Macromolecular substance, diffusion

When immobilizing biocatalysts within polymer gels using physical entrapment methods, we may take advantage of the great resistance to the diffusion of macromolecular substances due to the gel porosity. However, this limited diffusion within the gel phase also causes a reduced mass transfer rate for low... 

Similar molecular crystals can also occur with macromolecular substances. Spherically shaped and ellipsoidal proteins produce, for example, protein crystals, with protein molecules occupying the lattice positions. The quite large voids between the lattice points and the vacant spaces within the protein molecules are filled with water or aqueous salt solution. Protein crystals consist of up to 95% water or salt solution. The channels and holes so produced are often so large that low-molar-mass substrates can penetrate and enzymatically react in these spaces. Heavy metals can also diffuse into these spaces. This effect is made use of in X-ray crystallography, since the phases of the X-ray scattering distribution can then be evaluated, and this aids the determination of the internal structure of the protein molecule (see also Section 4.4.2). 

Let us consider the reaction in which particles P of a chemical substance diffuse in the medium, containing random located static non-saturated traps (growing macromolecular coils) T. At the contact of particle P with a trap T the particle disappears. It is usually considered that if the concentration of particles and traps is large or the reaction occurs with intensive stirring, the process can be considered as the classical reaction of the first order. In this case it can be assumed that the concentration of particles c(t) decay law will be the following [136] ... 

Equation (10.4-4) allows us to express / in terms of D2, the diffusion coefficient of the macromolecular substance, giving... 

A molecule in a liquid was pictured as partially confined in a cage made up of its nearest neighbors. This model and an assumed frictional force were related to diffusion in liquid solutions, to viscosity in pure liquids, and to sedimentation in solutions of macromolecular substances. 

The electron in the electron transport chain is not free like in a metal wire. Therefore the electron motion in each act involves surmounting an energy barrier. As was shown in Refs. 16 and 108-110, a substantial role in this process is played by the conformations of the macromolecular components of the electron transport chain. Nevertheless, the simplest model systems of electron transport realized on bilayer lipid membranes were virtually based on the concept of a membrane as a thin liquid hydrocarbon in which a substance capable of redox transformations is dissolved, the products of this reaction being able to diffuse inside the bilayer. The electron transport from the aqueous phase containing a reducer amounts to injection of charges into the nonaqueous phase if it contains an electron acceptor ... 

Let us consider the physical reasons of reactive medium ds change within the indicated above limits. Reactive medium itself presents Euclidean space with dimension d = 3, as and any solution of low-molecular substance in the same solvent [12]. The appearance of dimension d with values <3, which are specific for fractal mediums, is due to unevenness of monomer in solution distribution and c decreasing results to law-governed diffusion time increasing, which is necessary for reagent reaching one another. Let us note, that DMDAACh macromolecular coil fractal dimension in water solution is Dj. = 1.65 [13]. According to Kremer s formula the dimension dm of medium, in which such coil is formed, can be determined [14] ... 

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