Quantum Yield Of Reaction Research Articles

Efficient sunlight-driven photocatalytic behavior of zinc sulfide nanorods towards Rose Bengal degradation

In this study, zinc sulfide nanorods (ZSNRs) were successfully synthesized by the solvothermal route. The structural, morphological, elemental composition, chemical state, surface charge, particle size, optical and electrochemical characterizations using powder X-ray diffraction (P-XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy, dynamic light scattering (DLS), UV–Vis spectroscopy, steady-state and time-resolved photoluminescence spectroscopy (PL), electrochemical impedance spectroscopy (EIS) and Mott–Schottky (MS) confirmed that the prepared zinc sulfide (ZnS) exhibits hexagonal wurtzite structure, rod-like morphology, excellent optical absorption, fast charge carrier decay, surface charge transfer behavior, and flat band potential. The photocatalytic performance of prepared ZSNRs photocatalyst was tested by monitoring the degradation of Rose Bengal (RB) dye aqueous solution under direct sunlight irradiation. The effects of catalyst dosage and dye concentration were also considered for the effective degradation of RB dye. The optimum catalyst dosage and concentration of dye were found to be 0.02 mg/mL and 10 µM, respectively. A maximum of 93% photocatalytic degradation efficiency (DE%) was achieved at 60 min of direct sunlight irradiation. The standard deviation in photocatalytic performance is found to be ± 0.89%. From the reactive species trapping experiment, the photocatalyst performance of RB dye over ZSNRS mainly depends on the species of holes and hydroxyl radicals rather than electrons and superoxide radicals. A 0.72 ± 0.09 quantum yield for the photodegradation reaction of ZSNRs was noticed. To the best of our knowledge, the present work is the first study to utilize ZSNRs as a photocatalyst for the effective degradation of RB dye.

Influence of Electron Acceptors and Donors on the Dye-Photosensitized Decomposition of 2-Mercaptobenzothiazole

It has been shown that the quantum yield of the dye-photosensitized decomposition of 2-mercaptobenzothiazole (MBT) in aqueous solutions increases in the case of irradiation of dyes in the presence of electron acceptors. In the presence of electron donors, the quantum yields of the photosensitized decomposition reaction of MBT either remains unchanged or decreases. The donor thiocyanate and iodide ions were the exception; in this case, this was due to the formation of radical anions in the subsequent reactions of iodine and thiocyanate radicals with their anions, respectively. A mechanism has been suggested for the photosensitization of 2-mercaptobenzothiazole decomposition by dyes in the presence of electron acceptors and donors.

Extreme Kinetics of Chemiluminescence in the Initiated Oxidation of Vegetable Lipids

During the oxidation of sunflower oil initiated by 2,2'-azo-bis-isobutyronitrile, which was used in this study as the model lipid system of plant origin, the previously unobserved form of kinetic chemiluminescence curves has been discovered. At the end of the induction period, during which chemiluminescence was suppressed by the antioxidants present in sunflower oil, instead of the expected smooth S-shaped output of the luminescence intensity at a significantly higher stationary level, a sharp surge in intensity was observed with its subsequent decrease to the stationary level. The standard kinetic scheme, which is used in most works on the effect of antioxidants on chemiluminescence in the chain free-radical oxidation of hydrocarbons, cannot explain the shape of the obtained kinetic curves. To explain the discovered phenomenon, an extended kinetic scheme, which takes into account the reactions of the initiator isobutyronitrile-peroxide radicals and their conversion to methyl-peroxide radicals, is proposed. It is shown that the observed extreme kinetics is possible only in the case of quantum yields of the chemiluminescence from the reaction of the initiator isobutyronitrile-peroxide radicals with the substrate peroxide radicals, which are 1–2 orders of magnitude higher than the quantum yields of other chemiluminescent reactions.

Study of Phototoxic Properties of Retinal and Its Derivatives in a Photoreceptor Cell by the Method of Pulsed Photolysis

It is believed that one of the causes of photodamage to the retina is the accumulation of all-trans-retinal (ATR) in the visual cells. However, the ATR is formed during photolysis inside the disk of the photoreceptor cell and transferred to the cytoplasm of the cell, where it is converted with a high yield to retinol, a nonphototoxic compound. Inside the disk, where ATR can accumulate, it can form Schiff bases, which are also not phototoxic compounds, with the amino groups of proteins and lipids. In addition, the resulting free retinal (R) isomers bind to specific retinal-binding proteins that can shield them from oxygen. Thus, the question on the concentrations in which free ATR can accumulate inside a cell is ambiguous. In this study, it is proposed to evaluate the concentration of free ATR in a cell by the yield of the excited triplet state, since neither the Schiff bases of ATR nor retinol are transformed into an excited triplet state. It is shown that 70% of ATR form Schiff bases in the equilibrium state in the native cell. This significantly reduces the likelihood that ATR is the main inducer of photodamage. Moreover, it is shown that the quantum yield of the formation reaction of an excited triplet state of R when it is bound to interfotoreceptor proteins is significantly reduced.

Quantitative evaluation of luminescence intensity from enzymatic luminescence reaction of coelenterazine and analogues

Recent advances in bioluminescence technology rely on the discovery of luciferin-luciferase pairs having excellent luminescence activity. Here, we focus on coelenterazine (CTZ) and its analogues and quantitatively investigate reaction factors, including bioluminescence reaction quantum yield (φBL) and enzyme reaction kinetics (turnover rate, kcat), determining the luminescence intensity to design brighter reaction systems. Initially, it was confirmed that the CTZ was kept stable during the storage and the φBL value measuring experiment in terms of comparative study using benzyl-protected CTZ. Using a luminometer whose absolute responsivity is calibrated for each luminescence reaction spectrum, we absolutely measured φBL and other reaction factors of CTZ and 3 types of blue-shifted CTZ analogues, CTZ 400a, 6-pi-H-CTZ and 6-pi-Ph-CTZ. The results suggested that there was no significant difference in reaction kinetics, but a clear difference in φBL (up to 22-fold), which was presumably due to an improvement in fluorescence quantum yield (φFL) of the corresponding coelenteramide (CTMD), oxidized form of CTZ. Our evaluation suggests that the design of CTZ analogues considering φFL is important for developing a bright luminescent reaction system.

Peculiar synergetic effect of γ-Fe2O3 nanoparticles and graphene oxide on MIL-53 (Fe) for boosting photocatalysis

Special enhanced synergistic effect of ultra-small γ-Fe2O3 and graphene oxide (GO) on MIL-53 (Fe) was achieved for boosting photocatalysis. Compared to traditional methods of surface coverage, the incorporation of γ-Fe2O3 (average size 2–3 nm) inside MOFs particles not only increased the light absorption of catalyst, but also formed numerous micro-heterojunctions with MOFs units and thus effectively facilitated the separation of photogenerated carriers. By supplying attachment sites for MOFs crystal, the functionalized GO reduced the size of MOFs particles to 100–200 nm, meanwhile improved their dispersibility. The active sites and quantum yield of photocatalytic reaction were also intensified benefiting from the large surface area and high electronic conductivity of GO. Therefore, the novel γ-Fe2O3-MIL-53(Fe)-GO composite exhibited the highest photocatalytic activity towards norfloxacin, with a removal rate of 92.8% in 90 min. The kinetic constant was 4.49-fold higher than that using pure MIL-53 (Fe), and 1.43-time greater than that in the system of MIL-53 (Fe) and hydrogen peroxide, which usually acted as efficient electron acceptors to increase the quantum yield and final photocatalytic performance of MOFs. Based on the identified intermediates, three NOR degradation pathways including the cleavage of piperazine ring, defluorination and decarboxylation, as well as the conversion of quinolones group were proposed. Photocatalytic mechanism investigation revealed the holes and hydroxyl radicals came from the reaction of electrons with oxygen played the important role in γ-Fe2O3-MIL-53(Fe)-GO photocatalysis. Moreover, the utilization of magnetic nanoparticles improved the recovery and recyclability of ternary catalyst.

Palette of Luciferases: Natural Biotools for New Applications in Biomedicine.

Optoanalytical methods based on using genetically encoded bioluminescent enzymes, luciferases, allow one to obtain highly sensitive signals, are non-invasive, and require no external irradiation. Bioluminescence is based on the chemical reaction of oxidation of a low-molecular-weight substrate (luciferin) by atmospheric oxygen, which is catalyzed by an enzyme (luciferase). Relaxation of the luciferin oxidation product from its excited state is accompanied by a release of a quantum of light, which can be detected as an analytical signal. The ability to express luciferase genes in various heterological systems and high quantum yields of luminescence reactions have made these tools rather popular in biology and medicine. Among several naturally available luciferases, a few have been found to be useful for practical application. Luciferase size, the wavelength of its luminescence maximum, enzyme thermostability, optimal pH of the reaction, and the need for cofactors are parameters that may differ for luciferases from different groups of organisms, and this fact directly affects the choice of the application area for each enzyme. It is quite important to overview the whole range of currently available luciferases based on their biochemical properties before choosing one bioluminescent probe suitable for a specific application.

ВЛИЯНИЕ ОСМОЛИТОВ НА БИОЛЮМИНЕСЦЕНТНУЮ РЕАКЦИЮ БАКТЕРИЙ: СТРУКТУРНО-ДИНАМИЧЕСКИЕ АСПЕКТЫ

The effects of viscous media with glycerol and sucrose (10-40%) on the kinetics of the bacterial bioluminescent reaction have been investigated by stopped-flow technique. Increment of quantum yield in media with 10% of both osmolytes was shown. Higher concentrations of glycerol, up to 30-40%, were found to reduce the efficiency of the reaction, while this effect was not observed in the media with sucrose. The molecular dynamics simulation was used to study the structure of bacterial luciferase surrounded by either water molecules solely or by mixture of water with various numbers of glycerol/sucrose molecules. It was found that both cosolvents at studied concentrations did not cause a significant change in conformation of bacterial luciferase. The calculated root mean square fluctuations for Cα-atoms of bacterial luciferase α-subunit indicated that the higher flexibility of the enzyme mobile loop could be responsible for increment of quantum yield in the presence of 10% of both osmolytes. The active site of bacterial luciferase was found to be accessible for glycerol molecules while sucrose did not enter catalytic gorge. Moreover, at 30% and 40% concentration the glycerol molecules were found to locate in the active site of bacterial luciferase throughout the whole simulation time (40 ns) and to exclude water molecules, which can explain the experimentally obtained reaction quantum yield decrease.

Long-Lived Photocatalysis Centers Created in ZnO via Resonant Exciton Excitation

ZnO together with TiO2 is a main photocatalyst for various redox reactions to convert light energy into a chemical one and to purify the environment. Intrinsic surface defects in ZnO—the vacancies in anionic and cationic sublattices (F-type and V-type centers)—allow creation of long-lived (up to 103 s) photocatalysis centers and, therefore, tenfold increase in quantum yield of reactions. Slow surface states—the photocatalysis centers—appear via diffusion of electrons and holes generated during the interband transitions in the bulk of a photoactivated sample. The transfer efficiency, however, decreases sharply because of recombination of charge carriers and losses during overcoming the surface Schottky barrier. Neutral energy carriers—excitons—were used in this work to decrease these losses during the energy transfer to a surface. High exciton binding energy in ZnO (60 meV) allows it to move at room temperature without decay. The exciton energy loss for radiation is effectively decreased in our experiments via formation of a 2D surface structure. The results confirm high efficiency of exciton channel to form surface long-lived photocatalysis F-centers and V‑centers during the photoadsorption and photodesorption processes of oxygen, which simulate full cycle of a redox photocatalytic reaction.

Efficient Use of Photons in Photoredox/Enamine Dual Catalysis with a Peptide-Bridged Flavin-Amine Hybrid.

An isoalloxazine (flavin) ring system and a secondary amine have been integrated through a short peptide linker with the aim of using photons as efficiently as possible in photoredox/enamine dual catalysis. We herein report a peptide-bridged flavin-amine hybrid that can catalyze α-oxyamination of aldehydes with TEMPO under weak blue light irradiation to achieve an extremely high quantum yield of reaction (Φ = 0.80).

Intrinsic kinetic model of photoautotrophic microalgae based on chlorophyll fluorescence analysis

As photoautotrophic microorganisms, microalgae feature complex mechanisms of photosynthesis and light energy transfer and as such studying their intrinsic growth kinetics is fairly difficult. In this article, the quantum yield of photochemical reaction was introduced in a study of microalgal kinetics to establish an intrinsic kinetic model of photoautotrophic microalgal growth. The blue-green algae Synechococcus sp. PCC7942 was used to verify the kinetic model developed using chlorophyll fluorescence analysis and growth kinetics determination. Results indicate that the kinetic model can realistically reflect the light energy utilization efficiency of microalgae as well as their intrinsic growth kinetic characteristics. The model and method proposed in this article may be utilized in intrinsic kinetics studies of photoautotrophic microorganisms.

Determination of the quantum yield of a heterogeneous photocatalytic reaction employing a black body photoreactor

Abstract Quantum yields of the photocatalytic DCA degradation in aqueous titanium dioxide suspensions (Hombikat UV100, Aeroxide P25) were determined employing a black body like photoreactor. The amounts of photons absorbed by the photocatalysts per unit time were determined by chemical actinometry varying the photon flux and the photon flux density. The photocatalytic DCA degradation experiments were performed under zero order conditions regarding the concentration of the probe compound. The obtained results suggest that the quantum yield of the photocatalytic DCA degradation depends on the photon flux density. Only the low flux density resulting from a large surface area of the light inlet seems to allow the determination of a quantum yield as a photocatalyst-inherent property.

Kinetics of Direct Photoinduced Addition of Carbosilane Thiols with Bulky Groups to Polyallylcarbosilane

The kinetics of the addition of carbosilane thiols of various structures to a hyperbranched polyallylcarbosilane matrix in n-hexane solution under direct photoinitiation is studied. A kinetic scheme that makes it possible to describe the photoaddition reaction at the quantitative level is proposed. The reaction rate constants are determined, and the dependence of the differential quantum yield of the photochemical reaction on the kinetic parameters and the concentration of allyl groups in the polyallylcarbosilane matrix is obtained. The assignment of the absorption bands to the corresponding components of the reaction system is confirmed by the quantum-chemical calculations of transition energies and oscillator strengths of the chromophore groups of thiols and the resulting thioesters. It is shown that the lowest rate of thiol-ene addition is observed for thiol with the smallest length of a polymethylene spacer between sulfur and silicon atoms.

β-Selective Aroylation of Activated Alkenes by Photoredox Catalysis.

Late-stage synthesis of α,β-unsaturated aryl ketones remains an unmet challenge in organic synthesis. Reported herein is a photocatalytic non-chain-radical aroyl chlorination of alkenes by a 1,3-chlorine atom shift to form β-chloroketones as masked enones that liberate the desired enones upon workup. This strategy suppresses side reactions of the enone products. The reaction tolerates a wide array of functional groups and complex molecules including derivatives of peptides, sugars, natural products, nucleosides, and marketed drugs. Notably, addition of 2,6-di-tert-butyl-4-methyl-pyridine enhances the quantum yield and efficiency of the cross-coupling reaction. Experimental and computational studies suggest a mechanism involving PCET, formation and reaction of an α-chloro-α-hydroxy benzyl radical, and 1,3-chlorine atom shift.

Solvent Effects on the Absorption Profile, Kinetic Stability, and Photoisomerization Process of the Norbornadiene–Quadricyclanes System

Molecular photoswitches based on the norbornadiene-quadricyclane (NBD-QC) couple can be used to store solar energy and to release the stored energy as heat on demand. In this context, the energy storage time as well as the quantum yield of the energy storing reaction are important parameters. Here, we explore for the first time solvent effects on these processes for a series of four NBD-QC compounds in four different solvents with different polarity (acetonitrile, tetrahydrofuran, toluene, and hexane). We show that the energy storage time of the QC forms can vary by up to a factor of 2 when going from the most to the least polar solvent. Moreover, we show that for the norbornadiene derivatives with an asymmetric 1,2 substitution pattern, the quantum yield of conversion is highly solvent dependent, whereas this is not the case for the symmetrically substituted compounds. The spectroscopic observations are further rationalized using classical molecular dynamics (MD) simulations and time-dependent density functional theory (TDDFT) calculations. These demonstrate the importance of vibrational and rotational excitations for obtaining broad-band absorption, which is a prerequisite for capturing a wide range of the solar spectrum.

Effect of soil salinity on growth, metal distribution and photosynthetic performance of two Lycium species

The effect of salinity on gas exchange and fluorescence characteristics in Lycium barbarum and Lycium chinense grown on nonsaline and saline soils was investigated. The distribution of Na+ between three types of substrates and different organs showed acropetal concentration gradient for Na+ accumulation only in L. barbarum grown on peat-moss-perlite and saline soil. Selective uptake of K+ over Na+ in the L. barbarum leaves was established. All plants grown on saline soil showed a slight inhibition of PSII activity as revealed by the quantum yield of the primary photochemical reaction. Intersystem electron transport, reduction of the end electron acceptors, and the performance index of photosynthesis declined to a greater extent in L. barbarum than that in L. chinense. The higher tolerance of L. chinense to salt stress was accompanied with the higher overall photosynthetic performance.

QM/MM Photodynamics of Retinal in the Channelrhodopsin Chimera C1C2 with OM3/MRCI

AbstractThe photoisomerization of all‐trans retinal in channelrhodopsins triggers the opening of a cation channel in the membrane of certain green algae. The stimulus resulting from cell depolarization enables the algae to perceive and react to the present lighting conditions. This property makes channelrhodopsins especially interesting for neuroscientific applications in optogenetics. We investigate the initial photoreaction in the channelrhodopsin chimera C1C2 with a combined quantum mechanical/molecular mechanical (QM/MM) strategy. For geometry optimizations, the OM3/RHF and OM3/MRCI/Amber protocols are used. Trajectory surface hopping calculations are performed with OM3/MRCI/Amber and a statistically relevant number of molecules to obtain reaction rates and quantum yields. The utilized models include a direct hydrogen bond of the retinal Schiff base to the proposed counterions in C1C2, i. e. either toward glutamate or aspartate. Static and dynamic aspects are compared to experimental findings including time constants and spectral traces. The calculations provide a rationale for the observed short and long time components in the photokinetics of C1C2 and yield detailed insight into the photoreaction mechanisms that include bicycle pedal and hula twist motions.

Analysis of Correlations between the Indexes of Light-Dependent Reactions of Photosynthesis and the Photochemical Reflectance Index (PRI) in Pea Leaves under Short-Term Illumination

The photochemical reflectance index (PRI) is related to the conversion of violoxanthin into zeaxanthin in the xanthophyll cycle and thereby reflects the activity of electron-transport chain in chloroplasts. The PRI is recorded by a relatively simple and non-invasive technique; therefore it can be used in a perspective approach for the remote monitoring of photosynthetic processes and detection of photosynthetic stress. However, correlation coefficients between PRI and photosynthetic parameters vary widely in different studies; one of the possible causes of such variability under natural conditions may be the changes in illumination and the development of transient processes in the photosynthetic apparatus. In the present study, the influence of the duration of illumination (a minute interval) on the relationship between parameters of light-dependent reactions of photosynthesis and the PRI has been investigated. The photosynthetic parameters and PRI were determined in pea leaves. A high negative correlation has been found between changes of PRI induced by illumination and changes in the quantum yields of the photochemical reactions of photosystems I and II; the PRI changes did not correlate with changes of non-photochemical quenching. There was a positive correlation between the quantum yields of photochemical reactions and PRI averaged over the entire time range and a negative correlation in the case of non-photochemical quenching and PRI. The absolute value of the correlation coefficient of PRI with the parameters of the light-dependent reactions of photosynthesis increased with increasing duration of illumination. Thus, the correlation of PRI with the parameters of the light-dependent reactions of photosynthesis in a pea leaf may depend on the duration of illumination, at least in a minute interval.

Exploring the ultrafast dynamics of a diarylethene derivative using sub-10 fs laser pulses.

A diarylethene derivative, 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)perfluorocyclopentene (DMP), is a photoswitch molecule utilizing a reversible aromatic ring-opening reaction. The quantum yield of the ring-opening reaction is however remarkably low. We investigate the origin of this behaviour by means of ultrafast transient absorption spectroscopy utilizing sub-10 fs pulses, which is an invaluable tool for simultaneously studying both the electronic and the vibrational molecular dynamics. Namely, a noncollinear optical parametric amplifier (NOPA) generating sub-10 fs pulses in the spectral range 605-750 nm is employed. The transient absorption signal is modulated by several vibrational modes, which are compared with experimental and computational Raman spectra and then assigned to the ground or excited electronic state. We observe that the most pronounced vibrational mode - the ethylenic stretching mode at a frequency of 1501 cm-1 - exhibits instantaneous frequency and amplitude modulation. The observed modulations occur due to weak coupling with another 1431 cm-1 stretching mode mediated by a vibrational mode of low frequency, i.e. around 60 cm-1. Fast internal conversion S1 → S0 originates in a relaxation through a conical intersection (found by density-functional theory computations), facilitated by the two aforementioned stretching modes.

Долгоживущие центры фотокатализа, создаваемые в ZnO резонансным возбуждением экситона

Along with TiO_2, ZnO is the main photocatalyst for a wide class of redox reactions used to convert light energy into chemical and for environmental cleanup. It has been shown that the creation in ZnO of surface intrinsic defects in ZnO i.e. vacancies in the anionic and cationic sublattices (F-type and V-type centers) - makes it possible to create long-lived (up to 10^3 s) photocatalysis centers and thus fundamentally (tens of times) to increase the quantum yield of reactions. Slow surface states — photocatalysis centers — are created by the diffusion of electrons and holes generated during interband transitions in the volume of the photoactivated sample. However, the transfer efficiency is sharply reduced due to carrier recombination and losses when overcoming the Schottky surface barrier. In this work, In order to reduce these losses during energy transfer to the surface, we used in this work neutral energy carriers — excitons. The high (60 meV) exciton binding energy in ZnO allows it to move at room temperature without decay. The radiation loss of the exciton energy in our experiments is effectively reduced by the formation of a surface 2D structure. The results obtained confirm the high efficiency of the exciton channel for the formation of surface long-lived F and V centers of photocatalysis in the processes of oxygen photoadsorption and photodesorption, imitating the full cycle of the redox photocatalytic reaction.