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331.
A TLC fluorodensitometric method for the determination of total PAHs in aqueous and hydroalcoholic solutions at the parts per billion level has been developed. The PAHs are extracted into cyclohexane and separated as a class on a chemically bonded reversed-phase TLC plate using stepwise development. In the fluorescence scanning of the plate the PAHs are located by reference to a mixture of 16 PAHs designated by EPA as primary pollutants and measured as benzo(a)pyrene. 相似文献
332.
[reaction: see text] At 275 degrees C, 8-exo-methylbicyclo[4.2.0]oct-2-ene (1a) undergoes a [1,3] sigmatropic rearrangement to 5-methylbicyclo[2.2.2]oct-2-enes, of which the orbital symmetry-allowed si product is only marginally favored over the forbidden sr product; that is, si/sr is 2.4. Accompanying the [1,3] shift are significant amounts of epimerization and fragmentation. The 8-endo epimer 1b, which yields no [1,3] product, experiences primarily direct fragmentation and secondarily epimerization. A diradical intermediate can account for all such observations. 相似文献
333.
Evgeny I. Kvasyuk Tamara I. Kulak Igor A. Mikhailopulo Ramamurthy Charubala Wolfgang Pfleiderer 《Helvetica chimica acta》1995,78(7):1777-1784
The 5′-amino-5′-deoxy-2′,3′-O-isopropylideneadenosine ( 4 ) was obtained in pure form from 2′,3′-O-isopropylideneadenosine ( 1 ), without isolation of intermediates 2 and 3 . The 2-(4-nitrophenyl)ethoxycarbonyl group was used for protection of the NH2 functions of 4 (→7) . The selective introduction of the palmitoyl (= hexadecanoyl) group into the 5′-N-position of 4 was achieved by its treatment with palmitoyl chloride in MeCN in the presence of Et3N (→ 5 ). The 3′-O-silyl derivatives 11 and 14 were isolated by column chromatography after treatment of the 2′,3′-O-deprotected compounds 8 and 9 , respectively, with (tert-butyl)dimethylsilyl chloride and 1H-imidazole in pyridine. The corresponding phosphoramidites 16 and 17 were synthesized from nucleosides 11 and 14 , respectively, and (cyanoethoxy)bis(diisopropylamino)phosphane in CH2Cl2. The trimeric (2′–5′)-linked adenylates 25 and 26 having the 5′-amino-5′-deoxyadenosine and 5′-deoxy-5′-(palmitoylamino)adenosine residue, respectively, at the 5′-end were prepared by the phosphoramidite method. Similarly, the corresponding 5′-amino derivatives 27 and 28 carrying the 9-[(2-hydroxyethoxy)methyl]adenine residue at the 2′-terminus, were obtained. The newly synthesized compounds were characterized by physical means. The synthesized trimers 25–28 were 3-, 15-, 25-, and 34-fold, respectively, more stable towards phosphodiesterase from Crotalus durissus than the trimer (2′–5′)ApApA. 相似文献
334.
Richard J. Sundberg Rita Broome Claudia Powers Walters Dora Schnur 《Journal of heterocyclic chemistry》1981,18(4):807-809
Benzenesulfonylindole is converted to a dilithio derivative by 2.2 equivalents of lithiating reagent. The dilithio derivative gives rise to sultones on reaction with carbonyl compounds. This reaction proceeds by an intramolecular displacement of the indole group from the bis-adduct. Fair to poor yields of the 2-indolycarbinols can also be isolated. Benzoyl chloride forms a thiazine dioxide ring by addition at both the 2-indolyl and 2′-phenylsulfonyl positions. 3-Methyl-1-benzenesulfonylindole is also easily dilithiated. 相似文献
335.
Tamara Milivojević Damjana Drobne Tea Romih Lilijana Bizjak Mali Irena Marin Mojca Lunder Gorazd Drevenšek 《Journal of nanoparticle research》2016,18(10):309
The use of zinc oxide nanoparticles (ZnO NPs) in numerous products is increasing, although possible negative implications of their long-term consumption are not known yet. Our aim was to evaluate the chronic, 6-week oral exposure to two different concentrations of ZnO NPs on isolated rat hearts exposed to ischemic-reperfusion injury and on small intestine morphology. Wistar rats of both sexes (n = 18) were randomly divided into three groups: (1) 4 mg/kg ZnO NPs, (2) 40 mg/kg ZnO NPs, and (3) control. After 6 weeks of treatment, the hearts were isolated, the left ventricular pressure (LVP), the coronary flow (CF), the duration of arrhythmias and the lactate dehydrogenase release rate (LDH) were measured. A histological investigation of the small intestine was performed. Chronic exposure to ZnO NPs acted cardiotoxic dose-dependently. ZnO NPs in dosage 40 mg/kg maximally decreased LVP (3.3-fold) and CF (2.5-fold) and increased the duration of ventricular tachycardia (all P < 0.01) compared to control, whereas ZnO NPs in dosage 4 mg/kg acted less cardiotoxic. Goblet cells in the small intestine epithelium of rats, treated with 40 mg ZnO NPs/kg, were enlarged, swollen and numerous, the intestinal epithelium width was increased. Unexpectedly, ZnO NPs in both dosages significantly decreased LDH. A 6-week oral exposure to ZnO NPs dose-dependently increased heart injuries and caused irritation of the intestinal mucosa. A prolonged exposure to ZnO NPs might cause functional damage to the heart even with exposures to the recommended daily doses, which should be tested in future studies. 相似文献
336.
Tamara?A.?Vico Valeria?B.?Arce María?F.?FangioEmail author Liesel?B.?Gende Celso?A.?Bertran Daniel?O.?Mártire María?S.?ChurioEmail author 《Journal of nanoparticle research》2016,18(11):348
Silica nanoparticles attached to gallic acid were synthesized from 7-nm diameter fumed silica particles by different functionalization methods involving the condensation of hydroxyl or carboxyl groups. The particles were characterized by thermal analyses and UV–vis, FTIR, NMR, and EPR spectroscopies. In comparison to free gallic acid, enhanced stability and increased antimicrobial activity against Paenibacillus larvae were found for the functionalized nanoparticles. Thus, both derivatization strategies result in improved properties of the natural polyphenol as antimicrobial agent for the treatment of honeybee pathologies. 相似文献
337.
Gold(I)‐Catalyzed Generation of the Two Components of a Formal [4+2] Cycloaddition Reaction for the Synthesis of Tetracyclic Pyrano[2,3,4‐de]chromenes
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Dr. Tamara Arto Prof. Dr. Francisco J. Fañanás Prof. Félix Rodríguez 《Angewandte Chemie (International ed. in English)》2016,55(25):7218-7221
Ortho‐Alkynylbenzaldehydes have been widely used to generate isochromenylium derivatives through gold‐catalyzed cycloisomerization. These isochromenylium derivatives have been exploited as formal diene derivatives for reactions with different dienophiles. Herein, we describe the behavior of ortho‐alkynylsalicylaldehydes, a particular case of ortho‐alkynylbenzaldehydes. The gold‐catalyzed cycloisomerization of ortho‐alkynylsalicylaldehydes delivers an unusual heterodiene derivative that reacts with electron‐rich alkenes through a formal [4+2] cycloaddition. In this reaction, both the diene and dienophile are generated in situ through gold‐catalyzed cycloisomerization of appropriate alkynamines or alkynols. This reaction was used to synthesize complex tetracyclic pyrano[2,3,4‐de]chromenes from two very simple starting materials (an ortho‐alkynylsalicylaldehyde and an alkynamine or alkynol) with complete atom economy and with selective formation of bonds, cycles, and stereocenters. 相似文献
338.
339.
Tamara J. Bednarchuk Vasyl Kinzhybalo Adam Pietraszko 《Acta Crystallographica. Section C, Structural Chemistry》2016,72(5):432-441
The chemistry of organically templated metal sulfates has attracted interest from the materials science community and the development of synthetic strategies for the preparation of organic–inorganic hybrid materials with novel structures and special properties is of current interest. Sulfur–oxygen–metal linkages provide the possibility of using sulfate tetrahedra as building units to form new solid‐state materials. A series of novel organically templated metal sulfates of 2‐aminopyridinium (2ap) with aluminium(III), cobalt(II), magnesium(II), nickel(II) and zinc(II) were obtained from the respective aqueous solutions and studied by single‐crystal X‐ray diffraction. The compounds crystallize in centrosymmetric triclinic unit cells in three structure types: type 1 for 2‐aminopyridinium hexaaquaaluminium(III) bis(sulfate) tetrahydrate, (C5H7N2)[Al(H2O)6](SO4)2·4H2O, (I); type 2 for bis(2‐aminopyridinium) tris[hexaaquacobalt(II)] tetrakis(sulfate) dihydrate, (C5H7N2)2[Co(H2O)6]3(SO4)4·2H2O, (II), and bis(2‐aminopyridinium) tris[hexaaquamagnesium(II)] tetrakis(sulfate) dihydrate, (C5H7N2)2[Mg(H2O)6]3(SO4)4·2H2O, (III); and type 3 for bis(2‐aminopyridinium) hexaaquanickel(II) bis(sulfate), (C5H7N2)2[Ni(H2O)6](SO4)2, (IV), and bis(2‐aminopyridinium) hexaaquazinc(II) bis(sulfate), (C5H7N2)2[Zn(H2O)6](SO4)2, (V). The templating role of the 2ap cation in all of the reported crystalline substances is governed by the formation of characteristic charge‐assisted hydrogen‐bonded pairs with sulfate anions and the presence of π–π interactions between the cations. Additionally, both coordinated and uncoordinated water molecules are involved in hydrogen‐bond formation. As a consequence, extensive three‐dimensional hydrogen‐bonding patterns are formed in the reported crystal structures. 相似文献
340.
Christopher M. Lemon Michael Huynh Andrew G. Maher Bryce L. Anderson Dr. Eric D. Bloch Prof. Dr. David C. Powers Prof. Dr. Daniel G. Nocera 《Angewandte Chemie (International ed. in English)》2016,55(6):2176-2180
The ground state electronic structure of copper corroles has been a topic of debate and revision since the advent of corrole chemistry. Computational studies formulate neutral Cu corroles with an antiferromagnetically coupled CuII corrole radical cation ground state. X‐ray photoelectron spectroscopy, EPR, and magnetometry support this assignment. For comparison, CuII isocorrole and [TBA][Cu(CF3)4] were studied as authentic CuII and CuIII samples, respectively. In addition, the one‐electron reduction and one‐electron oxidation processes are both ligand‐based, demonstrating that the CuII centre is retained in these derivatives. These observations underscore ligand non‐innocence in copper corrole complexes. 相似文献