Lanthanum-selective membrane electrode based on 2,2′-dithiodipyridine

In this study, a new poly(vinyl chloride) (PVC) membrane sensor for La³⁺ ion based on 2,2′-dithiodipyridine as an ion carrier was prepared. This electrode revealed good selectivity for La³⁺ over a wide variety of other metal ions. Effects of experimental parameters such as membrane composition, nature and amount of plasticizer, the amount of additive and concentration of internal solution on the potential response of La³⁺ sensor were investigated. The electrode exhibited a Nernstian slope of 20.0 ± 1.0 mV per decade of La³⁺ over a concentration range of 7.1 × 10⁻⁶ to 2.2 × 10⁻² M of La³⁺ in the pH range 3.3-8.0. The response time was about 7 s and the detection limit was 3.1 × 10⁻⁶ M. The electrode can be used for at least 2 months without a considerable divergence in potential. The proposed electrode was used as an indicator electrode in potentiometric titration of oxalate and fluoride ions and was applied for determination of F⁻ ion in mouthwash solution.     

Synthesis of New (Pyrimido[4,5-e][1,3,4] thiadiazin-7-yl)hydrazine Derivatives

New (pyrimido[4,5-e][1,3,4]thiadiazin-7-yl)hydrazines were synthesized via the cyclocondensation of alkyl-2-phenylhydrazinecarbodithioates as bidentate nucleophiles with 5-bromo-2,4-dichloro-6-methylpyrimidine as an electrophile and further replacement of chlorine atom on the seven number position of pyrimido[4,5-e][1,3,4]thiadiazin by hydrazine in boiling ethanol.     

Studies of New Peroxyoxalate-H<Subscript>2</Subscript>O<Subscript>2</Subscript> Chemiluminescence System Using Quinoxaline Derivatives as Green Fluorophores

Quinoxaline derivatives are a great interest as fluorescent emitters for peroxyoxalate chemiluminescence. Reaction of peroxyoxalates such as bis-(2,4,6-trichlorophenyl) oxalate with H₂O₂ can transfer energy to fluorophore via formation of dioxetanedione intermediate. Two quinoxaline derivatives used as a fluorophore in this study which produce a green light in the chemiluminescence systems. The relationship between the chemiluminescence intensity and concentrations of fluorophore, peroxyoxalate, sodium salicylate and hydrogen peroxide was investigated. Kinetic parameters for the peroxyoxalate-chemiluminescence were also calculated from the computer fitting of the corresponding chemiluminescence intensity/time profiles. It was found that the biphenylquinoxaline can be used as an efficient green fluorescent emitter.     

N‐Inversion in N‐phenyloxaziridine: substituent and solvent effects via density functional theory

In this work, using density functional theory, the kinetic effects of the substitution of a t‐butyl group and\or the incorporation of an oxygen atom, and both, at the aziridine ring moiety were investigated for N‐inversion in N‐phenylaziridine. Then, for N‐inversion in 3‐t‐butyl‐N‐phenyloxaziridine, the kinetic Hammett substituent effects were studied using the different para‐substituted groups on the N‐phenyl ring moiety. The natural bond orbital (NBO) study was the last case in this work. The calculations were performed in the gas phase and solution (in carbon tetrachloride and dichloromethane). The incorporation of an oxygen atom in the aziridine ring strongly weakens the N‐inversion process. In addition, while both t‐butyl substituent and solvent slightly reinforce the N‐inversion of N‐phenyloxaziridine, in N‐phenylaziridine, they decrease the N‐inversion rate to some extent. In both phases, more pronounced in solution and especially in dichloromethane, and in agreement with the NBO results, the electron‐withdrawing groups on para position of the N‐phenyl ring strongly increase the rate of N‐inversion of 3‐t‐butyl‐N‐phenyloxaziridine molecule.     

Boundary Behavior of Functions in the de Branges–Rovnyak Spaces

This paper deals with the boundary behavior of functions in the de Branges–Rovnyak spaces. First, we give a criterion for the existence of radial limits for the derivatives of functions in the de Branges–Rovnyak spaces. This criterion generalizes a result of Ahern–Clark. Then we prove that the continuity of all functions in a de Branges–Rovnyak space on an open arc I of the boundary is enough to ensure the analyticity of these functions on I. We use this property in a question related to Bernstein’s inequality. Received: May 10, 2007. Revised: August 8, 2007. Accepted: August 8, 2007.     

An efficient explicit framework for determining the lowest structural buckling load using Dynamic Relaxation method

This paper develops an e?cient explicit algorithm for calculating buckling load of structures. Here, the modified Dynamic Relaxation method is utilized so that the first structural buckling load is achieved. The proposed algorithm does not require solving any eigenvalue problem and runs by full vector and iterative operations. Moreover, the suggested procedure is general so that it could be utilized for both symmetric and unsymmetric structures without any additional calculations. For numerical verification, some columns and portal frames are analyzed and the calculated buckling loads are compared with the exact solution and other available approaches. Results show that the proposed algorithm has suitable accuracy and e?ciency that is useful for determining the lowest buckling load of each structure. Moreover, the effect of initial imperfection and time step size on the suggested framework is studies numerically.