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Thiosemicarbazones are biologically active substances whose structural formula is formed by an azomethine, an hydrazine, and a thioamide fragments, to generate a R2C=N–NR–C(=S)–NR2 backbone. These compounds often act as ligands to generate highly stable metal–organic complexes. In certain experimental conditions, however, thiosemicarbazones undergo reactions leading to the cleavage of the chain. Sometimes, the breakage involves desulfurization processes. The present work summarizes the different chemical factors that influence the desulfurization reactions of thiosemicarbazones, such as pH, the presence of oxidant reactants or the establishment of redox processes as those electrochemically induced, the effects of the solvent, the temperature, and the electromagnetic radiation. Many of these reactions require coordination of thiosemicarbazones to metal ions, even those present in the intracellular environment. The nature of the products generated in these reactions, their detection in vivo and in vitro, together with the relevance for the biological activity of these compounds, mainly as antineoplastic agents, is discussed. [ABSTRACT FROM AUTHOR]

The reaction of silver acetate and silver nitrate with the new phosphinethiosemicarbazone ligand 2-(2-(diphenylphosphino)benzylidene)-N-ethylthiosemicarbazone (HLPEt) gave rise to the complexes [Ag(LPEt)][sub4]∙2MeOH (1) and [Ag[sub2](LPEt)(HLPEt)][sub2]∙(NO3)2 (3). Slow crystallization of the mother liquors obtained from the synthesis of 1 and 3 afforded suitable crystals of [Ag[sub2](LPEt)(HLPEt)][sub2](CH[sub3]COO)[sub2]∙6MeOH (2) and [Ag[sub2](LPEt)(HLPEt)][sub2](NO[sub3])[sub2]∙2MeOH∙2H[sub2]O (4), respectively. Complexes 2 and 4 are tetranuclear silver clusters displaying a similar Ag[sub4]S[sub4]P[sub4] core, but containing different sizes, conformations for the Ag[sub4]S[sub4] metallacycles, and crystal packings. The four complexes are strongly luminescent in methanol solutions. A comparison between the emission bands of compounds 1-4 lead us to conclude that the luminescence is notably affected by the charge and the counterion of the cluster. [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 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 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 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 reaction of silver acetate with a phosphinothiosemicarbazone ligand, HLPPh, yielded the tetranuclear silver compound [Ag4(LPPh)4] · 2MeOH (1), which after recrystallization results in the cocrystallization of two different silver clusters, [Ag4(LPPh)4]a- [Ag4(LPPh)4]b · 8MeOH (2). The factors involved in the assembly of tetranuclear compounds derived from thiosemicarbazone ligands and the structural differences between the two clusters are analyzed herein. Additionally, HLPPh and complex 1 exhibit photoluminescence in solution at room temperature. [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]

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]

The oxygen-evolving complex (OEC) is the native enzyme that catalyzes the oxidation of water in natural photosynthesis. Two new classes of manganese cluster complexes of formula Ba2Mn2L¹2(H3L¹)2(CH3OH)41 and Mn4L²6Cl2 2 were prepared (H4L¹ = N,N0-(ethane-1,2-diyl)bis (2-hydroxybenzamide); L² = methyl picolinimidate) and characterized by standard techniques including microanalysis, IR spectroscopy, ESI spectrometry, and magnetic susceptibility measurements. X-ray diffraction studies of these complexes revealed (i) a box-type structure for 1 formed by two redox-active manganese(III) ions and two barium(II) ions connected by two bridging bisamido-bisphenoxy ligand molecules; and (ii) a planar-diamond array for Mn4N6 cluster 2 where the picolinimidates act as chelating ligands through the two nitrogen atoms. The ability of 1 and 2 to split water has been studied by means of water photolysis experiments. In these experiments, the oxygen evolution was measured in aqueous media in the presence of p-benzoquinone (acting as the hydrogen acceptor), the reduction of which was followed by UV-spectroscopy. The relevant photolytic activity found for 1 is in contrast to the inactivity of 2 in the photolytic experiments. This different behavior is discussed on the basis of the structure of the biomimetic models and the proposed reaction mechanism for this process supported by DFT calculations. [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 use of perchlorate ancillary ligands with relatively low coordination ability nicely illustrates a rich structural diversity in thiosemicarbazone copper(II) (TSC-Cu(II)) systems. Five compounds with the formulae {[CuL(OH2)][CuL(OClO3)]}n·nClO4·2nH2O (1), [{CuL(OClO3)}2] (2), [Cu(HL)(OClO3)2(OH2)] H2O (3), [Cu2L3](ClO4)·2H2O (4) and [Cu(HL)(NCS)](ClO4) (5) are studied, where HL = pyridine-2-carbaldehyde thiosemicarbazone. The crystal structures show the presence of polynuclear species in the compounds containing an anionic L− thiosemicarbazone ligand: 1D chains (1) and dinuclear (2 and 4) arrangements. Meanwhile, complexes with a neutral HL ligand give rise to mononuclear entities (3 and 5). The chemical and structural parallelism of these complexes with the analogous TSC–Cu(II)–nitrate system is discussed. The thiocyanate ligand in compound 5 comes from partial desulfurization of the thiosemicarbazone in acid medium and results in an incommensurate modulated structure. On the other hand, it is proposed that [Cu2L3]+ species present in 4 could play a possible role in desulfurization reactions. Experimental evidence and theoretical calculations support a proposed mechanism for the partial desulfurization of preformed TSC-Cu(II) entities in basic and physiological media to yield the [CuL(LCN)] (HLCN = pyridine-2-ylmethylene(hydrazine carbonitrile)) and [{CuL(SH)}2)] compounds. [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]

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]

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]

We have developed an easy and flexible synthetic methodology to obtain lipid chains containing methanothiosulfonate terminal groups with the aim to attach them to natural proteins as functional groups. There are many proteins found in nature that are modified by lipids, and this is a key part of their function. For example, the prion protein is attached to the plasma membrane via a glycosylphosphatidylinositol (GPI) anchor, and this protein is thought to be the causative agent in diseases such as bovine spongiform encephalopathy (BSE; “mad cow disease”) and the human equivalent Creutzfeldt-Jakob disease. However, production of large amounts of protein in bacteria results in proteins that lack these lipid modifications. The lipid chains containing methanothiosulfonate terminal groups that we have synthesized here can be attached to these proteins through the thiol contained in the side chain of the cysteine residue, which can be incorporated into the protein sequence at the desired position. [ABSTRACT FROM AUTHOR]

Abstract: The neutral single-stranded monohelicate [Pd(HL)]·2(CH3CN) (1) aggregates in the solid state to give an infinite 1D supramolecular chain through either the cooperative action of hydrogen bonding and π-stacking interactions or by aromatic π-stacking alone. [Copyright &y& Elsevier]

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]

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 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]

In this work, four manganese(II) complexes derived from the ligands H 2 L1-H 2 L4, that incorporate dansyl or tosyl fluorescent dyes, have been investigated in term of their antioxidant properties. Two of the manganese(II) complexes have been newly prepared using the asymmetric half-salen ligand H 2 L2 and the thiosemicarbazone ligand H 2 L3. The four organic strands and the manganese complexes have been characterized by different analytical and spectroscopic techniques. The study of the antioxidant behaviour of these two new complexes and other two fluorophore-labelled analogues was tested in SH-SY5Y neuroblastoma cells. These four model complexes 1 – 4 were found to protect cells from oxidative damage in this human neuronal model, by reducing the release of reactive oxygen species. Complexes 1 – 4 significantly improved cell survival, with levels between 79.1 ± 0.8% and 130.9 ± 4.1%. Moreover, complexes 3 and 4 were able to restore the mitochondrial membrane potential at 1 μM, with 4 reaching levels higher than 85%, similar to the percentages obtained by the positive control agent cyclosporin A. The incorporation of the fluorescent label in the complexes allowed the study of their ability to enter the human neuroblastoma cells by confocal microscopy. Four manganese complexes that incorporate fluorescent dyes can protect cells from oxidative damage, induce a decrease in reactive oxygen species (ROS) release and ameliorate the mitochondrial function in a human neuronal model. The incorporation of the fluorescent labels allows the study of the ability of the complexes to enter cells. [Display omitted] • Four manganese complexes with fluorescent dyes behave like catalytic antioxidants. • Complexes improve cell survival against oxidative stress in a human neuronal model. • Complexes induce a significant decrease in reactive oxygen species release. • Two of the complexes can restore the mitochondrial membrane potential. • Fluorescent labels allow the study of the ability of the complexes to enter cells. [ABSTRACT FROM AUTHOR]

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]

Abstract: In this work we studied and compared the physicochemical properties of perfluorinated (sodium perfluoroheptanoate, C7FONa, and perfluorooctanoate, C8FONa) and hydrogenated (sodium octanoate, C8HONa, decanoate, C10HONa, and dodecanoate, C12HONa) amphiphiles. First, we determined their Krafft points to study the solubility and appropriate temperature range of micellization of these compounds. The critical micelle concentration (cmc) and ionization degree of micellization (β) as a function of temperature (T) were estimated from conductivity data. Plots of cmc vs T appear to follow the typical U-shaped curve with a minimum . The results show that the surfactants with CF2/CH2 ratio of 1.5 between alkyl chains (C12HONa–C8FONa and C10HONa–C7FONa) have nearly the same minimum value for cmc against temperature. The comparison between the cmc of hydrogenated amphiphiles and the corresponding perfluorinated amphiphiles must be done at this point. Thermodynamic functions of micellization were obtained by applying different theoretical models and choosing the one that best fit our experimental data. Although perfluorinated and hydrogenated amphiphiles present similar thermodynamic behavior, we have found a variation of 1.3 to 1.7 in the CF2/CH2 ratio, which did not remain constant with temperature. In the second part of this study the apparent molar volumes and adiabatic compressibilities were determined from density and ultrasound velocity measurements. Apparent molar volumes at infinite dilution presented the ratio 1.5 between alkyl chains again. However, apparent molar volumes upon micellization for sodium perfluoroheptanoate indicated a different aggregation pattern. [Copyright &y& Elsevier]

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]