Relative binding strength of terpyridine model complexes under matrix-assisted laser desorption/ionization mass spectrometry conditions

The relative binding strength of a series of terpyridine metal complexes of the type [M(II)L(2)](+) was investigated by using variable laser intensities in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). A model terpyridine ligand, 4'-(1,4,7-trioxa-octyl)-2,2':6',2"-terpyridine, was prepared and complexed with a series of transition metal ions including cadmium, cobalt, copper, iron, manganese, nickel and ruthenium. The relative binding strength of these complexes can be obtained by measuring MALDI mass spectra of the prepared compounds at different laser intensities. The ratio of the signal intensities belonging to the ligand [LH](+) and the complex [ML(2)](+) ([LH](+) /[ML(2)](+)) depends on the laser intensity utilized for the spectrum acquisition. By considering an [LH](+)/[ML(2)](+) ratio > 10 as the point of complete complex dissociation, it is possible to establish a row of complex stabilities depending on the kind of metal ion.     

Synthesis, structure and luminescence properties of Cu(ii), Zn(ii) and Cd(ii) complexes with 4'-terphenylterpyridine

The complexes [M(tptpy)(2)](ClO(4))(2) (M = Zn(ii) (1), Cd(ii) (2), and Cu(ii) (3)); tptpy = 4'-[1,1':4',1']terphenyl-4'-yl-[2,2':6',2']terpyridine = 4'-terphenylterpyridine) have been synthesized, structurally characterized by X-ray crystallography and subjected to preliminary luminescence studies. In the crystalline state, all the metal ions have an N(6) coordination sphere of distorted octahedral geometry and the structures of the Zn(ii) and Cd(ii) complexes are isomorphous but differ from that of the Cu(ii) complex, which also differs from the other two in that it is non-emissive. The structure determinations show that aromatic-aromatic interactions involving both the terpyridine heads and the terphenyl tails are important factors influencing the crystalline array. The emission spectra of the Zn(ii) and Cd(ii) complexes are very similar and show a considerable red-shift of the emission maximum compared to that of the free ligand.     

A terpyridyl-imidazole (tpy-HImzPh3) based bifunctional receptor for multichannel detection of Fe2+ and F- ions

The X-ray crystal structures of the tridentate ligand, 4'-[4-(4,5-diphenyl-1H-imidazol-2-yl)-phenyl]-[2,2':6',2']terpyridine (tpy-HImzPh(3)) and its bis-homoleptic iron(ii) complex of composition [Fe(tpy-HImzPh(3))(2)](2+) have been determined, showing that the ligand crystallized in a monoclinic form with the space group P2(1)/c while its Fe(II) complex crystallizes in an orthorhombic form with space group Fddd. Both the anion and cation binding properties of the receptor were thoroughly investigated in dimethylformamide-acetonitrile (1?:?9) solution using absorption, emission, and (1)H NMR spectral studies which revealed that the receptor acts as a sensor for both F(-) and Fe(2+). In the presence of excess F(-) ion, deprotonation of the imidazole N-H fragment of the receptor occurs, an event which is signaled by the development of a yellow color visible with the naked eye. The estimated value of the equilibrium constant of the receptor with F(-) is 1.9 × 10(4) M(-1). Deprotonation is also observed in the presence of hydroxide. The receptor also shows colorimetric and fluorimetric sensing ability towards Fe(2+) ions. The binding site for the metal ion in the system has been unambiguously established by single-crystal X-ray diffraction studies of the Fe(II) complex of the receptor. The influence of solvents on the absorption and fluorescence spectra of the receptor has been investigated in detail. Cyclic voltammetric (CV) and square wave voltammetric (SWV) measurements carried out in dimethylformamide-acetonitrile (2?:?3) provided evidence in favor of cation (Fe(2+)) and anion (F(-)) concentration dependent electrochemical responses, enabling the ligand to act as a suitable electrochemical sensor for F(-) and Fe(2+) ions.     

Effect of adenine moiety on DNA binding property of copper(II)-terpyridine complexes

Two novel copper(ii) terpyridine complexes, [Cu(atpy)(NO(3))(H(2)O)](NO(3)).3H(2)O () and [Cu(ttpy)(NO(3))(2)] () (atpy = 4'-p-N9-adeninylmethylphenyl-2,2':6,2'-terpyridine; ttpy = 4'-p-tolyl-2,2':6,2'-terpyridine) have been prepared and structurally characterized by X-ray crystallography. Both complexes show a CuN(3)O(2) coordination in a square pyramidal (4 + 1) geometry with terpyridine acting as an equatorial ligand. For complex , intermolecular AA base pairing interaction is observed between N(6) and N(1) of adjacent adenines with N(6)N(1) of 3.027(7) A. A molecular dynamics simulation of the DNA binding of two complexes showed that the adenine moiety plays an important role in the intercalation of into DNA. This is verified by UV, fluorescence, circular dichroism and flow linear dichroism studies. The promotional effect from the adenine moiety to the intracellular DNA binding of complex is also confirmed by the inductively coupled plasma mass (ICP-MS) spectrometry data which showed a significant higher copper content in DNA isolated from complex treated MCF-7 and HeLa cells.     

Terpyridine–Porphyrin Hetero‐Pacman Compounds

The two different coordination spheres afforded by Pacman architectures offer cooperativity derived from two different metal centers. A modular strategy is developed to produce a hetero‐Pacman scaffold featuring a porphyrin and terpyridine for metal‐ion binding. A double Suzuki reaction was employed to first attach a terpyridine moiety to a xanthene backbone and then attach a porphyrin. The new hetero‐Pacman scaffold has been characterized and all building blocks have been isolated and structurally characterized. The principle objective to incorporate different metal centers was confirmed by isolating a trinuclear complex comprising two porphyrinic units and a bis(terpyridine)–iron unit. The compounds described herein expand the Pacman scaffold concept by allowing for the incorporation of a terpyridine–metal complex proximate to a porphyrin‐cofactor active site for small‐molecule activation.     

Synthesis and characterisation of second-generation metallodithiolene complexes of the type [Tp*ME(dithiolene)](M=Mo, W; E=O, S) and a novel 'organoscorpionate' complex of tungsten

Paramagnetic, chalcogenido-M(v) dithiolene complexes, [Tp*ME{S2C2(CO2Me)2}][M=Mo, E=O, S; M=W, E=O, S; Tp*=hydrotris(3,5-dimethylpyrazol-1-yl)borate] are generated in the reactions of dimethyl acetylenedicarboxylate (DMAC) and the sulfur-rich complexes NEt4[Tp*MoS(S4)] and NEt4[Tp*WS3]; the oxo complexes result from hydrolysis of the initial sulfido products. As well, a novel 'organoscorpionate' complex, [W{S2C2(CO2Me)2}{SC2(CO2Me)2-Tp*}], has been isolated from the reactions of NEt4[Tp*WS3] with excess DMAC. Complexes , and have been isolated and characterised by microanalytical, mass spectrometric, spectroscopic and (for and) X-ray crystallographic techniques. Complexes and have been partially characterised by mass spectrometry and IR and EPR spectroscopy. Six-coordinate, distorted-octahedral contains a terminal sulfido ligand (W=S=2.108(3)A), a bidentate dithiolene ligand (S-Cav=1.758 A, C=C=1.332(10)A) and a fac-tridentate Tp* ligand. Seven-coordinate contains a planar, bidentate dithiolene ligand (S-Cav=1.746 A, C=C=1.359(5)A) and a novel pentadentate 'organoscorpionate' ligand formed by the melding of DMAC, sulfido and trispyrazolylborate units. The latter is coordinated through two pyrazolyl N atoms (kappa2-N,N') and a tridentate kappa3-S,C,C' unit appended to N-beta of the third (uncoordinated) pyrazolyl group. The second-generation [Tp*ME(dithiolene)] complexes represent a refinement on first-generation [Tp*ME(arene-1,2-dithiolate)] complexes and their synthesis affords an opportunity to compare and contrast the electronic structures of true vs. pseudo-dithiolene ligands in otherwise analogous complexes.     

Photophysical behavior of terpyridine-lanthanide ion complexes incorporated in a poly(N,N-dimethylacrylamide) hydrogel

Poly(N,N-dimethylacrylamide) hydrogel forms complexes with terpyridine and various trivalent ions, like Eu(3+), Tb(3+), Gd(3+), and In(3+). The hydrogel can be obtained in three different phases: swollen with water, lyophilized (i.e., dried by freeze-drying), where it loses the solvent but preserves the swollen configuration, and dried in the air where it shrinks. The three hydrogel phases affect the type of complex formed between terpyridine and the metal ion. Thus, in the swollen and lyophilized phases, metal-centered emission can be obtained by energy transfer from the excited ligand. In the shrunk phase, an intense green fluorescence is emitted, which is ligand-centered and is independent of the complexed ion. In the absence of any ion, the ligand emits blue luminescence, independently of the hydrogel phase. In the presence of europium(III) ions, blue, green, or red emission can be thus produced at appropriate compositions and hydrogel phases. Analysis of the photophysical behavior of the polymer-ligand-metal ion complex is related with the photophysical behavior of the ligand and its complexes in various pure solvents.     

A joint experimental and theoretical study of cation-pi interactions: multiple-decker sandwich complexes of ferrocene with alkali metal ions (Li+, Na+, K+, Rb+, Cs+)

A systematic study of cation-pi interactions between alkali metal ions and the cyclopentadienyl ring of ferrocene is presented. The alkali metal (Li+, Na+, K+, Rb+, Cs+) salts of the ditopic mono(pyrazol-1-yl)borate ligand [1,1'-fc(BMe2pz)2]2- crystallize from dimethoxyethane as multiple-decker sandwich complexes with the M+ ions bound to the pi faces of the ferrocene cyclopentadienyl rings in an eta5 manner (fc = (C5H4)2Fe; pz = pyrazolyl). X-ray crystallography of the lithium complex reveals discrete trimetallic entities with each lithium ion being coordinated by only one cyclopentadienyl ring. The sodium salt forms polyanionic zigzag chains where each Na+ ion bridges the cyclopentadienyl rings of two ferrocene moieties. Linear columns [-CpR-Fe-CpR-M+-CpR-Fe-CpR-M+-](infinity) (R = [-BMe2pz]-) are established by the K+, Rb+, and Cs+ derivatives in the solid state. According to DFT calculations, the binding enthalpies of M+-eta5(ferrocene) model complexes are about 20% higher as compared to the corresponding M+-eta6(benzene) aggregates when M+ = Li+ or Na+. For K+ and Rb+, the degree of cation-pi interaction with both aromatics is about the same. The binding sequence along the M+-eta5(ferrocene) series follows a classical electrostatic trend with the smaller ions being more tightly bound.     

Metal ion affinity-based biomolecular recognition and conjugation inside synthetic polymer nanopores modified with iron-terpyridine complexes

Here we demonstrate a novel biosensing platform for the detection of lactoferrin (LFN) via metal-organic frameworks, in which the metal ions have accessible free coordination sites for binding, inside the single conical nanopores fabricated in polymeric membrane. First, monolayer of amine-terminated terpyridine (metal-chelating ligand) is covalently immobilized on the inner walls of the nanopore via carbodiimide coupling chemistry. Second, iron-terpyridine (iron-terPy) complexes are obtained by treating the terpyridine modified-nanopores with ferrous sulfate solution. The immobilized iron-terPy complexes can be used as recognition elements to fabricate biosensing nanodevice. The working principle of the proposed biosensor is based on specific noncovalent interactions between LFN and chelated metal ions in the immobilized terpyridine monolayer, leading to the selective detection of analyte protein. In addition, control experiments proved that the designed biosensor exhibits excellent biospecificity and nonfouling properties. Furthermore, complementary experiments are conducted with multipore membranes containing an array of cylindrical nanopores. We demonstrate that in the presence of LFN in the feed solution, permeation of methyl viologen (MV(2+)) and 1,5-naphthalenedisulphate (NDS(2-)) is drastically suppressed across the iron-terPy modified membranes. On the basis of these findings, we envision that apart from conventional ligand-receptor interactions, the designing and immobilization of alternative functional ligands inside the synthetic nanopores would extend this method for the construction of new metal ion affinity-based biomimetic systems for the specific binding and recognition of other biomolecules.     

Coordination features of a terpyridine-containing polyamine receptor. Effect of protonation on the photophysical properties of the complexes

The synthesis of the new terpyridine-containing macrocycle 2,6,10,14-tetraaza[15](6,6')cyclo(2,2':6',2')terpyridinophane (L) is reported. The ligand contains a tetraamine chain linking the 6,6' positions of a terpyridine unit. A potentiometric, (1)H NMR, UV-vis spectrophotometric and fluorescence emission study on the basicity properties of in aqueous solutions shows that the first four protonation steps occur on the polyamine chain, while the terpyridine nitrogens are involved in proton binding only in the last protonation step at strongly acidic pH values. Cu(II), Zn(II), Cd(II) and Pb(II) complexation was studied in aqueous solution by means of potentiometric, spectrophotometric and spectrofluorimetric measurements. Cu(II) and Zn(II) can form both mono- and dinuclear complexes in solution, while the larger Cd(II) and Pb(II) give only mononuclear complexes. In the [ML](2+) complexes (M = Zn(II) or Cd(II)) the metal is unequivocally bound to the terpyridine unit. Some amine groups are not coordinated and can quench the fluorescence emission of the terpyridine unit thanks to an electron transfer process. Protonation of the unbound amine groups inhibits the eT process, affording fluorescent [MLH(x)]((2+x)+) complexes.     

New terpyridine-containing macrocycle for the assembly of dimeric Zn(II) and Cu(II) complexes coupled by bridging hydroxide anions and pi-stacking interactions

The synthesis of the new terpyridine-containing macrocycle 2,5,8,11,14-pentaaza[15](6,6' ')cyclo(2,2':6',2' ')terpyridinophane (L) is reported. The ligand contains a pentaamine chain linking the 6,6' ' positions of a terpyridine unit. A potentiometric, (1)H NMR, UV-vis spectrophotometric and fluorescence emission study on the acid-base properties of L in aqueous solutions shows that the first four protonation steps occur on the polyamine chain, whereas the terpyridine nitrogens are involved in proton binding only at strongly acidic pH values. L can form both mono- and dinuclear Cu(II), Zn(II), Cd(II), and Pb(II) complexes in aqueous solution. The crystal structures of the Zn(II) and Cd(II) complexes ([ZnLH](2)(micro-OH))(ClO(4))(5) (6) and ([CdLH](2)(micro-Br))(ClO(4))(5).4H(2)O (7) show that two mononuclear [MLH](3+) units are coupled by a bridging anion (OH(-) in 6 and Br(-) in 7) and pi-stacking interactions between the terpyridine moieties. A potentiometric and spectrophotometric study shows that in the case of Cu(II) and Zn(II) the dimeric assemblies are also formed in aqueous solution containing the ligand and the metals in a 1:1 molar ratio. Protonation of the complexes or the addition of a second metal ion leads to the disruption of the dimers due to the increased electrostatic repulsions between the two monomeric units.     

Dissociation of gas-phase dimeric complexes of lactic acid and transition-metal ions formed under electrospray ionization conditions; the role of reduction of the metal ion

Dimeric complex ions of the type [M(A-H)A]+, where M=metal ion (Co, Ni, Cu, and Zn) and A=ligand (lactic acid, methyl lactate or ethyl lactate), were generated in the gas phase under electrospray ionization conditions. The collision-induced dissociation spectra of [M(A-H)A]+ ions were recorded to study the behaviour of ligand and metal ions in decomposition of these dimeric complex ions. Based on the fragmentation pathways observed for complex ions of lactic acid, it is found that both the carboxylic and hydroxyl groups of lactic acid are involved in the complex formation following displacement of a proton by the metal ion. The dimeric complex ions of Co, Ni, and Zn dissociated to yield similar types of ions, whereas that of Cu behaved differently. The dissociations of Co-, Ni-, and Zn-bound dimeric complexes involved losses of neutral molecules while keeping the oxidation state of the metal ion unchanged. However, elimination of radicals is found in the dissociation of dimeric complex ions of Cu, and the oxidation state of copper is reduced from Cu(II) to Cu(I) in the resulting fragment ions. The deprotonated ligand is involved in the fragmentation pathway of Cu complexes, whereas it is intact in other complexes. The oxidation state of the metal ion, nature of the ligand, and site of attachment to the metal ion are found to control the dissociation of these dimeric complex ions.     

Transition metal complexes of 2-acetylpyridine o-hydroxybenzoylhydrazone (APo-OHBH): their preparation, characterisation and antimicrobial activity.

Coordination compounds of some transition metal ions with 2-acetylpyridene-o-hydroxybenzoylhydrazone (APo-OHBH) were synthesized. Their structures have been characterised by elemental analyses, electrical conductance, magnetic moments (at 25 degrees C) and spectral (IR, UV, NMR) studies. The fast atom bombardment (FAB) method was used for obtaining mass spectra of the positive ion FAB studies of the ligand and some metal complexes. The thermal behaviour of selected complexes was investigated by thermal gravimetrical analysis (TGA) and differential thermal analysis (DTA) techniques. The IR spectra show that the ligand acts in a neutral bidentate, neutral tridentate and/or mononegative tridentate fashion depending on the metal salt used and the medium of the reaction. Preliminary pharmacological tests on the ligand and its complexes showed some antimicrobial activity.     

Relative binding energies of gas-phase pyridyl ligand/metal complexes by energy-variable collisionally activated dissociation in a quadrupole ion trap

The relative binding energies of a series of pyridyl ligand/metal complexes of the type [M(I)L(2)](+) and [M(II)L(3)](2+) are investigated by using energy-variable collisionally activated dissociation in a quadrupole ion trap mass spectrometer. The pyridyl ligands include 1,10-phenanthroline and various alkylated analogues, 2,2'-bipyridine, 4,4'-dimethyl-2,2'-bipyridine, and 2,2':6',2' '-terpyridine, and the metal ions include cobalt, nickel, copper, zinc, cadmium, calcium, magnesium, lithium, sodium, potassium, rubidium, and cesium. The effect of the ionic size and electronic nature of the metal ion and the polarizability and degree of preorganization of the pyridyl ligands on the threshold activation voltages, and thus the relative binding energies of the complexes, are evaluated. Correlations are found between the binding constants of [M(II)L(3)](2+) complexes in aqueous solution and the threshold activation voltages of the analogous gas-phase complexes determined by collisionally activated dissociation.     

Structure and stability of complexes of thiohydantoin derivative

The formation constant of 4-phenylhydrazono-2-thiohydantoin with 3d transition metal ions has been determined. The factors affecting the stability of the metal chelates have been studied. Complexes of Ag(I), Cu(II), Cd(II) and Pd(II) with the ligand have been isolated and characterized by physico-chemical techniques. The ligand forms a 1∶1 complex with Ag(I) and 1∶2 complexes with the other metal ions.     

Dioxadiaza- and trioxadiaza-macrocycles containing one dibenzofuran unit selective for cadmium

The binding properties of dioxadiaza- ([17](DBF)N2O2) and trioxadiaza- ([22](DBF)N2O3), macrocyclic ligands containing a rigid dibenzofuran group (DBF), to metal cations and structural studies of their metal complexes have been carried out. The protonation constants of these two ligands and the stability constants of their complexes with Ca2+, Ba2+, and Mn2+, Co2+, Ni2+, Cu2+, Zn2+ and Cd2+, were determined at 298.2 K in methanol-water (1:1, v/v), and at ionic strength 0.10 mol dm-3 in KNO3. The values of the protonation constants of both ligands are similar, indicating that no cavity size effect is observed. Only mononuclear complexes of these ligands with the divalent metal ions studied were found, and their stability constants are lower than expected, especially for the complexes of the macrocycle with smaller cavity size. However, the Cd2+ complex with [17](DBF)N2O2 exhibits the highest value of stability constant for the whole series of metal ions studied, indicating that this ligand reveals a remarkable selectivity for cadmium(II) in the presence of all the metal ions studied, except copper(II), indicating that this ligand reveals a remarkable selectivity for cadmium(II) in the presence of the mentioned metal ions. The crystal structures of H2[17](DBF)N2O3(2+) (diprotonated form of the ligand) and of its cadmium complex were determined by X-ray diffraction. The Cd2+ ion fits exactly inside the macrocyclic cavity exhibiting coordination number eight by coordination to all the donor atoms of the ligand, and additionally to two oxygen atoms from one nitrate anion and one oxygen atom from a water molecule. The nickel(II) and copper(II) complexes with the two ligands were further studied by UV-vis-NIR and the copper(II) complexes also by EPR spectroscopic techniques in solution indicating square-pyramidal structures and suggesting that only one nitrogen and oxygen donors of the ligands are bound to the metal. However an additional weak interaction of the second nitrogen cannot be ruled out.     

Pyrazolyl methyls prescribe the electronic properties of iron(II) tetra(pyrazolyl)lutidine chloride complexes

A series of iron(II) chloride complexes of pentadentate ligands related to α,α,α',α'-tetra(pyrazolyl)-2,6-lutidine, pz(4)lut, has been prepared to evaluate whether pyrazolyl substitution has any systematic impact on the electronic properties of the complexes. For this purpose, the new tetrakis(3,4,5-trimethylpyrazolyl)lutidine ligand, pz**(4)lut, was prepared via a CoCl(2)-catalyzed rearrangement reaction. The equimolar combination of ligand and FeCl(2) in methanol gives the appropriate 1:1 complexes [FeCl(pz(R)(4)lut)]Cl that are each isolated in the solid state as a hygroscopic solvate. In solution, the iron(II) complexes have been fully characterized by several spectroscopic methods and cyclic voltammetry. In the solid state, the complexes have been characterized by X-ray diffraction, and, in some cases, by M?ssbauer spectroscopy. The M?ssbauer studies show that the complexes remain high spin to 4 K and exclude spin-state changes as the cause of the surprising solid-state thermochromic properties of the complexes. Non-intuitive results of spectroscopic and structural studies showed that methyl substitution at the 3- and 5- positions of the pyrazolyl rings reduces the ligand field strength through steric effects whereas methyl substitution at the 4-position of the pyrazolyl rings increases the ligand field strength through inductive effects.     

Bimetallic reactivity. Preparation and properties of bimetallic complexes formed by binucleating ligands bearing 4- and 6-coordinate sites

Four binucleating ligands bearing 4- and 6-coordinate sites employing phenolate bridges have been prepared. Bimetallic copper(II) and nickel(II) complexes of some of these ligands have been isolated and characterized. Crystal structures of two of the copper(II) complexes have been determined. A monometallic manganese(II) complex of one of these ligands was isolated. Upon exposure to dioxygen, acetonitrile solutions of the complex in the presence of chloride ions lead to the formation of a manganese(IV) complex. The crystal structure of this complex is reported, and it is shown that the metal is in the 4-coordinate ligand site and is bound to two chloride ions.     

M(III)Dy(III)3 (M = Fe(III), Co(III)) complexes: three-blade propellers exhibiting slow relaxation of magnetization

[Dy(III)(HBpz(3))(2)](2+) moieties (HBpz(3)(-) = hydrotris(pyrazolyl)borate) and a 3d transition-metal ion (Fe(III) or Co(III)) have been rationally assembled using an dithiooxalato dianion ligand into 3d-4f [MDy(3)(HBpz(3))(6)(dto)(3)]·4CH(3)CN·2CH(2)Cl(2) (M = Fe (1), Co (2) complexes. Single-crystal X-ray studies reveal that three eight-coordinated Dy(III) centers in a square antiprismatic coordination environment are connecting to a central octahedral trivalent Fe or Co ion forming a propeller-type complex. The dynamics of the magnetization in the two isostructural compounds, modulated by the nature of the central M(III) metal ion, are remarkably different despite their analogous direct current (dc) magnetic properties. The slow relaxation of the magnetization observed for 2 mainly originates from isolated Dy ions, since a diamagnetic Co(III) metal ion links the magnetic Dy(III) ions. In the case of 1, the magnetic interaction between S = 1/2 Fe(III) ion and the three Dy(III) magnetic centers, although weak, generates a complex energy spectrum of magnetic states with low-lying excited states that induce a smaller energy gap than for 2 and thus a faster relaxation of the magnetization.