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111.
Wyss HM Innerlohinger J Meier LP Gauckler LJ Glatter O 《Journal of colloid and interface science》2004,271(2):388-399
The aggregation of concentrated aqueous silica suspensions is characterized by means of static light scattering. We use an in situ destabilization mechanism based on the enzyme-catalyzed hydrolysis of urea. This method enables us to continuously and homogeneously change the interparticle potential from repulsive to attractive without disturbing the aggregation process. Moreover, our electrostatically stabilized suspensions can be destabilized by two different methods. In the first method, the pH is shifted toward the isoelectric point of the particles ( Delta pH method), thereby leading to a decrease of their surface charge. In the second method, the ionic strength is continuously increased at constant pH ( Delta I method), leading to a compression of the electrical double layer around the charged particles. A laboratory-built flat-cell light-scattering instrument is used, which allows fast data acquisition and an adjustment of the sample cell thickness. To circumvent multiple scattering effects, we use a very small sample thickness ( approximately 13 microm). In addition, the refractive index difference between the aqueous phase and the particles is reduced by adding sucrose to the liquid phase of our suspensions. We are able to characterize the structural changes at the very early stages of the destabilization process, where no significant effects are yet detected in macroscopic rheological measurements. While during the Delta pH destabilization, the scattering curve shows significant changes only after some characteristic delay time, it changes continuously during the Delta I destabilization. The latter is attributed to the formation of a weak pre-gel structure in the suspensions, as a shallow secondary minimum appears in the interparticle potential. Data are evaluated by using a HMSA square-well structure factor model. Results are in good agreement with those predicted from DLVO theory. 相似文献
112.
FTIR-spectroscopic investigations of catalytic reactions yield detailed information about the interaction of adsorbed molecules with the catalyst and kinetic data of the surface reaction, if the participating molecules show vibrations whose position and intensity in the IR-spectrum depend on the sorption state and the quantity adsorbed. In this paper, the possibilities and limitations of the method are represented by two examples. 相似文献
113.
(C2H10N2)[BPO4F2] — Strukturbeziehungen zwischen [BPO4F2]2— und [Si2O6]4— Colourless crystals of (C2H10N2)[BPO4F2] were prepared from mixture of ethylendiamine, H3BO3, BF3 · C2H5NH2, H3PO4 and HCl under mild hydrothermal conditions (220 °C). The crystal structure was determined by single crystal methods (triclinic, P1¯ (no. 2), a = 451.85(5) pm, b = 710.20(8) pm, c = 1210.2(2) pm, α = 86.08(1)°, β = 88.52(2)°, γ = 71.74(1)°, Z = 2) and contains infinite tetrahedral zweier‐single‐chains {[BPO4F2]2—} which are isoelectronic (48e—) with the polyanions {[Si2O6]4—} of the pyroxene family. 相似文献
114.
Complexes of Vanadium and Titanium with Salicylaldehyde benzoylhydrazone and 2-(2′-Hydroxyphenyl)-8-quinolinol. Crystal Structure of μ-Oxo-bis[oxo{2-(2′-hydroxyphenyl)-8-quinolinato(2-)}-vanadium(V)] . By reaction of titanium(IV)-isopropoxide and bis(acetylacetonato)-oxovanadium(IV) with salicylaldehyde benzoylhydrazone and 2-(2′hydroxyphenyl)-8-quinolinol, respectively, the metal complexes of the tridentate diacidic ligands were synthesized and characterized mass spectrometrically. The mass spectra of the titanium compounds correspond to the expected bisligand complexes whereas several species are demonstrable in the case of vanadium. Crystals of μ-oxo-bis[oxo{2-(2′-hydroxyphenyl)-8-quinolinolato(2-)}-vanadium(V)] were isolated and characterized by X-ray structural analysis. The complex exhibits C2 symmetry, accordingly the μ2-oxygen atom is situated on the 4 axis. The VOV bridge is angular with the unusually small bond angle of 107.3°. The coordination polyhedron is distorted octahedral. The compound additionally contains one molecule of chloroform per formula unit which is disordered in two positions. Crystallographic data see “Inhaltsübersicht”. 相似文献
115.
Gerhard Buchbauer Angela Fischlmayr Ernst Haslinger Wolfgang Robien Horst Völlenkle Carla Wassmann 《Monatshefte für Chemie / Chemical Monthly》1984,115(6-7):739-748
2-Hydroxy-13-oxo-tricyclo[7.3.1.02,7]tridecane derivatives can be obtained by reaction of cyclohexanone with alcohols under alkaline conditions. The unambiguous assignment of all signals of the1H-NMR- and13C-NMR-spectrum is possible by 2D-1H-13C-shift correlation and 2D-INADEQUATE. Compound1 crystallizes in space group P21/n witha=8.518 (1),b=14.789 (2),c=19.321 (2) Å, =94.91 (1)°,Z=8,D
c
=1.22 Mg cm–3. The structure refined toR=0.100 andR
w
=0.097 for 1719 observed reflections. Two independent molecules form centrosymmetric hydrogen-bonded dimers.Part V:Haslinger E.,Kalchhau-ser H.,Robien W.,Steindl H., Monatsh. Chem.115, 597 (1984). 相似文献
116.
Silvia Schaffner Ludwig Macko Markus Neubufger Margareta Zehnder 《Helvetica chimica acta》1997,80(2):463-471
Crystal and solution structures of the enantiomerically pure and the racemic pairs of (η3-allyl) {2-[2′-(diphenylphosphino)phenyl]-4,5-dihydro-4-phenyloxazole}palladium(II) hexafluorophosphates ( 1 , and rac- 1 , resp.) and tetraphenylborates ( 2 , and rac- 2 , resp.) as well as (η3-allyl){2-[2′-(diphenylphosphino)phenyl]-4,5-dihydro-4-isopropyloxazole}palladium(II) tetraphenylborate ( 3 ) were characterized by X-ray crystallography and 1H-NMR spectroscopy. In the solid state, rac- 1 and rac- 2 proved to be disordered with both diastereoisomeric complexes in the crystal. The complexes 2 and 3 exist only in the ‘exo’ form. The X-ray structures show that the [PdII(η3-allyl)] moiety may adopt different configurations between a nearly symmetrical three-electron PdII(π3-allyl) system and an asymmetrical allyl group with a η1- and a η2-bonding to the metal center. The [PdII(η3-allyl)] system of rac- 1 and of ‘endo’ rac- 2 is closer to the former, and that of 2 , ‘exo’-rac- 2 , and 3 closer to the later geometry. The 1H-NMR spectra of the hexafluorophosphates 1 and rac- 1 show two sets of signals of the allylic protons in an ‘exo’/‘endo’ ratio of 2:3. The tetraphenylborates 2, rac- 2 , and 3 give only one set of broad signals of the allylic protons. 相似文献
117.
Johann-Peter Melder Klaus Weber Andreas Weiler Emmerich Sackers Hans Fritz Dieter Hunkler Horst Prinzbach 《Research on Chemical Intermediates》1996,22(7):667-702
Methodological alternatives for the preparation of highly strained, highly pyramidalized dodecahedrene 2 (Estr=87.3 kcal mol?1; ?=43.5°, MM2) and 1,16-dodecahedradiene 3 (Estr=105.3 kcal mol?1; ?=42.9°, MM2) have been explored, protection/deprotection strategies have been tested—with the eye on their utilization for the generation of higher unsaturated dodecahedranes (e.g. 1,4, 16-triene 4, 1,4,10 (14),16-tetraene 5). For the acquisition of preparative quantities of monoene 2 the “P2F” catalyzed cis-β-elimination in bromododecahedrane, of diene 3 the FVP fragmentation of a “twofold protected” precursor (bis-furan adduct) have become the protocols of choice, which both profit from the recent synthetic advances along the pagodane → dodecahedrane scheme. Because of unusually effective steric protection the highly tilted C=C double bonds of 2 (λmax (CH3CN) = 254 nm, ν C=C = 1658 cm?1, δC=C = 164.4) and 3 (δC=C = 170.5) enter into thermal stabilization pathways (dimerization, oligomerization) only at higher temperatures (for 2 ca. 50% consumption after 5 h at 100°C in a 3·10?3 molar toluene solution); extreme sensitivity to oxygen is primarily attributed to kinetically and thermodynamically promoted allylic hydrogen abstraction. 相似文献
118.
Perfluoroorgano tin and lead compounds can be prepared in high yields from the reactions of (CH3)3SnOCOCF3 and (CH3)3Pb(OCOCF3) with perfluoroorgano cadmium complexes. (CH3)3SiOCOCF3 reacts with (CF3)2Cd complexes — probably via the intermediate (CH3)3SiCF3 and CF2 elimination — to form (CH3)3SiF and CF3CdOCOCF3 complexes. While the reaction of (CF3)2Cd·D with (CH3)3SnONO2 yields CF3NO as the only volatile product, (Rf)2Cd·D (Rf C2F5, iC3F7) forms RfCdONO2·D and (CH3)3SnRf. The preparations and properties of the partly new compounds as well as the n.m.r. spectra are described. 相似文献
119.
A special kind of partiality of heterogeneous algebraic structures is introduced. Every operator of a heterogeneous operator domain is associated with a set of term equations as necessary and sufficient domain condition.It is shown that some kind of hierarchy condition for the system of domain equations is equivalent to the condition that every injective weak homomorphism is a strong homomorphism which is equivalent to the statement that every bijective weak homomorphism is an isomorphism.On the base of this result the notions of a quasi-variety and of a variety of equationally partial heterogeneous algebras are suggested. The class of all small categories becomes a standard example of a variety of equational partial heterogeneous algebras.Presented by V. Trnková. 相似文献
120.
Yang Nan Subhash P. Upadhyaya Wei Xu Kathrine E. Hughes William J. Dunn Ludwig Bauer Hemendra N. Bhargava George A. Doss 《Journal of heterocyclic chemistry》1996,33(2):399-407
A number of (E)-7-arylidenenaltrexones were synthesized by azeotropic distillation of water from a benzene solution of naltrexone and an aromatic aldehyde (benzaldehyde, 4-chloro- and 4-fluorobenzaldehyde, 3-and 4-pyridinecarboxaldehyde and 1-methyl-2-imidazolecarboxaldehyde) using piperidine as a catalyst. In addition, (E)-7-benzylidenenaloxone was prepared by the previously published Claisen-Schmidt condensation using sodium hydroxide in methanol. The stereochemistry of these arylidene derivatives 3–9 was determined to be (E) by means of nuclear Overhauser enhancement experiments. The 13C nmr spectra of (E)- 3–9 are recorded in deuteriochloroform and those of the hydrochlorides in deuteriodimethyl sulfoxide. 相似文献