The only indisputable evidence on the occurrence of amino acids outside our planet is their detection in carbona- ceous chondrites. However only a small fraction was found in chemically free state, whereas hydrolyzable derivatives of unknown composition (possibly amides) is a major source of the detectable amino acids. The difference between carbona- ceous chondrites and the icy bodies (interstellar ices and comets) is the basic component, wich is water in the latter case. Thus it is reasonable to expect for a higher content of hydrolyzed derivatives (free amino acids as final products) in the icy bodies, as compared to the one in carbonaceous chondrites. As a preliminary test for energetic feasibility of this type of reactions, we studied theoretically the reaction of glycine amide hydrolysis, at the B3LYP/6-31++(d,p) level. We found that a very high activation barrier makes this reac- tion prohibited. Besides molecular water, a similar hydro- lytic effect might be produced by hydroxyl radicals (OH) generated under ionizing action of cosmic rays. Therefore we tested the reaction of glycine amide with OH radical as well. Nevertheless, althought the barrier height decreased signifi- cantly, by ca. 30 kcal/mol, it remained positive.

Micron-sized sample preparation for AFM and SEM

MARAS, Adriana;
2004

Abstract

The only indisputable evidence on the occurrence of amino acids outside our planet is their detection in carbona- ceous chondrites. However only a small fraction was found in chemically free state, whereas hydrolyzable derivatives of unknown composition (possibly amides) is a major source of the detectable amino acids. The difference between carbona- ceous chondrites and the icy bodies (interstellar ices and comets) is the basic component, wich is water in the latter case. Thus it is reasonable to expect for a higher content of hydrolyzed derivatives (free amino acids as final products) in the icy bodies, as compared to the one in carbonaceous chondrites. As a preliminary test for energetic feasibility of this type of reactions, we studied theoretically the reaction of glycine amide hydrolysis, at the B3LYP/6-31++(d,p) level. We found that a very high activation barrier makes this reac- tion prohibited. Besides molecular water, a similar hydro- lytic effect might be produced by hydroxyl radicals (OH) generated under ionizing action of cosmic rays. Therefore we tested the reaction of glycine amide with OH radical as well. Nevertheless, althought the barrier height decreased signifi- cantly, by ca. 30 kcal/mol, it remained positive.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11573/187821
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