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Evolving systems rely on the storage and replication of genetic information. Here we present an autonomous, purely thermally driven replication mechanism. A pool of hairpin molecules, derived from transfer RNA replicates the succession of a two-letter code. Energy is first stored thermally in metastable hairpins. Thereafter, energy is released by a highly specific and exponential replication with a duplication time of 30 s, which is much faster than the tendency to produce false positives in the absence of template. Our experiments propose a physical rather than a chemical scenario for the autonomous replication of protein encoding information in a disequilibrium setting. [ABSTRACT FROM AUTHOR]

How can molecules with short lifetimes preserve their information over millions of years? For evolution to occur, information-carrying molecules have to replicate before they degrade. Our experiments reveal a robust, reversible cooperation mechanism in oligonucleotide replication. Two inherently slow replicating hairpin molecules can transfer their information to fast crossbreed replicators that outgrow the hairpins. The reverse is also possible. When one replication initiation site is missing, single hairpins reemerge from the crossbreed. With this mechanism, interacting replicators can switch between the hairpin and crossbreed mode, revealing a flexible adaptation to different boundary conditions. [ABSTRACT FROM AUTHOR]

Thermophoresis is the movement of molecules in a temperature gradient. For aqueous solutions its microscopic basis is debated. Understanding thermophoresis for this case is, however, important since it proved very useful to detect the binding affinity of biomolecules and since thermophoresis could have played an important role in early molecular evolution. Here we discuss why the thermophoresis of single- and double-stranded oligonucleotides - DNA and RNA - is surprisingly similar. This finding is understood by comparing the spherical capacitor model for single-stranded species with the case of a rod-shaped model for double-stranded oligonucleotides. The approach describes thermophoresis of DNA and RNA with fitted effective charges consistent with electrophoresis measurements and explains the similarity between single- and double-stranded species. We could not confirm the sign change for the thermophoresis of single- versus double-stranded DNA in crowded solutions containing polyethylene glycol [Y. T. Maeda, T. Tlusty, and A. Libchaber, Proc. Natl. Acad. Sci. USA 109, 17972 (2012)], but find a salt-independent offset while the Debye length dependence still satisfies the capacitor model. Overall, the analysis documents the continuous progress in the microscopic understanding of thermophoresis. [ABSTRACT FROM AUTHOR]

Methods to move solvated molecules are rare. Apart from electric fields, only thermal gradients are effective enough to move molecules inside a fluid. This effect is termed thermophoresis, and the underlying mechanisms are still poorly understood. Nevertheless, it is successfully used to quantify biomolecule binding in complex liquids. Here we show experiments that reveal that thermophoresis in water is dominated by two electric fields, both established by the salt ions of the solution. A local field around the molecule drives molecules along an energy gradient, whereas a global field moves the molecules by a combined thermoelectrophoresis mechanism known as the Seebeck effect. Both mechanisms combined predict the thermophoresis of DNA and RNA polymers for a wide range of experimental parameters. For example, we correctly predict a complex, nonlinear size transition, a salt-species-dependent offset, a maximum of thermophoresis over temperature, and the dependence of thermophoresis on the molecule concentration. [ABSTRACT FROM AUTHOR]

The RNA world scenario posits replication by RNA polymerases. On early Earth, a geophysical setting is required to separate hybridized strands after their replication and to localize them against diffusion. We present a pointed heat source that drives exponential, RNA-catalyzed amplification of short RNA with high efficiency in a confined chamber. While shorter strands were periodically melted by laminar convection, the temperature gradient caused aggregated polymerase molecules to accumulate, protecting them from degradation in hot regions of the chamber. These findings demonstrate a size-selective pathway for autonomous RNA-based replication in natural nonequilibrium conditions. [ABSTRACT FROM AUTHOR]

We measure the thermophoresis of polysterene beads over a wide range of temperature gradients and find a pronounced nonlinear phoretic characteristic. The transition to the nonlinear behavior is marked by a drastic slowing down of thermophoretic motion and is characterized by a Péclet number of order unity as corroborated for different particle sizes and salt concentrations. The data follow a single master curve covering the entire nonlinear regime for all system parameters upon proper rescaling of the temperature gradients with the Péclet number. For low thermal gradients, the thermal drift velocity follows a theoretical linear model relying on the local-equilibrium assumption, while linear theoretical approaches based on hydrodynamic stresses, ignoring fluctuations, predict significantly slower thermophoretic motion for steeper thermal gradients. Our findings suggest that thermophoresis is fluctuation dominated for small gradients and crosses over to a drift-dominated regime for larger Péclet numbers in striking contrast to electrophoresis.

We calculate the thermophoretic drift of a charged single colloidal particle with hydrodynamically slipping surface immersed in an electrolyte solution in response to a small temperature gradient. Here we rely on a linearized hydrodynamic approach for the fluid flow and the motion of the electrolyte ions while keeping the full nonlinearity of the Poisson-Boltzmann equation of the unperturbed system to account for possible large surface charging. The partial differential equations are transformed into a coupled set of ordinary differential equations in linear response. Numerical solutions are elaborated for parameter regimes of small and large Debye shielding and different hydrodynamic boundary conditions encoded in a varying slip length. Our results are in good agreement with predictions from recent theoretical work and successfully describe experimental observations on thermophoresis of DNA. We also compare our numerical results with experimental data on polystyrene beads.

Thermophoresis is the movement of molecules in a temperature gradient. For aqueous solutions its microscopic basis is debated. Understanding thermophoresis for this case is, however, important since it proved very useful to detect the binding affinity of biomolecules and since thermophoresis could have played an important role in early molecular evolution. Here we discuss why the thermophoresis of single- and double-stranded oligonucleotides - DNA and RNA - is surprisingly similar. This finding is understood by comparing the spherical capacitor model for single-stranded species with the case of a rod-shaped model for double-stranded oligonucleotides. The approach describes thermophoresis of DNA and RNA with fitted effective charges consistent with electrophoresis measurements and explains the similarity between single- and double-stranded species. We could not confirm the sign change for the thermophoresis of single- versus double-stranded DNA in crowded solutions containing polyethylene glycol [Y. T. Maeda, T. Tlusty, and A. Libchaber, Proc. Natl. Acad. Sci. USA 109, 17972 (2012)], but find a salt-independent offset while the Debye length dependence still satisfies the capacitor model. Overall, the analysis documents the continuous progress in the microscopic understanding of thermophoresis.

A poorly understood step in the transition from a chemical to a biological world is the emergence of self-replicating molecular systems. We study how a precursor for such a replicator might arise in a hydrothermal RNA reactor, which accumulates longer sequences from unbiased monomer influx and random ligation. In the reactor, intra- and intermolecular base pairing locally protects from random cleavage. By analyzing stochastic simulations, we find temporal sequence correlations that constitute a signature of information transmission, weaker but of the same form as in a true replicator.

The hallmark of living matter is the replication of genetic molecules and their active storage against diffusion. We implement both in the simple nonequilibrium environment of a temperature gradient. Convective flow both drives the DNA replicating polymerase chain reaction while concurrent thermophoresis accumulates the replicated 143 base pair DNA in bulk solution. The time constant for accumulation is 92 s while DNA is doubled every 50 s. The experiments explore conditions in pores of hydrothermal rock which can serve as a model environment for the origin of life.

Two differing theories aim to describe fluidic thermophoresis, the movement of particles along a temperature gradient. While thermodynamic approaches rely on local equilibrium, hydrodynamic descriptions assume a quasi-slip-flow boundary condition at the particle's surface. Evidence for slip flow is presented for the case of thermal gradients exceeding (aS_(T)(-1) with particle radius a and Soret coefficient S_(T). Thermophoretic slip flow at spheres near a surface attracts or repels tracer particles perpendicular to the thermal gradient. Moreover, particles mutually attract and form colloidal crystals. Fluid dynamic slip explains the latter quantitatively.

The thermal expansion of a fluid combined with a temperature-dependent viscosity introduces nonlinearities in the Navier-Stokes equations unrelated to the convective momentum current. The couplings generate the possibility for net fluid flow at the microscale controlled by external heating. This novel thermomechanical effect is investigated for a thin fluid chamber by a numerical solution of the Navier-Stokes equations and analytically by a perturbation expansion. A demonstration experiment confirms the basic mechanism and quantitatively validates our theoretical analysis.

Thermophoresis moves molecules along temperature gradients, typically from hot to cold. We superpose fluid flow with thermophoretic molecule flow under well-defined microfluidic conditions, imaged by fluorescence microscopy. DNA is trapped and accumulated 16-fold in regions where both flows oppose each other. Strong 800-fold accumulation is expected, however, with slow trapping kinetics. The experiment is equally described by a three-dimensional and one-dimensional analytical model. As an application, we show how a radially converging temperature field confines short DNA into a 10 microm small spot.

Thermophoresis, also termed thermal diffusion or the Soret effect, moves particles along temperature gradients. For particles in liquids, the effect lacks a theoretical explanation. We present experimental results at moderate thermal gradients: (i) Thermophoretic depletion of 200 nm polystyrene spheres in water follows an exponential distribution over 2 orders of magnitude in concentration; (ii) Soret coefficients scale linearly with the sphere's surface area. Based on the experiments, it is argued that local thermodynamic equilibrium is a good starting point to describe thermophoresis.

It is shown that laminar thermal convection can drive a chain reaction of DNA replication. The convection is triggered by a constant horizontal temperature gradient, moving molecules along stationary paths between hot and cold regions. This implements the temperature cycling for the classical polymerase chain reaction (PCR). The amplification is shown to be exponential and reaches 100,000-fold gains within 25 min. Besides direct applications, the mechanism might have implications for the molecular evolution of life.

Thermophoresis depletes DNA from a heated spot. We quantify for the first time the thermal diffusion constant D(T)=0.4x10(-8) cm(2)/s K for DNA, using fluorescent dyes and laser heating. For 5 kB DNA we extrapolate a 1000-fold depletion from a temperature difference of 50 K. Surprisingly, convection generated by the same heating can turn the depletion into trapping of DNA. Trapped DNA can form point geometries 20 microm in diameter with more than 1000-fold enhanced concentrations. The accumulation is driven only by temperature gradients and offers a new approach to biological microfluidics and replicating systems in prebiotic evolution.