A novel octanuclear Mn(III) aggregate as a single-molecule magnet

The novel octanuclear cluster [Mn8O2(OH)2(OMe)12(OAc)2(Mesalim)4] (1) presents SMM behaviour with a relatively high experimental energy barrier (eff/kB= 36.0 K) as shown by its dc and ac magnetic properties.     

Parallel analysis of v-Src mutant protein function using reverse transfection cell arrays

The conversion of the genomic information produced by the recent sequencing projects into a comprehensive understanding of the human proteome has yet to occur. A new technology that represents a potential bridge between genomics and proteomics is reverse transfection. Reverse transfection cell microarrays are produced by overlaying cDNA arrays with mammalian cells, generating localized clusters of transfected cells with each cluster overexpressing a unique protein. This miniaturized cell-based microarray format affords parallel functional analysis of thousands of cDNA constructs in a high throughput format. In this report we document the development of a co-transfection methodology for reverse transfection applications. The demonstrated high co-transfection efficiency with a "marker" plasmid encoding for GFP enables the identification of transfected cells and eliminates the need for epitope-tagged constructs in cell-based high throughput screening applications using reverse transfection. This co-transfection method was used to study in parallel the structure/function of multiple versions of the v-Src protein using automated fluorescence microscopy. The wild-type v-Src protein and four mutants having insertions or deletions in the SH2 or SH3 domains displayed high levels of tyrosine kinase activity in HEK293T cells. Three other mutated v-Src proteins, including a kinase-dead version, were shown to be defective for tyrosine kinase activity. This reverse co-transfection approach is applicable for high throughput screening of both cDNA libraries and positional scanning recombinant protein libraries.     

On the problem of splitting deformations of super Riemann surfaces

Letters in Mathematical Physics - An odd deformation of a super Riemann surface $$\mathcal {S}$$ is a deformation of $$\mathcal {S}$$ by variables of odd parity. In this article, we study the...     

Synthesis of Ag/AgCl-mesoporous silica nanocomposites using a simple aqueous solution-based chemical method and a study of their antibacterial activity on E. coli

Simple aqueous solution-based chemical methods have been developed for the synthesis of Ag/AgCl nanoparticle-mesoporous silica nanocomposites. Ag loading in the mesoporous silica was accomplished using a wet-impregnation method. The AgCl-mesoporous silica nanocomposite material(AgCl-mSi) was synthesized by using a 'one pot' method. Synthesized materials were characterized using X-ray diffraction,N2 adsorption-desorption analysis and high-resolution transmission electron microscopy. Antibacterial activity of...     

Magnetic resonance studies of a gas–solids fluidised bed: Jet–jet and jet–wall interactions

Magnetic resonance imaging （MRI） gave images of air jets from orifices in the distributor plate of a bed of poppy seeds. Attention focused on two features：
（1） The interaction between nearby vertical jets from two, three or four orifices;
（2） Wall effects, where one or more orifices created vertical jets near the vertical wall of the cylinder containing the particle bed.
The results show that nearby jets are mutually attracted. Likewise a jet near a wall bends out of the vertical, towards the wall, For multiple adjacent jets, the jet lengths show dependence on orifice layout： the lengths are in reasonable agreement with published measurements, by other methods, for single jets. The MRI gives three-dimensional images of the single jets and of multiple jets, separate or merging.     

High-nuclearity manganese and iron complexes with the anionic ligand methyl salicylimidate

The three novel clusters [Mn6O4(OMe)2(OAc)4(Mesalim)4] (3), [Mn8O2(OH)2(OMe)12(OAc)2(Mesalim)4] (4), and [Fe10O4(OMe)14Cl2(Mesalim)6] (5) have been synthesized from a simple bidentate ligand HMesalim (HMesalim = methyl salicylimidate). Starting from the mononuclear complex [Mn(Mesalim)2(OAc)(MeOH)].MeOH (1), either the hexanuclear complex 3 or the octanuclear complex 4 is obtained after recrystallization, depending upon the reaction conditions and solvents used. Similarly, starting from the purple-colored mononuclear complex [Fe(Mesalim)2Cl] (2), the orange-colored decanuclear iron(III) cluster 5 has been obtained upon recrystallization from methanol. Complex 3, which could also be prepared directly from manganese acetate and the ligand, has a face-sharing double-cubane [Mn6O6] core, unique in transition metal chemistry. Compounds 4 and 5 are composed of [M3O4] partial cubanes. All complexes belong to a class of oxo-bridged cubic close-packed molecular clusters resembling the metal oxide/hydroxide ores. Complex 4 exhibits intramolecular ferromagnetic interactions, as evidenced from dc magnetic susceptibility studies (1.8-300 K), resulting in a high-spin ground state, probably with S(T) = 8. Complex 4 displays single molecule magnet behavior as indicated by frequency and temperature dependences of its ac susceptibility. An Arrhenius plot gave relatively large experimental activation energy of 36.0 K. The magnetic properties of complexes 3 and 5 are dominated by antiferromagnetic interactions leading to zero-spin ground states.     

Stereochemical influence of the ligand on the structure of manganese complexes: implications for catalytic epoxidations

Manganese complexes of the ligand HphoxCOOR (R=H or Me) have been synthesized and characterized by X-ray analysis, ESI-MS, ligand-field spectroscopy, electrochemistry, and paramagnetic 1H NMR. The ligands, chirally pure or racemic, influence the structures of the complexes formed. Manganese(III) complexes of the ligand HphoxCOOMe are square-pyramidal or octahedral with two ligands bound in a trans fashion in the solid state. The racemic ligand (RS-HphoxCOOMe) as well as the enantiopure ligand (R-HphoxCOOMe) forms manganese complexes with similar solid-state structures. Ligand-exchange reactions occur in solution giving rise to meso complexes as confirmed by ESI-MS and deuteration studies. The manganese(III) complex of R-HphoxCOOH is octahedral, with two dianionic ligands bound in a fac-cct fashion in a tridentate manner. The manganese(III) complex of RS-HphoxCOOH is also octahedral with two dianionic ligands now bound in a trans fashion in a didentate manner and with two water molecules occupying axial sites. The paramagnetic 1H NMR spectra of the complexes have been interpreted on the basis of the relaxation times with the help of the inversion-recovery pulse technique. The binding of imidazole with the metal center depends on the chirality of the ligands in the metal complexes of HphoxCOOMe. Imidazole coordination was found to occur with the metal complex that contains two ligands with the same chirality (R and R) (R-1), while no imidazole coordination was found upon reaction with the metal complex that contains two ligands with opposite chirality (R and S) (RS-1). Epoxidation reactions of various alkenes with H2O2 as the oxidant reveal that the complexes give turnover numbers in the range of 10-35, the epoxide being the major product. The catalytic activity depends on the additives used, and a clear base effect is observed. The turnover numbers have been found to be higher in the complexes where no binding of N-Meim is observed. The latter fact unambiguously shows that imidazole binding is not a prerequisite for higher turnover numbers, in contrast to the Mn-Schiff base catalysts.     

Entropically Favoured Assembly of Pyrazine‐Based Helical Fibers into Superstructures: Achiral/ Chiral Guest‐Induced Chirality Transformation

The development of synthetic helical structures undergoing stimuli‐responsive chirality transformations is important for an understanding of the role of chirality in natural systems. However, controlling supramolecular chirality in entropically driven assemblies in aqueous media is challenging. To develop stimuli‐responsive assemblies, we designed and synthesized pyrazine derivatives with l ‐alanine groups as chiral building blocks. These systems undergo self‐assembly in aqueous media to generate helical fibers and the embedded alanine groups transfer their chirality to the assembled structures. Furthermore, these helical fibers undergo a Ni²⁺‐induced chirality transformation. The study demonstrates the role of intermolecular hydrogen bonding, π–π stacking, and the hydrophobic effect in the Ni²⁺‐mediated transition of helical fibers to supercoiled helical ensembles which mimic the formation of superstructures in biopolymers.