Control of the electrode temperature for electrochemical studies: A new approach illustrated on porous anodizing of aluminium

A new approach for studying the effect of temperature on electrochemical processes is presented in this paper. Using an in-house developed electrode holder, experiments are performed under conditions of applied and controlled electrode temperature. This new approach provides an improved temperature control during the experimental study and, additionally, allows distinguishing both the influences of the electrolyte and electrode temperatures. The advantages of the applied electrode temperature approach are illustrated by considering porous anodizing of aluminium. In a broad temperature range the electrochemical behaviour of the aluminium electrodes, recorded during the new and the conventional way of anodizing, are compared. Differences between the anodic potential evolutions in both approaches are observed, and are explained by a heat flux to the surroundings during the experiments at uncontrolled electrode temperature. These results illustrate the advantage of applying the electrode temperature. If the influence of temperature on a process is investigated by merely varying the electrolyte temperature, the electrode temperature is only indirectly influenced and can significantly differ from the electrolyte temperature. Therefore, when evaluating the influence of temperature on an electrochemical system the electrode temperature should be considered, and preferentially also controlled.     

Synthesis of the bis-potassium salts of 5-hydroxy-3-oxopent-4-enoic acids and their use for the efficient preparation of 4-hydroxy-2H-pyran-2-ones and other heterocycles

5-Hydroxy-3-oxopent-4-enoic acid esters can be efficiently transformed into the stable bis-potassium salts of the corresponding 5-hydroxy-3-oxopent-4-enoic acids, from which the sensitive acids are released in situ, the latter being converted into substituted 4-hydroxy-2H-pyran-2-ones, pyrazoles and isoxazoles under mild conditions; the efficiency of this method is demonstrated by the first synthesis of two naturally occurring pyrones.     

Iron porphyrins catalyze the synthesis of non-protected amino acid esters from ammonia and diazoacetates

Iron complexes of porphyrins (and corroles to a lesser extent) are the first catalysts to utilize ammonia for the synthesis of N-free amino acid esters.     

Hydrogen bonding in dimers of tritolyl and tritosylurea derivatives of triphenylmethanes

The crystal structure of the homodimer formed by the tritolylurea 3a proves the existence of a belt of six bifurcated hydrogen bonds between both NH and the O=C groups of the adjacent urea residues. For the tritosylurea 3b, four additional three-center hydrogen bonds, also involving the SO2 oxygen, are found in the crystalline state. Molecular dynamics simulations in a chloroform box confirm these patterns of the hydrogen bonds and the resulting elongation of the dimer 3b. 3b in comparison to 3a x 3a. The calculated complexation energies for the three dimeric combinations are nearly identical in agreement with the simultaneous formation of heterodimer 3a x 3b in a mixture of 3a and 3b.     

Rapid reduction of pentavalent antimony by trypanothione: potential relevance to antimonial activation

The dithiol trypanothione can reduce an antiparasitic pentavalent antimony agent to trivalent rapidly; this reduction process is both pH and temperature dependent and trypanothione may therefore play an important role in the activation of the drug.     

Unusual conformations of 1,3‐dialk­oxy­thia­calix[4]arenes in the solid state

The structures of three syn‐1,3‐dialkoxy­thia­calix[4]arenes with unusual conformations in the solid state are reported. The pinched cone conformation of syn‐2²,4²‐dihydroxy‐1²,3²‐bis­(prop‐2‐enyl­oxy)thia­calix[4]arene, C₃₀H₂₄O₄S₄, (3a), is stabilized by two intra­molecular hydrogen bonds, remarkably formed from both OH groups to the same ether O atom. In syn‐2²,4²‐dihydroxy‐1⁵,2⁵,3⁵,4⁵‐tetra­nitro‐1²,3²‐bis­(prop‐2‐enyl­oxy)thia­calix[4]arene acetone disolvate, C₃₀H₂₀N₄O₁₂S₄·2C₃H₆O, (3b1), the mol­ecule is found in the 1,3‐alternate conformation. The crystallographic C2 symmetry is due to a twofold rotation axis running through the centre of the calixarene ring. The hydroxy groups cannot form intra­molecular hydrogen bonds as in (3a) and both are bonded to an acetone solvent mol­ecule. The mol­ecule of the pseudo‐polymorph of (3b1) in which the same compound crystallized without any solvent, viz. (3b2), is located on a crystallographic mirror plane. Only one of the two hydroxy groups forms a hydrogen bond, and this is with a nitro group of a neighbouring mol­ecule as acceptor. Mol­ecular mechanics calculations for syn‐1,3‐diethers suggest a preference of the 1,3‐alternate over the usual cone conformation for thia­calix[4]arene versus calix[4]arene and for para‐nitro versus para‐H derivatives.     

Templated metal catalysis for single nucleotide specific DNA sequence detection

A catalytic DNA-templated reaction of hydrolysis of an ester group in an N-modified peptide nucleic acid, which is activated by a Cu2+ complex-PNA, has been discovered and optimized. Both the ester-containing PNA and the metal complex PNA bind neighboring sites on a template DNA. This brings the reacting groups (the ester and the Cu2+ complex) in proximity to each other and accelerates the hydrolysis of the ester approximately 500 times in comparison with its hydrolysis in the absence of the template. The hydrolysis reaction provides >10(2)-fold kinetic discrimination between DNAs that are different from each other at a single nucleotide position. Natural enzyme T4 DNA ligase is slightly less selective. On the basis of this reaction a fully homogeneous and sensitive assay for sequence-specific DNA detection has been developed (10 fmol DNA). Identification of one of four DNAs (variation at one position) can be done in a single experiment. Since the Cu2+ ion is tightly bound in an associate containing the ester PNA, the metal complex PNA, and the template DNA, application of this method in buffers containing other Cu2+-binding ligands, e.g., PCR buffer and physiological buffer, is possible.