Chemical Basis of Biological Homochirality during the Abiotic Evolution Stages on Earth

Abstract

Spontaneous mirror symmetry breaking (SMSB), a phenomenon leading to non-equilibrium stationary states (NESS) that exhibits biases away from the racemic composition is discussed here in the framework of dissipative reaction networks. Such networks may lead to a metastable racemic non-equilibrium stationary state that transforms into one of two degenerate but stable enantiomeric NESSs. In such a bifurcation scenario, the type of the reaction network, as well the boundary conditions, are similar to those characterizing the currently accepted stages of emergence of replicators and autocatalytic systems. Simple asymmetric inductions by physical chiral forces during previous stages of chemical evolution, for example in astrophysical scenarios, must involve unavoidable racemization processes during the time scales associated with the different stages of chemical evolution. However, residual enantiomeric excesses of such asymmetric inductions suffice to drive the SMSB stochastic distribution of chiral signs into a deterministic distribution. According to these features, we propose that a basic model of the chiral machinery of proto-life would emerge during the formation of proto-cell systems by the convergence of the former enantioselective scenarios.

Chaotic oscillations, dissipation and mirror symmetry breaking in a chiral catalytic network

“…14 The racemic state becomes metastable along the so-called thermodynamic branch and the intrinsic statistical chiral fluctuations perturb the system, provoking a transition to one of two energetically degenerate final chiral states: a bifurcation to ordered scalemic states takes place with a consequent decrease in the symmetry, and for which the production of entropy is minimized with respect to the former racemic configuration. This bifurcation trend together with the minimization of entropy production has been confirmed via numerical simulations for a variety of model chemical systems capable of reaching non-equilibrium steady states; 22,[33][34][35][36][37] here we show it holds as well for chaotic dynamics.…”

“…This kinetic approximation of clamped concentrations for the chemical species exchanges with the environment overlooks the role of the boundary conditions of open flow systems for the correct description of non-equilibrium stationary states. 33 In open volumetric flow systems however (as in Fig. 2), the affinities, or chemical forces, depend on both the internal bulk system reactions as well as on the matter fluxes entering and leaving the system, just as in open flow reactors.…”

Handed Mirror Symmetry Breaking at the Photo-Excited State of π-Conjugated Rotamers in Solutions

“…It is commonly understood in chemistry that molecules in the photoexcited state lose energy via a non-radiative decay channel. In principle, the non-radiative loss can be curbed if molecular rotational and vibrational modes are restricted in viscous solvents [48,49]. To collect more evidence on the parity-violating (-)-sign CPL enhancement with the viscosity of the solvent, the mean excited state lifetime (τ)of luminophores and relative Φ f were measured as a function of viscosity in selected solvents (ethanol = The τ values for DSA, DSBA, and DSBP reduced linearly with an increase in the viscosity of the solvent (Figure 2b).…”

“…Additional theoretical models of real and imaginary molecules have been referred to in several innovative re-ports, along with experimental attempts [6][7][8][12][13][14][16][17][18]20,[25][26][27][28][29][41][42][43][44][45][46]. Recent reports highlight the advance in the realm of MPV [47][48][49][50].…”

“…Relationships between radiative decay rate (Kf), photoluminescence lifetime (τ), and quantum yield (Φf) of DSA (red filled circles and squares), DSBA (blue filled circles and squares), and DSBP (black filled circles and squares) (a), the relationship between Φf, τ and the viscosity of four alcohols (b), and the relationship between Kf and the solvent viscosity (c). The solvents are ethanol 1.19 cP (25 °C), n-pentanol 3.47 cP (25 °C), n-octanol 7.59 cP (25 °C), and n-undecanol 16.95 cP (25 °C))[48,49].…”