Photosynthetic models with maximum entropy production in irreversible charge transfer steps

Abstract

Steady-state bacterial photosynthesis is modelled as cyclic chemical reaction and is examined with respect to overall efficiency, power transfer efficiency, and entropy production. A nonlinear flux-force relationship is assumed. The simplest two-state kinetic model bears complete analogy with the performance of an ideal (zero ohmic resistance of the P-N junction) solar cell. In both cases power transfer to external load is much higher than the 50% allowed by the impedance matching theorem for the linear flux-force relationship. When maximum entropy production is required in the transition with a load, one obtains high optimal photochemical yield of 97% and power transfer efficiency of 91%. In more complex photosynthetic models, entropy production is maximized in all irreversible electron/proton (non-slip) transitions in an iterative procedure. The resulting steady-state is stable with respect to an extremely wide range of initial values for forward rate constants. Optimal proton current increases proportionally to light intensity and decreases with an increase in the proton-motive force (the backpressure effect). Optimal affinity transfer efficiency is very high and nearly perfectly constant for different light absorption rates and for different electrochemical proton gradients. Optimal overall efficiency (of solar into proton-motive power) ranges from 10% (bacteriorhodopsin) to 19% (chlorophyll-based bacterial photosynthesis). Optimal time constants in a photocycle span a wide range from nanoseconds to milliseconds, just as corresponding experimental constants do. We conclude that photosynthetic proton pumps operate close to the maximum entropy production mode, connecting biological to thermodynamic evolution in a coupled self-amplifying process.

A model of surface heat fluxes based on the theory of maximum entropy production

“…For example, Kleidon and Fraedrich [2004] have shown that global biotic productivity corresponds to the states of MEP. Juretic and Zupanovic [2003] found that the MEP may govern the photosynthetic processes. Evidence accumulated so far suggests that the MEP theory could explain transport phenomena in the far from equilibrium systems over a wide range of space and time scales [Kleidon and Schymanski, 2008].…”

Enzyme kinetics and the maximum entropy production principle

“…Although the MEP principle is rigorously valid only in a network of linear biochemical reactions they have found that this principle works very well even in the case of a non-linear network of biochemical reactions. Among other applications of the MEP principle we single out ones used to predict rate constants in relevant transitions of bacteriorhodopsin light-cycle and bacterial photosynthesis [40] and an optimal angular position for the ATP-binding transition in the ATPase nanomotor [41]. The successful applications of the MEP principle to these intramolecular transitions (predictions in qualitative agreement or close to experimental values) has encouraged us to test this principle as physical selection principle acting in concert with enzyme biological evolution.…”

A Simple Thermodynamic Analysis of Photosynthesis

“…In this section we will present a brief analysis of some photosynthetical reactions within the context of finite-time thermodynamics [2], [5][6][7][8], [10]. In particular, we will use the so-called ecological criterion [10].…”

“…De Vos [4], conceived the photosynthesis engine as composed by two parts: a photovoltaic component that absorbs the solar radiation and converts it into work, and a chemical reactor, which uses the work in order to keep a chemical reaction going on in the "reverse direction". A very complete model was proposed by Juretic and Zupanovic [5]. This model is based on a non-equilibrium thermodynamics approach provided by Meszena and Westerhoff [6].…”

“…This model is based on a non-equilibrium thermodynamics approach provided by Meszena and Westerhoff [6]. In the treatment of photosynthesis several design principles for biological systems have been used, such as maximum efficiency [7] & [8], minimum entropy production [2] and maximum entropy production [5]. Recently Lavergne [9] has disscused a photochemical energy transducer as a model for photosynthesis within a second law analysis.…”