Modelling the fractionation process in TREF systems: Thermodynamic simple approach

A simple thermodynamic model, based on an extension of Flory-Huggins theory, is applied to temperature rising elution fractionation (TREF). Dependence of the fractionation process on melting temperature, melting enthalpy, average crystallinity, average crystallizable sequence length, and polymer-solvent interaction parameter is predicted. Results from the model fit experimental TREF data, and correctly predict number-average branch points for TREF fractions. © 1995 John Wiley & Sons, Inc.     

Hydrogen Bonds, Tautomers, and Conformation in 2-Hydroxyphenyl 2-hydroxy-2-(β-naphthyl)vinyl Ketone

Single crystal X-ray diffraction and IR spectroscopy have been used to study the conformation of 2-hydroxyphenyl 2-hydroxy-2-(-naphthyl)vinyl ketone in solid state. It was found that one of the two possible enol tautomeric forms is stabilized in the crystal. The 1-hydroxy-3-oxo-1,3-propenylene moiety, O=C—CH=C—OH, shows a strong intramolecular H bond with a definite character of reasonance-assisted hydrogen bond in spite of being in competition with ring intermolecular hydrogen bonds. The comparison of the present results with solution NMR data indicates that the molecular geometry in solid state and in solution are similar.     

Scope of the formal [3+2] cycloaddition for the synthesis of substituted 3-arylindanes and related compounds

We report the single step synthesis of several 3-arylindanes and related compounds via a formal [3+2] cycloaddition. A study of the influence of the aromatic ring substitution pattern on the reaction was carried out.     

Internal pressure and cohesive energy density for binary non-electrolyte mixtures

Internal pressures and cohesive energy densities of binary liquid mixtures of n-pentane+dichloromethane, n-pentane+methylacetate, 2-propanol+methylacetate and n-bytylamine+1,4-dioxane at 25°C have been evaluated from molar volumes surface tensions and enthalpies. The data obtained provide information about interactions in the binary liquid mixtures which can be correlated with results from other thermodynamic properties.Presented at the VI Congreso Argentino de Fisicoquímica, Santiago del Estero, Argentina, 1989.     

Ultrasound Assisted Pictet–Spengler Synthesis of Tetrahydro‐β‐Carboline Derivatives

The synthesis of twelve tetrahydro‐β‐carboline derivatives 3a , 3b , 3c , 3d , 3e , 3f , 3g , 3h , 3i , 3j , 3k , 3l prepared via the Pictet–Spengler reaction is described. The reaction of tryptamine and a variety of arylaldehydes were carried out under ultrasonic irradiation and trifluoracetic acid catalysis at room temperature. These tetrahydro‐β‐carbolines have been synthesized in higher yields and shorter reaction times compared to the conventional method. Moreover, the reaction proceeded successfully even employing arylaldehydes with electron‐donating or electron‐attracting substituents which did not react under conventional method.     

3α‐Hydroxytirucalla‐7,24‐dien‐21‐oic acid: a triterpene from Protium crenatum Sandwith

The crystal structure of the title compound, C₃₀H₄₈O₃, a triterpene extracted from the resin of Protium crenatum Sandwith, is reported. The aliphatic acidic side chain is attached to the tirucallene four‐ring system on its α‐face and is extended by 7.248 (5) Å in the `left‐hand' orientation.     

On the existence of weak solutions of anisotropic generally restrained plates

This paper presents investigations of free vibration of anisotropic plates of different geometrical shapes and generally restrained boundaries. The existence and uniqueness of weak solutions of boundary value problems and eigenvalue problems which correspond to the statical and dynamical behaviour of the mentioned plates is demonstrated. It is determined that when the plates have corner points formed by the intersection of edges free or elastically restrained against translation, the corresponding bilinear forms maintain the V – ellipticity property.     

On Second-Order Optimality Conditions for Vector Optimization

In this article, two second-order constraint qualifications for the vector optimization problem are introduced, that come from first-order constraint qualifications, originally devised for the scalar case. The first is based on the classical feasible arc constraint qualification, proposed by Kuhn and Tucker (Proceedings of the Second Berkeley Symposium on Mathematical Statistics and Probability, vol. 1, pp. 481–492, University of California Press, California, 1951) together with a slight modification of McCormick’s second-order constraint qualification. The second—the constant rank constraint qualification—was introduced by Janin (Math. Program. Stud. 21:110–126, 1984). They are used to establish two second-order necessary conditions for the vector optimization problem, with general nonlinear constraints, without any convexity assumption.     

Nanoscale characterization of zein self-assembly

Zein, a major protein of corn, is rich in α-helical structure. It has an amphiphilic character and is capable of self-assembly. Zein can self-assemble into various mesostructures that may find applications in food, agricultural, and biomedical engineering. Understanding the mechanism of zein self-assembly at the nanoscale is important for further development of zein structures. In this work, high-resolution transmission electron microscopy (TEM) images revealed nanosize zein stripes, rings, and discs containing a 0.35 nm periodicity, which is characteristic of β-sheet. TEM images were interpreted in terms of the transformation of original α-helices into β-sheet conformation after evaporation-induced self-assembly (EISA). The presence of β-sheet was also detected by circular dichroism (CD) spectroscopy. Zein β-sheets self-assembled into stripes, which curled into rings. Rings formed discs and eventually spheres. The formation of zein nanostructures was believed to be the result of β-sheet orientation, alignment, and packing.