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131.
Irvine Masson P. V. Dupré Orme Masson R. W. Roberts und A. Fraser 《Fresenius' Journal of Analytical Chemistry》1911,50(12):765-767
Ohne Zusammenfassung 相似文献
132.
133.
Richard D Chambers Darren HollingGraham Sandford Horst PuschmannJudith A.K Howard 《Journal of fluorine chemistry》2002,117(2):99-101
Direct fluorination of various quinoline derivatives in acidic reaction media gives fluorinated quinoline products arising from selective, efficient electrophilic substitution processes. 相似文献
134.
Philip J. Bailey Dr. Laura Budd Dr. Filipa A. Cavaco Simon Parsons Prof. Felix Rudolphi Alejandro Sanchez‐Perucha Dr. Fraser J. White Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(9):2819-2829
The dimethylamine in the adducts [(HNMe2)B(azolyl)3] (azolyl=methimazolyl, pyrazolyl), obtained by reaction of the azole with B(NMe2)3, can readily be substituted with a range of nitrogen donors to provide new charge‐neutral, tripodal ligands in high yield. This observation has led to a revision of an earlier interpretation of the mechanism of the formation of these species. The donor properties of the ligands [(nmi)B(azolyl)3] (nmi=N‐methylimidazole) have been compared with their anionic analogues [HB(azolyl)3]? by synthesis of their manganese(I)–tricarbonyl complexes and comparison of their infrared νCO energies. This comparison indicates that the new neutral ligands are only marginally weaker donors than the corresponding anionic hydrotris(azolyl)borate ligands. This may be explained by the ability of the attached nmi ring to stabilize a positive charge remotely from the coordinated metal, which may also account for the fact that the [(nmi)B(pyrazolyl)3] ligand is a substantially stronger donor than the similarly neutral tris(pyrazolyl)methane ligand. 相似文献
135.
Cangelosi VM Carter TG Crossland JL Zakharov LN Johnson DW 《Inorganic chemistry》2010,49(21):9985-9992
A series of Group 15-containing homometallic (E(2)L(3), E = P, As, Sb, Bi) and heterometallic (AsSbL(3), AsBiL(3), PSbL(3)) supramolecular cryptands were prepared by the self-assembly of pnictogen halides with dithiolate ligand or by direct transmetalation from a heavier congener. Structural characterization by single crystal X-ray diffraction shows that the E-S bond distances and S-E-S bond angles are significantly affected by the identity of the pnictogen. (1)H NMR spectroscopy reveals that the homometallic cryptands are dynamic in solution: surprisingly one ligand "flips", perturbing the C(3) symmetry of the complex and giving a new asymmetric conformer. Density functional theory calculations were carried out on both the symmetric and the asymmetric conformations of the cryptands, and the energies were compared to those observed by NMR spectroscopy. It was found that the relative stability of the asymmetric cryptand to its symmetric conformer increases with increasing size of the Group 15 element. Finally, it is reported that if two metals are present during the self-assembly process, heterometallic cryptands form. These supramolecular cryptands are reminiscent of their organic analogues, but result from a self-assembly process rather than a stepwise synthesis. Surprisingly, they possess conformational isomerism and exhibit dynamic transmetalation in their reactivity which provides access to otherwise unattainable assemblies. 相似文献
136.
Catechol derivatives directly bonded to all-carbon quaternary stereocentres are prevalent in nature. An oxidative coupling strategy for the synthesis of this motif is described. Pivoting on the base-catalysed Michael addition of carbon-centred pro-nucleophiles to in situ generated ortho-benzoquinones, the method is broad in scope, high yielding and provides remarkably simple access to this challenging motif. The application of this methodology in the total synthesis of the crinane-type amaryllidaceae alkaloids (±)-powelline and (±)-buphanidrine is demonstrated and our efforts towards an enantioselective synthesis described. 相似文献
137.
Ghosh S Carty D Clarke SP Corr SA Tekoriute R Gun'ko YK Brougham DF 《Physical chemistry chemical physics : PCCP》2010,12(42):14009-14016
We report the physico-chemical characterisation of fatty acid stabilised aqueous magnetic fluids, which are ideal systems for studying the influence of nanoparticle aggregation on the emergent magnetic resonance properties of the suspensions. Stable colloids of superparamagnetic magnetite, Fe(3)O(4), nanoparticle clusters in the 80 to 100 nm size range were produced by in situ nanoparticle growth and stabilisation, and by suspending pre-formed nanoparticles. NMR relaxation analysis shows that the magnetic resonance properties of the two types of suspension differ substantially and provides new insights into how the relaxation mechanisms are determined by the organisation of the nanoparticles within the clusters. 相似文献
138.
Güneş Y Polat MF Sahin E Fleming FF Altundas R 《The Journal of organic chemistry》2010,75(21):7092-7098
Quaternary oxonitriles are stereoselectively generated from the union of five-, six-, and seven-membered 2-chloroalkenecarbonitriles with chiral alcohols via a Claisen rearrangement. The strategy rests on a new conjugate addition-elimination of allylic alkoxides to 2-chlorocycloalkenecarbonitriles to afford substituted 2-alkoxyalkenenitriles. Subsequent thermolysis unmasks a cyclic oxonitrile while selectively forming a new quaternary center with enantiomeric ratios typically greater than 9:1. The overall alkylation strategy addresses the challenge of enantioselectively generating hindered, quaternary centers while simultaneously installing ketone, nitrile, and olefin functionalities. 相似文献
139.
The setting of analytical quality specifications in laboratory medicine has attracted attention for many years. Over time,
many strategies were advocated and all had advantages and disadvantages. In the final decade of the last millennium, considerable
confusion existed on how to define analytical quality specifications correctly and how to apply them in everyday practice.
This led to wide professional interest. In 1999, a consensus conference sponsored by IUPAC, IFCC and WHO was held in Stockholm
on “Strategies to Set Global Analytical Quality Specifications in Laboratory Medicine”. The consensus set useful and well-documented
strategies for the setting of analytical quality specifications into a hierarchy with the best strategy at the highest level,
namely, (1) Evaluation of the effect of analytical performance on clinical outcomes in specific clinical situations, (2) Evaluation
of the effect of analytical performance on clinical decisions in general, (3) Published professional recommendations, (4)
Performance goals set by regulatory bodies and EQAS organisers, and (5) Goals based on the current state of the art. Much success has been achieved since the promulgation of the statement with the approach being adopted by many in laboratory
medicine for a very wide variety of purposes, particularly in quality management. However, there is a requirement for additional
investigation of, inter alia, quality specifications for examinations done on measurements performed on ordinal and nominal scales, pre-analytical factors
and matrix effects, examinations done as POCT, target values of control materials, and ways in which analytical quality specifications
can be used both to set what is the optimum performance and as a tool for assessment of everyday practice. 相似文献
140.
Rand DA Shaw SE Ochoa JR Ripin DJ Taylor A Fan TY Martin H Hawes S Zhang J Sarkisyan S Wilson E Lundquist P 《Optics letters》2011,36(3):340-342
A cryogenic Yb amplifier using two laser materials, Gd3Sc2Al3O12 and Y3Al5O12 (YAG), has been used to obtain 70 W average power at 5 kHz pulse repetition frequency; the output was compressed to 1.6 ps, compared with an input compressible to 1.4 ps. The gain broadening obtained by combining two media enables shorter pulses than using Yb:YAG alone but retains the power-scaling advantages of cryogenic Yb:YAG. 相似文献