Enzymes of Opuntia ficus-indica (L.) Miller with potential industrial applications-I

We report on the screening of different enzymes such as arylamidases, lipases, proteinases, and glucosidases in plant extracts of the Cactaceae family, genus Opuntia, as well as on a newly purified plant proteases from O. ficus-indica fruit extracts. These proteinases showed the maximum activity at pH 5.2 and 55°C and FTC-casein was the best of the escreened substrates. Proteolytic activities were activated by anti-oxidant compounds and by some divalent cations. These proteinases were efficiently inhibited by cystein proteinase inhibitors and by 1,10-phenanth roline. The estimated M _t for the main proteolytic activity was about 23.2 kDa. The results on milk clotting characteristics suggest a potential use of the fruit cystein enzymes of this plant in dairy industries.     

Thermal Characterization of Lapachol by Means of TG and DSC Coupled to a Photovisual System

Thermal characterization is proposed as analytical methodology for the purity assay of lapachol, and for determination of the quality parameters of capsules containing this molecule. The TG data revealed that lapachol is more stable in the presence of adjuvants, showing the good quality of the formulation. The kinetic parameters obtained were lower for lapachol drug than for the formulated lapachol. The DSC data demonstrated good compatibility between lapachol drug and the adjuvant in the formulated lapachol, and did not reveal impurities such as secondary products of the isolation and recrystallization processes. The data were confirmed by the DSC-photovisual findings. This revised version was published online in July 2006 with corrections to the Cover Date.     

Interfacial deposition of functionalized copolymers onto nanoemulsions produced by the solvent displacement method

Cationic nanoemulsions containing an oily core as potential carriers of nucleic acids were prepared by a solvent displacement method in the presence of a nonionic surfactant (Pluronic F68). With a view to functionalize such nanoemulsions for further incorporation of a fusogenic peptide, a poly(maleic anhydride-alt-methyl vinyl ether) (M _n=67,000) grafted with variable amount of acetylspermine (or acetylspermidine) and decylamine was nanodeposited during the nanoemulsion formation step. Functionalized nanoemulsions were characterized in terms of particle size (by quasi-elastic light scattering and electron microscopy), electrophoretic mobility and long-term stability as a function of the amount of polymer used in the formulation. It was found that increases in the level of the copolymer led to a reduction in the particle size and a decrease in colloidal stability. In addition, the incorporation of the grafted copolymers at the interface of the nanoemulsions was clearly evidenced, a shift towards low pH at the point of zero charge being attributed to the formation of carboxylic groups induced by hydrolysis of the residual maleic anhydride groups of the copolymer. Received: 1 September 2000 / in revised form: 29 November 2000 Accepted: 12 December 2000     

Excited-state Acidity of Bifunctional Compounds. 7. Long Distance, Solvent-assisted Excited-state Proton Transfer in Olivacine

Abstract— By use of fluorescence spectroscopy and time-correlated single photon counting, solvent-assisted excited-state proton transfer (ESPT) has been observed for olivacine in two organic solvents, 1,4-dioxane and methanol. Because of spectral overlap, factor analysis was used to determine the emission spectrum of the proton-transferred (PT) species. The ESPT is not observed in the nonpolar solvent n -hexane. For the first time in a system of this type, the individual excited-state rate constants have been calculated exactly from time-resolved single photon counting results. Because the PT process involves a path of more than 6 Å, its individual rate constant is extremely low, approximately 10⁷ s⁻¹.     

New advances on the characterisation of polymer surfaces by HREELS

Self assembled monolayers (SAMs) of thiols functionalised with oligothiophene functions were used as models for polymer surfaces. Thienyl functionalisation simulates the surface region and demonstrates that the analysed depth is of the order of 10 Å. Spectra of polystyrene (PS) films were recorded and show that impact mechanism dominates, which corroborates the high sensitivity of HREELS applied to polymer surfaces. Different orientation of phenyl groups is unravel for PS films deposited on platinum and silicon substrates, which is here related to a different conformation of the PS chains in the surface region of the film. To illustrate the state of the art of HREELS applied to organic films, spectra were recorded with old and new generation spectrometers.     

The Helmholtz equation in a quadrant with Robin's conditions

The boundary value problem for the Helmholtz equation in a quadrant with different Robin's or impedance‐type conditions is considered by the use of variational methods and boundary pseudodifferential equations. The coerciveness of the underlying sesquilinear form in dependence of the impedance parameters is proved. The equivalence between the boundary value problem and a scalar uniquely solvable Wiener–Hopf–Hankel equation is obtained. Copyright © 1999 John Wiley & Sons, Ltd.     

Physicochemical Characterization and Simulation of the Solid–Liquid Equilibrium Phase Diagram of Terpene-Based Eutectic Solvent Systems

The characterization of terpene-based eutectic solvent systems is performed to describe their solid–liquid phase transitions. Physical properties are measured experimentally and compared to computed correlations for deep eutectic solvents (DES) and the percentage relative error e_r for the density, surface tension, and refractive index is obtained. The thermodynamic parameters, including the degradation, glass transition and crystallization temperatures, are measured using DSC and TGA. Based on these data, the solid–liquid equilibrium phase diagrams are calculated for the ideal case and predictions are made using the semi-predictive UNIFAC and the predictive COSMO RS models, the latter with two different parametrization levels. For each system, the ideal, experimental, and predicted eutectic points are obtained. The deviation from ideality is observed experimentally and using the thermodynamic models for Thymol:Borneol and Thymol:Camphor. In contrast, a negative deviation is observed only experimentally for Menthol:Borneol and Menthol:Camphor. Moreover, the chemical interactions are analyzed using FTIR and ¹H-NMR to study the intermolecular hydrogen bonding in the systems.     

Molecular Ordering of Nematics Between Concentric Cylinders: Results and Perspectives

Abstract

We present a short overview of recent investigations of the equilibrium tilt angle profile in a cell limited by two concentric cylinders filled with nematic liquid crystals (NLC), both in presence and in absence of an external electric field. The analyses are carried out by recalling some recent results obtained in the framework of the elastic continuum theory and Monte Carlo (MC) simulations, or suitable combinations of both approaches. These are very powerful tools to face the richness of the configurations of NLC in complex geometries. In particular, they are helpful in providing a comprehension of the molecular organisation of these systems for what concerns the spontaneous Fréedericksz-like transition, connected with the phenomenon of escaping into the third dimension. Some concluding remarks and perspectives points towards some remarkable features of confined systems in soft matter.     

Evaluation of the structural characteristics and the fading effects of image plates

The photostimulated luminescence (PSL) is the basis for the digital image formation of image plates (IPs). However, the PSL decreases exponentially with the increasing of the elapsed time between the exposure and the IP scanning (t), and consequently, there is a fading of the digital image. The purpose of this paper is to investigate the relationship between IPs physical structure and elemental composition with the fading behavior. Three different types of IPs, with distinct resolutions, were analyzed. The fading behavior with the time, t, has been measured and correlated with their physical structure. Furthermore, micro X-ray fluorescence (μXRF) analysis was used to provide information on the elemental composition of this layer. The results showed that standard resolution plate have larger grains, thicker sensitive layer, and generate a bigger effect of image fading. The μXRF technique showed that, to compensate the low emission, the high-resolution IP has a higher concentration of Br and Sr.