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1.
Food Chem ; 304: 125446, 2020 Jan 30.
Artigo em Inglês | MEDLINE | ID: mdl-31491715

RESUMO

Fused coumarins recently attracted strong scientific interest due to their potent pharmacological activities. In this study, density functional theory (DFT) calculations were performed to evaluate the antiradical activities of a series of coumarin-fused coumarins. By calculating the thermodynamic parameters, three primary mechanisms including hydrogen atom transfer (HAT), electron transfer followed by proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET) were examined. It was found that in the gas and benzene phases, the studied compounds prefer to undergo HAT mechanism, while SPLET is more favored in polar media. The results also reveal the possibility of double HAT and double SPLET mechanisms for compound CC-6. Interestingly, a new polycyclic compound was generated by forming a new C5-O5' bond during the second HAT process at the 5'-OH in CC-6-R6 radical. In addition, the SPLHAT mechanism is proposed as a competitive pathway for radical scavenging by CC-4, CC-5 and CC-6.

2.
J Phys Chem A ; 122(43): 8520-8529, 2018 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-30296082

RESUMO

In view of the multifunctional features of coumarins and chalcones, coumarin-chalcone hybrids have attracted much attention in recent years. Herein, the free radical scavenging activities of a series of coumarin-chalcone hybrids were investigated using the density functional theory (DFT) method. Three main reaction mechanisms were explored: hydrogen atom transfer (HAT), electron transfer followed by proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET). Thermodynamic descriptors associated with these mechanisms were calculated in the gas phase and solvents. The results demonstrate that the predicted antioxidant efficiencies are generally in accordance with the experimental results. HAT is proposed as the thermodynamically favored mechanism in the gas phase and nonpolar solution, while SPLET is preferred in polar media. Our results indicate that compound MPHCC possesses potential for inactivating free radicals via double HAT and double SPLET mechanisms depending upon the polarity of environment. In addition, the SPLHAT mechanism provides an alternative pathway to HAT and SPLET for radical scavenging by MPHCC and OPHCC. The results confirmed the crucial role of hydroxyl groups on the chalcone moiety in trapping radicals. 4'-OH in the catechol group is proposed as the primary target for radical attack.

3.
Inorg Chem ; 54(4): 1215-7, 2015 Feb 16.
Artigo em Inglês | MEDLINE | ID: mdl-25602599

RESUMO

Polyanionic cluster [ß-As8V14O42(H2O)](4-) is well embedded in a large porous eight-membered cationic ring of the copper ligand, giving a stable host-guest supramolecular system. The assembly exhibits an efficient heterogeneous catalytic performance for the reduction of Cr(VI) using formic acid at ambient temperature.

4.
ACS Appl Mater Interfaces ; 6(12): 9160-72, 2014 Jun 25.
Artigo em Inglês | MEDLINE | ID: mdl-24844411

RESUMO

Single-composition white-emitting phosphors with superior intrinsic properties upon excitation by ultraviolet light-emitting diodes are important constituents of next-generation light sources. Borate-based phosphors, such as NaSrBO3:Ce(3+) and NaCaBO3:Ce(3+), have stronger absorptions in the near-ultraviolet region as well as better chemical/physical stability than oxides. Energy transfer effects from sensitizer to activator caused by rare-earth ions are mainly found in the obtained photoluminescence spectra and lifetime. The interactive mechanisms of multiple dopants are ambiguous in most cases. We adjust the doping concentration in NaSrBO3:RE (RE = Ce(3+), Tb(3+), Mn(2+)) to study the energy transfer effects of Ce(3+) to Tb(3+) and Mn(2+) by comparing the experimental data and theoretical calculation. The vacuum-ultraviolet experimental determination of the electronic energy levels for Ce(3+) and Tb(3+) in the borate host regarding the 4f-5d and 4f-4f configurations are described. Evaluation of the Ce(3+)/Mn(2+) intensity ratios as a function of Mn(2+) concentration is based on the analysis of the luminescence dynamical process and fluorescence lifetime measurements. The results closely agree with those directly obtained from the emission spectra. Density functional calculations are performed using the generalized gradient approximation plus an on-site Coulombic interaction correction scheme to investigate the forbidden mechanism of interatomic energy transfer between the NaSrBO3:Ce(3+) and NaSrBO3:Eu(2+) systems. Results indicate that the NaSrBO3:Ce(3+), Tb(3+), and Mn(2+) phosphors can be used as a novel white-emitting component of UV radiation-excited devices.

5.
Enzyme Microb Technol ; 48(6-7): 438-44, 2011 May 06.
Artigo em Inglês | MEDLINE | ID: mdl-22113014

RESUMO

With improved enzymatic activity and easy accessibility, the recombinant purine nucleoside phosphorylase (PNPase) could be a very promising alternative for nucleoside biosynthesis. In our work, the deoD gene encoding PNPase was successfully cloned from Escherichia coli MG1665 and overexpressed in E. coli BL 21(DE3). After optimization of expression conditions including temperature, induction timing and isopropyl-thio-ß-D-galactoside (IPTG) concentration, over 70% of expressed total protein was His-tagged PNPase, in the soluble and functional form. Followed assays indicated that the recombinant enzyme exhibited similar substrate specificity and pH preference as the wild type PNPase. Furthermore, the immobilization technology was applied to develop the possible application of recombinant enzyme. Agar from four different polymer carriers was selected as a suitable matrix for whole recombinant cell entrapment. Subsequent enzyme assays, kinetic analysis and stability evaluation of free and immobilized recombinant cells were compared. The results indicated that although the immobilization process reduced the substrate affinity and catalytic efficiency of recombinant cells, it could significantly enhance the stability and reusability of these cells. Finally, the immobilized whole cell biocatalyst was applied to produce ribavirin, as a model nucleoside synthesis reaction. The obtained relative high productivity of ribavirin and quick reaction time suggested the great potential and feasibility of immobilized PNPase in efficient and valuable industrial utilizations.


Assuntos
Células Imobilizadas , Proteínas de Escherichia coli/genética , Escherichia coli/enzimologia , Genes Bacterianos , Purina-Núcleosídeo Fosforilase/genética , Ribavirina/metabolismo , Ágar , Biocatálise , Clonagem Molecular , Proteínas de Escherichia coli/isolamento & purificação , Proteínas de Escherichia coli/metabolismo , Géis , Guanosina/metabolismo , Concentração de Íons de Hidrogênio , Cinética , Purina-Núcleosídeo Fosforilase/isolamento & purificação , Purina-Núcleosídeo Fosforilase/metabolismo , Proteínas Recombinantes de Fusão/isolamento & purificação , Proteínas Recombinantes de Fusão/metabolismo , Especificidade por Substrato , Temperatura Ambiente , Triazóis/metabolismo
6.
J Colloid Interface Sci ; 302(2): 530-6, 2006 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-16889789

RESUMO

Phase-pure, ultrafine nanocrystalline anatase with high specific surface area (up to 250 m(2) g(-1)) was obtained upon injection of a titanium alkoxide precursor into ethanol with designed volume of water under mild solvothermal conditions (<200 degrees C, 2 h). Primary particle sizes were tuned by adjusting various reaction parameters, with the smallest grain sizes occurring at low temperatures (140-150 degrees C), low initial alkoxide concentrations, and intermediate hydrolysis ratios (r identical with[H2O]/[Ti(OR)4]=5-10). Additionally, variations in the reaction temperature result in changes in particle morphology and distribution, with high-temperature samples exhibiting bimodal distributions of small spherical and larger cubic particles that suggest grain growth via Ostwald ripening. A crystalline product with high thermal stability and specific surface area up to 5 times that of commercial nano-titania can be obtained at a relatively low temperature of 150 degrees C. The physical properties of the titania samples obtained in this study suggest they might be well suited for catalytic applications.


Assuntos
Nanoestruturas/química , Temperatura Ambiente , Titânio/química , Adsorção , Tamanho da Partícula , Solventes/química , Propriedades de Superfície
7.
Toxicol Sci ; 92(1): 174-85, 2006 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-16613837

RESUMO

Nanocrystalline titanium dioxide (nano-TiO(2)) is an important material used in commerce today. When designed appropriately it can generate reactive species (RS) quite efficiently, particularly under ultraviolet (UV) illumination; this feature is exploited in applications ranging from self-cleaning glass to low-cost solar cells. In this study, we characterize the toxicity of this important class of nanomaterials under ambient (e.g., no significant light illumination) conditions in cell culture. Only at relatively high concentrations (100 microg/ml) of nanoscale titania did we observe cytotoxicity and inflammation; these cellular responses exhibited classic dose-response behavior, and the effects increased with time of exposure. The extent to which nanoscale titania affected cellular behavior was not dependent on sample surface area in this study; smaller nanoparticlulate materials had effects comparable to larger nanoparticle materials. What did correlate strongly to cytotoxicity, however, was the phase composition of the nanoscale titania. Anatase TiO(2), for example, was 100 times more toxic than an equivalent sample of rutile TiO(2). The most cytotoxic nanoparticle samples were also the most effective at generating reactive oxygen species; ex vivo RS species generation under UV illumination correlated well with the observed biological response. These data suggest that nano-TiO(2) samples optimized for RS production in photocatalysis are also more likely to generate damaging RS species in cell culture. The result highlights the important role that ex vivo measures of RS production can play in developing screens for cytotoxicity.


Assuntos
Pulmão/efeitos dos fármacos , Pele/efeitos dos fármacos , Titânio/química , Titânio/toxicidade , Linhagem Celular , Células Epiteliais/efeitos dos fármacos , Fibroblastos/efeitos dos fármacos , Humanos , Interleucina-8/biossíntese , L-Lactato Desidrogenase/metabolismo , Pulmão/citologia , Pulmão/enzimologia , Pulmão/metabolismo , Estrutura Molecular , Nanotecnologia , Tamanho da Partícula , Espécies Reativas de Oxigênio/metabolismo , Pele/citologia , Pele/enzimologia , Pele/metabolismo , Raios Ultravioleta , Difração de Raios X
8.
Nano Lett ; 5(5): 963-7, 2005 May.
Artigo em Inglês | MEDLINE | ID: mdl-15884903

RESUMO

Analytical ultracentrifugation (AU) provides a general way to probe the polydispersity of nanoparticles and the formation of bioconjugates in solution. Unconjugated gold nanocrystals show sedimentation coefficient distributions that are in agreement with size distributions as measured by TEM. AU is sensitive to the size/shape changes elicited by conjugation, in this case to lactose repressor (LacI). AU data reveal saturating protein concentrations for conjugates that correspond to the measured stoichiometry of the complex under these conditions.


Assuntos
Algoritmos , Materiais Revestidos Biocompatíveis/análise , Materiais Revestidos Biocompatíveis/química , Nanoestruturas/análise , Nanoestruturas/química , Nanotecnologia/métodos , Ultracentrifugação/métodos , Cristalização/métodos , Ouro/química , Nanoestruturas/ultraestrutura , Tamanho da Partícula , Proteínas Repressoras/análise , Proteínas Repressoras/química , Proteínas Repressoras/ultraestrutura
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