Water Adsorption on the Stoichiometric (001) and (010) Surfaces of Hydroxyapatite: A Periodic B3LYP Study

Abstract

H2O adsorption on hexagonal hydroxyapatite (001) and (010) stoichiometric surfaces has been studied at B3LYP level with a localized Gaussian basis set of polarized double-zeta quality using the periodic CRYSTAL06 code. Because four Ca2+ cations are available at both surfaces, the considered H2O coverages span the 1/4<or=theta<or=5/4 range. The affinity of both HA surfaces for H2O is large: on the (001) surface, H2O adsorbs molecularly (binding energies BE approximately 80 kJ mol(-1) per adsorbed molecule), whereas it dissociates on the (010) surface, giving rise to new surface terminations (CaOwHw and POHw). The highly negative reaction energy for H2O dissociation (between -250 and -320 kJ mol(-1) per adsorbed H2O molecule) strongly suggests that the pristine (010) surface "as cut" from the hydroxyapatite bulk cannot survive in aqueous environment. Conversely, on the reacted surface, H2O adsorbs molecularly with BE similar to those computed for the (001) surface. The B3LYP BEs have been contrasted to the experimental water adsorption enthalpies measured by microcalorimetry on polycrystalline hydroxyapatite samples, showing a fairly good agreement and supporting the suggestion that H2O vapor adsorbs on the already reacted (010) crystalline faces. Harmonic B3LYP vibrational features of adsorbed H2O show, when compared to modes of the gas-phase H2O, a hypsochromic shift of the HOH bending mode (Deltadelta(HOH)=49 cm(-1)) and a bathochromic shift of the OH stretching modes larger than 1700 cm(-1) (Deltanu(OH)=427 cm(-1)), which are both in good agreement with literature experimental data.

Coordination chemistry of Ca sites at the surface of nanosized hydroxyapatite: interaction with H2O and CO

“…As for water uptake on the investigated HA materials, asdsorbed amounts (per Ca 2+ cation) on dehydrated HA/573 are significantly larger than on hydrated HA/303, in agreement with the presence at the dehydrated surface of cus Ca 2+ cations acting as Lewis acidic sites [25,26,29], which are expected to be strong hydrophilic sites. The hydrated HA/303 surface is conversely made up of H 2 O molecules coordinated to the surface, which act as hydrophilic sites of medium strength in that they are able to bind a second layer of H 2 O molecules via H bonding.…”

“…The surface structure of stoichiometric HA as such [28], and in interaction with small molecules such as water [29,30] and glycine [30,31] was also studied by some of us by ab initio modelling, combined with experimental techniques (adsorption microcalorimetry and IR spectroscopy).…”

Interstellar H adsorption and H2formation on the crystalline (010) forsterite surface: a B3LYP-D2* periodic study

“…The above equation can be easily recast to include the BSSE correction, using the same counterpoise method adopted for intermolecular complexes. 40 The definition of the BSSE-corrected adsorption energy E C is:…”

“…For the sake of brevity, we refer to previous works for a complete discussion concerning the calculation of the E C and the associated BSSE values. 40 Kinetic constants k TST have been computed by standard transition state theory using partition functions and the activation free energy. H tunneling has also been considered in a rather crude way by means of the Wigner correction…”

Layered Water in Crystal Interfaces as Source for Bone Viscoelasticity: Arguments from a Multiscale Approach

“…The latter needs to be dissolved or rinsed off, as to see the collagen fibrils in atomic force microscopy (Lees et al 2008;Hamed et al 2010;Martinez-Reina et al 2010;Reisinger et al 2010;Sansalone et al 2010). In such extrafibrillar crystal agglomerates, single crystals are stuck together, their surfaces being covered with very thin water layers (Zahn and Hochrein 2003;deLeeuw 2004;Bhowmik et al 2007;Astala and Stott 2008;Bhowmik et al 2009;Corno et al 2009). These layers exhibit a mass density, which is higher than that of standard liquid water, they are made of structured 'ice-like' water (Pan et al 2007).…”