摘要:

AbstractSyntheses of the aglycones of gilvocarcins, gilvocarcin‐relatedC‐glycosides, and (+)‐gilvocarcin M are described. Variety of methodologies have been reported for the construction of the aglycones of gilvocarcins including Meerwein and Diels‐Alder reactions, nucleophilic aromatic substitution, palladium‐catalyzed coupling, Suzuki biaryl coupling, Dotz carbene chromium benzannulation, conjugate addition to naphthoquinone ketals, and Pechmann condensation. In the syntheses of gilvocarcin‐relatedC‐glycosides, only those reactions involving palladium‐mediated coupling, Lewis‐acid‐mediated condensation, cuprate reagents, and reductive aromatization of quinol k

ISSN:0165-0513    

DOI:10.1002/recl.19951140802

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe 1,3‐dipolar cycloadditions of 2,3,4,5‐tetrahydropyridine 1‐oxide (1) and 3,4‐dihydro‐2H‐pyrrole 1‐oxide (2) to methyl (E)‐6‐(benzyloxy)‐4‐hydroxy‐2‐hexenoate (3) and methyl (S)‐(E)‐3‐(2,2‐dimethyl‐1,3‐dioxolan‐4‐yl)propenoate (4) yield predominantly the adducts derived fromendotra

ISSN:0165-0513    

DOI:10.1002/recl.19951140803

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractAged porous 13 wt% silica hydrogel beads were characterized by measuring the freezing point depression of water in silica gel pores, which provides information about the ice crystal radius (Rn), the ice‐pore volume (Vn), the pore shape (F), and the ice‐surface area (An). Hydrothermal treatment at high temperatures increases both the pore size and apparent pore volume of not previously dried hydrogel beads. The ice crystal radius, is increased from 8.6 to 27 nm after ageing for 7 h at 473K, while the apparent ice‐pore volume increases from 0.9 to 1.4 ml/g. The pore size and pore volume decrease upon drying. AtRnvalues of 8.6 and 27 nm, the drop ΔRnon drying is 5.1 and 7 nm, respectively, and the decrease ofVn, ΔVn, is 0.4 and 0.6 ml/g, which amounts to 44 and 38%, respectively. The exceptionally small decrease of pore volume for a gel upon drying suggests that this measurement is underestimated by thermoporometry. The soft gel is compressed as liquid is drained from the network during freezing. The apparent increase of the pore volume of the hydrogel must be interpreted to indicate the effect of stiffening (through ageing) on the amount of compression during the measurement. Based on the probably real pore volumeVnof the hydrogel of 1.4 ml/g, instead of 0.9 ml/g, the pore volume decrease atRn= 8.6 nm would be 0.9, not 0.4 ml/g, so the percentage change would be 64%, rather than 44%. By contrast, at aRnvalue of 10.9 and 25 nm, the thermoporometric surface areaAn* of the hydrogels, which is the surface area of the ice crystals corrected for a non‐freezing layer of water, is equal to the BET surface areas of the xerogel measured by nitrogen sorption, which indicates that no pores are enclosed. The increase in pore volume of the aged xerogels by both mercury penetration and thermoporometry is real. It reflects the coarsening and stiffening by ageing, which leads to less shrinkage during drying. The xerogels are probably stiff enough that they experience little contraction on application of thermo

ISSN:0165-0513    

DOI:10.1002/recl.19951140804

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractA new surfactant with a branched monoalkyl chain and a malonate headgroup has been synthesized: 2‐(4‐butyloctyl)malonic acid (BOMA). From the geometry of the surfactant, reflected in a packing parameter (P), it was anticipated that the surfactant would preferably aggregate in bilayers. This expectation was borne out in practice by the aggregation behavior, as studied by transmission electron microscopy (TEM) with negatively stained samples and freeze‐fracture samples of aqueous vesicle dispersions. The structure of the surfactant headgroup has been varied by changes in pH of the vesicle dispersions. Over a wide pH range (pH 2.8‐12.8) small unilamellar vesicles with a size of 20–50 nm were observed. Multilamellar vesicles were observed as well in the pH range 2.8–5.1. Phase‐penetration experiments using an optical polarization microscope showed the birth and growth of myelins and multilamellar vesicles over a pH range 1.5‐13.1. At pH<2.8, a phase separation occured into a surfactant‐rich, optically isotropic phase and a surfactant‐lean phase. The physical and colloidal stability of the vesicular aggregates is high: up to one year as confirmed by TEM. The fusogenic properties of BOMA vesicles were examined. Upon the addition of Ca2+ions, aggregates tended to become larger, but the formation of Ca2+surfactant crystal

ISSN:0165-0513    

DOI:10.1002/recl.19951140805

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19951140806

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19951140809

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19951140811

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19951140801

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY