Radiolysis of aqueous solutions of hydrogen cyanide (pH∼6): Compounds of interest in chemical evolution studies

Abstract

Oxygen-free aqueous solutions of hydrogen cyanide, 0.1 M and pH ~6, were exposed to gamma rays from a 60Co source, the mixture of nonvolatile products was fractionated and the fractions were analysed. It has been found that the complex mixture contains oligomers and polymers with molecular weights up to 20,000 daltons, mainly polyamides with urea and peptidic fragments. Among the constituents are carbamyl glycinonitrile and carbamyl glycinamide that represent 6.4% and 3.1% of the total of unfracfionated material respectively. Urea content is 2.6%, but the derivatives of urea are more abundant. Acid hydrolysis releases several amino acids. Glycine is the most abundant (75% or more of total amino acid content), and its concentration considerably increases in some fractions when the hydrolysis is carried out at 130~ The role of free radicals in reactions leading to the formations of radiolytic products is considered. Some comparisons are made between findings in the present work, at initial pH ~6, and an earlier study of ammonium cyanide at pH 9.

Radiation chemistry of overirradiated aqueous solutions of hydrogen cyanide and ammonium cyanide

“…The amino acid analysis of hydrolysates of the dry residues showed the presence of amino acids that we saw at lower doses in previous work (Dra-gani6 et al 1977b(Dra-gani6 et al , 1980Niketi6 et al 1983): aspartic acid, threonine, serine, glutamic acid, alanine, #-alanine, and histidine. With the exception ofserine and histidine, they were all also confirmed by gas chromatography-mass spectrometry (GC-MS).…”

“…5) suggests that the absorbances of the biuret complex are much stronger than would be expected from the amino acid contents (molar absorptivity of the peptide bond in the biuret test was taken to be 800 M-~; Draganid et al 1980). Apart from the peptidic material, two oligomers that are already formed at low doses and were considered earlier (Dragani6 et al 1980;Niketi6 1983;Niketi6 et al 1983) are among the radiolytic products contributing to the formation of the absorbing complex: oligoamide and urea-aldehyde.…”

“…5 shows that glycine is by far the most abundant amino acid. It originates not only from peptidic material, but also in the hydrolyses of certain carbamyl-glycine radiolytic products that are known to represent at least about 11% of the mass of dry residue: N-carbamylglycinonitrile (HCN, 6.4%; NH4CN, 3%), N-carbamylglycinamide (HCN, 3.1%;Niketi6 et al 1983), N-carbamylglycinoureid (HCN, 1.1%), and bis(carbamyl-glycyno)oxotriazine (NH4CN, 8.3%; Niketi6 1983). The rapid decrease in total amino acid concentration with increasing dose at doses up to about 40 Mrad is mainly due to loss of glycine from carbamyl-glycine derivatives.…”

“…The bulk of the irradiated solution (100-400 ml) was evaporated at reduced pressure and 45"C to about 10 ml and the concentrate was transferred to a freeze-drier and lyophilized. After lyophilization the dry residue was weighed and used for further analyses: the biuret test (Ellman 1962), infrared spectra, determination of earboxylic acids after hydrolysis and esterification (Negr6n-Mendoza et al 1983), and search for amino acids upon acid hydrolysis (Dragani~ et al 1980;Niketi6 et al 1983). Molecular weight estimation was done on a 1 x 11.5 cm Bio-gel P-10 column using 4 M urea solution for elution (Niketi6 et al 1983).…”

Unearthing the Mechanism of Prebiotic Nitrile Bond Reduction in Hydrogen Cyanide through a Curious Association of Two Molecular Radical Anions

“…The abundance of the HCN ( 1 ) molecule in interstellar space, frozen comets and the atmosphere of planets certainly strengthens the likelihood of HCN playing a crucial rule in the chemical roadmap for the generation of molecules that are essential for the origin of life 9–11. Experiments over several decades have repeatedly demonstrated that the radiolysis of aqueous solutions of HCN and cyanides generates the very basic building blocks of life, namely nucleobases and amino acids 12–14. However, such radiolytic processes spawn several reactive species, namely radicals and solvated electrons, leading to a myriad possibilities and resulting in a multitude of products, thus preventing a thorough understanding of the underlying mechanisms.…”