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1.
J Phys Chem Lett ; 9(13): 3604-3611, 2018 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-29902010

RESUMO

We report an investigation of lead halide perovskite CH3NH3PbBr3 nanocrystals and associated ligand molecules by combining several different state-of-the-art experimental techniques, including synchrotron radiation-based XPS and VUV PES of free-standing nanocrystals isolated in vacuum. By using this novel approach for perovskite materials, we could directly obtain complete band alignment to vacuum of both CH3NH3PbBr3 nanocrystals and the ligands widely used in their preparation. We discuss the possible influence of the ligand molecules to apparent perovskite properties, and we compare the electronic properties of nanocrystals to those of bulk material. The experimental results were supported by DFT calculations.

2.
Colloids Surf B Biointerfaces ; 155: 341-348, 2017 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-28454063

RESUMO

The interaction of the tryptophan functionalized Ag nanoparticles and live Candida albicans cells was studied by synchrotron excitation deep-ultraviolet (DUV) fluorescence imaging at the DISCO beamline of Synchrotron SOLEIL. DUV imaging showed that incubation of the fungus with functionalized nanoparticles results in significant increase in the fluorescence signal. The analysis of the images revealed that the interaction of the nanoparticles with (pseudo)hyphae polymorphs of the diploid fungus was less pronounced than in the case of yeast cells or budding spores. The changes in the intensity of the fluorescence signals of the cells after incubation were followed in [327-353nm] and [370-410nm] spectral ranges that correspond to the fluorescence of tryptophan in non-polar and polar environment, respectively. As a consequence of the environmental sensitivity of the silver-tryptophan fluorescent nanoprobe, we were able to determine the possible accumulation sites of the nanoparticles. The analysis of the intensity decay kinetics showed that the photobleaching effects were more pronounced in the case of the functionalized nanoparticle treated cells. The results of time-integrated emission in the mentioned spectral ranges suggested that the nanoparticles penetrate the cells, but that the majority of the nanoparticles attach to the cells' surfaces.


Assuntos
Antifúngicos/farmacologia , Candida albicans/efeitos dos fármacos , Hifas/efeitos dos fármacos , Nanopartículas Metálicas/química , Prata/farmacologia , Esporos Fúngicos/efeitos dos fármacos , Antifúngicos/química , Antifúngicos/metabolismo , Candida albicans/crescimento & desenvolvimento , Candida albicans/metabolismo , Candida albicans/ultraestrutura , Hifas/crescimento & desenvolvimento , Hifas/metabolismo , Hifas/ultraestrutura , Cinética , Imagem Óptica/métodos , Prata/química , Prata/metabolismo , Esporos Fúngicos/crescimento & desenvolvimento , Esporos Fúngicos/metabolismo , Esporos Fúngicos/ultraestrutura , Síncrotrons , Triptofano/química , Raios Ultravioleta
3.
J Am Chem Soc ; 138(51): 16596-16599, 2016 12 28.
Artigo em Inglês | MEDLINE | ID: mdl-27992194

RESUMO

Biological entities, such as DNA bases or proteins, possess numerous tautomers and isomers that lie close in energy, making the experimental characterization of a unique tautomer challenging. We apply VUV synchrotron-based experiments combined with state-of-the-art ab initio methodology to determine the adiabatic ionization energies (AIEs) of specific gas-phase cytosine tautomers produced in a molecular beam. The structures and energetics of neutral and cationic cytosine tautomers were determined using explicitly correlated methods. The experimental spectra correspond to well-resolved bands that are attributable to the specific contributions of five neutral tautomers of cytosine prior to ionization. Their AIEs are experimentally determined for the first time with an accuracy of 0.003 eV. This study also serves as an important showcase for other biological entities presenting a dense pattern of isomeric and tautomeric forms in their spectra that can be investigated to understand the charge redistribution in these species upon ionization.


Assuntos
Citosina/química , Fótons , Isomerismo , Processos Fotoquímicos
4.
Colloids Surf B Biointerfaces ; 135: 742-50, 2015 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-26340364

RESUMO

Biocompatible fluorescent nanostructures were prepared by a functionalization of gold nanoparticles with the amino acid tryptophan. The gold-tryptophan bioconjugates were investigated by TEM and HRTEM and various spectroscopy methods (XPS, FTIR, UV-vis and photoluminescence). It was found that the gold nanoparticles, initially 8 nm in diameter, aggregate in the presence of the amino acid. From the XPS and FTIR spectroscopy results, it was concluded that the tryptophan gold interactions mainly take place via indole and carboxyl groups. Although the indole group is involved in the interaction with the gold surfaces, the tryptophan-gold hybrids showed strong fluorescence due to the presence of multilayers of tryptophan. Deep ultra violet (DUV) imaging performed at the SOLEIL synchrotron showed that it is possible to detect these hybrid nanostructures within Escherichia coli cells.


Assuntos
Escherichia coli/química , Ouro/química , Nanopartículas Metálicas , Espectrofotometria Ultravioleta/métodos , Triptofano/química , Microscopia Eletrônica de Transmissão
5.
Carbohydr Polym ; 90(2): 1139-46, 2012 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-22840051

RESUMO

A silver nanoparticle colloid was prepared by a modified Tollens method using d-glucose as the reduction agent. The obtained nanoparticles were used for the modification of pine, linter and recycled cellulose fibers. Although the silver contents were relatively low (0.05-0.13 wt.%), the cellulose-sheets prepared from the modified fibers show improved mechanical and viscoelastic properties. The tensile index (strength) increased with up to 30% in comparison to the index of the sheets obtained from the untreated fibers. The influence of the nanoparticles on the viscoelastic properties of the cellulose sheets was investigated by dynamic mechanical analysis (DMA) in the temperature range from -120 to 20 °C and with a force frequency of 100 Hz. A broad relaxation transition positioned at -80 °C was observed in the loss modulus spectrum of all the cellulose sheets, while the Ag-modified sheets exhibited higher storage moduli values in the whole temperature range. The antimicrobial activity tests show that the pine, silver and recycled cellulose fiber sheets with silver nanoparticles can be successfully employed to prevent the viability and growth of the common pathogens Staphylococcus aureus, Escherichia coli and Candida albicans.


Assuntos
Anti-Infecciosos/síntese química , Celulose/química , Nanopartículas Metálicas/química , Prata/química , Substâncias Viscoelásticas/síntese química , Anti-Infecciosos/química , Anti-Infecciosos/farmacologia , Candida albicans/efeitos dos fármacos , Candida albicans/crescimento & desenvolvimento , Coloides , Escherichia coli/efeitos dos fármacos , Escherichia coli/crescimento & desenvolvimento , Testes de Sensibilidade Microbiana , Nanofibras/química , Prata/farmacologia , Staphylococcus aureus/efeitos dos fármacos , Staphylococcus aureus/crescimento & desenvolvimento , Propriedades de Superfície , Temperatura Ambiente , Substâncias Viscoelásticas/química , Substâncias Viscoelásticas/farmacologia
6.
J Biomater Sci Polym Ed ; 22(17): 2343-55, 2011.
Artigo em Inglês | MEDLINE | ID: mdl-21092423

RESUMO

A sago starch biopolymer with embedded silver nanoparticles has been studied as a material for the prevention of microbial growth. Approximately 8 nm in size, silver nanoparticles have been synthesized by reduction of the silver salt in aqueous solution in the presence of sago starch using sodium borohydride as a reducing agent. The obtained solutions were cast on glass plates to obtain thin supported silver-starch nanocomposite films. The morphology of the nanocomposites was investigated by scanning and transmission electron microscopy. UV-Vis absorption spectroscopy showed that during the film formation a part of the silver nanoparticles has been trapped in the water present in the sample, which enabled their partial oxidation into active Ag(+) species. The oxidation of the silver nanoparticles was confirmed by X-ray photoelectron spectroscopy. The antimicrobial activity tests have shown that the nanocomposite material can be successfully employed to prevent the viability and growth of the common pathogens Staphylococcus aureus, Escherichia coli and Candida albicans.


Assuntos
Antibacterianos/farmacologia , Escherichia coli/efeitos dos fármacos , Nanocompostos , Prata/farmacologia , Staphylococcus aureus/efeitos dos fármacos , Amido/farmacologia , Antibacterianos/química , Boroidretos/química , Candida albicans/efeitos dos fármacos , Candida albicans/fisiologia , Escherichia coli/fisiologia , Nanopartículas Metálicas/química , Microscopia Eletrônica de Varredura , Microscopia Eletrônica de Transmissão , Nanocompostos/química , Espectroscopia Fotoeletrônica , Prata/química , Análise Espectral , Staphylococcus aureus/fisiologia , Amido/química , Temperatura Ambiente , Água/química
7.
Colloids Surf B Biointerfaces ; 73(1): 30-5, 2009 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-19477103

RESUMO

Adsorption of sulfide ions onto a surface of starch capped silver nanoparticles upon addition of thioacetamide was investigated. UV-vis absorption spectroscopy revealed that the adsorption of the sulfide ion on the surface of the silver nanoparticles induced damping as well as blue shift of the silver surface plasmon resonance band. Further increase in thioacetamide concentration led to shift of the resonance band toward higher wavelengths indicating the formation of the continuous Ag2S layer on the silver surface. Thus fabricated nanoparticles were investigated using electron microscopy techniques (TEM, HRTEM, and HAADF-STEM) and X-ray photoelectron spectroscopy (XPS), which confirmed their core-shell structure.


Assuntos
Biopolímeros/química , Nanopartículas/química , Prata/química , Amido/química , Enxofre/química , Adsorção , Microscopia Eletrônica de Transmissão , Nanopartículas/ultraestrutura , Espectrofotometria , Sulfetos/química , Ressonância de Plasmônio de Superfície , Propriedades de Superfície , Tioacetamida/química , Difração de Raios X
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