Binding of the Mn(III) complex of meso-tetrakis (4-N-methyl-pyridiniumyl) porphyrin to DNA. Effect of ionic strength

Interaction of MnTOEtPyP4 porphyrin with DNA

The binding of water-soluble meso-tetra-(4N-oxyethylpyridyl) porphyrin (H2TOEtPyP4) and its manganese (III) derivative (MnTOEtPyP4) with calf thymus DNA have been quantitatively studied using UV/Vis spectrophotometry, Circular Dichroism (CD), thermal melting curves and viscometry. The results show, that porphyrins interact with DNA via one binding mode at low relative concentrations (r) and two binding modes at high values of r. The binding constant (Kb) and stoichiometry (n) were determined from binding isotherms for both porphyrin-DNA complexes. The thermal melting analysis indicates that the double-helical structure of DNA molecules is stabilizing in presence of studied porphyrins. At certain concentrations of porphyrin, two-stage melting curves were observed, which indicates the existence of two different binding modes. Obtained results show that MnTOEtPyP4 associates with DNA duplex via outside binding mode.Communicated by Ramaswamy H. Sarma.

Hybrid Complexes of Photosensitizers with Luminescent Nanoparticles: Design of the Structure

Increasing the efficiency of the photodynamic action of the dyes used in photodynamic therapy is crucial in the field of modern biomedicine. There are two main approaches used to increase the efficiency of photosensitizers. The first one is targeted delivery to the object of photodynamic action, while the second one is increasing the absorption capacity of the molecule. Both approaches can be implemented by producing dye-nanoparticle conjugates. In this review, we focus on the features of the latter approach, when nanoparticles act as a light-harvesting agent and nonradiatively transfer the electronic excitation energy to a photosensitizer molecule. We will consider the hybrid photosensitizer-quantum dot complexes with energy transfer occurring according to the inductive-resonance mechanism as an example. The principle consisting in optimizing the design of hybrid complexes is proposed after an analysis of the published data; the parameters affecting the efficiency of energy transfer and the generation of reactive oxygen species in such systems are described.

A sensitive impedimetric platform biosensing protein: Insoluble precipitates based on the biocatalysis of manganese(III) meso-tetrakis (4-N-methylpyridiniumyl)-porphyrinin in HCR-assisted dsDNA

In this study, a sensitive biosensing interface for protein was reported based on nonconductive insoluble precipitates (IPs) by the biocatalysis of manganese(III) meso-tetrakis (4-N-methylpyridiniumyl)-porphyrin (MnTMPyP), which was intercalated into formed double-strand DNA (dsDNA) scaffold triggered by hybridization chain reaction (HCR). In the proposed impedimetric aptasensor, carcinoembryonic antigen (CEA) and its aptamer were used as testing model. PtPd nanowires (PtPdNWs) with large surface area and superior conductivity were employed as nanocarriers to greatly immobilize biomolecules (e.g. CEA aptamers). Then, two DNA hairpins H1 and H2 were introduced to trigger HCR with the assistance of DNA initiator, resulting in the formation of a long dsDNA scaffold. Meanwhile, mimicking enzyme MnTMPyP molecules were embedded into the resultant dsDNA, in situ generating the complex MnTMPyP-dsDNA with peroxidase-like activity. Under the biocatalysis of MnTMPyP-dsDNA, 3,3-diaminobenzidine (DAB) was oxidized to form nonconductive IPs. As a result, the electron transfer between electrode interface and redox probe was vastly hindered, leading to the significant amplification of electrochemical impedimetric signal. So, greatly improved analytical performances of the proposed aptasensor were achieved with a detection limit as low as 0.030pgmL(-1). And the successful assay of CEA in human serum samples enabled the developed biosensing platform to have promising potential in bioanalysis.

Synthesis, crystal structures, photoluminescence properties and DNA binding of triazine-nickel(II) complexes for DNA detection

We report here the synthesis of three new nickel(II) complexes: [Ni(PzTA)2CO3]·5H2O (PzTA=2,4-diamino-6-(2'-pyrazin)-1,3,5-triazine) in 1, [NiQ(PyTA)(H2O)2]Cl·H2O (HQ=8-hydroxyquinoline, PyTA=2,4-diamino-6-(2'-pyridyl)-1,3,5-triazine) in 2, [NiQ(PzTA)(H2O)2]Cl·H2O in 3, and they were characterized by UV spectroscopy, elemental analysis, molar conductivity and X-ray single crystal diffraction. Binding of the complexes to ct-DNA was investigated with electronic spectroscopy, ethidium bromide displacement from DNA, viscometry and cyclic voltammetry. The results depicted the DNA binding mode of the three complexes was intercalation, and complex 1 together with external static-electricity. Moreover, the three complexes also presented potential anti-oxidant activity. Interestingly, we found 1 was sensitive to oxygen and to the polarity of nonaqueous solvents in fluorescence spectroscopy. Fluorescence of 2 and 3 is weak in neutral aqueous solvents, but is greatly enhanced by addition of ct-DNA. Thus, 2 and 3 can be used to DNA detection as DNA fluorescence probes with a LOD of 1.61 ng mL(-1), 4.90 ng mL(-1) for the relative wide linear range of 0.01-20 μg mL(-1), 0.02-30 μg mL(-1), respectively. These findings indicate that 1 may be a potential optical probe for oxygen-free environments in nonaqueous form, while 2 and 3 were DNA-targeted probes.

Comparative study of the interaction of meso-tetrakis (N-para-trimethyl-anilium) porphyrin (TMAP) in its free base and Fe derivative form with oligo(dA.dT)15 and oligo(dG.dC)15

Interaction between a cationic porphyrin and its ferric derivative with oligo(dA.dT)15 and oligo(dG.dC)15 was studied by UV-vis spectroscopy, resonance light scattering (RLS), and circular dichroism (CD) at different ionic strengths; molecular docking and molecular dynamics simulation were also used for completion. Followings are the observed changes in the spectral properties of meso-tetrakis (N-para-trimethyl-anilium) porphyrin (TMAP), as a free-base porphyrin with no axial ligand, and its Fe derivative (FeTMAP) upon interaction with oligo(dA.dT)15 and oligo(dG.dC)15: (1) the substantial red shift and hypochromicity at the Soret maximum in the UV-vis spectra; (2) the increased RLS intensity by increasing the ionic strength; and (3) an intense bisignate excitonic CD signal. All of them are the reasons for TMAP and FeTMAP binding to oligo(dA.dT)15 and oligo(dG.dC)15 with the outside binding mode, accompanied by the self-stacking of the ligands along the oligonucleotide helix. The CD results demonstrated a drastic change from excitonic in monomeric behavior at higher ionic strengths, which indicates the groove binding of the ligands with oligonucleotides. Molecular docking also confirmed the groove binding mode of the ligands and estimated the binding constants and energies of the interactions. Their interaction trend was further confirmed by molecular dynamics technique and structure parameters obtained from simulation. It showed that TMAP reduced the number of intermolecular hydrogen bonds and increased the solvent accessible surface area in the oligonucleotide. The self-aggregation of ligands at lower concentrations was also confirmed.

Synthesis, crystal structures, DNA binding and photoluminescence properties of [Cu(pzta)2Cl]Cl⋅H2O for DNA detection

We report here the synthesis of a new copper(II) complex of 2,4-diamino-6-(2'-pyrazin)-1,3,5-triazine [Cu(pzta)2Cl]Cl·H2O and its characterization using UV and IR spectroscopy, elemental analysis, and X-ray diffraction. Fluorescence spectroscopy revealed that the complex was sensitive to oxygen and to the polarity of nonaqueous solvents. Binding of the complex to DNA was investigated using UV spectroscopy, ethidium bromide displacement from DNA, cyclic voltammetry, and viscometry. The results revealed the DNA binding mode was intercalation together with external static-electricity. However, the complex can be also used to DNA detection as DNA fluorescence probe with a LOD of 4.21 ng mL(-1) for the relative wide linear range between 0.2 and 17 μg mL(-1). In conclusion, that synthetic method of the complex was easy with low expense and was relatively rapid and sensitive compared to most toxic fluorescence dyes. This finding would indicate the complex may be a potential DNA-targeted probes and optical probes for oxygen-free environments in nonaqueous form.

Manganese porphyrin-dsDNA complex: a mimicking enzyme for highly efficient bioanalysis

Manganese porphyrin (MnTMPyP)-dsDNA complex was reported as an excellent mimicking enzyme of peroxidase. It possessed high catalytic activity and much quicker catalytic kinetics and better stability with exposure to light irradiation and high temperature than both horseradish peroxidase and hemin/G-quadruplex DNAzyme. The groove binding of MnTMPyP to the dsDNA scaffold efficiently maintained the catalytic activity of the MnTMPyP center and improved its stability. By combining with an isothermal hybridization chain reaction (HCR) and in situ formation of MnTMPyP-dsDNA, a highly efficient chemiluminescent (CL) immunosensing method was proposed. After a sandwich immunoreaction, a biotinylated DNA strand, which was bound to biotinylated signal antibody by streptavidin, triggered the HCR and growth of MnTMPyP-dsDNA on the immunocomplex. The in situ, HCR-assisted enzyme formation brought numerous enzymatic catalytic centers, MnTMPyP, on the immunocomplex, resulting in significant CL signal amplification and highly sensitive CL detection. Using carcinoembryonic antigen as the model target, the proposed CL immunoassay method showed a wide linear range from 10 pg/mL to 100 ng/mL with a detection limit of 6.8 pg/mL. The new MnTMPyP-dsDNA complex could be conveniently synthesized, functionalized, and combined with DNA amplification strategies, showing a promising potential in bioanalysis and other relative fields.

Spectral investigations of the solution properties of 5,10,15,20-tetrakis(4-N-benzyl-pyridyl)porphyrin (TBzPyP) and its interaction with human serum albumin (HSA)

The association behavior of 5,10,15,20-tetrakis(4-N-benzyl-pyridyl)porphyrin ( TBzPyP ) was investigated in aqueous solution at 27 °C and various ionic strengths by optical absorption, fluorescence and resonance light scattering (RLS) spectroscopies. The results show that TBzPyP exists as monomer at low ionic strength and as ill-defined aggregates at high ionic strength and does not show concentration dependent aggregation over an extended concentration range between 5 × 10−7 to 1 × 10−4 M in water. The interaction of the TBzPyP with human serum albumin (HSA) in 5 mM phosphate buffer, pH = 7.00, and at 27 °C, has been also studied by optical absorption, fluorescence and RLS spectroscopies. The formation of two types of complexes (HSA: TBzPyP and (HSA)2: TBzPyP ) has been demonstrated by analysis of optical absorption spectral patterns of TBzPyP at various concentrations of HSA. Based on absorption data, a binding model has been proposed and used to analyze the binding process. The calculated binding constant for formation of HSA: TBzPyP and ( HSA )2: TBzPyP are 3.79 × 106 M−1 and 1.46 × 105 M−1, respectively. The RLS spectra of TBzPyP at various concentration of HSA do not show any aggregation of TBzPyP in the presence of HSA. Due to the fact that binding of TBzPyP quenches the HSA fluorescence, a step-by-step aggregation model, which has been developed by Borissevich, I. E. et al, was used to determine the average aggregation number of HSA, < J >, from the fluorescence quenching. The < J > value is 1.4, which further confirms the formation of the two mentioned complexes at this concentration range of HSA.

Characterization of mesoscale coiled-coil peptide-porphyrin complexes

Photoelectronically conductive self-assembling peptide-porphyrin assemblies have great potential in their use as biomaterials, owing largely to their environmentally responsive properties. We have successfully designed a coiled-coil peptide that can self-assemble to form mesoscale filaments and serve as a scaffold for porphyrin interaction. In our earlier work, peptide-porphyrin-based biomaterials were formed at neutral pH, but the structures were irregular at the nano- to microscale size range, as judged by atomic force microscopy. We identified a pH in which mesoscale fibrils were formed, taking advantage of the types of porphyrin interactions that are present in well-characterized J-aggregates. We used UV-visible spectroscopy, circular dichroism spectropolarimetry, fluorescence spectroscopy, and atomic force microscopy to characterize these self-assembling biomaterials. We propose a new assembly paradigm that arises from a set of unique porphyrin-porphyrin and porphyrin-peptide interactions whose structure may be readily modulated by changes in pH or peptide concentration.

Excited state dynamics of meso-tetra(sulphonatophenyl) metalloporphyrins

The excited state dynamics of Zn2+, Fe3+, and Mn3+ meso-tetra(sulfonatophenyl) porphyrin complexes were investigated with a Z-scan technique at 532 nm using 70 ps and 120 fs single pulses and 200 ns pulse trains of a Q-switched and mode locked laser. We determined the characteristic interconversion and intersystem crossing times, quantum yields of the excited S1 state, and S1 --> Sn and T1 --> Tn transition cross-sections. The ground state cross-sections were obtained using UV-vis absorption spectroscopy, and a five-energy-level diagram was used to yield the photophysical parameters mentioned previously.

Enzymatic oxidation of dipyridamole in homogeneous and micellar solutions in the horseradish peroxidase–hydrogen peroxide system

Enzymatic oxidation of dipyridamole (DIP) by horseradish peroxidase-hydrogen peroxide system (HRP-H2O2) in aqueous and micellar solutions was carried out. The reaction was monitored by optical absorption and fluorescence techniques. In aqueous solution at pH 7.0 and pH 9.0, the disappearance of the characteristic bands of DIP centered at 400 nm and 280 nm was observed. A new strong band at 260 nm is observed for the oxidation product(s) with shoulders at 322 nm and 390 nm. A non-fluorescent product is formed upon oxidation. In cationic cethyl trimethyl-1-ammonium chloride (CTAC) and zwitterionic 3-(N-hexadecyl-N,N-dimethylammonium) propane sulfonate (HPS) micellar solutions the same results are observed: three, well-defined, isosbestic points in the optical spectra suggest the transformation between two species. In anionic micellar sodium dodecylsulfate solution (SDS), the appearance of a new band centered around 506 nm was observed, associated to a solution color change from the usual yellow to deep blue/violet, characteristic of a radical species associated to the one-electron oxidation of DIP to its cation radical (DIP*+), observed previously in electrochemical oxidation. Experiments of radical decay kinetics monitoring the absorbance change at 506 nm were performed and analyzed in the frame of a kinetic model taking into account the species both in homogeneous and micellar media. The reaction medium is composed of bulk solution, SDS micelle/solution interface and enzyme catalytic site(s). The variation of DIP*+ concentration was analyzed assuming: (1) synthesis of DIP*+ by HRP through one-electron oxidation; (2) decomposition of DIP*+ by further one-electron oxidation; (3) direct two-electron oxidation of DIP by HRP; (4) bimolecular DIP*+ disproportionation. The main results of the analysis are as follows: (1) kinetic data can be divided in two phases, an HRP active phase and another phase which proceeds in the absence of enzyme activity due to consumption of all H2O2; (2) the reactions of DIP*+ formation, DIP*+ decomposition and DIP two-electron oxidation are HRP concentration dependent; (3) since DIP*+ formation constant seems to be overestimated, it is proposed that two-electron oxidation is another source of DIP*+, through the comproportionation reaction. Evidences for this reaction were also observed previously in electrochemical experiments; and (4) the kinetic analysis provides evidences that the bimolecular reaction of DIP*+ takes place mainly in the absence of active HRP and in this phase the combination of, at least, two second-order kinetic processes is needed to model the experimental data. Our data suggest that HRP oxidizes DIP in general by a two-electron process or that the cation radical is very unstable so that the one-electron process is only detected in the presence of anionic surfactant, which stabilizes significantly the DIP*+ intermediate.

Spectroscopic studies of the interaction of bichromophoric cyanine dyes with DNA. Effect of ionic strength

Spectroscopic characteristics of a cyanine dye with two chromophores (biscyanine dye, BCD) in aqueous solutions and effects of NaCl and DNA upon these characteristics have been studied by optical absorption, circular dichroism (CD) and fluorescence spectroscopies. In homogeneous solutions, BCD is characterized by intense optical absorption (epsilon =1.33 x 10(5) M(-1) x cm(-1)) and weak fluorescence (phi(fl)=0.018) in the wavelength region greater than 600 nm. The dye forms H-aggregates at low concentrations (10(-6) M). NaCl stimulates the formation of both H- and J-aggregates of the dye at much lower dye concentrations, while DNA in low concentrations (<10(-6) M) stimulated the formation of just J-aggregates on the surface of the DNA molecule. Higher DNA concentrations induce the dye to disaggregate, and there exists an equilibrium between three dye forms: free monomers, J-aggregates and bound monomers, the maximum content of J-aggregates was observed at [DNA]/[BCD]=0.6+/-0.2 and total disaggregation at [DNA]/[BCD]=190+/-20. J-aggregates are characterized by phi(fl)=0.05 and bound monomers by phi(fl)=0.44. In the presence of NaCl, total disaggregation was observed at [DNA]/[BCD]=570+/-10 due to competition between Na(+) and the dye molecules for DNA electronegative binding sites.