The base-catalyzed keto-enol tautomerism of chrysophanol anthrone. A DFT investigation of the base-catalyzed reaction

The keto-enol tautomerization of chrysophanol anthrone was systematically investigated via a series of density functional theory computations using the M06-2X/6-31?+?G(d,p) level of theory. Bulk solvent effects were taken into account implicitly using the polarisable continuum model and explicitly with one pyridine molecule. Moreover, the tautomeric equilibrium was estimated by calculating the equilibrium constant. The pyridine-assisted tautomerism was found to be the energetically preferred pathway, where the pyridine acts as a proton carrier through a two-step reaction, in which the first one corresponds to the deprotonation of the chrysophanol anthrone and the second step to the protonation yielding the enol form. The results show, in accordance with experimental reports, that in the process of dissociation of the protonated pyridine and the aryloxylate anion, the ion is quite susceptible to oxidation. The highly dipolar structures of the transition states and intermediates are stabilised by pyridine up to 7.0?kcal/mol. The non-covalent interactions stabilising the transition states and the intermediates were analysed. Additionally, an intermolecular hydrogen bonding between the enol form of chrysophanol anthrone and the pyridine is formed at the last stage of the reaction. The keto-enol equilibrium analysis shows that the enol form of chrysophanol anthrone must be present in small amounts in basic solvents.     

A cytoplasmically inherited mutation in the fungus Phycomyces blakesleeanus

Fourteen mutants of the fungus Phycomyces blakesleeanus, showing high levels of resistance to copper, were isolated. In all the mutants, copper resistance behaved as a very variable and unstable trait. In the mutant strain MU102, the mutation was demonstrated to be cytoplasmically inherited. In addition, this mutant strain differed from the wild-type in growth, respiration rate, and shape and viability of spores.     

Isolation of the facA (acetyl-CoA synthetase) gene of Phycomyces blakesleeanus

A 5.6 kb DNA fragment from the fungus Phycomyces blakesleeanus has been cloned and sequenced. The fragment contains a gene that probably codes for the enzyme acetyl-coenzyme A synthetase (facA). The amino acid sequence deduced for the P. blakesleeanns protein is highly homologous to those of acetyl-coA-synthetases from other organisms. When placed under the control of a constitutive promoter from Aspergillus nidulans, the cloned gene complemented a facA mutation of this organism. In P. blakesleeanns, the expression of facA is induced by acetate.