Main group metal complexes of semicarbazones and thiosemicarbazones. A structural review

Synthesis and theoretical study of a mixed-ligand indium(III) complex for fabrication of β-In2S3 thin films via chemical vapor deposition

Two new heteroleptic indium aminothiolate compounds [InClSC2H4N(Me)SC2H4]3[1] and [InSC2H4N(Me)SC2H4(C8H5F3NO)] [2] were synthesized by in situ salt metathesis reaction involving indium trichloride, aminothiol, and N,O-β-heteroarylalkenol ligands. The complexes were subsequently purified and thoroughly characterized by nuclear magnetic resonance (NMR) analysis, elemental studies, mass spectroscopy, and X-ray diffraction single crystal analysis that showed a trigonal bipyramidal coordination of In(III) in both complexes. Thermogravimetric analysis of [1] revealed a multistep decomposition pathway and the formation of In2S3 at 350 °C, which differed from the pattern of [2] due to the lower thermal stability of [1]. Compound [2] exhibited a three-step decomposition process, resulting in the formation of In2S3 at 300 °C. The Chemical Vapor Deposition (CVD) experiment involving compound [2] was conducted on the FTO substrate, resulting in the production of singular-phase In2S3 deposits. A comprehensive characterization of these deposits, including crystal structure analysis via X-ray diffraction (XRD), and surface topography examination through scanning electron microscopy (SEM) has been completed. The presence of In-S units was also supported by the Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and energy dispersive spectroscopy (EDS) of the as-deposited films. Moreover, the electronic structure and thermal properties of compound [2] were investigated through DFT calculations. Electron density localization analysis revealed that the highest occupied molecular orbital (HOMO) exhibited dense concentration at the aminothiolate moiety of the complex, while the lowest unoccupied molecular orbital (LUMO) predominantly resided at the N,O-β-heteroarylalkenolate ligand. Furthermore, our computational investigation has validated the formation of indium sulfide by elucidating an intermediate state, effectively identified through EI-MS analysis, as one of the plausible pathways for obtaining In2S3. This intermediate state comprises the aminothiolate ligand (LNS) coordinated with indium metal.

Palladium(II) Complexes of 4-Phenyl-3-thiosemicarbazone Ligands: Insights Into Cytotoxic Properties and Mode of Cell Death

Reactions between sodium tetrachloropalladate and 2- (or 4-) substituted 4-phenyl-3-thiosemicarbazone ligands (HLR), with various electron-donating and electron-withdrawing substituents (R = OCH3, NO2, and Cl), afford square-planar complexes of the general formula [Pd(LR)2]. Ground-state geometry optimization and the vibrational analysis of cis- and trans-isomers of the complexes were carried out to get an insight into the stereochemistry of the complexes. Natural bond orbital analysis was used to analyze how the nature of the substituent affects the natural charge of the metal center, the type of hybridization, and the strength of the M-N and M-S bonds. Using spectrophotometry, the stability of the complexes, and their DNA binding abilities were assessed. The Pd(II) complexes showed moderate cytotoxicity against MCF-7 and Caco-2 cell lines, two of the assessed malignant cell lines, resulting in all known cell death types, including early apoptotic bodies and late apoptotic vacuoles as well as evident necrotic bodies.

Exploring spin states and ligand field splitting in metal complexes: a theoretical analysis of spin-orbital interactions and magnetic properties

Metal complexes are pivotal in diverse fields due to their wide array of functionalities, including magnetism, conductivity, and photoresponsiveness. These functionalities are intricately linked to the phenomenon of ligand field splitting, yet controlling the magnitude of this splitting within metal complexes presents a significant challenge. This study aims to address this challenge by developing a novel 2D spectrochemical series, integrating two critical parameters: metal ions and ligands. Employing the DV-Xα molecular orbital method, we directly calculated ligand field splitting width, enabling a detailed assessment of energy splitting trends. Our results reveal that the magnitude of ligand field splitting, encompassing 17 metal types and 29 ligand types, can be precisely controlled. This represents a significant advancement over traditional spectrochemical series, such as those proposed by R. Tsuchida, which predominantly focus on either ligands or metals in isolation. Additionally, our study extends to the calculation of spin states in these metal complexes, contributing valuable insights for the development of magnetic materials. We demonstrate that the relative ligand field splitting and spin polarization can be used to predict spin states, offering a new perspective in material design and functionality. These findings not only enhance our understanding of ligand field splitting in metal complexes but also provide a comprehensive framework for predicting their electronic and magnetic properties, paving the way for innovative applications in material science and coordination chemistry.

Role of the auxiliary ligand in determining the genotoxicity and mode of cell death of thiosemicarbazone Pd(II) complexes

A series of Pd(II) complexes of the general formula [PdX(NNS)] (X = Cl, Br, I, NCS and phenyl-tetrazole-thiolato; NNS = 2-quinolinecarboxyaldehyde-N4-phenylthiosemicarbazone) was tested against four malignant cell lines for their antiproliferative properties and the outcomes were compared to those seen in normal mouse splenocytes. Various auxiliary ligands were substituted in order to investigate the impact of the character of the ligand on the cytotoxicity of this class of Pd(II) complexes. The iodo complex was the most cytotoxic compound towards the Caco-2 cell line in this study. The improved apoptosis and necrosis cell modes were in accordance with the fragmentation results of DNA, which revealed increased fragmentation terminals, especially in isothiocyanate and tetrazole-thiolato complexes. After 24 hours, at half the IC50 of each complex, the complex-treated cells exhibited considerable genotoxicity when compared to the corresponding non-treated control especially in the case of isothiocyanate and tetrazole-thiolato complexes.

Green approach to synthesize novel thiosemicarbazide complexes, characterization; DNA-methyl green assay and in-silico studies against DNA polymerase

A thiosemicarbazide derivative as (E)-4-ethyl-1-(1-(naphthalen-1-yl) ethylidene) thiosemicarbazide (HAN) was synthesized then characterized to prepare [Co(HAN)Cl2·(H2O)2], [Ni(HAN)Cl2·(H2O)2]. H2O, and [Cd(HAN)Cl2] complexes. According to spectral and analytical data we could confirm the neutral bidentate mode of bonding via (C]S) and (C]N) groups to form 1:1 M ratio within the three complexes. The octahedral geometry was suggested for Co(II) and Ni(II) complexes according to electronic transitions assigned to 4T1g → 4T1g(P)(ʋ2) and 4T1g → 4A2g(F)(ʋ3) and 3A2g → 3T1g(P,υ3) and 3A2g → 3T1g(F,υ2), respectively. The values of nephelauetic ratio (β) in the ligand field parameters detect the ionic nature of new M-L bonds. The molecular ion peaks appeared in the mass spectra of two selected complexes confirming their molecular formulae. The conductometric study was performed for Cd(II) ion solution during variable additions of HAN to calculate association and formation constant of Cd(II)-HAN complex. DFT/B3LYP method was used to optimize the structures of the compounds and confirm the binding mode of the ligand. The distribution of C(5) = N(17) and C(13) = S(19) groups asserts their priority in coordination. Hirshfeld crystal properties were obtained via normalized contact distance (dnorm) and shape index in which the nitrogen atoms act as the best contact points in crystal packing. The biological screening was carried out against microbial strains as well as methyl green/DNA test. In vitro, the superiority of the ligand was clearly recorded in its biological effectiveness. In silico methods were implemented to confirm the activity of the ligand and to recognize the interaction features. The bioavailability, pharmacokinetics and drug-likeness were evaluated via Swiss-link. The data detect the ability of the ligand to penetrate barrier of brain (BBB) but not absorbed in gastrointestinal tract. Pharmit link and molecular docking were utilized to investigate the interaction of HAN with 1bna, 425d and 2k4l proteins. The best intercalation with protein pockets was observed with 2k4l protein, and searching the MolPort library detects a drug analog of MolPort-002-894-701. Finally, the results suggest the biological efficiency of the ligand, which may be asserted by specialists through intensive in-vivo studies.

Desulfurization of thiosemicarbazones: the role of metal ions and biological implications

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.

Recent advances in the synthesis and utility of thiazoline and its derivatives

Thiazolines and their derivatives hold significant importance in the field of medicinal chemistry due to their promising potential as pharmaceutical agents. These molecular entities serve as critical scaffolds within numerous natural products, including curacin A, thiangazole, and mirabazole, and play a vital role in a wide array of physiological reactions. Their pharmacological versatility encompasses anti-HIV, neurological, anti-cancer, and antibiotic activities. Over the course of recent decades, researchers have extensively explored and developed analogs of these compounds, uncovering compelling therapeutic properties such as antioxidant, anti-tumor, anti-microbial, and anti-inflammatory effects. Consequently, thiazoline-based compounds have emerged as noteworthy targets for synthetic endeavors. In this review, we provide a comprehensive summary of recent advancements in the synthesis of thiazolines and thiazoline-based derivatives, along with an exploration of their diverse potential applications across various scientific domains.

The synthesis and structural properties of a chlorido-bis-{N-[(4-meth-oxy-phen-yl)imino]-pyrrolidine-1-carboxamide}-zinc(II) (aceto-nitrile)-trichlorido-zincate coordination complex

The title complex, [ZnCl(C12H15N3O2)2][ZnCl3(CH3CN)], was synthesized and its structure was fully characterized through single-crystal X-ray diffraction analysis. The complex crystallizes in the ortho-rhom-bic system, space group Pbca (61), with a central zinc atom coordinating one chlorine atom and two pyrrolidinyl-4-meth-oxy-phenyl azoformamide ligands in a bidentate manner, utilizing both the nitro-gen and oxygen atoms in a 1,3-heterodiene (N=N-C=O) motif for coordinative bonding, yielding an overall positively (+1) charged complex. The complex is accompanied by a [(CH3CN)ZnCl3]- counter-ion. The crystal data show that the harder oxygen atoms in the heterodiene zinc chelate form bonding inter-actions with distances of 2.002 (3) and 2.012 (3) Å, while nitro-gen atoms are coordinated by the central zinc cation with bond lengths of 2.207 (3) and 2.211 (3) Å. To gain further insight into the inter-molecular inter-actions within the crystal, Hirshfeld surface analysis was performed, along with the calculation of two-dimensional fingerprint plots. This analysis revealed that H⋯H (39.9%), Cl⋯H/H⋯Cl (28.2%) and C⋯H/H⋯C (7.2%) inter-actions are dominant. This unique crystal structure sheds light on arrangement and bonding inter-actions with azo-formamide ligands, and their unique qualities over similar semicarbazone and azo-thio-formamide structures.

5-Nitrofuryl-Containing Thiosemicarbazone Gold(I) Compounds: Synthesis, Stability Studies, and Anticancer Activity

This work describes the synthesis of four gold(I) [AuClL] compounds containing chloro and biologically active protonated thiosemicarbazones based on 5-nitrofuryl (L=HSTC). The stability of the compounds in dichloromethane, DMSO, and DMSO/culture media solutions was investigated by spectroscopy, cyclic voltammetry, and conductimetry, indicating the formation overtime of cationic monometallic [Au(HTSC)(DMSO)]± or [Au(HTSC)2 ]± , and/or dimeric species. Neutral [{Au(TSC)}2 ] species were obtained from one of the compounds in dichlomethane/n-hexane solution and characterized by X-ray crystallography revealing a Au-Au bond, and deprotonated thiosemicarbazone (TSC). The cytotoxicity of the gold compounds and thiosemicarbazone ligands was evaluated against selected cancer cell lines and compared to that of Auranofin. Studies of the most stable, cytotoxic, and selective compound on a renal cancer cell line (Caki-1) demonstrated its relevant antimigratory and anti-angiogenic properties, and preferential accumulation in the cell nuclei. Its mode of action seems to involve interaction with DNA, and subsequent cell death via apoptosis.

Encapsulation and Biological Activity of Hesperetin Derivatives with HP-β-CD

The encapsulation of insoluble compounds can help improve their solubility and activity. The effects of cyclodextrin encapsulation on hesperetin's derivatives (HHSB, HIN, and HTSC) and the physicochemical properties of the formed complexes were determined using various analytical techniques. The antioxidant (DPPH•, ABTS•+ scavenging, and Fe2+-chelating ability), cytotoxic, and antibacterial activities were also investigated. The inclusion systems were prepared using mechanical and co-evaporation methods using a molar ratio compound: HP-β-CD = 1:1. The identification of solid systems confirmed the formation of two inclusion complexes at hesperetin (CV) and HHSB (mech). The identification of systems of hesperetin and its derivatives with HP-β-CD in solutions at pHs 3.6, 6.5, and 8.5 and at various temperatures (25, 37 and 60 °C) confirmed the effect of cyclodextrin on their solubility. In the DPPH• and ABTS•+ assay, pure compounds were characterized by higher antioxidant activity than the complexes. In the FRAP study, all hesperetin and HHSB complexes and HTSC-HP-β-CD (mech) were characterized by higher values of antioxidant activity than pure compounds. The results obtained from cytotoxic activity tests show that for most of the systems tested, cytotoxicity increased with the concentration of the chemical, with the exception of HP-β-CD. All systems inhibited Escherichia coli and Staphylococcus aureus.

Synthesis, Characterization, and Anticancer Activity of Phosphanegold(i) Complexes of 3-Thiosemicarbano-butan-2-one Oxime

Four novel phosphanegold(I) complexes of the type [Au(PR3)(DMT)].PF6 (1-4) were synthesized from 3-Thiosemicarbano-butan-2-one oxime ligand (TBO) and precursors [Au(PR3)Cl], (where R = methyl (1), ethyl (2), tert-butyl (3), and phenyl (4)). The resulting complexes were characterized by elemental analyses and melting point as well as various spectroscopic techniques, including FTIR and (1H, 13C, and 31P) NMR spectroscopy. The spectroscopic data confirmed the coordination of TBO ligands to phosphanegold(I) moiety. The solution chemistry of complexes 1-4 indicated their stability in both dimethyl sulfoxide (DMSO) and a mixture of EtOH:H2O (1:1). In vitro cytotoxicity of the complexes was evaluated relative to cisplatin using an MTT assay against three different cancer cell lines: HCT116 (human colon cancer), MDA-MB-231 (human breast cancer), and B16 (murine skin cancer). Complexes 2, 3, and 4 exhibited significant cytotoxic effects against all tested cancer cell lines and showed significantly higher activity than cisplatin. To elucidate the mechanism underlying the cytotoxic effects of the phosphanegold(I) TBO complexes, various assays were employed, including mitochondrial membrane potential, ROS production, and gene expression analyses. The data obtained suggest that complex 2 exerts potent anticancer activity against breast cancer cells (MDA-MB-231) through the induction of oxidative stress, mitochondrial dysfunction, and apoptosis. Gene expression analyses showed an increase in the activity of the proapoptotic gene caspase-3 and a reduction in the activity of the antiapoptotic gene BCL-xL, which supported the findings that apoptosis had occurred.

Ga(III) pyridinecarboxylate complexes: potential analogues of the second generation of therapeutic Ga(III) complexes?

A series of novel Ga(III)-pyridine carboxylates ([Ga(Pic)3]·H2O (GaPic; HPic = picolinic acid), H3O[Ga(Dpic)2]·H2O (GaDpic; H2Dpic = dipicolinic acid), [Ga(Chel)(H2O)(OH)]2·4H2O (GaChel; H2Chel = chelidamic acid) and [Ga(Cldpic)(H2O)(OH)]2 (GaCldpic; H2Cldpic = 4-chlorodipicolinic acid)) have been synthesized by simple one-step procedure. Vibrational spectroscopy (mid-IR), elemental analysis, thermogravimetric analysis and X-ray diffraction confirmed complexes molecular structure, inter and intramolecular interactions and their influence to spectral and thermal properties. Moreover, complex species speciation was described in Ga(III)-HPic and Ga(III)-H2Dpic systems by potentiometry and 1H NMR spectroscopy and mononuclear complex species were determined; [Ga(Pic)2]+ (logβ021 = 16.23(6)), [Ga(Pic)3] (logβ031 = 20.86(2)), [Ga(Dpic)2]- (logβ021 = 15.42(9)) and [Ga(Dpic)2(OH)]2- (logβ-121 = 11.08(4)). To confirm the complexes stability in 1% DMSO (primary solvent for biological testing), timescale 1H NMR spectra were measured (immediately after dissolution up to 96 h). Antimicrobial activity evaluated by IC50 (0.05 mM) is significant for GaDpic and GaCldpic against difficult to treat and multi-resistant P. aeruginosa. On the other hand, the GaPic complex is most effective against Jurkat, MDA-MB-231 and A2058 cancer cell lines and significantly also decreases the HepG2 cancer cells viability at 75 and 100 μM concentrations in a relatively short time (up to 48 h). In addition, fluorescence measurements have been used to elucidate bovine serum albumin binding activity between ligands, Ga(III) complexes and bovine serum albumin.

A new series of bioactive Mo(V)2O2S2-based thiosemicarbazone complexes: Solution and DFT studies, and antifungal and antioxidant activities

This paper deals with the synthesis, characterization, and studies of biological properties of a series of 5 coordination compounds based on binuclear core [Mo(V)2O2S2]2+ with thiosemicarbazones ligands bearing different substituents on the R1 position of the ligand. The complexes are first studied using MALDI-TOF mass spectrometry and NMR spectroscopy to determine their structures in solution in relation to single-crystal X-Ray diffraction data. In a second part, the antifungal and antioxidative activities are explored and the high potential of these coordination compounds compared to the uncoordinated ligands is demonstrated for these properties. Finally, DFT calculation provides important support to the solution studies by identifying the most stable isomers in each [Mo2O2S2]2+/Ligand system, while the determination of HUMO and LUMO levels is performed to explain the antioxidative properties of these systems.

Bioactive Thiosemicarbazone Coordination Metal Complexes: Synthesis, Characterization, Theoretical analysis, Biological Activity, Molecular Docking and ADME analysis

Mn(II) and Cu(II) complexes having the formula [M(L)2 ]X2 of ligand, i. e., 2-acetyl-5-methylfuranthiosemicarbazone were synthesized. Various analytical and spectroscopic techniques described the structure of synthesized complexes. Molar conductance confirmed the electrolytic nature of the complexes. The theoretical study of the complexes explained the structural property and reactivity. The chemical reactivity, interaction and stability of the ligand and metal complexes were studied with the help of global reactivity descriptors. MEP analysis was used to investigate the charge transfer in the ligand. The biological potency was evaluated against two bacteria and two fungi. Complexes demonstrated superior inhibitory action to ligand. The inhibitory effect was also checked at the atomic scale using molecular docking, which confirmed the experimental results. Cu(II) complex was shown to have the most inhibitory effect in experimental and theoretical studies. To check the bioavailability and drug-likeness, ADME analysis was also done.

The Effect of Metal Ions (Fe, Co, Ni, and Cu) on the Molecular-Structural, Protein Binding, and Cytotoxic Properties of Metal Pyridoxal-Thiosemicarbazone Complexes

Thiosemicarbazones and their transition metal complexes are biologically active compounds and anticancer agents with versatile structural properties. In this contribution, the structural features and stability of four pyridoxal-thiosemicarbazone (PLTSC) complexes with Fe, Co, Ni, and Cu were investigated using the density functional theory and natural bond orbital approach. Special emphasis was placed on the analysis of the donor atom-metal interactions. The geometry of compounds and crystallographic structures were further examined by Hirshfeld surface analysis, and the main intermolecular interactions were outlined. It has been shown that the geometry and the number of PLTSC units in the structure determine the type and contribution of the specific interactions. The binding of all four complexes to bovine and human serum albumin was investigated through spectrofluorometric titration. The dependency of the thermodynamic parameters on the present metal ion and geometry was explained by the possible interactions through molecular docking simulations. The binding of complexes to DNA, as one of the possible ways the compounds could induce cell death, was examined by molecular docking. The cytotoxicity was measured towards HCT116, A375, MCF-7, A2780, and MCF5 cell lines, with Cu-PLTSC being the most active, as it had the highest affinity towards DNA and proteins.

In vitro anti-proliferative, and in silico ribonucleotide reductase and pharmacokinetics studies of heteroleptic silver(I), nickel(II) and copper(II) complexes of 4-methyl-3-thiosemicarbazones and ibuprofen

OBJECTIVES

The present research focuses on the in vitro anti-proliferative, and in silico ribonucleotide reductase and pharmacokinetics studies of twelve heteroleptic metal complexes of the general formulae [Ag(L^1-4)(ibu)] (1-4) and [M(L^1-4)(ibu)₂] (5-12), where L^1-4 = 2-(1-(4-substitutedphenyl)ethylidene)-N-methylhydrazinecarbothioamide, ibu = non-steroidal anti-inflammatory drug (ibuprofen), and M = Cu(II) and Ni(II).

METHODS

Various spectroscopic techniques were used to authenticate the structure of the synthesized complexes. UV-Vis and cyclic voltammetry techniques were used to analyse the stability and the reducing ability of the complexes. In vitro anti-proliferative studies by MTT assay, apoptotic behaviour and cellular uptake studies were investigated followed by the in silico interaction with ribonucleotide reductase (RNR) enzyme.

RESULTS

The spectral studies predicted distorted tetrahedral geometry around silver(I) ion and distorted octahedral geometry around nickel(II) and copper(II) ions. The reducing ability of the copper(II) complexes was analysed using ascorbic acid by UV-Vis and cyclic voltammetry techniques, which authenticate the reducing ability of the complexes and the possible interactions within the cells. The in vitro anti-proliferative activity of the synthesized complexes against three cancerous (estrogen positive (MCF-7), estrogen negative (MDA-MB-231) and pancreatic (PANC-1)) and one normal (MCF-10a) cell lines by MTT assay showed enhanced activity for copper(II) complexes 11 and 12 containing the hydrophobic substituents. The apoptotic and cellular uptake studies showed that the complex 12 is readily taken up by PANC-1 cell lines and induces ROS-mediated mitochondrial and caspase-dependent apoptosis. The in silico studies indicated hydrogen bonding, hydrophobic and π-pair (π-π, π-σ and π-cation) interactions between the complexes and the ribonucleotide reductase (RNR) enzyme. The in silico pharmacokinetics studies of the complexes predicted the drug-likeness characteristics of the complexes.

CONCLUSION

The synthesized complexes are found to be less toxic to normal cells and inhibit the growth of cancerous cells by inducing mitochondrial-mediated and caspase dependent apoptotic pathway in PANC-1 cells.

Insights into the role of the cobalt(III)-thiosemicarbazone complex as a potential inhibitor of the Chikungunya virus nsP4

Chikungunya virus (CHIKV) is the causative agent of chikungunya fever, a disease that can result in disability. Until now, there is no antiviral treatment against CHIKV, demonstrating that there is a need for development of new drugs. Studies have shown that thiosemicarbazones and their metal complexes possess biological activities, and their synthesis is simple, clean, versatile, and results in high yields. Here, we evaluated the mechanism of action (MOA) of a cobalt(III) thiosemicarbazone complex named [CoIII(L1)2]Cl based on its in vitro potent antiviral activity against CHIKV previously evaluated (80% of inhibition on replication). Furthermore, the complex has no toxicity in healthy cells, as confirmed by infecting BHK-21 cells with CHIKV-nanoluciferase in the presence of the compound, showing that [CoIII(L1)2]Cl inhibited CHIKV infection with the selective index of 3.26. [CoIII(L1)2]Cl presented a post-entry effect on viral replication, emphasized by the strong interaction of [CoIII(L1)2]Cl with CHIKV non-structural protein 4 (nsP4) in the microscale thermophoresis assay, suggesting a potential mode of action of this compound against CHIKV. Moreover, in silico analyses by molecular docking demonstrated potential interaction of [CoIII(L1)2]Cl with nsP4 through hydrogen bonds, hydrophobic and electrostatic interactions. The evaluation of ADME-Tox properties showed that [CoIII(L1)2]Cl presents appropriate lipophilicity, good human intestinal absorption, and has no toxicological effect as irritant, mutagenic, reproductive, and tumorigenic side effects.

Exploring the Biological Properties of Zn(II) Bisthiosemicarbazone Helicates

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(L^Me)₂∙2H₂O 1, Zn₂(L^Ph)₂∙2H₂O 2 and Zn₂(L^PhNO2)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.

Thiosemicarbazonecopper/Halido Systems: Structure and DFT Analysis of the Magnetic Coupling

Experimental magnetic studies performed on the [{CuLX}2] system (HL = pyridine-2-carbaldehyde thiosemicarbazone, X = Cl−, Br−, I−) point to the larger electronegativity in X, the lower magnitude of the antiferromagnetic interactions. In order to confirm this and other trends observed and to dip into them, computational studies on the [{CuLX}2] (X = Cl− (1), I− (2)) compounds are here reported. The chemical and structural comparisons have been extended to the compounds obtained in acid medium. In this regard, chlorido ligands yield the [Cu(HL)Cl2]∙H2O (3) complex, whose crystal structure shows that thiosemicarbazone links as a tridentate chelate ligand to square pyramidal Cu(II) ions. On the other hand, iodido ligands provoke the formation of the [{Cu(H2L)I2}2] (4) derivative, which contains pyridine-protonated cationic H2L+ as a S-donor monodentate ligand bonded to Cu(I) ions. Crystallographic, infrared and electron paramagnetic resonance spectroscopic results are discussed. Computational calculations predict a greater stability for the chlorido species, containing both the neutral (HL) and anionic (L−) ligand. The theoretical magnetic studies considering isolated dimeric entities reproduce the sign and magnitude of the antiferromagnetism in 1, but no good agreement is found for compound 2. The sensitivity to the basis set and the presence of interdimer magnetic interactions are debated.

Estradiol-Based Salicylaldehyde (Thio)Semicarbazones and Their Copper Complexes with Anticancer, Antibacterial and Antioxidant Activities

A series of novel estradiol-based salicylaldehyde (thio)semicarbazones ((T)SCs) bearing (O,N,S) and (O,N,O) donor sets and their Cu(II) complexes were developed and characterized in detail by ¹H and ¹³C nuclear magnetic resonance spectroscopy, UV-visible and electron paramagnetic resonance spectroscopy, electrospray ionization mass spectrometry and elemental analysis. The structure of the Cu(II)-estradiol-semicarbazone complex was revealed by X-ray crystallography. Proton dissociation constants of the ligands and stability constants of the metal complexes were determined in 30% (v/v) DMSO/H₂O. Estradiol-(T)SCs form mono-ligand complexes with Cu(II) ions and exhibit high stability with the exception of estradiol-SC. The Cu(II) complexes of estradiol-TSC and its N,N-dimethyl derivative displayed the highest cytotoxicity among the tested compounds in MCF-7, MCF-7 KCR, DU-145, and A549 cancer cells. The complexes do not damage DNA according to both in vitro cell-free and cellular assays. All the Cu(II)-TSC complexes revealed significant activity against the Gram-positive Staphylococcus aureus bacteria strain. Estradiol-TSCs showed efficient antioxidant activity, which was decreased by complexation with Cu(II) ions. The exchange of estrone moiety to estradiol did not result in significant changes to physico-chemical and biological properties.

(Z)-2-(1-(5-Methyl-1-(4-nitrophenyl)-1H-1,2,3-triazol-4-yl)ethylidene)-N-phenylhydrazine-1-carbothioamide

Reaction of equimolar equivalents of 1-(5-methyl-1-(4-nitrophenyl)-1H-1,2,3-triazol-4-yl)ethan-1-one (1) and N-phenylhydrazinecarbothioamide (2) in boiling ethanol containing a catalytic amount of concentrated hydrochloric acid for 4 h gave (Z)-2-(1-(5-methyl-1-(4-nitrophenyl)-1H-1,2,3-triazol-4-yl)ethylidene)-N-phenylhydrazine-1-carbothioamide (3) with 88% yield. The structure of 3 was established using single-crystal X-ray diffraction and magnetic resonance spectroscopy.

Two Synthetic Approaches to Coinage Metal(I) Mesocates: Electrochemical versus Chemical Synthesis

We report two different approaches to isolate neutral and cationic mesocate-type metallosupramolecular architectures derived from coinage monovalent ions. For this purpose, we use a thiocarbohydrazone ligand, H₂L (1), conveniently tuned with bulky phosphine groups to stabilize the M^I ions and prevent ligand crossing to achieve the selective formation of mesocates. The neutral complexes [Cu₂(HL)₂] (2), [Ag₂(HL)₂] (3), and [Au₂(HL)₂] (4) were prepared by an electrochemical method, while the cationic complexes [Cu₂(H₂L)₂](PF₆)₂ (5), [Cu₂(H₂L)₂](BF₄)₂ (6), [Ag₂(H₂L)₂](PF₆)₂ (7), [Ag₄(HL)₂](NO₃)₂ (8), and [Au₂(H₂L)₂]Cl₂ (9) were obtained by using a metal salt as the precursor. All of the complexes are neutral or cationic dinuclear mesocates, except the silver nitrate derivative, which exhibits a tetranuclear cluster mesocate architecture. The crystal structures of the neutral and cationic copper(I), silver(I), and gold(I) complexes allow us to analyze the influence of synthetic methodology or the counterion role on both the micro- and macrostructures of the mesocates.

Conformational Properties of New Thiosemicarbazone and Thiocarbohydrazone Derivatives and Their Possible Targets

The structure assignment and conformational analysis of thiosemicarbazone KKI15 and thiocarbohydrazone KKI18 were performed through homonuclear and heteronuclear 2D Nuclear Magnetic Resonance (NMR) spectroscopy (2D-COSY, 2D-NOESY, 2D-HSQC, and 2D-HMBC) and quantum mechanics (QM) calculations using Functional Density Theory (DFT). After the structure identification of the compounds, various conformations of the two compounds were calculated using DFT. The two molecules showed the most energy-favorable values when their two double bonds adopted the E configuration. These configurations were compatible with the spatial correlations observed in the 2D-NOESY spectrum. In addition, due to the various isomers that occurred, the energy of the transition states from one isomer to another was calculated. Finally, molecular binding experiments were performed to detect potential targets for KKI15 and KKI18 derived from SwissAdme. In silico molecular binding experiments showed favorable binding energy values for all four enzymes studied. The strongest binding energy was observed in the enzyme butyrylcholinesterase. ADMET calculations using the preADMET and pKCSm software showed that the two molecules appear as possible drug leads.

Influence of the Reaction Conditions in the Crystal Structures of Zn(II) and Ni(II) Coordination Compounds with a Dissymmetric Bis(Thiosemicarbazone) Ligand

The new ligand HMeATSM, derived from condensation of 2-3-butanedione with 4-methyl-3-thiosemicarbazide and 2,4-dimethyl-3-thiosemicarbazide, has been synthesized. Its reactivity with nickel(II) and zinc(II) nitrates was explored and the resulting complexes were thoroughly characterized by elemental analysis, conductivity, mass spectrometry, IR, 1H and 13C NMR spectroscopies and their structures were confirmed by single-crystal X-ray diffraction. The results showed that the complex [Ni(MeATSM)]NO3 1 is formed under every reaction condition. In contrast, the reaction with zinc(II) nitrate depends on the temperature and the presence of LiOH.H2O, leading to the obtaining of complexes [Zn(MeATSM)(OH2)](NO3) 2 and [Zn(Me2TS)2(OH2)](NO3)2 3. The crystal structures of complexes 1 and 2 show that the dissymmetric ligand acts as a N2S2 tetradentate monoanionic ligand. The structural preferences of the metals also determine the structure of the complexes: whereas nickel(II) is in a square-planar environment, the zinc atom prefers a distorted square-base pyramid geometry imposed by the coordination mode and the planarity of the bis(thiosemicarbazone) ligand. In contrast, in complex 3, containing two bidentate Me2TS ligands, the Zn(II) is in a trigonal bipyramid arrangement. In all the complexes, the nitrate ion is not coordinated to the metal and acts as a counterion.

Structural characterization of benzketozone monohydrate

The structure of benzketozone monohydrate, C9H9N3O2S·H2O (BKZ), was studied by single-crystal X-ray diffraction, quantum chemical (DFT) and IR spectroscopy methods. The nitrogen atoms of the amino and imine groups of the thiosemicarbazide fragment are stabilized in the cis-configuration. The bond length N–C in the thiosemicarbazide group is unusually short (1.306(3) Å) as a result of the p,π-conjugation in that group. The hydrogen bonds and other weak interactions are studied by Hirshfeld surface calculations. The geometrical parameters of the structures were optimized by density functional theory.

An Efficient Synthesis, Spectroscopic Characterization, and Optical Nonlinearity Response of Novel Salicylaldehyde Thiosemicarbazone Derivatives

In this study, seven derivatives of salicylaldehyde thiosemicarbazones (1-7) were synthesized by refluxing substituted thiosemicarbazide and salicylaldehyde in an ethanol solvent. Different spectral techniques (UV-vis, IR, and NMR) were used to analyze the prepared compounds (1-7). Accompanied by the experimental study, quantum chemical studies were also carried out at the M06/6-311G(d,p) level. A comparative analysis of the UV-visible spectra and vibrational frequencies between computational and experimental findings was also performed. These comparative data disclosed that both studies were observed to be in excellent agreement. Furthermore, natural bond orbital investigations revealed that nonbonding transitions were significant for the stability of prepared molecules. In addition, frontier molecular orbital (FMO) findings described that a promising charge transfer phenomenon was found in 1-7. The energies of FMOs were further used to determine global reactivity parameters (GRPs). These GRP factors revealed that all synthesized compounds (1-7) contain a greater hardness value (η = 2.1 eV) and a lower softness value (σ = 0.24 eV), which indicated that these compounds were less reactive and more stable. Nonlinear optical (NLO) evaluation displayed that compound 5 consisted of greater values of linear polarizability ⟨α⟩ and third-order polarizability ⟨γ⟩ of 324.93 and 1.69 × 105 a.u., respectively, while compound 3 exhibited a larger value of second-order polarizability (βtotal) of 508.41 a.u. The NLO behavior of these prepared compounds may be significant for the hi-tech NLO applications.

Solvent-Induced Formation of Novel Ni(II) Complexes Derived from Bis-Thiosemicarbazone Ligand: An Insight from Experimental and Theoretical Investigations

In this work, we report solvent-induced complexation properties of a new N₂S₂ tetradentate bis-thiosemicarbazone ligand (H₂L^I), prepared by the condensation of 4-phenylthiosemicarbazide with bis-aldehyde, namely 2,2'-(ethane-1,2-diylbis(oxy)dibenzaldehyde, towards nickel(II). Using ethanol as a reaction medium allowed the isolation of a discrete mononuclear homoleptic complex [NiL^I] (1), for which its crystal structure contains three independent molecules, namely 1-I, 1-II, and 1-III, in the asymmetric unit. The doubly deprotonated ligand L^I in the structure of 1 is coordinated in a cis-manner through the azomethine nitrogen atoms and the thiocarbonyl sulfur atoms. The coordination geometry around metal centers in all the three crystallographically independent molecules of 1 is best described as the seesaw structure. Interestingly, using methanol as a reaction medium in the same synthesis allowed for the isolation of a discrete mononuclear homoleptic complex [Ni(L^II)₂] (2), where L^II is a monodeprotonated ligand 2-(2-(2-(2-(dimethoxymethyl)phenoxy)ethoxy)benzylidene)-N-phenylhydrazine-1-carbothioamide (HL^II). The ligand L^II was formed in situ from the reaction of L^I with methanol upon coordination to the metal center under synthetic conditions. In the structure of 2, two ligands L^II are coordinated in a trans-manner through the azomethine nitrogen atom and the thiocarbonyl sulfur atom, also yielding a seesaw coordination geometry around the metal center. The charge and energy decomposition scheme ETS-NOCV allows for the conclusion that both structures are stabilized by a bunch of London dispersion-driven intermolecular interactions, including predominantly N-H∙∙∙S and N-H∙∙∙O hydrogen bonds in 1 and 2, respectively; they are further augmented by less typical C-H∙∙∙X (where X = S, N, O, π), CH∙∙∙HC, π∙∙∙π stacking and the most striking, attractive long-range intermolecular C-H∙∙∙Ni preagostic interactions. The latter are found to be determined by both stabilizing Coulomb forces and an exchange-correlation contribution as revealed by the IQA energy decomposition scheme. Interestingly, the analogous long-range C-H∙∙∙S interactions are characterized by a repulsive Coulomb contribution and the prevailing attractive exchange-correlation constituent. The electron density of the delocalized bonds (EDDB) method shows that the nickel(II) atom shares only ~0.8|e| due to the σ-conjugation with the adjacent in-plane atoms, demonstrating a very weak σ-metalloaromatic character.

Complex formation of an estrone-salicylaldehyde semicarbazone hybrid with copper(II) and gallium(III): Solution equilibria and biological activity

The solution chemical properties such as proton dissociation, complex formation with copper(II) and gallium(III) ions in addition to antibacterial and antitumor activity of a novel tridentate salicyaldehyde semicarbazone-estrone hybrid (estrone-SC) and a related bicyclic compound (thn-SC) were investigated. The crystal structure of complex [Cu(thn-SCH_-1)Cl] was studied by single crystal X-ray diffraction method. Estrone-SC and thn-SC form mono-ligand complexes with Cu(II) characterized by relatively high stability, however, they are much less stable than their thiosemicarbazone analogues. The neutral Cu(II) complexes with (O^-,N,O^-)(H₂O) coordination mode predominate at physiological pH. Estrone-SC and thn-SC are more efficient Ga(III) binders in comparison with thiosemicarbazones, although the complexes also suffer dissociation at pH 7.4. The Cu(II) complex of estrone-SC displayed significant cytotoxicity in A549, SW480 and CH1/PA cancer cells, and moderate apoptosis induction and ROS formation. The semicarbazone compounds did not exhibit antibacterial effect; unlike the related Cu(II)-thiosemicarbazone complexes represented by the fairly low MIC values (3-50 μM) obtained on the Gram-positive Staphylococcus aureus and Enterococcus faecalis bacteria.

Ni, Pd, and Pt complexes of a tetradentate dianionic thiosemicarbazone-based O^N^N^S ligand

New tetradentate phenolate O^N^N^S thiosemicarbazone (TSC) ligands and their Ni(ii), Pd(ii) and Pt(ii) complexes were studied. The diamagnetic and square planar configured orange or red complexes show reversible reductive electrochemistry and in part reversible oxidative electrochemistry at very moderate potentials. DFT calculations show essentially pyridyl-imine centred lowest unoccupied molecular orbitals (LUMO) while the highest occupied molecular orbitals (HOMO) receive contributions from the phenolate moiety, the metal d orbitals and the TSC thiolate atom in keeping with UV-vis spectroelectrochemistry. DFT calculations in conjunction with IR spectra showed details of the molecular structures, the UV-vis absorptions were modelled through TD-DFT calculation with very high accuracy. UPS is fully consistent with UV-vis absorption and TD-DFT calculated data and shows decreasing HOMO-LUMO gaps along the series Pd > Pt > Ni.

Influence of Complexation of Thiosemicarbazone Derivatives with Cu (II) Ions on Their Antitumor Activity against Melanoma Cells

A series of thiosemicarbazone derivatives was prepared and their anti-tumor activity in vitro was tested. The X-ray investigation performed for compounds T2, T3 and T5 confirmed the synthesis pathway and assumed molecular structures of analyzed thiosemicarbazones. The conformational preferences of the thiosemicarbazone system were characterized using theoretical calculations by AM1 method. Selected compounds were converted into complexes of Cu (II) ions. The effect of complexing on anti-tumor activity has been investigated. The copper(II) complexes, with Schiff bases T1, T10, T12, T13, and T16 have been synthesized and characterized by chemical and elemental analysis, FTIR spectroscopy and TGA method. Thermal properties of coordination compounds were studied using TG-DTG techniques under dry air atmosphere. G361, A375, and SK-MEL-28 human melanoma cells and BJ human normal fibroblast cells were treated with tested compounds and their cytotoxicity was evaluated with MTT test. The compounds with the most promising anti-tumour activity were then selected and their cytotoxicity was verified with cell cycle analysis and apoptosis/necrosis detection. Additionally, DNA damages in the form of a basic sites presence and the expression of oxidative stress and DNA damage response genes were evaluated. The obtained results indicate that complexation of thiosemicarbazone derivatives with Cu (II) ions improves their antitumor activity against melanoma cells. The observed cytotoxic effect is associated with DNA damage and G2/M phase of cell cycle arrest as well as disorders of the antioxidant enzymes expression.

Condensed-phase relative Gibbs free energy and E/Z descriptors for 2-acetylthiophene and 2-acetylthiophene-N1-phenyl thiosemicarbazones

Thiosemicarbazones (TSCs) encompasses a class of compounds relevant in the pharmacological context. Their specific applicability varies in function of the appropriated chemical modification and their binding to different transition metals. In the present work, we apply current standards functionals, B3LYP and B97D, with triple zeta basis set quality, 6-311++G(d,p), to investigate the relative stability of the various possible spatial arrangements for 2-acetylthiophene and 2-acetylthiophene-N1-phenyl thiosemicarbazones, denoted ATTSC and ATTSC-Ph, respectively. The relative stability of neutral and deprotonated species at ethanol described by an implicit solvent model was investigated. For ATTSC, the relative Gibbs energy changed significantly upon deprotonation, and for ATTSC-Ph, a novel global minimum was identified. Based on the present study, deprotonation determines population in condensed-media. Such information, valid for ATTSC and ATTSC-Ph, can be crucial in studying other thiosemicarbazones.

Gallium and indium complexes with new hexadentate bis(semicarbazone) and bis(thiosemicarbazone) chelators

The synthesis of two new hexadentate potentially tetra-anionic acyclic chelators, an N2O4-donor bis(semicarbazone) (H4bsc) and an N2O2S2-donor bis(thiosemicarbazone) (H4btsc), is described. Coordination reactions of the ligands with gallium and indium precursors were investigated and yielded the complexes [Ga(Hbsc)] (1) and [In(Hbtsc)] (2), respectively. Ligands and complexes structures were confirmed by several techniques, including FTIR, NMR (1H, 13C, COSY, HSQC), ESI(+)-MS and single crystal X-ray diffraction analysis. The radioactive congeners [67Ga(Hbsc)] (1*) and [111In(Hbtsc)] (2*) were also synthesized and their radiolabeling yield and radiochemical purity were certified by HPLC and ITLC analyses. Biodistribution assays in groups of CD-1 mice showed a high uptake of both radiocomplexes in liver and intestine where 1* presented higher retention. In vitro and in vivo assays revealed higher stability of 1* compared with 2*, namely in the blood. The results suggest that radiocomplex 1* is a candidate for further investigation as it could be prepared in high yields (>95%), at low temperature (20-25 °C) and at fast reaction time (15 min), which are very desirable synthesis conditions for potential new radiopharmaceuticals.