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211.
Single-armed, 15- and 18-membered lariat ether receptor systems having indolylethyl side arms bind Na+ and K+ in the ring. The indole residue serves as a pi-donor to the ring-bound cation. Whether the five- or six-membered ring interacts most directly with Na+ or K+ depends on whether the sidearm is attached to indole's 3- or 5-position. This suggests that structural as well as electronic factors are important in pi-complexation of alkali metal cations. 相似文献
212.
Comparative study of photodynamic properties of 13,15-N-cycloimide derivatives of chlorin p6 总被引:1,自引:0,他引:1
Feofanov A Sharonov G Grichine A Karmakova T Pljutinskaya A Lebedeva V Ruziyev R Yakubovskaya R Mironov A Refregier M Maurizot JC Vigny P 《Photochemistry and photobiology》2004,79(2):172-188
Comparative study of 13,15-[N-(2-hydroxyethyl)]cycloimide chlorin p6 (2), 13,15-(N-acetoxy)cycloimide chlorin p6 (3), 13,15-(N-hydroxy)cycloimide chlorin p6 methyl ester (4) and 13,15-(N-methoxy)cycloimide chlorin p6 methyl ester (5) together with the previously investigated 13,15-[N-(3-hydroxypropyl)]cycloimide chlorin p6 (1) was performed. The dependence of the key photodynamic properties of 1-5 on the introduced substituents was analyzed. The photoinduced cell-killing activity of 4 is 100- and 280-fold higher than that of chlorin p6 and Photogem, respectively, as estimated on A549 human lung adenocarcinoma cells. The activity is reduced eight times in the order 4 > 5 > 1 > 2 > 3. The intracellular accumulation of 1-5 occurs in cytoplasm in a monomeric form bound to the lipids of cellular membranes. This form of 1, 2, 3, 4 and 5 is characterized by the high quantum yield of singlet oxygen generation, which depends on the introduced substituents, 0.66, 0.59, 0.35, 0.51 and 0.73, respectively. The photostability is two-fold less for 1 and four-fold less for 2, 3 and 5 than for 4. The rates of cellular uptake and efflux of 1-5 vary widely, thus providing the way to optimize the pharmacological properties of the photosensitizer (PS) using the respective substituents. Modifying the substituents, 1-5 were targeted to different cellular organelles. The enhanced accumulation in the Golgi apparatus and mitochondria complemented with diffuse staining of intracellular membranous structures is a property of 1-4. Compound 5 accumulates selectively in the lipid droplets and stains weakly perinuclear structures. Temperature-sensitive mechanisms of transport are responsible for the 1-4 uptake. Diffusion can play a role in the internalization of 5 but not of 1-4. Endocytosis via caveolae, clathrin-dependent and adenosine triphosphate-dependent pathways are not noticeably involved in the 1-5 internalization. Independently from their intracellular localization 1, 4 and 5 are highly efficient near-IR PS, which induce predominantly an apoptotic type of cell death under conditions providing ca 50% level of phototoxicity and necrosis at the 100% level of phototoxicity. 相似文献
213.
Mousumi Sannigrahi Patrick Pinto T.M. Chan Neng-Yang Shih F. George Njoroge 《Tetrahedron letters》2006,47(28):4877-4880
An efficient and practical synthesis of sterically hindered N-substituted lactams has been developed starting from simple starting materials. The stereochemistry of the synthetically useful N,N acetal intermediate has been established. 相似文献
214.
Two new types of iso-oxacephems have been synthesized in which a phosphonate group replaces either the carboxyl group or C(3). The latter compound exists as a stable trialkoxyphosphonium ylide. Potassium thioacetate and O2 in DMF are transformed in an autocatalytic, probably sulfur-catalyzed process to CH3COOK and sulfur; the latter two reagents are sufficient to transform the methanesulfonate 7 to the isopenam 15 . 相似文献
215.
A quantitative compressed pellet infrared method used together with a micro-distillation to effect separation of the isomer has been developed and reported here for the analysis of ortho-, meta-, and para-terphonyl. The terphenyl content is determined on fractions isolated by distillation from radiation damaged samples. The compressed pellet infrared method is preferred instead of the more conventional solution technique since smaller quantities of isolated terphcnyl are required. The pellet method is applicable also to polyphenyls higher than the terphenyls. The solution technique is not due to the insolubility of the polyphenyls. It is expected that the compressed pellet spectral method developed here might well find application in the analysis of compounds other than polyphenyls. Results presented here appear to be the, first quantitative infrared data reported in the literaturu on polyphenyl compounds. 相似文献
216.
Bashiardes G Chaussebourg V Laverdan G Pornet J 《Chemical communications (Cambridge, England)》2004,(1):122-123
A new synthesis of benzo[1,2]oxasiloles is described, wherein an unprecedented intramolecular allylic transposition takes place probably involving a pentavalent silicon intermediate. 相似文献
217.
George Holinga 《Tetrahedron letters》2005,46(47):8245-8247
Dibromocarbene reacts with tertiary-butylisocyanide to form a ketenimine. The absolute rate constant of the reaction (kTBI = 2.3 × 109 M−1 s−1) was determined by laser flash photolysis techniques with UV-vis detection of the dibromocarbene-pyridine ylide. The ketenimine was detected by TRIR spectroscopy at 2040 cm−1. Isocyanide trapping of carbenes to form ketenimines is proposed as a general method of studying IR silent carbenes by TRIR spectroscopy. 相似文献
218.
Phenol is quantified rapidly and accurately by the 4-aminoantipyrine spectrophotometric method after adding 15 g of sodium chloride to a 25-ml sample and distilling in a Semimicro steam distillation apparatus of the Pregl—Parnas—Wagner type. The large amount of sodium chloride provides a saturated solution of the salt during the course of the distillation and causes most of the phenol to be contained in the first few milliliters of distillate. The method has been used to quantify up to 25 mg of phenol per 25 ml. 相似文献
219.
Volumetric heat capacities of the six binary mixtures formed from cyclopentane, cyclohexane, cycloheptane and cyclooctane were determined at 298.15 K in a Picker flow microcalorimeter. Excess heat capacities obtained from the results are compred with the temperature variation of excess enthalpies from the literature. 相似文献
220.
VOF3 is soluble in acetonitrile but is slowly reduced to give a vanadyl (IV) species as one product. It reacts rapidly with Me3SiNet2 in MeCN below ambient temperature; fluorine is replaced by -NEt2 ligands but the spectroscopic and magnetic properties of the products indicate that, in addition, reduction to VIV occurs not some extent. The products are formulated as VOF3-n(NEt2)n containing small quantities of VOF2-m(NEt2)m(NEt2H) (n = 1-3, m = 0-2). A similar reaction occurs between VOF3 and Me3SiOMe but with Me3SiOSiMe3 only VO2F is formed. 相似文献