Naphthyl benzoates versus phenyl benzoates A molecular structure-liquid crystal and ferroelectric behaviour relationship study

A comparative study of the liquid crystal and ferroelectric properties of several achiral, racemic and non-racemic 2,6-naphthyl benzoates and their 1,4-phenyl benzoate analogues is reported. In terms of pure compounds, both central core structures give rise to similar mesophase sequences; however, the naphthalene derivatives exhibit broader and more thermally stable liquid crystalline states. On the other hand, both central core units give rise to equivalent electric and optoelectronic properties when the compounds are used as chiral dopants in ferroelectric liquid crystal mixtures.     

Reproductivity for a nematic liquid crystal model

In this paper we prove existence of weak solution with the reproductivity in time property, for a penalized PDE’s system related to a nematic liquid crystal model. This problem is relatively explict when time-independent Dirichlet boundary conditions are imposed for the orientation of crystal molecules. Nevertheless, for the time-dependent case, the treatment of the problem is completely different. The verification of a maximum principle for weak reproductive solutions is fundamental in the argument. Finally, the relation between reproductive and periodic in time (regular) solutions will be pointed out, differenting the 2D and 3D cases. Basically, in two-dimensional domains every reproductive solution is regular and time periodic, whereas the problem remains open for three-dimensional domains.     

On-line characterisation of apple polyphenols by liquid chromatography coupled with mass spectrometry and ultraviolet absorbance detection

Apple polyphenols were characterised by means of hyphenated techniques such as HPLC coupled to UV photodiode array detection (LC-DAD) and to mass spectrometry (LC-MS). LC-MS using atmospheric pressure ionisation (APCI) in the positive ion mode provided the molecular weight, the number of hydroxyl groups, the number of sugars and an idea about the substitution pattern of the polyphenols. LC-DAD with postcolumn addition of UV shift reagents afforded precise structural information about the position of the free hydroxyl groups in the polyphenolic nucleus. Five isorhamnetin glycosides, two hydroxyphloretin glycosides and quercetin were reported in apple peel for the first time. Postcolumn addition of UV shift reagents in LC-DAD analysis confirmed the presence of isorhamnetin glycosides and not the isomeric glycosides of rhamnetin. Moreover, isorhamnetin-3-O-rhamnoglucoside was identified unambiguously by comparison with a standard. These results are relevant not only from a chemotaxonomic point of view, but also in the control of authenticity of fruit derived products in order to detect fraudulent admixtures.     

The Stokes equations with Fourier boundary conditions on a wall with asperities

We study the effect of the rugosity of a wall on the solution of the Stokes system complemented with Fourier boundary conditions. We consider the case of small periodic asperities of size ε. We prove that the velocity field, pressure and drag, respectively, converge to the velocity field, pressure and drag of a homogenized Stokes problem, where a different friction coefficient appears. This shows that, contrarily to the case of Dirichlet boundary conditions, rugosity is dominant here. Copyright © 2001 John Wiley & Sons, Ltd.     

Multicomponent synthesis of 4-aryl-NH-1,2,3-triazoles in the presence of Al-MCM-41 and sulfated zirconia

The acid properties of Al-MCM-41 and sulfated zirconia were used to develop a strategy for the synthesis of 4-aryl-NH-1,2,3-triazoles via a multicomponent reaction involving various benzaldehydes, sodium azide and nitromethane. The efficiency of the process is analysed from the perspective of the difference in acids among the catalysts used.