The mechanism and kinetics of the atmospheric oxidation of CF(CF)CHCH (HFC-1447fz) by hydroxyl radicals: investigation.

The oxidation of 3,3,4,4,5,5,5-heptafluoro-1-pentene (HFC-1447fz) by hydroxyl radicals plays a crucial role in atmospheric conditions. By employing the CCSD(T)/cc-pVTZ//M06-2X/6-311++G(d,p) level of theory, the detailed reaction mechanism, kinetics and atmospheric implications of the degradation of HFC-1447fz by hydroxyl radicals were investigated. Compared to H-abstraction channels, the OH addition reaction is determined to be more favorable initial pathways in the degradation processes of HFC-1447fz.

Size-controlled growth of ZnSe nanocrystals for high-performance photocatalytic HO production in pure water.

Semiconductor photocatalysis is deemed as a novel and promising process that can produce HO from earth-abundant water and gaseous dioxygen using sunlight as the energy supply. The searching of novel catalysts for photocatalytic HO production has received increasing attention in the last few years. Herein, size-controlled growth of ZnSe nanocrystals was realized a solvothermal method by varying the amount of Se and KBH.

The Mechanism and Kinetics Model of Degradation of Dicarboxylic Acids by Hydroxyl Radicals under Atmospheric Conditions.

The atmospheric degradation mechanism of dicarboxylic acids (DCAs) initiated by hydroxyl radicals has been theoretically investigated at the DLPNO-CCSD(T)/def2-TZVP//BH&HLYP/6-311++G(d,p) level of theory. In the presence of O, the degradation of DCAs by hydroxyl radicals takes place through a two-step mechanism: the α-H elimination and the degradation of the peroxyl radical intermediate. The latter degradation mechanism is easy to proceed for the exothermic process of radical recombination.

True Grit in Learning Math: The Math Anxiety-Achievement Link Is Mediated by Math-Specific Grit.

In this study, we tested a possible mechanism of the association between math anxiety and math achievement: the mediating role of math-specific grit (i.e., sustaining effort in the face of adversity when learning math).

Evidence and evolution of Criegee intermediates, hydroperoxides and secondary organic aerosols formed via ozonolysis of α-pinene.

α-Pinene, the most abundant monoterpene in the atmosphere, accounts for more than 50% of global monoterpene emission. Though its reaction with ozone has been generally perceived as a major source of secondary organic aerosols (SOAs), direct evidence of its reaction intermediates (RI) and their evolution remain lacking. Here we study the ozonolysis of α-pinene between 180 and 298 K using a long-path, temperature-variable aerosol cooling chamber coupled to a rapid-scan time-resolved Fourier transform infrared spectrometer.

Phthalide Derivatives from Angelica Sinensis Decrease Hemoglobin Oxygen Affinity: A New Allosteric-Modulating Mechanism and Potential Use as 2,3-BPG Functional Substitutes.

Angelica sinensis (AS), one of the most versatile herbal medicines remains widely used due to its multi-faceted pharmacologic activities. Besides its traditional use as the blood-nourishing tonic, its anti-hypertensive, anti-cardiovascular, neuroprotective and anti-cancer effects have been reported. Albeit the significant therapeutic effects, how AS exerts such diverse efficacies from the molecular level remains elusive.

Molecular Basis of the Antioxidant Capability of Glutathione Unraveled via Aerosol VUV Photoelectron Spectroscopy.

Glutathione (GSH), the most abundant nonenzymatic antioxidant in living systems, actively scavenges various exogenous/endogenous oxidizing species, defending important biomolecules against oxidative damages. Although it is well established that the antioxidant activity of GSH originates from the cysteinyl thiol (-SH) group, the molecular origin that makes the thiol group of GSH a stronger reducing agent than other thiol-containing proteins is unclear. To gain insights into the molecular basis underlying GSH's superior antioxidant capability, here we report, for the first time, the valence electronic structures of solvated GSH in the aqueous aerosol form via the aerosol vacuum ultraviolet photoelectron spectroscopy technique.

VUV Photoelectron Spectroscopy of Cysteine Aqueous Aerosols: A Microscopic View of Its Nucleophilicity at Varying pH Conditions.

Cysteine (Cys) is unique due to its highly reactive thiol group. It often regulates the biological function of proteins by acting as the redox site. Despite its biological significance, however, the valence electronic structure of Cys under the aqueous environments remains unavailable.

Time-resolved and mechanistic study of the photochemical uncaging reaction of the o-hydroxycinnamic caged compound.

The o-hydroxycinnamic derivatives represent efficient caged compounds that can realize quantification of delivery upon uncaging, but there has been lack of time-resolved and mechanistic studies. We used time-resolved infrared (TRIR) spectroscopy to investigate the photochemical uncaging dynamics of the prototype o-hydroxycinnamic compound, (E)-3-(2-hydroxyphenyl)-acrylic acid ethyl ester (HAAEE), leading to coumarin and ethanol upon uncaging. Taking advantage of the specific vibrational marker bands and the IR discerning capability, we have identified and distinguished two key intermediate species, the cis-isomers of HAAEE and the tetrahedral intermediate, in the transient infrared spectra, thus providing clear spectral evidence to support the intramolecular nucleophilic addition mechanism following the trans-cis photoisomerization.

Mechanism of the deamination reaction of isoguanine: a theoretical investigation.

Mechanisms of the deamination reactions of isoguanine with H2O, OH(-), and OH(-)/H2O and of protonated isoguanine (isoGH(+)) with H2O have been investigated by theoretical calculations. Eight pathways, paths A-H, have been explored and the thermodynamic properties (ΔE, ΔH, and ΔG), activation energies, enthalpies, and Gibbs energies of activation were calculated for each reaction investigated. Compared with the deamination reaction of isoguanine or protonated isoguanine (isoGH(+)) with water, the deamination reaction of isoguanine with OH(-) shows a lower Gibbs energy of activation at the rate-determining step, indicating that the deamination reaction of isoguanine is favorably to take place for the deprotonated form isoG(-) with water.

Formation of guanine-6-sulfonate from 6-thioguanine and singlet oxygen: a combined theoretical and experimental study.

As an end metabolism product of the widely used thiopurine drugs, 6-thioguanine (6-TG) absorbs UVA and produces (1)O2 by photosensitization. This unusual photochemical property triggers a variety of DNA damage, among which the oxidation of 6-TG itself by (1)O2 to the promutagenic product guanine-6-sulfonate (G(SO3)) represents one of the major forms. It has been suspected that there exists an initial intermediate, G(SO), prior to its further oxidation to G(SO2) and G(SO3), but G(SO) has never been observed.

[2+2] Photocycloaddition reaction dynamics of triplet pyrimidines.

Taking the 266 nm excited pyrimidine (uracil or thymine) with cyclopentene as model reaction systems, we have examined the photoproduct formation dynamics from the [2 + 2] photocycloaddition reactions of triplet pyrimidines in solution and provided mechanistic insights into this important DNA photodamage reaction. By combining two compliment methods of nanosecond time-resolved transient IR and UV-vis laser flash-photolysis spectroscopy, the photoproduct formation dynamics as well as the triplet quenching kinetics are measured. Characteristic IR absorption bands due to photoproduct formation have been observed and product quantum yields are determined to be ∼0.

Reaction mechanisms of a photo-induced [1,3] sigmatropic rearrangement via a nonadiabatic pathway.

Time-resolved Fourier transform infrared absorption spectroscopy measurements and B3LYP/cc-pVDZ calculations have been conducted to characterize the reaction dynamics of a remarkable photoinduced 1,3-Cl sigmatropic rearrangement reaction upon 193 or 266 nm excitation of the model systems acryloyl chloride (CH(2)CHCOCl) and crotonyl chloride (CH(3)CHCHCOCl) in solution. The reaction is elucidated to follow nonadiabatic pathways via two rapid ISC processes, S(1) --> T(1) and T(1) --> S(0), and the S(1)/T(1) and T(1)/S(0) surface intersections are found to play significant roles leading to the nonadiabatic pathways. The S(1) --> T(1) --> S(0) reaction pathway involving the key participation of the T(1) state is the most favorable, corresponding to the lowest energy path.

Theoretical investigation of direct amination of beta-ketoesters catalyzed by copper(II)-bisoxazoline(BOX).

The mechanism of the direct amination of beta-keto esters catalyzed by copper(II)-bisoxazoline has been studied by means of density functional theory of B3LYP method. The computational results support the present mechanism, which involves (i) the generation of the enol from beta-keto esters, which coordinates to copper(II)-bisoxazoline. The coordination step appears to be fast, exothermic, and irreversible.