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931.
A novel pentacyclic saturated sesterpene condensed with hydroxyhydroquinone moiety, which we named disidein (1), has been isolated from the marine sponge Disidea pallescens as disulfate sodium calcium salt. A minor accompaining compound, which seems a likely precursor of disidein, has been identified as 2-pentaprenylbenzoquinone (7). 相似文献
932.
The reaction between mercury(II) chloride and azoles(pyrazole, 3,5-dimethylpyrazole, benzotriazole, 1,2,4-triazole) afforded mainly N-chloro mercury derivatives, although other reactions, such as the well known ring mercuration or the formation of a complex, were observed simultaneously. Therefore, no simple generalization explains the observed reactivity of azoles towards mercury(II) chloride, each reaction investigated being a different case. 相似文献
933.
Luca Brandolini Alex Iosevich Giancarlo Travaglini 《Journal of Fourier Analysis and Applications》2001,7(4):359-372
Let Γ be a smooth compact convex planar curve with arc length dm and let dσ=ψ dm where ψ is a cutoff function. For Θ∈SO (2)
set σΘ(E) = σ(ΘE) for any measurable planar set E. Then, for suitable functions f in ℝ2, the inequality.
represents an average over rotations, of the Stein-Tomas restriction phenomenon. We obtain best possible indices for the
above inequality when Γ is any convex curve and under various geometric assumptions. 相似文献
934.
The capacitated Economic Order Quantity problem (capacitated EOQ) is a well-known problem where products have to be shipped between two points with a vehicle of given capacity. Each shipment has a fixed cost, independent of the shipped quantity, and an inventory cost is generated in the two points. The problem consists in finding the optimal time between consecutive shipments, which minimizes the total cost. The problem is a capacitated variant of the EOQ problem and has a closed form solution. Since such solution is often irrational, it is often rounded to an integer value. In this paper we investigate the errors which are generated by rounding procedures to integer and powers-of-two values. We show that, although in the worst case a tight general relative error of 2 is generated by all the considered rounding procedures, the procedure which rounds to the best between the lower and upper values (integer or powers-of-two) has a performance of $\frac{1}{2}$ ( $\sqrt 2 + 1/\sqrt 2 $ )≈1.06 on classes of instances of high practical relevance. 相似文献
935.
In this note, we show that if is a positive integer satisfying the congruence , then .
936.
Sadow AD Haller I Fadini L Togni A 《Journal of the American Chemical Society》2004,126(45):14704-14705
The dicationic Ni(II) complex [Ni(Pigiphos)(THF)](ClO4)2, [1](ClO4)2 ((R)-(S)-Pigiphos = bis-{(R)-1-[(S)-2-(diphenylphosphino)ferrocenyl]ethyl}cyclohexylphosphine), catalyzes the addition of bulky aliphatic secondary phosphines to methaacrylonitrile. This hydrophosphination reaction reaches TON = 900 and enantioselectivities up to 94%. A catalytic cycle involving 1,4-conjugate addition of R2PH to methacrylonitrile is supported by the isolation and characterization of a catalytically active N-coordinated, methacrylonitrile Ni complex. 相似文献
937.
Bernardi L Bonini BF Capito E Dessole G Comes-Franchini M Fochi M Ricci A 《The Journal of organic chemistry》2004,69(23):8168-8171
A nitrogen-containing superbase such as TMG was found to be an effective catalyst for the reaction between N-diphenylphosphinoyl imines and nitroalkanes. Exploiting a protocol that avoids the use of any solvent also during workup procedure, we synthesized a series of beta-nitroamines in excellent yields and high diastereomeric ratios. These results, combined with the capability of the indium in conjunction with Zn as the stoichiometric reducing agent to perform in aqueous medium reduction of the nitro group under mild reaction conditions, led us to devise a three-step, one-pot synthesis of a range of 1,2-diamines, making use of environmentally friendly procedures in the various steps. 相似文献
938.
By doping CoSb(3) with Sn, Ba, and La, several structural outcomes are possible. The effect these different structures have on the electronic transport properties of the resulting materials is evaluated by means of an ab initio electronic structure approach and by using the semiclassical Boltzmann theory to derive the electronic transport properties from the band structure. It is shown that the calculated Seebeck coefficient is a very useful indicator of both the actual content of the dopant element and of where it mainly locates into the CoSb(3) structure. The use of such an indicator, along with geometrical considerations, demonstrates that the Sn atom occupies both the interstitial and the pnicogen ring positions with relative occupancies and ensuing thermoelectric properties, which heavily depend on the synthesis' conditions. The same indicator also suggests that the La atom, which occupies only interstitial positions, has a far lower maximal solubility in CoSb(3) than that claimed experimentally. 相似文献
939.
Carru C Zinellu A Sotgia S Serra R Usai MF Pintus GF Pes GM Deiana L 《Biomedical chromatography : BMC》2004,18(6):360-366
Neopterin, a pyrazinopyrimidine compound, serves as a marker of cellular immune system activation, and it can be used as a prognostic predictor for certain types of diseases. We propose a new simple HPLC method to measure serum neopterin with highly sensitive fluorimetric detection. After TCA serum protein precipitation, the supernatant was diluted five times, injected into a C18 reversed-phase column and eluted at a flow rate of 1.5 mL/min by an isocratic water-acetonitrile (99:1) mobile phase. The natural fluorescence of the molecule was detected at excitation wavelength 353 nm and emission 438 nm. In these conditions the neopterin retention time was about 4 min. Our proposed method was compared with a validated chromatographic separation, and the obtained data of the serum neopterin from 35 healthy volunteers were analysed by Passing-Bablok regression and Bland-Altman test. Neopterin measurement in healthy subjects was also employed to investigate on its potential relationships with plasma thiols levels. 相似文献
940.