Conformation and Dynamics of Organic Tethers Bound to MCM41-Type Surfaces from Solid State NMR Measurements

Abstract

The conformation and motions of organic chains bound to the surface of MCM41-type mesoporous silica materials are investigated in molecular detail. 2D heteronuclear correlation measurements in conjunction with relaxation measurements are used to infer both the orientation and the motions of the organic chains on the silica surface. In octyl-MCM41, proximity of octyl tether carbons to silanols is observed with the exception of the terminal carbons, pointing to slight chain bending which positions the center carbons in the chain closer to neighboring silanols. In aminopropyl-MCM41, the carbon directly bound to the amine group is the closest to silanol protons and physisorbed water protons, indicating a tilted orientation of the tail allowing for the amine group to interact with the silanol. Motions in the two chains are characterized by using 13C longitudinal and rotating frame relaxation measurements. Substantial differences in the T 1 and T 1ρ times of the two materials are shown to be the result of differences in activation energy for respective rotation and libration motions between the two materials. The shorter tether in aminopropyl-MCM41, characterized by larger kinetic barriers for libration motions, demonstrates higher chain rigidity. The longer chain in octyl-MCM41 is characterized by faster librations and slower bond rotations in the center carbons. Evidence from structural and dynamical data jointly provides a detailed view of the chain behavior and underscores differences in the physical properties of the two tethers bound to the MCM41-type surface.

Spectroscopic Characterization of Adsorbed 13CO2 on 3-Aminopropylsilyl-Modified SBA15 Mesoporous Silica

“…It is worthwhile to note the ammonium propylsilane present may also arise from protonation by the silanol groups and residual water on the silica surface . The pendent APS species have been previously shown to hydrogen bond with such silanol groups . Notably, the 15 N resonance at 44 ppm is not found in samples of APS-SBA15 synthesized by the more traditional route, via grafting 3-aminopropyl silane species, yet its chemical shift is consistent with an alkyl amine .…”

“…The pendent APS species have been previously shown to hydrogen bond with such silanol groups. 31 Notably, the 15 N resonance at 44 ppm is not found in samples of APS-SBA15 synthesized by the more traditional route, via grafting 3aminopropyl silane species, 12 yet its chemical shift is consistent with an alkyl amine. 32 Postgrafting amination was conducted by grafting bromopropylsilanes onto the surface of SBA15 and reacting it with ammonia gas.…”

Solid-state NMR studies of proteins immobilized on inorganic surfaces

“…This review primarily focuses on studies published after the previously reported review articles on solid state NMR of biomineralization proteins [11–14], discussing other proteins which have now been well studied, describing new techniques which are being implemented, and providing a look to the future of both methodology and systems. Work investigating interactions of non-protein based molecules such as citrate [15], succinate [16], tethered chains [17], or liposomes [18] on or with inorganic materials provide interesting venues for comparison, have recently been reviewed [19], and are outside the scope of this review. Additionally, the inorganic mineral of the biominerals has been studied in some detail [16,20–25], but that will also not be covered here.…”

Synthesis of a core–shell–shell structured acid–base bifunctional mesoporous silica nanoreactor (MS-SO3H@MS@MS-NH2) and its application in tandem catalysis

“…Solid-state NMR spectroscopy provided convincing spectroscopic evidence for the presence of the desired functional groups. [36][37][38] Fig. 5 shows the 29 Si solid-state NMR spectra of the samples; the three signals at À90, À100 ppm and À109 ppm were attributed to the Q 2 , Q 3 and Q 4 peaks.…”