78 research outputs found
Interaction of the Pd(II) complex of 5,10,15,20-tetrakis(1-methyl-4-pyridiyl)-porphyne with natural DNA
No full textA mechanistic, thermodynamic and kinetic analysis of the binding of the Pd(II)/5,10,15,20-tetrakis(1-methyl-4-pyridiyl)-porphyrine metal complex is done. Fluorescence and absorbance titrations under different conditions of temperature and salt content concur in indicating that the binding is strong. Kinetic and equilibrium parameters for the complex interaction with the nucleic acid are obtained and the binding mechanism is discussed. An intercalative binding is found to be active
Diorganotin(IV) and triorganotin(IV complexes of meso tetra (4 sulfonatophenyl) porphine: do they bind DNA?
No full textIt was observed that organometallic porphyrin systems, where the Sn(IV) residue is in side chains, coordinated via sulphonatophenyl groups of porphyrin, show interesting
and peculiar in vitro activity, in agreement with the anti-tumour activity of organotin complexes
(meso-Tetrakis(1-methyl-4-pyridinium)porphyrinato)Pd(II) complex: kinetics of formation and DNA binding
No full textAbsorbance variation in time, connected to complex formation, is spectrophotometrically observed at two different temperatures. Spectra broadening upon reaction suggests some aggregation of the formed metal complex.
Due to the presence of high metal ion amounts respect to ligand (pseudo-first order conditions) the curves can be analysed by a mono-exponential equation, yielding for each curve amplitude (amp) and reciprocal relaxation time (1/t) parameters. The initial rate (slope of the very first part of the plot) can also be obtained. Constancy of the curves amplitude and zero intercept of the 1/t vs. [Pd] plot indicate a quantitative process taking place (kd = 0).
The slope of the dilogarithmic plot of the initial rates values is equal to one, indicating a first order reaction respect to palladium in agreement with formation of a 1:1 complex.
The above considerations are true both at 25 °C and at 40°C.Addition of DNA produces bathochromic and hypochromic effects consistent with intercalation of the metal complex between DNA base pairs. However, the non-perfect isosbestic points suggest non-simple equilibria i.e. complex mechanism of interaction.
Calculations on the binding isotherm resulting form titrations indicate quantitative binding, even in the presence of relatively high salt content (1.0 M NaCl)
Studies on DNA interaction of organotin(IV) complexes of meso-tetra(4-sulfonatophenyl)porphine that show cellular activity
No full textThe interaction of the diorgano- and triorganotin(IV) derivatives of meso-tetra-(4-sulfonatophenyl)porphine (Me2Sn)2TPPS, (Bu2Sn)2TPPS, (Me3Sn)4TPPS and (Bu3Sn)4TPPS to natural DNA was analysed (together with free meso-tetra-(4-sulfonatophenyl)porphine (TPPS4-) for comparison purposes). Particular attention was paid to (Bu3Sn)4TPPS, a species that shows significant cellular action. Preliminary tests were done on the solution properties of the organotin(IV) compounds (pKA and possible self-aggregation). Spectrophotometric and spectrofluorometric experiments showed that all the investigated organotin(IV) derivatives strongly interact with DNA, the binding energy depending on the dye steric hindrance. In all cases experimental data concur in indicating that external binding mode prevails. Interestingly, fluorescence quenching and viscosity experiments show that the Bu-containing species, and in particular (Bu3Sn)4TPPS, are able to noticeably alter the DNA conformation
Kinetic and thermodynamic studies on Gold extraction by using micellar system: the PADA/SDS and PADA/DTAC systems
No full textMetal-Complex Formation and DNA Interaction of 5,10,15,20-Tetrakis(1-methyl-4-pyridiy1)-porphine: Study of the Mechanistic Aspects
No full textThe macrocyclic porphyrin 5,10,15,20-tetrakis(1-methyl-4-pyridiyl)-porphine is studied in its ability to coordinate Cu(II) even at very low pH values and to interact, as a copper complex, with calf-thymus (CT-DNA). The kinetics and equilibria for metal-ligand complexes formation are spectrophotometrically studied, particularly focussing on the mechanistic information provided by the kinetic approach. The rate constants of complex formation is much lower than that of water exchange at Cu(II), this behavior is ascribed to an equilibrium between two porphyrin populations, only one of them being reactive. Concerning the interaction of the copper-porphyrin complex (D) with CT-DNA, it has been found that the complex binds to G-C base pairs by intercalation while forms external complex with the A-T base pairs. The kinetic results agree with a reaction mechanism that takes into account the slow shuffling from an AT-bound form (DAT) to a GC-bound form (DGC) of the copper complex (D), finally leading to a more stable DGC* intercalated form. Kinetic and equilibrium parameters for the copper complex binding to the nucleic acid are obtained, and the binding mechanism is discussed. A mechanism is proposed where D reacts simultaneously with (G-C) and (A-T) base pairs. The resulting bound forms interconvert according to a "shuffling" process, which involves formation of an intermediate (DGC) form. (C) 2009 Wiley Periodicals, Inc
Metal complex formation and DNA interaction of 5,10,15,20-tetrakis(1-methyl-4-pyridiyl)-porphyne: study of the mechanistic aspects
No full textEffects of micelle nature and concentration on the acid dissociation constants of the metal extractor PADA
No full textThe pyridine-2-azo-p-dimethylaniline (PADA) ligand presents two acid dissociation constants, being pKa1 related to the pyridinium and pKa2 related to the anilinium residue. These have been measured by spectrophotometric titrations in aqueous solutions containing either the anionic (SDS), or the non–ionic (Triton X-100) or the cationic (DTAC) surfactants. The pKai shifts of the charged systems from that of the PADA/Triton X-100 reference (∆pKai0) are compared. For PADA/DTAC ∆pKa10 = 0.05 and ∆pKa20 = 0.6. For PADA/SDS ∆pKa10 = 2.1 and ∆pKa20 = 2.1 both yielding the value of -126 mV for the surface potential (ψ) of SDS. The ψ value, lying between the calculated Stern potential and the zeta potential, indicates that the dye is located on the SDS micelles between the fixed and the shear layer. In contrast, the behaviour of PADA/DTAC is explained assuming that the positively charged deprotonation sites of PADA are forced to protrude towards the bulk solvent by the positive charges of DTAC micelles. The shifts of the apparent pKai from the aqueous values (∆pKaiw) have also been analysed. Concerning PADA/Triton X-100, the shifts ∆pKa1w = -0.1 and ∆pKa2w = -0.9 are rationalized in terms of dielectric constant reduction at the reaction sites. Concerning PADA/DTAC, ∆pKa1w= -0.05 and ∆pKa2w= -0.3 whereas, for PADA/SDS, ∆pKa1w = 2.0 and ∆pKa2w = 1.2. The pKa2w values decrease on raising the surfactant concentrations for all the investigated systems. This behaviour is explained assuming that the increase of the overall micellar surface and, by consequence, of the reaction sites number, results in a site dilution effect which disfavours proton association. The addition of NaCl induces changes of pKa1 and pKa2 which are explained in terms of (large) reduction of ψ for PADA/SDS and of (small) reduction of the dielectric constant for the other systems
Effects of micelle charge and concentration on acid dissociation constants of ligands suitable for metal extraction: the PADA/SDS and PADA/DTAC systems
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