Restriction of CaCO3 polymorph by NH⋯O hydrogen-bonded poly(methacryloylaminocarboxylate) ligands: induced polymorph change by strength and/or formation manner of hydrogen bond

Abstract

Novel poly(methacryloylaminocarboxylate) ligands were synthesized as models for an acidic peptide in CaCO₃ biominerals. Syndiotactic poly[3-methyl-2-(methacryloylamino)butyrate], isotactic-rich poly[3-(methacryloylamino)propionate], and syndiotactic poly[4-(methacryloylamino)butyrate] form 5-, 6-, and 7-membered-ring intra-side-chain NH⋯O hydrogen bonds, respectively, between a carboxylate oxyanion and the neighboring amide NH proton, while syndiotactic poly[3-(methacryloylamino)propionate] forms intermolecular NH⋯O hydrogen bonds. These polymer ligands strongly bind to CaCO₃ crystals because of the NH⋯O hydrogen bonds. In polymer ligand–CaCO₃ composites, the strength and/or mode of hydrogen bonding in the polymer ligands affects the CaCO₃ polymorphs. Five-membered-ring intra-side-chain and intermolecular hydrogen-bonded polymers have weak hydrogen bonds and produce calcite crystals, whereas other ligands with 6- and 7-membered-ring intra-side-chain hydrogen bonds have strong hydrogen bonds and yield vaterite crystals. Polymorph change of CaCO₃ crystal is induced by differences of strength and/or mode of the NH⋯O hydrogen bond.