Synthesis of novel types of copper-bipyridyl porphyrins and characterization of their interactions and reactivity with DNA

Nucleobase (A, T, G and C) appended tri-cationic water-soluble porphyrins: synthesis, characterization, binding and photocleavage studies with DNA

A series of nucleobase appended tri-cationic porphyrins ( AT 4, TT 4, GT 4 and CT 4) have been synthesized and their binding and cleaving ability of DNA were investigated in this present study. UV-vis, fluorescence, circular dichroism and thermal melting studies were carried out to investigate binding of the porphyrin with calf thymus DNA (CTDNA). The apparent binding constant ( K app ) and the intrinsic binding constant ( K b) values calculated from UV-vis and fluorescence titrations, respectively, were comparable to 5,10,15,20-tetra(N-methylpyridinium-4-yl) porphyrin ( H 2 T 4) or slightly more for few compounds. Circular dichroism spectra of these porphyrins with DNA show variation in their mode of binding. Among the nucleobase appended tri-cationic porphyrins, the porphyrin in GT4 and TT4 exhibit strong intercalating ability in the DNA duplex whereas the porphyrin in AT 4 and CT 4 exhibit very less ability for intercalation. The intercalating efficiency of the porphyrin in GT 4 is even stronger than that of the H 2 T 4. The steric strain exists between the tri-cationic porphyrin moiety and the DNA may decrease depending on (a) the ease to exhibit keto-enol tautomerism due to the more acidic protons in guanine and thymine, (b) extended conjugation and (c) hydrogen bonding capability of the nucleobase moieties. Photocleavage proclivities with pBR322 DNA in the presence of light reveal that AT 4, TT 4 and CT 4 show same amount of cleavage but GT 4 shows more cleaving efficiency than H 2 T 4 due to the stacked guanine moieties those are more reducing than a single guanine residue. The singlet oxygen mechanism that is responsible for the photocleavage was confirmed with various inhibitors and interestingly with Tiron (disodium salt of 1,2-dihydroxy-3,5-benzenedisulfonic acid) the photocleaving efficiency increases due to the inhibition of superoxide formation.

The CdCl2 effects on synthetic DNAs encaged in the nanodomains of a cationic water-in-oil microemulsion

The present work is dedicated to the study of the interactions of CdCl(2) with the synthetic polynucleotides polyAT and polyGC confined in the nanoscopic aqueous compartment of the water-in-oil microemulsion CTAB/pentanol/hexane/water, with the goal to mimic in vitro the situation met by the nucleic acids in vivo. In biological structures, in fact, very long strings of nucleic acids are segregated into very small compartments having a radius exceedingly smaller than the length of the encapsulated macromolecule. For comparison, the behaviour of polyGC was also studied in aqueous solutions of matched composition. The conformational and thermal stabilities of both polynucleotides enclosed in the inner compartment of the microemulsion are scarcely affected by the presence of CdCl(2), whereas in solution immediate and large effects were observed also at room temperature. The lack of effects of CdCl(2) on the properties of the biopolymers entrapped in the aqueous core of the microemulsion has been attributed to the peculiar characteristics of the medium (low dielectric constant, in particular) which cause a total repression of the CdCl(2) dissociation that is not complete even in water. In fact, several of the numerous effects of CdCl(2) observed on the conformational stability of polyGC in aqueous solutions have also been ascribed to the limited dissociation of the cadmium salt.

The interaction of taurine-salicylaldehyde Schiff base copper(II) complex with DNA and the determination of DNA using the complex as a fluorescence probe

The interaction of taurine-salicylaldehyde Schiff base copper(II) (Cu(TSSB)2(2+)) complex with DNA was explored by using UV-vis, fluorescence spectrophotometry, and voltammetry. In pH 7.4 Tris-HCl buffer solution, the binding constant of the Cu(TSSB)2(2+) complex interaction with DNA was 3.49 x 10(4) L mol(-1). Moreover, due to the fluorescence enhancing of Cu(TSSB)2(2+) complex in the presence of DNA, a method for determination of DNA with Cu(TSSB)2(2+) complex as a fluorescence probe was developed. The fluorescence spectra indicated that the maximum excitation and emission wavelength were 389 nm and 512 nm, respectively. Under optimal conditions, the calibration graphs are linear over the range of 0.03-9.03 microg mL(-1) for calf thymus DNA (CT-DNA), 0.10-36 microg mL(-1) for yeast DNA and 0.01-10.01 microg mL(-1) for salmon DNA (SM-DNA), respectively. The corresponding detection limits are 7 ng mL(-1) for CT-DNA, 3 ng mL(-1) for yeast DNA and 3 ng mL(-1) for SM-DNA. Using this method, DNA in synthetic samples was determined with satisfactory results.

Metal Cu(II) and Zn(II) bipyridyls as inhibitors of lactate dehydrogenase

Metal complex-protein interaction is an evolving concept for determining cellular targets of metallodrugs. Lacatate dehydrogenase (LDH) is critically implicated in tumor growth and therefore, considered to be an important target protein for anti-tumor metal complexes. Due to efficient biocompatibility of copper (Cu(2+)) and zinc (Zn(2+)), we synthesized CubpyAc(2) . H(2)O (Cu-bpy) and ZnbpyAc(2) . H(2)O (Zn-bpy; where bpy = 2,2' bipyridine, Ac = CH(3)COO(-)) complexes and evaluated their interaction with and modulation of LDH in mouse tissues. The increasing concentration of both the complexes showed a significant shift in UV-Vis spectra of LDH. The binding constant data (Kc = 1 x 10(3) M(-1) for Cu-bpy and 7 x 10(6) M(-1) for Zn-bpy) suggested that Zn-bpy-LDH interaction is stronger than that of Cu-bpy-LDH. LDH modulating potential of the complexes were monitored by perfusing the mice tissues with non-toxic doses of Cu-bpy and Zn-bpy followed by activity measurement and analysis of LDH isozymes on non-denaturing polyacrylamide gel electrophoresis (PAGE). As compared to the control sets, Cu-bpy caused a significant decline (P < 0.05-0.001) in the activity of LDH in all the tissues studied. However, Zn-bpy showed inhibition of LDH only in liver (P < 0.01), kidney (P < 0.001) and heart (P < 0.01), but with no effect in spleen, brain and skeletal muscle tissues. PAGE analysis suggested that all the five LDH isozymes are equally sensitive to both the complexes in the respective tissues. The results suggest that Cu- and Zn-bpy are able to interact with and inhibit LDH, a tumor growth supportive target protein at tissue level.

The interaction of native DNA with Zn(II) and Cu(II) complexes of 5-triethyl ammonium methyl salicylidene orto-phenylendiimine

The interaction of native calf thymus DNA with the Zn(II) and Cu(II) complexes of 5-triethyl ammonium methyl salicylidene orto-phenylendiimine (ZnL(2+) and CuL(2+)), in 1 mM Tris-HCl aqueous solutions at neutral pH, has been monitored as a function of the metal complex-DNA molar ratio by UV absorption spectrophotometry, circular dichroism (CD) and fluorescence spectroscopy. The results support for an intercalative interaction of both ZnL(2+) and CuL(2+) with DNA, showing CuL(2+) an affinity of approximately 10 times higher than ZnL(2+). In particular, the values of the binding constant, determined by UV spectrophotometric titration, equal to 7.3x10(4) and 1.3x10(6)M(-1), for ZnL(2+) and CuL(2+), respectively, indicate the occurrence of a marked interaction with a binding size of about 0.7 in base pairs. The temperature dependence of the absorbance at 258 nm suggests that both complexes strongly increase the DNA melting temperature (Tm) already at metal complex-DNA molar ratios equal to 0.1. As evidenced by the quenching of the fluorescence of ethidium bromide-DNA solutions in the presence of increasing amounts of metal complex, ZnL(2+) and CuL(2+) are able to displace the ethidium cation intercalated into DNA. A tight ZnL(2+)-DNA and CuL(2+)-DNA binding has been also proven by the appearance, in both metal complex-DNA solutions, of a broad induced CD band in the range 350-450 nm. In the case of the CuL(2+)-DNA system, the shape of the CD spectrum, at high CuL(2+) content, is similar to that observed for psi-DNA solutions. Such result allowed us to hypothesize that CuL(2+) induces the formation of supramolecular aggregates of DNA in aqueous solutions.

Synthetic metallomolecules as agents for the control of DNA structure

This tutorial review summarises B-DNA structure and metallomolecule binding modes and illustrates some DNA structures induced by molecules containing metallic cations. The effects of aquated metal ions, cobalt amines, ruthenium octahedral metal complexes, metallohelicates and platinum complexes such as cis-platin are discussed alongside the techniques of NMR, X-ray crystallography, gel electrophoresis, circular dichroism, linear dichroism and molecular dynamics. The review will be of interest to people interested in both DNA structure and roles of metallomolecules in biological systems.

DNA-binding and cleavage studies of novel copper(II) complex with l-phenylalaninate and 1,4,8,9-tetra-aza-triphenylene ligands

DNA-binding properties of novel copper(II) complex [Cu(l-Phe)(TATP)(H(2)O)](+), where L-Phe=L-phenylalaninate and TATP=1,4,8,9-tetra-aza-triphenylene are investigated using electronic absorption spectroscopy, fluorescence spectroscopy, voltammetry and viscosity measurement. It is found that the presence of calf thymus DNA results in a hypochromism and red shift in the electronic absorption, a quenching effect on fluorescence nature of ethidium bromide-DNA system, an enhanced response on voltammograms of [Co(phen)(3)](3+/2+)-DNA system, and an obvious change in viscosity of DNA. From absorption titration, fluorescence analysis and voltammetric measurement, the binding constant of the complex with DNA is calculated. The latter two methods reveal the stronger binding of [Cu(l-Phe)(TATP)(H(2)O)](+) complex to double strand DNA by the moderate intercalation than [Co(phen)(3)](3+). Such a binding induces the cleavage of plasmid pBR322 DNA in the presence of H(2)O(2).