Have photosynthetic pigments been formulated for chemical stability? A cursory insight into the reactivity of magnesium porphyrinoids

Abstract

Magnesium complexes with reduced tetrapyrrolic ligands are active compounds of plant and bacteria photosystems. However, also the porphyrin complex appears as an intermediate on the biosynthetic pathway of the photosynthetic pigments. Its transformations, in particular the reduction of pyrrole rings, lead to the acquisition of the properties that are primary for activity in antenna systems and reaction centers. On the other hand, modifications of the porphyrin system must affect the resistance to destructive processes, such as loss of metal ion and its substitution. In order to compare the stability of three natural Mg complexes, namely Mg protoporphyrin IX, chlorophyll a, and bacteriochlorophyll a, spectroscopic studies in solution were performed. The difference in the electronic structure of the macrocyclic ligand was the basic variable in testing the action against d-electron metal salts and acetic acid. The spectroscopic studies were supplemented with calculations using the Density Functional Theory which provided insight into the stability of M(II)-N bonds depending on the dimension of the delocalized electron system. The results indicate the decreasing stability of Mg(II) complexes on the biosynthetic pathway, thereby providing an additional justification for incorporation of the metal ion into porphyrin prior to the electronic modifications of the tetrapyrrolic system.     

Gel Chromatographic Behavior of Labile Metal Complexes Trimeta- And Tetrametaphosphate Complexes with Bivalent Metal Cations

Abstract

The gel chromatographic behavior of metal ions in a labile complex formation system was expressed as a function of the ligand concentration in an eluent and the stability constants of the complexes. Trimeta- and tetrametaphosphate complexes with bivalent metal ions were used as examples. The retention volumes of the metal complexes were found to be always greater than those of the corresponding free ligands.     

Comparative study of two new grid complexes: synthesis,X-ray structure characterization,thermogravimetric, and spectroscopic properties

The synthesis and characterization of two new grid complexes, [Ni₄(L)₄(DMF)₄]?·?2H₂O (1) and [Mn₄(L)₄(DMF)₄] (2) (where L is the anion of 3,5-dichlorosalicylaldehyde pyridine-2-formyl hydrazone), were investigated. X-ray crystal structure analysis reveals that the metal centers in both complexes exhibit slightly distorted square-bipyramidal coordination geometry. The dominating interaction of two adjacent grids for 1 and 2 is Cl?···?H hydrogen bonds. The halogen–hydrogen bond is a key factor to stabilize the crystal structure of chloro-substituted grid compounds. Thermogravimetric curves of 1 and 2 exhibit distinct weight loss stages at different temperatures and reflect the thermal stability of the complexes. Both UV-visible and fluorescence spectra of 1 and 2 indicate they have a stronger conjugated system and the same significant quenching ability compared with H₂L. The ESI-MS spectra of 1 and 2 prove that the tetranuclear grids decompose in methanol/water solution.     

Polarography of Alkali Metal ion Complexes of Macrotetrolides: Complex ion Size and Stability

Abstract

The stability constants of several alkali metal ion complexes with the macrotetrolides were determined polarographically in acetonitrile. For any single alkali metal ion the stability constant increased in the order nonactin < monactin < dinactin < trinactin. Their values are larger than those found in methanol. The Stoke's radii estimated from the limiting diffusion currents of the complexes increase with increasing crystallographic radius of the cation. The increasing strain on the ligand causes a decrease of stability constant for Rb⁺ and Cs⁺.     

Capillary complexation gas chromatography in analysis of cyclic and aromatic hydrocarbons

Summary Results of studies on stationary phases containing copper(II), nickel(II) and cobalt(II) chloride chemically bonded via cyano—or thiol groups are presented. The retention parameters—i.e. retention factor (k), retention index (I) and molecular retention index (ΔMe) and specific retention volume (Vg)-enabled the characteristics of specific interaction between aromatic and cyclic hydrocarbons and metal complexes chemically bonded to stationary phases to be determined. Presented at Balaton Symposium on High Performance Separation Methods, Siófok, Hungary, September 1–3, 1999     

THEORETICAL INVESTIGATION OF KETENE BONDING MODES IN BIS(PHOSPHINE) PALLADIUM KETENE COMPLEXES

Abstract

Theoretical studies were carried out on a series of bis(phosphine) palladium ketene complexes (PR₃)₂Pd(CH₂=C=O), and on the related CH₂=C=O and Pd(PR₃)₂ molecular fragments in order to investigate the electronic structure and the bonding of the ketene ligand to the metal fragment in these complexes. An analysis of the frontier MOs has been performed in order to understand the interactions between the ketene and the metal fragments. The calculated results have shown that the η²-(C,C) mode is preferred over the η²-(C,O) mode by 10–15 kcal/mol in bis(phosphine) palladium ketene complexes. The basicity and bulkiness of the phosphine ligands PR₃ have little effect on the bonding mode in (PR₃)₂Pd(CH₂=C=O) complexes. The most stable structure was calculated to be the η²-(C,C) square planar geometry with the CH₂ group of ketene out of the molecular plane. Comparison and discussion between the two bonding modes were also presented in this paper.     

Complex Formation Between Hydroxy Naphthol Blue and First Row Transition Metal Cyanide Complexes

Abstract

It has been found that cyanide complexes of first row transition metal elements exhibit enhanced binding to hydroxy naphthol blue (HNB) relative to the binding of corresponding aquo-ions. HNB forms a 2:1 complex with Fe³⁺ and Cu²⁺ cyanides, and 1:1 complexes with all other transition metal cyanide complexes studied; formation constants have been calculated from the spectrophotometric data in each case. It is possible to use HNB as a spectrophotometric reagent for transition metal cyanide complexes, lower limits of detection being determined for each complex.     

Synthesis,characterization, potentiometry,and antimicrobial studies of transition metal complexes of a tridentate ligand

Complexes of Cu(II), Ni(II), Co(II), Mn(II), and Fe(III) with the tridentate Schiff base, 4-hydroxy-3(1-{2-(benzylideneamino)-phenylimino}-ethyl)-6-methyl-2H-pyran-2-one (HL) derived from 3-acetyl-6-methyl-(2H)-pyran-2,4(3H)-dione (dehydroacetic acid or DHA), o-phenylenediamine, and benzaldehyde were characterized by elemental analysis, molar conductivity, magnetic susceptibility, thermal analysis, X-ray diffraction, IR, ¹H-NMR, UV-Vis spectroscopy, and mass spectra. From analytical data, the stiochiometry of the complexes was found to be 1?:?2 (metal?:?ligand) with octahedral geometry. The molar conductance values suggest nonelectrolytes. X-ray diffraction data suggest monoclinic crystal systems. IR spectral data suggest that the ligand is dibasic tridentate with ONN donors. To investigate the relationship between formation constants of metal complexes and antimicrobial activity, the dissociation constants of Schiff base and stability constants of its binary metal complexes have been determined potentiometrically in THF–water (60?:?40) at 30?±?1°C and at 0.1?mol?L^?1 NaClO₄ ionic strength. The potentiometric titrations suggest 1?:?1 and 1?:?2 complexation. Antibacterial and antifungal activities in vitro were performed against Staphylococcus aureus, Escherichia coli, Aspergillus niger, and Trichoderma with determination of minimum inhibitory concentrations of ligand and metal complexes. The structure–activity correlation based on stability constants of metal complexes is discussed. Activity enhances upon complexation and the order of activity is in accord with the stability order of metal ions.     

COMPLEX FORMATION BETWEEN HEAVY METAL CATIONS AND DIAZA CROWN ETHERS AND CRYPTANDS IN AQUEOUS SOLUTION

Abstract

Complexation of some heavy metal cations in aqueous solution by diaza crown ethers and cryptands has been studied using pH-metric titrations. In most cases, macrobicyclic cryptands form more stable complexes than diaza crown ethers. The size of the cavity aiso influences the stability of the complexes formed.     

SPECTROPHOTOMETRIC STUDY OF COMPLEX FORMATION BETWEEN SOME ALKALI AND ALKALINE EARTH CATIONS AND SEVERAL CONVENTIONAL (N,N), (N,O) AND (O,O) LIGANDS IN 95% ETHANOL

Abstract

The complexation of Li⁺, Na⁺, Mg²⁺ and Ca²⁺ with 1,10-phenanthroline, 2,2′-bipyridine, 1,2-phenylenediamine, 2-aminopyridine, 8-hydroxyquinoline, catechol and ethylene glycol was studied in 95% ethanol by means of a competitive spectrophotometric method using murexide as indicator. Formation constants of 1:1 conplexes were determined. In the case of all ligands used, the stability of the complexes was found to vary in the order Mg²⁺ > Ca²⁺ > Li⁺ > Na⁺. It was found that the structure influences the formation and stability of resulting complexes. Effects of various parameters on complexation are discussed.     

Studies on mononuclear transition metal chelates derived from a novel ( E,E )-dioxime: synthesis,characterization and biological activity

A novel vic-dioxime ligand with a thiourea moiety, (4E,5E)-1,3-bis{4-[(4-bromophenylamino)methylene]phenyl}-2-thiooxaimidazoline-4,5-dione dioxime (4) (bmdH₂) has been synthesized from N,N′-bis{4-[(4-bromophenylamino)methylene]phenyl}thiourea and (E,E)-dichloroglyoxime. The bmdH₂ ligand (4) forms transition metal complexes [M(bmdH)₂] with a metal?:?ligand ratio of 1?:?2 with M?=?Ni(II), Co(II), and Cu(II). The mononuclear Ni(II), Co(II) and Cu(II) complexes, [Ni(bmdH)₂] (5), [Co(bmdH)₂] (6) and [Cu(bmdH)₂] (7) have the metal ions coordinated through the two N,N atoms, as do most vic-dioximes. Elemental analyses, molar conductivity, magnetic susceptibility, IR, ¹H NMR spectra, and UV-Visible spectroscopy were used to elucidate the structures of the ligand and its complexes. Conductivity measurements have shown that the mononuclear complexes are non-electrolytes. In addition, the ligands and metal complexes were screened for antibacterial and antifungal activities by agar well diffusion techniques using DMF as solvent.     

Synthesis and characterization of chiral trinuclear cobalt and nickel complexes supported by binaphthol-derived bis(salicylaldimine) ligands

Chiral bis(salicylaldimine) ligands derived from binaphthol (LH₂) were synthesized by condensation of (R/S) 2,2′-dihydroxy-1,1′-binaphthyl-3,3′-dicarbaldehyde with 2-anisidine. Cobalt and nickel complexes (CoL)₂(OAc)₂Co (1) and (NiL)₂(OAc)₂Ni (2) were synthesized via reactions of the ligand with the corresponding metal acetate salt. Both complexes were characterized by elemental analysis, IR, MS, and single-crystal X-ray diffraction analysis. The X-ray analysis reveals linear trinuclear for 1 and 2 and the metal ions in both complexes are octahedral coordination. The two acetates separately bridge the center metal with one of the terminal metals in M–O–C–O–M manner. The magnetic susceptibility of 1 below 150?K suggests the existence of a weak ferromagnetic exchange at low temperatures, while antiferromagnetic interactions among Co(II) cores were observed above 150?K. Complex 2 shows similar magnetic behavior to that of 1.     

Structural and Antimicrobial Studies of Some Divalent Transition Metal Complexes with Some New Symmetrical Bis (7-Formylanil Substituted-Sulfoxine) Schiff Base Ligands

Symmetrical bis (7-formyanil substituted-8-hydroxyquinoline-5-sulfonic acid), Schiff bases, react with Co(II), Ni(II) and Cu(II) ions to give M_nL (n=1, 2) complexes as established by conductometric titration in 1 : 1 DMF: H₂O. The complexes were identified by elemental analyses, molecular weight determination, thermal analysis, infrared, magnetic moments, electronic absorption, and electron spin resonance spectra. The suggested general geometry for these complexes may have a tetrahedral crystal structure and the general formula is [M₂L(OH₂4], where M(II) = Co, Ni and Cu and L = 7―X―H₂ L(―X―= dimethyl, p-phenyl, o-phenyl), while for the, trimethyl, ligand and the tetrahedral crystal structure has the general formula [M₂L(OH₂)₂].Antimicrobial activity of these ligands and their transition metal complexes has been investigated on some common fungi and bacteria. A considerable increase in the biocide acticity of these ligands has been observed on coordination with transition metal ions, therefore, these complexes can be used in the chemotherapy of candidiaces and other fungal skin diseases.     

THE INTERACTIONS BETWEEN PERIPHERAL AND CENTRAL UNITS IN SUPRAMOLECULAR AND METALLOSUPRAMOLECULAR STRUCTURES: THE CHARACTERIZATION OF SOME MONO-, DI- AND TRINUCLEAR COMPLEXES OF A VICINAL OXIME-IMINE LIGAND

Abstract

The 1:1 molar ratio reaction of p-phenylenediamine with isonitrosoacetylacetone in chloroform led to the formation of the half unit ligand (HL); (1). Two types of the trans octahedral (L)₂Ni 2H₂O complex were characterized; the green molecular complex (2) and the associated supramolecular dark brown complex (3). Molecular association in (3) took place via inter-molecular hydrogen bonding between the amino group of a molecule and the oxygen sites of an adjacent molecule. The 1:1 molar ratio reactions of (2) with the metal acetates M(OAc)₂ (M = divalent nickel, copper or cobalt) produced the self-assembly structure (4) whereby the metal acetate is coordinated to the amino groups of the nickel(II) complex. Reaction of the dinuclear (4) with another metal acetate (1:1 molar ratio) gave the trinuclear terminated structure (5). Similar reactions of (3) with nickel acetate (1:1 or 1:2) led to formation of complexes with metallosupramolecular structures. An antiferromagnetic interaction between the peripheral and central paramagnetic units was observed from those complexes with copper(II) at the peripheral location. In all these cases the metal ions are bridged via the aromatic Schiff-base moiety. The suggested structures of the mono-, di- and trinuclear coordination compounds are in accordance with the analytical, spectral and magnetic moment data.     

Synthesis,characterization, reactivity,and electrochemical studies of manganese(IV) complexes of bis(2-hydroxy-1-naphthaldehyde)adipoyldihydrazone

Manganese(IV) complexes [Mn^IV(npah)(H₂O)₂] (1) and [Mn^IV(npah)(A)₂]?·?nH₂O (where A?=?py (2), 2-pic (3), 3-pic (4), 4-pic (5)) and Mn^IV(npah)(NN)] (NN?=?bpy (6) and phen (7)) have been synthesized from bis(2-hydroxy-1-naphthaldehyde)adipoyldihydrazone in methanol. The composition of the complexes has been established by elemental analyses. Complex 3 has been characterized by mass spectral data also. Structural assessment of the complexes has been based on data from molar conductance, magnetic moment, electronic, electron paramagnetic resonance, and infrared (IR) spectral studies. Molar conductances of the complexes in DMSO suggest non-electrolytes. Magnetic moment and EPR studies suggest +4 oxidation state for manganese in these complexes. Electronic spectral studies suggest six-coordinate octahedral geometry around the metal ions. IR spectra reveal that H₄npah coordinates to the metal in enol form. Reaction of the complexes with benzyl alcohol and SO₂ has been investigated. Cyclic voltammetric studies of the complexes have also been carried out.     

THE INFLUENCE OF STRUCTURAL EFFECTS ON THE COMPLEXING ABILITY OF CROWN ETHERS

Abstract

Simple regression including interaction energies of the cation-ligand systems explains to some extent the variability in logarithms of stability constants of complexes formed by a series of nine 18-crown-6 ethers with potassium cations in methanol. The atomic charges were calculated for energy minimized structures, found during molecular dynamics computations. In order to mimic the residual solvation of complexed cations, two CH₃OH molecules were incorporated above and below the macrocyclic plane. Polarization effects of the metal cation on the resulting atomic charges were considered in calculations and found to be crucial for satisfactory correlations with experimental data.     

Synthesis,DNA-binding,and cytotoxic studies on three copper(II) complexes of unsymmetrical synthetic analogues of curcumin

Copper(II) chelates of three unsymmetrical synthetic analogs of curcumin, namely (2E)-2-(4-hydroxy-3-methoxybenzylidene)-5-((E)-3-(4-hydroxy-3-methoxyphenyl)acryloyl)cyclopentanone(1), (2E)-2-(3,4-dihydroxybenzylidene)-5-((E)-3-(3,4-dihydroxyphenyl)acryloyl)cyclopentanone(2), and (2E)-2-(3,4-dimethoxybenzylidene)-5-((E)-3-(3,4-dimethoxyphenyl)acryloyl)cyclopeantanone(3) have been synthesized and characterized by physicochemical and spectroscopic methods. The ligands were in their enolic form and metal complexes have 1 : 2 metal:ligand stoichiometry. The DNA-binding properties of the ligands and their metal complexes were studied by absorption titrations, fluorescence quenching experiments, and viscosity measurements with calf-thymus DNA. The interactions of copper(II) complexes were higher than that of free ligands. The observed intrinsic binding constants reveal moderate interaction of copper(II) complexes with calf-thymus DNA. The binding involves intercalative mode through non-covalent interactions and produced conformational changes in the structure of DNA. The compounds were investigated for their possible cytotoxic and antitumor activities. All the compounds were cytotoxic towards Dalton’s lymphoma ascites cells. It was found that copper chelates are remarkably active compared to free curcumin analogs. Concentrations needed for 50% cell death were 10–22 μg mL^?1 for copper complexes and 27–52 μg mL^?1 for curcumin analogs. Copper complex of 2 with two hydroxyl groups in the phenyl ring was most active towards Dalton’s lymphoma ascites cells (increase in life span 77.91%). Copper(II) complex of 3, which possesses methoxy groups in the phenyl ring system, showed the lowest activity towards increase in lifespan of tumor-bearing mice (increase in lifespan 60.14%). Copper chelates of all curcuminoid analogs showed a significant reduction in solid tumor volume in mice.     

Eco-friendly energetic complexes based on transition metal nitrates and 3,4-diamino-1,2,4-triazole (DATr)

Four eco-friendly energetic metal complexes of 3,4-diamino-1,2,4-triazole (DATr), including manganese (1), cobalt (2), nickel (3), and zinc (4), were synthesized by reacting DATr·HCl with the corresponding metal (Mn(II), Co(II), Ni(II), and Zn(II)) nitrate in aqueous solution and characterized by using Fourier transform-infrared spectroscopy and elemental analyses. The single crystals of 2, 3, and 4 were obtained and determined by X-ray single-crystal diffraction analysis. All three complexes crystallize in the monoclinic crystal system and belong to P2(1)/n space group. The thermal decomposition processes were investigated by differential scanning calorimeter (DSC) and thermogravimetry–derivative thermogravimetry analyses. The results show that the decomposition temperatures of 1–4 are above 260 °C, depending upon their onset DSC peaks. It can be predicted that these complexes based on 3,4-diamino-1,2,4-triazole have good thermal stability. The nonisothermal kinetic parameters of decomposition were calculated by using Kissinger and Ozawa–Doyle’s methods. Furthermore, the sensitivities of these complexes to impact, friction, and flame were determined. Sensitivity tests revealed that 2 was more sensitive to external stimuli compared to the other three complexes.     

SYNTHESIS OF 5-DODECANOYLAMINE-8-HYDROXY-1,4-NAPHTHOQUINONE AND STUDY OF SOME OF ITS BIVALENT METAL CHELATES

Abstract

Two new naphthoquinone derivatives, 5-dodecanoylamine-8-hydroxy-l,4-naphthoquinone (1) and 5-dodecanoylamine-8-acetoxy-l,4-naphthoquinone (2), have been prepared and characterized. Their chelating ability with Ni(II) and Co(II) have been studied. Compound (1) coordinates to the divalent metal ions as a monoanionic bidentate ligand. The complexes were found to contain two ligands and two molecules of coordinated water. The structure and bonding of the chelates are discussed based on the spectroscopic data.     

基于四齿配体的蓝光d8金属配合物及其OLED应用的研究进展

用于有机发光二极管(OLED)的红光和绿光磷光金属配合物材料在稳定性和发光效率方面均已达到了目前产业化应用的要求,而蓝光磷光配合物则在稳定性方面无法达到应用条件。高能量的激发态以及d-d态引起的配合物分解是造成蓝光磷光OLED器件稳定性差的原因之一。采用四齿配体开发d~8金属配合物是同时提升配合物发光效率和稳定性的途径之一,有望在蓝光磷光材料和器件应用方面取得突破。本文总结了基于四齿配体的蓝光铂(Ⅱ)和钯(Ⅱ)配合物的研究进展,通过探讨配体结构对配合物光物理性质和稳定性的影响,为继续开发具有应用前景的蓝光金属配合物材料提供了指导性方向。