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Chemical Science Feb 2024Rhenium(i) complexes c-[Re(diimine)(CO)(L)] are mostly used and evaluated as photocatalysts and catalysts in both photochemical and electrochemical systems for CO...
Rhenium(i) complexes c-[Re(diimine)(CO)(L)] are mostly used and evaluated as photocatalysts and catalysts in both photochemical and electrochemical systems for CO reduction. However, the selective reduction mechanism of CO to CO is unclear, although numerous mechanistic studies have been reported. A Ru(ii)-Re(i) supramolecular photocatalyst with -[Re(diimine)(CO){OC(O)OCHCHNR}] (R = CHOH) as a catalyst unit (RuC2Re) exhibits very high efficiency, selectivity, and durability of CO formation in photocatalytic CO reduction reactions. In this work, the reaction mechanism of photocatalytic CO reduction using RuC2Re is fully clarified. Time-resolved IR (TR-IR) measurements using rapid-scan FT-IR spectroscopy with laser flash photolysis verify the formation of RuC2Re(COOH) with a carboxylic acid unit, , -[Re(diimine)(CO)(COOH)], in the photocatalytic reaction solution. Additionally, this important intermediate is detected in an actual photocatalytic reaction using steady state irradiation. Kinetics analysis of the TR-IR spectra and DFT calculations demonstrated the reaction mechanism of the conversion of the one-electron reduced species of RuC2Re with a -[Re(diimine˙)(CO){OC(O)OCHCHNR}] unit, which was produced the photochemical reduction of RuC2Re by 1,3-dimethyl-2-phenyl-2,3-dihydro-1-benzo[]imidazole (BIH), to RuC2Re(COOH). The kinetics of the recovery processes of the starting complex RuC2Re from RuC2Re(COOH) accompanying the release of CO and OH was also clarified. As a side reaction of RuC2Re(COOH), a long-lived carboxylate-ester complex with a -[Re(diimine)(CO)(COOCHNR)] unit, which was produced by the nucleophilic attack of TEOA to one of the carbonyl ligands of RuC2Re(CO) with a -[Re(diimine)(CO)] unit, was formed during the photocatalytic reaction. This complex works not only as a precursor in another minor CO formation process but also as an external photosensitiser that photochemically reduces the other complexes , RuC2Re, RuC2Re(COOH), and the intermediate that is reductively converted to RuC2Re(COOH).
PubMed: 38332814
DOI: 10.1039/d3sc06059d -
The Journal of Physical Chemistry. A Feb 2024Broad-band ultraviolet photolysis (λ > 200 nm) of (cyanomethylene)cyclopropane () in an argon matrix at 20 K generates 1-cyano-2-methylenecyclopropane (), a previously...
Broad-band ultraviolet photolysis (λ > 200 nm) of (cyanomethylene)cyclopropane () in an argon matrix at 20 K generates 1-cyano-2-methylenecyclopropane (), a previously unknown compound. This product was initially identified by comparison of its infrared spectrum to that predicted by an anharmonic MP2/6-311+G(2d,p) calculation. This assignment was unambiguously confirmed by the synthesis of 1-cyano-2-methylenecyclopropane () and observation of its authentic infrared spectrum, which proved identical to that of the observed photoproduct. We investigated the singlet and triplet potential energy surfaces associated with this isomerization process using density functional theory and multireference calculations. The observed rearrangement of compound to compound is computed to be endothermic (3.3 kcal/mol). We were unable to observe the reverse reaction ( → ) under the photochemical conditions.
PubMed: 38329215
DOI: 10.1021/acs.jpca.3c08001 -
Chemosphere Mar 2024Natural organic matter (NOM) is a complex mixture of heterogeneous compounds with varying functional groups and molecular sizes. Understanding the impact of NOM on the...
Natural organic matter (NOM) is a complex mixture of heterogeneous compounds with varying functional groups and molecular sizes. Understanding the impact of NOM on the generation of photochemically produced reactive intermediates (PPRIs) and their potential inhibitory effects on photolysis has remained challenging due to the variations in the reactivities and concentrations of these functional groups. To address this gap, tannic acid (TA), gallic acid (GA), catechin (CAT), and tryptophan (Trp), were chosen as potential substitutes for NOM. Their effects on the photochemical transformation process were evaluated and compared with the widely used Suwannee River NOM (SRNOM). Atrazine (ATZ) was selected as a probe organic micropollutant (OMP). In this investigation, a significantly higher concentration of HO was observed compared to O1, and the triplet excited state ( NOM*3). The findings suggest that the substituted phenols, particularly those with carboxylate-substitutions, played a substantial role in HO formation, while electron-rich moieties acted as antioxidants, consuming NOM3. Hydroxyl, carboxylic, and amino acid were the active groups for O21 formation. However, the inhibitory effects induced by the NOM surrogates were significant and mainly attributed to the direct photolysis inhibition caused by the inner filter effect. The scope of this work was further extended to include SRNOM, where similar trends with less pronounced formation of PPRIs and inner filter effects were observed. Therefore, this study sheds some light on the role of the functional groups in NOM during photochemical transformations of OMPs, thereby deepening our understanding of their fate in aqueous systems.
Topics: Photolysis; Atrazine; Water Pollutants, Chemical; Phenols; Polyphenols
PubMed: 38325617
DOI: 10.1016/j.chemosphere.2024.141390 -
ChemistryOpen Feb 2024We present a first spectroscopic characterization of the homoatomic polyhalogen tetrabromine, Br , in the gas phase. Photolysis of CHBr at 248 nm is used to generate...
We present a first spectroscopic characterization of the homoatomic polyhalogen tetrabromine, Br , in the gas phase. Photolysis of CHBr at 248 nm is used to generate atomic bromine radicals in a flow tube reactor. Resulting combination products are detected by photoionization mass spectrometry at the Advanced Light Source of the Lawrence Berkeley National Laboratory. Interpretation of the experimental mass spectra is informed by calculated adiabatic ionization energies carried out at the CCSD(T)/aug-cc-pVTZ//M06-2X/aug-cc-pVTZ and CCSD(T)/aug-cc-pVTZ//cam-B3LYP/6-311++g** levels of theory. Tunable VUV synchrotron radiation enables the collection of the mass-selected photoionization spectra by which Br is assigned using Franck-Condon simulations of a Br dimer with a stretched tetrahedral geometry.
PubMed: 38308191
DOI: 10.1002/open.202300266 -
Journal of Molecular Biology Mar 2024Adaptation to rapid environmental changes is crucial for maintaining optimal photosynthetic efficiency and is ultimately key to the survival of all photosynthetic...
Adaptation to rapid environmental changes is crucial for maintaining optimal photosynthetic efficiency and is ultimately key to the survival of all photosynthetic organisms. Like most of them, cyanobacteria protect their photosynthetic apparatus against rapidly increasing light intensities by nonphotochemical quenching (NPQ). In cyanobacteria, NPQ is controlled by Orange Carotenoid Protein (OCP) photocycle. OCP is the only known photoreceptor that uses carotenoid for its light activation. How carotenoid drives and controls this unique photoactivation process is still unknown. However, understanding and potentially controlling the OCP photocycle may open up new possibilities for improving photosynthetic biomass. Here we investigate the effect of the carbonyl group in the β2 ring of the carotenoid on the OCP photocycle. We report microsecond to minute OCP light activation kinetics and Arrhenius plots of the two OCP forms: Canthaxanthin-bound OCP (OCP) and echinenone-bound OCP (OCP). The difference between the two carotenoids is the presence of a carbonyl group in the β2-ring located in the N-terminal domain of the protein. A combination of temperature-dependent spectroscopy, flash photolysis, and pump-probe transient absorption allows us to report the previously unresolved OCP intermediate associated primarily with the absorption bleach (OCP). OCP dominates the photokinetics in the μs to subms time range for OCP and in the μs to ms range for OCP. We show that in OCP the OCP photocycle steps are always faster than in OCP: from 2 to almost 20 times depending on the step. These results suggest that the presence of the carbonyl group in the β2-ring of the carotenoid accelerates the OCP photocycle.
Topics: Bacterial Proteins; Light; Photoreceptors, Microbial; Photosynthesis; Spectrum Analysis; Kinetics
PubMed: 38307159
DOI: 10.1016/j.jmb.2024.168463 -
Chemosphere Jan 2024In this study, we prepared and tested a carbon-modified, Fe-loaded bismuth oxychloride (Fe-BiOCl/CS) photocatalyst for photocatalytic degradation of perfluorooctane...
In this study, we prepared and tested a carbon-modified, Fe-loaded bismuth oxychloride (Fe-BiOCl/CS) photocatalyst for photocatalytic degradation of perfluorooctane sulfonate (PFOS). Structural analyses revealed a (110) facet-dominated sheet-type BiOCl crystal structure with uniformly distributed Fe and confirmed carbon modification of the photocatalyst. The presence of d-glucose facilitated the growth control of BiOCl particles and enhanced the adsorption of PFOS via added hydrophobic interaction. Adsorption kinetic and equilibrium tests showed rapid uptake rates of PFOS and high adsorption capacity with a Langmuir Q of 1.51 mg/g. When used for directly treating PFOS in solution, Fe-BiOCl/CS was able to mineralize or defluorinate 83% of PFOS (C = 100 μgL) under UV (254 nm, intensity = 21 mW cm) in 4 h; and when tested in a two-step mode, i.e., batch adsorption and subsequent photodegradation, Fe-BiOCl/CS mineralized 65.34% of PFOS that was pre-concentrated in the solid phase under otherwise identical conditions; while the total degradation percentages of PFOS were 83.48% and 80.50%, respectively, for the two experimental modes. The photoactivated electrons and/or hydrated electrons and superoxide radicals primarily initiated the desulfonation of PFOS followed by decarboxylation and defluorination, through a stepwise chain-subsiding mechanism. The elevated photocatalytic activity can be attributed to the effective separation of e/h pairs facilitated by the (110) interlayer electrostatic field, Fe doping, and the presence of oxygen vacancies. This work reveals the potential of carbon-modified and Fe-co-catalyzed BiOCl for concentrating and degrading PFOS and possibly other persistent organic pollutants.
Topics: Carbon; Water Pollutants, Chemical; Photolysis; Bismuth; Water; Fluorocarbons; Alkanesulfonic Acids
PubMed: 38303393
DOI: 10.1016/j.chemosphere.2023.140585 -
The Journal of Physical Chemistry. B Feb 2024Polarized time-resolved X-ray absorption spectroscopy at the Co K-edge is used to probe the excited-state dynamics and photolysis of base-off methylcobalamin and the...
Polarized time-resolved X-ray absorption spectroscopy at the Co K-edge is used to probe the excited-state dynamics and photolysis of base-off methylcobalamin and the excited-state structure of base-off adenosylcobalamin. For both molecules, the final excited-state minimum shows evidence for an expansion of the cavity around the Co ion by ca. 0.04 to 0.05 Å. The 5-coordinate base-off cob(II)alamin that is formed following photodissociation has a structure similar to that of the 5-coordinate base-on cob(II)alamin, with a ring expansion of 0.03 to 0.04 Å and a contraction of the lower axial bond length relative to that in the 6-coordinate ground state. These data provide insights into the role of the lower axial ligand in modulating the reactivity of B coenzymes.
Topics: Coenzymes; X-Ray Absorption Spectroscopy; Vitamin B 12; Photolysis
PubMed: 38301132
DOI: 10.1021/acs.jpcb.3c07779 -
Water Research Mar 2024UV light emitting diodes (LEDs) are considered the new frontier of UV water disinfection. As UV technologies continue to evolve, so does the need to understand...
UV light emitting diodes (LEDs) are considered the new frontier of UV water disinfection. As UV technologies continue to evolve, so does the need to understand disinfection mechanisms to ensure that UV treatment continues to adequately protect public health. In this research, two Escherichia coli (E. coli) strains (the wild type K12 MG1655 and K12 SP11 (ThiI E342K)) were irradiated with UV-C at 268 nm both independently and after exposure to UV-A (365 nm). A synergistic effect was found on the viability of the wild type E. coli K12 strain when UV-A irradiation was applied prior to UV-C. Sublethal UV-A doses, which had a negligible effect on cell viability alone, enhanced UV-C inactivation by several orders of magnitude. This indicated a specific cellular response mechanism to UV-A irradiation, which was traced to direct photolysis of the transfer RNA (tRNA), which are critical links in the translation of messenger RNA to proteins. The wild type K12 strain MG1655, containing tRNAs with a thiolated uridine, directly absorbs the UV-A light, which leads to a reduction in protein synthesis, making them more susceptible to UV-C induced damage. However, the K12 strain SP11 (ThiI E342K), with a point mutation in the thiI gene that prevents a post-transcriptional modification of tRNA, experienced less inactivation upon subsequent irradiation by UV-C. The growth rate of cells, which was inhibited by sublethal UV-A doses, was not inhibited in this mutant strain with the modified tRNA. Time-lapse microscopy with microfluidics showed that sub-lethal UV-A caused a transient, reversible, growth arrest in E. coli. However, once the growth resumed, the cell division time resembled that of unirradiated cells. Damage induced by UV-A impaired the recovery of damage induced by UV-C. Depending on the UV-A dose applied, the synergistic effect remained even when there was a time delay of several hours between UV-A and UV-C exposures. The effect of sublethal UV-A was reversible over time; therefore, the synergistic effect was strongest when UV-C was applied immediately after UV-A. Combining UV-A and UV-C irradiation may serve as a practical tool to increase UV disinfection efficacy, which could potentially reduce costs while still adequately protecting public health.
Topics: Escherichia coli; Ultraviolet Rays; Disinfection; Water Purification; RNA, Transfer
PubMed: 38295454
DOI: 10.1016/j.watres.2024.121189 -
Environmental Science & Technology Feb 2024Solar photoexcitation of chromophoric groups in dissolved organic matter (DOM), when coupled to photoreduction of ubiquitous Fe(III)-oxide nanoparticles, can...
Solar photoexcitation of chromophoric groups in dissolved organic matter (DOM), when coupled to photoreduction of ubiquitous Fe(III)-oxide nanoparticles, can significantly accelerate DOM degradation in near-surface terrestrial systems, but the mechanisms of these reactions remain elusive. We examined the photolysis of chromophoric soil DOM coated onto hematite nanoplatelets featuring (001) exposed facets using a combination of molecular spectroscopies and density functional theory (DFT) computations. Reactive oxygen species (ROS) probed by electron paramagnetic resonance (EPR) spectroscopy revealed that both singlet oxygen and superoxide are the predominant ROS responsible for DOM degradation. DFT calculations confirmed that Fe(II) on the hematite (001) surface, created by interfacial electron transfer from photoexcited chromophores in DOM, can reduce dioxygen molecules to superoxide radicals (O) through a one-electron transfer process. H nuclear magnetic resonance (NMR) and electrospray ionization Fourier-transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) spectroscopies show that the association of DOM with hematite enhances the cleavage of aromatic groups during photodegradation. The findings point to a pivotal role for organic matter at the interface that guides specific ROS generation and the subsequent photodegradation process, as well as the prospect of using ROS signatures as a forensic tool to help interpret more complicated field-relevant systems.
Topics: Reactive Oxygen Species; Dissolved Organic Matter; Ferric Compounds; Superoxides; Photolysis
PubMed: 38294779
DOI: 10.1021/acs.est.3c08752 -
The Science of the Total Environment Mar 2024We use the Community Multiscale Air Quality (CMAQv5.4) model to examine the potential impact of particulate nitrate (pNO) photolysis on air quality over the Northern...
We use the Community Multiscale Air Quality (CMAQv5.4) model to examine the potential impact of particulate nitrate (pNO) photolysis on air quality over the Northern Hemisphere. We estimate the photolysis frequency of pNO by scaling the photolysis frequency of nitric acid (HNO) with an enhancement factor that varies between 10 and 100 depending on pNO and sea-salt aerosol concentrations and then perform CMAQ simulations without and with pNO photolysis to quantify the range of impacts on tropospheric composition. The photolysis of pNO produces gaseous nitrous acid (HONO) and nitrogen dioxide (NO) over seawater thereby increasing atmospheric HONO and NO mixing ratios. HONO subsequently undergoes photolysis, producing hydroxyl radicals (OH). The increase in NO and OH alters atmospheric chemistry and enhances the atmospheric ozone (O) mixing ratio over seawater, which is subsequently transported to downwind continental regions. Seasonal mean model O vertical column densities without pNO photolysis are lower than the Ozone Monitoring Instrument (OMI) retrievals, while the column densities with the pNO photolysis agree better with the OMI retrievals of tropospheric O burden. We compare model O mixing ratios with available surface observed data from the U.S., Japan, the Tropospheric Ozone Assessment Report - Phase II, and OpenAQ; and find that the model without pNO photolysis underestimates the observed data in winter and spring seasons and the model with pNO photolysis improves the comparison in both seasons, largely rectifying the pronounced underestimation in spring. Compared to measurements from the western U.S., model O mixing ratios with pNO photolysis agree better with observed data in all months due to the persistent underestimation of O without pNO photolysis. Compared to the ozonesonde measurements, model O mixing ratios with pNO photolysis also agree better with observed data than the model O without pNO photolysis.
PubMed: 38281631
DOI: 10.1016/j.scitotenv.2024.170406