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41.
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
42.
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
43.
A beta-CD-based biodegradable polyrotaxane was prepared by capping both terminals of polypseudorotaxane consisting of hydrazide-terminated PEG-block-PPG-block-PEG (Pluronic P-105) and beta-CD-succinates with mono-aldehyde alpha-CDs. By decreasing pH, the fluorescent intensity of TNS was increased with time, indicating cleavage of the terminal hydrazone bonds followed by beta-CD-succinate release. The terminal alpha-CD moieties of the polyrotaxane are useful for self-assembled formation with some guest molecules. [Diagram: see text] 相似文献
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By means of a high pressure d.t.a. method, a new crystalline phase of tetramethylsilane which forms below its melting point has been observed at pressures above 20 MPa. This is a verification of the prediction from earlier calorimetric data at ordinary pressures. 相似文献
48.
Takeshi Saito Toshihide Ihara Tooru Miura Yuuko Yamada Koichi Chiba 《Accreditation and quality assurance》2011,16(8-9):421-428
The accurate quantification of pesticide residues in food is an important factor in assuring the quality of life of our citizens. In general, chromatographic methods are used, which require certified reference materials (CRMs) for each analyte of interest for accurate quantitative analysis. Recently, regulation of pesticides in food, limiting the positive maximum residue (positive list system) has been brought into effect in Japan. Furthermore, ISO/IEC 17025 requires calibration and testing laboratories to program calibrations and measurements traceable to the International System of Units (SI). Accordingly, these laboratories need a suite of CRMs that are traceable to the SI. In order to address these requirements for every analyte of interest in an efficient manner, a new approach to producing SI traceable CRMs is required. Nuclear magnetic resonance (NMR) has been used widely in chemical analysis. One of the well known characteristics of NMR is the proportional relationship between peak area and the number of nuclei contributing to the peak. If accurate relative intensities of peak areas are obtained, this provides an attractive quantitative tool for organic compounds. The area of a signal from an analyte can be measured with respect to another signal originating from a comparator that has been added to the sample solution. The chosen comparator should not react with the analyte or resonate at any chemical shift similar to that of the analyte. This enables us to produce SI traceable CRMs more effectively. In this paper, we demonstrate a new approach for producing CRMs for pesticides using quantitative NMR??an SI traceable quantitative technique. 相似文献
49.
Jiří Málek Takefumi Mitsuhashi Naoki Ohashi Yuki Taniguchi Hitoshi Kawaji Tooru Atake 《The Journal of chemical thermodynamics》2011,43(3):405-409
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
50.
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