Zn Metal Center Research Articles

Exploring the effect of chain length of bridging ligands in coordination complexes and polymers derived from mixed ligand systems of pyridylnicotinamides and dicarboxylates

The supramolecular structural diversities in mixed ligand systems derived from a series of dicarboxylate anions with varying chain lengths and N-donor exo-bidentate ligand equipped with hydrogen bonding capable amide backbone with Co(II)/Zn(II) metal centers are analyzed. In this context, two complexes namely (Co( L1) 2(malonate)(H 2O) 2} ( 1a), {Zn( L1) 2(malonate)(H 2O) 2} ( 1b) and one coordination polymer namely {[Co(μ- L1)(μ-glutarate)(H 2O)] · H 2O} n ( 4) (where L1 = N-(4-pyridyl)nicotinamide) have been synthesized and crystallographically characterized. The main aim of this work is to explore the effects of chain lengths of the anionic carboxylate ligands such as malonate, succinate, maleate, and glutarate, in determining the final architecture of coordination compounds based on the mixed ligands. Analyses of the structures revealed that the length of the bridging ligands have prominent effect in the formation of hierarchical structures.

Zinc(II) complexes derived from pyridine-2-carbaldehyde thiosemicarbazone and (1 E)-1-pyridin-2-ylethan-1-one thiosemicarbazone. Synthesis, crystal structures and antiproliferative activity of zinc(II) complexes

The complexes [ZnCl 2(HFoTsc) · H 2O], [Zn(FoTsc) 2], [ZnCl 2(HAcTsc) · H 2O] and [Zn(AcTsc) 2], where HFoTsc and HAcTsc is pyridine-2-carbaldehyde thiosemicarbazone and (1 E)-1-pyridin-2-ylethan-1-one thiosemicarbazone respectively, have been prepared and structurally characterized by means vibrational, and NMR ( 1H and 13C) spectroscopy. The crystal structures of the complexes [ZnCl 2(HFoTsc) · H 2O], [Zn(AcTsc) 2] and [ZnCl 2(HAcTsc) · H 2O] have been determined by X-ray crystallography. The metal co-ordination geometry of [ZnCl 2(HFoTsc) · H 2O] and [ZnCl 2(HAcTsc) · H 2O] is described as distorted square pyramidal and the two complexes are self-assembled via π → π stacking interactions and intermolecular hydrogen bonds. In these two cases molecular recognition of the hydrogen bonds leads to aggregation and a supramolecular assembly of infinite two-dimensional network. The metal co-ordination geometry of [Zn(AcTsc) 2] is described as distorted octahedral configuration in a trans-N(2)- cis-N(1)- cis-S configuration. HFoTsc and HAcTsc and the zinc complexes have been evaluated for antiproliferative activity in vitro against the cells of two human cancer cell lines: MCF-7 (human breast cancer cell line), T24 (bladder cancer cell line) and a mouse fibroblast L-929 cell line. The cytotoxic activity shown by these compounds indicates that coupling of HFoTsc and HAcTsc to Zn(II) metal center result in metallic complexes with important biological properties since they display IC 50 values in a μM range similar to or better than that of the antitumor drug cis-platin and are considered as agents with potential antitumor activity candidates for further stages of screening in vitro and/or in vivo.

Terpyridine Zn(II), Ru(III), and Ir(III) Complexes: The Relevant Role of the Nature of the Metal Ion and of the Ancillary Ligands on the Second-Order Nonlinear Response of Terpyridines Carrying Electron Donor or Electron Acceptor Groups

Coordination of 4'-(C6H4-p-X)-2,2':6',2''-terpyridines [X = NO2, NBu2, (E)-CH=CH-C6H4-p-NBu2, (E,E)-(CH=CH)2-C6H4-p-NMe2] to Zn(II), Ru(III), and Ir(III) metal centers induces a significant enhancement of the absolute value of the second-order nonlinear optical (NLO) response of the terpyridine, measured by means of both electric field induced second harmonic generation and solvatochromic methods. By varying the nature of the metal center, the enhanced second-order NLO response shifts from positive to negative. Such a shift is controlled by electronic charge-transfer transitions, such as metal-to-ligand or ligand-to-metal transitions, in addition to the intraligand charge transfer. The enhancement generated by coordination is also controlled by the chelation effect and by fine-tuning of the ancillary ligands.

Oxazoline chemistry IX. Synthesis and characterisation of the first Zinc oxazoline dialkyldithiocarbamato complexes; X-ray crystal structure determinations of [Zn(S 2CNR 2-κ 2S) 2(2-R′-4,4-R″-2-oxazoline-κ 1N)] (R = R′ = Me, R″ = H; R = Et, R′ = Me, Et or Ph, R″ = H; R = Bz; R′ = R″ = Me)

The synthesis and characterisation (NMR, IR, X-ray diffraction and elemental analysis) of a series of zinc dialkyldithiocarbamato complexes incorporating a monodentate oxazoline ligand are described. These compounds represent the first known examples of oxazolines that are bound to a [Zn(S 2CNR 2) 2] fragment. The syntheses of the title materials involves the treatment of solutions of [Zn(S 2CNR 2) 2] n (R = Me: 1, Et: 2 or benzyl (Bz): 3) with oxazolines (L) of general formula 2-R′-4,4-R″-2-oxazoline (R′ = Me, Et or Ph; R″ = H or Me). The compounds can be isolated in yields ranging from 17% to 82% and all of the complexes are assumed to be mononuclear species of general formula [Zn(S 2CNR 2-κ 2 S) 2(L)]. The nature of the bonding in several examples has been further elucidated in the solid-state by single crystal X-ray diffraction; specifically the cases of R = Me, L = 2-methyl-2-oxazoline: 12; R = Et, L = 2-R′-2-oxazoline: R′ = Me: 9, Et: 10 or Ph: 11 and R = Bz, L = 2,4,4-trimethyl-2-oxazoline: 16. The structurally characterised materials contain two chelating dialkyldithiocarbamato groups and a single oxazoline ligand bound through the N-atom. The disposition of donor atoms around the formally Zn(II) metal centre is best described as distorted trigonal bipyramidal. Complex 16 is the first known N-donor complex of 3 to be fully characterised. In case of the common commercial oxazoline, viz. 4,4-dimethyl-2-phenyl-2-oxazoline, none of the zinc compounds tested forms a stable complex. Some aspects of the steric and electronic effects on oxazoline adduct formation within this series of complexes is discussed. The relationship of these new compounds to other structurally similar and industrially relevant zinc dialkyldithiocarbamate complexes is also detailed.

Synthesis and characterization of new coordination polymers generated from oxadiazole-containing ligands and IIB metal ions

The coordination chemistry of the oxadiazole-containing rigid bidentate ligands 2,5-bis(4-pyridyl)-1,3,4-oxadiazole (L1) and 2,5-bis(3-pyridyl)-1,3,4-oxadiazole (L2) with inorganic IIB metal salts have been investigated. Five new coordination polymers ( 1–5) were prepared by solution reactions and fully characterized by infrared spectroscopy, elemental analysis, and single-crystal X-ray diffraction. Cd(L1) 2(CH 3CN) 2](ClO 4) 2 · (CH 3CN) 2 ( 1) crystallized in the monoclinic space group P2 1/ c, a = 8.4028(5) Å, b = 21.3726(13) Å, c = 10.5617(7) Å, β = 95.1200(10)°, and Z = 2. In the solid state, it adopts an infinite two-dimensional polymeric structural motif with effective cross section of ca. 14.31 × 14.31 Å. Cd(L2)(H 2O)(NO 3) 2 ( 2) crystallized in the monoclinic space group Ia, a = 7.1203(5) Å, b = 22.2475(15) Å, c = 20.2652(16) Å, β = 90.6080(10)°, and Z = 8. In the solid state, the two Cd(II) centers are connected to each other by L2 ligands and bridging nitrates into a two-dimensional network. [ZnCl 2(L1)] ( 3) and [HgI 2(L1)] · CH 3CN ( 4) crystallized in the monoclinic crystal system ( 3: P2 1/ c, a = 5.3702(3) Å, b = 20.4800(11) Å, c = 12.4093(7) Å, β = 94.7930(10)°, and Z = 4; 4: P2/ n, a = 17.2733(11) Å, b = 5.2173(3) Å, c = 20.4069(13) Å, β = 102.8690(10)°, and Z = 4). In the solid state, Zn(II) and Hg(II) metal centers are connected to each other by L1 ligands into a zigzag chain motif. Compound 5 (HgBr 2(L2) is different from 3 and 4, monoclinic, P2(1)/ n, a = 5.470(4) Å, b = 16.271(13) Å, c = 16.486(12) Å, β = 93.197(15)°, and Z = 4) adopts a novel one-dimensional helical chain motif which resulted from the relative different coordinated orientation of the two N-donors on L2 ligand.

Purification, substrate range, and metal center of AtzC: the N-isopropylammelide aminohydrolase involved in bacterial atrazine metabolism.

N-Isopropylammelide isopropylaminohydrolase, AtzC, the third enzyme in the atrazine degradation pathway in Pseudomonas sp. strain ADP, catalyzes the stoichiometric hydrolysis of N-isopropylammelide to cyanuric acid and isopropylamine. The atzC gene was cloned downstream of the tac promoter and expressed in Escherichia coli, where the expressed enzyme comprised 36% of the soluble protein. AtzC was purified to homogeneity by ammonium sulfate precipitation and phenyl column chromatography. It has a subunit size of 44,938 kDa and a holoenzyme molecular weight of 174,000. The K(m) and k(cat) values for AtzC with N-isopropylammelide were 406 micro M and 13.3 s(-1), respectively. AtzC hydrolyzed other N-substituted amino dihydroxy-s-triazines, and those with linear N-alkyl groups had higher k(cat) values than those with branched alkyl groups. Native AtzC contained 0.50 eq of Zn per subunit. The activity of metal-depleted AtzC was restored with Zn(II), Fe(II), Mn(II), Co(II), and Ni(II) salts. Cobalt-substituted AtzC had a visible absorbance band at 540 nm (Delta epsilon = 84 M(-1) cm(-1)) and exhibited an axial electron paramagnetic resonance (EPR) signal with the following effective values: g((x)) = 5.18, g((y)) = 3.93, and g((z)) = 2.24. Incubating cobalt-AtzC with the competitive inhibitor 5-azacytosine altered the effective EPR signal values to g((x)) = 5.11, g((y)) = 4.02, and g((z)) = 2.25 and increased the microwave power at half saturation at 10 K from 31 to 103 mW. Under the growth conditions examined, our data suggest that AtzC has a catalytically essential, five-coordinate Zn(II) metal center in the active site and specifically catalyzes the hydrolysis of intermediates generated during the metabolism of s-triazine herbicides.

A tetranuclear heterobimetallic square formed from the cooperative ligand binding properties of square planar and tetrahedral metal centers.

Reaction of Rh(I) and Zn(II) metal centers with a ligand containing salicylaldiminato and thioether-phosphine moieties resulted in the formation of a tetranuclear heterobimetallic molecular square. The directionality required to form these structures is imparted by both the tetrahedral and square planar metal centers acting in concert with one another.

Solvent effects in tandem mass spectrometry: mechanistic studies indicating how a change in solvent conditions and pH can dramatically alter CID spectra.

Dramatically different CID (collision-induced dissociation) spectra are obtained when the complex [Zn(dien-glucose)](+) is electrosprayed from acidic and basic solutions. To understand this peculiar phenomenon, an in-depth mechanistic study was performed on one of the product ions that is present when the initial complex is diluted in basic solution but absent when the complex is diluted with acidic solution. On the basis of the results of this study, the differences in the CID spectra can be rationalized by the fact that the complex electrosprayed from basic solution was kinetically trapped, with the deprotonation site distal from the metal center. Under acidic conditions, the deprotonation site is at a hydroxyl group coordinated to the metal ion. A variety of experiments support this hypothesis. The studies herein underscore the importance of using identical solvent conditions when comparing sets of CID spectra. The data also highlight a very interesting phenomenon involving deprotonation of a hydroxyl group, which was several atoms away from the Zn(II) metal center.

Conformational studies of Zn-ligand-hexose diastereomers using ion mobility measurements and density functional theory calculations

Ion mobility studies and density functional theory calculations were used to study the structures of [Zn/diethylenetriamine/Hexose/Cl] + complexes in an effort to probe differences in the three-dimensional conformations. This information allows us to gain insight into the structure of these complexes before collisional activation, which is the first step in understanding the stereoselective dissociations observed under collisionally activated conditions. The collision cross sections obtained from the ion mobility measurements showed that the mannose structure is more compact than the galactose and glucose complexes, respectively. Using density functional theory, candidate structures for each of the experimentally observed complexes were generated. Two criteria were used to determine the most likely structures of these complexes before activation: (1) The allowed relative energies of the molecules (between 0–90 kJ/mol) and (2) collision cross section agreement (within 2%) between the theoretically determined structures and the experimentally determined cross section. It was found that the identity of the monosaccharide made a difference in the overall conformation of the metal–ligand–monosaccharide complex. For glucose and galactose, metal coordination to O(6) was found to be favorable, with the monosaccharide occupying the 4C 1 chair conformation, while for mannose, O(2) metal coordination was found with the monosaccharide in a B 3,0 conformation. Coordination numbers varied between four and six for the Zn(II) metal centers. Given these results, it appears that the stereochemistry of the monosaccharide influences the conformation and metal coordination sites of the Zn(II)/monosaccharide/dien complex. These differences may influence the dissociation products observed under collisionally activated conditions.

ZnCl 2(4,4′-bpy): a one-dimensional coordination polymer with two isomorphic phases

Two isomorphic phases of one-dimensional coordination polymer ZnCl 2(4,4′-bpy) were prepared from hydrothermal reactions of ZnCl 2 and 4,4′-bipyridyl (4,4′-bpy). α-ZnCl 2(4,4′-bpy) ( I) crystallizes in the monoclinic space group C2/c, with a=15.821(3) Å, b=5.109(1) Å, c=14.612(3) Å, β=110.33(3)°, V=1107.5(4) Å 3, Z=4. β-ZnCl 2(4,4′-bpy) ( II) crystallizes in the orthorhombic space group Pnma, with a=17.349(3) Å, b=12.407(2) Å, c=5.114(1) Å, V=1100.8(3) Å 3, Z=4. The crystal structures of the two compounds are closely related to each other. In both phases, the Zn metal center is tetrahedrally coordinated to two terminal Cl and two bridging 4,4′-bpy. Each 4,4′-bpy acts as a bifunctional ligand and is bonded to two Zn to give rise to a Zn(4,4′-bpy) zig-zag chain. The extended Hückel (EH) calculations were performed on both structures to analyze the bonding. The solubility of the title compounds was also tested.

Complexation of Bis-2-(benzylideneamino)Phenol to Cobalt(II) and Zinc(II), and their Spectroscopic Studies

A bis-Schiff base of bis-2-(benzylideneamino)phenol (SB1) was synthesized via condensation reaction ofterephthaldehyde and 2-aminophenol in ethanol. SB1 was then reacted with respective MX2 salt (M = Co & Zn,X = Cl & OAc) in the ligand to metal ratio of 1:2 under refluxing condition in ethanolic KOH solution for sixhours. All synthesized complexes were characterized using FT-IR and UV-vis spectroscopy. The formation ofcomplexes with Co and Zn was indicated by the shifts observed from the IR peaks and λmax of the UV absorptionbands for the C=N bond. The IR peak at 1621 cm-1 in SB1 was shifted to around 1638 and 1619 cm-1 afterforming its complexes with Co and Zn, respectively. The absorption band of C=N bond was blue shifted fromλmax of 384 nm to 307 nm in Co(II) complex, whereas this band was red-shifted to 389 nm in the Zn(II) complex.Therefore, SB1 was confirmed to coordinate with the Co(II) and Zn(II) metal centres via the imine nitrogen.