Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 15 de 15
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Molecules ; 27(14)2022 Jul 21.
Artigo em Inglês | MEDLINE | ID: mdl-35889526

RESUMO

Copolymers are valuable supports for obtaining heterogeneous catalysts that allow their recycling and therefore substantial savings, particularly in the field of asymmetric catalysis. This contribution reports the use of two comonomers: Azido-3-propylmethacrylate (AZMA) bearing a reactive azide function was associated with 2-methoxyethyl methacrylate (MEMA), used as a spacer, for the ATRP synthesis of copolymers, and then post-functionalized with a propargyl chromium salen complex. The controlled homopolymerization of MEMA by ATRP was firstly described and proved to be more controlled in molar mass than that of AZMA for conversions up to 63%. The ATRP copolymerization of both monomers made it possible to control the molar masses and the composition, with nevertheless a slight increase in the dispersity (from 1.05 to 1.3) when the incorporation ratio of AZMA increased from 10 to 50 mol%. These copolymers were post-functionalized with chromium salen units by click chemistry and their activity was evaluated in the asymmetric ring opening of cyclohexene oxide with trimethylsilyl azide. At an equal catalytic ratio, a significant increase in enantioselectivity was obtained by using the copolymer containing the largest part of salen units, probably allowing, in this case, the more favorable bimetallic activation of both the engaged nucleophile and electrophile. Moreover, the catalytic polymer was recovered by simple filtration and re-engaged in subsequent catalytic runs, up to seven times, without loss of activity or selectivity.


Assuntos
Etilenodiaminas , Polímeros , Catálise , Cromo , Etilenodiaminas/química , Polímeros/química
2.
Anal Bioanal Chem ; 413(5): 1417-1428, 2021 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-33388848

RESUMO

Surface-enhanced Raman scattering (SERS), based on the enhancement of the Raman signal of molecules positioned within a few nanometres from a structured metal surface, is ideally suited to provide bacterial-specific molecular fingerprints which can be used for analytical purposes. However, for some complex structures such as bacteria, the generation of reproducible SERS spectra is still a challenging task. Among the various factors influencing the SERS variability (such as the nature of SERS-active substrate, Raman parameters and bacterial specificity), we demonstrate in this study that the environment of Gram-positive and Gram-negative bacteria deposited on ultra-thin silver films also impacts the origin of the SERS spectra. In the case of densely packed bacteria, the obtained SERS signatures were either characteristic of the secretion of adenosine triphosphate for Staphylococcus aureus (S. aureus) or the cell wall and the pili/flagella for Escherichia coli (E. coli), allowing for an easy discrimination between the various strains. In the case of isolated bacteria, SERS mapping together with principal component analysis revealed some variabilities of the spectra as a function of the bacteria environment and the bactericidal effect of the silver. However, the variability does not preclude the SERS signatures of various E. coli strains to be discriminated.


Assuntos
Escherichia coli/química , Análise Espectral Raman/métodos , Staphylococcus aureus/química , Escherichia coli/citologia , Infecções por Escherichia coli/microbiologia , Humanos , Prata/química , Infecções Estafilocócicas/microbiologia , Staphylococcus aureus/citologia , Propriedades de Superfície
3.
Langmuir ; 36(46): 13908-13917, 2020 11 24.
Artigo em Inglês | MEDLINE | ID: mdl-33166140

RESUMO

The association of a mycotoxin-ochratoxin A (OTA)-with a high-affinity DNA aptamer (anti-OTA) immobilized on a functionalized surface has been investigated at the molecular level. Anti-OTA aptamers are coupled by aminolysis in several steps on an acid-terminated alkyl monolayer grafted on a silicon substrate, and Fourier transform infrared spectroscopy in attenuated total reflection geometry is used to assess the immobilization of anti-OTA (in its unfolded single-strand form) and determine its areal density (ca. 1.4/nm2). IR spectra further demonstrate that the OTA/anti-OTA association is efficient and selective and that several association/dissociation cycles may be conducted on the same surface. The areal density of OTA measured after association on the surface (IR spectroscopy) and after dissociation from the surface (UV-vis spectroscopy) falls in the range 0.16-0.3/nm2 which is close to the areal density of a closed-packed monolayer of anti-OTA aptamers folded to form their G-quadruplex structure. The interactions between OTA and its aptamer at the surface are discussed with the help of density functional theory calculations-to identify the complex IR vibrational modes of OTA in solution-and UV-vis spectroscopy-to determine the protonation state of the adsorbing species (i.e., OTA dissolved in the buffer solution).

4.
ACS Appl Mater Interfaces ; 9(3): 3075-3084, 2017 Jan 25.
Artigo em Inglês | MEDLINE | ID: mdl-27977928

RESUMO

Silicon nitride is used for many technological applications, but a quantitative knowledge of its surface chemistry is still lacking. Native oxynitride at the surface is generally removed using fluorinated etchants, but the chemical composition of surfaces still needs to be determined. In this work, the thinning (etching efficiency) of the layers after treatments in HF and NH4F solutions has been followed by using spectroscopic ellipsometry. A quantitative estimation of the chemical bonds found on the surface is obtained by a combination of infrared absorption spectroscopy in ATR mode, X-ray photoelectron spectroscopy, and colorimetry. Si-F bonds are the majority species present at the surface after silicon nitride etching; some Si-OH and a few Si-NHx bonds are also present. No Si-H bonds are present, an unfavorable feature for surface functionalization in view of the interest of such mildly reactive groups for achieving stable covalent grafting. Mechanisms are described to support the experimental results, and two methods are proposed for generating surface SiH species: enriching the material in silicon, or submitting the etched surface to a H2 plasma treatment.

5.
J Colloid Interface Sci ; 464: 198-205, 2016 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-26619130

RESUMO

Essential to the success of any surface-based carbohydrate biochip technology is that interactions of the particular interface with the target protein be reliable and reproducible and not susceptible to unwanted nonspecific adsorption events. This condition is particularly important when the technology is intended for the evaluation of low-affinity interactions such as those typically encountered between lectins and their monomeric glycan ligands. In this paper, we describe the fabrication of glycan (mannoside and lactoside) monolayers immobilized on hydrogenated crystalline silicon (111) surfaces. An efficient conjugation protocol featuring a key "click"-based coupling step has been developed which ensures the obtention of interfaces with controlled glycan density. The adsorption behavior of these newly developed interfaces with the lectins, Lens culinaris and Peanut agglutinin, has been probed using quantitative IR-ATR and the data interpreted using various isothermal models. The analysis reveals that protein physisorption to the interface is more prevalent than specific chemisorption for the majority of washing protocols investigated. Physisorption can be greatly suppressed through application of a strong surfactinated rinse. The coexistence of chemisorption and physisorption processes is further demonstrated by quantification of the amounts of adsorbed proteins distributed on the surface, in correlation with the results obtained by atomic force microscopy (AFM). Taken together, the data demonstrates that the nonspecific adsorption of proteins to these glycan-terminated surfaces can be effectively eliminated through the proper control of the chemical structure of the surface monolayer combined with the implementation of an appropriate surface-rinse protocol.


Assuntos
Lectinas/química , Polissacarídeos/química , Silício/química , Estrutura Molecular , Tamanho da Partícula , Especificidade por Substrato , Propriedades de Superfície
6.
Anal Chem ; 87(7): 3721-8, 2015 Apr 07.
Artigo em Inglês | MEDLINE | ID: mdl-25729928

RESUMO

Carbohydrate arrays are potentially one of the most attractive tools to study carbohydrate-based interactions. This paper describes a new analytical platform that exploits metal-enhanced fluorescence for the sensitive and selective screening of carbohydrate-lectin interactions. The chip consists of a glass slide covered with gold nanostructures, postcoated with a thin layer of amorphous silicon-carbon alloy (a-Si0.8C0.2:H). An immobilization strategy based on the formation of a covalent bond between propargyl-terminated glycans and surface-linked azide groups was used to attach various glycans at varying surface densities onto the interface and to fabricate a carbohydrate array via efficient local "click" chemistry strategy. The specific association of the new interface with fluorescently labeled lectins was assessed by fluorescence imaging and an excellent selectivity to specific proteins was achieved. Optimization of the surface architecture and the plasmonic transducer resulted in an enhancement of the fluorescence intensity by 1 order of magnitude, when compared to the corresponding substrate devoid of gold nanostructures. The limit of detection (LOD) of such microarrays is in the picomolar range, making it a promising system for development in pharmaceutical or biomedical applications.


Assuntos
Ouro/química , Lectinas/metabolismo , Análise em Microsséries/instrumentação , Nanoestruturas/química , Imagem Óptica/instrumentação , Polissacarídeos/metabolismo , Azidas/química , Química Click , Desenho de Equipamento , Corantes Fluorescentes/análise , Corantes Fluorescentes/metabolismo , Lectinas/análise , Polissacarídeos/química
7.
Anal Chem ; 86(20): 10340-9, 2014 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-25216376

RESUMO

A key challenge in the development of glycan arrays is that the sensing interface be fabricated reliably so as to ensure the sensitive and accurate analysis of the protein-carbohydrate interaction of interest, reproducibly. These goals are complicated in the case of glycan arrays as surface sugar density can influence dramatically the strength and mode of interaction of the sugar ligand at any interface with lectin partners. In this Article, we describe the preparation of carboxydecyl-terminated crystalline silicon (111) surfaces onto which are grafted either mannosyl moieties or a mixture of mannose and spacer alcohol molecules to provide "diluted" surfaces. The fabrication of the silicon surfaces was achieved efficiently through a strategy implicating a "click" coupling step. The interactions of these newly fabricated glycan interfaces with the lectin, Lens culinaris, have been characterized using quantitative infrared (IR) spectroscopy in the attenuated total geometry (ATR). The density of mannose probes and lectin targets was precisely determined for the first time by the aid of special IR calibration experiments, thus allowing for the interpretation of the distribution of mannose and its multivalent binding with lectins. These experimental findings were accounted for by numerical simulations of lectin adsorption.


Assuntos
Carboidratos/química , Técnicas de Química Analítica/métodos , Proteínas/metabolismo , Silício/química , Estrutura Molecular , Proteínas/química , Espectroscopia de Infravermelho com Transformada de Fourier , Propriedades de Superfície
8.
Langmuir ; 28(41): 14654-64, 2012 Oct 16.
Artigo em Inglês | MEDLINE | ID: mdl-22988984

RESUMO

Various poly(ethylene glycol) monomethyl ether moieties were grafted onto hydrogenated silicon surfaces in order to investigate the influence of the molecular design on the antifouling performance of such coatings. The grafted chains were either oligo(ethylene oxide) chains (EG)(n)OMe bound to silicon via Si-O-C covalent bonds, or hybrid alkyl/oligo(ethylene oxide) chains C(p)(EG)(n)OMe bound via Si-C covalent bonds (from home-synthesized precursors). Quantitative IR spectroscopy gave the molecular coverage of the grafted layers, and AFM imaging demonstrated that a proper surfactinated rinse yields C(p)(EG)(n)OMe layers free of unwanted residues. The protein-repellent character of these grafted layers (here, toward BSA) was studied by IR and AFM imaging. C(p)(EG)(n)OMe layers exhibit a lower surface concentration than (EG)(n)OMe layers, because of the presence of a solvent in the grafting solution; they however demonstrate high resistance against BSA adsorption for high values of the n/p ratio and a higher stability than (EG)(n)OMe. This behavior is consistently explained by the poor ordering capability of the alkyl part of the layer, contrary to what is observed for similar layers on Au, and the key role of an entangled arrangement of the ethylene oxide chains which forms when these chains are long enough.


Assuntos
Incrustação Biológica/prevenção & controle , Polietilenoglicóis/química , Soroalbumina Bovina/química , Silício/química , Adsorção , Animais , Bovinos , Interações Hidrofóbicas e Hidrofílicas , Estrutura Molecular , Propriedades de Superfície
9.
Nanoscale Res Lett ; 6(1): 412, 2011 Jun 06.
Artigo em Inglês | MEDLINE | ID: mdl-21711937

RESUMO

In this work, a Glycyl-Histidyl-Glycyl-Histidine (GlyHisGlyHis) peptide is covalently anchored to the porous silicon PSi surface using a multi-step reaction scheme compatible with the mild conditions required for preserving the probe activity. In a first step, alkene precursors are grafted onto the hydrogenated PSi surface using the hydrosilylation route, allowing for the formation of a carboxyl-terminated monolayer which is activated by reaction with N-hydroxysuccinimide in the presence of a peptide-coupling carbodiimide N-ethyl-N'-(3-dimethylaminopropyl)-carbodiimide and subsequently reacted with the amino linker of the peptide to form a covalent amide bond. Infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy are used to investigate the different steps of functionalization.The property of peptides to form stable complexes with metal ions is exploited to achieve metal-ion recognition by the peptide-modified PSi-based biosensor. An electrochemical study of the GlyHisGlyHis-modified PSi electrode is achieved in the presence of copper ions. The recorded cyclic voltammograms show a quasi-irreversible process corresponding to the Cu(II)/Cu(I) couple. The kinetic factors (the heterogeneous rate constant and the transfer coefficient) and the stability constant of the complex formed on the porous silicon surface are determined. These results demonstrate the potential role of peptides grafted on porous silicon in developing strategies for simple and fast detection of metal ions in solution.

10.
Langmuir ; 27(9): 5498-505, 2011 May 03.
Artigo em Inglês | MEDLINE | ID: mdl-21480606

RESUMO

Monolayers of metal complexes were covalently attached to the surface of lamellar SPR interfaces (Ti/Ag/a-Si(0.63)C(0.37)) for binding histidine-tagged peptides with a controlled molecular orientation. The method is based on the activation of surface acid groups with N-hydroxysuccinimide (NHS), followed by an amidation reaction with (S)-N-(5-amino-1-carboxypentyl)iminodiacetic acid (NTA). FTIR and X-ray photoelectron spectroscopy (XPS) were used to characterize each surface modification step. The NTA modified SPR interface effectively chelated Cu(2+) ions. Once loaded with metal ions, the modified SPR interface was able to bind specifically to histidine-tagged peptides. The binding process was followed by surface plasmon resonance (SPR) in a droplet based configuration. The Cu(2+)-NTA modified interface showed protein loading comparable to commercially available NTA chips based on dextran chemistry and can thus be regarded as an interesting alternative. The sensor interface can be reused several times due to the easy regeneration step using ethylenediaminetetraacetic acid (EDTA) treatment.


Assuntos
Quelantes/química , Histidina/química , Metais/química , Peptídeos/química , Ressonância de Plasmônio de Superfície/métodos , Aminas/química , Sequência de Aminoácidos , Bradicinina/química , Bradicinina/metabolismo , Proteínas Imobilizadas/química , Proteínas Imobilizadas/metabolismo , Dados de Sequência Molecular , Ácido Nitrilotriacético/química
11.
Analyst ; 136(9): 1859-66, 2011 May 07.
Artigo em Inglês | MEDLINE | ID: mdl-21437320

RESUMO

The use of an amorphous silicon-carbon alloy overcoating on silver nanostructures in a localized surface plasmon resonance (LSPR) sensing platform allows for decreasing the detection limit by an order of magnitude as compared to sensors based on gold nanostructures deposited on glass. In addition, silver based multilayer structures show a distinct plasmonic behaviour as compared to gold based nanostructures, which provides the sensor with an increased short-range sensitivity and a decreased long-range sensitivity.


Assuntos
Ligas/química , Técnicas Biossensoriais/métodos , Nanopartículas Metálicas/química , Hibridização de Ácido Nucleico/métodos , Silício/química , Prata/química , Técnicas Biossensoriais/instrumentação , DNA/química , Vidro/química , Ouro/química , Ressonância de Plasmônio de Superfície/métodos
12.
Biosens Bioelectron ; 25(12): 2579-85, 2010 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-20483582

RESUMO

Versatile and highly-sensitive detection of DNA hybridization is described using metal nanostructures-enhanced fluorescence (MEF) emission intensity when fluorescently-labeled DNA oligomers are covalently immobilized on a nanometer-thin amorphous silicon-carbon layer capping the metal nanostructures. The MEF structures are formed by thermal deposition of silver, gold or silver/gold thin films on glass surfaces and post-annealing at 500 degrees C. The choice of the metal film allows for tuning the optical properties of the interface. The metallic nanostructures are subsequently coated with an amorphous thin silicon-carbon alloy (a-Si(0.80)C(0.20): H) layer deposited by PECVD. Carboxydecyl groups are attached on these surfaces through hydrosilylation then reacted with amine-terminated single-stranded DNA oligomers, forming a covalent link. The immobilized DNA is hybridized with its complementary strand carrying a fluorescent label. Through optimization of the thickness of the a-Si(0.80)C(0.20): H alloy overlayer and by working close to resonance conditions for plasmon and fluorophore excitation, the hybridization of very dilute oligomers (5 fM) is easily detected, and the hybridization kinetics can be monitored in situ and in real-time.


Assuntos
DNA/química , Hibridização de Ácido Nucleico/métodos , Espectrometria de Fluorescência/métodos , Ressonância de Plasmônio de Superfície/métodos , Sequência de Bases , Carbono , DNA/genética , DNA de Cadeia Simples/química , DNA de Cadeia Simples/genética , Corantes Fluorescentes , Ouro , Nanopartículas Metálicas , Silício , Prata
13.
Langmuir ; 26(8): 6058-65, 2010 Apr 20.
Artigo em Inglês | MEDLINE | ID: mdl-20131832

RESUMO

The paper reports on a novel surface plasmon resonance (SPR) substrate architecture based on the coating of a gold (Au) or silver (Ag) substrate with 5 nm thin amorphous silicon-carbon alloy films. Ag/a-Si(1-x)C(x):H and Au/a-Si(1-x)C(x):H multilayers are found to provide a significant advantage in terms of sensitivity over both Ag and Au for SPR refractive index sensing. The possibility for the subsequent linking of stable organic monolayers through Si-C bonds is demonstrated. In a proof-of-principle experiment that this structure can be used for real-time biosensing experiments, amine terminated biotin was covalently linked to the acid-terminated SPR surface and the specific streptavidin-biotin interaction recorded.


Assuntos
Ligas/química , Carbono/química , Ouro/química , Membranas Artificiais , Silício/química , Prata/química , Ressonância de Plasmônio de Superfície/métodos , Modelos Químicos , Estrutura Molecular
14.
Biosens Bioelectron ; 25(5): 1199-203, 2010 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-19959351

RESUMO

This paper describes a novel platform for preparing localized surface plasmon resonance (LSPR) sensing surfaces. It is based on the coating of gold nanostructures deposited on glass with an amorphous silicon-carbon alloy overcoating. The interest in coating the Au NSs with an amorphous silicon-carbon alloy resides in the possibility of incorporating carboxyl functions directly onto the surface via Si-C covalent bonds. This permits the use of hyrdosilylation reactions to modify the sensor surface. The use of this multilayer structure for the detection of hybridization events is discussed.


Assuntos
Técnicas Biossensoriais/instrumentação , Carbono/química , DNA/química , DNA/genética , Hibridização In Situ/instrumentação , Silício/química , Ressonância de Plasmônio de Superfície/instrumentação , Ligas , Desenho de Equipamento , Análise de Falha de Equipamento , Reprodutibilidade dos Testes , Sensibilidade e Especificidade
15.
Langmuir ; 22(1): 153-62, 2006 Jan 03.
Artigo em Inglês | MEDLINE | ID: mdl-16378414

RESUMO

This work demonstrates that well-defined mixed carboxyl-terminated/methyl-terminated alkyl monolayers can be prepared in one step on H-terminated Si(111) via direct photochemical hydrosilylation of undecylenic acid and 1-decene mixtures. As evidenced by AFM imaging and IR spectroscopy, a final rinse in hot acetic acid leaves the functionalized surface atomically smooth and perfectly free of physisorbed contaminants while unwanted material remains atop the monolayer with most other common solvents. The compositional surface chemistry was determined from a truly quantitative IR (ATR geometry) study in the range of 900-4000 cm(-)(1). Results prove that neither surface oxidation nor grafting through the carboxyl end groups occurs. Monolayers are fairly dense for such bulky end groups, with a total molecular surface density of approximately 2.7 10(14) cm(-)(2) corresponding to a surface coverage of 0.35 (maximum theoretical value approximately 0.5). Careful analysis of the CH- and COOH-related IR bands reveals that the composition of the grafted layers is richer in acid chains than the starting grafting mixture. A simple model is presented that shows that the grafting kinetics is about twice as fast for undecylenic acid as for 1-decene. Complementary electrochemical impedance measurements indicate the excellent electronic properties of the interface with a very low density of gap states. They also show that the acid terminal groups promote the penetration of water in the outer part of the organic film.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...