Spectroscopic Study and Local Coordination of Polyphosphate Colloidal Systems

Abstract

The interaction between metaphosphate chains and the metal ions Ca2+ and Eu3+ has been studied in water by Eu3+ luminescence, infrared absorption, and 31P NMR spectroscopy. Two main families of sites could be identified for the metal ions in the aqueous polyphosphate colloidal systems: (1) cagelike sites provided by the polyphosphate chain and (2) a family which arises following saturation of cagelike sites. Occupation of this second family leads to supramolecular interactions between polyphosphate chains and the consequent destabilization of the colloidal system. In the polyphosphate-Ca2+ system, this destabilization appears as a coacervation process. Equilibrium existing between colloidal species as a function of the compositions could be reasoned based on the spectroscopic measurements. The determination of coordination numbers and the correlation of the results with the observation of coacervates show that Eu3+ luminescence properties can be used to probe in a unique way the coacervation process.

Characterisation of phosphate coacervates for potential biomedical applications

“…11–14 In general, the coacervation process involves the liquid–liquid phase separation of a homogeneous solution of charged macromolecules resulting in a dense, polymer-rich ‘coacervate’ phase which coexists with its supernatant. In relation to PBG, the process entails the addition of a solution of polyvalent cations to a concentrated solution of sodium polyphosphate (Graham salt).…”

“…In relation to PBG, the process entails the addition of a solution of polyvalent cations to a concentrated solution of sodium polyphosphate (Graham salt). 11–13,15–17 Graham salt is a water soluble polyphosphate composed of long metaphosphate chains. 18 When in solution, electrostatic interactions between the long polyphosphate chains and polyvalent cations lead to the formation of the dense coacervate phase.…”

“…19 Further to this, phosphate coacervates have found a wide range of other applications including the anticorrosion protection of metals and the immobilisation of asbestos. 12 …”

“…studied the interactions between metaphosphate chains and Ca 2+ and Eu 3+ cations in aqueous solution using Eu 3+ luminescent measurements, and infrared and 31 P nuclear magnetic resonance (NMR) spectroscopies. 12 Their results revealed that the cations occupy two types of sites: cage-like sites within the polyphosphate chains and sites outside the chains which only become occupied once all the cage-like sites are taken. The authors concluded that it is the occupation of the second type of site that leads to supramolecular interactions between the chains that result in the formation of the coacervate.…”

Calcium polyphosphate precipitation – A strategy to tune the chain length of the glass and control the subsequent release of vancomycin

“…One existing theory on the interaction of calcium with polyphosphate is that, at low Ca/P ratios, the calcium ions will be located in "cage-like" sites (site 1) [43]. Upon saturation of site 1, the calcium ions may cross-link between adjacent chains (site 2) and allow for the polyphosphates to precipitate out of solution.…”