Mn Centers Research Articles

Anion-Responsive Manganese Porphyrin Facilitates Chloride Transport and Induces Immunogenic Cell Death

Anion-Responsive Manganese Porphyrin Facilitates Chloride Transport and Induces Immunogenic Cell Death

Multifunctional Coordination Polymer Exhibiting Reversible Mechanical Motion Allowing Selective Uptake of Guests and Leading to Enhanced Electrical Conductivity.

A remarkably flexible, multifunctional, 2D coordination polymer exhibiting an unprecedented mode of reversible mechanical motion, enabling pores to open and close, is reported. Such multifunctional materials are highly sought after, owing to the potential to exploit coexisting electronic and mechanical functionalities that underpin useful technological applications such as actuators and ultrasensitive detectors. The coordination polymer, of composition Mn(F4TCNQ)(py)2 (F4TCNQ = 2,3,5,6-tetrafluoro-7,7,8,8-tetracycanoquinodimethane; py = pyridine), consists of Mn(II) centers bridged by F4TCNQ dianions and coordinated by py molecules that extend above and below the 2D network. Exposure of Mn(F4TCNQ)(py)2, in its collapsed state, to carbon dioxide results in a pore-opening process at a threshold pressure for a given temperature. In addition to carbon dioxide, a variety of volatile guests may be incorporated into the pores, which are lined with electron-rich F4TCNQ dianions. The inclusion of electron-deficient guests such as 1,4-benzoquinone, nitrobenzene, maleic anhydride, and iodine into the pores is accompanied by a striking color change associated with a new host-guest charge-transfer interaction and an improvement in the semiconductor behavior, with the iodine adduct showing an increase in conductivity of almost 5 orders of magnitude. Experimental and density functional theory calculations on this remarkable multifunctional material demonstrate a reduction in the optical band gap with increasing electron affinity of the guest.

A novel manganese(II) bisthiocarbohydrazone complex: Crystal structures, Hirshfeld surface analysis, DFT and molecular docking study with SARS-CoV-2

A novel Mn(II) complex [Mn(H2L)Cl2]•H2O (1) of a ditopic ligand 1,5-bis(2-benzoylpyridine) thiocarbohydrazone (H2L) was synthesized and characterised physico-chemically. A part of the mother solution of the complex 1 and THF yielded single crystals in a triclinic space group and are found same from the crystals obtained from another mixture of the mother solution and ethyl acetate. Single crystal XRD studies have confirmed the mononuclear complex formation and absence of any interactions between the Mn(II) centers. A solution of the complex 1 in chloroform, conversely, yielded a crystallographically different complex [Mn(H2L)Cl2]•CHCl3 (1a) in monoclinic and is also characterised with single crystal XRD. The ligand is coordinated through thione sulfur atom to form a square pyramidal geometry around Mn(II) center in both the complexes. The molecular packing of the complexes is found influenced by the nature of solvent inclusion, and are stabilized by different non-covalent interactions in the lattice. The intermolecular interactions are quantified by Hirshfeld surface analyses, which reveal that H•••Cl interactions has maximum contribution to the total Hirshfeld surface in the complex 1a. This is the first crystal structure study of a manganese(II) complex of a bisthiocarbohydrazone ligand. The molecular and electronic structures of the complexes are studied by DFT quantum chemical calculations. The band gap (Eg) of the complex 1 was estimated as 2.45 eV using Kubelka-Munk model and is in agreement with the electronic spectral calculations of the complex at TD-DFT level. Molecular docking studies of both the ligand and the complex reveal their greater propensity towards SARS-CoV-2 main protease compared to B-DNA dodecamer. Also, the binding potential of the ligand and the complex with SARS-CoV-2 main protease is found higher than that with chloroquine and hydroxychloroquine.

Recent Advances in Crystalline Oxidopolyborate Complexes of d-Block or p-Block Metals: Structural Aspects, Syntheses, and Physical Properties.

Crystalline materials containing hybrid inorganic–organic metal borates (complexes with oxidoborate ligands) display a variety of novel framework building blocks. The structural aspects of these hybrid metallaoxidoborates containing Cd(II), Co(II), Cu(II), Ga(III), In(III), Mn(II), Ni(II) or Zn(II) metal centers are discussed in this review. The review describes synthetic approaches to these hybrid materials, their physical properties, their spectroscopic properties and their potential applications.

Rare nuclearities in Mn/oxo cluster chemistry: Synthesis and characterization of a mixed-valence {MnII/III11} complex bearing acetate and salicylhydroximate(-3) bridging/chelating ligands

The one-pot reaction between Mn(O2CMe)2·4H2O, salicylhydroxamic acid (shaH2) and Me4NOH·5H2O in a molar ratio of 2:1:2, and a solvent mixture comprising MeCN and MeOH, affords the new mixed-valence cluster compound (Me4N)4[MnII2MnIII9O4(O2CMe)9(shi)6] (1) in moderate yields. The anion of the tetradentate (N,O,O,O) chelating/bridging ligand shi3− resulted from the in-situ metal ion-assisted amide-iminol tautomerism of shaH2. The [MnII2MnIII9(μ3-O)4(μ-OR)3(μ3-NO)6]14+ core of 1 comprises four vertex-sharing {MnIII3(μ3-O2−)}7+ triangular subunits of different types, which are linked to each other and the MnII atoms through the oximato arms and the carboxylate O-atoms of six η1:η1:η1:η2:μ3 shi3− and three η1:η2:μ3 MeCO2− groups, respectively. Peripheral ligation about the core is provided by six η1:η1:μ MeCO2− groups and the chelating parts of the shi3− ligands. Solid-state direct-current (dc) magnetic susceptibility studies revealed the presence of predominant antiferromagnetic exchange interactions between the Mn centers, mainly promoted by the coplanarity of the μ3-O2− within the {Mn3} triangular planes and the insignificant distortion of the MnNOMn bridging units. Low-lying excited states precluded obtaining a good fit from the magnetization data, and the ground state was instead determined from the alternating-current (ac) data, which indicated an S = 3 ground state for 1. The combined results emphasize the continuing supply from the use of the salicylhydroxime chelating/bridging ligand of new 3d-metal clusters of very rare nuclearities and beautiful molecular structures.

Unusual redox activity of the central heteroatom manganese in Anderson anion: Modulating its oxidation state in a gas solid reaction

The orange crystalline [N(C4H9)4]3[MnIIIMo6O18{(OCH2)3CNH2}2] (1) with central Mn(III), on exposure to vapors of conc. HCl is converted to green colour solid of tentative formula, [N(C4H9)4]2[MnIIMo6O18{(OCH2)3CNH3}2] ∙ [N(C4H9)4]Cl (1red). Compound 1, on exposure to conc. HNO3 vapours is converted to brown solid, which has tentatively been formulated as [MnIVMo6O18{(OCH2)3CNH3}2] ∙ 3[N(C4H9)4]NO3 (1ox). The color changes are associated with oxidation of central Mn(III) center of compound 1 into Mn(IV) in compound 1ox and reduction of central Mn(III) center of compound 1 into Mn(II) in compound 1red. Both solid state reduction and oxidation of Mn(III) center are accompanied by the protonation of amino group of tris(hydroxymethyl) aminomethane during the gas–solid interface reactions. The conversion of compound 1 into compounds 1red and 1ox in gas solid redox reactions has been characterized by various spectroscopic techniques, e.g., FT-IR, PXRD, EPR, DRS, 1H NMR, 13C NMR and XPS. Also, electrochemical analyses were carried out for all the compounds.

Electron paramagnetic spectrum of dimanganic human serum transferrin

An EPR signal for Mn(III) bound to the metal transport protein transferrin has been detected for the first time. The temperature dependence and simulations of the EPR signal are consistent with the Mn(III) centers being six-coordinate in an elongated tetragonal environment. Thus, the incorporation of Mn(III) within the Tf active site does not vastly alter the coordination number or active site geometry relative to native Fe(III)2-Tf. This parallel mode EPR signal for Mn(III)2-Tf could prove valuable for future studies aimed at determining the physiological relevance of Mn(III)2-Tf.

Synthesis and characterization of a 30-membered decanuclear manganese metallacrown containing cyclopentane-carboxyl salicylhydrazide ligand

A new macrocyclic 30-metallacrown-10, [Mn10(cpshz)10(CH3OH)10]·2CH2Cl2·10CH3OH, has been prepared by supramolecular self-assembly using N-cyclopentane-carboxyl salicylhydrazide (H3cpshz) as the pentadentate ligands. Ten ligands chelate ten manganese(III) ions through the diaza bridging groups into a 30-membered [Mn–N–N]10 cyclic structure. The Mn(III) centers in the decanuclear ring exhibit alternating Λ and Δ configurations. The temperature-dependent magnetic behavior indicated that there are weakly antiferromagnetic couplings between the paramagnetic centers.

The Role of the -OH Groups within Mn12 Clusters in Electrocatalytic Water Oxidation.

The formidable reactivity of the oxygen-evolving center near photosystem II is largely based on its protein environment that stabilizes it during catalysis. Inspired by this concept, the water-soluble Mn12 clusters Mn12 O12 (O2 CC6 H3 (OH)2 )16 (H2 O)4 (3,5DHMn12 ) and Mn12 O12 (O2 CC6 H3 (OH)3 )16 (H2 O)4 (3,4,5THMn12 ) were developed as efficient electrocatalysts for water oxidation. In this work, the role of the -OH groups in the electrocatalytic process was explored by describing the structural and electrocatalytic properties of two new Mn12 clusters, 3,4DHMn12 and 2,3DHMn12 , having one -OH group in the meta position relative to the benzoate-Mn moiety, and one at the para or ortho position, respectively. The Mn centers in 3,4DHMn12 were discovered to have lower oxidation potential compared with those in 2,3DHMn12 , and thus, 3,4DHMn12 can catalyze water oxidation with higher rate and TON than 2,3DHMn12 . Hence, the role of the -OH groups in the electrocatalysis was established, being involved in electronic stabilization of the Mn centers or in proton shuttling.

A global record of particulated metals on the southwestern Atlantic shelf (Argentine Sea)

The Argentine Sea (Southwestern Atlantic) is one of the most productive ecosystem in the Southern Hemisphere. Research on metals in this region is scarce or null. In this study, we evaluated the concentrations of some metals in the suspended particulate matter (SPM), to provide baseline data that would enable us to understand the role of the SPM in the transport of metals in the Argentine Sea. Sampling was carried out during the austral summer 2016 at 20 stations distributed in the Argentine Sea. Surface seawater samples were collected and then filtered by vacuum through Millipore® HAWP 04,700 filters (0.45 µm). The samples were acid-digested (HNO3 and HClO4, 5:1) and the metal concentrations were determined with ICP-OES Optima 2100 DV (Perkin Elmer). Significant spatial variations were detected due to the extension of the study area, with the highest levels of metals in the stations next to large urban centers (Cd, Cu, Cr, Fe, Mn, Ni, Pb and Zn: 13.9, 154.9, 48.7, 54,470, 7646, 49.2, 58.6 and 509.5 μg g−1 d.w. respectively), which was supported by the nMDS and Cluster analyses. According to PCA analysis, two groups of metals that could have similar behavior were stablished: one group integrated by Cu, Zn, Pb and Ni, and the other group integrated by Cr, Fe and Mn. Metals that act as micronutrients and the toxic ones were present in all the sampling stations, highlighting the need to reinforce the study of these elements in this extensive and productive area of the South Atlantic Ocean.

A Zn-based metal–organic framework as bifunctional chemosensor for the detection of nitrobenzene and Fe3+

In this report, three metal-organic frameworks (MOFs) were synthesized by hydrothermal reactions with 4,4′,4″-nitrilotribenzoic acid (H3NTB), 1,10-phenanthroline (phen) and water by introducing Zn(Ⅱ), Mn(Ⅱ) and Cu(Ⅱ) center ions, namely, [Zn(HNTB)(phen)]n (Ⅰ), [Mn(HNTB)(phen)•H2O]n (Ⅱ) and {[Cu(HNTB)(phen)•H2O]•H2O}n (Ⅲ). Single-crystal X-ray diffraction data analyses demonstrate that Ⅰ-Ⅲ are assembled into three-dimensional frameworks based on the building blocks of {ZnO4N2}, {MnO3N2} and {CuO4N2} through the connections of HNTB2−, intermolecular hydrogen bonds and the π … π interactions between pyridine rings, respectively. The fluorescent properties of Ⅰ-Ⅲ have been systematically studied in different solutions containing certain metal ions and organic molecules. As a result, Zn-MOF (I) exhibits a dual-responsive fluorescent sensor toward nitrobenzene (NB) and Fe3+ with high selectivity, stability and anti-interference ability at the existence of other corresponding analytes originating from its excellent fluorescent quenching efficiency. Moreover, the possible sensing mechanisms for the above analytes have also been elucidated, which are testified by PXRD analysis, ICP-AES, UV–vis spectra, XPS and the density functional theory (DFT).

Cationic PCP and PCN NHC Core Pincer-Type Mn(I) Complexes: From Synthesis to Catalysis

The coordination chemistry of NHC core pincer-type PCP and PCN ligands with Mn(I) center was systematically investigated. The reaction of [Mn(CO)5Br] with free carbenes, conveniently prepared from the corresponding imidazolium salts and a strong base, lead to the initial formation of bidentate fac-[MnBr(CO)3(κ 2 P,C,L)] complexes bearing a pending phosphine or pyridine donor extremity (L), which upon bromide abstraction, afford cationic [Mn(CO)3(κ 3 P,C,L)](OTf) derivatives exhibiting a meridional or a facial coordinating geometry of tridentate NHC core ligand depending on its relative flexibility. All bi-and tridentate Mn(I) complexes were characterized by X-ray diffraction analysis. The impact of the tridentate ligand structure on catalytic performance was illustrated in the Mn-catalyzed hydrogenation of acetophenone revealing fac-[Mn(CO)3(κ 3 P,C,N)](OTf) based on a 5,6-membered metallacyclic architecture to be the most active, thus evidencing the role of the pyridine arm lability in the catalytic cycle.

Syntheses, structures, and fluorescent and magnetic properties of four metal–organic coordination polymers constructed from dicarboxylate ligands

Four new coordination polymers, namely [Cd(OBA)(H2O)3]n (1), [Zn2(OBA)2(PBHB)2]n (2), [Mn(OBA)(BBHB)2]n (3), and [Co(MIP)(BPP)]n (4) (H2OBA = 4-oxyacetate-benzoic acid, PBHB = 1,1′-(1,3-propanediyl)bis-1H-benzimidazole, BBHB = 1,1′-(1,4-butanediyl)bis-1H-benzimidazole, H2MIP = 5-methylisophthalic acid, and BPP = 1,3-bis(4-pyridyl)propane)), were prepared and structurally characterized by single-crystal X-ray diffraction. In complex 1, the Cd(II) atoms are bridged by OBA2− anions to give 1D zigzag chain, and the 1D chains are stacked into 2D network through the O–H–O hydrogen bonds. The Mn(II) and Zn(II) centers in 2 and 3 are connected by OBA2− anions to form 1D chains, which are further bridged by N-donor ligands to generate 2D layer. Complex 4 shows twofold 3D interpenetrating network. Furthermore, the fluorescence of complexes 1 and 2 and magnetic properties of 3 and 4 have also been investigated.

De Novo Design, Solution Characterization, and Crystallographic Structure of an Abiological Mn-Porphyrin-Binding Protein Capable of Stabilizing a Mn(V) Species.

De novo protein design offers the opportunity to test our understanding of how metalloproteins perform difficult transformations. Attaining high-resolution structural information is critical to understanding how such designs function. There have been many successes in the design of porphyrin-binding proteins; however, crystallographic characterization has been elusive, limiting what can be learned from such studies as well as the extension to new functions. Moreover, formation of highly oxidizing high-valent intermediates poses design challenges that have not been previously implemented: (1) purposeful design of substrate/oxidant access to the binding site and (2) limiting deleterious oxidation of the protein scaffold. Here we report the first crystallographically characterized porphyrin-binding protein that was programmed to not only bind a synthetic Mn-porphyrin but also maintain binding site access to form high-valent oxidation states. We explicitly designed a binding site with accessibility to dioxygen units in the open coordination site of the Mn center. In solution, the protein is capable of accessing a high-valent Mn(V)-oxo species which can transfer an O atom to a thioether substrate. The crystallographic structure is within 0.6 Å of the design and indeed contained an aquo ligand with a second water molecule stabilized by hydrogen bonding to a Gln side chain in the active site, offering a structural explanation for the observed reactivity.

Construction of an Asymmetric Porphyrinic Zirconium Metal-Organic Framework through Ionic Postchiral Modification.

Herein, one kind of neutral chiral zirconium metal-organic framework (Zr-MOF) was reported from the porphyrinic MOF (PMOF) family with a metallolinker (MnIII-porphyrin) as the achiral polytopic linker [free base tetrakis(4-carboxyphenyl)porphyrin] and chiral anions. Achiral Zr-MOF was chiralized through the exchange of primitive anions with new chiral organic anions (postsynthetic exchange). This chiral functional porphyrinic MOF (CPMOF) was characterized by several techniques such as powder X-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, 1H NMR, energy-dispersive X-ray spectroscopy, scanning electron microscopy, and Brunauer-Emmett-Teller measurements. In the resulting structure, there are two active metal sites as Lewis acid centers (Zr and Mn) and chiral species as Brønsted acid sites along with their cooperation as nucleophiles. This CPMOF shows considerable bimodal porosity with high surface area and stability. Additionally, its ability was investigated in asymmetric catalyses of prochiral substrates. Interactions between framework chiral species and prochiral substrates have large impacts on the catalytic ability and chirality induction. This chiral catalyst proceeded asymmetric epoxidation and CO2 fixation reactions at lower pressure with high enantioselectivity due to Lewis acids and chiral auxiliary nucleophiles without significant loss of activity up to the sixth step of consecutive cycles of reusability. Observations revealed that chiralization of Zr-MOF could happen by a succinct strategy that can be a convenient method to design chiral MOFs.

From antiferromagnetic to ferromagnetic exchange in a family of phenoxido-bridged heterodinuclear Cu(II)-Mn(II) complexes: A magneto-structural theoretical study

Density functional theory with a broken symmetry approach was performed on phenoxido-bridged heterodinuclear complexes [LCuMn(NO3)2], for which magneto-structural correlations were developed. Satisfactory results were obtained at the B3LYP*/TZV level, and the calculated J value of the magnetic coupling constant was − 35.24 cm−1, which is consistent with the experimental result of − 35.80 cm−1. The analysis of spin populations indicated that the paramagnetic centers Cu(II) and Mn(II) exhibit a spin delocalization mechanism. The study of magneto-structural correlations indicated that the magnetic coupling constant J value shows a linear correlation with the bond angle (θ) of Cu–O-Mn; for θ < 97.20°, the magnetic coupling effect between Cu(II) and Mn(II) transformed from an anti-ferromagnetic to a ferromagnetic interaction.

Synthesis and Spectro-Electrochemical Properties of New Metallophthalocyanines Having High Electron Transfer Capability

It is important to synthesis and examine the redox properties of phthalocyanines and related macrocycles in order to reveal their possible applications. In this paper, new Zn2+, Co2+ and Mn2+ phthalocyanine complexes containing substituted 1,2,4-triazole groups on peripheral positions have been prepared and characterized by classical methods and electrochemistry in detail. The use of triethylamine and acetone combination in the synthesis of nitrile structures 3a and 3b, the starting compounds for phthalocyanines, both increased yield of products and shortened reaction time compared to classical synthesis of nitrile structures. The electron transfer capability of new metallophthalocyanines (ZnPcs, CoPcs and MnPcs) was investigated in detail via cyclic voltammetry (CV), square wave voltammetry (SWV) and in situ UV–vis spectroelectrochemistry. For ZnPcs, these experiments demonstrated that the complexes exhibited three well-defined reductions and two oxidations waves based on the Pc ring electroinactive nature of the Zn metal coordinated to the macrocycle. For CoPcs showed three reductions and one oxidation based on both the Pc ring and electroactive nature of Co center. Furthermore, MnPcs displayed three well-defined reductions and two oxidations waves based on either the Pc ring or electroactive Mn center.

Chemical Switching of the Magnetic Coupling in a MnPc Dimer by Means of Chemisorption and Axial Ligands

We present an ab initio density functional theory study of the magnetic properties of manganese phthalocyanine dimers, where we focus on the magnetic coupling between the Mn centers and on how it is affected by external factors like chemisorption or atomic axial ligands. We have studied several different configurations for the gas phase dimers, which resulted in ferromagnetic couplings of different magnitudes. For the bare dimer we find a significant ferromagnetic coupling between the Mn centers, which decreases by about 20% when a H atom is adsorbed on one of the Mn atoms and is reduced to about 7% when a Cl atom is adsorbed. The magnetic coupling is almost fully quenched when the dimer, bare or with the H ligand, is deposited on the ferromagnetic substrate Co(001). Our calculations indicate that the coupling between the two Mn atoms principally occurs via a superexchange interaction along two possible paths within a Mn–N–Mn–N four-atom loop. When these electrons get involved in chemical bonding outside the dimer itself, an appreciable alteration of the overlap between Mn and N molecular orbitals along the loop occurs, and consequently, the magnetic interaction between the Mn centers varies. We show that this is reflected by the electronic structure of the dimer in various configurations and is also visible in the structure of the atomic loop. The chemical tuning of the magnetic coupling is highly relevant for the design of nanodevices like molecular spin valves, where the molecules need to be anchored to a support.

EPR Spectral Studies of Manganese(I) Based Molecular Squares

Manganese(I) based molecular squares of type [Mn(CO)3Br(μ-L)]4 where L = pyrazine, 4,4′-bipyridine, trans-1,2-bis(4-pyridyl)ethylene were synthesized and studied in detail by EPR spectroscopy. The continuous wave electron paramagnetic resonance (CW EPR) spectrum of these compounds consists of a broad transition at g = 2.006 and 4.16 that corresponds to an interacting low spin Mn(II) center and a narrow transition at g = 2.004 that corresponds to a nitrogen center radical. These results are discussed in detail and the observation of these characteristic EPR spectral signals is attributed to a partial transfer of an electron from Mn(I) center to the nitrogenous ligand through MLCT.

Zinc(II) and manganese(II) complexes with 1,3-bis(1-allylbenzimidazol-2-yl)-2-oxapropane: synthesis, crystal structures, antioxidant activities and DNA-binding properties

Two new zinc(II) and manganese(II) complexes with the ligand 1,3-bis(1-allylbenzimidazol-2-yl)-2-oxopropane (aobb), with composition [Zn(aobb)2](pic)2·DMF·CH3OH (1) and [Mn(aobb)(DMF)2(H2O)] (pic)2 (2) (pic = picrate; DMF = N,N-dimethylformamide), have been synthesized and characterized by elemental analysis, electrical conductivities, X-ray single-crystal diffraction, IR, and UV–vis spectra. Single-crystal X-ray revealed that Zn(II) and Mn(II) centers are both located in the six-coordinate distorted octahedral geometry. The DNA-binding modes of the ligand and the complexes were investigated by electronic absorption titration, competitive binding with ethidium bromide and viscosity measurements. The experimental evidence indicated the ligand and complexes interact with calf thymus DNA through intercalation. The binding strength follows the order 2 > 1 > aobb. Additionally, 2 displays potential superoxide dismutase activity in vitro studies.