Condensed thymine films at the mercury/water interface

Adsorption of Cytosine on a Mercury Electrode

The electrosorption behavior of cytosine at the mercury electrode/acetic buffer of pH 4 and 5 interfaces was determined from the double-layer differential capacity measurements extrapolated to zero frequency. Solutions of cytosine were prepared to cover the range from 1 × 10-4 to 6 × 10-3 mol dm-3. Adsorption of cytosine was described by the adsorption isotherms constants derived from the surface pressure data as a function of electrode charge density and bulk concentration. The obtained values of the relative surface excesses Γ′ were higher in the acetic buffer of pH 4 than of pH 5. Maximum of cytosine adsorption in the mentioned buffers was at -581 and -551 mV, respectively. The values of the standard Gibbs energy ∆G° obtained from the Frumkin isotherm were higher in the buffer of pH 4 than of pH 5. The values of the interaction parameter A indicated weaker repulsive interaction between adsorbed molecules of cytosine in the former buffer. The adsorption parameters obtained from the virial isotherm confirmed corresponding parameters obtained from the Frumkin isotherm. The dependences of ΦM-2 on the relative surface excess at a constant charge density were analyzed in order to calculate the electrostatic parameters of the inner layer.

Condensation of nucleobases at mercury/aqueous solution interface--a structural perspective using hydrogen bonding considerations

The two-dimensional condensation behavior exhibited by nucleobases at a mercury/aqueous solution interface is analyzed on the basis of their hydrogen-bonded quadruplex structures, and the experimentally observed critical temperatures are rationalized incorporating different types of hydrogen bonding, surface coordination effects, and stacking considerations. The proposed methodology provides a structural basis for the interpretation of critical temperatures and enables the calculation of the same pertaining to different modified nucleobases. The applicability of the procedure to order-disorder transitions of water dipoles at Hg electrodes is also indicated.

Life before RNA

The hypothesis that life originated and evolved from linear informational molecules capable of facilitating their own catalytic replication is deeply entrenched. However, widespread acceptance of this paradigm seems oblivious to a lack of direct experimental support. Here, we outline the fundamental objections to the de novo appearance of linear, self-replicating polymers and examine an alternative hypothesis of template-directed coding of peptide catalysts by adsorbed purine bases. The bases (which encode biological information in modern nucleic acids) spontaneously self-organize into two-dimensional molecular solids adsorbed to the uncharged surfaces of crystalline minerals; their molecular arrangement is specified by hydrogen bonding rules between adjacent molecules and can possess the aperiodic complexity to encode putative protobiological information. The persistence of such information through self-reproduction, together with the capacity of adsorbed bases to exhibit enantiomorphism and effect amino acid discrimination, would seem to provide the necessary machinery for a primitive genetic coding mechanism.

Origins of life: a route to nanotechnology

The origins of life and nanotechnology are two seemingly disparate areas of scientific investigation. However, the fundamental questions of life's beginnings and the applied construction of a Drexlerian nanotechnology both share a similar problem; how did and how can self-reproducing molecular machines originate? Here we draw attention to the coincidence between nanotechnology and origins research with particular attention paid to the spontaneous adsorption and scanning tunneling microscopy investigation of purine and pyrimidine bases self-organized into monolayers, adsorbed to the surfaces of crystalline solids. These molecules which encode biological information in nucleic acids, can form supramolecular architectures exhibiting enantiomorphism with the complexity to store and encode putative protobiological information. We conclude that the application of nanotechnology to the investigation of life's origins, and vice versa, could provide a viable route to an evolution-driven synthetic life.

Differential adsorption of nucleic acid bases: Relevance to the origin of life

The adsorption of organic molecules onto the surfaces of inorganic solids has long been considered a process relevant to the origin of life. We have determined the equilibrium adsorption isotherms for the nucleic acid purine and pyrimidine bases dissolved in water on the surface of crystalline graphite. The markedly different adsorption behavior of the bases describes an elutropic series: guanine > adenine > hypoxanthine > thymine > cytosine > uracil. We propose that such differential properties were relevant to the prebiotic chemistry of the bases and may have influenced the composition of the primordial genetic architecture.