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41.
A functional polyrotaxane of a PEI-b-PEG-b-PEI copolymer is synthesized in aqueous solution in a one-pot sequence. To obtain a polyrotaxane with PEG-block-selective inclusion complexes, the solution pH of the polypseudorotaxane is lowered to 4.4 in the presence of 9-anthraldehyde (AN), which triggers the expulsion of the alpha-cyclodextrins (alpha-CDs) from the flank PEI chains. Synthetic strategy of a block-selective polyrotaxane between a PEI-b-PEG-b-PEI copolymer and alpha-cyclodextrins.  相似文献   
42.
Structural changes in cristobalite and silica glass and melt are investigated at high temperatures by molecular dynamics simulations. The calculated interaction energies are analyzed employing a new method called ‘atomistic energy distribution analysis’. Each pair-interaction energy is divided into equal halves which are allocated to each atom. Therefore, each atom has the summed-up value (‘atomistic potential energy’) of half the pair-interaction energies. First, an analysis of atomistic energy distribution functions show a correspondence with structural changes such as α–β phase transition, cristobalite melting and glass transition of SiO2, in harmony with the results obtained in our preceding study. Moreover, this study demonstrates the different roles of oxygen and silicon in terms of structural changes. Finally, newly defined order parameters offer the possibility of distinguishing structures resulting from different thermal histories through introduction of higher moments.  相似文献   
43.
The heat capacity of polycrystalline germanium disulfide α-GeS2 has been measured by relaxation calorimetry, adiabatic calorimetry, DSC and heat flux calorimetry from T = (2 to 1240) K. Values of the molar heat capacity, standard molar entropy and standard molar enthalpy are 66.191 J · K?1 · mol?1, 87.935 J · K?1 · mol?1 and 12.642 kJ · mol?1. The temperature of fusion and its enthalpy change are 1116 K and 23 kJ · mol?1, respectively. The thermodynamic functions of α-GeS2 were calculated over the range (0 ? T/K ? 1250).  相似文献   
44.
We have prepared a hydrophilic molecularly imprinted polymer (MIP) for the hydrophobic compound bisphenol A (BPA) in aqueous solution using 3-acrylamido-N,N,N-trimethylpropan-1-aminium chloride (AMTC) as the functional monomer. Under redox-polymerization conditions, BPA forms an ion-pair with AMTC, which was confirmed by 1H-NMR titration. The imprinting effect in aqueous solution was evaluated by comparison of this material with the corresponding non-imprinted polymer (NIP) and with a control polymer (CP) bearing no AMTC. The MIP showed the highest activity among the three polymers, and the imprinting factors as calculated from the amount of BPA bound to the MIP divided by the amounts bound to NIP and CP, respectively, are 1.8 and 6.0. The MIP was selective for BPA in aqueous solution, while structurally related compounds are not recognized. Such a selectivity for a hydrophobic compound is rarely observed in aqueous medium because non-specific binding of BPA inevitably leads to hydrophobic interaction.
Figure
A hydrophilic molecularly imprinted polymer (MIP) for bisphenol A (BPA) recognition was prepared in aqueous solution. The obtained MIP (BPA-MIP) showed good selectivity under aqueous conditions  相似文献   
45.
A palladium-catalyzed CO(2)-recycling reaction has been developed. Reaction of 4-methoxycarbonyloxy-2-butyn-1-ols with phenols, carried out in the presence of a palladium catalyst, produces phenoxy-substituted cyclic carbonates by way of a pathway involving a CO(2) elimination-fixation. A variety of propargylic alcohols and phenols participate in these reactions which yield cyclic carbonates with high efficiencies. Stereoselective construction of trans-cyclic carbonates is achieved by using nonsymmetric substrates. Highly enantioselective reactions occur when (S)-BINAP is used as a ligand. Reaction of 4-phenoxycarbonyloxy-2-butyn-1-ol in the presence of the palladium catalyst yields the corresponding cyclic carbonates via a three-component decomposition-reconstruction process.  相似文献   
46.
47.
We disclosed a novel ‘racemization-free segment condensation’ based on the ‘O-acyl isopeptide method’ in which an N-segment including C-terminal O-acyl isopeptide structure with urethane-protected Ser/Thr residue was employed for the segment condensation, suggesting that the use of this method contributes to the effective convergent synthesis of long peptides/proteins.  相似文献   
48.
Kuroiwa  Y.  Aoyagi  S.  Sawada  A.  Ikawa  H.  Yamashita  I.  Inoue  N.  Atake  T. 《Journal of Thermal Analysis and Calorimetry》2002,69(3):933-938
The crystal structures of BaTiO3 and PbTiO3 fine particles have been investigated by powder diffraction using synchrotron radiation high energy X-rays. It is revealed that a BaTiO3 fine particle essentially consists of tetragonal and cubic structure components at 300 K, whereas a PbTiO3 fine particle consists of a tetragonal structure. Adopting a structure model for the BaTiO3 particle that a cubic shell covers a tetragonal core, the thickness of cubic BaTiO3 shell is estimated at almost constant irrespective of particle sizes. Successive phase transitions are detected in 100 nm particles of BaTiO3 near the phase-transition temperatures of a bulk crystal. The changes in diffraction profiles are small, but they are apparent for a most up-to-date powder diffractometry. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
49.
Supramolecular hydrogels have been prepared on the basis of polymer inclusion complex (PIC) formation between poly(ethylene glycol) (PEG)-modified chitosans and alpha-cyclodextrin (alpha-CD). A series of PEG-modified chitosans were synthesized by coupling reactions between chitosan and monocarboxylated PEG using water-soluble carbodiimide (EDC) as coupling agent. With simple mixing, the resultant supramolecular assembly of the polymers and alpha-CD molecules led to hydrogel formation in aqueous media. The supramolecular structure of the PIC hydrogels was confirmed by differential scanning calorimetry (DSC), X-ray diffraction, and (13)C cross-polarized/magic-angle spinning (CP/MAS) NMR characterization. The PEG side-chains on the chitosan backbones were found to form inclusion complexes (ICs) with alpha-CD molecules, resulting in the formation of channel-type crystalline micro-domains. The IC domains play an important role in holding together hydrated chitosan chains as physical junctions. The gelation property was affected by several factors including the PEG content in the polymers, the solution concentration, the mixing ratio of host and guest molecules, temperature, pH, etc. All the hydrogels in acidic conditions exhibited thermo-reversible gel-sol transitions under appropriate conditions of mixing ratio and PEG content in the mixing process. The transitions were induced by supramolecular association and dissociation. These supramolecular hydrogels were found to have phase-separated structures that consist of hydrophobic crystalline PIC domains, which were formed by the host-guest interaction between alpha-CD and PEG, and hydrated chitosan matrices below the pK(a).The formation of inclusion complexes between alpha-cyclodextrin and PEG-modified chitosan leads to the formation of hydrogels that can undergo thermo-reversible supramolecular dissociation.  相似文献   
50.
Summary: Specific temperature‐responsive biodegradable hydrogels were synthesized and characterized in terms of their regulation of enzymatic accessibility based on the physical properties of the temperature‐responsive polymers. The hydrogels consist of glycidyl methacrylate‐modified dextran grafted with the poly(N‐isopropylacrylamide) (PNIPAAm) homopolymer, and cross‐linked by co‐polymerization with NIPAAm and N,N‐dimethylacrylamide (DMAAm). The coil‐globule change in the grafted poly(NIPAAm) chains and only a slight dehydration of the poly(NIPAAm‐co‐DMAAm) cross‐linkers are effective in controlling the enzymatic degradation over a specific temperature range.

The thermo‐responses of the graft chains (steric hindrance) and the crosslinkers (slight deswelling of the hydrogel networks) control the enzymatic degradation of the hydrogel.  相似文献   

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