Template synthesis and characterization of hexaaza nickel(II) complex nanoparticles entrapped within the zeolite-Y

Some complexes containing “[Ni([18]py₂N₄)]²⁺, [Ni([20]py₂N₄)]²⁺, [Ni(Bzo₂[18]py₂N₄)]²⁺ and [Ni(Bzo₂[20]py₂N₄)]²⁺” were successfully prepared by the template synthesis of 2,6-diacetylpyridine with [bis(diamine)nickel(II)]; [Ni(N-N)₂]²⁺; within the zeolite-Y. These complexes were entrapped in the supercage of Y-zeolite by a two-step process in the liquid phase: (i) inclusion of a Ni(II) precursor complex, [Ni(diamine)₂]²⁺@NaY, and (ii) template synthesis of the nickel(II) precursor complex with 2,6-diacetylpyridine. The new complex nanoparticles entrapped within the zeolite-Y “[Ni([18]py₂N₄)]²⁺@NaY, [Ni([20]py₂N₄)]²⁺@NaY, [Ni(Bzo₂[18]py₂N₄)]²⁺@NaY, [Ni(Bzo₂[20]py₂N₄)]²⁺@NaY” were characterized by several techniques: chemical analysis and spectroscopic methods (FT-IR, UV-Vis, XRD, BET, DRS). Analysis of the data indicates that the Ni(II) complexes are encapsulated within the zeolite-Y and exhibit different property from those of the free complexes, which can arise from distortions caused by steric effects due to the presence of sodium cations, or from interactions with the zeolite matrix.     

Dipeptide interactions with Zn(II)–cyclen artificial model for molecular recognition

The Zn(II)–cyclen–dipeptide ternary systems (where cyclen is abbreviated as L and dipeptide is glycylglycine (HL¹) or glycyl‐(S)‐alanine (HL²)) were investigated by potentiometry applying both “out‐of‐cell” and direct titrations and by ¹H NMR spectroscopy. Especially, the ¹H NMR study was found to be very efficient to estimate speciation in the systems. The results obtained under full equilibria indicated two main species, [Zn(L)(HL^1,2)]²⁺ and [Zn(L)(L^1,2)]⁺, in both the systems. In the [Zn(L)(HL^1,2)]²⁺ complex, presence of carbonyl‐carboxylate chelate was confirmed, and in the [Zn(L)(L^1,2)]⁺ species, the peptide coordination is re‐organized to carbonyl‐amine chelate or only terminal amino group is coordinated. Equilibrium constants describing [Zn(L)]²⁺–dipeptide interaction are relatively low, log K = 3.4 for Gly‐Gly and 4.1 for Gly‐(S)‐Ala, respectively. Nevertheless, the values are slightly higher than stability constants for interaction of Zn(II) with the dipeptides (i.e. [Zn(L^1,2)]⁺ species) where a chelate formation is expected. It indicates that interaction between Zn(II) ion in [Zn(L)]²⁺ and the dipeptides should be supported by some additional interactions. Potentiometry carried out under non‐equilibrum condition showed different species where these additional stabilizing forces play more important role. Copyright © 2015 John Wiley & Sons, Ltd.     

Reversible ring opening and closure reactions of the triazine ligands derived from 1-phenylazo-2-naphthylamine and pyridine-2-aldehyde or quinoline-2-aldehyde - structure and reactivity of the palladium (II) complexes

New ligands containing a heterocyclic ring, L¹ (1-anilino-2-(2-pyridyl)-naphth[1,2-d]imidazol-1-io-3-ide), L² (2-phenyl-3-(2-pyridyl)-3,4-dihydro-naphtho[2,1-e][1,2,4]triazin-1-io-4-ide), and L³ (1-anilino-2-(2-quinolyl)-naphth[1,2-d]imidazol-1-io-3-ide), and their palladium (II) complexes have been prepared. Structures of the ligands and the complexes were determined by X-ray crystallography. The mononuclear square-planar complexes of [PdCl₂(Lⁿ)] (n = 1 (1), n = 2 (2) and n = 3 (3)) had didentate Lⁿ (n = 1-3) ligands. The Lⁿ (n = 1-3) ligands were stable and their absorption spectra did not change in dichloromethane and methanol. On the other hand, the absorption spectrum of [PdCl₂(L²)] (2) in dichloromethane changed rapidly when methanol was added to the solution, and [PdCl(L^4b)] (5) (L^4b = N-[methoxy(2-pyridyl)methyl]-1-(phenylazo)-2-naphthylamide) was obtained from the concentrated reaction mixture. In this reaction, the dihydrotriazine ring of the didentate L² ligand in complex 2 opened and the resulting tridentate L^4b ligand coordinated to the Pd atom in complex 5. When an excess amount of (ⁿBu)₄NCl was added to complex 5 in dichloromethane, the absorption spectrum reverted to that of complex 2. Thus, the reversible ring opening and closure reactions of the coordinating dihydrotriazine ligand were observed. We also prepared [PdCl₂(L⁵)] (9) (L⁵ = 1-(phenylazo)-N-[1-(2-pyridyl)ethylidene]-2-naphthylamine) and determined the structure. It is noted that neither the ring closure reaction nor the coordination of the azo nitrogen atom of the L⁵ ligand occurred in complex 9.     

Metal-directed synthesis of a chiral acyclic pentaamine and pendant-arm macrocyclic hexaamine derived from an amino acid

l-3-Phenylpropane-1,2-diamine (dapp) was prepared by a three-step synthesis based on l-phenylalanine and characterized, including determination of stability constants with M²⁺ ions (Ni, Cu, Zn, Cd). The reaction of L-3-phenylpropane-1,2-diamine as the [Cu(dapp)₂]²⁺ complex ion with formaldehyde and nitroethane in basic solution yields the acyclic (5-methyl-5-nitro-1,9-diphenyl-3,7-diazanonane-1,9-diamine)copper(II) complex ion, [Cu(1)]²⁺, as the major product. In addition, small amounts of the macrocyclic complex ion (2,10-diphenyl-6,13-dimethyl-6,13-dinitro-1,4,8,11-tetraazacyclotetradecane)copper(II), [Cu(2)]²⁺, form. Reduction of the [Cu(1)]²⁺ ion with zinc in aqueous acid yields the acyclic polyamine 5-methyl-1,9-diphenyl-3,7-diazanonane-1,5,9-triamine (3), an analogue of the previously reported pentaamine 5-methyl-3,7-diazanonane-1,5,9-triamine. Using the bis(l-3-phenylpropane-1,2-diamine)palladium(II) as precursor and an excess of other reagents, the macrocyclization reaction to produce [Pd(2)]²⁺ proved more successful. Reduction and recomplexation to copper(II) allowed isolation of the 2,9-dibenzyl-6,13-diammonio-6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane)copper(II) ion, [Cu(4H₂²⁺)]⁴⁺. The acyclic complex [Cu(1)]²⁺ promotes the hydrolytic cleavage of plasmid DNA modestly; a mechanism to support this observation is presented.     

An exploratory scandium-45 NMR study into the complexation of alanine and oligopeptides

The 87.5 MHz ⁴⁵Sc NMR spectrum of 0.025 M aqueous Sc(NO₃)₃ exhibits two resonance signals, separated by ca. 25 ppm, attributable to [Sc(H₂O)₆]³⁺ and [Sc(H₂O)₅OH]²⁺. Acidification leads to a single, comparatively sharp line (W_1/2 = 160 Hz) for the hexaqua complex, the temperature dependence (temperature gradient = 0.076 ppm/deg) of which indicates that relaxation is dominated by the quadrupole mechanism. Addition of α-alanine gives rise to an additional broad signal at ca. +70 ppm (relative to [Sc(H₂O)₆]³⁺), which is assigned to a carboxylato complex [Sc(H₂O)_6−n(ala)_n]³⁺ or [Sc(H₂O)_5−nOH- (ala)_n]²⁺ (1 < n < 2). At ambient temperatures, these species are in slow exchange with the hexaqua and pentaqua-hydroxo complex, progressing through medium towards fast exchange as the temperature increases, and giving rise to an exchange contribution to relaxation. W_1/2 becomes a measure for the stability of the complexes, which increases in the order ala < (ala)₄ ∼ (ala)₂ < ala-val-leu. The pronounced stability of the latter is due to the formation of a chelate-five ring structure (participation of the NH- function of the peptide bond in coordination to Sc³⁺). 1 M aqueous ScCl₃ probably contains the two species [Sc(H₂O)₆]³⁺ and [Sc(H₂O)₅Cl]²⁺, separated by 33 ppm.     

Coordination abilities of substituted β-aminophosphonates towards Cu and Zn ions

The formation constants of equimolar and bis-chelate copper(II) and zinc(II) complexes with three aliphatic and four aromatic-substituted β-aminophosphonates have been determined in water solution by potentiometric studies. Spectroscopic parameters clearly indicate involvement of {NH₃, PO₃ ²⁻} in both metal ions coordination. The comparison of the stability constants reveals slightly higher coordination power of the aliphatic-substituted β-aminophosphonic acids, which may be due to the higher basicity of their amino groups. All studied ligands are more effective in Cu²⁺ and Zn²⁺ coordination than phosphonic analogue of simple β-amino acid.     

Biosynthetic Origin of [R-(Z)]-4-Amino-3-chloro-2-pentenedioic Acid in Streptomyces viridogenes

The biosynthesis of the chlorinated amino acid [R-(Z)]-4-amino-3-chloro-2-pentenedioic acid (ACPA) was investigated. Feeding studies with Streptomyces viridogenes were conducted in resting cells. Substantial incorporation from [¹⁵N]- and [¹³C]-enriched glutamate and proline indicated that the biosynthetic origin of ACPA is one of these amino acids. Experiments with deuterated glutamate and proline imply that chlorination does not occur via a radical mechanism, but rather suggest that a FADH₂-dependent halogenase is involved.     

Copper(II), nickel(II) and zinc(II) complexes of N-acetyl-His-Pro-His-His-NH2: equilibria, solution structure and enzyme mimicking

The copper(II), nickel(II) and zinc(II) binding ability of the multi-histidine peptide N-acetyl-His-Pro-His-His-NH₂ has been studied by combined pH-potentiometry and visible, CD and EPR spectroscopies. The internal proline residue, preventing the metal ion induced successive amide deprotonations, resulted in the shift of this process toward higher pH values as compared to other peptides. The metal ions in the parent [ML]²⁺ complexes are exclusively bound by the three imidazole side chains. In [CuH₋₁L]⁺, formed between pH 6-8, the side chains of the two adjacent histidines and the peptide nitrogen between them are involved in metal ion binding. The next deprotonation results in the proton loss of the coordinated water molecule (CuH₋₁L(OH)). The latter two species exert polyfunctional catalytic activity, since they possess superoxide dismutase-, catecholase- (the oxidation of 3,5-di-tert-butylcatechol) and phosphatase-like (transesterification of the activated phosphoester 2-hydroxypropyl-4-nitrophenyl phosphate) properties. On further increase of the pH rearrangement of the coordination sphere takes place leading to the [CuH₋₃L]⁻ species, the deprotonated amide nitrogen displaces a coordinated imidazole nitrogen from the equatorial position of the metal ion. The shapes of the visible and CD spectra reflect a distorted arrangement of the donor atoms around the metal ion. In presence of zinc(II) the species [ZnL]²⁺ forms only above pH 6, which is shortly followed by precipitation. On the other hand, the [NiL]²⁺ complex is stable over a wide pH range, its deprotonation takes place only above pH 8. At pH 10 an octahedral NiH₋₂L species is present at first, which transforms slowly to a yellow square planar complex.     

Metal-dependent dimensionality in coordination polymers of a semi-rigid dicarboxylate ligand with additional amide groups: Syntheses, structures and luminescent properties

Three new coordination polymers, [CdL(H₂O)₃·H₂O]_n (1), [MnL(H₂O)₂]_n (2) and [ZnL]_n (3) (L = 2,2′-[1,4-bis(-benzamido)]diacetate) have been hydrothermally synthesized. Complex 1 and complex 2 are 1-D infinite zigzag chain and 2-D rectangular grid networks, respectively, in which are further stabilized by hydrogen bonds, thus affording two 3-D supramolecular frameworks. Complex 3 exhibits a (4, 4)-connected PtS topology. Moreover, an unusual phenomenon has been observed that the dimension of these coordination polymers gradually increases with the decrease of coordination numbers of metal ions. In addition, complex 1 exhibits a strong blue luminescence in the solid state at room temperature and may be potential candidate for luminescent materials.     

DNA cleavage promoted by trigonal-bipyramidal zinc(II) and copper(II) complexes formed by asymmetric tripodal tetradendate 2-[bis(2-aminoethyl)amino]ethanol

Asymmetric trigonal-bipyramidal Zn(II) complex 1 formed by 2-[bis(2-aminoethyl)amino]ethanol (L) was found to be able to promote the cleavage of supercoiled plasmid DNA pBR322 to the nicked and linear DNA via a hydrolytic manner but only in neutral Tris-HCl buffer, no cleavage was observed in HEPES or NaH₂PO₄/Na₂HPO₄ buffer. However, the copper complex 2 of L, possessing the similar coordination geometry, can only promote DNA cleavage via an oxidative mechanism in the presence of ascorbic acid. ESI-MS study implies that complex 1 exist mainly as [Zn(L)]²⁺/[Zn(L-H)]⁺ in neutral Tris-HCl buffer. Moreover, there is no discriminable species for complex 1 in HEPES or NaH₂PO₄/Na₂HPO₄ buffer. A phosphate activation mechanism via phosphate coordinating to Zn(II) center of [Zn(L)]²⁺/[Zn(L-H)]⁺ to form the stable trigonal-bipyramidal structure is proposed for the hydrolytic cleavage promote by complex 1. For complex 2, the abundance of [Cu(L)Cl]⁺ is higher than that of [Cu(L)]²⁺/[Cu(L-H)]⁺ in Tris-HCl buffer. The lower phosphate binding/activating ability of Cu(II) in complex 2 may be the origin for its incapability to promote the hydrolytic DNA cleavage. However, the readily accessible redox potential of Cu(II) makes complex 2 promote the oxidative DNA cleavage. Although the DNA cleavage promoted by complex 1 has no specificity, trigonal-bipyramidal Zn(II) complexes formed by asymmetric tripodal polyamine with ethoxyl pendent should be a novel potential model for practical artificial nuclease.     

Alkylated poly(amino acids). I. Conformational properties of poly(Nε-trimethyl-L-lysine) and poly(Nδ-trimethyl-L-ornithine)

Poly(N^ε-trimethyl-L -lysine), [Lys(Me₃)]_n, and poly(N^δ-trimethyl-L -ornithine), [Orn(Me₃)]_n, in sodium dodecylsulfate do not assume the β-structure or α-helix, respectively, of their parent polymers. In 0.5M Ca(ClO₄)₂ both [Lys(Me₃)]_n and [Orn(Me₃)]_n are aggregated and display CD spectra indicative of a regular, perhaps helical, structure. For [Lys]_n and [Lys(Me₃)]_n, the T₁ of the α-hydrogens are 0.379 and 0.230 sec, respectively, indicating greater rigidity for [Lys(Me₃)]_n. The CD spectrum of [Lys(Me₃)]_n at pH 8 is more heat resistant than that of [Lys]_n. It is suggested that apolar interactions are more important in the methylated polymers than in the parent polymers.     

Silver(I) complexes with hydantoins and allantoin: synthesis, crystal and molecular structure, cytotoxicity and pharmacokinetics

Coordination polymers [Ag(L^1,3)]_n (L¹ = hydantoin, L³ = 5,5-dimethylhydantoin), {[Ag(L²)]^.0.5H₂O}_n (L² = 1-methylhydantoin) and [Ag(NH₃)(L⁴)]_n (L⁴ = allantoin) were prepared and characterized by elemental analysis, spectroscopic (IR, FTIR and NMR), thermal and mass spectrometry methods. The crystal structure of {[Ag(1-methylhydantoin)]·0,5H₂O}_n was determined and analyzed. Three 1-methylhydantoinate ligands create a T-shape (CN = 3) coordination sphere around the Ag⁺ ion. Additionally, a short Ag?Ag distance of 2.997 Å was found in the structure resulting in the expanded [3 + 2] environment of a distorted square shape. The [Ag(L²)] entities are bound to each other by the bridging organic ligands. Thus a two-dimensional coordination polymer is created with water molecules located between the layers. In contrast to hydantoins, the allantoin complex contains an additional ammonia molecule in the coordination sphere. Moreover, in the Ag-alla complex the M-organic ligand binding site is shifted to the N-atom of the ureid chain. Free ligands are cytotoxically inactive against human MCF-7 and A549 cancer cell lines and mouse fibroblasts Balb/3T3. The silver hydantoin complexes exhibit a very strong activity against these lines. (The introduction of the methyl groups to the ring slightly increases resistance only against the A549 cell line.) In contrast, the silver complex of allantoin shows only a weak activity which may be related to the presence of the cytotoxic ammonia group in the composition of the compound and/or the different binding site of the ligand. Calculated in silico physiochemical parameters are promising for the future application of the complexes as drugs.     

Nickel(II) and copper(II) complexes of Schiff base ligands containing N4O2 and N4S2 donors with pyrrole terminal binding groups: Synthesis, characterization, X-ray structures, DFT and electrochemical studies

A series of hexadentate ligands, H₂L^m (m = 1−4), [1H-pyrrol-2-ylmethylene]{2-[2-(2-{[1H-pyrrol-2-ylmethylene]amino}phenoxy)ethoxy]phenyl}amine (H₂L¹), [1H-pyrrol-2-ylmethylene]{2-[4-(2-{[1H-pyrrol-2-ylmethylene]amino}phenoxy)butoxy]phenyl}amine (H₂L²), [1H-pyrrol-2-ylmethylene][2-({2-[(2-{[1H-pyrrol-2-ylmethylene]amino}phenyl)thio]ethyl}thio)phenyl]amine (H₂L³) and [1H-pyrrol-2-ylmethylene][2-({4-[(2-{[1H-pyrrol-2-lmethylene]amino}phenyl)thio]butyl}thio) phenyl]amine (H₂L⁴) were prepared by condensation reaction of pyrrol-2-carboxaldehyde with {2-[2-(2-aminophenoxy)ethoxy]phenyl}amine, {2-[4-(2-aminophenoxy)butoxy]phenyl}amine, [2-({2-[(2-aminophenyl)thio]ethyl}thio)phenyl]amine and [2-({4-[(2-aminophenyl)thio]butyl}thio)phenyl]amine respectively. Reaction of these ligands with nickel(II) and copper(II) acetate gave complexes of the form ML^m (m = 1−4), and the synthesized ligands and their complexes have been characterized by a variety of physico-chemical techniques. The solid and solution states investigations show that the complexes are neutral. The molecular structures of NiL³ and CuL², which have been determined by single crystal X-ray diffraction, indicate that the NiL³ complex has a distorted octahedral coordination environment around the metal while the CuL² complex has a seesaw coordination geometry. DFT calculations were used to analyse the electronic structure and simulation of the electronic absorption spectrum of the CuL² complex using TDDFT gives results that are consistent with the measured spectroscopic behavior of the complex. Cyclic voltammetry indicates that all copper complexes are electrochemically inactive but the nickel complexes with softer thioethers are more easily oxidized than their oxygen analogs.     

Silver(I) complexes of dibenzo-18-crown-6-ether having cation-π and π-π interactions

Three silver(I) complexes of dibenzo-18-crown-6-ether (DB[18]C6), [Ag(DB[18]C6)(ClO₄)](THF) (1), [Ag(DB[18]6)(CF₃SO₃)]₂(acetone)₂ (2) and [Ag(DB[18]C6)(CF₃COO)]₂(AgCF₃COO)₂ (3) have been synthesized in different solvents and characterized structurally. In each complex, silver ions prefer an octahedral coordination geometry and form close dinuclear complex with DB[18]C6 based on cation-π interaction in η²-fashion. In particular, the coordination unit involving σ bonding at an oxygen group and π-π bonding between two benzene rings is quite unique.     

A hypothesis for the basis of the pro-oxidant nature of calcium ions

A new hypothesis describing the role of the redox inactive Ca²⁺ ion in the expression of physiological oxidative damage is described. The hypothesis is based on the optimization of the chelation characteristics of iron complexes for pro-oxidant activity. In a previous investigation it was found that an excess of ligand kinetically hindered the Fenton reaction activity of the Fe^II/IIIEDTA complex (Bobier et al. 2003). EDTA, citrate, NTA, and glutamate were selected as models for the coordination sites likely encountered by mobile iron, i.e. proteins. The optimal [EDTA]:[Fe^III] ratio for Fenton reaction activity as measured by electrocatalytic voltammetry in a solution was found to be 1:1. An excess of EDTA in the amount of 10:1 [ligand]:[metal] suppresses the Fenton reaction activity to nearly the control. It is expected that the physiological coordination characteristics of mobile Fe would have a very large excess of [ligand]:[metal] and thus not be optimized for the Fenton reaction. Introduction of Ca²⁺ in to a ratio of 10:10:1 [Ca²⁺]:[EDTA]:[Fe^III] to the system reinvigorated the Fenton reaction activity to nearly the value of the optimal 1:1 [EDTA]:[Fe^III] complex. The pH distribution diagrams of Ca²⁺ in the presence of EDTA and Fe^II/III indicate that Ca²⁺ has the ability to uptake excess EDTA without displacing either Fe^II of Fe^III from their respective complexed forms. The similarity in the presence for hard ligand sites albeit with a lower binding constant for Ca²⁺ accounts for this action.     

Blood plasma model predictions for the proposed bone-seeking radiopharmaceutical [Sn]Sn(IV)-N,N′,N′-trimethylenephosphonate-poly(ethyleneimine)

In an attempt to elucidate the in vivo stability of the prospective radiopharmaceutical [^117mSn]Sn(IV)-PEI-MP, where PEI-MP stands for N,N′,N′-trimethylenephosphonate-polyethyleneimine, glass electrode potentiometry was used to determine the stability constants of the Sn⁴⁺ ion as complexed with a variety of physiological amino acids. In addition, linear free energy relationship (LFER) correlation plots were used to extrapolate the constants of the major blood plasma ligands, based on data from Cu²⁺, Pb²⁺, and Zn²⁺. In so doing, a thermodynamic model of blood plasma was established for Sn⁴⁺ from which the complexation tendencies of Sn⁴⁺ were predicted in the event of the intravenous administration of such a drug. It was found that the Sn(IV)-PEI-MP could succumb to competition by the glutamine amino acid, which forms more stable complex(es), whilst the PEI-MP gets taken up largely by Ca²⁺. Also, this study shows the value of the in vitro experiments and modeling performed for radiopharmaceutical research and for attempts to reduce the number of animal experiments.     

Specificity of DNA-basic polypeptide interactions. III. Sequential and random copolymers of lysine and aromatic amino acids.

Sequential and random lysine copolymers containing various amounts of different aromatic amino acids were synthesized. The sequential copolypeptides exhibited strong dependence of yield and degree of polymerization on the amino acid sequence of the repeating unit. To elucidate the specific contributions of aromatic side chains to the interaction of these copolymers with DNA, direct-mixed complexes were studied by thermal denaturation and CD. The melting behaviour of peptide-bound DNA was found to be strongly affected by amino acid composition and sequence. The contribution of the different aromatic amino acids to thermal stability decreased in the order: polylysine > [Lys, Tyr]_n > [Lys,Phe]_n > [Lys,(OMe)Tyr]_n. The CD spectrum of DNA was altered by random copolymers, whereas sequential copolymers exhibited no changes. The influence of the random copolymers on the CD spectrum of DNA decreased in the series: polylysine > [Lys,Phe]_n > [Lys,(OMe)Tyr]_n > [Lys,Tyr]_n. The contribution of the different aromatic amino acids to thermal stability is interpreted as stacking tendencies toward denatured and, in the case of Tyr, H-bond formation with native DNA. The differences found for the random and the sequential polypeptides can best be explained by assuming a cooperative action of rather small peptide segments.     

Heterometallic complex formation on p-sulfonatothiacalix[4]arene platform resulting in pH- and redox-modification of [Ru(bpy)3] luminescence

The pH-dependent heterometallic complex formation with p-sulfonatothiacalix[4]arene (TCAS) as bridging ligand in aqueous solutions was revealed by the use of spectrophotometry, nuclear magnetic relaxation and fluorimetry methods. The novelty of the structural motif presented is that the appendance of emission metal center ([Ru(bpy)₃]²⁺) is achieved through the cooperative non-covalent interactions with the upper rim of TCAS. The second metal block (Fe(III), Fe(II) and Mn(II)), bound with the lower rim of TCAS in the inner sphere coordination mode is serving as quencher of [Ru(bpy)₃]²⁺ emission. The difference between the complex ability of Fe(III) and Fe(II) ions provides pH conditions for redox-dependent emission of [Ru(bpy)₃]²⁺.     

pH Dependent photophysics and role of medium on photoinduced electron transfer between ruthenium polypyridyl complex and anthraquinone

The spectroscopic and photophysical properties of a synthetically versatile ruthenium complex [Ru(bpy)₂(LH₂)]²⁺ where LH₂ is 2-(4-carboxyphenyl)imidazo[4,5-f][1,10]phenanthroline and bpy is 2,2-bipyridyl and its analogue, [Ru(bpy)₂(LOMe)]²⁺ where the carboxyphenyl functionality is methylated are reported. Both complexes exhibit long-lived luminescence which for [Ru(bpy)₂(LH₂)]²⁺ is remarkably enhanced in aqueous compared to organic media. The pH dependence of the electronic absorption and emission spectra in water and acetonitrile are described and the influence of the protonation state of the 2-(4-carboxyphenyl)imidazo[4,5-f][1,10]phenanthroline ligand on the electronic structure of [Ru(bpy)₂(LH₂)]²⁺ is discussed. Oxidative quenching of the excited state of the complex by anthraquinone-2-carboxylic acid is investigated for both complexes. In polar media, this is a dynamic process suggesting that the quenching rate is controlled by bimolecular collision with a quenching rate constant, k_q, of approximately 6.7 × 10⁹ M⁻¹ s⁻¹ for [Ru(bpy)₂(LH₂)]²⁺. In contrast in aprotic solvent, dichloromethane, quenching occurs through a purely static mechanism indicating association between the luminophore and quencher, most likely through hydrogen bonding, between the carboxylic acid moieties of the ruthenium complex and the anthraquinone carboxylic derivative. The association constant for formation of the dyad was determined to be 565 L mol⁻¹ in dichloromethane and the rate of electron transfer was estimated to be 4.7 × 10⁷ s⁻¹. By contrast, for the analogous complex in which the carboxylate is methyl protected mixed static and dynamic quenching behaviour in aprotic solvent.     

DNA binding behaviors and cleavage properties of a Ru(II) polypyridyl complex

A novel complex, [Ru(phen)₂pzip]²⁺1 (phen = 1,10-phenanthroline; pzip = 2-(pyrazine-2-yl)imidazo-[4,5-f][1,10]phenanthroline]), has been synthesized and characterized by elemental analysis, ES-MS, ¹H NMR. The DNA-binding behaviors of this complex were studied by spectroscopic methods and viscosity measurements. The results indicate that the complex can bind to CT-DNA in an intercalative mode. When irradiated at 365 nm, complex 1 can promote the cleavage of plasmid pBR322DNA. Furthermore, Zn²⁺ can trigger the DNA cleavage of complex 1 without irradiation. The mechanism studies revealed that the DNA cleavage by complex 1 in the presence of Zn²⁺ is likely to proceed via a hydrolytic cleavage process.