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51.
Schoonbeek FS van Esch JH Hulst R Kellogg RM Feringa BL 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(14):2633-2643
Several geminal bis-urea compounds were synthesised by means of an acid-catalysed condensation of various benzaldehydes with different monoalkylureas. Many of these compounds form thermoreversible gels with a number of organic solvents at very low concentrations (<3mM) and which are stable to temperatures higher than 100 degrees C. Electron microscopy revealed a three-dimensional (3D) network of intertwined fibres, which are several tens of micrometers long and have a width ranging from approximately 30 to 300 nm. The possible aggregate forms and aggregate symmetries were evaluated by means of molecular mechanics calculations. 1H NMR, 2D NMR, 13C NMR and 13C-CP/MAS NMR techniques were used to obtain information about the aggregation and possible aggregate symmetry of geminal bis-ureas in solution, in the gel state, and in the solid state. 相似文献
52.
Africh C Lin H Corso M Esch F Rosei R Hofer WA Comelli G 《Journal of the American Chemical Society》2005,127(32):11454-11459
By means of scanning tunneling microscopy and density functional theory calculations, we studied the water formation reaction on the Rh(110) surface when exposing the (2 x 1)p2mg-O structure to molecular hydrogen, characterizing each of the structures that form on the surface during the reaction. First the reaction propagates on the surface as a wave front, removing half of the initial oxygen atoms. The remaining 0.5 monolayers of O atoms rearrange in pairs, forming a c(2 x 4) structure. Second, as the reaction proceeds, areas of an intermediate structure with c(2 x 2) symmetry appear and grow at the expense of the c(2 x 4) phase, involving all the oxygen atoms present on the surface. Afterward, the c(2 x 2) islands shrink, indicating that complete hydrogenation occurs at their edges, leaving behind a clean rhodium substrate. Two possible models for the c(2 x 2) structure, where not only the arrangement but also the chemical identity is different, are given. The first one is a mixed H + O structure, while the second one resembles the half-dissociated water layer already proposed on other metal surfaces. In both models, the high local oxygen coverage is achieved by the formation of a hexagonal network of hydrogen bonds. 相似文献
53.
Browne WR de Jong JJ Kudernac T Walko M Lucas LN Uchida K van Esch JH Feringa BL 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(21):6430-6441
The electrochemical and spectroelectrochemical properties of a series of C5-substituted dithienylhexahydro- and dithienylhexafluorocyclopentenes are reported. The effect of substitution at C5 of the thienyl moiety on the redox properties is quite dramatic, in contrast to the effect on their photochemical properties. The efficiency of electrochemical switching is dependent both on the central cyclopentene unit and on the nature of the substituents, whereby electron-donating moieties favour oxidative electrochemical ring-closure and vice versa. Asymmetrically substituted dithienylcyclopentenes were investigated to explore the ring-closure process in more detail. The results indicate that electrochemically induced ring-closure occurs via the monocation of the open form. In the presence of electroactive groups at C5 of the thienyl ring (e.g., methoxyphenyl) initial oxidation of these groups is followed by intermolecular electron transfer, which drives ring-closure of the open forms. 相似文献
54.
Hurenkamp JH de Jong JJ Browne WR van Esch JH Feringa BL 《Organic & biomolecular chemistry》2008,6(7):1268-1277
The synthesis and characterisation of a coumarin-dithienylcyclopentene-coumarin symmetric triad (CSC) and a perylene bisimide-dithienylcyclopentene-coumarin asymmetric triad (PSC) are reported. In both triads the switching function of the photochromic dithienylcyclopentene unit is retained. For CSC an overall 50% quenching of the coumarin fluorescence is observed upon ring-closure of the dithienylcyclopentene component, which, taken together with the low PSS (<70%), indicates that energy transfer quenching of the coumarin component by the dithienylcyclopentene in the closed state is efficient. Upon ring opening of the dithienylcyclopentene unit the coumarin emission is restored fully. The PSC triad shows efficient energy transfer from the coumarin to the perylene bisimide unit when the dithienylcyclopentene unit is in the open state. When the dithienylcyclopentene is in the closed (PSS) state a 60% decrease in sensitized perylene bisimide emission intensity is observed due to competitive quenching of the coumarin excited state and partial quenching of the perylene excited state by the closed dithienylcyclopentene unit. This modulation of energy transfer is reversible over several cycles for both the symmetric and asymmetric tri-component systems. 相似文献
55.
Qian Liu Zhenyu Yuan Xuhong Guo Jan H. van Esch 《Angewandte Chemie (International ed. in English)》2020,59(33):14076-14080
In cancer therapy, the selective targeting of cancer cells while avoiding side effects to normal cells is still full of challenges. Here, we developed dual‐functionalized crescent microgels, which selectively captured and killed lung cancer cells in situ without killing other cells. Crescent microgels with the inner surface of the cavity functionalized with antibody and containing glucose oxidase (GOX) in the gel matrix have been produced in a microfluidic device. These microgels presented high affinity and good selectivity to lung cancer cells and retained them inside the cavities for extended periods of time. Exposing the crescent hydrogels to physiological concentrations of glucose leads to the production of a locally high concentration of H2O2 inside the microgels’ cavities, due to the catalytic action by GOX inside the gel matrix, which selectively killed 90 % cancer cells entrapped in the microgel cavities without killing the cells outside. Our strategy to create synergy between different functions by incorporating them in a single microgel presents a novel approach to therapeutic systems, with potentially broad applications in smart materials, bioengineering and biomedical fields. 相似文献
56.
van Bommel KJ Stuart MC Feringa BL van Esch J 《Organic & biomolecular chemistry》2005,3(16):2917-2920
An enzymatically cleavable low molecular weight gelator-(model) drug conjugate system can be employed to effect a two-step enzyme mediated drug release, demonstrating the potential of LMWG systems for the development of drug delivery devices. 相似文献
57.
J. D'Ans G. Dorfmüller J. Großfeld H. Leonhardt Ph. Naoúm A. Berthman G. Jayme R. Korn F. Burgstaller H. Sommer H. Mendrzyk W. Weltzien Karin Windeck-Schulze E. Ristenpart E. Sauer A. Küntzel S. Reissinger W. Esch W. Toeldte H. P. Kaufmann S. Funke W. Halden B. Wurzschmitt H. Thomas E. van Hulle E. Messmer P. Rabe H. van Haasy G. Hamann T. Berglund M. Sartori Gebührenaussehuß für chemische Arbeiten 《Analytical and bioanalytical chemistry》1940,119(11-12):422-425
58.
F. Willy Hinrichsen Erich Kindscher J. Marcusson Fendler Schneider Spence Budde Kuhn Harries C. R. Boggs S. Axelrod Hinrichsen Manasse Gasparini Frank Marckwald W. A. Ducca Gerhard Hübener Memmler Werner Esch Jules Bock Galletly Scott F. Kirchhof A. Tschirch W. Schmitz W. J. Britland H. E. Potts Weber Ditmar Paul Goldberg Frank Birkner Coolbaugb Betterton D. Spence J. Young John A. Schaeffer 《Analytical and bioanalytical chemistry》1919,58(10-11):490-504
59.
Schaaf O Jarvis AP van der Esch SA Giagnacovo G Oldham NJ 《Journal of chromatography. A》2000,886(1-2):89-97
Based on reversed-phase high-performance liquid chromatography (RP-HPLC) and atmospheric pressure chemical ionization (APCI) mass spectrometry, a HPLC-MS method was developed to permit the rapid qualitative and quantitative analysis of azadirachtin and related tetranortriterpenoids from seeds and tissue cultures of Neem (Azadirachta indica). APCI+ standard scanning mass spectra of the major Neem triterpenoids were recorded and utilized to select suitable ions for selected ion monitoring (SIM). Transitions for selective reaction monitoring (SRM) were based on MS-MS experiments. Using SIM, major Neem triterpenoids were detected in callus culture material and seed kernels of A. indica. The limit of detection for azadirachtin in extract samples (approximately 1 ng ml(-1) or 10 pg in SIM mode) was determined to be (with respect to injected absolute amounts) approximately 1000-times lower than values quoted in the literature for existing HPLC methods (approximately 200 ng ml(-1) or 10 ng). In addition to high sensitivity, the HPLC-MS method is able to tolerate minimal sample preparation and purification, dramatically reducing total analysis time. 相似文献
60.
Kai Zhang Sander Oldenhof Yiming Wang Jan H. van Esch Eduardo Mendes 《Angewandte Chemie (International ed. in English)》2020,59(22):8601-8607
Supramolecular assemblies are promising building blocks for the fabrication of functional soft devices for high‐tech applications. However, there is a lack of effective methods for large‐scale manipulation and integration of nano‐sized supramolecular structures on soft substrate. Now, functional soft devices composed of micellar filaments and hydrogels can be created through a versatile approach involving guided dewetting, transfer‐printing, and laser‐assisted patterning. Such an approach enables unprecedented control over the location and alignment of the micellar filaments on hydrogel substrates. As examples, freely suspended micellar fishnets immobilized on hydrogels are formed, showing the capability of trapping and releasing micro‐objects and the piconewton force sensitivity. By incorporating responsive moieties into hydrogels, shape‐morphing actuators with micelle‐controlled rolling directionality are constructed. 相似文献