108 research outputs found
The Gallium (III)/4-(2-pyridylazo)resorcinol System in Water and SDS Solution: Kinetics and Thermodynamic
No full textThe equilibria and kinetics of the complex formation and dissociation reaction between gallium(III) and PAR
[4-(2-pyridylazo)resorcinol] have been investigated in water and in the presence of SDS micelles. The reactive form
of Ga(III) is GaOH2+ in both cases. The addition of SDS results in an increase of both the binding affinity and velocity,
the maximum accelerating effect being observed just above the cmc value of SDS that, under the conditions of the
experiments, is 5.6 10-3 M. At pH ) 3.2, the maximum value of the equilibrium constant ratio Kapp(SDS)/Kapp(H2O)
is 27.4, whereas that of the binding rate constants kf(SDS)/kf(H2O) is 16. The results are interpreted in terms of
increased concentrations of the reactants on the micelle surface and on competition of PAR and SDS for GaOH2+
Kinetic and Thermodynamic Studies on Ga3+/PAR Complex Formation in SDS Surfactant Solutions
No full textIn recent years, owing to the awareness on environmental hazards in the wide use of organic solvents for metal ion extraction, selective extraction and concentration of toxic and precious metals from aqueous streams and liquid wastes by new smart technologies has been the object of intense studies. Between these new strategies, micellar media were found to have significant advantages over a two-phase water-organic solvent system for the extraction process.1,2 In addition of lower environmental impact, the micelles are distributed uniformly through the medium as very small (nano-sized) aggregates, therefore avoiding mixing problems due to unhomogeneity. In the presence of a negatively charged surface, such as is provided by the head groups of the surfactant, the metal ion will be electrostatically attracted to the micelle surface and the extractant will concentrate in the hydrophobic core of the micelle. Under these conditions the extent of extraction will be enhanced as the result of a local concentration effect on both reactants.A study on the kinetics and thermodynamics of the reaction between Ga(III) and ligand 4-(2-pyridylazo)resorcinol (PAR) has been done in sodium dodecyl sulphate (SDS) surfactant solutions, by means of the stopped-flow technique and by UV-vis spectroscopy. A rate promotion effect is found for the forward reaction and for the equilibrium constant in the presence of micelles. The maximum catalysis effect is found when the surfactant concentration is just above the cmc (critical micellar concentration), followed by a decrease at higher SDS concentrations. The kinetic constant of complex formation in SDS solutions at pH=4 is much lower that the one measured at pH=6. In fact, under the latter pH conditions, the neutral PAR species prevails. Such a neutral molecule will have lower tendency to condensate on the negative micelle surface than the protonated H3PAR+ species. Further mechanistic details will be discussed
DNA binding of a proflavine derivative bearing a platinum hanging residue
No full textNew platinum(II) complex of 3,6-diamine-9-[6,6-bis(2-aminohethyl)-1,6-diaminohexyl]acridine, AzaPt, has been synthesised and characterised. Behaviour of AzaPt in solution (protonation and possible self-aggregation phenomena) has been investigated by spectral methods (absorbance and fluorescence) at I=0.1 M and 25 degrees C, and the equilibrium parameters of binding to calf thymus DNA have been established. Two different modes of DNA binding by the complex were detected, which depend on the polymer to dye molar ratio (P/D). At relatively low P/D values the mode was interpreted as binding by the polyamine residue external to the base pairs, while at high P/D values the binding corresponds to intercalation of the proflavine residue. Such interpretation is supported by the observed salt effect on binding and the temperature variation of the binding constants, which allowed estimating the Delta H and Delta S values contributions. Spectrophotometric analysis of the long time range binding revealed that AzaPt is involved in a slow reaction, interpreted as an attack by the platinum ion on the nucleobases. The time constant for such interaction was calculated and found to be the same order of magnitude as for processes responsible for the action of anti-tumour drugs that do covalently bind to polynucleotides. (C) 2010 Elsevier Inc. All rights reserved
New aspects of the interaction of the antibiotic coralyne with RNA: coralyne induces triple helix formation in poly(rA)poly(rU)
No full textThe interaction of coralyne with poly(A)poly(U), poly(A)2poly(U), poly(A) and poly(A)poly(A) is analysed using spectrophotometric, spectrofluorometric, circular dichroism (CD), viscometric, stopped-flow and temperature-jump techniques. It is shown for the first time that coralyne induces disproportionation of poly(A)poly(U) to triplex poly(A)2poly(U) and single-stranded poly(A) under suitable values of the [dye]/[polymer] ratio (C(D)/C(P)). Kinetic, CD and spectrofluorometric experiments reveal that this process requires that coralyne (D) binds to duplex. The resulting complex (AUD) reacts with free duplex giving triplex (UAUD) and free poly(A); moreover, ligand exchange between duplex and triplex occurs. A reaction mechanism is proposed and the reaction parameters are evaluated. For C(D)/C(P)> 0.8 poly(A)poly(U) does not disproportionate at 25 degrees C and dye intercalation into AU to give AUD is the only observed process. Melting experiments as well show that coralyne induces the duplex disproportionation. Effects of temperature, ionic strength and ethanol content are investigated. One concludes that triplex formation requires coralyne be only partially intercalated into AUD. Under suitable concentration conditions, this feature favours the interaction of free AU with AUD to give the AUDAU intermediate which evolves into triplex UAUD and single-stranded poly(A). Duplex poly(A)poly(A) undergoes aggregation as well, but only at much higher polymer concentrations compared to poly(A)poly(U)
New metal complexes containing a proflavine pendant arm as bifunctional DNA binding agent
No full textNo abstract availabl
In situ observations on the dentition and oral cavity of the Neanderthal skeleton from Altamura (Italy)
No full textThe Neanderthal specimen from Lamalunga Cave, near Altamura (Apulia, Italy), was discovered during a speleological survey in 1993. The specimen is one of the most complete fossil hominins in Europe and its state of preservation is exceptional, although it is stuck in calcareous concretions and the bones are mostly covered by calcite depositions. Nevertheless, it is possible to carry out some observations on craniodental features that have not previously been described. In this work, we present an account of the oral cavity, made possible by the use of a videoscope, which allowed us to reach some hidden parts of the mandible and palate. This is the first detailed overview of the teeth and maxillary bones of the Neanderthal skeleton from Altamura. The dentition is almost complete. However, two teeth (upper right P3 and upper left M1) were lost ante mortem and four teeth (lower right I1 and P3 and lower left I1 and I2) were lost most probably post mortem. Dental wear is marked. The erupted M3s and the inversion of the compensating curve of Wilson in the M1s and M2s but not in the M3s suggest that the individual is fully adult, but not old. Although most of the teeth have their roots exposed for several millimeters, the periodontal bone appears to be in good condition overall, except in correspondence of the two ante-mortem tooth losses. X-rays of the anterior teeth show a periapical lesion, probably linked to the advanced dental wear. We also observed a weak expression of taurodontism in the posterior dentition and the presence of a retromolar space, features consistent with an attribution to the Neanderthal hypodigm; this attribution is also supported by aspects of the cranial morphology, the morphometric analysis of the scapula and preliminary mtDNA data. There is also a well-developed palatine torus, to the best of our knowledge a feature not previously described in Neanderthals
A new cyanine dye with potential groove binding features: characterisation and interaction with DNA
No full textPhysical ageing reduction in PES through the incorporation of rigid non-interacting PTFE nanoparticles
No full textThe enthalpy relaxation of PES in the presence of PTFE nanoparticles was investigated and discussed. The increase in the PES glass transition temperature with increasing the PTFE content was explained assuming a frictional effect exerted by the rigid PTFE domains on the PES segmental motions. The presence of constraints on the PES segmental motions caused by the PTFE crystalline domains was confirmed by the analysis of the enthalpy relaxation process. A significant increase in the activation energy and a reduction in the enthalpy lost during PES structural relaxation was observed as a consequence of the PTFE nanoparticles addition, which proves that a potential strategy to reduce physical ageing of non-equilibrium glasses could be the incorporation of rigid, even if non-interacting, fillers
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