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A mononuclear air-stable and water soluble six coordinated cadmium (II) complex [Cd(HL)6](ClO4)2 (1) with bi-dentate phenol based ligand [HL = 2-(benzylimino)methyl)phenol] have been synthesized. The complex has been characterized by various spectroscopic techniques. The solid-state structure, by single crystal X-ray diffraction, revealed that Cd(II) complex crystallizes in trigonal space group R-3. Interestingly, single crystal Xray structure data show that the Schiff base in the complex is present in a zwitterionic form and coordinated through the phenolic oxygen atom only, providing the first example of more than four monodendate Schiff base in zwitterionic form to be coordinated with the central metal ion. Cyclic voltamogram of the cadmium (II) complex (1) exhibits a quasi-reversible oxidation peak in the positive potential region. The redox process occurs due to the generation of phenoxyl radical from the pheolate group of the attached ligand with the central metal ion. Luminescence spectra show a strong emission band around 500 nm. Additionally, the mononuclear cadmium complex (1) shows catechol oxidase activity in methanol under aerobic conditions. The turnover number of the process is 2.766 × 103 h–1. The oxidation process occurs via formation of ligand oriented phenoxyl radical species.

Journal of Molecular Structure

A protonated imine-based water-soluble cadmium complex with N, O donor chelating agent: Synthesis, structure, fluorescence efficiency and catecholase activity

The design of amino acid sensors have significant applications in biomarkers. Herein, we have developed an achiral Fe(III)-complex [FeIIIL(bzac)] (complex 1) (H2L = N,N′-dimethyl-N,N′-bi(2-hydroxy-3,5-dichlorobenzyl)-ethylenediamine (H2L) that shows highly selective sensing of histidine over others in an aqueous methanolic solution. The complex has been synthesized by a simple stirring method using H2L and benzylacetone (bzac) as the ancillary ligand and characterized by single crystal X-ray diffraction analysis along with other spectroscopic studies. Structural study shows that it is a simple mononuclear complex though the single molecule is chiral; however, the overall crystalline lattice is achiral in nature. In the complex, Fe(III) shows distorted octahedral geometry, and each discrete complex is connected by supramolecular hydrogen bonding interactions to form achiral 3D supramolecular structure. Both the absorption spectral analyses reveal that the complex has peaks at 484 nm due to ligand-to-metal charge transfer (LMCT) and emission spectra have a peak at 566 nm. In the presence of histidine, there is a red-shift of about 70 nm and peaks arise at about 564 nm, while the emission spectra shows that the peak at 566 nm disappears completely and a new peak at 603 nm appears. In the presence of other amino acids, there is no such distinct change in both the absorption and emission spectra of the complex. It also acts as an effective catalyst toward the oxidation of 3,5-di-tert-butylcatechol in methanol solvent.

New Journal of Chemistry

A new mononuclear Fe(iii) Mannich-base complex with selective histidine binding and catechol oxidase activity

A square-planar Cu(II) complex [Cu(L)Cl], 1, with sterically constrained tridentate phenol-based ligand (HL= N,N,N′-trimethyl-N′-(2-hydroxy-3,5-di-tert-butylbenzyl)-ethylenediamine) with N, N, O donor sites has been synthesized. The complex is characterized by single crystal X-ray diffraction study as well as other spectroscopic techniques. The reported complex crystallizes in monoclinic space group C2/c with a = 30.248(6), b = 13.750(3) and c = 11.410(2) Å with β = 110.232(2)°. The Cu(II) ion adopts a square planar environment in this complex. Electrochemical study of the complex 1 gives quasi-reversible reductive response at E1/2 ≈ −0.5 V due to the reduction of the Cu(II) center along with a reversible oxidation peak at E1/2 ≈ 0.75 V. The oxidation peak arises due to the ligand-based oxidation of phenolate group to phenoxyl radical in the complex. The Cu(II) complex exhibits catechol oxidase activity in methanol as observed by the UV–vis spectroscopy of the aerial oxidation of 3,5-DTBC to 3,5-DTBQ and the reaction proceeds via the formation of ligand phenoxyl radical. The turnover number for complex 1 is 2560 h−1.

Fulltext

Crystals

Synthesis, Structure and Catechol Oxidase Activity of Mono Nuclear Cu(II) Complex with Phenol-Based Chelating Agent with N, N, O Donor Sites

Two new monomeric copper(II) complexes based on 1,3-dimethyl-5-(4′/3′-pyridylazo)-6-aminouracil (HL1: 4′-pyridylazo, complex 1: cis-CuIIL12.MeOH; HL2: 3′-pyridylazo, complex 2: cis-CuIIL12.H2O) were synthesized, characterized and investigated for redox, magnetic and protein-binding properties. The complex 1 is in monoclinic space group C2/c, Z = 4 whereas the complex 2 is in triclinic space group P-1, Z = 2. The complexes hold similar structure in solid and solution state as could be infered from the EPR spectra of 1 having well-resolved hyperfine features, g|| &gt; g┴ &gt; ge (g|| =2.20 and g┴ =2.05). The E½ values for oxidative response of Cu(III)/Cu(II) couple are 1.030 V (ΔE = 133 mV) for 1 and 0.982 V (ΔE = 128 mV) for 2, indicating high redox stability of Cu(II) ions in the complex environment. Direct current (DC) variable-temperature magnetic susceptibility measurements on polycrystalline sample of 1 were carried out in the temperature range 1.8-300 K. The magnetic behavior indicates a weak antiferromagnetic interaction between Cu(II) ions in the crystal lattice below 25 K. The study of Bovin Serum Albumin (BSA)-complex interactions reveals that the BSA binds the complexes through the sites of tryptophan residues in 1:1 manner (n = 0.9007 &amp; KA = 1.482 × 104M−1 for 1 and 0.7433 &amp; KA =2.394×103M−1 for 2). Thus, the developed complexes could be treated as muti-functional materials. © 2021 Elsevier B.V. &nbsp;

<figure class="table"><table><tbody><tr><td>Copper(II) complexes of 1,3-dimethyl-5-(4′/3′-pyridylazo)-6-aminouracil: Structures, redox, magnetic and protein binding properties</td></tr></tbody></table></figure>

Ruthenium complexes are being studied extensively as anticancer drugs following the inclusion of NAMI-A and KP1019 in phase II clinical trials for the treatment of metastatic phase and primary tumors. Herein, we designed and synthesized four organometallic Ru(II)-arene complexes [Ru(η6-p-cymene)(L)Cl] (1), [Ru(η6-benzene)(L)Cl] (2), [Ru(η6-p-cymene)(L)N3] (3) and [Ru(η6-benzene)(L)N3] (4) [HL = (E)-N′-(pyren-1-ylmethylene)thiopene-2-carbohydrazide] that have anticancer, antimetastatic and two-photon cell imaging abilities. Moreover, in the transfer hydrogenation of NADH to NAD+, these compounds also display good catalytic activity. All the complexes, 1–4, are well characterized by spectroscopic techniques (NMR, mass, FTIR, UV-vis and fluorescence). The single crystal X-ray diffraction technique proved that the ligand L coordinates through an N,O-bidentate chelating fashion in the solid-state structures of complexes 1 and 2. The stability study of the complexes was performed through UV-visible spectroscopy. The cytotoxicities of all the complexes were screened through MTT assay and the results revealed that the complexes have potential anticancer activity against various cancerous cells (HeLa, MCF7 and A431). Studies with spectroscopic techniques revealed that complexes 1–4 exhibit strong interactions with biological molecules i.e. proteins (HSA and BSA) and CT-DNA. The density functional theory (DFT-D) method has been employed in the present study to know the interaction between DNA and complexes by calculating the HOMO and LUMO energy. A plausible mechanism for NADH oxidation has also been explored and the DFT calculations are found to be in accord with the experimental observation. Furthermore, we have investigated intracellular reactive oxygen species (ROS) generation capabilities in the MCF7 breast cancer cell line. The Hoechst/PI dual staining method confirmed the apoptosis mode of cell death. Meanwhile, complexes 1–4 show capabilities to prevent the metastasis phase of cancer cells by inhibiting cell migration.

Dalton Transactions

Pyrene-based fluorescent Ru(ii)-arene complexes for significant biological applications: catalytic potential, DNA/protein binding, two photon cell imaging and in vitro cytotoxicity

Inorganic macrocycles remain challenging synthetic targets due to the limited number of strategies reported for their syntheses. Among these species, large fully inorganic cyclodiphosphazane macrocycles have been experimentally and theoretically highlighted as promising candidates for supramolecular chemistry. In contrast, their hybrid organic–inorganic counterparts are lagging behind due to the lack of synthetic routes capable of controlling the size and topological arrangement (i.e., folded vs unfolded) of the target macrocycle, rendering the synthesis of differently sized macrocycles a tedious screening process. Herein, we report—as a proof-of-concept—the combination of pre-arranged building blocks and a two-step synthetic route to rationally enable access a large unfolded tetrameric macrocycle, which is not accessible via conventional synthetic strategies. The obtained macrocycle hybrid cyclodiphosphazane macrocycle, cis-[μ-P(μ-NtBu)]2(μ-p-OC6H4C(O)O)]4[μ-P(μ-NtBu)]2 (4), displays an unfolded open-face cavity area of 110.1 Å2. Preliminary theoretical host–guest studies with the dication [MeNC5H4]22+ suggest compound 4 as a viable candidate for the synthesis of hybrid proto-rotaxanes species based on phosphazane building blocks.

Communications Chemistry

Pre-arranged building block approach for the orthogonal synthesis of an unfolded tetrameric organic–inorganic phosphazane macrocycle

A mononuclear octahedral mixed-ligand cobalt (II) complex [Co(H2L)(PhCOO)2] (1) has been prepared by using H2L (N,N′-dimethyl-N,N′-bi(2-hydroxy-3,5-di methyl benzyl)-ethylenediamine) as a facially coordinating tetradentate ligand with a N2O2 donor center along with sodium benzoate as an ancillary ligand. Complex 1 has been characterized by a single-crystal X-ray diffraction study, as well as by other spectroscopic tools. The complex crystallizes in the monoclinic space group C2 with a = 31.73(3) Å, b = 7.868(3) Å, c = 19.131(15) Å, and β = 125.25(3)°. The single-crystal X-ray diffraction study shows that in the mononuclear cobalt (II) complex [Co(H2L)(PhCOO)2] (1), the metal center adopts an octahedral environment. © 2022 by the authors.

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MolBank

Synthesis, Characterization, and Structure of Mixed-Ligand Cobalt (II) Complex with N, O Donor Sites

We present a new approach to study the one-dimensional Dirac equation in the background of a position-dependent mass m. Taking the Fermi velocity v f to be a local variable, we explore the resulting structure of the coupled equations and arrive at an interesting constraint of m turning out to be the inverse square of v f. We address several solvable systems that include the free particle, shifted harmonic oscillator, Coulomb and nonpolynomial potentials. In particular, in the supersymmetric quantum mechanics context, the upper partner of the effective potential yields a new form for an inverse quadratic functional choice of the Fermi velocity. © 2021 IOP Publishing Ltd.

Journal of Physics A: Mathematical and Theoretical

Position-dependent mass Dirac equation and local Fermi velocity

Background: Malaria remains one of the most virulent and deadliest parasitic disease in the world, particularly in Africa and Southeast Asia. Widespread occurrence of artemisinin-resistant Plasmodium falciparum strains from the Greater Mekong Subregion is alarming. This hinders the national economies, as well as being a major drawback in the effective control and elimination of malaria worldwide. Clearly, an effective anti-malarial drug is urgently needed. Methods: The dinuclear and mononuclear copper(II) and zinc(II) complexes were synthesized in ethanolic solution and characterized by various physical measurements (FTIR, CHN elemental analysis, solubility, ESI-MS, UV-Visible, conductivity and magnetic moment, and NMR). X-ray crystal structure of the dicopper(II) complex was determined. The in vitro haemolytic activities of these metal complexes were evaluated spectroscopically on B+ blood while the anti-malarial potency was performed in vitro on blood stage drug-sensitive Plasmodium falciparum 3D7 (Pf3D7) and artemisinin-resistant Plasmodium falciparum IPC5202 (Pf5202) with fluorescence dye. Mode of action of metal complexes were conducted to determine the formation of reactive oxygen species using PNDA and DCFH-DA dyes, JC-1 depolarization of mitochondrial membrane potential, malarial 20S proteasome inhibition with parasite lysate, and morphological studies using Giemsa and Hoechst stains. Results: Copper(II) complexes showed anti-malarial potency against both Pf3D7 and Pf5202 in sub-micromolar to micromolar range. The zinc(II) complexes were effective against Pf3D7 with excellent therapeutic index but encountered total resistance against Pf5202. Among the four, the dinuclear copper(II) complex was the most potent against both strains. The zinc(II) complexes caused no haemolysis of RBC while copper(II) complexes induced increased haemolysis with increasing concentration. Further mechanistic studies of both copper(II) complexes on both Pf3D7 and Pf5202 strains showed induction of ROS, 20S malarial proteasome inhibition, loss of mitochondrial membrane potential and morphological features indicative of apoptosis. Conclusion: The dinuclear [Cu(phen)-4,4′-bipy-Cu(phen)](NO3)4 is highly potent and can overcome the total drug-resistance of Pf5202 towards chloroquine and artemisinin. The other three copper(II) and zinc(II) complexes were only effective towards the drug-sensitive Pf3D7, with the latter causing no haemolysis of RBC. Their mode of action involves multiple targets. Graphical Abstract: [Figure not available: see fulltext.]. © 2022, The Author(s).

Malaria Journal

Dinuclear and mononuclear metal(II) polypyridyl complexes against drug-sensitive and drug-resistant Plasmodium falciparum and their mode of action

Visible-light driven photoreactions using transition metal complexes as catalysts are currently a research hotspot in developing environmentally friendly sustainable processes. To develop a potential copper-based photocatalyst, a binuclear Cu(ii) complex has been synthesized using a Mannich base ligand viz. 2,4-dichloro-6-((4-(2-hydroxyethyl)piperazin-1-yl)methyl)phenol (H2L). The photocatalyst has been characterized using ESI-MS and single crystal X-ray diffraction. Under the irradiation of visible light, the catalyst can catalyze hydrogen auto-transfer in N-alkylated amine formation and benzyl alcohol oxidation reactions with excellent conversion. A plausible mechanistic pathway for catalytic reactions has been explored through ESI-MS spectrometric, UV-Vis spectroscopic and computational studies. © 2022 The Royal Society of Chemistry.