Thermal Wet Decomposition of Prussian Blue: Implications for Prebiotic Chemistry by Marta Ruiz-Bermejo* a ), Celia Rogero a ), Ce ´sar Menor-Salva ´n a ), Susana Osuna-Esteban a ), Jose ´A ´ ngel Martín-Gago a ) b ), and Sabino Veintemillas-Verdaguer a ) b ) a ) Centro de Astrobiología (Consejo Superior de Investigaciones Científicas-Instituto Nacional de Te ´cnica Aeroespacial (CSIC-INTA)), Carretera Torrejo ´n-Ajalvir, Km. 4.2, ES-28850 Torrejo ´ n de Ardoz, Madrid (phone: þ 34 91 520 6402/6458; fax: þ 34 91 5206410; e-mail: ruizbm@inta.es) b ) Instituto de Ciencias de Materiales de Madrid (CSIC), C/ Sor Juana Ine ´s de la Cruz, 3, Cantoblanco, ES-28049 Madrid The complex salt named Prussian Blue, Fe 4 [Fe(CN) 6 ] 3 · 15 H 2 O, can release cyanide at pH > 10. From the point of view of the origin of life, this fact is of interest, since the oligomers of HCN, formed in the presence of ammonium or amines, leads to a variety of biomolecules. In this work, for the first time, the thermal wet decomposition of Prussian Blue was studied. To establish the influence of temperature and reaction time on the ability of Prussian Blue to release cyanide and to subsequently generate other compounds, suspensions of Prussian Blue were heated at temperatures from room temperature to 1508 at pH 12 in NH 3 environment for several days. The NH 3 wet decomposition of Prussian Blue generated hematite, a-Fe 2 O 3 , the soluble complex salt (NH 4 ) 4 [Fe(CN 6 ) ] · 1.5 H 2 O, and several organic compounds, the nature and yield of which depend on the experimental conditions. Urea, lactic acid, 5,5- dimethylhydantoin, and several amino acids and carboxylic acids were identified by their trimethylsilyl (TMS) derivatives. HCN, cyanogen (C 2 N 2 ), and formamide (HCONH 2 ) were detected in the gas phase by GC/MS analysis. Introduction. – It has been suggested that HCN could act as an important prebiotic precursor of purines, pyrimidines, and amino acids, as well as of other compounds such as oxalic acid and guanidine [1]. In the presence of a base media, such as amine or ammonia [2], concentrated solutions of HCN ( < 0.01 m ) can polymerize and produce nucleic acid bases and amino acids, whereas, in dilute solutions, hydrolysis becomes dominant [3]. Taking into account the production rates of HCN in the primitive atmosphere and the experimental hydrolysis rates, the steady-state concentration of HCN in the primitive ocean could be in the range of 4  10 6 –2  10 8 m at pH 8 between 08 and 258 [4]. Miyakawa et al. [5] estimated this concentration to be ca. 2  10  6 m at pH 8 and 08. Therefore, if HCN polymerization was actually important for the production of the first and essential biomolecules, there must have been routes by which diluted HCN solutions were efficiently concentrated. Since HCN is more volatile than H 2 O, it cannot be concentrated by evaporation, if the pH is lower than the pK a of HCN (9.2 at 258 ). An alternative and plausible mechanism is, therefore, eutectic freezing. Miller and co-workers achieved the synthesis of several purine and pyrimidine bases from a frozen NH 4 CN solution (HCN 0.15m plus NH 3 0.1 m ) that had been held at  788 for 27 years [5]. CHEMISTRY & BIODIVERSITY – Vol. 6 (2009) 1309  2009 Verlag Helvetica Chimica Acta AG, Zürich