Manganese Complexes Research Articles

Macrocyclic pseudo crown-ether- manganese (II) complex coated on nanomagnetic LDH- catalyzed Biginelli annulation reactions

A single-site macrocyclic pseudo crown ether-manganese complex was generated from the complexation of a new tetradentate ligand brought from a synthetic procedure with manganese (II) halide precursor in an electron-transfer process. The prepared [γ-Fe2O3@LDH/PCE-Mn(II)] acts as an efficient heterogeneous Mn-based catalyst – exhibiting efficient catalytic activity in the synthesis of the functionalized chromeno-pyrimidines via a Biginelli-like annulation process. Moreover, Biginelli reaction of a variety of aryl aldehydes and carbamide/thiocarbamide with a β-ketoester moiety was achieved in ethanol at 60 °C with 65–92% yield in 10–40 min. This catalytic process can be initiated using the Mn(II)-catalyzed in situ generation of an imine intermediate. Subsequently, the addition of a β-ketoester moiety – followed by the ring-closure reaction and removal of a water molecule – forms a library of new chromeno-pyrimidine-2,5-diones/thione products with a broad substrate scope.

A macrocyclic quinol-containing ligand enables high catalase activity even with a redox-inactive metal at the expense of the ability to mimic superoxide dismutase.

Previously, we found that linear quinol-containing ligands could allow manganese complexes to act as functional mimics of superoxide dismutase (SOD). The redox activity of the quinol enables even Zn(ii) complexes with these ligands to catalyze superoxide degradation. As we were investigating the abilities of manganese and iron complexes with 1,8-bis(2,5-dihydroxybenzyl)-1,4,8,11-tetraazacyclotetradecane (H4qp4) to act as redox-responsive contrast agents for magnetic resonance imaging (MRI), we found evidence that they could also catalyze the dismutation of H2O2. Here, we investigate the antioxidant behavior of Mn(ii), Fe(ii), and Zn(ii) complexes with H4qp4. Although the H4qp4 complexes are relatively poor mimetics of SOD, with only the manganese complex displaying above-baseline catalysis, all three display extremely potent catalase activity. The ability of the Zn(ii) complex to catalyze the degradation of H2O2 demonstrates that the use of a redox-active ligand can enable redox-inactive metals to catalyze the decomposition of reactive oxygen species (ROS) besides superoxide. The results also demonstrate that the ligand framework can tune antioxidant activity towards specific ROS.

Chemoselective C(sp)–H borylation of terminal alkynes catalyzed by a bis(N-heterocyclicsilylene) manganese complex

The manganese(ii) complex [Mn(SiNSi)Cl2] (SiNSi = 2,6-[EtNSi(NtBu)2CPh]2C5H3N) is an efficient catalyst for the chemoselective C(sp)–H borylation of terminal alkynes.

Spin-state switching: chemical modulation and the impact of intermolecular interactions in manganese(III) complexes.

A series of mononuclear manganese(III) complexes [Mn(X-sal2-323)](ReO4) (X = 5 Cl, 1; X = 5 Br, 2; X = 3,5 Cl, 3; X = 3,5 Br, 4; and X = 5 NO2, 5), containing hexadentate ligands prepared using the condensation of N,N'-bis(3-aminopropyl)ethylenediamine and 5- or 3,5-substituted salicylaldehyde, has been synthesized. Variable temperature single-crystal X-ray diffraction, magnetic, spectroscopic, electrochemical, and spectroelectrochemical analyses, and theoretical calculations have been used to explore the role of various ligand substituents in the spin-state switching behavior of the prepared manganese(III) complexes. All five complexes consist of an analogous distorted octahedral monocationic MnN4O2 surrounding offered by the flexible hexadentate ligand and ReO4- as the counter anion. However, a disordered water molecule was detected in complex 4. Complexes 1 (X = 5 Cl) and 5 (X = 5 NO2) show gradual and complete spin-state switching between the high-spin (HS) (S = 2) and the low-spin (LS) (S = 1) state with T1/2 values of 146 and 115 K respectively, while an abrupt and complete transition at 95 K was observed for complex 2 (X = 5 Br). Alternatively, complex 3 (X = 3, 5 Cl) exhibits an incomplete and sharp transition between the HS and LS states at 104 K, while complex 4 (X = 3, 5 Br) (desolvated) remains almost LS up to 300 K and then displays gradual and incomplete SCO at a higher temperature. The nature of the spin-state switch and transition temperature suggest that the structural effect (cooperativity) plays a more significant role in comparison with the electronic effect coming from various substituents (Cl, Br, and NO2), which is further supported by the detailed structural, electrochemical, and theoretical studies.

Biologically important 26-32-membered macrocyclic complexes of manganese (II): In situ one pot template synthesis (IOPTS), characterization and bio-efficacy

Twenty six to thirty two membered tetraazamacrocyclic complexes of manganese (II) have been synthesized by template condensation of MnCl2.4H2O with dicarboxylic acid (malonic, succinic, glutaric or adipic acid) and 1,8-diaminooctane in 1:2:2 molar ratios. The new products with octahedral geometry have been characterized by elemental analyses, molecular weight determinations, molar conductance, magnetic moment and spectral studies viz., infrared and electronic. On the basis of the spectral studies the binding sites are proposed as the nitrogen atom of the macrocycles. The formulation of the complexes as [Mn(Macn)Cl2] (where n = 1 - 4) has been established on the basis of chemical composition. To assess the growth inhibiting potential of the manganese (II) complexes biological screening has been undertaken.

COORDINATION BEHAVIOUR AND COMPUTATIONAL STUDIES OF 3-FORMYL CHROMONE N(4)-METHYL-N(4)- PHENYLTHIOSEMICARBAZONE AND ITS TRANSITION METAL COMPLEXES

This article reports on the 3-formylchromone N(4)-substituted thiosemicarbazone’s coordination behavior towards transition metal ions. CHNS analysis, magnetic moment, thermal analysis, IR, UV, NMR, and EPR spectroscopy were used to characterize the compounds. Moreover, DFT, insilico ADME, and docking studies of the ligand were done. Based on the spectral results, copper, cobalt, and nickel complexes had square planar geometry. Conversely, the manganese complex has octahedral geometry. The Gaussian 09 program is utilized for DFT studies. The GLIDE program was used for docking calculations. As receptor molecules, histone deacetylase, ribonucleotide reductase, and DNA methyltransferase were chosen. The SwissADME tool was used to evaluate the pharmacokinetics of the ligand. Based on Lipinski's rules, the estimation of insilico ADMET discovered that ligands procure significant drug-likeness characteristics. Its ability to block histone deacetylase 8 (PDB ID 1T69) protein is shown by docking calculations, and its proper action can be further confirmed in wet lab tests.

Interactions of Mn complexes with DNA: the relevance of therapeutic applications towards cancer treatment.

Manganese (Mn) is one of the most significant bio-metals that helps the body to form connective tissue, bones, blood clotting factors, and sex hormones. It is necessary for fat and carbohydrate metabolism, calcium absorption, blood sugar regulation, and normal brain and nerve functions. It accelerates the synthesis of proteins, vitamin C, and vitamin B. It is also involved in the catalysis of hematopoiesis, regulation of the endocrine level, and improvement of immune function. Again, Mn metalloenzymes like arginase, glutamine synthetase, phosphoenolpyruvate decarboxylase, and Mn superoxide dismutase (MnSOD) contribute to the metabolism processes and reduce oxidative stress against free radicals. Recent investigations have revealed that synthetic Mn-complexes act as antibacterial and antifungal agents. As a result, chemists and biologists have been actively involved in developing Mn-based drugs for the treatment of various diseases including cancer. Therefore, any therapeutic drugs based on manganese complexes would be invaluable for the treatment of cancer/infectious diseases and could be a better substitute for cisplatin and other related platinum based chemotherapeutic drugs. From this perspective, attempts have been made to discuss the interactions and nuclease activities of Mn(II/III/IV) complexes with DNA through which one can evaluate their therapeutic applications.

A manganese complex on a gas diffusion electrode for selective CO2 to CO reduction

A gas diffusion electrode based on a Mn complex gives good selectivity for CO production from CO2 at both near neutral pH in a flow cell configuration and when in contact with the acidic cation exchange layer of a bipolar membrane.

Microwave synthesis of cationic ABAB di-imidazolyl fluorinated porphyrins and manganese complexes

ABAB porphyrins are promising platforms for potential use in several applications, particularly in medical imaging. Herein, the synthetic optimization studies for preparing such porphyrins via the statistical condensation of 4-trifluoromethylphenyl and 1-methylimidazol-2-yl aldehydes with pyrrole, are described, with emphasis on the use of microwave irradiation as heating source, against conventional heating. Then, the preparation of the corresponding Mn(III) complex and cationization of the imidazole groups, using microwave irradiation, were also carried out and the photophysical, photochemical, and electrochemical properties were further assessed. The compounds revealed interesting features, including adequate log P, singlet oxygen yield, redox potentials, and excellent photostability, which pave the way for potential use as imaging probes in MRI or PET, or as photosensitizing molecules.

Metallo-dithiaporphyrin pigments for bulk-heterojunction solar cell applications: ab initio investigation of structural and optoelectronic properties.

Metallo-dithiaporphyrin small molecules have been designed by substituting Ru(ii) with various transition metals at the same oxidation state (M = Mn, Fe, Ni, Cu) as donor materials for Bulk Heterojunction Organic Solar Cells (BHJ-OSCs). Density functional theory (DFT) and time-dependent DFT (TD-DFT) have been used to study the optoelectronic properties of metallo-dithiaporphyrin at various functionals and basis sets. We discovered that the open-circuit voltage (VOC) value increases when Ru(ii) in Ru(S2TTP)Cl2 (S2TTP = tetra-p-tolyldithiaporphyrin) is substituted. In addition, the light harvesting efficiency (LHE) of nickel, manganese, and iron complexes was found to be similar to that of ruthenium, and the iron complex furthermore presented a comparable charge transfer in the excited state corresponding to the Q-band, compared to Ru(S2TTP)Cl2. Hence M(S2TTP)Cl2 (M = Mn, Fe, Ni) appear to be potential low cost candidate donor molecules within a bulk heterojunction solar cell. We further propose suitable engineered acceptor pigments, fitted to provide a good overall solar cell efficiency.

Manganese(ii) complexes stimulate antitumor immunity via aggravating DNA damage and activating the cGAS-STING pathway.

Activating the cyclic GMP-AMP synthase-stimulator of the interferon gene (cGAS-STING) pathway is a promising immunotherapeutic strategy for cancer treatment. Manganese(ii) complexes MnPC and MnPVA (P = 1,10-phenanthroline, C = chlorine, and VA = valproic acid) were found to activate the cGAS-STING pathway. The complexes not only damaged DNA, but also inhibited histone deacetylases (HDACs) and poly adenosine diphosphate-ribose polymerase (PARP) to impede the repair of DNA damage, thereby promoting the leakage of DNA fragments into cytoplasm. The DNA fragments activated the cGAS-STING pathway, which initiated an innate immune response and a two-way communication between tumor cells and neighboring immune cells. The activated cGAS-STING further increased the production of type I interferons and secretion of pro-inflammatory cytokines (TNF-α and IL-6), boosting the tumor infiltration of dendritic cells and macrophages, as well as stimulating cytotoxic T cells to kill cancer cells in vitro and in vivo. Owing to the enhanced DNA-damaging ability, MnPC and MnPVA showed more potent immunocompetence and antitumor activity than Mn2+ ions, thus demonstrating great potential as chemoimmunotherapeutic agents for cancer treatment.

Manganese(ii) complexes of hexaazatrinaphthylene and hexaazatrianthracene: synthesis, structure and properties

A series of complexes containing dianionic and radical-trianionic hexaazatriphenylene (HATNA) and hexazatrianthracene (HATA) ligands and high-spin MnII ions (S = 5/2) were obtained. It is shown that elongation of the Mn–N bonds results in a decrease of both Mn–ligand and Mn–Mn couplings.

Synthesis, Crystal Structure and Thermal decomposition of Copper(II) and Manganese(II) Complexes Based on Bipyridine Dicarboxylate and 1,10-Phenanthroline

Two novel transition metal complexes of the formulae [Cu(5,5′-bpdc)(phen)]n (1) and [Mn(6,6′-bpdc)(phen)(H2O)]·H2O (2) (where phen = 1,10-phenanthroline, 5,5′-H2bpdc = 2,2′-bipyridine-5,5′-dicarboxylic acid, 6,6′-H2bpdc = 2,2′-bipyridine-6,6′-dicarboxylic acid) were synthesized by hydrothermal reaction. The complexes were characterized by elemental analysis, X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetry and differential scanning calorimetry. The X-ray crystallographic investigation reveals that 1 is a coordination polymer, and its asymmetric structural units are connected by oxygen atoms in the carboxyl group of 5,5′-bpdc2– anion. 2 is a heptacoordination monomer complex with mono-capped trigonal prismatic configuration and its mononuclear molecules are connected by hydrogen bonds to form supramolecular structure. The result of fluorescence shows that 2 has fluorescent property.

An insight into the hydrogen bonding, halogen bonding and chalcogen bonding interactions in manganese(iii) complexes with N2O2donor salicylidine Schiff base ligands.

Four manganese(iii) complexes, [MnL1(H2O)2]ClO4·H2O (1), [MnL2(H2O)2]ClO4 (2), [MnL3(DMSO)(H2O)]ClO4 (3) and [MnL4(DMSO)(H2O)]ClO4 (4), where H2L1 = N,N'-bis(5-bromosalicylidene)-1,3-diaminopropane, H2L2 = 2,2-dimethyl-N,N-bis(3-methyloxysalicylidene)-1,3-diaminopropane, H2L3 = N,N'-bis(5-chlorosalicylidene)-2,2-dimethyl-1,3-diaminopropane and H2L4 = 2-hydroxy-N,N'-bis(3-ethyloxysalicylidene)-1,3-diaminopropane are tetradentate N2O2-donor ligands and DMSO = dimethyl sulfoxide, have been synthesized and characterised by elemental analysis, IR and UV-vis spectroscopy and single-crystal X-ray diffraction studies. All are monomeric complexes. Complex 1 crystallises in orthorhombic space group P212121, complex 3 crystallises in triclinic space group P-1, whereas complexes 2 and 4 crystallize in monoclinic space groups, C2/c and C2/m respectively. In all the complexes, manganese(iii) has a six-coordinated pseudo-octahedral geometry in which imine nitrogen atoms and phenolate oxygen atoms of the deprotonated di-Schiff base constitute the equatorial plane. In complexes 1 and 2, water molecules are present in the fifth and sixth coordination sites in the axial positions while in complexes 3 and 4 they are occupied by one water and one DMSO. The coordinated water molecules initiate hydrogen-bonded networks in all complexes. DFT calculations have been carried out to analyze two aspects of these complexes viz. the formation of halogen (HaB) and chalcogen bonding (ChB) interactions in complexes 1 and 3 where the electron donor is the perchlorate anion and the acceptor either bromine or chlorine atoms for the HaBs and the sulfur atom of the coordinated DMSO for the ChB. In addition, other intermolecular effects are discussed in the solid state for complexes 1, 2 and 4, where the hydrogen atoms of the coordinated water molecules interact with the electron rich cavities formed by the phenolate and alkyloxy oxygen atoms of the Schiff-base ligand.

Manganese(III) complexes stabilized with N-heterocyclic carbene ligands for alcohol oxidation catalysis.

The chemistry of N-heterocyclic carbenes with Earth-abundant manganese has largely focused on low-valent systems for reductive catalysis. Here, we have decorated imidazole- and triazole-derived carbenes with phenol substituents to access higher-valent Mn(III) complexes [Mn(O,C,O)(acac)], where acac = acetylacetonato, and O,C,O = bis(phenolate)imidazolylidene (1) or bis(phenolate)triazolylidene (2). Both complexes catalyze the oxidation of alcohols in the presence of tBuOOH as terminal oxidant. Complex 2 is slightly more active than 1 (TOF up to 540 h-1vs. 500 h-1), yet significantly more robust towards deactivation. Secondary and primary alcohols are oxidized, the latter with high selectivity and essentially no overoxidation of the aldehyde product to carboxylic acids unless the reaction time is substantially extended. Mechanistic investigations using Hammett parameters, IR spectroscopy, isotope labelling experiments, and specific substrates and oxidants as probes support the formation of a manganese(V) oxo system as the active species and subsequent turnover-limiting hydrogen atom abstraction.

Synthesis, structures, and properties of manganese(i) complexes featuring tridentate amidine-toting protic amine ligands

Cationic Mn(CO)3 complexes having a protic amine ligand with cyclic amidine side arms were prepared and their catalytic properties of transfer hydrogenation of acetophenone and electrochemical reduction of CO2 were compared.

Catalytic fate of structurally characterized manganese(iii)–salen complexes towards efficient transformation of primary amides to amines or nitriles using hydrosilane

Simple salen-based manganese(iii) complexes show excellent catalytic activity towards the hydrosilylative transformation of primary amides to their corresponding primary amines under mild reaction conditions.

Discovery of metal complexes with antibacterial properties in aqueous extracts of Radix scutellariae and a study of the antibacterial properties of the baicalin–manganese complex

In the process of extraction with hot water, many organic components in Radix scutellariae form complexes with metal ions. Among them, baicalin–manganese has good antibacterial activity and less tendency to cause resistance.

Unprecedented pseudo-zeroth-order kinetics of the catecholase-like activity of mixed-valence MnIIMn2III complexes

The pseudo-zero-order kinetics of the catecholase-like activity of biologically active linear trinuclear mixed-valence manganese complexes have been explored; the formation of singlet oxygen is thought to be the rate-limiting step.

Mechanistic insights into CO2 conversion to CO using cyano manganese complexes.

Without the use of a photosensitizer, [Mn(bpy)(CO)3(CN)] (MnCN) can photochemically form [Mn(bpy)(CO)3]-, the active species for CO2 reduction. While cases of the axial X-ligand dissociating upon irradiation of fac-[M(N-N)(CO)3X] complexes (M = Mn or Re; N-N = bipyridine (bpy) ligand; X = halogen or pseudohalogen) are well documented, the axial cyanide ligand is retained when either [Mn(bpy)(CO)3(CN)] or [Mn(mesbpy)(CO)3(CN)], MnCN(mesbpy), are irradiated anaerobically. Infrared and UV-vis spectroscopies indicate the formation of [Mn(bpy)(CO)2(MeCN)(CN)] (s-MnCN) as the primary product during the irradiation of MnCN. An in-depth analysis of the photochemical mechanism for the formation of [Mn(bpy)(CO)3]- from MnCN is presented. MnCN(mesbpy) is too sterically hindered to undergo the same photochemical mechanism as MnCN. However, MnCN(mesbpy) is found to be electrocatalytically active for CO2 reduction to CO. Thus providing an interesting distinction between photochemical and electrochemical charge transfer.