Electrochemically controlled formation/dissociation of phosphonate-cavitand/methylpyridinium complexes

The phosphorus-bridged cavitand 1 self-assembles very efficiently in CH2Cl2 with either the monopyridinium guest 2+ or the bispyridinium guest 3(2+). In the first case a 1:1 complex is obtained, whereas in the second case both 1:1 and 2:1 host-guest complexes are observed. The association between 1 and either one of the guests causes the quenching of the cavitand fluorescence; in the case of the adduct between 1 and 3(2+), the fluorescence of the latter is also quenched. Cavitand complexation is found to affect the reduction potential values of the electroactive guests. Voltammetric and spectroelectrochemical measurements show that upon one-electron reduction both guests are released from the cavity of 1. Owing to the chemical reversibility of such redox processes, the supramolecular complexes can be re-assembled upon removal of the extra electron from the guest. Systems of this kind are promising for the construction of switchable nanoscale devices and self-assembling supramolecular materials, the structure and properties of which can be reversibly controlled by electrochemical stimuli.     

Rethinking polyhedrality for lindenstrauss spaces

We present a Lindenstrauss space with an extreme point that does not contain a subspace linearly isometric to c. This example disproves a result stated by Zippin in a paper published in 1969 and it shows that some classical characterizations of polyhedral Lindenstrauss spaces, based on Zippin’s result, are false, whereas some others remain unproven; then we provide a correct proof for those characterizations. Finally, we also disprove a characterization of polyhedral Lindenstrauss spaces given by Lazar, in terms of the compact norm-preserving extension of compact operators, and we give an equivalent condition for a Banach space X to satisfy this property.     

Thrombin allostery

Thrombin is a Na(+)-activated, allosteric serine protease that plays multiple functional roles in blood pathophysiology. Binding of Na(+) is the major driving force behind the procoagulant, prothrombotic and signaling functions of the enzyme. This review summarizes our current understanding of the molecular basis of thrombin allostery with special emphasis on the kinetic aspects of Na(+) activation. The molecular mechanism of thrombin allostery is a remarkable example of long-range communication that offers a paradigm for many other biological systems.     

Chemoselective and efficient carbomethoxylation of the alcoholic chain of phenols by dimethyl carbonate (DMC)

The efficiency of dimethyl carbonate (DMC) as chemoselective carbomethoxylating agent of the alcoholic chain of phenols has been investigated. In the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) or sulfuric acid as catalysts, new carbomethoxylated phenolic compounds were obtained in quantitative yields. A new efficient derivatization of the aliphatic alcoholic chain of the precious natural hydroxytyrosol is described, which increases the lipophilicity of the hydroxytyrosol. The antioxidant activity of this new carboxymethylated hydroxytyrosol 8 has been investigated using DPPH radical scavenging test. The results showed that this new compound has an antioxidant activity similar to hydroxytyrosol.     

Monitoring the traceability of the pH of a primary tetraborate buffer: comparison of results from primary and secondary apparatus

This paper reports evaluation of the behaviour of different combined glass electrodes applied to measurement of the pH of a primary, 0.01 mol kg⁻¹, tetraborate buffer. Measurements were first performed by use of a primary Harned cell (at 15, 25, and 37 °C); these results were then compared with those obtained for the same solution by use of three combined glass electrodes (25 °C) with different membranes and liquid-junction designs, calibrated by use of commercial pH-metric buffers. The pH of the same solution was also measured in terms of the molal concentration of hydrogen ions, using acid–base titration to evaluate the formal potential difference K of each cell at fixed ionic strength, I, adjusted by addition of KCl or Et₄NI (tetraethylammonium iodide). The reference value from primary measurement, paH = 9.171, was slightly closer to the mean value obtained by determination of concentration, rather than that obtained by direct measurement of activity; the differences were smaller than the extended uncertainty characteristics of the secondary measurements. The importance of evaluation of the ionic strength of the solution under study is emphasised. We verified that for tetraborate buffer slight modification of the value of I used to calculate γ _i (the activity coefficient of a single ion) in the calculation of paH from the acidity function at zero molality of chloride can significantly affect the reference value of the calibrator tool. This is true, in general, for low values of the ionic strength, such as those considered in this work; an approximate value of I can then cause distortions along the pH traceability chain. Application of the concepts of thermodynamics to this traceability chain is discussed.     

A supramolecular approach to sub-ppb aromatic VOC detection in air

Micromachining technology is coupled to a selective pre-concentration material for the development of a portable sub-ppb level monitoring system for aromatic volatile organic compounds (VOC); the high sensitivity of Metal Oxide (MOX) gas sensors is combined with a supramolecular concentration unit to increase selectivity and reduce the detection limits.