title: Single molecule investigation of the onset and minimum size of the calcium-mediated junction zone in alginate.
abstract: One of the principal roles of alginate, both natively and in commercial applications, is gelation via Ca(2+)-mediated crosslinks between blocks of guluronic acid. In this work, single molecule measurements were carried out between well-characterised series of nearly monodisperse guluronic acid blocks ('oligoGs') using dynamic force spectroscopy. The measurements provide evidence that for interaction times on the order of tens of milliseconds the maximum crosslink strength is achieved by pairs of oligoGs long enough to allow the coordination of 4Ca(2+) ions, with both shorter and longer oligomers forming weaker links. Extending the interaction time from tens to hundreds of milliseconds allows longer oligoGs to achieve much stronger crosslinks but does not change the strength of individual links between shorter oligoGs. These results are considered in light of extant models for the onset of cooperative crosslinking in polyelectrolytes and an anisotropic distribution of oligoGs on interacting surfaces and provide a timescale for the formation and relaxation of alginate gels at the single crosslink level.
authors.affiliation: University of East Anglia, School of Pharmacy, United Kingdom.
authors.forename: Kate A
authors.initials: KA
authors.lastname: Bowman
authors.affiliation: Norwegian University of Science and Technology, Department of Biotechnology, Norway.
authors.forename: Olav Andreas
authors.initials: OA
authors.lastname: Aarstad
authors.affiliation: University of East Anglia, School of Pharmacy, United Kingdom; University of São Paulo, Ribeirão Preto School of Pharmaceutical Sciences, Brazil.
authors.forename: Marcela
authors.initials: M
authors.lastname: Nakamura
authors.affiliation: Norwegian University of Science and Technology, Department of Physics, Norway.
authors.forename: Bjørn Torger
authors.initials: BT
authors.lastname: Stokke
authors.affiliation: Norwegian University of Science and Technology, Department of Biotechnology, Norway.
authors.forename: Gudmund
authors.initials: G
authors.lastname: Skjåk-Bræk
authors.affiliation: University of East Anglia, School of Pharmacy, United Kingdom. Electronic address: a.round@uea.ac.uk.
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Round
mesh_terms: D000464:Alginates / Q000737:chemistry*; D002118:Calcium / Q000378:metabolism*; D005782:Gels / Q000737:chemistry*
chemical_list: D000464:Alginates; D005782:Gels; D002118:Calcium
keywords: AFM; Alginate; Gel; Junction zone; Single molecule