Magnetic property studies of manganese-phosphate complexes

Microwave-assisted one-step synthesis of water-soluble manganese-carbon nanodot clusters

Using metal coordination to assemble carbon nanodots (CND) into clusters can enhance their photophysical properties for applications in sensing and biomedicine. Water-soluble clusters of CNDs are prepared by one-step microwave synthesis starting from ethylenediaminetetraacetic acid, ethylenediamine and MnCl2·4H2O as precursors. Transmission electron microscopy and powder X-Ray diffraction techniques indicate that the resulting clusters form spherical particles of 150 nm constituted by amorphous CNDs joined together with Mn ions in a laminar crystalline structure. The nanomaterial assemblies show remarkable fluorescence quantum yields (0.17-0.20) and magnetic resonance imaging capability (r1 = 2.3-3.8 mM-1.s-1). In addition, they can be stabilized in aqueous solutions by phosphate ligands, providing a promising dual imaging platform for use in biological systems.

Synergistic effect of manganese (II) phosphate & diamond nanoparticles in electrochemical sensors for reactive oxygen species determination in seminal plasma

In this work, we explore the ability of manganese (II) phosphate (MnP) as a catalytic element for the determination of reactive oxygen species (ROS) in seminal plasma, when MnP is employed as modifier of a glassy carbon electrode. The electrochemical response of the manganese (II) phosphate-modified electrode shows a wave at around +0.65 V due to the oxidation of Mn²⁺ to MnO₂⁺, which is clearly enhanced after addition of superoxide, the molecule considered as the mother of ROS. Once proved the suitability of manganese (II) phosphate as catalyst, we evaluate the effect of including a 0D (diamond nanoparticles) or a 2D (ReS₂) nanomaterial in the sensor design. The system consisting of manganese (II) phosphate and diamond nanoparticles yielded the largest improvement of the response. The morphological characterization of the sensor surface was performed by scanning electron microscopy and atomic force microscopy, while cyclic and differential pulse voltammetry were employed for the electrochemical characterization of the sensor. After optimizing the sensor construction, calibration procedures by chronoamperometry were performed, leading to a linear relation between peak intensity and the superoxide concentration in the range of 1.1 10^-4 M - 1.0 10^-3 M with a limit of detection of 3.2 10^-5 M. Seminal plasma samples were analysed by the standard addition method. Moreover, the analysis of samples fortified with superoxide at the μM level leads to recoveries of 95%.

Impacts of environmental levels of hydrogen peroxide and oxyanions on the redox activity of MnO2 particles

Despite the widespread presence of hydrogen peroxide (H₂O₂) in surface water and groundwater systems, little is known about the impact of environmental levels of H₂O₂ on the redox activity of minerals. Here we demonstrate that environmental concentrations of H₂O₂ can alter the reactivity of birnessite-type manganese oxide, an earth-abundant functional material, and decrease its oxidative activity in natural systems across a wide range of pH values (4-8). The H₂O₂-induced reductive dissolution generates Mn(II) that will re-bind to MnO₂ surfaces, thereby affecting the surface charge of MnO₂. Competition of Bisphenol A (BPA), used as a target compound here, and Mn(II) to interact with reactive surface sites may cause suppression of the oxidative ability of MnO₂. This suppressive effect becomes more effective in the presence of oxyanions such as phosphate or silicate at concentrations comparable to those encountered in natural waters. Unlike nitrate, adsorption of phosphate or silicate onto birnessite increased in the presence of Mn(II) added or generated through H₂O₂-induced reduction of MnO₂. This suggests that naturally occurring anions and H₂O₂ may have synergetic effects on the reactivity of birnessite-type manganese oxide at a range of environmentally relevant H₂O₂ amounts. As layered structure manganese oxides play a key role in the global carbon cycle as well as pollutant dynamics, the impact of environmental levels of hydrogen peroxide (H₂O₂/MnO₂ molar ratio ≤ 0.3) should be considered in environmental fate and transport models.

Inhibition of Oxyanions on Redox-driven Transformation of Layered Manganese Oxides

Layered manganese (Mn) oxides, such as birnessite, can reductively transform into other phases and thereby affect the environmental behavior of Mn oxides. Solution chemistry strongly influences the transformation, but the effects of oxyanions remain unknown. We determined the products and rates of Mn(II)-driven reductive transformation of δ-MnO₂, a nanoparticulate hexagonal birnessite, in the presence of phosphate or silicate at pH 6-8 and a wide range of Mn(II)/MnO₂ molar ratios. Without the oxyanions, δ-MnO₂ transforms into triclinic birnessite (T-bir) and 4 × 4 tunneled Mn oxide (TMO) at low Mn(II)/MnO₂ ratios (0.09 and 0.13) and into δ-MnOOH and Mn₃O₄ with minor poorly crystallized α- and γ-MnOOH at high Mn(II)/MnO₂ ratios (0.5 and 1). The presence of phosphate or silicate substantially decreases the rate and extent of the above transformation, probably due to adsorption of the oxyanions on layer edges or the formation of Mn(II,III)-oxyanion ternary complexes on vacancies of δ-MnO₂, adversely interfering with electron transfer, Mn(III) distribution, and structural rearrangements. The oxyanions also reduce the crystallinity and particle sizes of the transformation products, ascribed to adsorption of the oxyanions on the products, preventing their further particle growth. This study enriches our understanding of the solution chemistry control on redox-driven transformation of Mn oxides.

Galvanic oxidation processes (GOPs): An effective direct electron transfer approach for organic contaminant oxidation

The activation of peroxymonosulfate (PMS) for organic contaminant oxidation usually relies on the formation of reactive oxygen species (ROSs). However, the ubiquitous anions and natural organic matter can easily scavenge ROSs and/or PMS, resulting in lower efficiencies and/or the formation of toxic byproducts. Relying on the unique long-distance electron transfer property, the recently developed Galvanic Oxidation Process (GOP) successfully achieved bisphenol A (BPA) degradation when BPA and PMS were physically separated in two reactors. In this study, we systematically investigated the performance of GOP at different PMS or BPA concentrations, pH, and ionic strength (IS) in both PMS and BPA solutions. The kinetic modeling employing the Langmuir-Hinshelwood model at different BPA concentrations suggested that although BPA and PMS were physically separated, the oxidation of the adsorbed BPA and reduction of the adsorbed PMS still followed a similar mechanism to that in traditional heterogeneous catalytic processes. The anions in the target water showed little impact on BPA degradation; higher IS enhanced the solution conductivity but inhibited BPA and electrode interactions, resulting in increased and then decrease BPA degradation rate. The electrodes presented high stability with a rate increase of 12% after 13 times of uses, and their hydration significantly facilitated BPA degradation but reduced the current by decreasing the potential difference between the anode and cathode. The graphite sheet itself without catalyst coating was also capable of shuttling electrons, while the use of a graphite fiber anode increased the BPA degradation by near 100% because of the larger surface area. The developed continuous stirred-tank reactor coupled with GOP (CSTR-GOP) achieved stable BPA degradation in less than 35 min and its scaling up is promising for future applications.

Preparation and characterization of manganese, cobalt and zinc DNA nanoflowers with tuneable morphology, DNA content and size

Recently reported DNA nanoflowers are an interesting class of organic-inorganic hybrid materials which are prepared using DNA polymerases. DNA nanoflowers combine the high surface area and scaffolding of inorganic Mg₂P₂O₇ nanocrystals with the targeting properties of DNA, whilst adding enzymatic stability and enhanced cellular uptake. We have investigated conditions for chemically modifying the inorganic core of these nanoflowers through substitution of Mg²⁺ with Mn²⁺, Co²⁺ or Zn²⁺ and have characterized the resulting particles. These have a range of novel nanoarchitectures, retain the enzymatic stability of their magnesium counterparts and the Co²⁺ and Mn²⁺ DNA nanoflowers have added magnetic properties. We investigate conditions to control different morphologies, DNA content, hybridization properties, and size. Additionally, we show that DNA nanoflower production is not limited to Ф29 DNA polymerase and that the choice of polymerase can influence the DNA length within the constructs. We anticipate that the added control of structure, size and chemistry will enhance future applications.

Tumor acidity-activatable manganese phosphate nanoplatform for amplification of photodynamic cancer therapy and magnetic resonance imaging

Amorphous biodegradable metal phosphate nanomaterials are considered to possess great potential in cancer theranostic application due to their promise in providing ultra-sensitive pH-responsive therapeutic benefits and diagnostic functions simultaneously. Here we report the synthesis of photosensitising and acriflavine-carrying amorphous porous manganese phosphate (PMP) nanoparticles with ultra-sensitive pH-responsive degradability and their application for a photoactivable synergistic nanosystem that imparts reactive oxygen species (ROS) induced cytotoxicity in synchrony with hypoxia-inducible factor 1α/vascular endothelial growth factor (HIF1α/VEGF) inhibitor that suppresses tumor growth and treatment escape signalling pathway. Carboxymethyl dextran (CMD) is chemically anchored on the surface of porous manganese phosphate theranostic system through the pH-responsive boronate esters. Upon the stimulus of the tumor acid microenvironment, manganese phosphate disintegrates and releases Mn²⁺ ions rapidly, which are responsible for the magnetic resonance imaging (MRI) effect. Meanwhile, the released photosensitizer chlorin e6 (Ce6) produces ROS under irradiation while acriflavine (ACF) inhibits the HIF-1α/VEGF pathway during the burst release of VEGF in tumour induced by photodynamic therapy (PDT), resulting in increased therapeutic efficacy. Considering the strong pH responsivity, MRI signal amplification and drug release profile, the PMP nanoparticles offer new prospects for tumor acidity-activatable theranostic application by amplifying the PDT through inhibiting the HIF-1α /VEGF pathway timely while enhancing the MRI effect.

STATEMENT OF SIGNIFICANCE

In this study, we report the synthesis of the tumor acidity-activatable amorphous porous manganese phosphate nanoparticles and their application for a photoactivable synergistic nanosystem that imparts reactive oxygen species (ROS) induced cytotoxicity in synchrony with hypoxia-inducible factor 1α/vascular endothelial growth factor (HIF-1α/VEGF) inhibitor that suppresses tumor growth and treatment escape signalling pathway. Besides, upon the stimulus of the tumor acid microenvironment, the manganese phosphate nanoparticles finally disintegrate and release Mn²⁺ ions rapidly, which are responsible for the magnetic resonance imaging (MRI) effect. This nanoplatform is featured with distinctive advantages such as ultra pH-responsive drug release, MRI function and rational drug combination exploiting the blockage of the treatment escape signalling pathway.

Models to predict the magnetic properties of single- and multiple-bridged phosphate CuII systems: a theoretical DFT insight

Models for the 1,1 and 1,3-bridging modes of phosphate for copper(ii) compounds were developed. Using unrestricted corresponding orbitals (UCO), a graphical identification of the predominant exchange pathway was described.

A facile electrochemical approach for the deposition of iron–manganese phosphate composite coatings on aluminium

Cathodic electrochemical treatment is a facile approach for the deposition of iron–manganese phosphate composite coatings on Al.

Manganese acquisition and homeostasis at the host-pathogen interface

Pathogenic bacteria acquire transition metals for cell viability and persistence of infection in competition with host nutritional defenses. The human host employs a variety of mechanisms to stress the invading pathogen with both cytotoxic metal ions and oxidative and nitrosative insults while withholding essential transition metals from the bacterium. For example, the S100 family protein calprotectin (CP) found in neutrophils is a calcium-activated chelator of extracellular Mn and Zn and is found in tissue abscesses at sites of infection by Staphylococcus aureus. In an adaptive response, bacteria have evolved systems to acquire the metals in the face of this competition while effluxing excess or toxic metals to maintain a bioavailability of transition metals that is consistent with a particular inorganic "fingerprint" under the prevailing conditions. This review highlights recent biological, chemical and structural studies focused on manganese (Mn) acquisition and homeostasis and connects this process to oxidative stress resistance and iron (Fe) availability that operates at the human host-pathogen interface.

Hydrogen Bonding and Multiphonon Structure in Copper Pyrazine Coordination Polymers

We report a systematic investigation of the temperature-dependent infrared vibrational spectra of a family of chemically related coordination polymer magnets based upon bridging bifluoride (HF(2)-) and terminal fluoride (F-) ligands in copper pyrazine complexes including Cu(HF(2))(pyz)(2)BF(4), Cu(HF(2))(pyz)(2)ClO(4), and CuF(2)(H(2)O)(2)(pyz). We compare our results with several one- and two-dimensional prototype materials including Cu(pyz)(NO(3))(2) and Cu(pyz)(2)(ClO(4))(2). Unusual low-temperature hydrogen bonding, local structural transitions associated with stronger low-temperature hydrogen bonding, and striking multiphonon effects that derive from coupling of an infrared-active fundamental with strong Raman-active modes of the pyrazine building-block molecule are observed. On the basis of the spectroscopic evidence, these interactions are ubiquitous to this family of coordination polymers and may work to stabilize long-range magnetic ordering at low temperature. Similar interactions are likely to be present in other molecule-based magnets.

Highly Selective Ferric Ion Sorption and Exchange by Crystalline Metal Phosphonates Constructed from Tetraphosphonic Acids

With the motivation of searching for highly selective ferric ion sorbents, two open-framework and microporous materials, {[Pb7(HEDTP)2(H2O)] x 7H2O}n (1) and {[Zn2(H4EDTP)] x 2H2O}n (2) [H8EDTP = N,N,N',N'-ethylenediaminetetrakis(methylenephosphonic acid)], have been synthesized and structurally characterized. The structure of compound 1 results from the seven crystallographically different lead atoms that are bridged by two HEDTP(7-) ligands to yield a three-dimensional microporous framework with tunnels along the a and b axes. Compound 2 features a layer architecture built of square waves along the a axis. The layers are connected by hydrogen bonds between uncoordinated phosphonate oxygen atoms to form a three-dimensional supramolecular network, with one-dimensional tunnels along the a axis. Both compounds 1 and 2 exhibited high ion sorption and exchange capacities for millimolar concentrations of Fe(III). Specifically, when 0.01 g of 1 (or 2) was added to 5 mL of a 1 mM metallic chloride aqueous solution and the mixture was allowed to stand for 2 days at room temperature, compound 1 adsorbed nearly 100% of Fe(III) and compound 2 adsorbed 96.8% of Fe(III). They were also found to adsorb ferric ions selectively over other metal ions, such as Ca(II), Cr(II), Mn(II), Cu(II), Zn(II), Cd(II), etc. Their special ferric ion uptake capacities may be attributed to the cation exchange, coordination bonding, and electrostatic attraction between ferric ions and metal phosphonates.

Old materials with new tricks: multifunctional open-framework materials

The literature on open-framework materials has shown numerous examples of porous solids with additional structural, chemical, or physical properties. These materials show promise for applications ranging from sensing, catalysis and separation to multifunctional materials. This critical review provides an up-to-date survey to this new generation of multifunctional open-framework solids. For this, a detailed revision of the different examples so far reported will be presented, classified into five different sections: magnetic, chiral, conducting, optical, and labile open-frameworks for sensing applications. (413 references.)

XPS Study of Interface and Ligand Effects in Supported Cu2O and CuO Nanometric Particles

This paper reports an analysis of the changes in the photoemission parameters of copper in small particles of copper oxides deposited on silicon dioxide. This study is of relevance for investigations in the fields of heterogeneous catalysis and coordination chemistry. Copper oxides (Cu2O and CuO) have been deposited on the surface of a flat SiO2 substrate by evaporation of copper and subsequent oxidization of the deposited particles. XPS has been used to analyze the chemical and coordination state of copper. Large variations in the Cu 2p(3/2) binding energy (BE) and Auger parameter (alpha') have been found as a function of the type and amount of deposited copper oxide. The differences in BE calculated from the values of the lowest amount of deposited material and those of the bulk compounds were -0.4 eV (Cu2O) and -1.9 eV (CuO), while those in alpha' amounted to 2.9 (Cu2O) and 1.6 eV (CuO). The observed changes have been described in terms of the chemical state vector (CSV) concept in a Wagner plot and rationalized by considering the characteristics of bonding and electronic interactions that occur at a given oxide/oxide interface. These interactions have been modeled by means of quantum mechanical calculations with cluster models simulating the Cu-O-Si bonding at the interface. The effect of the polarization of the surrounding media around the copper cations has been also estimated for both the dispersed clusters supported on the SiO2 substrate and for the copper oxide materials in bulk form. A change in the values of alpha' and BE of copper (ie., delta alpha' = 1.1 eV, deltaBE = 0.1 eV) upon adsorption on the Cu+ species of Cu2O moieties dispersed on SiO2 of a phenyl-acetylene molecule illustrates the use of XPS to study the formation of cation-ligand complexes in heterogeneous systems. A detailed description of the bonding interactions of these coordinated Cu+ species in terms of initial and final state effects of the photoemission process has been also carried out by means of quantum mechanical calculations and cluster models.