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97166 ATOMIC FORCE MICROSCOPY AND MOLECULAR MODELING OF BRANCHED AND UNBRANCHED POLYASPARTATE BOUND TO CALCITE AND MICA

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Product Number: 51300-97166-SG
ISBN: 97166 1997 CP
Author: C.S. Sikes, Andrzej Wierzbicki
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Polyaspartate molecules made by dry, thermal polycondensation of aspartic acid are thought to be moderately branched. Polyaspartates made by thermal polycondensation in the presence of phosphoric acid as a solvent/catalyst are thought to be linear, unbranched molecules. Examples of these two forms of polyaspartate were synthesized. When viewed by atomic force microscopy (AFM) on mica, the polyaspartates did appear to be different, but there was no evidence for or against the presence of branching as such. When viewed by AFM on calcite, the phosphoric-catalyzed, thermal polyasparates did exhibit a linear, unbranched appearance that was not seen in the presence of dry, thermal polyaspartates. In addition, the transition to the linear appearance was dependent on the concentration of phosphoric acid used in the synthesis. Studies of inhibition of calcium carbonate and calcium phosphate formation by the polyaspartates revealed that the putatively branched polyaspartate was an effective inhibitor, especially of calcium phosphate crystallization. Molecular modeling showed that a moderate number of branches of moderate length may dramatically affect the morphology and therefore the binding energies of polyaspartate. Linear molecules are predicted to have stereospecific, high-affinity binding to calcite that the branched molecules may not have. The presence of both alpha and beta residues also can weaken the interactions somewhat of polyaspartates with calcite. The results suggested that although branching may occur in thermal polyaspartate, it is probably not very extensive.
Polyaspartate molecules made by dry, thermal polycondensation of aspartic acid are thought to be moderately branched. Polyaspartates made by thermal polycondensation in the presence of phosphoric acid as a solvent/catalyst are thought to be linear, unbranched molecules. Examples of these two forms of polyaspartate were synthesized. When viewed by atomic force microscopy (AFM) on mica, the polyaspartates did appear to be different, but there was no evidence for or against the presence of branching as such. When viewed by AFM on calcite, the phosphoric-catalyzed, thermal polyasparates did exhibit a linear, unbranched appearance that was not seen in the presence of dry, thermal polyaspartates. In addition, the transition to the linear appearance was dependent on the concentration of phosphoric acid used in the synthesis. Studies of inhibition of calcium carbonate and calcium phosphate formation by the polyaspartates revealed that the putatively branched polyaspartate was an effective inhibitor, especially of calcium phosphate crystallization. Molecular modeling showed that a moderate number of branches of moderate length may dramatically affect the morphology and therefore the binding energies of polyaspartate. Linear molecules are predicted to have stereospecific, high-affinity binding to calcite that the branched molecules may not have. The presence of both alpha and beta residues also can weaken the interactions somewhat of polyaspartates with calcite. The results suggested that although branching may occur in thermal polyaspartate, it is probably not very extensive.
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