A study of the sintering effect on ultrafine silver particles by means of positron annihilation

Angular correlation curves of two-photon annihilation in ultrafine silver particles are shown to become similar to that of bulk silver with increasing degree of sintering.     

Bio‐reduction of Redox‐Sensitive Albumin Conjugates in FcRn‐Expressing Cells

Disulfide‐containing IgG‐, Fc‐, or albumin‐based prodrugs that rely on FcRn‐trafficking by endothelial cells for prolonged circulation in the body might be hampered by premature bio‐reduction processes during FcRn‐mediated recycling events. A detailed bio‐reduction analysis of redox‐sensitive albumin conjugates in two FcRn‐expressing cell lines has been performed. The obtained results indicate that the FcRn‐mediated recycling pathway is not (or is only poorly) bio‐reducing.     

Cysteine cyclic pyrrole-imidazole polyamide for sequence-specific recognition in the DNA minor groove

Pyrrole-imidazole (PI) polyamides are small DNA-binding molecules that can recognize predetermined DNA sequences with high affinity and specificity. Hairpin PI polyamides have been studied intensively; however, cyclic PI polyamides have received less attention, mainly because of difficulties with their synthesis. Here, we describe a novel cyclization method for producing PI polyamides using cysteine and a chloroacetyl residue. The cyclization reaction is complete within 1 h and has a high conversion efficiency. The method can be used to produce long cyclic PI polyamides that can recognize 7 bp DNA sequences. A cyclic PI polyamide containing two β-alanine molecules had higher affinity and specificity than the corresponding hairpin PI polyamide, demonstrating that the cyclic PI polyamides can be used as a new type of DNA-binding molecule.     

Role of O?H bonding in catalytic activity of Nb2O5 during the course of dehydrogenation of MgH2

The hydrogen desorption reaction of MgH₂, MgH₂ → Mg + H₂, is accelerated by the addition of metal oxide catalysts (e.g., Nb₂O₅). From our theoretical calculation of electronic structure, it was predicted that the catalytic activities of metal oxides are related closely to the O? H interaction operating at the interface between oxide catalyst and MgH₂. In this study, the O? H vibration on the Nb₂O₅‐catalyzed MgH₂ was investigated experimentally using FTIR spectroscopy. The broad absorption band due to the O? H stretching mode was observed in the region of 2,800–3,600 cm^?1 in the FTIR spectra of the specimens when hydrogen desorption reaction was in progress. The absorbance of the band decreased monotonously with decreasing hydrogen content in the specimen during the course of dehydrogenation of MgH₂. This experimental result was in agreement with our prediction for the existence of O? H interaction in the hydrogen desorption process. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Three‐component polyaddition of diamines,carbon disulfide,and diacrylates in water

The three‐component polyaddition of diamines, carbon disulfide (CS₂), and diacrylates in water was successfully achieved without the use of a surfactant or catalyst. Appropriate reaction conditions (i.e., reaction temperature, reaction time, and CS₂ feed) enabled the polyaddition of 1,3‐di‐4‐piperidylpropane ( 1a ), CS₂, and 1,6‐hexanediol diacrylate ( 2a ) to afford the corresponding poly(dithiourethane‐amine) containing 83% of dithiourethane units in 84% yield. Polyaddition of other monomers also proceeded under the optimum conditions to afford various poly(dithiourethane‐amine)s. Unsuccessful results for polyaddition in organic solvents such as toluene, tetrahydrofuran, and N,N‐dimethylformamide revealed that the polyaddition is accelerated in water. The obtained poly(dithiourethane‐amine)s adsorbed Au (III) efficiently under acidic conditions, due to the strong interaction of the thiocarbonyl sulfur in the dithiourethane unit with Au (III). The poly(dithiourethane‐amine)s also showed selective adsorption for Au (III) from a mixture of metal ions [Au (III), Fe (III), Mn (II), and Zn (II)], which indicates their potential utilization for the collection of gold. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 845–851, 2010     

Gel formation in cationic polymerization of divinyl ethers. III. Effect of oligooxyethylene chain versus oligomethylene chain as central spacer units

Cationic polymerizations of two series of divinyl ethers were carried out to clarify the effects of their central spacer chain structure on their crosslinking polymerization behavior. One series of the monomers involves divinyl ethers with an oligooxyethylene central spacer chain: diethylene glycol divinyl ether ( O‐3 ), triethylene glycol divinyl ether ( O‐4 ), tetraethylene glycol divinyl ether ( O‐5 ), pentaethylene glycol divinyl ether ( O‐6 ), and heptaethylene glycol divinyl ether ( O‐8 ) (see Scheme 1 ). The other series includes divinyl ethers with an oligomethylene central spacer chain: 1,4‐butanediol divinyl ether ( C‐4 ), 1,6‐hexanediol divinyl ether ( C‐6 ), and 1,8‐octanediol divinyl ether ( C‐8 ). Cationic polymerizations of these monomers were carried out with the hydrogen chloride/zinc chloride (HCl/ZnCl₂) initiating system in methylene chloride (CH₂Cl₂) at ?30 °C ([Monomer]₀ = 0.15 M; [HCl]₀ = 5.0 mM; [ZnCl₂]₀ = 0.5 mM). The polymerizations of the oligomethylene‐based divinyl ethers C‐6 and C‐8 caused gel formation at high monomer conversions (～90%), whereas C‐4 formed soluble polymers even at almost 100% monomer conversion. The oligooxyethylene‐based divinyl ethers O‐3 , O‐4 , O‐5 , and O‐6 underwent gel‐free polymerizations up to 100% monomer conversion and O‐8 did so at least up to ～80% conversion. The content of unreacted pendant vinyl groups of the obtained soluble polymers was measured by ¹H NMR spectroscopy. In the polymerizations of the oligomethylene‐based divinyl ethers ( C‐4 , C‐6 , and C‐8 ), the vinyl contents of the polymers decreased monotonously with increasing monomer conversion, and their number‐average molecular weights (M_n's) and polydispersity ratios (M_w/M_n's) increased considerably just before the gelation occurred. On the contrary, the vinyl contents of the polymers obtained from the oligooxyethylene‐based divinyl ethers ( O‐3 , O‐4 , O‐5 , O‐6 , and O‐8 ) decreased steeply even in the early stage of the polymerizations and almost all the pendant vinyl ether groups were consumed in the soluble polymers at the final stage of the polymerizations. The oligooxyethylene spacer units adjacent to the pendant unreacted vinyl ether groups may solvate intramolecularly with the carbocationic active center to accelerate frequent occurrence of intramolecular crosslinking reactions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3729–3738, 2004     

A study of the fermi surface of α-brass

Fermi surface of α-brass was investigated up to 24.6 at.% Zn by the rotatingspecimen method in the annihilation radiation. The anisotropy in the Fermi surface of α-brass was found to be similar to that of pure copper. It was also noted that the 〈111〉-neck radius of the alloys increase monotonically with increasing content of zinc.     

Doping effects on proton incorporation and conduction in SrZrO3

The doping effects on the proton incorporation and protonic conductivity of perovskite-type SrZrO3 were investigated using the density functional theory (DFT) with the generalized gradient approximation (GGA). The optimized geometries, formation energies of hydrogen defect and activation energies for hydrogen diffusion in SrZrO3 doped with Al, Sc, Ga, Y, Rh, In, and Yb were calculated. It was shown that the doping leads to large local distortions around hydrogen and dopant ion, affecting the protonic conduction in these oxides. The alignment of hydrogen levels varies with the dopant introduced into the SrZrO3. In In-, Y-, Sc-, Ga-, and Al-doped SrZrO3, the H+ is the lowest energy state in all the bandgap. But for Yb- and Rh-doped SrZrO3, the H+ is the lowest energy state only when the Fermi energy below 2.37 and 2.66 eV, respectively. The estimates of the activation energy show good agreement between the measured and calculated activation energies. Also, the hydrogen diffusion seems to become more difficult as the distance between hydrogen and dopant ion decreases.