| Abstract
| - Succinoglycan, a high molar mass polysaccharide, undergoes conformational transformationsas a function of ionic strength. The nature of the transitions and the presence of intermolecular associationshave been described previously using solution-based techniques. In this work, we have determined theconformation of succinoglycan macromolecules at the solution−mica interface using atomic forcemicroscopy (AFM) and compared these data to the measurements obtained in solution. Molecularcharacteristics such as chain length, end-to-end distances, polymer heights (diameters), and chain rigiditywere determined as a function of ionic strength. Individual chains and dimers were found for succinoglycandeposited from pure water, whereas only individual chains were found for 0.01 M KCl. In 0.5 M KCl,succinoglycan formed a gel-like structure at the mica surface. Analysis of persistence lengths from theAFM images indicated that succinoglycan became more rigid with increasing ionic strength. Flexiblechains corresponding to a disordered conformation were observed in water while ordered, single helicalchains were imaged in 0.01 M KCl. In comparison to bulk solution measurements, molecular conformationsdetermined by AFM were shown to be affected by local concentration increases due to the AFM dryingstep and by the strength of the interaction between the macromolecules and the mica substrate. In waterand 0.01 M KCl, comparison of the measured end-to-end distances, with calculated 2D or projected end-to-end distances, revealed that the polysaccharide was not at equilibrium with the mica surface. Thesefindings demonstrate the potential of AFM as a polymer characterization technique that is complementaryto classical solution-based techniques and able to provide specific information on the polymer conformationsat the solid−water interface.
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