RESUMEN
The effect of a double hydrophilic block-copolymer additive (made of polyaspartic acid and polyethyleneglycol, pAsp(10)-b-PEG(110)) on the initial formation of calcium carbonate from a supersaturated salt solution has been studied in situ by means of time-resolved synchrotron small-angle X-ray scattering (SAXS). A stopped-flow cell was used for rapidly mixing the 20 mM aqueous reactant solutions of calcium chloride and sodium carbonate. In reference measurements without polymer additive the very rapid formation of primary, overall spherical CaCO(3) particles with a radius of ca. 19 nm and a size polydispersity of ca. 26% was observed within the first 10 ms after mixing. A subsequent, very rapid aggregation of these primary particles was evidenced by a distinct upturn of the SAXS intensity at smallest angles. During the aggregation process the size of the primary particles remained unchanged. From an analysis of the absolute scattering intensity the mass density of these particles was determined to 1.9 g/cm(3). From this rather low density it is concluded that those precursor particles are amorphous, which has been confirmed by simultaneous wide-angle X-ray diffraction measurements. Upon adding 200 pm of the block-copolymer no influence on the size, the size polydispersity and morphology of the primary particles, nor on the kinetics of their formation and growth, was found. On the other hand, the subsequent aggregation and precipitation process is considerably slowed down by the additive and smaller aggregates result. The crystalline morphology of the sediment was studied in situ by WAXS ca. 50 min after mixing the reactants. Several diffraction rings could be detected, which indicate that a transformation of the metastable, amorphous precursor particles to randomly oriented vaterite nanocrystallites has taken place. In addition, a few isolated Bragg spots of high intensity were detected, which are attributed to individual, oriented calcite microcrystals that nucleated at the wall of the capillary.
RESUMEN
We use small-angle x-ray scattering (SAXS) as a tool to study the binding of proteins to spherical polyelectrolyte brushes (SPB) in situ. The SPB consists of a solid core of approximately 100 nm diam onto which long polyelectrolyte chains [poly(styrene sulfonic acid, PSS) and poly(acrylic acid, PAA)] have been densely grafted. The proteins used in this investigation, Bovine Serum Albumine (BSA) and Bovine Pancreatic Ribonuclease A (RNase A), adsorb strongly to these SPB if the ionic strength is low despite their negative charge. Virtually no adsorption takes place at high ionic strength. SAXS demonstrates that both proteins are distributed within the brush. The findings reported here give further evidence that the strong adsorption of proteins to SPB is due to the "counterions release forces": The patches of positive charge on the surface of the proteins become multivalent counterions of the polyelectrolyte chains. Thus, a concomitant number of co- and counterions is thereby released and the entropy of the entire system is increased. The repulsive Coulombic interaction as well as the steric repulsion between the proteins and the brush layer are counterbalanced by this effect. The data discussed here demonstrate that the adsorption of proteins in SPB presents a new principle for the immobilization of proteins.
Asunto(s)
Electrólitos/química , Polímeros/química , Proteínas/química , Adsorción , Animales , Bovinos , Modelos Químicos , Dispersión de Radiación , Soluciones/química , Propiedades de SuperficieRESUMEN
With reference to an observation, thirty-four cases of systemic mastocytosis with intestinal malabsorption are reviewed. The most characteristic intestinal anomalies are the steatorrhea, partial villous atrophy and deficiency in secretory IgA. Routine investigations for mastocytosis may be warranted in patients with malabsorption. A markedly telangiectatic and angiomatous aspect of cutaneous lesions may be suggestive of the association.
