[en] Short communication

[en] The origin of chirality is closely related to the evolution of life on the Earth. Until now, no proposed mechanism has been able to explain how the completely asymmetric roles of mirror-image biological molecules could arise. Recently, Salam proposed that due to the attractive character of the parity violating force in electro-weak interactions, a phase transition at low temperature could eventually lead to enantiomeric purity. Specific heat measurement is one of the powerful method to investigate the mechanism of second order phase transitions. A series of experimental tests has been undertaken and we have studied the differential specific heats of D and L Valine in single crystal state with sample mass being 100mg and 30mg respectively by differential scanning calorimetry in the temperature range 77-320K. Experimental data are presented on the temperature dependence of the specific heat in Figure. The specific heat jump at Tc 272K indicates the symmetry breaking of D-Valine. There is a smooth line of Cp-T(K) with L-Valine sample in the same temperature range. Furthermore, a specific heat peak at 272K has also been found with L-Valine as the reference sample and D-Valine. It seems to undergo a phase transition only in D-Valine. (author). 4 figs. Abstract only

[en] Short communication

[en] Unexpectedly, scalemic mixtures (>0% ee) show a significant discrimination during distillation. The most pronounced effects were observed for (S>R)-N-TFA-amino acid esters (valine, leucine, alanine), with differences of up to 20% ee in the fractions, as determined by GC on L- and D-Chirasil-Val. We define the kinetic enantioselectivity α_k of the phase transition on the basis of the relative rates: α_k = K_R/K_S where (K_R = -Δ[R]/[R]/Δt) ≥ (k_S = -Δ[S]/[S]/Δt). In contrast, a merely thermodynamic interpretation was ruled out by vapor pressure measurements: The boiling points of RS- and S-N-TFA-Val-OMe differ by no more than ΔT < 0.25 deg. C, whereas thermodynamic calculations would demand for ΔT > 7.5 deg. C. In the course of the distillation, a gradient of ee is built up along the column. The picture of two-dimensional homochiral domains at the liquid gas interface is corroborated by physicochemical studies in the neat liquid, including ¹H- and ¹³C-NMR spectra, surface tensions and excess volumes of mixing of the enantiomers. Like in living systems, non-equilibrium effects driven by a flux of energy manifest themselves in transient local ordering of the system. (author). 1 ref., 3 figs. Abstract only

[en] The report includes 17 summaries of the papers presented at the Third Trieste Conference on Chemical Evolution concerning the structure and model of the first cell which was the central theme of the conference. A separate indexing is provided for each summary. Refs and figs

[en] Short communication. 1 fig

[en] Short communication

[en] Short communication

[en] Short communication. 4 refs

[en] A review is presented within the framework of the theory of evolution, after it has been extrapolated from the population level to the cellular and molecular levels. From Darwin's seminal and persuasive insight - the theory of common descent - we assume, with him, that ''probably all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed''. We are now aware that this primordial cell may have been a protocyanobacterium, but it has often been called 'a last universal ancestor', a 'breakthrough organism', or a 'progenote', a term introduced by Woese which has gained wide acceptance. Strictly speaking, in the 'intermediate period', ranging from the first living cell to the progenote, life may have evolved in the absence of significant diversity, effectively as a single phylum, incorporating organisms whose genetic systems were already based on DNA. Earlier still, prior to the encapsulation of nucleic acids in microspheres, evolution may already have been at work on RNA molecules (the 'RNA world'). This takes our discussion into the period of chemical evolution, a concept first put forward by Oparin, whose principal merit is to have formulated the underlying problem in clear scientific terms. This review does not attempt to be comprehensive. It is mainly devoted to the discussion of certain concepts that may have played a relevant role in the pathway that led to the origin and evolution of the progenote. We do not dwell on the main events of the intermediate period. The topics that we have chosen to include are: the origin of chirality of protein amino acids, the origin of translation, and the origin of the genome. We conclude with some comments on one further aspect of the evolutionary process - the development of biodiversity - by considering the origin of the first eukaryotic cell, an event which, according to the fossil record, may have preceded the evolutionary radiation in the early Cambrian by over a billion years. (author). Abstract only