Thermodynamic characterization of the prevailing molecular interactions in mixed floating monolayers of phospholipids and usnic acid

The investigation of the characteristics of mixed floating monolayers of phospholipids and usnic acid (UA), an active metabolite from lichens, can provide valuable information on how to prepare stable liposomes that could serve as carriers of UA for therapeutic proposes. The present paper is concerned with the thermodynamic analysis of the behavior of Langmuir monolayers formed by mixing different phospholipids (dibehenoylphosphatidylcholine, DBPC, dipalmitoylphosphatidylcholine, DPPC, and dioleoylphosphatidylcholine, DOPC) and UA at varied molar fractions. Relevant thermodynamic parameters such as excess areas, excess free energies and free energy of mixing were derived from the surface pressure data obtained from compression measurements performed in a Langmuir trough. For the largest lateral pressure examined (25 mN/m), negative values of the excess free energy were found only for the DOPC/UA monolayer, which should be the most stable of them. Based on the calculated values of the free energy of mixing, we note that the DBPC/UA and DPPC/UA systems present the best mixed character at low pressures and when the molar fraction of the UA is 0.5; at that relative concentration and at low values of the external pressure, the UA molecules can better mix and interact with the phospholipid molecules. The compression isotherms for mixed monolayers show no visible transitions, exhibiting a more organized phase that corresponds to a negative free energy of mixing. We have established that the most stable monolayers were those corresponding to DOPC/UA mixtures with a UA molar fraction of 0.75.     

Structure and crises of fractal basin boundaries

We discuss the structure of fractal basin boundaries in typical nonanalytic maps of the plane and describe a new type of crisis phenomenon.     

Selective light-induced modulation of bcl-XL and bax expressions in indocyanine green-loaded U937 cells: effects of continuous or intermittent photo-sensitization with low IR-light using a 805-nm diode laser

The present study is concerned with the effects of an IR diode laser source emitting at 805 nm on a human leukaemic cell strain from a histiocytic lymphoma (U937) pre-loaded with the dye indocyanine green (ICG). The first aim of this work was the assessment of the earliest cellular defense events occurring upon ICG photosensitization. To this purpose, photosensitization was performed at low ICG concentration and low light energy density. The second aim was the comparative evaluation of the effects produced by continuous or fragmented irradiation. Independent of the irradiation method employed (continuous or fragmented), we could demonstrate that cells are forced to apoptosis, as indicated by the appearance in cell extracts of the 85-kDa proteolytic fragment of the poly(ADP-ribose)polymerase (PARP). This proteolysis, however, could be entirely prevented by a specific Caspase-3 inhibitor benzyloxycarbonyl-Asp-Glu-Val-Asp-fluoromethylketone (Z-DEVD-fmk). Indeed the only perceptible change in the expression of pro/antiapoptotic proteins produced by continuous photostimulation was a small, albeit reproducible, increase in Bax. In contrast, when the photostimulation was achieved by means of several consecutive pulses, we observed not only a remarkable increase in Bax but also a noticeable abatement in Bcl-XL expression. The potential involvement of singlet oxygen in this process has been directly demonstrated by ICG photo-mediated oxidation of dithiothreitol in water. It has also been demonstrated that this oxidation is apparently more efficient when ICG is photostimulated by light pulses.     

Asymmetric reduction of prochiral ketones using in situ generated oxazaborolidine derived from (1S,2S,3R,4R)-3-amino-7,7-dimethoxynorbornan-2-ol. An efficient synthesis of enantiopure (R)-tomoxetine

Catalytic asymmetric reduction of prochiral ketones was examined in the presence of chiral oxazaborolidine catalyst 2 prepared in situ from (1S,2S,3R,4R)-3-amino-7,7-dimethoxynorbornan-2-ol (1). The optically active secondary alcohols were generally obtained in moderate to high enantiomeric excesses (ee 43-95%) and good yields (75-94%), except for ketones bearing electron-withdrawing groups. The methodology was applied to the synthesis of enantiopure (R)-tomoxetine, a potent anti-depressant drug.     

Effects of self-assembly process of latex spheres on the final topology of macroporous silica

This paper surveys the topology of macroporous silica prepared using latex templates covering the submicrometric range (0.1-0.7 mum). The behavior of latex spheres in aqueous dispersion has been analyzed by dynamic light scattering (DLS) measurement indicating the most appropriate conditions to form well-defined cubic arrays. The optical behavior of latex spheres has been analyzed by transmittance and reflectance measurements in order to determine their diameter and filling factor when they were assembled in bidimensional arrays. Macroscopic templates have been obtained by a centrifugation process and their crystalline ordering has been confirmed by porosimetry and scanning electron microscopy. These self-assembled structures have been used to produce macroporous silica, whose final topology depends on the pore size distribution of the original template. It has been seen that latex spheres are ordered in a predominant fcc arrangement with slipping of tetragonal pores due to the action of attractive electrostatic interactions. The main effect is to change the spherical shape of voids in macroporous silica into a hexagonal configuration with possible applications to fabricate photonic devices with novel optical properties.     

TS-FF-AAS and multivariate calibration: A proposition for sewage sludge slurry sample analyses

This work describes a methodology for Cd and Pb determination in sewage sludge slurry samples using thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS). The TS-FF-AAS system was equipped with a Ni tube atomizer placed on an oxidizing air/acetylene flame. Two multivariate calibration models based on partial least squares (PLS) were proposed using total peak profiles (recorded during 57 s). Metals concentration in the sewage sludge samples were from 1.87 to 6.26 mg kg⁻¹ for Cd and from 101 to 327 mg kg⁻¹ for Pb. The limits of detection and quantification were, respectively, 0.2 and 0.7 μg kg⁻¹ for Cd and 8 and 26 μg kg⁻¹ for Pb. These values were three times lower than the limits found when these metals were calibrated using linear calibration with aqueous standard solutions.     

Energy requirements for the indirect formation of cluster ions in the gas phase: the ion-molecule reaction of negative ions with esters of formic acid

Negative ions are shown to lead to solvated ions in the gas phase by reaction with esters of formic acid when two requirements are met: (1) the bond energy of the cluster is greater than 9.3 kcal/mole, and (2) the proton affinity of the negative ion is greater than 349 kcal/mole. A likely mechanism for the bimolecular process is suggested based on these results.     

Indecomposable continua in dynamical systems with noise: Fluid flow past an array of cylinders

Standard dynamical systems theory is based on the study of invariant sets. However, when noise is added, there are no bounded invariant sets. Our goal is then to study the fractal structure that exists even with noise. The problem we investigate is fluid flow past an array of cylinders. We study a parameter range for which there is a periodic oscillation of the fluid, represented by vortices being shed past each cylinder. Since the motion is periodic in time, we can study a time-1 Poincare map. Then we add a small amount of noise, so that on each iteration the Poincare map is perturbed smoothly, but differently for each time cycle. Fix an x coordinate x(0) and an initial time t(0). We discuss when the set of initial points at a time t(0) whose trajectory (x(t),y(t)) is semibounded (i.e., x(t)>x(0) for all time) has a fractal structure called an indecomposable continuum. We believe that the indecomposable continuum will become a fundamental object in the study of dynamical systems with noise. (c) 1997 American Institute of Physics.     

Spectroscopic characterization of SnO2 gels

Excitation and dynamic emission spectra of Eu³⁺ ions were simultaneously used with FTIR and Raman spectroscopy to study the structural evolution during SnO₂ sol gel xerogel conversion. Results make evident an increase of the surroundings symmetry for the Eu³⁺ ions dissolved in SnO₂ matrix and a decrease of the amount of hydroxo groups (Sn-OH) during drying. These phenomena were associated to the pursuit of the condensation reaction after gelation.