The “True” Affinities of Metal Cations to p‐Sulfonatocalix[4]arene: A Thermodynamic Study at Neutral pH Reveals a Pitfall Due to Salt Effects in Microcalorimetry

A microcalorimetric study on the inclusion of monovalent and divalent metal cations by p‐sulfonatocalix[4]arene was performed. The thermodynamic parameters for the complexation of alkali metal cations and Ag⁺ were obtained for the first time at neutral pH. The Na⁺ cation is routinely present as counterion of the calixarene in neutral aqueous solution, and this must be taken into account in the determination of the thermodynamic parameters for the complexation of Na⁺ and the other cations by considering a sequential or a competitive binding scheme. The ΔH° and ΔS° values show that the inclusion process is entropically driven, although an influence of the temperature on the complexation reaction indicates that the enthalpic term is also an important contributor. The results also reveal that enthalpy/entropy compensation balances the gain in one contribution against a corresponding loss in the other. The obtained thermodynamic data are in contrast to the results from previous microcalorimetric studies, which showed binding constants that were orders of magnitude smaller and complexations, which were in part enthalpically driven but which neglected the influence of the alkali metal counterions.     

微孔草新品系种子油中脂肪酸成分的比较

以气相色谱法(GC)测定了微孔草种子油中脂肪酸的含量。发现微孔草种子油中多不饱和脂肪酸含量在84.49%—85.73%之间;其中α-亚麻酸含量在13.74%—16.66%之间,微孔草新品系种子油中α亚麻酸含量均大于北微1号;γ-亚麻酸含量在6.46%—7.64%之间,微孔草新品系种子油中γ-亚麻酸含量均小于北微1号。     

The Sliding Bifurcations in Planar Piecewise Smooth Differential Systems

In this paper we are mainly interested in the bifurcation phenomena for a class of planar piecewise smooth differential systems, where a new phenomenon, i.e. sliding heteroclinic bifurcation, is found. Furthermore we will show that the involved systems can present many interesting bifurcation phenomena, such as the (sliding) heteroclinic bifurcation, sliding (homoclinic) cycle bifurcation and semistable limit cycle bifurcation and so on. The system can have two hyperbolic limit cycles, which are bifurcated in one way from a semistable limit cycle, and in another way from a heteroclinic cycle and a sliding cycle. In the proof of our main results, we will use the geometric singular perturbation theory to analyze the dynamics near the sliding region.     

Photoisomerization of a Maleonitrile‐Type Salen Schiff Base and Its Application in Fine‐Tuning Infinite Coordination Polymers

Strategically designed salen ligand 2,3‐bis[4‐(di‐p‐tolylamino)‐2‐hydroxybenzylideneamino]maleonitrile ( 1 ), which has pronounced excited‐state charge‐transfer properties, shows a previously unrecognized form of photoisomerization. On electronic excitation (denoted by an asterisk), 1Z *→ 1E isomerization takes place by rotation about the C2? C3 bond, which takes on single‐bond character due to the charge‐transfer reaction. The isomerization takes place nonadiabatically from the excited‐state ( 1Z ) to the ground‐state ( 1E ) potential‐energy surface in the singlet manifold; 1Z and 1E are neither thermally inconvertible at ambient temperature (25–30 °C), nor does photoinduced reverse 1E *→ 1Z (or 1Z *) isomerization occur. Isomers 1Z and 1E show very different coordination chemistry towards a Zn^II precursor. More prominent coordination chemistry is evidenced by a derivative of 1 bearing a carboxyl group, namely, N,N′‐dicyanoethenebis(salicylideneimine)dicarboxylic acid ( 2 ). Applying 2Z and its photoinduced isomer 2E as building blocks, we then demonstrate remarkable differences in morphology (sphere‐ and needlelike nanostructure, respectively) of their infinite coordination polymers with Zn^II.     

Analytical and experimental studies on out-of-plane dynamic instability of shallow circular arch based on parametric resonance

Nonlinear Dynamics - Little research about the out-of-plane dynamic stability of arches under in-plane loading has been reported in the literature hitherto. This paper presents analytical and...     

Determination of trans-resveratrol in grapes by pressurised liquid extraction and fast high-performance liquid chromatography

A study has been made of the extraction of trans-resveratrol from grapes using pressurised liquids (PLE); for this, the first stage was to determine the stability of this compound during extractions at different temperatures (50, 100, 150 degrees C), with quantitative recoveries being obtained up to 150 degrees C. By employing solid-phase extraction (SPE) it was possible to retain this compound and separate it from other interfering substances present in the grape. The method developed comprises a sequential extraction of the sample adsorbed (0.5g) on a polystyrene-divinylbenzene based sorbent in the extraction chamber, first with water at 40 degrees C and 40atm of pressure (three cycles of 5min), and then with methanol at 150 degrees C and 40atm (three cycles of 5min). The trans-resveratrol content of the methanolic extract is determined by means of liquid chromatography. A rapid (5min) chromatographic method employing a monolithic column, with fluorescence detection, has been developed; for this, the conditions for detection of the compound were optimised (excitation at 310nm and emission at 403nm). The analytical parameters of the method of chromatographic analysis developed have been calculated: linear range (0.11-2.75mg/L), detection limit (0.003mg/L), quantification limit (0.004mg/L). Using this method, three varieties of grape have been analysed and the concentration of trans-resveratrol in these has been determined.