Diacetyl-2-(4-methyl-3-thiosemicarbazonato)-3-(2-hydrazinatopyridine)(methanol) zinc(II) (ZnL10(MeOH)) and related structures use metal-ligand cooperativity to capture atmospheric CO2 under ambient conditions. However, the low solubility in protic solvents limits their practical use in direct air capture systems. This study reports the synthesis, characterization, and CO2 binding affinity of a series of new alkylthiocarbamato-hydrizinato(pyridine) ZnLn(MeOH) complexes (n = 1-9) and assesses the solubility and CO2 binding affinity of each complex. Replacement of the thiosemicarbazonato functional group with alkylthiocarbamato groups leads to increased Lewis acidity and CO2 binding affinity relative to ZnL10(MeOH). Additionally, the solubility of the complexes increased as a function of the alkylthiocarbamato group. In comparison to the structurally related thiosemicarbazonato complex, ZnL11(MeOH), the solubility of the ZnL1(MeOH) to ZnL9(MeOH) complexes was more than 100 times higher, accompanied by excellent binding affinities. The CO2 equilibrium binding constant (K1) showed an increase from 33,600 ± 1700 for ZnL1(MeOH) to 69,000 ± 7900 for ZnL8(MeOH) with the addition of the backbone phenyl group. Overall, the study revealed that the total amount of CO2 captured per unit volume is influenced by both the CO2 binding constant (K1) and the solubility of the complex, with the solubility being the dominant factor.

Spectroelectrochemical signature associated with the corrosion of copper and nickel metal strips have been investigated using chronoamperometry, UV-Visible spectroscopy and electrochemical impedance spectroscopy (EIS) techniques. Inspired by gel electrophoresis, an in-situ method (named EPIX) was developed using 2 wt% gel prepared in 3.58 wt% NaCl to follow the movement of metal ions resulting from the corrosion of copper and nickel metal strips under an applied oxidative current bias and detected in the UV-Visible spectrophotometer beam. The progression of the corrosion processes for both nickel and copper were further analyzed by applying different voltages and by using gel matrices of different pHs and salt concentrations. From the chronoamperometric responses, it was observed that for all the cases current density decreased with time initially and eventually plateaued except for the case of acidic gel solution where current density was found to increase initially before becoming plateaued during corrosion of copper metal strip whereas for the corrosion of nickel metal strip, current density was found to increase initially with time and eventually plateauing to a constant current density value for all the cases. All the characteristic absorption bands associated with octahedral copper(II) and nickel(II) ions were observed during the corrosion of the metal strips in the gel medium. The decay rate of the metal strips during the corrosion event was calculated and found to increase with decreasing potential, increasing applied potential, and higher salt concentration in the reaction medium.

Green hydrogen, generated through the electrolysis of water using renewable energy sources, is recognized as a highly promising alternative to fossil fuels in the pursuit of net-zero carbon emissions. Electrocatalysts are crucial for reducing overpotentials and enhancing the efficiency of the hydrogen evolution reaction (HER) for the production of green hydrogen. Homogeneous HER serves as a primary method to assess the activity and mechanisms of novel non-precious molecular electrocatalysts in pursuit of replacing precious platinum standards. However, these catalysts can sometimes exhibit instability under reductive and acidic conditions during homogeneous HER. Thus, it is also essential to evaluate catalysts through heterogeneous HER for initial assessment and practical application. In this study, we examine a series of structurally related N2S2 chelated Ni(ii) complexes, which are tailored to optimize the basicity of the catalyst for heterogeneous HER activity. These complexes are insoluble in 0.5 M H2SO4, and the films formed after catalyst deposition on glassy carbon electrodes (GCEs) exhibit catalytic currents during HER, demonstrating moderate to good overpotentials, Tafel slopes, and charge transfer resistance. Furthermore, we observe the anticipated structure-activity relationship that arises from tuning the catalyst structure. The complexes maintain stability over extended reductive cycling, as confirmed by various surface characterization techniques, including SEM, EDX, XPS, and XRD. This study highlights the potential of utilizing catalyst basicity to develop efficient and robust heterogeneous HER catalysts.

A series of thiosemicarbazonato-hydrazinatopyridine zinc(II) complexes were evaluated as direct air CO2 capture agents. The complexes sequester CO2 in a methanol solution as a metal-coordinated methylcarbonate. The reaction is reversible upon sparging of solutions with an inert gas (N2 or Ar). The capture process involves metal-ligand cooperativity with the noncoordinating nitrogen of the hydrazinatopyridine functional group serving as a Brønsted-Lowry base and the zinc acting as a Lewis acid. In this study, the pendent amine of the thiosemicarbazonato group was varied to include 4-phenyl (ZnL5), 4-(trifluoromethyl)phenyl (ZnL6), 4-cyanophenyl (ZnL7), 4-tolyl (ZnL8), and 4-naphthyl (ZnL9). Hyperconjugation between the pendent group and the ligand core resulted in modulation of the metal ion acidity, as quantified by ligand exchange equilibrium constants (K3 = 193-511) and ligand basicity (pKa,MeOH = 11.09-11.94). Variations in electronic structure that decreased ligand basicity were more than offset by increases in Lewis acidity. The equilibrium constant (K1) for CO2 capture varied from 46300 to 73700. Overall, the value of K1 was directly related to the relative Lewis acidity of the complexes (K3). Notably, there was an overall inverse relationship between K1 and the ligand basicity. The results provide insights into ligand design to further improve CO2 capture.

Molecular catalysts with N2S2 chelates and earth abundant metals have been used in different applications. With their versatile nature to modulate activity through changes in the ligand framework, they are excellent candidates to generate low-cost and sustainable energy as electrocatalysts for the hydrogen evolution reaction (HER). Herein we demonstrate the modulation of the reduction potential and basicity across a series of six square planar Ni(II) complexes with bis(thiosemicarbazonato) (BTSC), hybrid thiosemicarbazonato-alkylthiocarbamato (TSTC), and bis(alkylthiocarbamato) (BATC) ligands and evaluate their activity as homogenous HER catalysts. The redox active ligands have been designed to modulate the electronic structure of the N2S2Ni core and to systematically alter their respective pKa values. Cyclic voltammograms of all six complexes show two reversible reduction events in acetonitrile that systematically shift to more anodic potentials when the pendent methylthiosemicarbazonato (-NN=C(S)NHMe) groups are substituted with ethylthiocarbamato (-NN=C(S)OEt) groups and/or when the 2,4-butanedione backbone is replaced by 1-phenyl-1,2-propandione. Ligand basicity was evaluated by spectroscopic titration in acetonitrile and found to vary systematically across the series. Within the series of complexes the reduction potentials vary over an 500 mV range and the ligand basicity over 7 pKa units. Density functional theory (DFT) computations are consistent with experimental changes in redox potential and pKa values across the series of complexes. The results demonstrate a unique example in which electronic properties of the complexes are modulated via small ligand structure variations. The complexes are stable under acidic conditions or upon reduction, but they degrade upon reduction in the presence of acid limiting their application as homogeneous HER electrocatalysts.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

A series of isomeric bis(alkylthiocarbamate) copper complexes have been synthesized, characterized, and evaluated for antiproliferation activity. The complexes were derived from ligand isomers with 3-methylpentyl (H2L2) and cyclohexyl (H2L3) backbone substituents, which each yield a pair of linkage isomers. The thermodynamic products CuL2a/3a have two imino N and two S donors resulting in three five-member chelate rings (555 isomers). The kinetic isomers CuL2b/3b have one imino and one hydrazino N donor and two S donors resulting in four-, six-, and five-member rings (465 isomers). The 555 isomers have more accessible CuII/I potentials (E1/2 = -811/-768 mV vs. ferrocenium/ferrocene) and lower energy charge transfer bands than their 465 counterparts (E1/2 = -923/-854 mV). Antiproliferation activities were evaluated against the lung adenocarcinoma cell line (A549) and nonmalignant lung fibroblast cell line (IMR-90) using the MTT assay. CuL2a was potent (A549EC50 = 0.080 μM) and selective (IMR-90EC50/A549EC50 = 25) for A549. Its linkage isomer CuL2b had equivalent A549 activity, but lower selectivity (IMR-90EC50/A549EC50 = 12.5). The isomers CuL3a and CuL3b were less potent with A549EC50 values of 1.9 and 0.19 μM and less selective with IMR-90EC50/A549EC50 ratios of 2.3 and 2.65, respectively. There was no correlation between reduction potential and A549 antiproliferation activity/selectivity.

A series of hybrid thiosemicarbazone-alkylthiocarbamate copper complexes with similar electronic environments but distinct physical structures have been prepared, characterized, and evaluated for antiproliferation activity. The complexes include the constitutional isomers (1-phenylpropane-1-imine-(O-ethylthiocarbamato)-2-one-(N-methylthiosemicarbazonato))copper(II) (CuL1) and (1-phenylpropane-1-one-(N-methylthiosemicarbazonato)-2-imine-(O-ethylthiocarbamato))copper(II) (CuL2) along with (1-propane-1-imine-(O-ethylthiocarbamato)-2-one-(N-methylthiosemicarbazonato))copper(II) (CuL3). Complexes CuL1 and CuL2 differ in the positions of the pendent thiosemicarbazone (TSC) and alkylthiocarbamate (ATC) moieties on the 1-phenylpropane backbone. Complex CuL3 employs a propane backbone with the TSC in the 2-position as in CuL1. The isomer pair CuL1 and CuL2 have equivalent electronic environments with indistinguishable CuII/I potentials (E1/2 = -0.86 V vs. ferrocenium/ferrocene) and electron paramagnetic resonance (EPR) spectra (g∥ = 2.26, g⊥ = 2.08). The electronic structure of CuL3 has a similar E1/2 of -0.84 V and identical EPR parameters to CuL1, 2. Single crystal X-ray diffraction studies confirm a consistent donor environment with no substantial variation in the CuN or CuS bond distances and angles between the complexes. The antiproliferation activities of the CuL1–3 were evaluated against the lung adenocarcinoma cell line (A549) and nonmalignant lung fibroblast cell line (IMR-90) using the MTT assay. CuL1 had the highest A549 activity (A549EC50 = 0.065 μM) and selectivity (IMR-90EC50/A549EC50 = 20). The constitutional isomer CuL2 displayed decreased A549 activity (0.18 μM) and selectivity (10.6). The complex CuL3 displayed activity (0.009 μM) similar to CuL1 but with a lack of selectivity (1.0). Cellular copper loading determined by ICP-MS was consistent with the activity and selectivity trends. The complexes CuL1–3 did not induce reactive oxygen species (ROS) generation.

In this study, a series of thiosemicarbazonato-hydrazinatopyridine metal complexes were evaluated as CO2 capture agents. The complexes incorporate a non-coordinating, basic hydrazinatopyridine nitrogen in close proximity to a Lewis acidic metal ion allowing for metal-ligand cooperativity. The coordination of various metal ions with (diacetyl-2-(4-methyl-thiosemicarbazone)-3-(2-hydrazinopyridine) (H2L1) yielded ML1 (M = Ni(II), Pd(II)), ML1(CH3OH) (M = Cu(II), Zn(II)), and [ML1(PPh3)2]BF4 (M = Co(III)) complexes. The ML1(CH3OH) complexes reversibly capture CO2 with equilibrium constants of 88 ± 9 and 6900 ± 180 for Cu(II) and Zn(II), respectively. Ligand effects were evaluated with Zn(II) through variation of the 4-methyl-thiosemicarbazone with 4-ethyl (H2L2), 4-phenethyl (H2L3), and 4-benzyl (H2L4) derivatives. The equilibrium constant for CO2 capture increased to 11,700 ± 300, 15,000 ± 400, and 35,000 ± 200 for ZnL2(MeOH), ZnL3(MeOH), and ZnL4(MeOH), respectively. Quantification of ligand basicity and metal ion Lewis acidity shows that changes in CO2 capture affinity are largely associated with ligand basicity upon substitution of Cu(II) with Zn(II), while variation of the thiosemicarbazone ligand enhances CO2 affinity by tuning the metal ion Lewis acidity. Overall, the Zn(II) complexes effectively capture CO2 from dilute sources with up to 90%, 86%, and 65% CO2 capture efficiency from 400, 1000, and 2500 ppm CO2 streams.

Linkage isomers are coordination compounds with the same composition but different donor atoms, resulting in distinct physical and electronic structures. A pair of linkage isomers, CuL555 and CuL465, derived from phenylglyoxal bis(ethylthiocarbamate) were synthesized, isolated, and characterized by structural, electrochemical, and spectroscopic methods. The isomers are stable in solution under ambient conditions, but CuL465 converts to CuL555 in acid, consistent with quantum-chemical calculations. The complexes were screened against a lung adenocarcinoma cell line (A549) and a nonmalignant lung fibroblast cell line (IMR-90) to evaluate the antiproliferation activity. CuL555 and CuL465 possessed EC50 values of 0.113 ± 0.030 and 0.115 ± 0.038 μM for A549 and 1.87 ± 0.29 and 0.77 ± 0.22 μM for IMR-90, respectively.

In this study, we report a pair of electrocatalysts for the hydrogen evolution reaction (HER) based on the noninnocent ligand diacetyl-2-(4-methyl-3-thiosemicarbazone)-3-(2-pyridinehydrazone) (H2DMTH, H2L1). The neutral complexes NiL1 and PdL1 were synthesized and characterized by spectroscopic and electrochemical methods. The complexes contain a non-coordinating, basic hydrazino nitrogen that is protonated during the HER. The pKa of this nitrogen was determined by spectrophotometric titration in acetonitrile to be 12.71 for NiL1 and 13.03 for PdL1. Cyclic voltammograms of both NiL1 and PdL1 in acetonitrile exhibit diffusion-controlled, reversible ligand-centered events at -1.83 and -1.79 V (vs ferrocenium/ferrocene) for NiL1 and PdL1, respectively. A quasi-reversible, ligand-centered event is observed at -2.43 and -2.34 V for NiL1 and PdL1, respectively. The HER activity in acetonitrile was evaluated using a series of neutral and cationic acids for each catalyst. Kinetic isotope effect (KIE) studies suggest that the precatalytic event observed is associated with a proton-coupled electron transfer step. The highest turnover frequency values observed were 6150 s-1 at an overpotential of 0.74 V for NiL1 and 8280 s-1 at an overpotential of 0.44 V for PdL1. Density functional theory (DFT) computations suggest both complexes follow a ligand-centered HER mechanism where the metals remain in the +2 oxidation state.

Pencil substrates are promising ideal durable carbon support also amenable for post characterization for evaluation of hydrogen evolution reaction catalysts.

Fungi are ubiquitous in nature, and typically cause little or no environmental or pathogenic damage to their plant, animal, and human hosts. However, a small but growing number of pathogenic fungi are spreading world-wide at an alarming rate threatening global ecosystem health and proliferation. Many of these emerging pathogens have developed multi-drug resistance to front line therapeutics increasing the urgency for the development of new antifungal agents. This review examines the development of thiosemicarbazones, bis(thiosemicarbazones), and their metal complexes as potential antifungal agents against more than 65 different fungal strains. The fungistatic activity of the compounds are quantified based on the zone of inhibition, minimum inhibitory concentration, or growth inhibition percentage. In this review, reported activities were standardized based on molar concentrations to simplify comparisons between different compounds. Of all the fungal strains reported in the review, A. niger in particular was very resistant towards a majority of tested compounds. Our analysis of the data shows that metal complexes are typically more active than non-coordinated ligands with copper(II) and zinc(II) complexes generally displaying the highest activity.

A series of new bis(thiosemicarbazonato) Cu(II) complexes with pendent polyamines, diacetyl-(N, -dimethylethylenediaminothiosemicarbazonato)-(N'-methyl-3-thio-semicarbazonato)butane-2,3-diimine)-copper(II) (Cu-1), diacetyl-bis(N-dimethylethylenediamino-3-thiosemicarbazonato)butane-2,3-diimine)-copper(II) (Cu-3), and their cationic derivatives Cu-2 and Cu-4, have been synthesized and fully characterized by spectroscopic, electrochemical, and X-ray diffraction methods. Complexes Cu-1-Cu-4 are analogues of Cu(ATSM), which contains a similar N2S2 donor core with terminal non-coordinating amines. Substitution of the methyl group(s) of the terminal amines of H(2)ATSM with N,N-dimethylethylenediamine followed by alkylation generates a charged quaternary amine in the ligand framework. The charged site tunes the redox potentials of the complexes with minimal changes in their physical and electronic properties. The HER activity of all four copper complexes were evaluated in acetonitrile with glacial acetic acid. All of the complexes have lower HER overpotentials than Cu(ATSM), which is attributed to charge effects. The pendent amines of Cu-1 and Cu-3 have the lowest HER overpotential as the pendent tertiary amine also serves as a proton relay to enhance proton rearrangement under catalytic conditions. Complex Cu-3 showed the highest activity with a TOF of 12 x 10(3) s(-1), an overpotential of 0.65 V, and faradaic efficiency of 100 %.

This study evaluates the effect of water vapor pressure on the surface conductivity of a hydrated small molecule crystal under dry and wet conditions. The crystal contains a discrete metal complex with waters of hydration in structural positions and in 1D water wires. Under dry conditions, the surface of the hydrated crystal behaves as a near ideal capacitor. Under wet conditions, the waters of hydration serve as a template to assemble surface water networks by organization of water from the environment. The surface water provides pathways for charge transfer attributed to proton mobility that increases conductivity by > 3 orders in magnitude. Modulation between wet and dry conditions tunes the conductivity of the crystal surface via a two-step process, which has been evaluated kinetically as a function of the water vapor pressure. (C) 2020 Elsevier Ltd. All rights reserved.

As atmospheric levels of carbon dioxide (CO2) continue to increase, there is an immediate need to balance the carbon cycle. Current approaches require multiple processes to fix CO2 from the atmosphere or flue gas and then reduce it to value-added products. The zinc(II) catalyst Zn(DMTH) (DMTH = diacetyl-2-(4-methyl-3-thiosemicarbazonate)-3-(2-pyridinehydrazonato)) reduces CO2 from air to formate with a faradaic efficiency of 15.1% based on total charge. The catalyst utilizes metal-ligand cooperativity and redox-active ligands to fix, activate, and reduce CO2. This approach provides a new strategy that incorporates sustainable earth-abundant metals that are oxygen and water tolerant.

A series of hybrid ligands (H2L1-H2L3) derived from 4-methyl-3-thiosemicarbazide and hydrazinecarbothioic acid O-alkyl esters were synthesized and characterized by NMR. The ligands were chelated with copper (4-6), nickel (7-9), and zinc (10-12) and characterized by spectroscopy, electrochemistry, and single crystal X-ray crystallography. The chelated metals displayed substantial anodic shifts in the CuII/I reduction potential of ∼160 mV relative to their bis(thiosemicarbazone) analogues. The metal chelates 4-12 were evaluated for potential anticancer activity by MTT assays, and selected results were confirmed by clonogenic and trypan blue assays. The copper derivatives 4 and 6 were found to have potent and cancer-selective antiproliferative effects, with GI50 values less than 100 nM in A549 lung adenocarcinoma cells compared with at least 20-fold less activity in IMR90 nonmalignant lung fibroblasts. In comparison, the nickel complexes were much less active and had little cancer-selectivity. Varying by ligand, the zinc complexes were less potent or had comparable activity compared to that of the corresponding copper complex. UV-visible spectroscopy indicated that zinc complex 10 was transmetalated in the presence of equimolar copper, whereas nickel complex 7 was not. Copper complexes 4 and 6 were also assessed in the NCI60 screen and were found to have cytotoxic activity against most solid tumor cell lines. In MTT assays, 4 and 6 were substantially more active against A549 cancer cells than Cu(ATSM) and were more cancer-selective (for A549 compared to IMR-90) than Cu(GTSM). Our results suggest that hybrid thiosemicarbazone-alkylthiocarbamate copper complexes have potential for development as new anticancer agents.

The molecular catalyst diacetyl-bis(N-4-methyl-3-thiosemi-carbazonato)nickel(ii) (NiATSM) was integrated with Si for light-driven hydrogen evolution from water. Compared to an equivalent loading of Ni metal, the NiATSM/p-Si electrode performed better. Durability of the surface-bound catalyst under operation in acid was achieved without covalent attachment by using Nafion binding.

The zinc(II) complex of diacetyl-2-(4-methyl-3-thiosemicarbazone)-3-(2-hydrazonepyridine), ZnL1 (1), was prepared and evaluated as a precatalyst for the hydrogen evolution reaction (HER) under homogeneous conditions in acetonitrile. Complex 1 is protonated on the noncoordinating nitrogen of the hydrazonepyridine moiety to yield the active catalyst Zn(HL1)OAc (2) upon addition of acetic acid. Addition of methyl iodide to 1 yields the corresponding methylated derivative ZnL2I (3). In solution, partial dissociation of the coordinated iodide yields the cationic derivative 3'. Complexes 1-3 were characterized by 1H NMR, FT-IR, and UV-visible spectroscopies. The solid-state structures of 2 and 3 were determined by single crystal X-ray diffraction. HER studies conducted in acetonitrile with acetic acid as the proton source yield a turnover frequency (TOF) of 7700 s-1 for solutions of 1 at an overpotential of 1.27 V and a TOF of 6700 s-1 for solutions of 3 at an overpotential of 0.56 V. For both complexes, the required potential for catalysis, Ecat/2, is larger than the thermodynamic reduction potential, E1/2, indicative of a kinetic barrier attributed to intramolecular proton rearrangement. The effect is larger for solutions of 1 (+440 mV) than for solutions of 3 (+160 mV). Controlled potential coulometry studies were used to determine faradaic efficiencies of 71 and 89% for solutions of 1 and 3, respectively. For both catalysts, extensive cycling of potential under catalytic conditions results in the deposition of a film on the glassy carbon electrode surface that is active as an HER catalyst. Analysis of the film of 3 by X-ray photoelectron spectroscopy indicates the complex remains intact upon deposition. A proposed ligand-centered HER mechanism with 1 as a precatalyst to 2 is supported computationally using density functional theory (DFT). All catalytic intermediates in the mechanism were structurally and energetically characterized with the DFT/B3LYP/6-311g(d,p) in solution phase using a polarizable continuum model (PCM). The thermodynamic feasibility of the mechanism is supported by calculation of equilibrium constants or reduction potentials for each proposed step.