Silicon-29 NMR

Marsmann, H.C.

doi:10.1002/9780470034590.emrstm0505

Cited by 4 publications

(4 citation statements)

References 52 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…First, a resonance between silanol proton and D 2 can be discerned in Figure 3d. Second, the presence of Si-Cl bonds should have caused a larger downfield shift, by about 20 ppm, 25 than has been observed in our spectra. Third, these findings are supported by the DFT predicted chemical shifts, as discussed later.…”

Section: Resultsmentioning

confidence: 46%

“…[18][19][20][21][22][23][24] In addition to Q n sites, the functionalized materials may contain silicon atoms in positions denoted as T n (m ) 1; n ) 0, 1, 2, 3) and D n (m ) 2; n ) 0, 1, 2), where X ) OH, OCH 3 , Cl, etc. 25 Identification of these groups and their structures is an important challenge. The templated mesoporous silicas are usually uniform but never crystalline and thus cannot be examined in depth with X-ray diffraction.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Characterization of Covalent Linkages in Organically Functionalized MCM-41 Mesoporous Materials by Solid-State NMR and Theoretical Calculations

et al. 2007

View full text Add to dashboard Cite

The covalent linkages formed during functionalization of MCM-41 mesoporous molecular sieves with five chloroalkylsilanes ((EtO)3Si(CH2Cl), (MeO)3Si(CH2CH2CH2Cl), Cl3Si(CH2CH2CH3), Cl2Si(CH3)(CH2Cl) and Cl2Si(CH3)2) have been investigated using high-resolution solid-state NMR spectroscopy and DFT calculations. Structural information was obtained from 1H-13C and 1H-29Si heteronuclear (HETCOR) NMR spectra, in which high resolution in the 1H dimension was obtained by using fast MAS. The 1H-13C HETCOR results provided the assignments of 1H and 13C resonances associated with the surface functional groups. Sensitivity-enhanced 1H-29Si HETCOR spectra, acquired using Carr-Purcell-Meiboom-Gill refocusing during data acquisition, revealed the identity of 29Si sites (Qn, Tn, and Dn) and the location of functional groups relative to these sites. Optimal geometries of local environments representing the Qn, Tn and Dn resonances were calculated using molecular mechanics and ab initio methods. Subsequently, DFT calculations of 29Si, 13C, and 1H chemical shifts were performed using Gaussian 03 at the B3LYP/6-311++G(2d,2p) level. The theoretical calculations are in excellent accord with the experimental chemical shifts. This work illustrates that state-of-the-art spectroscopic and theoretical tools can be used jointly to refine the complex structures of inorganic-organic hybrid materials.

show abstract

Section: Resultsmentioning

confidence: 46%

Section: Introductionmentioning

confidence: 99%

Characterization of Covalent Linkages in Organically Functionalized MCM-41 Mesoporous Materials by Solid-State NMR and Theoretical Calculations

et al. 2007

View full text Add to dashboard Cite

show abstract

“…In addition to the discussed signals present in the spectra of all studied polyHIPEs, the 29 Si MAS-NMR spectra of the V3_1:1 and V3_1:1.5 samples show the lines of low intensities at δ = ∼−65 and ∼−56 ppm (Figure ). They are because of the [SiO 3 CH 3 ], that is, T, and [SiO 2 (CH 3 )OH], that is, D OH units of polysiloxanes, respectively . These lines prove that during the preparation of V3_1:1 and V3_1:1.5 polyHIPEs, which involved the use of higher amounts of D 4 H than in the remaining systems, hydrolysis of some Si–H groups leading to silanol (Si–OH) moieties and their subsequent condensation resulting in T units took place.…”

Section: Results and Discussionmentioning

confidence: 87%

Poly(methylvinylsiloxane)-Based High Internal Phase Emulsion-Templated Materials (polyHIPEs)—Preparation, Incorporation of Palladium, and Catalytic Properties

Mrówka

Gackowski

Lityńska‐Dobrzyńska

et al. 2020

Ind. Eng. Chem. Res.

View full text Add to dashboard Cite

Poly(methylvinylsiloxane) (V 3 polymer) obtained by kinetically controlled anionic ring-opening polymerization of 1,3,5-trimethyl-1,3,5-trivinylcyclotrisiloxane was cross-linked with various amounts of 1,3,5,7-tetramethylcyclotetrasiloxane (D 4 H ) in w/o high internal phase emulsions (HIPEs). PolyHIPEs thus prepared differed in the polymer cross-linking degree, which affected their porous morphology and total porosity. The obtained V 3 polymer-based polyHIPEs were applied as matrices for the incorporation of Pd from the Pd(OAc) 2 solution in tetrahydrofuran. This process involved the conversion of Si−H groups remaining in the polymer networks and resulted in the formation of crystalline, metallic Pd in the systems. Mean sizes of the generated Pd crystallites were lower in polyHIPEs of higher than in those of lower polymer cross-linking degrees and porosities (∼5 nm vs ∼8 nm, respectively). The Pd-containing polyHIPEs showed activity in catalytic hydrogenation of the triple carbon−carbon bond in phenylacetylene giving the unsaturated product, styrene with a selectivity of ca. 80%. To the best of our knowledge, this is the first work devoted to polysiloxane-based polyHIPEs with dispersed metallic particles.

show abstract

“…The spectra of the functionalized material prove that the functionalization was successful. Not only the spectra of the functionalized material exhibit resonances at about −67 and −59 ppm, which can be assigned to T 3 (RSi(OSi) 3 ) and T 2 (RSi(OSi) 2 (OH)) units, the relative intensities of the Q 4 , Q 3 , and Q 2 signals are also substantially changed as compared to the original spectrum. The decrease of the density of “free” silanol groups unambiguously confirms that APTES molecules had attached to the surface.…”

Section: Resultsmentioning

confidence: 99%

Structural and Dynamical Properties of Indomethacin Molecules Embedded within the Mesopores of SBA-15: A Solid-State NMR View

et al. 2012

View full text Add to dashboard Cite

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.

show abstract

Silicon-29 NMR

Cited by 4 publications

References 52 publications

Characterization of Covalent Linkages in Organically Functionalized MCM-41 Mesoporous Materials by Solid-State NMR and Theoretical Calculations

Characterization of Covalent Linkages in Organically Functionalized MCM-41 Mesoporous Materials by Solid-State NMR and Theoretical Calculations

Poly(methylvinylsiloxane)-Based High Internal Phase Emulsion-Templated Materials (polyHIPEs)—Preparation, Incorporation of Palladium, and Catalytic Properties

Structural and Dynamical Properties of Indomethacin Molecules Embedded within the Mesopores of SBA-15: A Solid-State NMR View

Contact Info

Product

Resources

About