Methylene blue diffusibility

Release of tetracycUne hydrochloride from PCL fibers was evaluated as a means of controlled administration to periodontal pockets (69). Only small amounts of the drug were released rapidly in vitro or in vivo, and poly(ethylene-co-vinyl acetate) gave superior results. Because Fickian diffusion of an ionic hydrochloride salt in a UpophiUc polymer is unlikely, and because PCL and EVA have essentially identical Fickian permeabilities, we attribute this result to leaching of the charged salt by a mechanism similar to release of proteins from EVA (73). Poly-e-caprolactone pellets have been found unsuitable for the release of methylene blue, another ionic species (74,75). In this case, blending PCL with polyvinyl alcohol (75% hydrolyzed) increased the release rate. 

Graph in paper of A+e vs. NBc 1 5-2400 Diffusion of methylene blue in water... 

Nitrate intoxication has been described in a patient receiving hemodialysis at home. Using well water contaminated with nitrates, the patient developed dyspnea, sweating, and cyanosis. The venous blood acquired a brownish color and the arterial p02 decreased and failed to rise with the administration of 02. His condition reversed with the intravenous administration of methylene blue. Nitrate must be converted to nitrite before it can convert hemoglobin (ferrous) to methe-moglobin (ferric). The authors of this case report postulated that nitrate must have diffused from the blood into the gut, where the resident bacteria reduced it to nitrite, which then diffused back into the blood (C3). 

Dissolving 0 to 2x 10-4 mole/liter of KMnC>4 in water decreases the diffusion coefficient by 25%. A very large change in the diffusion coefficient is observed in solutions of methylen-blue (the molecular weight m = 317) the presence of 6 x 10-4 mole/liter of this substance decreases the diffusion coefficient to half the original value at room temperature. 

U.V. Stabilizers.—Many of the papers discussed in preceding sections contain discussion of the nature and mechanism of u.v. stabilizers. A brief survey of antioxidants and stabilizers used in the plastics industry has appeared,28 and some new photostabilizers, including a polymeric u.v. absorber and a surface-grafted antioxidant, have been proposed.280 The mechanism of nickel chelate stabilizers has been further discussed,281 and the diffusion of and loss of light stabilizers in poly(olefins) described.282 As part of an attempt to understand the transformations of stabilizers during the ageing of polymers, the photooxidation of 2,6-di-t-butyl-4-methylphenol sensitized by Methylene Blue has been studied.283 U.v. light protection by sunscreens, with mechanisms of interest to the polymer field, has been described.284... 

The next paper we will comment on in this section is a letter by Nakatami et al. [147] in which they describe a microscale technique to study the dynamics of adsorption. This technique, the single-microparticle injection, is basically an optical method that uses Lambert-Beer law to follow the concentration of methylene blue on the surface of a silica gel microparticle. Their main conclusions are that equilibrium is attained within 20 min, Langmuir equation describes the experimental adsorption isotherm, methylene blue molecules penetrate into the pores and the whole process is controlled by adsorbate diffusion in water. 

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