Binding of meso-Tetrakis(N-methylpyridinium-4-yl)porphyrin to Double Helical RNA and DNA.RNA Hybrids

Binding of a Tricationic meso-Substituted Porphyrin to poly(A)⋅poly(U): an Experimental Study

The porphyrins are macrocyclic compounds widely used as photosensitizers in anticancer photodynamic therapy. The binding of a tricationic meso-tris(N-methylpyridinium)-porphyrin, TMPyP3+, to poly(A)⋅poly(U) polynucleotide has been studied in neutral buffered solution, pH6.9, of low and near-physiological ionic strength in a wide range of molar phosphate-to-dye ratios (P/D). Effective TMPyP3+ binding to the biopolymer was established using absorption spectroscopy, polarized fluorescence, fluorimetric titration and resonance light scattering. We propose a model in which TMPyP3+ binds to the polynucleotide in two competitive binding modes: at low P/D ratios (< 4) external binding of the porphyrin to polynucleotide backbone without self-stacking dominates, and at higher P/D (> 30) the partially stacked porphyrin J-dimers are embedded into the polymer groove. Enhancement of the porphyrin emission was observed upon binding in all P/D range, contrasting the binding of this porphyrin to poly(G)⋅poly(C) with significant quenching of the porphyrin fluorescence at low P/D ratios. This observation indicates that TMPyP3+ can discriminate between poly(A)⋅poly(U) and poly(G)⋅poly(C) polynucleotides at low P/D ratios. Formation of highly scattering extended porphyrin aggregates was observed near the stoichiometric in charge binding ratio, P/D = 3. It was revealed that the efficiency of the porphyrin external binding and aggregation is reduced in the solution of near-physiological ionic strength.

Combined spectroscopic and theoretical analysis of the binding of a water-soluble perylene diimide to DNA/RNA polynucleotides and G-quadruplexes

We present here a combined spectroscopic and theoretical analysis of the binding of N,N'-bis(2-(1-piperazino)ethyl)-3,4,9,10-perylenetetracarboxylic acid diimide dichloride (PZPERY) to different biosubstrates. Absorbance titrations and circular dichroism experiments, melting studies and isothermal calorimetry (ITC) titrations reveal a picture where the binding to natural double-stranded DNA is very different from that to double and triple-stranded RNAs (poly(A)∙poly(U) and poly(U)∙poly(A)⁎poly(U)). As confirmed also by the structural and energetic details clarified by density functional theory (DFT) calculations, intercalation occurs for DNA, with a process driven by the combination of aggregates disruption and monomers intercalation. Oppositely, for RNAs, no intercalation but groove binding with the formation of supramolecular aggregates is observed. Among all the tested biosubstrates, the affinity of PZPERY towards DNA G-quadruplexes (G4) is the greatest one with a preference for human telomeric G4s. Focusing on hybrid G4 forms, either sitting-atop ("tetrad-parallel") or lateral ("groove-parallel") binding modes were considered in the discussion of the experimental results and molecular dynamics (MD) simulations. Both turned out to be possible concurrently, in agreement also with the experimental binding stoichiometries higher than 2:1.

One-pot synthesis of a new 2-substituted 1,2,3-triazole 1-oxide derivative from dipyridyl ketone and isonitrosoacetophenone hydrazone: Nickel(II) complex, DNA binding and cleavage properties

An efficient and simple one-pot synthesis of a new 1,2,3-triazole-1-oxide via reaction between isonitrosoacetophenone hydrazone and dipyridyl ketone in the EtOH/AcOH at room temperature has been developed smoothly in high yield. The reaction proceeds via metal salt free, in-situ formation of asymmetric azine followed by cyclization to provide 1,2,3-triazole 1-oxide compound. It has been structurally characterized. The 1:1 ratio reaction of the 1,2,3-triazole 1-oxide ligand with nickel(II) chloride gives the mononuclear complex [Ni(L)(DMF)Cl₂], hexa-coordinated within an octahedral geometry. Characterization of the 1,2,3-triazole compound and its Ni(II) complex with FTIR, ¹H and ¹³C NMR, UV-vis and elemental analysis also confirms the proposed structures of the compounds. The interactions of the compounds with Calf thymus DNA (CT-DNA) have been investigated by UV-visible spectra and viscosity measurements. The results suggested that both ligand and Ni(II) complex bind to DNA in electrostatic interaction and/or groove binding, also with a slight partial intercalation in the case of ligand. DNA cleavage experiments have been also investigated by agarose gel electrophoresis in the presence and absence of an oxidative agent (H₂O₂). Both 1,2,3-triazole 1-oxide ligand and its nickel(II) complex show nuclease activity in the presence of hydrogen peroxide. DNA binding and cleavage affinities of the 1,2,3-triazole 1-oxide ligand is stronger than that of the Ni(II) complex.

Interaction of a tricationic meso-substituted porphyrin with guanine-containing polyribonucleotides of various structures

The interaction of a tricationic water-soluble meso-(N-methylpyridinium)-substituted porphyrin, TMPyP³⁺, derived from classic TMPyP4, with double-stranded poly(G)  ⋅  poly(C) and four-stranded poly(G) polyribonucleotides has been studied in aqueous buffered solutions, pH 6.9, of low and near-physiological ionic strengths in a wide range of molar phosphate-to-dye ratios (P/D). To clarify the binding modes of TMPyP³⁺ to biopolymers various spectroscopic techniques, including absorption and polarized fluorescence spectroscopy, Raman spectroscopy, and resonance light scattering, were used. As a result, two competitive binding modes were revealed. In solution of low ionic strength outside binding of the porphyrin to the polynucleotide backbone with self-stacking prevailed at low P/D ratios (P/D  <  3.5). It manifested itself by the substantial quenching of porphyrin fluorescence. Also the formation of large-scale porphyrin aggregates was observed near the stoichiometric binding ratio. The spectral changes observed at P/D  >  30 including emission enhancement were supposed to be caused by the embedding of partially stacked porphyrin J-dimers into the polymer groove. TMPyP³⁺ binding to poly(G) induced a fluorescence increase 2.5 times as large as that observed for poly(G)  ⋅  poly(C). In solution of near-physiological ionic strength the efficiency of external porphyrin binding was reduced substantially due to the competitive binding of Na⁺ ions with the polymer backbone. The spectroscopic characteristics of porphyrin bound to polynucleotides at different conditions were compared with those for free porphyrin.

Photocytotoxicity, cellular uptake and subcellular localization of amidinophenylporphyrins as potential photodynamic therapeutic agents: An in vitro cell study

The cell-based studies of 5, 10, 15, 20-Tetrakis (4-amidinophenyl) porphyrin (Por1), its Zn complex (Por2) and amidinophenyl bisporphyrin (Por3) were carried out to examine their photocytotoxicity, cellular uptake and sub-cellular localization with human nasopharyngeal carcinoma cell (HK-1), using 5, 10, 15, 20-Tetrakis (N-methyl-4-pyridyl) porphyrin (H2TMPyP) as a reference. These porphyrins showed low dark-cytotoxicity and high photo-cytotoxicity against HK-1. The amphiphilic amidinophenyl bisporphyrin (Por3) displayed better cellular uptake than the single hydrophilic Por1, Por2 and H2TMPyP. As seen from the extent of overlapping of the fluorescence profiles, lysosomal localization of amidinophenylporphyrin Por1-Por3 and mito/lyso localization of the H2TMPyP occurred in the cells. The results suggest these porphyrins with amidine group could be used as potential agents in photodynamic therapy.

Selective G-quadruplex stabilizers: Schiff-base metal complexes with anticancer activity

Molecular dynamics simulations and quantum mechanics/molecular mechanics calculations provided a mechanism for G-quadruplex binding of three transition metal complexes.

DNA oligonucleotide templated nanohybrids using electronic type sorted carbon nanotubes for light harvesting

Light harvesting nanostructure hybrids have been designed and demonstrated using single-wall carbon nanotubes (SWCNTs) and porphyrin chromophores. DNA oligonucleotides are used to conjugate SWCNTs with light-absorbing chromophores for transparent films which generate photocurrents. High-purity semiconducting SWCNTs demonstrate significant enhancement in the photocurrent compared to metallic or unsorted tubes.

Electrospray mass spectrometry of isomeric tetrakis(N-alkylpyridyl)porphyrins and their manganese(III) and iron(III) complexes

Manganese(III) complexes of isomeric tetrakis(N-alkylpyridyl)porphyrins (N- alkyl = N- methyl , M or N- ethyl , E ), MnTM ( E )-2(3,4)- PyP5+, are being developed as superoxide dismutase (SOD) mimics. Simultaneously, techniques for their purification, identification and characterization are being pursued. Electrospray mass spectrometry ( ESMS ) proved to be an excellent method for identification and characterization of this group of water-soluble cationic porphyrins. The multiply charged parent ion is observed for both the metal-free ligands and their corresponding manganese complexes. The other major peaks in the mass spectra result from loss of N-alkyl groups, reduction of the metal center, axial coordination of chloride or hydroxo ion in the case of the Fe porphyrin, loss of metal and deprotonation of pyrrolic nitrogens. As a result of inductive and resonance effects, which stabilize the ortho isomer, almost no loss of N-alkyl groups from the manganese complex or from its parent ligand was observed. The relative intensity of the multiply charged molecular ion MnIIITM -3(4)- PyP5+/5 was 100% in the case of the meta and para isomers. Although manganese porphyrins display a low preference toward axial ligation, favorable electrostatics at the metal center of the ortho isomer gives rise to 100% relative intensity of the species that has chloride axially ligated at the manganese site, MnIIITM ( E )-2- PyPCl4+/4. When the stronger preference of iron porphyrins toward axial ligation combines with the ortho effect, the monohydroxo iron porphyrin FeIIITM -2- PyP ( OH )4+/4 dominates the ESMS of an aqueous acetonitrile solution at pH 7.8.

Interactions of tetracationic mercury(II), cadmium(II) and lead(II) porphyrins with DNA and their effects on DNA cleavage

The effects of tetrakis(1-methylpyridinium-4-yl)porphyrinatomercury(II) [ Hg ( TMPyP )]4+(6) along with [ Pb ( TMPyP )]4+(7), [ Cd ( TMPyP )]4+(8), and [ H2( TMPyP )]4+(1) (free base porphyrin) on DNA cleavage by Haemophilus aegyptius (HaeIII) have been studied using gel electrophoresis, UV-vis absorption spectroscopy, and circular dichroism (CD) spectroscopy. The gel electrophoresis results indicate that in the absence of 6, HaeIII restriction enzyme could not cleave plasmid DNA at a low concentration of 0.2 units μl-1after 1 h incubation at 37 °C. However, DNA cleavage occurred in the presence of 6 at the concentrations of 1.0 × 10-6and 1.0 × 10-7M and 0.2 units μl-1of HaeIII under the same conditions. In addition, acceleration of DNA cleavage occurred at a higher concentration of HaeIII (0.4 units μl-1) in the presence of a wider concentration range of 6 from 1.0 × 10-5to 1.0 × 10-7M . 8, 7, and 1 could not enhance DNA cleavage in the presence of HaeIII (0.2 units μl-1). However, when the concentration of HaeIII was increased to 0.4 units μl-1, only 8 inhibited DNA cleavage by HaeIII at higher concentrations (1.0 × 10-5-10-6M ) whereas 6, 7, and 1 did not. The UV-vis and CD spectroscopic results indicate that these porphyrins interact differently with DNA based on their binding modes. 6 enhanced DNA cleavage due to the synergistic effect of the Hg2+ions and the free base porphyrin 1 that dissociated from the mercury(II) porphyrin complex upon binding to DNA which resulted in the enhanced transformation of the DNA conformation from the original B-form to a Z-like conformation, while 8 inhibited HaeIII activity at higher concentrations and 7 and 1 neither enhanced nor inhibited DNA cleavage. A mechanism for this phenomenon is suggested.

Nucleic acid interaction and antibacterial behaviours of a ternary palladium(II) complexes

The bidentate ligands and Pd(II) complexes have been synthesized and characterized using elemental analysis (C, H, N), (1)H NMR, (13)C NMR, electronic spectra, FT-IR and FAB mass spectroscopy. The binding of palladium complexes with calf thymus DNA (CT DNA) has been explored using absorption titration, DNA melting temperature and viscosity measurements. The cleavage reaction on pUC19 DNA has been monitored by agarose gel electrophoresis. The results suggest that complexes can bind to DNA by intercalative modes and exhibit nuclease activities in which supercoil form is converted to open circular form. The antibacterial activity of ligands and complexes has been performed against three Gram(-ve) and two Gram(+ve) microorganisms and the study indicates that all the complexes show better microbial inhibition activity than ligands and palladium salt.

Synthesis of novel long wavelength cationic chlorins via stereoselective aldol-like condensation

Using stereoselective aldol-like condensation as a key methodology, a series of chlorophyll a-based long wavelength cationic chlorins were synthesized using methyl pyropheophorbide a (MPPa) and purpurin-18-N-methoxylimide methyl ester as starting materials. Such long wavelength cationic chlorins possess covalently linked cationic moieties (pyridinium or quinolinium) on the peripheral of their tetrapyrrole macrocycles. It was found that all long wavelength cationic chlorins showed their longest absorption maxima in the range of 712-763nm, making them potential photosensitizers in photodynamic therapy. The results of preliminary experiments probing in vitro photodynamic effects showed that the purpurinimide derivatives exhibit relatively high phototoxicity in HeLa cells as compared to MPPa derivatives.

Synthesis of tetra(trimethylammonio)phthalocyanato zinc tetraiodide, [ZnPc(NMe3)4]I4, and a spectrometric investigation of its interaction with calf thymus DNA

The phthalocyanine salt [ ZnPc(NMe3)4]I4was synthesized from 4-nitrophthalonitrile using a three-step procedure. The interaction of [ ZnPc(NMe3)4]4+with calf thymus DNA (CT DNA) has been investigated by UV-vis and fluorescence spectrometric methods. [ ZnPc(NMe3)4]4+exists in a non-monomeric form, proposed to be a dimer, in phosphate buffer solution (pH 6.82). Spectral changes show that in the presence of high concentrations of CT DNA added to the solution, [ ZnPc(NMe3)4]4+is bound in a monomeric state with evidence suggesting it is located in a DNA groove. At lower concentrations of DNA there is evidence of stacking of non-monomeric [ ZnPc(NMe3)4]4+onto the DNA. Two intrinsic binding constants for the interaction of [ ZnPc(NMe3)4]4+with CT DNA, 1.33 × 105and 2.56 × 104M-1have been obtained. Electrostatic binding is shown to play an important role in the interaction of [ ZnPc(NMe3)4]4+with nucleic acids.

Specific visible spectral changes induced by guanine binding to cytosine-derivatized porphyrin

The interaction of the free nucleic acid bases adenine, cytosine, and thymidine with meso-tri(4-sulfonatophenyl) meso 4-phenyl porphyrin cytosine amide (TPSC) trisodium salt at pH 5.9, 7.4, and 9.3 results is a decrease in the absorbance of the Soret (B-band) at 413 nm of TPSC. A decrease in Soret band absorbance is observed with guanine below pH 8; at higher pH values a new absorbance band at 424 nm is observed. The appearance of the band is consistent with hydrogen bonding between the cytosine-functionalized porphyrin and guanine and the resulting perturbation of the electron orbitals of the porphyrin.

DNA Interaction Studies of a New Platinum(II) Complex Containing Different Aromatic Dinitrogen Ligands

A new mononuclear Pt(II) complex, [Pt(DMP)(DIP)]Cl(2).H(2)O, in which DMP is 4,4-dimethyl-2,2-bipyridine and DIP is 4,7-diphenyl-1,10-phenantroline, has been synthesized and characterized by physicochemical and spectroscopic methods. The binding interaction of this complex with calf thymus DNA (CT-DNA) was investigated using fluorimetry, spectrophotometry, circular dichroism, viscosimetry and cyclic voltametry (CV). UV-VIS spectrum showed 4 nm bathochromic shift of the absorption band at 280 nm along with significant hypochromicity for the absorption band of the complex. The intrnisic binding constant (K(b) = 2 × 10(4) M(-1)) is more in keeping with intercalators and suggests this binding mode. The viscosity measurements showed that the complex-DNA interaction can be hydrophobic and confirm intercalation. Moreover, the complex induced detectable changes in the CD spectrum of CT-DNA. The fluorescence studies revealed that the probable quenching mechanism of fluorescence of the complex by CT-DNA is static quenching. The thermodynamic parameters (ΔH > 0 and ΔS > 0) showed that main interaction with hydrogenic forces occurred that is intercalation mode. Also, CV results confirm this mode because, with increasing the CT-DNA concentration, shift to higher potential was observed.

Structural insights into G-quadruplexes: towards new anticancer drugs

DNA G-quadruplexes are DNA secondary structures formed in specific G-rich sequences. DNA sequences that can form G-quadruplexes have been found in regions with biological significance, such as human telomeres and oncogene-promoter regions. DNA G-quadruplexes have recently emerged as a new class of novel molecular targets for anticancer drugs. Recent progress on structural studies of the biologically relevant G-quadruplexes formed in human telomeres and in the promoter regions of human oncogenes will be discussed, as well as recent advances in the design and development of G-quadruplex-interactive drugs. DNA G-quadruplexes can readily form in solution under physiological conditions and are globularly folded nucleic acid structures. The molecular structures of intramolecular G-quadruplexes appear to differ from one another and, therefore, in principle may be differentially regulated and targeted by different proteins and drugs.

DNA interaction studies of a platinum(II) complex, PtCl(2)(NN) (NN=4,7-dimethyl-1,10-phenanthroline), using different instrumental methods

The Pt(II) complex, PtCl(2)(4,7-Me(2)phen) (4,7-Me(2)phen=chelating dinitrogen ligand: 4,7-dimethyl-1,10-phenanthroline) was synthesized and characterized by spectroscopic ((1)H, (13)C NMR) and elemental analysis techniques. Binding interaction of this complex with calf thymus (CT) DNA has been investigated by emission, absorption, circular dichroism, viscosity and DNA thermal denaturation studies. The complex displays significant binding properties to the CT DNA. In fluorimeteric studies, the binding mode of complex with CT DNA was studied by using methylene blue as a fluoresce probe. As evidenced by the increasing fluorescence of methylene blue-DNA solutions in presence of increasing amount of complex, PtCl(2)(NN) complex is able to displace the methylene blue intercalated into DNA completely as to indicate intercalation. Furthermore, mentioned complex induces detectable changes in the CD spectrum of CT-DNA, an increase in T(m) value, and an increase in its viscosity. The experimental results showed that Pt(II) complex bound to DNA by an intercalative mode of binding.

Spectroscopic study of the interaction of Ni(II)-5-triethyl ammonium methyl salicylidene ortho-phenylendiiminate with native DNA

The interaction of native calf thymus DNA with the cationic Ni(II) complex of 5-triethyl ammonium methyl salicylidene ortho-phenylendiimine (NiL(2+)), in 1mM 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 dramatic modification of the DNA CD spectrum, the appearance of a broad induced CD band in the range 350-400nm, the strong increase of the DNA melting temperature (T(m)) and the fluorescence quenching of ethidium bromide-DNA solutions, in the presence of increasing amounts of the NiL(2+) metal complex, support the existence of a tight intercalative interaction of NiL(2+) with DNA, analogous to that recently reported for both ZnL(2+) and CuL(2+). The intrinsic binding constant (K(b)) and the interaction stoichiometry (s), determined by UV spectrophotometric titration, are equal to 4.3x10(6)M(-1) and 1.0 base pair per metal complex, respectively. Interestingly, the value of K(b) is slightly higher and 10 times higher than that relative to the CuL(2+)-DNA and the ZnL(2+)-DNA systems, respectively. Speculations can be performed to rationalize the observed trend, on the basis of the electronic and geometrical structures of the three complexes of the same ligand. Analogously to what previously observed for CuL(2+), the shape of the CD of the NiL(2+)-DNA system at NiL(2+)-DNA molar ratios higher than 0.5 is indicative of the formation of supramolecular aggregates in solutions, as a possible consequence of the electrostatic interaction between the cationic complex and the negatively charged phosphate groups of DNA.

Experimental and DFT studies on DNA binding and photocleavage of two cationic porphyrins. Effects of the introduction of a carboxyphenyl into pyridinium porphyrin

The DNA-binding affinities and DNA photocleavage abilities of cationic porphyrin, 5-(4-carboxyphenyl)-10,15,20-tris(4-methylpyridiniumyl)porphyrin (CTMPyP), and its reference compound meso-tetrakis(N-methyl-4-pyridiniumyl)porphyrin (H2TMPyP) have been investigated. The DNA-binding behaviors of the two compounds in NaH2PO4 buffer were compared systematically by using absorption, fluorescence and circular dichroism (CD) spectra, thermal denaturation as well as viscosity measurements. The experimental results show that CTMPyP binds to DNA in an outside binding mode, while H2TMPyP in an intercalative mode. Photocleavage experiments reveal that both two compounds employ 1O2-mediated mechanism in cleaving DNA and H2TMPyP can cleave DNA more efficiently than CTMPyP. Theoretical calculations were carried out with the density functional theory (DFT), and the calculated results indicate that the character and energies of some frontier orbitals of CTMPyP are quite different from those of H2TMPyP. These theoretical results can be used to explain their different DNA-binding modes and affinities to a certain extent.

Binding of cationic bis-porphyrins linked with p- or m-xylylenediamine and their zinc(II) complexes to duplex DNA

Spectroscopic, viscometric, and molecular docking analysis of binding of cationic bis-porphyrins linked with p- or m-xylylenediamine (H₂pXy and H₂mXy) and their zinc(II) complexes (ZnpXy and ZnmXy) to duplex DNA are described. H₂pXy and H₂mXy bound to calf thymus DNA (CTDNA) stronger than unichromophoric H₂TMPyP, and showed exciton-type induced circular dichroism spectra of their Soret bands. The H₂TMPyP-like units of the metal-free bis-porphyrins did not intercalate into CTDNA, and thus the binding mode is outside binding with intramolecular stacking. ZnpXy showed favorable binding to A·T over G·C region, and should lie in the major groove of A·T region.

2070-DTI, A Topoisomerase Inhibitor Produced byStreptomycessp. Strain No. 2070

A novel inhibitor of topoisomerase II designated as 2070-DTI was isolated from the culture filtrate of Streptomyces sp. strain No. 2070. The structure was determined to be that of the known soyasaponin I on the basis of spectroscopic methods (NMR and MS). 2070-DTI strongly inhibited the decatenation activity of human placenta topoisomerase II in a noncompetitive manner, and weakly inhibited or was inert towards the relaxation activities of various topoisomerase I's and DNA-related enzymes. 2070-DTI is an inhibitor belonging to the cleavable complex-nonforming type without DNA intercalation.

Photodynamic Therapy: Porphyrins and Phthalocyanines as Photosensitizers

The present work is focussed on the principles of photodynamic therapy (PDT), emphasizing the photochemical mechanisms of reactive oxygen species formation and the consequent biochemical processes generated by the action of reactive oxygen species on various biological macromolecules and organelles. This paper also presents some of the most used photosensitizers, including Photofrin, and the new prototypes of photosensitizers, analysing their physicochemical and spectroscopic properties. At this point, the review discusses the therapeutic window of absorption of specific wavelengths involving first- and second-generation photosensitizers, as well as the principal light sources used in PDT. Additionally, the aggregation process, which consists in a phenomenon common to several photosensitizers, is studied. J-aggregates and H-aggregates are discussed, along with their spectroscopic effects. Most photosensitizers have a significant hydrophobic character; thus, the study of the types of aggregation in aqueous solvent is very relevant. Important aspects of the coordination chemistry of metalloporphyrins and metallophthalocyanines used as photosensitizers are also discussed. The state-of-the-art in PDT is evaluated, discussing recent articles in this area. Furthermore, macrocyclic photosensitizers, such as porphyrins and phthalocyanines, are specifically described. The present review is an important contribution, because PDT is one of the most auspicious advances in the therapy against cancer and other non-malignant diseases.

Synthetic control of interchromophoric interaction in cationic bis-porphyrins toward efficient DNA photocleavage and singlet oxygen production in aqueous solution

We have synthesized cationic bis-porphyrins and their zinc(II) complexes with two TMPyP-like chromophores bridged by p- or m-xylylenediamine to develop effective DNA photocleaving agents. The xylylene linkers and zinc ion were introduced to control interchromophoric interaction that should be involved in photosensitization of the cationic bis-porphyrins. The molar absorptivities of all the bis-porphyrins in aqueous solution remained unchanged over a wide range of concentrations, indicating the absence of self-aggregation property. In particular, the molar absorptivity of the zinc(II) complex of the p-xylylenediamine-linked bis-porphyrin in aqueous solution was 2.0 times as large as that of unichromophoric ZnTMPyP, suggesting the absence of both intermolecular and intramolecular interchromophoric interaction. The metal-free p-xylylenediamine-linked bis-porphyrin showed the more efficient conversion ability of supercoiled to nicked circular pUC18 plasmid DNA by photosensitization than the metal-free m-xylylenediamine-linked one. Furthermore, the zinc complexes of the bis-porphyrins exhibited the more potent DNA photocleavage than did the metal-free bis-porphyrins. Singlet oxygen productivity of the four cationic bis-porphyrins was determined by measuring the decomposition rate of 1,3-diphenylisobenzofuran. The amount of singlet oxygen generated by photosensitization of the zinc(II) complex of the p-xylylenediamine-linked bis-porphyrin in aqueous solution was 2.1 times as large as ZnTMPyP, indicating the full singlet oxygen productivity. A significant relationship between the DNA photocleaving abilities and the singlet oxygen productivities of the cationic porphyrins in aqueous solution was found. Hence, the degree of the intramolecular interchromophoric interaction, the DNA photocleaving ability, and the singlet oxygen productivity of the cationic bis-porphyrins in aqueous solution were successfully controlled by means of the introduction of the appropriate linker and metal ion.

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.