Direct minimization of the energy functional in LCAO-MO density matrix formalism

A general theory is presented for the optimization of the coefficients of orbitals and configuration interaction expansion in the case of multiconfiguration wavefunctions containing all single excitations. The orbital coefficients are optimized by suitable orthogonal transformations of the atomic basis; the Cl coefficients are determined solving the usual secular problem. The energy minimization is performed directly by a gradient approach. The method works both for ground and excited states and no convergence difficulties are met. Computational examples are given for H₂O and H₂S molecules.     

Design of highly active heterogeneous palladium catalysts for the activation of aryl chlorides in Heck reactions

In situ generation of highly active palladium species by intermediate dissolution of Pd from solid supported catalysts has been demonstrated to be a very successful approach for the activation of aryl chlorides in Heck reactions. The new ‘heterogeneous’ Pd catalysts act as reservoir for molecular Pd species with unsaturated coordination sphere in solution. Crucial Pd leaching and re-deposition onto the support can be controlled by optimization of reaction conditions and by the properties of the catalysts. Pd is re-deposited onto the support at the end of the reaction. The catalysts, palladium supported on activated carbon, on various metal oxides or fluorides and Pd complexes in zeolites, are easy to prepare, though the preparation conditions are crucial. The catalysts convert all aryl bromides completely within minutes (TON 100,000). Aryl chlorides (even deactivated ones) are converted with high yields, within 2-6 h. The catalysts belong to the most active ones in Heck reactions at all (including best homogeneous systems) and fulfill all relevant requirements for practical applications in laboratory and industry.     

Biopolymer-metal complex wool-Pd as a highly active heterogeneous catalyst for Heck reaction in aqueous media

Heterogeneous palladium catalysts, a biopolymer complex wool-Pd, have been applied in water-mediated coupling reactions of aryl bromides without assistance of any phosphine ligands. The catalyst was characterized by XPS, ICP. The results showed that aryl bromides could carry out the coupling reaction with a variety of alkenes at 80 °C, in aqueous media under atmospheric condition. More importantly, the cheap catalyst is stable, which shows negligible metal leaching, and retain good activity for at least ten successive runs without any additional activation treatment. This approach would be very useful from a practical viewpoint.     

Fickian diffusion in glassy polymer-solvent systems

A free-volume theory is developed for the analysis of Fickian diffusion processes in glassy polymers. Equations are presented for the prediction of mutual diffusion coefficients in concentrated glassy polymer-penetrant systems. The concentration dependence of the mutual diffusion coefficient is dependent on how much free volume the solvent contributes to the system and on how the addition of solvent affects the densification of the polymer matrix. © 1992 John Wiley & Sons, Inc.     

Spectroscopic studies of tin ethyl etiopurpurin in homogeneous and heterogeneous systems

Tin ethyl etiopurpurin is a promising second generation photosensitizer for photodynamic treatment of cancer. This compound is only poorly soluble in aqueous media and, therefore, needs a delivery system for administration to animals. Successful tumor eradication has previously been reported, following light exposure of rats previously administered with the purpurin formulated as a Cremophor El emulsion, in dipalmitoyl—phosphatidyl—choline liposomes or with gamma cyclodextrins. In this paper, we describe some absorbance and fluorescence studies of tin ethyl etiopurpurin in homogeneous and heterogeneous systems. In general, absorption and emission maxima were found to be red shifted as the environment changed from polar to non-polar. The viscosity and dielectric constant of the medium affected the purpurin fluorescence intensity. The liposome preparations were characterized by particle size determination, differential scanning calorimetry and by sensitizer fluorescence quenching studies. Photobleaching studies also showed variation owing to changes in the environment in which the dye was located.     

Highly efficient C-H insertion reactions of hydrogen peroxide catalyzed by homogeneous and heterogeneous methyltrioxorhenium systems in ionic liquids

A convenient and efficient C-H insertion reaction of environment friendly H₂O₂ into representative hydrocarbon derivatives by homogeneous methyltrioxorhenium (MTO), heterogeneous poly(4-vinylpyridine)/methyltrioxorhenium (PVP/MTO) and microencapsulated polystyrene/methyltrioxorhenium (PS/MTO) systems in ionic liquids, is described. In some cases a higher activity was observed if compared with the same reaction in molecular solvents. The heterogeneous catalysts are stable systems under the reaction conditions and can be recycled for more transformations.     

The conjugation of ionic flows in the diffusion layers of electrodialysis systems

Fundamental regularities of the ion interference in diffusion layers of electrodialysis systems are revealed, as well as their effect on the electrical field strength, through which the ionic flows in their turn affect each other.     

Sevelamer as an efficient and reusable heterogeneous catalyst for the Knoevenagel reaction in water

A catalyst system of Sevelamer, a phosphate-binding drug, has been prepared and used in the Knoevenagel reaction of aromatic aldehydes in water to produce substituted electrophilic alkenes. The products were obtained in excellent yields. Several novel, related catalytic systems showed promising catalytic properties for aromatic and heterocyclic aldehydes. The Sevelamer catalyst can be recovered using simple filtration and reused numerous times（up to 15 times） in the aqueous Knoevenagel reaction without any significant lowering of activity.     

Some comments on diffusion in ternary systems

The diffusion coefficients in the ternary system NaCl (0.3 m)–NH₄Cl (0.3 m)–H₂O at 25° C have been measured. Some aspects of the diffusion equations for ternary systems are discussed within the range of applicability of the Gouy technique and based on the gravitational stability of free diffusion layers.     

Influence of concentration on the activation energy for diffusion in polymer-solvent systems

The self-diffusion of benzene, toluene, and ethylbenzene in polystyrene have been analyzed using the Vrentas/Duda free-volume diffusion model. Diffusion coefficient predictions suggest an exponential concentration dependence of the activation energy required to overcome attractive forces, E. Without the use of any diffusion data approximating E as zero over the entire concentration range yields self-diffusion coefficient predictions which are in good agreement with experimental data. © 1992 John Wiley & Sons, Inc.     

MCM-41 anchored sulfonic acid (MCM-41-R-SO3H): A mild, reusable and highly efficient heterogeneous catalyst for the Biginelli reaction

An efficient three-component synthesis of 3A-dihydropyrimidinones using MCM-41 anchored sulfonic acid (MCM-41-R-SO3H) as a mild, heterogeneous catalyst for Biginelli reaction in CH3CN under reflux condition is described.     

Recent developments in the application of nanoparticles prepared from w/o microemulsions in heterogeneous catalysis

This paper reviews the use of microemulsions, especially the water-in-oil (w/o) microemulsions, for preparation of nanoparticles that are employed as catalyst components in heterogeneous catalytic reactions. The objective is to show the growing interest of using microemulsions in the preparation of different types of materials such as metals, single metal oxides or mixed metal oxides with a broad range of application in heterogeneous catalysis and also in electrocatalysis. In most cases, the catalytic material showed improved catalytic properties as a result of the special synthesis environment created by the microemulsions. Still, research is needed for a better understanding of such beneficial effects. In addition, this method needs improvements in order to produce, in an environmentally friendly way, a suitable amount of material for use in industrial-scale catalytic processes.     

Silica supported perchloric acid(HClO4-SiO2):A mild,reusable and highly efficient heterogeneous catalyst for the synthesis of axidoalkyl naphthols

An efficient and direct procedure has been developed for the preparation of amidoalkyl naphthols by a one-pot condensation of aryl aldehydes,2-naphthol and urea or amides,in the presence of HClO4-SiO2 as a heterogeneous catalyst.The reactions were carried out under reflux and solvent-free conditions.The present methodology offers several advantages such as excellent yields,simple procedure,easy work-up and ecofriendly reaction condition.The catalystis easily prepared,stable,reusable and efficient under the reaction conditions.     

Gas diffusion in partially crystalline polymers part I: Concentration dependence

In this work, a phenomenological model for the gas diffusion in partially crystalline polymers using differential effective medium theory is presented. By making an analogy with the power law known as Archie's law which relates the d.c. conductivity of a brine saturated porous rock to its porosity; we show that gas diffusion through semicrystalline polymers can be described in a similar way. It is assumed that the diffusion coefficient in the crystalline region is zero, while in the amorphous region it is given by a free volume model, and an effective diffusion coefficient D^eff, is obtained using the mentioned analogy. The variation of D^eff upon concentration is analyzed through its free volume dependence. The crystallinity dependence is considered through an average chain immobilization factor 〈β〉 which is explicitely derived. Finally, the results of this model are compared with experimental data given by Kreituss and Frisch, obtaining a good agreement. © 1996 John Wiley & Sons, Inc.     

Application of highly sulfonated single-walled carbon nanotubes: An efficient heterogeneous catalyst for the one-pot synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes under solvent-free conditions

Highly sulfonated single-walled carbon nanotube-catalyzed synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes in excellent yields and very short reaction times. Sulfonated single-walled carbon nanotubes are prepared using a chemical and simple process and it characterized by Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, Thermal gravimetric analysis (TGA) and acid-base titration. The sulfonated single-walled carbon nanotube was easily separated by simple filtration and was recycled eight consecutive times without any loss in its activity.     

Employing Theories Far beyond Their Limits—The Case of the (Boguer‐) Beer–Lambert Law

For spectroscopists, the (Bouguer‐)Beer–Lambert law is unquestionably an essential principle, since it is inseparably linked with one of the most important quantities in spectroscopy, the absorbance. In spite of its importance, a quantitative discussion of the legitimacy of relating the transmittance, the quantity that is usually measured, to the absorbance by assuming a logarithmic relation between both quantities cannot be found in literature. In this contribution, we quantitatively discuss, based on examples, the errors that can be introduced by disregarding the exact solution based on Maxwell's equations and show that these errors can easily exceed one order of magnitude. We also re‐derive the Beer–Lambert law, thereby providing guidance as how to convert transmittance into absorbance properly.     

Orthogonal projection to latent structures solution properties for chemometrics and systems biology data

Partial least squares (PLS) is a widely used algorithm in the field of chemometrics. In calibration studies, a PLS variant called orthogonal projection to latent structures (O‐PLS) has been shown to successfully reduce the number of model components while maintaining good prediction accuracy, although no theoretical analysis exists demonstrating its applicability in this context. Using a discrete formulation of the linear mixture model known as Beer's law, we explicitly analyze O‐PLS solution properties for calibration data. We find that, in the absence of noise and for large n, O‐PLS solutions are simpler but just as accurate as PLS solutions for systems in which analyte and background concentrations are uncorrelated. However, the same is not true for the most general chemometric data in which correlations between the analyte and background concentrations are nonzero and pure profiles overlap. On the contrary, forcing the removal of orthogonal components may actually degrade interpretability of the model. This situation can also arise when the data are noisy and n is small, because O‐PLS may identify and model the noise as orthogonal when it is statistically uncorrelated with the analytes. For the types of data arising from systems biology studies, in which the number of response variables may be much greater than the number of observations, we show that O‐PLS is unlikely to discover orthogonal variation whether or not it exists. In this case, O‐PLS and PLS solutions are the same. Copyright © 2011 John Wiley & Sons, Ltd.     

MCM-41 anchored sulfonic acid （MCM-41-R-SO3H）： A mild,reusable and highly efficient heterogeneous catalyst for the Biginelli reaction

An efficient three-component synthesis of 3,4-dihydropyrimidinones using MCM-41 anchored sulfonic acid （MCM-41-R-SO3H） as a mild, heterogeneous catalyst for Biginelli reaction in CH3CN under reflux condition is described.     

Efficient dehydrative C-N bond formation using alcohols and amides in the presence of silica supported perchloric acid as a heterogeneous catalyst

Silica supported perchloric acid has been utilized as an efficient heterogeneous recyclable catalyst for N-alkylation of amides (sulfonamides and carboxamides) using alcohols (primary and secondary aliphatic as well as benzylic). The products are formed in high yields within 2-3 h.     

玻璃态PET的有序结构与解偏振光的记忆效应

聚合物的非晶态结构究竟是完全无序的 ,还是局部有序的 ,目前存在两种对立的学说 ,即 Flory的无规线团模型和 Yeh的两相球粒模型 [1] .Siegmann等 [2 ]在研究低于玻璃化转变温度 (Tg≈ 3 4 3 K)下的退火对 PET热谱 (DSC)中玻璃化转变的影响时发现 ,未经退火后的 PET在 Tg范围内仅表现出一个拐折 ,而在 3 2 7K退火时 ,随时间的增加 ,出现了类似于吸热峰的转变过程 ,并认为是由玻璃态中有序程度的增加所致 .本文通过解偏振光方法 (DLI)的研究发现 ,在玻璃态的 PET中确实存在着一定的有序结构 ,与晶态 PET中的有序结构不同的是 ,玻璃…