title: Computational Study of Acidic and Basic Functionalized Crystalline Silica Surfaces as a Model for Biomaterial Interfaces.
abstract: In silico modeling of acidic (CH2COOH) or basic (CH2NH2) functionalized silica surfaces has been carried out by means of a density functional approach based on a gradient-corrected functional to provide insight into the characterization of experimentally functionalized surfaces via a plasma method. Hydroxylated surfaces of crystalline cristobalite (sporting 4.8 OH/nm(2)) mimic an amorphous silica interface as unsubstituted material. To functionalize the silica surface we transformed the surface Si-OH groups into Si-CH2COOH and Si-CH2NH2 moieties to represent acidic/basic chemical character for the substitution. Structures, energetics, electronic, and vibrational properties were computed and compared as a function of the increasing loading of the functional groups (from 1 to 4 per surface unit cell). Classical molecular dynamics simulations of selected cases have been performed through a Reax-FF reactive force field to assess the mobility of the surface added chains. Both DFT and force field calculations identify the CH2NH2 moderate surface loading (1 group per unit cell) as the most stable functionalization, at variance with the case of the CH2COOH group, where higher loadings are preferred (2 groups per unit cell). The vibrational fingerprints of the surface functionalities, which are the ν(C═O) stretching and δ(NH2) bending modes for acidic/basic cases, have been characterized as a function of substitution percentage in order to guide the assignment of the experimental data. The final results highlighted the different behavior of the two types of functionalization. On the one hand, the frequency associated with the ν(C═O) mode shifts to lower wavenumbers as a function of the H-bond strength between the surface functionalities (both COOH and SiOH groups), and on the other hand, the δ(NH2) frequency shift seems to be caused by a subtle balance between the H-bond donor and acceptor abilities of the NH2 moiety. Both sets of data are in general agreement with experimental measurements on the corresponding silica-functionalized materials and provide finer details for a deeper interpretation of experimental spectra.
authors.affiliation: †Dipartimento di Chimica and NIS - Nanostructured Interfaces and Surfaces - Centre, Università degli Studi di Torino, via P. Giuria 7, 10125 Torino, Italy.
authors.forename: Marta
authors.initials: M
authors.lastname: Corno
authors.affiliation: †Dipartimento di Chimica and NIS - Nanostructured Interfaces and Surfaces - Centre, Università degli Studi di Torino, via P. Giuria 7, 10125 Torino, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Delle Piane
authors.affiliation: ‡CNR Institute of Chemistry of Organometallic Compounds, Area della Ricerca, via G. Moruzzi l, I-56124 Pisa, Italy.
authors.forename: Susanna
authors.initials: S
authors.lastname: Monti
authors.affiliation: §Materials Research and Technology Department (MRT), Luxembourg Institute of Science and Technology (LIST), 5 avenue des Hauts-Fourneaux, L-4362 Esch/Alzette, Luxembourg.
authors.forename: Maryline
authors.initials: M
authors.lastname: Moreno-Couranjou
authors.affiliation: §Materials Research and Technology Department (MRT), Luxembourg Institute of Science and Technology (LIST), 5 avenue des Hauts-Fourneaux, L-4362 Esch/Alzette, Luxembourg.
authors.forename: Patrick
authors.initials: P
authors.lastname: Choquet
authors.affiliation: †Dipartimento di Chimica and NIS - Nanostructured Interfaces and Surfaces - Centre, Università degli Studi di Torino, via P. Giuria 7, 10125 Torino, Italy.
authors.forename: Piero
authors.initials: P
authors.lastname: Ugliengo
mesh_terms: D000143:Acids; D000327:Adsorption; D000468:Alkalies; D004583:Electrons; D006900:Hydroxylation; D056004:Molecular Dynamics Simulation; D011789:Quantum Theory; D012822:Silicon Dioxide / Q000737:chemistry*; D013499:Surface Properties; D013816:Thermodynamics; D014732:Vibration; D014867:Water / Q000737:chemistry*
chemical_list: D000143:Acids; D000468:Alkalies; D014867:Water; D012822:Silicon Dioxide