In Situ Visualizing Oxidase-Mimicking Activity of Single MnOOH Nanotubes with Mie Scattering-Based Absorption Microscopy.

Imaging the catalytic activity at the single-particle level can greatly promote the screening and rational design of highly efficient nanozymes, but conventional techniques are based on ensemble analysis. Here, we present a new absorption microscopy for in situ visualizing oxidase-mimicking activity of single MnOOH nanotubes. The particle with a size more than 700 nm roughly equally scatters all wavelengths of visible light via Mie scattering, and the scattering light is collected by dark-field optical microscopy. When the particles absorb a single color of the scattering light, each individual nanoparticle shows its complementary color, enabling a form of absorption microscopy that we name Mie scattering-based absorption microscopy. We find that MnOOH nanotubes can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to generate polyTMB nanowires at their tips. There are multiple active sites on the surface of the individual nanotube, and the nanozyme activity shows a large heterogeneity as well as pH-dependent characteristic.

Preparation of SiO2-MnFe2O4 Composites via One-Pot Hydrothermal Synthesis Method and Microwave Absorption Investigation in S-Band.

MnFe2O4 NPs are successfully decorated on the surface of SiO2 sheets to form the SiO2-MnFe2O4 composite via one-pot hydrothermal synthesis method. The phase identification, morphology, crystal structure, distribution of elements, and microwave absorbing properties in S-band (1.55~3.4 GHz) of the as-prepared composite were investigated by XRD, SEM, TEM, and Vector Network Analyzer (VNA) respectively. Compared with the pure MnFe2O4 NPs, the as-prepared SiO2-MnFe2O4 composite exhibits enhanced microwave absorption performance in this frequency band due to the strong eddy current loss, better impedance matching, excellent attenuation characteristic, and multiple Debye relaxation processes. The maximum reflection loss of -14.87 dB at 2.25 GHz with a broader -10 dB bandwidth over the frequency range of 1.67~2.9 GHz (1.23 GHz) can be obtained at the thickness of 4 mm. Most importantly, the preparation method used here is relatively simple, hence such composite can be served as a potential candidate for effective microwave absorption in S-band.

MnO nanoparticles with unique excitation-dependent fluorescence for multicolor cellular imaging and MR imaging of brain glioma.

The authors describe MnO nanoparticles (NPs) with unique excitation-dependent fluorescence across the entire visible spectrum. These NPs are shown to be efficient optical nanoprobe for multicolor cellular imaging. Synthesis of the NPs is accomplished by a thermal decomposition method. The MnO NPs exhibit a high r1 relaxivity of 4.68 mM-1 s-1 and therefore give an enhanced contrast effect in magnetic resonance (MR) studies of brain glioma. The cytotoxicity assay, hemolysis analysis, and hematoxylin and eosin (H&E) staining tests verify that the MnO NPs are biocompatible. In the authors' perception, the simultaneous attributes of multicolor fluorescence and excellent MR functionality make this material a promising dual-modal nanoprobe for use in bio-imaging. Graphical abstract A direct method to synthesize fluorescent MnO NPs is reported. The NPs are biocompatible and have been successfully applied for multicolor cellular imaging and MR detection of brain glioma.

In vitro study on apoptotic cell death by effective magnetic hyperthermia with chitosan-coated MnFe2O4.

Magnetic nanoparticles (MNPs) have been widely investigated as a hyperthermic agent for cancer treatment. In this study, thermally responsive Chitosan-coated MnFe2O4 (Chitosan-MnFe2O4) nanoparticles were developed to conduct localized magnetic hyperthermia for cancer treatment. Hydrophobic MnFe2O4 nanoparticles were synthesized via thermal decomposition and modified with 2,3-dimercaptosuccinic acid (DMSA) for further conjugation of chitosan. Chitosan-MnFe2O4 nanoparticles exhibited high magnetization and excellent biocompatibility along with low cell cytotoxicity. During magnetic hyperthermia treatment (MHT) with Chitosan-MnFe2O4 on MDA-MB 231 cancer cells, the targeted therapeutic temperature was achieved by directly controlling the strength of the external AC magnetic fields. In vitro Chitosan-MnFe2O4-assisted MHT at 42 °C led to drastic and irreversible changes in cell morphology and eventual cellular death in association with the induction of apoptosis through heat dissipation from the excited magnetic nanoparticles. Therefore, the Chitosan-MnFe2O4 nanoparticles with high biocompatibility and thermal capability can be an effective nano-mediated agent for MHT on cancer.

Manganese oxides supported on gold nanoparticles: new findings and current controversies for the role of gold.

We synthesized manganese oxides supported on gold nanoparticles (diameter <100 nm) by the reaction of KMnO4 with gold nanoparticles under hydrothermal conditions. In this green method Mn oxide is deposited on the gold nanoparticles. The compounds were characterized by scanning electron microscopy, energy-dispersive spectrometry, high-resolution transmission electron microscopy, X-ray diffraction, UV-Vis spectroscopy, Fourier transform infrared spectroscopy, and atomic absorption spectroscopy. In the next step, the water-oxidizing activities of these compounds in the presence of cerium(IV) ammonium nitrate as a non-oxo transfer oxidant were studied. The results show that these compounds are good catalysts toward water oxidation with a turnover frequency of 1.0 ± 0.1 (mmol O2/(mol Mn·s)). A comparison with other previously reported Mn oxides and important factors influencing the water-oxidizing activities of Mn oxides is also discussed.

Ball milling synthesized MnOx as highly active catalyst for gaseous POPs removal: significance of mechanochemically induced oxygen vacancies.

A rapid (1.5 h) one-step ball milling (BM) method was developed not only to modify commercial MnO2 via top-down approaches (BM0), but also to bottom-up synthesize MnO(x) by cogrinding of KMnO4 and MnC4H6O4 (BM1) or KMnO4 and MnSO4 (BM2). Catalysts activity on gaseous POPs removal was tested using hexachlorobenzene (HCBz) as surrogate. Catalytic performance decreases in the order of BM2 ≈ BM1 (T90% = 180-200 °C) > BM0 (260 °C) > CMO ≈ cryptomelane MnO2 (>300 °C). Both adsorption and destruction contribute to HCBz removal at 180 °C while destruction prevails at 200-300 °C. Mechanism studies show that destruction activity is lineally correlated with the amount of surface reactive oxygen species (Oads); stability is determined by the removal of surface chloride, which is associated with the mobility of bulk lattice oxygen (Olat); adsorption capacities are linearly correlated with surface area and pore structure. With the aid of extensive characterizations the excellent performance of BM prepared samples can be explained as (1) abundant surface vacancies enhance the generation of Oads; (2) massive bulk vacancies promote the mobility of bulk Olat; (3) large surface area and uniform pore size distribution facilitate the physisorption of HCBz.

Synthesis, crystal structure, and biological activities of two chiral mononuclear Mn((III)) complexes.

Two new chiral mononuclear Mn((III)) complexes, [MnL((R)) Cl (C2 H5 OH)]•C2 H5 OH () and [MnL((S)) (CH3 OH)2 ]Cl•CH3 OH (), {H2 L = (R,R)-or (S,S)-N,N'-bis-(2-hydroxy-1-naphthalidehydene)-cyclohexanediamine} were synthesized and characterized by various physicochemical techniques. Bond valence sum (BVS) calculations and the Jahn-Teller effect indicate that the Mn centers are in a +3 oxidation state. The statuses of the two complexes in the solution were confirmed as a pair of enantiomers by electrospray ionization, mass spectrometry (ESI-MS) spectrum. The binding ability of the complexes with calf thymus CT-DNA was investigated by spectroscopic and viscosity measurements. Both of the complexes could interact with CT-DNA via an intercalative mode with the order of (R-enantiomer) > (S-enantiomer). Under the physiological conditions, the two compounds exhibit efficient DNA cleavage activities without any external agent, which also follows the order of R-enantiomer > S-enantiomer. Interestingly, the concentration-dependent DNA cleavage experiments indicate an optimal concentration of 17.5 µM. In addition, the interaction of the compounds with bovine serum albumin (BSA) was also investigated, which indicated that the complexes could quench the intrinsic fluorescence of BSA by a static quenching mechanism.

Synthesis of Ordered Mesoporous Manganese Oxides with Various Oxidation States.

Ordered mesoporous MnO, MnO4, Mn2O3 and MnO2 materials with 3-D pore structure were suc- cessfully synthesized via a nano-replication method by using ordered mesoporous silica, KIT-6 (Cubic Ia3d space group mesostructure) as the template under specific oxidation and reduction conditions. Notably, ordered mesoporous MnO with a crystalline wall (rock salt structure) was syn- thesized for the first time, to the best of our knowledge. The synthesis of the ordered mesoporous MnO was achieved by reducing the ordered mesoporous Mn3O4 under an H2 atmosphere, while preserving the ordered mesostructure and crystalline wall throughout the solid/solid transformation. All of the ordered mesoporous manganese oxides with different crystal structures and oxidation states demonstrated almost the same spherical-like morphology with several hundred nanometers of particles. The synthesized ordered mesoporous manganese oxides had uniform dual mesopores (2-3 nm, and ~20 nm) and crystalline frameworks with large surface areas (86-140 m2/g) and pore volumes (0.27-0.33 cm3/g).

Sorption of arsenic on manganese dioxide synthesized by solid state reaction.

Arsenic in groundwater is a major concern in many parts of the world and suitable sorbents are required for removal of arsenic from ground water. Removal of arsenic from groundwater has been studied using manganese dioxide, synthesized by solid state reaction of manganese acetate with potassium permanganate. Manganese dioxide was characterized by X-ray diffraction (XRD), zeta potential, surface area, particle size measurements and thermal analysis. XRD measurement showed that the manganese dioxide had α-MnO2 structure. Sorption of As(III) and As(V) on manganese dioxide was studied by radiotracer technique using (76)As radio isotope. Arsenic removal efficiency for both As(III) and As(V) at concentration of 2 mg L(-1) was ∼99% in the pH range of 3-9. The sorption capacities for As(III) and As(V) were ∼60 mg g(-1). Kinetic studies showed that the equilibrium was reached within 30 s. Arsenic sorbed on manganese dioxide was present as As(V) irrespective of initial oxidation state. The presence of Ca(2+), Mg(2+), Cl(-) and SO4(2-) up to a concentration of 1000 mg L(-1) had no significant effect on arsenic sorption. The sorption of arsenic decreased significantly in the presence of phosphate and bicarbonate anions above 10 mg L(-1). Arsenic sorbed on manganese dioxide was desorbed by 0.1M NaOH. Arsenic was effectively removed by manganese dioxide from groundwater samples collected from arsenic contaminated areas of West Bengal, India.

Two-dimensional nanosheets associated with one-dimensional single-crystalline nanorods self-assembled into three-dimensional flower-like Mn3O4 hierarchical architectures.

Three-dimensional (3D) flower-like hausmannite architectures of Mn3O4 with uniform morphology have been successfully synthesized by a novel chemical reaction route using cetyltrimethylammonium bromide as the template. Micro/nanostructures of the as-synthesized 3D flower-like Mn3O4 architectures were investigated in detail by a series of analytical techniques. The geometrical shape of 3D flower-like Mn3O4 architectures is structurally perfect, and they are produced with diameters in the range of several hundred nanometers to a few micrometers. Experimental results indicate that two-dimensional nanosheets associated with one-dimensional single-crystalline nanorods self-assembled into three-dimensional flower-like Mn3O4 architectures. The single-crystalline Mn3O4 nanorods are a few hundred nanometers long and several tens of nanometers wide. Different dimensional systems, such as two-dimensional nanosheets, one-dimensional nanorods, and three-dimensional nanoflowers, could provide different building blocks to constitute nanostructured materials. These specific building blocks, which constituted the complex hierarchical architectures with nanostructural features, may offer exciting opportunities for both fundamental research and technological applications.

Enhanced catalytic and supercapacitor activities of DNA encapsulated ß-MnO2 nanomaterials.

A new approach is developed for the aqueous phase formation of flake-like and wire-like ß-MnO2 nanomaterials on a DNA scaffold at room temperature (RT) within a shorter time scale. The ß-MnO2 nanomaterials having a band gap energy ∼3.54 eV are synthesized by the reaction of Mn(II) salt with NaOH in the presence of DNA under continuous stirring. The eventual diameter of the MnO2 particles in the wire-like and flake-like morphology and their nominal length can be tuned by changing the DNA to Mn(ii) salt molar ratio and by controlling other reaction parameters. The synthesized ß-MnO2 nanomaterials exhibit pronounced catalytic activity in organic catalysis reaction for the spontaneous polymerization of aniline hydrochloride to emeraldine salt (polyaniline) at RT and act as a suitable electrode material in electrochemical supercapacitor applications. From the electrochemical experiment, it was observed that the ß-MnO2 nanomaterials showed different specific capacitance (Cs) values for the flake-like and wire-like structures. The Cs value of 112 F g(-1) at 5 mV s(-1) was observed for the flake-like structure, which is higher compared to that of the wire-like structure. The flake-like MnO2 nanostructure exhibited an excellent long-term stability, retaining 81% of initial capacitance even after 4000 cycles, whereas for the wire-like MnO2 nanostructure, capacitance decreased and the retention value was only 70% over 4000 cycles. In the future, the present approach can be extended for the formation of other oxide-based materials using DNA as a promising scaffold for different applications such as homogeneous and heterogeneous organic catalysis reactions, Li-ion battery materials or for the fabrication of other high performance energy storage devices.

Characterization strategies for Mn2O3 nanomaterials.

Transition metal oxides belong to a class of versatile materials that are vitally important for developing new materials with functionality and smartness. Research on manganese oxides has been a key topic among studies on transition metal oxides. This is due to their potential applications in diverse areas, including rechargeable lithium ion batteries, catalysis, molecular adsorption, gas sensors, energy storage, and magnetics. In this review, we will elucidate in detail various characterization strategies, including temperature-dependent growth, micro/nanostructures, Raman, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and electron spin resonance, for Mn2O3 nanocrystals, highlighting contributions from our laboratory. This review article mainly focuses on the wide-ranging research effort on the development of preparation methodologies and the assessment of various characterization strategies in Mn2O3 nanomaterials. The main purpose is to provide the readers a comprehensive understanding of the research progress of manganese oxides. This is an interdisciplinary work that integrates the areas of physics, chemistry, materials science, and nanotechnology.

Sorption of As(III) and As(V) on chemically synthesized manganese dioxide.

Sorption of As(III) and As(V) on manganese dioxide was studied by batch equilibration method using (76)As radioactive tracer. Manganese dioxide was prepared by two different methods viz. reacting (a) KMnO(4) solution with MnSO(4) solution, and (b) KMnO(4) solution with concentrated hydrochloric acid. Manganese dioxide was characterized by zeta potential measurement, surface area measurement, thermogravimetry (TG), differential thermal analysis (DTA) and X-ray diffraction (XRD) techniques. Point of zero charge (PZC) for manganese dioxide was between pH 3 and 4. Radioactive tracer ((76)As) was prepared by neutron irradiation of arsenious oxide in self serve facility of CIRUS reactor followed by conversion to As(III) and As(V), by appropriate chemical methods. Sorption of As(III) and As(V) were studied separately, between pH 1 to 11, using (i) freshly prepared, (ii) air-dried and (iii) aged manganese dioxide. Sorption of As(III) and As(V) on freshly prepared as well as aged manganese dioxide, from both the methods was greater than 98% between pH 1 to 9 and decreased above pH 9. Percentage sorption was comparable for manganese dioxide prepared by both the methods in different batches. Sorption capacity was ∼2 mg g(-1) for both As(III) and As(V). Arsenic was desorbed from the manganese dioxide by 0.1 M sodium hydroxide and oxidation state of desorbed arsenic was determined by solvent extraction method. It was found that the desorbed arsenic was present in As(V) oxidation state, independent of the initial oxidation states. This simple and direct chemical evidence, establishing that As(III) is converted to As(V) by manganese dioxide, is reported for the first time. Sorption of As(III) and As(V) on manganese dioxide did not cause an increase in manganese concentration above solubility limit confirming that Mn(2+), formed during oxidation of As(III) to As(V), was re-adsorbed.

Polydisulfide manganese(II) complexes as non-gadolinium biodegradable macromolecular MRI contrast agents.

PURPOSE: To develop safe and effective manganese(II) -based biodegradable macromolecular MRI contrast agents. MATERIALS AND METHODS: In this study, we synthesized and characterized two polydisulfide manganese(II) complexes, Mn-DTPA cystamine copolymers and Mn-EDTA cystamine copolymers, as new biodegradable macromolecular MRI contrast agents. The contrast enhancement of the two manganese-based contrast agents were evaluated in mice bearing MDA-MB-231 human breast carcinoma xenografts, in comparison with MnCl(2) . RESULTS: The T(1) and T(2) relaxivities were 4.74 and 10.38 mM(-1) s(-1) per manganese at 3T for Mn-DTPA cystamine copolymers (M(n) = 30.50 kDa) and 6.41 and 9.72 mM(-1) s(-1) for Mn-EDTA cystamine copolymers (M(n) = 61.80 kDa). Both polydisulfide Mn(II) complexes showed significant liver, myocardium and tumor enhancement. CONCLUSION: The manganese-based polydisulfide contrast agents have a potential to be developed as alternative non-gadolinium contrast agents for MR cancer and myocardium imaging.

Thermoelectric properties of Ca(1-x)Gd(x)MnO(3-δ) (0.00, 0.02, and 0.05) systems.

Polycrystalline samples of Ca(1-x)Gd(x)MnO(3-δ) (x = 0.00, 0.02, and 0.05) have been studied by X-ray diffraction (XRD), electrical resistivity (ρ), thermoelectric power (S), and thermal conductivity (κ). All the samples were single phase with an orthorhombic structure. The Seebeck coefficient of all the samples was negative, indicating that the predominant carriers are electrons over the entire temperature range. The iodometric titration measurements indicate that the electrical resistivity of Ca(1-x)Gd(x)MnO(3-δ) correlated well with the average valence of Mn(v+) and oxygen deficiency. Among the doped samples, Ca0.98Gd0.02MnO(3-δ) had the highest dimensionless figure of merit 0.018 at 300 K, representing an improvement of about 125% with respect to the undoped GaMnO(3-δ) sample at the same temperature.

Electrochemical insertion of lithium in mechanochemically synthesized Zn2SnO4.

We studied the electrochemical insertion of Li in mechanochemically prepared Zn(2)SnO(4). The mechanism of the electrochemical reaction was investigated by using X-ray diffraction, nuclear magnetic resonance spectroscopy, and Mössbauer spectroscopy. Changes in the morphology of the Zn(2)SnO(4) particles were studied by in situ scanning electron microscopy. The results were compared with mixtures of SnO(2) + ZnO and with Zn(2)SnO(4) prepared by conventional solid-state synthesis and showed that the mechanochemically prepared Zn(2)SnO(4) exhibits the best cyclic stability of these samples.

Microwave-assisted synthesis of NaMnF3 particles with tuneable morphologies.

Here, the synthesis of sub-micron MMnF3 (M = Na or K) particles by a rapid microwave-assisted approach is reported. Adjustment of the Na+-to-Mn2+ ratio in the reaction mixture yielded tuneable morphologies, i.e., rods, ribbons, and plates. Relaxometric results indicated that poly(acrylic acid)-capped MMnF3 particles exhibited characteristic magnetic properties, which endows them with potential T1-weighted contrast agent capabilities.

Improving the sensitivity of T1 contrast-enhanced MRI and sensitive diagnosing tumors with ultralow doses of MnO octahedrons.

Rationale: Sensitive and accurate imaging of cancer is essential for early diagnosis and appropriate treatment. For generally employed magnetic resonance imaging (MRI) in clinic, comprehending how to enhance the contrast effect of T1 imaging is crucial for improving the sensitivity of cancer diagnosis. However, there is no study ever to reveal the clear mechanism of how to enhance the effect of T1 imaging and accurate relationships of influencing factors. Herein, this study aims to figure out key factors that affect the sensitivity of T1 contrast-enhanced MRI (CE-MRI), thereby to realize sensitive detection of tumors with low dose of CAs. Methods: Manganese oxide (MnO) nanoparticles (NPs) with various sizes and shapes were prepared by thermal decomposition. Factors impacting T1 CE-MRI were investigated from geometric volume, surface area, crystal face to r2/r1 ratio. T1 CE-MR imaging of liver, hepatic and subcutaneous tumors were conducted with MnO NPs of different shapes. Results: The surface area and occupancy rate of manganese ions have positive impacts on the sensitivity of T1 CE-MRI, while volume and r2/r1 ratio have negative effects. MnO octahedrons have a high r1 value of 20.07 mM-1s-1 and exhibit an excellent enhanced effect in liver T1 imaging. ZDS coating facilitates tumor accumulation and cellular uptake, hepatic and subcutaneous tumors could be detected with MnO octahedrons at an ultralow dose of 0.4 mg [Mn]/kg, about 1/10 of clinical dose. Conclusions: This work is the first quantitative study of key factors affecting the sensitivity of T1 CE-MRI of MnO nanoparticles, which can serve as a guidance for rational design of high-performance positive MRI contrast agents. Moreover, these MnO octahedrons can detect hepatic and subcutaneous tumors with an ultralow dose, hold great potential for sensitive and accurate diagnosis of cancer with lower cost, less dosages and side effects in clinic.

Boosting Chemodynamic Therapy via a Synergy of Hypothermal Ablation and Oxidation Resistance Reduction.

Chemodynamic therapy (CDT), deemed as a cutting-edge antineoplastic therapeutic tactics, efficaciously suppresses tumors via catalytically yielding hydroxyl radicals (•OH) in tumor regions. Nevertheless, its biomedical applications are often restricted by the limited hydrogen peroxide (H2O2) level and upregulated antioxidant defense. Herein, a versatile nanoreactor is elaborately designed via integrating Cu2-xS and MnO2 for T1-weighted magnetic resonance (MR) imaging-guided CDT, synergistically enhanced through hypothermal ablation and oxidation resistance reduction, thereby displaying splendid antitumor efficiency as well as suppression on pulmonary metastasis. The as-synthesized Cu2-xS@MnO2 nanoreactors afford acid-dependent Cu-based and glutathione (GSH)-activated Mn-based catalytic properties for bimodal CDT. Owing to excellent absorbance at the second near-infrared (NIR-II) window, the Cu2-xS furnishes hypo-photo-thermal therapy (PTT) against tumor growth and ameliorates the catalytic performance for thermal-enhanced CDT. Additionally, MnO2 significantly downregulates GSH and glutathione peroxidase 4, which synergistically boosts CDT via promoting oxidative stress, simultaneously generating Mn2+ for MR contrast improvement and activatable tumor imaging. Therefore, this study proffers a new attempt centered on the collaborative strategy integrating NIR-II hypothermal PTT and synergistically enhanced CDT for tumor eradication.

Mesoporous MnO2/carbon aerogel composites as promising electrode materials for high-performance supercapacitors.

MnO(2) as one of the most promising candidates for electrochemical supercapacitors has attracted much attention because of its superior electrochemical performance, low cost, and environmentally benign nature. In this Letter, we explored a novel route to prepare mesoporous MnO(2)/carbon aerogel composites by electrochemical deposition assisted by gas bubbles. The products were characterized by energy-dispersive spectrometry (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The MnO(2) deposits are found to have high purity and have a mesoporous structure that will optimize the electronic and ionic conductivity to minimize the total resistance of the system and thereby maximize the performance characteristics of this material for use in supercapacitor electrodes. The results of nitrogen adsorption-desorption experiments and electrochemical measurements showed that these obtained mesoporous MnO(2)/carbon aerogel composites had a large specific surface area (120 m(2)/g), uniform pore-size distribution (around 5 nm), high specific capacitance (515.5 F/g), and good stability over 1000 cycles, which give these composites potential application as high-performance supercapacitor electrode materials.