Two-dimensional (2D) solid-state nuclear magnetic resonance (SSNMR) experiments on samples loaded with C-labeled CO, "under controlled partial pressures", have been performed in this work, revealing unprecedented structural details about the formation of CO adducts from its reaction with various amine-functionalized SBA-15 containing amines having distinct steric hindrances (e.g., primary, secondary) and similar loadings. Three chemisorbed CO species were identified by NMR from distinct carbonyl environments resonating at δ ≈ 153, 160, and 164 ppm. The newly reported chemisorbed CO species at δ ≈ 153 ppm was found to be extremely moisture dependent. A comprehensive H-based SSNMR study [1DH and 2D H-X heteronuclear correlation (HETCOR, X =C, Si) experiments] was performed on samples subjected to different treatments. It was found that all chemisorbed CO species are involved in hydrogen bonds (HBs) with either surface silanols or neighboring alkylamines. H chemical shifts up to 11.8 ppm revealed that certain chemisorbed CO species are engaged in very strong HBs. We effectively demonstrate that NMR may help in discriminating among free and hydrogen-bonded functional groups. C{N} dipolar-recoupling NMR showed that the formation of carbonate or bicarbonate is excluded. Density functional theory calculations on models of alkylamines grafted into the silica surface assisted the H/C assignments and validated various HB arrangements that may occur upon formation of carbamic acid. This work extends the understanding of the chemisorbed CO structures that are formed upon bonding of CO with surface amines and readily released from the surface by pressure swing.

The wealth of site-selective structural information on CO speciation, obtained by spectroscopic techniques, is often hampered by the lack of easy-to-control synthetic routes. Herein, an alternative experimental protocol that relies on the high sensitivity of C chemical shift anisotropy (CSA) tensors to proton transfer, is presented to unambiguously distinguish between ionic/charged and neutral CO species, formed upon adsorption of CO in amine-modified porous materials. Control of the surface amine spacing was achieved through the use of amine protecting groups during functionalisation prior to CO adsorption. This approach enabled the formation of either "isolated" or "paired" carbamate/carbamic acid species, providing a first experimental NMR proof towards the identification of both aggregation states. Computer modelling of surface CO -amine adducts assisted the solid-state NMR assignments and validated various hydrogen-bond arrangements occurring upon formation of isolated/aggregated carbamic acid and alkylammonium carbamate ion species. This work extends the understanding of chemisorbed CO structures formed at pore surfaces and reveals structural insight about the protonation source responsible for the proton-transfer mechanism in such aggregates.

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Two types of preformed alginate wet gels, one with a low (30−35%) and the other with a high (65−75%) content of glucuronic acid, were reacted with an aliphatic triisocyanate that was priorly allowed to diffuse in the pores. This reaction formed urethane groups on the surface of the alginate framework and also formed a polyurea (PUA) network connecting these urethane groups via respective reactions of the triisocyanate with alginate surface −OH groups or with gelation water remaining adsorbed on the inner surfaces of the wet gels. These processes formed a conformal nanothin film of PUA around the alginate network. After drying the wet gels with the supercritical fluid CO 2 , we obtained PUA/polyurethane-crosslinked alginate (X-alginate) aerogels. Although X-alginate aerogels are essentially copolymers, unlike all copolymers mentioned in previous literature reports, the relative topology of the alginate and the cross-linker is defined at the nanoscopic scale rather than at the molecular level. For the systematic study of X-alginate aerogels as a function of synthetic conditions, the experimental protocol was designed according to the central circumscribed rotatory design model using the alginate and the triisocyanate concentration as independent variables. Empirical models were derived for all relevant material properties by fitting experimental data to the two independent variables. The chemical identity of all samples was confirmed with attenuated total reflectance−Fourier transform infrared spectroscopy and solid-state 13 C and 15 N cross-polarization magic angle spinning NMR spectroscopy. The percentage of PUA uptake in X-alginate aerogels (58−98%) was calculated from skeletal density data. Scanning electron microscopy showed that all samples were nanofibrous, indicating that PUA coated conformally the skeletal network of both alginates, and the micromorphology remained the same as in the native (non-cross-linked) samples. X-alginate aerogels are mechanically strong materials, in contrast to their native counterparts, which are extremely weak mechanically. Compared to various organic aerogels from the literature, X-alginate aerogels can be as stiff as many other polymeric aerogels with 2 or 3 times higher densities. In addition, X-alginate aerogels are good candidates for sound insulation applications, as the speed of sound in most samples was estimated to be significantly lower than the speed of sound in dry air.

The structural properties of the mesoscopically confined drug and drug–drug and drug–matrix interactions were investigated in model drug-delivery systems prepared from nonfunctionalized and functionalized SBA-15 mesoporous silicate matrices, loaded with different amounts of indomethacin molecules. 1H MAS and 1H–13C CPMAS NMR spectroscopy indicated that only when the concentration of indomethacin within the mesopores becomes sufficiently high (when the mass fraction of indomethacin within the sample exceeds ∼0.15) do hydrogen bonds between the drug molecules become abundant. Nitrogen sorption analysis and comparison of 1H spin–lattice relaxation times in progressively loaded SBA-15 matrices suggested that at low loading concentrations indomethacin forms a layer on the silicate walls of the mesopores and that at moderate or high loading concentrations rigid nanoparticles that extend throughout the entire mesopore cross section are formed. 1H–29Si HETCOR NMR spectra indicated that the interaction between the indomethacin molecules and the silicate surface was moderate to weak. The 1H–13C CPMAS NMR spectrum of indomethacin embedded within the mesopores of SBA-15 closely resembled the spectrum of the bulk amorphous indomethacin and did not allow to draw firm conclusions about the molecular conformation and the packing of the drug molecules within the pores. On the contrary, variable-temperature 1H spin–lattice relaxation measurements showed that the mesoscopically confined indomethacin is significantly different from the bulk amorphous indomethacin. It does not become rubbery, and it exhibits a solid–solid transition at 363 K that is similar to the phase transition of the crystalline indomethacin solvate with tetrahydrofuran. When indomethacin is incorporated into the functionalized SBA-15 matrix, the interactions between the embedded drug molecules and the walls of the matrix are enhanced.

Polyurea-crosslinked alginate (X-M-alginate; M: Co, Ni, Cu) aerogels, prepared from the corresponding M-alginate wet-gels and the aromatic triisocyanate Desmodur RE, are precursors for metal- and nitrogen-doped carbon (X-M-C) aerogels.

Polyurea-crosslinked calcium alginate and chitosan aerogel beads: novel fibrous biopolymer-based aerogels.

A HKUST-1 metal–organic framework was crystallized in the NH2-modified mesostructured silica FDU-12 in order to improve its structural stability upon water exposure.