Kinetics of vesicle formation

 The kinetics of vesicle formation from a hydrotrope (sodium xylenesulfonate) solution of a surfactant (Laureth 4) is studied by the use of a stopped-flow apparatus combined with a dynamic light scattering device to determine vesicle size in the system. The hydrotrope system studied presents a system with a high surfactant solubilization combined with vesicle formation simply by dilution with water. The kinetic results show a single exponential decay time. The kinetic analysis indicates that the vesicles are formed from a molecular solution which resulted from the shear in the stopped-flow device and grow by monomeric association. Received: 1 October 1996 Accepted: 22 November 1996     

TRANSIENT PHOTOCHEMISTRY OF SAFRANIN-O

Abstract— We have characterized the spectra, acidity constants and decay kinetics of the triplet and semireduced radical species of Safranin-O. Between pH 3.0 and 10.6, there are three triplet species denoted ³DH^{2 +}₂, ³DH⁺ and ³D, the p K _as being 7.5 and 9.2. All three triplet species exhibit first order decay, the rate constant for ³DH⁺ being ca. 5-fold lower than the rate constants of ³DH⁺ and ³D. Ascorbic acid and ethylenediaminetetraacetic acid (EDTA) quench the triplet state under appropriate pH conditions and the pH dependencies of the yield of semireduced dye indicate that ³DH⁺ is more reactive than ³DH⁺ or ³D. With EDTA as the reducing agent, there is the additional requirement that at least one of the amino nitrogens be deprotonated to obtain a significant yield of semireduced dye. In these reactions, ascorbic acid is oxidized reversibly, but EDTA is oxidized irreversibly, so that with the latter reducing agent photolysis causes buildup of the leucodye, which on subsequent photolysis can reduce triplet state dye. With ascorbic acid as the reducing agent, the regeneration of the ground state dye is reversible, the decay of the semireduced radical being second order. In general, the transient photochemistry of Safranin-O resembles that of Thionine, the major difference being that the lifetimes of ³DH^{2 +}₂ and ³DH⁺ are much longer for Safranin-O than for Thionine.     

Narrow band quantitative and multivariate electroencephalogram analysis of peri-adolescent period

ABSTRACT: BACKGROUND: The peri-adolescent period is a crucial developmental moment of transition from childhood to emergent adulthood. The present report analyses the differences in Power Spectrum (PS) of the Electroencephalogram (EEG) between late childhood (24 children between 8 and 13 years old) and young adulthood (24 young adults between 18 and 23 years old). RESULTS: The narrow band analysis of the Electroencephalogram was computed in the frequency range of 0--20 Hz. The analysis of mean and variance suggested that six frequency ranges presented a different rate of maturation at these ages, namely: low delta, delta-theta, low alpha, high alpha, low beta and high beta. For most of these bands the maturation seems to occur later in anterior sites than posterior sites. Correlational analysis showed a lower pattern of correlation between different frequencies in children than in young adults, suggesting a certain asynchrony in the maturation of different rhythms. The topographical analysis revealed similar topographies of the different rhythms in children and young adults. Principal Component Analysis (PCA) demonstrated the same internal structure for the Electroencephalogram of both age groups. Principal Component Analysis allowed to separate four subcomponents in the alpha range. All these subcomponents peaked at a lower frequency in children than in young adults. CONCLUSIONS: The present approaches complement and solve some of the incertitudes when the classical brain broad rhythm analysis is applied. Children have a higher absolute power than young adults for frequency ranges between 0-20 Hz, the correlation of Power Spectrum (PS) with age and the variance age comparison showed that there are six ranges of frequencies that can distinguish the level of EEG maturation in children and adults. The establishment of maturational order of different frequencies and its possible maturational interdependence would require a complete series including all the different ages.     

POLYMERIC SURFACTANTS BASED ON OLEIC ACID III. Copolymerization of Sodium Acrylamidostearate and Oleic Acid in a Lamellar Liquid Crystal

Copolymerization of sodium acrylamidostearate (NaAAS) and oleic acid was performed in the lamellar liquid crystal (LLC) formed by NaAAS, oleic acid and water, in the absence of N.N’-methylenebisacrylamide (MBAA) and in the presence of MBAA, respectively. In the absence of MBAA, after the polymerization the lamellar structure remained, and the disorder of the lamellar liquid crystal was, to some extent, enhanced. Surface tension, small-angle X-ray diffraction, viscosity, and fluorescence methods were used to study the properties of the linear copolymer. The linear polymeric surfactant behaves like     

Integral equation formulation for buoyancy-driven convection problems

An integral equation formulation for buoyancy-driven convection problems is developed and illustrated. Buoyancy-driven convection in a bounded cylindrical geometry with a free surface is studied for a range of aspect ratios and Nusselt numbers. The critical Rayleigh number, the nature of the cellular motion, and the heat transfer enhancement are computed using linear theory. Green's functions are used to convert the linear problem into linear Fredholm integral equations. Theorems are proved which establish the properties of the eigenvalues and eigenfunctions of the linear integral operator which appears in these equations.     

Density functional analysis of geometries and electronic structures of gold-phosphine clusters. The case of Au4(PR3)42+ and A(u4μ2-I)2(PR3)4

Geometries, ligand binding energies, electronic structure, and excitation spectra are determined for Au(4)(PR(3))(4)(2+) and Au(4)(μ(2)-I)(2)(PR(3))(4) clusters (R = PH(3), PMe(3), and PPh(3)). Density functionals including SVWN5, Xα, OPBE, LC-ωPBE, TPSS, PBE0, CAM-B3LYP, and SAOP are employed with basis sets ranging from LANL2DZ to SDD to TZVP. Metal--metal and metal--ligand bond distances are calculated and compared with experiment. The effect of changing the phosphine ligands is assessed for geometries and excitation spectra. Standard DFT and hybrid ONIOM calculations are employed for geometry optimizations with PPh(3) groups. The electronic structure of the gold--phosphine clusters examined in this work is analyzed in terms of cluster ("superatom") orbitals and d-band orbitals. Transitions out of the d band are significant in the excitation spectra. The use of different basis sets and DFT functionals leads to noticeable variations in the relative intensities of strong transitions, although the overall spectral profile remains qualitatively unchanged. The replacement of PMe(3) with PPh(3) changes the nature of the electronic transitions in the cluster due to low-lying π*-orbitals. To reproduce the experimental geometries of clusters with PPh(3) ligands, computationally less expensive PH(3) or PMe(3) ligands are sufficient for geometry optimizations. However, to predict cluster excitation spectra, the full PPh(3) ligand must be considered.     

Effect of Pr-Ca substitution on the transport and magnetic behavior of LaMnO3 perovskite

The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO₃ perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good example of these properties is (La_1−2x Pr _x Ca _x )MnO₃ (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T _c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for understanding the structural, transport and magnetic properties are discussed in detail.     

Copper and iron interactions with angiotensin-converting enzyme inhibitors. A study by fast-atom bombardment tandem mass spectrometry

Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd.