Understanding the interactions among polyelectrolytes by using inorganic polyoxometalate molecular clusters as model systems
Nanometer-scaled polyoxometalate (POM) molecular clusters exist as hydrophilic, highly soluble macroions in water and other polar solvents. Very interestingly, they do not stay as discrete ions even in very dilute solutions. Instead, we find that they universally tend to self-assemble into highly stable, monodispersed, hollow, spherical, single-layered shell-like structures (we call them “blackberries”), by using laser light scattering, TEM, SEM and SAXS studies.
The blackberry size can be accurately tuned by adjusting solution content and/or solution pH. The transitions between discrete macroions to blackberry structures, and between blackberries with different sizes, can be also achieved. The driving forces of the blackberry formation are not due to hydrophobic interaction, van der Waals forces or chemical interactions. Instead, we believe that the counter-ion effects and hydrogen bonds are critical. Synchrotron SAXS studies clearly show the radial distribution of small cations around large POM anions and the relation between the counter-ion association and the blackberry formation. › Continue reading
Reversible Self-Assembly of Hydrophilic Inorganic Polyelectrolytes into Highly Conservative, Vesicle-like Structures
The hydrophilic polyoxometalate (POM) macroanions are inorganic polyelectrolytes which offer a direct connection between simple ions and organic polyelectrolytes. POM solutions are perfect model systems for studying polyelectrolyte solutions because they are identical in size, shape, mass and charges, with easily tunable charge density.
Many types of POM macroanions are highly soluble but undergo reversible self-assembly to form uniform, stable, soft, single-layer vesicle-like blackberry structures containing >1000 individual POMs in dilute solutions. The driving force of the blackberry formation is likely counterion-mediated attraction (like-charge attraction). The blackberry size can be accurately controlled by solvent quality, or the charge density on macroions. Many unexpected phenomena have been observed in these novel systems. Blackberry structures may be analogous to virus shell structures formed by capsid proteins.
References:
Nature, 2003, 426, 59; JACS, 2002, 124, 10942; 2003, 125, 312; 2004, 126, 16690; 2005, 127, 6942; 2006, 128, 10103.
Strong Attractions with Controllable Size between Hydrophilic Inorganic Macroanions and Reversible Supramolecular Formations
The polyoxometalate (POM) hydrophilic macroionic solutions, offer a direct connection between traditional fields of simple inorganic ions, colloidal suspensions, polyelectrolytes, particularly proteins and DNAs.
Many types of POM macroanions are highly soluble, but undergo reversible self-assembly to form uniform, stable, soft, single-layer vesicle-like blackberry structures containing >1000 individual POMs in dilute solutions. Blackberry structures represent a new state of soluble inorganic ions. The driving forces of the POM self-assembly are unlike those of surfactant micelles or colloid aggregates. The POM driving forces are most likely counterion-mediated attraction (like-charge attraction). Blackberry size is controlled by the solvent quality, or the charge density of macroions. Blackberry structures may be analogous to virus shell structures formed by capsid proteins. Unexpected phenomena have been observed in the novel POM systems.
References:
JACS. 2005, 127, 6942; 2003, 125, 312; 2002, 124, 10942.
Nature, 2003, 426, 59.
J. Clust. Sci, 2006, 17, 427.