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排序方式: 共有105条查询结果,搜索用时 187 毫秒
51.
Björne B. Mollet Yoko Nakano Pieter C. M. M. Magusin A. J. H. Spiering Jef A. J. M. Vekemans Patricia Y. W. Dankers E. W. Meijer 《Journal of polymer science. Part A, Polymer chemistry》2016,54(1):81-90
Supramolecular polymers based on ureido‐pyrimidinone (UPy) represent a promising class of biocompatible materials for medical applications. Here, the chemical modification effect of UV irradiation, used to sterilize these materials, is studied. Besides anticipated crosslinking effects, UV irradiation causes telechelic UPy‐polymers to become fluorescent. UPy‐model compounds confirm a relation between UV‐induced changes and the UPy‐moiety. UV‐induced fluorescence and IR‐spectral changes are (partially) reversible by heat and/or solvent treatment. The results indicate the presence of at least two distinct UV‐induced molecular species. UPy‐model compounds with specific tautomeric forms directly relate fluorescence to UPy‐enol tautomers. Photo‐enolization is hypothesized to occur via an excited‐state intermolecular double proton transfer. Changes in UPy‐tautomeric equilibrium and crosslinking are factors that influence the dynamics of UPy‐based materials. Identification and understanding of such factors will aid in the successful application of these materials, for example as biomaterial in tissue engineering applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 81–90 相似文献
52.
Wu T Froeyen M Schepers G Mullens K Rozenski J Busson R Van Aerschot A Herdewijn P 《Organic letters》2004,6(1):51-54
[structure: see text] Nucleotide building blocks with two base moieties were synthesized and incorporated into oligonucleotides. One of the two bases is involved in base pairing within the double helix, while the other base is sticking out of the minor groove. This system may be used for presenting sequence information at the outside of the helix. 相似文献
53.
F. Dross J. Robbelein B. Vandevelde E. Van Kerschaver I. Gordon G. Beaucarne J. Poortmans 《Applied Physics A: Materials Science & Processing》2007,89(1):149-152
A new implantation-free lift-off process is presented. We deposit a layer with mismatched thermal expansion coefficient with
respect to the substrate. Upon cooling, the differential contraction induces a large stress field which is released by the
initiation and the propagation of a crack parallel to the surface. The principle is demonstrated on both single and multi-crystalline
silicon. Films with an area of 25 cm2 and a thickness of 30–50 μm have been obtained. Some Si layers were further processed into solar cells. An energy conversion
efficiency of 9.9% was reached on a 1 cm2 sample.
PACS 62.20.Mk; 68.55.Jk; 68.60.Bs; 84.60.Jt 相似文献
54.
C.R. Jungmann H. Weigmann L. Mewissen F. Poortmans E. Cornelis J.P. Theobald 《Nuclear Physics A》1982,386(2):287-307
Neutron transmission experiments were performed on 32S between 0.18 MeV and 19 MeV and differential elastic scattering experiments up to 2 MeV. The resonance parameters, including spin and parity, were determined up to 1.7 MeV. The distribution of neutron strength was determined for s, P, P, d, d and f-wave levels, and is compared to recent model calculations. The isotopic purity of some possible isobaric analog states was deduced from their neutron widths. 相似文献
55.
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57.
van Buijtenen J van As BA Verbruggen M Roumen L Vekemans JA Pieterse K Hilbers PA Hulshof LA Palmans AR Meijer EW 《Journal of the American Chemical Society》2007,129(23):7393-7398
Novozym 435-catalyzed ring-opening of a range of omega-methylated lactones demonstrates fascinating differences in rate of reaction and enantioselectivity. A switch from S- to R-selectivity was observed upon going from small (ring sizes or=8). This was attributed to the transition from a cisoid to a transoid conformational preference of the ester bond on going from small to large lactones. The S-selectivity of the ring-opening of the small, cisoid lactones was low to moderate, while the R-selectivity of the ring-opening of the large transoid lactones was surprisingly high. The S-selectivity of the ring-opening of the small, cisoid lactones combined with the established R-selectivity of the transesterification of (aliphatic) secondary alcohols prevented polymerization from taking place. Ring-opening of the large, transoid lactones was R-selective with high enantioselectivity. As a result, these lactones could be polymerized, without exception, by straightforward kinetic resolution polymerization, yielding the enantiopure R-polyester with excellent enantiomeric excess (>99%). 相似文献
58.
van den Hout KP Martín-Rapún R Vekemans JA Meijer EW 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(29):8111-8123
C3-symmetrical molecules are described which consists of a 1,3,5-benzenetricarboxamide core extended with dipeptide fragments bearing peripheral mesogenic groups. Small structural modifications in the dipeptide fragment have been performed to demonstrate their influence on the stability of the stacks and on the order within the self-assemblies formed. Seven C3-symmetrical discs have been investigated, all with different combinations of glycine, L- and/or D-phenylalanine in the dipeptide fragments. Characterization of these discotics in the neat state using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and polarized optical microscopy (POM) and in solution with circular dichroism (CD), UV-visible spectroscopy, low-concentration proton nuclear magnetic resonance and IR spectroscopy reveals that there is a clear trend in the stack stability, going from the glycine-phenylalanine motifs to the phenylalanine-phenylalanine ones. The combination of a larger hydrophobic core, more confinement of space and the possibility of additional pi-pi interactions leads to more stable stacks. Surprisingly, the weakest stacks consist of discotics of which the center is extended with L-phenylalanyl-glycines and not of discotics of which the center is extended with the glycyl-L-phenylalanine sequences. Furthermore, the XRD investigations show that it is difficult to form well-ordered self-assemblies in the neat state. And, CD measurements point out that some of the discs have a very complex energy landscape in solution. These observations suggest that small differences in the balance between the secondary interactions originating from the benzenetricarboxamide core and the dipeptide fragments, have a strong influence on the order within the stack. From these results it can be concluded that subtle modifications in the peptide fragments of the discs cause significant changes in the stacking properties, stressing the importance of understanding the self-assembly mechanism of each discotic in order to clarify its self-assembly behavior. 相似文献
59.
60.
EkaterinaV. Efimtseva GeorgiiV. Bobkov SergeyN. Mikhailov Arthur VanAerschot Guy Schepers Roger Busson Jef Rozenski Piet Herdewijn 《Helvetica chimica acta》2001,84(8):2387-2397
Disaccharide nucleosides with 2′‐O‐(D ‐arabinofuranosyl), 2′‐O‐(L ‐arabinofuranosyl), 2′‐O‐(D ‐ribopyranosyl), 2′‐O‐(D ‐erythrofuranosyl), and 2′‐O‐(5‐azido‐5‐deoxy‐D ‐ribofuranosyl) substituents were synthesized. These modified nucleosides were incorporated into oligonucleotides (see Table). Single substitution resulted in a ΔTm of +0.5 to −1.4° for DNA/RNA and a ΔTm of −0.8 to −4.7° for DNA/DNA duplexes. These disaccharide nucleosides can be well accommodated in RNA/DNA duplexes, and the presence of a NH2−C(5″) group has a beneficial effect on duplex stability. 相似文献