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This review aims to analyze the emerging number of studies on biological media that describe the unexpected effects of different natural bioactive antioxidants. Hormetic effects, with a biphasic response depending on the dose, or activities that are apparently non-dose-dependent, have been described for compounds such as resveratrol, curcumin, ferulic acid or linoleic acid, among others. The analysis of the reported studies confirms the incidence of these types of effects, which should be taken into account by researchers, discarding initial interpretations of imprecise methodologies or measurements. The incidence of these types of effects should enhance research into the different mechanisms of action, particularly those studied in the field of basic research, that will help us understand the causes of these unusual behaviors, depending on the dose, such as the inactivation of the signaling pathways of the immune defense system. Antioxidative and anti-inflammatory activities in biological media should be addressed in ways that go beyond a mere statistical approach. In this work, some of the research pathways that may explain the understanding of these activities are revised, paying special attention to the ability of the selected bioactive compounds (curcumin, resveratrol, ferulic acid and linoleic acid) to form metal complexes and the activity of these complexes in biological media. [ABSTRACT FROM AUTHOR]

A [4+4] double-stranded cadmium dihelicate was afforded from an easily accessible thiosemicarbazone ligand; its crystal structure reveals the assembly of two enantiomers into dihelicate pairs, these pairs being further connected into infinite linear chains. [ABSTRACT FROM AUTHOR]

The ligand design factors that may influence the isolation of metallosupramolecular helicates or mesocates still deserve to be investigated. In this sense, dinuclear nickel(II), copper(II) and zinc(II) compounds were obtained by electrochemical synthesis using a family of five Schiff base ligands, H2Ln (n = 1–5), derived from bisphenylmethane and functionalized with bulky tert-butyl groups in the periphery and ethyl groups in the spacer. Six of the new complexes were characterized by X-ray crystallography, thus demonstrating that the helicate structure is predominant in the solid state. 1H NMR studies were performed for the zinc complexes to analyze if the helical architecture of the metal complexes is retained in solution. These studies reveal that the presence of a tert-butyl group in the ortho position with respect to the OH group is an essential factor identified for the existence of a helicate conformation in solution. [ABSTRACT FROM AUTHOR]

In the present work, we report a neutral dinuclear copper(II) complex, [Cu2(L1)(OH)], derived from a new [N,O] donor Schiff base ligand L1 that was formed after the endogenous hydroxylation of an initial carbamate Schiff base H2L coordinated with copper ions in an electrochemical cell. The copper(II) complex has been fully characterized using different techniques, including X-ray diffraction. Direct current (DC) magnetic susceptibility measurements were also performed at variable temperatures, showing evidence of antiferromagnetic behavior. Its catalase-like activity was also tested, demonstrating that this activity is affected by temperature. [ABSTRACT FROM AUTHOR]

The study of the inherent factors that influence the isolation of one type of metallosupramolecular architecture over another is one of the main objectives in the field of Metallosupramolecular Chemistry. In this work, we report two new neutral copper(II) helicates, [Cu2(L1)2]·4CH3CN and [Cu2(L2)2]·CH3CN, obtained by means of an electrochemical methodology and derived from two Schiff-based strands functionalized with ortho and para-t-butyl groups on the aromatic surface. These small modifications let us explore the relationship between the ligand design and the structure of the extended metallosupramolecular architecture. The magnetic properties of the Cu(II) helicates were explored by Electron Paramagnetic Resonance (EPR) spectroscopy and Direct Current (DC) magnetic susceptibility measurements. [ABSTRACT FROM AUTHOR]

The design of artificial helicoidal molecules derived from metal ions with biological properties is one of the objectives within metallosupramolecular chemistry. Herein, we report three zinc helicates derived from a family of bisthiosemicarbazone ligands with different terminal groups, Zn2(LMe)2∙2H2O 1, Zn2(LPh)2∙2H2O 2 and Zn2(LPhNO2)23, obtained by an electrochemical methodology. These helicates have been fully characterized by different techniques, including X-ray diffraction. Biological studies of the zinc(II) helicates such as toxicity assays with erythrocytes and interaction studies with proteins and oligonucleotides were performed, demonstrating in all cases low toxicity and an absence of covalent interaction with the proteins and oligonucleotides. The in vitro cytotoxicity of the helicates was tested against MCF-7 (human breast carcinoma), A2780 (human ovarian carcinoma cells), NCI-H460 (human lung carcinoma cells) and MRC-5 (normal human lung fibroblasts), comparing the IC50 values with cisplatin. We will try to demonstrate if the terminal substituent of the ligand precursor exerts any effect in toxicity or in the antitumor activity of the zinc helicates. [ABSTRACT FROM AUTHOR]

A dinuclear Pb(ii) mesocate has been prepared with an unprecedented four-coordinated kernel in which the Pb(ii) lone pair is stereochemically active. This is the first time that this effect has been observed in a supramolecular Pb(ii) helicate or meso-helicate. [ABSTRACT FROM AUTHOR]

The mechanism of carbamate activation promoted by different metal ions has been explored in this work. The reaction of the carbamate ligand H2L with chloride metal salts (M = Ni, Cu, Zn, Cd) leads to the coordination of the metal ions to the ligand, causing hydrolysis of the systems. This self-immolation process results in mononuclear dihydrazone complexes, carbon dioxide and the release of alcohol species from the pendant groups of the carbamate ligand. The conditions under which this process occurs have been studied in detail. [ABSTRACT FROM AUTHOR]

Abstract: A series of Mn(III) nitrate complexes have been synthesized from dianionic hexadentate Schiff bases obtained by condensation of 3-methoxy-2-hydroxybenzaldehyde with different diamines. The complexes have been characterised by elemental analysis, ESI mass spectrometry, IR and 1H NMR spectroscopy. Magnetic studies and molar conductivity measurements were also performed. Complexes [MnL1(H2O)2]2·2NO3·2CH3OH (1), [MnL2(H2O)2]2·2NO3·2CH3OH (2) and [MnL5(H2O)2]2·2NO3·6H2O (5) were crystallographically characterised. The X-ray structures show an octahedral geometry around the metal with the Schiff base in the equatorial plane acting as tetradentate and water or methanol molecules in the axial positions. The octahedron entities are linked in pairs by μ-aquo bridges between neighbouring axial water molecules and also by π–π stacking interactions, establishing dimeric and polymeric structures. Nitrate anions are accommodated in the cavities of the framework and form hydrogen bonds with the aqua ligands and the methanol or crystal water, leading to infinite supramolecular aggregates of the complexes. Comparison of chloride, perchlorate and nitrate complexes indicate that the nature of the anions is the key factor directing the structural topologies. [Copyright &y& Elsevier]

Abstract: The interaction of manganese(II) carboxylate salts [Mn(O2CR)2, where R=ethane, pentane] with H2L1 [N,N′-bis(3-methoxy-2-hydroxybenzaldehyde)-1,2-phenylenediamine] and H2L2 [N,N′-bis(3-ethoxy-2-hydroxybenzaldehyde)-1,2-phenylenediamine] was studied. MnL1(O2CEt)(H2O) (1), MnL1(O2CPe n )(H2O) (2), MnL2(O2CEt)(H2O)2 (3) and MnL2(O2CPe n )(H2O)2 (4) were isolated and thoroughly characterised by elemental analysis, FAB mass spectrometry, infrared and 1H NMR spectroscopy, magnetic susceptibility measurements, molar conductivities, and cyclic and normal pulse voltammetry. Compounds 1 and 2 were crystallographically characterised revealing a tetragonally elongated octahedral geometry for the manganese coordination sphere and also a dimeric nature through μ-aqua bridges. Complexes 1–4 behave as efficient peroxidase mimics in the presence of the water-soluble trap ABTS, probably due to their ease to coordinate the substrate molecule. A correlation between rhombicity of the complexes and peroxidase activity has also been established. [Copyright &y& Elsevier]

A unique case of a grid-of-mesocates sequentially assembled by supramolecular cobalt(ii) meso-helical units connected through hydrogen bonding is reported. [ABSTRACT FROM AUTHOR]

Water reduction can be electrochemically promoted by zinc under very mild conditions, as demonstrated by the formation of the complex [Zn(H2O)6][Zn3(L)3(μ3-O)], whose anion consists of a Zn3O4cluster incorporating a μ3-oxo anion. [ABSTRACT FROM AUTHOR]

A cobalt(II) thiosemicarbazonate mesocate has been structurally characterized as an unexpected mixture of conformational and linkage isomers. Moreover, we have shown that the absence of a nitrogen atom in the spacer of the helicand ligand H2La, enables the assembly of an achiral mesohelical complex in the case of Co(ll) ions. [ABSTRACT FROM AUTHOR]

The condensation of 3-methoxy-2-hydroxybenzaldehyde and the diamines 1,2-diphenylendiamine, 1,2-diamine-2-methylpropane and 1,3-propanediamine yielded the dianionic tetradentate Schiff base ligands N,N′-bis(2-hydroxy-4-methoxybenzylidene)-1,2-diphenylendiimine (H2L1), N,N′-bis(2-hydroxy-4-methoxybenzylidene)-1,2-diamino-2-methylpropane (H2L2) and N,N′-bis(2-hydroxy-4-methoxybenzylidene)-1,3-diaminopropane (H2L3) respectively. The organic compounds H2L1 and H2L2 have been characterized by elemental analysis, IR, 1H and 13C NMR spectroscopies and mass spectrometry electrospray (ES). The crystal structure of H2L2 in solid state, solved by X-ray crystallography, is highly conditioned in the solid state by two N-H•••N intramolecular interactions. The synthesis of three new manganese(III) complexes 1–3, incorporating these ligands, H2L1–H2L3, and dicyanamide (DCA), is reported. The complexes 1–3 have been physicochemically characterized by elemental analysis, IR and paramagnetic 1H NMR spectroscopy, ESI mass spectrometry, magnetic moment at room temperature and conductivity measurements. Complex 1 has been crystallographically characterized. The X-ray structure shows the self-assembly of the Mn(III)-Schiff base-DCA complex through µ-aquo bridges between neighbouring axial water molecules and also by π-π stacking interactions, establishing a dimeric structure. The manganese complexes were also tested as peroxidase mimics for the H2O2-mediated reaction with the water-soluble trap ABTS, showing complexes 1-2 relevant peroxidase activity in contrast with 3. The rhombicity around the metal ion can explain this catalytic behaviour. [ABSTRACT FROM AUTHOR]

The effect of the metal ion and ligand design on the enantioselectivity and linkage isomerization of neutral cobalt and zinc bisthiosemicarbazone metallohelicates has been investigated in this work. The electrochemical synthesis has afforded the enantioselective formation of chirally pure cobalt helicates, and the ΛΛ isomer of a single enantiomer has been crystallized as only product for the cobalt methyl-substituted thiosemicarbazone helicate. Interestingly linkage isomers have been formed from zinc ethyl-substituted thiosemicarbazone helicate enantiomers for the first time. The co-existence of these isomers has been evaluated from the point of view of both experimental results and computational calculations. [ABSTRACT FROM AUTHOR]

The ability to organize functional molecules into higher dimensional arrays with well-defined spatial relationships between the components is one of the major goals in supramolecular chemistry. We report here a new route for the preparation of supramolecular boxes, incorporating two types of metal ions: (i) alkali-metal ions, which induce the supramolecular architecture and essentially play a structural role in the final compounds; (ii) manganese(III) ions, which are redox-active systems and give functionality to the new cages. Our results evidence that the size of the cavity inside the box can be tuned depending on the alkali metal used, a characteristic that gives this new family of compounds the potential to act selectively against different substrates. These compounds behave as active catalysts for disproportionation of H2O2 or for water photolysis, but they catalyze neither catecholase reaction nor peroxidase action upon using bulky organic substrates. [ABSTRACT FROM AUTHOR]

Abstract: The first [5+5] coordination isomer of a zinc helical dimer derived from a pentadentate bisthiosemicarbazone Schiff base ligand was obtained by means of a new route. This compound was synthesised using a template procedure, spectroscopically characterised and recrystallised in a 1:1 v/v dichloromethane/acetonitrile mixture. The geometry showed by this compound is new for well-known dimer zinc complexes derived from pentadentate thiosemicarbazones and suggests that the experimental procedure could be an important factor in defining the stereochemistry of the metal atoms in such helical dimers. [Copyright &y& Elsevier]

The electrochemical oxidation of a tin plate in the presence of an acetonitrile suspension of the ligand bis-(4-N-methylthiosemicarbazone)-2,6-diacetylpyridine, H4DAPTsz-Me, yields the complex Sn(H2DAPTsz-Me)(H2O)2 (1). Recrystallisation of 1 in a methanol/acetone solution leads us to isolate yellow crystals of [Sn(H2DAPTsz-Me)(CH3OH)2] · CH3OH (2), structurally characterised. To the best of our knowledge, 2 is the first neutral Sn(II) complex derived from a pentadentate thiosemicarbazone Schiff base ligand. This complex shows a distorted pentagonal bipyramidal geometry for Sn(II), being the metal surrounded by the N3S2 donor set of the bideprotonated ligand [H2DAPTsz-Me]2−. This compound self-assembles into a 3D network through intermolecular hydrogen bonds. [Copyright &y& Elsevier]

A method to modulate the strength of the superexchange coupling interaction in dinuclear helical assemblies based on the coordination preferences of the metal centres is described. [ABSTRACT FROM AUTHOR]

A series of phosphino-thiosemicarbazone gold(I) dinuclear complexes obtained by two different synthetic procedures have been prepared. All the compounds have been spectroscopically characterized including single crystal X ray diffraction analysis in some of cases. [Au 2 (HL 1 )Cl 2 (1), [Au 2 (HL 2 ) 2 Cl 2 (2) and [Au 2 (HL 3 ) 2 Cl 2 (3) have been prepared by chemical synthesis using a gold(III) salt as precursor; while [Au 2 (L 1 ) 2 (4), [Au 2 (L 2 ) 2 ∙2CH 3 CN (5) and [Au 2 (L 3 ) 2 (6) have been isolated from an electrochemical synthesis (HLn = 2-[2-(diphenylphosphanyl)-benzylidene]- N -R-thiosemicarbazone; HL1: R = methyl, HL2: R = methoxyphenyl, HL3: R = nitrophenyl). The in vitro cytotoxic activity of these gold(I) complexes was tested against some human tumor cell lines: HeLa 229 (cervical epithelial carcinoma), MCF-7 (ovarian adenocarcinoma), NCI-H460 (non-small-cell lung cancer) and MRC5 (normal human lung fibroblast), and the IC 50 values compared with those of cisplatin. The neutral methyl-substituted complexes 1 and 4 and methoxyphenyl 5 displayed significant cytotoxic activities in all investigated cancer cell lines, being 1 and 4 the most effective. The ability of complexes 1 and 4 to induce cell death by apoptosis in Hela 229 was also investigated by fluorescence microscopy using the apoptotic DNA fragmentation as marker. These results indicated that the inhibition of cell proliferation is mainly due to an apoptotic process. In order to obtain more information about the mechanism of action of these metallocompounds, the interactions of complexes 1 and 4 with the thioredoxin reductase (TrxR) enzyme were analyzed. Both complexes exhibited a strong inhibition of the thioredoxin reductase activity. Unlabelled Image • Gold(I) complexes obtained by traditional and a electrochemical procedures were studied. • Electrochemical synthesis makes available a new arsenal of neutral gold(I) compounds. • Complexes containing the methyl group are the most cytotoxic against the investigated cancer cell lines. • These complexes exhibit a strong inhibition of the thioredoxin reductase activity. [ABSTRACT FROM AUTHOR]