Structural studies on γ-MnO2 by transmission electron microscopy

Single-crystal electron diffraction patterns were obtained on five specimens of -MnO₂: one natural, two electrolytical (EMD) and two chemical (CMD) samples. EMDs are best described by the orthorhombic structure proposed by De Wolff which is derived from the ramsdellite structure. A CMD prepared from MnCO₃ fits the hexagonal cell of -MnO₂. Flaky grains from the natural sample and fibres from a CMD prepared from Mn(NO₃)₂ are hexagonal with a new cell:a 0.494,c 0.539 nm. No simple relation between chemical composition, morphology and structure could be found.     

Analysis of weather data measured in Valencia during the years 1989, 1990, 1991 and 1992

Monthly average daily data over the period 1989–1992 for eight meteorological parameters in Valencia are presented. Using a multiple regression method, equations to calculate the monthly average daily data for six parameters as a function of the month of the year were obtained.     

Preparation of a New Oligomeric Surfactant: N,N,N′,N″,N″-Pentamethyl Diethyleneamine—N,N″-Di-[Tetradecylammonium Bromide] and the Study of its Thermodynamic Properties

A new oligomeric surfactant: N,N,N′,N″,N″- pentamethyl diethyleneamine—N,N″-di-[tetradecylammonium bromide] referred to as 14-2-N(CH₃)-2-14 was synthesized, purified and characterized by Elemental Analysis, ¹H and ¹³C NMR and Electrospray. The micellar properties of this compound were determined by electrical conductivity and surface tension methods. Optical microscopy was also employed to study the behavior of anhydrous surfactant and the binary water/surfactant system as a function of temperature. The critical micellar concentration (cmc), degree of counterion binding and thermodynamic parameters of micellization (standard molar Gibbs energy, enthalpy and entropy of micellization) were determined by electrical conductivity measurements in the temperature range [24–54 °C]. Surface tension measurements also provide information about the dependence of the surface tension at the cmc (γ_cmc), pC₂₀ (negative logarithm of the surfactant’s molar concentration C₂₀, required to reduce the surface tension by 20 mN/m, the surface excess (Γ_max) at air/solution interface, the minimum area per surfactant molecule at the air/solution interface (Amin), surface pressure at the cmc (П_cmc), critical packing parameter(CPP) and the standard free energies of micellization ( \Updelta G_m⁰\Updelta G_{m}^{0}) and of adsorption ( \Updelta G_\textads⁰ \Updelta G_{\text{ads}}^{0} ).     

Heat conduction in multilayer spherical products by transfer functions

The development of a computer program is presented in order to determine the heat conduction transfer in multilayer spherical products, hollow or solid, by means of the transfer function method. We can establish a methodology in order to determine heat flux and inner and/or outer temperatures for spherical solid multilayer products, and heat flux and temperatures in any intermediate point of the spherical multilayer products both hollow and solid. The program developed is designed for variable intervals and it allows for the inclusion of the superficial convection coefficient in the cases where it remains constant, or its exclusion from the mathematical model in the cases where it does not remain constant, as well as in the cases in which it does not exist (heating or cooling by superficial contact). The method was validated with oranges of average diameters between 7.73 and 7.89 cm and thickness of rind between 4.7 and 6.8 mm, and these showed good results.     

Aggregation Behavior,Antibacterial Activity and Biocompatibility of Catanionic Assemblies Based on Amino Acid-Derived Surfactants

The surface activity, aggregates morphology, size and charge characteristics of binary catanionic mixtures containing a cationic amino acid-derived surfactant N(π), N(τ)-bis(methyl)-L-Histidine tetradecyl amide (DMHNHC₁₄) and an anionic surfactant (the lysine-based surfactant N^α-lauroyl-N^εacetyl lysine (C₁₂C₃L) or sodium myristate) were investigated for the first time. The cationic surfactant has an acid proton which shows a strong pK_a shift irrespective of aggregation. The resulting catanionic mixtures exhibited high surface activity and low critical aggregation concentration as compared with the pure constituents. Catanionic vesicles based on DMHNHC₁₄/sodium myristate showed a monodisperse population of medium-size aggregates and good storage stability. According to Small-Angle X-Ray Scattering (SAXS), the characteristics of the bilayers did not depend strongly on the system composition for the positively charged vesicles. Negatively charged vesicles (cationic surfactant:myristate ratio below 1:2) had similar bilayer composition but tended to aggregate. The DMHNHC₁₄-rich vesicles exhibited good antibacterial activity against Gram-positive bacteria and their bactericidal effectivity declined with the decrease of the cationic surfactant content in the mixtures. The hemolytic activity and cytotoxicity of these catanionic formulations against non-tumoral (3T3, HaCaT) and tumoral (HeLa, A431) cell lines also improved by increasing the ratio of cationic surfactant in the mixture. These results indicate that the biological activity of these systems is mainly governed by the cationic charge density, which can be modulated by changing the cationic/anionic surfactant ratio in the mixtures. Remarkably, the incorporation of cholesterol in those catanionic vesicles reduces their cytotoxicity and increases the safety of future biomedical applications of these systems.     

Anti-Trypanosoma cruzi Activity of Metabolism Modifier Compounds

Chagas disease is caused by the protozoan parasite Trypanosoma cruzi and affects over 6 million people worldwide. Development of new drugs to treat this disease remains a priority since those currently available have variable efficacy and frequent adverse effects, especially during the long regimens required for treating the chronic stage of the disease. T. cruzi modulates the host cell-metabolism to accommodate the cell cytosol into a favorable growth environment and acquire nutrients for its multiplication. In this study we evaluated the specific anti-T. cruzi activity of nine bio-energetic modulator compounds. Notably, we identified that 17-DMAG, which targets the ATP-binding site of heat shock protein 90 (Hsp90), has a very high (sub-micromolar range) selective inhibition of the parasite growth. This inhibitory effect was also highly potent (IC₅₀ = 0.27 μmol L⁻¹) against the amastigote intracellular replicative stage of the parasite. Moreover, molecular docking results suggest that 17-DMAG may bind T. cruzi Hsp90 homologue Hsp83 with good affinity. Evaluation in a mouse model of chronic T. cruzi infection did not show parasite growth inhibition, highlighting the difficulties encountered when going from in vitro assays onto preclinical drug developmental stages.     

Turbidimetric analysis of amine oxides and amine oxide-anionic surfactant mixtures

Automatic turbidimetric analysis has been shown to be a simple and accurate method to determine the actives in anionic surfactants as well as the actives in amine oxides. This technique has been applied to dilute solutions of these surfactants in the μM range. Solutions containing mixtures of anionic surfactants and amine oxides can be positively resolved by turbidimetric titration without interferences. Performing two titrations at different pH values ensures that the amine oxide is completely in its nonionic form or totally protonated and behaving as a cationic surfactant.     

Synthesis and properties of cationic surfactants containing a disulfide bond

Two new cationic surfactants containing a disulfide bond were synthesized, and the physical chemical characteristics and the fundamental surface-active properties were determined. These new surfactants have potential applications in the textile and cosmetic field. These compounds have been prepared by condensation of a commercial N^α,N^α-dimethyl amino betaine with cystine dimethyl ester or cystamine by means of the mixed anhydride method. The study of their properties revealed that these molecules are soluble in water (stable at pH⩽8) and show surface activity with similar low critical micelle concentration values. Microscopic examination of water/surfactant systems containing these compounds shows that they form liquid crystals with patterns corresponding to typical hexagonal and lamellar structures.     

The Experiences of Retired Managers Acting as Volunteers in an Entrepreneurial Mentoring Organization

Volunteering in later life is an important way of staying involved in one’s community and engaging in a meaningful activity that has a positive impact on others. Previous research has mainly described the antecedents and consequences of volunteering; the process and experiences associated with performing this role has been less studied. The aim of this study was to assess the positive and negative experiences of older managers involved in an entrepreneurial mentoring organization. Fourteen older male volunteers were administered a semi-structured interview and the data obtained were analyzed thematically. The themes that emerged were the importance of the final result as a filter to assess the whole mentoring experience, the mentor-mentee bond, and the self-attribution of successes and failures. These themes were discussed using the generativity theory as a framework to understand the experiences of older adults keen to pass on their skills and knowledge to a younger generation.     

A comparative study of SPCTRAL2 and SMARTS2 parameterised models based on spectral irradiance measurements at Valencia, Spain

Results obtained using the parametric models SPCTRAL2 and SMARTS2 for the urban area of Valencia, Spain, have been analysed and compared with experimental measurements at ground level obtained with two Li-cor 1800 spectroradiometers with a 6 nm resolution. The study used two different input parameters in both models for the aerosol characterisation: the aerosol optical thickness at 0.5 μm, τ_aλ(0.5), and the Angstrom turbidity coefficient β. The results obtained show that both algorithms reproduce quite correctly the spectral irradiance experimental values when an urban aerosol model parameterised by the τ_aλ(0.5) value is considered. In all the cases the deviations are lower when SMARTS2 code is used.