Field-Control, Phase-Transitions, and Life's Emergence

Abstract

Instances of critical-like characteristics in living systems at each organizational level (bio-molecules to ecosystems) as well as the spontaneous emergence of computation (Langton), do suggest the relevance of self-organized criticality (SOC). But extrapolating complex bio-systems to life's origins, brings up a paradox: how could simple organics - lacking the "soft-matter" response properties of today's complex bio-molecules - have dissipated energy from primordial reactions (eventually reducing CO(2)) in a controlled manner for their "ordering"? Nevertheless, a causal link of life's macroscopic irreversible dynamics to the microscopic reversible laws of statistical mechanics is indicated via the "functional-takeover" of a soft magnetic scaffold by organics (c.f. Cairns-Smith's "crystal-scaffold"). A field-controlled structure offers a mechanism for boot-strapping - bottom-up assembly with top-down control: its super-paramagnetic colloidal components obey reversible dynamics, but its dissipation of magnetic (H)-field energy for aggregation breaks time-reversal symmetry. The responsive adjustments of the controlled (host) mineral system to environmental changes would bring about mutual coupling between random organic sets supported by it; here the generation of long-range correlations within organic (guest) networks could include SOC-like mechanisms. And, such cooperative adjustments enable the selection of the functional configuration by altering the inorganic dipolar network's capacity to assist a spontaneous process. A non-equilibrium dynamics could now drive the kinetically oriented system (trimming the phase-space via sterically coupled organics) toward a series of phase-transitions with appropriate organic replacements "taking-over" its functions. Where available, experiments are cited in support of these speculations and for designing appropriate tests.

Keywords: feedback; field-controlled colloids; long-range correlation; organic “takeover,” phase-transition; proto-metabolic cycle; slow driving.

Figure 1

Toward facilitating the evolution of organic reactions/interactions (guest-level-II) via a controlled inorganic scaffold (host-level-I) a la Cairns-Smith. (A) The probability of forming complex stable dynamical patterns decreases with increasing number of organic molecules. This can be aided via selection by a pre-existing functioning organization – the crystal-scaffold or level-I (represented by a white pin board) acting as “traps” for functioning assembled modules from level-II (represented by a “bottom-up assembly” of colored beads). For, e.g., a variety of recognition-like interactions between organic “building blocks” are required (not all are shown) to construct the unit leading up to the fourfold symmetric structure. Shown on top is the new organic organization which has functionally replaced the original crystal one at level-I. (B) To make this scenario compatible with soft colloidal dynamics and facilitate the “takeover” of level-I by a hierarchy of functioning modules, we suggest a reversible field-stabilized scaffold with a modular organization – represented by a transparent pin board. A stable inorganic scaffold is also compatible with the simultaneous emergence of (and replacement by) different types of organic spatio-temporal correlations, and as each of these would be dependent on the scaffold, any external tinkering with the latter’s degrees of freedom (d.o.f.s), would also impact the different organic networks and facilitate their mutual coupling (see text).

Figure 2

Monte Carlos simulation in 2D: (A) clustering without H-field; (B) chaining under H-field. Reprinted with permission from Chantrell et al., . Copyright 1982, American Institute of Physics; see also Rosensweig, .

Figure 3

Speculated asymmetric interactive diffusion in aqueous medium of further incoming organic ligand (O.L.)-linked MNPs – indicated by red-green arrows – through a field-induced MNP aggregate – indicated by blue arrows – in response to a gentle gradient (say, non-homogeneous rock field). Here particles comprising the MNP-aggregate could have differences in associated magnetic moment size (see blue arrow length), diameter, composition (see circle-colour – green, blue, yellow, pink), etc. State 1/ State 2 correspond to lower/higher template-affinity states of the diffusing O.L.-linked MNP, indicated by a grey circle having darker/brighter red-green coloured arrow, respectively. A spatially non-homogeneous H-field (direction indicated on top) provides both detailed-balance breaking non-equilibrium and asymmetry, to a diffusing magnetic dipole undergoing infinitesimal spin-alignment changes. In addition to the external field and the bath fluctuations, its orientational state is influenced by the local H-fields of its “template” partners (forming the aggregate) that would periodically perturb its directed diffusion; this magnetic interaction in State 2 is represented by green lines. Thus the dipole’s magnetic d.o.f. would enable alternating unbound and bound states, like isothermal release/attachment cycles of molecular machines on nucleic acid/protein templates, respectively. These changes would be similarly facilitated by thermal excitations from bath – indicated by dotted brown arrows – with rectification by either the gentle H-field gradient or local template-partner H-fields (Mitra-Delmotte and Mitra 2010a; see text).

Figure 4

Patterning of magnetically labeled cells by Slater and coworkers (Ho et al., 2009). (A) Schematics of the procedure for magnetic cell labeling and patterning. A: Magnetic cell labeling. Cell membrane proteins were first biotinylated and subsequently labeled with streptavidin paramagnetic particles. B: Magnetic cell patterning. A star-shaped magnet was attached under the culture dish. Magnetically labeled cells were added and patterned onto the plate by the magnetic field. (B) Magnetic cell patterning of biotinylated human monocytes (HMs) labeled with streptavidin paramagnetic particles. A: Magnetically labeled HMs were successfully patterned by the star-shaped magnetic template. B: Magnetically labeled HMs were not patterned in the absence of the magnetic template. C: The non-labeled biotinylated HMs were patterned unsuccessfully by the magnetic template. D: Original magnetic template used to pattern HMs. E: Magnetic field profile of the magnetic star template used, as visualized by using iron filings to locate magnetic field maxima. Figures and legends taken from Ho et al. (2009) with kind permission from Prof. Nigel Slater; “Copyright (2009) Royal Society of Medicine Press, UK.”

Figure 5

Three size-scales observed in framboids (Adapted from Sawlowicz, with permission, see text). As a contrast, the top left shows a framboidal aggregate without sufficient surface minimizing forces.

Figure 6

The hydrothermal mound as an acetate and methane generator. Steep physicochemical gradients are focused at the margin of the mound. The inset (cross section of the surface) illustrates the sites where anionic organic molecules are produced, constrained, react, and automatically organize to emerge as protolife (from Russell and Martin, ; Russell and Hall, , with kind permission). Compartmental pore space may have been partially filled with rapidly precipitated dendrites. The walls to the pores comprised nanocrystals of iron compounds, chiefly of FeS (Wolthers et al., 2003) but including greigite, vivianite, and green rust occupying a silicate matrix. Tapping the ambient protonmotive force the pores and bubbles acted as catalytic culture chambers for organic synthesis, open to H₂, NH₃, ${\text{CH}}_{\text{3}}^{-}$ at their base, selectively permeable and semi-conducting at their upper surface. The font size of the chemical symbols gives a qualitative indication of the concentration of the reactants.

Figure 7

Framboids in chimney: Sheaf system, formed from coalescing rods of anastamosing microcrystalline pyrite. Black areas (in reflected ore microscopy of transverse section) are empty spaces; central regions are framboidal pyrite with an exterior of crystalline pyrite (picture by Dr. Adrian Boyce reproduced with his kind permission; source: Boyce et al., ; Boyce, ; see Mitra-Delmotte and Mitra, 2010b).

Figure A1

The feedback-coupling between the control-network (level-I) and the metabolic-network (level-II), is extrapolated to the pre-biotic era to rephrase Orgel’s (2000) concerns regarding plausible assumptions on the nature of minimal information-processing capabilities of mineral surfaces for hosting/organizing a proto-metabolic cycle. A capacity for interactions enabling long-range energy and electron transfers (represented by bold orange and dashed blue arrows, respectively) is needed at level-I – the hosting surface, depicted as a green parallelogram, – for proto-metabolic reaction cycles to organize at level-II – depicted as green hexagon. Did the host-surface at level-I have the ability to capture and channel the thermal energy released into it, say at point P (i.e., from an exothermic reaction taking place at level-II), to another spatio/temporal location, say point Q, where potential reactants (for endothermic reaction at level-II) could get recruited into the expanding cycle? Similarly electrons, required for some reactions of the cycle, would have led to exchanges (shown in blue dashed arrows) with the level-I catalytic colloids. (B) The possibility of percolation through an inorganic network of dipolar interactions makes it interesting to consider a field-controlled network of magnetic mineral-particles as a hosting surface to pre-biotic attractor cycles a la level-I. (B) Is a top view of (A), where the green parallelogram representing the hosting surface is a “layer” of field-structured colloids, adapted from Figure 2, main text. We speculate that transfers of electrons and heat energy through the dipolar network (see Percolation of Heat, Electrons) could drive the magnetic system out of equilibrium. This is since each individual particle’s composite magnetic moment in turn is directly affected by its redox state, and also the local temperature, thus affecting their collective dynamics. Taken above a threshold these feedback effects have the potential to cause phase-transitions to regimes with new types of collective ordering, leading to a long-range correlation.