Stimulated and co-operative electron transfer in energy conversion and catalysis.

A new mechanism of electron transfer, stimulated electron transfer, is postulated, in which an electronic feedback is drastically increasing both the rate of electron transfer and the propagation of free energy along electron transferring molecular pathways. In principle, the idea of pushing a system far from equilibrium to achieve a high reaction rate and co-operative phenomena is applied to molecular electron transfer. The effect is calculated from a semiclassical kinetic model of a chain redox reaction with autocatalytic feedback on individual rate constants, where the steps have subsequently been minimized to obtain a continuous electron transfer pathway with electronic feedback. The influence of inhomogeneities and asymmetries in the electron transfer path and of vectorial components (electrical field, gradient of redox potential) are discussed as well as the acceleration of individual and multiple electron transfer as a function of feedback. Examples of autocatalytic feedback are provided including mechanisms involving electron transfer proteins and multi-centre electron transfer catalysts. Such a phenomenon can be described for molecular and interfacial electron transfer in analogy to stimulated and coherent light emission. The results suggest that autocatalytic or stimulated electron transfer may be a key to the understanding of efficient electron transfer and co-operative multi-electron transfer catalysis in biology and a challenge for fuel production mechanisms in artificial photosynthesis and fuel cycles.     

Photoelectrochemical Power,Chemical Energy and Catalytic Activity for Organic Evolution on Natural Pyrite Interfaces

Natural pyrite (FeS₂) has frequently been discussed as a material involved in CO₂ fixation in presence of H₂S and as a possible catalyst for the origin of life. A straightforward chemical fixation of carbon dioxide as proposed by Wächtershäuser could not be verified from thermo-chemical equilibrium calculations by minimizing Gibb's Free Energy in the system C, O, H, S, Fe and appears unlikely dueto the experimentally encountered large overpotentials involved in CO₂ fixation. However, the hypothesis, by W. R. Edwards, that pyrite in shallow coastal waters may have been involved, canbe sustained. In this case, daily available photoelectrochemical power from FeS₂/Fe^2+/3+ interfaces could have made thedifference in combination with electrochemical processes, such ashydrogen insertion, and the solubilization of pyrite by the aminoacid cysteine to yield dissolved chemical energy. Periodical changes in energy supply could also have entrained primitive self-organization processes for organic-biological evolution.Natural samples from thirteen ore deposits have been investigatedphotoelectrochemically. Efficient light-induced current generation has been found with several of these samples so thatphotoelectrochemical processes generated by pyrite have to be considered as naturally occurring phenomena, which could have been even more pronounced in oxygen deficient environments. Pyrite from the Murgul mine in Turkey of suboceanic volcanicorigin was closer examined as a model system to understand the morphology and chemistry of pyrite photoactivity.     

Morphology of bacterial leaching patterns by Thiobacillus ferrooxidans on synthetic pyrite

Thiobacillus ferrooxidans has been cultivated on synthetic pyrite (FeS₂) single crystals as the only energy source and the pyrite interface investigated with respect to characteristic morphological changes using scanning electron microscopy. Corrosion patterns of bacterial size were identified in different stages of development and correlated with bacterial activity. It appears that bacterial attack of the sulfide interface starts by secretion of organic substances around the contact area between the bacterial cell and the sulfide energy source. They might either be part of a pseudo capsule which shields the contact area or may form a sulfur absorbing and transporting organic film. Degradation of the sulfide occurs in the contact area below the bacterial cell leading to a corrosion pit which the bacterium may abandon after it has reached a depth of bacterial dimension. Electron spectroscopic (XPS) and X-ray fluorescence studies indicate a layer of organic substances covering the sulfide surface under bacterial leaching conditions, which is sufficiently thick for consideration in interfacial chemical mechanisms.     

Novel technique for investigation and quantification of bacteriol leaching by Thiobacillus ferrooxidans

A novel, efficient, and simple technique for the in situ study and quantification of the heterogeneous Bacteriol activity and the Bacteriol degradation of metal sulfides by Thiobacillus ferrooxidans is presented. It consists of exposing an ultrathin (300-2500 A) metal sulfide layer, FeS(2) in the experiments, to Thiobacillus f. grown in Touvinen media and visually following the Bacteriol attack and development of Bacteriol corrosion patterns under a light microscope. The uniform pyrite layer, partially transparent for visible light, permits the optical characterization of Bacteriol attack in remarkable detail. Several open or little understood questions concerning Bacteriol leaching, such as those on the kinetics of adhesion, the interfacial Bacteriol reproduction, the density of surface active bacteria, and the rate and morphology of sulfide degradation can also be studied. The degree of Bacteriol activity can be distinguished on the basis of development of variable sizes of spots and halos around Bacteriol cells produced by light passing through differently sized corrosion pits. The information obtained and identification of microorganisms has additionally been accentuated by immunofluorescence techniques (FA). It is concluded that the described method can be developed as a convenient testing and control technique for use in mine laboratories and bioleaching operations.     

Bacterial leaching patterns on pyrite crystal surfaces

Selected pyrite crystals were placed as a bacterial energy source into stationary cultures of Thiobacillus ferroxidans. Scanning electron microscope studies performed after a period of 2 years on these crystals revealed bacterial etching pits in characteristic patterns; they include pit arrangements in loose statistical disorder, in pairs, in clusters, and most remarkably in pearl-string-like chains. It has previously been confirmed that the chemical processes of bacterial leaching occur mainly in the region of contact between bacteria and the sulfide surface. The evidence presented in this experiment strongly suggests that the observed bacterial distributions are critically dependent on crystal structure and on deviations in the crystal order (fracture lines, dislocations) of the leachable substrate.     

Parametric energy conversion--a possible, universal approach to bioenergetics in biological structures.

It is shown that the mechanism of parametric energy conversion—a non-linear phenomenon which is known to occur in all branches of physics—may play a fundamental role in energy conversion in biological structures. Parametric energy conversion means pumping of energy through the variation of an energy storing quantity (a parameter). In biological systems the energy storing parameter is the membrane itself, the structure and composition of which is varied by proceeding structure bound biochemical reactions. The principle of parametric energy conversion is introduced into a molecular kinetical model and three coupled differential equations are derived, which interconnect chemical, electrical and mechanical energy in biological structures. It is shown that they describe parametric pumping of energy. It is a particular mechanism, which is also found in the physical phenomenon of Bethenod. The mechanism is tested with the derivation and explanation of various important bioenergetical functions as special cases of parametric energy conversion, of ATP synthesis, the pumping of ions and molecules during active transport, the excitability of nerve membranes and the dynamics of oscillatory muscles. A new interpretation of the connection of structure and function in striated muscles is also derived and signal transformation in receptors discussed. It is suggested that parametric energy conversion may be the uniform basis of energy conversion in biological structures and that the path of bioenergetic evolution might have essentially followed the line marked by the characteristic properties of this flexible mechanism. The parametric hypothesis offers an elegant ordering scheme and reasonable explanation for evolution and function of a large variety of important bioenergetic mechanisms. In order to handle the intricate mechanism properly it would be necessary to give up the conventional, intuitive way of formulating and understanding biochemical mechanisms and to develop a new dimension of chemical thinking.     

Application of electrochemical kinetics to photosynthesis and oxidative phosphorylation: The redox element hypothesis and the principle of parametric energy coupling

It is suggested that the transfer of electrons within the biological electron transfer chain is subject to the laws of electrochemical kinetics, when membrane-bound electron carriers are involved. Consequently, small tightly bound molecular complexes of two or more electron transfer proteins of different redox potential within an energy transducing membrane, which accept electrons from a donor at one membrane surface and donate it to an acceptor at the other, may be regarded as real and functioning molecular redox elements, which convert the free energy of electrons into electrochemical energy. Especially, the transfer of an electron from excited chlorophyll to an electron acceptor can be looked upon as an electrochemical oxidation of excited chlorophyll at such a complex. In this reaction the electron acceptor complex behaves like a polarized electrode, in which the electrochemical potential gradient is provided by a gradient of redox potential of its constituents.Calculations and qualitative considerations show that this concept leads to a consistent understanding of both primary and secondary reactions in photosynthesis (electron capture, delayed light emission, ion transfer, energy conversion) and can also be applied to oxidative phosphorylation. Within the proposed concept, ion transfer and the development of ion gradients have to be considered as results of electrochemical activity—not as intermediates for energy conversion. For energetic reasons, a non steady state, periodic energy coupling mechanism is postulated which functions by periodic changes of the capacity of the (electrochemically) charged energy transducing membrane, during which capacitive surplus energy is released as chemical energy. Energy transducing membranes may thus be considered as electrochemical parametric energy transformers. This concept explains active periodic conformation changes and mechanochemical processes of energy transducing membranes as energetically essential events, which trigger energy conversion according to the principle of variable parameter energy transformers.The electrochemical approach presented here has been suggested and is supported by the observation, that with respect to electron capture and conversion of excitation energy into electrochemical energy, the behaviour of excited chlorophyll at suitable solid state (semiconductor) electrodes is very similar to that of chlorophyll in photosynthetic reaction centers.     

Sulfur colloids as temporary energy reservoirs for Thiobacillus ferrooxidans during pyrite oxidation

Thiobacillus ferrooxidans was cultivated on 100-nm-thick synthetic pyrite (FeS₂) films. The steps of biooxidation were studied with high-resolution transmission electron microscopy. The crystallized sulfide was transformed into colloidal sulfur (4–70 nm, depending on the age of the cell and the degree of substrate oxidation; 70nm initially and 4nm after oxidation of the pyrite substrate), which was taken up and distributed over an organic capsule around the bacteria. This colloidal sulfur acted as intermediate energy storage and was transferred by contact to daughter cells not directly attached to the sulfide substrate.     

Bionic Photovoltaic Panels Bio-Inspired by Green Leaves

In strong solar light, silicon solar panels can heat up by 70℃ and, thereby, loose approximately one third of their efficiencyfor electricity generation. Leaf structures of plants on the other hand, have developed a series of technological adaptations,which allow them to limit their temperature to 40-45℃ in full sunlight, even if water evaporation is suppressed. This is accomplishedby several strategies such as limitation of leaf size, optimization of aerodynamics in wind, limitation of absorbedsolar energy only to the useful fraction of radiation and by efficient thermal emission. Optical and infrared thermographicmeasurements under a solar simulator and in a streaming channel were used to investigate the corresponding properties of leavesand to identify suitable bionic model systems. Experiments started with the serrated structure of ordinary green leaves distributedover typical twig structures and finally identified the Australian palm tree Licuala ramsayi as a more useful bionic model. Itcombines a large area for solar energy harvesting with optimized aerodynamic properties for cooling and is able to restructureitself as a protection against strong winds. The bionic models, which were constructed and built, are analyzed and discussed.