DNA binding studies of new valine derived chiral complexes of tin(IV) and zirconium(IV)

Valine derived chiral complexes of SnCl4 (1) and ZrCl4 (2) were designed as potent antitumor agents. These complexes were characterized by elemental analysis, IR, 1H NMR, 119Sn NMR and ESI mass spectroscopy. In vitro binding studies of complexes 1 and 2 under physiological conditions at room temperature with CT-DNA were carried out employing UV-vis absorption titration, fluorescence studies and viscosity measurements. The extent of binding was quantified by Kb values of complexes 1 and 2 which were found to be 1.97×10(4) and 1.17×10(3) M(-1), respectively, suggesting that complex 1 has significantly greater DNA binding propensity in contrast to the complex 2. The mode of action at the molecular level was ascertained by the interaction of complex 1 with 5'GMP and 5'TMP which revealed that complex 1 binds via electrostatic mode with the oxygen of the negatively charged surface phosphate group of the DNA helix. The supercoiled pBR322 plasmid DNA cleavage activity of complex 1 was ascertained by gel electrophoresis assay.     

Synthesis, singlet oxygen photogeneration and DNA photocleavage of porphyrins with nitrogen heterocycle tails

Eight novel compounds were prepared by reaction of 5-(bromo- propoxyphenyl)-10,15,20-triphenylporphyrin with oxazole thiols, 1,3,4-oxadiazole thiols and 1,3,4-thiadiazole thiols, and their structures confirmed by UV-vis, IR, 1H-NMR, MS and elemental analysis. The assessment of indirectly measured 1O(2) production rates against 5,10,15,20-tetraphenyl porphyrin (H(2)TPP) were described and the relative singlet oxygen production yields were：porphyrin 5 > porphyrins 1, 3, 4, 6-8, H(2)TPP > porphyrin 2. Porphyrin 4 and porphyrin 7 showed substantial photocleavage activities toward DNA, with over 75% cleavage observed at 40 μM. It suggested that these those porphyrins with nitrogen heterocycle tails are potential photosensitive agents.     

Interaction between certain porphyrins and CdS colloids: a steady state and time resolved fluorescence quenching study

The interaction between porphyrins namely, meso-tetrakis (4-methoxyphenyl)porphyrin (TMeOPP), protoporphyrin IX (PPIX) and Zinc(II) meso-tetraphenylporphyrin (ZnTPP) with colloidal CdS has been studied by using steady state and time resolved fluorescence quenching measurements. The porphyrins adsorbed on the surface of colloidal CdS due to electrostatic interaction. This adsorption leads to changes in the absorption spectra related to the complex formation. The apparent association constant (Kapp) was in the order of 4.34-5.58 x 10(5) M(-1) from the effect of colloidal CdS on the absorption spectra and 0.64-1.6 x 10(5) M(-1) from fluorescence quenching data. Quenching is attributable mainly to static mechanism through ground state complex formation as confirmed by lifetime measurements.     

Binding studies of porphyrins to human serum albumin using affinity capillary electrophoresis

The present work demonstrates that affinity capillary electrophoresis (ACE) can be employed as a valuable and powerful tool for studying the interactions between porphyrins and proteins in biological and biomedical research, such as the development of porphyrins and related compounds as efficient and selective photosensitizers in the photodynamic therapy of cancers. Binding constants of human serum albumin (HSA) to four biological porphyrins (uroporphyrin I, heptacarboxylporphyrin, coproporphyrin I, protoporphyrin IX), which possess a wide range of hydrophobicity, were estimated by ACE. Based on 1:1 molecular association between these individual porphyrins and HSA, the change of the electrophoretic mobility of HSA as a function of porphyrin concentration in the run buffer was measured and the binding constants were calculated from the slope of the Scatchard plots. The binding constant values were found to be 8.80 +/- 0.51 x 10(4) M(-1), 2.39 +/- 0.16 x 10(5) M(-1), 1.61 +/- 0.11 x 10(6) M(-1), and 9.34 +/- 0.30 x 10(6) M(-1) for uroporphyrin I, heptacarboxylporphyrin, coproporphyrin I, and protoporphyrin IX, respectively, and most of these results are in good agreement with those reported in the literature using conventional methods for binding measurements. Additionally, experimental binding constant data obtained using ACE was found to exhibit very good correlation with theoretical hydrophobicity values calculated using the Rekker's hydrophobic fragmental constant method, thus further supporting the hypothesis that the hydrophobicity of the porphyrin side chains play an important role in governing the hydrophobic interaction of porphyrins with serum proteins such as HSA.     

Synthesis, crystal structure, and DNA-binding study on the trinitrate{2,2'-[2,3-naphthylenebis(oxy)]-bis(N,N-diisopropyl(acetamide))} gadolinium(III) complex

A 2,2'-[2,3-naphthylenebis(oxy)]-bis(N,N-diisopropyl(acetamide)) ligand (L) and its Gd(III) complex have been prepared and characterized. The crystal and molecular structure of the complex was determined by single-crystal X-ray diffraction. The interactions of complex with calf thymus DNA were investigated by UV-vis, fluorescence and viscosity measurements. Experimental results indicated that the complex can bind to DNA by intercalation modes. Its intrinsic binding constant is 1.03 x 10(6) M(-1).     

Kinetic and mechanistic studies on the reaction of nitric oxide with a water-soluble octa-anionic iron(III) porphyrin complex

The polyanionic water-soluble and non-mu-oxo-dimer-forming iron porphyrin iron(III) 5(4),10(4),15(4),20(4)-tetra-tert-butyl-5(2),5(6),15(2),15(6)-tetrakis[2,2-bis(carboxylato)ethyl]-5,10,15,20-tetraphenylporphyrin, (P(8-))Fe(III) (1), was synthesized as an octasodium salt by applying well-established porphyrin and organic chemistry procedures to bromomethylated precursor porphyrins and characterized by standard techniques such as UV-vis and (1)H NMR spectroscopy. A single pK(a1) value of 9.26 was determined for the deprotonation of coordinated water in (P(8-))Fe(III)(H(2)O)(2) (1-H(2)()O) present in aqueous solution at pH <9. The porphyrin complex reversibly binds NO in aqueous solution to give the mononitrosyl adduct, (P(8-))Fe(II)(NO(+))(L), where L = H(2)O or OH(-). The kinetics of the binding and release of NO was studied as a function of pH, temperature, and pressure by stopped-flow and laser flash photolysis techniques. The diaqua-ligated form of the porphyrin complex binds and releases NO according to a dissociative interchange mechanism based on the positive values of the activation parameters DeltaS() and DeltaV() for the "on" and "off" reactions. The rate constant k(on) = 6.2 x 10(4) M(-1) s(-1) (24 degrees C), determined for NO binding to the monohydroxo-ligated (P(8-))Fe(III)(OH) (1-OH) present in solution at pH >9, is markedly lower than the corresponding value measured for 1-H(2)O at lower pH (k(on) = 8.2 x 10(5) M(-1) s(-1), 24 degrees C, pH 7). The observed decrease in the reactivity is contradictory to that expected for the diaqua- and monohydroxo-ligated forms of the iron(III) complex and is accounted for in terms of a mechanistic changeover observed for 1-H(2)O and 1-OH in their reactions with NO. The mechanistic interpretation offered is further substantiated by the results of water-exchange studies performed on the polyanionic porphyrin complex as a function of pH, temperature, and pressure.     

DNA interaction with Al-N,N'-bis(salicylidene)2,2'-phenylendiamine complex

The Al(III) complex, [Al(salophen)2H2O]NO3, was synthesized and characterized by spectroscopic (NMR and FT-IR) techniques. Then the binding of Schiff base complex of [Al(salophen)]+ type, where salophen denotes N,N'-bis(salicylidene) 2,2-phenylendiamine to calf thymus DNA, has been investigated by spectrophotometric, circular dichroism, spectrofluorometric, melting temperature and viscosimetric techniques. This Al(III) complex showed absorption hyperchromism in the range of 310-390 nm, increase in melting temperature, some structural changes in specific viscosity, when bound to calf thymus DNA. The binding constant has been determined using absorption measurement and found to be 1.82 x 10(3)M(-1) and 1.31 x 10(3)M(-1) in HEPES and Tris-HCl buffers, respectively. Also the fluorescence spectral characteristics and interaction of Al-salophen complex with DNA have been studied. Al-salophen bound to DNA showed a marked increase in the fluorescence intensity along with a bathochromic shift (5 nm). The intersection point of the binding isotherm indicated a binding site size of 12 bp per bound complex molecule in both HEPES and Tris-HCl buffers. The experimental results showed that the Al-salophen complex bound to DNA by non-intercalative mode and major groove binding was the preferred mode of interaction.     

Study on the interaction of 5-pyridine-10,15,20-tris-(p-chlorophenyl)porphyrin with cyclodextrins and DNA by spectroscopy

The interaction of 5-pyridine-10,15,20-tris-(p-chlorophenyl)porphyrin (PyTPP) with beta-CD and TM-beta-CD were examined by UV-vis absorption, fluorescence and (1)H NMR spectroscopy. PyTPP prefers to form the 1:1 inclusion complex with TM-beta-CD but hardly form inclusion complex with beta-CD. An inclusion constant (K) for the formation of PyTPP-TM-beta-CD inclusion complex has been evaluated to be 4.4x10(3)L/mol from the absorbance changes. This K value is nearly the same as that 4.5x10(3)L/mol obtained from the fluorescence intensity changes. Compared to beta-CD, the inclusion ability of TM-beta-CD with PyTPP is stronger. It indicates that the hydrophobic effect plays an important role in the inclusion procedure. The mechanism of inclusion interaction was carried out by 1H NMR technique. Furthermore, the interaction of PyTPP with DNA is shown here. It can bind DNA by out-side stacking along the DNA helix but not by intercalation because of the high electron density in the porphyrin core. The binding constant and binding number of PyTPP to DNA are 4.3x10(3) and 1.3, respectively. The interaction of PyTPP with DNA was further carried out in the presence of TM-beta-CD. The significant decrease of the binding constant and binding number were observed and the interaction of porphyrin-bound DNA has been inhibited, which was due to the fact that PyTPP inter into the cavity of TM-beta-CD and influence binding affinity of PyTPP to DNA.     

Photoinduced electron transfer in a hexaphenylbenzene-based self-assembled porphyrin-fullerene triad

A hexaphenylbenzene-based zinc porphyrin dyad forms a 1:1 complex with a fullerene bearing two pyridyl groups via coordination of the pyridyl nitrogens with the zinc atoms. The fullerene is symmetrically located between the two zinc porphyrins. The binding constant for the complex is 7.3 x 10(4) M(-1) in 1,2-difluorobenzene. Photoinduced electron transfer from a porphyrin first excited singlet state to the fullerene occurs with a time constant of 3 ps, and the resulting charge-separated state has a lifetime of 230 ps. This self-assembled construct should form a basis for the construction of more elaborate model photosynthetic antenna-reaction center systems.     

Fluorescence and absorption spectroscopic studies on the interaction of porphyrins with snake gourd (Trichosanthes anguina) seed lectin

The interaction of several free-base porphyrins and their corresponding copper(II) and zinc(II) derivatives with the galactose-specific lectin from snake gourd (Trichosanthes anguina) seeds has been investigated by absorption and fluorescence spectroscopic techniques. The lectin dimer contains two apparently equivalent binding sites for the porphyrins. Association constants obtained for the interaction of various porphyrins with the lectin are in the range 1.7 x 10(4)-6.2 x 10(5) M(-1), with the metalloporphyrins being seen to have higher affinity for the lectin compared with the free-base analogues. Both positively charged and negatively charged porphyrins bind to snake gourd seed lectin (SGSL) with comparable affinities, suggesting that binding occurs primarily via hydrophobic interactions. Further, binding of porphyrins is found to be largely unaffected by the presence of the sugar ligand, lactose, indicating that the binding sites for the carbohydrate and porphyrin are different. This study thus suggests that the lectin may serve as a receptor for some endogenous non-carbohydrate, hydrophobic ligand in vivo, in addition to the saccharide ligands. It also opens up the possibility of employing the T. anguina lectin in applications such as photodynamic therapy, which involve the use of porphyrins.     

Aggregation and solution behavior of 5-(1-(4-carboxybutyl) pyridinum-4-yl) 10,15,20-tris (1-methylpyridinium-4-yl) porphyrin: A resonance light scattering, fluorescence and absorption spectroscopic study

Aggregation behavior of water soluble porphyrins, 5-(1-(4-carboxybutyl) pyridinum-4-yl) 10,15,20-tris (1-methylpyridinium-4-yl) porphyrin (5-CBPyP) in the presence of various concentrations of calf thymus DNA (ct-DNA) and sodium chloride were studied in comparison with meso-tetrakis (4-N-methyl pyridinum) porphyrin (TMPyP), by optical absorption, fluorescence and resonance light scattering (RLS) spectroscopies. Both porphyrins obey Beer’s law in extended range of concentration. Optical absorption and RLS measurements demonstrated nonaggregation for both porphyrins under increasing concentration of ct-DNA and NaCl. However, in comparison, 5-CBPyP had less tendency for aggregation that may be taken as an advantage for its probable application in photodynamic therapy of cancer. The trend of changes in absorption spectra of both porphyrins in the presence of ct-DNA indicates the homogeneous intercalation binding mode. The values of (2.81 ± 0.28) × 10⁶ M^?1 and (0.95 ± 0.09) × 10⁶ M^?1 were obtained for apparent binding constant of TMPyP and 5-CBPyP from analysis of optical absorption data, respectively. This indicates the less affinity of 5-CBPyP to ct-DNA in comparison with TMPyP. The binding of both porphyrins to ct-DNA quenches fluorescence emission of Ethidium bromide (EB) that is bound to ct-DNA. The quenching process obeys linear Stern-Volmer relationship indicating the displacement of EB from its binding sites by these porphyrins. The results of this technique also represent the intercalation mode of binding for both porphyrins and higher binding affinity of TMPyP compared with 5-CBPyP.     

Spectra and DNA-binding affinities of Copper(II), Nickel(II) complexes with a novel glycine Schiff base derived from chromone

New [CuL.(H(2)O)(3)]NO(3).H(2)O and [NiL.H(2)O]NO(3).2H(2)O complexes with Schiff base (LNa) derived from 6-hydroxy-3-carbaldehyde chromone (CDC) and glycine are reported. Two complexes have been characterized by elemental analysis, IR data, TG/DTA and molar conductivity. The binding of these two complexes to calf thymus DNA (CT-DNA) has been investigated, respectively, with UV-vis spectroscopy, fluorescence spectroscopy and viscosity measurements. The experiment results indicate that the two complexes may bind to CT-DNA through an intercalative mode and [CuL.(H(2)O)(3)]NO(3).H(2)O intercalates into DNA more deeply than [NiL.H(2)O]NO(3).2H(2)O. Their intrinsic binding constants (K) with DNA are 6.08 x 10(5) and 2.76 x 10(5)M(-1).     

A comparative mechanistic study of the reversible binding of NO to a water-soluble octa-cationic Fe(III) porphyrin complex

The water-soluble, non-mu-oxo dimer-forming porphyrin, [5,10,15,20-tetrakis-4'-t-butylphenyl-2',6'-bis-(N-methylene-(4'-t-butylpyridinium))porphyrinato]iron(III) octabromide, (P(8+))Fe(III), with eight positively charged substituents in the ortho positions of the phenyl rings, was characterized by UV-vis and 1H NMR spectroscopy and 17O NMR water-exchange studies in aqueous solution. Spectrophotometric titrations of (P(8+))Fe(III) indicated a pKa1 value of 5.0 for coordinated water in (P(8+))Fe(III)(H2O)2. The monohydroxo-ligated (P(8+))Fe(III)(OH)(H2O) formed at 5 < pH < 12 has a weakly bound water molecule that undergoes an exchange reaction, k(ex) = 2.4 x 10(6) s(-1), significantly faster than water exchange on (P(8+))Fe(III)(H2O)2, viz. k(ex) = 5.5 x 10(4) s(-1) at 25 degrees C. The porphyrin complex reacts with nitric oxide to yield the nitrosyl adduct, (P(8+))Fe(II)(NO+)(L) (L = H2O or OH-). The diaqua-ligated (P(8+))Fe(III)(H2O)2 binds and releases NO according to a dissociatively activated mechanism, analogous to that reported earlier for other (P)Fe(III)(H2O)2 complexes. Coordination of NO to (P(8+))Fe(III)(OH)(H2O) at high pH follows an associative mode, as evidenced by negative deltaS(double dagger)(on) and deltaV(double dagger)(on) values measured for this reaction. The observed ca. 10-fold decrease in the NO binding rate on going from six-coordinate (P(8+))Fe(III)(H2O)2 (k(on) = 15.1 x 10(3) M(-1) s(-1)) to (P(8+))Fe(III)(OH)(H2O) (k(on) = 1.56 x 10(3) M(-1) s(-1) at 25 degrees C) is ascribed to the different nature of the rate-limiting step for NO binding at low and high pH, respectively. The results are compared with data reported for other water-soluble iron(III) porphyrins with positively and negatively charged meso substituents. Influence of the porphyrin periphery on the dynamics of reversible NO binding to these (P)Fe(III) complexes as a function of pH is discussed on the basis of available experimental data.     

Studies of interaction of emodin and DNA in the presence of ethidium bromide by spectroscopic method

Emodin interacting with deoxyribonucleic acid (DNA) has been studied by different spectroscopic techniques, such as fluorescence, ultraviolet and visible (UV-vis), and fourier transform infared (FT-IR) spectroscopies, using ethidium bromide (EB) as a fluorescence probe of DNA. The decrease in the fluorescence of DNA-EB system on addition of emodin shows that the fluorescence quenching of DNA-EB complex by emodin occurs. The binding constants of emodin with DNA in the presence of EB are 6.02x10(4), 9.20x10(4) and 1.17x10(5)Lmol(-1) at 20, 35 and 50 degrees C, respectively. FT-IR spectrum further suggests that both the phosphate groups and the bases of DNA react with emodin. The reaction of DNA with emodin in the presence of EB is affected by ionic strength and temperature. The values of melting temperature (T(m)) of DNA-EB complex and emodin-DNA-EB complexes were determined, respectively. From the experiment evidences, the major binding mode of emodin with DNA should be the groove binding.     

Recognition through self-assembly. A quadruply-hydrogen-bonded, strapped porphyrin cleft that binds dipyridyl molecules and a [2]rotaxane

Quadruply-hydrogen-bonded porphyrin homodimer Zn1.Zn1 has been designed, assembled, and evaluated as a supramolecular cleft-featured receptor for its ability to bind dipyridyl guests in chloroform-d. Monomer Zn1 consists of a 2-ureidopyrimidin-4(1H)-one unit, which was initially reported by Meijer et al., and a zinc porphyrin unit. The zinc porphyrin is strapped with an additional aliphatic chain for controlling the atropisomerization of porphyrin. The 2-ureidopyrimidin-4(1H)-one unit dimerizes exclusively in chloroform even at the dilute concentration of 10(-)(4) M, while the two "strapped" zinc porphyrin units of the homodimer provide additional binding sites for selective guest recognition. (1)H NMR studies indicate that the new homodimer Zn1.Zn1 adopts an S-type conformation due to strong donor-acceptor interaction between the electron-rich porphyrin units and the electron-deficient 2-ureidopyrimidin-4(1H)-one unit. (1)H NMR, UV-vis, and vapor pressure osmometry investigations reveal that Zn1.Zn1 could function as a new generation of assembled supramolecular cleft, to be able to not only efficiently bind linear dipyridyl molecules 14-17, resulting in the formation of stable termolecular complexes, with K(aasoc) values ranging from 3.8 x 10(6) to 8.9 x 10(7) M(-)(1), but also strongly complex a hydrogen-bond-assembled [2]rotaxane, 18, which consists of a rigid fumaramide thread and a pyridine-incorporated tetraamide cyclophane, with K(aasoc) = 1.2 x 10(4) M(-)(1). (1)H NMR competition experiments reveal that complexation to the dipyriyl guests also promotes the stability of the quadruply-hydrogen-bonded dimeric receptor.     

Investigation on DNA Binding and Photo-Cleavage Properties of Water-Soluble Porphyrin and Metalloporphyrins

A water-soluble porphyrin, tetrakis[4-(trimethylammonium)phenyl]porphyrin (TAPP), and its metal complexes with Zn(II), (ZnTAPP), have been synthesized and characterized by elemental analyses and u.v.-vis. spectra. The binding of the two complexes with calf thymus DNA has been investigated by absorption spectra, luminescence titrations, and viscosity measurements. The changes of the u.v.-vis. absorption spectra during the titration of these porphyrins with calf thymus DNA revealed a large bathochromic shift (upto 8–12 nm) and a hypochromicity of the porphyrins soret bands. The intensity of the fluorescence spectra of these porphyrins was enhanced. The cytotoxicity of the series of porphyrins TAPP and MTAPP [M = Zn(II), Cu(II), Fe(III), Co(III), Ni(II), Mn(III)] complexes was determined for Madin–Darby Canine Kindney (MDCK) cells and Vero cells with the method of cell culture, and were evaluated as anti-virus activity for influenza virus type A (H3N2), B and Herpes simplex virus type-1 (HSV-1, strain SM44), type-2 (HSV-2, strain 333) in vitro. Among the complexes evaluated, inhibited viral cytopathogenicity at lower concentrations that were found cytotoxic for the MDCK cells. Differences were observed in the 50% effective doses (based on inhibition of viral cytopathogenicity) of these complexes for a number of influenza viruses type A, B, and HSV-1, HSV-2 strains. It was found that CoTAPP displayed good inhibitory action against the virus in vitro.     

A Ru(II) complex with 2-(4-(methylsulfonyl)phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline: synthesis, characterization, and acid-base and DNA-binding properties

A new Ru(II) complex of [Ru(bpy)2(Hmspip)]Cl2 {in which bpy=2,2'-bipyridine, Hmspip=2-(4-(methylsulfonyl)phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline} have been synthesized and characterized. The ground- and excited-state acid-base properties of [Ru(bpy)2(Hmspip)]Cl2 and its parent complex of [Ru(bpy)2(Hpip)]Cl2 {Hpip=2-phenyl-1H-imidazo[4,5-f][1,10]phenanthroline} have been studied by UV-visible (UV-vis) and emission spectrophotometric pH titrations. [Ru(bpy)2(Hmspip)]Cl2 acts as a calf thymus DNA intercalators with a binding constant of 4.0×10(5) M(-1) in buffered 50 mM NaCl, as evidenced by UV-vis and luminescence titrations, steady-state emission quenching by [Fe(CN)6]4-, DNA competitive binding with ethidium bromide, reverse salt titrations and viscosity measurements.     

New route to the synthesis of bis[N-(2-aminoethyl) salicylaldiminato] chromium(III) chloride monohydrate Spectroscopic characterization, crystal structure and interaction with DNA

The reaction of [Cr(urea)(6)]Cl(3).3H(2)O with H(2)salen (H(2)salen=N,N(')-ethylenebis(salicylaldimine) in water-methanol mixture (40:60v/v) under reflux yielded the complex bis[N-(2-aminoethyl)salicylaldiminato]chromium(III) chloride monohydrate, [Cr(aesaldmn)(2)]Cl.H(2)O. The complex was characterized by elemental analysis, molar conductance, magnetic susceptibility, spectroscopic (UV-vis and IR) data and X-ray diffraction studies. The new ligand, N-(2-aminoethyl)salicylaldimine, Haesaldmn, possibly resulted from the hydrolytic cleavage of one end of the H(2)salen ligand during reflux. Binding of this chromium(III) complex to CT DNA has been studied using UV-vis spectroscopy with an apparent binding constant of 2.68 x 10(3)M(-1). It shows that the binding mode is electrostatic while the emission of ethidium bromide to CT DNA in the absence and in the presence of the complex show that it binds DNA with partial intercalation.     

The pH-induced emission switching and interesting DNA-binding properties of a novel dinuclear ruthenium(II) complex

A novel dinuclear Ru(II) complex, [(bpy)(2)Ru(ebipcH(2))Ru(bpy)(2)](ClO(4))(4), where bpy = 2,2'-bipyridine and ebipcH(2) = N-ethyl-4,7-bis([1,10]-phenanthroline[5,6-f]imidazol-2-yl)carbazole, has been newly synthesized. The pH effects on UV-vis absorption and emission spectra of the complex are studied, and ground- and excited-state ionization constants of the complex are derived. The binding of the complex to calf thymus (ct) DNA is investigated with absorption and luminescence titrations, steady-state emission quenching, and viscosity measurements. The complex acts as a pH-induced "on-off" emission switch between pH 8.0 and pH 10.0 with a maximum on-off ratio of approximately 100 which is favorably compared with the other imidazole-containing Ru(II) complex congeners, and a strong ct-DNA intercalator with an intrinsic binding constant of 1.31(+/-0.08) x 10(6) M(-)(1) in buffered 50 mM NaCl.     

Dipyrrolylquinoxaline-bridged Schiff bases: a new class of fluorescent sensors for mercury(II)

Novel 2,3-bis(1H-pyrrol-2-yl)quinoxaline-functionalized Schiff bases were prepared and characterized as new fluorescent sensors for mercury(II) ion. The X-ray crystal structures of compounds 4, 5, 4a and 5a were determined. The binding properties of 4 and 5 for cations were examined by UV-vis and fluorescence spectroscopy. The UV-vis and fluorescence data indicate that a 1 : 1 stoichiometric complex is formed between compound 4 (or 5) and mercury(II) ion, and the association constant is (3.81 +/- 0.7) x 10(5) M(-1) for 4 and (3.43 +/- 0.53) x 10(5) M(-1) for 5. The recognition mechanism between compound 4 (or 5) and metal ion was discussed based on their chemical construction and the fluorescence quenching effect when they interact with each other. Competition experiments revealed that compound 4 (or 5) has a highly selective response to mercury(II) ion in aqueous solution.