排序方式: 共有17条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
5.
Joseph A. N. Zasadzinski Paul C. Vosejpka Wilmer G. Miller 《Journal of colloid and interface science》1986,110(2)
Polymerized liposomes and vesicles are under close scrutiny as long-lived, stable substitutes for their natural and synthetic unpolymerized counterparts. The monomer surfactant, which contains one or more polymerizable groups, is dispersed in water at the proper temperature and concentration to form the lyotropic liquid crystalline phase of interest and polymerized while in the liquid crystalline state. In addition to their applications to slow-release and site-specific drug delivery, membrane-mediated chemistry, artificial photosynthesis, etc., polymerized surfactant liposomes and vesicles hold great promise as model systems for TEM investigations of lamellar liquid crystal structure. One such model polymerizable surfactant is DBPAl, or N,N-dimethyl-N,N-bis(1,3-pentadecadienyl-carbonyloxyethyl) ammonium iodide. Polarized light microscopy and differential scanning calorimetry (DSC) confirm that DBPAI forms lamellar liquid crystalline liposomes in water. The DBPAI liposomes were polymerized while in the liquid crystalline state by ultraviolet (UV) irradiation. The DBPAI liposomes were shown to be identical in structure before and after polymerization by a combination of X-ray diffraction and freeze-fracture TEM. However, turbidity measurements showed that the polymerized DBPAI liposomes were much more stable in acetone and ethanol than the monomer DBPAI liposomes, demonstrating that the chemical nature of the surfactant in the liposome had changed. The combination of structural preservation and enhanced chemical stability makes DBPAI a natural choice for TEM thin-sections. A method of preparing DBPAI liposomes for thin-section TEM is outlined and bilayer resolution images of the DBPAI liposomes are presented. Polymerized bilayers in thin-section TEM promise the enhanced resolution required to answer many important structural questions left unresolved by freeze-fracture TEM. 相似文献
6.
Catarina IV Ramos Flávio Figueira Marcelo D Polêto Francisco ML Amado Hugo Verli João PC Tomé M Graça PMS Neves 《Journal of mass spectrometry : JMS》2016,51(5):342-349
Electrospray mass spectrometry/mass spectrometry was used to investigate the gas‐phase properties of protonated expanded porphyrins, in order to correlate those with their structure and conformation. We have selected five expanded meso‐pentafluorophenyl porphyrins, respectively, a pair of oxidized/reduced fused pentaphyrins (22 and 24 π electrons), a pair of oxidized/reduced regular hexaphyrins (26 and 28 π electrons) and a regular doubly N‐fused hexaphyrin (28 π electrons). The gas‐phase behavior of the protonated species of oxidized and reduced expanded porphyrins is different. The oxidized species (aromatic Hückel systems) fragment more extensively, mainly by the loss of two HF molecules. The reduced species (Möbius aromatic or Möbius‐like aromatic systems) fragment less than their oxidized counterparts because of their increased flexibility. The protonated regular doubly fused hexaphyrin (non‐aromatic Hückel system) shows the least fragmentation even at higher collision energies. In general, cyclization through losses of HF molecules decreases from the aromatic Hückel systems to Möbius aromatic or Möbius‐like aromatic systems to non‐aromatic Hückel systems and is related to an increase in conformational distortion. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
7.
8.
9.
PC. M. Gubbens G. J. Boender A. M. van der Kraan K. H. J. Buschow 《Hyperfine Interactions》1992,68(1-4):329-332
DyFe12?xMx (M=Si,Ti,Cr) were studied with57Fe and161Dy Mössbauer spectroscopy. The deduced coupling constants JRFe of these compounds are about equal. It is found that Si is substituting one particular Fe-site, while Cr is substituting Fe randomly. In DyFe10Si2 two Fe-sites favour a c-axis anisotropy, while the third one favours the basal plane. 相似文献
10.