title: Calcium carbonate crystal growth beneath Langmuir monolayers of acidic β-hairpin peptides.
abstract: Four amphiphilic peptides with designed hairpin structure were synthesized and their monolayers were employed as model systems to study biologically inspired calcium carbonate crystallization. Langmuir monolayers of hairpin peptides were investigated by surface pressure area isotherms, surface potential isotherms, Brewster angle microscopy (BAM), atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy. A β-hairpin conformation was found for all peptides at the air-water interface although their packing arrangements seem to be different. Crystallization of calcium carbonate under these peptide monolayers was investigated at different surface pressures and growth times both by in situ optical microscopy, BAM and ex situ investigations such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM). An amorphous calcium carbonate precursor was found at the initial crystallization stage. The crystallization process occurred in three stages. It starts from the nucleation of amorphous particles being a kinetically controlled process. Crystal nuclei subsequently aggregate to large particles and vaterite crystals start to form inside the amorphous layer, with the monolayer fluidity exerting an important role. The third process includes the re-crystallization of vaterite to calcite, which is thermodynamically controlled by monolayer structural factors including the monolayer flexibility and packing arrangement of the polar headgroups. Thus, the kinetic factors, monolayer fluidity and flexibility as well as structure factors govern the crystal morphology and polymorph distribution simultaneously and synergistically.
authors.affiliation: Institute of Physics, Chair of Solid State and Materials Chemistry, Augsburg University, Universitätsstrasse 1, D-86159 Augsburg, Germany. dirk.volkmer@physik.uni-augsburg.de.
authors.forename: Haofei
authors.initials: H
authors.lastname: Gong
authors.forename: Yi
authors.initials: Y
authors.lastname: Yang
authors.forename: Manuela
authors.initials: M
authors.lastname: Pluntke
authors.forename: Othmar
authors.initials: O
authors.lastname: Marti
authors.forename: Zsuzsa
authors.initials: Z
authors.lastname: Majer
authors.forename: Norbert
authors.initials: N
authors.lastname: Sewald
authors.forename: Dirk
authors.initials: D
authors.lastname: Volkmer
mesh_terms: D002119:Calcium Carbonate / Q000737:chemistry*; D003460:Crystallization; D006863:Hydrogen-Ion Concentration; D018625:Microscopy, Atomic Force; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D010455:Peptides / Q000737:chemistry*; D011487:Protein Conformation; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D010455:Peptides; D002119:Calcium Carbonate