated spectrophotometer for precise measurements of the LED photon flux. The initial slope in time-resolved absorbance profiles provides the quantum yield. We show the feasibility of our methodology for the kinetic analysis of photochemical reactions and quantum yield determination. The typical chemical actinometers, ferrioxalate and ortho-nitrobenzaldehyde, as well as riboflavin, a spiro-compound, phosphorus- and germanium-based photoinitiators for radical polymerizations and the frequently utilized photo-switch azobenzene serve as paradigms. The excellent agreement of our results with published data demonstrates the high potential of the proposed method as a convenient alternative to the time-consuming chemical actinometry.

An infrared study of the nitro—nitrito linkage isomerization in solid nitro- and nitritopentamminecobalt(III) chloride

NASA Astrophysics Data System (ADS)

Heyns, A. M.; de Waal, D.

1989-01-01

The photochemical isomerization reaction of [Co(NH 3) 5NO 2]Cl 2 to [Co(NH 3) 5ONO]Cl 2 has been studied in the solid state by means of i.r. spectroscopy. The reaction is first order with k = 2.53±0.05 × 10 -4s -1 and is much faster ( t1/2=49min) than the well-known spontaneous nitrito → nitro isomerization ( t1/2 = 6 days). The i.r. bands of both the NH 3 and ONO - -groups in the range 4000-50 cm -1 indicate minor differences between the structures of freshly and photochemically prepared [Co(NH 3) 5ONO]Cl 2. The far i.r. spectra indicate the disorder existing in the intermediate products during the isomerization processes.

PHOTOCHEMICAL REACTION OF NITRO-POLYCYCLIC AROMATIC HYDROCARBONS: EFFECT BY SOLVENT AND STRUCTURE

PubMed Central

Stewart, Gernerique; Smith, Keonia; Chornes, Ashley; Harris, Tracy; Honeysucker, Tiffany; Dasary, Suman Raj; Yu, Hongtao

2010-01-01

Photochemical degradation of 1-nitropyrene, 2-nitrofluorene, 2,7-dinitrofluorene, 6-nitrochrysene, 3-nitrofluoranthene, 5-nitroacenaphthene, and 9-nitroanthracene were examined in CHCl3, CH2Cl2, DMF, DMF/H2O (80/20), CH3CN, or CH3CN/H2O (80/20). The degradation follows mostly the 1st order kinetics; but a few follow 2nd order kinetics or undergo self-catalysis. The photodegradation rates follow the order: CHCl3 > CH2Cl2 > DMF > DMF/H2O > CH3CN > CH3CN/H2O. DMF is an exceptional solvent because 3 of the 7 compounds undergo self-catalytic reaction. 9-Nitroanthracene, which has a perpendicular nitro group, is the fastest, while the more compact 1-nitropyrene and 3-nitrofluoranthene, are the slowest degrading compounds. PMID:21170286

Factors controlling the redox potential of ZnCe6 in an engineered bacterioferritin photochemical 'reaction centre'.

PubMed

Mahboob, Abdullah; Vassiliev, Serguei; Poddutoori, Prashanth K; van der Est, Art; Bruce, Doug

2013-01-01

Photosystem II (PSII) of photosynthesis has the unique ability to photochemically oxidize water. Recently an engineered bacterioferritin photochemical 'reaction centre' (BFR-RC) using a zinc chlorin pigment (ZnCe6) in place of its native heme has been shown to photo-oxidize bound manganese ions through a tyrosine residue, thus mimicking two of the key reactions on the electron donor side of PSII. To understand the mechanism of tyrosine oxidation in BFR-RCs, and explore the possibility of water oxidation in such a system we have built an atomic-level model of the BFR-RC using ONIOM methodology. We studied the influence of axial ligands and carboxyl groups on the oxidation potential of ZnCe6 using DFT theory, and finally calculated the shift of the redox potential of ZnCe6 in the BFR-RC protein using the multi-conformational molecular mechanics-Poisson-Boltzmann approach. According to our calculations, the redox potential for the first oxidation of ZnCe6 in the BRF-RC protein is only 0.57 V, too low to oxidize tyrosine. We suggest that the observed tyrosine oxidation in BRF-RC could be driven by the ZnCe6 di-cation. In order to increase the efficiency of tyrosine oxidation, and ultimately oxidize water, the first potential of ZnCe6 would have to attain a value in excess of 0.8 V. We discuss the possibilities for modifying the BFR-RC to achieve this goal.

Nature and kinetic analysis of carbon-carbon bond fragmentation reactions of cation radicals derived from SET-oxidation of lignin model compounds.

PubMed

Cho, Dae Won; Parthasarathi, Ramakrishnan; Pimentel, Adam S; Maestas, Gabriel D; Park, Hea Jung; Yoon, Ung Chan; Dunaway-Mariano, Debra; Gnanakaran, S; Langan, Paul; Mariano, Patrick S

2010-10-01

Features of the oxidative cleavage reactions of diastereomers of dimeric lignin model compounds, which are models of the major types of structural units found in the lignin backbone, were examined. Cation radicals of these substances were generated by using SET-sensitized photochemical and Ce(IV) and lignin peroxidase promoted oxidative processes, and the nature and kinetics of their C-C bond cleavage reactions were determined. The results show that significant differences exist between the rates of cation radical C1-C2 bond cleavage reactions of 1,2-diaryl-(β-1) and 1-aryl-2-aryloxy-(β-O-4) propan-1,3-diol structural units found in lignins. Specifically, under all conditions C1-C2 bond cleavage reactions of cation radicals of the β-1 models take place more rapidly than those of the β-O-4 counterparts. The results of DFT calculations on cation radicals of the model compounds show that the C1-C2 bond dissociation energies of the β-1 lignin model compounds are significantly lower than those of the β-O-4 models, providing clear evidence for the source of the rate differences.

Atmospheric chemistry and transport modeling in the outer solar system

NASA Astrophysics Data System (ADS)

Lee, Yuan-Tai (Anthony)

2001-11-01

This thesis consists of 1-D and 2-D photochemical- dynamical modeling in the upper atmospheres of outer planets. For 1-D modeling, a unified hydrocarbon photochemical model has been studied in Jupiter, Saturn, Uranus, Neptune, and Titan, by comparing with the Voyager observations, and the recent measurements of methyl radicals by ISO in Saturn and Neptune. The CH3 observation implies a kinetically sensitive test to the measured and estimated hydrocarbon rate constants at low temperatures. We identify the key reactions that control the concentrations of CH3 in the model, such as the three-body recombination reaction, CH3 + CH3 + M --> C 2H6 + M, and the recycling reaction H + CH3 + M --> CH4 + M. The results show reasonable agreement with ISO values. In Chapter 4, the detection of PH3 in the lower stratosphere and upper troposphere of Jupiter has provided a photochemical- dynamical coupling model to derive the eddy diffusion coefficient in the upper troposphere of Jupiter. Using a two-layers photochemical model with updated photodissociation cross-sections and chemical rate constants for NH3 and PH 3, we find that the upper tropospheric eddy diffusion coefficient <10 5 cm2 sec-1, and the deeper tropospheric value >106 cm2 sec-1, are required to match the derived PH3 vertical profile by the observation. The best-fit functional form derivation of eddy diffusion coefficient in the upper troposphere of Jupiter above 400 mbar is K = 2.0 × 104 (n/2.2 × 1019)-0.5 cm 2 sec-1. On the other hand, Chapter 5 demonstrates a dynamical-only 2-D model of C2H6 providing a complete test for the current 2-D transport models in Jovian lower stratosphere and upper troposphere (270 to 0.1 mbar pressure levels). Different combinations of residual advection, horizontal eddy dispersion, and vertical eddy mixing are examined at different latitudes.

Molecular transformations of phenolic SOA during photochemical aging in the aqueous phase: Competition among oligomerization, functionalization, and fragmentation

DOE PAGES

Yu, Lu; Smith, Jeremy; Laskin, Alexander; ...

2016-04-13

Organic aerosol is formed and transformed in atmospheric aqueous phases (e.g., cloud and fog droplets and deliquesced airborne particles containing small amounts of water) through a multitude of chemical reactions. Understanding these reactions is important for a predictive understanding of atmospheric aging of aerosols and their impacts on climate, air quality, and human health. In this study, we investigate the chemical evolution of aqueous secondary organic aerosol (aqSOA) formed during reactions of phenolic compounds with two oxidants – the triplet excited state of an aromatic carbonyl ( 3C *) and hydroxyl radical ( • OH). Changes in themore » molecular composition of aqSOA as a function of aging time are characterized using an offline nanospray desorption electrospray ionization mass spectrometer (nano-DESI MS) whereas the real-time evolution of SOA mass, elemental ratios, and average carbon oxidation state (OS C) are monitored using an online aerosol mass spectrometer (AMS). Our results indicate that oligomerization is an important aqueous reaction pathway for phenols, especially during the initial stage of photooxidation equivalent to ~2 h irradiation under midday winter solstice sunlight in Northern California. At later reaction times functionalization (i.e., adding polar oxygenated functional groups to the molecule) and fragmentation (i.e., breaking of covalent bonds) become more important processes, forming a large variety of functionalized aromatic and open-ring products with higher OS C values. Fragmentation reactions eventually dominate the photochemical evolution of phenolic aqSOA, forming a large number of highly oxygenated ring-opening molecules with carbon numbers ( n C) below 6. The average n C of phenolic aqSOA decreases while average OS C increases over the course of photochemical aging. In addition, the saturation vapor pressures ( C *) of dozens of the most abundant phenolic aqSOA molecules are estimated. A wide range of C * values is observed, varying from < 10 –20 µg m –3 for functionalized phenolic oligomers to > 10 µg m –3 for small open-ring species. Furthermore, the detection of abundant extremely low-volatile organic compounds (ELVOC) indicates that aqueous reactions of phenolic compounds are likely an important source of ELVOC in the atmosphere.« less

Molecular transformations of phenolic SOA during photochemical aging in the aqueous phase: Competition among oligomerization, functionalization, and fragmentation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Lu; Smith, Jeremy; Laskin, Alexander

Organic aerosol is formed and transformed in atmospheric aqueous phases (e.g., cloud and fog droplets and deliquesced airborne particles containing small amounts of water) through a multitude of chemical reactions. Understanding these reactions is important for a predictive understanding of atmospheric aging of aerosols and their impacts on climate, air quality, and human health. In this study, we investigate the chemical evolution of aqueous secondary organic aerosol (aqSOA) formed during reactions of phenolic compounds with two oxidants – the triplet excited state of an aromatic carbonyl ( 3C *) and hydroxyl radical ( • OH). Changes in themore » molecular composition of aqSOA as a function of aging time are characterized using an offline nanospray desorption electrospray ionization mass spectrometer (nano-DESI MS) whereas the real-time evolution of SOA mass, elemental ratios, and average carbon oxidation state (OS C) are monitored using an online aerosol mass spectrometer (AMS). Our results indicate that oligomerization is an important aqueous reaction pathway for phenols, especially during the initial stage of photooxidation equivalent to ~2 h irradiation under midday winter solstice sunlight in Northern California. At later reaction times functionalization (i.e., adding polar oxygenated functional groups to the molecule) and fragmentation (i.e., breaking of covalent bonds) become more important processes, forming a large variety of functionalized aromatic and open-ring products with higher OS C values. Fragmentation reactions eventually dominate the photochemical evolution of phenolic aqSOA, forming a large number of highly oxygenated ring-opening molecules with carbon numbers ( n C) below 6. The average n C of phenolic aqSOA decreases while average OS C increases over the course of photochemical aging. In addition, the saturation vapor pressures ( C *) of dozens of the most abundant phenolic aqSOA molecules are estimated. A wide range of C * values is observed, varying from < 10 –20 µg m –3 for functionalized phenolic oligomers to > 10 µg m –3 for small open-ring species. Furthermore, the detection of abundant extremely low-volatile organic compounds (ELVOC) indicates that aqueous reactions of phenolic compounds are likely an important source of ELVOC in the atmosphere.« less

Molecular transformations of phenolic SOA during photochemical aging in the aqueous phase: competition among oligomerization, functionalization, and fragmentation

NASA Astrophysics Data System (ADS)

Yu, L.; Smith, J.; Laskin, A.; George, K. M.; Anastasio, C.; Laskin, J.; Dillner, A. M.; Zhang, Q.

2015-10-01

Organic aerosol is formed and transformed in atmospheric aqueous phases (e.g., cloud and fog droplets and deliquesced airborne particles containing small amounts of water) through a multitude of chemical reactions. Understanding these reactions is important for a predictive understanding of atmospheric aging of aerosols and their impacts on climate, air quality, and human health. In this study, we investigate the chemical evolution of aqueous secondary organic aerosol (aqSOA) formed during reactions of phenolic compounds with two oxidants - the triplet excited state of an aromatic carbonyl (3C*) and hydroxyl radical (•OH). Changes in the molecular composition of aqSOA as a function of aging time are characterized using an offline nanospray desorption electrospray ionization mass spectrometer (nano-DESI MS) whereas the real-time evolution of SOA mass, elemental ratios, and average carbon oxidation state (OSC) are monitored using an online aerosol mass spectrometer (AMS). Our results indicate that oligomerization is an important aqueous reaction pathway for phenols, especially during the initial stage of photooxidation equivalent to ∼ 2 h irradiation under midday, winter solstice sunlight in northern California. At later reaction times functionalization (i.e., adding polar oxygenated functional groups to the molecule) and fragmentation (i.e., breaking of covalent bonds) become more important processes, forming a large variety of functionalized aromatic and open-ring products with higher OSC values. Fragmentation reactions eventually dominate the photochemical evolution of phenolic aqSOA, forming a large number of highly oxygenated open-ring molecules with carbon numbers (nC) below 6. The average nC of phenolic aqSOA decreases while average OSC increases over the course of photochemical aging. In addition, the saturation vapor pressures C*) of dozens of the most abundant phenolic aqSOA molecules are estimated. A wide range of C* values is observed, varying from < 10-20 μg m-3 for functionalized phenolic oligomers to > 10 μg m-3 for small open-ring species. The detection of abundant extremely low volatile organic compounds (ELVOC) indicates that aqueous reactions of phenolic compounds are likely an important source of ELVOC in the atmosphere.

Molecular transformations of phenolic SOA during photochemical aging in the aqueous phase: competition among oligomerization, functionalization, and fragmentation

NASA Astrophysics Data System (ADS)

Yu, Lu; Smith, Jeremy; Laskin, Alexander; George, Katheryn M.; Anastasio, Cort; Laskin, Julia; Dillner, Ann M.; Zhang, Qi

2016-04-01

Organic aerosol is formed and transformed in atmospheric aqueous phases (e.g., cloud and fog droplets and deliquesced airborne particles containing small amounts of water) through a multitude of chemical reactions. Understanding these reactions is important for a predictive understanding of atmospheric aging of aerosols and their impacts on climate, air quality, and human health. In this study, we investigate the chemical evolution of aqueous secondary organic aerosol (aqSOA) formed during reactions of phenolic compounds with two oxidants - the triplet excited state of an aromatic carbonyl (3C∗) and hydroxyl radical (•OH). Changes in the molecular composition of aqSOA as a function of aging time are characterized using an offline nanospray desorption electrospray ionization mass spectrometer (nano-DESI MS) whereas the real-time evolution of SOA mass, elemental ratios, and average carbon oxidation state (OSC) are monitored using an online aerosol mass spectrometer (AMS). Our results indicate that oligomerization is an important aqueous reaction pathway for phenols, especially during the initial stage of photooxidation equivalent to ˜ 2 h irradiation under midday winter solstice sunlight in Northern California. At later reaction times functionalization (i.e., adding polar oxygenated functional groups to the molecule) and fragmentation (i.e., breaking of covalent bonds) become more important processes, forming a large variety of functionalized aromatic and open-ring products with higher OSC values. Fragmentation reactions eventually dominate the photochemical evolution of phenolic aqSOA, forming a large number of highly oxygenated ring-opening molecules with carbon numbers (nC) below 6. The average nC of phenolic aqSOA decreases while average OSC increases over the course of photochemical aging. In addition, the saturation vapor pressures (C∗) of dozens of the most abundant phenolic aqSOA molecules are estimated. A wide range of C∗ values is observed, varying from < 10-20 µg m-3 for functionalized phenolic oligomers to > 10 µg m-3 for small open-ring species. The detection of abundant extremely low-volatile organic compounds (ELVOC) indicates that aqueous reactions of phenolic compounds are likely an important source of ELVOC in the atmosphere.

Photochemical Transformation of Graphene Oxide in Sunlight

EPA Science Inventory

Graphene oxide (GO) is a graphene derivative that is more easily manufactured in large scale and used to synthesize reduced graphene oxide (rGO) with properties analogous to graphene. In this study, we investigate the photochemical fate of GO under sunlight conditions. The resu...

Volatile Organic Compounds from Logwood Combustion: Emissions and Transformation under Dark and Photochemical Aging Conditions in a Smog Chamber.

PubMed

Hartikainen, Anni; Yli-Pirilä, Pasi; Tiitta, Petri; Leskinen, Ari; Kortelainen, Miika; Orasche, Jürgen; Schnelle-Kreis, Jürgen; Lehtinen, Kari E J; Zimmermann, Ralf; Jokiniemi, Jorma; Sippula, Olli

2018-04-17

Residential wood combustion (RWC) emits high amounts of volatile organic compounds (VOCs) into ambient air, leading to formation of secondary organic aerosol (SOA), and various health and climate effects. In this study, the emission factors of VOCs from a logwood-fired modern masonry heater were measured using a Proton-Transfer-Reactor Time-of-Flight Mass Spectrometer. Next, the VOCs were aged in a 29 m 3 Teflon chamber equipped with UV black lights, where dark and photochemical atmospheric conditions were simulated. The main constituents of the VOC emissions were carbonyls and aromatic compounds, which accounted for 50%-52% and 30%-46% of the detected VOC emission, respectively. Emissions were highly susceptible to different combustion conditions, which caused a 2.4-fold variation in emission factors. The overall VOC concentrations declined considerably during both dark and photochemical aging, with simultaneous increase in particulate organic aerosol mass. Especially furanoic and phenolic compounds decreased, and they are suggested to be the major precursors of RWC-originated SOA in all aging conditions. On the other hand, dark aging produced relatively high amounts of nitrogen-containing organic compounds in both gas and particulate phase, while photochemical aging increased especially the concentrations of certain gaseous carbonyls, particularly acid anhydrides.

Mechanistic details for cobalt catalyzed photochemical hydrogen production in aqueous solution: Efficiencies of the photochemical and non-photochemical steps

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shan, Bing; Baine, Teera; Ma, Xuan Anh N.

2013-04-17

The use of sunlight to drive chemical reactions that lead to the reduction of water to produce hydrogen is a potential avenue of solar energy utilization. There are many individual steps that take place in this process. This paper reports the investigation of a particular system that involves light absorbing molecules, electron donating agents and a catalyst for water reduction to hydrogen. We evaluated the efficiency of the light induced formation of a strong electron donor, the use of this donor to reduce the catalyst and finally the efficiency of the catalyst to produce hydrogen from water. From this, themore » sources of loss of efficiency could be clearly identified and used in the design of better systems to produce hydrogen from water.« less

Additive and Photochemical Manufacturing of Copper

PubMed Central

Yung, Winco K. C.; Sun, Bo; Meng, Zhengong; Huang, Junfeng; Jin, Yingdi; Choy, Hang Shan; Cai, Zhixiang; Li, Guijun; Ho, Cheuk Lam; Yang, Jinlong; Wong, Wai Yeung

2016-01-01

In recent years, 3D printing technologies have been extensively developed, enabling rapid prototyping from a conceptual design to an actual product. However, additive manufacturing of metals in the existing technologies is still cost-intensive and time-consuming. Herein a novel platform for low-cost additive manufacturing is introduced by simultaneously combining the laser-induced forward transfer (LIFT) method with photochemical reaction. Using acrylonitrile butadiene styrene (ABS) polymer as the sacrificial layer, sufficient ejection momentum can be generated in the LIFT method. A low-cost continuous wave (CW) laser diode at 405 nm was utilized and proved to be able to transfer the photochemically synthesized copper onto the target substrate. The wavelength-dependent photochemical behaviour in the LIFT method was verified and characterized by both theoretical and experimental studies compared to 1064 nm fiber laser. The conductivity of the synthesized copper patterns could be enhanced using post electroless plating while retaining the designed pattern shapes. Prototypes of electronic circuits were accordingly built and demonstrated for powering up LEDs. Apart from pristine PDMS materials with low surface energies, the proposed method can simultaneously perform laser-induced forward transfer and photochemical synthesis of metals, starting from their metal oxide forms, onto various target substrates such as polyimide, glass and thermoplastics. PMID:28000733

Additive and Photochemical Manufacturing of Copper

NASA Astrophysics Data System (ADS)

Yung, Winco K. C.; Sun, Bo; Meng, Zhengong; Huang, Junfeng; Jin, Yingdi; Choy, Hang Shan; Cai, Zhixiang; Li, Guijun; Ho, Cheuk Lam; Yang, Jinlong; Wong, Wai Yeung

2016-12-01

In recent years, 3D printing technologies have been extensively developed, enabling rapid prototyping from a conceptual design to an actual product. However, additive manufacturing of metals in the existing technologies is still cost-intensive and time-consuming. Herein a novel platform for low-cost additive manufacturing is introduced by simultaneously combining the laser-induced forward transfer (LIFT) method with photochemical reaction. Using acrylonitrile butadiene styrene (ABS) polymer as the sacrificial layer, sufficient ejection momentum can be generated in the LIFT method. A low-cost continuous wave (CW) laser diode at 405 nm was utilized and proved to be able to transfer the photochemically synthesized copper onto the target substrate. The wavelength-dependent photochemical behaviour in the LIFT method was verified and characterized by both theoretical and experimental studies compared to 1064 nm fiber laser. The conductivity of the synthesized copper patterns could be enhanced using post electroless plating while retaining the designed pattern shapes. Prototypes of electronic circuits were accordingly built and demonstrated for powering up LEDs. Apart from pristine PDMS materials with low surface energies, the proposed method can simultaneously perform laser-induced forward transfer and photochemical synthesis of metals, starting from their metal oxide forms, onto various target substrates such as polyimide, glass and thermoplastics.

Investigation of power-plant plume photochemistry using a reactive plume model

NASA Astrophysics Data System (ADS)

Kim, Y. H.; Kim, H. S.; Song, C. H.

2016-12-01

Emissions from large-scale point sources have continuously increased due to the rapid industrial growth. In particular, primary and secondary air pollutants are directly relevant to atmospheric environment and human health. Thus, we tried to precisely describe the atmospheric photochemical conversion from primary to secondary air pollutants inside the plumes emitted from large-scale point sources. A reactive plume model (RPM) was developed to comprehensively consider power-plant plume photochemistry with 255 condensed photochemical reactions. The RPM can simulate two main components of power-plant plumes: turbulent dispersion of plumes and compositional changes of plumes via photochemical reactions. In order to evaluate the performance of the RPM developed in the present study, two sets of observational data obtained from the TexAQS II 2006 (Texas Air Quality Study II 2006) campaign were compared with RPM-simulated data. Comparison shows that the RPM produces relatively accurate concentrations for major primary and secondary in-plume species such as NO2, SO2, ozone, and H2SO4. Statistical analyses show good correlation, with correlation coefficients (R) ranging from 0.61 to 0.92, and good agreement with the Index of Agreement (IOA) ranging from 0.70 to 0.95. Following evaluation of the performance of the RPM, a demonstration was also carried out to show the applicability of the RPM. The RPM can calculate NOx photochemical lifetimes inside the two plumes (Monticello and Welsh power plants). Further applicability and possible uses of the RPM are also discussed together with some limitations of the current version of the RPM.

Laboratory simulation of photochemistry on Titan

NASA Astrophysics Data System (ADS)

Ferris, J.; Tran, B.; Force, M.; Briggs, R.; Vuitton, V.

Solar UV radiation is the principal energy source driving the chemistry in Titan's atmosphere ....(Sagan and Thompson, 1984). We have investigated the photochemical reactions in Titan's atmosphere in a flow reactor using the 185 and 254 nm UV emissions from a low-pressure mercury lamp ....(Clarke, et al., 2000) .....(Tran, et al., 2003). A solid product is formed using this apparatus and its optical properties have been measured since it is an analog of the haze layer on Titan. The complex refractive index of the solid material was determined and compared with the corresponding refractive index derived from the optical data obtained from Voyager 1 .......(Tran, et al., 2003). The current research focuses on the volatile reaction products. The principal gaseous compounds that absorb 185 nm light in Titan's atmosphere (acetylene, ethylene, and cyanoacetylene) were irradiated individually and in the presence of other atmospheric constituents at their mixing ratios in the Titan atmosphere. The objectives of this study are to determine the reaction pathways and to construct a model that reproduces the experimental results. Quantum yields for the loss of reactants and the formation of products were determined from the rates measured by gas chromatographic analysis. Irradiation of a mixture of acetylene, ethylene, cyanoacetylene, methane, hydrogen and nitrogen generated over 120 compounds. The structures of about 100 of these compounds were determined by GC/MS. The structures of many of these compounds were confirmed by use of authentic samples. The similarities and difference in the products obtained photochemically and by plasma discharges will be discussed. Clarke D. W., J. C. Joseph and J. P. Ferris, 2000, The design and use of a photochemical flow reactor: A laboratory study of the atmospheric chemistry of cyanoacetylene on Titan, Icarus, 282-291. Sagan C. and W. R. Thompson, 1984, Production and condensation of organic gases in the atmosphere of Titan, Icarus, 59, 133-161. Tran B. N., J. P. Ferris and J. J. Chera, 2003, The photochemical formation of a Titan haze analog. Structural analysis by X-ray photoelectron and infrared spectroscopy, Icarus, 162, 114-124. Tran B. N., J. C. Joseph, J. P. Ferris, P. D. Persans and J. J. Chera, 2003, Simulation of Titan haze formation using a photochemical flow reactor: The Optical constants of the polymer. Icarus, 165, 379-390.

Lasers: A Valuable Tool for Chemists.

ERIC Educational Resources Information Center

Findsen, E. W.; Ondrias, M. R.

1986-01-01

Discusses the properties of laser light, reviews types of lasers, presents operating principles, and considers mechanical aspects of laser light production. Applications reviewed include spectroscopy, photochemical reaction initiation, and investigation of biological processes involving porphyrins. (JM)

ROLE OF THE PHOTO-FENTON REACTION IN THE PRODUCTION OF HYDROXYL RADICALS AND PHOTOBLEACHING OF COLORED DISSOLVED ORGANIC MATTER IN A COASTAL RIVER OF THE SOUTHEASTERN UNITED STATES

EPA Science Inventory

Photochemical reactions involving colored dissolved organic matter (CDOM) in natural waters are important determinants of nutrient cycling, trace gas production and control of light penetration into the water column. In this study the role of the hydroxyl radical ((OH)-O-.) in CD...

Blue light induced free radicals from riboflavin on E. coli DNA damage.

PubMed

Liang, Ji-Yuan; Yuann, Jeu-Ming P; Cheng, Chien-Wei; Jian, Hong-Lin; Lin, Chin-Chang; Chen, Liang-Yu

2013-02-05

The micronutrients in many cellular processes, riboflavin (vitamin B(2)), FMN, and FAD are photo-sensitive to UV and visible light to generate reactive oxygen species (ROS). The riboflavin photochemical treatment with UV light has been applied for the inactivation of microorganisms to serve as an effective and safe technology. Ultra-violet or high-intensity radiation is, however, considered as a highly risky practice. This study was working on the application of visible LED lights to riboflavin photochemical reactions to development an effective antimicrobial treatment. The photosensitization of bacterial genome with riboflavin was investigated in vitro and in vivo by light quality and irradiation dosage. The riboflavin photochemical treatment with blue LED light was proved to be able to inactivate E. coli by damaging nucleic acids with ROS generated. Riboflavin is capable of intercalating between the bases of bacterial DNA or RNA and absorbs lights in the visible regions. LED light illumination could be a more accessible and safe practice for riboflavin photochemical treatments to achieve hygienic requirements in vitro. Copyright © 2013 Elsevier B.V. All rights reserved.

Coupling photochemical reaction detection based on singlet oxygen sensitization to capillary electrochromatography

PubMed

Dickson; Odom; Ducheneaux; Murray; Milofsky

2000-07-15

Despite the impressive separation efficiency afforded by capillary electrochromatography (CEC), the detection of UV-absorbing compounds following separation in capillary dimensions remains limited by the short path length (5-75 microm) through the column. Moreover, analytes that are poor chromophores present an additional challenge with respect to sensitive detection in CEC. This paper illustrates a new photochemical reaction detection scheme for CEC that takes advantage of the catalytic nature of type II photooxidation reactions. The sensitive detection scheme is selective toward molecules capable of photosensitizing the formation of singlet molecular oxygen (1O2). Following separation by CEC, UV-absorbing analytes promote groundstate 3O2 to an excited state (1O2) which reacts rapidly with tert-butyl-3,4,5-trimethylpyrrolecarboxylate, which is added to the running buffer. Detection is based on the loss of pyrrole. The reaction is catalytic in nature since one analyte molecule may absorb light many times, producing large amounts of 1O2. The detection limit for 9-acetylanthracene, following separation by CEC, is approximately 6 x 10(-9) M (S/N = 3). Optimization of the factors effecting the S/N for four model compounds is discussed.

$sup 18$O enrichment process in UO$sub 2$F$sub 2$ utilizing laser light

DOEpatents

DePoorter, G.L.; Rofer-DePoorter, C.K.

1975-12-01

Photochemical reaction induced by laser light is employed to separate oxygen isotopes. A solution containing UO$sub 2$F$sub 2$, HF, H$sub 2$O and a large excess of CH$sub 3$OH is irradiated with laser light of appropriate wavelength to differentially excite the UO$sub 2$$sup 2+$ ions containing $sup 16$O atoms and cause a reaction to proceed in accordance with the reaction 2 UO$sub 2$F$sub 2$ + CH$sub 3$OH + 4 HF $Yields$ 2 UF$sub 4$ down arrow + HCOOH + 3 H$sub 2$O. Irradiation is discontinued when about 10 percent of the UO$sub 2$F$sub 2$ has reacted, the UF$sub 4$ is filtered from the reaction mixture and the residual CH$sub 3$OH and HF plus the product HCOOH and H$sub 2$O are distilled away from the UO$sub 2$F$sub 2$ which is thereby enriched in the $sup 18$O isotope, or the solution containing the UO$sub 2$F$sub 2$ may be photochemically processed again to provide further enrichment in the $sup 18$O isotope.

Photochemical Hydrogen Doping Induced Embedded Two-Dimensional Metallic Channel Formation in InGaZnO at Room Temperature.

PubMed

Kim, Myeong-Ho; Lee, Young-Ahn; Kim, Jinseo; Park, Jucheol; Ahn, Seungbae; Jeon, Ki-Joon; Kim, Jeong Won; Choi, Duck-Kyun; Seo, Hyungtak

2015-10-27

The photochemical tunability of the charge-transport mechanism in metal-oxide semiconductors is of great interest since it may offer a facile but effective semiconductor-to-metal transition, which results from photochemically modified electronic structures for various oxide-based device applications. This might provide a feasible hydrogen (H)-radical doping to realize the effectively H-doped metal oxides, which has not been achieved by thermal and ion-implantation technique in a reliable and controllable way. In this study, we report a photochemical conversion of InGaZnO (IGZO) semiconductor to a transparent conductor via hydrogen doping to the local nanocrystallites formed at the IGZO/glass interface at room temperature. In contrast to thermal or ionic hydrogen doping, ultraviolet exposure of the IGZO surface promotes a photochemical reaction with H radical incorporation to surface metal-OH layer formation and bulk H-doping which acts as a tunable and stable highly doped n-type doping channel and turns IGZO to a transparent conductor. This results in the total conversion of carrier conduction property to the level of metallic conduction with sheet resistance of ∼16 Ω/□, room temperature Hall mobility of 11.8 cm(2) V(-1) sec(-1), the carrier concentration at ∼10(20) cm(-3) without any loss of optical transparency. We demonstrated successful applications of photochemically highly n-doped metal oxide via optical dose control to transparent conductor with excellent chemical and optical doping stability.

Photosensitized degradation of acetaminophen in natural organic matter solutions: The role of triplet states and oxygen.

PubMed

Li, Yanyun; Pan, Yanheng; Lian, Lushi; Yan, Shuwen; Song, Weihua; Yang, Xin

2017-02-01

The photolysis of acetaminophen, a widely used pharmaceutical, in simulated natural organic matter solutions was investigated. The triplet states of natural organic matter ( 3 NOM*) were found to play the dominant role in its photodegradation, while the contributions from hydroxyl radicals and singlet oxygen were negligible. Dissolved oxygen (DO) plays a dual role. From anaerobic to microaerobic (0.5 mg/L DO) conditions, the degradation rate of acetaminophen increased by 4-fold. That suggests the involvement of DO in reactions with the degradation intermediates. With increasing oxygen levels to saturated conditions (26 mg/L DO), the degradation rate became slower, mainly due to DO's quenching effect on 3 NOM*. Superoxide radical (O 2 - ) did not react with acetaminophen directly, but possibly quenched the intermediates to reverse the degradation process. The main photochemical pathways were shown to involve phenoxyl radical and N-radical cations, finally yielding hydroxylated derivatives, dimers and nitrosophenol. A reaction mechanism involving 3 NOM*, oxygen and O 2 - is proposed. Copyright © 2016 Elsevier Ltd. All rights reserved.

Photochemical transformation of graphene oxide in sunlight (journal)

EPA Science Inventory

Graphene oxide (GO) is a graphene derivative that is more easily manufactured in large scale and used to synthesize reduced graphene oxide (rGO) with properties analogous to graphene. In this study, we investigate the photochemical fate of GO under sunlight conditions. The resu...

Enhanced Ga2O3-photocatalyzed and photochemical degradation of the Fipronil insecticide by UVC irradiation in mixed aqueous/organic media under an inert atmosphere.

PubMed

Hidaka, Hisao; Tsukamoto, Tohru; Mitsutsuka, Yoshihiro; Oyama, Toshiyuki; Serpone, Nick

2015-05-01

Agrochemicals such as the insecticide Fipronil that bear fluoro groups are generally fat-soluble and nearly insoluble in water, so that their photodegradation in a heterogeneous aqueous gallium oxide dispersion presents some challenges. This article examined the photodegradation of this insecticide by solubilizing it through the addition of organic solvents (EtOH, MeOH, THF, 1,4-dioxane and ethylene glycol) to an aqueous medium and then subjecting the insecticide to 254 nm UVC radiation under photocatalytically inert (Ga2O3/N2) and air-equilibrated (Ga2O3/O2) conditions, as well as photochemically in the absence of Ga2O3 but also under inert and air-equilibrated conditions. Defluorination, dechlorination, desulfonation and denitridation of Fipronil were examined in mixed aqueous/organic media (10, 25 and 50 vol% in organic solvent). After 3 h of UVC irradiation (50 vol% mixed media) defluorination with Ga2O3/N2 was ∼65% greater than in aqueous media, and ca. 80% greater than the direct photolysis of Fipronil under inert (N2) conditions; under air-equilibrated conditions both Ga2O3-photocatalyzed and photochemical defluorination were significantly lower than in aqueous media. Dechlorination of Fipronil was ∼160% (Ga2O3/N2) and 140% (photochemically, N2) greater than in aqueous media; under air-equilibrated conditions, both photocatalyzed and photochemical formation of Cl(-) ions in mixed media fell rather short relative to aqueous media. The photocatalyzed (Ga2O3/N2) and photochemical (N2) conversion of the sulfur group in Fipronil to SO4(2(-)) ions was ca. 20% and 30% greater, respectively, in mixed media, while under air-equilibrated conditions photocatalyzed desulfonation was nearly twofold less than in the aqueous phase; direct photolysis showed little variations in mixed media. Denitridation of the nitrogens in Fipronil occurred mostly through the formation of ammonia (as NH4(+)) under all conditions with negligible quantities of NO3(-); again mixed media offered enhanced denitridation, particularly under inert N2 conditions. Time-of-flight electrospray (TOF-MS/ESI(-)) mass spectrometry revealed a fairly large number of intermediates formed in the degradation of Fipronil, particularly under photocatalytic conditions. Only a couple of intermediates were identified in the photodegradation and the presence of Ga2O3 enhanced the complexity of an already cumbersome problem owing to the involvement of organic solvents.

A Simple Photochemical Conversion of Perfluoroalkyl Hydrides to Perfluoroalkyl Bromides Using Interhalogen Compounds.

DTIC Science & Technology

1983-05-31

slower (100 hrs) than the ambient temperature chlorination of that compound (10 minutes). The reaction was followed by gas phase infrared spectroscopy...excess of bromine to chlorine and a slightly shorter (254 hrs) reaction time slightly increases the yield of bromo-F-neopentane. The 19F NMR data (Table... chlorination products, however, optimal bromina- tion (4.4:1) occurred for reaction 4 which produced predominately 1-bromo-3- hydryl-F-neopentane (48%). It

PEM-West trajectory climatology and photochemical model sensitivity study prepared using retrospective meteorological data

NASA Technical Reports Server (NTRS)

Merrill, John T.; Rodriguez, Jose M.

1991-01-01

Trajectory and photochemical model calculations based on retrospective meteorological data for the operations areas of the NASA Pacific Exploratory Mission (PEM)-West mission are summarized. The trajectory climatology discussed here is intended to provide guidance for flight planning and initial data interpretation during the field phase of the expedition by indicating the most probable path air parcels are likely to take to reach various points in the area. The photochemical model calculations which are discussed indicate the sensitivity of the chemical environment to various initial chemical concentrations and to conditions along the trajectory. In the post-expedition analysis these calculations will be used to provide a climatological context for the meteorological conditions which are encountered in the field.

Photochemical Conversion of Surrogate Emissions for Use in Toxicological Studies: Role of Particulate- and Gas-Phase Products

EPA Science Inventory

The production of photochemical atmospheres under controlled conditions in an irradiated chamber permits the manipulation of a variety of parameters that influences resulting air pollutant chemistry and potential biological effects. To date no studies have examined how contrastin...

Gas-phase Precursors to Anthropogenic SOA: Using the MCM to Probe Detailed Observations of Aromatic Photo-oxidation

NASA Astrophysics Data System (ADS)

Rickard, A. R.; Wyche, K. P.; Metzger, A.; Monks, P. S.; Ellis, A. M.; Baltensperger, U.; Pilling, M. J.; Jenkin, M. E.

2008-12-01

The formation of photochemical ozone and particulate matter are major priorities in the determination of European air quality policies. Predictions of the future state of the atmosphere and the development of appropriate mitigation strategies rely on models, which necessarily incorporate chemistry. The Master Chemical Mechanism (MCM, http://mcm.leeds.ac.uk/MCM) is a near-explicit chemical mechanism originally conceived to model ozone formation in Europe but now also employed as a benchmark mechanism in a wide variety of applications where chemical detail is required. The MCM currently describes the detailed gas- phase tropospheric degradation of a 135 primary emitted volatile organic compounds (VOCs) leading to a mechanism containing ca. 5900 species and 13500 reactions. In order that the MCM continues to be a state-of-the-art resource for the atmospheric science community it resides under a constant regime of evaluation, development and improvement. Individual VOC photochemical mechanisms are evaluated using data obtained, under a variety of atmospheric conditions, from highly instrumented smog chambers. Smog chamber experiments are crucial, not only for mechanism evaluation, but also for mechanism development. Findings obtained from combined model and chamber studies can additionally provide key insight for guiding the directions of future laboratory experiments. Recently, the MCM was updated to MCMv3.1 in order to take into account recent advancements in the understanding of aromatic photo-oxidation, an important class of anthropogenic VOCs. As well as constituting precursors to secondary organic aerosol (SOA), aromatics generally have high photochemical ozone creation potentials (POCPs) and hence contribute significantly towards tropospheric ozone formation. In the work presented, a detailed gas-phase photochemical chamber box model, incorporating the MCMv3.1 degradation mechanism for 1,3,5-trimethylbenzene (TMB), has been used to simulate data measured during a series of chamber experiments carried out at the Paul Scherrer Institute Aerosol Chamber in order to evaluate the mechanism under a variety of VOC/NOx conditions. More specifically, the model was used in the interpretation of data recorded by the University of Leicester's Chemical Ionisation Reaction Time-of- Flight Mass Spectrometer (CIR-TOF-MS), a novel instrument used to provide comprehensive, high (mass and time) resolution measurements of the organic gaseous oxidation products formed from the TMB precursor. Additional supporting gas and aerosol measurements also enable us to explore the "missing link" between the gas and aerosol phases. Model-measurement comparisons have been used to gain an insight into the complex array of oxygenated products formed, including the peroxide bicyclic ring opening products (gamma-dicarbonyls and furanones) and the O2-bridged peroxide bicyclic ring retaining products (diol, ketone and nitrate). To our knowledge this is the first time these O2-bridged species have been identified in the gas-phase. The model was also used to give insights into which gas-phase species were participating in SOA formation, with the primary and secondary peroxide products, formed primarily under NOx-limiting conditions ([NO] approaches zero), identified as likely candidates.

Comparison of femtosecond laser and continuous wave UV sources for protein-nucleic acid crosslinking.

PubMed

Fecko, Christopher J; Munson, Katherine M; Saunders, Abbie; Sun, Guangxing; Begley, Tadhg P; Lis, John T; Webb, Watt W

2007-01-01

Crosslinking proteins to the nucleic acids they bind affords stable access to otherwise transient regulatory interactions. Photochemical crosslinking provides an attractive alternative to formaldehyde-based protocols, but irradiation with conventional UV sources typically yields inadequate product amounts. Crosslinking with pulsed UV lasers has been heralded as a revolutionary technique to increase photochemical yield, but this method had only been tested on a few protein-nucleic acid complexes. To test the generality of the yield enhancement, we have investigated the benefits of using approximately 150 fs UV pulses to crosslink TATA-binding protein, glucocorticoid receptor and heat shock factor to oligonucleotides in vitro. For these proteins, we find that the quantum yields (and saturating yields) for forming crosslinks using the high-peak intensity femtosecond laser do not improve on those obtained with low-intensity continuous wave (CW) UV sources. The photodamage to the oligonucleotides and proteins also has comparable quantum yields. Measurements of the photochemical reaction yields of several small molecules selected to model the crosslinking reactions also exhibit nearly linear dependences on UV intensity instead of the previously predicted quadratic dependence. Unfortunately, these results disprove earlier assertions that femtosecond pulsed laser sources provide significant advantages over CW radiation for protein-nucleic acid crosslinking.

Photochemical dimerization of organic compounds

DOEpatents

Crabtree, Robert H.; Brown, Stephen H.; Muedas, Cesar A.; Ferguson, Richard R.

1992-01-01

At least one of selectivity and reaction rate of photosensitized vapor phase dimerizations, including dehydrodimerizations, hydrodimerizations and cross-dimerizations of saturated and unsaturated organic compounds is improved by conducting the dimerization in the presence of hydrogen or nitrous oxide.

Applying green chemistry to the photochemical route to artemisinin

NASA Astrophysics Data System (ADS)

Amara, Zacharias; Bellamy, Jessica F. B.; Horvath, Raphael; Miller, Samuel J.; Beeby, Andrew; Burgard, Andreas; Rossen, Kai; Poliakoff, Martyn; George, Michael W.

2015-06-01

Artemisinin is an important antimalarial drug, but, at present, the environmental and economic costs of its semi-synthetic production are relatively high. Most of these costs lie in the final chemical steps, which follow a complex acid- and photo-catalysed route with oxygenation by both singlet and triplet oxygen. We demonstrate that applying the principles of green chemistry can lead to innovative strategies that avoid many of the problems in current photochemical processes. The first strategy combines the use of liquid CO2 as solvent and a dual-function solid acid/photocatalyst. The second strategy is an ambient-temperature reaction in aqueous mixtures of organic solvents, where the only inputs are dihydroartemisinic acid, O2 and light, and the output is pure, crystalline artemisinin. Everything else—solvents, photocatalyst and aqueous acid—can be recycled. Some aspects developed here through green chemistry are likely to have wider application in photochemistry and other reactions.

Organic chemistry on Titan

NASA Technical Reports Server (NTRS)

Chang, S.; Scattergood, T.; Aronowitz, S.; Flores, J.

1979-01-01

Features taken from various models of Titan's atmosphere are combined in a working composite model that provides environmental constraints within which different pathways for organic chemical synthesis are determined. Experimental results and theoretical modeling suggest that the organic chemistry of the satellite is dominated by two processes: photochemistry and energetic particle bombardment. Photochemical reactions of CH4 in the upper atmosphere can account for the presence of C2 hydrocarbons. Reactions initiated at various levels of the atmosphere by cosmic rays, Saturn 'wind', and solar wind particle bombardment of a CH4-N2 atmospheric mixture can account for the UV-visible absorbing stratospheric haze, the reddish appearance of the satellite, and some of the C2 hydrocarbons. In the lower atmosphere photochemical processes will be important if surface temperatures are sufficiently high for gaseous NH3 to exist. It is concluded that the surface of Titan may contain ancient or recent organic matter (or both) produced in the atmosphere.

Applying green chemistry to the photochemical route to artemisinin.

PubMed

Amara, Zacharias; Bellamy, Jessica F B; Horvath, Raphael; Miller, Samuel J; Beeby, Andrew; Burgard, Andreas; Rossen, Kai; Poliakoff, Martyn; George, Michael W

2015-06-01

Artemisinin is an important antimalarial drug, but, at present, the environmental and economic costs of its semi-synthetic production are relatively high. Most of these costs lie in the final chemical steps, which follow a complex acid- and photo-catalysed route with oxygenation by both singlet and triplet oxygen. We demonstrate that applying the principles of green chemistry can lead to innovative strategies that avoid many of the problems in current photochemical processes. The first strategy combines the use of liquid CO2 as solvent and a dual-function solid acid/photocatalyst. The second strategy is an ambient-temperature reaction in aqueous mixtures of organic solvents, where the only inputs are dihydroartemisinic acid, O2 and light, and the output is pure, crystalline artemisinin. Everything else-solvents, photocatalyst and aqueous acid-can be recycled. Some aspects developed here through green chemistry are likely to have wider application in photochemistry and other reactions.

Annihilation of photochemical reactivity of photo-alignment layer.

PubMed

Hong, S H; Hwang, Y J; Lee, S G; Shin, D M

2008-09-01

The gas-polymer and liquid-polymer interfacial reactions of photosensitive polyimide can annihilate photo-reactive carbon-carbon double bonds, which remain after photo-alignment process. The annihilation processes dramatically affect voltage holding ratio and reorientation of photo-active functional groups. Photochemical dimerizations were identified using UV-visible and FT-IR spectroscopy. Polyimide films containing cinnamate groups were irradiated by linear polarized ultra violet (LPUV) light. Schadt et al. claims that the photo-alignment results from the anisotropy depletion of the cinnamate side chains as a consequence of the (2+2) cycloaddition reactions. The photo-aligned polyimide induces the orientation of nematic liquid crystals perpendicular to the polarization axis. However, the un-reacted photo-sensitive functional groups generate problems such as image sticking and reduced contrast ratio. Voltage holding ratio and photo-fading observed from photo-alignment layer can be dramatically improved by annihilation process of remnant photoreactive groups.

A sterilization system using ultraviolet photochemical reactions based on nitrous oxide and oxygen gases.

PubMed

Ohnishi, Yasutaka; Matsumoto, Hiroyuki; Iwamori, Satoru

2016-03-01

Active oxygen species (AOS) generated under ultraviolet (UV) lamps can be applied for various industrial processes owing to extremely strong oxidative abilities. We have already reported on an application of the AOS for a sterilization process of microorganisms. Here, a sterilization method using active oxygen generated under ultraviolet (UV) lamps introducing nitrous oxide (N2O) and oxygen gases into a vacuum chamber was investigated. Nitrogen dioxide (NO2) gas was readily produced from N2O by UV photochemical reactions under the low-pressure mercury lamp and then used to sterilize medical devices. We compared the ability of the N2O gas to sterilize Geobacillus stearothermophilus spores with those of conventional methods. Successful sterilization of spores on various biological indicators was achieved within 60 min, not only in sterilization bags but also in a lumen device. Copyright © 2016 Elsevier B.V. All rights reserved.

Degradation and mineralization of 2,4,6-trinitroresorcine in various photochemical systems.

PubMed

Khue, Do Ngoc; Chat, Nguyen Van; Minh, Do Binh; Lam, Tran Dai; Lan, Pham Hong; Loi, Vu Duc

2013-05-01

Comparison was observed for degradation and mineralization of the explosive 2,4,6-trinitroresorcine (TNR) in different photochemical systems TNR/UV, TNR/UV/TiO2, TNR/UV/H2O2, TNR/UV/O3, TNR/UV/TiO2/H2O2 and TNR/UV/TiO2/O3 using High Performance Liquid Chromatography coupled with Mass Spectrometry (HPLC/MS) and Total Organic Carbon (TOC) analysis. Addition of oxidizing agents such as H2O2 or O3 accelerated the rate of TNR conversion and mineralization. Highest reaction rate was obtained in TNR/UV/TiO2/H2O2 system. The intermediate products were characterized and identified by LS-MS technique. The similarity in intermediate products of TNR suggested the analogous reaction pathways of the TNR degradation by these different systems. Copyright © 2013 Elsevier B.V. All rights reserved.

A novel solid state photocatalyst for living radical polymerization under UV irradiation

NASA Astrophysics Data System (ADS)

Fu, Qiang; McKenzie, Thomas G.; Ren, Jing M.; Tan, Shereen; Nam, Eunhyung; Qiao, Greg G.

2016-02-01

This study presents the development of a novel solid state photocatalyst for the photoinduced controlled radical polymerization of methacrylates under mild UV irradiation (λmax ≈ 365 nm) in the absence of conventional photoinitiators, metal-catalysts or dye sensitizers. The photocatalyst design was based on our previous finding that organic amines can act in a synergistic photochemical reaction with thiocarbonylthio compounds to afford well controlled polymethacrylates under UV irradiation. Therefore, in the current contribution an amine-rich polymer was covalently grafted onto a solid substrate, thus creating a heterogeneous catalyst that would allow for facile removal, recovery and recyclability when employed for such photopolymerization reactions. Importantly, the polymethacrylates synthesized using the solid state photocatalyst (ssPC) show similarly excellent chemical and structural integrity as those catalysed by free amines. Moreover, the ssPC could be readily recovered and re-used, with multiple cycles of polymerization showing minimal effect on the integrity of the catalyst. Finally, the ssPC was employed in various photo-“click” reactions, permitting high yielding conjugations under photochemical control.

Biologically Enhanced Energy and Carbon Cycling on Titan?

NASA Astrophysics Data System (ADS)

Schulze-Makuch, Dirk; Grinspoon, David H.

2005-08-01

With the Cassini-Huygens Mission in orbit around Saturn, the large moon Titan, with its reducing atmosphere, rich organic chemistry, and heterogeneous surface, moves into the astrobiological spotlight. Environmental conditions on Titan and Earth were similar in many respects 4 billion years ago, the approximate time when life originated on Earth. Life may have originated on Titan during its warmer early history and then developed adaptation strategies to cope with the increasingly cold conditions. If organisms originated and persisted, metabolic strategies could exist that would provide sufficient energy for life to persist, even today. Metabolic reactions might include the catalytic hydrogenation of photochemically produced acetylene, or involve the recombination of radicals created in the atmosphere by ultraviolet radiation. Metabolic activity may even contribute to the apparent youth, smoothness, and high activity of Titan's surface via biothermal energy.

Biologically enhanced energy and carbon cycling on Titan?

PubMed

Schulze-Makuch, Dirk; Grinspoon, David H

2005-08-01

With the Cassini-Huygens Mission in orbit around Saturn, the large moon Titan, with its reducing atmosphere, rich organic chemistry, and heterogeneous surface, moves into the astrobiological spotlight. Environmental conditions on Titan and Earth were similar in many respects 4 billion years ago, the approximate time when life originated on Earth. Life may have originated on Titan during its warmer early history and then developed adaptation strategies to cope with the increasingly cold conditions. If organisms originated and persisted, metabolic strategies could exist that would provide sufficient energy for life to persist, even today. Metabolic reactions might include the catalytic hydrogenation of photochemically produced acetylene, or involve the recombination of radicals created in the atmosphere by ultraviolet radiation. Metabolic activity may even contribute to the apparent youth, smoothness, and high activity of Titan's surface via biothermal energy.

L-Cysteine Capped CdSe Quantum Dots Synthesized by Photochemical Route.

PubMed

Singh, Avinash; Kunwar, Amit; Rath, M C

2018-05-01

L-cysteine capped CdSe quantum dots were synthesized via photochemical route in aqueous solution under UV photo-irradiation. The as grown CdSe quantum dots exhibit broad fluorescence at room temperature. The CdSe quantum dots were found to be formed only through the reactions of the precursors, i.e., Cd(NH3)2+4 and SeSO2-3 with the photochemically generated 1-hydroxy-2-propyl radicals, (CH3)2COH radicals, which are formed through the process of H atom abstraction by the photoexcited acetone from 2-propanol. L-Cysteine was found to act as a suitable capping agent for the CdSe quantum dots and increases their biocompatability. Cytotoxicty effects of these quantum dots were evaluated in Chinese Hamster Ovary (CHO) epithelial cells, indicated a significant lower level for the L-cysteine capped CdSe quantum dots as compare to the bare ones.

A review of iron and cobalt porphyrins, phthalocyanines, and related complexes for electrochemical and photochemical reduction of carbon dioxide

DOE PAGES

Manbeck, Gerald F.; Fujita, Etsuko

2015-03-30

This review summarizes research on the electrochemical and photochemical reduction of CO₂ using a variety of iron and cobalt porphyrins, phthalocyanines, and related complexes. Metalloporphyrins and metallophthalocyanines are visible light absorbers with extremely large extinction coefficients. However, yields of photochemically-generated active catalysts for CO₂ reduction are typically low owing to the requirement of a second photoinduced electron. This requirement is not relevant to the case of electrochemical CO₂ reduction. Recent progress on efficient and stable electrochemical systems includes the use of FeTPP catalysts that have prepositioned phenyl OH groups in their second coordination spheres. This has led to remarkable progressmore » in carrying out coupled proton-electron transfer reactions for CO₂ reduction. Such ground-breaking research has to be continued in order to produce renewable fuels in an economically feasible manner.« less

Characterization of a trinuclear ruthenium species in catalytic water oxidation by Ru(bda)(pic)2 in neutral media.

PubMed

Zhang, Biaobiao; Li, Fei; Zhang, Rong; Ma, Chengbing; Chen, Lin; Sun, Licheng

2016-06-30

A Ru(III)-O-Ru(IV)-O-Ru(III) type trinuclear species was crystallographically characterized in water oxidation by Ru(bda)(pic)2 (H2bda = 2,2'-bipyridine-6,6'-dicarboxylic acid; pic = 4-picoline) under neutral conditions. The formation of a ruthenium trimer due to the reaction of Ru(IV)[double bond, length as m-dash]O with Ru(II)-OH2 was fully confirmed by chemical, electrochemical and photochemical methods. Since the oxidation of the trimer was proposed to lead to catalyst decomposition, the photocatalytic water oxidation activity was rationally improved by the suppression of the formation of the trimer.

Photochemically enhanced binding of small molecules to the tumor necrosis factor receptor-1 inhibits the binding of TNF-[alpha

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carter, Percy H.; Scherle, Peggy A.; Muckelbauer, Jodi K.

2010-03-05

The binding of tumor necrosis factor alpha (TNF-{alpha}) to the type-1 TNF receptor (TNFRc1) plays an important role in inflammation. Despite the clinical success of biologics (antibodies, soluble receptors) for treating TNF-based autoimmune conditions, no potent small molecule antagonists have been developed. Our screening of chemical libraries revealed that N-alkyl 5-arylidene-2-thioxo-1,3-thiazolidin-4-ones were antagonists of this protein-protein interaction. After chemical optimization, we discovered IW927, which potently disrupted the binding of TNF-{alpha} to TNFRc1 (IC{sub 50} = 50 nM) and also blocked TNF-stimulated phosphorylation of I{kappa}-B in Ramos cells (IC{sub 50} = 600 nM). This compound did not bind detectably to themore » related cytokine receptors TNFRc2 or CD40, and did not display any cytotoxicity at concentrations as high as 100 {micro}M. Detailed evaluation of this and related molecules revealed that compounds in this class are 'photochemically enhanced' inhibitors, in that they bind reversibly to the TNFRc1 with weak affinity (ca. 40-100 mM) and then covalently modify the receptor via a photochemical reaction. We obtained a crystal structure of IV703 (a close analog of IW927) bound to the TNFRc1. This structure clearly revealed that one of the aromatic rings of the inhibitor was covalently linked to the receptor through the main-chain nitrogen of Ala-62, a residue that has already been implicated in the binding of TNF-{alpha} to the TNFRc1. When combined with the fact that our inhibitors are reversible binders in light-excluded conditions, the results of the crystallography provide the basis for the rational design of nonphotoreactive inhibitors of the TNF-{alpha}-TNFRc1 interaction.« less

Photochemical behavior of carbon nanotubes in natural waters: reactive oxygen species production and effects on •OH generation by Suwannee River fulvic acid, nitrate, and Fe (III).

PubMed

Zhou, Lei; Zhang, Ya; Wang, Qi; Ferronato, Corinne; Yang, Xi; Chovelon, Jean-Marc

2016-10-01

The photochemical activities of three kinds of carbon nanotubes (CNTs) were investigated in the present study. Efficient procedures of dispersing the three kinds of carbon nanotubes in water were established, and the quantitative analysis methods were also developed by TOC-absorbance method. High pH value or low ionic strength of the colloidal solutions facilitated the dispersion of CNTs. The suspensions of three kinds of CNTs could generate singlet oxygen ((1)O2) and hydroxyl radical (•OH) under irradiation of simulated sunlight, while superoxide radical (O2 (•-)) was not detected. The steady-state concentrations of (1)O2 and •OH generated by these CNTs were also determined. The presence of CNTs in natural waters can affect the photochemical behavior of water constituents, such as nitrate, dissolved organic matter, and Fe(3+). Specifically, in nitrate solution, the presence of CNTs could inhibit the generation of •OH by nitrate through light screening effect, while the quenching effect of hydroxyl radicals by CNTs was not observed. Besides light screening effect, the three kinds of CNTs used in the experiments also have a strong inhibiting effect on the ability of DOM to produce •OH by binding to the active sites. Moreover, the adsorption of Fe(3+) on MWCNT-OH and MWCNT-COOH could lead to its inactivation of formation of •OH in acidic conditions. However, the presence of the three kinds of CNTs did not affect the ligand-to-metal charge transfer (LMCT) reaction of DOM-Fe (III) complex.

Long term atmospheric deposition as the source of nitrate and other salts in the Atacama Desert, Chile: New evidence from mass-independent oxygen isotopic compositions

USGS Publications Warehouse

Michalski, Greg; Böhlke, J.K.; Thiemens , Mark

2004-01-01

Isotopic analysis of nitrate and sulfate minerals from the nitrate ore fields of the Atacama Desert in northern Chile has shown anomalous 17O enrichments in both minerals. Δ17O values of 14–21 ‰ in nitrate and 0.4 to 4 ‰ in sulfate are the most positive found in terrestrial minerals to date. Modeling of atmospheric processes indicates that the Δ17O signatures are the result of photochemical reactions in the troposphere and stratosphere. We conclude that the bulk of the nitrate, sulfate and other soluble salts in some parts of the Atacama Desert must be the result of atmospheric deposition of particles produced by gas to particle conversion, with minor but varying amounts from sea spray and local terrestrial sources. Flux calculations indicate that the major salt deposits could have accumulated from atmospheric deposition in a period of 200,000 to 2.0 M years during hyper-arid conditions similar to those currently found in the Atacama Desert. Correlations between Δ17O and δ18O in nitrate salts from the Atacama Desert and Mojave Desert, California, indicate varying fractions of microbial and photochemical end-member sources. The photochemical nitrate isotope signature is well preserved in the driest surficial environments that are almost lifeless, whereas the microbial nitrate isotope signature becomes dominant rapidly with increasing moisture, biologic activity, and nitrogen cycling. These isotopic signatures have important implications for paleoclimate, astrobiology, and N cycling studies.

Improved vacuum-UV (VUV)-initiated photomineralization of organic compounds in water with a xenon excimer flow-through photoreactor (Xe2* lamp, 172 nm) containing an axially centered ceramic oxygenator.

PubMed

Oppenländer, Thomas; Walddörfer, Carsten; Burgbacher, Jens; Kiermeier, Martin; Lachner, Klaus; Weinschrott, Helga

2005-07-01

Xenon excimer (Xe2*) lamps can be used for the oxidation and mineralization of organic compounds in aqueous solution. This vacuum-ultraviolet (VUV) photochemical method is mainly based on the photochemically initiated homolysis of water that produces hydrogen atoms and hydroxyl radicals. The efficiency of substrate oxidation and mineralization is limited markedly due to the high absorbance of water at the emission maximum of the Xe2* lamp (lambda(max)=172 nm). This photochemical condition generates an extreme heterogeneity between the irradiated volume V(irr) and the non-irradiated ("dark") bulk solution. During VUV-initiated photomineralization of organic substrates, the fast scavenging of hydrogen atoms and of carbon-centered radicals by dissolved molecular oxygen produces a permanent oxygen deficit within V(irr) and adjacent compartments. Hence, at a constant photon flux the concentration of dissolved molecular oxygen within the zones of photo and thermal radical reactions limits the rate of mineralization, i.e. the rate of TOC diminution. Thus, a simple and convenient technique is presented that overcomes this limitation by injection of molecular oxygen (or air) into the irradiated volume by use of a ceramic oxygenator (aerator). The tube oxygenator was centered axially within the xenon excimer flow-through lamp. Consequently, the oxygen or air bubbles enhanced the transfer of dissolved molecular oxygen into the VUV-irradiated volume leading to an increased rate of mineralization of organic model compounds, e.g. 1-heptanol, benzoic acid and potassium hydrogen phthalate.

Spectral Dependence of Chlorophyll Biosynthesis Pathways in Plant Leaves.

PubMed

Belyaeva, O B; Litvin, F F

2015-12-01

This review covers studies on the dependence of chlorophyll photobiosynthesis reactions from protochlorophyllide on the spectral composition of actinic light. A general scheme of the reaction sequence for the photochemical stage in chlorophyll biosynthesis for etiolated plant leaves is presented. Comparative analysis of the data shows that the use of light with varied wavelengths for etiolated plant illumination reveals parallel transformation pathways of different protochlorophyllide forms into chlorophyllide, including a pathway for early photosystem II reaction center P-680 pigment formation.

High-yielding and photolabile approaches to the covalent attachment of biomolecules to surfaces via hydrazone chemistry.

PubMed

Lee, Ju Hun; Domaille, Dylan W; Noh, Hyunwoo; Oh, Taeseok; Choi, Chulmin; Jin, Sungho; Cha, Jennifer N

2014-07-22

The development of strategies to couple biomolecules covalently to surfaces is necessary for constructing sensing arrays for biological and biomedical applications. One attractive conjugation reaction is hydrazone formation--the reaction of a hydrazine with an aldehyde or ketone--as both hydrazines and aldehydes/ketones are largely bioorthogonal, which makes this particular reaction suitable for conjugating biomolecules to a variety of substrates. We show that the mild reaction conditions afforded by hydrazone conjugation enable the conjugation of DNA and proteins to the substrate surface in significantly higher yields than can be achieved with traditional bioconjugation techniques, such as maleimide chemistry. Next, we designed and synthesized a photocaged aryl ketone that can be conjugated to a surface and photochemically activated to provide a suitable partner for subsequent hydrazone formation between the surface-anchored ketone and DNA- or protein-hydrazines. Finally, we exploit the latent functionality of the photocaged ketone and pattern multiple biomolecules on the same substrate, effectively demonstrating a strategy for designing substrates with well-defined domains of different biomolecules. We expect that this approach can be extended to the production of multiplexed assays by using an appropriate mask with sequential photoexposure and biomolecule conjugation steps.

APEX (Aqueous Photochemistry of Environmentally occurring Xenobiotics): a free software tool to predict the kinetics of photochemical processes in surface waters.

PubMed

Bodrato, Marco; Vione, Davide

2014-04-01

The APEX software predicts the photochemical transformation kinetics of xenobiotics in surface waters as a function of: photoreactivity parameters (direct photolysis quantum yield and second-order reaction rate constants with transient species, namely ˙OH, CO₃(-)˙, (1)O₂ and the triplet states of chromophoric dissolved organic matter, (3)CDOM*), water chemistry (nitrate, nitrite, bicarbonate, carbonate, bromide and dissolved organic carbon, DOC), and water depth (more specifically, the optical path length of sunlight in water). It applies to well-mixed surface water layers, including the epilimnion of stratified lakes, and the output data are average values over the considered water column. Based on intermediate formation yields from the parent compound via the different photochemical pathways, the software can also predict intermediate formation kinetics and overall yield. APEX is based on a photochemical model that has been validated against available field data of pollutant phototransformation, with good agreement between model predictions and field results. The APEX software makes allowance for different levels of knowledge of a photochemical system. For instance, the absorption spectrum of surface water can be used if known, or otherwise it can be modelled from the values of DOC. Also the direct photolysis quantum yield can be entered as a detailed wavelength trend, as a single value (constant or average), or it can be defined as a variable if unknown. APEX is based on the free software Octave. Additional applications are provided within APEX to assess the σ-level uncertainty of the results and the seasonal trend of photochemical processes.

Temperature-dependent responses of the photosynthetic and chlorophyll fluorescence attributes of apple (Malus domestica) leaves during a sustained high temperature event.

PubMed

Greer, Dennis H

2015-12-01

The objective of this study was to follow changes in the temperature-dependent responses of photosynthesis and photosystem II performance in leaves of field-grown trees of Malus domestica (Borkh.) cv. 'Red Gala' before and after exposure to a long-term heat event occurring late in the growing season. Light-saturated photosynthesis was optimal at 25 °C before the heat event. The high temperatures caused a reduction in rates at low temperatures (15-20 °C) but increased rates at high temperatures (30-40 °C) and a shift in optimum to 30 °C. Rates at all temperatures increased after the heat event and the optimum shifted to 33 °C, indicative of some acclimation to the high temperatures occurring. Photosystem II attributes were all highly temperature-dependent. The operating quantum efficiency of PSII during the heat event declined, but mostly at high temperatures, partly because of decreased photochemical quenching but also from increased non-photochemical quenching. However, a further reduction in PSII operating efficiency occurred after the heat event subsided. Non-photochemical quenching had subsided, whereas photochemical quenching had increased in the post-heat event period and consistent with a greater fraction of open PSII reaction centres. What remained uncertain was why these effects on PSII performance appeared to have no effect on the process of light-saturated photosynthesis. However, the results provide an enhanced understanding of the impacts of sustained high temperatures on the photosynthetic process and its underlying reactions, notably photochemistry. Copyright © 2015 Elsevier Masson SAS. All rights reserved.

Arbuscular mycorrhizal symbiosis ameliorates the optimum quantum yield of photosystem II and reduces non-photochemical quenching in rice plants subjected to salt stress.

PubMed

Porcel, Rosa; Redondo-Gómez, Susana; Mateos-Naranjo, Enrique; Aroca, Ricardo; Garcia, Rosalva; Ruiz-Lozano, Juan Manuel

2015-08-01

Rice is the most important food crop in the world and is a primary source of food for more than half of the world population. However, salinity is considered the most common abiotic stress reducing its productivity. Soil salinity inhibits photosynthetic processes, which can induce an over-reduction of the reaction centres in photosystem II (PSII), damaging the photosynthetic machinery. The arbuscular mycorrhizal (AM) symbiosis may improve host plant tolerance to salinity, but it is not clear how the AM symbiosis affects the plant photosynthetic capacity, particularly the efficiency of PSII. This study aimed at determining the influence of the AM symbiosis on the performance of PSII in rice plants subjected to salinity. Photosynthetic activity, plant gas-exchange parameters, accumulation of photosynthetic pigments and rubisco activity and gene expression were also measured in order to analyse comprehensively the response of the photosynthetic processes to AM symbiosis and salinity. Results showed that the AM symbiosis enhanced the actual quantum yield of PSII photochemistry and reduced the quantum yield of non-photochemical quenching in rice plants subjected to salinity. AM rice plants maintained higher net photosynthetic rate, stomatal conductance and transpiration rate than nonAM plants. Thus, we propose that AM rice plants had a higher photochemical efficiency for CO2 fixation and solar energy utilization and this increases plant salt tolerance by preventing the injury to the photosystems reaction centres and by allowing a better utilization of light energy in photochemical processes. All these processes translated into higher photosynthetic and rubisco activities in AM rice plants and improved plant biomass production under salinity. Copyright © 2015 Elsevier GmbH. All rights reserved.

Formulation design and photochemical studies on nanocrystal solid dispersion of curcumin with improved oral bioavailability.

PubMed

Onoue, Satomi; Takahashi, Haruki; Kawabata, Yohei; Seto, Yoshiki; Hatanaka, Junya; Timmermann, Barbara; Yamada, Shizuo

2010-04-01

Considerable interest has been focused on curcumin due to its use to treat a wide variety of disorders, however, the therapeutic potential of curcumin could often be limited by its poor solubility, bioavailability, and photostability. To overcome these drawbacks, efficacious formulations of curcumin, including nanocrystal solid dispersion (CSD-Cur), amorphous solid dispersion (ASD-Cur), and nanoemulsion (NE-Cur), were designed with the aim of improving physicochemical and pharmacokinetic properties. Physicochemical properties of the prepared formulations were characterized by scanning/transmission electron microscope for morphological analysis, laser diffraction, and dynamic light scattering for particle size analysis, and polarized light microscope, powder X-ray diffraction and differential scanning calorimetry for crystallinity assessment. In dissolution tests, all curcumin formulations exhibited marked improvement in the dissolution behavior when compared with crystalline curcumin. Significant improvement in pharmacokinetic behavior was observed in the newly developed formulations, as evidenced by 12- (ASD-Cur), 16- (CSD-Cur), and 9-fold (NE-Cur) increase of oral bioavailability. Upon photochemical characterization, curcumin was found to be photoreactive and photodegradable in the solution state, possibly via type 2 photochemical reaction, whereas high photochemical stability was seen in the solid formulations, especially CSD-Cur. On the basis of these observations, taken together with dissolution and pharmacokinetic behaviors, CSD strategy would be efficacious to enhance bioavailability of curcumin with high photochemical stability. 2009 Wiley-Liss, Inc. and the American Pharmacists Association

Phototransformation of the sunlight filter benzophenone-3 (2-hydroxy-4-methoxybenzophenone) under conditions relevant to surface waters.

PubMed

Vione, Davide; Caringella, Rosalinda; De Laurentiis, Elisa; Pazzi, Marco; Minero, Claudio

2013-10-01

The UV filter benzophenone-3 (BP3) has UV photolysis quantum yield ΦBP3=(3.1±0.3)·10(-5) and the following second-order reaction rate constants: with (•)OH, k(BP3,(•)OH)=(2.0±0.4)·10(10) M(-1) s(-1); with the triplet states of chromophoric dissolved organic matter ((3)CDOM*), K(BP3,(3)CDOM*)=(1.1±0.1)·10(9) M(-1) s(-1); with (1)O2, k(BP3,(1)O2)=(2.0±0.1)·10(5) M(-1) s(-1), and with CO3(-•), k(BP3,CO3(-•))<5·10(7) M(-1) s(-1). These data allow the modelling of BP3 photochemical transformation, which helps filling the knowledge gap about the environmental persistence of this compound. Under typical surface-water conditions, direct photolysis and reactions with (•)OH and (3)CDOM* would be the main processes of BP3 phototransformation. Reaction with (•)OH would prevail at low DOC, direct photolysis at intermediate DOC (around 5 mg C L(-1)), and reaction with (3)CDOM* at high DOC. If the reaction rate constant with CO3(-•) is near the upper limit of experimental measures (5·10(7) M(-1) s(-1)), the CO3(-•) degradation process could be somewhat important for DOC<1 mg C L(-1). The predicted half-life time of BP3 in surface waters under summertime conditions would be of some weeks, and it would increase with increasing depth and DOC. BP3 transformation intermediates were detected upon reaction with (•)OH. Two methylated derivatives were tentatively identified, and they were probably produced by reaction between BP3 and fragments arising from photodegradation. The other intermediates were benzoic acid (maximum concentration ~10% of initial BP3) and benzaldehyde (1%). Copyright © 2013 Elsevier B.V. All rights reserved.

Chemical and Isotopic Analysis of Trace Organic Matter on Meteorites and Interstellar Dust Using a Laser Microprobe Instrument

NASA Technical Reports Server (NTRS)

Zare, Richard N.; Boyce, Joseph M. (Technical Monitor)

2001-01-01

Polycyclic Aromatic Hydrocarbons (PAHs) are of considerable interest today because they are ubiquitous on Earth and in the interstellar medium (ISM). In fact, about 20% of cosmic carbon in the galaxy is estimated to be in the form of PAHs. Investigation of these species has obvious uses for determining the cosmochemistry of the solar system. Work in this laboratory has focused on four main areas: 1) Mapping the spatial distribution of PAHs in a variety of meteoritic samples and comparing this distribution with mineralogical features of the meteorite to determine whether a correlation exists between the two. 2) Developing a method for detection of fullerenes in extraterrestrial samples using microprobe Laser Desorption Ionization Mass Spectroscopy and utilizing this technique to investigate fullerene presence, while exploring the possibility of spatially mapping the fullerene distribution in these samples through in situ detection. 3) Investigating a possible formation pathway for meteoritic and ancient terrestrial kerogen involving the photochemical reactions of PAHs with alkanes under prebiotic and astrophysically relevant conditions. 4) Studying reaction pathways and identifying the photoproducts generated during the photochemical evolution of PAH-containing interstellar ice analogs as part of an ongoing collaboration with researchers at the Astrochemistry Lab at NASA Ames. All areas involve elucidation of the solar system formation and chemistry using microprobe Laser Desorption Laser Ionization Mass Spectrometry. A brief description of microprobe Laser Desorption Ionization Mass Spectroscopy, which allows selective investigation of subattomole levels of organic species on the surface of a sample at 10-40 micrometer spatial resolution, is given.

Effects of the antioxidant moieties of dissolved organic matter on triplet-sensitized phototransformation processes: Implications for the photochemical modeling of sulfadiazine.

PubMed

Vione, Davide; Fabbri, Debora; Minella, Marco; Canonica, Silvio

2018-01-01

Previous studies have shown that the photodegradation of some pollutants, induced by the excited triplet states of chromophoric dissolved organic matter ( 3 CDOM*), can be inhibited by back-reduction processes carried out by phenolic antioxidants occurring in dissolved organic matter (DOM). Here, for the first time to our knowledge, we included such an inhibition effect into a photochemical model and applied the model predictions to sulfadiazine (SDZ), a sulfonamide antibiotic that occurs in surface waters in two forms, neutral HSDZ and anionic SDZ - (pK a  = 6.5). The input parameters of the photochemical model were obtained by means of dedicated experiments, which showed that the inhibition effect was more marked for SDZ - than for HSDZ. Compared to the behavior of 2,4,6-trimethylphenol, which does not undergo antioxidant inhibition when irradiated in natural water samples, the back-reduction effect on the degradation of SDZ was proportional to the electron-donating capacity of the DOM. According to the model results, direct photolysis and OH reaction would account for the majority of both HSDZ and SDZ - photodegradation in waters having low dissolved organic carbon (DOC < 1 mgC L -1 ). With higher DOC values (>3-4 mgC L -1 ) and despite the back-reduction processes, the 3 CDOM* reactions are expected to account for the majority of HSDZ phototransformation. In the case of SDZ - at high DOC, most of the photodegradation would be accounted for by direct photolysis. The relative importance of the triplet-sensitized phototransformation of both SDZ - and (most importantly) HSDZ is expected to increase with increasing DOC, even in the presence of back reduction. An increase in water pH, favoring the occurrence of SDZ - with respect to HSDZ, would enhance direct photolysis at the expense of triplet sensitization. SDZ should be fairly photolabile under summertime sunlight, with predicted half-lives ranging from a few days to a couple of months depending on water conditions. Copyright © 2017 Elsevier Ltd. All rights reserved.

Photochemical degradation of PCBs in snow.

PubMed

Matykiewiczová, Nina; Klánová, Jana; Klán, Petr

2007-12-15

This work represents the first laboratory study known to the authors describing photochemical behavior of persistent organic pollutants in snow at environmentally relevant concentrations. The snow samples were prepared by shock freezing of the corresponding aqueous solutions in liquid nitrogen and were UV-irradiated in a photochemical cold chamber reactor at -25 degrees C, in which simultaneous monitoring of snow-air exchange processeswas also possible. The main photodegradation pathway of two model snow contaminants, PCB-7 and PCB-153 (c approximately 100 ng kg(-1)), was found to be reductive dehalogenation. Possible involvement of the water molecules of snow in this reaction has been excluded by performing the photolyses in D2O snow. Instead, trace amounts of volatile organic compounds have been proposed to be the major source of hydrogen atom in the reduction, and this hypothesis was confirmed by the experiments with deuterated organic cocontaminants, such as d6-ethanol or d8-tetrahydrofuran. It is argued that bimolecular photoreduction of PCBs was more efficient or feasible than any other phototransformations under the experimental conditions used, including the coupling reactions. The photodegradation of PCBs, however, competed with a desorption process responsible for the pollutant loss from the snow samples, especially in case of lower molecular-mass congeners. Organic compounds, apparently largely located or photoproduced on the surface of snow crystals, had a predisposition to be released to the air but, at the same time, to react with other species in the gas phase. It is concluded that physicochemical properties of the contaminants and trace co-contaminants, their location and local concentrations in the matrix, and the wavelength and intensity of radiation are the most important factors in the evaluation of organic contaminants' lifetime in snow. Based on the results, it has been estimated that the average lifetime of PCBs in surface snow, connected exclusively to the photoreductive dechlorination process, is 1-2 orders of magnitude longer than that in surface waters when subjected to the equivalent solar radiation. However, in case that the concentration of the hydrogen peroxide in natural snow is sufficient, the photoinduced oxidation process could succeed the photoreductive dechlorination and evaporative fluxes as the major sink.

Exploring mechanisms of a tropospheric archetype: CH{sub 3}O{sub 2} + NO

DOE Office of Scientific and Technical Information (OSTI.GOV)

Launder, Andrew M.; Agarwal, Jay; Schaefer, Henry F., E-mail: ccq@uga.edu

Methylperoxy radical (CH{sub 3}O{sub 2}) and nitric oxide (NO) contribute to the propagation of photochemical smog in the troposphere via the production of methoxy radical (CH{sub 3}O) and nitrogen dioxide (NO{sub 2}). This reaction system also furnishes trace quantities of methyl nitrate (CH{sub 3}ONO{sub 2}), a sink for reactive NO{sub x} species. Here, the CH{sub 3}O{sub 2} + NO reaction is examined with highly reliable coupled-cluster methods. Specifically, equilibrium geometries for the reactants, products, intermediates, and transition states of the ground-state potential energy surface are characterized. Relative reaction enthalpies at 0 K (ΔH{sub 0K}) are reported; these values are comprisedmore » of electronic energies extrapolated to the complete basis set limit of CCSDT(Q) and zero-point vibrational energies computed at CCSD(T)/cc-pVTZ. A two-part mechanism involving CH{sub 3}O and NO{sub 2} production followed by radical recombination to CH{sub 3}ONO{sub 2} is determined to be the primary channel for formation of CH{sub 3}ONO{sub 2} under tropospheric conditions. Constrained optimizations of the reaction paths at CCSD(T)/cc-pVTZ suggest that the homolytic bond dissociations involved in this reaction path are barrierless.« less

T.E. KLEINDIENST, E.W. CORSE, F.T. BLANCHARD, W.A. LONNEMAN

EPA Science Inventory

Carbonyl compounds are important constituents in urban and global atmospheres. n urban atmospheres these compounds frequently serve to initiate photochemical smog and certainly sustain the chain reactions leading to ozone formation. easurement of carbonyl compounds under atmosphe...

Photochemical production of H2SO4 aerosols on Venus

NASA Technical Reports Server (NTRS)

Yuk, L. Yung

1986-01-01

The quantum yields for producing O2(a (1 delta g)) and O2(b(1 sigma g +)) for the reaction, O + ClO yields Cl + O2, are summarized. Also included are results for other simple reactions capable of producing the singlet oxygen states. An episodic injection of SO2 into the upper atmosphere of Venus is considered as a possible explanation for the airglow values.

Thermotolerance of apple tree leaves probed by chlorophyll a fluorescence and modulated 820 nm reflection during seasonal shift.

PubMed

Duan, Ying; Zhang, Mengxia; Gao, Jin; Li, Pengmin; Goltsev, Vasilij; Ma, Fengwang

2015-11-01

During the seasonal shift from June to August, air temperatures increase. To explore how apple trees improve their thermotolerance during this shift, we examined the photochemical reaction capacity of apple tree leaves by simultaneous measurement of prompt chlorophyll fluorescence, delayed chlorophyll fluorescence, and modulated 820 nm reflection at varying temperatures. It was found that the reaction centers and antennae of photosystem II (PSII) and photosystem I (PSI), the donor side of PSII, the electron transfer capacity from QA to QB, and the reoxidation capacity of plastoquinol were all sensitive to heat stress, particularly in June. As the season shifted, apple tree leaves improved in thermotolerance. Interestingly, the acclimation to seasonal shift enhanced the thermotolerance of PSII and PSI reaction centers more than that of their antennae, and the activity of PSII more than that of PSI. This may be a strategy for plant adaptation to changes in environmental temperatures. In addition, results from prompt and delayed fluorescence, as well as modulated 820 nm reflection corroborate each other. We suggest that the simultaneous measurement of the three independent signals may provide more information on thermal acclimation mechanisms of photochemical reactions in plant leaves. Copyright © 2015 Elsevier B.V. All rights reserved.

An accessible visible-light actinometer for the determination of photon flux and optical pathlength in flow photo microreactors.

PubMed

Roibu, Anca; Fransen, Senne; Leblebici, M Enis; Meir, Glen; Van Gerven, Tom; Kuhn, Simon

2018-04-03

Coupling photochemistry with flow microreactors enables novel synthesis strategies with higher efficiencies compared to batch systems. Improving the reproducibility and understanding of the photochemical reaction mechanisms requires quantitative tools such as chemical actinometry. However, the choice of actinometric systems which can be applied in microreactors is limited, due to their short optical pathlength in combination with a large received photon flux. Furthermore, actinometers for the characterization of reactions driven by visible light between 500 and 600 nm (e.g. photosensitized oxidations) are largely missing. In this paper, we propose a new visible-light actinometer which can be applied in flow microreactors between 480 and 620 nm. This actinometric system is based on the photoisomerization reaction of a diarylethene derivative from its closed to the open form. The experimental protocol for actinometric measurements is facile and characterized by excellent reproducibility and we also present an analytical estimation to calculate the photon flux. Furthermore, we propose an experimental methodology to determine the average pathlength in microreactors using actinometric measurements. In the context of a growing research interest on using flow microreactors for photochemical reactions, the proposed visible-light actinometer facilitates the determination of the received photon flux and average pathlength in confined geometries.

Assessing the phototransformation of diclofenac, clofibric acid and naproxen in surface waters: Model predictions and comparison with field data.

PubMed

Avetta, Paola; Fabbri, Debora; Minella, Marco; Brigante, Marcello; Maurino, Valter; Minero, Claudio; Pazzi, Marco; Vione, Davide

2016-11-15

Phototransformation is important for the fate in surface waters of the pharmaceuticals diclofenac (DIC) and naproxen (NAP) and for clofibric acid (CLO), a metabolite of the drug clofibrate. The goal of this paper is to provide an overview of the prevailing photochemical processes, which these compounds undergo in the different conditions found in freshwater environments. The modelled photochemical half-life times of NAP and DIC range from a few days to some months, depending on water conditions (chemistry and depth) and on the season. The model indicates that direct photolysis is the dominant degradation pathway of DIC and NAP in sunlit surface waters, and potentially toxic cyclic amides were detected as intermediates of DIC direct phototransformation. With modelled half-life times in the month-year range, CLO is predicted to be more photostable than DIC or NAP and to be degraded mainly by reaction with the • OH radical and with the triplet states of chromophoric dissolved organic matter ( 3 CDOM*). The CLO intermediates arising from these processes and detected in this study (hydroquinone and 4-chlorophenol) are, respectively, a chronic toxicant to aquatic organisms and a possible carcinogen for humans. Hydroquinone is formed with only ∼5% yield upon CLO triplet-sensitised transformation, but it is highly toxic for algae and crustaceans. In contrast, the formation yield of 4-chlorophenol reaches ∼50% upon triplet sensitisation and ∼10% by · OH reaction. The comparison of model predictions with field data from a previous study yielded a very good agreement in the case of DIC and, when using 4-carboxybenzophenone as proxy for triplet sensitisation by CDOM, a good agreement was found for CLO as well. In the case of NAP, the comparison with field data suggests that its direct photolysis quantum yield approaches or even falls below the lower range of literature values. Copyright © 2016 Elsevier Ltd. All rights reserved.

Molecular weight growth in Titan's atmosphere: Branching pathways for the reaction of 1-propynyl radical (H 3CC≡C˙) with small alkenes and alkynes

DOE PAGES

Kirk, Benjamin B.; Savee, John D.; Trevitt, Adam J.; ...

2015-07-16

The reaction of small hydrocarbon radicals (i.e. ˙CN, ˙C 2H) with trace alkenes and alkynes is believed to play an important role in molecular weight growth and ultimately the formation of Titan's characteristic haze. Current photochemical models of Titan's atmosphere largely assume hydrogen atom abstraction or unimolecular hydrogen elimination reactions dominate the mechanism, in contrast to recent experiments that reveal significant alkyl radical loss pathways during reaction of ethynyl radical (˙C 2H) with alkenes and alkynes. In this study, the trend is explored for the case of a larger ethynyl radical analogue, the 1-propynyl radical (H3CC≡C˙), a likely product frommore » the high-energy photolysis of propyne in Titan's atmosphere. Using synchrotron vacuum ultraviolet photoionization mass spectrometry, product branching ratios are measured for the reactions of 1-propynyl radical with a suite of small alkenes (ethylene and propene) and alkynes (acetylene and d 4-propyne) at 4 Torr and 300 K. Reactions of 1-propynyl radical with acetylene and ethylene form single products, identified as penta-1,3-diyne and pent-1-en-3-yne, respectively. These products form by hydrogen atom loss from the radical-adduct intermediates. The reactions of 1-propynyl radical with d4-propyne and propene form products from both hydrogen atom and methyl loss, (–H = 27%, –CH 3 = 73%) and (–H = 14%, –CH 3 = 86%), respectively. Altogether, these results indicate that reactions of ethynyl radical analogues with alkenes and alkynes form significant quantities of products by alkyl loss channels, suggesting that current photochemical models of Titan over predict both hydrogen atom production as well as the efficiency of molecular weight growth in these reactions.« less

Molecular weight growth in Titan's atmosphere: branching pathways for the reaction of 1-propynyl radical (H3CC≡C˙) with small alkenes and alkynes.

PubMed

Kirk, Benjamin B; Savee, John D; Trevitt, Adam J; Osborn, David L; Wilson, Kevin R

2015-08-28

The reaction of small hydrocarbon radicals (i.e.˙CN, ˙C2H) with trace alkenes and alkynes is believed to play an important role in molecular weight growth and ultimately the formation of Titan's characteristic haze. Current photochemical models of Titan's atmosphere largely assume hydrogen atom abstraction or unimolecular hydrogen elimination reactions dominate the mechanism, in contrast to recent experiments that reveal significant alkyl radical loss pathways during reaction of ethynyl radical (˙C2H) with alkenes and alkynes. In this study, the trend is explored for the case of a larger ethynyl radical analogue, the 1-propynyl radical (H3CC[triple bond, length as m-dash]C˙), a likely product from the high-energy photolysis of propyne in Titan's atmosphere. Using synchrotron vacuum ultraviolet photoionization mass spectrometry, product branching ratios are measured for the reactions of 1-propynyl radical with a suite of small alkenes (ethylene and propene) and alkynes (acetylene and d4-propyne) at 4 Torr and 300 K. Reactions of 1-propynyl radical with acetylene and ethylene form single products, identified as penta-1,3-diyne and pent-1-en-3-yne, respectively. These products form by hydrogen atom loss from the radical-adduct intermediates. The reactions of 1-propynyl radical with d4-propyne and propene form products from both hydrogen atom and methyl loss, (-H = 27%, -CH3 = 73%) and (-H = 14%, -CH3 = 86%), respectively. Together, these results indicate that reactions of ethynyl radical analogues with alkenes and alkynes form significant quantities of products by alkyl loss channels, suggesting that current photochemical models of Titan over predict both hydrogen atom production as well as the efficiency of molecular weight growth in these reactions.

Molecular weight growth in Titan's atmosphere: Branching pathways for the reaction of 1-propynyl radical (H 3CC≡C˙) with small alkenes and alkynes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kirk, Benjamin B.; Savee, John D.; Trevitt, Adam J.

The reaction of small hydrocarbon radicals (i.e. ˙CN, ˙C 2H) with trace alkenes and alkynes is believed to play an important role in molecular weight growth and ultimately the formation of Titan's characteristic haze. Current photochemical models of Titan's atmosphere largely assume hydrogen atom abstraction or unimolecular hydrogen elimination reactions dominate the mechanism, in contrast to recent experiments that reveal significant alkyl radical loss pathways during reaction of ethynyl radical (˙C 2H) with alkenes and alkynes. In this study, the trend is explored for the case of a larger ethynyl radical analogue, the 1-propynyl radical (H3CC≡C˙), a likely product frommore » the high-energy photolysis of propyne in Titan's atmosphere. Using synchrotron vacuum ultraviolet photoionization mass spectrometry, product branching ratios are measured for the reactions of 1-propynyl radical with a suite of small alkenes (ethylene and propene) and alkynes (acetylene and d 4-propyne) at 4 Torr and 300 K. Reactions of 1-propynyl radical with acetylene and ethylene form single products, identified as penta-1,3-diyne and pent-1-en-3-yne, respectively. These products form by hydrogen atom loss from the radical-adduct intermediates. The reactions of 1-propynyl radical with d4-propyne and propene form products from both hydrogen atom and methyl loss, (–H = 27%, –CH 3 = 73%) and (–H = 14%, –CH 3 = 86%), respectively. Altogether, these results indicate that reactions of ethynyl radical analogues with alkenes and alkynes form significant quantities of products by alkyl loss channels, suggesting that current photochemical models of Titan over predict both hydrogen atom production as well as the efficiency of molecular weight growth in these reactions.« less

Quadrupole type mass spectrometric study of the abstraction reaction between hydrogen atoms and ethane.

PubMed

Bayrakçeken, Fuat

2008-02-01

The reactions of photochemically generated deuterium atoms of selected initial translational energy with ethane have been investigated. At each initial energy the relative probability of the atoms undergoing reaction or energy loss on collision with ethane was investigated, and the phenomenological threshold energy was measured as 30+/-5kJmol(-1) for the abstraction from the secondary C-H bonds. The ratio of relative yields per bond, secondary:primary was approximately 3 at the higher energies studied. The correlation of threshold energies with bond dissociation energies, heats of reaction and activation energies is discussed for abstraction reactions with several hydrocarbons.

Preparation of Low Molecular Weight Heparin by Microwave Discharge Electrodeless Lamp/TiO2 Photo-Catalytic Reaction.

PubMed

Lee, Do-Jin; Kim, Byung Hoon; Kim, Sun-Jae; Kim, Jung-Sik; Lee, Heon; Jung, Sang-Chul

2015-01-01

An MDEL/TiO2 photo-catalyst hybrid system was applied, for the first time, for the production of low molecular weight heparin. The molecular weight of produed heparin decreased with increasing microwave intensity and treatment time. The abscission of the chemical bonds between the constituents of heparin by photo-catalytic reaction did not alter the characteristics of heparin. Formation of by-products due to side reaction was not observed. It is suggested that heparin was depolymerized by active oxygen radicals produced during the MDEL/TiO2 photo-chemical reaction.

Prebiotic synthesis of carboxylic acids, amino acids and nucleic acid bases from formamide under photochemical conditions⋆

NASA Astrophysics Data System (ADS)

Botta, Lorenzo; Mattia Bizzarri, Bruno; Piccinino, Davide; Fornaro, Teresa; Robert Brucato, John; Saladino, Raffaele

2017-07-01

The photochemical transformation of formamide in the presence of a mixture of TiO2 and ZnO metal oxides as catalysts afforded a large panel of molecules of biological relevance, including carboxylic acids, amino acids and nucleic acid bases. The reaction was less effective when performed in the presence of only one mineral, highlighting the role of synergic effects between the photoactive catalysts. Taken together, these results suggest that the synthesis of chemical precursors for both the genetic and the metabolic apparatuses might have occurred in a simple environment, consisting of formamide, photoactive metal oxides and UV-radiation.

Efficiency of photochemical stages of photosynthesis in purple bacteria (a critical survey).

PubMed

Borisov, A Yu

2014-03-01

Based on currently available data, the energy transfer efficiency in the successive photophysical and photochemical stages has been analyzed for purple bacteria. This analysis covers the stages starting from migration of the light-induced electronic excitations from the bulk antenna pigments to the reaction centers up to irreversible stage of the electron transport along the transmembrane chain of cofactors-carriers. Some natural factors are revealed that significantly increase the rates of efficient processes in these stages. The influence on their efficiency by the "bottleneck" in the energy migration chain is established. The overall quantum yield of photosynthesis in these stages is determined.

Multiscale model of light harvesting by photosystem II in plants

DOE PAGES

Amarnath, Kapil; Bennett, Doran I. G.; Schneider, Anna R.; ...

2016-01-19

The first step of photosynthesis in plants is the absorption of sunlight by pigments in the antenna complexes of photosystem II (PSII), followed by transfer of the nascent excitation energy to the reaction centers, where long-term storage as chemical energy is initiated. Quantum mechanical mechanisms must be invoked to explain the transport of excitation within individual antenna. However, it is unclear how these mechanisms influence transfer across assemblies of antenna and thus the photochemical yield at reaction centers in the functional thylakoid membrane. In this paper, we model light harvesting at the several-hundred-nanometer scale of the PSII membrane, while preservingmore » the dominant quantum effects previously observed in individual complexes. We show that excitation moves diffusively through the antenna with a diffusion length of 50 nm until it reaches a reaction center, where charge separation serves as an energetic trap. The diffusion length is a single parameter that incorporates the enhancing effect of excited state delocalization on individual rates of energy transfer as well as the complex kinetics that arise due to energy transfer and loss by decay to the ground state. The diffusion length determines PSII’s high quantum efficiency in ideal conditions, as well as how it is altered by the membrane morphology and the closure of reaction centers. Finally, we anticipate that the model will be useful in resolving the nonphotochemical quenching mechanisms that PSII employs in conditions of high light stress.« less

Atmospheric photochemistry at a fatty acid coated air/water interface

NASA Astrophysics Data System (ADS)

George, Christian; Rossignol, Stéphanie; Passananti, Monica; Tinel, Liselotte; Perrier, Sebastien; Kong, Lingdong; Brigante, Marcello; Bianco, Angelica; Chen, Jianmin; Donaldson, James

2017-04-01

Over the past 20 years, interfacial processes have become increasingly of interest in the field of atmospheric chemistry, with many studies showing that environmental surfaces display specific chemistry and photochemistry, enhancing certain reactions and acting as reactive sinks or sources for various atmospherically relevant species. Many molecules display a free energy minimum at the air-water interface, making it a favored venue for compound accumulation and reaction. Indeed, surface active molecules have been shown to undergo specific photochemistry at the air-water interface. This presentation will address some recent surprises. Indeed, while fatty acids are believed to be photochemically inert in the actinic region, complex volatile organic compounds (VOCs) are produced during illumination of an air-water interface coated solely with a monolayer of carboxylic acid. When aqueous solutions containing nonanoic acid (NA) at bulk concentrations that give rise to just over monolayer NA coverage are illuminated with actinic radiation, saturated and unsaturated aldehydes are seen in the gas phase and more highly oxygenated products appear in the aqueous phase. This chemistry is probably initiated by triplet state NA molecules excited by direct absorption of actinic light at the water surface. As fatty acids covered interfaces are ubiquitous in the environment, such photochemical processing will have a significant impact on local ozone and particle formation. In addition, it was shown recently that a heterogeneous reaction between SO2 and oleic acid (OA; an unsaturated fatty acid) takes place and leads efficiently to the formation of organosulfur products. Here, we demonstrate that this reaction proceeds photochemically on various unsaturated fatty acids compounds, and may therefore have a general environmental impact. This is probably due to the chromophoric nature of the SO2 adduct with C=C bonds, and means that the contribution of this direct addition of SO2 could be in excess of 5%.

VOLATILE ORGANIC COMPOUNDS (VOCS) CHAPTER 31.

EPA Science Inventory

The term "volatile organic compounds' (VOCs) was originally coined to refer, as a class, to carbon-containing chemicals that participate in photochemical reactions in the ambient (outdoor) are. The regulatory definition of VOCs used by the U.S. EPA is: Any compound of carbon, ex...

A Tractable Numerical Model for Exploring Nonadiabatic Quantum Dynamics

ERIC Educational Resources Information Center

Camrud, Evan; Turner, Daniel B.

2017-01-01

Numerous computational and spectroscopic studies have demonstrated the decisive role played by nonadiabatic coupling in photochemical reactions. Nonadiabatic coupling drives photochemistry when potential energy surfaces are nearly degenerate at avoided crossings or truly degenerate at unavoided crossings. The dynamics induced by nonadiabatic…

Photolysis of Indole-Containing Mycotoxins to Fluorescent Products

USDA-ARS?s Scientific Manuscript database

Photochemical reaction of the non-fluorescent mycotoxin cyclopiazonic acid (CPA) to fluorescent products was recently reported. Because CPA contains an indole moiety, believed to contribute to the fluorescence, it was of interest to determine whether the effect might be more generally applicable to ...

Overhead Projector Demonstrations.

ERIC Educational Resources Information Center

Kolb, Doris, Ed.

1988-01-01

Provides two demonstrations: (1) electrolyte migration of ions using colored ions which cross a strip of gelatin allowing for noticeable migration; and (2) photochemical reduction of Fe+3 by the citrate ion. Points out both reactions can be done in a Petri dish using common lab materials. (MVL)

Nitrogen Oxides in Early Earth's Atmosphere as Electron Acceptors for Life's Emergence

NASA Astrophysics Data System (ADS)

Wong, Michael L.; Charnay, Benjamin D.; Gao, Peter; Yung, Yuk L.; Russell, Michael J.

2017-10-01

We quantify the amount of nitrogen oxides (NOx) produced through lightning and photochemical processes in the Hadean atmosphere to be available in the Hadean ocean for the emergence of life. Atmospherically generated nitrate (NO3-) and nitrite (NO2-) are the most attractive high-potential electron acceptors for pulling and enabling crucial redox reactions of autotrophic metabolic pathways at submarine alkaline hydrothermal vents. The Hadean atmosphere, dominated by CO2 and N2, will produce nitric oxide (NO) when shocked by lightning. Photochemical reactions involving NO and H2O vapor will then produce acids such as HNO, HNO2, HNO3, and HO2NO2 that rain into the ocean. There, they dissociate into or react to form nitrate and nitrite. We present new calculations based on a novel combination of early-Earth global climate model and photochemical modeling, and we predict the flux of NOx to the Hadean ocean. In our 0.1-, 1-, and 10-bar pCO2 models, we calculate the NOx delivery to be 2.4 × 105, 6.5 × 108, and 1.9 × 108 molecules cm-2 s-1. After only tens of thousands to tens of millions of years, these NOx fluxes are expected to produce sufficient (micromolar) ocean concentrations of high-potential electron acceptors for the emergence of life.

Light-activated control of protein channel assembly mediated by membrane mechanics

NASA Astrophysics Data System (ADS)

Miller, David M.; Findlay, Heather E.; Ces, Oscar; Templer, Richard H.; Booth, Paula J.

2016-12-01

Photochemical processes provide versatile triggers of chemical reactions. Here, we use a photoactivated lipid switch to modulate the folding and assembly of a protein channel within a model biological membrane. In contrast to the information rich field of water-soluble protein folding, there is only a limited understanding of the assembly of proteins that are integral to biological membranes. It is however possible to exploit the foreboding hydrophobic lipid environment and control membrane protein folding via lipid bilayer mechanics. Mechanical properties such as lipid chain lateral pressure influence the insertion and folding of proteins in membranes, with different stages of folding having contrasting sensitivities to the bilayer properties. Studies to date have relied on altering bilayer properties through lipid compositional changes made at equilibrium, and thus can only be made before or after folding. We show that light-activation of photoisomerisable di-(5-[[4-(4-butylphenyl)azo]phenoxy]pentyl)phosphate (4-Azo-5P) lipids influences the folding and assembly of the pentameric bacterial mechanosensitive channel MscL. The use of a photochemical reaction enables the bilayer properties to be altered during folding, which is unprecedented. This mechanical manipulation during folding, allows for optimisation of different stages of the component insertion, folding and assembly steps within the same lipid system. The photochemical approach offers the potential to control channel assembly when generating synthetic devices that exploit the mechanosensitive protein as a nanovalve.

Analysis of the Electronic Structure of the Special Pair of a Bacterial Photosynthetic Reaction Center by 13 C Photochemically Induced Dynamic Nuclear Polarization Magic-Angle Spinning NMR Using a Double-Quantum Axis.

PubMed

Najdanova, Marija; Gräsing, Daniel; Alia, A; Matysik, Jörg

2018-01-01

The origin of the functional symmetry break in bacterial photosynthesis challenges since several decades. Although structurally very similar, the two branches of cofactors in the reaction center (RC) protein complex act very differently. Upon photochemical excitation, an electron is transported along one branch, while the other remains inactive. Photochemically induced dynamic nuclear polarization (photo-CIDNP) magic-angle spinning (MAS) 13 C NMR revealed that the two bacteriochlorophyll cofactors forming the "Special Pair" donor dimer are already well distinguished in the electronic ground state. These previous studies are relying solely on 13 C- 13 C correlation experiments as radio-frequency-driven recoupling (RFDR) and dipolar-assisted rotational resonance (DARR). Obviously, the chemical-shift assignment is difficult in a dimer of tetrapyrrole macrocycles, having eight pyrrole rings of similar chemical shifts. To overcome this problem, an INADEQUATE type of experiment using a POST C7 symmetry-based approach is applied to selectively isotope-labeled bacterial RC of Rhodobacter (R.) sphaeroides wild type (WT). We, therefore, were able to distinguish unresolved sites of the macromolecular dimer. The obtained chemical-shift pattern is in-line with a concentric assembly of negative charge within the common center of the Special Pair supermolecule in the electronic ground state. © 2017 The American Society of Photobiology.

Photochemical versus Thermal Synthesis of Cobalt Oxyhydroxide Nanocrystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alvarado, Samuel R.; Guo, Yijun; Ruberu, T. Purnima A.

2012-04-18

Photochemical methods facilitate the generation, isolation, and study of metastable nanomaterials having unusual size, composition, and morphology. These harder-to-isolate and highly reactive phases, inaccessible using conventional high-temperature pyrolysis, are likely to possess enhanced and unprecedented chemical, electromagnetic, and catalytic properties. We report a fast, low-temperature and scalable photochemical route to synthesize very small (3 nm) monodisperse cobalt oxyhydroxide (Co(O)OH) nanocrystals. This method uses readily and commercially available pentaamminechlorocobalt(III) chloride, [Co(NH3)5Cl]Cl2, under acidic or neutral pH and proceeds under either near-UV (350 nm) or Vis (575 nm) illumination. Control experiments showed that the reaction proceeds at competent rates only in themore » presence of light, does not involve a free radical mechanism, is insensitive to O2, and proceeds in two steps: (1) Aquation of [Co(NH3)5Cl]2+ to yield [Co(NH3)5(H2O)]3+, followed by (2) slow photoinduced release of NH3 from the aqua complex. This reaction is slow enough for Co(O)OH to form but fast enough so that nanocrystals are small (ca. 3 nm). The alternative dark thermal reaction proceeds much more slowly and produces much larger (250 nm) polydisperse Co(O)OH aggregates. UV–Vis absorption measurements and ab initio calculations yield a Co(O)OH band gap of 1.7 eV. Fast thermal annealing of Co(O)OH nanocrystals leads to Co3O4 nanocrystals with overall retention of nanoparticle size and morphology. Thermogravimetric analysis shows that oxyhydroxide to mixed-oxide phase transition occurs at significantly lower temperatures (up to ΔT = 64 °C) for small nanocrystals compared with the bulk.« less

Extraterrestrial cold chemistry. A need for a specific database.

NASA Astrophysics Data System (ADS)

Pernot, P.; Carrasco, N.; Dobrijevic, M.; Hébrard, E.; Plessis, S.; Wakelam, V.

2008-09-01

The major resource databases for building chemical models for photochemistry in cold environments are mainly based on those designed for Earth atmospheric chemistry or combustion, in which reaction rates are reported for temperatures typically above 300 K [1,2]. Kinetic data measured at low temperatures are very sparse; for instance, in stateoftheart photochemical models of Titan atmosphere, less than 10% of the rates have been measured in the relevant temperature range (100200 K) [35]. In consequence, photochemical models rely mostly on lowT extrapolations by Arrheniustype laws. There is more and more evidence that this is often inappropriate [6], and low T extrapolations are hindered by very high uncertainty [3] (Fig.1). The predictions of models based on those extrapolations are expected to be very inaccurate [4,7]. We argue that there is not much sense in increasing the complexity of the present models as long as this predictivity issue has not been resolved. Fig. 1 Uncertainty of low temperature extrapolation for the N(2D) +C2H4 reaction rate, from measurements in the range 225 292 K [10], assuming an Arrhenius law (blue line). The sample of rate laws is generated by Monte Carlo uncertainty propagation after a Bayesian Data reAnalysis (BDA) of experimental data. A dialogue between modellers and experimentalists is necessary to improve this situation. Considering the heavy costs of low temperature reaction kinetics experiments, the identification of key reactions has to be based on an optimal strategy to improve the predictivity of photochemical models. This can be achieved by global sensitivity analysis, as illustrated on Titan atmospheric chemistry [8]. The main difficulty of this scheme is that it requires a lot of inputs, mainly the evaluation of uncertainty for extrapolated reaction rates. Although a large part has already been achieved by Hébrard et al. [3], extension and validation requires a group of experts. A new generation of collaborative kinetic database is needed to implement efficiently this scheme. The KIDA project [9], initiated by V. Wakelam for astrochemistry, has been joined by planetologists with similar prospects. EuroPlaNet will contribute to this effort through the organization of comities of experts on specific processes in atmospheric photochemistry.

Variation of iron redox kinetics and its relation with molecular composition of standard humic substances at circumneutral pH.

PubMed

Lee, Ying Ping; Fujii, Manabu; Kikuchi, Tetsuro; Terao, Koumei; Yoshimura, Chihiro

2017-01-01

Oxidation and reduction kinetics of iron (Fe) and proportion of steady-state Fe(II) concentration relative to total dissolved Fe (steady-state Fe(II) fraction) were investigated in the presence of various types of standard humic substances (HS) with particular emphasis on the photochemical and thermal reduction of Fe(III) and oxidation of Fe(II) by dissolved oxygen (O2) and hydrogen peroxide (H2O2) at circumneutral pH (pH 7-8). Rates of Fe(III) reduction were spectrophotometrically determined by a ferrozine method under the simulated sunlight and dark conditions, whereas rates of Fe(II) oxidation were examined in air-saturated solution using luminol chemiluminescence technique. The reduction and oxidation rate constants were determined to substantially vary depending on the type of HS. For example, the first-order rate constants varied by up to 10-fold for photochemical reduction and 7-fold for thermal reduction. The degree of variation in Fe(II) oxidation was larger for the H2O2-mediated reaction compared to the O2-mediated reaction (e.g., 15- and 3-fold changes for the former and latter reactions, respectively, at pH 8). The steady-state Fe(II) fraction under the simulated sunlight indicated that the Fe(II) fraction varies by up to 12-fold. The correlation analysis indicated that variation of Fe(II) oxidation is significantly associated with aliphatic content of HS, suggesting that Fe(II) complexation by aliphatic components accelerates Fe(II) oxidation. The reduction rate constant and steady-state Fe(II) fractions in the presence of sunlight had relatively strong positive relations with free radical content of HS, possibly due to the reductive property of radical semiquinone in HS. Overall, the findings in this study indicated that the Fe reduction and oxidation kinetics and resultant Fe(II) formation are substantially influenced by chemical properties of HS.

Photochemical reactions of metal nitrosyl complexes. Mechanisms of NO reactions with biologically relevant metal centers

DOE PAGES

Ford, Peter C.

2001-01-01

Tmore » he discoveries that nitric oxide (a.k.a. nitrogen monoxide) serves important roles in mammalian bioregulation and immunology have stimulated intense interest in the chemistry and biochemistry of NO and derivatives such as metal nitrosyl complexes. Also of interest are strategies to deliver NO to biological targets on demand. One such strategy would be to employ a precursor which displays relatively low thermal reactivity but is photochemically active to release NO. his proposition led us to investigate laser flash and continuous photolysis kinetics of nitrosyl complexes such as the Roussin's iron-sulfur-nitrosyl cluster anions Fe 2 S 2 ( NO ) 4 2 − and Fe 4 S 3 ( NO ) 7 − and several ruthenium salen and porphyrin nitrosyls. hese include studies using metal-nitrosyl photochemistry as a vehicle for delivering NO to hypoxic cell cultures in order to sensitize γ -radiation damage. Also studied were the rates and mechanisms of NO “on” reactions with model water soluble heme compounds, the ferriheme protein met-myoglobin and various ruthenium complexes using ns laser flash photolysis techniques. An overview of these studies is presented.« less

Selective Catalytic Combustion Sensors for Reactive Organic Analysis

NASA Technical Reports Server (NTRS)

Innes, W. B.

1971-01-01

Sensors involving a vanadia-alumina catalyst bed-thermocouple assembly satisfy requirements for simple, reproducible and rapid continuous analysis or reactive organics. Responses generally increase with temperature to 400 C and increase to a maximum with flow rate/catalyst volume. Selectivity decreases with temperature. Response time decreases with flow rate and increases with catalyst volume. At chosen optimum conditions calculated response which is additive and linear agrees better with photochemical reactivity than other methods for various automotive sources, and response to vehicle exhaust is insensitive to flow rate. Application to measurement of total reactive organics in vehicle exhaust as well as for gas chromatography detection illustrate utility. The approach appears generally applicable to high thermal effect reactions involving first order kinetics.

Phototransformation of the herbicide sulcotrione on maize cuticular wax.

PubMed

Ter Halle, Alexandra; Drncova, Daniela; Richard, Claire

2006-05-01

Vegetation plays a key role in environmental cycling and the fate of many organic pollutants. This is especially the case for pesticides because plant leaves are their first reaction environment after application. It is commonly accepted that photochemical reactions of pollutants on plants predominantly take place in the cuticular wax coating of the leaves. Thus, we used films made of either cuticular wax extracted from maize or carnauba gray wax as a model support. Under simulated sunlight irradiation, sulcotrione (a new class of triketone herbicides) sorbed on cuticular wax films was photolyzed and mainly underwent an intramolecular cyclization. The photoproduct is a chromone derivative which was isolated and fully characterized. It is reported for the first time as a sulcotrione degradation product. The photoreactivity of formulated sulcotrione at the surface of cuticular waxes was investigated too. It photodegraded more rapidly than nonformulated sulcotrione. This study also shows that the rate of sulcotrione photolysis was much faster than the rate of penetration into the wax; photolysis should be, thus, a relevant process in real conditions.

Degradation of pharmaceuticals in UV (LP)/H₂O₂ reactors simulated by means of kinetic modeling and computational fluid dynamics (CFD).

PubMed

Wols, B A; Harmsen, D J H; Wanders-Dijk, J; Beerendonk, E F; Hofman-Caris, C H M

2015-05-15

UV/H2O2 treatment is a well-established technique to degrade organic micropollutants. A CFD model in combination with an advanced kinetic model is presented to predict the degradation of organic micropollutants in UV (LP)/H2O2 reactors, accounting for the hydraulics, fluence rate, complex (photo)chemical reactions in the water matrix and the interactions between these processes. The model incorporates compound degradation by means of direct UV photolysis, OH radical and carbonate radical reactions. Measurements of pharmaceutical degradations in pilot-scale UV/H2O2 reactors are presented under different operating conditions. A comparison between measured and modeled degradation for a group of 35 pharmaceuticals resulted in good model predictions for most of the compounds. The research also shows that the degradation of organic micropollutants can be dependent on temperature, which is relevant for full-scale installations that are operated at different temperatures over the year. Copyright © 2015 Elsevier Ltd. All rights reserved.

The Path of Carbon in Photosynthesis XX. The Steady State

DOE R&D Accomplishments Database

Calvin, M.; Massini, Peter

1952-09-01

The separation of the phenomenon of photosynthesis in green plants into a photochemical reaction and into the light-dependent reduction of carbon dioxide is discussed, The reduction of carbon dioxide and the fate of the assimilated carbon were investigated with the help of the tracer technique (exposure of the planks to the radioactive C{sup 14}O{sub 2}) and of paper chromatography. A reaction cycle is proposed in which phosphoglyceric acid is the first isolable assimilations product. Analyses of the algal extracts which had assimilated radioactive carbon dioxide in a stationary condition ('steady-state' photosynthesis) for a long time provided further information concerning the proposed cycle and permitted the approximate estimation, for a number of compounds of what fraction of each compound was taking part in the cycle. The earlier supposition that light influences the respiration cycle was confirmed. The possibility of the assistance of {alpha}-lipoic acid, or of a related substance, in this influence and in the photosynthesis cycle, is discussed.

PHOTOREACTIONS IN SURFACE WATERS AND THEIR ROLE IN BIOGEOCHEMICAL CYCLES

EPA Science Inventory

During the past decade significant interest has developed in the influence of photochemical reactions on biogeochemical cycles in surface waters of lakes and the sea. A major portion of recent research on these photoreactions has focused on the colored component of dissolved org...

COMPARISONS OF SPATIAL PATTERNS OF WET DEPOSITION TO MODEL PREDICTIONS

EPA Science Inventory

The Community Multiscale Air Quality model, (CMAQ), is a "one-atmosphere" model, in that it uses a consistent set of chemical reactions and physical principles to predict concentrations of primary pollutants, photochemical smog, and fine aerosols, as well as wet and dry depositi...

Middle Atmosphere Program. Handbook for MAP, volume 4

NASA Technical Reports Server (NTRS)

Sechrist, C. F., Jr. (Editor)

1982-01-01

Topics include winter in the Northern Hemisphere, temperature measurement, geopotential heights, wind measurement, atmospheric motions, photochemical reactions, solar spectral irradiance, trace constituents, tides, gravity waves, and turbulence. Highlights from the Map Steering Committee and a Map Open Meeting including organizational structure are also given.

INTERACTIONS OF SOLAR ULTRAVIOLET RADIATION AND DISSOLVED ORGANIC MATTER IN FRESHWATER AND MARINE ENVIRONMENTS

EPA Science Inventory

Solar radiation provides the primary driving force for the biogeochemical cycles upon which life and climate depend. Recent studies have demonstrated that the absorption of solar radiation, especially 'm the ultraviolet spectral region, results in photochemical reactions that can...

Effects of Isoprene- and Toluene-Generated Smog on Allergic Inflammation in Mice

EPA Science Inventory

Reactions of organic compounds with nitric oxide (NO) and sunlight produce complex mixtures of pollutants including secondary organic aerosol (SOA), ozone (O3), nitrogen dioxide (NO2), and reactive aldehydes. The health effects of these photochemical smog mixtures in susceptible ...

Removal of sulfur compounds from diesel using ArF laser and oxygen.

PubMed

Gondal, M A; Siddiqui, M N; Al-Hooshani, K

2013-01-01

A laser-based technique for deep desulfurization of diesel and other hydrocarbon fuels by removal of dimethyldibenzothiophene (DMDBT), a persistent sulfur contaminant in fuel oils has been developed. We report a selective laser excitation of DMDBT in diesel and model compounds such as n-hexane in a reaction chamber under oxygen environment where oxidative reactions can take place. ArF laser emitting at 193 nm was employed for excitation of oxygen and DMDBT, while for process optimization, the laser energy was varied from 50 to 200 mJ/cm(2). The laser-irradiated DMDBT solution under continuous oxygen flow was analyzed by UV absorption spectrometer to determine the photochemical oxidative degradation of DMDBT. In just 5 min of laser irradiation time, almost 95% DMDBT was depleted in a diesel containing 200 ppm of DMDBT. This article provides a new method for the removal of sulfur compounds from diesel by laser based photochemical process.

Visible-light excitation of iminium ions enables the enantioselective catalytic β-alkylation of enals

NASA Astrophysics Data System (ADS)

Silvi, Mattia; Verrier, Charlie; Rey, Yannick P.; Buzzetti, Luca; Melchiorre, Paolo

2017-09-01

Chiral iminium ions—generated upon condensation of α,β-unsaturated aldehydes and amine catalysts—are used extensively by chemists to make chiral molecules in enantioenriched form. In contrast, their potential to absorb light and promote stereocontrolled photochemical processes remains unexplored. This is despite the fact that visible-light absorption by iminium ions is a naturally occurring event that triggers the mechanism of vision in higher organisms. Herein we demonstrate that the direct excitation of chiral iminium ions can unlock unconventional reaction pathways, enabling enantioselective catalytic photochemical β-alkylations of enals that cannot be realized via thermal activation. The chemistry uses readily available alkyl silanes, which are recalcitrant to classical conjugate additions, and occurs under illumination by visible-light-emitting diodes. Crucial to success was the design of a chiral amine catalyst with well-tailored electronic properties that can generate a photo-active iminium ion while providing the source of stereochemical induction. This strategy is expected to offer new opportunities for reaction design in the field of enantioselective catalytic photochemistry.

Photochemical reactions in interstellar grains photolysis of CO, NH3, and H2O

NASA Technical Reports Server (NTRS)

Agarwal, V. K.; Ferris, J. P.; Schutte, W.; Greenberg, J. M.; Briggs, R.

1985-01-01

The interstellar grains are currently considered to be the basic building blocks of comets and, possibly, meteorites. To test this theory, a simulation of the organic layer accreted onto interstellar dust particles was prepared by slow deposition of a CO:NH3:H2O gas mixture on an Al block at 10 K, with concomitant irradiation with vacuum UV. The results of the HPLC and IR analyses of the nonvolatile residue formed by photolysis at 10 K are compared with those observed at 77 K and 298 K. Some of the compounds that may be present on the surfaces of interstellar dust particles have been identified, and some specific predictions concerning the types of molecular species present in comets could be drawn. The results also suggest that photochemical reactions may have been important for the formation of meteorite components. The implication of the findings to the questions of the source of organic matter on earth and the origin of life are discussed.

UV-induced photochemical heterogeneity of dissolved and attached organic matter associated with cyanobacterial blooms in a eutrophic freshwater lake.

PubMed

Xu, Huacheng; Jiang, Helong

2013-11-01

Cyanobacterial blooms represent a significant ecological and human health problem worldwide. In aquatic environments, cyanobacterial blooms are actually surrounded by dissolved organic matter (DOM) and attached organic matter (AOM) that bind with algal cells. In this study, DOM and AOM fractionated from blooming cyanobacteria in a eutrophic freshwater lake (Lake Taihu, China) were irradiated with a polychromatic UV lamp, and the photochemical heterogeneity was investigated using fluorescence excitation-emission matrix (EEM)-parallel factor (PARAFAC) analysis and synchronous fluorescence (SF)-two dimensional correlation spectroscopy (2DCOS). It was shown that a 6-day UV irradiation caused more pronounced mineralization for DOM than AOM (59.7% vs. 41.9%). The EEM-PARAFAC analysis identified one tyrosine-, one humic-, and two tryptophan-like components in both DOM and AOM, and high component photodegradation rates were observed for DOM versus AOM (k > 0.554 vs. <0.519). Moreover, SF-2DCOS found that the photodegradation of organic matters followed the sequence of tyrosine-like > humic-like > tryptophan-like substances. Humic-like substances promoted the indirect photochemical reactions, and were responsible for the higher photochemical rate for DOM. The lower photodegradation of AOM benefited the integrality of cells in cyanobacterial blooms against the negative impact of UV irradiation. Therefore, the photochemical behavior of organic matter was related to the adaptation of enhanced-duration cyanobacterial blooms in aquatic environments. Copyright © 2013 Elsevier Ltd. All rights reserved.

Identification of nutrient deficiency in maize and tomato plants by in vivo chlorophyll a fluorescence measurements.

PubMed

Kalaji, Hazem M; Oukarroum, Abdallah; Alexandrov, Vladimir; Kouzmanova, Margarita; Brestic, Marian; Zivcak, Marek; Samborska, Izabela A; Cetner, Magdalena D; Allakhverdiev, Suleyman I; Goltsev, Vasilij

2014-08-01

The impact of some macro (Ca, S, Mg, K, N, P) and micro (Fe) nutrients deficiency on the functioning of the photosynthetic machinery in tomato (Solanum lycopersicum L.) and maize (Zea mays L.) plants grown in hydroponic cultures were investigated. Plants grown on a complete nutrient solution (control) were compared with those grown in a medium, which lacked one of macro- or microelements. The physiological state of the photosynthetic machinery in vivo was analysed after 14-days of deficient condition by the parameters of JIP-test based on fast chlorophyll a fluorescence records. In most of the nutrient-deficient samples, the decrease of photochemical efficiency, increase in non-photochemical dissipation and decrease of the number of active photosystem II (PSII) reaction centres were observed. However, lack of individual nutrients also had nutrient-specific effects on the photochemical processes. In Mg and Ca-deficient plants, the most severe decrease in electron donation by oxygen evolving complex (OEC) was indicated. Sulphur deficiency caused limitation of electron transport beyond PSI, probably due to decrease in the PSI content or activity of PSI electron acceptors; in contrary, Ca deficiency had an opposite effect, where the PSII activity was affected much more than PSI. Despite the fact that clear differences in nutrient deficiency responses between tomato and maize plants were observed, our results indicate that some of presented fluorescence parameters could be used as fluorescence phenotype markers. The principal component analysis of selected JIP-test parameters was presented as a possible species-specific approach to identify/predict the nutrient deficiency using the fast chlorophyll fluorescence records. Copyright © 2014 Elsevier Masson SAS. All rights reserved.

Evidence for in situ production of chlorinated polycyclic aromatic hydrocarbons on tidal flats: environmental monitoring and laboratory scale experiment.

PubMed

Sankoda, Kenshi; Nomiyama, Kei; Yonehara, Takayuki; Kuribayashi, Tomonori; Shinohara, Ryota

2012-07-01

This study investigated environmental distributions and production mechanisms of chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs) in the sediments from some tidal flats located in Asia. Cl-PAHs were found in sediments taken from Arao tidal flat, Kikuchigawa River and Shirakawa River. The range of ∑Cl-PAHs was from 25.5 to 483 pg g(-1) for Kikuchigawa River and Arao tidal flat, respectively. Concentrations of PAHs and Cl-PAHs showed no significant correlations (r=0.134). This result suggests that the origins of these compounds differ. In the identified Cl-PAH isomers, the most abundant Cl-PAH isomer was 9,10-dichloroanthracene (9,10-di-Cl-ANT) in the three sites. In general, concentrations of Cl-ANTs in the coastal environment are about 3-5 orders of magnitude lower than those of anthracene (ANT). However, concentration ratios between Cl-ANTs and ANT (Cl-ANTs/ANT) in the sediments ranged from 4.1% to 24.6%. This result indicated that Cl-PAHs were not generated under industrial processes but the high concentration ratios have resulted from the contribution of photochemical production of Cl-ANTs in the sediments because ANT is known to have high photochemical reactivity. For examining this phenomenon, ANT adsorbed onto glass beads was irradiated with UV under the mimicked field conditions of tidal flats. As a result, it was noticed that, while chlorinated derivatives were negligible in a light-controlled group, production of 2-Cl-ANT, 9-Cl-ANT and 9,10-diCl-ANT on the irradiated surface were found in this study. These results suggest that photochemical reaction of PAHs can be a potential source of the occurrence of Cl-PAHs in the coastal environment. Copyright © 2012 Elsevier Ltd. All rights reserved.

[Response and adaptation of photosynthesis of cucumber seedlings to high temperature stress].

PubMed

Sun, Sheng Nan; Wang, Qiang; Sun, Chen Chen; Liu, Feng Jiao; Bi, Huan Gai; Ai, Xi Zhen

2017-05-18

Cucumber seedlings (Cucumis sativus Jinyou 35) were used to study the effects of high temperature (HT: 42 ℃/32 ℃) and sub-high temperature (SHT: 35 ℃/25 ℃) on its photosynthesis and growth. The results showed that the growth of cucumber seedlings was dramatically inhibited by the high and sub-high temperature stresses. The photosynthetic rate (P n ) was gradually reduced, while intercellular CO 2 concentration (C i ) was increased as heat stress lasted. Under heat stress, stomatal conductance (g s ), transpiration rate (T r ), photorespiration rate (P r ) and dark respiration rate (D r ) showed a trend from rise to decline in cucumber seedlings, which implied that heat-induced decline of photosynthesis was mainly due to non-stomatal limitation. Maximal photochemical efficiency of PS2 in darkness (F v /F m ), actual photochemical efficiency (χ PS 2 ), photochemical quenching (q P ) and electron transport rate (ETR) were severely hampered, while initial fluorescence (F o ) and non-chemical quenching (NPQ) were increased as a result of high and sub-high temperature stresses. Under extended high temperature stress, the activities of RuBP carboxylase (RuBPCase) and Rubisco activase (RCA) as well as the mRNA abundance of Rubisco and RCA were in the trend of decrease, while they were reduced 3 days following the sub-high temperature treatment. The activities and mRNA expressions of sedoheptulose-1,7-bisphosphatase (SBPase) and fructose 1,6-bisphosphate aldolase (FBA) increased initially, but decreased afterwards under heat stress. Taken together, our data suggested that short-term sub-high temperature did not cause photoinhibition under optimal light conditions, however, high temperature led to severe damage to PS2 reaction center in cucumber seedlings. The photosynthetic enzymes were induced by high temperature stress and the induction was affected by temperature and stress duration.

Boosting the catalytic performance of MoSx cocatalysts over CdS nanoparticles for photocatalytic H2 evolution by Co doping via a facile photochemical route

NASA Astrophysics Data System (ADS)

Lei, Yonggang; Hou, Jianhua; Wang, Fang; Ma, Xiaohua; Jin, Zhiliang; Xu, Jing; Min, Shixiong

2017-10-01

Low-crystalline or amorphous molybdenum sulfides (MoSx), bearing abundant unsaturated active sites, have been identified as efficient catalysts for electrocatalytic and photocatalytic H2 evolution reactions, however, their intrinsic activity is still low and need to be further improved for large-scale applications. In this paper, we report that low-crystalline MoSx doped with Co (Co-MoSx) as efficient cocatalysts could be loaded on CdS nanoparticles through a facile and controllable photochemical reduction method and showed high performances in catalyzing H2 evolution under visible light irradiation (≥420 nm). The photochemical loading of Co-MoSx was accomplished by using an in-situ formed molecular complex precursor and photogenerated electrons on CdS as reductants under mild conditions. The optimized CdS/Co-MoSx (Co:Mo = 1:4, 2 mol% loading) photocatalyst exhibited a catalytic H2 evolution rate of 535 μmol h-1, which is 1.8 times higher than that of CdS/MoSx, and an apparent quantum efficiency (AQE) of 23.5% was achieved over CdS/Co-MoSx photocatalyst at 420 nm. Co-MoSx catalyst also shows a long-term stability without noticeable activity degradation. Notably, Co-MoSx cocatalyst was found more efficient than that of noble metals in catalyzing photocatalytic H2 evolution on CdS. The formation of CoMoS phase, the enhanced electrocatalytic activity as well as reduced electron transfer resistance due to the doping effects of Co ions, account for the enhanced catalytic activity of this Co-MoSx cocatalyst.

Photochemical Escape of Atomic Carbon from Mars

NASA Astrophysics Data System (ADS)

Fox, J. L.; Hac, A. B.

2009-12-01

Determining the escape rate of C over time is necessary to reconstructing the time-dependent history of volatiles on Mars. We report initial results from a one-dimensional spherical Monte Carlo calculation of photochemical escape fluxes and rates of atomic carbon from the Martian atmosphere. This model has recently been used to estimate the photochemical escape flux of O from Mars. We include as sources photodissociation of CO, dissociative recombination of CO+, photoelectron-impact dissociation of CO, photodissociative ionization and photoelectron impact dissociative ionization. Dissociative recombination of CO2+ has been suggested as a source of C (in the channel that produces C + O2) but later studies have found that the yield of this channel is negligible. We test the potential importance of this reaction by comparing the final results produced by including it and excluding it. Finally we compare the range of the escape rate to that of C in ions that have been modeled or measured by ASPERA instruments on MEX and Phobos.

A metal-organic cage incorporating multiple light harvesting and catalytic centres for photochemical hydrogen production

NASA Astrophysics Data System (ADS)

Chen, Sha; Li, Kang; Zhao, Fang; Zhang, Lei; Pan, Mei; Fan, Yan-Zhong; Guo, Jing; Shi, Jianying; Su, Cheng-Yong

2016-11-01

Photocatalytic water splitting is a natural but challenging chemical way of harnessing renewable solar power to generate clean hydrogen energy. Here we report a potential hydrogen-evolving photochemical molecular device based on a self-assembled ruthenium-palladium heterometallic coordination cage, incorporating multiple photo- and catalytic metal centres. The photophysical properties are investigated by absorption/emission spectroscopy, electrochemical measurements and preliminary DFT calculations and the stepwise electron transfer processes from ruthenium-photocentres to catalytic palladium-centres is probed by ultrafast transient absorption spectroscopy. The photocatalytic hydrogen production assessments reveal an initial reaction rate of 380 μmol h-1 and a turnover number of 635 after 48 h. The efficient hydrogen production may derive from the directional electron transfers through multiple channels owing to proper organization of the photo- and catalytic multi-units within the octahedral cage, which may open a new door to design photochemical molecular devices with well-organized metallosupramolecules for homogenous photocatalytic applications.

Violaxanthin de-epoxidase is rate-limiting for non-photochemical quenching under subsaturating light or during chilling in Arabidopsis.

PubMed

Chen, Zhong; Gallie, Daniel R

2012-09-01

In response to conditions of excess light energy, plants induce non-photochemical quenching (NPQ) as a protective mechanism to prevent over reduction of photosystem II and the generation of reactive oxygen species (ROS). The xanthophyll cycle, which contributes significantly to reversible NPQ to thermally dissipate excess absorbed light energy, involves de-epoxidation of violaxanthin and antheraxanthin to zeaxanthin in response to excess light energy. The activation of violaxanthin de-epoxidase (VDE), which catalyzes the de-epoxidation reaction, requires the generation of a light-induced, transthylakoid pH gradient. In this work, we overexpressed or repressed the expression of VDE in Arabidopsis (Arabidopsis thaliana) to examine whether VDE is rate-limiting for the induction of NPQ. Increasing VDE expression increased the de-epoxidation state of xanthophyll pigments, the rate of NPQ induction, and the level of NPQ achieved under subsaturating light. In saturating light, however, overexpression of VDE did not increase the xanthophyll pigment de-epoxidation state, the level of NPQ achieved following its initial induction, or substantially improve tolerance to high light. Only under chilling, which reduces VDE activity, did an increase in VDE expression provide slightly greater phototolerance. Repression of VDE expression impaired violaxanthin de-epoxidation, reduced the generation of NPQ, and lowered the level of NPQ achieved while increasing photosensitivity. These results demonstrate that the endogenous level of VDE is rate-limiting for NPQ in Arabidopsis under subsaturating but not saturating light and can become rate-limiting under chilling conditions. These results also show that increasing VDE expression confers greater phototolerance mainly under conditions which limit endogenous VDE activity. Copyright © 2012 Elsevier Masson SAS. All rights reserved.

Photochemical processing of diesel fuel emissions as a large secondary source of isocyanic acid (HNCO)

NASA Astrophysics Data System (ADS)

Link, M. F.; Friedman, B.; Fulgham, R.; Brophy, P.; Galang, A.; Jathar, S. H.; Veres, P.; Roberts, J. M.; Farmer, D. K.

2016-04-01

Isocyanic acid (HNCO) is a well-known air pollutant that affects human health. Biomass burning, smoking, and combustion engines are known HNCO sources, but recent studies suggest that secondary production in the atmosphere may also occur. We directly observed photochemical production of HNCO from the oxidative aging of diesel exhaust during the Diesel Exhaust Fuel and Control experiments at Colorado State University using acetate ionization time-of-flight mass spectrometry. Emission ratios of HNCO were enhanced, after 1.5 days of simulated atmospheric aging, from 50 to 230 mg HNCO/kg fuel at idle engine operating conditions. Engines operated at higher loads resulted in less primary and secondary HNCO formation, with emission ratios increasing from 20 to 40 mg HNCO/kg fuel under 50% load engine operating conditions. These results suggest that photochemical sources of HNCO could be more significant than primary sources in urban areas.

MAVEN in situ measurements of photochemical escape of oxygen from Mars

NASA Astrophysics Data System (ADS)

Lillis, Robert; Deighan, Justin; Fox, Jane; Bougher, Stephen; Lee, Yuni; Cravens, Thomas; Rahmati, Ali; Mahaffy, Paul; Benna, Mehdi; Groller, Hannes; Jakosky, Bruce

2016-04-01

One of the primary goals of the MAVEN mission is to characterize rates of atmospheric escape from Mars at the present epoch and relate those escape rates to solar drivers. One of the known escape processes is photochemical escape, where a) an exothermic chemical reaction in the atmosphere results in an upward-traveling neutral particle whose velocity exceeds planetary escape velocity and b) the particle is not prevented from escaping through subsequent collisions. At Mars, photochemical escape of oxygen is expected to be a significant channel for atmospheric escape, particularly in the early solar system when extreme ultraviolet (EUV) fluxes were much higher. Thus characterizing this escape process and its variability with solar drivers is central to understanding the role escape to space has played in Mars' climate evolution. We use near-periapsis (<400 km altitude) data from three MAVEN instruments: the Langmuir Probe and Waves (LPW) instrument measures electron density and temperature, the Suprathermal And Thermal Ion Composition (STATIC) experiment measures ion temperature and the Neutral Gas and Ion Mass Spectrometer (NGIMS) measures neutral and ion densities. For each profile of in situ measurements, we make several calculations, each as a function of altitude. The first uses electron and temperatures and simulates the dissociative recombination of both O2+ and CO2+ to calculate the probability distribution for the initial energies of the resulting hot oxygen atoms. The second is a Monte Carlo hot atom transport model that takes that distribution of initial O energies and the measured neutral density profiles and calculates the probability that a hot atom born at that altitude will escape. The third takes the measured electron and ion densities and electron temperatures and calculates the production rate of hot O atoms. We then multiply together the profiles of hot atom production and escape probability to get profiles of the production rate of escaping atoms. We integrate with respect to altitude to give us the escape flux of hot oxygen atoms for that periapsis pass. We have sufficient coverage in solar zenith angle (SZA) to estimate total escape rates for two intervals with the obvious assumption that escape rates are the same at all points with the same SZA. We estimate total escape rates of 3.5-5.8 x 1025 s-1 for Ls = 289° to 319° and 1.6-2.6 x 1025 s-1 for Ls = 326° to 348°. The latter is the most directly comparable to previous model-based estimates and is roughly in line with several of them. Total photochemical loss over Mars history is not very useful to calculate from such escape fluxes derived over a limited area and under limited conditions. A thicker atmosphere and much higher solar EUV in the past may change the dynamics of escape dramatically. In the future, we intend to use 3-D Monte Carlo models of global atmospheric escape, in concert with our in situ and remote measurements, to fully characterize photochemical escape under current conditions and carefully extrapolate back in time using further simulations with new boundary conditions.

Photochemical synthesis of simple organic free radicals on simulated planetary surfaces - An ESR study

NASA Technical Reports Server (NTRS)

Tseng, S.-S.; Chang, S.

1975-01-01

Electron spin resonance (ESR) spectroscopy provided evidence for formation of hydroxyl radicals during ultraviolet photolysis (254 nm) at -170 C of H2O adsorbed on silica gel or of silica gel alone. The carboxyl radical was observed when CO or CO2 or a mixture of CO and CO2 adsorbed on silica gel at -170 C was irradiated. The ESR signals of these radicals slowly disappeared when the irradiated samples were warmed to room temperature. However, reirradiation of CO or CO2, or the mixture CO and CO2 on silica gel at room temperature then produced a new species, the carbon dioxide anion radical, which slowly decayed and was identical with that produced by direct photolysis of formic acid adsorbed on silica gel. The primary photochemical process may involve formation of hydrogen and hydroxyl radicals. Subsequent reactions of these radicals with adsorbed CO or CO2 or both yield carboxyl radicals, CO2H, the precursors of formic acid. These results confirm the formation of formic acid under simulated Martian conditions and provide a mechanistic basis for gauging the potential importance of gas-solid photochemistry for chemical evolution on other extraterrestrial bodies, on the primitive earth, and on dust grains in the interstellar medium.

Isotopic evidence for oxygenated Mesoarchaean shallow oceans

NASA Astrophysics Data System (ADS)

Eickmann, Benjamin; Hofmann, Axel; Wille, Martin; Bui, Thi Hao; Wing, Boswell A.; Schoenberg, Ronny

2018-02-01

Mass-independent fractionation of sulfur isotopes (MIF-S) in Archaean sediments results from photochemical processing of atmospheric sulfur species in an oxygen-depleted atmosphere. Geological preservation of MIF-S provides evidence for microbial sulfate reduction (MSR) in low-sulfate Paleoarchaean (3.8-3.2 billion years ago (Ga)) and Neoarchaean (2.8-2.5 Ga) oceans, but the significance of MSR in Mesoarchaean (3.2-2.8 Ga) oceans is less clear. Here we present multiple sulfur and iron isotope data of early diagenetic pyrites from 2.97-Gyr-old stromatolitic dolomites deposited in a tidal flat environment of the Nsuze Group, Pongola Supergroup, South Africa. We identified consistently negative Δ33S values in pyrite, which indicates photochemical reactions under anoxic atmospheric conditions, but large mass-dependent sulfur isotope fractionations of 30‰ in δ34S, identifying active MSR. Negative pyrite δ56Fe values (-1.31 to -0.88‰) record Fe oxidation in oxygen-bearing shallow oceans coupled with biogenic Fe reduction during diagenesis, consistent with the onset of local Fe cycling in oxygen oases 3.0 Ga. We therefore suggest the presence of oxygenated near-shore shallow-marine environments with ≥5 μM sulfate at this time, in spite of the clear presence of an overall reduced Mesoarchaean atmosphere.

Mechanistic consideration of the photochemical transformation of domoic acid (algal toxin) in DOM-Rich brackish water.

PubMed

Jin, Hangxing; Lian, Lushi; Zhou, Huaxi; Yan, Shuwen; Song, Weihua

2018-06-14

Domoic acid (DA) is a neurotoxin generated by several diatom species in harmful algae blooms (HABs). We report the photo-induced transformation products (TPs) and degradation mechanisms of DA in dissolved organic matter (DOM)-rich freshwater and brackish water. High-resolution quadrupole time-of-flight mass spectrometry (QTOF-MS) and the multivariate statistical strategy orthogonal partial least-squares discriminant analysis (OPLS-DA) identified 36 and 23 potential TPs in DOM-rich freshwater and brackish water, respectively. The main reactive sites of DA are the conjugated double bond and proline ring. Isomerization is the predominant transformation pathway induced by excited-state triplet DOM ( 3 DOM ∗ ). The second-order rate constant of the isomerization reaction was measured as (3.8 ± 0.2) × 10 8  M -1  s -1 . The inverse correlation between the dissolved oxygen (DO) concentration and the rate of photo-induced DA isomerization was revealed. Furthermore, under halide-present conditions, halide radicals are mainly responsible for the differentiation of products by quenching hydroxyl radicals and generating unique organic peroxide products. Our results indicated that halide radicals could be important in the photochemical transformation of organic contaminants in high saline environments. Copyright © 2018 Elsevier Ltd. All rights reserved.

Production of hydrogen peroxide in the atmosphere of a Snowball Earth and the origin of oxygenic photosynthesis

PubMed Central

Liang, Mao-Chang; Hartman, Hyman; Kopp, Robert E.; Kirschvink, Joseph L.; Yung, Yuk L.

2006-01-01

During Proterozoic time, Earth experienced two intervals with one or more episodes of low-latitude glaciation, which are probable “Snowball Earth” events. Although the severity of the historical glaciations is debated, theoretical “hard Snowball” conditions are associated with the nearly complete shutdown of the hydrological cycle. We show here that, during such long and severe glacial intervals, a weak hydrological cycle coupled with photochemical reactions involving water vapor would give rise to the sustained production of hydrogen peroxide. The photochemical production of hydrogen peroxide has been proposed previously as the primary mechanism for oxidizing the surface of Mars. During a Snowball, hydrogen peroxide could be stored in the ice; it would then be released directly into the ocean and the atmosphere upon melting and could mediate global oxidation events in the aftermath of the Snowball, such as that recorded in the Fe and Mn oxides of the Kalahari Manganese Field, deposited after the Paleoproterozoic low-latitude Makganyene glaciation. Low levels of peroxides and molecular oxygen generated during Archean and earliest Proterozoic non-Snowball glacial intervals could have driven the evolution of oxygen-mediating and -using enzymes and thereby paved the way for the eventual appearance of oxygenic photosynthesis. PMID:17138669

Alterations of pigment composition and their interactions in response to different light conditions in the diatom Chaetoceros gracilis probed by time-resolved fluorescence spectroscopy.

PubMed

Nagao, Ryo; Ueno, Yoshifumi; Yokono, Makio; Shen, Jian-Ren; Akimoto, Seiji

2018-07-01

Maintenance of energy balance under changeable light conditions is an essential function of photosynthetic organisms to achieve efficient photochemical reactions. Among the photosynthetic organisms, diatoms possess light-harvesting fucoxanthin chlorophyll (Chl) a/c-binding protein (FCP) as peripheral antennas. However, how diatoms regulate excitation-energy distribution between FCP and the two photosystem cores during light adaptation is poorly understood. In this study, we examined spectroscopic properties of a marine diatom Chaetoceros gracilis adapted in the dark and at photosynthetic photon flux density at 30 and 300 μmol photons m -2  s -1 . Absorption spectra at 77 K showed significant changes in the Soret region, and 77-K steady-state fluorescence spectra showed significant differences in the spectral shape and relative fluorescence intensity originating from both PSII and PSI, among the cells grown under different light conditions. These results suggest alterations of pigment composition and their interactions under the different light conditions. These alterations affected the excitation-energy dynamics monitored by picosecond time-resolved fluorescence analyses at 77 K significantly. The contributions of Chls having lower energy levels than the reaction center Chls in the two photosystems to the energy dynamics were clearly identified in the three cells but with presumably different roles. These findings provide insights into the regulatory mechanism of excitation-energy balance in diatoms under various light conditions. Copyright © 2018 Elsevier B.V. All rights reserved.

Determination of Double Bond Positions in Polyunsaturated Fatty Acids Using the Photochemical Paternò-Büchi Reaction with Acetone and Tandem Mass Spectrometry.

PubMed

Murphy, Robert C; Okuno, Toshiaki; Johnson, Christopher A; Barkley, Robert M

2017-08-15

The positions of double bonds along the carbon chain of methylene interrupted polyunsaturated fatty acids are unique identifiers of specific fatty acids derived from biochemical reactions that occur in cells. It is possible to obtain direct structural information as to these double bond positions using tandem mass spectrometry after collisional activation of the carboxylate anions of an acetone adduct at each of the double bond positions formed by the photochemical Paternò-Büchi reaction with acetone. This reaction can be carried out by exposing a small portion of an inline fused silica capillary to UV photons from a mercury vapor lamp as the sample is infused into the electrospray ion source of a mass spectrometer. Collisional activation of [M - H] - yields a series of reverse Paternò-Büchi reaction product ions that essentially are derived from cleavage of the original carbon-carbon double bonds that yield an isopropenyl carboxylate anion corresponding to each double bond location. Aldehydic reverse Paternò-Büchi product ions are much less abundant as the carbon chain length and number of double bonds increase. The use of a mixture of D 0 /D 6 -acetone facilitates identification of these double bonds indicating product ions as shown for arachidonic acid. If oxygen is present in the solvent stream undergoing UV photoactivation, ozone cleavage ions are also observed without prior collisional activation. This reaction was used to determine the double bond positions in a 20:3 fatty acid that accumulated in phospholipids of RAW 264.7 cells cultured for 3 days.

PRODUCTION OF HYDRATED ELECTRONS FROM PHOTOIONIZATION OF DISSOLVED ORGANIC MATTER IN NATURAL WATERS

EPA Science Inventory

Under UV irradiation, an important primary photochemical reaction of colored dissolved organic matter (CDOM) is electron ejection, producing hydrated electrons (e-aq). The efficiency of this process has been studied in both fresh and seawater samples with both steady-state scave...

INTERACTIONS OF SOLAR UV RADIATION AND DISSOLVED ORGANIC MATTER IN AQUATIC ENVIRONMENTS

EPA Science Inventory

Changes in the ozone layer over the past two decades have resulted in increases in solar ultraviolet (UV) radiation that reaches the surface of aquatic environments. Recent studies have demonstrated that these UV increases cause changes in photochemical reactions that affect the...

Methyl transfer from Fe (and Mo) to Sn: formation of (eta(5)-C(5)H(5))M(CO)(n)Sn(t)Bu(2)Me (M = Fe, n = 2; M = Mo, n = 3) complexes from photochemical irradiation of (eta(5)-C(5)H(5))M(CO)(n)Me and (t)Bu(2)SnH(2).

PubMed

Sharma, Hemant K; Arias-Ugarte, Renzo; Metta-Magana, Alejandro; Pannell, Keith H

2010-07-07

Formation of an Sn-CH(3) bond, concomitantly with an Sn-M (M = Fe, Mo), is readily achieved from the photochemical reactions of (t)Bu(2)SnH(2) with (eta(5)-C(5)H(5))M(CO)(n)Me (M = Fe, n = 2; M = Mo, n = 3) via the intermediacy of (eta(5)-C(5)H(5))M(CO)(n)Sn(t)Bu(2)H.

Photocatalytic Iron Oxide Micro-Swimmers for Environmental Remediation

NASA Astrophysics Data System (ADS)

Richard, Cynthia; Simmchen, Juliane; Eychmüller, Alexander

2018-05-01

Harvesting energy from photochemical reactions has long been studied as an efficient means of renewable energy, a topic that is increasingly gaining importance also for motion at the microscale. Iron oxide has been a material of interest in recent studies. Thus, in this work different synthesis methods and encapsulation techniques were used to try and optimize the photo-catalytic properties of iron oxide colloids. Photodegradation experiments were carried out following the encapsulation of the nanoparticles and the Fenton effect was also verified. The end goal would be to use the photochemical degradation of peroxide to propel an array of swimmers in a controlled manner while utilizing the Fenton effect for the degradation of dyes or waste in wastewater remediation.

And There Was Light: Prospects for the Creation of Micro- and Nanostructures through Maskless Photolithography.

PubMed

Rühe, J

2017-09-26

In photolithographic processes, the light inducing the photochemical reactions is confined to a small volume, which enables direct writing of micro- and nanoscale features onto solid surfaces without the need of a predefined photomask. The direct writing process can be used to generate topographic patterns through photopolymerization or photo-cross-linking or can be employed to use light to generate chemical patterns on the surface with high spatial control, which would make such processes attractive for bioapplications. The prospects of maskless photolithography technologies with a focus on two-photon lithography and scanning-probe-based photochemical processes based on scanning near-field optical microscopy or beam pen lithography are discussed.

Photochemical reactions of water and carbon monoxide in earth's primitive atmosphere

NASA Technical Reports Server (NTRS)

Bar-Nun, A.; Chang, S.

1983-01-01

The gas-phase photolysis of H2O at 1849 A in the presence of CO yields mainly CO2 and H2 and a variety of organic compounds, including C1-C3 hydrocarbons, alcohols, aldehydes, acetone, and acetic acid. The overall quantum yield for conversion of CO to organic compounds varies between 0.23 and 0.03 as a function of the CO abundance. These results indicate that even if primitive earth's atmosphere initially contained no molecular hydrogen and contained carbon only in the form of CO or a mixture of CO and CO2, the prebiotic environment would have become enriched with a variety of organic compounds produced by photochemical processes.

Net ozone photochemical production over the eastern and central North Pacific as inferred from GTE/CITE 1 observations during fall 1983

NASA Technical Reports Server (NTRS)

Chameides, W. L.; Davis, D. D.; Rodgers, M. O.; Bradshaw, J.; Sandholm, S.; Sachse, G.; Hill, G.; Gregory, G.

1987-01-01

The role of photochemistry in the budget of tropospheric ozone is studied. Measurements of O3, NO, CO, H2O vapor, and temperature obtained during the fall of 1983 during the GTE/CITE project over the eastern and central North Pacific Ocean are analyzed. The effect of altitude on the measurements is discussed. The analysis reveals a correlation between ozone and NO levels; both increase in concentration and variability with altitude. It is observed that an additional source of secondary importance associated wih CO-rich air parcels exists. A photochemical model is utilized to calculate the net rate of ozone production by photochemical reactions. A net photochemical source of ozone in the free troposphere and a net sink in the boundary layer are detected. The relation between the ozone source in the free troposphere and NO is examined. It is estimated that photochemistry provides a net ozone source to the free troposphere overlying the eastern and central North Pacific Ocean of about 5 x 10 to the 10th molecules/sq cm sec and a net sink of ozone to the boundary layer overlying this region of about 3 x 10 to the 10th molecules/sq cm sec.

Increased Sensitivity of HIV-1 p24 ELISA Using a Photochemical Signal Amplification System.

PubMed

Bystryak, Simon; Santockyte, Rasa

2015-10-01

In this study we describe a photochemical signal amplification method (PSAM) for increasing of the sensitivity of enzyme-linked immunosorbent assay (ELISA) for determination of HIV-1 p24 antigen. The photochemical signal amplification method is based on an autocatalytic photochemical reaction of a horseradish peroxidase (HRP) substrate, orthophenylenediamine (OPD). To compare the performance of PSAM-boosted ELISA with a conventional colorimetric ELISA for determination of HIV-1 p24 antigen we employed a PerkinElmer HIV-1 p24 ELISA kit, using conventional ELISA alongside ELISA + PSAM. In the present study, we show that PSAM technology allows one to increase the analytical sensitivity and dynamic range of a commercial HIV-1 p24 ELISA kit, with and without immune-complex disruption, by a factor of approximately 40-fold. ELISA + PSAM is compatible with commercially available microtiter plate readers, requires only an inexpensive illumination device, and the PSAM amplification step takes no longer than 15 min. This method can be used for both commercially available and in-house ELISA tests, and has the advantage of being considerably simpler and less costly than alternative signal amplification methods. This method can be used for both commercially available and in-house ELISA tests, and has the advantage of being considerably simpler and less costly than alternative signal amplification methods.

A practical approach to calculate the time evolutions of magnetic field effects on photochemical reactions in nano-structured materials.

PubMed

Yago, Tomoaki; Wakasa, Masanobu

2015-04-21

A practical method to calculate time evolutions of magnetic field effects (MFEs) on photochemical reactions involving radical pairs is developed on the basis of the theory of the chemically induced dynamic spin polarization proposed by Pedersen and Freed. In theory, the stochastic Liouville equation (SLE), including the spin Hamiltonian, diffusion motions of the radical pair, chemical reactions, and spin relaxations, is solved by using the Laplace and the inverse Laplace transformation technique. In our practical approach, time evolutions of the MFEs are successfully calculated by applying the Miller-Guy method instead of the final value theorem to the inverse Laplace transformation process. Especially, the SLE calculations are completed in a short time when the radical pair dynamics can be described by the chemical kinetics consisting of diffusions, reactions and spin relaxations. The SLE analysis with a short calculation time enables one to examine the various parameter sets for fitting the experimental date. Our study demonstrates that simultaneous fitting of the time evolution of the MFE and of the magnetic field dependence of the MFE provides valuable information on the diffusion motions of the radical pairs in nano-structured materials such as micelles where the lifetimes of radical pairs are longer than hundreds of nano-seconds and the magnetic field dependence of the spin relaxations play a major role for the generation of the MFE.

Second-order advantage with excitation-emission photoinduced fluorimetry for the determination of the antiepileptic carbamazepine in environmental waters.

PubMed

Lozano, Valeria A; Escandar, Graciela M

2013-06-11

A photochemically induced fluorescence system combined with second-order chemometric analysis for the determination of the anticonvulsant carbamazepine (CBZ) is presented. CBZ is a widely used drug for the treatment of epilepsy and is included in the group of emerging contaminant present in the aquatic environment. CBZ is not fluorescent in solution but can be converted into a fluorescent compound through a photochemical reaction in a strong acid medium. The determination is carried out by measuring excitation-emission photoinduced fluorescence matrices of the products formed upon ultraviolet light irradiation in a laboratory-constructed reactor constituted by two simple 4 W germicidal tubes. Working conditions related to both the reaction medium and the photoreactor geometry are optimized by an experimental design. The developed approach enabled the determination of CBZ at trace levels without the necessity of applying separation steps, and in the presence of uncalibrated interferences which also display photoinduced fluorescence and may be potentially present in the investigated samples. Different second-order algorithms were tested and successful resolution was achieved using multivariate curve resolution-alternating least-squares (MCR-ALS). The study is employed for the discussion of the scopes and yields of each of the applied second-order chemometric tools. The quality of the proposed method is probed through the determination of the studied emerging pollutant in both environmental and drinking water samples. After a pre-concentration step on a C18 membrane using 50.0 mL of real water samples, a prediction relative error of 2% and limits of detection and quantification of 0.2 and 0.6 ng mL(-1) were respectively obtained. Copyright © 2013 Elsevier B.V. All rights reserved.

HYDROXYL RADICAL AND OZONE INITIATED PHOTOCHEMICAL REACTIONS OF 1,3-BUTADIENE. (R826247)

EPA Science Inventory

1,3-Butadiene, classified as hazardous in the 1990 Clean Air Act Amendments, is an important ambient air pollutant. Understanding its atmospheric transformation is useful for its own sake, and is also helpful for eliciting isoprene's fate in the atmosphere (isoprene dominates ...

Demonstrating the Antioxidative Capacity of Substances with Lightsticks

ERIC Educational Resources Information Center

Wieczorek, Robert R.; Sommer, Katrin

2011-01-01

The antioxidative capacity of phytochemical compounds is often discussed in life science courses (to prevent or slow cancer) and food science courses (to prevent the oxidation of sensitive ingredients). Thus, we developed a laboratory experiment where the photochemical reaction of lightsticks is used to qualitatively demonstrate the antioxidative…

Long term impact of anthropogenic emissions of halogenated hydrocarbons on stratospheric ozone level

NASA Technical Reports Server (NTRS)

1977-01-01

Reaction kinetics are studied for stratospheric chlorine atoms, OH initiated degradation of carbon-chlorine compounds, the chemical decomposition of stratospheric HCl and ClONO2. A photochemical study is made of the decomposition of O3 over the wavelength range 2935 to 3165 deg A.

ROLE OF HUMIC SUBSTANCES ON THE PHOTOCHEMICAL REDUCTION OF MERCURY

EPA Science Inventory

Solutions containing mercury and fulvic acids (isolated from the Florida Everglades) were exposed to simulated sunlight from a 1000-W Xenon lamp. In the ensuing reaction, ionic mercury was reduced to elemental mercury, which was collected on a gold trap and measured on a cold va...

Synthesis and Photophysical Characterization of an Artificial Photosynthetic Reaction Center Exhibiting Acid-Responsive Regulation of Charge Separation

NASA Astrophysics Data System (ADS)

Pahk, Ian

Non-photochemical quenching (NPQ) is a photoprotective regulatory mechanism essential to the robustness of the photosynthetic apparatus of green plants. Energy flow within the low-light adapted reaction centers is dynamically optimized to match the continuously fluctuating light conditions found in nature. Activated by compartmentalized decreases in pH resulting from photosynthetic activity during periods of elevated photon flux, NPQ induces rapid thermal dissipation of excess excitation energy that would otherwise overwhelm the apparatus's ability to consume it. Consequently, the frequency of charge separation decreases and the formation of potentially deleterious, high-energy intermediates slows, thereby reducing the threat of photodamage by disallowing their accumulation. Herein is described the synthesis and photophysical analysis of a molecular triad that mimics the effects of NPQ on charge separation within the photosynthetic reaction centers. Steady-state absorption and emission, time-resolved fluorescence, and transient absorption spectroscopies were used to demonstrate reversible quenching of the first singlet excited state affecting the quantum yield of charge separation by approximately one order of magnitude. As in the natural system, the populations of unquenched and quenched states and, therefore, the overall yields of charge separation were found to be dependent upon acid concentration.

Development of fibrin-free intraocular lens with photochemical surface modification

NASA Astrophysics Data System (ADS)

Sato, Yuji; Tanizawa, Katsuya; Anai, Hiroyuki; Sato, Nobuhiro; Sato, Yuki; Ajiki, Tooru; Parel, Jean-Marie; Murahara, Masataka

2004-07-01

Having substituted the hydrophilic and hydrophobic groups alternately on the soft acrylic resin intraocular lens (IOL) surface by using an ArF excimer laser and a Xe2 excimer lamp, we have developed the IOL that is free from fibrin. Acrylic resin or PMMA lens has been used as an intraocular lens for 50 years. However, protein and fat are stuck onto the IOL surface after a long implantation, which opacifies the surface (after-cataract). Thus, we designed the micro domain structures of hydrophilic and hydrophobic groups on the IOL surface for fibrin-free. Firstly, the IOL was irradiated with the Xe2 excimer lamp in the presence of perfluoropolyether in order to make it hydrophobic. By this photochemical reaction, the CF3 functional groups were substituted on the IOL surface. Secondly, the ArF laser was projected on the IOL through the mask pattern in reduced size in the presence of water in order to be hydrophilic. With the photochemical reaction, the OH groups were substituted at the part exposed. The fibrin adsorption test of the modified IOL surface was carried out with FT-IR; which revealed that the fibrin-sticking rate of the treated sample has decreased by 23% compared with that of the non-treated sample. As a result, the fibrin-free IOL has been made by modifying the surface of the IOL to have the micro domain structures of the hydrophilic and hydrophobic groups that are arrayed alternately. In conclusion, the ideal intraocular lens has been demonstrated.

Nitrogen Oxides in Early Earth's Atmosphere as Electron Acceptors for Life's Emergence.

PubMed

Wong, Michael L; Charnay, Benjamin D; Gao, Peter; Yung, Yuk L; Russell, Michael J

2017-10-01

We quantify the amount of nitrogen oxides (NOx) produced through lightning and photochemical processes in the Hadean atmosphere to be available in the Hadean ocean for the emergence of life. Atmospherically generated nitrate (NO 3 - ) and nitrite (NO 2 - ) are the most attractive high-potential electron acceptors for pulling and enabling crucial redox reactions of autotrophic metabolic pathways at submarine alkaline hydrothermal vents. The Hadean atmosphere, dominated by CO 2 and N 2 , will produce nitric oxide (NO) when shocked by lightning. Photochemical reactions involving NO and H 2 O vapor will then produce acids such as HNO, HNO 2 , HNO 3 , and HO 2 NO 2 that rain into the ocean. There, they dissociate into or react to form nitrate and nitrite. We present new calculations based on a novel combination of early-Earth global climate model and photochemical modeling, and we predict the flux of NOx to the Hadean ocean. In our 0.1-, 1-, and 10-bar pCO 2 models, we calculate the NOx delivery to be 2.4 × 10 5 , 6.5 × 10 8 , and 1.9 × 10 8 molecules cm -2 s -1 . After only tens of thousands to tens of millions of years, these NOx fluxes are expected to produce sufficient (micromolar) ocean concentrations of high-potential electron acceptors for the emergence of life. Key Words: Nitrogen oxides-Nitrate-Nitrite-Photochemistry-Lightning-Emergence of life. Astrobiology 17, 975-983.

Two mechanisms for dissipation of excess light in monomeric and trimeric light-harvesting complexes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dall'Osto, Luca; Cazzaniga, Stefano; Bressan, Mauro

Oxygenic photoautotrophs require mechanisms for rapidly matching the level of chlorophyll excited states from light harvesting with the rate of electron transport from water to carbon dioxide. These photoprotective reactions prevent formation of reactive excited states and photoinhibition. The fastest response to excess illumination is the so-called non-photochemical quenching which, in higher plants, requires the luminal pH sensor PsbS and other yet unidentified components of the photosystem II antenna. Both trimeric light-harvesting complex II (LHCII) and monomeric LHC proteins have been indicated as site(s) of the heat-dissipative reactions. Different mechanisms have been proposed: Energy transfer to a lutein quencher inmore » trimers, formation of a zeaxanthin radical cation in monomers. Here, we report on the construction of a mutant lacking all monomeric LHC proteins but retaining LHCII trimers. Its non-photochemical quenching induction rate was substantially slower with respect to the wild type. A carotenoid radical cation signal was detected in the wild type, although it was lost in the mutant. Here, we conclude that non-photochemical quenching is catalysed by two independent mechanisms, with the fastest activated response catalysed within monomeric LHC proteins depending on both zeaxanthin and lutein and on the formation of a radical cation. Trimeric LHCII was responsible for the slowly activated quenching component whereas inclusion in supercomplexes was not required. Finally, this latter activity does not depend on lutein nor on charge transfer events, whereas zeaxanthin was essential.« less

Preparation of Low Molecular Weight Gelatin Using Microwave Discharge Electrodeless Lamp/TiO2 Photocatalyst Hybrid System.

PubMed

Lee, Do-Jin; Kim, Hangun; Park, Young-Kwon; Kim, Byung Hoon; Lee, Heon; Jungf, Sana-Chul

2016-02-01

In this study, an MDEL/TiO2 photocatalyst hybrid system was applied to the production of low molecular weight gelatin. The molecular weight of produed gelatin decreased with increasing microwave intensity and increasing treatment time. The abscission of the chemical bonds between the con- stituents of gelatin by photocatalytic reaction did not alter the characteristics of gelatin. Formation of any by-products due to side reaction was not observed. It is suggested that gelatin was depolymerized by hydroxyl radicals produced during the MDEL/TiO2 photochemical reaction.

Transformation of triclosan to 2,8-dichlorodibenzo-p-dioxin by iron and manganese oxides under near dry conditions.

PubMed

Ding, Jiafeng; Su, Mian; Wu, Cuiwei; Lin, Kunde

2015-08-01

Triclosan (TCS) is a broad-spectrum antibacterial agent widely used in household and personal care products and is frequently detected in the environment. Previous studies have shown that TCS could be converted to the more toxic compound 2,8-dichlorodibenzo-p-dioxins (2,8-DCDD) in photochemical reactions and incineration processes. In this study, we demonstrated the formation of 2,8-DCDD from the oxidation of TCS by α-FeOOH and a natural manganese oxides (MnOx) sand. Experiments at room temperature and under near dry conditions showed that Fe and Mn oxides readily catalyzed the conversion of TCS to 2,8-DCDD and other products. Approximately 5.5% of TCS was transformed to 2,8-DCDD by α-FeOOH in 45 d and a higher conversion percentage (6.7%) was observed for MnOx sand in 16d. However, the presence of water in the samples significantly inhibited the formation of 2,8-DCDD. Besides 2,8-DCDD, 2,4-dichlorphenol (2,4-DCP), 4-chlorobenzene-1,2-diol, 2-chloro-5-(2,4-dichlorophenoxy)benzene-1,4-diol, and 2-chloro-5-(2,4-dichlorophenoxy)-1,4-benzoquinone were identified in the reactions. The possible pathways for the formation of reaction products were proposed. This study suggests that Fe and Mn oxides-mediated transformation of TCS under near dry conditions might be another potential pathway for the formation of 2,8-DCDD in the natural environment. Copyright © 2015 Elsevier Ltd. All rights reserved.

Full-scale chamber investigation and simulation of air freshener emissions in the presence of ozone.

PubMed

Liu, Xiaoyu; Mason, Mark; Krebs, Kenneth; Sparks, Leslie

2004-05-15

Volatile organic compound (VOC) emissions from one electrical plug-in type of pine-scented air freshener and their reactions with O3 were investigated in the U.S. Environmental Protection Agency indoor air research large chamber facility. Ozone was generated from a device marketed as an ozone generator air cleaner. Ozone and oxides of nitrogen concentrations and chamber conditions such as temperature, relative humidity, pressure, and air exchange rate were controlled and/or monitored. VOC emissions and some of the reaction products were identified and quantified. Source emission models were developed to predict the time/concentration profiles of the major VOCs (limonene, alpha-pinene, beta-pinene, 3-carene, camphene, benzyl propionate, benzyl alcohol, bornyl acetate, isobornyl acetate, and benzaldehyde) emitted bythe air freshener. Gas-phase reactions of VOCs from the air freshener with O3 were simulated by a photochemical kinetics simulation system using VOC reaction mechanisms and rate constants adopted from the literature. The concentration-time predictions were in good agreement with the data for O3 and VOCs emitted from the air freshener and with some of the primary reaction products. Systematic differences between the predictions and the experimental results were found for some species. Poor understanding of secondary reactions and heterogeneous chemistry in the chamber is the likely cause of these differences. The method has the potential to provide data to predict the impact of O3/VOC interactions on indoor air quality.

Method of producing metallized chloroplasts and use thereof in the photochemical production of hydrogen and oxygen

DOEpatents

Greenbaum, Elias

1987-01-01

The invention is primarily a metallized chloroplast composition for use in a photosynthetic reaction. A catalytic metal is precipitated on a chloroplast membrane at the location where a catalyzed reduction reaction occurs. This metallized chloroplast is stabilized by depositing it on a support medium such as fiber so that it can be easily handled. A possible application of this invention is the splitting of water to form hydrogen and oxygen that can be used as a renewable energy source.

Improving the throughput of batch photochemical reactions using flow: Dual photoredox and nickel catalysis in flow for C(sp2)C(sp3) cross-coupling.

PubMed

Abdiaj, Irini; Alcázar, Jesús

2017-12-01

We report herein the transfer of dual photoredox and nickel catalysis for C(sp 2 )C(sp 3 ) cross coupling form batch to flow. This new procedure clearly improves the scalability of the previous batch reaction by the reactor's size and operating time reduction, and allows the preparation of interesting compounds for drug discovery in multigram amounts. Copyright © 2016 Elsevier Ltd. All rights reserved.

Visible-light sensitization of vinyl azides by transition-metal photocatalysis.

PubMed

Farney, Elliot P; Yoon, Tehshik P

2014-01-13

Irradiation of vinyl and aryl azides with visible light in the presence of Ru photocatalysts results in the formation of reactive nitrenes, which can undergo a variety of C-N bond-forming reactions. The ability to use low-energy visible light instead of UV in the photochemical activation of azides avoids competitive photodecomposition processes that have long been a significant limitation on the synthetic use of these reactions. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Structural diversity through intramolecular cycloaddition and modulation of chemical reactivity in excited state. Synthesis and photoreactions of 3-oxa-tricyclo[5.2.2.0(1,5)]undecenones: novel stereoselective route to oxa-triquinanes and oxa-sterpuranes.

PubMed

Singh, V; Alam, S Q

2000-11-20

Synthesis of 11-methyl-3-oxa-tricyclo[5.2.2.0(1,5)]undecenones by intramolecular Diels-Alder reaction of highly labile spiroepoxycyclohexa-2,4-dienones and its photochemical reactions upon triplet (3T) and singlet (1S) excitation leading to a stereoselective route to oxa-triquinane and oxa-sterpurane, respectively, is described.

Photochemical cycloaddition reagents for rigidly attaching the 1, 4-dimethoxynaphthalene chromophore to scaffold alkenes

PubMed

Margetic; Russell; Warrener

2000-12-14

The norbornanecyclobutene epoxides 1a-1c containing a fused 1, 4-dimethoxynaphthalene chromophore have been reacted with cyclobutenes, cyclohexenes, norbornenes, 7-isopropylidenenorbornenes, 7-azanorbornenes, and other cyclic or electron-deficient alkenes at room temperature to form 1:1 adducts in stereoselective 1,3-dipolar cycloaddition reactions; alkynes can also participate in this reaction. The ability to form 2:1 adducts has also been demonstrated, thereby opening up opportunities for preparing functionalized products with large chromophore separations.

A quantitative structure–function relationship for the Photosystem II reaction center: Supermolecular behavior in natural photosynthesis

PubMed Central

Barter, Laura M. C.; Durrant, James R.; Klug, David R.

2003-01-01

Light-induced charge separation is the primary photochemical event of photosynthesis. Efficient charge separation in photosynthetic reaction centers requires the balancing of electron and excitation energy transfer processes, and in Photosystem II (PSII), these processes are particularly closely entangled. Calculations that treat the cofactors of the PSII reaction center as a supermolecular complex allow energy and electron transfer reactions to be described in a unified way. This calculational approach is shown to be in good agreement with experimentally observed energy and electron transfer dynamics. This supermolecular view also correctly predicts the effect of changing the redox potentials of cofactors by site-directed mutagenesis, thus providing a unified and quantitative structure–function relationship for the PSII reaction center. PMID:12538865

Criegee intermediate-hydrogen sulfide chemistry at the air/water interface.

PubMed

Kumar, Manoj; Zhong, Jie; Francisco, Joseph S; Zeng, Xiao C

2017-08-01

We carry out Born-Oppenheimer molecular dynamic simulations to show that the reaction between the smallest Criegee intermediate, CH 2 OO, and hydrogen sulfide (H 2 S) at the air/water interface can be observed within few picoseconds. The reaction follows both concerted and stepwise mechanisms with former being the dominant reaction pathway. The concerted reaction proceeds with or without the involvement of one or two nearby water molecules. An important implication of the simulation results is that the Criegee-H 2 S reaction can provide a novel non-photochemical pathway for the formation of a C-S linkage in clouds and could be a new oxidation pathway for H 2 S in terrestrial, geothermal and volcanic regions.

Fractal growth mechanism of sp3-bonded 5H-BN microcones by plasma-assisted pulsed-laser chemical vapor deposition

NASA Astrophysics Data System (ADS)

Komatsu, Shojiro; Kazami, Daisuke; Tanaka, Hironori; Moriyoshi, Yusuke; Shiratani, Masaharu; Okada, Katsuyuki

2006-08-01

Here we propose a repetitive photochemical reaction and diffusion model for the fractal pattern formation of sp3-bonded 5H-BN microcones in laser-assisted plasma chemical vapor deposition, which was observed experimentally and reported previously. This model describing the behavior of the surface density of precursor species gave explanations to (1) the "line-drawing" nature of the patterns, (2) the origin of the scale-invariant self-similarity (fractality) of the pattern, and (3) the temperature-dependent uniform to fractal transition. The results have implications for controlling the self-organized arrangements of electron-emitter cones at the micro-and nanoscale by adjusting macroscopically the boundary condition (LX,LY) for the deposition, which will be very effective in improving the electron field emission properties.

Photochemical Synthesis of Carbazoles Using an [Fe(phen)3](NTf2)2/O2 Catalyst System: Catalysis toward Sustainability.

PubMed

Parisien-Collette, Shawn; Hernandez-Perez, Augusto C; Collins, Shawn K

2016-10-07

An increasingly sustainable photochemical synthesis of carbazoles was developed using a catalytic system of Fe(phen) 3 (NTf 2 ) 2 /O 2 under continuous flow conditions and was demonstrated on gram-scale using a numbering-up strategy. Photocyclization of triaryl and diarylamines into the corresponding carbazoles occurs in general in higher yields than with previously developed photocatalysts.

In search of efficient 5-endo-dig cyclization of a carbon-centered radical: 40 years from a prediction to another success for the Baldwin rules.

PubMed

Alabugin, Igor V; Timokhin, Vitaliy I; Abrams, Jason N; Manoharan, Mariappan; Abrams, Rachel; Ghiviriga, Ion

2008-08-20

Despite being predicted to be stereoelectronically favorable by the Baldwin rules, efficient formation of a C-C bond through a 5-endo-dig radical cyclization remained unknown for more than 40 years. This work reports a remarkable increase in the efficiency of this process upon beta-Ts substitution, which led to the development of an expedient approach to densely functionalized cyclic 1,3-dienes. Good qualitative agreement between the increased efficiency and stereoselectivity for the 5-endo-dig cyclization of Ts-substituted vinyl radicals and the results of density functional theory analysis further confirms the utility of computational methods in the design of new radical processes. Although reactions of Br atoms generated through photochemical Ts-Br bond homolysis lead to the formation of cyclic dibromide side products, the yields of target bromosulfones in the photochemically induced reactions can be increased by recycling the dibromide byproduct into the target bromosulfones through a sequence of addition/elimination reactions at the exocyclic double bond. Discovery of a relatively efficient radical 5-endo-dig closure, accompanied by a C-C bond formation, provides further support to stereoelectronic considerations at the heart of the Baldwin rules and fills one of the last remaining gaps in the arsenal of radical cyclizations.

Fabrication of copper decorated tungsten oxide-titanium oxide nanotubes by photochemical deposition technique and their photocatalytic application under visible light

NASA Astrophysics Data System (ADS)

Momeni, Mohamad Mohsen

2015-12-01

Copper decorated WO3-TiO2 nanotubes (Cu/WTNs) with a high photocatalytic activity were prepared by anodizing and photochemical deposition. Highly ordered WO3-TiO2 nanotubes (WTNs) on pure titanium foils were successfully fabricated by electrochemical anodizing and copper deposited on these nanotubes (Cu/WTNs) by photoreduction method. The resulting samples were characterized by various methods. Only the anatase phase was detected by X-ray diffraction analysis. The presence of copper in the structure of thin films was confirmed by energy dispersive X-ray spectrometry and X-ray diffraction. The extension of optical absorption into the visible region of as-prepared films was indicated by UV/Vis spectroscopy. The degradation of methylene blue was used as a model reaction to evaluate the photocatalytic activity of the obtained samples. Results showed that the photocatalytic activity of Cu/WTNs samples is higher than bare WTNs sample. Kinetic research showed that the reaction rate constant of Cu/WTNs is approximately 2.5 times higher than the apparent reaction rate constant of bare WTNs. These results not only offer an economical method for constructing Cu/WTNs photocatalysts, but also shed new insight on the rational design of a low cost and high-efficiency photocatalyst for environmental remediation.

Process for light-driven hydrocarbon oxidation at ambient temperatures

DOEpatents

Shelnutt, John A.

1990-01-01

A photochemical reaction for the oxidation of hydrocarbons uses molecular oxygen as the oxidant. A reductive photoredox cycle that uses a tin(IV)- or antimony(V)-porphyrin photosensitizer generates the reducing equivalents required to activate oxygen. This artificial photosynthesis system drives a catalytic cycle, which mimics the cytochrome P.sub.450 reaction, to oxidize hydrocarbons. An iron(III)- or manganese(III)-porphyrin is used as the hydrocarbon-oxidation catalyst. Methylviologen can be used as a redox relay molecule to provide for electron-transfer from the reduced photosensitizer to the Fe or Mn porphyrin. The system is long-lived and may be used in photo-initiated spectroscopic studies of the reaction to determine reaction rates and intermediates.

Photoperiod and temperature constraints on the relationship between the photochemical reflectance index and the light use efficiency of photosynthesis in Pinus strobus

PubMed Central

Fréchette, Emmanuelle; Chang, Christine Yao-Yun; Ensminger, Ingo

2016-01-01

The photochemical reflectance index (PRI) is a proxy for the activity of the photoprotective xanthophyll cycle and photosynthetic light use efficiency (LUE) in plants. Evergreen conifers downregulate photosynthesis in autumn in response to low temperature and shorter photoperiod, and the dynamic xanthophyll cycle-mediated non-photochemical quenching (NPQ) is replaced by sustained NPQ. We hypothesized that this shift in xanthophyll cycle-dependent energy partitioning during the autumn is the cause for variations in the PRI–LUE relationship. In order to test our hypothesis, we characterized energy partitioning and pigment composition during a simulated summer–autumn transition in a conifer and assessed the effects of temperature and photoperiod on the PRI–LUE relationship. We measured gas exchange, chlorophyll fluorescence and leaf reflectance during the photosynthetic downregulation in Pinus strobus L. seedlings exposed to low temperature/short photoperiod or elevated temperature/short photoperiod conditions. Shifts in energy partitioning during simulated autumn were observed when the pools of chlorophylls decreased and pools of photoprotective carotenoids increased. On a seasonal timescale, PRI was controlled by carotenoid pool sizes rather than xanthophyll cycle dynamics. Photochemical reflectance index variation under cold autumn conditions mainly reflected long-term pigment pool adjustments associated with sustained NPQ, which impaired the PRI–LUE relationship. Exposure to warm autumn conditions prevented the induction of sustained NPQ but still impaired the PRI–LUE relationship. We therefore conclude that alternative zeaxanthin-independent NPQ mechanisms, which remain undetected by the PRI, are present under both cold and warm autumn conditions, contributing to the discrepancy in the PRI–LUE relationship during autumn. PMID:26846980

Photoperiod and temperature constraints on the relationship between the photochemical reflectance index and the light use efficiency of photosynthesis in Pinus strobus.

PubMed

Fréchette, Emmanuelle; Chang, Christine Yao-Yun; Ensminger, Ingo

2016-03-01

The photochemical reflectance index (PRI) is a proxy for the activity of the photoprotective xanthophyll cycle and photosynthetic light use efficiency (LUE) in plants. Evergreen conifers downregulate photosynthesis in autumn in response to low temperature and shorter photoperiod, and the dynamic xanthophyll cycle-mediated non-photochemical quenching (NPQ) is replaced by sustained NPQ. We hypothesized that this shift in xanthophyll cycle-dependent energy partitioning during the autumn is the cause for variations in the PRI-LUE relationship. In order to test our hypothesis, we characterized energy partitioning and pigment composition during a simulated summer-autumn transition in a conifer and assessed the effects of temperature and photoperiod on the PRI-LUE relationship. We measured gas exchange, chlorophyll fluorescence and leaf reflectance during the photosynthetic downregulation in Pinus strobus L. seedlings exposed to low temperature/short photoperiod or elevated temperature/short photoperiod conditions. Shifts in energy partitioning during simulated autumn were observed when the pools of chlorophylls decreased and pools of photoprotective carotenoids increased. On a seasonal timescale, PRI was controlled by carotenoid pool sizes rather than xanthophyll cycle dynamics. Photochemical reflectance index variation under cold autumn conditions mainly reflected long-term pigment pool adjustments associated with sustained NPQ, which impaired the PRI-LUE relationship. Exposure to warm autumn conditions prevented the induction of sustained NPQ but still impaired the PRI-LUE relationship. We therefore conclude that alternative zeaxanthin-independent NPQ mechanisms, which remain undetected by the PRI, are present under both cold and warm autumn conditions, contributing to the discrepancy in the PRI-LUE relationship during autumn. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

A one-dimensional photochemical model of the troposphere with planetary boundary-layer parameterization

NASA Technical Reports Server (NTRS)

Fishman, J.; Carney, T. A.

1984-01-01

A time-dependent, one-dimensional photochemical model of the troposphere is used to describe the vertical distribution of atmospheric trace constituents for summer-time conditions at midlatitudes in the Northern Hemisphere. The model incorporates a planetary boundary layer (PBL) parametrization and a detailed chemical mechanism that includes the photochemistry of important nonmethane hydrocarbon species formed during the oxidation process. One result of the parametrized PBL is that the concentrations of some trace species in the free troposphere are 20-30 percent higher than when mixing processes are described by a vertical eddy diffusion coefficient which is held constant with respect to height and time. The lifetime of the oxides of nitrogen against photochemical conversion to nitric acid during summertime conditions is on the order of six hours. This lifetime is short enough to deplete most of the NO(x) in the PBL so that other reactive nitrogen species are more abundant than NO(x) throughout the free troposphere.

Energetic Metastable Oxygen and Nitrogen Atoms in the Terrestrial Atmosphere

NASA Technical Reports Server (NTRS)

Kharchenko, Vasili

2003-01-01

We have investigated the energy distributions of the metastable oxygen atoms in the terrestrial thermosphere. Nascent O(lD) atoms play a fundamental role in the energy balance and chemistry of the terrestrial atmosphere, because they are produced by photo-chemical reactions in the excited electronic states and carry significant translational energies.

Mutation of Photosystem II D1 protein that empower efficient phenotypes of Chlamydomonas Reinhardtii under extreme environment in space

USDA-ARS?s Scientific Manuscript database

Oxygenic photosynthesis involves capture and conversion of light energy into chemical energy, a process fundamental to life including plant productivity on Earth. Photosynthetic electron transport is catalyzed by two photochemical reaction centres in series, photosystem II (PS II) and photosytem I (...

40 CFR 60.711 - Definitions, symbols, and cross reference tables.

Code of Federal Regulations, 2011 CFR

2011-07-01

... audio or video recording or information storage. (14) Natural draft opening means any opening in a room... control device. (18) Utilize refers to the use of solvent that is delivered to coating mix preparation... participate in atmospheric photochemical reactions or that are measured by Method 18, 24, 25, or 25A or an...

40 CFR 60.711 - Definitions, symbols, and cross reference tables.

Code of Federal Regulations, 2013 CFR

2013-07-01

... audio or video recording or information storage. (14) Natural draft opening means any opening in a room... control device. (18) Utilize refers to the use of solvent that is delivered to coating mix preparation... participate in atmospheric photochemical reactions or that are measured by Method 18, 24, 25, or 25A or an...

40 CFR 60.711 - Definitions, symbols, and cross reference tables.

Code of Federal Regulations, 2012 CFR

2012-07-01

... audio or video recording or information storage. (14) Natural draft opening means any opening in a room... control device. (18) Utilize refers to the use of solvent that is delivered to coating mix preparation... participate in atmospheric photochemical reactions or that are measured by Method 18, 24, 25, or 25A or an...

40 CFR 60.711 - Definitions, symbols, and cross reference tables.

Code of Federal Regulations, 2010 CFR

2010-07-01

... audio or video recording or information storage. (14) Natural draft opening means any opening in a room... control device. (18) Utilize refers to the use of solvent that is delivered to coating mix preparation... participate in atmospheric photochemical reactions or that are measured by Method 18, 24, 25, or 25A or an...

40 CFR 60.711 - Definitions, symbols, and cross reference tables.

Code of Federal Regulations, 2014 CFR

2014-07-01

... audio or video recording or information storage. (14) Natural draft opening means any opening in a room... control device. (18) Utilize refers to the use of solvent that is delivered to coating mix preparation... participate in atmospheric photochemical reactions or that are measured by Method 18, 24, 25, or 25A or an...

A MECHANISTIC MODEL FOR MERCURY CAPTURE WITH IN-SITU GENERATED TITANIA PARTICLES: ROLE OF WATER VAPOR

EPA Science Inventory

A mechanistic model to predict the capture of gas phase mercury species using in-situ generated titania nanosize particles activated by UV irradiation is developed. The model is an extension of a recently reported model1 for photochemical reactions that accounts for the rates of...

Preparation and Analysis of Potassium Tris(Oxalato)Ferrate(III)Trihydrate: A General Chemistry Experiment.

ERIC Educational Resources Information Center

Olmsted, John

1984-01-01

Describes a five-period experiment which: (1) integrates preparative and analytical techniques; (2) utilizes a photochemical reaction that excites student interest both from visual impact and as an introduction to photoinduced processes; (3) provides accurate results; and (4) costs less than $0.20 per student per laboratory session. (JN)

Studies on the nature of the primary reactions of photosystem II in photosynthesis. I. The electrochromic 515 nm absorption change as an appropriate indicator for the functional state of the photochemical active centers of system II in DCMY poisoned chloroplasts.

PubMed

Renger, G; Wolff, C

1975-01-01

The field indicating electrochromic 515 nm absorption change has been measured under different excitation conditions in DCMU poisoned chloroplasts in the presence of benzylviologen as electron acceptor. It has been found: 1. The amplitude of the 515 nm absorption change is nearly completely suppressed under repetitive single turnover flash excitation conditions which kinetically block the back reaction around system II (P. Bennoun, Biochim. Biophys. Acta 216, 357 [1970]). 2. The amplitude of the 515 nm absorption change measured under repetitive single turnover flash excitation conditions which allow the completion of the back reaction during the dark time between the flashes (measuring light beam switched off) amounts in the presence of 2 mum DCMU nearly 50% of the electrochromic 515 nm amplitude obtained in the absence of DCMU. In DCMU poisoned chloroplasts this amplitude is significantly decreased by hydroxylaminhydrochloride, but nearly doubled in the presence of CDIP+ascorbate. 3. The dependence of the 515 nm amplitude on the time td between the flashes kinetically resembles the back reaction around system ?II. The time course of the back reaction can be fairly described either by a second order reaction or by a two phase exponential kinetics. 4. 1,3-dinitrobenzene (DNE) or alpha-bromo-alpha-benzylmalodinitril (BBMD) reduce the 515 nm amplitude in DCMU poisoned chloroplasts, but seem to influecne only slightly the kinetics of the back reaction. 5. The dependence of the 515 nm amplitude on the flash light intensity (the amplitude normalized to 1 at 100% flash light intensity) is not changed by DNB. Based on these experimental data it has been concluded that in DCMU poisoned chloroplasts the amplitude of the 515 nm absorption change reflects the functional state of photosystem II centers (designated as photoelectric dipole generators II) under suitable excitation conditions. Furthermore, it is inferred that in DCMU poisoned chlorplasts the photoelectric dipole generators II either cooperate (probably as twin-pairs) or exist in two functionally different forms. With respect to BBMD and DNB it is assumed that these agents transform the phtooelectric dipole generators II into powerful nonphotochemical quenchers, which significantly reduce the variable fluorescence in DCMU-poisoned chloroplasts.

Raising the shields: PCR in the presence of metallic surfaces protected by tailor-made coatings.

PubMed

Scherag, Frank D; Brandstetter, Thomas; Rühe, Jürgen

2014-10-01

The implementation of PCR reactions in the presence of metallic surfaces is interesting for the generation of novel bioanalytical devices, because metals exhibit high mechanical stability, good thermal conductivity, and flexibility during deformation. However, metallic substrates are usually non-compatible with enzymatic reactions such as PCR due to poisoning of the active center of the enzyme or nonspecific adsorption of the enzymeto the metal surface, which could result in protein denaturation. We present a method for the generation of polymer coatings on metallic surfaces which are designed to minimize protein adsorption and also prevent the release of metal ions. These coatings consist of three layers covalently linked to each other; a self-assembled monolayer to promote adhesion, a photochemically generated barrier layer and a photochemically generated hydrogel. The coatings can be deposited onto aluminum, stainless steel, gold and copper surfaces. We compare PCR efficiencies in the presence of bare metallic surfaces with those of surfaces treated with the novel coating system. Copyright © 2014 Elsevier B.V. All rights reserved.

15N photo-CIDNP MAS NMR analysis of reaction centers of Chloracidobacterium thermophilum.

PubMed

Zill, Jeremias C; He, Zhihui; Tank, Marcus; Ferlez, Bryan H; Canniffe, Daniel P; Lahav, Yigal; Bellstedt, Peter; Alia, A; Schapiro, Igor; Golbeck, John H; Bryant, Donald A; Matysik, Jörg

2018-03-30

Photochemically induced dynamic nuclear polarization (photo-CIDNP) has been observed in the homodimeric, type-1 photochemical reaction centers (RCs) of the acidobacterium, Chloracidobacterium (Cab.) thermophilum, by 15 N magic-angle spinning (MAS) solid-state NMR under continuous white-light illumination. Three light-induced emissive (negative) signals are detected. In the RCs of Cab. thermophilum, three types of (bacterio)chlorophylls have previously been identified: bacteriochlorophyll a (BChl a), chlorophyll a (Chl a), and Zn-bacteriochlorophyll a' (Zn-BChl a') (Tsukatani et al. in J Biol Chem 287:5720-5732, 2012). Based upon experimental and quantum chemical 15 N NMR data, we assign the observed signals to a Chl a cofactor. We exclude Zn-BChl because of its measured spectroscopic properties. We conclude that Chl a is the primary electron acceptor, which implies that the primary donor is most likely Zn-BChl a'. Chl a and 8 1 -OH Chl a have been shown to be the primary electron acceptors in green sulfur bacteria and heliobacteria, respectively, and thus a Chl a molecule serves this role in all known homodimeric type-1 RCs.

Key role of pH in the photochemical conversion of NO2 to HONO on humic acid

NASA Astrophysics Data System (ADS)

Han, Chong; Yang, Wangjin; Wu, Qianqian; Yang, He; Xue, Xiangxin

2016-10-01

The heterogeneous photochemical reactions of NO2 with humic acid (HA) were performed using a flow tube reactor coupled to a NOx analyzer. The effects of the pH on the uptake coefficient (γ) of NO2 and HONO and NO yields were investigated in detail. With increasing the pH in the range of 2-12, γ was almost constant with an average value of (4.21 ± 0.46) × 10-6, whereas the HONO yield and NO yield linearly decreased from (81.07 ± 4.07)% and (10.35 ± 3.86)% to (13.87 ± 9.15)% and (1.51 ± 0.94)%, respectively. According to the characterization of HA compositions and possible reaction paths, it can be concluded that the pH may influence the transfer of protons and the equilibrium of HONO with NO2- by varying the contents of carboxyl and phenol groups in HA, which should primarily contribute to the change in the HONO yield with the pH.

Plasmon inducing effects for enhanced photoelectrochemical water splitting: X-ray absorption approach to electronic structures.

PubMed

Chen, Hao Ming; Chen, Chih Kai; Chen, Chih-Jung; Cheng, Liang-Chien; Wu, Pin Chieh; Cheng, Bo Han; Ho, You Zhe; Tseng, Ming Lun; Hsu, Ying-Ya; Chan, Ting-Shan; Lee, Jyh-Fu; Liu, Ru-Shi; Tsai, Din Ping

2012-08-28

Artificial photosynthesis using semiconductors has been investigated for more than three decades for the purpose of transferring solar energy into chemical fuels. Numerous studies have revealed that the introduction of plasmonic materials into photochemical reaction can substantially enhance the photo response to the solar splitting of water. Until recently, few systematic studies have provided clear evidence concerning how plasmon excitation and which factor dominates the solar splitting of water in photovoltaic devices. This work demonstrates the effects of plasmons upon an Au nanostructure-ZnO nanorods array as a photoanode. Several strategies have been successfully adopted to reveal the mutually independent contributions of various plasmonic effects under solar irradiation. These have clarified that the coupling of hot electrons that are formed by plasmons and the electromagnetic field can effectively increase the probability of a photochemical reaction in the splitting of water. These findings support a new approach to investigating localized plasmon-induced effects and charge separation in photoelectrochemical processes, and solar water splitting was used herein as platform to explore mechanisms of enhancement of surface plasmon resonance.

Role of bonding mechanisms during transfer hydrogenation reaction on heterogeneous catalysts of platinum nanoparticles supported on zinc oxide nanorods

NASA Astrophysics Data System (ADS)

Al-Alawi, Reem A.; Laxman, Karthik; Dastgir, Sarim; Dutta, Joydeep

2016-07-01

For supported heterogeneous catalysis, the interface between a metal nanoparticle and the support plays an important role. In this work the dependency of the catalytic efficiency on the bonding chemistry of platinum nanoparticles supported on zinc oxide (ZnO) nanorods is studied. Platinum nanoparticles were deposited on ZnO nanorods (ZnO NR) using thermal and photochemical processes and the effects on the size, distribution, density and chemical state of the metal nanoparticles upon the catalytic activities are presented. The obtained results indicate that the bonding at Pt-ZnO interface depends on the deposition scheme which can be utilized to modulate the surface chemistry and thus the activity of the supported catalysts. Additionally, uniform distribution of metal on the catalyst support was observed to be more important than the loading density. It is also found that oxidized platinum Pt(IV) (platinum hydroxide) provided a more suitable surface for enhancing the transfer hydrogenation reaction of cyclohexanone with isopropanol compared to zero valent platinum. Photochemically synthesized ZnO supported nanocatalysts were efficient and potentially viable for upscaling to industrial applications.

Coherent fifth-order visible-infrared spectroscopies: ultrafast nonequilibrium vibrational dynamics in solution.

PubMed

Lynch, Michael S; Slenkamp, Karla M; Cheng, Mark; Khalil, Munira

2012-07-05

Obtaining a detailed description of photochemical reactions in solution requires measuring time-evolving structural dynamics of transient chemical species on ultrafast time scales. Time-resolved vibrational spectroscopies are sensitive probes of molecular structure and dynamics in solution. In this work, we develop doubly resonant fifth-order nonlinear visible-infrared spectroscopies to probe nonequilibrium vibrational dynamics among coupled high-frequency vibrations during an ultrafast charge transfer process using a heterodyne detection scheme. The method enables the simultaneous collection of third- and fifth-order signals, which respectively measure vibrational dynamics occurring on electronic ground and excited states on a femtosecond time scale. Our data collection and analysis strategy allows transient dispersed vibrational echo (t-DVE) and dispersed pump-probe (t-DPP) spectra to be extracted as a function of electronic and vibrational population periods with high signal-to-noise ratio (S/N > 25). We discuss how fifth-order experiments can measure (i) time-dependent anharmonic vibrational couplings, (ii) nonequilibrium frequency-frequency correlation functions, (iii) incoherent and coherent vibrational relaxation and transfer dynamics, and (iv) coherent vibrational and electronic (vibronic) coupling as a function of a photochemical reaction.

Validation of photosynthetic-fluorescence parameters as biomarkers for isoproturon toxic effect on alga Scenedesmus obliquus.

PubMed

Dewez, David; Didur, Olivier; Vincent-Héroux, Jonathan; Popovic, Radovan

2008-01-01

Photosynthetic-fluorescence parameters were investigated to be used as valid biomarkers of toxicity when alga Scenedesmus obliquus was exposed to isoproturon [3-(4-isopropylphenyl)-1,1-dimethylurea] effect. Chlorophyll fluorescence induction of algal cells treated with isoproturon showed inactivation of photosystem II (PSII) reaction centers and strong inhibition of PSII electron transport. A linear correlation was found (R2>or=0.861) between the change of cells density affected by isoproturon and the change of effective PSII quantum yield (PhiM'), photochemical quenching (qP) and relative photochemical quenching (qP(rel)) values. The cells density was also linearly dependent (R2=0.838) on the relative unquenched fluorescence parameter (UQF(rel)). Non-linear correlation was found (R2=0.937) only between cells density and the energy transfer efficiency from absorbed light to PSII reaction center (ABS/RC). The order of sensitivity determined by the EC-50% was: UQF(rel)>PhiM'>qP>qP(rel)>ABS/RC. Correlations between cells density and those photosynthetic-fluorescence parameters provide supporting evidence to use them as biomarkers of toxicity for environmental pollutants.

Effect of dipolar fields, surface termination, and surface orientation on photochemical reactions on transition metal oxides

NASA Astrophysics Data System (ADS)

Giocondi, Jennifer Lynn

Experiments have been conducted to determine the effects of dipolar fields, surface termination, and surface orientation on the photochemical reactivity of several transition metal oxides. These compounds include BaTiO3, SrTiO3, BaTi4O9, Sr2Nb2O 7, and Sr2Ta2O7 which were studied as polycrystalline ceramics, single crystals, micron-sized faceted particles, or some combination of these forms. The reduction of Ag+ from an aqueous AgNO3 solution (Ag0 product) and the oxidation of Pb2+ from an aqueous lead acetate solution (PbO 2 product) were selected as probe reactions because they leave insoluble products on the oxide surfaces. The reactivity of ferroelectric BaTiO3 was dominated by the effect of dipolar fields on the transport of photogenerated charge carriers. Silver was reduced on domains with a positive surface charge while lead was oxidized on domains with a negative surface charge. This reactivity implies that the dipolar field in individual domains drives photogenerated charge carriers to oppositely charged surfaces. This reaction mechanism results in a physical separation of the photogenerated charge carriers and the locations of the oxidation and reduction half reactions on the catalyst surface. Experiments performed on polycrystalline ceramics, single crystals, and micron-sized particles all showed this domain specific reactivity. SrTiO3 has the ideal cubic perovskite structure from which the tetragonally distorted ferroelectric BaTiO3 phase is derived. Polished and annealed surfaces of randomly oriented grain surfaces were bound by some combination of the following three planes: {110}, {111}, and a complex facet inclined approximately 24° from {100}. Surfaces with the complex {100} facet were found to be the most active for Ag reduction. Single crystal studies also showed that the nonpolar (100) surface is the most reactive and that the composition of the termination layer does not influence this reaction. However, the polar (111) and (110) surfaces had a non-uniform distribution of reaction products. For these orientations, the location of the reduction and oxidation reactions is determined by the chemical and charge terminations of the different terraces or facets. The reactivity for silver reduction on the faceted particles is ranked as (100) > (111) > (110) while the (100) surface was least reactive for lead oxidation. Overall, these results show that the photochemical reactivity of SrTiO3 is anisotropic and that on polar surfaces, dipolar fields arising from charged surface domains influence the transport of photogenerated charge carriers and promote spatially selective oxidation and reduction reactions. (Abstract shortened by UMI.)

Early inner solar system origin for anomalous sulfur isotopes in differentiated protoplanets.

PubMed

Antonelli, Michael A; Kim, Sang-Tae; Peters, Marc; Labidi, Jabrane; Cartigny, Pierre; Walker, Richard J; Lyons, James R; Hoek, Joost; Farquhar, James

2014-12-16

Achondrite meteorites have anomalous enrichments in (33)S, relative to chondrites, which have been attributed to photochemistry in the solar nebula. However, the putative photochemical reactions remain elusive, and predicted accompanying (33)S depletions have not previously been found, which could indicate an erroneous assumption regarding the origins of the (33)S anomalies, or of the bulk solar system S-isotope composition. Here, we report well-resolved anomalous (33)S depletions in IIIF iron meteorites (<-0.02 per mil), and (33)S enrichments in other magmatic iron meteorite groups. The (33)S depletions support the idea that differentiated planetesimals inherited sulfur that was photochemically derived from gases in the early inner solar system (<∼2 AU), and that bulk inner solar system S-isotope composition was chondritic (consistent with IAB iron meteorites, Earth, Moon, and Mars). The range of mass-independent sulfur isotope compositions may reflect spatial or temporal changes influenced by photochemical processes. A tentative correlation between S isotopes and Hf-W core segregation ages suggests that the two systems may be influenced by common factors, such as nebular location and volatile content.

[PS II photochemical efficiency in flag leaf of wheat varieties and its adaptation to strong sun- light intensity on farmland of Xiangride in Qinghai Province, Northwest China].

PubMed

Shi, Sheng-Bo; Chen, Wen-Jie; Shi, Rui; Li, Miao; Zhang, Huai-Gang; Sun, Ya-Nan

2014-09-01

Taking four wheat varieties developed by Northwest Institute of Plateau Biology, Chinese Academy of Sciences, as test materials, with the measurement of content of photosynthetic pigments, leaf area, fresh and dry mass of flag leaf, the PS II photochemistry efficiency of abaxial and adaxial surface of flag leaf and its adaptation to strong solar radiation during the period of heading stage in Xiangride region were investigated with the pulse-modulated in-vivo chlorophyll fluorescence technique. The results indicated that flag leaf angle mainly grew in horizontal state in Gaoyuan 314, Gaoyuan 363 and Gaoyuan 584, and mainly in vertical state in Gaoyuan 913 because of its smaller leaf area and larger width. Photosynthetic pigments were different among the 4 varieties, and positively correlated with intrinsic PS II photochemistry efficiencies (Fv/Fm). In clear days, especially at noon, the photosynthetic photoinhibition was more serious in abaxial surface of flag leaf due to directly facing the solar radiation, but it could recover after reduction of sunlight intensity in the afternoon, which meant that no inactive damage happened in PS II reaction centers. There were significant differences of PS II actual and maximum photochemical efficiencies at the actinic light intensity (ΦPS II and Fv'/Fm') between abaxial and adaxial surface, and their relative variation trends were on the contrary. The photochemical and non-photochemical quenching coefficients (qP and NPQ) had a similar tendency in both abaxial and adaxial surfaces. Although ΦPS II and qP were lower in adaxial surface of flag leaf, the Fv'/Fm' was significantly higher, which indicated that the potential PS II capture efficiency of excited energy was higher. The results demonstrated that process of photochemical and non-photochemical quenching could effectively dissipate excited energy caused by strong solar radiation, and there were higher adaptation capacities in wheat varieties natively cultivated in Qinghai-Tibetan Plateau area.

Intraspecific variation in Pinus pinaster PSII photochemical efficiency in response to winter stress and freezing temperatures.

PubMed

Corcuera, Leyre; Gil-Pelegrin, Eustaquio; Notivol, Eduardo

2011-01-01

As part of a program to select maritime pine (Pinus pinaster Ait.) genotypes for resistance to low winter temperatures, we examined variation in photosystem II activity by chlorophyll fluorescence. Populations and families within populations from contrasting climates were tested during two consecutive winters through two progeny trials, one located at a continental and xeric site and one at a mesic site with Atlantic influence. We also obtained the LT₅₀, or the temperature that causes 50% damage, by controlled freezing and the subsequent analysis of chlorophyll fluorescence in needles and stems that were collected from populations at the continental trial site.P. pinaster showed sensitivity to winter stress at the continental site, during the colder winter. The combination of low temperatures, high solar irradiation and low precipitation caused sustained decreases in maximal photochemical efficiency (F(v)/F(m)), quantum yield of non-cyclic electron transport (Φ(PSII)) and photochemical quenching (qP). The variation in photochemical parameters was larger among families than among populations, and population differences appeared only under the harshest conditions at the continental site. As expected, the environmental effects (winter and site) on the photochemical parameters were much larger than the genotypic effects (population or family). LT₅₀ was closely related to the minimum winter temperatures of the population's range. The dark-adapted F(v)/F(m) ratio discriminated clearly between interior and coastal populations.In conclusion, variations in F(v)/F(m), Φ(PSII), qP and non-photochemical quenching (NPQ) in response to winter stress were primarily due to the differences between the winter conditions and the sites and secondarily due to the differences among families and their interactions with the environment. Populations from continental climates showed higher frost tolerance (LT₅₀) than coastal populations that typically experience mild winters. Therefore, LT₅₀, as estimated by F(v)/F(m), is a reliable indicator of frost tolerance among P. pinaster populations.

Intraspecific Variation in Pinus Pinaster PSII Photochemical Efficiency in Response to Winter Stress and Freezing Temperatures

PubMed Central

Corcuera, Leyre; Gil-Pelegrin, Eustaquio; Notivol, Eduardo

2011-01-01

As part of a program to select maritime pine (Pinus pinaster Ait.) genotypes for resistance to low winter temperatures, we examined variation in photosystem II activity by chlorophyll fluorescence. Populations and families within populations from contrasting climates were tested during two consecutive winters through two progeny trials, one located at a continental and xeric site and one at a mesic site with Atlantic influence. We also obtained the LT50, or the temperature that causes 50% damage, by controlled freezing and the subsequent analysis of chlorophyll fluorescence in needles and stems that were collected from populations at the continental trial site. P. pinaster showed sensitivity to winter stress at the continental site, during the colder winter. The combination of low temperatures, high solar irradiation and low precipitation caused sustained decreases in maximal photochemical efficiency (Fv/Fm), quantum yield of non-cyclic electron transport (ΦPSII) and photochemical quenching (qP). The variation in photochemical parameters was larger among families than among populations, and population differences appeared only under the harshest conditions at the continental site. As expected, the environmental effects (winter and site) on the photochemical parameters were much larger than the genotypic effects (population or family). LT50 was closely related to the minimum winter temperatures of the population's range. The dark-adapted Fv/Fm ratio discriminated clearly between interior and coastal populations. In conclusion, variations in Fv/Fm, ΦPSII, qP and non-photochemical quenching (NPQ) in response to winter stress were primarily due to the differences between the winter conditions and the sites and secondarily due to the differences among families and their interactions with the environment. Populations from continental climates showed higher frost tolerance (LT50) than coastal populations that typically experience mild winters. Therefore, LT50, as estimated by Fv/Fm, is a reliable indicator of frost tolerance among P. pinaster populations. PMID:22220195

Field-cycling NMR with high-resolution detection under magic-angle spinning: determination of field-window for nuclear hyperpolarization in a photosynthetic reaction center.

PubMed

Gräsing, Daniel; Bielytskyi, Pavlo; Céspedes-Camacho, Isaac F; Alia, A; Marquardsen, Thorsten; Engelke, Frank; Matysik, Jörg

2017-09-21

Several parameters in NMR depend on the magnetic field strength. Field-cycling NMR is an elegant way to explore the field dependence of these properties. The technique is well developed for solution state and in relaxometry. Here, a shuttle system with magic-angle spinning (MAS) detection is presented to allow for field-dependent studies on solids. The function of this system is demonstrated by exploring the magnetic field dependence of the solid-state photochemically induced nuclear polarization (photo-CIDNP) effect. The effect allows for strong nuclear spin-hyperpolarization in light-induced spin-correlated radical pairs (SCRPs) under solid-state conditions. To this end, 13 C MAS NMR is applied to a photosynthetic reaction center (RC) of the purple bacterium Rhodobacter (R.) sphaeroides wildtype (WT). For induction of the effect in the stray field of the magnet and its subsequent observation at 9.4 T under MAS NMR conditions, the sample is shuttled by the use of an aerodynamically driven sample transfer technique. In the RC, we observe the effect down to 0.25 T allowing to determine the window for the occurrence of the effect to be between about 0.2 and 20 T.

The affects on Titan atmospheric modeling by variable molecular reaction rates

NASA Astrophysics Data System (ADS)

Hamel, Mark D.

The main effort of this thesis is to study the production and loss of molecular ions in the ionosphere of Saturn's largest moon Titan. Titan's atmosphere is subject to complex photochemical processes that can lead to the production of higher order hydrocarbons and nitriles. Ion-molecule chemistry plays an important role in this process but remains poorly understood. In particular, current models that simulate the photochemistry of Titan's atmosphere overpredict the abundance of the ionosphere's main ions suggesting a flaw in the modeling process. The objective of this thesis is to determine which reactions are most important for production and loss of the two primary ions, C2H5+ and HCNH+, and what is the impact of uncertainty in the reaction rates on the production and loss of these ions. In reviewing the literature, there is a contention about what reactions are really necessary to illuminate what is occurring in the atmosphere. Approximately seven hundred reactions are included in the model used in this discussion (INT16). This paper studies what reactions are fundamental to the atmospheric processes in Titan's upper atmosphere, and also to the reactions that occur in the lower bounds of the ionosphere which are used to set a baseline molecular density for all species, and reflects what is expected at those altitudes on Titan. This research was conducted through evaluating reaction rates and cross sections available in the scientific literature and through conducting model simulations of the photochemistry in Titan's atmosphere under a range of conditions constrained by the literature source. The objective of this study is to determine the dependence of ion densities of C2H5+ and HCNH+ on the uncertainty in the reaction rates that involve these two ions in Titan's atmosphere.

Delayed photolysis of liposomes: a strategy for the precision timing of bolus drug release using ex-vivo photochemical sensitization

NASA Astrophysics Data System (ADS)

Kozikowski, Raymond T.; Sorg, Brian S.

2012-03-01

Chemotherapy is a standard treatment for metastatic cancer. However drug toxicity limits the dosage that can safely be used, thus reducing treatment efficacy. Drug carrier particles, like liposomes, can help reduce toxicity by shielding normal tissue from drug and selectively depositing drug in tumors. Over years of development, liposomes have been optimized to avoid uptake by the Reticuloendothelial System (RES) as well as effectively retain their drug content during circulation. As a result, liposomes release drug passively, by slow leakage, but this uncontrolled drug release can limit treatment efficacy as it can be difficult to achieve therapeutic concentrations of drug at tumor sites even with tumor-specific accumulation of the carriers. Lipid membranes can be photochemically lysed by both Type I (photosensitizer-substrate) and Type II (photosensitizer-oxygen) reactions. It has been demonstrated in red blood cells (RBCs) in vitro that these photolysis reactions can occur in two distinct steps: a light-initiated reaction followed by a thermally-initiated reaction. These separable activation steps allow for the delay of photohemolysis in a controlled manner using the irradiation energy, temperature and photosensitizer concentration. In this work we have translated this technique from RBCs to liposomal nanoparticles. To that end, we present in vitro data demonstrating this delayed bolus release from liposomes, as well as the ability to control the timing of this event. Further, we demonstrate for the first time the improved delivery of bioavailable cargo selectively to target sites in vivo.

Photodegradation and ecotoxicology of acyclovir in water under UV254 and UV254/H2O2 processes.

PubMed

Russo, Danilo; Siciliano, Antonietta; Guida, Marco; Galdiero, Emilia; Amoresano, Angela; Andreozzi, Roberto; Reis, Nuno M; Li Puma, Gianluca; Marotta, Raffaele

2017-10-01

The photochemical and ecotoxicological fate of acyclovir (ACY) through UV 254 direct photolysis and in the presence of hydroxyl radicals (UV 254 /H 2 O 2 process) were investigated in a microcapillary film (MCF) array photoreactor, which provided ultrarapid and accurate photochemical reaction kinetics. The UVC phototransformation of ACY was found to be unaffected by pH in the range from 4.5 to 8.0 and resembled an apparent autocatalytic reaction. The proposed mechanism included the formation of a photochemical intermediate (ϕ ACY  = (1.62 ± 0.07)·10 -3  mol ein -1 ) that further reacted with ACY to form by-products (k' = (5.64 ± 0.03)·10 -3  M -1  s -1 ). The photolysis of ACY in the presence of hydrogen peroxide accelerated the removal of ACY as a result of formation of hydroxyl radicals. The kinetic constant for the reaction of OH radicals with ACY (k OH/ACY ) determined with the kinetic modeling method was (1.23 ± 0.07)·10 9  M -1  s -1 and with the competition kinetics method was (2.30 ± 0.11)·10 9  M -1  s -1 with competition kinetics. The acute and chronic effects of the treated aqueous mixtures on different living organisms (Vibrio fischeri, Raphidocelis subcapitata, D. magna) revealed significantly lower toxicity for the samples treated with UV 254 /H 2 O 2 in comparison to those collected during UV 254 treatment. This result suggests that the addition of moderate quantity of hydrogen peroxide (30-150 mg L -1 ) might be a useful strategy to reduce the ecotoxicity of UV 254 based sanitary engineered systems for water reclamation. Copyright © 2017 Elsevier Ltd. All rights reserved.

Quantum entanglement at ambient conditions in a macroscopic solid-state spin ensemble.

PubMed

Klimov, Paul V; Falk, Abram L; Christle, David J; Dobrovitski, Viatcheslav V; Awschalom, David D

2015-11-01

Entanglement is a key resource for quantum computers, quantum-communication networks, and high-precision sensors. Macroscopic spin ensembles have been historically important in the development of quantum algorithms for these prospective technologies and remain strong candidates for implementing them today. This strength derives from their long-lived quantum coherence, strong signal, and ability to couple collectively to external degrees of freedom. Nonetheless, preparing ensembles of genuinely entangled spin states has required high magnetic fields and cryogenic temperatures or photochemical reactions. We demonstrate that entanglement can be realized in solid-state spin ensembles at ambient conditions. We use hybrid registers comprising of electron-nuclear spin pairs that are localized at color-center defects in a commercial SiC wafer. We optically initialize 10(3) identical registers in a 40-μm(3) volume (with [Formula: see text] fidelity) and deterministically prepare them into the maximally entangled Bell states (with 0.88 ± 0.07 fidelity). To verify entanglement, we develop a register-specific quantum-state tomography protocol. The entanglement of a macroscopic solid-state spin ensemble at ambient conditions represents an important step toward practical quantum technology.

Model study of greenline dayglow emission under geomagnetic storm conditions.

NASA Astrophysics Data System (ADS)

Singh, V.; Bag, T.; Sunil Krishna, M. V.

2016-12-01

A comprehensive model is developed to study the influences of geomagnetic storms on greenline (557.7 nm) dayglow emission during the solar active and solar quiet conditions in thermosphere. This study is based on a photochemical model which is developed using the latest reaction rate coefficients, quantum yields and collisional cross-sections obtained from the experimental observations and empirical models. This study is for a low latitude station Tirunelveli (8.7N,77.8E), India. The volume emission rate (VER) has been calculated using the densities and temperature from NRLMSISE-00 and IRI-2012 models. The modeled VER shows a positive correlation with the Dst index, and a negative correlation with the number densities of O, O2, and N2. The VER calculated at the peak emission altitude shows depletion during the main phase of the storm. The peak emission altitude doesn't show any appreciable variation during storm period. On the other hand, the peak emission altitude shows an upward movement with the increase in F10.7 solar index.

Photophysical and photochemical effects of UV and VUV photo-oxidation and photolysis on PET and PEN

NASA Astrophysics Data System (ADS)

Morgan, Andrew

Polyethylene Terephthalate (PET) is a widely used polymer in the bottling, packaging, and clothing industry. In recent years an increasing global demand for PET has taken place due to the Solar Disinfection (SODIS) process. SODIS is a method of sterilizing fresh water into drinkable water. The PET bottles are used in the process to contain the water during solar irradiation due to its highly transparent optical property. Alongside PET, polyethylene 2,6-napthalate (PEN) is used in bottling and flexible electronic applications. The surface of PEN would need to be modified to control the hydrophilicity and the interaction it exudes as a substrate. The UV light absorption properties of PET and PEN are of great importance for many applications, and thus needs to be studied along with its photochemical resistance. The optical and chemical nature of PET was studied as it was treated by UV photo-oxidation, photo-ozonation, and photolysis under atmospheric pressure. Another investigation was also used to study PEN and PET as they are treated by vacuum UV (VUV) photo-oxidation, VUV photolysis, and remote oxygen reactions. The extent of the photoreactions' effect into the depth of the polymers is examined as treatment conditions are changed. The different experimental methods established the rate of several competing photoreactions on PET and PEN during irradiance, and their effect on the optical quality of the polymers.

Photochemical Cycling of Humic-Like Substances in Atmospheric Aerosols

NASA Astrophysics Data System (ADS)

Rincon, A. G.; Guzman, M. I.; Hoffmann, M. R.; Colussi, A. J.

2007-12-01

Colored, humic-like substances (HULIS) arising from the biodegradation of organic detritus are widespread in natural surface waters, where they ultimately undergo solar photolysis into small alpha-dicarbonylic species, such as glyoxal, glyoxylic and pyruvic acids. Diversely generated and chemically dissimilar HULIS are also found in the atmospheric aerosol. How are significant levels of colored HULIS produced and sustained in the concentrated aerosol phase under intense solar irradiation? Here, this issue is tackled by investigating the solar photolysis of aqueous pyruvic acid (PA) solutions at concentrations representative of the atmospheric aerosol using UV-absorption, high resolution electrospray mass, and nuclear magnetic resonance spectrometries. Under such conditions, PA is not photodegraded but yields polyfunctional polymers, whose mass and UV-absorption spectra remain unaffected after 3, 8 and 22 h photolysis. Unless diluted, these polymers undergo condensation/polymerization in the post-photolysis period into mass < 700 Da species that absorb in the visible, and are bleached upon resuming irradiation. The re- photolyzed solutions recover the mass and UV-absorption spectra of first photolyzed solutions. Whereas initial pH has no effect on the mechanism of reaction, ammonium bisulfate, a major component of the aerosol, markedly influences these processes. These findings suggest that the chemical identity and concentration levels of complex organic substances in the aerosol are the result of dynamic photochemical processing in the condensed phase.

Photochemical Grafting of Organic Alkenes to Single-Crystal TiO2 Surfaces: A Mechanistic Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Franking, Ryan A.; Kim, Heesuk; Chambers, Scott A.

2012-08-21

The UV-induced photochemical grafting of terminal alkenes has emerged as a versatile way to form molecular layers on semiconductor surfaces. Recent studies have shown that grafting reactions can be initiated by photoelectron emission into the reactant liquid as well as by excitation across the semiconductor bandgap, but the relative importance of these two processes is expected to depend on the nature of the semiconductor and the reactant alkene and the excitation wavelength. Here we report a study of the wavelength-dependent photochemical grafting of alkenes onto single-crystal TiO2 samples. Trifluoroacetamide-protected 10-aminododec-1-ene (TFAAD), 10-N-BOC-aminodec-1-ene (t-BOC) and 1-dodecene were used as model alkenes.more » On rutile(110), photons with energy above the bandgap but below the expected work function are not effective at inducing grafting, while photons with energy sufficient to induce electronic transitions from the TiO2 Fermi level to electronic acceptor states of the reactant molecules induce grafting. A comparison of rutile (110), rutile(001), anatase (001), and anatase(101) samples shows slightly enhanced grafting for rutile but no difference between crystal faces for a given crystal phase. Hydroxylation of the surface increases the reaction rate by lowering the work function and thereby facilitating photoelectron ejection into the adjacent alkene. These results demonstrate that photoelectron emission is the dominant mechanism responsible for grafting when using short-wavelength (~254 nm) light and suggest that photoemission events beginning on mid-gap states may play a crucial role.« less

Photochemical Aging of α-pinene and β-pinene Secondary Organic Aerosol formed from Nitrate Radical Oxidation: New Insights into the Formation and Fates of Highly Oxygenated Gas- and Particle-phase Organic Nitrates

NASA Astrophysics Data System (ADS)

Nah, T.; Sanchez, J.; Boyd, C.; Ng, N. L.

2015-12-01

The nitrate radical (NO3), one of the most important oxidants in the nocturnal atmosphere, can react rapidly with a variety of biogenic volatile organic compounds (BVOCs) to form high mass concentrations of secondary organic aerosol (SOA) and organic nitrates (ON). Despite its critical importance in aerosol formation, the mechanisms and products from the NO3 oxidation of BVOCs have been largely unexplored, and the fates of their SOA and ON after formation are not well characterized. In this work, we studied the formation of SOA and ON from the NO3 oxidation of α-pinene and β-pinene and investigated for the first time how they evolve during dark and photochemical aging through a series of chamber experiments performed at the Georgia Tech Environmental Chamber (GTEC) facility. The α-pinene and β-pinene SOA are characterized using real-time gas- and particle-phase measurements, which are used to propose mechanisms for SOA and organic nitrate formation and aging. Highly oxygenated gas- and particle-phase ON (containing as many as 9 oxygen atoms) are detected during the NO3 reaction. In addition, the β-pinene SOA and α-pinene SOA exhibited drastically different behavior during photochemical aging. Our results indicate that nighttime ON formed by NO3+monoterpene chemistry can serve as either NOx reservoirs or sinks depending on the monoterpene precursor. Results from this study provide fundamental data for evaluating the contributions of NO3+monoterpene reactions to ambient OA measured in the Southeastern U.S.

Photochemical CVD of Ru on functionalized self-assembled monolayers from organometallic precursors

NASA Astrophysics Data System (ADS)

Johnson, Kelsea R.; Arevalo Rodriguez, Paul; Brewer, Christopher R.; Brannaka, Joseph A.; Shi, Zhiwei; Yang, Jing; Salazar, Bryan; McElwee-White, Lisa; Walker, Amy V.

2017-02-01

Chemical vapor deposition (CVD) is an attractive technique for the metallization of organic thin films because it is selective and the thickness of the deposited film can easily be controlled. However, thermal CVD processes often require high temperatures which are generally incompatible with organic films. In this paper, we perform proof-of-concept studies of photochemical CVD to metallize organic thin films. In this method, a precursor undergoes photolytic decomposition to generate thermally labile intermediates prior to adsorption on the sample. Three readily available Ru precursors, CpRu(CO)2Me, (η3-allyl)Ru(CO)3Br, and (COT)Ru(CO)3, were employed to investigate the role of precursor quantum yield, ligand chemistry, and the Ru oxidation state on the deposition. To investigate the role of the substrate chemistry on deposition, carboxylic acid-, hydroxyl-, and methyl-terminated self-assembled monolayers were used. The data indicate that moderate quantum yields for ligand loss (φ ≥ 0.4) are required for ruthenium deposition, and the deposition is wavelength dependent. Second, anionic polyhapto ligands such as cyclopentadienyl and allyl are more difficult to remove than carbonyls, halides, and alkyls. Third, in contrast to the atomic layer deposition, acid-base reactions between the precursor and the substrate are more effective for deposition than nucleophilic reactions. Finally, the data suggest that selective deposition can be achieved on organic thin films by judicious choice of precursor and functional groups present on the substrate. These studies thus provide guidelines for the rational design of new precursors specifically for selective photochemical CVD on organic substrates.

Modelling study of boundary-layer ozone over northern China - Part II: Responses to emission reductions during the Beijing Olympics

NASA Astrophysics Data System (ADS)

Tang, Guiqian; Zhu, Xiaowan; Xin, Jinyuan; Hu, Bo; Song, Tao; Sun, Yang; Wang, Lili; Wu, Fangkun; Sun, Jie; Cheng, Mengtian; Chao, Na; Li, Xin; Wang, Yuesi

2017-09-01

The implementation of emission reduction measures during the Olympics provided a valuable opportunity to study regional photochemical pollution over northern China. In this study, the fifth-generation Pennsylvania State University/National Centre for Atmospheric Research Mesoscale Model and Community Multiscale Air Quality model system was applied to conduct two sets of modelling analyses of the period from July 20 to September 20, 2008, to illustrate the influences of emission reduction measures on regional photochemical pollution over northern China during the Beijing Olympics. The results indicated that the implementation of emission control measures decreased the concentrations of ozone (O3) precursors, namely nitrogen oxide (NOx) and volatile organic compounds (VOCs), throughout the boundary layer. The concentrations of these compounds were reduced by 45% in the central urban area of Beijing at the ground level. Although the average O3 concentration in the central urban area increased by more than 8 ppbv, the total oxidant concentration decreased significantly by more than 5 ppbv. Greater O3 concentrations mainly occurred during periods with weak photochemical reactions. During periods of strong photochemical production, the O3 concentration decreased significantly due to a weakening vertical circulation between the lower and upper boundary layer. Consequently, the number of days when the O3 concentration exceeded 100 ppbv decreased by 25% in Beijing. The emission control measures altered the sensitivity of the regional O3 production. The coordinated control region of NOx and VOCs expanded, and the control region of VOCs decreased in size. The reduction of non-point-source emissions, such as fugitive VOCs and vehicles, was more useful for controlling regional photochemical pollution over northern China.

Composition/bandgap selective dry photochemical etching of semiconductor materials

DOEpatents

Ashby, Carol I. H.; Dishman, James L.

1987-01-01

A method of selectively photochemically dry etching a first semiconductor material of a given composition and direct bandgap Eg.sub.1 in the presence of a second semiconductor material of a different composition and direct bandgap Eg.sub.2, wherein Eg.sub.2 >Eg.sub.1, said second semiconductor material substantially not being etched during said method, comprises subjecting both materials to the same photon flux and to the same gaseous etchant under conditions where said etchant would be ineffective for chemical etching of either material were the photons not present, said photons being of an energy greater than Eg.sub.1 but less than Eg.sub.2, whereby said first semiconductor material is photochemically etched and said second material is substantially not etched.

Photochemical degradation of an anionic surfactant by TiO2 nanoparticle doped with C, N in aqueous solution

NASA Astrophysics Data System (ADS)

Zamiri, M.; Giahi, M.

2016-12-01

Novel C,N-doped TiO2 nanoparticles were prepared by a solid phase reaction. The catalyst was characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). The results showed that crystallite size of synthesized C,N-doped TiO2 particles were in nanoscale. UV light photocatalytic studies were carried out using sodium naphthalenesulfonate formaldehyde condensate (SNF) as a model pollutant. The effects of initial concentration of surfactant, catalyst amount, pH, addition of oxidant on the reaction rate were ascertained and optimum conditions for maximum degradation was determined. The results indicated that for a solution of 20 mg/L of SNF, almost 98.7% of the substance were removed at pH 4.0 and 0.44 g/L photocatalyst load, with addition of 1 mM K2S2O8 and irradiation time of 90 min. The kinetics of the process was studied, and the photodegradation rate of SNF was found to obey pseudo-first-order kinetics equation represented by the Langmuir-Hinshelwood model.

Rhodium-Coordinated Poly(arylene-ethynylene)-alt-Poly(arylene-vinylene) Copolymer Acting as Photocatalyst for Visible-Light-Powered NAD+/NADH Reduction

PubMed Central

2014-01-01

A 2,2′-bipyridyl-containing poly(arylene-ethynylene)-alt-poly(arylene-vinylene) polymer, acting as a light-harvesting ligand system, was synthesized and coupled to an organometallic rhodium complex designed for photocatalytic NAD+/NADH reduction. The material, which absorbs over a wide spectral range, was characterized by using various analytical techniques, confirming its chemical structure and properties. The dielectric function of the material was determined from spectroscopic ellipsometry measurements. Photocatalytic reduction of nucleotide redox cofactors under visible light irradiation (390–650 nm) was performed and is discussed in detail. The new metal-containing polymer can be used to cover large surface areas (e.g. glass beads) and, due to this immobilization step, can be easily separated from the reaction solution after photolysis. Because of its high stability, the polymer-based catalyst system can be repeatedly used under different reaction conditions for (photo)chemical reduction of NAD+. With this concept, enzymatic, photo-biocatalytic systems for solar energy conversion can be facilitated, and the precious metal catalyst can be recycled. PMID:25130570

Photochemically induced carbon dioxide production as a mechanism for carbon loss from plant litter in arid ecosystems

NASA Astrophysics Data System (ADS)

Brandt, L. A.; Bohnet, C.; King, J. Y.

2009-06-01

We investigated the potential for abiotic mineralization to carbon dioxide (CO2) via photodegradation to account for carbon (C) loss from plant litter under conditions typical of arid ecosystems. We exposed five species of grass and oak litter collected from arid and mesic sites to a factorial design of ultraviolet (UV) radiation (UV pass, UV block), and sterilization under dry conditions in the laboratory. UV pass treatments produced 10 times the amount of CO2 produced in UV block treatments. CO2 production rates were unaffected by litter chemistry or sterilization. We also exposed litter to natural solar radiation outdoors on clear, sunny days close to the summer solstice at midlatitudes and found that UV radiation (280-400 nm) accounted for 55% of photochemically induced CO2 production, while shortwave visible radiation (400-500 nm) accounted for 45% of CO2 production. Rates of photochemically induced CO2 production on a per-unit-mass basis decreased with litter density, indicating that rates depend on litter surface area. We found no evidence for leaching, methane production, or facilitation of microbial decomposition as alternative mechanisms for significant photochemically induced C loss from litter. We conclude that abiotic mineralization to CO2 is the primary mechanism by which C is lost from litter during photodegradation. We estimate that CO2 production via photodegradation could be between 1 and 4 g C m-2 a-1 in arid ecosystems in the southwestern United States. Taken together with low levels of litter production in arid systems, photochemical mineralization to CO2 could account for a significant proportion of annual carbon loss from litter in arid ecosystems.

Iodide-induced organothiol desorption and photochemical reaction, gold nanoparticle (AuNP) fusion, and SERS signal reduction in organothiol-containing AuNP aggregates

USDA-ARS?s Scientific Manuscript database

Gold nanoparticles (AuNPs) have been used extensively as surface-enhanced Raman spectroscopic (SERS) substrates for their large SERS enhancements and widely believed chemical stability. Presented is the finding that iodide can rapidly reduce the SERS intensity of the ligands, including organothiols ...

From containers to catalysts: supramolecular catalysis within cucurbiturils.

PubMed

Pemberton, Barry C; Raghunathan, Ramya; Volla, Sabine; Sivaguru, Jayaraman

2012-09-24

Cucurbiturils are a family of molecular container compounds with superior molecular recognition properties. The use of cucurbiturils for supramolecular catalysis is highlighted in this concept. Both photochemical reactions as well as thermal transformations are reviewed with an eye towards tailoring substrates for supramolecular catalysis mediated by cucurbiturils. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis of Stereoisomeric - Metal Complexes Using Phase-Transfer Catalysis and Photochemical Transforms.

DTIC Science & Technology

1984-05-25

bonded arrangement (2) as depicted in Figure 1-1. Fe Fe.’. % V3 1 2 Figure I-1 Proposed Structures of Ferrocene In order to understand clearly the... phosphines (PR3) or methanol (CH3OH) results in the formation nf o-alkylmetal complexes (Scheme Ill-1, 1). If stable, further reaction of these

The Catalytic Enantioselective Total Synthesis of (+)-Liphagal**

PubMed Central

Day, Joshua J.; McFadden, Ryan M.; Virgil, Scott C.; Kolding, Helene; Alleva, Jennifer L.; Stoltz, Brian M.

2012-01-01

Ring a ding: The first catalytic enantioselective total synthesis of the meroterpenoid natural product (+)-liphagal is disclosed. The approach showcases a variety of technology including enantioselective enolate alkylation, a photochemical alkyne-alkene [2+2] reaction, microwave-assisted metal catalysis, and an intramolecular aryne capture cyclization reaction. Pivotal to the successful completion of the synthesis was a sequence involving ring expansion from a [6-5-4] tricycle to a [6-7] bicyclic core followed by stereoselective hydrogenation of a sterically occluded tri-substituted olefin to establish the trans homodecalin system found in the natural product. PMID:21671325

Enantioselective syntheses of carbanucleosides from the Pauson-Khand adduct of trimethylsilylacetylene and norbornadiene.

PubMed

Vázquez-Romero, Ana; Rodríguez, Julia; Lledó, Agustí; Verdaguer, Xavier; Riera, Antoni

2008-10-16

A new enantioselective approach to carbanucleosides from Pauson-Khand (PK) adduct 1 is disclosed. The chiral cyclopentenone 1 is readily accessible in enantiomerically pure form via PK reaction of trimethylsilylacetylene and norbornadiene using N-benzyl-N-diphenylphosphino-tert-butyl-sulfinamide as a chiral P,S ligand. (-)-Carbavir and (-)-Abacavir were enantioselectively synthesized starting from (-)-1. The key steps of the sequence are a photochemical conjugate addition of a hydroxymethyl radical, a retro-Diels-Alder reaction, and a palladium catalyzed allylic substitution to introduce the nucleobase.

Thiol-ene and photo-cleavage chemistry for controlled presentation of biomolecules in hydrogels.

PubMed

Grim, Joseph C; Marozas, Ian A; Anseth, Kristi S

2015-12-10

Hydrogels have emerged as promising scaffolds in regenerative medicine for the delivery of biomolecules to promote healing. However, increasing evidence suggests that the context that biomolecules are presented to cells (e.g., as soluble verses tethered signals) can influence their bioactivity. A common approach to deliver biomolecules in hydrogels involves physically entrapping them within the network, such that they diffuse out over time to the surrounding tissues. While simple and versatile, the release profiles in such system are highly dependent on the molecular weight of the entrapped molecule relative to the network structure, and it can be difficult to control the release of two different signals at independent rates. In some cases, supraphysiologically high loadings are used to achieve therapeutic local concentrations, but uncontrolled release can then cause deleterious off-target side effects. In vivo, many growth factors and cytokines are stored in the extracellular matrix (ECM) and released on demand as needed during development, growth, and wound healing. Thus, emerging strategies in biomaterial chemistry have focused on ways to tether or sequester biological signals and engineer these bioactive scaffolds to signal to delivered cells or endogenous cells. While many strategies exist to achieve tethering of peptides, protein, and small molecules, this review focuses on photochemical methods, and their usefulness as a mild reaction that proceeds with fast kinetics in aqueous solutions and at physiological conditions. Photo-click and photo-caging methods are particularly useful because one can direct light to specific regions of the hydrogel to achieve spatial patterning. Recent methods have even demonstrated reversible introduction of biomolecules to mimic the dynamic changes of native ECM, enabling researchers to explore how the spatial and dynamic context of biomolecular signals influences important cell functions. This review will highlight how two photochemical methods have led to important advances in the tissue regeneration community, namely the thiol-ene photo-click reaction for bioconjugation and photocleavage reactions that allow for the removal of protecting groups. Specific examples will be highlighted where these methodologies have been used to engineer hydrogels that control and direct cell function with the aim of inspiring their use in regenerative medicine. Copyright © 2015 Elsevier B.V. All rights reserved.

Lignin Contribution to the Global Carbon Pool: Investigating the Abiotic Modification of Lignin by Reactive Oxygen Species

NASA Astrophysics Data System (ADS)

Waggoner, Derek Charles

Evidence suggests that reactive oxygen species (ROS), largely generated through photochemical processes, are important in transforming the chemical composition of the large pool of terrestrially-derived dissolved organic matter (DOM) exported from land to water annually. However, due to the challenges inherent in isolating the effects of individual ROS on DOM composition, the role of ROS in the photochemical alteration of DOM remains poorly characterized. The main focus of the studies within this dissertation aim to more thoroughly characterize the alterations to lignin, used as an analog for terrestrial DOM, resulting from reactions with ROS. To investigate the possibility that the alteration of lignin, through reactions involving ROS, could lead to the production of compounds not recognized as having terrestrial origin, lignin-derived DOM was prepared from a sample of Atlantic white cedar (Chamaecyparis thyoides) and used for a number of studies. Lignin-derived DOM was independently exposed to hydroxyl radical (•OH) generated by Fenton reaction, singlet oxygen (1O2) produced using the photosensitizer Rose Bengal, and superoxide (O2-•) via stable potassium superoxide solution, under controlled laboratory conditions to accentuate how each ROS is responsible for the alteration of lignin. Advanced analytical techniques including high performance liquid chromatography (HPLC), nuclear magnetic resonance (NMR), and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS), were employed to characterize alteration to lignin taking place following various ROS treatments. Results of these studies have shown distinct differences in the types of new compounds observed from exposure to each ROS as well as ROS reactivity. The alteration of lignin to compounds not typically associated with terrestrial DOM has been demonstrated upon exposure to ROS. It is also suggested that ROS could selectively react with different fractions of lignin like compounds based largely on oxygen content. Additionally, results indicate that partially oxidized lignin could react further with ROS to generate compounds resembling condensed aromatic-like compounds, previously believed to be primarily pyrogenic in origin, as well as alicyclic compounds commonly observed in marine DOM.

Loss Process for the C2H5 Radical in the Atmospheres of Jupiter and Saturn: First Direct, Absolute Measurement of the Rate Constant for the Reaction H + C2H5 at Low Pressure and Temperature

NASA Astrophysics Data System (ADS)

Stief, L. J.; Pimentel, A. S.; Payne, W. A.; Nesbitt, F. L.; Cody, R. J.

2003-05-01

Photochemical models of the atmospheres of Jupiter and Saturn predict the reaction H + C2H5 to be the most important loss process for C2H5 in these atmospheres. In addition, the reaction channel H + C2H5 -> 2 CH3 is a significant source of the methyl radical. There are only two relatively modern studies of the H + C2H5 reaction, both of which depend on extensive modeling involving eight elementary reactions. The motivation for the present study is the lack of direct, absolute measurements of the rate constant for the H + C2H5 reaction at low pressures and temperatures appropriate for outer planet models. In the present experiments the reactants H and C2H5 are rapidly and simultaneously generated by reaction of F with appropriate mixtures of H2 and C2H6. Using the technique of discharge-flow with collision-free sampling to a mass spectrometer, we monitor the decay of C2H5 in excess H. In contrast to previous studies of this reaction, the primary H + C2H5 reaction is isolated and the radical decays only by reaction with H and by loss at the wall. Secondary reactions such as the self-reaction of C2H5 are negligible. At P = 1 Torr He we measure k (298K) = 1.13 x 10-10 cm3 molecule-1 s-1 and k (202K) = 1.18 x 10-10 cm3 molecule-1 s-1. Experiments at T = 155 K are in progress. The reaction is temperature independent as expected based on studies of other atom-radical reactions. Our result at T = 298 K lies between those of the two relatively modern but complex studies of this reaction. The present total rate constant data and planned product yield studies at low pressures and temperatures will then be available for use in future photochemical models of the atmospheres of the outer planets. The Planetary Atmospheres Program of NASA Headquarters is supporting this research.

Photoclickable dendritic molecular glue: noncovalent-to-covalent photochemical transformation of protein hybrids.

PubMed

Uchida, Noriyuki; Okuro, Kou; Niitani, Yamato; Ling, Xiao; Ariga, Takayuki; Tomishige, Michio; Aida, Takuzo

2013-03-27

A water-soluble dendron with a fluorescein isothiocyanate (FITC) fluorescent label and bearing nine pendant guanidinium ion (Gu(+))/benzophenone (BP) pairs at its periphery (Glue(BP)-FITC) serves as a "photoclickable molecular glue". By multivalent salt-bridge formation between Gu(+) ions and oxyanions, Glue(BP)-FITC temporarily adheres to a kinesin/microtubule hybrid. Upon subsequent exposure to UV light, this noncovalent binding is made permanent via a cross-linking reaction mediated by carbon radicals derived from the photoexcited BP units. This temporal-to-permanent transformation by light occurs quickly and efficiently in this preorganized state, allowing the movements of microtubules on a kinesin-coated glass plate to be photochemically controlled. A fundamental difference between such temporal and permanent bindings was visualized by the use of "optical tweezers".

Primary photochemical processes for Pt(iv) diazido complexes prospective in photodynamic therapy of tumors.

PubMed

Shushakov, Anton A; Pozdnyakov, Ivan P; Grivin, Vjacheslav P; Plyusnin, Victor F; Vasilchenko, Danila B; Zadesenets, Andrei V; Melnikov, Alexei A; Chekalin, Sergey V; Glebov, Evgeni M

2017-07-25

Diazide diamino complexes of Pt(iv) are considered as prospective prodrugs in oxygen-free photodynamic therapy (PDT). Primary photophysical and photochemical processes for cis,trans,cis-[Pt(N 3 ) 2 (OH) 2 (NH 3 ) 2 ] and trans,trans,trans-[Pt(N 3 ) 2 (OH) 2 (NH 3 ) 2 ] complexes were studied by means of stationary photolysis, nanosecond laser flash photolysis and ultrafast kinetic spectroscopy. The process of photolysis is multistage. The first stage is the photosubstitution of an azide ligand to a water molecule. This process was shown to be a chain reaction involving redox stages. Pt(iv) and Pt(iii) intermediates responsible for the chain propagation were recorded using ultrafast kinetic spectroscopy and nanosecond laser flash photolysis. The mechanism of photosubstitution is proposed.

Efficient Photochemical Dihydrogen Generation Initiated by a Bimetallic Self-Quenching Mechanism

DOE PAGES

Chambers, Matthew B.; Kurtz, Daniel A.; Pitman, Catherine L.; ...

2016-09-27

Artificial photosynthesis relies on coupling light absorption with chemical fuel generation. A mechanistic study of visible light-driven H 2 production from [Cp*Ir(bpy)H] + (1) has revealed a new, highly efficient pathway for integrating light absorption with bond formation. The net reaction of 1 with a proton source produces H 2, but the rate of excited state quenching is surprisingly acid-independent and displays no observable deuterium kinetic isotopic effect. Time-resolved photoluminescence and labeling studies are consistent with diffusion-limited bimetallic self-quenching by electron transfer. Accordingly, the quantum yield of H 2 release nearly reaches unity as the concentration of 1 increases. Furthermore,more » this unique pathway for photochemical H 2 generation provides insight into transformations catalyzed by 1.« less

Fabrication of gallium nitride nanowires by metal-assisted photochemical etching

NASA Astrophysics Data System (ADS)

Zhang, Miao-Rong; Jiang, Qing-Mei; Zhang, Shao-Hui; Wang, Zu-Gang; Hou, Fei; Pan, Ge-Bo

2017-11-01

Gallium nitride (GaN) nanowires (NWs) were fabricated by metal-assisted photochemical etching (MaPEtch). Gold nanoparticles (AuNPs) as metal catalyst were electrodeposited on the GaN substrate. SEM and HRTEM images show the surface of GaN NWs is smooth and clean without any impurity. SAED and FFT patterns demonstrate GaN NWs have single crystal structure, and the crystallographic orientation of GaN NWs is (0002) face. On the basis of the assumption of localized galvanic cells, combined with the energy levels and electrochemical potentials of reactants in this etching system, the generation, transfer and consumption of electron-hole pairs reveal the whole MaPEtch reaction process. Such easily fabricated GaN NWs have great potential for the assembly of GaN-based single-nanowire nanodevices.

Photochemical Dual-Catalytic Synthesis of Alkynyl Sulfides.

PubMed

Santandrea, Jeffrey; Minozzi, Clémentine; Cruché, Corentin; Collins, Shawn K

2017-09-25

A photochemical dual-catalytic cross-coupling to form alkynyl sulfides via C(sp)-S bond formation is described. The cross-coupling of thiols and bromoalkynes is promoted by a soluble organic carbazole-based photocatalyst using continuous flow techniques. Synthesis of alkynyl sulfides bearing a wide range of electronically and sterically diverse aromatic alkynes and thiols can be achieved in good to excellent yields (50-96 %). The simple continuous flow setup also allows for short reaction times (30 min) and high reproducibility on gram scale. In addition, we report the first application of photoredox/nickel dual catalysis towards macrocyclization, as well as the first example of the incorporation of an alkynyl sulfide functional group into a macrocyclic scaffold. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Influence of Intense secondary aerosol formation and long range transport on aerosol chemistry and properties in the Seoul Metropolitan Area during spring time: Results from KORUS-AQ

NASA Astrophysics Data System (ADS)

Kim, H.; Zhang, Q.

2017-12-01

Non-refractory submicrometer particulate matter (NR-PM1) was measured in the Seoul Metropolitan Area (SMA), Korea, using an HR-ToF-AMS from April 14 to June 15, 2016, as a part of the KORUS-AQ campaign. The average concentration of PM1 was 22.1 µg m-3, which was composed of 44% organics, 20% SO4, 17% NO3, and 12 % NH4. Organics had an average O/C ratio of 0.49 and an average OM/OC ratio of 1.82. Four distinct sources of OA were identified via PMF analysis of the HR-ToF-AMS data: hydrocarbon like OA (HOA), cooking OA (COA),semi-volatile oxygenated OA (SV-OOA) and a low volatility oxygenated OA (LV-OOA). Our results indicate that air quality in SMA during KORUS-AQ was influenced strongly by secondary aerosol formation with SO4, NO3, NH4, SV-OOA, and LV-OOA together accounting for 76% of the PM1 mass. Due to high temperature and elevated ozone concentrations, photochemical reactions during daytime promoted the formation of SV-OOA, LV-OOA and SO4. In addition, aqueous-phase or heterogeneous reactions likely promoted efficient formation of NO3 whereas gas-to-particle partitioning processes appeared to have enhanced nighttime SV-OOA and NO3 formation. From May 20 to May 23, LV-OOA was significantly enhanced and accounted for up to 41% of the PM1 mass. Since this intense LV-OOA formation event was associated with large enhancement of VOCs, high concentration of Ox , strong solar radiation, and stagnant conditions, it appeared to be related to local photochemical formation. We also have investigated the formation and evolution mechanisms of severe haze episodes. Unlike the cases observed in winter when haze episodes were mainly caused by intense local emissions coupled with stagnant meteorological conditions, the spring haze events observed in this study appeared to be attributed by both regional and local factors. For example, episodes of long range transport of plumes were followed by calm meteorology conditions, which promoted the formation and accumulation of local secondary species, thus led to high concentrations of PM. Overall, our results indicate that PM pollutants in urban Korea originate from complex emission sources and atmospheric processes and that their concentrations and composition are controlled by various factors including meteorological conditions, local anthropogenic emissions, and upwind sources.

Wintertime peroxyacetyl nitrate (PAN) in the megacity Beijing: role of photochemical and meteorological processes.

PubMed

Zhang, Hualong; Xu, Xiaobin; Lin, Weili; Wang, Ying

2014-01-01

Previous measurements of peroxyacetyl nitrate (PAN) in Asian megacities were scarce and mainly conducted for relative short periods in summer. Here, we present and analyze the measurements of PAN, O3, NO(x), etc., made at an urban site (CMA) in Beijing from 25 January to 22 March 2010. The hourly concentration of PAN averaged 0.70 x 10(-9) mol/mol (0.23 x 10(-9) -3.51 x 10(-9) mol/mol) and was well correlated with that of NO2 but not O3, indicating that the variations of the winter concentrations of PAN and 03 in urban Beijing are decoupled with each other. Wind conditions and transport of air masses exert very significant impacts on O3, PAN, and other species. Air masses arriving at the site originated either from the boundary layer over the highly polluted N-S-W sector or from the free troposphere over the W-N sector. The descending free-tropospheric air was rich in O3, with an average PAN/O3 ratio smaller than 0.031, while the boundary layer air over the polluted sector contained higher levels of PAN and primary pollutants, with an average PAN/O3 ratio of 0.11. These facts related with transport conditions can well explain the observed PAN-O3 decoupling. Photochemical production is important to PAN in the winter over Beijing. The concentration of the peroxyacetyl (PA) radical was estimated to be in the range of 0.0014 x 10(-12) -0.0042 x 10(-12) mol/mol. The contributions of the formation reaction and thermal decomposition to PAN's variation were calculated and found to be significant even in the colder period in air over Beijing, with the production exceeding the decomposition.

Brassica rapa plants adapted to microgravity with reduced photosystem I and its photochemical activity

NASA Technical Reports Server (NTRS)

Jiao, Shunxing; Hilaire, Emmanuel; Paulsen, Avelina Q.; Guikema, James A.

2004-01-01

The photosynthetic apparatus contains several protein complexes, many of which are regulated by environmental conditions. In this study, the influences of microgravity on PSI and PSII in Brassica rapa plants grown aboard the space shuttle were examined. We found that Brassica plants grown in space had a normal level of growth relative to controls under similar conditions on Earth. Upon return to Earth, cotyledons were harvested and thylakoid membranes were isolated. Analysis of chlorophyll contents showed that the Chl a/b ratio (3.5) in flight cotyledons was much higher than a ratio of 2.42 in the ground controls. The flight samples also had a reduction of PSI complexes and a corresponding 30% decrease of PSI photochemical activity. Immunoblotting showed that the reaction centre polypeptides of PSI were more apparently decreased (e.g. by 24-33% for PsaA and PsaB, and 57% for PsaC) than the light-harvesting complexes. In comparison, the accumulation of PSII complex was less affected in microgravity, thus only a slight reduction in D1, D2 and LHCII was observed in protein blots. However, there was a 32% decrease of OEC1 in the flight samples, indicating a defective OEC subcomplex. In addition, an average 54% increase of the 54 kDa CF1-beta isoform was found in the flight samples, suggesting that space-grown plants suffered from certain stresses, consistent with implications of the increased Chl a/b ratio. Taken together, the results demonstrated that Brassica plants can adapt to spaceflight microgravity, but with significant alterations in chloroplast structures and photosynthetic complexes, and especially reduction of PSI and its activity.

Evaluating the impact of new observational constraints on P-S/IVOC emissions, multi-generation oxidation, and chamber wall losses on SOA modeling for Los Angeles, CA

NASA Astrophysics Data System (ADS)

Ma, Prettiny K.; Zhao, Yunliang; Robinson, Allen L.; Worton, David R.; Goldstein, Allen H.; Ortega, Amber M.; Jimenez, Jose L.; Zotter, Peter; Prévôt, André S. H.; Szidat, Sönke; Hayes, Patrick L.

2017-08-01

Secondary organic aerosol (SOA) is an important contributor to fine particulate matter (PM) mass in polluted regions, and its modeling remains poorly constrained. A box model is developed that uses recently published literature parameterizations and data sets to better constrain and evaluate the formation pathways and precursors of urban SOA during the CalNex 2010 campaign in Los Angeles. When using the measurements of intermediate-volatility organic compounds (IVOCs) reported in Zhao et al. (2014) and of semi-volatile organic compounds (SVOCs) reported in Worton et al. (2014) the model is biased high at longer photochemical ages, whereas at shorter photochemical ages it is biased low, if the yields for VOC oxidation are not updated. The parameterizations using an updated version of the yields, which takes into account the effect of gas-phase wall losses in environmental chambers, show model-measurement agreement at longer photochemical ages, even though some low bias at short photochemical ages still remains. Furthermore, the fossil and non-fossil carbon split of urban SOA simulated by the model is consistent with measurements at the Pasadena ground site. Multi-generation oxidation mechanisms are often employed in SOA models to increase the SOA yields derived from environmental chamber experiments in order to obtain better model-measurement agreement. However, there are many uncertainties associated with these aging mechanisms. Thus, SOA formation in the model is compared to data from an oxidation flow reactor (OFR) in order to constrain SOA formation at longer photochemical ages than observed in urban air. The model predicts similar SOA mass at short to moderate photochemical ages when the aging mechanisms or the updated version of the yields for VOC oxidation are implemented. The latter case has SOA formation rates that are more consistent with observations from the OFR though. Aging mechanisms may still play an important role in SOA chemistry, but the additional mass formed by functionalization reactions during aging would need to be offset by gas-phase fragmentation of SVOCs. All the model cases evaluated in this work show a large majority of the urban SOA (70-83 %) at Pasadena coming from the oxidation of primary SVOCs (P-SVOCs) and primary IVOCs (P-IVOCs). The importance of these two types of precursors is further supported by analyzing the percentage of SOA formed at long photochemical ages (1.5 days) as a function of the precursor rate constant. The P-SVOCs and P-IVOCs have rate constants that are similar to highly reactive VOCs that have been previously found to strongly correlate with SOA formation potential measured by the OFR. Finally, the volatility distribution of the total organic mass (gas and particle phase) in the model is compared against measurements. The total SVOC mass simulated is similar to the measurements, but there are important differences in the measured and modeled volatility distributions. A likely reason for the difference is the lack of particle-phase reactions in the model that can oligomerize and/or continue to oxidize organic compounds even after they partition to the particle phase.

Temperature Dependence of the Rate Constant for the CH3 Recombination Reaction: A Loss Process in Outer Planet Atmospheres

NASA Technical Reports Server (NTRS)

Cody, R. J.; Payne, W. A.; Thorn, R. P., Jr.; Romani, P. N.; Stief, L. J.; Nesbitt, F. L.; Iannone, M. A.; Tardy, D. C.

2002-01-01

The methyl free radical (CH3) has been observed in the atmospheres of Saturn and Neptune by the ISO satellite. There are discrepancies between the column densities for the CH3 radical derived from the ISO observations and the column densities derived from atmospheric photochemical models. For Neptune the model column density is 1.5 times that derived from ISO. For Saturn the model is 6 times that from ISO. The recombination of methyl radicals is the major loss process for methyl in these atmospheres. The serious disagreement between observed and calculated levels of CH3 has led to suggestions that the atmospheric models greatly underestimated the loss of CH3 due to poor knowledge of the rate of the reaction (1) CH3 + CH3 + M goes to C2H6 + M at the low temperatures and pressures of these atmospheric systems. Although the reaction CH3 + CH3 + M goes to C2H6 + M has been extensively studied both theoretically and experimentally, the laboratory conditions have been, with only a few exceptions, higher temperatures (T greater than 298K), higher pressures (P greater than or equal to 10 Torr - 13.3 mbar) or M=Ar rather than H2 or He as the bath gas.

Use of high-volume outdoor smog chamber photo-reactors for studying physical and chemical atmospheric aerosol formation and composition

NASA Astrophysics Data System (ADS)

Borrás, E.; Ródenas, M.; Vera, T.; Muñoz, A.

2015-12-01

The atmospheric particulate matter has a large impact on climate, biosphere behaviour and human health. Its study is complex because of large number of species are present at low concentrations and the continuous time evolution, being not easily separable from meteorology, and transport processes. Closed systems have been proposed by isolating specific reactions, pollutants or products and controlling the oxidizing environment. High volume simulation chambers, such as EUropean PHOtoREactor (EUPHORE), are an essential tool used to simulate atmospheric photochemical reactions. This communication describes the last results about the reactivity of prominent atmospheric pollutants and the subsequent particulate matter formation. Specific experiments focused on organic aerosols have been developed at the EUPHORE photo-reactor. The use of on-line instrumentation, supported by off-line techniques, has provided well-defined reaction profiles, physical properties, and up to 300 different species are determined in particulate matter. The application fields include the degradation of anthropogenic and biogenic pollutants, and pesticides under several atmospheric conditions, studying their contribution on the formation of secondary organic aerosols (SOA). The studies performed at the EUPHORE have improved the mechanistic studies of atmospheric degradation processes and the knowledge about the chemical and physical properties of atmospheric particulate matter formed during these processes.

Impacts of Lateral Boundary Conditions on U.S. Ozone Modeling Analyses

EPA Science Inventory

Chemical boundary conditions are a key input to regional-scale photochemical models. In this study, we perform annual simulations over North America with chemical boundary conditions prepared from two global models (GEOS-CHEM and Hemispheric CMAQ). Results indicate that the impac...

Exogenous Melatonin Mitigates Photoinhibition by Accelerating Non-photochemical Quenching in Tomato Seedlings Exposed to Moderate Light during Chilling

PubMed Central

Ding, Fei; Wang, Meiling; Liu, Bin; Zhang, Shuoxin

2017-01-01

Melatonin plays an important role in tolerance to multiple stresses in plants. Recent studies have shown that melatonin relieves photoinhibition in plants under cold stress; however, the mechanisms are not fully understood. Non-photochemical quenching (NPQ) is a key process thermally dissipating excess light energy that plants employ as a protective mechanism to prevent the over reduction of photosystem II. Here, we report the effects of exogenous melatonin on NPQ and mitigation of photoinhibition in tomato seedlings exposed to moderate light during chilling. In response to moderate light during chilling, the maximum quantum yield (Fv/Fm) and the effective photochemical efficiency (F′v/F′m) of PSII were both substantially reduced, showing severe photoinhibition in tomato seedlings, whereas exogenous application of melatonin effectively alleviated the photoinhibition. Further experiment showed that melatonin accelerated the induction of NPQ in response to moderate light and maintained higher level of NPQ upon longer exposure to light during chilling. Consistent with the increased NPQ was the elevated de-epoxidation state of xanthophyll pigments in melatonin-pretreated seedlings exposed to light during chilling. Enzyme activity assay showed that violaxanthin de-epoxidase (VDE), which catalyzes the de-epoxidation reaction in the xanthophyll cycle, was activated by light and the activity was further enhanced by application of melatonin. Further analysis revealed that melatonin induced the expression of VDE gene in tomato seedlings under moderate light and chilling conditions. Ascorbic acid is an essential cofactor of VDE and the level of it was found to be increased in melatonin-pretreated seedlings. Feeding tomato seedlings with dithiothreitol, an inhibitor of VDE, blocked the effects of melatonin on the de-epoxidation state of xanthophyll pigments and the induction of NPQ. Collectively, these results suggest that exogenous melatonin mitigates photoinhibition by accelerating NPQ through the stimulation of VDE activity and the enhancement of de-epoxidation state of xanthophyll pigments. PMID:28265283

Exogenous Melatonin Mitigates Photoinhibition by Accelerating Non-photochemical Quenching in Tomato Seedlings Exposed to Moderate Light during Chilling.

PubMed

Ding, Fei; Wang, Meiling; Liu, Bin; Zhang, Shuoxin

2017-01-01

Melatonin plays an important role in tolerance to multiple stresses in plants. Recent studies have shown that melatonin relieves photoinhibition in plants under cold stress; however, the mechanisms are not fully understood. Non-photochemical quenching (NPQ) is a key process thermally dissipating excess light energy that plants employ as a protective mechanism to prevent the over reduction of photosystem II. Here, we report the effects of exogenous melatonin on NPQ and mitigation of photoinhibition in tomato seedlings exposed to moderate light during chilling. In response to moderate light during chilling, the maximum quantum yield (Fv/Fm) and the effective photochemical efficiency (F'v/F'm) of PSII were both substantially reduced, showing severe photoinhibition in tomato seedlings, whereas exogenous application of melatonin effectively alleviated the photoinhibition. Further experiment showed that melatonin accelerated the induction of NPQ in response to moderate light and maintained higher level of NPQ upon longer exposure to light during chilling. Consistent with the increased NPQ was the elevated de-epoxidation state of xanthophyll pigments in melatonin-pretreated seedlings exposed to light during chilling. Enzyme activity assay showed that violaxanthin de-epoxidase (VDE), which catalyzes the de-epoxidation reaction in the xanthophyll cycle, was activated by light and the activity was further enhanced by application of melatonin. Further analysis revealed that melatonin induced the expression of VDE gene in tomato seedlings under moderate light and chilling conditions. Ascorbic acid is an essential cofactor of VDE and the level of it was found to be increased in melatonin-pretreated seedlings. Feeding tomato seedlings with dithiothreitol, an inhibitor of VDE, blocked the effects of melatonin on the de-epoxidation state of xanthophyll pigments and the induction of NPQ. Collectively, these results suggest that exogenous melatonin mitigates photoinhibition by accelerating NPQ through the stimulation of VDE activity and the enhancement of de-epoxidation state of xanthophyll pigments.

Composition/bandgap selective dry photochemical etching of semiconductor materials

DOEpatents

Ashby, C.I.H.; Dishman, J.L.

1985-10-11

Disclosed is a method of selectively photochemically dry etching a first semiconductor material of a given composition and direct bandgap Eg/sub 1/ in the presence of a second semiconductor material of a different composition and direct bandgap Eg/sub 2/, wherein Eg/sub 2/ > Eg/sub 1/, said second semiconductor material substantially not being etched during said method. The method comprises subjecting both materials to the same photon flux and to the same gaseous etchant under conditions where said etchant would be ineffective for chemical etching of either material were the photons not present, said photons being of an energy greater than Eg/sub 1/ but less than Eg/sub 2/, whereby said first semiconductor material is photochemically etched and said second material is substantially not etched.

The production of trace gases by photochemistry and lightning in the early atmosphere

NASA Technical Reports Server (NTRS)

Levine, J. S.; Tennille, G. M.; Towe, K. M.; Khanna, R. K.

1986-01-01

Recent atmospheric calculation suggest that the prebiological atmosphere was most probably composed of nitrogen, carbon dioxide, and water vapor, resulting from volatile outgassing, as opposed to the older view of a strongly reducing early atmosphere composed of methane, ammonia, and hydrogen. Photochemical calculations indicate that methane would have been readily destroyed via reaction with the hydroxyl radical produced from water vapor and that ammonia would have been readily lost via photolysis and rainout. The rapid loss of methane and ammonia, coupled with the absence of a significant source of these gases, suggest that atmospheric methane and ammonia were very short lived, if they were present at all. An early atmosphere of N2, CO2, and H2O is stable and leads to the chemical production of a number of atmospheric species of biological significance, including oxygen, ozone, carbon monoxide, formaldehyde, and hydrogen cyanide. Using a photochemical model of the early atmosphere, the chemical productionof these species over a wide range of atmospheric parameters were investigated. These calculations indicate that early atmospheric levels of O3 were significantly below the levels needed to provide UV shielding. The fate of volcanically emitted sulfur species, e.g., sulfur dioxide and hydrogen sulfide, was investigated in the early atmosphere to assess their UV shielding properties. The photochemical calculations show that these species were of insufficient levels, due in part to their short photochemical lifetimes, to provide UV shielding.

A photochemical proposal for the preparation of ZnAl{sub 2}O{sub 4} and MgAl{sub 2}O{sub 4} thin films from β-diketonate complex precursors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cabello, G., E-mail: gerardocabelloguzman@hotmail.com; Lillo, L.; Caro, C.

2016-05-15

Highlights: • ZnAl{sub 2}O{sub 4} and MgAl{sub 2}O{sub 4} thin films were prepared by photo-chemical method. • The Zn(II), Mg(II) and Al(III) β-diketonate complexes were used as precursors. • The photochemical reaction was monitored by UV–vis and FT-IR spectroscopy. • The results reveal spinel oxide formation and the generation of intermediate products. - Abstract: ZnAl{sub 2}O{sub 4} and MgAl{sub 2}O{sub 4} thin films were grown on Si(100) and quartz plate substrates using a photochemical method in the solid phase with thin films of β-diketonate complexes as the precursors. The films were deposited by spin-coating and subsequently photolyzed at room temperaturemore » using 254 nm UV light. The photolysis of these films results in the deposition of metal oxide thin films and fragmentation of the ligands from the coordination sphere of the complexes. The obtained samples were post-annealed at different temperatures (350–1100 °C) for 2 h and characterized by FT-Infrared spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force miscroscopy (AFM), and UV–vis spectroscopy. The results indicate the formation of spinel-type structures and other phases. These characteristics determined the quality of the films, which were obtained from the photodeposition of ternary metal oxides.« less

FIGAERO ToF CIMS measurements of chlorine photochemical activation by nitryl chloride chemistry at a semi-rural site in Beijing

NASA Astrophysics Data System (ADS)

Le Breton, Michael; Hallquist, Åsa M.; Kant Pathak, Ravi; Simpson, David; Wang, Yujue; Zheng, Jing; Yang, Yudong; Shang, Dongjie; Wang, Haichao; Lu, Keding; Guo, Song; Hu, Min; Hallquist, Mattias

2017-04-01

Severe pollution events across China pose a major threat to air quality and climate through the direct emission of pollutants, but also via the production of photochemically induced secondary pollutants. Nitryl chloride (ClNO2), produced from heterogeneous reactions of dinitrogen pentoxide (N2O5) and aerosols containing chloride, is photolysed rapidly in sunlight and activates chlorine. Subsequent daytime oxidation via the chlorine atom can proceed orders of magnitude faster than that of the hydroxyl radical and therefore significantly perturb radical budgets and concentrations of ozone and secondary pollutants. Knowledge of the formation pathways, abundance and fate of these secondary pollutants, which can depend on ClNO2 abundance, is not fully understood but is necessary to support abatement strategies which will efficiently account for both primary and secondary pollutants. A Time of Flight Chemical Ionisation Mass Spectrometer (ToF CIMS) utilising the Filter Inlet for Gases and AEROsols (FIGAERO) was deployed in Changping, Beijing, during June and July, 2016 as part of an intercollaborative project to assess the photochemical smog in China. Concentrations of ClNO2 regularly exceeded 500 ppt throughout the campaign and reached a maximum concentration of 2.8 ppb, whereas relatively low N2O5 concentrations were observed, indicating a rapid heterogeneous production of ClNO2. Correlation of particulate chloride and carbon monoxide during the campaign suggests an anthropogenic chlorine source, also supported by high daytime Cl2 concentrations. Observations of ClNO2 desorptions using the FIGAERO suggest a possible unaccounted particulate reservoir of active chlorine in highly polluted regions. The persistence of ClNO2 several hours passed sunrise significantly increases the atomic chlorine production rate throughout the day further perturbing standard daytime oxidation processes. Simultaneous ToF CIMS measurements of Cl2, ClNO2, HCl, HOCl, OClO and ClONO2 were implemented into steady state calculations using the Master Chemical Mechanism (MCM) to assess how the daytime activation of chlorine competes with OH as a dominant oxidant in this heavily polluted region. The reactions of atomic chlorine with VOCs are traced and assessed via the gas and particle phase measurements of chlorinated VOCs and supporting Proton Transfer Reaction Mass Spectrometer (PTR MS) VOC measurements. This provides the first high frequency measurements of unique tracers for chlorine atom chemistry, several of which are represented in the MCM, in both the gas and particle phase and enable the detailed assessment of their diurnal variation and importance for photochemical smog formation.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Henderson, Michael A.; Lyubinetsky, Igor

The field of heterogeneous photocatalysis has grown considerably in the decades since Fujishima and Honda's ground-breaking publications of photoelectrochemistry on TiO2. Numerous review articles continue to point to both progress made in the use of heterogeneous materials (such as TiO2) to perform photoconversion processes, and the many opportunities and challenges in heterogeneous photocatalysis research such as solar energy conversion and environmental remediation. The past decade has also seen an increase in the use of molecular-level approaches applied to model single crystal surfaces in an effort to obtain new insights into photocatalytic phenomena. In particular, scanning probe techniques (SPM) have enabledmore » researchers to take a ‘nanoscale’ approach to photocatalysis that includes interrogation of the reactivities of specific sites and adsorbates on a model photocatalyst surface. The rutile TiO2(110) surface has become the prototypical oxide single crystal surface for fundamental studies of many interfacial phenomena. In particular, TiO2(110) has become an excellent model surface for probing photochemical and photocatalytic reactions at the molecular level. A variety of experimental approaches have emerged as being ideally suited for studying photochemical reactions on TiO2(110), including desorption-oriented approaches and electronic spectroscopies, but perhaps the most promising techniques for evaluating site-specific properties are those of SPM. In this review, we highlight the growing use of SPM techniques in providing molecular-level insights into surface photochemistry on the model photocatalyst surface of rutile TiO2(110). Our objective is to both illustrate the unique knowledge that scanning probe techniques have already provided the field of photocatalysis, and also to motivate a new generation of effort into the use of such approaches to obtain new insights into the molecular level details of photochemical events occurring at interfaces. Discussion will start with an examination of how scanning probe techniques are being used to characterize the TiO2(110) surface in ways that are relevant to photocatalysis. We will then discuss specific classes of photochemical reaction on TiO2(110) for which SPM has proven indispensible in providing unique molecular-level insights, and conclude with discussion of future areas in which SPM studies may prove valuable to photocatalysis on TiO2. This work was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. I.L. was partially supported by a Pacific Northwest National Laboratory (PNNL) Chemical Imaging Initiative project. PNNL is a multiprogram national laboratory operated for DOE by Battelle.« less

Comparison of scientific findings from major ozone field studies in North America and Europe

NASA Astrophysics Data System (ADS)

Solomon, Paul; Cowling, Ellis; Hidy, George; Furiness, Cari

During the past decade, nearly 600 million dollars were invested in more than 30 major field studies in North America and Europe examining tropospheric ozone chemistry, meteorology, precursor emissions, and modeling. Most of these studies were undertaken to provide new or refined knowledge about ozone accumulation and to assist in the development of economical and effective emissions management practices for ozone. In this paper, we describe a selection of field research programs conducted under a wide range of geographical and climatological conditions in North America and Europe. The designs of these studies were generally similar, employing a combination of ground-based observation networks, upper-air sampling, and meteorological observations. Analysis and interpretation of the resulting data were combined with improved inventories of ozone precursor emissions and air quality modeling to develop new or enhanced knowledge about photochemical processes under various tropospheric conditions. The scientific results from these studies contained few surprises; in fact, they generally affirmed the conclusions in the review by the US National Research Council (NRC, 1999). Key findings include: (1) reaffirmation that tropospheric ozone is a multi-scale phenomenon extending to continental boundaries; (2) aerometric conditions aloft are important to ground-level ozone; (3) biogenic sources make important contributions to VOC and NO x emissions in parts of eastern North America and southern Europe; (4) emissions estimates are among the more uncertain components of predictive models for ozone; (5) recirculating flow over complex terrain and large water bodies are universally important factors affecting accumulation of ozone at the ground; (6) nonlinearities in ozone response to precursor changes create important degrees of freedom in management strategies - VOC and NO x sensitivities vary extensively in urban and rural areas, making decisions about emissions management complicated; (7) measurement methods for many precursors, intermediates, and products of photochemical reactions have improved greatly; and (8) additional analysis and interpretation of existing data from many of these field studies should pay handsome dividends at relatively modest cost.

Organic reactions for the electrochemical and photochemical production of chemical fuels from CO2--The reduction chemistry of carboxylic acids and derivatives as bent CO2 surrogates.

PubMed

Luca, Oana R; Fenwick, Aidan Q

2015-11-01

The present review covers organic transformations involved in the reduction of CO2 to chemical fuels. In particular, we focus on reactions of CO2 with organic molecules to yield carboxylic acid derivatives as a first step in CO2 reduction reaction sequences. These biomimetic initial steps create opportunities for tandem electrochemical/chemical reductions. We draw parallels between long-standing knowledge of CO2 reactivity from organic chemistry, organocatalysis, surface science and electrocatalysis. We point out some possible non-faradaic chemical reactions that may contribute to product distributions in the production of solar fuels from CO2. These reactions may be accelerated by thermal effects such as resistive heating and illumination. Copyright © 2015 Elsevier B.V. All rights reserved.

Chemical reactions directed Peptide self-assembly.

PubMed

Rasale, Dnyaneshwar B; Das, Apurba K

2015-05-13

Fabrication of self-assembled nanostructures is one of the important aspects in nanoscience and nanotechnology. The study of self-assembled soft materials remains an area of interest due to their potential applications in biomedicine. The versatile properties of soft materials can be tuned using a bottom up approach of small molecules. Peptide based self-assembly has significant impact in biology because of its unique features such as biocompatibility, straight peptide chain and the presence of different side chain functionality. These unique features explore peptides in various self-assembly process. In this review, we briefly introduce chemical reaction-mediated peptide self-assembly. Herein, we have emphasised enzymes, native chemical ligation and photochemical reactions in the exploration of peptide self-assembly.

Chemical Reactions Directed Peptide Self-Assembly

PubMed Central

Rasale, Dnyaneshwar B.; Das, Apurba K.

2015-01-01

Fabrication of self-assembled nanostructures is one of the important aspects in nanoscience and nanotechnology. The study of self-assembled soft materials remains an area of interest due to their potential applications in biomedicine. The versatile properties of soft materials can be tuned using a bottom up approach of small molecules. Peptide based self-assembly has significant impact in biology because of its unique features such as biocompatibility, straight peptide chain and the presence of different side chain functionality. These unique features explore peptides in various self-assembly process. In this review, we briefly introduce chemical reaction-mediated peptide self-assembly. Herein, we have emphasised enzymes, native chemical ligation and photochemical reactions in the exploration of peptide self-assembly. PMID:25984603

Influence of Boundary Conditions on Simulated U.S. Air Quality

EPA Science Inventory

One of the key inputs to regional-scale photochemical models frequently used in air quality planning and forecasting applications are chemical boundary conditions representing background pollutant concentrations originating outside the regional modeling domain. A number of studie...

Role of nitrite in the photochemical formation of radicals in the snow.

PubMed

Jacobi, Hans-Werner; Kleffmann, Jörg; Villena, Guillermo; Wiesen, Peter; King, Martin; France, James; Anastasio, Cort; Staebler, Ralf

2014-01-01

Photochemical reactions in snow can have an important impact on the composition of the atmosphere over snow-covered areas as well as on the composition of the snow itself. One of the major photochemical processes is the photolysis of nitrate leading to the formation of volatile nitrogen compounds. We report nitrite concentrations determined together with nitrate and hydrogen peroxide in surface snow collected at the coastal site of Barrow, Alaska. The results demonstrate that nitrite likely plays a significant role as a precursor for reactive hydroxyl radicals as well as volatile nitrogen oxides in the snow. Pollution events leading to high concentrations of nitrous acid in the atmosphere contributed to an observed increase in nitrite in the surface snow layer during nighttime. Observed daytime nitrite concentrations are much higher than values predicted from steady-state concentrations based on photolysis of nitrate and nitrite indicating that we do not fully understand the production of nitrite and nitrous acid in snow. The discrepancy between observed and expected nitrite concentrations is probably due to a combination of factors, including an incomplete understanding of the reactive environment and chemical processes in snow, and a lack of consideration of the vertical structure of snow.

The Comparative Photodegradation Activities of Pentachlorophenol (PCP) and Polychlorinated Biphenyls (PCBs) Using UV Alone and TiO2-Derived Photocatalysts in Methanol Soil Washing Solution

PubMed Central

Zhou, Zeyu; Zhang, Yaxin; Wang, Hongtao; Chen, Tan; Lu, Wenjing

2014-01-01

Photochemical treatment is increasingly being applied to remedy environmental problems. TiO2-derived catalysts are efficiently and widely used in photodegradation applications. The efficiency of various photochemical treatments, namely, the use of UV irradiation without catalyst or with TiO2/graphene-TiO2 photodegradation methods was determined by comparing the photodegadation of two main types of hydrophobic chlorinated aromatic pollutants, namely, pentachlorophenol (PCP) and polychlorinated biphenyls (PCBs). Results show that photodegradation in methanol solution under pure UV irradiation was more efficient than that with either one of the catalysts tested, contrary to previous results in which photodegradation rates were enhanced using TiO2-derived catalysts. The effects of various factors, such as UV light illumination, addition of methanol to the solution, catalyst dosage, and the pH of the reaction mixture, were examined. The degradation pathway was deduced. The photochemical treatment in methanol soil washing solution did not benefit from the use of the catalysts tested. Pure UV irradiation was sufficient for the dechlorination and degradation of the PCP and PCBs. PMID:25254664

Temperature-assisted photochemical construction of CdS-based ordered porous films with photocatalytic activities on solution surfaces.

PubMed

Huang, Zhenxun; Sun, Fengqiang; Zhang, Yu; Gu, Kaiyuan; Zou, Xueqiong; Huang, Yuying; Wu, Qingsong; Zhang, Zihe

2011-04-15

Taking a colloidal monolayer floating on the surface of a precursor solution as template, free-standing CdS/Cd composites and pure CdS (CdS-based) ordered porous films had been prepared by a temperature-assisted photochemical strategy. After irradiation with UV-light and heat treatment, the films formed hemi-spherical pores due to the preferable deposition of CdS and Cd onto the PS spheres during the photochemical and interfacial reactions. When the temperature increased from 15 to 60°C, the air/water interface gradually changed into a vapor/water interface on the surface of the solution, resulting in variations of the final compositions. The optical properties of the films were hence changed. Because of the free-standing characteristic, the ordered porous films were first transferred on surface of polluted solutions as photocatalysts, which was a new mode in application of photocatalysts. The photocatalytic activities of films showed regular variations with the compositions in photodegradation of Rhodamine B. This method provides a simple route for tuning the properties of porous films through control of its composition and a flexible application of films on any surface. Copyright © 2011 Elsevier Inc. All rights reserved.

Balloon-Borne Measurements of Stratospheric Radicals and their Precursors: Implications for the Production and Loss of Ozone

NASA Technical Reports Server (NTRS)

Osterman, G. B.; Salawitch, R. J.; Sen, B.; Toon, G. C.; Stachnik, R. A.; Pickett, H. M.; Margitan, J. J.; Blavier, J.-F.; Peterson, D. B.

1997-01-01

Measurements of hydrogen, nitrogen and chlorine radicals from a balloon flight on 25 September 1993 from Ft. Sumner, NM provide an opportunity to quantify photochemical production and loss of stratospheric ozone. Ozone loss rates determined using measured radical concentrations agree fairly well with loss rates calculated using a photochemical model. Catalytic cycles involving OH and HO2 are shown to dominate photochemical loss of ozone for altitudes between 44 and 50 km. Reactions involving NO and NO2 are the dominant sink for ozone between 25 and 38 km. The total ozone loss rate determined from the measurements balances calculated production rates for altitudes between 30 and 40 km. However, loss of ozone exceeds production by -35% between 42 and 50 km. The imbalance between production and loss of ozone above 42 km is larger than the uncertainty of any one of the critical kinetic parameters or species concentrations. No single adjustment to any of these parameters can simultaneously resolve the imbalance and satisfy constraints imposed by measured OH, HO2, NO2 and ClO. Our results are consistent with an additional mechanism for ozone production above 40 km other than photolysis of ground state O2.

Unexpected effect of catalyst concentration on photochemical CO2 reduction by trans(Cl)–Ru(bpy)(CO)2Cl2: new mechanistic insight into the CO/HCOO– selectivity† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c5sc00199d Click here for additional data file.

PubMed Central

Kuramochi, Yusuke; Itabashi, Jun; Fukaya, Kyohei; Enomoto, Akito; Yoshida, Makoto

2015-01-01

Photochemical CO2 reduction catalysed by trans(Cl)–Ru(bpy)(CO)2Cl2 (bpy = 2,2′-bipyridine) efficiently produces carbon monoxide (CO) and formate (HCOO–) in N,N-dimethylacetamide (DMA)/water containing [Ru(bpy)3]2+ as a photosensitizer and 1-benzyl-1,4-dihydronicotinamide (BNAH) as an electron donor. We have unexpectedly found catalyst concentration dependence of the product ratio (CO/HCOO–) in the photochemical CO2 reduction: the ratio of CO/HCOO– decreases with increasing catalyst concentration. The result has led us to propose a new mechanism in which HCOO– is selectively produced by the formation of a Ru(i)–Ru(i) dimer as the catalyst intermediate. This reaction mechanism predicts that the Ru–Ru bond dissociates in the reaction of the dimer with CO2, and that the insufficient electron supply to the catalyst results in the dominant formation of HCOO–. The proposed mechanism is supported by the result that the time-course profiles of CO and HCOO– in the photochemical CO2 reduction catalysed by [Ru(bpy)(CO)2Cl]2 (0.05 mM) are very similar to those of the reduction catalysed by trans(Cl)–Ru(bpy)(CO)2Cl2 (0.10 mM), and that HCOO– formation becomes dominant under low-intensity light. The kinetic analyses based on the proposed mechanism could excellently reproduce the unusual catalyst concentration effect on the product ratio. The catalyst concentration effect observed in the photochemical CO2 reduction using [Ru(4dmbpy)3]2+ (4dmbpy = 4,4′-dimethyl-2,2′-bipyridine) instead of [Ru(bpy)3]2+ as the photosensitizer is also explained with the kinetic analyses, reflecting the smaller quenching rate constant of excited [Ru(4dmbpy)3]2+ by BNAH than that of excited [Ru(bpy)3]2+. We have further synthesized trans(Cl)–Ru(6Mes-bpy)(CO)2Cl2 (6Mes-bpy = 6,6′-dimesityl-2,2′-bipyridine), which bears bulky substituents at the 6,6′-positions in the 2,2′-bipyridyl ligand, so that the ruthenium complex cannot form the dimer due to the steric hindrance. We have found that this ruthenium complex selectively produces CO, which strongly supports the catalytic mechanism proposed in this work. PMID:28706681