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31.
Yasuyuki Takeda Chihiro Takagi 《Journal of inclusion phenomena and macrocyclic chemistry》1994,17(1):93-97
The theory is derived to determine the dimer-formation constant,K
2, of a crown ethermetal salt 111 complex in organic solvents of low dielectric constant by solvent extraction. The theoretical predictions are verified experimentally by extraction of sodium picrate (NaA) with 15-crown-5 (15C5) into carbon tetrachloride. All the experiments were conducted at 25°C. The logK
2 value of the Na(15C5)A complex in carbon tetrachloride has been determined to be 4.05±0.11. Moreover, the partition constant of the complex is calculated. 相似文献
32.
Akihiko Sugie Hiromi Shimomura Junki Katsube Hisao Yamamoto 《Tetrahedron letters》1979,20(28):2607-2610
A stable PGI2 analog (methanoprostacyclin ) was synthesized starting from 5-norbornene-2,3-dicarboxylic anhydride. 相似文献
33.
Mohammed Akhter Hossain Keiko Takahashi Hisakazu Mihara Akihiko Ueno 《Journal of inclusion phenomena and macrocyclic chemistry》2002,43(3-4):271-277
-Helix peptides bearing one unit of -cyclodextrin (-CD), one unit of pyrene and one unit of nitrobenzene (NB) in their side chains have been designed and synthesized as novel molecule-responsive devices.In both the CD-peptides,
-PR17 and
-PL17, the NB unit is separated from the CD unit by two turns of the helix. Two reference peptides (PL17, and -P17,) have also been synthesized. The circular dichroism studies in the peptide absorption region (200–250 nm)of
-PR17 and
-PL17 suggestthat the CD-peptides form stable-helixstructures (83–77%), which was destabilized by accommodating guest molecules (e.g., n-pentanol) into the CD cavity. It suggests that formation of intramolecular host–guest(CD–NB) complex stabilized thehelical structure and exogenous guest molecule excluded the appending NB moiety from inside to outside of the CD cavity, thereby causing destabilization of the helical structure and increasing the random coil content. The ICD spectra of the peptides in the pyrene and nitrobenzene absorption region (250–40 nm) suggest that NB forms inclusion complex with CD. The fluorescence studies revealed that the fluorescence of the pyrene unit is quenched by the NB unit in
-PR17 and
-PL17. The fluorescence intensity increases with increasing guest concentration for the CD-peptides.This guest-responsiveenhancement in the fluorescence intensity can be explained in terms of increased distance between the pyrene and NB moieties, which is caused by exclusion of the NB moiety from the CD cavity by guest accommodation. Using the guest-responsive fluorescence quenching properties of the CD-peptides, we have obtained binding constants for various short chain alkanols.
-PL17 has higher binding affinity to the guest molecules than its isomer,
-PR17, indicating that the location of functional groups on the peptide scaffold is important in molecule detection. 相似文献
34.
Various amounts of n-alkylbenzenes (Cn: C6H5-CnH2n+1 (n = 3-16)) were doped into poly(methyl methacrylate) (PMMA) films, and the emission and thermal properties of each film were measured in detail together with their solid-state 13C NMR spectra. The aim of the present work was to estimate the size distribution of free volume in amorphous regions of polymer solids heavily doped with plasticizers by using Cn as models of a plasticizer. The excimer fluorescence yields of Cn in PMMA were found to depend on both the amount of Cn and the length of the alkyl chains of Cn, although the fluorescence spectra of all of the Cns in dilute fluid solution were almost the same. The quantitative analysis showed: (1) Cn with n ? 12 induces a phase separation in PMMA, in which almost all of the Cn molecules are in a separated phase, and thus they cannot penetrate regions in which PMMA chains are aggregated. This means that Cn with n ? 12 cannot enlarge the space between PMMA chains. (2) Smaller Cn (n < 11) can enter free volumes between PMMA chains that correspond to their molecular size, but they can enlarge them only to a limited extent. Thus, the amount by which plasticization can increase the free volume of PMMA is limited by the size of the dopant and the inherent free volume of the polymer matrix. (3) The efficiency of excimer formation was found to reveal the maximum amount of Cn that could fit in the free volume of PMMA. Thus our fluorescence measurements showed that PMMA solids that were plasticized to their limit had a free volume that was larger than the volume occupied by all the conformers of C5 and smaller than the volume occupied by almost all the conformers of C12. In conclusion, we were able to obtain information on plasticization and to demonstrate a method of monitoring microenvironments in polymer solids after they have been doped with plasticizers. 相似文献
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The total synthesis of a new platelet aggregation-inhibiting gamma-lactam PI-091 (1) gave a 1:1 diastereomeric mixture at the gamma-ketal carbon. The high-yielding aldol reaction of an appropriately protected 1,3,4-trihydroxy-4-methyldecan-2-one 42, prepared from D-glucose, with the kinetically generated enolate of 3-methyl-2-butanone provided 43. The resulting diastereomeric mixture of the aldol adduct 43 was converted to a 2,4-alkylated furan 45 via an intramolecular ketalization followed by dehydration. The addition of a singlet oxygen to the alpha-trimethylsilylated furan 48derived from 45 under photochemical conditions efficiently provided an alpha,gamma-dialkylated gamma-hydroxy gamma-lactone 47. The transformation of methyl ketal 52 prepared from 47 into gamma-hydroxy gamma-lactam 53 was achieved by exposure to liquid ammonia in MeOH. The total synthesis of 1 was achieved from 52 through the Dess-Martin periodinane oxidation of the secondary hydroxy group in the side chain. The present total synthesis revealed that the stereogenic carbon center in the side chain in natural 1 is S. 相似文献