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The Journal of Physical Chemistry. B Feb 2023Characterization of short-lived reaction intermediates is essential for elucidating the mechanism of the reaction catalyzed by metalloenzymes. Here, we demonstrated that...
Characterization of short-lived reaction intermediates is essential for elucidating the mechanism of the reaction catalyzed by metalloenzymes. Here, we demonstrated that the photolysis of a caged compound under cryogenic temperature followed by thermal annealing is an invaluable technique for trapping of short-lived reaction intermediates of metalloenzymes through the study of membrane-integrated nitric oxide reductase (NOR) that catalyzes reductive coupling of two NO molecules to NO at its heme/nonheme Fe binuclear center. Although NO produced by the photolysis of caged NO did not react with NOR under cryogenic temperature, annealing to ∼160 K allowed NO to diffuse and react with NOR, which was evident from the appearance of EPR signals assignable to the = 3/2 state. This indicates that the nonheme Fe-NO species can be trapped as the intermediate. Time-resolved IR spectroscopy with the use of the photolysis of caged NO as a reaction trigger showed that the intermediate formed at 10 μs gave the NO stretching frequency at 1683 cm typical of nonheme Fe-NO, confirming that the combination of the cryo-photolysis of caged NO and annealing enabled us to trap the reaction intermediate. Thus, the cryo-photolysis of the caged compound has great potential for the characterization of short-lived reaction intermediates.
Topics: Nitric Oxide; Photolysis; Oxidoreductases; Metalloproteins
PubMed: 36602896
DOI: 10.1021/acs.jpcb.2c05852 -
Chemosphere Feb 2022In this work, the photo reactivity of ferric oxalate (Fe(III)-Ox) complex in atmospheric particles was investigated. Raman spectroscopy was used to explore the mechanism...
In this work, the photo reactivity of ferric oxalate (Fe(III)-Ox) complex in atmospheric particles was investigated. Raman spectroscopy was used to explore the mechanism and kinetics of Fe(III)-Ox photolysis occurring at the aqueous/gas interface, inside the droplet and in bulk solution. Ferrous carbonate (FeCO) was detected indicating that carbonate ion (CO) formed inside the droplets would compete with oxalate ligands for iron complexation. A higher concentration of photoproduct Fe(II)-Ox was observed at the surface and inside of the droplets than in bulk solution. In particular, Fe(III)-Ox on the droplet surface was quickly reduced with light and Fe(II)-Ox concentration gradually decreased with irradiation time. The evolution of Fe(II)-Ox concentration was similar inside the droplet and in bulk solution with a trend of first increasing and then gradually decreasing during irradiation time. Although FeCO would hinder Fenton intermediate reaction, the photolysis rate of Fe(III)-Ox in droplets was almost two orders of magnitude times faster than that observed during bulk experiment. In general, the photolysis mechanism and kinetics of Fe(III)-Ox in aqueous/air interface, inside of droplet and bulk solution were distinct, and the production of oxide species from the atmospheric Fe(III)-Ox droplets was underestimated.
Topics: Ferric Compounds; Ferrous Compounds; Iron; Oxalic Acid; Photolysis
PubMed: 34864008
DOI: 10.1016/j.chemosphere.2021.133127 -
British Journal of Pharmacology Aug 19961. We studied the effects of flash photolysis on the novel enantiomeric cardiac inotropes EMD 57033 (a calcium sensitizer) and EMD 57439 (a phosphodiesterase III...
1. We studied the effects of flash photolysis on the novel enantiomeric cardiac inotropes EMD 57033 (a calcium sensitizer) and EMD 57439 (a phosphodiesterase III inhibitor) in rat isolated ventricular trabeculae. 2. In skinned trabeculae, EMD 57439 had no effect on force production, consistent with lack of an active cyclic AMP system in this preparation. In contrast, EMD 57033 potentiated force at partial and maximal activation. A single flash of near u.v. light given at partial activation (30-70%) reduced force potentiation by 52.4 +/- 5.2%. No effect was produced by flashes in the presence of EMD 57439 or in the absence of either drug. 3. The time course of relaxation induced by EMD 57033 photolysis was indistinguishable from that obtained on deactivating the muscle by rapidly lowering Ca2+ using photolysis of the caged chelator of calcium, diazo-2. 4. In intact, twitching trabeculae, EMD 57033 increased diastolic and peak force and slowed relaxation. These effects were simultaneously reduced by a light flash. In these muscles EMD 57439 reduced force, without affecting the twitch time course. These effects were also reduced by a light flash. 5. The u.v. absorbance spectra of EMD 57033 and EMD 57439 were identical. After photolysis optical density decreased substantially and the peak shifted from 320 nm to 280 nm. 6. The proton n.m.r. spectra of these compounds were identical. The main change post-photolysis was a decrease in the proton signal associated with the enantiomeric carbon atom. 7. This novel manipulation of the molecular structure of EMD 57033 and EMD 57439 within an experiment thus provides direct evidence linking calcium sensitization to a particular molecular structure. The three main effects of the sensitizer on the twitch were simultaneously abolished and may be mechanistically linked. Flash photolysis may be a useful tool for further investigations of the actions of these compounds. In particular, flash photolysis of the sensitizer represents a novel method of rapidly deactivating cardiac muscle.
Topics: Animals; Calcium; Male; Phosphodiesterase Inhibitors; Photolysis; Quinolines; Rats; Rats, Wistar; Thiadiazines
PubMed: 8864540
DOI: 10.1111/j.1476-5381.1996.tb15641.x -
Chemosphere Jun 2007The photolysis of nonylphenol ethoxylates with an average oligomers length of ten ethoxylate units (NPEO(10)) in aqueous solution under UV, as well as the influence of...
The photolysis of nonylphenol ethoxylates with an average oligomers length of ten ethoxylate units (NPEO(10)) in aqueous solution under UV, as well as the influence of humic acid (HA) on the photolysis was studied. A 125W high-pressure mercury lamp was employed as the light source. The intermediate products from the photolysis were determined by LC-MS. The results indicated that NPEO(10) underwent direct photolysis upon exposed to UV. The degradation pathway was complex. Besides the generally proposed degradation pathway of ethylene oxide (EO) side chains shortening, the oxidation of alkyl chain and EO chain led to intermediates having both a carboxylated (as well as carbonylated) ethoxylate and alkyl chain of varying lengths. The hydrogenation of benzene ring was also detected. The kinetics data showed that the first order reaction kinetics could be well used to describe the kinetics of NPEO(10) degradation. In the presence of dissolved organic matter by HA addition, the performance of NPEO(10) photodegradation was reduced. The photolysis rate decreased with increased HA concentration.
Topics: Environmental Pollutants; Ethylene Glycols; Humic Substances; Kinetics; Photolysis; Ultraviolet Rays
PubMed: 17280701
DOI: 10.1016/j.chemosphere.2006.12.055 -
The Science of the Total Environment Apr 2020In this work, nine types of combination advanced oxidation processes/zero-valent iron (AOP-ZVI) were tested, in order to determine if any of these combinations...
In this work, nine types of combination advanced oxidation processes/zero-valent iron (AOP-ZVI) were tested, in order to determine if any of these combinations demonstrate good chances as pretreatment for the biological degradation processes of organochlorinated pollutants. To do this, the changes undergone in the respirometric behavior, toxicity and short-term biodegradability were compared. The three AOPs studied were anodic oxidation with mixed metal oxides anodes (AO-MMO), with boron doped diamond anodes (AO-BDD) and photolysis and they were evaluated in three different modes: without any addition of ZVI, with ZVI-dehalogenation as pre-treatment and with ZVI-dehalogenation simultaneous to the AOP treatment. Clopyralid has been used as a model of chlorinated hydrocarbon pollutant. Results show that technologies proposed can successfully treat wastes polluted with clopyralid and the biological characteristics of the waste are significantly modified by dehalogenating the waste with ZVI, either previously to the treatment or simultaneously to the treatment, being the information provided by the three techniques very important in order to evaluate later combinations of the advanced oxidation technologies with biological treatments.
Topics: Boron; Diamond; Electrodes; Electrolysis; Oxidation-Reduction; Photolysis
PubMed: 31955107
DOI: 10.1016/j.scitotenv.2020.136647 -
The Science of the Total Environment Sep 2022Excited triplet species play an important role in the photolytic formation of O from carbonyls, but the related mechanism is still uncertain, due to lack of direct...
Excited triplet species play an important role in the photolytic formation of O from carbonyls, but the related mechanism is still uncertain, due to lack of direct evidence. In this study, steady-state and transient photolysis of eleven carbonyls to produce O was investigated. Dicarbonyl displayed greater O production ability than monocarbonyl, while dicarbonyl containing both ketone and carboxyl groups connected by CC bond (i.e., pyruvic acid (PA)) showed the highest O steady-state concentration ([O]). For the first time, the production of PA* from PA with narrow energy gap was confirmed by laser flash photolysis technique and the second-order decay rate constant of PA* was 2.78 × 10 M s. Quenching results verified the dominant contribution of PA* to O production from PA. Addition of inorganic salt or increase in solution pH showed negligible effect on PA*, but significantly decreased the [O] of PA by up to two orders of magnitude, due to reduction of hydrate content. Photolysis of methylglyoxal and dimethylamine mixture led to higher content of excited triplet species at pH ≈ 11 and remarkably enhanced [O], which was 2.3 times of that from PA and dimethylamine mixture. These findings provide direct evidence for the contribution of transient species from carbonyls or their product to O formation in atmospheric environment.
Topics: Dimethylamines; Oxygen; Photolysis
PubMed: 35508234
DOI: 10.1016/j.scitotenv.2022.155464 -
Scientia Sinica. Series B, Chemical,... Apr 1984The transient absorption spectra of the initial UV-photolysis products of insulin and des-pentapeptide (B26-30)-insulin (DPI) were determined and compared with that of...
The transient absorption spectra of the initial UV-photolysis products of insulin and des-pentapeptide (B26-30)-insulin (DPI) were determined and compared with that of free tyrosine. The far-UV band of the spectra (less than 300 nm) has not been reported before. Their main initial photoproducts are p-alanylphenoxyl radical (lambda max = 410,390 nm) and an unidentified radical (lambda max = 270 nm). The photolysis yields are closely correlative with the dissociation rate of hydroxyl group on phenol ring of tyrosine residues, which in turn depends on the exposed degree of these residues. The quantum yields of the phenoxyl radicals formed in photolysis of insulin and DPI were determined and compared with that of free tyrosine. Based on the comparison, the number of light accessible tyrosine residue in insulin and DPI can be calculated, which provides more quantitative information on the exposed degree of tyrosine residues in these two proteins.
Topics: Hydrogen-Ion Concentration; Insulin; Photolysis; Protein Conformation; Tyrosine
PubMed: 6379874
DOI: No ID Found -
The Journal of Physical Chemistry. A Nov 2011Two different reaction types for the photolysis of pyridoxine-aromatic ring-opening and photodissociation-have been studied in the Density Functional Theory (DFT)...
Two different reaction types for the photolysis of pyridoxine-aromatic ring-opening and photodissociation-have been studied in the Density Functional Theory (DFT) framework. Our results show that neither photolytic ring-opening, dehydroxymethylation, demethylation nor dehydroxylation from the aromatic ring can be induced spontaneously in UV-irradiated pyridoxine, due to the high barriers along the reaction coordinates in the excited states. However, the simultaneous dehydroxylation of the C4-bound hydroxymethyl group and dehydrogenation of the ring bound hydroxyl substituent, selectively generating ortho-quinone methide and water, does occur after UV exposure. The findings correlate very well with available experimental data. The geometries of pyridoxine, its various transition states and products are optimized in the ground and first excited states in vacuum within the TD-DFT formalism.
Topics: Molecular Structure; Photolysis; Pyridoxine; Quantum Theory
PubMed: 21995706
DOI: 10.1021/jp205724k -
Bioresource Technology Mar 2018In this study, bacterium Pseudomonas sp. strain D was proved to be the main partner assisting Chlamydomonas reinhardtii in improving photolysis-mediated H production and...
In this study, bacterium Pseudomonas sp. strain D was proved to be the main partner assisting Chlamydomonas reinhardtii in improving photolysis-mediated H production and a good partner for promoting H production by the green algae Chlorella and Scenedesmus. In strain D partnered algal-bacterial co-culture, the relative O content in the headspace plus the dissolved oxygen in the culture medium were rapidly consumed by bacterial growth, resulting in a completely anaerobic environment that proved suitable for the activation of algal hydrogenase. Moreover, algal-bacterial cooperation was able to slow the reduction of chlorophyll, enhance starch accumulation, and maintain protein content, which are the potential factors whose control provides an opportunity for improving algal H production. This study systematically analyzed the main pathway responsible for H production by algal-bacterial cooperation and the potential mechanisms for improvement, and proposed an efficient and durable algal-bacterial cooperation system for improving photolysis-mediated H production by green algae.
Topics: Chlamydomonas reinhardtii; Chlorella; Hydrogen; Hydrogenase; Photolysis
PubMed: 29291532
DOI: 10.1016/j.biortech.2017.12.072 -
Photochemical & Photobiological... May 2022Although reported several decades ago, 3,3',5,5'-tetramethoxybenzoin esters have not been used as a common photolabile protecting group, contrary to their unsymmetrical...
Although reported several decades ago, 3,3',5,5'-tetramethoxybenzoin esters have not been used as a common photolabile protecting group, contrary to their unsymmetrical 3',5'-dimethoxybenzoin analogues. While the properties of the latter are superior, their tedious synthesis and chemical instability represent a drawback. In this article, we describe a reliable synthetic access to the symmetrical tetramethoxybenzoin derivatives, and show that their photochemical behaviour remain interesting, in particular chromatically orthogonality with respect to nitroveratryl esters.
Topics: Esters; Photochemistry; Photolysis
PubMed: 35028893
DOI: 10.1007/s43630-021-00150-7