One of the major public health problems worldwide is cancer followed by a significant number of deaths due to the resistance developed by bacteria or protozoan to the currently employed treatments. This generates an immediate need to develop drugs to treat these afflictions (illnesses, diseases). It has recently been identified that tumor cell, bacteria or protozoa are quite sensitive to oxidative stress induced by the same drugs. Due to this, it is important to develop new drugs to attend them, in this case, by using metals to increase the concentration of oxidative species. In the present work, the ligand 2,9-diformyl-4,7-diphenyl-1,10-phenanthroline and its corresponding coordination compounds with essential metals such as iron(II), cobalt( II), nickel(II), copper(II) and zinc(II) were synthesized. The electrochemical study shows that these compounds present three redox processes, all of them associated to the ligand. The compounds have shown inhibitory activity in vitro against human neuroblastoma CHP-212 cells, Escherichia coli and trophozoites of Entamoeba histolytica HM1: IMSS. It has been found that the inhibitory activity of the compounds studied is related to the first reduction process of the ligand. The correlation between the inhibitory activity and the red ox potential was linear. The inhibitory activity in CHP-212 increased with the increase of the compounds' redox potential values, in contrast with the behavior observed in Escherichia coli, where the compounds with lowest redox potential values have had significantly higher inhibitory activity. Many of these coordination compounds have shown a higher inhibitory activity than those typically used in the treatment of cancer (cisplatin). The next step is to prove these compounds in vitro against healthy cells in order to verify its selectivity or cytotoxicity in these systems.

Schiff bases derived from o-hydroxyaldehydes present keto and enol tautomeric forms; the relative equilibrium between these two tautomers depending on the particular aldehyde the Schiff bases is derived from. Thus benzaldehyde produces a stable enol tautomer, while a naphthaldehyde produces a mixture of keto and enol tautomers. The energy difference between these tautomers is very small (∼5kJ/mol) and therefore close to current precision limits of ab initio and DFT based quantum calculations. NMR spectroscopy results, which allows for the determination of the stable structure when one tautomer is prevalent, can be very difficult to interpret when both tautomers are present. We calculate energy differences between the tautomers and demonstrate that the precision of current DFT calculations is not sufficient to predict the most stable structure. On the other hand, DFT calculations of the NMR chemical shifts (using the GIAO technique) can properly interpret the spectroscopy results allowing the characterization of the experimentally present tautomers and the estimation of the relative abundance of each when both are present.

The dithiosalicylidenediamine Ni II complexes [Ni(L)] (R=tBu, R'=CH2C(CH3)2CH2 1, R'=C6H4 2; R=H, R'=CH2C(CH3)2CH2 3, R'=C6H4 4) have been prepared by transmetallation of the tetrahedral complexes [Zn(L)] (R=tBu, R'=CH2C(CH3)2CH2 7, R'=C6H4 8; R=H, R'=CH2C(CH3)2CH2 9, R'=C6H4 10) formed by condensation of 2,4-di-R-thiosalicylaldehyde with diamines H2N-R'-NH2 in the presence of Zn II salts. The diamagnetic mononuclear complexes [Ni(L)] show a distorted square-planar N2S2 coordination environment and have been characterized by 1H- and 13C NMR and UV/Vis spectroscopies and by single-crystal X-ray crystallography. Cyclic voltammetry and coulombic measurements have established that complexes 1 and 2, incorporating tBu functionalities on the thiophenolate ligands, undergo reversible one-electron oxidation processes, whereas the analogous redox processes for complexes 3 and 4 are not reversible. The one-electron oxidized species, 1+ and 2+, can be generated quantitatively either electrochemically or chemically with 70 % HClO4. EPR and UV/Vis spectroscopic studies and supporting DFT calculations suggest that the SOMOs of 1+ and 2+ possess thiyl radical character, whereas those of 1(py)2 + and 2(py)2 + possess formal Ni III centers. Species 2+ dimerizes at low temperature, and an X-ray crystallographic determination of the dimer [(2)2](ClO4)2.2 CH2Cl2 confirms that this dimerization involves the formation of a S-S bond (S...S=2.202(5) A).

The binuclear [Ni(L)Fe(CO)3], , and trinuclear [Ni(L){Fe(CO)3}2], , complexes adopt unusual structural motifs whereby Fe(CO)3 units bind to [Ni(L)] via mu2-S bridging modes, C=N imine pi-bonds and potential Ni-Fe bonding interactions.

The binuclear [Ni(L)Fe(CO)(3)], 1, and trinuclear [Ni(L){Fe(CO)(3)}(2)], 2, complexes adopt unusual structural motifs whereby Fe(CO)(3) units bind to [Ni(L)] via mu(2)-S bridging modes, C=N imine pi-bonds and potential Ni-Fe bonding interactions.

ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTNew Thiolate−Cobalt(II) Complexes for Catalytic Chain Transfer Polymerization of Methyl MethacrylateWenxin Wang, Philip A. Stenson, Armando Marin-Becerra, Jonathan McMaster, Martin Schröder, Derek J. Irvine, David Freeman, and Steven M. HowdleView Author Information School of Chemistry, University of Nottingham, University Park, Nottingham, NG7 2RD, U.K., and Uniqema R&D Department, The Wilton Research Centre, Wilton, Redcar, TS10 4RF, U.K. Cite this: Macromolecules 2004, 37, 18, 6667–6669Publication Date (Web):August 12, 2004Publication History Received15 April 2004Revised20 July 2004Published online12 August 2004Published inissue 1 September 2004https://doi.org/10.1021/ma049267zCopyright © 2004 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views489Altmetric-Citations29LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (46 KB) Get e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Catalysts,Organic compounds,Polymerization,Polymers,Radical polymerization Get e-Alerts

The structures of four neutral binuclear Zn-II complexes of the Schiff-base macrocycles formed by the [2 + 2] template condensation of 2,6-diformyl-4-methylphenol with 1,2-diaminoethane: [H2L1], 1,3-diaminopropane: [H2L2], 1,4-diaminobutane: [H2L3] and 2,6-diacetyl-4-methylphenol with 1,2-diaminoethane: [H2L4] have been determined. The complexes [Zn-2(L-1)(OAc)(2)].2CHCl(3),[Zn-2(L-2)(OAc)(2)].2CHCl(3) and [Zn-2(L-4)Cl-2] each contain two five coordinate Zn-II centres with each metal ion bound to the N2O2 donor set of the macrocyclic ligand and to an anion molecule. Two different coordination environments are observed in [Zn-2(L-3)(mu-OAc)(OAc)].CHCl3 which contains both a five- and a six-coordinate Zn-II centre, with one acetate bridging two metal ions and a monodentate acetate bound to the six-coordinate Zn-II ion. Significantly, the reaction of pre-formed macrocyclic ligands [H4L2](PF6)(2) and [H4L4](PF6)(2) with Zn(OAc)(2).2H(2)O affords [Zn-2(L-2)(mu-OAc)](PF6).MeCN and [Zn(H2L4)(MeCN)](PF6)(2), respectively. The former shows two five-coordinate Zn-II centres in which an acetate bridges both metal ions. In the latter complex the macrocyclic ligand binds only one five-coordinate Zn-II ion with a molecule of MeCN bound at an apical position.

Reaction of dichlorotris(triphenylphosphine) ruthenium(II) [RuCl(2)(PPh(3))(3)] with 1,8-bis(2-pyridyl)-3,6-dithiaoctane (pdto), a (N(2)S(2)) tetradentate donor, yields a new compound [Ru(pdto)(PPh(3))Cl]Cl (1), which has been fully characterized. (1)H and (31)P NMR studies of 1 in acetonitrile at several temperatures show the substitution of both coordinated chloride and triphenylphosphine with two molecules of acetonitrile, as confirmed by the isolation of the complex [Ru(pdto)(CH(3)CN)(2)]Cl(2) (2). Cyclic voltammetric and spectroelectrochemical techniques allowed us to determine the electrochemical behavior of compound 1. The substitution of the chloride and triphenylphosphine by acetonitrile molecules in the Ru(II) coordination sphere of compound 1 was also established by electrochemical studies. The easy substitution of this complex led us to use it as starting material to synthesize the substituted phenanthroline coordination compounds with (pdto) and ruthenium(II), [Ru(pdto)(4,7-diphenyl-1,10-phenanthroline)]Cl(2).4H(2)O (3), [Ru(pdto)(1,10-phenanthroline)]Cl(2).5H(2)O (4), [Ru(pdto)(5,6-dimethyl-1,10-phenanthroline)]Cl(2).5H(2)O (5), [Ru(pdto)(4,7-dimethyl-1,10-phenanthroline)]Cl(2).3H(2)O (6), and [Ru(pdto)(3,4,7,8-tetramethyl-1,10-phenanthroline)]Cl(2).4H(2)O (7). These compounds were fully characterized, and the crystal structure of 4 was obtained. Cyclic voltammetric and spectroelectrochemical techniques allowed us to determine their electrochemical behavior. The electrochemical oxidation processes in these compounds are related to the oxidation of ionic chlorides, and to the reversible transformation from Ru(II) to Ru(III). On the other hand, a single reduction process is associated to the reduction of the substituted phenanthroline in the coordination compound. The E(1/2) (phen/phen(-)) and E(1/2) (Ru(II)/Ru(III)) for the compounds (3-7) were evaluated, and, as expected, the modification of the substituted 1,10-phenanthrolines in the complexes also modifies the redox potentials. Correlations of both electrochemical potentials with pK(a) of the free 1,10-phenathrolines, lambda(max) MLCT transition band, and chemical shifts of phenanthrolines in these complexes were found, possibly as a consequence of the change in the electron density of the Ru(II) and the coordinated phenanthroline.

Multi-frequency EPR spectroscopy on 61Ni-labelled samples of [Ni2(L)]3+ confirms extensive charge-delocalisation between the Ni(III) centre and thiolate donors in the Ni(II)Ni(III) complex.

The dinuclear [CoIIICoIII] complexes [Co2(L1)(μ-OAc)(OAc)(NH3)](PF6)2 and [(Co2(L2)2(μ-OAc)](PF6), incorporating the rare Co(μ-SR)2Co moiety associated with Schiff-base co-ligands, are protected by bridging μ-OAc− units situated within a domed cavity formed by the complexes; increasing the steric bulk of the ligand, as in [L3]2−, affords the mononuclear species [Co(L3)(OAc)]. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The dinuclear [Co III Co III ] complexes [Co 2 (L 1 )(μ‐OAc)(OAc)(NH 3 )](PF 6 ) 2 and [(Co 2 (L 2 ) 2 (μ‐OAc)](PF 6 ), incorporating the rare Co(μ‐SR) 2 Co moiety associated with Schiff‐base co‐ligands, are protected by bridging μ‐OAc − units situated within a domed cavity formed by the complexes; increasing the steric bulk of the ligand, as in [L 3 ] 2− , affords the mononuclear species [Co(L 3 )(OAc)]. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The tetranuclear cluster [Zn(2)L(mu-OH)](2)[ClO4](2) . 2H(2)O (L = dianion of the condensation product of 1,3-diaminopropane and 2,6-diformyl-4-methylthiophenol) shows two unique dinuclear Zn-II units linked by two Ir-hydroxy bridges; the structure of the Cu-II complex [Cu(2)L(HOMe)(2)](NO3)]PF6 shows square-pyramidal coordination at the Cu centres with two thiolate bridges and two terminal N-donors, with a Cu ... Cu separation of 3.264(2) Angstrom.

The synthesis of a range of new compartmental macrocyclic complexes based on 2,6-diformyl and -diketo phenol groups is described. The metal-free ligands have been prepared and structurally characterised for the first time, and this has led to the synthesis of novel cubane and platinum-group metal complexes. The synthesis of related dithiophenolato-bridged compartmental complexes of Ni-II Cu-II and Zn-II has been achieved and the relevance of these species to metalloproteins is discussed.