Identification and Quantification of Tocopherols in Vegetable Oils by Thin-Layer Chromatography

JPC – Journal of Planar Chromatography – Modern TLC -     

Global Minimization of a Multivariate Polynomial using Matrix Methods

The problem of minimizing a polynomial function in several variables over R ⁿ is considered and an algorithm is given. When the polynomial has a minimum the algorithm returns the global minimal value and finds at least one point in every connected component of the set of minimizers. A characterization of such points is given. When the polynomial does not have a minimum the algorithm computes its infimum. No assumption is made on the polynomial.     

Kinetic data on the curing of an epoxy polymer in the presence of lignin

In the present study, dynamic differential scanning calorimetry has been used to investigate the effect of an alkali lignin in amounts up to 20% by weight, on the crosslinking kinetics of an epoxy prepolymer cured with an aliphatic polyamine. Lignin presence does not significantly affect the overall reaction order, but the activation energy increases and the slowing of the overall curing process with lignin content could be explained by the interaction between lignin and the polyamine hardener. The possibility of having a “false compensation” in the case of the use of single DSC scans is also discussed.     

Thermodynamics of binary mixtures: Volumes,heat capacities,and dilution enthalpies for then-pentanol+2-methyl-2-butanol system

The densities, heat capacities, and dilution enthalpies ofn-pentanol+2-methyl-2-butanol mixtures have been measured, in many cases as a function of temperature, over the complete mole fraction range. Excesses thermodynamic properties, apparent and partial molar heat capacities, volumes and expansibilities were derived. The concentration and temperature dependences of these functions are discussed in terms of the variations of the structure of the system caused by the participation of the two alcohol molecules (with quite different steric hindrance of the alkyl chain around the-OH group) in the dynamic intermolecular association process through hydrogen bonding.     

Quest for zeolite-like metal-organic frameworks: on pyrimidinecarboxylate bis-chelating bridging ligands

Two novel porous zeolitelike metal-organic frameworks (ZMOFs) were constructed via the single metal ion-based molecular building block approach from rigid and directional tetrahedral building units and pyrimidinecarboxylate bridging ligands; their ion exchange and hydrogen sorption properties were evaluated.     

A set of homologous hetarylenediyne macrocycles by oxidative acetylene-acetylene coupling

The synthesis of a set of bipyridine-containing macrocycles by oxidative acetylene-acetylene dimerization is described. The cycles are separated by preparative GPC, and the smallest homologue is analyzed by single-crystal X-ray diffraction, which shows a layered structure with channels that are partially filled with parts of the flexible chains of adjacent macrocycles. The cyclic trimer has a D3h symmetry and is a possible candidate for the formation of metal organic supramolecular assemblies on surfaces.     

On the <Emphasis Type="Italic">L</Emphasis><Superscript><Emphasis Type="Italic">p</Emphasis></Superscript>-Poisson Semigroup Associated with Elliptic Systems

We study the infinitesimal generator of the Poisson semigroup in L ^p associated with homogeneous, second-order, strongly elliptic systems with constant complex coefficients in the upper-half space, which is proved to be the Dirichlet-to-Normal mapping in this setting. Also, its domain is identified as the linear subspace of the L ^p -based Sobolev space of order one on the boundary of the upper-half space consisting of functions for which the Regularity problem is solvable. Moreover, for a class of systems containing the Lamé system, as well as all second-order, scalar elliptic operators, with constant complex coefficients, the action of the infinitesimal generator is explicitly described in terms of singular integral operators whose kernels involve first-order derivatives of the canonical fundamental solution of the given system. Furthermore, arbitrary powers of the infinitesimal generator of the said Poisson semigroup are also described in terms of higher order Sobolev spaces and a higher order Regularity problem for the system in question. Finally, we indicate how our techniques may be adapted to treat the case of higher order systems in graph Lipschitz domains.     

Influence of the nature of the chain breaker on the thermal stability of phthalic anhydride-based polyesters

This study presents the synthesis of polyesters obtained from phthalic anhydride as acidic components and one mixture of monoethylene glycol and monohydric alcohol (in ratio 1.1:0.15). Molar ratio of the acid component and alcohol component was 1:1.25. n-Propanol, n-butanol, n-octanol and isoamyl alcohol were used as monohydric alcohol. Physicochemical characterization was performed by elemental analysis, FTIR/UATR spectroscopy of polyesters and char, EGA (evolved gas analysis), thermal analysis in synthetic air and in nitrogen atmosphere.     

A Substrate-Driven Approach to Determine Reactivities of α,β-Unsaturated Carboxylic Esters Towards Asymmetric Bioreduction

The degree of C?C bond activation in the asymmetric bioreduction of α,β-unsaturated carboxylic esters by ene-reductases was studied, and general recommendations to render these "borderline-substrates" more reactive towards enzymatic reduction are proposed. The concept of "supported substrate activation" was developed. In general, an additional α-halogenated substituent proved to be beneficial for enzymatic activity, whereas β-alkyl or β-aryl substituents were detrimental for the reactivity of nonhalogenated substrates, and α-cyano groups showed little effect. The alcohol moiety of the ester functionality was found to have a strong influence on the reaction rate. Overall, activities were determined by both steric and electronic effects.