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1.
J Phys Chem B ; 111(20): 5651-7, 2007 May 24.
Artigo em Inglês | MEDLINE | ID: mdl-17469863

RESUMO

The 2D complex formed at the air-water interface between the dialkyl chain cationic surfactant, dihexadecyldimethylammonium bromide, and the anionic porphyrin, tetrakis-(4-sulfonatophenyl) porphine, was studied using surface pressure-area isotherms as well as X-ray and neutron reflection measurements. The surface structure of these films was determined by the use of simultaneously constrained analysis of the neutron and X-ray reflectometry data and BAM images. Isotopic contrast variation methods were employed to enhance the information content of the neutron reflection data. The rigid complex forms at the interface due to the electrostatic interaction between the cationic headgroups of the surfactant and the anionic functional groups at the meso position of the porphyrin. The surface pressure-area isotherms show three distinct regions on compression: an initial condensed phase that ends with a pressure peak at 36 mN m-1, a second plateau region of high compressibility, and a final condensed phase. BAM images show that at the beginning of the plateau region in the isotherm there is complete surface coverage by a monolayer. The constrained simultaneous fitting of neutron and X-ray data measured just prior to and after the pressure peak shows a structurally similar 2D complex at the interface. Modeling of X-ray reflectometry data also reveals that in the final high-pressure phase the film has folded to form a trilayer. The conclusion is that the plateau region of the isotherm is due to the formation of trilayer surface coverage through localized buckling or folding, and that after this is complete there is some condensation before final film collapse.


Assuntos
Membranas Artificiais , Porfirinas/química , Compostos de Amônio Quaternário/química , Tensoativos/química , Estrutura Molecular , Propriedades de Superfície
2.
J Inorg Biochem ; 100(5-6): 963-71, 2006 May.
Artigo em Inglês | MEDLINE | ID: mdl-16624414

RESUMO

XANES spectroscopy has been used to investigate whether it is possible to determine the oxidation state and coordination environment of Co complexes following treatment of cancer cells with Co(III) or Co(II) complexes. Our results show that the variation of the XANES with coordination geometry make it impossible to do this in a completely reliable way which is in contrast to the situation for platinum and chromium. It was established that the XANES spectrum obtained from cells treated with [Co(diNOsar)]Br(3) remained unchanged with respect to its XANES spectrum obtained in solution, demonstrating that the [Co(diNOsar)]Br(3) complex remained intact after 24h in cellular media (diNOsar=1,8-dinitro-3,6,10,13,16,19-hexaazabicyclo[6.6.6]eicosane). In contrast, the XANES spectra obtained from cells treated with Na[Co(acac)(3)] and [Co(acac)(3)] differed from the XANES spectra of the respective complexes obtained in solution, indicating a change in co-ordination environment for both complexes upon uptake in cells. The similarity of these spectra suggests that appearance of this XANES can be used as an indication of loss of the carrier ligands, a useful indicator in the study of hypoxia selective complexes. The results obtained for Na[Co(acac)(3)] and [Co(acac)(3)] are consistent with the intracellular coordination of cobalt(III) to sulfur ligands upon cellular uptake.


Assuntos
Cobalto/química , Análise Espectral/métodos , Oxirredução , Soluções , Raios X
3.
Metallomics ; 4(6): 568-75, 2012 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-22569908

RESUMO

The platinum(II) drugs cisplatin, carboplatin and oxaliplatin are usefully employed against a range of malignancies, but toxicities and resistance have spurred the search for improved analogs. This has included investigation of the platinum(IV) oxidation state, which provides greater kinetic inertness. It is generally accepted that Pt(IV) complexes must be reduced to Pt(II) for activation. As such, the ability to monitor reduction of Pt(IV) complexes is critical to guiding the design of candidates, and providing mechanistic understanding. Here we report in full that the white line height of X-ray absorption near-edge spectra (XANES) of Pt complexes, normalized to the post-edge minima, can be used to quantitatively determine the proportion of each oxidation state in a mixture. A series of Pt(IV) complexes based on the Pt(II) complexes cisplatin and transplatin were prepared with chlorido, acetato or hydroxido axial ligands, and studies into their reduction potential and cytotoxicity against A2780 human ovarian cancer cells were performed, demonstrating the relationship between reduction potential and cytotoxicity. Analysis of white line height demonstrated a clear and consistent difference between Pt(II) (1.52 ± 0.05) and Pt(IV) (2.43 ± 0.19) complexes. Reduction of Pt(IV) complexes over time in cell growth media and A2780 cells was observed by XANES, and shown to correspond with their reduction potentials and cytotoxicities. We propose that this method is useful for monitoring reduction of metal-based drug candidates in complex biological systems.


Assuntos
Carboplatina/química , Cisplatino/química , Compostos Organoplatínicos/química , Antineoplásicos/química , Antineoplásicos/farmacologia , Carboplatina/farmacologia , Linhagem Celular Tumoral , Sobrevivência Celular/efeitos dos fármacos , Cisplatino/farmacologia , Meios de Cultura , Humanos , Compostos Organoplatínicos/farmacologia , Oxaliplatina , Oxirredução , Espectroscopia por Absorção de Raios X/métodos
5.
Inorg Chem ; 45(12): 4743-54, 2006 Jun 12.
Artigo em Inglês | MEDLINE | ID: mdl-16749839

RESUMO

Transition-metal complexes with redox-active catecholato ligands are of interest as models of bioinorganic systems and as potential molecular materials. This work expands our recent X-ray absorption spectroscopic (XAS) studies of Cr(V/IV/III) triscatecholato complexes (Levina, A.; Foran, G. J.; Pattison, D. I.; Lay, P. A. Angew. Chem., Int. Ed. 2004, 43, 462-465) to a Cr(III) monocatecholato complex, [Cr(tren)(cat)]+ (tren = tris(2-aminoethyl)amine, cat = catecholato2-), and its oxidized analogue, as well as to a series of V(V/IV/III) triscatecholato complexes ([VL3]n-, where L = cat, 3,5-di-tert-butylcatecholato2-, or tetrachlorocatecholato2-, and n = 1-3). Various oxidation states of these complexes in solutions were generated by bulk electrolysis directly in the XAS cell. Increases in the edge energies and pre-edge absorbance intensities in XANES spectra, as well as decreases in the average M-O bond lengths (M = Cr or V) revealed by XAFS data analyses, are consistent with predominantly metal-based oxidations in both the Cr(V/IV/III) and V(V/IV/III) triscatecholato series, but the degree of electron delocalization between the metal ion and the ligands was higher in the case of Cr complexes. By contrast, oxidation of [Cr(III)(tren)(cat)]+ was mainly ligand-based and led to [Cr(III)(tren)(sq)]2+ (sq = semiquinonato-), as shown by the absence of significant changes in the pre-edge and edge features and by an increase in the average Cr-O bond length. The observed differences in electron-density distribution in various oxidation states of Cr and V mono- and triscatecholato complexes have been discussed on the basis of the results of density functional calculations. A crystal and molecular structure of (Et3NH)2[V(IV)(cat)3] has been determined at 25 K and the same complex with an acetonitrile of crystallization at 150 K.

6.
Langmuir ; 22(2): 681-6, 2006 Jan 17.
Artigo em Inglês | MEDLINE | ID: mdl-16401117

RESUMO

The behavior of monolayer films of free base 5,10,15,20-tetrapyridylporphinato (TPyP) and 5,10,15,20-tetrapyridylporphinato zinc(II) (ZnTPyP) on pure water, 0.1 M CdCl2, and 0.1 M CuCl2 subphases was investigated by surface pressure-area isotherms, specular X-ray reflectometry, and polarized total reflection X-ray absorption spectroscopy (PTRXAS). Surface pressure-area isotherms showed significant differences in the area per molecule on pure water compared to that on salt subphases, with a marked increase in the area observed on the salt solutions. This behavior was noted for both forms of the porphyrin and both salts investigated. Modeling of specular X-ray reflectometry data indicated that thinner and more electron dense layers on salt subphases best fit the observed profiles. These data suggest that the porphyrin macrocycle is oriented parallel to the interface on salt subphases and takes on a tilted conformation on pure water. In the case of ZnTPyP, PTRXAS was used to determine the orientation of the porphyrin moiety relative to the surface and to probe the coordination of the central Zn ion. In agreement with the pressure-area isotherms and reflectometry, the PTRXAS data indicate a change in orientation on the salt subphases.

7.
Dalton Trans ; (40): 4805-13, 2006 Oct 28.
Artigo em Inglês | MEDLINE | ID: mdl-17033705

RESUMO

Electronic coupling between the porphyrin units of a laterally-bridged dimanganese(III) bis-porphyrin 2 is explored using electrochemistry, spectroelectrochemistry and resonance-Raman spectroscopy. It is found that strong electronic interactions between the manganese(III) ion and the porphyrin macrocycle enhance the perturbations experienced by these bis-porphyrin systems when compared to related monomer porphyrin systems. In turn this leads to effective electronic communication between the manganese ions in the bis-porphyrin. This finding has importance in the design of molecular wires based on laterally-bridged oligo-metallo-porphyrins.

8.
J Am Chem Soc ; 125(25): 7524-5, 2003 Jun 25.
Artigo em Inglês | MEDLINE | ID: mdl-12812486

RESUMO

Here we describe the use of X-ray absorption near edge spectroscopy (XANES) to provide information about the relative proportions of platinum(II) and platinum(IV) complexes by analyzing the XANES edge height. The intracellular reduction of platinum(IV) complexes in cancer cells has been observed directly, and the proportion of reduction after 2 h was found to correlate with the reduction potentials of the complexes.


Assuntos
Antineoplásicos/farmacocinética , Compostos Organoplatínicos/farmacocinética , Neoplasias Ovarianas/metabolismo , Platina/farmacocinética , Antineoplásicos/química , Feminino , Humanos , Compostos Organoplatínicos/química , Neoplasias Ovarianas/química , Neoplasias Ovarianas/tratamento farmacológico , Oxirredução , Platina/química , Espectrometria por Raios X , Células Tumorais Cultivadas
9.
J Synchrotron Radiat ; 10(Pt 4): 332-6, 2003 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-12824934

RESUMO

A controlled-atmosphere furnace has been constructed for X-ray absorption spectroscopy experiments under imposed oxygen fugacities at temperatures up to 1773 K. The use of the furnace is demonstrated in a study of the oxidation state of Cr in a basaltic silicate melt (mid-ocean ridge basalt) by K-edge XANES spectroscopy. This is the first time the Cr(2+)/Cr(3+) ratio has been identified directly in an Fe-bearing melt. At typical terrestrial oxygen fugacities around half the Cr is present as Cr(2+), even though this oxidation state has never been identified in a terrestrial material and only Cr(3+) is observed after quenching to a glass. Cr(2+) oxidizes to Cr(3+) on cooling in the presence of Fe(3+) according to the electron exchange reaction Cr(2+) + Fe(3+) --> Cr(3+) + Fe(2+). This illustrates the importance of the in situ determination of metal oxidation states in melts.

10.
Inorg Chem ; 43(3): 1046-55, 2004 Feb 09.
Artigo em Inglês | MEDLINE | ID: mdl-14753827

RESUMO

Structures of the complexes [Cr(V)O(ehba)(2)](-), [Cr(IV)O(ehbaH)(2)](0), and [Cr(III)(ehbaH)(2)(OH(2))(2)](+) (ehbaH(2) = 2-ethyl-2-hydroxybutanoic acid) in frozen aqueous solutions (10 K, [Cr] = 10 mM, 1.0 M ehbaH(2)/ehbaH, pH 3.5) have been determined by single- and multiple-scattering fitting of X-ray absorption fine structure (XAFS) data. An optimal set of fitting parameters has been determined from the XAFS calculations for a compound with known crystal structure, Na[Cr(V)O(ehba)(2)] (solid, 10 K). The structure of the Cr(V) complex [Cr(V)O(ehba)(2)](-) does not change in solution in the presence of excess ligand. Contrary to the earlier suggestions made from the kinetic data (Ghosh, M. C.; Gould, E. S. J. Chem. Soc., Chem. Commun. 1992, 195-196), the structure of the Cr(IV) complex (generated by the Cr(VI) + As(III) + ehbaH(2) reaction) is close to that of the Cr(V) complex (five-coordinate, distorted trigonal bipyramidal) and different from that of the Cr(III) complex (six-coordinate, octahedral). For both Cr(V) and Cr(IV) complexes, some disorder in the position of the oxo group is observed, which is consistent with but not definitive for the presence of geometric isomers. The structure of the Cr(IV) complex differs from that of Cr(V) by protonation of alcoholato groups of the ligands, which leads to significant elongation of the corresponding Cr-O bonds (2.0 vs 1.8 A). This is reflected in the different chemical properties reported previously for the Cr(IV) and Cr(V) complexes, including their reactivities toward DNA and other biomolecules in relation to Cr-induced carcinogenicity.


Assuntos
Cromo/química , Compostos Organometálicos/química , Compostos Organometálicos/síntese química , Cristalografia por Raios X , Indicadores e Reagentes , Ligantes , Modelos Moleculares , Fotoquímica , Espectrofotometria Ultravioleta
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