RESUMO
Nanocomposites with bimetallic monolayers of porphyrins were prepared. The well-ordered metalloporphyrin monolayers covalently linked to the gold surface produce an important increase of the B band (â¼400 nm) shifted 20 nm relative to that of the related high-spin iron(III) complexes in solution. The position of the B band in the bimetallic architectures is highly dependent on the relative amount of the two porphyrins, showing the most significant shift for the SiO2/APTES/AuNp/Fe-TPyP&M-TPyP (1:1) (30 nm, M = Ni(II) or Cu(II)). Resonance Raman based on the oxidation state marker bands (1553, 1354, and 390 cm(-1)) indicates that Fe-TPyP attached on gold nanoparticles adopts a low-spin Fe(II) conformation, which changes to Fe(II) intermediate spin or a low-spin Fe(III) in the presence of Cu-TPyP or Ni-TPyP. Surface-enhanced Raman scattering studies confirmed the hypothesis. MALDI-TOF analysis of the composites on gold nanoparticles was very useful in the detection of oxygenated forms of the metal complexes.
RESUMO
Poly [Ni-Protoporphyrin] film (pNiPP), containing multiwall carbon nanotubes (MWCNT) was used to cover a glassy carbon electrode. The hybrid material (pNiPP/MWCNT) successfully combines the permselectivity of pNiPP with the high conductivity of MWCNT. The modified electrode was used to perform amperometric detection of long chain aliphatic amines (LCAA) in order to prevent the passivation effect of the aliphatic chain. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) demonstrated that the pNiPP/MWCNT facilitates the electron transfer reaction. The charge transfer resistance (Rct) values were significantly lower by up to one order of magnitude compared to the bare electrode. Differential pulse polarography (DPP) showed a marked decrease of the overpotential generated by the aliphatic chain. The calibration of the amperometric peak area vs. concentrations of derivatized LCAA exhibits a linear response within the range of 0.018 and 28 µM and correlation coefficient (R(2)) higher than 0.999 (n=5). The quantitation limit of the pNiPP/MWCNT electrode is about 400 times lower than the UV-visible detection. RSD of 7.2%, 5.8%, 2.5% and 2.3% was obtained for concentrations of 0.028, 0.28, 2.8 and 28 µM of ferrocenyl octadecylamine. A solution of sphingosine, 0.23 µM, was exclusively detected with HPLC-ECD with pNiPP/MWCNT electrode.
Assuntos
Aminas/análise , Metaloporfirinas/química , Nanocompostos/química , Nanotubos de Carbono/química , Níquel/química , Protoporfirinas/química , Aminas/química , Condutividade Elétrica , EletroquímicaRESUMO
We report a new method of immobilization of gold nanoparticles (AuNPs) on a fused-silica capillary through covalent binding. The resulting modified capillary was applied to electrophoretic systems to improve the efficiency of separation and the selectivity of selected solutes. The immobilization of AuNPs on the capillary wall was performed in a very simple and fast way without requiring heating. The surface features of an AuNP-coated capillary column were determined using the scanning electron microscopy. The chromatographic properties of AuNP-coated capillaries were investigated through variation of the buffer pH and separation voltage. Effective separations of synthetic peptides mixture were obtained on the AuNP-coated capillaries. The method shows a remarkable stability since it was reused about 900 times. The capacity factor was duplicated. Therefore, this modification is stable and can be applied to different separation purposes. A complex mixture of tryptic peptide fragments of HSA was analyzed in both the bare- and the AuNP-coated capillaries. Better electrophoretic peptide profile was observed when using the AuNP-coated capillary.
Assuntos
Eletrocromatografia Capilar/instrumentação , Eletrocromatografia Capilar/métodos , Ouro/química , Nanopartículas Metálicas/química , Peptídeos/análise , Proteínas/análise , Humanos , Concentração de Íons de Hidrogênio , Microscopia Eletrônica de Varredura , Fragmentos de Peptídeos/análise , Fragmentos de Peptídeos/isolamento & purificação , Peptídeos/isolamento & purificação , Proteínas/isolamento & purificação , Espectrofotometria Ultravioleta , Tripsina/químicaRESUMO
The inner surface of fused silica capillaries has been covalently modified with different porphyrins (deuteroporphyrin, complexes of deuteroporphyrin with metal ions Fe(III), Cu(II), Zn(II), Ni(II), and Cu(II)-meso-tetra (carboxyphenyl) porphyrin) and it was applied for the separation of biologically active peptides by open-tubular capillary electrochromatography. Separations were performed in a mobile phase composed of 25 mM potassium phosphate, pH 4.0, 5% v/v ACN and 10 mM hydroquinone. Changes in the effective electrophoretic mobility of peptides were studied concerning porphyrin central metal atom, attachment geometry, and the presence of coordinating or aromatic amino acid residues in the peptide sequence. The results showed that differences in metal core on the porphyrin and the spatial conformation of attached porphyrin result in changes in the analyte interaction with the stationary phase.
Assuntos
Eletrocromatografia Capilar/instrumentação , Deuteroporfirinas/química , Mesoporfirinas/química , Metais Pesados/química , Neuropeptídeos/análise , Eletrocromatografia Capilar/métodos , Modelos Moleculares , Neuropeptídeos/química , Estatísticas não ParamétricasRESUMO
The separation of seven biologically active peptides was attempted by open-tubular capillary electrochromatography in fused-silica capillaries chemically modified with iron (III)-deuteroporphyrin using UV-absorption detection at 214 nm. The effect of BGE pH and content of organic solvent modifier was investigated. The best separations were obtained in 25 mM phosphate (BGE), pH 4.0, containing 5% v/v ACN and 10 mM hydroquinone, which was added to prevent gas bubble formation. Considering the method sensitivity, lower concentration LODs were obtained for all peptides in their open-tubular capillary electrochromatography separation as compared with their CZE separation in bare fused-silica capillary. The iron (III)-deuteroporphyrin column proved to be highly stable over time and showed acceptable precision of migration times and corrected peak areas (RSD in the range 2-4%).