Study of the internal morphology of cation-exchange membranes by means of electroosmotic permeability relaxations.

The effect of an ac sinusoidal perturbation of known amplitude and frequency superimposed to the usual dc applied electric voltage difference on the electroosmotic flow through three cation-exchange membranes with different morphology has been studied. A dispersion of the electroosmotic permeability on the frequency of the applied ac signal has been found for the three membranes investigated, observing that the electroosmotic permeability reaches maximum values for some characteristic values of the frequency. These characteristic frequency values, which are related to relaxation processes in heterogeneous media, depend on the membrane system and permit to obtain information about the different structures of the membrane system. Thus, the study of the electroosmotic permeability relaxation can be used as a method to study the internal morphology of a cation-exchange membrane in a given electrolyte medium.

Experimental estimation of equilibrium and transport properties of sulfonated cation-exchange membranes with different morphologies.

Solvent uptake, hydraulic and electroosmotic permeabilities, true cation transport number, effective fixed charge concentration, and limiting current values have been determined in aqueous LiCl solutions for three commercial cation-exchange membranes with different morphologies and similar electric properties. The differences found in the equilibrium and transport properties of the membranes have been analyzed on the basis of their different structures. The experimental results show that the membrane morphology has an influence on the effect that the presence of an electrolyte has in the solvent uptake and in the liquid permeation. Differences have also been found in the polarization concentration effects, and on the loss of the membrane selectivity with the increase of the electrolyte concentration.

Preparation and application of dense poly(phenylene oxide) membranes in pervaporation.

Dense flat-sheet membranes were prepared from poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) using the casting solvents chloroform and 1,1,2-trichloroethylene. X-ray diffraction, tapping mode atomic force microscopy (TM-AFM), and contact angle studies were used to characterize the membranes. The surface energy and the solubility parameters of the PPO membranes were determined from the measured contact angles and compared with the predicted ones from the group contribution method. Swelling experiments and pervaporation separation of methanol from its mixture with ethylene glycol over the entire range of concentration, 0-100%, were conducted using these membranes. Flory-Huggins theory was used to predict the sorption selectivity. The results are discussed in terms of the solubility parameter approach and as function of the morphological characteristics of the membranes. It was found that PPO membranes prepared with chloroform exhibited better pervaporation performance than PPO membranes prepared with 1,1,2-trichloroethylene.

[Familiar chronic progressive external ophthalmoplegia of mitochondrial origin]. / Oftalmoplejía crónica progresiva externa familiar de origen mitocondrial.

INTRODUCTION: The syndrome of chronic progressive external ophthalmoplegia (CPEO) is a mitochondrial disease characterized by ptosis and ophthalmoplegia has that has been associated to the presence of large deletion, single or multiple, in the mitochondrial DNA of skeletal muscle. CASE REPORT: We report a familiar case of chronic progressive external ophthalmoplegia of maternal inheritance that began at birth, and developed with slow progression but with no multisystemic involvement. Non of the affected individuals had ragged-red fibers in skeletal muscle. Genetic analysis of mitochondrial DNA revealed the presence of a single deletion of 4,977 bp that encompasses the nucleotide positions 8,482 to 13,460, flanked by a direct repeat sequence. CONCLUSIONS: The amount of deleted mitochondrial DNA (15%) in this patient's muscle suggests, even if the percentage of the mutation is low, that this deletion is the molecular cause of the phenotypic presentation of this patient. This is one of the few cases described in the literature of CPEO maternally inherited.

[Glutaric aciduria type I]. / Aciduria glutárica tipo I.

We report three patients with glutaric aciduria type I. The biochemical diagnosis of two cases was revealed by determination of free glutaric acid in urine, by using the CG/EM method. In the third patient, however, these levels were only slightly increased and the diagnosis was attained by the determination of total glutaric acid and glutaryl-carnitine. Serum carnitine levels were decreased in two cases. Clinical symptoms of this type of organic acidemia are highlighted by an acute or subacute presentation with signs of dysfunction of the neostriatum, simulating a cerebral paralysis with extrapyramidal signs. Homozygous patients have been reported with the same biochemical and enzymatic activity findings, but these patients were neurologically asymptomatic throughout life. Other features suggestive of the disease are macrocephaly associated with a widening of the subarachnoid spaces. Riboflavin and carnitine administration to these patients seems to prevent new bouts of neurological dysfunction.