Artificial oxygen-transporting systems

To that end, an important idea contributed by Robertson and Michaels was that oxygen reduction on Pt could potentially be co-limited by adsorption and diffusion rather than by just one or the other. In modeling the system, they noted that it is not possible for adsorbed oxygen to be in chemical equilibrium with the gas at the gas-exposed Pt surface while at the same time being in electrochemical equilibrium with the applied potential at the three-phase boundary. To resolve this singularity, prior (and several subsequent) models for diffusion introduce an artificial fixed diffusion length governing transport from the gas-equilibrated surface to the TPb.56,57,59,64,65,70 coutrast, Robertsou and Michaels... 

The mechanisms of transfer of molecules and ions across the wall of tubules are more complicated than in the artificial apparatus. In addition to osmosis and simple passive transport viz., ordinary downhill mass transfer due to concentration gradients), renal mass transfer involves active transport viz., uphill mass transport against gradients). The mechanism of active transport, which often occurs in living systems, is beyond the scope of this text. Active transport requires a certain amount of energy, as can be seen from the fact that live kidneys require an efficient oxygen supply. 

As mentioned above, the liposome-embedded hemes are promising as an artificial blood in many ways, but they are not yet usable as substitutes for the red blood cell in living animals. Trats conducted in rodents showed that the liposome/heme indeed transports oxygen in vivo, but only for several hours After that, the animals died, presumably because of a severe immune system reaction in the animal. Further experiments are being carried out by our group to try to overcome that problem. 

Depending on the system under study, oxygen production or consumption is measured. In both cases the use of artificial electron acceptors and electrondonors is necessary (2). The classical electron acceptor for the whole electron transport chain with water as electron donor is methyl-viologen. The same acceptor is used when one measures the photosystem I (PSI) electron transport but now with different artificial electron donors after inhibition of photosystem 2 (PS2) with DCMU (2). In both cases an oxygen consumption is registered due to the auto-oxidation of the reduced methylviologen (3). 

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