A comprehensive laboratory experiment suitable for advanced undergraduate organic chemistry students has been designed. The experiment is based on the dienone-phenol rearrangement reaction of the sesquiterpene santonin to give -desmotroposantonin acetate. It challenges students to solve an earlier controversial stereochemical problem. The students carry out the reaction and analyze spectroscopic data to determine the stereochemistry of the starting material and the product. In addition, they perform simple molecular modeling calculations, which enable them to rationalize the stereochemical outcome of the transformation and discuss the mechanism of the dienone-phenol rearrangement and related rearrangements reported in the literature. 相似文献
The crystal structure of Nd[Fe(CN)6]·4H2O has been refined by Rietveld analysis using high resolution synchrotron powder X-ray diffraction data. It belonged to the orthorhombic crystal system, Cmcm space group, with cell parameters: , and . The change in space group from P63/m which is observed in the pentahydrates (LnFe(CN)6·5H2O) to Cmcm in the tetrahydrates has been analyzed to be a consequence of the change in 9-fold coordination of Nd3+ in the pentahydrates to 8-fold coordination in the tetrahydrates, which changes the Nd3+ environment from tricapped trigonal prism to a distorted tricapped trigonal prism or square antiprism. Its decomposition process in air to produce NdFeO3 has been followed by thermogravimetric and differential thermal analysis, IR spectroscopy and laboratory powder XRD. We found that it is possible to synthesize crystalline NdFeO3 at temperatures as low as 380 °C and refine the structure of single phase crystalline NdFeO3 synthesized by this method at 600 °C. 相似文献
Differential scanning calorimetry (DSC), isothermal stress testing–Fourier transform infrared spectroscopy (IST–FTIR), isothermal stress testing–high-performance liquid chromatography, and powder X-ray diffraction (PDRX) were used as screening techniques for assessing the compatibility of tobramycin with some currently employed ophthalmic excipients. In the first phase of the study, DSC was used as a tool to detect any interaction. The absolute value of the difference between the enthalpy of the pure tobramycin melting peak and that of its melting peak in the different analyzed mixtures was chosen as a parameter of the drug–excipient interaction degree. DSC results demonstrated that benzalkonium chloride, monobasic sodium phosphate, boric acid, edetate disodium, sodium metabisulfite, thimerosal, and potassium sorbate interact with tobramycin. Taking into account these results, it could be suggested that some of the changes observed in the IST–FTIR spectra of binary blends of tobramycin and some of the excipients would account for a possible interaction between the mixture component. In this study, PDRX did not provide much information, since only tobramycin–thimerosal interactions could be detected. DSC and IST–FTIR are suitable and simple methods for the detection of potential incompatibilities between active pharmaceutical ingredient (API) and excipients.
Simple and efficient route to the title compounds by using diethyl aluminium cyanide in benzene for the epoxide ring opening and the electrophilic assistance of LiCIO4 during the isomerization-elimination process. 相似文献
Heat capacity measurements have been made down to 5 mK for 3He fluid films adsorbed in one-dimensional (1D) nanometer-scale pores, 28 A in diameter, preplated with 4He of 1.47 atomic layers. At low 3He density, the heat capacity shows a density-dependent, Schottky-like peak near 150 mK asymptoting to the value corresponding to a 2D Boltzmann gas at high temperatures. The peak behavior is attributed to the crossover from a 2D gas to a 1D state at low temperatures. The degenerate state of the 1D 3He fluid is indicated by a predominantly linear temperature dependence below about 30 mK. 相似文献
A solid-phase extraction methodology, followed by high-performance liquid chromatography (HPLC) quantification with UV absorbance
detection (λ=267 nm), was developed in order to study the stability of 3′-azido-3′-deoxy-5′-O-isonicotinoylthymidine (AZT-Iso), a novel derivative of the antiretroviral AZT, in different matrixes. The half-lives (t1/2) for AZT-Iso were 1.19, 1.13 and 0.30 h for human, rat and rabbit plasma, respectively, and 14.91 and 25.49 h for potassium
phosphate buffer (pH 7.4) and human serum albumin solution, respectively. The HPLC method proved to be selective, sensitive
and accurate. Good recovery, linearity and precision were achieved using p-fluorophenol as an internal standard. The validity of this method was tested using synthetic mixtures of the intact drug
with its decomposition products. In conclusion, the method presented is applicable to in vivo pharmacokinetics studies of
AZT-Iso in rats. 相似文献
We report Monte Carlo simulations of the solvation pressure between two planar surfaces, which represent the interface of spherical silica nanoparticles in supercritical carbon dioxide. Carbon dioxide (CO2) was modeled as an atomistic dumbbell or a spherical Lennard-Jones particle. The interaction between CO2 molecules and silica surfaces was characterized by the standard Steele potential with energetic heterogeneities representing the hydrogen bonds. The parameters for the solid-fluid interaction potentials were obtained by fitting our simulations to the experimental isotherms of CO2 sorption on mesoporous siliceous materials. We studied the dependence of the solvation force on the distance between planar silica surfaces at T = 318 K, at equilibrium bulk pressures p(bulk) ranging from 69 to 200 atm. At 69 atm, we observed a long-range attraction between the two surfaces, and it vanished when the pressure was increased to 102 and then 200 atm. The results obtained with different fluid models were consistent with each other. According to our observations, energetic heterogeneities of the surface have negligible influence on the solvation pressure. Using the Derjaguin approximation, we calculated the solvation forces between spherical silica nanoparticles in supercritical CO2 from the solvation pressures between the planar surfaces. 相似文献
In this paper, the numerical treatment of magnetic loss of NiZn, MnZn, Ni2Y, and NiZnCu ferrite and their composites, by using Krameres-Kronig relations, is investigated. The complex magnetic permeability spectra for ferromagnetic materials have been studied. Due to the principle of causality and time independence in the relation between magnetic induction B and magnetic field H, the real and the imaginary part of the complex magnetic permeability are mutually dependent, and the correlation is given by the Krameres-Kronig equations. Through them, it is possible to measure the real component of the complex magnetic permeability, assuming the real component is given, and by the Hilbert transform, the imaginary part of the magnetic permeability can be calculated. Magnetic circuit model has been studied theoretically, focusing on the model's poles in the complex plane to verify the principle of causality and the temporary independence. 相似文献
In this paper we study integral operators of the form
1 + ... + m = n. We obtain the Lp(w) boundedness for them, and a weighted (1, 1) inequality for weights w in Ap satisfying that there exists c 1 such that w(aix) cw(x) for a.e. xn, 1 im. Moreover, we prove
for a wide family of functions fL (n).Partially supported by CONICET, Agencia Cordoba Ciencia and SECYT-UNC. 相似文献