X-ray Crystallography Research Articles

Synthesis and characterization of Cu(II) complexes supported by a pyridylamide ligand

In our effort to understand the impact of ligand platforms on the structure diversity and chemical properties of copper clusters, a tripod pyridylamide ligand H3tpmbc was used in this work. Two one-dimensional polymeric Cu(II) complexes [Cu(H3tpmbc)Cl2]n (1) and [Cu2(H3tpmbc)Cl4]n (2) were isolated and characterized. X-ray crystallography analysis showed that both structures have a similar one-dimensional backbone. The main structure difference of the two complexes is the presence of a second Cu(II) site in complex 2. Hirshfeld analysis revealed the presence of interesting C–H⋅⋅⋅π and π⋅⋅⋅π interaction networks in both complexes. Spectroscopic characterization of both complexes and [CuPyCl2] suggests the source of the color difference between the two polymers at the solid state. Computational studies based on the X-ray crystal structures were performed and the results provided a deeper understanding of the electronic structures of the Cu(II) site(s) in both complexes. Thermal gravimetric analysis (TGA) demonstrated that the two complexes have the similar thermal behavior, and this could be attributed to the similar one-dimensional backbone structure.

Phosphorus–nitrogen compounds: part 75—design, synthesis, stereogenic and conformational properties of chiral dispiro(N/N)cyclotriphosphazenes: structural analysis and photophysical and bioactivity studies

Multiheterocyclic inorganic–organic hybrid phosphazenes have robust inorganic ring systems with the stabilities of the phosphorus nitrogen skeleton and many different substituents bonded to the P atoms. In present study, unsymmetrical dispirocyclotriphosphazenes were prepared due to their potential to depict steric hindrance and electronic rearrangement in creating permanent chirality for certain conformational and configurational isomers. These isomers may have an effect on DNA bindings and activitiy against selected fungi and bacteria, remarkably. Herein, tetrachlorocyclotriphosphazenes (1 and 2) were reacted with 9-ethyl-N-methyl-3-carbazolyl-1,2-diaminoethane (3), 9-ethyl-N-ethyl-3-carbazolyl-1,2-diaminoethane (4) and 9-ethyl-N-methyl-3-carbazolyl-1,3-diaminopropane (5) to give the new unsymmetrical cis/trans-dispirocyclotriphosphazenes, [(ClBz/BzSpiro-6)R1(N3P3)(CzSpiro-n)R2]Cl2 (Cz: Carbazolyl; R1:Me R2:Me or Et; n = 5 or 6; trans 6a–11a and cis 6b–11b). Characterizations, chiralities, and photophysical and biological properties of the new compounds were examined. The molecular and crystal structures of cis-6b, cis-7b, trans-9a, cis-9b, trans-10a and cis-10b were determined by single crystal X-ray crystallography. The chiralities of these compounds with unsymmetrical spiro-architectures were confirmed by X-ray crystallography. These results were further proven by 31P NMR data recorded with the addition of a chiral solvent (CSA). Additionally, circular dichroism (CD) spectra also supported the results. Photophysical measurements indicate that these compounds show emission with lifetimes of approximately 5.6–5.9 ns. In addition, the bioactivities of some isomers were found to be different and quite high against some bacterial and yeast strains. Trans-8a was very active against B. cereus (MBC = 78.1 µM), while cis-6b, trans-9a and cis-9b were very active against the pathogenic yeast C. albicans (MFC = 156.3 µM).Graphical abstract

Structural Analysis of the Macrocyclic Inhibitor BI-4020 Binding to EGFR Kinase.

A novel macrocyclic inhibitor of mutant EGFR (BI-4020) has shown promise in pre-clinical studies of T790M and C797S drug-resistant non-small cell lung cancer. To better understand the molecular basis for BI-4020 selectivity and potency, we have carried out biochemical activity assays and structural analysis with X-ray crystallography. Biochemical potencies agree with previous studies indicating that BI-4020 is uniquely potent against drug-resistant L858R/T790M and L858R/T790M/C797S variants. X-ray structures with wild-type (2.4 Å) and T790M/V948R (3.1 Å) EGFR kinase domains show that BI-4020 is likely rendered selective due to interactions with the kinase domain hinge region as well as T790M, akin to Osimertinib. Additionally, BI-4020 is also rendered more potent due to its constrained macrocycle geometry as well as additional H-bonds to conserved K745 and T845 residues in both active and inactive conformations. These findings taken together show how this novel macrocyclic inhibitor is both highly potent and selective for mutant EGFR in a reversible mechanism and motivate structure-inspired approaches to developing targeted therapies in medicinal oncology.

Simulations predict preferred Mg2+ coordination in a nonenzymatic primer-extension reaction center

The mechanism by which genetic information was copied prior to the evolution of ribozymes is of great interest because of its importance to the origin of life. The most effective known process for the nonenzymatic copying of an RNA template is primer extension by a two-step pathway in which 2-aminoimidazole-activated nucleotides first react with each other to form an imidazolium-bridged intermediate that subsequently reacts with the primer. Reaction kinetics, structure-activity relationships, and X-ray crystallography have provided insight into the overall reaction mechanism, but many puzzles remain. In particular, high concentrations of Mg2+ are required for efficient primer extension, but the mechanism by which Mg2+ accelerates primer extension remains unknown. By analogy with the mechanism of DNA and RNA polymerases, a role for Mg2+ in facilitating the deprotonation of the primer 3′-hydroxyl is often assumed, but no catalytic metal ion is seen in crystal structures of the primer-extension complex. To explore the potential effects of Mg2+ binding in the reaction center, we performed atomistic molecular dynamics simulations of a series of modeled complexes in which a Mg2+ ion was placed in the reaction center with inner-sphere coordination with different sets of functional groups. Our simulations suggest that coordination of a Mg2+ ion with both O3′ of the terminal primer nucleotide and the pro-Sp nonbridging oxygen of the reactive phosphate of an imidazolium-bridged dinucleotide would help to pre-organize the structure of the primer/template substrate complex to favor the primer-extension reaction. Our results suggest that the catalytic metal ion may play an important role in overcoming electrostatic repulsion between a deprotonated O3′ and the reactive phosphate of the bridged dinucleotide and lead to testable predictions of the mode of Mg2+ binding that is most relevant to catalysis of primer extension.

Unveiling a Novel Solvatomorphism of Anti-inflammatory Flufenamic Acid: X-ray Structure, Quantum Chemical, and In Silico Studies.

This paper delves into the polymorphism of 2-[3-(trifluoromethyl)anilino]benzoic acid, commonly referred to as flufenamic acid (FA), a pharmaceutical agent employed in treating inflammatory conditions. The central focus of the study is on a newly unearthed solvatomorphic structure of FA in methanol (FAM), and a thorough comparison is conducted with the commercially available standard structure. Employing a comprehensive approach, including X-ray crystallography, Hirshfeld surface analysis, density functional theory (DFT), molecular docking, and molecular dynamics (MD) simulations, the research aims to unravel the structural and functional implications of solvatomorphism. The X-ray crystal structure analysis brings to light notable differences between the standard FA and solvatomorphic FAM, showcasing variations in intermolecular interactions and crystal packing. Key features such as hydrogen bonding, π···π stacking, and C-H···π interactions are identified as influential factors shaping the stability and conformation of the compounds. Hirshfeld surface analysis further quantifies the nature and contribution of intermolecular interactions, providing a comprehensive perspective on molecular stability. Density functional theory offers valuable electronic structure insights, highlighting disparities in frontier molecular orbitals between FA and FAM. Molecular docking studies against prostaglandin D2 11-ketoreductase explore potential drug interactions, unveiling distinct binding modes and hydrogen bonding patterns that shed light on how the solvatomorphic structure may impact drug-target interactions. In-depth molecular dynamics simulations over 100 ns investigate the stability of the protein-ligand complex, with root mean square deviation and root mean square fluctuation analyses revealing minimal deviations and affirming the stability of FAM within the active site of the target protein.

Unexpected One-Pot Synthesis of 3-Cinnamoyl-3-hydroxyphthalide Derivatives

AbstractA new and simple method to prepare 3-cinnamoyl-3-hydroxyphthalide derivatives from 2-hydroxy-3-methyl-1,4-naphthoquinone and substituted benzaldehydes was unexpectedly uncovered. The reaction was conveniently performed in DMSO at 100 °C with K3PO4 as a base and AlCl3 as a catalyst. We propose that the reaction proceeds by a cascade process involving nucleophilic addition followed by demethylation and rearrangement. The products were typically obtained in moderate to good yields. The highest yield (95%) was obtained when the reaction of 2-bromobenzaldehyde was performed for 24 hours. X-ray crystallography of the product derived from 2-fluorobenzaldehyde unequivocally confirmed the structure of the hydroxyphthalide derivatives.

Why are the luminescent properties of the mononuclear and binuclear Eu/Tb-2-hydroxybenzoate complexes with 1,10-phenanthroline so different? An experimental-theoretical study

This study presents a comprehensive investigation into the structural and luminescent properties of lanthanide 2-hydroxybenzoate compounds, focusing on Eu3+ and Tb3+ ions in both single and mixed systems. The X-ray structures of (Hphen)2[Eu2(2-OHBz)8(H2O)2]·2H2O (1a·2H2O) and [Eu(2-OHBz)3(phen)2]·PhMe (2a·PhMe) were determined, where 2-OHBz: 2-hydroxybenzoate and phen: 1,10-phenantroline, revealing triclinic crystal structures with distinct coordination geometries. Compound 1a·2H2O displayed a centrosymmetric dinuclear anion with a coordination number of eight for each Eu3+ center, while compound 2a·PhMe exhibited a neutral mononuclear complex with a decacoordinated Eu3+ center. A comparative analysis of luminescent properties between these compounds unveiled significant differences in the nonradiative decay rates of the 5D0 level of Eu3+ ions, suggesting potential luminescence-quenching channels. The investigation is extended to mixed Eu3+-Tb3+ systems, demonstrating efficient Tb3+ to Eu3+ energy transfer, especially at room temperature. Three models, including two novel ones proposed in this study, were considered to rationalize energy transfer in the mixed systems. Our theoretical-experimental investigation reveals that variations in lifetimes of the emitting level 5D0 of Eu-2-OHBz mononuclear and binuclear complexes, or mixed Eu/Tb-2-OHBz complexes, with 1,10-phenanthrolines, primarily result from multiphonon decay processes; however, low-energy ligand-to-metal charge transfer (LMCT) states play a key role in suppressing luminescence in the binuclear complex compare to the mononuclear ones.

Oxidovanadium(V) complexes with tridentate hydrazone ligands as oxygen atom transfer catalysts

Four isostructural oxovanadium(V) complexes with hydrazone ligands have been synthesised, characterised, and evaluated as epoxidation and sulfoxidation catalysts. The reactions between [VO(acac)2] (acac– = acetylacetonate) and H2Ln (n = 1–4), precursors for monoanionic tridentate hydrazone ligands, afford complexes formulated as [VO(Ln)(bzh)·MeOH] (1–4) when bidentate benzohydroxamic acid (Hbzh) is included as a co-ligand. Single crystal X-ray structure analyses showed that complexes 1–3 have a distorted octahedral coordination geometry with an O5N coordination environment. Cyclic voltammetry showed that all complexes undergo two quasi-irreversible reduction peaks and a single irreversible oxidation peak. The bonding in 1 has been investigated by electronic structure calculations, and these data are discussed with respect to the electrochemical results. Complexes 1–4 were tested as catalysts for the epoxidation of cis-cyclooctene at 50 °C and sulfoxidation of methyl-p-tolylsulfide at room temperature using tert-butyl hydroperoxide (tBuOOH) and aqueous H2O2 as the terminal oxidants.

Reduction of Thorium Tris(amido)arene Complexes: Reversible Double and Single C-C Couplings.

The reduction chemistry of thorium complexes is less explored compared to that of their uranium counterparts. Here, we report the synthesis, characterization, and reduction chemistry of two thorium(IV) complexes, (AdTPBN3)ThCl (1) and (DtbpTPBN3)ThCl(THF) (4) [RTPBN3 = 1,3,5-[2-(RN)C6H4]3C6H3; R = 1-adamantyl (Ad) or 3,5-di-tert-butylphenyl (Dtbp); THF = tetrahydrofuran], supported by tripodal tris(amido)arene ligands with different N-substituents. Reduction of 1 with excessive potassium in n-pentane yielded a double C-C coupling product, [(AdTPBN3)ThK(Et2O)2]2 (3), featuring a unique tetraanionic tricyclic core. On the other hand, reduction of 4 with 1 equiv of KC8 in hexanes/1,2-dimethoxyethane (DME) afforded a single C-C coupling product, [(DtbpTPBN3)Th(DME)]2 (5), with a dianionic bis(cyclohexadienyl) core. The solid- and solution-state structures of dinuclear thorium(IV) complexes 3 and 5 were established by X-ray crystallography and NMR spectroscopy. In addition, reactivity studies show that 3 and 5 can behave as thorium(II) and thorium(III) synthons to reduce organic halides. For instance, 3 and 5 are able to reduce 4 and 2 equiv of benzyl chloride, respectively, to regenerate 1 and 4 with concomitant formation of dibenzyl. Reversible C-C couplings under redox conditions provide an alternative approach to exploiting the potential of thorium arene complexes in redox chemistry.

Fluorotrifluoromethylation of Alkenes Mediated by a Hypervalent Trifluoromethyl-Iodine(III) Reagent.

Herein, we present a novel strategy for synthesizing polyfluorinated compounds by the fluorotrifluoromethylation of olefins, which was achieved through a new trifluoromethyl-iodine(III) reagent TFNI-1. TFNI-1 was readily synthesized via a three-step process, and its structure was characterized by NMR spectroscopy and X-ray crystallography. It is shown by radical trapping and radical clock experiments that the reaction involves the CF3 radical intermediate.

Synthesis, Spectroscopic Characterization, and Photophysical Studies of Heteroleptic Silver Complexes Bearing 2,9-Bis(styryl)-1,10-phenanthroline Ligands and Bis[(2-diphenylphosphino)phenyl] Ether

Three new heteroleptic Ag(I) complexes, labeled as [AgL(POP)]BF4 (1–3), were successfully synthesized and comprehensively characterized. Here, L represents 2,9-bis((E)-4-methoxystyryl)-1,10-phenanthroline (L1), 2,9-bis((E)-4-methylthiostyryl) -1,10-phenanthroline (L2), and 2,9-bis((E)-4-diethylaminostyryl)-1,10-phenanthroline (L3), while POP stands for Bis[(2-diphenylphosphino)phenyl] ether. The stability of these compounds in solution was confirmed through multinuclear 1D (1H, 13C, 31P) and 2D NMR (COSY, NOESY, HMBC, HSQC) spectroscopies. Additionally, their molecular structure was elucidated via X-ray crystallography. The photophysical properties of the complexes were assessed both in the solid state and in solution (dichloromethane). Compounds 1–3 demonstrated moderate emissions in solution, with quantum yields ranging from 11–23%. Interestingly, their solid-state luminescent behavior differed. Large bathochromic shifts (42–75 nm) of the emission maxima and a decrease in quantum yields (2.5–9.5%) were evident, possibly due to the presence of excimers. Compound 3 stands out as a rare example of an Ag(I) red-color emitter.

X-ray crystal structure of a designed rigidified imaging scaffold in the ligand-free conformation.

Imaging scaffolds composed of designed protein cages fused to designed ankyrin repeat proteins (DARPins) have enabled the structure determination of small proteins by cryogenic electron microscopy (cryo-EM). One particularly well characterized scaffold type is a symmetric tetrahedral assembly composed of 24 subunits, 12 A and 12 B, which has three cargo-binding DARPins positioned on each vertex. Here, the X-ray crystal structure of a representative tetrahedral scaffold in the apo state is reported at 3.8 Å resolution. The X-ray crystal structure complements recent cryo-EM findings on a closely related scaffold, while also suggesting potential utility for crystallographic investigations. As observed in this crystal structure, one of the three DARPins, which serve as modular adaptors for binding diverse `cargo' proteins, present on each of the vertices is oriented towards a large solvent channel. The crystal lattice is unusually porous, suggesting that it may be possible to soak crystals of the scaffold with small (≤30 kDa) protein cargo ligands and subsequently determine cage-cargo structures via X-ray crystallography. The results suggest the possibility that cryo-EM scaffolds may be repurposed for structure determination by X-ray crystallography, thus extending the utility of electron-microscopy scaffold designs for alternative structural biology applications.

Tailoring the dielectric properties of bentonite for advanced capacitor Applications: The role of ruthenium and strontium incorporation

This study utilized incipient wetness impregnation to synthesize bentonite materials and to enhance their physical characteristics with ruthenium (Ru) and strontium (Sr) ions. The atomic composition of the materials was confirm confirmed via the analysis of the EDX measurements. X-ray crystallography indicates that the materials have almost similar diffraction peak profiles, and that the addition of Sr increases the crystallinity of the bentonite grains. Dielectric and electrical properties, measured between 25 °C and 55 °C at frequencies of 1 kHz −1 MHz, revealed that the real and imaginary impedances increased upon the introduction of 5 % Ru and 5 % Sr, possibly due to Ru and Sr segregation into the grain boundaries, increasing the resistance of the bentonite granular structure. For all materials, the observed saturation of the real electric modulus at high frequencies, and the reduction of the permittivity with increasing frequency, may be explained by the Maxwell-Wagner interfacial polarization and Koop's empirical theory. This trend is more pronounced for the bentonite with Sr, highlighting the essence of the present work for engineering interfacial polarisation applications associated with supercapacitors and batteries.

Template-free hierarchical TiO2/rGO nanocomposites for enhanced photocatalytic performance

This work utilized a simple, cost-effective, one-pot, template-free hydrothermal technique to form a hierarchical nanocomposite having TiO2 and reduced graphene oxide (rGO). The hierarchical TiO2/rGO nanocomposite demonstrates a large surface area, resulting in higher adsorption of photons and effective charge generation, separation, and migration. As a result, the synthesized nanocomposite shows effective degradation of Rhodamine-B dye. The optimal amount of rGO effectively minimizes the charge recombination, which plays a significant role in dye degradation. The morphological, photoelectrochemical, and photocatalytic characteristics were studied by scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray crystallography, photoluminescence spectra, electrochemical impedance spectroscopy, and UV–Vis spectrophotometer.

DNA and bovine serum albumin protein (BSA) interaction of antitumor supramolecular nickel(II) complex: Inference for drug design

To explore the therapeutic potential of supramolecular nickel(II) Schiff base self-assemble complexes, the Schiff base ligand (N, N′-bis(salicylidene)-1,3-diamino-2-propanol) and its Ni(II) complex [Ni2(H2L)2(NCS)2(CH3OH)2](CH3OH)2 were synthesized. Characterization by X-ray crystallography (for the complex), FT-IR, UV–Vis spectroscopy, 1HNMR and elemental analysis (CHN) were performed. Single-crystal X-ray structure of the complex exhibited a distorted octahedral geometry in which each nickel(II) center, in the asymmetric unit, was six coordinated with three N atoms and three O atoms (from Schiff base ligand, methanol and NCS). In vitro Fish Sperm DNA (FS-DNA) and Bovine Serum Albumin (BSA) binding studies of the complex employed UV–Vis and fluorescence spectroscopy, cyclic voltammetry, viscosity measurement and molecular docking. The complex indicated a good binding propensity to BSA and was also bound to FS-DNA, preferably via intercalation. The outputs of the molecular docking study confirmed the experimental results. The complex was found to exert high anticancer activity against the gastric and prostate cancerous cells with putative selective anticancer properties. The death-induced mechanism underlying the complex is mainly related to the intercalator interactions, which may result in apoptosis-programmed cell death.

Animal-derived food allergen: A review on the available crystal structure and new insights into structural epitope.

Immunoglobulin E (IgE)-mediated food allergy is a rapidly growing public health problem. The interaction between allergens and IgE is at the core of the allergic response. One of the best ways to understand this interaction is through structural characterization. This review focuses on animal-derived food allergens, overviews allergen structures determined by X-ray crystallography, presents an update on IgE conformational epitopes, and explores the structural features of these epitopes. The structural determinants of allergenicity and cross-reactivity are also discussed. Animal-derived food allergens are classified into limited protein families according to structural features, with the calcium-binding protein and actin-binding protein families dominating. Progress in epitope characterization has provided useful information on the structural properties of the IgE recognition region. The data reveals that epitopes are located in relatively protruding areas with negative surface electrostatic potential. Ligand binding and disulfide bonds are two intrinsic characteristics that influence protein structure and impact allergenicity. Shared structures, local motifs, and shared epitopes are factors that lead to cross-reactivity. The structural properties of epitope regions and structural determinants of allergenicity and cross-reactivity may provide directions for the prevention, diagnosis, and treatment of food allergies. Experimentally determined structure, especially that of antigen-antibody complexes, remains limited, and the identification of epitopes continues to be a bottleneck in the study of animal-derived food allergens. A combination of traditional immunological techniques and emerging bioinformatics technology will revolutionize how protein interactions are characterized.

Antimony complexes with SNN thiosemicarbazones: Synthesis, structural studies and cytotoxicity against bacterial and cancer cells

Addition of antimony(III) chloride to ligands {HL1 = 4-(4-nitrophenyl)-1-((pyridin-2-yl)methylene)thiosemicarbazide and HL2 = 4-(2-methoxyphenyl)-1-((pyridin-2-yl)methylene)thiosemicarbazide} produced the complexes [Sb(L1)Cl2] (C1) and [Sb(L2)Cl2] (C2), respectively. These complexes were formulated based on elemental, spectroscopic and solution conductivity data. X-ray crystallography elucidated the packing of C2 in the triclinic P-1 space group and the exhibition of pseudo octahedral geometry around the antimony cation. The complexes (20 mg/ml) showed the largest inhibition zones in Staphylococcus aureus (34 mm for C1 and 36 mm for C2) and Escherichia coli (33 mm for C1 and 36 mm for C2) strains. HL1 showed no inhibition in the bacterial strains and HL2 inhibited the strains of Staphylococcus aureus and E. coli at 11 and 10 mm, while ampicillin inhibited these strains at 21 and 25 mm, respectively. The ligands' cytotoxic effects were investigated on four human cancer cells and the greatest effect was on the breast MCF-7 cells. The compounds HL1, HL2, C1, C2 and doxorubicin revealed cytotoxicity with IC50 values of 52.4 ± 0.38, 153.7 ± 1.05, 37.5 ± 0.32, 21.8 ± 0.20 and 9.66±0.25 μM in the MCF-7 cancer cells and of 54.8 ± 0.85, 82.7 ± 0.44, 176.5 ± 0.70, 196.7 ± 1.16 and 36.42±0.08 μM in normal baby hamster kidney (BHK) cells.

Visualizing the Active Site Oxyanion Loop Transition Upon Ensitrelvir Binding and Transient Dimerization of SARS-CoV-2 Main Protease

N-terminal autoprocessing from its polyprotein precursor enables creating the mature-like stable dimer interface of SARS-CoV-2 main protease (MPro), concomitant with the active site oxyanion loop equilibrium transitioning to the active conformation (E*) and onset of catalytic activity. Through mutagenesis of critical interface residues and evaluating noncovalent inhibitor (ensitrelvir, ESV) facilitated dimerization through its binding to MPro, we demonstrate that residues extending from Ser1 through Glu14 are critical for dimerization. Combined mutations G11A, E290A and R298A (MPro™) restrict dimerization even upon binding of ESV to monomeric MPro™ with an inhibitor dissociation constant of 7.4 ± 1.6 µM. Contrasting the covalent inhibitor NMV or GC373 binding to monomeric MPro, ESV binding enabled capturing the transition of the oxyanion loop conformations in the absence of a reactive warhead and independent of dimerization. Characterization of complexes by room-temperature X-ray crystallography reveals ESV bound to the E* state of monomeric MPro as well as an intermediate approaching the inactive state (E). It appears that the E* to E equilibrium shift occurs initially from G138-F140 residues, leading to the unwinding of the loop and formation of the 310-helix. Finally, we describe a transient dimer structure of the MPro precursor held together through interactions of residues A5-G11 with distinct states of the active sites, E and E*, likely representing an intermediate in the autoprocessing pathway.

Thiosalicylanilide complexes of nickel(II), palladium(II) and platinum(II)

Reactions of the complexes cis-[PtCl2(PPh3)2], [PtCl2(dppf)] {dppf = Fe(C5H4PPh2)2}, [PdCl2(PPh3)2], [PdCl2(dppe)] (dppe = Ph2PCH2CH2PPh2) and [NiCl2(dppe)] with thiosalicylanilide (HSC6H4CONHPh, H2-1a) and its substituted derivatives H2-1b to H2-1d (where H2-1b = p-Cl-HSC6H4CONHPh, H2-1c = p-CH3-HSC6H4CONHPh, and H2-1d = m-OCH3-HSC6H4CONHPh) gave a series of square-planar MS2P2-type complexes. The complexes were characterised by ESI MS, 1H and 31P{1H} NMR, FTIR, and microelemental analyses, and in some cases by single crystal X-ray crystallography. The predominant coordination mode is through bonding of deprotonated thiol group of two ligands. However, the tendency to form complexes with a single, chelating S,N- and S,O-donor ligand was observed by 31P{1H} NMR in some reactions. In addition, cis/trans isomerisation was observed in some complexes by 31P{1H} NMR and confirmed by X-ray structure determinations on trans-[Pt(H-1b)2(PPh3)2] and trans-[Pd(H-1b)2(PPh3)2]. A comparison of the energetics of the reaction systems involving [Pt(1b)(PPh3)2]/[Pt(H-1b)2(PPh3)2], [Pt(1d)(PPh3)2]/[Pt(H-1d)2(PPh3)2] and [Pd(1b)(dppe)]/[Pd(H-1b)2(dppe)] using Density Functional Theory (DFT) revealed that the MS2P2 systems [Pt(H-1b)2(PPh3)2], [Pt(H-1d)2(PPh3)2] and [Pd(H-1b)2(dppe)] have lower Gibbs free energies than the S,N-chelate systems [Pt(1b)(PPh3)2], [Pt(1d)(PPh3)2] and [Pd(1b)(dppe)], and are thermodynamically favoured. Intermolecular interactions quantified and visualized on Hirshfeld surfaces for trans-[Pt(H-1b)2(PPh3)2], [Pt(H-1d)2(PPh3)2].H2O, and [Pd(H-1a)2(dppe)] revealed the dominant contribution of H···H contacts to crystal packing.

Anticancer, antimicrobial and photocatalytic activities of a new pyrazole containing thiosemicarbazone ligand and its Co(III) and Ni(II) complexes: Synthesis, spectroscopic characterization and X-ray crystallography

A new pyrazole based thiosemicarbazone ligand, 5-methyl-3-formylpyrazole-N(4)-isopropylthiosemicarbazone, (HMPzNHPri) (compound I), and its cobalt(III) and nickel(II) complexes, [Co(MPzNHPri)2]Cl (compound II) and [Ni(HMPzNHPri)2]Br2 (compound III), respectively, have been synthesized and characterized through various physico-chemical and spectroscopic studies. Both the reported Co(III) and Ni(II) complexes are cationic in nature and behave as 1:1 and 1:2 electrolytes in MeOH, respectively. Electronic spectral features of the complexes have classified them as distorted octahedral ones. IR spectral data (4000–450 cm−1) have suggested a monoprotic tridentate (NNS) function of compound I coordinating to the Co(III) ion via the pyrazolyl (tertiary) ring nitrogen, azomethine nitrogen and thiolato sulphur atom; while for compound III, compound I has been found to act as neutral NNS tridentate one, coordinating to Ni(II) via the pyrazolyl iminic nitrogen, azomethine nitrogen and thioketo sulphur. Structural features of all the compounds are confirmed by the single crystal X-ray data. All the compounds reported here have been found to exhibit significant photocatalytic activity towards degradation of Methylene Blue (MB) under UV radiation. Anticancer activity of all the three compounds against cancer cell lines (HeLa and A549) and a normal cell line (HEK293) have been investigated. Compound II has been found to be more efficient against the human cervical cancer cell (HeLa) and the lung cancer cell (A549) than compounds I and III. The ligand and both the complexes display potential activities against both gram-positive (Bacillus subtilis MTCC 7193) and gram-negative bacteria (E. coli MTCC 1610).