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151.
Xiabing Li Dr. Daniele Leonori Dr. Nadeem S. Sheikh Prof. Iain Coldham 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(24):7724-7730
The lithiation of N‐tert‐butoxycarbonyl (N‐Boc)‐1,2,3,4‐tetrahydroisoquinoline was optimized by in situ IR (ReactIR) spectroscopy. Optimum conditions were found by using n‐butyllithium in THF at ?50 °C for less than 5 min. The intermediate organolithium was quenched with electrophiles to give 1‐substituted 1,2,3,4‐tetrahydroisoquinolines. Monitoring the lithiation by IR or NMR spectroscopy showed that one rotamer reacts quickly and the barrier to rotation of the Boc group was determined by variable‐temperature NMR spectroscopy and found to be about 60.8 kJ mol?1, equating to a half‐life for rotation of approximately 30 s at ?50 °C. The use of (?)‐sparteine as a ligand led to low levels of enantioselectivity after electrophilic quenching and the “poor man’s Hoffmann test” indicated that the organolithium was configurationally unstable. The chemistry was applied to N‐Boc‐6,7‐dimethoxy‐1,2,3,4‐tetrahydroisoquinoline and led to the efficient synthesis of the racemic alkaloids salsolidine, carnegine, norlaudanosine and laudanosine. 相似文献
152.
We report experimental data on the highly excited states of zinc in the energy range 74,625-75,740 cm−1 using two-step laser excitation scheme in conjunction with a thermionic diode ion detector. The 4s4p 3P1 inter-combination level at 32501.399 cm−1 was populated using a frequency doubled dye laser. The 4s5s 3S1 level at 53672.28 cm−1 gets populated from the ASE (amplified spontaneous emission) of the second step dye laser. The Rydberg series 4snp 3P2 (12 ? n ? 60), 4snp 1P1 (16 ? n ? 30) and parity forbidden transitions 4sns 3S1 (19 ? n ? 44) have been observed. A two parameter fit to excitation energies of the observed series yields the binding energy of the 4s5s 3S1 level as 22097.03 ± 0.03 cm−1 and consequently, the first ionization potential of zinc is determined as 75769.31 ± 0.05 cm−1, that is in excellent agreement with the earlier work. 相似文献
153.
154.
Magnetization of sol-gel prepared zinc ferrite nanoparticles: Effects of inversion and particle size
Nanoparticles of ZnFe2O4 have been prepared by using sol-gel method in two different mediums (acidic and basic) in order to observe the influence of the medium on the magnetic properties of the obtained nanoparticles. X-ray diffraction and Mössbauer studies of these samples show the presence of single-phase spinel structure. The average size of the particles as determined by X-ray diffraction increases with the annealing temperature from 18 to 52 nm. With the increase in particle size, magnetization decreases while the magnetization blocking temperature increases. Magnetization studies show that the samples prepared in basic medium have more ferrimagnetic nature as compared to those prepared in acidic medium. We understand this increase in magnetization as reflective of the increased degree of inversion (transfer of Fe3+ ions from octahedral to tetrahedral sites) in the particles of smaller size unit cells. From lattice parameter calculations on different particles it is determined that inversion is more favorable in the particles prepared in a basic medium than in the acidic medium due to the smaller cell size in the former. 相似文献
155.
M. A. Chaudhri Q. Nadeem M. N. Chaudhri Q. Jabbar 《Journal of Radioanalytical and Nuclear Chemistry》2007,271(3):697-700
By making use of the 19F(p,αγ)16O reaction the F-concentrations of different varieties of tea leaves, of some international geochemical reference materials,
and of the bones and teeth of some experimental animals have been determined. The tea leaves from Ceylon (ordinary), Orange
Pekoe (special Ceylon), China (ordinary black), Lapsang Souchong (special smoked Chinese) and Darjeeling (India) were found
to contain 170 ppm, 170 ppm, 120 ppm, 160 ppm and 100 ppm of fluorine, respectively, The F-concentrations of established geochemical
reference materials, NIM-D, NIM-N, NIM-P and NIM-S, from the National Institute of Metallurgy, South Africa were determined
to be 60 ppm, 120 ppm, 130 ppm and 190 ppm, respectively. The bones of rabbits, who were given fluoridated water, were found
to contain much higher amount of fluorine than the bones of the control rabbit. Furthermore, the rabbits who were kept on
fluoridated water for 45 days, had almost double the amount of F in their bones than the rabbits who were given fluoridated
water for only 15 days. Similarly, the teeth of grown-up monkeys who were given fluoridated water since birth had double the
amount of fluorine than those of the control monkey. 相似文献
156.
Atomistic static computer simulation techniques have been applied to investigate the energetics of defects and dopants in Sr2RuO4 (SRO) and Ca2RuO4 (CRO). Interatomic potentials have been derived which reproduced the crystal structures of these systems. Solution energies are calculated for different dopant ions to ascertain the site occupied by the dopant ion in the host lattice. Monovalent and divalent ions are predicted to substitute preferentially at the alkaline-earth site in both the systems. Trivalent cations of smaller ionic radii substitute at the Ru sites while those having larger ionic radii prefer to substitute at the Sr or Ca sites in SRO or CRO systems, respectively. In addition, there is a possibility of self-compensation, where a trivalent cation can substitute at both Sr(Ca) and Ru sites. Tetravalent dopants are found to substitute at the ruthenium sites in both systems. 相似文献
157.
Nadeem MA Thornton AW Hill MR Stride JA 《Dalton transactions (Cambridge, England : 2003)》2011,40(13):3398-3401
A microporous metal-organic framework [Cu(3)(ipO)(2)(pyz)(2)](n), (ipO = 2-hydroxyisophthalic acid, pyz = pyrazine) was synthesized via an in situ. ligand transformation reaction. The microporous framework displays helical arrays of ipo ligands holding the Cu atoms in 2D sheets, whilst the coordination of pyz molecules acts to arrange these sheets into a microporous 3D structure. Remarkable selective sorption behaviour (>5) for H(2) over N(2) is observed and explained with molecular dynamics simulations. 相似文献
158.
Phytochemical investigations on the methanolic extract of Melicope ptelefolia Champ ex Benth. resulted in the isolation of three new compounds, identified as 3beta-stigmast-5-en-3-ol butyl tridecanedioate (melicoester) (1), (2Z, 6Z, 10Z, 14Z, 18Z, 22Z, 26E)-3', 7', 11', 15', 19', 23', 27', 31'-octamethyldotriaconta-2, 6, 10, 14, 18, 22, 26, 30-octadecanoate (melicopeprenoate) (2) and p-O-geranyl-7"-acetoxy coumaric acid (3). The compounds were isolated along with twenty-one other known compounds, lupeol (4), oleanolic acid (5), kokusaginine (6) genistein (7), p-O-geranyl coumaric acid (8), 4-stigmasten-3-one (9), 3beta-hydroxystigma-5-en-7-one (10) cis-phytyl palmitate (11), dodecane, dodecan-1-ol, ceryl alcohol, hentriacontanoic acid, eicosane, n-amyl alcohol, caprylic alcohol, octatriacontane, nonatriacontane, hexatriencontan-1-ol, methyl octacosanoate, beta-sitosterol, beta-sitosterol glucoside. Structures of all the compounds were established on the basis of MS and 1D and 2D NMR spectral data, as well as comparison with reported data. 相似文献
159.
We demonstrate that commercially available plasters (band aids), usually used for wound healing, can be electrolytically modified with a range of electro-catalytic metals for analytical sensing purposes. These 'Plaster-trodes' consist of a mesh type surface which have star-shaped type microelectrodes of ~150 micron radius in a hexagonal pattern which are separated from its nearest neighbours by ~1250 microns with interlinking connections between each microelectrode which are generally electrochemically active resulting in micro-band-type connections. Proof-of-concept is shown where the Plaster-trode is electrolytically modified with palladium for the sensing of hydrazine and nickel for the direct oxidation of ethanol. Given the low cost of the Plaster-trode which can be readily modified with electro-catalytic metals, we expect this new electrode to be widely utilised in electro-analysis. 相似文献
160.
In the present investigation we have presented the peristaltic flow of a linear Maxwell model through porous boundaries in
a porous medium. The governing non-dimensional partial differential are solved in wave frame by using regular perturbation
method and assumed form of solution. We have discussed the problem only for free pumping case. The effects of various physical
parameters involved in the problem have been investigated and shown graphically. 相似文献