Complex coacervation

Guest editors Paul Dubin and Russell J. Stewart introduce this Soft Matter themed collection on complex coacervation.

Glycosaminoglycans as polyelectrolytes

One of the barriers to understanding structure-property relations for glycosaminoglycans has been the lack of constructive interplay between the principles and methodologies of the life sciences (molecular biology, biochemistry and cell biology) and the physical sciences, particularly in the field of polyelectrolytes. To address this, we first review the similarities and differences between the physicochemical properties of GAGs and other statistical chain polyelectrolytes of both natural and abioitic origin. Since the biofunctionality and regulation of the structures of GAGs is intimately connected with interactions with their cognate proteins, we particularly compare and contrast aspects of protein binding, i.e. effects of both GAGs and other polyelectrolytes on protein stability, protein aggregation and phase behavior. The protein binding affinities and their dependences on pH and ionic strength for the two groups are discussed not only in terms of observable differences, but also with regard to contrasting descriptions of the bound state and the role of electrostatics. We conclude that early studies of the heparin-Antithromin system, proceeding to a large extent through the methods and models of protein chemistry and drug discovery, established not only many enabling precedents but also constraining paradigms. Current studies on heparan sulfate and chondroitin sulfate seem to reflect a more ecumenical view likely to be more compatible with concepts from physical and polymer chemistry.

Effect of EO Chain Length of Dodecanol Ethoxylates (C12En) on the Complexation of C12En/SDS Mixed Micelles with an Oppositely Charged Polyelectrolyte

Turbidimetry, dynamic light scattering, and capillary electrophoresis were used to study the complexation of polydiallyldimethylammonium chloride (PDADMAC) with mixed micelles of sodium dodecyl sulfate (SDS) and dodecanol ethoxylates (C12En). The effect of EO chain length and its distribution was examined using various combinations of C12En (n = 4, 6, 8, 12). The results show that the onset of the complexation of PDADMAC with the mixed micelles is affected by the EO chain length of C12En: the mole fraction (Y) of SDS in the mixed micelle required to form the complex (Yc) increases with n. The effect of EO chain length on the onset of bulk phase separation shows the same trend. Although Yc varies with n, the electrophoretic mobility of mixed micelles with composition corresponding to Yc is independent of n. We propose that the effect of EO chain length has two aspects: (1) an increase in the average distance between bound polycation segments and the SDS sulfate groups, and (2) an increase in the distance between SDS head groups, which causes a decrease in the surface charge density (sigma) of the micelle. Therefore, the electrical potential at the mean locus of bound polymer segments, psi0, decreases with increasing n; in order for complexation to occur, this effect must be compensated for by a larger value of Y. Broader distributions of EO chain length lead to an increase in the range of Y over which the soluble complex is stable. We suggest that polycations initially bind to micelles which are rich in shorter EO chains and thus have higher "surface" potential, psi0. However, additional SDS may go preferentially into micelles rich in longer chains with lower psi0. This delays the formation of micelles which have sufficiently large psi0 to cause phase separation.

[Acute pancreatitis from obstruction of Wirsung's canal by Taenia saginata (author's transl)]

A case is reported of acute edematous pancreatitis due to obstruction of Wirsung's canal by Taenia saginata rings. The patients recovered after release of the obstruction by sphincterotomy followed by drainage of the biliary tract.

Reduction of azo food dyes in cultures of Proteus vulgaris

1. Rates of reduction of a number of azo food dyes were measured in anaerobic cultures of Proteus vulgaris. The rates of colour loss were found to be zero order under conditions in which the concentration of viable cells remained constant. 2. A significant increase in the rate of reduction followed the onset of cell mortality. 3. The zero-order rates correlate with the redox potentials of the dyes. A mechanism consistent with these observations involes an extracellular non-enzymic reducing agent which acts as an electron shuttle between dye and cellular reducing enzymes.