PubMed · 5434344
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B B Edelstein. 1970. Instabilities associated with dissipative structure.. https://doi.org/10.1016/s0022-5193(70)80014-5
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The diffusion model for percutaneous absorption is developed for the specific case of delivery to the skin being limited by the application of a finite amount of solute. Two cases are considered; in the first, there is an application of a finite donor (vehicle) volume, and in the second, there are solvent-deposited solids and a thin vehicle with a high partition coefficient. In both cases, the potential effect of an interfacial resistance at the stratum corneum surface is also considered. As in the previous paper, which was concerned with the application of a constant donor concentration, clearance limitations due to the viable eqidermis, the in vitro sampling rate, or perfusion rate in vivo are included. Numerical inversion of the Laplace domain solutions was used for simulations of solute flux and cumulative amount absorbed and to model specific examples of percutaneous absorption of solvent-deposited solids. It was concluded that numerical inversions of the Laplace domain solutions for a diffusion model of the percutaneous absorption, using standard scientific software (such as SCIENTIST, MicroMath Scientific software) on modern personal computers, is a practical alternative to computation of infinite series solutions. Limits of the Laplace domain solutions were used to define the moments of the flux-time profiles for finite donor volumes and the slope of the terminal log flux-time profile. The mean transit time could be related to the diffusion time through stratum corneum, viable epidermal, and donor diffusion layer resistances and clearance from the receptor phase. Approximate expressions for the time to reach maximum flux (peak time) and maximum flux were also derived. The model was then validated using reported amount-time and flux-time profiles for finite doses applied to the skin. It was concluded that for very small donor phase volume or for very large stratum corneum-vehicle partitioning coefficients (e.g., for solvent deposited solids), the flux and amount of solute absorbed are affected by receptor conditions to a lesser extent than is obvious for a constant donor constant donor concentrations.
Quantitative kinetic models have been developed for the reaction between peroxynitrite and membrane lipids in vesicles and for transmembrane oxidation of reactants located within their inner aqueous cores. The models were used to analyze TBARS formation and oxidation of entrapped Fe(CN)(6)(4)(-) ion in egg lecithin liposomes and several artificial vesicles. The analyses indicate that permeation of the bilayers by ONOOH and NO(2)(*), a radical formed by homolysis of the ONOOH bond, is unusually rapid but that permeation by ONOO(-) and CO(3)(*)(-), a radical formed when CO(2) is present, is negligible. Bicarbonate protects the vesicles against both membrane and Fe(CN)(6)(4)(-) oxidation by rapid competitive CO(2)-catalyzed isomerization of ONOOH to NO(3)(-); this effect is partially reversed by addition of nitrite ion, which reacts with CO(3)(*)(-) to generate additional NO(2)(*). Under medium conditions mimicking the physiological milieu, a significant fraction of the oxidants escape to inflict damage upon the vesicular assemblies. Rate constants for several elementary reaction steps, including transmembrane diffusion rates for ONOOH and NO(2)(*), were estimated from the bicarbonate dependence of the oxidative reactions.
The methods have been developed for studying oxygen mobility by donor quenching in solutions with uniform concentration and in geminate pairs in a solid phase. It is shown that the kinetics of luminescence variations with time is described by a diffusion model. Oxygen mobility has been studied at low temperatures (77 K) in hard polymer matrices. squalane. glasses of low-molecular hydrocarbons and alcohols. The methods can be used to measure very low oxygen mobility with a diffusion coefficient of about 10(-23) cm2 s(-1).