Investigation of electrocatalytic activity of a new mononuclear Mn(II) complex for water oxidation in alkaline media.

Water splitting is a promising way to alleviate the energy crisis. In nature, water oxidation is done by a tetranuclear manganese cluster in photosystem II. Therefore, the study of water oxidation by Mn complexes is attractive in water splitting systems. In this report, a new mononuclear Mn(II) complex, MnL2 (HL = (E)-3-hydroxy-N'-(pyridin-2-ylmethylene)-2-naphthohydrazide) was prepared and characterized by spectroscopic techniques and single-crystal X-ray diffraction. Crystallographic analysis indicated that the geometry around the Mn(II) ion is distorted octahedral. The MnN4O2 coordination moiety is achieved by bounding of oxygen and two nitrogen donor atoms of two hydrazone ligands. The synthesized complex was also investigated for electrochemical water oxidation using electrochemical techniques, scanning electron microscopy, energy dispersive spectrometry, and PXRD analysis. Linear sweep voltammetry experiment showed that the modified carbon paste electrode by the complex displays high activity for water oxidation reaction with an overpotential of 565 mV at a current density of 10 mA cm-2 and Tafel slope of 105 mV dec-1 in an alkaline solution. It was found that the complex structure finally changes during the reaction and converts to Mn oxide nanoparticles which act as active catalytic species and oxidize the water.

A novel [Mn2(µ-(C6H5)2CHCOO)2(bipy)4](bipy)(ClO4)2 complex loaded solid lipid nanoparticles: synthesis, characterization and in vitro cytotoxicity on MCF-7 breast cancer cells.

Manganese (Mn)-based complexes have been drawing attention due to the fact that they are more effective than other metal complexes. However, the use of Mn(II)-based complexes in medicine remains limited because of certain side effects. The aim of this study was to investigate the cytotoxic and apoptotic effects of a novel Mn(II) complex [Mn2(µ-(C6H5)2CHCOO)2(bipy)4](bipy)(ClO4)2 and Mn(II) complex loaded solid lipid nanoparticles (SLNs) on MCF-7 and HUVEC control cells. The average diameter of Mn(II) complex was about 1120 ± 2.43 nm, while the average particle size of Mn(II) complex-SLNs was ∼340 ± 2.27 nm. The cytotoxic effects of Mn(II) complex and Mn(II)-SLNs were 86.8 and 66.4%, respectively (p < .05). Additionally, both Mn(II) complex (39.25%) and Mn(II)-SLNs (38.05%) induced apoptosis and increased the arrest of G0/G1 phase. However, Mn(II) complex exerted toxic effects on the HUVEC control cell (63.4%), whereas no toxic effects was observed when treated with Mn(II)-SLNs at 150 µM. As a consequence, SLNs might be potentially used for metal-based complexes in the treatment of cancer due to reducing size and toxic effects of metal-based complexes.

Apigenin-Mn(II) loaded hyaluronic acid nanoparticles for ulcerative colitis therapy in mice.

Ulcerative colitis (UC) is a chronic idiopathic inflammatory bowel disease characterized by rapid progression and frequent comorbidities that make its treatment challenging. Nanomaterial-based strategies have been extensively studied to target the GI mucosal immune system in recent years. Herein, we propose a novel apigenin-Mn(II) loaded sodium hyaluronate nanoparticles where apigenin (API) was incorporated in the Mn2+ ramework, coated with hyaluronic acid. The apigenin-Mn(II) loaded sodium hyaluronate nanoparticles (API-Mn(II)@HA NPs) exhibited a diameter of 200 nm and were effective against UC. The preparation of the API-Mn(II) complex was relatively simple, and the mechanism underlying its therapeutic effect on UC induced by sodium dextran sulfate (DSS) was studied in detail. We found that API-Mn(II)@HA nanoparticles could effectively repair the intestinal barrier and significantly improve the damaged colon tissue by mediating inflammatory factors. This study provides novel insights on a new kind of active targeted nanoparticle for improving the efficacy of drugs for UC treatment.

Porous Silica Nanospheres with a Confined Mono(aquated) Mn(II)-Complex: A Potential T1-T2 Dual Contrast Agent for Magnetic Resonance Imaging.

Magnetic resonance imaging has emerged as an indispensable imaging modality for the early-stage diagnosis of many diseases. The imaging in the presence of a contrast agent is always advantageous, as it mitigates the low-sensitivity issue of the measurements and provides excellent contrast in the acquired images even in a short acquisition time. However, the stability and high relaxivity of the contrast agents remained a challenge. Here, molecules of a mononuclear, mono(aquated), thermodynamically stable [log KMnL = 14.80(7) and pMn = 8.97] Mn(II)-complex (1), based on a hexadentate pyridine-picolinate unit-containing ligand (H2PyDPA), were confined within a porous silica nanosphere in a noncovalent fashion to render a stable nanosystem, complex 1@SiO2NP. The entrapped complex 1 (complex 1@SiO2) exhibited r1 = 8.46 mM-1 s-1 and r2 = 33.15 mM-1 s-1 at pH = 7.4, 25 °C, and 1.41 T in N-(2-hydroxyethyl)piperazine-N'-ethanesulfonic acid buffer. The values were about 2.9 times higher compared to the free (unentrapped)-complex 1 molecules. The synthesized complex 1@SiO2NP interacted significantly with albumin protein and consequently boosted both the relaxivity values to r1 = 24.76 mM-1 s-1 and r2 = 63.96 mM-1 s-1 at pH = 7.4, 37 °C, and 1.41 T. The kinetic inertness of the entrapped molecules was established by recognizing no appreciable change in the r1 value upon challenging complex 1@SiO2NP with 30 and 40 times excess of Zn(II) ions at pH 6 and 25 °C. The water molecule coordinated to the Mn(II) ion in complex 1@SiO2 was also impervious to the physiologically relevant anions (bicarbonate, biphosphate, and citrate) and pH of the medium. Thus, it ensured the availability of the inner-coordination site of complex 1 for the coordination of water molecules in the biological media. The concentration-dependent changes in image intensities in T1- and T2-weighted phantom images and uptake of the nanoparticles by the HeLa cell put forward the biocompatible complex 1@SiO2NP as a potential dual-mode MRI contrast agent, an alternative to Gd(III)-containing contrast agents.

Treatment of the breast cancer by using low frequency electromagnetic fields and Mn(II) complex of a Schiff base derived from the pyridoxal.

The breast cancer is the most common type of cancer in women. In this project, the breast cancer was transplanted in vivo with the TUBO cells. Then, the cancerous mice were treated by radiation of low frequency electromagnetic fields and injection of the Mn(II) complex of the N,N'-dipyridoxyl(1,2-diaminobenzene) Schiff base. Three different concentrations of the Mn(II) complex were used. Cytotoxicity and morphological alterations caused by the Mn(II) complex in the TUBO breast cancer cell line have been evaluated. Apoptotic properties of the Mn(II) complex was studied using the flow cytometry. The Mn(II) complex has a cytotoxic effect on cancer cells. Also, both of the Mn(II) complex and low frequency electromagnetic field induced apoptosis, which was confirmed by flow cytometry. Both of them result in considerable changes in the treated tissues such as decrease of the tumor mass, induction of apoptosis and decrease in number of the blood vessels.

Construction and characterization of a theranostic system based on graphene/manganese chelate.

Construction of hybrid systems that combine the cancer treatment and diagnosis agents on a single platform, known as theranostic systems, have received great attentions in the field of nanobiomedicine. Here, construction and characterization of a new multifunctional hybrid theranostic system based on RGO, PDA, BSA, DTPA-Mn(II), and MTX constituents, is presented. Accordingly, GO is partially reduced and simultaneously functionalized by dopamine, leading to reduced graphene oxide/polydopamine, RGO-PDA system; and then, the bovine serum albumin protein (BSA) is grafted onto this system. The obtained system, RGO-PDA-BSA, is further decorated with diethylenetriaminepentaacetic acid-Mn(II) as diagnostic system and methotrexate as anticancer drug. Physicochemical characteristics of the RGO-PDA-BSA-DTPA-Mn(II)/MTX system are studied by Fourier transform infrared spectroscopy, atomic force microscopy, and electrochemical methods. The capturing ability of the prepared system for the cancer cells is evaluated through electrochemical impedance spectroscopy (EIS) and by using the 4T1 cancer cells in comparison with L929 normal cells. The EIS results indicate that a degree of selectivity as 6.23 for GC-RGO-PDA-BSA-DTPA-Mn(II)/MTX electrode system toward 4T1 cells, which is larger than that obtained for this system toward the L929 cells. Similar analysis performed using the GC-RGO-PDA-DTPA-Mn(II)/MTX system (having no BSA) indicate that the selectivity degree of the system is increased only by a factor of 1.6, implying that presence of BSA has increased the selectivity of the system for 4T1 cells by a factor of four. This behavior supports the crucial role of BSA in this process for 4T1 cells. Finally, the drug release study of RGO-PDA-BSA-DTPA-Mn(II)/MTX system is performed successfully at pH 7.4.

Electrochemical Behavior and Voltammetric Determination of a Manganese(II) Complex at a Carbon Paste Electrode.

Investigation of the electrochemical behavior using cyclic voltammetry and detection of [Mn(2+)(thiophenyl-2-carboxylic acid)2 (triethanolamine)] with adsorptive stripping differential pulse voltammetry. The electrochemical behavior of a manganese(II) complex [Mn(2+)(thiophenyl-2-carboxylic acid)2(triethanolamine)] (A) was investigated using cyclic and differential pulse voltammetry in an acetate buffer of pH 4.6 at a carbon paste electrode. Further, an oxidation-reduction mechanism was proposed. Meanwhile, an adsorptive stripping differential pulse voltammetric method was developed for the determination of manganese(II) complex.

Molecular structure, natural bond analysis, vibrational and electronic spectra, surface enhanced Raman scattering and Mulliken atomic charges of the normal modes of [Mn(DDTC)2] complex.

Theoretical and experimental bands have been assigned for the Fourier Transform Infrared and Raman spectra of the bis(diethyldithiocarbamate)Mn(II) complex, [Mn(DDTC)2]. The calculations have been based on the DFT/B3LYP method, second derivative spectra and band deconvolution analysis. The UV-vis experimental spectra were measured in acetonitrile solution, and the calculated electronic spectrum was obtained using the TD/B3LYP method with 6-311G(d, p) basis set for all atoms. Charge transfer bands and those d-d spin forbidden were assigned in the UV-vis spectrum. The natural bond orbital analysis was carried out using the DFT/B3LYP method and the Mn(II) hybridization leading to the planar geometry of the framework was discussed. Surface enhanced Raman scattering (SERS) was also performed. Mulliken charges of the normal modes were obtained and related to the SERS enhanced bands.

Structural comparative studies on new Mn(II), Cr(III) and Ru(III) complexes derived from 2,4,6-tri-(2-pyridyl)-1,3,5-triazine (TPTZ).

The structure of a new Mn(II) complex, [Mn(TPTZ)Cl2(H2O)]⋅H2O, was established by a single crystal X-ray diffraction. Crystal data are as follow: monoclinic, P21/c,a = 8.7202 (3)Å, b = 11.5712 (4)Å, c = 20.8675 (9)Å, ß=11 (18) × 1010, V = 2029.27 (13)Å(3), Z = 4. The HOMO, LUMO and other DFT parameters on the atoms have been calculated to confirm the geometry of the ligand and its complexes using material studio program. The complexes were characterized by elemental analyses, spectral, magnetic, thermal and cyclic voltammetry measurements. Electronic spectra and magnetic moments of the complexes suggest distorted-octahedral structures around the metal ions (Mn(II), Cr(III) and Ru(III)). The redox properties were investigated by cyclic voltammetry. Kinetic parameters were determined using Coats-Redfern and Horowitz-Metzger methods. The results of DNA studies of the metal complexes promised to be effective in tumour treatment.