From Democritus to Schrödinger: a reflection on quantum molecular modeling

This review describes the saga of the atom and molecules, from the atomic concept as it was introduced 25 centuries ago by Leucippus and Democritus, to the modern Quantum Molecular Modeling. Quantum methods that have given rise to the contemporary Molecular Modeling are briefly presented. Chosen examples illustrate the performance and the predictions of Quantum Modeling in the following topics: conformational analysis, electrostatics, molecular spins and radicals, infrared and Raman spectra, thermochemistry, and electrophilicity properties derived from the molecular chemical potential.     

Micropolarity and microviscosity of Pluronics L62 and L64 core–shell aggregates in water at various concentrations and additives examined by absorption and fluorescence probes

The microstructure of aggregates formed in aqueous solutions of the triblock copolymers poly(ethylene oxide) (PEO)–poly(propylene oxide)–PEO, Pluronics L62 and L64, and the effect of additives (n-butanol, n-hexanol, and o-xylene) on the local polarity and viscosity were investigated using several absorption and fluorescence probes with different hydrophilic/hydrophobic trade-offs. The absorption probe was 2,2,6,6-tetramethylpiperidine-1-oxyl and the fluorescence probes pyrene (P), 1-anilinonaphthalene-8-sulfonic acid (ANS), 1,10-bis(1-pyrene) decane (PD), and N-[5-(dimethylamino)naphthalene-1-sulfonyl]hexadecylamine (Dansyl). The specific absorption and fluorescence parameters, sensitive to changes in micropolarity and microviscosity, were related to the hydration calibration curves carried out in homogeneous tetraethylene glycol/water mixtures. Thus, the effective local hydration of the molecular probe solubilized in the guest aggregate was quantified, and at the same time, the probe location is established with respect of the corona and core aggregate. The ANS and PD probes evidence differences in microviscosity and track the effect of the block copolymer structure and additive concentration on microviscosity.     

Energy Transfer from the Aminophthalate Dianion to Fluorescein

Energy transfer from the excited aminophthalate dianion species to fluorescein at pH 8.32 (Tris-HCl buffer) was studied. The excited aminophthalate dianion species was obtained either by excitation with UV radiation (330 nm), with fluorescence emission, or by the well-known chemical reaction luminol-hydrogen peroxide in an alkaline medium, with chemiluminescent emission, both with _max at 425 nm. The influence of Co²⁺ and Mg²⁺ on fluorescence and chemiluminescence (CL) was studied. It was found that at low concentrations (10^–7–10^–9 M), these ions do not modify the fluorescein fluorescence, however, the CL is strong affected. The effect of the concentration of these elements, which exert an influence on CL even at a high dilution (nanomolar concentration), was determined. In the case of Co²⁺ the prooxidant character is stronger than in the case of Mg²⁺, and therefore the CL enhancer effect is higher. Compared to the system without catalyst, their presence ensures stronger, prolonged, and stable light emission. The emission spectra, in the presence of fluorescein, show two bands with maxima at 425 and 520 nm, the second one being specific to fluorescein emission. The intensity of aminophthalate dianion luminescence is lower and the duration shorter in the presence of fluorescein. The influence of Co²⁺ and Mg²⁺ catalyst and fluorescein concentration on the energy transfer process was studied. The efficiency of the energy transfer process for these two situations (fluorescence and CL) was compared. An attempt was made to replace hydrogen peroxide with superoxide anion (solubilized by means of crown ether) and its effect upon the energy transfer process was observed.     

Quantitative determination of vitamin b12 by cyan dosage,with infrared absorption spectrophotometry

Microchimica Acta - Vitamin B12 has been determined by measurement of the infrared absorption of the cyano-group band at 2137 cm?1, the samples being pelleted with KBr. The error is within...     

Hybrid polymer inorganic materials prepared from ternary microemulsions

The microemulsion system containing vinyl acetate (Vac), silane derivatives tetraethoxysilane (TEOS), methacryloxypropyltrimethoxysilane (MPTS), vinyltriethoxysilane (VTES), methyltriethoxysilane (MeTES), octyltriethoxysilane (OTES), nonylphenol etoxylated with 25 mol of ethylene oxyde (NPEO₂₅) and water was studied. It was established that the probability of microemulsion formation increases with surfactant concentration. The microenviroment of the solubilization of the VAc and of silane derivatives in the aggregates of NPEO₂₅ was affected by their polarity. Hybrid materials were obtained by sol-gel reaction of silane derivatives combined with free-radical polymerization of VAc. The change of the glass transition temperature and of thermal stability of the polymer chains in the presence of the inorganic one proved the formation of simultaneous polymer inorganic hybrids.     

Monitoring of titanium base alloys-biofluids interface

Monitoring of the titanium, Ti-5Al-4V, Ti-6Al-4Fe implant materials--Ringer 1 and Ringer 2 solutions (of different pH values) interface for long term was studied in this work. In Ringer 1 solution (with high chloride ion content) all biomaterials present self-passivation. On Ti-6Al-4Fe alloy, the breakdown of the passive film was registered but at high pitting potential; pitting protection potential is very noble and can not be reached in human fluids. In Ringer 2 solution was obtained more electropositive corrosion potential values than in Ringer 1 solution; pitting corrosion of Ti-6Al-4Fe alloy is characterised by nobler breakdown and pitting protection potential values, therefore a better pitting corrosion resistance and tendency. Ion release increases in time, for the first 400-600 immersion hours and then tend to a constant level with very low values, non-dangerous for human body. All open circuit potentials oscillate around some electropositive values. The potential gradients calculated for extreme pH values have low values during 20,000 exposure hours and can not accelerate the corrosion. Atomic Force Microscopy images obtained after different exposure periods in Ringer 1 solution revealed that the roughness increased in time, suggesting a dynamic process at biomaterial-biofluid interface. X-ray Photoelectron spectra obtained after 2880 immersion hours in Ringer 2 solution show the existence of protective titanium dioxide TiO(2) and TiO and Ti(2)O(3) oxides both for titanium and Ti-5Al-4V alloy. Also, Al(2)O(3) oxide was detected.     

Structural characterization of amorphous and nanostructured bismuth silicate xerogels

Bismuth silicate xBi₂O₃·(1 − x)SiO₂ xerogels, 0 ≤ x ≤ 0.5, doped with gadolinium have been synthesized by sol–gel method. The study aims to evidence by X-ray diffraction (XRD), electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) the structural changes in amorphous Bi₂O₃–SiO₂ xerogels, function of Bi₂O₃ content and heat treatment. As was proved by XRD, nanostructured samples were obtained after 30 min heat treatment at 400 °C of the as-prepared samples with x > 0, in the mainly amorphous matrices nanocrystals of Bi_5.6Si_0.5O_9.4 phase being developed. The dimension of the nanocrystallites are function of the bismuth content, and vary from few nanometers to 25 nm for samples with x = 0.14 and x = 0.5 respectively. The local order around silicon, reflected by 29Si MAS NMR spectra, is less dependent on both composition and thermal history of the samples, showing that an amorphous silicon rich phase is present in all samples. The changes in the local order around Gd³⁺ ions, as reflected by the EPR spectra dependence on composition and especially on the heat treatment, support the assumption that a part of these paramagnetic ions is incorporated in the bismuth rich phase.     

Hamburger and Stieltjes moment problems in several variables

In this paper we give solutions to the Hamburger and Stieltjes moment problems in several variables, in algebraic terms, via extended sequences. Some characterizations of the uniqueness of the solutions are also presented.

     

Spectroscopic study on nystatin conformational modifications generated by its interaction with the solvent

Conformational transformations of the tetraenic nystatin chromophore under the influence of solvents and UV irradiation have been studied by absorption, fluorescence and wide-line NMR spectroscopy.