Oxidation,Redox Disproportionation and Chain Termination Reactions Catalysed by the Pd‐561 Giant Cluster

Redox disproportionation of benzyl alcohol to benzaldehyde and toluene catalysed by the Pd₅₆₁phen₆₀(OAc)₁₈₀ (phen=1,10‐phenanthroline) giant cluster 1 under anaerobic conditions was found, whereas in an O₂ atmosphere cluster 1 catalyses the oxidation of benzyl alcohol to benzaldehyde and inhibits further oxidation of the latter. A study of the AIBN‐initiated and non‐initiated oxidation of benzyl alcohol, sec‐butyl alcohol and styrene in the presence of cluster 1 revealed that cluster 1 performs three functions in the oxidation reactions: 1) catalysis of polar oxidation of the substrates with O₂, 2) termination of the chains of radical oxidation, and 3) catalysis of redox disproportionation.     

Temporal Control of Seed Development in Dicots: Molecular Bases,Ecological Impact and Possible Evolutionary Ramifications

In flowering plants, seeds serve as organs of both propagation and dispersal. The developing seed passes through several consecutive stages, following a conserved general outline. The overall time needed for a seed to develop, however, may vary both within and between plant species, and these temporal developmental properties remain poorly understood. In the present paper, we summarize the existing data for seed development alterations in dicot plants. For genetic mutations, the reported cases were grouped in respect of the key processes distorted in the mutant specimens. Similar phenotypes arising from the environmental influence, either biotic or abiotic, were also considered. Based on these data, we suggest several general trends of timing alterations and how respective mechanisms might add to the ecological plasticity of the families considered. We also propose that the developmental timing alterations may be perceived as an evolutionary substrate for heterochronic events. Given the current lack of plausible models describing timing control in plant seeds, the presented suggestions might provide certain insights for future studies in this field.     

Hyaluronan/Diethylaminoethyl Chitosan Polyelectrolyte Complexes as Carriers for Improved Colistin Delivery

Improving the therapeutic characteristics of antibiotics is an effective strategy for controlling the growth of multidrug-resistant Gram-negative microorganisms. The purpose of this study was to develop a colistin (CT) delivery system based on hyaluronic acid (HA) and the water-soluble cationic chitosan derivative, diethylaminoethyl chitosan (DEAECS). The CT delivery system was a polyelectrolyte complex (PEC) obtained by interpolymeric interactions between the HA polyanion and the DEAECS polycation, with simultaneous inclusion of positively charged CT molecules into the resulting complex. The developed PEC had a hydrodynamic diameter of 210–250 nm and a negative surface charge (ζ-potential = −19 mV); the encapsulation and loading efficiencies were 100 and 16.7%, respectively. The developed CT delivery systems were characterized by modified release (30–40% and 85–90% of CT released in 15 and 60 min, respectively) compared to pure CT (100% CT released in 15 min). In vitro experiments showed that the encapsulation of CT in polysaccharide carriers did not reduce its antimicrobial activity, as the minimum inhibitory concentrations against Pseudomonas aeruginosa of both encapsulated CT and pure CT were 1 μg/mL.     

Interaction of a copper oxide particle with copper in drawing

The forming of copper near a copper oxide particle is determined during multiple-pass drawing. The interaction of the copper oxide particle with copper is studied by the calculation of the state of stress in a finite element formulation and using scanning electron microscopy data. The results obtained demonstrate that pores appear around copper oxide particles when strain accumulates in multiple-pass drawing machines. The pore length increases with the accumulated strain, which can result in breaks of a wire in a highly cold-worked state.     

Emission properties of colloidal quantum dots on polyelectrolyte multilayers

We present steady state and time-resolved photoluminescence (PL) characteristics of differently charged CdTe quantum dots (QDs) adsorbed onto a polyelectrolyte (PE) multilayer. The PE multilayer is built up using a layer-by-layer assembly technique. We find that the diffusion of the QDs into the PE multilayer is an important factor in the case of 3-mercapto-1, 2-propanediol stabilized QDs (neutral surface charge), resulting in a ～31-fold enhancement in PL intensity accompanied by a blue shift in the PL spectra and an increase in decay lifetime from 3.74?ns to a maximum of 11.65?ns. These modified emission properties are attributed to the enhanced surface related emission resulting from the interaction of the QD's surface with the PE. We find that diffusion does not occur for thioglycolic acid (TGA) stabilized QDs (negative surface charge) or 2-mercaptoethylamine stabilized QDs (positive surface charge), indicating localization of the QDs on top of the PE multilayer. However, the PL lifetime of the TGA stabilized QDs decreases from 9.58 to 5.78?ns with increasing PE multilayer thickness. This provides evidence for increased intrinsic exciton recombination relative to surface related emission, which results in an overall reduction in the average lifetime. Our studies indicate the importance of the QD surface charge in determining the interaction with the PE multilayers and the subsequent modification of the QD emission properties.     

Filter diagonalization method-based mass spectrometry for molecular and macromolecular structure analysis

Molecular and macromolecular structure analysis by high resolution and accurate mass spectrometry (MS) is indispensable for a number of fundamental and applied research areas, including health and energy domains. Comprehensive structure analysis of molecules and macromolecules present in the extremely complex samples and performed under time-constrained experimental conditions demands a substantial increase in the acquisition speed of high resolution MS data. We demonstrate here that signal processing based on the filter diagonalization method (FDM) provides the required resolution for shorter experimental transient signals in ion cyclotron resonance (ICR) MS compared to the Fourier transform (FT) processing. We thus present the development of a FDM-based MS (FDM MS) and demonstrate its implementation in ICR MS. The considered FDM MS applications are in bottom-up and top-down proteomics, metabolomics, and petroleomics.     

Multifrequency imaging in the intermittent contact mode of atomic force microscopy: beyond phase imaging

The cantilever dynamics in single-frequency scanning probe microscopy (SPM) are undefined due to having only two output variables, which leads to poorly understood image contrast. To address this shortcoming, generalized phase imaging scanning probe microscopy (GP-SPM), based on broad band detection and multi-eigenmode operation, is developed and demonstrated on diamond nanoparticles with different functionalization layers. It is shown that rich information on tip-surface interactions can be acquired by separating the response amplitude, instant resonance frequency, and quality factor. The obtained data allow high-resolution imaging even in the ambient environment. By tuning the strength of tip-surface interaction, different surface functionalizations can be discerned.     

Synthesis of poly(methyl methacrylate)-block-poly(L-histidine) and its use as a hybrid silver nanoparticle conjugate

Poly[(methyl methacrylate)-block-poly(L-histidine)] (PMMA-b-PHIS) was synthesized by combining atom transfer radical polymerization and living ring-opening polymerization of alpha-amino acid-N-carboxyanhydride. The resulting hybrid block copolymer forms reverse micelles in the mixture solution of water and N,N-dimethylformamide (DMF) and self-assembles into PHIS/PMMA core/shell spheres with controllable size in the range of 80 to 250 nm depending on the micellization temperature. The self-assembly of PMMA-b-PHIS was carried out in H2O/DMF (3/7) mixture in the presence of AgNO3. Reduction of the resulting Ag ions encapsulated inside of the reverse micelles yielded an attractive Ag nanoparticle core/polymer shell conjugate system.     

Reinforcing of a calcium phosphate cement with hydroxyapatite crystals of various morphologies

A series of biocomposite materials was successfully prepared by reinforcing advanced calcium phosphate cement with hydroxyapatite fibrous and elongated plate-like particles. Powder X-ray diffraction showed that ball-milled biocomposite precursors (dicalcium and tetracalcium phosphates) entirely transform to a single phase hydroxyapatite end product within 7 h at 37 °C. Electron microscopy showed that the resultant biocomposites are constituted of nanoscaled cement particles intimately associated with the reinforcement crystals. The influence of shape, size, and concentration of the hydroxyapatite filler on the compression strength of reinforced cements is discussed. The best compression strength of 37 ± 3 MPa (enhancement of ～50% compared to pure cement) was achieved using submicrometer-sized hydroxyapatite crystals with complementary shapes. Nanoindentation revealed that averaged elastic modulus and hardness values of the cements are consistent with those reported for trabecular and cortical human bones, indicating a good match of the micromechanical properties for their potential use for bone repair. The stiffness of the biocomposites was confirmed to gradate-compliant cement matrix, cement-filler interface, and stiff filler-as a result of the structuring at the nanometer-micrometer level. This architecture is critical in conditioning the final mechanical properties of the functional composite biomaterial. In vitro cell culture experiments showed that the developed biomaterial system is noncytotoxic.