The effect of increasing the excitation level of the sodium atom on the structure of the NaArn polyatomic exciplexes

In this work, the geometrical structures, the formation energies, and electronic states of the Na(ms)Ar_n polyatomic exciplexes with m = 3-6 and n = 2-5 are studied by using a quantum-classical method. The interaction potential between an electronically excited sodium atom and argon atoms are calculated by using a one-electron model involving electron-Ar and electron-Na⁺ pseudopotentials, in which the Hamiltonian is diagonalized at every optimization step in the Basin Hopping algorithm. The relationship between the position of the electronically excited levels and the cluster geometry is investigated as a function of the excitation level and of the spatial extension of the excited electron orbital. We show that the equilibrium structures of the ground state Na(3s)Ar_n and those of the electronically excited states Na(4s)Ar_n, Na(5s)Ar_n, and Na(6s)Ar_n are significantly different. As a result of the detailed examination of the relationships between the geometrical structure and density distribution of the Na valence electron of the Na^∗Ar_n with n = 2-5 polyatomic exciplexes, we can see that for the Na(4s)Ar_n polyatomic exciplexes, the two extreme geometries, neutral Na(3s)Ar_n and ionic Na⁺Ar_n compete. It appears that none of them is the actual one. For Na(5s)Ar_n and Na(6s)Ar_n the valence electron is very weakly bound to the ionic core and described by a more diffused orbital so that the geometry and the formation energies of this excited state called Rydberg states converge towards those of the ionic cores.     

A Spectrophotometric Method for the Determination of Buclizine Hydrochloride Using the Charge-Transfer Spectrum of Buclizine-Iodine Complex

Abstract

A simple and sensitive spectrophotometric method is described for the determination of buclizine hydrochloride in bulk and tablets form. The method is based on the formation of charge-transfer complex between buclizine, as n-donor, and iodine, as Δ acceptor, which measured spectrophotometrically at 295 and 355 nm. A Job's plot indicated a 1:1 complex between the drug and iodine and Beer's law was obeyed in a concentration range of 4–30 μg ml^?1. A more detailed investigation of the complex was made with respect to its association constant and the free energy change. The method is simple and sensitive and has been applied successfully to the analysis of laboratory-made tablets without any interference from the tablet excipients. To validate the method, the results obtained were compared statistically with a newly developed uv-derivative spectrophotometric method. The charge-transfer method was favored due to its higher sensitivity, cheap coast and available equipments.     

New method for strength improvement of silica optical fibers

The reliability and the expected lifetime of optical fibers used in telecommunication technologies are closely related to the chemical environment action on the silica network. To ensure the long-term mechanical strength of the optical fibers, a polymer coating was applied onto the fiber surface during fiber fabrication. This external coating is vital to ensure a long optical fiber lifetime. Its protective action includes several functions, such as to protect glass fiber from any external damage, to limit chemical attack, in particular that of water, and finally to ensure fatigue protection and bending insensitivity, especially during handling and in-service installation. Since the mechanical strength of the fiber is controlled by its surface characteristics, we propose a new method for increasing fiber strength.The silica optical fibers used were 125 μm in diameter, with a 62.5 μm thick epoxy-acrylate coating. Fibers were rolled up around two similar cylinders. Using a screw, these cylinders moved away from one another and thus subjected the fibers to stretching. Submitted to this mechanical loading, the distended fibers were plunged into hot water at 65 or 85 °C and aged for several days. Then, the fibers were removed from the water and various weights were suspended on the fiber ends. Thus, the fibers were subjected to a tensile loading in static fatigue for several days. Just before fiber rupture, the fibers were unloaded and subjected to dynamic tensile tests at different velocities.Result analysis proved that the aging in hot water increased the fiber strength. The Weibull's diagram study shows a bimodal dispersion of defects on the fiber surface and the important role of polymer coating.     

The use of Omega Chrome Fast Blue 2G in the microdetermination of some metals

Summary Omega Chrome Fast Blue 2G has been found to be a suitable indicator for the detection of the equivalence point of calcium, magnesium and manganese in the presence of cadmium, nickel, and aluminium, when they are masked by the addition of cyanide or triethanolamine. It is also a suitable indicator for the back titration of aluminium using calcium or magnesium as a back titrant.This dye has also been found to be a suitable reagent for the colorimetric determination of calcium, magnesium, manganese and thorium.     

A convenient synthesis of pyrazolo[3,4‐d]pyrimidine‐4,6‐dione and pyrazolo[4,3‐d]pyrimidine‐5,7‐dione derivatives

Pyrazolo‐[3,4‐d]pyrimidine‐4,6‐diones 5 and pyrazolo[4,3‐d]pyrimidine‐5,7‐diones 7 were synthesized by Curtius rearrangement of pyrazolic mono‐esters 2 and 3 followed by hetero‐cyclization via the ureas derivatives 4 and 6 under alkaline conditions.     

Synthesis and reactivity of 2-(furan-2-yl)benzo[<Emphasis Type="Italic">e</Emphasis>][1,3]benzothiazole

N-(1-Naphthyl)furan-2-carboxamide was synthesized by the coupling of naphthalen-1-amine with furan-2-carbonyl chloride in propan-2-ol and then treated with excess P2S5 in anhydrous toluene to obtain the corresponding thioamide. The latter was oxidized with potassium ferricyanide in an alkaline medium by the Jakobson procedure to synthesize 2-(furan-2-yl)benzo[e][1,3]benzothiazole which was subjected to electrophilic substitution reactions: nitration, bromination, formylation, and acylation.     

Electrical conductivity of 2,4-dinitrosoresorcinol and its complexes

Electrical conductivity measurements of 2,4-dinitrosoresorcinol (DNR) and its complexes were measured in the temperature range 20–115°C to give faint semiconducting behaviour for these systems. The conductivity values of the bis Co, Ni, Cu and Zn systems indicated that the metal ion forms a bridge between the two ligands facilitating the transfer of current carriers with some degree of delocalization in the excited state. As the iron content in the complexes increased, a gradual increase of electrical conductivity occurred, that might be due to lattice imperfections.     

Some considerations to optimize the synthesis procedure and the structural quality of mesostructured silicas

Two methods for the preparation of highly ordered MCM-41 silica are discussed. The quality of the structure was optimized by adequate stirring of the reaction mixture containing low concentration of surfactant, followed by heating at 70 °C for 3 h under stirring. Besides this energetically favorable procedure allowed to obtain structures very stable upon calcination. The role of the ethanol and the hydroxide source in the synthesis process is also analyzed.     

Crystal Structure and IR Study of (C<Subscript>6</Subscript>H<Subscript>5</Subscript>NH<Subscript>3</Subscript>)[ZnCl(HPO<Subscript>3</Subscript>)]

Abstract  

A new hybrid phosphate, (C₆H₅NH₃)[ZnCl(HPO₃)], has been synthesized and its structure characterized from single-crystal X-ray diffraction. The title compound crystallizes in the orthorhombic space group Pbca (n. 61) with the unit-cell parameters: a = 9.8635(2) ?, b = 9.4516(10) ?, c = 22.2430(4) ?, Z = 8 and V = 2,073.62(6) ?³. The final R factors were R/ωR = 0.0361/0.0924. Its framework might be described as a layered structure with two (010)-parallel cationic and anionic layers. The IR spectrum of this phase shows characteristic bands of phosphite and anilinium groups.