ABSTRACT
The emergence of the citric acid cycle is one of the most remarkable occurrences with regard to understanding the origin and evolution of metabolic pathways. Although the chemical steps of the cycle are preserved intact throughout nature, diverse organisms make wide use of its chemistry, and in some cases organisms use only a selected portion of the cycle. However, the origins of this cycle would have arisen in the more primitive anaerobic organism or even back in the proto-metabolism, which likely arose spontaneously under favorable prebiotic chemical conditions. In this context, we report that UV irradiation of formamide in the presence of titanium dioxide afforded 6 of the 11 carboxylic acid intermediates of the reductive version of the citric acid cycle. Since this cycle is the central metabolic pathway of contemporary biology, this report highlights the role of photochemical processes in the origin of the metabolic apparatus.
Subject(s)
Citric Acid Cycle , Titanium/chemistry , Biological Evolution , Catalysis , Formamides/chemistry , Gas Chromatography-Mass Spectrometry , Metabolic Networks and Pathways , Oxidation-Reduction , Photosynthesis , Ultraviolet RaysABSTRACT
Designing large Schmidt cameras using the polynomial expansion may yield a not-perfect spherical aberration correction. We indicate an alternative method to design the corrector, whose integration in a software package is in progress. The shape of the corrector can be determined with a simple recursive method. The incidence point can also be calculated for any ray, as well as the corresponding unitary vector normal to the surface.
