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1.
Inorg Chem ; 2020 Apr 10.
Artigo em Inglês | MEDLINE | ID: mdl-32275143

RESUMO

Macrocyclic molecules with multiple coordination sites have been widely used as promising ligands to build polynuclear metal clusters; however, cyclic silsesquioxane-based metal clusters are still rare. Herein, we report a new octanuclear Co-silsesquioxane cluster [Co8(OH)2{(MeSiO2)6}2(bpy)2(Obpy)2] (SD/Co8c; SD = SunDi), wherein the Co8 disc-like core is sandwiched by two hexamethylcyclohexasiloxanolate ligands (MeSiO2)6 at two poles and finally encircled by two bpy (bpy = 2,2'-bipyridine) and two Obpy (HObpy = 6-hydroxy-2,2'-bipyridine) ligands at the equatorial region. Interestingly, both MeSi(OMe)3 and bpy undergo in situ transformations to generate hexameric cyclic (MeSiO2)6 and Obpy, respectively. The unusual hydroxylation of bpy and the OH- anion in the center of Co8 core provide additional binding sites to induce the formation of the larger cluster instead of the traditional hexanuclear cluster. The solution stability and fragmentation route in the gas phase were studied by cold-spray ionization and collision-induced dissociation mass spectrometry, respectively. Both results reveal that the Co8 core is quite stable in solution as well as in the gas phase, even with increased collision voltage. Magnetic susceptibility studies of SD/Co8c show the slow magnetization relaxation indicative of single-molecule magnet (SMM) behavior. This work not only presents the multiple in situ ligand-transformation-assisted assembly of polynuclear cobalt cluster but also provides some new insights into the magnetism-structure relationship for SMMs.

2.
Inorg Chem ; 2020 Apr 24.
Artigo em Inglês | MEDLINE | ID: mdl-32330029

RESUMO

A molecule-based ferroelectric triethylmethylammonium tetrachloroferrate(III) ([N(C2H5)3CH3][FeCl4]) powder was designed as a multifunctional material exhibiting excellent multiple bistability. Prepared by the slow evaporation method at room temperature, the compound crystallizes in the non-centrosymmetric assembly of hexagonal symmetry (P63mc space group) which undergoes a reversible temperature-triggered phase transition pinpointed at 363 K to the centrosymmetric packing within the P63/mmc space group. Aside from the inseparable role of the symmetry-breaking process smoothly unveiled from the X-ray powder diffraction data, a striking change in the dielectric permittivity observed during the paraelectric-to-ferroelectric phase transition directly discloses the bistable dielectric behavior-an exceptionally high increase in the dielectric permittivity of about 360% at 100 kHz across the heating and cooling cycles is direct proof showing the highly desirable stimuli-responsive electric ordering in this improper ferroelectric architecture. Due to the magnetically modulated physical properties resulting in the coupling of magnetic and electric orderings, the flexible assembly of [N(C2H5)3CH3][FeCl4] could be used to boost the design and development of novel magnetoelectric devices.

3.
Inorg Chem ; 2020 Feb 19.
Artigo em Inglês | MEDLINE | ID: mdl-32073840

RESUMO

Most of polyoxometallates (POMs) templated silver nanoclusters recorded so far are polyoxomolybdates and polyoxotungstates; however, as congeneric polyoxochromates, they are rarely observed in silver nanoclusters. Herein, a high-nuclearity polyoxochromate, (CrIII4CrVI8O36)12-, is uncovered in a novel silver nanocluster (SD/Ag56a) as an anion template. The mixed-valent (CrIII4CrVI8O36)12- consists of four edge-sharing CrIIIO6 octahedra and eight CrVIO4 tetrahedra, which are fused together by sharing one or two vertexes. The (CrIII4CrVI8O36)12- is the by far highest nuclearity polyoxochromate and is trapped by outer Ag56 bracelet-like shell coprotected by quaternary ligands including iPrS-, NapCOO- (2-naphthalenecarboxylate), CF3COO-, and CH3CN. The antiferromagnetic property and solution behavior of SD/Ag56a are discussed in detail.

4.
Inorg Chem ; 58(6): 3800-3806, 2019 Mar 18.
Artigo em Inglês | MEDLINE | ID: mdl-30816713

RESUMO

The search for functional materials, for example those aiming at microelectronics, magnetic recording, and catalysis, often ventures into mixed metal systems to achieve optimization of the properties. Thus, understanding site preference and self-organization is crucial but hard to implement. Herein, we present a system whereby MgII, MnII, and MnIII ions selectively locate exact positions within the Brucite-structured cluster, Mn13Mg6, [MnIII⊂MgII6⊂MnII9MnIII3( L)18(OH)12(N3)6](ClO4)6·12CH3CN, H L = 1-(hydroxymethyl)-3,5-dimethylpyrazolate). The MnIII being small (78 pm) takes up the core position; while 6 MgII (86 pm) are located in the inner ring, and the 9 large MnII (97 pm) and 3 MnIII occupy the outer ring. The factors (a) ionic radii, (b) regularity in coordination geometry, oxophilicity, and softness of MgII compared to MnII, and (c) Jahn-Teller distortion of MnIII may all be implicated synergistically. Electrospray ionization mass spectrometry reveals the M19 disc remains an integral unit when crystals are dissolved, and exchange between Mg and Mn occurs within the disc during its formation. Diamagnetic MgII doping insulates the magnetic exchange between the central MnIII and those in the outer ring, thus giving an overall antiferromagnetic exchange interaction between nearest-neighbors of the outer ring. The work reveals the underlying rule for site-preference of main group metal versus transition metal in disc-like Brucite-structured cluster and provides an elegant new avenue to assemble heterometallic clusters in a stepwise fashion.

5.
Beilstein J Nanotechnol ; 9: 1613-1622, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-29977695

RESUMO

Nanocomposites with a high, uniform loading of magnetic nanoparticles are very desirable for applications such as electromagnetic shielding and cancer treatment based on magnetically induced hyperthermia. In this study, a simple and scalable route for preparing nanocomposites with a high, uniform loading of magnetic nanoparticles is presented. The magnetic iron-oxide nanoparticles were functionalized with a methacrylate-based monomer that copolymerized in a toluene solution with the methyl methacrylate (MMA) monomer. The resulting suspension of magnetic nanoparticles decorated with poly(methyl methacrylate) (PMMA) chains in toluene were colloidal, even in the presence of a magnetic field gradient. Nanocomposites were precipitated from these suspensions. The transmission electron microscopy investigation of the prepared nanocomposites revealed that the magnetic nanoparticles were homogeneously dispersed in the PMMA matrix, even in amounts up to 53 wt %. The uniform dispersion of the nanoparticles in the PMMA matrix was attributed to the good solvation of the grafted PMMA chains from the magnetic nanoparticles by the PMMA chains of the matrix. The nanocomposites were superparamagnetic and exhibited large values for the saturation magnetization of up to 36 emu/g. Moreover, the nanocomposite with the largest amount of incorporated nanoparticles exhibited relatively large values for the specific power loss when subjected to alternating magnetic fields, giving this material great potential for the magnetically induced hyperthermia-based treatment of cancer.

6.
Inorg Chem ; 56(5): 2481-2489, 2017 Mar 06.
Artigo em Inglês | MEDLINE | ID: mdl-28199094

RESUMO

Two novel POM-based inorganic-organic hybrids, [Cu6II(2,2'-bipy)6(Mo6O22)(SiW12O40)]n (1), and {[Cu6II(ppz)6(H2O)5(MoO4)(SiW12O40)]·4H2O}n (2) (2,2'-bipy = 2,2'-bipyridine, Hppz = 3-(pyrid-2-yl)pyrazole), have been constructed from heteropolytungstates and molybdates. Two compounds have been identified by single crystal X-ray diffraction, elemental analysis, and FT-IR. Compound 1 shows a 1D (one-dimensional) chain structure constructed from classical Keggin heteropolytungstate [SiW12O40]4- clusters and [Cu6(2,2'-bipy)6] modified isopolymolybdates [Mo6O22]8-. Compound 2 also represents a 1D chain-like motif built from classical Keggin heteropolytungstate [SiW12O40]4- clusters and [Cu8(ppz)6(H2O)5] modified molybdates MoO42-. Compound 1 represents the first example of POM-based inorganic-organic hybrid with mixed heteropolytungstates and isopolymolybdates. ESI-MS (electrospray ionization mass spectrometry) technique was employed to reveal the species and their evolutions in the hydrothermal reaction, whereby trivacant [SiW9] building block gradually transforms to classical Keggin [SiW12] during assembly process. Furthermore, the electrocatalytic and magnetic properties were discussed in details.

7.
Dalton Trans ; 45(20): 8404-11, 2016 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-27108482

RESUMO

Modified classical trivacant Wells-Dawson α-[P2W15O56](12-) and the assembly of related sandwiched transition metal clusters are of interest, but surprisingly few reports of these materials exist because of the sensitivity of α-[P2W15O56](12-) to the assembly environment. Herein, we describe the pH-controlled assembly of two novel Dawson-sandwiched clusters, (H2bpz)6[Co2(P2W16O57)2]·22H2O (1, bpz = 3,3',5,5'-tetramethyl-4,4'-bipyrazole) and (H2bpz)6[Co3H2(P2W16O57)(P2W15O56)(H2O)]·12H2O (2), involving the in situ transformation of α-[P2W15O56](12-). Both clusters were characterized by X-ray single-crystal diffraction, FT-IR spectroscopy, UV-Visible spectroscopy, thermogravimetric analysis, powder X-ray diffraction, and elemental analyses. X-ray crystallography showed that both heteropolytungstates become divacant α-[P2W16O57](8-) and symmetrically encapsulate two edge-shared CoO6 octahedra in the interior in 1, while only one divacant α-[P2W16O57](8-) is observed in 2, which combined with another trivacant α-[P2W15O56](12-) to asymmetrically clamp three edge-shared CoO6 octahedra. The α-[P2W16O57](8-) heteropolytungstate should be generated in situ from α-[P2W15O56](12-)via self-decomposition equilibria in solution. Their electrochemical behaviors reveal characteristic multi-electron redox processes related to W(VI) centers. The electrocatalytic reduction performances toward nitrite, hydrogen peroxide, chlorate, bromate and iodate were fully measured and discussed; among these species, both clusters exhibit the best electrocatalytic activity towards the reduction of bromate. Magnetic measurements indicate weak ferromagnetic exchange interactions between Co atoms sandwiched by vacant polyoxometalates.

8.
Philos Trans R Soc Lond B Biol Sci ; 365(1545): 1397-403, 2010 May 12.
Artigo em Inglês | MEDLINE | ID: mdl-20368258

RESUMO

Entropy production is calculated for bacterial chemotaxis in the case of a migrating band of bacteria in a capillary tube. It is found that the speed of the migrating band is a decreasing function of the starting concentration of the metabolizable attractant. The experimentally found dependence of speed on the starting concentration of galactose, glucose and oxygen is fitted with power-law functions. It is found that the corresponding exponents lie within the theoretically predicted interval. The effect of the reproduction of bacteria on band speed is considered, too. The acceleration of the band is predicted due to the reproduction rate of bacteria. The relationship between chemotaxis, the maximum entropy production principle and the formation of self-organizing structure is discussed.


Assuntos
Bactérias/crescimento & desenvolvimento , Bactérias/metabolismo , Quimiotaxia , Entropia , Modelos Biológicos , Aceleração , Metabolismo Energético/fisiologia
9.
J Chem Inf Model ; 45(6): 1605-9, 2005.
Artigo em Inglês | MEDLINE | ID: mdl-16309261

RESUMO

The mathematical model presented here describes the interactions among Ca2+, calmodulin (CaM), and myosin light chain kinase (MLCK) and consists of a kinetic scheme taking into account 7 reactions instead of 12 as proposed previously. We derive a system of 5 nonlinear ordinary differential equations. Solving it yields the prediction of active MLCK as a function of [Ca2+] whereby the active MLCK is defined to be proportional to the Ca4CaM.MLCK complex concentration. The model predictions are compared with other theoretical and experimental predictions of active MLCK as well as with the results of our previously proposed complex model.


Assuntos
Quinase de Cadeia Leve de Miosina/metabolismo , Algoritmos , Cálcio/fisiologia , Calmodulina/metabolismo , Ativação Enzimática/fisiologia , Transferência Ressonante de Energia de Fluorescência , Cinética , Modelos Estatísticos , Músculo Liso/enzimologia
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