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531.
Denitsa Momekova Stanislav Rangelov Nikolay Lambov Gőran Karlsson Mats Almgren 《Journal of Dispersion Science and Technology》2013,34(8):1106-1113
Amphiphilic, nonionic diblock copolymers based on poly(ethylene glycol) (PEG 2000–5000), comprising short blocks of lipid-mimetic units, where tested for their ability to afford steric stabilization of distearoylphosphathydilcholine:cholesterol liposomes. The copolymers bear 1–4 lipid-mimetic anchors per copolymer chain. Effects on liposomes size depend on copolymer type and content. Cryo-TEM reveals well-separated, intact, predominantly spherical liposomes at copolymer contents up to 5 mol%. A “flat” liposomes fraction occurs upon incorporation of above 7.5 mol% of copolymers bearing 2 or 4 lipid anchors. 5,6-carboxyfluorescein assay indicates lower leakage of stabilized vs. plain liposomes up to concentration 7.5 mol%. Leakage from liposomes with higher copolymer concentration is insignificantly greater. 相似文献
532.
Jonas Rydfjord Fredrik Svensson Dr. Alejandro Trejos Dr. Per J. R. Sjöberg Dr. Christian Sköld Dr. Jonas Sävmarker Dr. Luke R. Odell Prof. Dr. Mats Larhed 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(41):13803-13810
A fast and convenient synthesis of aryl amidines starting from carboxylic acids and cyanamides is reported. The reaction was achieved by palladium(II)‐catalysis in a one‐step microwave protocol using [Pd(O2CCF3)2], 6‐methyl‐2,2′‐bipyridyl and trifluoroacetic acid (TFA) in N‐methylpyrrolidinone (NMP), providing the corresponding aryl amidines in moderate to excellent yields. The protocol is very robust with regards to the cyanamide coupling partner but requires electron‐rich ortho‐substituted aryl carboxylic acids. Mechanistic insight was provided by a DFT investigation and direct ESI‐MS studies of the reaction. The results of the DFT study correlated well with the experimental findings and, together with the ESI‐MS study, support the suggested mechanism. Furthermore, a scale‐out (scale‐up) was performed with a non‐resonant microwave continuous‐flow system, achieving a maximum throughput of 11 mmol h?1 by using a glass reactor with an inner diameter of 3 mm at a flow rate of 1 mL min?1. 相似文献
533.
A. A. Barabanov N. V. Semikolenova M. A. Mats’ko L. G. Echevskaya V. A. Zakharov 《Kinetics and Catalysis》2011,52(2):217-221
Changes in the molecular-weight characteristics of the product of ethylene polymerization in the course of reaction in the
presence of a homogeneous catalytic system and in the number and reactivity of catalyst active sites were studied. The catalytic
system consisted of bis[N-(3-tert-butylsalicylidene)anilinato]zirconium dichloride and methylalumoxane as an activator. This catalytic system exhibited the
signs of unsteady-state conditions: the rate of polymerization dramatically decreased as the reaction time increased. At the
onset of polymerization (to 5 min), the catalyst was single-site, and it produced low-molecular-weight polyethylene with M
w = (4–10) × 103 g/mol. The fraction of active sites at the initial point in time was as high as 11% based on the initial amount of the zirconium
complex. The reactivity of these centers was very high (the rate constant of polymer chain growth was 5.4 × 104 l mol−1 s−1 at 35°C). As the polymerization time increased, the number of active sites decreased and the molecular-weight distribution
of polyethylene broadened because of the decay of a portion of initial centers and the formation of new centers that produced
high-molecular-weight polyethylene with M
w to 130 × 104 g/mol. The propagation rate constant measured at a sufficiently long polymerization time (20 min) was lower than that at
the initial point in time; this fact suggests the much lower reactivity of the new active sites. 相似文献
534.
Nordqvist A Björkelid C Andaloussi M Jansson AM Mowbray SL Karlén A Larhed M 《The Journal of organic chemistry》2011,76(21):8986-8998
Cinnamaldehyde derivatives were synthesized in good to excellent yields in one step by a mild and selective, base-free palladium(II)-catalyzed oxidative Heck reaction starting from acrolein and various arylboronic acids. Prepared α,β-unsaturated aldehydes were used for synthesis of novel α-aryl substituted fosmidomycin analogues, which were evaluated for their inhibition of Mycobacterium tuberculosis 1-deoxy-D-xylulose 5-phosphate reductoisomerase. IC(50) values between 0.8 and 27.3 μM were measured. The best compound showed activity comparable to that of the most potent previously reported α-aryl substituted fosmidomycin-class inhibitor. 相似文献
535.
The copper coordination geometry in the blue copper proteins plastocyanin, nitrite reductase, cucumber basic protein, and azurin has been studied by combined density functional (B3LYP) and molecular mechanical methods. Compared to quantum chemical vacuum calculations, a significant improvement of the geometry is seen (toward the experimental structures) not only for the dihedral angles of the ligands but also for the bond lengths and angles around the copper ion. The flexible Cu–SMet bond is well reproduced in the oxidized structures, whereas it is too long in some of the reduced complexes (too short in vacuum). The change in the geometry compared to the vacuum state costs 33–66 kJ/mol. If the covalent bonds between the ligands and the protein are broken, this energy decreases by ∼25 kJ/mol, which is an estimate of the covalent strain. This is similar to what is found for other proteins, so the blue copper proteins are not more strained than other metalloproteins. The inner‐sphere self‐exchange reorganization energy of all four proteins are ∼30 kJ/mol. This is 30–50 kJ/mol lower than in vacuum. The decrease is caused by dielectric and electrostatic effects in the protein, especially the hydrogen bond(s) to the cysteine copper ligands and not by covalent strain. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 81: 335–347, 2001 相似文献
536.
Mats Johnsson Karl W. Trnroos 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(6):i53-i54
Single crystals of dizinc tellurium dichloride trioxide, Zn2(TeO3)Cl2, were synthesized via a transport reaction in sealed evacuated glass tubes. The compound has a layered structure in which the building units are [ZnO4Cl] square pyramids, distorted [ZnO2Cl2] tetrahedra and [TeO3E] tetrahedra (E is the 5s2 lone pair of the TeIV atom), joined through shared edges and corners to form charge‐neutral layers. Cl atoms and Te‐atom lone pairs protrude from the surfaces of each layer towards adjacent layers, and the layers are held together by dispersion forces only. The compound is isostructural with the synthetic compound CuZn(TeO3)Cl2 and the mineral sophiite, Zn2(SeO3)Cl2. 相似文献
537.
Hyperbranched, aliphatic polyesters of theoretically calculated molar masses 1 200–44 300 (2–7 generations) were synthesized in the molten state from 2, 2-bis(hydroxymethyl)propionic acid (bis-MPA) (repeating unit of ABx-type) and 2-ethyl-2-(hydroxymethyl)-1, 3-propanediol (TMP) (core molecule) using acid catalysis. The synthetic procedure was a pseudo-one-step divergent reaction. The degree of branching was found to be near 80 %. A study has also been made with respect to the rheological properties of the hyperbranched aliphatic polyesters. The polymers exhibit an almost newtonian behaviour in the molten state. They also exhibit a lower increase in viscosity with molecular weight than linear polymers. The surface functionality is shown to greatly affect the viscosity of the polymers. 相似文献
538.
The microstructure and rheological behaviour of inhomogeneous biopolymer gels was studied using a model system of β-lactoglobulin. It can form both fine-stranded and particulate gels which can be homogeneous or inhomogeneous depending on pH and heating rate. The dense and loose regions of the fine-stranded gels had different relaxation times which significantly influenced the mechanical spectrum. The particulate gels showed coarser inhomogeneities influencing the fracture properties of the gels. 相似文献
539.