Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 61
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
J Hazard Mater ; 416: 125897, 2021 08 15.
Artigo em Inglês | MEDLINE | ID: mdl-34492835

RESUMO

Interconnected macro-porous cryogels with robust and pore-tunable structures have been fabricated using chemically crosslinked microfibrillated cellulose (MFC). Periodate oxidation was initially conducted to introduce aldehyde groups into the MFC surface, followed by the freeze-induced chemical crosslinking via the formation of hemiacetal bonds between aldehyde and hydroxyl at -12 °C. The cryogels with pore-tunable structures and sharply enhanced mechanical strengths were finally achieved by re-assembly of MFCs through soaking in NaIO4 solution. Furthermore, the MFC cryogels were post-crosslinked by polyethyleneimine (PEI), bestowing the cryogels with the capability of adsorbing anionic dyes. The stress of the PEI-MFC cryogel at the 80% strain was determined to be 304.5 kPa, which is the maximum value for the nanocellulose-based cryogels reported so far. Finally, the adsorption performances of PEI-MFC cryogels for methyl orange (MO) were evaluated. Maximum adsorption capacity of 500 mg/g could be obtained by the Langmuir model, outperforming that of previous absorbent materials. Reuse experiments indicated that over 90% of adsorption capacity was retained after 6 cycles. Continuous clean-up experiments demonstrated excellent MO removal abilities of the PEI-MFC cryogel. This study shows that the novel, green strategy to fabricate the robust cryogel extends the practical applications of nanocellulose adsorbents for environmental remediation.


Assuntos
Criogéis , Nanofibras , Adsorção , Compostos Azo , Celulose , Corantes , Porosidade
2.
BMC Cardiovasc Disord ; 21(1): 350, 2021 07 22.
Artigo em Inglês | MEDLINE | ID: mdl-34294029

RESUMO

BACKGROUND: Primary aldosteronism (PA), as a cause of secondary hypertension, can cause more serious cardiovascular damage than essential hypertension. The aldosterone-to-renin ratio (ARR) is recommended as the most reliable screening method for PA, but ARR screening is often influenced by many factors. PA cannot be easily excluded when negative ARR. CASE PRESENTATION: We report the case of a 45-year-old Chinese man with resistant hypertension. Three years ago, he underwent a comprehensive screening for secondary hypertension, including the ARR, and the result was negative. After that, the patient's blood pressure was still poorly controlled with four kinds of antihypertensive drugs, the target organ damage of hypertension progressed, and hypokalaemia was difficult to correct. When the patient was hospitalized again for comprehensive examination, we found that aldosterone levels had significantly increased, although the ARR was negative. An inhibitory test with saline was further carried out, and the results suggested that aldosterone was not inhibited; therefore, PA was diagnosed. We performed a unilateral adenoma resection for this patient, and spironolactone was continued to control blood pressure. After the operation, blood pressure is well controlled, and hypokalaemia is corrected. CONCLUSION: When the ARR is negative, PA cannot be easily excluded. Comprehensive analysis and diagnosis should be based on the medication and clinical conditions of patients.


Assuntos
Adenoma/complicações , Neoplasias das Glândulas Suprarrenais/complicações , Aldosterona/sangue , Hiperaldosteronismo/sangue , Hipertensão/etiologia , Renina/sangue , Adenoma/sangue , Adenoma/diagnóstico , Adenoma/cirurgia , Neoplasias das Glândulas Suprarrenais/sangue , Neoplasias das Glândulas Suprarrenais/diagnóstico , Neoplasias das Glândulas Suprarrenais/cirurgia , Adrenalectomia , Anti-Hipertensivos/uso terapêutico , Biomarcadores/sangue , Pressão Sanguínea/efeitos dos fármacos , Humanos , Hiperaldosteronismo/diagnóstico , Hiperaldosteronismo/etiologia , Hipertensão/diagnóstico , Hipertensão/tratamento farmacológico , Hipertensão/fisiopatologia , Masculino , Pessoa de Meia-Idade , Resultado do Tratamento
3.
Nanomedicine ; 35: 102390, 2021 07.
Artigo em Inglês | MEDLINE | ID: mdl-33857685

RESUMO

This study aimed to fabricate a hierarchical tantalum scaffold mimicking natural bone structure to enhance osseointegration. Porous tantalum scaffolds (p-Ta) with microgradients were fabricated by selective laser melting according to a computer-aided design model. Electrochemical anodization produced nanotubes on the p-Ta surface (p-Ta-nt). SEM verified the construction of a unique nanostructure on p-Ta-nt. Contact angle and protein adsorption measurements demonstrated that p-Ta-nt have enhanced hydrophilicity and protein absorption. MC3T3-E1 preosteoblasts showed increased filamentous pseudopods and comparable cell proliferation when cultured on p-Ta-nt. Osteogenic marker gene (Osterix, Runx2, COL-I) transcription was significantly upregulated in MC3T3-E1 cells cultured on p-Ta-nt after 7 days. After implantation into the femurs of New Zealand white rabbits for 2 weeks, histological examination found improved early osseointegration in the p-Ta-nt group. This study showed that a hierarchical tantalum structure could enhance early osteogenic effects in vitro and in vivo.

4.
Biotechnol Lett ; 43(3): 711-717, 2021 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-33386498

RESUMO

OBJECTIVES: To select a microbial consortium from intertidal sludge and evaluate its ability to convert crude glycerol from biodisel to high value-added products such as 1,3-propanediol (1,3-PDO) and lactic acid (LA). RESULTS: A microbial consortium named CJD-S was selected from intertidal sludge and exhibited excellent performance for the conversion of crude glycerol to 1,3-PDO and LA. The composition of CJD-S was determined to be 85.99% Enterobacteriaceae and 13.75% Enterococcaceae by 16S rRNA gene amplicon high-throughput sequencing. In fed-batch fermentation with crude glycerol under nonsterile conditions, the highest concentrations of 1,3-PDO and LA were 41.47 g/L and 45.86 g/L, respectively. CONCLUSIONS: The selected microbial consortium, CJD-S, effectively converted crude glycerol to 1,3-PDO and LA under nonsterile conditions and can contribute to the sustainable development of the biodiesel industry.


Assuntos
Glicerol/metabolismo , Ácido Láctico/metabolismo , Consórcios Microbianos/fisiologia , Propilenoglicóis/metabolismo , Esgotos/microbiologia , Biocombustíveis , Reatores Biológicos , Fermentação , Ácido Láctico/análise , Propilenoglicóis/análise
5.
Xenobiotica ; 51(3): 262-267, 2021 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-33115303

RESUMO

Ophiopogonin D is a commonly used herb in cardiology and pediatrics for its variuos pharmacological effects. It is necessary to investigate the effect of ophiopogonin D on the activity of cytochrome P450 enzymes (CYP450s) to provide more guidance for the clinical application of ophiopogonin D. Eight isoforms of CYP450s, including CYP1A2, 2A6, 2C8, 2C9, 2C19, 2D6, 2E1, and 3A4 were incubated with 100 µM ophiopogonin D in pooled human liver microsomes. The inhibition model and corresponding parameters were also investigated. Ophiopogonin D exerted a significant inhibitory effect on the activity of CYP3A4, 2C9, and 2E1 in a dose-dependent manner with the IC50 values of 8.08, 12.92, and 22.72 µM, respectively (p < 0.05). The inhibition of CYP3A4 by ophiopogonin D was performed non-competitively and time-dependently with the Ki value of 4.08 µM and the KI/Kinact value of 5.02/0.050 min-1·µM-1. Whereas, ophiopogonin D acts as a competitive inhibitor of CYP2E1 and 2C9 with the Ki value of 6.69 and 11.07 µM, respectively. The inhibitory effect of ophiopogonin D on the activity of CYP3A4, 2C9, and 2E1 indicated the potential drug-drug interaction between ophiopogonin D and drugs metabolized by these CYP450s, which needs further in vivo investigation and validation.


Assuntos
Inibidores das Enzimas do Citocromo P-450/farmacologia , Microssomos Hepáticos/efeitos dos fármacos , Saponinas/farmacologia , Espirostanos/farmacologia , Sistema Enzimático do Citocromo P-450 , Humanos , Microssomos Hepáticos/enzimologia
6.
Lab Chip ; 20(19): 3544-3551, 2020 10 07.
Artigo em Inglês | MEDLINE | ID: mdl-32895671

RESUMO

A surface wetting-driven droplet generation microfluidic chip was developed, and could produce droplets spontaneously once adding a drop of oil and an aqueous sample on the chip without any power source and equipment. The chip is simply composed of three drilled holes connected by a single microchannel. The aqueous sample dropped in the middle hole could be converged and segmented into monodispersed droplets spontaneously by preloading oil in the side hole, and then flow into the other side hole through the microchannel. To address the high throughput and stability in practical applications, a siphon pump was further integrated into the microfluidic chip by simply connecting oil-filled tubing also acting as a collector. In this way, droplets can be generated spontaneously with a high uniformity (CV < 3.5%) and adjustable size (30-80 µm). Higher throughput (280 Hz) and multi-sample emulsification are achieved by parallel integration of a multi-channel structure. Based on that, the microfluidic chip was used as the droplet generator for the ddPCR to absolutely quantify S. mutans DNA. This is the first time that the feasibility of droplet generation driven only by oil wettability on hydrophobic surfaces is demonstrated. It offers great opportunity for self-sufficient and portable W/O droplet generation in biomedical samples, thus holding the potential for point-of-care testing (POCT).

7.
Med Sci Monit ; 26: e924748, 2020 Aug 28.
Artigo em Inglês | MEDLINE | ID: mdl-32855380

RESUMO

BACKGROUND Chronic hypertension changes the function and structure of the heart and blood vessels. This study aimed to explore the role of the NOD1/Rip2 (nucleotide-binding oligomerization domain 1/receptor-interacting protein 2) signaling pathway in myocardial remodeling in spontaneously hypertensive rats (SHRs). MATERIAL AND METHODS Blood pressure was measured using a tail cuff. The cardiac structure was observed using echocardiography. Slices of the myocardium were stained with hematoxylin and eosin. The expression of NOD1 and Rip2 was detected using real-time polymerase chain reaction, western blot, and immunohistochemistry. The content and distribution of collagen in the myocardium were observed using Van Gieson staining. Enzyme-linked immunosorbent assay was used to detect the interleukin-1 (IL-1) concentrations. SHRs were treated with the NOD1 agonist iE-DAP and NOD1 inhibitor ML130. RESULTS The NOD1 agonist increased blood pressure in SHRs, and the NOD1 inhibitor decreased blood pressure; the interventricular septum thickness (IVST) and left ventricular posterior wall thickness (LVPWT) of the agonist-treated group were thicker than those of the control group, and the antagonist exerted the opposite effects. The levels of the NOD1 and Rip2 mRNAs and proteins, serum IL-1 concentration, and myocardial collagen volume fraction (CVF%) increased in SHRs in the NOD1 agonist group, but the levels of NOD1 and Rip2, serum IL-1 concentration, and myocardial collagen volume fraction (CVF%) decreased in SHRs in the NOD1 inhibitor group. CONCLUSIONS NOD1/Rip2 expression increased during the progression of myocardial remodeling in SHRs. The NOD1 agonist increased NOD1 expression and promoted myocardial remodeling, while the NOD1 antagonist reduced NOD1/Rip2 expression and protected against myocardial remodeling.


Assuntos
Proteína Adaptadora de Sinalização NOD1/metabolismo , Proteína Serina-Treonina Quinase 2 de Interação com Receptor/metabolismo , Transdução de Sinais , Remodelação Ventricular , Animais , Pressão Sanguínea/efeitos dos fármacos , Masculino , Proteína Adaptadora de Sinalização NOD1/agonistas , Proteína Adaptadora de Sinalização NOD1/antagonistas & inibidores , Ratos , Ratos Endogâmicos SHR , Ratos Endogâmicos WKY , Reação em Cadeia da Polimerase em Tempo Real
8.
J Phys Chem A ; 124(32): 6411-6419, 2020 Aug 13.
Artigo em Inglês | MEDLINE | ID: mdl-32692170

RESUMO

Photochromic phenylhydrazones are one of the most promising candidates for a photoswitchable fluorescent probe with potential applications in various fields, but mechanistic understanding of the origin of this unique behavior is limited. In this work, we explored the emission nature and switching mechanism of a model phenylhydrazone-based fluorescent photoswitch, DMA-PHA, by means of TD-DFT and CASPT2 calculations. The fluorescence-emitting Z configuration of DMA-PHA does not involve an excited-state intramolecular proton transfer process since the resonance effect between the DMA group and the rest part of the molecule in the excited state strengthens the hydrogen bond and thus stabilizes the emissive state. The light-induced fluorescence toggling results from E↔Z interconversion driven by an out-of-plane C═N bond torsion and assisted by a N-N single bond rotation, which in total lead to a charge separation process losing the fluorescence activity. The N-N bond rotation in phenylhydrazone further enhances the competitive nonradiative decay and reduces the photoisomerization yields. The theoretical results will provide the guidance for the rational design of novel and improved photoswitchable fluorescent probes with desired performances.

9.
Phys Chem Chem Phys ; 22(27): 15295-15302, 2020 Jul 21.
Artigo em Inglês | MEDLINE | ID: mdl-32618986

RESUMO

The substitution effect in chemistry is a concept that is probably too common to mention, while for a molecule with an elusive electronic structure, substitution can introduce an unusual effect that dramatically tunes the chemical process. To reveal the substitution effects on the photodynamics of Criegee Intermediates (CIs), we carried out the multireference CASSCF trajectory surface-hopping (TSH) molecular dynamics and CASPT2 electronic-structure calculations for a methyl-substituted CI (MCI) and a vinyl-substituted CI (VCI). The results show that for different substituents, the hydrogen bond, ring tension and π-conjugation not only alter the relative stabilities of the conformers/configurations, but also dramatically change the photo-induced channel of CIs. For an anti-MCI, the dominant channel starting from the S1 state is the ring-closure process leading to dioxirane, while in the syn configuration, the intramolecular CHO hydrogen bond hinders the rotation around the C-O bond and thus leads to a high yield of in-plane O-O dissociation towards acetaldehyde (X1A') and the O(1D) atom. In a VCI with an unsaturated substituent, the π-conjugation greatly strengthens the O-O bond and therefore no O-O dissociation is observed in all configurations. In addition, the CHO hydrogen bond in the syn(CO)-VCI further stabilizes the S1-state intermediates and makes them less reactive; in contrast, isomerization to dioxirane becomes the globally dominant channel in the anti(CO)-VCI. The dramatic substitution effects by saturated and unsaturated substituents on CIs found here will deepen the understanding of Criegee-intermediate chemistry.

10.
Biomed Pharmacother ; 129: 110364, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32531678

RESUMO

Cardiac hypertrophy and remodeling are among the major health challenges facing countries around the world today. Neohesperidin plays an important role in influencing cell apoptosis, cell growth, tumorigenesis and tumor microenvironment, but the mechanism and role of Neohesperidin in cardiac hypertrophy and remodeling caused by Angiotensin II has not been fully elucidated. This study used Angiotensin II to induce cardiac hypertrophy and cardiac remodeling in mice. Echocardiography was used to evaluate cardiac function, H&E and Masson trichrome staining were used to detect myocardial histological changes. Cardiac cell size was determined by WGA staining. The protein content of the signaling pathway was detected by Western blot, and the mRNA expression of fibrosis and hypertrophy markers was detected by qPCR. DHE staining was used to detect oxidative stress. We also observed the effect of Neohesperidin on Ang II-induced NRCMs. The results showed that neohesperidin can significantly inhibit Ang II-induced myocardial contractile dysfunction, cardiac hypertrophy, myocardial fibrosis, myocardial oxidative stress and inflammation. These results suggest that Neohesperidin can alleviate cardiac hypertrophy and remodeling caused by Ang II, and its mechanism may be related to the inhibition of multiple signaling pathways.


Assuntos
Angiotensina II , Hesperidina/análogos & derivados , Hipertrofia Ventricular Esquerda/prevenção & controle , Miócitos Cardíacos/efeitos dos fármacos , Função Ventricular Esquerda/efeitos dos fármacos , Remodelação Ventricular/efeitos dos fármacos , Animais , Células Cultivadas , Modelos Animais de Doenças , Fibrose , Regulação da Expressão Gênica , Hesperidina/farmacologia , Hipertrofia Ventricular Esquerda/metabolismo , Hipertrofia Ventricular Esquerda/patologia , Hipertrofia Ventricular Esquerda/fisiopatologia , Mediadores da Inflamação/metabolismo , Masculino , Camundongos Endogâmicos C57BL , Miócitos Cardíacos/metabolismo , Miócitos Cardíacos/patologia , Estresse Oxidativo/efeitos dos fármacos , Ratos Sprague-Dawley , Transdução de Sinais
11.
Phys Chem Chem Phys ; 22(18): 10212-10218, 2020 May 13.
Artigo em Inglês | MEDLINE | ID: mdl-32350491

RESUMO

Photo-involving aryl halide activation plays a pivotal role in organic synthesis and materials science. Revealing the mechanism and understanding the photophysical and photochemical processes in the activation is of great importance. Here, we found that aryl halides could be directly activated to form aryl radicals via halogen bonding under visible light irradiation without using photocatalysts or high power light. The interaction between the aryl halide and Lewis base (Et3N), as well as the triplet state formation, play crucial roles. Halogen bonding between aryl halide and Et3N facilitates intersystem crossing (ISC) and leads to an abundance of the triplet aryl halide/Et3N complex, where the carbon-halogen bond is much lengthened and prone to fracture. Therefore, visible light-driven photoredox catalyst-free C-C coupling reaction and radical-initiated polymerization were achieved. Avoiding the use of a catalyst not only brings convenience for low-cost operation, but also facilitates further purification. Meanwhile, the wide scope of aryl halide tolerance provides opportunities for chemical synthesis and polymerization.

12.
Angew Chem Int Ed Engl ; 59(31): 12714-12719, 2020 Jul 27.
Artigo em Inglês | MEDLINE | ID: mdl-32281220

RESUMO

A highly effective C-O coupling reaction of (hetero)aryl electrophiles with primary and secondary alcohols is reported. Catalyzed by a NiII -aryl complex under long-wave UV (390-395 nm) irradiation in the presence of a soluble amine base without any additional photosensitizer, the reaction enables the etherification of aryl bromides and aryl chlorides as well as sulfonates with a wide range of primary and secondary aliphatic alcohols, affording synthetically important ethers. Intramolecular C-O coupling is also possible. The reaction appears to proceed via a NiI -NiIII catalytic cycle.

13.
Angew Chem Int Ed Engl ; 59(22): 8579-8585, 2020 May 25.
Artigo em Inglês | MEDLINE | ID: mdl-32080956

RESUMO

The origin of the positive temperature effect in fluorescence emission of a newly designed perylene bisimide (PBI) derivative with two naphthyl units containing ortho-methoxy group (NM) at its bay positions (PBI-2NM) was elucidated. A key point is the finding of a weak hydrogen bond (<5.0 kcal mol-1 ) between the methoxy group of the NM unit and a nearby hydrogen atom of the PBI core. It is the bonding that drives co-planarization of the different aromatic units, resulting in delocalization of the π-electrons of the compound as synthesized, inducing fluorescence quenching via intramolecular charge transfer (ICT). With increasing temperature, the co-planar structure could be distorted in part, resulting in a decreased degree of ICT, and hence leading to enhanced fluorescence emission. The unique positive temperature effect in emission induced by H-bond-driven co-planarization may pave a new avenue in designing functional molecular systems complementary to conventional methods.

14.
J Environ Sci (China) ; 89: 125-135, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-31892385

RESUMO

Glycine (Gly) is ubiquitous in the atmosphere and plays a vital role in new particle formation (NPF). However, the potential mechanism of its on sulfuric acid (SA) - ammonia (A) clusters formation under various atmospheric conditions is still ambiguous. Herein, a (Gly)x·(SA)y·(A)z (z ≤ x + y ≤ 3) multicomponent system was investigated by using density functional theory (DFT) combined with Atmospheric Cluster Dynamics Code (ACDC) at different temperatures and precursor concentrations. The results show that Gly, with one carboxyl (-COOH) and one amine (-NH2) group, can interact strongly with SA and A in two directions through hydrogen bonds or proton transfer. Within the relevant range of atmospheric concentrations, Gly can enhance the formation rate of SA-A-based clusters, especially at low temperature, low [SA], and median [A]. The enhancement (R) of Gly on NPF can be up to 340 at T = 218.15 K, [SA] = 104, [A] = 109, and [Gly] = 107 molecules/cm3. In addition, the main growth paths of clusters show that Gly molecules participate into cluster formation in the initial stage and eventually leave the cluster by evaporation in subsequent cluster growth at low [Gly], it acts as an important "transporter" to connect the smaller and larger cluster. With the increase of [Gly], it acts as a "participator" directly participating in NPF.


Assuntos
Amônia , Glicina , Modelos Químicos , Atmosfera , Ácidos Sulfúricos
15.
Chemosphere ; 244: 125538, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-31835047

RESUMO

The effect of hydration on the formation mechanism of clusters consisting of methanesulfonic acid (MSA) and methylamine (MA) is investigated by quantum chemistry (Density Functional Theory, DFT) and kinetics simulation (Atmospheric Chemical Dynamic Code, ACDC) methods. The results showed that the process of hydration is favorable from the thermodynamic point of view, and the presence of water molecules can promote proton transfer significantly. Although MA has a significant influence on the formation rate of MSA-based clusters at the parts per trillion (ppt) levels, the effective nucleation of MSA-MA anhydrous clusters hardly seems to occur under common typical atmospheric conditions. The high concentrations of precursors ([MSA] > 6 × 107 molecules·cm-3 and [MA] > 1 ppt or [MSA] > 1 × 106 molecules·cm-3 and [MA] > 100 ppt) is necessary for the effective nucleation of the MSA-MA system. The formation rate of the MSA-MA system is enhanced significantly by hydration. The formation rate increases with the relative humidity (RH) and reached up to a factor of 2700 at RH = 40%. The formation mechanism of the hydrous system is different from the anhydrous system. The formation of (MSA)2 and (MSA)(MA) dimers is the rate-determining step of the anhydrous and hydrous systems, respectively. In addition, the growth pathway of clusters was complicated by low temperature and simplified by high humidity, respectively. In general, although humidity is a very favorable factor for the formation of the MSA-MA system, the involvement of other species (such as sulfuric acid) may be more effective to promote the nucleation of the MSA-MA system under typical atmospheric environment.


Assuntos
Atmosfera/química , Mesilatos/síntese química , Metilaminas/síntese química , Modelos Teóricos , Água/química , Umidade , Cinética , Prótons , Ácidos Sulfúricos , Temperatura , Termodinâmica
16.
Glob Chall ; 3(2): 1800067, 2019 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31565360

RESUMO

Biocompatible luminescent hydrogels containing covalently linked terbium complexes with a macrocyclic ligand are prepared by a facile method. The environmentally friendly preparation procedure is carried out at room temperature using water as a solvent. These new hybrid materials can act as luminescent sensors to detect Fe3+ with relative selectivity and high sensitivity. The hydrogels also show pH sensing with a wide range.

17.
J Chem Theory Comput ; 15(10): 5440-5447, 2019 Oct 08.
Artigo em Inglês | MEDLINE | ID: mdl-31436414

RESUMO

A combination of excited-state intramolecular proton transfer (ESIPT) and aggregation-induced emission (AIE) has opened new opportunities to develop color-tunable luminescent materials with high quantum yield. Understanding the emission mechanism of these luminophores is essential for the molecular design and construction of a functional system. Herein, we report QM (MS-CASPT2//TD-DFT, MS-CASPT2//CASSCF) and ONIOM (QM/MM) studies on the fluorescence quenching and AIE mechanisms of 2-(2-hydroxy-phenyl)-4(3H)-quinazolinone with typical characteristics of AIE and ESIPT as an example. The computational results indicate that in the tetrahydrofuran solution, once being excited to the S1 state, the molecule tends to undergo an ultrafast, barrierless ESIPT from enol to keto tautomer and then accesses a S1/S0 conical intersection in the vicinity of a C═C bond twisted intramolecular charge-transfer (TICT) intermediate, leading to a nonradiative decay from the excited to ground state. Hence, the TICT-induced nonadiabatic transition, which has been further confirmed by the on-the-fly trajectory surface hopping dynamics simulations, accounts for the fluorescence quenching in solution. In contrast, in the solid state, the nonradiative relaxation pathway via the C═C bond rotation is suppressed due to environmental hindrance, leaving the ESIPT-induced enol-keto tautomerization as the only excited-decay channel, thus the fluorescence is observably enhanced in the crystal.

18.
J Phys Chem A ; 123(14): 3205-3213, 2019 Apr 11.
Artigo em Inglês | MEDLINE | ID: mdl-30888818

RESUMO

The OH-initiated oxidation of vinyl alcohol (VA) produced by phototautomerization of acetaldehyde is thought to be a source of formic acid (FA) in the atmosphere. A recent theoretical study predicted that the VA + OH + O2 reaction 1 proceeds by OH addition at α-C (66%) and ß-C (33%) of VA and that FA is a main product of reaction 1. However, the metastable reactant ( anti-VA, ∼18% at 298 K, 1.42 kcal mol-1 higher than syn in energy) used in that study inspired us to reinvestigate reaction 1. Using the state-of-the-art quantum-chemical and kinetic calculations, we first found that a conformer of VA has a significant influence on the rate coefficient and branching ratio of reaction 1. Upon derivation, it is found that ∼84% of reaction 1 takes place through the ß-C-addition channel and ∼16% of reaction 1 happens by the α-C-addition channel. The calculated total initial rate coefficient at 298 K is 1.48 × 10-11 cm3 molecule-1 s-1, which is in reasonable agreement with the experimental values of similar systems (vinyl ethers + OH reactions). The predicted main products of reaction 1 are glycolaldehyde and the HO2 radical, whereas FA is just a byproduct.

19.
Chemistry ; 25(16): 4194-4201, 2019 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-30653755

RESUMO

The working mechanism including the photoisomerization and thermal isomerization steps of a chiral N-alkyl imine-based motor synthesized by Lehn et al. are revealed by MS-CASPT2//CASSCF and MS-CASPT2//(TD-)DFT methods. For the photoisomerization process of the imine-based motor, it involves both the bright (π,π*) state and the dark (n,π*) state. In addition, the MECI has similar geometry and energy to the minimum of the S1 state, which shows that the process is barrierless and keeps the unidirectionality of rotation well; the result confirms the imine-based motor is a good candidate for a light-driven molecular rotary motor. For the thermal isomerization process of the imine-based motor, there are two even isomerization paths: one with the mechanism of the in-plane N inversion, the energy barriers of which are 29.6 kcal mol-1 at MS3-CASPT2//CAM-B3LYP level and 29.2 kcal mol-1 at MS3-CASPT2//CASSCF level; the other with the mechanism of ring inversion of the cycloheptatriene moiety, with energy barriers of 28.1 kcal mol-1 at MS3-CASPT2//CAM-B3LYP level and 18.1 kcal mol-1 at MS3-CASPT2//CASSCF level. According to the structural feature of the stator moiety, the imine molecule can be used as a two-step or a four-step light-driven rotary motor.

20.
J Phys Chem Lett ; 9(5): 978-981, 2018 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-29420035

RESUMO

The photochemistry of Criegee intermediates plays a significant role in atmospheric chemistry, but it is relatively less explored compared with their thermal reactions. Using multireference CASPT2 electronic structure calculations and CASSCF trajectory surface-hopping molecular dynamics, we have revealed a dark-state-involved A1A → X1A photoisomerization channel of the simple Criegee intermediate (CH2OO) that leads to a cyclic dioxirane. The excited molecules on the A1A state, which can have either originated from the B1A state via B1A → A1A internal conversion or formed by state-selective electronic excitation, is driven by the out-of-plane motion toward a perpendicular A/X1A minimal-energy crossing point (MECI) then radiationless decay to the ground state with an average time constant of ∼138 fs, finally forming dioxirane at ∼254 fs. The dynamics starting from the A1A state show that the quantum yield of photoisomerization from the simple Criegee intermediate to dioxirane is 38%. The finding of the A1A → X1A photoisomerization channel is expected to broaden the reactivity profile and deepen the understanding of the photochemistry of Criegee intermediates.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...