Effect of Ca<sup>2+</sup>on the self assembly of a nonionic peptide aggregate

Moses, Julia P.; Inayathullah, Mohammed; Murugesan, Muthu; Andrews, Maneesha E.; Balasubramanian, M.; Jayakumar, R.

doi:10.1023/b:lips.0000014007.74872.d7

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“…3 Previous studies have shown that divalent counterions can lead to a surface charge reversal of a negatively charged solid surface, 4,5 while for bulk macromolecular solution, it has been demonstrated that they can induce aggregation or precipitation of charged surfactants and proteins by screening the electrostatic repulsion. 6 Although divalent ions have commonly been added to solutions to help the polyelectrolyte adsorb to solid surfaces, 7,8 for example in the application of lime to soil clay 9 and EDTA on glassware cleaning, 10 most studies on their effect of modulating the forces and interactions between charged polymers and surfaces are indirect, relying on theoretical simulations or observations made with scanning microscopy. 4,8,11,12 There were only a few direct force measurements in which only the counterion valency is varied.…”

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confidence: 99%

Interactions of Hyaluronan Layers with Similarly Charged Surfaces: The Effect of Divalent Cations

2013

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We used colloidal probe atomic force microscopy to measure the normal forces between the surface of a silica colloidal particle and a sparse layer of hyaluronan (hyaluronic acid, HA, MW ≈ 10(6) Da) covalently attached to a planar silica surface, both across pure water and following the addition of 1 mM MgCl2. It was found that in the absence of salt the HA layer repelled the colloidal silica surface during both approach and retraction. The addition of the MgCl2, however, changes the net force between the negatively charged HA layer and the opposing negatively charged silica surface from repulsion to adhesion. This interaction reversal is attributed to the bridging effect of the added Mg(2+) ions. Our results provide first direct force data to support earlier simulation and predictions that such divalent cations could bridge between negative charges on opposing surfaces, leading to an overall reversal of force from repulsion to attraction.

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