Molecular Synchronization Enhances Molecular Interactions: An Explanatory Note of Pressure Effects

In this study, we investigated a unique aspect of the supramolecular polymerization of tetrakis (4-sulfonatophenyl) porphyrin (TPPS), a self-assembling porphyrin, under non-equilibrium conditions by subtracting the effects of back-pressure on its polymerization. We focused on the enhanced self-assembly abilities of TPPS under a process of rapid proton diffusion in a microflow channel. Rapid protonation caused synchronization of many sets of protonation/deprotonation equilibria on the molecular scale, leading to the production of many sets of growing suparmolecular spices. Pressure effects in the microflow channel, which could potentially promote self-assembly of TPPS, were negligible, becoming predominant only when the system was in the synchronized state.

Kinetics and Mechanism of the Reaction between Chromium(III) and 3,4-Dihydroxy-Phenyl-Propenoic Acid (Caffeic Acid) in Weak Acidic Aqueous Solutions

Our study of the complexation of 3,4-dihydroxy-phenyl-propenoic acid by chromium(III) could give information on the way that this metal ion is available to plants. The reaction between chromium(III) and 3,4-dihydroxy-phenyl-propenoic acid in weak acidic aqueous solutions has been shown to take place by at least three stages. The first stage corresponds to substitution (Idmechanism) of water molecule from the Cr(H2O)5OH2+coordination sphere by a ligand molecule. A very rapid protonation equilibrium, which follows, favors the aqua species. The second and the third stages are chromium(III) and ligand concentration independent and are attributed to isomerisation and chelation processes. The corresponding activation parameters areΔH2(obs)≠= 28.6±2.9 kJmol−1,ΔS2(obs)≠=−220 ±10 JK−1mol−1,ΔH3(obs)≠= 62.9±6.7 kJmol−1andΔS3(obs)≠=−121 ±22 JK−1mol−1. The kinetic results suggest associative mechanisms for the two steps. The associatively activated substitution processes are accompanied by proton release causing pH decrease.

Nucleophilic and acid-catalyzed cleavage of the cyclopropane rings of β,γ-unsaturated α-spirocyclopropyl ketones

Treatment of isophorone (8) with sodium amide and 1,2-dibromomethane gives 6,6-dimethyl-8-methylenespiro[2.5]octan-4-one (9) and 6,6,8-trimethylspiro[2.5]oct-7-en-4-one (10); similar treatment of 3-methylcyclohex-2-en-1-one (5) gives analogous spiro compounds 6 and 7 together with 8-methylenedispiro[2.1.2.3]decan-4-one (11) and 8-methyldispiro[2.1.2.3]dec-8-en-4-one (12). The spiro ketones 6, 7, 9, and 10 undergo homoconjugate nucleophilic addition on being heated in morpholine with cleavage of the cyclopropane rings to give 2-[2-(4-morpholinyl)ethyl]cyclohex-2-en-1-ones. The rates of reaction are much greater for the exo methylene compounds 6 and 9 than for their endo isomers 7 and 10, but the rate of reaction of 10 is only slightly greater than that of the corresponding saturated compound, 6,6,8-trimethylspiro[2.5]octan-4-one (15). A corresponding rate differential between 9 and 10 is observed in their reactions with isophorone (8) and sodium hydride to give 2,2′-(ethanediyl)bis[3,5,5-trimethylcyclohex-2-en-1-one] (18). The acceleration in the cases of 6 and 9 relative to that of 15 is attributed to spiroactivation by both the carbonyl and exocyclic ethylenic groups; the much smaller effect of the endocyclic ethylenic groups in the cases of 7 and 10 is ascribed to torsional strain in the transition states for ring opening. The spiro ketones 6, 7, 9, and 10 also undergo acid-catalyzed cyclopropane ring cleavage in ethanol, giving 2-(2-ethoxyethyl)cyclohex-2-en-1-ones. Again the exo methylene compounds 6 and 9 react much more rapidly than their endo isomers 7 and 10; this is considered to be due to factors analogous to those operative in the nucleophilic addition reactions and/or the more rapid protonation of the exo methylene compounds.

The involvement of the bridging imidazolate in the catalytic mechanism of action of bovine superoxide dismutase

The pulse-radiolysis method has been used to study the catalytic mechanism of O2 leads to dismutation by the Co(II)-substituted bovine erythrocuprein (superoxide dismutase, EC 1.15.1.1). Catalysis is accompanied by spectral changes that may be interpreted in terms of rapid protonation and deprotonation of the Cu-facing nitrogen atom of the imidazolate that bridges the Cu(II) and the Co(II) [or Zn(II)] in the oxidized enzyme. This rapid change permits the possibility that the imidazole is a proton donor in the catalytic reduction of O2 leads to.