Synthetic analogues of the histidine–chlorophyll complex: a NMR study to mimic structural features of the photosynthetic reaction center and the light-harvesting complex

Mg(II)–porphyrin–ligand and (bacterio)chlorophyl–ligand coordination interactions have been studied by solution and solid-state MAS NMR spectroscopy. ¹H, ¹³C and ¹⁵N coordination shifts due to ring currents, electronic perturbations and structural effects are resolved for imidazole (Im) and 1-methylimidazole (1-MeIm) coordinated axially to Mg(II)-OEP and (B)Chl a. As a consequence of a single axial coordination of Im or 1-MeIm to the Mg(II) ion, 0.9–5.2 ppm ¹H, 0.2–5.5 ppm ¹³C and 2.1–27.2 ppm ¹⁵N coordination shifts were measured for selectively labeled [1,3-¹⁵N]-Im, [1,3-¹⁵N,2-¹³C]-Im and [1,3-¹⁵N,1,2-¹³C]-1-MeIm. The coordination shifts depend on the distance of the nuclei to the porphyrin plane and the perturbation of the electronic structure. The signal intensities in the ¹H NMR spectrum reveal a five-coordinated complex, and the isotropic chemical shift analysis shows a close analogy with the electronic structure of the BChl a–histidine in natural light harvesting 2 complexes. The line broadening of the ligand responses support the complementary IR data and provide evidence for a dynamic coordination bond in the complex.Abbreviations (B)Chl a (bacterio)chlorophyll a - HMBC heteronuclear multiple bond correlation - Im imidazole - LH light-harvesting - 1-MeIm 1-methylimidazole - Mg(II)-Por Mg(II)-porphyrin macrocycle - OEP 2,3,7,8,12,13,17,18-octaethylporphyrin     

Studies on the synthesis,characterisation and antimicrobial activity of new Co(II), Ni(II) and Zn(II) complexes of Schiff base derived from ninhydrin and glycine

Summary For the first time, Co(II), Ni(II) and Zn(II) complexes have been synthesized involving an intermediate Schiff base, indane-1,3-dione-2-imine-N-acetic acid the condensed product of ninhydrin and glycine. These coloured complexes were characterised by elemental analysis, molar conductivity, thermogravimetric analyses/differential thermal analysis, infrared, magnetic susceptibility, NMR and electronic spectral studies. Mechanisms for their formation have been proposed. The experimental studies reveal that the complexes possess octahedral stereochemistry whereas the Schiff base behaves as a monobasic tridentate ligand. A molecular structure for the metal complexes is also proposed. A comparative study of the antimicrobial activity of ninhydrin and the corresponding metal complexes againstEscherichia coli, Proteus mirabilis, Staphylococcus aureus andStreptococcus faecalis has been undertaken and the results are discussed.     

Biologically relevant tetraazamacrocyclic complexes of manganese: synthetic, spectral, antimicrobial, antifertility and antiinflammatory approach

The testicular sperm density, sperm morphology, sperm motility, density of cauda epididymis spermatozoa and fertility in mating trials and biochemical parameters of reproductive organs have been examined and discussed for [Mn(N(4)MacL(n))(NO(3))(2)] (where N(4)MacL(n) represents the tetraazamacrocyclic ligand molecule with n=1-4) type of complexes. An attempt also has been made to correlate the structural aspects of the compounds with their anti-inflammatory activity. The 14-18 membered tetraamide macrocyclic ligands N(4)L(1)-N(4)L(4) used during these investigations have been prepared by the condensation of 1,2-diaminoethane or 1,3-diaminopropane with malonic or succinic acid in the presence of condensing reagents, dicyclohexylcarbodiimide and 4-dimethylaminopyridine. On reduction, these macrocyclic ligands give a new series of tetraazamacrocyles [N(4)MacL(n)] and their complexes with manganese(II) nitrate. The ligands and their complexes were characterized by elemental analyses, molecular weight determinations, infrared, electronic, mass and X-ray structural analyses. An octahedral geometry for these complexes has been confirmed by spectral studies. On the basis of the chemical composition, the representation of the complexes as [Mn(N(4)MacL(n))(NO(3))(2)] has been established. The ligands and their complexes have been screened in vitro against a number of pathogenic fungi and bacteria to assess their growth inhibiting potential.     

Electronic structure of platinum(II) antitumor complexes and their interactions with nucleic acid bases. I

Using the semi-empirical all-valence method (GRINDOL) (recently modified and extended to transition series elements), electronic structure and intermolecular interactions of the model antitumor Pt(II) compounds with guanine and thioguanine have been calculated. Several possible models of antitumor action of platinum compounds are discussed. It is concluded that cis-Pt(II) complexes with guanine form stable intrastrand N7N7 cross-links (but chelation to the O6 atom is also possible). The trans-isomers of platinum(II) exclusively form interstrand cross-links, but the cis-Pt(II) complexes with thioguanine form almost entirely the N7S five-membered chelates.     

Octahedral Nickel(II) dithiocarboxylates

Two nickel(II) complexes, NiL₂Cl₂ and NiL₂– (NO₃)₂·0.3EtOH, with the ligand 1,3-dimethyl- imidazoliumdithiocarboxyalato (L) have been synthesized and characterized by infrared and electronic spectroscopy and magnetic susceptibilities. The complexes exhibit the normal paramagnetism characteristic of octahedral nickel(II). The magnetic moments decrease with falling temperature, indicative of antiferromagnetic coupling, which is greater for the chloride than for the nitrate adduct. Columnar structures with chloro and nitrato bridging are proposed.     

New copper(II), nickel(II) and zinc(II) complexes with 1,2,4-triazolo[1,5-a]pyrimidines and the chelating ligand 1,3-propanediamine: An unexpected coordination behavior for the 7-amine-derivative

Five new metal complexes with the metal ions Cu(II), Ni(II) and Zn(II) and containing 1,2,4-triazolo[1,5-a]pyrimidine derivatives and 1,3-propanediamine (tn) are described. The structural morphology of these coordination compounds depends on the triazolopyrimidine derivative used, being mononuclear for 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine (dmtp) and 5-methyl-1,2,4-triazolo[1,5-a]pyrimidin-7(4H)-one (HmtpO), and 1D-polymeric for 7-amine-1,2,4-triazolo[1,5-a]pyrimidine (7atp). In the 7atp case, this ligand does not coordinate through N3 atom, as expected, but through N1, N4 and N71 in a bridging fashion. This unexpected coordination mode seems to be induced by the stability of the polynuclear metal complex in presence of tn ligand. All isolated metal complexes have been characterized by single-crystal X-ray diffraction, IR and UV-Vis spectroscopies, and EPR measurements. Moreover, luminescence measurements have been carried out for 7atp ligand and its polynuclear complex with Zn(II).     

Synthesis, spectroscopic characterization and structural studies of mixed ligand complexes of Sr(II) and Ba(II) with 2-hydroxybenzophenone and salicylaldehyde, hydroxyaromatic ketones or β-diketones: Crystal structure of 2-HOC6H4C(O)C6H5

Reactions of Sr(II) and Ba(II) chlorides with 2-hydroxybenzophenone and salicylaldehyde, hydroxyaromatic ketones or β-diketones in 1:1:1 molar ratios have resulted in the formation of mixed ligand complexes of the type [MLL′(H₂O)₂] (M = Sr(II) or Ba(II); HL = 2-hydroxybenzophenone and HL′ = salicylaldehyde, 2-hydroxyacetophenone, 2-hydroxypropiophenone, pentane-2,4-dione, 1-phenylbutane-1,3-dione or 1,3-diphenylpropane-1,3-dione). These complexes have been characterized by elemental analyses, TLC, IR and ¹H NMR spectroscopy.     

Synthesis,characterization of some transition metal(II) complexes of acetone <Emphasis Type="Italic">p-</Emphasis>amino acetophenone salicyloyl hydrazone and their anti microbial activity

Complexes of the type [M(apash)Cl] and [M(Hapash)(H2O)SO4], where M = Mn(II), Co(II), Ni(II), Cu(II) and Zn(II); Hapash = acetone p-amino acetophenone salicyloyl hydrazone have been synthesized and characterized by elemental analyses, molar conductance, magnetic moments, electronic, ESR and IR spectra, thermal studies (TGA & DTA) and X-ray diffraction studies. The ligand coordinates through two >C=N and a deprotonated enolate group in all the chloro complexes, whereas through two >C=N- and a >C=O group in all the sulfato complexes. The electronic spectra suggest a square planar geometry for Co(II), Ni(II) and Cu(II) chloride complexes and an octahedral geometry for the sulfate complexes. ESR data show an isotropic symmetry for [Cu(apash)Cl] and [Cu(Hapash)(H2O)SO4] in solid state. However, ESR spectra of both Cu(II) complexes indicate the presence of unpaired electron in d x2-y2. The X-ray diffraction parameters for [Co(apash)Cl] and [Cu(Hapash)(H2O)SO4] complexes correspond to a tetragonal and an orthorhombic crystal lattices, respectively. Thermal studies of [Co(apash)Cl] complex shows a multi-step decomposition pattern. Most of the complexes show better antifungal activity than the standard miconazole against a number of pathogenic fungi. The antibacterial activity of these complexes has been evaluated against E. coli and Clostridium sp. which shows a moderate activity.     

Synthesis,physico-chemical characterization and antimicrobial activity of cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) complexes with some acyldihydrazones

Complexes of the type [M(bssdh)]Cl and [M(dspdh)]Cl, where M = Co(II), Ni(II), Cu(II), Zn(II) and Cd(II); Hbssdh = benzil salicylaldehyde succinic acid dihydrazone, Hdspdh = diacetyl salicylaldehyde phthalic acid dihydrazone have been synthesized and characterized with the help of elemental analyses, electrical conductance, magnetic susceptibility measurements, electronic, ESR and IR spectra and X–ray diffraction studies. Magnetic moment values and electronic spectral transitions indicate a spin free octahedral structure for Co(II), Ni(II) and Cu(II) complexes. IR spectral studies suggest that both the ligands behave as monobasic hexadentate ligands coordinating through three > C = O, two > C = N– and a phenolate group to the metal. ESR spectra of Cu(II) complexes are axial type and suggest as the ground state. X–ray powder diffraction parameters for [Co(bssdh)]Cl and [Co(dspdh)]Cl complexes correspond to an orthorhombic crystal lattice. The ligands as well as their metal complexes show a significant antifungal and antibacterial activity against various fungi and bacteria. The metal complexes are more active than the parent ligands.     

Physico-chemical study of first row transition metal ions coordination compounds with N,N′-bis(2-tosylaminobenzylidene)-1,3-diaminopropanol. The crystal structure of bis-azomethine and its cobalt(II) complex

The novel Cu(II), Ni(II), Zn(II), Co(II) coordination compounds with Schiff base ligand - N,N′-bis(2-tosylaminobenzylidene)-1,3-diaminopropanol have been synthesized and studied. The structures of bis-azomethine as well as Co(II) and Zn(II) mononuclear metallochelates have been determined by X-ray analysis. The magnetic properties of all complexes were studied and interpreted in terms of HDVV theory. It was shown that exchange interaction in binuclear copper(II) complexes was affected by tosyl groups.     

Biologically active macrocyclic complexes derived from diaminonaphthalene and glyoxal: Template synthesis and spectroscopic approach

A novel series of complexes of the type [M(C(24)H(16)N(4))X(2)]; where M = Co(II), Ni(II), Cu(II), Zn(II) and Cd(II); X = Cl(-1), NO(-1)(3), CH(3)COO(-1) has been synthesized by template condensation of 1,8-diaminonaphthalene and glyoxal in the presence of divalent metal salts in methanolic medium. The complexes have been characterized with the help of elemental analyses, conductance measurements, molecular weight determination, magnetic measurements, electronic, NMR, infrared and far infrared spectral studies. The low value of molar conductance indicates them to be non-electrolytes. On the basis of various studies a distorted octahedral geometry may be proposed for all of these complexes. These metal complexes were also tested for their in vitro antibacterial and antifungal activities to assess their inhibiting potential.     

New manganese complexes with 2-salicyloylhydrazono-1,3-dithiolane ligand and various coordination solvents

The new complexes with 2-salicyloylhydrazono-1,3-dithiolane ligand (H₂L) have been obtained with good yields (≈85%) by reacting manganese (II) acetate tetrahydrate or manganese (II) acetylacetonate with 2-salicyloylhydrazono-1,3-dithiolane ligand in DMF, THF or Py (L′). These compounds have been fully characterized by spectroscopic methods and single crystal X-ray diffraction. In the solid state, supramolecular networks are described and discussed in terms of weak H-bonds and short contacts. The new monomeric complexes will be considered as candidates to obtain polynuclear complexes.     

Unprecedented sugar-dependent in vivo antitumor activity of carbohydrate-pendant cis-diamminedichloroplatinum(II) complexes.

Eight carbohydrate-pendant platinum(II) complexes have been synthesized from carbohydrate-diamine conjugates. D-Glucose, D-mannose, D-galactose, D-xylose, and L-glucose are attached to the dichloroplatinum(II) moiety by 1,3- or 1,2-diaminopropane chelates through with an O-glycoside bond. All the carbohydrate moieties reduced the toxicity inherent with platinum(II) complexes.     

Main group metal halide complexes with sterically hindered thioureas. IX. New complexes of selected post-transition metals and 1,3-dimethyl-2(3H)-imidazolethione and a structural investigation of infrared peak shifts associated with coordination

Five new complexes of sterically hindered 1,3- dimethyl-2(3H)-imidazolethione (dmit) with the chlorides of Cd(II), Hg(II), Te(II), Sn(IV) and Sb(V) have been synthesized and characterized. The previously reported Zn(II) adduct was also synthesized and further characterized. These complexes were of the general formula MX_n(dmit)_m where n = 2 and m = 2 when M = Zn, Cd, Hg and Sn; and n = 2 and m = 4 for Te(II). The only 1:1 adduct observed was SbCl₅dmit, and its chemistry is more complex giving rise to unique redox products upon heating in solution. Solid state spectra of these complexes as well as for dmit complexes are reported and discussed with regard to the coordination sensitive NCN asymmetric stretch and the CS stretch observed not only for dmit complexes but for tetramethylthiourea (tmtu) complexes reported in the literature as well. Greatest shifts on coordination are observed with the NCN asymmetric stretch for tmtu causing shifts to higher wave numbers ranging from 55 to 95 cm⁻¹ relative to free tmtu. Shifts are explained on the basis of observed crystal structures of tmtu adducts showing a greater CN double bond character. Dmit adducts show much smaller shifts both to higher and lower wave numbers for this mode relative to free ligand, and the CS stretch shows little change also. Comparison to known crystal structures show little change in the bond distances of the dmit ligand upon coordination. Inductive effects based on correlations of shift magnitude to the Sanderson group electronegativity (SGEN) of the acceptor seem to be unrelated with the exception of a small positive correlation observed for the NCN asymmetric stretch of tmtu.     

Biologically important coordination compounds of 4-acetyl-2-(acetylamino)-5-dimethyl-δ2-1,3,4-thiadiazole with manganese(II), iron(II), cobalt(II) and nickel(II)

The complexes of 4-Acetyl-2-(acetylamino)-5- dimethyl-δ²-1,3,4-thiadiazole (AAT) with Mn(II), Fe(II), Co(Il) and Ni(II) have been prepared and characterized on the basis of elemental analyses, molar conductance, magnetic moments, electronic and infrared spectral studies. The most probable structures of the complexes have been proposed on the basis of their physicochemical properties. The fungitoxicity of AAT and its complexes has been evaluated on pathogenic fungi.     

Synthesis, characterization, crystal structure and biological activity of a novel heterotetranuclear complex: [NiLPb(SCN)2(DMF)(H2O)]2, bis-{[mu-N,N'-bis(salicylidene)-1,3-propanediaminato-aqua-nickel(II)](thiocyanato)(mu-thiocyanato)(mu-N,N'-dimethylformamide)lead(II)}

The mononuclear nickel complex NiL (LH2 = N,N'-bis(salicylidene)-1,3-diaminopropane) can be transformed into the tetranuclear complex [NiL(H2O)Pb(SCN)2(DMF)]2 in the aid of SCN-, DMF (dimethylformamide) and Pb(II) ions. The complex was characterized by elemental analysis and FTIR investigation. The crystal structure reveals it is a nonlinear Ni(II)-Pb(II)-Pb(II)i-Ni(II)i (i: 1-x, 1-y, 1-z) heterotetranuclear complex and crystallizes in the triclinic space group P1. The Ni(II) and Pb(II) ions have a distorted octahedral coordination geometry. There are three kinds of mu-bridge in the molecule between the metal ions. Each pair of Ni and Pb ions in the asymmetric unit is equatorially linked by two phenolic oxygen bridging atoms of N,N'-bis(salicylidene)-1,3-propanediaminato (salpd(2-), C17H16N2O2(2-)) ligand. The dinuclear centres from tetranuclear clusters Ni-Pb(i) and Ni(i)-Pb pairs are bridged by two mu-1,3-SCN groups. Pb(II) and Pb(II)i ions are also bridged by the oxygen atoms of DMF molecules. The tetranuclear units are hydrogen bonded by two O-H...N intermolecular interactions along the c-axis. The complex was screened for antibacterial and antifungal activities by the disc diffusion and microtiter plate techniques using DMF as solvent. The minimum inhibitory concentration values were calculated. It has been found that antimicrobial activities of the complexes are higher than the free ligand.     

Metal-based new sulfonamides: Design,synthesis, antibacterial,antifungal, and cytotoxic properties

Cobalt(II), copper(II), nickel(II) and zinc(II) metal complexes with 5-chlorosalicyladehyde derived Schiff base sulfonamides have been synthesized and characterized. Structure and bonding nature of all the synthesized compounds have been deduced from physical, analytical, and spectral (IR, ¹H NMR, ¹³C NMR, Mass, electronic) data. An octahedral geometry has been proposed for all the metal complexes. The ligands and their metal complexes have been screened for their in vitro antibacterial, antifungal, and cytotoxic properties and results are reported.     

Transition metal complexes with N, S donor ligands as synthetic antioxidants: synthesis, characterization and antioxidant activity

Transition metal complexes containing bidentate N, S donor ligands i.e., carvone thiosemicarbazone [(RS)-5-isopropenyl-2-methylcyclohex-2-en-1-one thiosemicarbazone (IPMCHTSC)] and carvone N(1)-phenylthiosemicarbazone [(RS)-5-isopropenyl-2-methylcyclohex-2-en-1-one phenylthiosemicarbazone (IPMCHPhTSC)] have been synthesized. All the metal complexes (1-8) have been characterized by elemental analysis, molar conductance measurement and various spectral studies [infrared (IR), electronic, fast-atom bombardment (FAB) mass and NMR (for ligands)] and thermogravimetric analysis. FAB mass spectroscopic studies of (1), (3), (4), (5), (6) (7), and (8) suggest their monomeric nature. Metal complexes are [M(LH)Cl(2)] and [M(LH)(2)Cl(2)] type, where M?=?Fe(III), Co(II), and Cu(II) and LH?=?IPMCHTSC and IPMCHPhTSC. The proposed geometries of the complexes were octahedral for 1:2 complexes, square planar for 1:1 complexes and distorted octahedral for Cu(II) complexes (1:2). The free radical scavenging activity of ligands (IPMCHTSC and IPMCHPhTSC) and their metal complexes have been determined at the concentration range of 10-400 μg/mL by means of their interaction with the stable free radical 2,2'-diphenyl-1-picrylhydrazyl and 5-200 μg/mL by 2,2'-Azinobis-3-ethylbenzothiazoline-6-sulphonic acid. All the compounds have shown encouraging antioxidant activities.     

Some bivalent metal complexes of Schiff bases containing N and S donor atoms

Schiff bases have been synthesized by the reaction of p-nitrobenzaldehyde, o-nitrobenzaldehyde and p-toluyaldehyde with 4-amino-5-mercapto-1,2,4-triazole. The ligands react with Co(II), Ni(II) and Zn(II) metals to yield (1:1) and (1:2) [metal:ligand] complexes. Elemental analyses, IR, ¹H NMR, electronic spectral data, magnetic susceptibility measurements, molar conductivity measurements and thermal studies have investigated the structure of the ligands and their metal complexes. The electronic spectral data suggests octahedral geometry for Co(II), Ni(II) and Zn(II). The antibacterial activities of the ligands and their metal complexes have been screened in vitro against three Gram-positive (Staphylococcus aureus, Staphylococcus epidermidis and Bacillus subtilis) and two Gram-negative (Salmonella typhi and Pseudomonas aeruginosa) organisms. The coordination of the metal ion had a pronounced effect on the microbial activities of the ligands and the metal complexes have higher antimicrobial effect than the free ligands.