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Zach N Nilsson, Brian L Mandella, Kakali Sen, Demet Kekilli, Michael A Hough, Pierre Moënne-Loccoz, Richard W Strange, Colin R Andrew
Nitrite coordination to heme cofactors is a key step in the anaerobic production of the signaling molecule nitric oxide (NO). An ambidentate ligand, nitrite has the potential to coordinate via the N- (nitro) or O- (nitrito) atoms in a manner that can direct its reactivity. Distinguishing nitro vs nitrito coordination, along with the influence of the surrounding protein, is therefore of particular interest. In this study, we probed Fe(III) heme-nitrite coordination in Alcaligenes xylosoxidans cytochrome c' (AXCP), an NO carrier that excludes anions in its native state but that readily binds nitrite (Kd ∼ 0...
October 20, 2017: Inorganic Chemistry
Elitsour Rozen, Yaron Erlich, Megan E Reesbeck, Patrick L Holland, Chaim N Sukenik
The application of synthetic organic chemistry to the surface chemistry of monolayer arrays adds a novel dimension to the power of these systems for surface modification. This paper describes the elaboration of simple functionalized monolayers into dialdimine and dialdiminate ligands tethered to the monolayer surface. These ligands are then used to coordinate metal ions in an effort to form diiminate complexes with control over their environment and orientation. Ligand anchoring is best achieved through either thiol-ene photochemistry or azide-acetylene "click" chemistry...
October 19, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
Nicholas C Pflug, Madeline K Hankard, Stephanie M Berg, Meghan O'Connor, James B Gloer, Edward P Kolodziej, David M Cwiertny, Kristine H Wammer
Potent trienone and dienone steroid hormones undergo a coupled photohydration (in light)-thermal dehydration (in dark) cycle that ultimately increases their environmental persistence. Here, we studied the photolysis of dienogest, a dienone progestin prescribed as a next-generation oral contraceptive, and used high resolution mass spectrometry and both 1D and 2D nuclear magnetic resonance spectroscopy to identify its phototransformation products. Dienogest undergoes rapid direct photolysis (t1/2 ∼ 1-10 min), forming complex photoproduct mixtures across the pH range examined (pH 2 to 7)...
October 16, 2017: Environmental Science. Processes & Impacts
Rebecca J Rapf, Michael R Dooley, Keaten Kappes, Russell J Perkins, Veronica Vaida
α-Keto acids are important atmospherically-relevant species, and their photochemistry has been considered in the formation and processing of aerosols. Despite their atmospheric relevance, the photochemistry of these species has primarily been studied under extremely low pH conditions. Using a variety of analytical techniques, we characterize the extent of hydration and deprotonation for solution of two α-keto acids, pyruvic acid and 2-oxooctanoic acid, as a function of pH. We find that changes in the initial solution composition govern the accessibility of different photochemical pathways, resulting in slowed photolysis under high pH conditions and a shift in photoproducts that can be predicted based on reaction mechanisms...
October 14, 2017: Journal of Physical Chemistry. A
Mao-Chang Liang, Sasadhar Mahata, Amzad H Laskar, Mark H Thiemens, Sally Newman
The abundance variations of near surface atmospheric CO2 isotopologues (primarily (16)O(12)C(16)O, (16)O(13)C(16)O, (17)O(12)C(16)O, and (18)O(12)C(16)O) represent an integrated signal from anthropogenic/biogeochemical processes, including fossil fuel burning, biospheric photosynthesis and respiration, hydrospheric isotope exchange with water, and stratospheric photochemistry. Oxygen isotopes, in particular, are affected by the carbon and water cycles. Being a useful tracer that directly probes governing processes in CO2 biogeochemical cycles, Δ(17)O (=ln(1 + δ(17)O) - 0...
October 13, 2017: Scientific Reports
Jack Saltiel, Shipra Gupta, David W Eaker, Andrew M Kropp, V K Ratheesh Kumar
The photochemical and photophysical properties of the extended conformers of trans- and cis-1-(2-naphthyl)-2-phenylethenes (t- and c-NPEB ) are strikingly different than those of their rigid analogues, trans- and cis-3-styrylidenebenz[e]indane (t- and c-BPE). The fluorescence quantum yield and lifetime at 25 °C in methylcyclohexane drop from 0.76 and 22.2 ns in t-NPEB to 0.0051 and 0.25 ns in t-BPE and there are complementary changes in the photoisomerization quantum yields. In both cases photoisomerization occurs in S2 , a stilbenic excited state...
October 10, 2017: Photochemistry and Photobiology
Michael L Wong, Benjamin D Charnay, Peter Gao, Yuk L Yung, Michael J Russell
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...
October 12, 2017: Astrobiology
Stefano Crespi, Stefano Protti, Davide Ravelli, Daniele Merli, Maurizio Fagnoni
Irradiation of the three isomeric chlorobenzylphophonic acids in aqueous buffer led to a pH dependent photochemistry. Under acidic conditions (pH = 2.5) photocleavage of the Ar-Cl bond occurred and a phenyl cation chemistry resulted. Moving to basic conditions (pH = 11), a photoinduced release of chloride anion followed by the detachment of metaphosphate anion gave α,n-didehydrotoluene diradicals α,n-DHTs), potential DNA cleaving intermediates. At physiological pH (pH = 7.2) both a cationic and a diradical reactivity took place depending on the phosphonic acid used...
October 11, 2017: Journal of Organic Chemistry
Taylor B Dorsey, Alexander Grath, Cancan Xu, Yi Hong, Guohao Dai
There are many biological stimuli that can influence cell behavior and stem cell differentiation. General cell culture approaches rely on soluble factors within the medium to control cell behavior. However, soluble additions cannot mimic certain signaling motifs, such as matrix-bound growth factors, cell-cell signaling, and spatial biochemical cues, which are common influences on cells. Furthermore, biophysical properties of the matrix, such as substrate stiffness, play important roles in cell fate, which is not easily manipulated using conventional cell culturing practices...
September 15, 2017: Journal of Visualized Experiments: JoVE
Wuyuan Zhang, Bastien O Burek, Elena Fernández-Fueyo, Miguel Alcalde, Jonathan Z Bloh, Frank Hollmann
Selective oxyfunctionalisation of inert C-H bonds under mild conditions can be achieved using peroxygenases. This approach, however, is impaired by the poor robustness of these enzymes in the presence of hydrogen peroxide as the stoichiometric oxidant. Here, we demonstrate that inorganic photocatalysts such as gold-titanium dioxide efficiently provide H2O2 from methanol-driven reductive activation of ambient oxygen in suitable amounts to ensure high reactivity and robustness of the enzyme. Using this approach stereoselective hydroxylation of ethyl benzene to (R)-1-phenyl ethanol in high enantioselectivity (>98% ee) and excellent turnover numbers of the biocatalyst (>71...
October 10, 2017: Angewandte Chemie
Alexander P Demchenko, Vladimir I Tomin, Pi-Tai Chou
This paper provides a systematic review and analysis of different phenomena that violate a basic principle, Kasha's rule, when applied to photochemical reactions. In contrast to the classical route of ultrafast transition to the lowest energy excited state and photochemical reaction starting therein, in some cases, these reactions proceed directly from high-energy excited states. Nowadays, this phenomenon can be observed for a number of major types of excited-state reactions: harvesting product via intersystem crossing; photoisomerizations; bond-breaking; and electron, proton, and energy transfers...
October 9, 2017: Chemical Reviews
Jennifer E Vernia, Mary R Warmin, Jeanette A Krause, David L Tierney, Michael J Baldwin
The tripodal amine chelate with two pyridyl groups and an α-hydroxy acid (AHA) group, Pyr-TPA-AHA, was synthesized. Different Fe(III) complexes form with this chelate depending upon the counterion of the Fe(III) source used in the synthesis. A dinuclear complex, Fe(III)2(Pyr-TPA-AHA)2(μ-O), 1, and mononuclear complexes Fe(III)(Pyr-TPA-AHA)X (X = Cl(-) or Br(-), 2 and 3, respectively) were synthesized. 2 can be easily converted to 1 by addition of silver nitrate or a large excess of water. The structure of 1 was solved by X-ray crystallography (C32H34N6O7Fe2·13H2O, a = 14...
October 9, 2017: Inorganic Chemistry
Isabelle M Dixon, Jean-Louis Heully, Fabienne Alary, Paul I P Elliott
We have identified highly novel photoreactive (3)MC states of ruthenium(ii) 4,4'-bi-1,2,3-triazolyl (btz) complexes of the form [Ru(N^N)(btz)2](2+) and have elucidated the mechanism of the highly unusual experimental observations of photochemical ligand dechelation and concomitant ligand rearrangement reactivity to form unusual photoproducts trans-[Ru(N^N)(κ(2)-btz)(κ(1)-btz)(solvent)](2+). The triplet metal-to-ligand charge-transfer ((3)MLCT) states and classical Jahn-Teller type triplet metal-centred ((3)MC) states of the series of complexes [Ru(N^N)3-n(btz)n](2+) (btz = 4,4'-bi-1,2,3-triazolyl; N^N = 2,2'-bipyridyl (bpy), n = 0 (1), 1 (2), 2 (3), 3 (5); N^N = 4-(pyrid-2-yl)-1,2,3-triazole (pytz), n = 1 (4)) have been optimised by density functional theory (DFT) and characterised...
October 18, 2017: Physical Chemistry Chemical Physics: PCCP
Ilya N Ioffe, Martin Quick, Michael T Quick, Alexander L Dobryakov, Celin Richter, Alex A Granovsky, Falko Berndt, Rainer Mahrwald, Nikolaus P Ernsting, Sergey A Kovalenko
Spontaneous polarization of a nonpolar molecule upon photoexcitation (the sudden polarization effect) earlier discussed for 90°-twisted alkenes is observed and calculated for planar ring-fluorinated stilbenes, trans-2,3,5,6,2',3',5',6'-octofluorostilbene (tF2356) and trans-2,3,4,5,6,2',3',4',5',6'-decafluorostilbene (tF23456). Due to the fluorination, Franck-Condon states S1(FC) and S2(FC) are dominated by the quasi-degenerate HOMO-1 → LUMO and HOMO-2 → LUMO excitations, while their interaction gives rise to a symmetry-broken zwitterionic S1 state...
October 16, 2017: Journal of the American Chemical Society
Yang-Er Chen, Jun-Mei Cui, Yan-Qiu Su, Chao-Ming Zhang, Jie Ma, Zhong-Wei Zhang, Ming Yuan, Wen-Juan Liu, Huai-Yu Zhang, Shu Yuan
Reversible phosphorylation of proteins and the assembly of thylakoid complexes are the important protective mechanism against environmental stresses in plants. This research was aimed to investigate the different responses of the antioxidant defense system and photosystem II (PSII) to osmotic stress between drought-resistant and drought-susceptible wheat cultivars. Results showed that the decrease in PSII photochemistry and six enzyme activities was observed in drought-susceptible wheat compared with drought-resistant wheat under osmotic stress...
October 5, 2017: Scientific Reports
Mandy L Slate, Todd N Rosenstiel, Sarah M Eppley
Background and Aims: Dioecy and sexual dimorphism occur in many terrestrial plant species but are especially widespread among the bryophytes. Despite the prevalence of dioecy in non-vascular plants, surprisingly little is known about how fine-scale sex-specific cell and leaf morphological traits are correlated with sex-specific physiology and population sex ratios. Such data are critical to understanding the inter-relationship between sex-specific morphological and physiological characters and how their relationship influences population structure...
July 10, 2017: Annals of Botany
Peter A Alpert, Raluca Ciuraru, Stéphanie Rossignol, Monica Passananti, Liselotte Tinel, Sebastien Perrier, Yoan Dupart, Sarah S Steimer, Markus Ammann, D James Donaldson, Christian George
Organic interfaces that exist at the sea surface microlayer or as surfactant coatings on cloud droplets are highly concentrated and chemically distinct from the underlying bulk or overlying gas phase. Therefore, they may be potentially unique locations for chemical or photochemical reactions. Recently, photochemical production of volatile organic compounds (VOCs) was reported at a nonanoic acid interface however, subsequent secondary organic aerosol (SOA) particle production was incapable of being observed...
October 4, 2017: Scientific Reports
A C Eriksson, C Wittbom, P Roldin, M Sporre, E Öström, P Nilsson, J Martinsson, J Rissler, E Z Nordin, B Svenningsson, J Pagels, E Swietlicki
Fresh and aged diesel soot particles have different impacts on climate and human health. While fresh diesel soot particles are highly aspherical and non-hygroscopic, aged particles are spherical and hygroscopic. Aging and its effect on water uptake also controls the dispersion of diesel soot in the atmosphere. Understanding the timescales on which diesel soot ages in the atmosphere is thus important, yet knowledge thereof is lacking. We show that under cold, dark and humid conditions the atmospheric transformation from fresh to aged soot occurs on a timescale of less than five hours...
September 28, 2017: Scientific Reports
Joshua A Snyder, Peter Grüninger, Holger F Bettinger, Arthur E Bragg
Boron-nitrogen doping of polyaromatic hydrocarbon (PAH) materials can be used to tune their electronic properties while preserving the structural characteristics of pure hydrocarbons. Many multicycle PAHs can be synthesized photochemically; in contrast, very little is known about the photochemistry of their BN-doped counterparts. We present results of fs, ns, and μs time-resolved spectroscopic studies on the photoinduced dynamics of hexaphenyl benzene and hexaphenyl borazine in order to examine how BN-doping alters photochemical C-C bond formation via 6π electrocyclization as well as the stability of resulting cyclized structures...
September 26, 2017: Journal of Physical Chemistry. A
Lars Kohler, Leona Nease, Pascal Vo, Jenna Garofolo, David K Heidary, Randolph P Thummel, Edith C Glazer
Light-activated compounds are powerful tools and potential agents for medical applications, as biological effects can be controlled in space and time. Ruthenium polypyridyl complexes can induce cytotoxic effects through multiple mechanisms, including acting as photosensitizers for singlet oxygen ((1)O2) production, generating other reactive oxygen species (ROS), releasing biologically active ligands, and creating reactive intermediates that form covalent bonds to biological molecules. A structure-activity relationship (SAR) study was performed on a series of Ru(II) complexes containing isomeric tetramethyl-substituted bipyridyl-type ligands...
September 26, 2017: Inorganic Chemistry
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