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1.
JACS Au ; 4(2): 419-431, 2024 Feb 26.
Artigo em Inglês | MEDLINE | ID: mdl-38425917

RESUMO

The synthesis of 1-aminonorbornane (1-aminoNB), a potential aniline bioisostere, through photochemistry or photoredox catalysis signifies a remarkable breakthrough with implications in organic chemistry, pharmaceutical chemistry, and sustainable chemistry. However, an understanding of the underlying mechanisms involved in these reactions remains limited and ambiguous. Herein, we employ high-precision CASPT2//CASSCF calculations to elucidate the intricate mechanisms regulating the intramolecular photo-(3 + 2)-cycloaddition reactions for the synthesis of 1-aminoNB in the presence or absence of the Ir-complex-based photocatalyst. Our investigations delve into radical cascades, stereoselectivity, particularly single-electron-transfer (SET) events, etc. Furthermore, we innovatively introduce and compare two SET models integrating Marcus electron-transfer theory and transition-state theory. These models combined with kinetic data contribute to recognizing the critical control factors in diverse photocatalysis, thereby guiding the design and manipulation of photoredox catalysis as well as the improvement and modification of photocatalysts.

2.
IEEE Trans Image Process ; 33: 42-57, 2024.
Artigo em Inglês | MEDLINE | ID: mdl-37988212

RESUMO

As compared to standard dynamic range (SDR) videos, high dynamic range (HDR) content is able to represent and display much wider and more accurate ranges of brightness and color, leading to more engaging and enjoyable visual experiences. HDR also implies increases in data volume, further challenging existing limits on bandwidth consumption and on the quality of delivered content. Perceptual quality models are used to monitor and control the compression of streamed SDR content. A similar strategy should be useful for HDR content, yet there has been limited work on building HDR video quality assessment (VQA) algorithms. One reason for this is a scarcity of high-quality HDR VQA databases representative of contemporary HDR standards. Towards filling this gap, we created the first publicly available HDR VQA database dedicated to HDR10 videos, called the Laboratory for Image and Video Engineering (LIVE) HDR Database. It comprises 310 videos from 31 distinct source sequences processed by ten different compression and resolution combinations, simulating bitrate ladders used by the streaming industry. We used this data to conduct a subjective quality study, gathering more than 20,000 human quality judgments under two different illumination conditions. To demonstrate the usefulness of this new psychometric data resource, we also designed a new framework for creating HDR quality sensitive features, using a nonlinear transform to emphasize distortions occurring in spatial portions of videos that are enhanced by HDR, e.g., having darker blacks and brighter whites. We apply this new method, which we call HDRMAX, to modify the widely-deployed Video Multimethod Assessment Fusion (VMAF) model. We show that VMAF+HDRMAX provides significantly elevated performance on both HDR and SDR videos, exceeding prior state-of-the-art model performance. The database is now accessible at: https://live.ece.utexas.edu/research/LIVEHDR/LIVEHDR_index.html. The model will be made available at a later date at: https://live.ece.utexas.edu//research/Quality/index_algorithms.htm.

3.
J Chem Theory Comput ; 19(1): 122-136, 2023 Jan 10.
Artigo em Inglês | MEDLINE | ID: mdl-36534617

RESUMO

We present a comprehensive excited-state benchmark for the state-averaged (SA) driven similarity renormalization group (DSRG) [Li, C.; Evangelista, F. A. J. Chem. Phys. 2018, 148, 124106]. Following the QUEST database [Véril, M.; Scemama, A.; Caffarel, M.; Lipparini, F.; Boggio-Pasqua, M.; Jacquemin, D.; Loos, P.-F. Wiley Interdiscip. Rev. Comput. Mol. Sci. 2021, 11, e1517], 280 vertical transition energies of 35 medium-sized molecules are computed using the SA-DSRG derived second- and third-order perturbation theories (PT2/PT3) along with a nonperturbative approach [sq-LDSRG(2)]. Comparing to the theoretical best estimates, the optimal flow parameter is found to be 0.35 and 2.0 Eh-2 for SA-DSRG-PT2 and SA-DSRG-PT3, respectively. For SA-sq-LDSRG(2), a flow parameter of 1.5 Eh-2 provides converged equations without compromising the accuracy. We then assess the accuracy of the SA-DSRG hierarchy using these parameters. The SA-DSRG-PT2 scheme outperforms the level-shifted CASPT2 by 0.10 eV in mean absolute error (MAE), yet this accuracy is slightly inferior than that of CASPT2 with the ionization-potential-electron-affinity shift. Both SA-DSRG-PT3 and SA-sq-LDSRG(2) yield a MAE of 0.10 eV, which is comparable to that of CASPT3 (0.09 eV). Finally, we compute vertical excitation energies of several low-lying singlet states of nucleobases. The SA-sq-LDSRG(2) approach provides highly accurate results for π → π* excitations, while n → π* transitions are better described by SA-DSRG-PT3.


Assuntos
Benchmarking , Elétrons
4.
Technol Health Care ; 30(6): 1359-1369, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-35599519

RESUMO

BACKGROUND: Arteriosclerosis is one of the diseases that endanger human health. There is a large amount of information in pulse wave signals to reflect the degree of arteriosclerosis. OBJECTIVE: The degree of arteriosclerosis is assessed by analyzing pulse wave signal and calculating multi-scale entropy values. METHODS: A method based on the multiscale cross-approximate entropy of the pulse wave of the human finger is proposed to assess the degree of arteriosclerosis. A total of 86 subjects were divided into three groups. The data of 1000 pulse cycles were selected in the experiment, and the multiscale cross-approximate entropy was calculated for the climb time and pulse wave peak interval. Independent sample t-test analysis gives the small-scale cross-approximate entropy of the two time series of climb time and pulse wave peak interval as p< 0.001 in Groups 1 and 2. The large-scale cross-approximate entropy of the two time series of climb time and pulse wave peak interval is p< 0.017 in Groups 2 and 3. RESULTS: Using the proposed algorithm, the results showed that the small-scale cross-approximate entropy of climb time and pulse wave peak interval could reflect the degree of arteriosclerosis in the human body from the perspective of autonomic nerve function. The large-scale cross-approximate entropy of climb time and pulse wave peak interval confirmed the effect of diabetes on the degree of arteriosclerosis. CONCLUSIONS: The results demonstrate the multiscale cross-approximate entropy is a comprehensive index to evaluate the degree of human arteriosclerosis.


Assuntos
Arteriosclerose , Processamento de Sinais Assistido por Computador , Humanos , Entropia , Frequência Cardíaca/fisiologia , Algoritmos
5.
Front Public Health ; 10: 844015, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-35462844

RESUMO

This article is aimed to examine the effect of economic growth on the health of residents from the perspective of local government behavior. First of all, it is theoretically proved that in an economy with economic decentralization and political centralization, because the local government implements the central planner's "people-oriented" and "people-centered" requirements, the local government pays attention to both its own consumption and the health of residents. For this reason, he prefers public health investment, and the conclusion is that there is a stable and balanced relationship between residents' health and economic growth. When the local government's relative importance to people's livelihood is greater than its own consumption, the economic growth will have a significant and positive impact on residents' health. And the internal mechanism of economic growth affecting residents' health is combed mathematically. Secondly, using panel data from China's 31 inland provinces from 2003 to 2019, empirical tests show that the hypothesis that China's economic growth promotes residents' health is established. The work of this article means that the improvement of residents' health depends not only on the total amount of available resources brought about by economic growth, but also on the government's livelihood preferences. The public health investment behavior of local governments in China is an important clue to explains that China's economic growth can promote residents' health.


Assuntos
Desenvolvimento Econômico , Governo Local , China , Humanos , Investimentos em Saúde , Saúde Pública
6.
Zhongguo Zhong Yao Za Zhi ; 47(3): 819-828, 2022 Feb.
Artigo em Chinês | MEDLINE | ID: mdl-35178965

RESUMO

The purpose of the study is to analyze the outcomes of randomized controlled trial(RCT) of Chinese herbal medicine formula(CHMF) in the treatment of gastrointestinal dysfunction in sepsis in recent two years. We systematically searched four Chinese databases, three English databases, and two clinical trial registries to analyze the reports of outcome indicators of clinical trials, and evaluated the risk of bias by using the ROB tool of Cochrane Collaboration. After screening, 55 clinical RCTs were included. The results showed that the current clinical studies of gastrointestinal dysfunction in sepsis reported the efficacy and safety indicators. The efficacy indicators included APACHE Ⅱ scores, gastrointestinal dysfunction scores, bowel sound scores, and inflammatory indicator such as C-reactive protein and procalcitonin. The safety indicators mainly include gastrointestinal reactions, skin reactions, and other adverse events and adverse reactions. However, there was no distinction between primary and secondary outcomes. The relevant indicators of health economics were not reported, and the quality of research methodology was poor. Therefore, we suggest that future researchers should be well prepared in the top-level design stage and actively construct the core outcome set, so as to improve the quality of clinical trials.


Assuntos
Medicamentos de Ervas Chinesas , Gastroenteropatias , Sepse , Medicamentos de Ervas Chinesas/uso terapêutico , Gastroenteropatias/tratamento farmacológico , Humanos , Medicina Tradicional Chinesa , Ensaios Clínicos Controlados Aleatórios como Assunto , Projetos de Pesquisa , Sepse/tratamento farmacológico
7.
Artigo em Inglês | MEDLINE | ID: mdl-34682445

RESUMO

Facing the increasingly severe environmental problems, the development of a green and sustainable low-carbon economy has become an international trend. In China, the core issue of low-carbon economic development is effectively resolving the contradiction between the exploitation and utilization of fossil energy and greenhouse gas emissions (mainly carbon emissions). Based on the SAM matrix, we established a static Computable General Equilibrium (CGE) model to simulate the impact of carbon tax policies on energy consumption, carbon emissions, and macroeconomics variables under 10, 20, and 30% emission reductions. Meanwhile, we analyze the impact of different carbon tax recycling mechanisms under the principle of tax neutrality. We find that the carbon tax effectively reduces carbon emissions, but it will negatively impact economic development and social welfare. A reasonable carbon tax recycling system based on the principle of tax neutrality can reduce the negative impact of carbon tax implementation. Among the four simulated scenarios of carbon tax cycle, the scenario of reducing residents' personal income tax is most conducive to realizing the "double dividend" of carbon tax.


Assuntos
Carbono , Desenvolvimento Econômico , Carbono/análise , Dióxido de Carbono , China , Políticas , Impostos
8.
Front Public Health ; 9: 833961, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-35141198

RESUMO

Using national dynamic panel data from 21 emerging markets between 1999 and 2020 and bidirectional fixed effect and threshold regression methods, this paper evaluated the impact of health investment on industrial structure upgrading from two aspects of economic output and economic structure. The results showed that: (1) public health investment and private health investment have a crowding out effect on the added value of primary and secondary industries, and the crowding out effect of public health investment is greater than that of private health investment; (2) Public health investment and private health investment have a spillover effect on the added value of the tertiary industry, and the spillover effect of public health investment is greater than that of private health investment; (3) Both public and private health investment contribute to the transfer of the labor force to the tertiary industry, and tests showed the baseline regression results were robust and reliable; (4) The relationship between health investment and industrial structure upgrading was non-linear. As per capital GDP increases, the inhibition effect of public health investment on industrial structure upgrading gradually weakens whilst the promotion effect of private health investment on industrial structure upgrading gradually increases. The results of this study clarify how health investment affects industrial structure, and offers new guidance for health investment policy formulation in emerging market countries.


Assuntos
Desenvolvimento Econômico , Investimentos em Saúde , Indústrias , Saúde Pública
9.
Acta Radiol ; 62(8): 1016-1024, 2021 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32811159

RESUMO

BACKGROUND: Contrast-enhanced ultrasound (CEUS) is considered an attractive imaging technique to evaluate tumor microcirculation. However, the validity of CEUS for assessing laryngeal carcinoma is unclear. PURPOSE: To compare the performance of CEUS with conventional US and contrast-enhanced computed tomography (CECT) in the diagnosis and preoperative T-staging of laryngeal carcinoma. MATERIAL AND METHODS: Forty-one consecutive patients with laryngeal carcinoma underwent conventional high-frequency US, CEUS, and CECT before surgery. The CEUS characteristics of laryngeal carcinoma were recorded. The imaging findings of CEUS and conventional US were compared with CECT findings and the postoperative pathological examination. RESULTS: CEUS showed hyperenhancement in 38 cases and isoenhancement in three cases. Homogeneous distribution of contrast agent was found in 20 cases and heterogeneous distribution in 21 cases, of which 16 cases showed local perfusion defects. In the enhanced phase, rapid entry was observed in 37 cases, synchronous entry was observed in two cases, and slow entry was observed in two cases. Rapid exit was observed in 25 cases and slow exit was observed in 16 cases. The pretherapeutic T-staging accuracy was not significantly different between conventional US, CEUS, and CECT (P ≥ 0.500). A high sensitivity and specificity were achieved by CEUS in the evaluation of involvement of thyroid cartilage. CONCLUSION: Compared with conventional US and CECT, CEUS has a reliable initial T-staging accuracy and diagnostic properties for detecting laryngeal cartilage invasion.


Assuntos
Neoplasias Laríngeas/diagnóstico por imagem , Adulto , Idoso , Idoso de 80 Anos ou mais , Humanos , Neoplasias Laríngeas/patologia , Neoplasias Laríngeas/cirurgia , Laringe/diagnóstico por imagem , Laringe/patologia , Laringe/cirurgia , Masculino , Pessoa de Meia-Idade , Estadiamento de Neoplasias , Tomografia Computadorizada por Raios X , Ultrassonografia/métodos
10.
Ultrasound Med Biol ; 45(9): 2309-2316, 2019 09.
Artigo em Inglês | MEDLINE | ID: mdl-31202455

RESUMO

We investigated the value of combined acoustic radiation force impulse (ARFI) imaging and conventional ultrasound (US) in identifying renal histopathological fibrosis with immunoglobulin A nephropathy. A total of 146 patients with immunoglobulin A nephropathy, pathologically confirmed by renal biopsy were grouped according to Oxford classification and Katafuchi grading, were included in the test group, and 39 healthy volunteers were included in the control group. Receiver operating characteristic (ROC) curves were constructed to compare the diagnostic accuracy of ARFI, renal lengths, parenchymal thicknesses and interlobular arterial resistance index (RI) and their combinations in identifying Katafuchi grading at renal biopsy. Shear wave velocity (SWV), renal length, renal parenchyma thickness and the interlobular arterial RI were correlated with Katafuchi grading, mesangial hypercellularity (M) and tubular atrophy/interstitial fibrosis (T) (r = -0.504 to -0.407, p < 0.01) but were not correlated with endocapillary hypercellularity (E) or segmental glomerulosclerosis (S). The area under the curves of SWV value + conventional US index (renal length, renal parenchyma thickness and interlobular arterial RI) was higher than those of the SWV value or of the conventional US index alone. The combination of ARFI imaging and conventional US can improve the diagnostic performance in quantitative evaluation pathologic damage in patients with immunoglobulin A nephropathy.


Assuntos
Técnicas de Imagem por Elasticidade/métodos , Glomerulonefrite por IGA/diagnóstico por imagem , Ultrassonografia Doppler/métodos , Adolescente , Adulto , Idoso , Criança , Feminino , Humanos , Masculino , Pessoa de Meia-Idade
11.
J Phys Chem Lett ; 8(23): 5771-5778, 2017 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-29129078

RESUMO

Two-dimensional transition metal dichalcogenides (TMDs) heterojunctions are appealing candidates for optoelectronics and photovoltaics. Using time-domain density functional theory combined with nonadiabatic (NA) molecular dynamics, we show that photoexcitation dynamics exhibit a significant difference in the vertical and lateral MoS2/WSe2 heterojunctions arising from the disparity in the donor-acceptor interaction and fundamental band alignment. The obtained electron transfer time scale in the vertical heterojunction shows excellent agreement with experiment. Hole transfer proceeds 1.5 times slower. The electron-hole recombination is 3 orders of magnitude longer than the charge separation, which favors solar cell applications. On the contrary, the lateral heterojunction shows no band offsets steering charge separation. The excited electron is localized at the interface that attracts holes to form an exciton-like state due to Coulomb interaction, suggesting potential applications in light-emitting devices. The coupled electron and hole wave functions increase NA coupling and the coherence time, accelerating electron-hole recombination by a factor of 3 compared with the vertical case. The atomistic studies advance our understanding of the photoinduced charge-phonon dynamics in TMDs heterojunctions.

12.
Environ Monit Assess ; 189(11): 541, 2017 Oct 06.
Artigo em Inglês | MEDLINE | ID: mdl-28986766

RESUMO

Heavy metals do not degrade and can remain in the environment for a long time. In this study, we analyzed the effects of Cu, Cd, Pb, Zn, Hg, and As, on environmental quality, pollutant enrichment, ecological hazard, and source identification of elements in sediments using data collected from samples taken from Shuangtai tidal wetland. The comprehensive pollution indices were used to assess environmental quality; fuzzy similarity analysis and geoaccumulation index were used to analyze pollution accumulation; correlation matrix, principal component analysis, and clustering analysis were used to analyze pollution source; environmental risk index and ecological risk index were used to assess ecological risk. The results showed that the environmental quality was either clean or almost clean. Pollutant enrichment analysis showed that the four sub-regions had similar pollution-causing metals to the background values of the soil element of the Liao River Plain, which were ranked according to their similarity. Source identification showed that all the elements were correlated. Ecological hazard analysis showed that the environmental risk index in the study area was less than zero, posing a low ecological risk. Ecological risk of the six elements was as follows: As > Cd > Hg > Cu > Pb > Zn.


Assuntos
Monitoramento Ambiental , Estuários , Metais/análise , Poluentes Químicos da Água/análise , Arsênio/análise , Cádmio/análise , China , Cobre/análise , Ecologia , Poluição Ambiental/análise , Sedimentos Geológicos/química , Chumbo/análise , Mercúrio/análise , Metais Pesados/análise , Medição de Risco , Rios , Solo , Áreas Alagadas , Zinco/análise
13.
PLoS One ; 11(2): e0149075, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-26862757

RESUMO

OBJECTIVE: To prepare arginine-glycine-aspartate (RGD)-targeted ultrasound contrast microbubbles (MBs) and explore the feasibility of their use in assessing dynamic changes in αvß3 integrin expression in a murine model of tumor angiogenesis. METHODS: RGD peptides were conjugated to the surfaces of microbubbles via biotin-avidin linkage. Microbubbles bearing RADfK peptides were prepared as controls. The RGD-MBs were characterized using an Accusizer 780 and optical microscopy. The binding specificity of the RGD-MBs for ανß3-expressing endothelial cells (bEnd.3) was demonstrated in vitro by a competitive inhibition experiment. In an in vivo study, mice bearing tumors of three different stages were intravenously injected with RGD-MBs and subjected to targeted, contrast-enhanced, high-frequency ultrasound. Subsequently, tumors were harvested and sectioned for immunofluorescence analysis of ανß3 expression. RESULTS: The mean size of the RGD-MBs was 2.36 ± 1.7 µm. The RGD-MBs showed significantly higher adhesion levels to bEnd.3 cells compared to control MBs (P < 0.01). There was rarely binding of RGD-MBs to αvß3-negative MCF-7 cells. Adhesion of the RGD-MBs to the bEnd.3 cells was significantly inhibited following treatment with anti-alpha(v) antibodies. The quantitative acoustic video intensity for high-frequency, contrast-enhanced ultrasound imaging of subcutaneous human laryngeal carcinoma (Hep-2) tumor xenografts was significantly higher in small tumors (19.89 ± 2.49) than in medium tumors (11.25 ± 2.23) and large tumors (3.38 ± 0.67) (P < 0.01). CONCLUSIONS: RGD-MBs enable noninvasive in vivo visualization of changes in tumor angiogenesis during tumor growth in subcutaneous cancer xenografts.


Assuntos
Meios de Contraste/química , Integrina alfaVbeta3/metabolismo , Microbolhas , Neovascularização Patológica/diagnóstico por imagem , Oligopeptídeos/química , Acústica , Animais , Avidina/química , Ligação Competitiva , Biotina/química , Adesão Celular , Linhagem Celular , Linhagem Celular Tumoral , Modelos Animais de Doenças , Células Endoteliais/citologia , Feminino , Humanos , Células MCF-7 , Camundongos , Camundongos Endogâmicos BALB C , Camundongos Nus , Microscopia de Fluorescência , Transplante de Neoplasias , Peptídeos/química , Ligação Proteica , Ultrassonografia/métodos , Gravação em Vídeo
15.
PLoS One ; 9(12): e115051, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-25546304

RESUMO

OBJECTIVE: To investigate the stiffness values obtained by acoustic radiation force impulse (ARFI) quantification in assessing renal histological fibrosis of chronic kidney disease (CKD). METHODS: 163 patients with CKD and 32 healthy volunteers were enrolled between June 2013 and April 2014. ARFI quantification, given as shear wave velocity (SWV), was performed to measure renal parenchyma stiffness. Diagnostic performance of ARFI imaging and conventional ultrasound (US) were compared with histologic scores at renal biopsy. Intra- and inter-observer reliability of SWV measurement was analyzed. RESULTS: In CKD patients, SWV measurements correlated significantly with pathological parameters (r = -0.422--0.511, P<0.001), serum creatinine (r = -0.503, P<0.001), and glomerular filtration rate (r = 0.587, P<0.001). The mean SWV in kidneys with severely impaired (histologic score: ≥19 points) was significant lower than that mildly impaired (histologic score: ≤9 points), moderately impaired (histologic score: 10-18 points), and control groups (all P<0.001). Receiver operating characteristic (ROC) curves analyses indicated that the area under the ROC curve for the diagnosis of renal histological fibrosis using ARFI imaging was superior to these conventional US parameters. Using the optimal cut-off value of 2.65 m/s for the diagnosis of mildly impaired kidneys, 2.50 m/s for moderately impaired kidneys, and 2.33 m/s for severely impaired kidneys, the corresponding area under the ROC curves were 0.735, 0.744, and 0.895, respectively. Intra- and intre-observer agreement of SWV measurements were 0.709 (95% CI: 0.390-0.859, P<0.001) and 0.627 (95% CI: 0.233-0.818, P = 0.004), respectively. CONCLUSIONS: ARFI may be an effective tool for evaluating renal histological fibrosis in CKD patients.


Assuntos
Técnicas de Imagem por Elasticidade/métodos , Insuficiência Renal Crônica/diagnóstico por imagem , Adolescente , Adulto , Idoso , Estudos de Casos e Controles , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Insuficiência Renal Crônica/patologia , Sensibilidade e Especificidade
16.
Carbohydr Polym ; 114: 183-189, 2014 Dec 19.
Artigo em Inglês | MEDLINE | ID: mdl-25263880

RESUMO

MDG-1, a water-soluble polysaccharide extracted from Ophiopogon japonicus, has potent hypoglycemic and weight control effects. We investigated the impact of MDG-1 on body weight, indirect calorimetry, body composition, plasma biochemical indices and obesity-related mitochondrial activity in diet-induced obese mice. Obese C57BL/6 mice induced by a high fat diet were given either vehicle or vehicle plus MDG-1 at 300 mg per body weight for 16-weeks. MDG-1 could evoked weight loss and reduce adipose tissue mass (by up to ∼ 50%) in the obese animals by increasing oxygen consumption and energy expenditure without inhibiting appetite or increasing physical activity. In addition, MDG-1 could ameliorate plasma lipid profiles, decrease leptin secretion, attenuate hepatic lipid accumulation and increased the expressions of genes related to lipid and energy metabolism in the liver. MDG-1 is a promising candidate drug to treat obesity-related metabolic diseases.


Assuntos
Dieta Hiperlipídica/efeitos adversos , Metabolismo Energético/efeitos dos fármacos , Obesidade/induzido quimicamente , Obesidade/tratamento farmacológico , Ophiopogon/química , Polissacarídeos/química , Polissacarídeos/uso terapêutico , Animais , Metabolismo dos Lipídeos/efeitos dos fármacos , Masculino , Camundongos , Camundongos Endogâmicos C57BL
17.
J Chem Phys ; 133(6): 064302, 2010 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-20707565

RESUMO

2-Aminopyridine dimer has frequently been used as a model system for studying photochemistry of DNA base pairs. We examine here the relevance of 2-aminopyridine dimer for a Watson-Crick adenine-thymine base pair by studying UV-light induced photodynamics along two main hydrogen bridges after the excitation to the localized (1)pi pi(*) excited-state. The respective two-dimensional potential-energy surfaces have been determined by time-dependent density functional theory with Coulomb-attenuated hybrid exchange-correlation functional (CAM-B3LYP). Different mechanistic aspects of the deactivation pathway have been analyzed and compared in detail for both systems, while the related reaction rates have also be obtained from Monte Carlo kinetic simulations. The limitations of the 2-aminopyridine dimer as a model system for the adenine-thymine base pair are discussed.


Assuntos
Adenina/química , Aminopiridinas/química , Pareamento de Bases , Timina/química , Dimerização , Ligação de Hidrogênio , Modelos Químicos , Modelos Moleculares , Método de Monte Carlo , Fotoquímica , Termodinâmica
18.
J Phys Chem A ; 114(4): 1980-4, 2010 Feb 04.
Artigo em Inglês | MEDLINE | ID: mdl-20050619

RESUMO

In the present work, density functional theory and canonical nonadiabatic Monte Carlo transition state theory have been used to investigate the histidine dissociation process from hexacoordinate heme in Ngb protein. The potential energy surfaces (PES) of the lowest singlet, triplet, and quintet states are calculated by stepwise optimization along with the histidine dissociation pathway. Based on the calculated two-dimensional PES, the histidine dissociation rates for the spin-forbidden processes via singlet to triplet and singlet to quintet transitions have been calculated by the nonadiabatic Monte Carlo transition state theory in canonical ensemble. The present study provides a quantitative description on spin-forbidden histidine dissociation processes.


Assuntos
Globinas/química , Heme/química , Histidina/química , Proteínas do Tecido Nervoso/química , Teoria Quântica , Simulação por Computador , Modelos Moleculares , Método de Monte Carlo , Neuroglobina
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