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Electron-Transfer Oxidation of Chlorophenols by Uranyl Ion Excited State in Aqueous Solution. Steady-State and Nanosecond Flash Photolysis Studies

Sarakha, Mohamed; Bolte, Michèle; Burrows, Hugh D.
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
ENG
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462.1827%
The oxidation of chlorophenols by photoexcited uranyl ion was studied in aqueous solution at concentrations where the ground-state interactions were negligible. Nanosecond flash photolysis showed that a clean electron-transfer process from the chlorophenols to the excited uranyl ion is involved. This is suggested to lead to the formation of a U(V)/chlorophenoxyl radical pair complex. The efficiency of this charge-transfer process is unity for the three chlorophenols. However, low product yields suggest that in the absence of oxygen, back electron transfer, both within the radical pair and from separated uranium(V) to phenoxyl radicals, appears to be the major reaction pathway. In the presence of oxygen the quantum yields of disappearance of chlorophenol and of photoproduct formation increased. This leads to the conclusion that oxygen favors reaction with uranium(V) and/or the uranium(V)−phenoxyl radical pair, leading to the formation of the superoxide anion and its conjugate acid, HO2•, which then regenerate UO22+. Based on this, a catalytic cycle for chlorophenol photooxidation involving uranyl ion and molecular oxygen is proposed.; http://dx.doi.org/10.1021/jp993676t

Changes in Hydration of Lanthanide Ions on Binding to DNA in Aqueous Solution

Costa, Diana; Burrows, Hugh D.; Miguel, M. da Graça
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
462.1827%
The interaction of the trivalent lanthanides Ce(III), Eu(III), and Tb(III) with sodium deoxyribonucleic acid (DNA) in aqueous solution has been studied using their luminescence spectra and decays. Complexation with DNA is indicated by changes in luminescence intensity. In the system terbium(III)−DNA, changes in luminescence with pH are suggested to be due to the protonation of phosphate groups. The degree of hydration of Tb(III) on binding to DNA is followed by luminescence lifetime measurements in water and deuterium oxide solutions, and it is found that the lanthanide ion loses at least one hydration water on binding to long double stranded DNA at pH 4.7 and pH 7. Rather different behavior is observed on binding to long or short single stranded DNA, where six water molecules are lost, independent of pH. It is suggested that in this case the lanthanide probably binds to the bases of the DNA backbone. The DNA conformation seems to be an important factor in the binding. In addition, the isotopic effect on terbium luminescence lifetime may provide a useful method to distinguish between single and double stranded DNA. DSC results are consistent with cleavage of the double helix of DNA at pH 9 in the presence of terbium.; http://dx.doi.org/10.1021/la051493u

Interaction between the Conjugated Polyelectrolyte Poly{1,4-phenylene[9,9-bis(4-phenoxybutylsulfonate)]fluorene-2,7-diyl} Copolymer and the Lecithin Mimic 1-O-(l-Arginyl)-2,3-O-dilauroyl-sn-glycerol in Aqueous Solution

Tapia, María J.; Burrows, Hugh D.; Knaapila, Matti; Monkman, Andrew P.; Arroyo, Antonio; Pradhan, Swapna; Scherf, Ullrich; Pinazo, Aurora; Pérez, Lourdes; Morán, Carmen
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
462.1827%
In this paper, the interaction between the water-soluble conjugated polyelectrolyte poly{1,4-phenylene[9,9-bis(4-phenoxybutylsulfonate)]fluorene-2,7-diyl} copolymer and the amino acid glyceride conjugate 1-O-(l-arginyl)-2,3-O-dilauroyl-sn-glycerol dichlorohydrate (a mimic for the phospholipid lecithin) has been studied in aqueous solution by electronic spectroscopy (absorption and fluorescence) and small-angle neutron scattering (SANS). A significant increase in the polymer fluorescence and blue shift in its emission are observed on association with the surfactant. This is suggested to be due to breakup of polymer aggregates. In addition, the spectroscopic and photophysical data suggest this is followed by the vesicle to ribbon transition characteristic of this surfactant, leading to incorporation of single chains of the polymer within mixed polymer−surfactant aggregates. Support for this comes from preliminary SANS measurements, from which evidence for polymer dissolution and formation of two-dimensional structures has been obtained.; http://dx.doi.org/10.1021/la0612217

Multinuclear NMR study of the interaction of the shift reagent lanthanide(III) bis(triphosphate) with alkali-metal ions in aqueous solution and in the solid state

Ramasamy, Ravichandran; Freitas, Duarte Mota de; Geraldes, Carlos F. G. C.; Peters, Joop A.
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
462.1827%
The paramagnetic ion-induced relaxation rate enhancements of 6Li in adducts of Li+ and Ln(PPP)J- complexes (Ln = Dy, Tm) in aqueous solution show that up to seven monovalent counterions can coordinate in the second coordination sphere of the Ln(II1) ion to the outer oxygens of the triphosphate ligands. However, the pseudocontact ’Li NMR shift data suggest that in the second coordination sphere some preference of the counterions for the axial region opposite the water ligand may exist. The estimated Ln3+-Li+ distances range from 5.1 to 5.9 A for [Li+]/[Ln(PPP)J-] ratios of 0.2-7. This is supported by a two-dimensional nutation spectrum of a polycrystalline sample of Na,La(PPP),, which indicates coordination of all Na+ ions to phosphate oxygens.; http://dx.doi.org/10.1021/ic00016a016