Fission tracks as a key to biomolecular chirogenesis

With regard to the origin of life, any putative role of naturally etched nuclear particle tracks under early Precambrian weathering conditions has not yet been addressed. Chemical building blocks of life, as for example amino acids, peptides, and sugar molecules, are almost exclusively incorporated in one of two mirror image forms, i.e. either left-handed or right-handed. Polymers or any other chemical systems are called homochiral, when the involved chiral (i.e. handed) units consist of only one molecular species, either left-handed or right-handed. It is generally assumed that such homochirality of organic molecules was a basic pre-requisite for self-replication of the very early living systems. Several alternative hypotheses for the origin of lifes homochirality were discussed. They can be grouped in extraterrestrial (interstellar) and terrestrial (planetary) models, as well as in determinate and random processes. A determinate process might be due to the weak nuclear interaction which has been proven to be asymmetric. Another way to chiral excess could be due to the interaction of circularly polarized radiation with organic molecules in the interstellar space. Random models for the appearance of biomolecular homochirality are based on the assumption that a small asymmetry during initial nucleation of crystals is amplified by autocatalytic crystallization. HEJL (2017) has proposed a new hypothesis for molecular separation in course of the chemical etching process of nuclear particle tracks, as for example fission tracks originating from the spontaneous or induced fission of 238U or 235U, respectively. The hypothesis relies on the principle of liquid chromatography, i.e. on different residence probabilities (partition) of dissolved molecular species on the walls of a capillary tube. When such tubes occur in an enantiomorphic crystal either left-handed or right- handed they should produce a slight separation of left-handed and right-handed molecules. Testing this hypothesis is the main goal of this research project. The project is dedicated to the revelation of uranium fission tracks in minerals which occur in a left-handed and right-handed form. It includes neutron irradiation, etching and infiltration experiments with dissolved mixtures of biomolecules, and chemical analysis of right-handed and left-handed molecular species.

Fission tracks in enantiomorphic minerals as a putative key to biomolecular chirogenesis With regard to the origin of life, any putative role of naturally etched nuclear particle tracks under early Precambrian weathering conditions has not yet been addressed. Chemical building blocks of life, as for example amino acids, peptides, and sugar molecules, are almost exclusively incorporated in one of two mirror image forms, i.e. either left-handed or right-handed. Polymers or any other chemical systems are called homochiral, when the involved chiral (i.e. handed) units consist of only one molecular species, either left-handed or right-handed enantiomers. It is generally assumed that such homochirality of organic molecules was a basic pre-requisite for self-replication of the very early living systems. Several alternative hypotheses for the origin of life's homochirality were discussed. They can be grouped in extraterrestrial (interstellar) and terrestrial (planetary) models, as well as in determinate and random processes. A determinate process might be due to the weak nuclear interaction which has been proven to be asymmetric. Another way to chiral excess could be due to the interaction of circularly polarized radiation with organic molecules in the interstellar space. Random models for the appearance of biomolecular homochirality are based on the assumption that a small asymmetry during initial nucleation of crystals is amplified by autocatalytic crystallization. This project was dedicated to the question if and how strong selective adsorption of either left-handed or right-handed biomolecules may occur on the surfaces of right-handed or left-handed quartz. In addition, a putative alteration of this effect by strong radiation damage (i.e. nuclear particle tracks in quartz) was considered. The experiments were conducted with aqueous solutions of the amino acids alanine and leucine. In this way, rather high enantiomeric excesses far above the limits of detection were obtained. Enantiomeric excesses of up to 15 % were obtained for alanine, and even 56 % for leucine. In the case of alanine, this effect was higher when pre-irradiated quartz with etched nuclear particle tracks was used, but in the case of leucine, the enantioselective adsorption was diminished when pre-irradiated quartz with etched nuclear particle tracks was used. Anyway, local enantioselective separation of biomolecules can be expected in the pores of natural quartz sand.