Highly enantioselective conjugate addition of thiols using mild scandium triflate catalysis

A Sc complex of (4S,5S)-diphenyl PYBOX 1 was found to serve as a catalyst for the asymmetric conjugate addition reactions between various thiols and 3-crotonoyl-2-oxazolidinone, affording the corresponding adducts in good yields and high enantioselectivies (up to 92% ee). A new improved method for making (4S,5S)-diphenyl PYBOX is presented.     

Studies of interactions between silane coupling agents and cellulose fibers with liquid and solid-state NMR

The hydrolysis of three alkoxy-silane coupling agents, gamma-methacryloxypropyl trimethoxy silane (MPS), gamma-aminopropyl triethoxy silane (APS), and gamma-diethylenetriaminopropyl trimethoxy silane (TAS), was carried out in ethanol/water solutions (80/20 w/w) at different pH values and followed by 1H, 13C and 29Si NMR spectroscopy. Acidic media were found to stabilize the hydrolyzed forms. As expected, the formation of silanol groups was followed by their self-condensation to generate oligomeric structures, yielding, ultimately, solid homopolycondensated structures, as analyzed by 29Si and 13C high-resolution solid-state NMR. Hydrolyzed MPS in acidic media was then successfully adsorbed onto a cellulose surface and the ensuing substrates submitted to thermal treatment at 110-120 degrees C under reduced pressure, in order to create covalent bonds between cellulose and the coupling agent.     

Further investigation of the mechanism of Doxorubicin release from P105 micelles using kinetic models

The kinetics of the release of Doxorubicin from Pluronic P105 micelles during ultrasonication and its subsequent re-encapsulation upon cessation of insonation were investigated. Four mechanisms are proposed to explain the acoustically-triggered Doxorubicin (Dox) release and re-encapsulation from Pluronic P105 micelles. The four mechanisms are: micelle destruction; destruction of cavitating nuclei; reassembly of micelles, and the re-encapsulation of Dox. The first mechanism, the destruction of micelles during insonation, causes the release of Dox into solution. The micelles are destroyed because of cavitation events produced by collapsing nuclei, or bubbles in the insonated solution. The second mechanism, the slow destruction of cavitating nuclei, results in a slow partial recovery phase, when a small amount of Dox is re-encapsulated. The third and fourth mechanisms, the reassembly of micelles and the re-encapsulatin of Dox, are independent of ultrasound. These two mechanism are responsible for maintaining the drug release at a partial level, and for recovery after insonation ceases. A normal distribution was used to describe micellar size. Parameters for the model were determined based upon the best observed fit to experimental data. The resulting model provides a good approximation to experimental data for the release of Dox from Pluronic P105 micelles.     

Mössbauer spectroscopy of Al substituted Fe in holmium iron garnet

A Mössbauer spectroscopy study was made on Ho₃Fe_5-xAl_xO₁₂ (x=0.0, 0.05, 0.7). X‐ray diffraction patterns indicate that the samples with x=0.0 and 0.05 have the garnet structure, while the sample with x=0.7 has an additional noncubic structural phase. The room temperature spectrum for samples with x=0.0 and 0.05 consists of two magnetic components corresponding to the octahedral and tetrahedral sites with hyperfine magnetic fields (B_hf) of 50 T and 40 T, respectively. For x=0.7 we observe a new magnetic component with B_hf= 45 T, a reduction in the intensity and broadening of the tetrahedral component, and the evolution of a nonmagnetic central component. These variations are evidently due to the addition of aluminium to the system. At liquid nitrogen temperature the samples with x=0.0 and 0.05 are nearly identical. It was also observed that the increase in B_hf for the octahedral site is smaller than that for the tetrahedral site as the temperature is lowered to 80 K.     

Thiophenylhydrazonoacetates in heterocyclic synthesis

Benzo[b]thiophen-2-yl-hydrazonoesters 4 were synthesized by coupling of 2-diazo-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carboxamide ( 1 ) with either ethyl cyanoacetate or ethyl acetoacetate. The reactivity of 4 toward a variety of nitrogen nucleophiles was investigated to yield pyrazole, isoxazole, pyrimidine, triazine, pyrazolopyridine, and pyrazolopyrimidine derivatives. © 2003 Wiley Periodicals, Inc. 15:15–20, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/.hc10205     

A New Generator of Probability Models: The Exponentiated Sine-G Family for Lifetime Studies

In this article, we propose the exponentiated sine-generated family of distributions. Some important properties are demonstrated, such as the series representation of the probability density function, quantile function, moments, stress-strength reliability, and Rényi entropy. A particular member, called the exponentiated sine Weibull distribution, is highlighted; we analyze its skewness and kurtosis, moments, quantile function, residual mean and reversed mean residual life functions, order statistics, and extreme value distributions. Maximum likelihood estimation and Bayes estimation under the square error loss function are considered. Simulation studies are used to assess the techniques, and their performance gives satisfactory results as discussed by the mean square error, confidence intervals, and coverage probabilities of the estimates. The stress-strength reliability parameter of the exponentiated sine Weibull model is derived and estimated by the maximum likelihood estimation method. Also, nonparametric bootstrap techniques are used to approximate the confidence interval of the reliability parameter. A simulation is conducted to examine the mean square error, standard deviations, confidence intervals, and coverage probabilities of the reliability parameter. Finally, three real applications of the exponentiated sine Weibull model are provided. One of them considers stress-strength data.     

Unprecedented Biodegradable Cellulose-Derived Polyesters with Pendant Citronellol Moieties: From Monomer Synthesis to Enzymatic Degradation

Levoglucosenone (LGO) is a cellulose-derived molecule that is present commercially on a multi-ton/year scale. Taking advantage of the α,β-conjugated ketone of LGO, a new citronellol-containing 5-membered lactone (HBO-citro) was synthesized through a one-pot two-step pathway involving oxa-Michael addition and Baeyer-Villiger oxidation. The solvent-free treatment of HBO-citro with NaBH₄ at room temperature led to the full reduction of the lactone moiety which gave a novel fully renewable triol monomer having a citronellol side chain (Triol-citro). Noticeably, by simply changing the reducing agent, temperature and reaction duration, the partial reduction of HBO-citro can be achieved to yield a mixture of 5- and 6-membered Lactol-citro molecules. Triol-citro was chosen to prepare functional renewable polyesters having citronellol pendant chains via polycondensation reactions with diacyl chlorides having different chain lengths. Good thermal stability (T_d5% up to 170 °C) and low glass transition temperatures (as low as −42 °C) were registered for the polyesters obtained. The polymers were then hydrolyzed using a commercial lipase from Thermomyces lanuginosus (Lipopan^® 50 BG) to assess their biodegradability. A higher degradation profile was found for the polyesters prepared using co-monomers (acyl chlorides) having longer chain lengths. This is likely due to the decreased steric hindrance around the ester bonds which allowed enhanced accessibility of the enzyme.     

Magnetocaloric properties in the Cr-doped La0.7Sr0.3MnO3 manganites

Single-phase polycrystalline samples of La_0.7Sr_0.3Mn_1-xCr_xO₃ with nominal composition of x=0.00, 0.20, 0.40 and 0.50 were prepared by a conventional solid-state reaction method in air. Investigations of magnetization were carried out in the temperature range 5-400 K and magnetic field range 0-8 T. It was found that the Curie temperature T_C decreases with increasing x and the maximum magnetic entropy change (−ΔS_M) for x=0.20 is ∼1.203 and ∼2.653 J/kg K, respectively for 2 and 6 T magnetic field near the temperature of 280 K.