CO2 activation and functionalization

• Main Author: Barradas, Sean
• Published: 2012
• Subjects: Carbon dioxide; Reduction (Chemistry); Acinetobacter
• Online Access: http://hdl.handle.net/10210/5754

M.Sc. === An Acinetobacter sp. strain RFB1 isolated in our laboratory has been shown to have the ability to metabolise inorganic cyanide salts, CO 2, and bicarbonate. The enzyme aggregate responsible for the conversion of these substrates, is located extra-cellularly. Resolution of the extra-cellular complex, a crude enzyme filtrate, was attempted in order to characterise the protein responsible for the reduction of CO 2. The crude enzyme filtrate was separated by means of molecular exclusion chromatography and afforded three fractions with molecular masses ranging from 76 000 to 191 000. Analysis by SDS-electrophoresis, showed that the first protein fraction contained more than ten proteins. Certain of these proteins were identified in the second fraction and other proteins in the third protein fraction. This implies that some denaturation already occurred during molecular exclusion separation. The functionali7ation of CO 2 by protein fractions 1 and 3 supports this argument, and, in addition , cyanide ions were only reduced by fractions 1 and 2. Fatty acids, ranging with chainlengths between C5 and C25, were shown to be present and certain fatty acids were unequivocally identified by GC-mass spectroscopy as the products resulting from CO2 functionali7ation and carbon-carbon bond formation. Ferrous ions, in an optimal concentration of 250 gg cm', were necessary and served as an essential ingredient of the reaction mixture. A rather unusual result was, however, that apart from an initial, relatively small uptake of Fe(II), significant amounts of Fe(III) were not formed and the Fe(II) concentration remained approximately constant during the reaction. This implies that the formed Fe(M) is rapidly reduced to Fe(II) again. Spectroscopic measurements, furthermore, strongly suggested the involvement of an iron-sulphur cluster in a cyclic redox process wherein both Fe(II) and Fe(III) are involved. Carefully conducted experiments pointed to light as the outside source of energy. Qualitative similarities with an artificial photosynthetic process, formulated earlier by J-M. Lehlliii, can be drawn and used partly to explain the experimental results.