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81.
82.
The reaction of [Cp*MCl4] (M = Nb, Ta; Cp* = C5Me5) with PH2R in toluene at room temperature gives the primary phosphine complexes [Cp*MCl4(PH2R)] [Cp* = C5Me5; M = Nb: R = But ( 1a ), Ad ( 2a ), Cy ( 3a ), Ph ( 4a ), 2, 4, 6‐Me3C6H2 (Mes) ( 5a ); M = Ta: R = But ( 1b ), Ad ( 2b ), Cy ( 3b ), Ph ( 4b ), Mes ( 5b )] in high yield. 1—5 were characterized spectroscopically (NMR, IR, MS) and by crystal structure determinations. The starting material [Cp*TaCl4] is monomeric in the solid state, as shown by crystal structure determination. 相似文献
83.
Matthias Stender Hannes Oesen Steffen Blaurock Evamarie Hey‐Hawkins 《无机化学与普通化学杂志》2001,627(5):980-984
Synthesis and Molecular Structure of [{Cp′(μ‐η1 : η5‐C5H3Me)Mo(μ‐AlRH)}2] (Cp′ = C5H4Me, R = iBu, Et) [Cp′2MoH2] reacts with HAlR2 to give [{Cp′(μ‐η1 : η5‐C5H3Me)Mo(μ‐AlRH)}2] (Cp′ = C5H4Me, R = iBu ( 1 ), Et ( 2 )). Crystal structure determinations were carried out on [Cp′2MoH2] and 1 . 1 exhibits a direct Mo–Al bond (2.636(2) Å). 相似文献
84.
Insertion and Substitution Reaction of Methyl Formate with [Cp′2ZrCl(PHTipp)] – Molecular Structure of meso‐trans ‐[Cp′2ZrCl{OCH(PHTipp)2}] (Cp′ = η5‐C5MeH4, Tipp = 2,4,6‐Pri3C6H2) [Cp′2ZrCl(PHTipp)] ( 1 ) (Cp′ = η5‐C5MeH4, Tipp = 2,4,6‐Pri3C6H2) reacts with methyl formate with insertion and substitution to give [Cp′2ZrCl{OCH(PHTipp)2}] ( 2 ). 2 was characterized spectroscopically (1H, 31P NMR, IR, MS) and by X‐ray structure determination. Only the meso‐trans isomer is present in the solid state. 相似文献
85.
Assessing model fit by cross-validation 总被引:8,自引:0,他引:8
Hawkins DM Basak SC Mills D 《Journal of chemical information and computer sciences》2003,43(2):579-586
When QSAR models are fitted, it is important to validate any fitted model-to check that it is plausible that its predictions will carry over to fresh data not used in the model fitting exercise. There are two standard ways of doing this-using a separate hold-out test sample and the computationally much more burdensome leave-one-out cross-validation in which the entire pool of available compounds is used both to fit the model and to assess its validity. We show by theoretical argument and empiric study of a large QSAR data set that when the available sample size is small-in the dozens or scores rather than the hundreds, holding a portion of it back for testing is wasteful, and that it is much better to use cross-validation, but ensure that this is done properly. 相似文献
86.
Ribière P Bravo-Altamirano K Antczak MI Hawkins JD Montchamp JL 《The Journal of organic chemistry》2005,70(10):4064-4072
[reaction: see text] A new nickel-based catalytic system has been developed for phosphorus-carbon bond formation. The addition of alkyl phosphinates to alkynes is catalyzed by nickel chloride in the absence of added ligand. The reaction generally proceeds in high yields, even with internal alkynes, which were poor substrates in our previously reported palladium-catalyzed hydrophosphinylation of alkyl phosphinates. The method is useful for the preparation of H-phosphinate esters and their derivatives. The one-pot synthesis of various important organophosphorus compounds is also demonstrated. The reaction can be conducted with microwave heating. 相似文献
87.
Cold preservation of endothelial cells was studied, comparing primary endothelial cells (human umbilical vein endothelial cells - HUVECs) and a continuously growing cell line (ECV304 cells). Viability at the end of 24h cold preservation was measured by dye exclusion, whilst metabolism was assessed by Alamar blue conversion. Two preservation solutions were studied (UW solution) and sucrose-based (SbS) in both cell types. The response was similar in both cell types to preservation under normoxic conditions (with percentage dye exclusion maintained at about 80 percent in both preservation solutions) whereas under hypoxic conditions ECV304 were more sensitive to preservation in UW solution (dye exclusion reduced to 43.5+/-1.4 percent versus 73.6+/-14 percent (P<0.01). Metabolism assessed by Alamar blue conversion after cold preservation and rewarming was similar in both ECV304 and HUVECs after storage under normoxic conditions in UW solution, but in both cell types, metabolism was higher in SbS (P<0.05 and p<0.01) than in UW solution. Under hypoxic conditions, both cell types showed similar recovery of metabolism after storage in either UW or SbS. If the cells (in this case ECV304 under aerobic conditions) were stored for 24h and then allowed to rewarm in either of the respective preservation solutions (UW or SbS for 1h) before the Alamar blue test, metabolism was higher (p less than 0.01) in those exposed to SbS. UW solution and SbS provide similar protection for endothelial cells under hypoxic conditions, but SbS has some advantages under normoxic storage or if the cells experience variable temperatures in the presence of residual preservation solution at the end of cold preservation period. 相似文献
88.
89.
90.
Thomas Hawkins 《Historia Mathematica》1975,2(1):1-29
It is well-known that Cauchy (1829) provided the first general proof that the eigenvalues of a symmetric matrix are real. Furthermore, Cauchy's paper initiated the developments that resulted in the creation of a substantial spectral theory of matrices by the early 1870's. The following essay relates Cauchy's work and its historical significance to the consideration of eigenvalue problems during the 18th century. 相似文献