Effect of the Electrochemistry Oxidation and Ultraviolet Irradiation on the Formation of Biomolecules from Ammonium Thiocyanate under Prebiotic Conditions

Author(s)

Vítor Alexandre Nunes de Carvalho

• Document type: Doctoral Thesis
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Instituto de Química de São Carlos (IQSC/BT)
• Defense date: 2016-10-27

Examining board members

Frank Nelson Crespilho; Adalgisa Rodrigues de Andrade; Daniel Rodrigues Cardoso

• Advisor: Frank Nelson Crespilho

Abstract

Since the classic Miller experiment in 1953 evidencing the amino acids formation under early Earth conditions, the chemistry of the prebiotic period is still very discussed. It is cited, for example, the role of sulfocyanic theory, which describes the origin of organic molecules from sulfur-containing compounds such as ammonium thiocyanate (NH4SCN). In this context, this thesis shows a study about the investigation of NH4SCN in prebiotic conditions. Thereby, experiments of electrochemical oxidation and ultraviolet (UV) irradiation were carried out with samples containing NH4SCN in different experimental conditions. By using electrochemistry coupled to Fourier transform infrared spectroscopy (FTIR in situ), the dimer thiocyanogen (SCN)2 was identified as the first oxidation product of NH4SCN, which is a recognized precursor of the oligomers from prebiotic period. In counterpart, UV irradiation of the NH4SCN led to the formation of orthorhombic sulfur (S8) and the nitrogenous bases 4-(3H)-pyrimidinone, cytosine, adenine and purine, besides other molecules. Probably, hydrogen cyanide (HCN) is one of the precursors of the biomolecules abovementioned, contradicting a possible route via (SCN)2. The results of this study also reinforce the hypothesis that there is no direct formation of amino acids by irradiation of NH4SCN. Thus, it is proposed here that the formation of DNA blocks, the nitrogenous bases, can also be inserted in the context of sulfocyanic theory. (AU)

• FAPESP's process: 12/07358-5 - Electrochemical Study of the Interface between Metal Oxides Nanostructures and Organic Molecules in Pre-Biotic Chemical Conditions
• Grantee: Vítor Alexandre Nunes de Carvalho
• Support Opportunities: Scholarships in Brazil - Doctorate