Dyeing process diffusion phenomena

Biosorption is a general phenomenon that can occur in either dead or living biomass. However, this process usually refers to a passive uptake mechanism carried out by nonviable microorganisms (dead yeasts). The biosorption process involves physical-chemical interactions between the yeast surface and the azo dyes, as well as possible passive diffusion inside dead cells. 

A comparison of the experimental data on quenching of triplet states of dyes in solutions in the absence and in the presence of DNA permits estimation of the steric complexation effect on the quenching process and conclusions about the structure of the dye-DNA complexes formed. In the case of dye K4, we may conclude that complexation with the biopolymer has relatively weak effect on the kq value. This is probably due to the fact that the quenching process for K4 occurs in the kinetic regime (kc k a, see reaction (2)), and diffusion of the quencher to dye molecules boimd to DNA exerts no substantial effect on kq (another assumed reason for this phenomenon could be partial decomposition of the dye(T)-DNA complex and the presence of free triplet dye molecules in the solution however, the experiments on quenching of the K4 triplet state by iodide ion considered above reject this possibility). 

Polymers are not homogeneous in a microscopic scale and a number of perturbed states for a dye molecule are expected. As a matter of fact, non-exponential decay of luminescence in polymer systems is a common phenomenon. For some reaction processes (e.g, excimer and exciplex formation), one tries to fit the decay curve to sums of two or three exponential terms, since this kind of functional form is predicted by kinetic models. Here one has to worry about the uniqueness of the fit and the reliability of the parameters. Other processes can not be analyzed in this way. Examples include transient effects in diffusion-controlled processes, energy transfer in rigid matrices, and processes which occur in a distribution of different environments, each with its own characteristic rate. This third example is quite common when solvent relaxation about polar excited states occurs on the same time scale as emission from those states. Careful measurement of time-resolved fluorescence spectra is an approach to this problem. These problems and many others are treated in detail in recent books (9,11), including various aspects of data analysis. 

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