Ligands L1 Research Articles

Formation of a Decanuclear Organometallic Dysprosium Complex via a Radical–Radical Cross–Coupling Reaction

AbstractOver the years, polynuclear cyclic or torus complexes have attracted increasing interest due to their unique metal topologies and properties. However, the isolation of polynuclear cyclic organometallic complexes is extremely challenging due to their inherent reactivity, which stems from the labile and reactive metal‐carbon bonds. In this study, the pyrazine ligand undergoes a radical‐radical cross‐coupling reaction leading to the formation of a decanuclear [(Cp*)20Dy10(L1)10] ⋅ 12(C7H8) (1; where L1 = anion of 2‐prop‐2‐enyl‐2H‐pyrazine; Cp* = pentamethylcyclopentadienyl) complex, where all DyIII metal centres are bridged by the anionic L1 ligand. Amongst the family of polynuclear Ln organometallic complexes bearing CpR2Lnx units (CpR = substituted cyclopentadienyl), 1 features the highest nuclearity obtained to date. In‐depth computational studies were conducted to elucidate the proposed reaction mechanism and formation of L1, while probing of the magnetic properties of 1, revealed slow magnetic relaxation upon application of a static dc field.

Synergizing Steric Hindrance and Stacking Interactions To Facilitate the Controlled Assembly of Multiple 41 Metalla‐Knots and Pseudo‐Solomon Links

AbstractIn this work, a noncoplanar terphenyl served as a building block to synthesize a novel 3,3′‐substituted bipyridyl ligand (L1) which further reacted with binuclear half‐sandwich units A/B, giving rise to two aesthetic 41 metalla‐knots in high yields via a coordination‐driven self‐assembly strategy. Furthermore, given the inherent compactness of the 41 metalla‐knots, it creates favorable conditions for the emergence of steric repulsion. We focused on progressively introducing nitrogen atoms featuring a lone pair of electrons (LPEs) into ligand L1 to manipulate the balance of H⋅⋅⋅H/LPEs⋅⋅⋅LPEs steric repulsion during the assembly process, ultimately achieving controlled assembly from 41 metalla‐knots to the pseudo‐Solomon link and then to molecular tweezer‐like assembly facilitated by stacking interactions. All the assemblies were well characterized by solution‐state NMR techniques, ESI‐TOF/MS, and single‐crystal X‐ray diffraction. The evolutionary process of the topological architectures is equivalent to visualizing the synergistic effect of steric hindrance and stacking interactions on structural assembly, providing a new avenue for achieving the controlled synthesis of different topologies.

Synergizing Steric Hindrance and Stacking Interactions To Facilitate the Controlled Assembly of Multiple 41 Metalla-Knots and Pseudo-Solomon Links.

In this work, a noncoplanar terphenyl served as a building block to synthesize a novel 3,3'-substituted bipyridyl ligand (L1) which further reacted with binuclear half-sandwich units A/B, giving rise to two aesthetic 41 metalla-knots in high yields via a coordination-driven self-assembly strategy. Furthermore, given the inherent compactness of the 41 metalla-knots, it creates favorable conditions for the emergence of steric repulsion. We focused on progressively introducing nitrogen atoms featuring a lone pair of electrons (LPEs) into ligand L1 to manipulate the balance of H⋅⋅⋅H/LPEs⋅⋅⋅LPEs steric repulsion during the assembly process, ultimately achieving controlled assembly from 41 metalla-knots to the pseudo-Solomon link and then to molecular tweezer-like assembly facilitated by stacking interactions. All the assemblies were well characterized by solution-state NMR techniques, ESI-TOF/MS, and single-crystal X-ray diffraction. The evolutionary process of the topological architectures is equivalent to visualizing the synergistic effect of steric hindrance and stacking interactions on structural assembly, providing a new avenue for achieving the controlled synthesis of different topologies.

High-temperature stable chromium complexes bearing fluorinated PNP ligands for selective ethylene tetramerization toward 1-octene

A series of new fluorinated PNP ligands of bis(ortho-fluorophenyl)-type (L1-L2) and ortho-fluorophenyl-type (L3-L4) have been synthesized and assessed for the selectivity of ethylene oligomerization. Compared to the non-fluorinated analogue ligand L6, the fluorinated ligand L1 exhibited approximately three times high catalytic activity. The bis(ortho-fluorophenyl)-type ligand L2 with a diethylphosphine substituent offered the highest catalytic performance of 3548 kg∙g−1∙h−1 and the 1-octene selectivity is 67.6 %. Both the L1 and L2 ligands exhibited excellent the activity of catalyst at a high temperature of 100 ℃, with ligand L2 providing the catalytic performance of 1587 kg∙g−1∙h−1 and good selectivity of 47.5 % for 1-C8=. The ortho-fluorophenyl substituent enhances the catalytic activity, while the para-fluorophenyl substituent reduces the catalytic activity. In addition, density functional theory (DFT) calculations and UV–vis spectroscopy have been used to rationalize the role of the fluorine effect in promoting catalytic performance. Our results indicated that the strong inductive effect of fluorine atoms and the non-covalent interaction between fluorine atoms and active centers jointly enhance the stability of the ortho-fluorophenyl-based catalyst and promote its overall activity.

Enhancing enantioselectivity of manganese catalyst for asymmetric transfer hydrogenation of ketones through P,N,N-chelation of a cyclooctyl pyridine

A new ferrocene-based chiral PNN pincer ligand (L1) was successfully applied in Mn-catalyzed asymmetric transfer hydrogenation (ATH) of ketones (37 examples), leading to high activities (up to 4000 TON with 48 h) and excellent enantioselectivities (up to >99 % ee) for their product alcohols. The combined coordination and catalytic studies led to the conclusion that PNN pincer ligand L1 proved higher enantioselectivity in ATH than that observed by PN bidentate analogue L0. Furthermore, DFT calculations and control experiments highlighted the significance of the cyclooctyl group among these cycloalkyl motifs in the Mn-catalysts, resulting in enhanced enantioselectivity (up to 99 % ee), and disclosed the stereocontrol with the assistance of an attractive aromatic π-π stacking interaction between substrate and catalyst in the catalytic process.

Chemo-, regio- and enantioselective hydroformylation of trisubstituted cyclopropenes: access to chiral quaternary cyclopropanes

Catalytic asymmetric synthesis of polysubstituted chiral cyclopropane presents a significant challenge in organic synthesis due to the difficulty in enantioselective control. Here we report a rhodium-catalyzed highly chemo-, regio- and enantioselective hydroformylation of trisubstituted cyclopropenes affording chiral quaternary cyclopropanes. Importantly, the easy made sterically bulky ligand L1 can effectively suppress hydrogenation and decomposition reactions and give quaternary cyclopropanes with high regio- and enantioselectivities for both aryl and alkyl functionalized substrates. Control experiments and computational studies reveal the sterically hindered well-defined chiral pocket instead of the substrates bearing electron-withdrawing diester groups is important for controlling the enantioselectivity and regioselectivity. Scale-up reaction and follow-up diverse transformations are also presented. Density Functional theory (DFT) computations suggest that the regio- and enantio-selectivities originate from the cyclopropene insertion to the Rh-H bond. The high regioselectivity is found to benefit from the presence of more efficient noncovalent interactions (NCIs) manifesting in the form of C–H···Cl, C–H···N, and l.p(Cl)···π contacts.

Two one‐dimensional cuprous iodide coordination polymers: Efficient and robust electrocatalysts for hydrogen evolution and glucose‐sensing

Development of efficient, low‐cost, robust, and structure tunability electrocatalysts for hydrogen evolution reaction (HER) is one of the main subjects of present study in renewable energies. In this work, two new cuprous iodide coordination polymers (Cu‐CPs) containing bisbenzimidazole‐derived ligand, namely, {[Cu2(L1)(μ2‐I)2]·DMF}n (1) and {[Cu(L2)0.5(μ2‐I)]·DMF} (2) (L1 = (2,2′‐(1,3‐propanediyl)‐6,6′‐bis(3‐methylpyridine)bis‐1,3‐benzimidazole); L2 = (2,2′‐(1,4‐butanediyl)‐7,7′‐bis(3‐methylpyridine)bis‐1,3‐benzimidazole); DMF = dimethyl formamide), were prepared under solvothermal conditions and structurally characterized. Single‐crystal structural analysis showed that although two Cu‐CPs have a one‐dimensional (1D) chain backbone structure, the coordination environment of cuprous is different. It is found that different coordination modes of ligands L1 and L2 lead to different coordination environments of central ions in two cuprous CPs. Electrocatalytic HER of modified electrodes (CP‐1~2/glassy carbon electrode [GCE]) prepared by coating the mixed solution of acetylene black, CPs 1–2, and Nafion on the surface of GCE was investigated in 0.5 M H2SO4 electrolyte. The HER measurements show that the overpotential η10293K of CP‐1~2/GCE positively shifted 113 and 74 mV compared with bare GCE (blank electrode, −930 mV), and the Tafel slope of bare/GCE and CP‐1~2/GCE were 298, 101, and 138 mV dec−1, respectively. The results indicate that CP‐1~2/GCE could effectively catalyze and accelerate the HER behavior, with electrocatalytic activity order being CP‐1/GCE > CP‐2/GCE > bare/GCE. The higher HER activity of the CP‐1/GCE can be attributed to that the coordination deformability of cuprous ion in CP 1 is greater. Furthermore, the recognition performance of CP‐1~2/GCE for glucose was further studied by chronoamperometry in 0.1 M NaOH. The two sensors can detect glucose in a linear range from 1 μM to 4 mM with sensitivities of 13.736 and 18.945 μA mM−1, and also revealed long‐term stability and good selectivity. These results indicate that cuprous CPs deserve further investigation as potential electrocatalyst candidates.

Platinum complexes with pyridyl derivatives of 1,2,4-triazole

The chemistry of platinum(II) and platinum(IV) with the ligands 3,4,5-tris(2-pyridyl)-4-H-1,2,4-triazole, L1, and 3,5-di(2-pyridyl)-4-(4-pyridyl)-4-H-1,2,4-triazole, L2, is described. The ligand L1 forms platinum(II) complexes [PtXY(κ2-N,N’-L1)] (X,Y = Cl,Cl; Cl,Me; Me,Me) by chelation while ligand L2 forms either analogous chelate complexes [PtXY(κ2-N,N’-L2)] (X,Y = Cl,Me; Me,Me) or acts as a monodentate ligand in forming trans-[PtCl2(SMe2)(κ1-N-L2)], in which only the 4-pyridyl group is coordinated. The electron-rich dimethylplatinum(II) complexes undergo oxidative addition reactions with methyl iodide to give [PtIMe3(κ2-N,N’-L1)], or with dichloromethane to give [PtClMe2(CH2Cl)(κ2-N,N’-L1)] or [PtClMe2(CH2Cl)(κ2-N,N’-L2)], each of which is formed as a mixture of three isomers. Structure determinations of several of these complexes are reported.

Bifunctional Ligands: Evaluating the Role of Acidic Protons in the Secondary Coordination Sphere.

To evaluate bifunctional ligand reactivity involving NH acidic sites in the secondary coordination sphere, complexes where the proton has been substituted with a methyl group (NMe) are often investigated. An alternative strategy involves substitution of the NH group for an O. This contribution considers and compares the merits of these approaches; the synthesis and characterization of cationic square-planar Rh carbonyl complexes bearing diprotic bispyrazole pyridine ligand L1, and the bis-methylated pyrazole pyridine ligand L1Me are described. The syntheses and characterization of the novel monoprotic pyrazole isoxazole pyridine ligand L2 and aprotic bisisoxazole pyridine ligand L3, and their corresponding Rh carbonyl complexes are also described. Comparison of the CO stretching frequencies of the four Rh complexes suggest that substitutions of NH with NMe, as well as with O, lead to significant electronic differences. These electronic differences result in different reactivities with respect to ligand addition/substitution of the Rh carbonyl complexes. Overall, the data suggest that electronic differences arising due to the NH substitutions can be significant and should be considered when the NH group is substituted in investigations of the participation of the NH proton in a reaction.

Preparation, characterization, single-crystal analysis, and cytotoxic assessment of complexes formed by Schiff base and 8-hydroxyquinoline co-ligand with Co(II), Ni(II), and Mn(II) metal ions

This study focuses on the preparation of mixed ligand complexes of Ni(II), Co(II), and Mn(II) by combining the co-ligands 2-(((4-fluorophenyl)imino)methyl)-4-methoxy-6-nitrophenol (L1) and 8-hydroxyquinoline (L2). The chemical structures of the all compounds were examined using various techniques, including 1H and 13C NMR, FT-IR, UV–Vis, TGA, molar conductivity, LC-MS/MS, elemental analysis and magnetic susceptibility. The crystal structure of the ligand L1 was determined using single crystal X-ray analysis revealing that the ligand favors the phenol-imine tautomeric form in the solid state. All complexes are suggested to have an octahedral structure. Finally, the MTT assay was used to determine the toxicity level of the mixed ligand complexes in human non-small cell lung cancer (A549) and normal bronchial epithelial cell lines (BEAS-2B). The results showed that the [Ni(L1)(L2).(H2O)2] complex (IC50: 5.97 µM) exhibited high cytotoxic activity at a lower dose than cisplatin compared to the other compounds. In contrast, the [Ni(L1)(L2).(H2O)2] complex was shown to exhibit significantly lower cytotoxic activity (IC50 > 100 s µM) in the BEAS-2B (normal bronchial epithelial cell) cell line. The other compounds [Co(L1)(L2).(H2O)2] and [Mn(L1)(L2).(H2O)2] were shown to have no significant anticancer activity in A549 cells due to their cytotoxic activity at higher doses than cisplatin (IC50 > 100 s µM).

Elucidating the crystal structures of heteronuclear salen complexes CuL-CdX2 with experimental and computational methods

Two novel heteronuclear salen-type complexes, CuL1-CdCl2 and CuL2-CdI2, have been successfully synthesized and characterized. The characterization processes utilized single-crystal X-ray diffraction, elemental, and FT-IR analysis, revealing the structural properties of the complexes. In both complexes, the Cu(II) ion exhibited an approximate square planar geometry (CuN2O2), where the deprotonated phenoxide-type ligand L2− coordinated to form N2O2. Conversely, For CuL1-CdCl2, the Cd(II) ion displayed a trigonal prismatic geometry, surrounded by two chlorine atoms and four oxygen atoms. Intermolecular and intramolecular interactions within the complex were facilitated by CH···Cl, CH···N, and CH···O hydrogen bondings. For CuL2-CdCl2, the Cd(II) ion displayed a trigonal prismatic geometry, surrounded by two iodine atoms and four oxygen atoms. Intermolecular interactions within the complex were facilitated by weak CH···I hydrogen bonding, while the overall stability of the framework was ensured through weak π···π stacking interactions. According to the Hirshfeld surface analysis results, the H···H contacts constitute a large part of the total surface area for both complexes; this highlights the importance of hydrogen bond interactions in stabilizing the crystal arrangement. The theoretical analysis of the complexes was executed by using Becke's three-parameter hybrid functional for the exchange component and the Lee-Yang-Parr (LYP) correlation function with the LanL2DZ basis set to achieve the optimized geometrical parameters. The results showed that experimental and theoretical calculations were in agreement.

Formation of a Decanuclear Organometallic Dysprosium Complex via a Radical-Radical Cross-Coupling Reaction.

Over the years, polynuclear cyclic or torus complexes have attracted increasing interest due to their unique metal topologies and properties. However, the isolation of polynuclear cyclic organometallic complexes is extremely challenging due to their inherent reactivity, which stems from the labile and reactive metal-carbon bonds. In this study, the pyrazine ligand undergoes a radical-radical cross-coupling reaction leading to the formation of a decanuclear [(Cp*)20Dy10(L1)10] ⋅ 12(C7H8) (1; where L1 = anion of 2-prop-2-enyl-2H-pyrazine; Cp* = pentamethylcyclopentadienyl) complex, where all DyIII metal centres are bridged by the anionic L1 ligand. Amongst the family of polynuclear Ln organometallic complexes bearing CpR 2Lnx units (CpR = substituted cyclopentadienyl), 1 features the highest nuclearity obtained to date. In-depth computational studies were conducted to elucidate the proposed reaction mechanism and formation of L1, while probing of the magnetic properties of 1, revealed slow magnetic relaxation upon application of a static dc field.

Estimation of Programed Death Ligand_1 Concentrations in Serum and Tissue Among Iraqi Breast Diseases

Abstract Background: A programed death ligand L1 is the particular PD-1 ligand that is primarily found in lymphoid, epithelial, and myeloid cells. In order to activate the PD-1/PD-L1 pathway, which suppresses the production of cytokines and controls immune function, PD-1 must bind to PD-L1. Objectives: Estimating the concentration of PDL_1 in serum and breast tissue of patients with breast tumors. Materials and Methods: Case–control study included 100 women (17–60 years old) undergoing breast surgery at Babylon Province’s Al-Hilla Teaching Hospital and Al-Fayhaa Al Ahly Hospital provided blood and breast tissue samples. Hospital histology lab performed histological confirmation of breast diseases, including benign and malignant tumors. Twenty blood samples were taken as controls from women and men who appeared to be in good health. The enzyme-linked immunosorbent assay was used to determine PDL_1 in both patient and control serum and in the cell supernatant from the patient’s breast tissues. Results: The mean level of PDL_1 in serum of patient was 549.37 ng/L while control was 594.22 ng/L with found significant differences where P value was 0.05. While tissue of patients was 464.97 ng/L. The results appeared concentrations of PDL-L1 were significantly higher in serum compared with tissues at P ≥ 0.05. The results found no significantly differences in concentrations of PDL_1 among types of diseases in sera of patients except in fat necrosis patients. Perhaps as a result of our small sample size, the difference in PD-L1 expression between the various subtypes was not statistically significant. Conclusion: This study found concentration of PDL-1 decreased with primary breast diseases and it might be diagnostic marker.

2‐Pyridinyl/quinolyl‐phenylamino‐quinoline Complexes With CF3 and C2F5 Ligated Ni

A new ligand architecture based on quinoline/pyridine attached ortho to the amine functionality on an aniline, which is coupled to another quinoline unit has been prepared. Ligands L1 and L2 have been complexed with CF3 and C2F5 ligated nickel centers. The resulting complexes have been extensively studied by NMR spectroscopy (on 1H, 13C{1H}, and 19F nuclei) and single‐crystal X‐ray crystallography. A poorly defined mixture of complexes obtained from L1 and nickel bis‐trifluoromethyl complex was moderately active in C‐H trifluoromethylation with the Umemoto I reagent.

Insights into Metabolites Profiling and Pharmacological Investigation of Aconitum heterophyllum wall ex. Royle Stem through Experimental and Bioinformatics Techniques.

The Aconitum genus is a leading source of a wide range of structurally diverse metabolites with significant pharmacological implications. The present study investigated metabolite profiling, pharmacological investigation, anticancer potential, and molecular docking analysis of the stem part of Aconitum heterophyllum (AHS). The metabolite profiling of the AHS extract was experimentally examined using LC-MS/MS-orbitrap in both modes (ESI+/ESI-) and GC-MS in EI mode. The in vitro MTT model was used to study the anticancer potential, while the in vivo animal model was used to study the anti-inflammatory and antinociceptive activities. The MOE software was used for the molecular docking study. A total of 118 novel and previously known metabolites, among 44 metabolites (26 in ESI+ positive mode and 18 in ESI- negative mode) in the MeOH extract, while 74 metabolites (46 in ESI+ and 28 in ESI- mode) were identified in the n-hexane extract via LCMS/MS. The identified metabolites include 24 phenolic compounds, 18 alkaloids, 10 flavonoids, 24 terpenoids, 2 coumarins, 2 lignans, and 38 other fatty acids and organic compounds. The major bioactive metabolites identified were hordenine, hernagine, formononetin, chrysin, N-methylhernagine, guineesine, shogaol, kauralexin, colneleate, zerumbone, medicarpin, boldine, miraxinthin-v, and lariciresinol-4-O-glucoside. Furthermore, the GC-MS study helped in the identification of volatile and nonvolatile chemical constituents based on the mass spectrum and retention indices. The methanol extract significantly inhibited tumor progression in H9c2 and MDCK cancer cells with IC50 values of 186.39 and 199.63 μg/mL. In comparison, the positive control aconitine exhibited potent IC50 values (132.32 and 141.58 μg/mL) against H9c2 and MDCK cell lines. The anti-inflammatory (carrageenan-induced hind paw edema) and antinociceptive (acetic acid-induced writhing) effects were significantly dose-dependent, (p < 0.001) and (p < 0.05), respectively. In addition, a molecular docking study was conducted on identified ligands against the anti-inflammatory enzyme (COX-2) (PDB ID: 5JVZ) and the cancer enzyme ADAM10 (PDB ID: 6BDZ) which confirmed the anti-inflammatory and anticancer effects in an in silico model. Among all ligands, L2, L3, and L7 exhibit the most potent potential for inhibiting COX-2 inflammation with binding energies of -7.3424, -7.0427, and -8.3562 kcal/mol. Conversely, against ADAM10 cancer protein, ligands L1, L4, L6, and L7, with binding energies of -8.0650, -7.7276, -7.0454, and -7.2080 kcal/mol, demonstrated notable effectiveness. Overall, the identified metabolites revealed in this AHS research study hold promise for discovering novel possibilities in the disciplines of chemotaxonomy and pharmacology.

Ocean alkalinity enhancement using sodium carbonate salts does not lead to measurable changes in Fe dynamics in a mesocosm experiment

Abstract. The addition of carbonate minerals to seawater through an artificial ocean alkalinity enhancement (OAE) process increases the concentrations of hydroxide, bicarbonate, and carbonate ions. This leads to changes in the pH and the buffering capacity of the seawater. Consequently, OAE could have relevant effects on marine organisms and in the speciation and concentration of trace metals that are essential for their physiology. During September and October 2021, a mesocosm experiment was carried out in the coastal waters of Gran Canaria (Spain), consisting on the controlled variation of total alkalinity (TA). Different concentrations of carbonate salts (NaHCO3 and Na2CO3) previously homogenized were added to each mesocosm to achieve an alkalinity gradient between Δ0 to Δ2400 µmol L−1. The lowest point of the gradient was 2400 µmol kg−1, being the natural alkalinity of the medium, and the highest point was 4800 µmol kg−1. Iron (Fe) speciation was monitored during this experiment to analyse total dissolved iron (TdFe, unfiltered samples), dissolved iron (dFe, filtered through a 0.2 µm pore size filter), soluble iron (sFe, filtered through a 0.02 µm pore size filter), dissolved labile iron (dFe′), iron-binding ligands (LFe), and their conditional stability constants (KFeL′) because of change due to OAE and the experimental conditions in each mesocosm. Observed iron concentrations were within the expected range for coastal waters, with no significant increases due to OAE. However, there were variations in Fe size fractionation during the experiment. This could potentially be due to chemical changes caused by OAE, but such an effect is masked by the stronger biological interactions. In terms of size fractionation, sFe was below 1.0 nmol L−1, dFe concentrations were within 0.5–4.0 nmol L−1, and TdFe was within 1.5–7.5 nmol L−1. Our results show that over 99 % of Fe was complexed, mainly by L1 and L2 ligands with kFe′L′ ranging between 10.92 ± 0.11 and 12.68 ± 0.32, with LFe ranging from 1.51 ± 0.18 to 12.3 ± 1.8 nmol L−1. Our data on iron size fractionation, concentration, and iron-binding ligands substantiate that the introduction of sodium salts in this mesocosm experiment did not modify iron dynamics. As a consequence, phytoplankton remained unaffected by alterations in this crucial element.

A Bichromophoric Approach to Induce Luminescence - A Blend of Experimental and Theoretical Studies.

Two homoleptic terpyridyl complexes of Ru(II), 1 and Fe(II), 2 were synthesized using a ligand L1 that contained a phenyl spacer between an anthracenyl (An) and a terpyridyl (tpy) moiety. An equilibrated-bichromophoric strategy was adopted to induce photoluminescence in 1 and 2. A glimpse into the excited state photophysical properties of 1 and 2 revealed that 1 exhibited NIR emission at ~700 nm with an excited state lifetime components of 1.33 and 6.52 ns. On the other hand, 2 was found to be non-luminescent. The origin of emission in case of 1 was attributed to the effect of phenyl spacer which rendered the 3An state to be nearly isoenergetic to the emissive 3MLCT state of 1 facilitating 3MLCT-3An equilibrium. This fact was supported by experimental (photocurrent generation) and theoretical (potential energy diagram) evidences.

Antibacterial and cytotoxicity studies of pyrrolo-based organic scaffolds and their binding interaction with bovine serum albumin.

Two pyrrolo-based compounds, 1H-pyrrolo[3,2-b]pyridine-3-carboxylic acid (L1) and 1H-pyrrolo[3,2-c]pyridine-4-carboxylic acid (L2), were employed for the detection of bovine serum albumin (BSA) by UV-Vis and fluorescence spectroscopic methods in phosphate buffer solution (pH = 7). In the presence of L1 and L2, the fluorescence emission of BSA at 340 nm was quenched and concomitantly a red-shifted emission band appeared at 420 nm (L1)/450 nm (L2). The fluorescence spectral changes indicate the protein-ligand complex formation between BSA and L1/L2. An isothermal titration calorimetry (ITC) experiment was conducted to determine the binding ability between BSA and L1/L2. The binding constants are found to be 4.45 ± 0.22 × 104 M-1 for L1 and 2.29 ± 0.11 × 104 M-1 for L2, respectively. The thermodynamic parameters were calculated from ITC measurements (i.e. ∆rH = -40 ± 2 kcal/mol, ∆rG = -4.57 ± 0.22 kcal/mol and -T∆rS = 35.4 ± 1.77 kcal/mol), which indicated that the protein-ligand complex formation between L1/L2 with BSA is mainly due to the electrostatic interactions. The protein-ligand interactions were studied by performing molecular docking. Further, the antibacterial assay of L1 and L2 was conducted against gram-positive and gram-negative bacterial strains in an effort to address the difficulties caused by the co-occurrence of antimicrobial and multidrug-resistant bacteria. E. coli and S. aureus were significantly inhibited by L1 and L2. The L1 exhibits 13, 12 and 15 mm, whereas L2 exhibits a 2, 3 and 5 mm zone of inhibition against S. aureus, S. pyogenesand E. coli, respectively. In silico molecular docking of L1 and L2 was performed with bacterial DNA gyrase to establish the intermolecular interactions. Finally, the in vitro cytotoxicity activities of the ligands L1 and L2 have been carried out using drosophila.

Mononuclear Fe(III) Schiff Base Complex with Trans-FeO4N2 Chromophore of o-Aminophenol Origin: Synthesis, Characterisation, Crystal Structure, and Spin State Investigation

A new iron(III) complex (Et3NH)2[Fe(L)2](ClO4)·MeOH (1) where H2L = 2-{(E)-[2-hydroxyphenyl)imino]methyl}phenol has been synthesised and characterised by single crystal XRD, elemental analysis and DC magnetic susceptibility measurements. The dianionic ligands L2− coordinate in a tridentate fashion with the Fe(III) through their deprotonated phenolic oxygens and azomethine nitrogen atoms, resulting in a trans-FeO4N2 chromophore. Variable-temperature magnetic measurements were performed between 300 and 5 K under an applied field of 0.1 T and show that 1 is in the high spin state (S = 5/2) over the whole measured temperature range. This is confirmed by Mössbauer spectroscopy at 77 and 300 K.

Platinum(II) phosphoryl-substituted thiourea complexes with bis-phosphine ligands and some triphenylarsine and triphenylstibine analogues

Reactions between the phosphorylthiourea ligands (EtO)2PONHC(S)NHPh (L1), (EtO)2PONHC(S)NHCH(CH3)3) (L2) and (EtO)2PONHC(S)NHCH2CH3 (L3) and cis-[PtCl2(PPh3)2] gave complexes in which the ligands bind to the platinum(II) centre as dianionic ligands. For ligands L1 and L3, the ligand binds through the thiourea sulfur and the N-alkyl nitrogen atoms, giving the distal isomer. In contrast, the ligand L2, on account of the bulky t-butyl substituent on the ligand, coordinates via the sulfur and N-phosphoryl nitrogen atoms, giving the proximal isomer. The identities of the isomers were confirmed by single crystal X-ray analysis and 31P{1H} NMR spectroscopy. The latter showing that the appearance or absence of 3J(PP) couplings between the ligand and ancillary ligands provides indicative isomeric information. Further reactions between the ligand L1 and a series of bis-phosphine, triphenylarsine and triphenylstibine platinum(II) starting complexes gave the corresponding products also as the distal linkage isomer. Computational analysis reveals a possible chalcogen bond non-covalent interaction that may be responsible for the preference for the distal isomer.