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991.
Minisci F Punta C Recupero F Fontana F Pedulli GF 《The Journal of organic chemistry》2002,67(8):2671-2676
The oxidation of N-alkylamides by O(2), catalyzed by N-hydroxyphthalimide (NHPI) and Co(II) salt, leads under mild conditions to carbonyl derivatives (aldehydes, ketones, carboxylic acids, imides) whose distribution depends on the nature of the alkyl group and on the reaction conditions. Primary N-benzylamides lead to imides and aromatic aldehydes at room temperature without any appreciable amount of carboxylic acids, while under the same conditions nonbenzylic derivatives give carboxylic acids and imides with no trace of aldehydes, even at very low conversion. These results are explained through hydrogen abstraction by the phthalimide-N-oxyl (PINO) radical, whose reactivity with benzyl derivatives is governed by polar effects, so that benzylamides are much more reactive than the corresponding aldehydes. The enthalpic effect is, however, dominant with nonbenzylic amides, making the corresponding aldehydes much more reactive than the starting amides. The importance of the bond dissociation energy (BDE) of the O-H bond in NHPI is emphasized. 相似文献
992.
Roberto Gazzi Francesca Perazzolo Arlen Ferrari 《Journal of organometallic chemistry》2005,690(8):2071-2077
The electronic features and photochemistry of TpTiCl3 (1) (Tp = hydrotris(pyrazol-1-yl)borate) and Tp*TiCl3 (2) (Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate) were studied in THF. Reactive decay of the excited states produced either (or ) and metal center Ti(III) radicals via homolytic cleavage of the Tp → Ti (Tp* → Ti) bond. Cleavage of the Tp → Ti and the Tp* → Ti bond as a primary photoprocess is shown to be consistent with LMCT Tp → Ti and Tp* → Ti excitation. TpTiCl2(THF) (3) and Tp*TiCl2(THF) (4) were also prepared by stoichiometric reduction of 1 and 2 with Li3N. The THF ligand in 3 and 4 was replaced by the stable nitroxyl radical TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) to provide the new complexes TpTiCl2(TEMPO) (5) and Tp*TiCl2(TEMPO) (6) in which the TEMPO ligand is η1 coordinated to Ti(IV). Photolysis of 5 and 6 generate Ti(III) and the TEMPO radical in the primary photochemical step. 相似文献
993.
Bruno Crociani Francesca Dibianca Amalia Giovenco Alberto Scrivanti 《Journal of organometallic chemistry》1985,291(2):259-272
The oxidative addition of 2-chloropyrimidine or 2-chloropyrazine to [Pd(PPh3)4] yields a mixture of trans-[PdCl(C4H3N2-C2)(PPh3)2] (I) and [PdCl(μ-C4H3N2-C2,N1)(PPh3 (II) (C4H3N2 = 2-pyrimidyl or 2-pyrazyl group). The mononuclear complexes I are quantitatively converted into the binuclear species II upon treatment with H2O2. The reaction of II with HCl gives the N-monoprotonated derivatives cis-[PdCl2(C4H4N2-C2)(PPh3)] (III), from which the cationic complexes trans-[PdCl(C4H4N2-C2)(L) (L = PPh3, IV; PMe2Ph, V; PEt3, VI) can be prepared by ligand substitution reactions. Reversible proton dissociation occurs in solution for III–VI. The low-temperature 1H NMR spectra of trans-[PdCl(C4H4N2-C2)(PMe2Ph)2]ClO4 show that the heterocyclic moiety undergoes restricted rotation around the PdC2 bond and that the 2-pyrazyl group is protonated predominantly at the N1 atom. These results and the 13C NMR data for the PEt3 derivatives are interpreted on the basis of a significant dπ → π★ back-bonding contribution to the palladium—carbon bond of the protonated ligands. 相似文献
994.
A reliable micellar electrokinetic capillary chromatographic method was developed and validated for the determination of lamotrigine and its metabolites in human plasma and urine. The variation of different parameters, such as pH of the background electrolyte (BGE) and Sodium dodecyl sulfate (SDS) concentration, were evaluated in order to find optimal conditions. Best separation of the analytes was achieved using a BGE composed of 10 mM borate and 50 mM SDS, pH 9.5; melatonin was selected as the internal standard. Isolation of lamotrigine and its metabolites from plasma and urine was accomplished with an original solid-phase extraction procedure using hydrophilic-lypophilic balance cartridges. Good absolute recovery data and satisfactory precision values were obtained. The calibration plots for lamotrigine and its metabolites were linear over the 1-20 microg/mL concentration range. Sensitivity was satisfactory; the limits of detection and quantitation of lamotrigine were 500 ng/mL and 1 microg/mL, respectively. The application of the method to real plasma samples from epileptic patients under therapy with lamotrigine gave good results in terms of accuracy and selectivity, and in agreement with those obtained with an high-performance liquid chromatography (HPLC) method. 相似文献
995.
Amorati R Lucarini M Mugnaini V Pedulli GF Minisci F Recupero F Fontana F Astolfi P Greci L 《The Journal of organic chemistry》2003,68(5):1747-1754
Bond dissociation enthalpies (BDE) of hydroxylamines containing alkyl, aryl, vinyl, and carbonyl substituents at the nitrogen atom have been determined by using the EPR radical equilibration technique in order to study the effect of the substituents on the O-H bond strength of these compounds. It has been found that substitution of an alkyl group directly bonded to the nitrogen atom with vinyl or aryl groups has a small effect, while substitution with acyl groups induces a large increase of the O-H BDE value. Thus, dialkyl hydroxylamines have O-H bond strengths of only ca. 70 kcal/mol, while acylhydroxylamines and N-hydroxyphthalimide (NHPI), containing two acyl substituents at nitrogen, are characterized by BDE values of ca. 80 and 88 kcal/mol, respectively. Since the phthalimide N-oxyl radical (PINO) has been recently proposed as an efficient oxidation catalyst of hydrocarbons or other substrates, the large BDE value found for the parent hydroxylamine (NHPI) justifies this proposal. Kinetic studies, carried out in order to better understand the mechanism of the NHPI-catalyzed aerobic oxidation of cumene, are consistent with a simple kinetic model where the rate-determining step is the hydrogen atom abstraction from the hydroxylamine by cumylperoxyl radicals. 相似文献
996.
Tessore F Locatelli D Righetto S Roberto D Ugo R Mussini P 《Inorganic chemistry》2005,44(7):2437-2442
To evidentiate the role of the nature of sulfonate ancillary ligands on the value of the quadratic hyperpolarizability of Zn(II) complexes with stilbazole-like ligands, the second-order nonlinear optical (NLO) properties of [ZnY(2)(4,4'-trans-NC5H4CH=CHC6H4NMe2)2] complexes (Y = CF3SO3, CH3SO3, or p-CH3C6H4SO3) are investigated. By working at relatively high concentrations (>3 x 10(-4) M), the positive effect of the triflate ligand remains unique while, with nonfluorinated sulfonate ligands, the second-order NLO response is comparable to that of the related complexes with acetate or trifluoroacetate as ancillary ligands. However, at dilutions higher than 10(-4) M, all of the sulfonate complexes reach huge quadratic hyperpolarizabilities because of solvolysis with the formation of cationic species such as [ZnY(4,4'-trans-NC5H4CH=CHC6H4NMe2)2]+, characterized by a large second-order NLO response. This view is supported by careful conductivity measurements. The same behavior occurs if 4,4'-trans-NC5H4CH=CHC6H4NMe2 is substituted by 4,4'-trans,trans-NC5H4(CH=CH)2C6H4NMe2. 相似文献
997.
Five substituted tartaric acid derivatives are studied using density functional theory, both isolated and adsorbed onto an oxidized GaAs cluster, to model molecular layers on semiconductor surfaces. The structures, energies, and electronic properties are computed to clarify the interactions responsible for the electric behavior of the modified surfaces, used in semiconductor/metal junction devices. The chemical structure of the molecule/GaAs adducts is optimized ab initio and discussed for the first time. A strong binding scheme is found, providing useful insights about the microscopic structure of the molecular layer. A widely used model based on molecular dipole layers is discussed and verified, by computing the dipole moment for the isolated systems and estimating the charge separation in the adducts; moreover the molecular orbitals energies are analyzed and correlated to the experimental measures of the modified surface electron affinity. 相似文献
998.
Gonçalves Adilson R. Costa Sirlene M. Esposito Elisa 《Applied biochemistry and biotechnology》2002,98(1-9):373-382
Three strains of the white-rot fungus Panus tigrinus (FTPT-4741, FTPT-4742, and FTPT-4745) were cultivated on sugarcane bagasse prior to kraft pulping. Pulp yields, kappa number,
and viscosity of all pulps were determined and Fourier transform infrared (FTIR) spectra from the samples were recorded. The
growth of P. tigrinus strains in plastic bags increased the manganese peroxide and xylanase activities. Lignin peroxidase was not detected in the
three systems (shaken and nonshaken flasks and plastic bags). FTIR spectra were reduced to their principal components, and
a clear separation between FTPT-4742 and the control was observed. Strain FTPT-4745 decayed lignin more selectively in the
three systems utilized. Yields of kraft pulping were low, ranging from 20 to 45% for the plastic bag samples and from 12 to
38% for the flask samples. Kappa numbers were 1–18 and viscosity ranged from 2.3 to 6.8 cP. 相似文献
999.
Bjørgen M Bonino F Kolboe S Lillerud KP Zecchina A Bordiga S 《Journal of the American Chemical Society》2003,125(51):15863-15868
Experimental evidence of protonation of an aromatic ring by a zeolite is hereby presented for the first time. The changes in vibrational properties and electronic transitions of the highest polymethylbenzene homologue, that is, hexamethylbenzene, were investigated after introducing the compound directly into a H-beta zeolite. Protonation of the aromatic ring, and thus the loss of symmetry, activated a vibrational ring mode at 1600 cm(-)(1). Furthermore, an electronic transition around 26 000 cm(-)(1), which was totally absent for the neutral species, was an obvious consequence of protonation. A parallel study of hexamethylbenzene adsorbed on a beta zeolite virtually free from protons did not show those distinctive spectral features. On the basis of the gas-phase proton affinity of hexamethylbenzene, a complete proton transfer from the zeolite framework to the molecule is, according to conventional considerations, not expected. The hexamethylbenzenium ion is stable in the zeolite cavities at least up to 200 degrees C. The remarkable persistence of this carbenium ion may be attributed to spatial constraints imposed by the tight fit of the cation inside the zeolite channels. Hexamethylbenzene is a relevant reaction intermediate in the methanol-to-hydrocarbons reaction and also plays a central role as a coke precursor in zeolite-catalyzed reactions that involve polymethylbenzenes. 相似文献
1000.
Synthesis of Highly Selective Submicromolar Microcystin‐Based Inhibitors of Protein Phosphatase (PP)2A over PP1
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Miriam Fontanillo Ivan Zemskov Maximilian Häfner Dr. Ulrike Uhrig Dr. Francesca Salvi Dr. Bernd Simon Prof. Dr. Valentin Wittmann Dr. Maja Köhn 《Angewandte Chemie (International ed. in English)》2016,55(45):13985-13989
Research and therapeutic targeting of the phosphoserine/threonine phosphatases PP1 and PP2A is hindered by the lack of selective inhibitors. The microcystin (MC) natural toxins target both phosphatases with equal potency, and their complex synthesis has complicated structure–activity relationship studies in the past. We report herein the synthesis and biochemical evaluation of 11 MC analogues, which was accomplished through an efficient strategy combining solid‐ and solution‐phase approaches. Our approach led to the first MC analogue with submicromolar inhibitory potency that is strongly selective for PP2A over PP1 and does not require the complex lipophilic Adda group. Through mutational and structural analyses, we identified a new key element for binding, as well as reasons for the selectivity. This work gives unprecedented insight into how selectivity between these phosphatases can be achieved with MC analogues. 相似文献