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1.
Chemosphere ; 349: 140796, 2024 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-38029936

RESUMEN

Atmospheric humic-like substances (HULIS) could affect regional climate due to their strong light-absorbing capacity. Daily fine particulate matter (PM2.5) samples were collected from December 18, 2016 to January 8, 2017 at an urban site in Chongqing, Southwest China. The mean concentration of HULIS in terms of carbon (HULIS-C) was 6.4 ± 3.4 µg m-3, accounting for 72% of water-soluble organic carbon. The mass absorption efficiency at 365 nm (MAE365) and absorption Ångström index (AAE) of atmospheric HULIS were 2.8 ± 0.30 m2 g-1 C and 4.6 ± 0.37, respectively. Good correlations between the light absorption coefficients of HULIS at 365 nm (Abs365) and the concentrations of K+, elemental carbon, NO3-, and NH4+ were observed, with correlation coefficients higher than 0.83, indicating that biomass burning and secondary formation were potential sources of light-absorbing HULIS, as evidenced by abundant fluorescent components related to less-oxygenated HULIS. Comparing the changes in Abs365 values, concentrations of major water-soluble inorganic ions and carbonaceous compounds in PM2.5, and environmental factors during the clean and pollution periods, we found that extensive biomass burning during the pollution period contributed significantly to the increase of Abs365 values. Moreover, the aerosol pH during the pollution period was close to 4, and NO2 concentration and aerosol water content were about 1.6 and 2.7 times higher than those during the clean period, respectively, which were favorable to form secondary HULIS through aqueous phase reactions in the presence of high NOx, resulting in an evident increase in its light absorption. Knowledge generated from this study is critical for evaluating the regional radiative forcing of brown carbon in southwest China.


Asunto(s)
Contaminantes Atmosféricos , Contaminantes Atmosféricos/análisis , Sustancias Húmicas/análisis , Agua/química , Monitoreo del Ambiente/métodos , Material Particulado/análisis , Carbono/análisis , Aerosoles/análisis
2.
Chemosphere ; 363: 142845, 2024 Sep.
Artículo en Inglés | MEDLINE | ID: mdl-39004144

RESUMEN

Nitroaromatic compounds (NACs) in ambient particles are of great concern due to their adverse effects on human health and climate. However, investigations on the characteristics and potential sources of NACs in Southwest China are still scarce. In this study, a field sampling campaign was carried out in the winter of 2022 at a suburban site in Mianyang, Southwest China. A direct injection liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed to rapidly determine 10 NACs in fine particulate matter (PM2.5) extracts. The method was sensitive for the quantification of the NACs, with a limit of quantification (LOQ) in the range of 0.092-0.52 ng mL-1. Then, the developed method was applied to determine the concentrations of nitrophenols (NPs), nitrocatechols (NCs), nitrosalicylic acids (NSAs), and nitronaphthol in PM2.5 in Mianyang. The average concentration of total NACs was 78.2 ± 31.2 ng m-3, with daily concentrations ranging from 20.7 to 127.9 ng m-3. Among the measured NACs, 4-nitrocatechol was the most abundant, accounting for 57.8% of the NACs in winter. The five NPs compounds together contributed to 14% of the NACs, which was lower than in other Chinese cities due to the warm climate in winter in Southwest China. NSAs and nitronaphthol each accounted for less than 5% of the NACs. Three major sources of NACs were identified based on the principal component analysis, including vehicle emissions, biomass burning, and secondary formation. The significant correlation between individual NACs and NO2 supported their secondary formation sources. The good correlation between NPs and cloud amount further suggested that gas-phase oxidation was the possible NPs formation mechanism. Our findings revealed the important role of nitrocatechols in NACs in Southwest China, implying that more measures should be taken to control biomass burning and aromatic volatile organic compounds emissions to reduce the level of NACs.


Asunto(s)
Aerosoles , Contaminantes Atmosféricos , Monitoreo del Ambiente , Material Particulado , Espectrometría de Masas en Tándem , Espectrometría de Masas en Tándem/métodos , China , Contaminantes Atmosféricos/análisis , Material Particulado/análisis , Monitoreo del Ambiente/métodos , Cromatografía Liquida , Aerosoles/análisis , Nitrocompuestos/análisis , Atmósfera/química
3.
J Chem Phys ; 139(18): 184309, 2013 Nov 14.
Artículo en Inglés | MEDLINE | ID: mdl-24320276

RESUMEN

Nonradiative energy dissipation in electronically excited polyatomic molecules proceeds through conical intersections, loci of degeneracy between electronic states. We observe a marked enhancement of laser-induced double ionization in the vicinity of a conical intersection during a non-radiative transition. We measured double ionization by detecting the kinetic energy of ions released by laser-induced strong-field fragmentation during the ring-opening transition between 1,3-cyclohexadiene and 1,3,5-hexatriene. The enhancement of the double ionization correlates with the conical intersection between the HOMO and LUMO orbitals.

4.
Phys Rev Lett ; 108(25): 253006, 2012 Jun 22.
Artículo en Inglés | MEDLINE | ID: mdl-23004597

RESUMEN

We report the first study of UV-induced photoisomerization probed via core ionization by an x-ray laser. We investigated x-ray ionization and fragmentation of the cyclohexadiene-hexatriene system at 850 eV during the ring opening. We find that the ion-fragmentation patterns evolve over a picosecond, reflecting a change in the state of excitation and the molecular geometry: the average kinetic energy per ion fragment and H(+)-ion count increase as the ring opens and the molecule elongates. We discuss new opportunities for molecular photophysics created by optical pump x-ray probe experiments.


Asunto(s)
Alquenos/química , Ciclización/efectos de la radiación , Ciclohexenos/química , Polienos/química , Procesos Fotoquímicos , Espectrofotometría Ultravioleta , Termodinámica , Rayos X
5.
J Phys Chem A ; 116(11): 2758-63, 2012 Mar 22.
Artículo en Inglés | MEDLINE | ID: mdl-22082319

RESUMEN

We have studied the photoinduced isomerization from 1,3-cyclohexadiene to 1,3,5-hexatriene in the presence of an intense ultrafast laser pulse. We find that the laser field maximally suppresses isomerization if it is both polarized parallel to the excitation dipole and present 50 fs after the initial photoabsorption, at the time when the system is expected to be in the vicinity of a conical intersection that mediates this structural transition. A modified ab initio multiple spawning (AIMS) method shows that the laser induces a resonant coupling between the excited state and the ground state, i.e., a light-induced conical intersection. The theory accounts for the timing and direction of the effect.

6.
J Chem Phys ; 134(5): 054313, 2011 Feb 07.
Artículo en Inglés | MEDLINE | ID: mdl-21303126

RESUMEN

We have previously reported experimental evidence for conformationally selective dissociation of propanal cation that was interpreted, on the basis of ab initio multiple spawning calculations, as arising from distinct dynamics in the excited state manifold of the cation. Two conical intersections (CIs) are accessible from Franck-Condon points on the dark state; however, different conformers prefer different CIs and quench to different regions on the ground state. In this paper, we extend our initial report to include experimental results for the partially deuterated propanal cation as well as detailed characterization of the ground state potential energy surface and statistical calculations of the ground state dissociation dynamics. The DC slice imaging experiments show a bimodal velocity distribution for H elimination with the observed branching ratio of the two channels different for the cis and gauche conformers. H(D)-elimination experiments from deuterated propanal cation support the dissociation mechanism proposed in the earlier report. We further investigate reaction rates on the ground state using Rice-Ramsperger-Kassel-Marcus theory. We find that the experimental results are consistent with a mechanistic picture where the ground state dissociation is statistical, and conformer specificity of the dissociation products arises because of the different populations in distinct ground state isomers after photoexcitation due to ultrafast quenching to the ground state.


Asunto(s)
Aldehídos/química , Cationes/química , Deuterio/química , Modelos Moleculares , Conformación Molecular , Procesos Fotoquímicos , Teoría Cuántica
7.
Int J Mol Med ; 45(2): 441-450, 2020 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-31894288

RESUMEN

Parkinson's disease (PD) is the second most common neurodegenerative disorder. miR­384­5p expression has been shown to be increased in an in vitro model of PD; however, it remains unknown whether there are other molecules that can be regulated by miR­384­5p in in vivo and in vitro models of PD; thus, the present study aimed to elucidate this matter. Rotenone was applied for the establishment of in vitro and in vivo models of PD in the present study. Motor disability and equilibrium were determined by a swimming test and traction test, respectively. mRNA and protein levels were detected by reverse transcription­quantitative polymerase chain reaction (RT­qPCR) and western blot analysis, respectively. The association between miR­384­5p and Sirtuin 1 (SIRT1) expression was verified by dual luciferase reporter assay. The α­synuclein aggregation was evaluated by immunofluorescence. The results from the in vitro model of PD demonstrated that, the mice in the PD group exhibited decreased scores in the swimming test and traction test, which were accompanied by increased α­synuclein aggregation. In addition, the expression of miR­384­5p, which targeted the 3'untranslated region (3'UTR) of SIRT1, was verified to be increased in mice and SH­SY5Y cells in the PD group, whereas SIRT1 exhibited the opposite changes. Moreover, increased mRNA and protein levels of p53 and FOXO1 were observed in mice and SH­SY5Y cells in the PD group. In addition, the SH­SY5Y cells in the PD group exhibited a higher cell apoptotic rate. On the whole, the findings of this study demonstrate that miRNA­384­5p promotes the progression of PD by targeting SIRT1.


Asunto(s)
MicroARNs/genética , Enfermedad de Parkinson/genética , Sirtuina 1/genética , Regiones no Traducidas 3' , Animales , Línea Celular Tumoral , Progresión de la Enfermedad , Regulación de la Expresión Génica , Humanos , Masculino , Ratones , Ratones Endogámicos C57BL , Enfermedad de Parkinson/patología
8.
J Am Chem Soc ; 131(18): 6377-9, 2009 May 13.
Artículo en Inglés | MEDLINE | ID: mdl-19378993

RESUMEN

We use ab initio steered molecular dynamics to investigate the mechanically induced ring opening of cyclobutene. We show that the dynamical results can be considered in terms of a force-modified potential energy surface (FMPES). We show how the minimal energy paths for the two possible competing conrotatory and disrotatory ring-opening reactions are affected by external force. We also locate minimal energy pathways in the presence of applied external force and show that the reactant, product, and transition state geometries are altered by the application of external force. The largest effects are on the transition state geometries and barrier heights. Our results provide a framework for future investigations of the role of external force on chemical reactivity.

9.
J Phys Chem A ; 113(49): 13656-62, 2009 Dec 10.
Artículo en Inglés | MEDLINE | ID: mdl-19888736

RESUMEN

We have implemented multi-state second-order perturbation theory (MS-CASPT2) in the ab initio multiple spawning (AIMS) method for first-principles molecular dynamics including nonadiabatic effects. The nonadiabatic couplings between states are calculated numerically using an efficient method which requires only two extra energy calculations per time step. As a representative example, we carry out AIMS-MSPT2 calculations of the excited state dynamics of ethylene. Two distinct types of conical intersections, previously denoted as the twisted-pyramidalized and ethylidene intersections, are responsible for ultrafast population transfer from the excited state to the ground state. Although these two pathways have been observed in prior dynamics simulations, we show here that the branching ratio is affected by dynamic correlation with the twisted-pyramidalized intersection overweighting the ethylidene-like intersection during the decay process at the AIMS-MSPT2 level of description.

10.
Science ; 315(5818): 1561-5, 2007 Mar 16.
Artículo en Inglés | MEDLINE | ID: mdl-17363670

RESUMEN

Ion imaging reveals distinct photodissociation dynamics for propanal cations initially prepared in either the cis or gauche conformation, even though these isomers differ only slightly in energy and face a small interconversion barrier. The product kinetic energy distributions for the hydrogen atom elimination channels are bimodal, and the two peaks are readily assigned to propanoyl cation or hydroxyallyl cation coproducts. Ab initio multiple spawning dynamical calculations suggest that distinct ultrafast dynamics in the excited state deposit each conformer in isolated regions of the ground-state potential energy surface, and, from these distinct regions, conformer interconversion does not effectively compete with dissociation.

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