Dissipation-Driven Selection under Finite Diffusion: Hints from Equilibrium and Separation of Time Scales

When exposed to a thermal gradient, reaction networks can convert thermal energy into the chemical selection of states that would be unfavourable at equilibrium. The kinetics of reaction paths, and thus how fast they dissipate available energy, might be dominant in dictating the stationary populations of all chemical states out of equilibrium. This phenomenology has been theoretically explored mainly in the infinite diffusion limit. Here, we show that the regime in which the diffusion rate is finite, and also slower than some chemical reactions, might bring about interesting features, such as the maximisation of selection or the switch of the selected state at stationarity. We introduce a framework, rooted in a time-scale separation analysis, which is able to capture leading non-equilibrium features using only equilibrium arguments under well-defined conditions. In particular, it is possible to identify fast-dissipation sub-networks of reactions whose Boltzmann equilibrium dominates the steady-state of the entire system as a whole. Finally, we also show that the dissipated heat (and so the entropy production) can be estimated, under some approximations, through the heat capacity of fast-dissipation sub-networks. This work provides a tool to develop an intuitive equilibrium-based grasp on complex non-isothermal reaction networks, which are important paradigms to understand the emergence of complex structures from basic building blocks.

Substantiation of the calculation methods of the nitrogen removing (nitrification) in bioreactors with using on the biofilm models

The mathematic model and calculations of the waste waters cleaning parameters from the compounds ammonium nitrogen (nitrification) in bioreactors with additional using in theirs volume the fixed biocenosis as the biofilm are presented. The valuation of the different influence factors on the waste waters cleaning parameters is given. The kinetics of reaction according to Monod nonlinear equation is used that allow to calculate the nitrogen concentrations on the external and in the interior biofilm surfaces and to evaluate the efficiency of the biofilm work of the given thickness relative to penetration character of the nitrogen pollutions in it. As showed the biofilm thickness and the flow in it are decreasing as the tearing off velocity of the biomass from its surface is increasing where as at increasing of the nitrogen concentrations these parameters are increasing. At this the substrate flow and the penetration depth into the biofilm are the functions of the substrate concentration on the biofilm surface, velocity of the reaction within it and the diffusive masstransfer. As a main parameter for evaluation of the oxygen influence for control of the process of ammonium oxidation to nitrite the relation of the concentrations oxygen to ammonium nitrogen is proposed. The specific examples and calculations have showed the given relation may be better alternative for control of the nitrification processes in reactor in comparison with oxygen concentration.

Evaluating Alternatives to Water as Solvents for Life: The Example of Sulfuric Acid

The chemistry of life requires a solvent, which for life on Earth is water. Several alternative solvents have been suggested, but there is little quantitative analysis of their suitability as solvents for life. To support a novel (non-terrestrial) biochemistry, a solvent must be able to form a stable solution of a diverse set of small molecules and polymers, but must not dissolve all molecules. Here, we analyze the potential of concentrated sulfuric acid (CSA) as a solvent for biochemistry. As CSA is a highly effective solvent but a reactive substance, we focused our analysis on the stability of chemicals in sulfuric acid, using a model built from a database of kinetics of reaction of molecules with CSA. We consider the sulfuric acid clouds of Venus as a test case for this approach. The large majority of terrestrial biochemicals have half-lives of less than a second at any altitude in Venus’s clouds, but three sets of human-synthesized chemicals are more stable, with average half-lives of days to weeks at the conditions around 60 km altitude on Venus. We show that sufficient chemical structural and functional diversity may be available among those stable chemicals for life that uses concentrated sulfuric acid as a solvent to be plausible. However, analysis of meteoritic chemicals and possible abiotic synthetic paths suggests that postulated paths to the origin of life on Earth are unlikely to operate in CSA. We conclude that, contrary to expectation, sulfuric acid is an interesting candidate solvent for life, but further work is needed to identify a plausible route for life to originate in it.

Fate of elemental Selenium in Sulfur dominated environments

<p>Selenium (Se) is an essential yet toxic trace element with one of the narrowest nutritional optimums of all elements. Se speciation plays a crucial role in its mobility, bioavailability, bioaccumulation, and toxicity. The current perception of Se environmental cycling encompasses a linear series of successive, bi-directional redox processes. Elemental Se is seen as a central species thermodynamically favored in redox conditions found in most environments. Most studies on Se environmental transformations focused on systems characterized by high Se concentrations. In nature though, sulfur (S) concentrations are in general orders of magnitude higher than those of Se. This work investigated elemental selenium reactivity in sulfur dominated environments. A set of laboratory experiments were conducted to determine the reaction rates of elemental selenium with sulfur in various environmental conditions. Our data clearly indicates that an abiotic reaction was occurring between elemental Se and S at neutral to alkaline conditions under anaerobic conditions, solubilizing elemental Se. At neutral pH (pH = 7), the reaction rates were low, whereas at high pH (pH = 12), the reaction was fast and all elemental Se was consumed by the reaction within 12 h. We present for the first time the detailed kinetics of reaction at various environmental conditions and discuss the control exerted by sulfur on selenium cycling.</p>