Investigating the Interaction of Water Vapour with Aminopropyl Groups on the Surface of Mesoporous Silica Nanoparticles

Abstract

The interaction of water molecules with the surface of hybrid silica-based mesoporous materials is studied by Si, H and C solid-state NMR and IR spectroscopy, with the support of ab initio calculations. The surface of aminopropyl-grafted mesoporous silica nanoparticles is studied in the dehydrated state and upon interaction with controlled doses of water vapour. Former investigations described the interactions between aminopropyl and residual SiOH groups; the present study shows the presence of hydrogen-bonded species (SiOH to NH ) and weakly interacting "free" aminopropyl chains with restricted mobility, together with a small amount of protonated NH groups. The concentration of the last-named species increased upon interaction with water, and this indicates reversible and fast proton exchange from water molecules to a fraction of the amino groups. Herein, this is discussed and explained for the first time, by a combination of experimental and theoretical approaches.

Hyaluronated mesoporous silica nanoparticles for active targeting: influence of conjugation method and hyaluronic acid molecular weight on the nanovector properties

“…All samples were measured in transmission mode on self-supporting pellets, after RT evacuation necessary to remove adsorbed impurities and water, which would influence the spectral analysis (see for instance Refs. [28] and [57]). The spectrum of HA 200 kDa (measured in KBr) is reported for comparison in the Supplementary Material (Figure S5).…”

“…Infrared spectroscopy is a powerful tool to investigate interface interactions in hybrid organicinorganic materials. It can be used to assess the molecular structure of surface grafted functionalizing groups, and the weak interactions taking place between silica surface and adsorbed/encapsulated drug molecules [28,[50][51][52][53][54][55][56][57][58]. The spectra of parent NH2-MSN and HA conjugated samples are reported in Figure 3, in the high and low frequency ranges (top and bottom panel, respectively).…”

Combined solid-state NMR, FT-IR and computational studies on layered and porous materials

“…379 Paul et al have applied multi-technique approach on the investigation of interaction of water vapour with aminopropyl groups on the surface of mesoporous silica nanoparticles. 380 The application of rotor-synchronised spin-echo magic angle spinning 1 H NMR methodology provided the substantial suppression of broad probe background signal as well as the signals from strongly dipolar coupled terms (other broad signals) in partly hydrated samples delivering an opportunity to obtain the signal of surface groups. They have judiciously chosen the delay time (τ) as an optimised compromise between the signal decay owing to relaxation and the resolution gain owing to longer delay times.…”

“…This point was discussed in detail with the help of ab initio simulations, showing the conditions for the protonation of amino groups on the silica surface in the presence of water. 380 Andreev et al further developed the spin-echo sequence with the insertion of a dipolar filter prior to the sequence. 381…”

Supramolecular Organization in Confined Nanospaces

“…By a judicious choice of template and synthesis conditions, it is possible to tune the size of the channel according to the size of specific pre‐selected guests ,. Also, mesoporous silicas can incorporate additional functionalities into their matrix via 1) “one‐pot” synthesis, i. e., by co‐condensation of a functional organosilane with the silica precursor, or 2) “post‐condensation”, which consists in the binding (“grafting”) of the functional organosilane to the walls of the mesoporous material, usually by impregnation or through the vapor phase (Figure ) ,. The presence of a great number of surface silanols on the inner pore walls favors post‐synthesis functionalization approaches.…”