Thermodynamic analysis of POPs interaction with biosubstrates

Persistent organic pollutants (POPs) as polycyclic aromatic hydrocarbons (PAH), pesticides and herbicides are nowadays ubiquitous [1]. These species are highly lipophilic and all at least suspected of carcinogenic effects [2,3]. However, information on their toxic activity is often related to in vitro/in vivo studies, whereas a detailed analysis of the mechanistic/chemical aspects of the binding to biosubstrates is sometimes missing. To contribute to this field and in the frame of our participation to PNRA (National Antarctic Research Program) we have done some tests on the binding of model targets (two PAHs, two pesticides and two herbicides, Fig. 1) to biosubstrates (natural DNA and bovine serum albumin - BSA). The interaction with micelles and liposomes was also tested, both as to scale the lipophilicity and to get information on the possible accumulation on membranes. The results collected show that the high hydrophobicity of these species turns into very high affinity for DNA. Absorbance and fluorescence titrations suggest complex binding modes that are discussed in relation with the different pollutant/DNA ratio. BSA binding is also found to occur. Ultrafiltration coupled with absorbance spectroscopy enables the percentage of retention (R%) on the micelle/liposome be measured. R% dependence on the molecule and on the type of system (sodium dodecyl sulphate anionic micelles, TritonX-100 neutral micelles, dodecyl trimethyl ammonium chloride positive micelles and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine liposomes) is discussed. References: [1] A. Lo Giudice, P. Casella, V. Bruni, L. Michaud, Ecotoxicology 2013, 22, 240-250. [2] H. Yu, Journal of Enviromental Science and Health 2002, 20, 149-183. [3] M.C.R. Alavanja, M.R. Bonner, Journal of Toxicology and Environmental Health B 2012, 15, 238-263

Mechanistic details on Pd(II)/5,10,15,20-tetrakis(1-methyl-4-pyridyl)porphyrin complex formation and reactivity in the presence of DNA

Abstract: Kinetics of coordination of Pd(II) by the macrocyclic porphyrin 5,10,15,20-tetrakis(1-methyl-4-pyridyl)porphyrin (H2P4+) is investigated and confirms quantitative formation of a planar PdP4+complex at room temperature (formation rate 0.19 M-1 s-1 at 25 °C, 0.2 M NaCl, pH 3). Then, the binding ability to DNA of the pre-formed PdP4+complex is analysed. To achieve this aim, spectrophotometry, spectrofluorometry and viscometry are used. Thermodynamic parameters for binding, obtained by the temperature dependence of the equilibrium constants, are deltaH = -71 kJ mol-1 and deltaS = -134 J mol-1 K-1. These values, being both highly negative, agree with full PdP4+intercalation into DNA. Moreover, kinetics of the binding reaction is analysed by the T-jump technique (reaction times in the 1-5 ms range). Experiments on the porphyrin ligand retention on negative SDS and positive DTAC micellar surfaces are also done. Taken altogether, these data provide mechanistic details on complex formation and on DNA binding and relevant energies and driving forces. It is found that interaction between PdP4+and base pairs is very strong (KabsDNA = 8.0E5 M-1 at 25 °C, 1.0 M NaCl), not only owing to the high positive charge borne by the complex, but also to the contribution of high hydrophobicity of the porphyrin ring. In the dye/DNA complex, PdP4+is buried into the helix, as confirmed also by fluorescence quenching tests. Both presence and type of metal ion play a major role, as lower affinity and lower induced helix conformation changes are found in the case of the H2P4+/DNA and CuP4+/DNA systems

The kinetics of gold(III) extraction by pyridine-2-azo-p-dimethylaniline in water and in micellar systems

The kinetics of reaction between AuCl4−and the azo-dye pyridine-2-azo-p-dimethylaniline (PADA) havebeen investigated in water and in the presence of DTAC micelles, using classical spectrophotometryand the stopped-flow technique. PADA reacts with different chloro/hydroxo gold(III) complexes, in turnformed as the pH and Cl−concentration were changed, according to a network of parallel paths. In aqueoussolution, at low pH values, a fast step is observed which is ascribed to the ligand induced expulsion ofa labile water molecule from the reacting species Au(H2O)Cl3which forms at low pH values. At highervalues of pH, the reaction is much slower because, in the key step, PADA has to replace the more inertCl−ions in the gold coordination shell. In the presence of DTAC a remarkable catalytic effect is observed,owing to the absorption and attraction of the reactants on the micelle surface. Moreover, DTAC favors theformation of aquochloro aurates, thus inducing a change in the gold(III) speciation compared to that inwater. The analysis of the data suggests that the aquo species Au(H2O)Cl3and Au(H2O)2Cl2+play a majorrole in the reaction mechanism

The mechanism of the reaction between Au(III) and PADA in Sodium dodecylsulphate

The PADA/SDS system provides an excellent tool to selectively extract metal ions using the ligand-modified micellar-enhanced ultrafitration (LM-MEUF) technique. Application of this method to the extraction of Au(III) has required a detailed knowledge of the conditions under which the interaction of the metal ion with the extractor are optimal. For this purpose the kinetics and the equilibria of the reaction between tetrachloro-aurate ion and PADA have been investigated in water/SDS medium, exploring wide ranges of pH values and NaCl concentrations. Addition of PADA to the water/SDS medium results in the full adsorption of the ligand on the micelle and, in the presence of Au(III), the resulting Au-PADA complex is fully retained on the SDS surface. The binding process is, in fact, a ligand displacement reaction where PADA interacts with different Au(III) chloro-aquo complexes, displacing Cl− or OH− or H2O molecules, depending on pH. The reaction is biphasic and its mechanism is discussed. Experiments at different SDS concentrations show that the reaction of complex formation is retarded on going from pure water to a water/SDS mixture with [SDS] just above the cmc, while for further increases of the SDS content the reaction rate tends to stay constant. The obtained results enabled to establish that the reaction occurs on the SDS surface while the aquo-species, Au(H2O)Cl3 and Au(OH)3(H2O), which are not involved in the binding process in pure water, play an important kinetic role in the H2O/SDS medium

Synthesis and DNA binding tests of a fluorescent pyrene bearing a Pt(II) pyridineimino complex

Despite the long time gone respect to the discovery of cis-platinum anticancer activity, still a huge amount of research is devoted to the design of new Pt(II) complexes with enhanced biological activity [1-3]. The here presented work concerns the synthesis of a fluorescent pyridinimino platinum(II) complex, where the presence of a cis-platinum moiety linked to an extended aromatic residue could provide interesting properties as for binding to biosubstrates. In fact, covalent Pt(II) binding can occur, which would be strengthened by the anchoring offered by possible intercalation in nucleic acids of the pyrene fragment. Antiproliferative properties have been described for some pyridinimino [4] and pyridinamino [5] platinum(II) complexes. Moreover, similar bifunctional systems have already been tested with interesting performances [7,8]. The chelating iminopyridine ligand was prepared by a condensation reaction between pyridine-2-carboxyaldehyde and the suitably O-alkylated aminoalcohol. The platinum complex was then synthesized starting from cis-[PtCl2(DMSO)2], and purified by crystallization. The pure complex (elemental analysis) was spectroscopically (IR, 1H-, 13C and 195Pt NMR) characterized. It is well soluble in DMSO and in DMSO/H2O mixtures, where its stability was checked by 1H- and 195Pt NMR. The absorbance and fluorescence optical features of the dye were also checked. Afterwards, the target Pt(II) complex was let interact with natural double stranded DNA to check its reactivity towards this biosubstrate. Spectrophotometric and spectrofluorometric titrations show that the binding does indeed occur. As for absorbance data, hypochromic and bathochromic effects suggest intercalative binding. However, the absence of a defined isosbestic point indicates multiple equilibria. Interestingly and in agreement with this observation, the light emission behavior of the dye/DNA system is complex. Opposite fluorescence change trends are observed at different temperatures, likely related to a different contribution of DNA-templated dye aggregation. Under the (until now) explored conditions, the binding is so strong to turn to be quantitative. Further experiments are ongoing to better enlighten the binding mechanism. References: [1] S. X. Chong, S. C. F. Au-Yeung, K. K. W. To, Current Medicinal Chemistry 2016, 23(12), 1268-12. [2] L. Cai, C. Yu, L. Ba, Q. Liu, Y. Qian, B. Yang, C. Gao, Applied Organometallic Chemistry 2018, 32(4). [3] M. Hanif, C. G. Hartinger, Future Medicinal Chemistry 2018, 10(6), 615-617. [4] B. A. Miles, A. E. Patterson, C. M. Vogels, A. Decken, J. C. Waller, P. Jr. Morin, S. A. Westcott, Polyhedron 2016, 108, 23-29. [5] S. Karmakar, K. Purkait, S. Chatterjee, A. Mukherjee, Dalton Trans. 2016, 45, 3599-3615. [6] S. Hochreuther, R. van Eldik, Inorg. Chem., 2012, 51 (5), 3025-3038. [7] C. Bazzicalupi, A. Bencini, A. Bianchi, T. Biver, A. Boggioni, S. Bonacchi, A. Danesi, C. Giorgi, P. Gratteri, A. Marchal Ingraín, F. Secco, C. Sissi, B. Valtancoli, M. Venturini, Chemistry – A European Journal 2008, 14(1), 184-196. [8] S. Biagini, A. Bianchi, T. Biver, A. Boggioni, I.V. Nikolayenko, F. Secco, M. Venturini, Journal of Inorganic Biochemistry 2011, 105, 558-562

Gold(III) extraction and recovery and gold(III)/copper(II) separation using micelles

Gold extraction from aqueous solutions has been performed by micellar enhanced ultrafiltration (MEUF), using SDS and DTAC micelles. DTAC entraps 92-100% of the metal, which is present in form of AuCl4-, owing to electrostatic interaction. Using SDS the extraction of gold is unsuccessful. However, addition of PADA, as a metal extractor agent, according to the ligand modified micellar enhanced ultrafiltration (LM-MEUF) procedure, makes the extraction yield to approach 100% also with SDS. The recovery of gold entrapped in the micellar pseudo-phase has also been investigated. Different stripping agents have been used, the most efficient of them being a mixture of NaCl and NH3 which allowed the metal to be expelled from the micelle with a yield of 85%. Finally, Au(III)/Cu(II) separation is achieved with DTAC or SDS between pH 3 and 5. Almost 100% of Au(III) is retained on DTAC micelles while all Cu(II) remains in the aqueous medium, while the opposite occurs in SDS

Studies on DNA interaction of organotin(IV) complexes of meso-tetra(4-sulfonatophenyl)porphine that show cellular activity

The 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

Synthesis of new bis[1-(thiophenyl)propynones] as potential organic dyes for colorless luminescent solar concentrators (LSCs)

New luminophores having different aryl nuclei and propynones moieties have been obtained via Sonogashira reactions. Their optical properties were evaluated and indicated that carbonyl groups are responsible for significant bathochromic effects and high Stokes shifts. The insertion of -OMe groups on the central benzene unit gives to the fluorophore high optical efficiency (7.7%) when homogeneously dispersed in a poly(cyclohexyl methacrylate) (PCMA) film and connected to a PV cell

Mg(II) and Ni(II) induce aggregation of poly(rA)poly(rU) to either tetra-aggregate or triplex depending on the metal ion concentration

The ability of magnesium(II) and nickel(II) to induce dramatic conformational changes in the synthetic RNA poly(rA)poly(rU) has been investigated. Kinetic experiments, spectrofluorometric titrations, melting experiments and DSC measurements contribute in shedding light on a complex behaviour where the action of metal ions (Na+, Mg2+, Ni2+), in synergism with other operators as the intercalating dye coralyne and temperature, all concur in stabilising a peculiar RNA form. Mg2+ and Ni2+ (M) bind rapidly and almost quantitatively to the duplex (AU) to give a RNA/metal ion complex (AUM). Then, by the union of two AUM units, an unstable tetraaggregate (UAUA(M2)*) is formed which, in the presence of a relatively modest excess of metal, evolves to the UAUM triplex by releasing a single AM strand. On the other hand, under conditions of high metal content, the UAUA(M2)* intermediate rearranges to give a more stable tetra-aggregate (UAUA(M2)). As concerns the role of coralyne (D), it is found that D strongly interacts with UAUA(M2). Also, in the presence of coralyne, the ability of divalent ions to promote the transition of AUD into UAUD is enhanced, according to the efficiency sequence [Ni2+]≫[Mg2+]≫[Na+]

Intercalation of Zn(II) and Cu(II) complexes of the cyclic polyamine Neotrien into DNA: equilibria and kinetics

The equilibria and kinetics of the interaction of the Zn(II) and Cu(II) complexes of the macrocyclic polyamine 2,5,8,11-tetraaza[12]-[12](2,9)[1,10]-phenanthrolinophane (Neotrien) with calf thymus DNA have been investigated at pH = 7.0 and T = 25 degreesC by spectrophotometry, spectrofluorimetry and stopped-flow method. At low dye/polymer ratios both complexes bind to DNA according to the excluded site model. At high dye/polymer ratios the binding displays cooperative features. The logarithm of the binding constant depends linearly on - log[NaCl]. The kinetic results suggest the D + S reversible arrow D, S reversible arrow DS mechanism where the metal complexes (D) react with the DNA sites (S) leading to fast formation of an externally bound form (D, S) which, in turn, is converted into internally bound complex (DS) by intercalation. The binding constants, evaluated as ratios of rate constants, agree with those obtained from equilibrium binding experiments, thus confirming the validity of the proposed model. Fluorescence titrations, where the metal-Neotrien complexes were added to DNA previously saturated with ethidium bromide (EB), show that both complexes displace EB from the DNA cavities. The reverse process, i.e. the addition of excess ethidium to the DNA/metal Neotrien systems, leads to fluorescence recovery for DNA/ZnNeotrien but not for DNA/CuNeotrien. This observation suggests that the binding of CuNeotrien induces deep alterations in the DNA structure. Experiments with Poly(dA-dT) . Poly(dA-dT) and Poly(dG-dC) . Poly(dG-dC) reveal that CuNeotrien mainly affects the structure of the latter polynucleotide. (C) 2004 Elsevier Inc. All rights reserved