Influence of the nature of the metal ion on the rate of reduction of coordinated azomethine group

The kinetics of reduction of the azomethine bond in various Schiff bases and their transition metal complexes with sodium borohydride in dimethylformamide and ethanol solutions was studied. The reduction rate depends on both the structure of the starting Schiff bases and the nature of the metal ion. In transition metal N-phenylsalicylaldiminates, the rate of reduction of the azomethine group increases in the order Zn(II) < Ni(II) < Cu(II) < Co(II) < VO(II) < Mn(II). Similar trend is observed in other series of metal complexes with Schiff bases. The revealed trends are opposite to the Irving-Williams series of stability of complexes. This fact suggests that the major factor affecting the rate of reduction of the coordinated azomethine bond is the strength of its bonding with the metal ion. Depending on particular metal ion, the complexation can either decelerate or accelerate the reduction.     

Comparison of freshwater biofilms grown on polycarbonate substrata in Lake Velence (Hungary) and Lake Mogan (Turkey)

Freshwater biofilms grown on polycarbonate substrata in Lake Velence (Hungary) and Lake Mogan (Turkey) were studied by applying total reflection X-ray fluorescence spectrometry and taxonomical techniques. Concentration of calcium, which stabilizes the structure of the exopolymer matrix, was identical in the biofilms, independently of the fact that its concentration in the lake waters differs by a factor of 2.5. Enrichment factors calculated as concentration ratios of elements (Ca, K, Fe, Mn, Zn, and Sr) measured in biofilm and water varied from 3×10⁴ to 1.5×10². The highest enrichment factors were observed for micronutrients of manganese and iron. Although the dominant alga species were different in the Hungarian and Turkish biofilms, the enrichment factors for these two elements differ only slightly. These results demonstrate that the accumulation of these micronutrients is similar within the diatom species. The lowest enrichment factors were measured for potassium.     

Palladium pincer complex catalyzed cross-coupling of vinyl epoxides and aziridines with organoboronic acids

Palladium-catalyzed cross-coupling of vinyl epoxides and aziridines with organoboronic acids was performed by using 0.5-2.5 mol % pincer-complex catalyst. The reactions proceed under mild conditions affording allyl alcohols and amines with high regioselectivity and in good to excellent yields. Under the applied reaction conditions aromatic chloro-, bromo- and iodo substituents are tolerated. Our results indicate that the mechanism of the pincer complex catalyzed and the corresponding palladium(0) catalyzed process is substantially different. It was concluded that the transformations proceed via transmetalation of the organoboronic acids to the pincer-complex catalyst followed by an S(N)2'-type opening of the vinyl epoxide or aziridine substrate. In this process the palladium atom is kept in oxidation state +2 under the entire catalytic process, and therefore oxidative side reactions can be avoided.     

Stability-Indicating HPTLC Analysis of Flurbiprofen in Pharmaceutical Dosage Forms

JPC – Journal of Planar Chromatography – Modern TLC - A sensitive, selective, precise, and stability-indicating high-performance thin-layer chromatographic (HPTLC) method has been...     

Determination of mineral phosphate species in sedimentary phosphate rock in Mardin, SE Anatolia, Turkey by sequential extraction

The importance of the effect of phosphate rock depends on the chemical form of phosphorus in which this element is combined. The paper presents the results of inorganic and organic forms of phosphorus in the phosphate rock from Mazidag-Derik, Semikan deposit located at Mardin city at SE Anatolia of Turkey. Total phosphorus concentration in the rock is an average 18.5%. The inorganic phosphorus mean % contents were 99.98% for studied sedimentary phosphate rock. Speciation of inorganic phosphorus was carried out using a method based on sequential extractions of the sedimentary phosphate rock each releasing four forms of inorganic phosphorus: loosely sorbed phosphorus, phosphorus bound to aluminium (P-Al), phosphorus bound to calcium (P-Ca) and phosphorus bound to iron (P-Fe). Calcium bound phosphorus is the dominant form of inorganic phosphorus in the studied sedimentary phosphate rock. Aluminium bound phosphorus is the second, iron bound phosphorus is the third most prevailing form. Loosely bound phosphorus is present in the lowest amounts. Analyses of phosphorus forms in sedimentary phosphate rock using a UV spectrophotometric method and ICP-AES are reported here. For the phosphorus the two methods give the same results and the concentrations are in good agreement with the reference values.     

Elasto-plastic buckling analysis for perforated steel plates subject to uniform compression

This study investigates the elasto-plastic buckling behaviour of simply supported square and rectangular thin steel plates having elliptic cut-outs by means of finite element method. Plates with simply supported in the out-of-plane direction are applied uniform compression in long-edge direction. A50 steel was used in the analysis and the focus was on the effect of plate aspect ratio, elliptical hole size, elliptical hole angle, elliptical hole location and slenderness ratio on buckling behaviour. It was found in the study that as the plate slenderness ratio increases, the critical buckling stress decreases for all the perforated plates.     

Kinetics of Thermal Decomposition of Plumbo-jarosite

An investigation was carried out on the kinetics of thermal decomposition of plumbo-jarosite. The kinetic models of dissociation of the compounds in the ore were identified. The results of the kinetic studies and the mechanism of the process are discussed. The thermal decomposition of plumbo-jarosite occurs in three stages: the first up to 763, the second up to 1023 and the third up to 1223 K, the corresponding activation energy values being 62.2, 60.3 and 98.0 kJ mol^–1 , respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Boundary value problems for nonlinear second-order difference equations with impulse

In this paper, we consider a boundary value problem with impulse （BVPI）for nonlinear second-order difference equations. Existence and uniqueness of solutions of the considered BVPI are established.     

Elastic buckling of rectangular plates under linearly varying in-plane normal load with a circular cutout

The elastic buckling behavior of rectangular perforated plates was studied by using the finite element method in this study. Circular cutout was chosen at different locations along the principal x-axis of plates subjected to linearly varying loading in order to evaluate the effect of cutout location on the buckling behavior of plates. The results show that the center of a circular hole should not be placed at the end half of the outer panel for all loading patterns. Furthermore, the presence of a circular hole always causes a decrease in the elastic buckling load of plates subjected to bending, even if the circular hole is not in the outer panel.     

Ball mill–assisted synthesis of carbon-free SnSe nanoparticles for sodium-ion battery anodes

Journal of Solid State Electrochemistry - Tin selenide (SnSe) is a potential candidate for sodium-ion battery anodes owing to its high theoretical capacity, environmental benignity, and abundant...