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41.
A technique for fitting a free-form scattering length density profile to reflectivity data via least-squares minimization is presented. The approach combines aspects of simulated annealing with a parametrized representation of the scattering length density profile. The ability of the algorithm to accurately recover the scattering length density profile from arbitrary initial parameter values is demonstrated for simulated and experimental data. 相似文献
42.
We show that for any positive integer k?4, if R is a (2k-1)×(2k-1) partial Latin square, then R is avoidable given that R contains an empty row, thus extending a theorem of Chetwynd and Rhodes. We also present the idea of avoidability in the setting of partial r-multi Latin squares, and give some partial fillings which are avoidable. In particular, we show that if R contains at most nr/2 symbols and if there is an n×n Latin square L such that δn of the symbols in L cover the filled cells in R where 0<δ<1, then R is avoidable provided r is large enough. 相似文献
43.
44.
Cooksey J Gunn A Kocienski PJ Kuhl A Uppal S Christopher JA Bell R 《Organic & biomolecular chemistry》2004,2(12):1719-1731
Two adjacent stereogenic centres and a pendant alkene were constructed via nucleophilic addition of a 1,3-dioxan-4-ylcopper(I) reagent to a cationic eta3-allylmolybdenum complex as part of a synthesis of (2E,5S,6R,7E)-6-methyl-8-phenylocta-2,7-dienoic acid, a key component of the Cryptophycins. Oxidative addition of Mo(CO)(4)(THF)(2) to allyl benzoates provides an efficient synthesis of eta3-allylmolybdenum(dicarbonyl) complexes. 相似文献
45.
Peter Kuhl Günter Döring Klaus Neubert Hans-Dieter Jakubke 《Monatshefte für Chemie / Chemical Monthly》1984,115(4):423-430
Papain and -chymotrypsin were used for the protease-catalyzed assembly ofBoc-protected eledoisin (6–11)-hexapeptide by (2+4)- and (3+3)-segment condensation, respectively, in aqueous-organic solvent systems. As C-components, chemically synthesizedBoc-protected peptide methyl esters were employed. The nucleophilic tetrapeptide amide was prepared by papain-catalyzed (2+2)-segment coupling, while theZ-protected C-terminal dipeptide amide could be obtained by -chymotrypsin- and thermolysin-catalyzed peptide bond formation. In addition, the influence of various reaction conditions, such as solvent composition, nucleophile concentration and reaction time, on the yield of theBoc-protected eledoisin (6–11)-hexapeptide was determined.
Abkürzungen: Es wurden die IUPAC/IUB-Regeln für Aminosäure- und Peptidderivate befolgt; vgl. Eur. J. Biochem.53, 1 (1975). Die verwendeten Aminosäuren hatten mit Ausnahme von GlycinL-Konfiguration.Boc=tetr-Butyloxycarbonyl-,Z=Benzyloxycarbonyl-,Ac=Acetyl-, –OMe=Methylester. 相似文献
46.
Peter Kuhl Nina P. Zapevalova Andreas Könnecke Hans-Dieter Jakubke 《Monatshefte für Chemie / Chemical Monthly》1983,114(3):343-347
Carboxypeptidase Y catalyzes in a biphasic system containing carbon tetrachloride and carbonate buffer the reaction ofZ-Phe-OMe and variousZ-andBoc-protected dipeptide methyl esters with Val-NH2 and Leu-NH2, respectively. This method has been applied to the synthesis of the corresponding N-protected tripeptide amides on a preparative scale. Using a substrate—nucleophile ratio of only 1:2 or 1:3 the peptide derivatives are obtained in yields of 56–97%.Abbreviations: IUPAC-IUB rules for peptides are followed, see Eur. J. Biochem.27, 201 (1972).Boc=tert-butyloxycarbonyl,Z=benzyloxycarbonyl,-OMe=methyl ester, HPLC=high performance liquid chromatography, TLC=thin layer chromatography,CPD-Y=carboxypeptidase Y. 相似文献
47.
Rigler P Ulrich WP Vogel H 《Langmuir : the ACS journal of surfaces and colloids》2004,20(19):7901-7903
We show that it is possible to immobilize membrane proteins uniformly and reversibly as self-assembled (sub)monolayers on nitrilotriacetic acid-covered sensor surfaces via hexahistidine sequences present either in the protein or in lipid membranes. Fourier transform infrared spectra of such self-assembled (sub)monolayers deliver important structural information of the membrane proteins and are suited to screen the function of cellular receptors. 相似文献
48.
S. W. Hui T. L. Kuhl Y. Q. Guo J. Israelachvili 《Colloids and surfaces. B, Biointerfaces》1999,14(1-4):213-222
Although poly(ethylene glycol) (PEG) has been widely used as an agent to induce cell aggregation and fusion, the physicochemical principles of its function are only becoming understood recently. PEG has an extremely high affinity for water. The PEG commonly used for these applications is in the molecular weight range of 8000 to 10 000. At low concentrations (0–15 wt.%), PEG in this molecular weight range tends to deplete from cell or lipid surfaces, creating an osmotic gradient which brings cells or lipid vesicles together. The depletion force is measured using a surface force apparatus. The corresponding reduction of surface viscosity is verified by shear viscosity measurements and by vesicle tumbling experiments. At higher concentrations (15–45 wt.%), the extremely high osmotic pressure generated by PEG compresses apposing surfaces of aggregated cells or vesicles to within limits where the membrane is no longer stable, and fusion occurs at point defects. A fusion lumen is formed with the help of cell swelling. If PEG is adsorbed or covalently link to the cell or vesicle surface, the surface force profile becomes entirely repulsive, and aggregation and fusion is inhibited. The repulsion is accountable by steric and electrostatic forces. Therefore, the fusogenic function of PEG can be explained quantitatively by colloidal stability theories. 相似文献
49.
The reaction of 1,5-diphenylpentanetrione, 4-chlorobenzaldehyde, and acetone in the presence of methylamine resulted in 2,6-dibenzoyl-5-(4-chlorphenyl)-3-methyl-cyclohex-2-en-1-one, which was formed by a sequence of a Knoevenagel reaction, an aldol condensation, and a Michael addition in a one-pot reaction. 相似文献
50.
Surface forces and shape changes were simultaneously measured during the approach and coalescence of two liquid-liquid and liquid-air interfaces. Large normal and lateral deformations were observed that are nevertheless consistent with a simple theoretical analysis of the long-range effects of short-range attractive van der Waals forces. The results imply that two fluidlike structures such as liquid droplets and soft biological cells can sense each other at much larger separations than previously assumed based on criteria taken from the interactions of hard particles. 相似文献