For Whom a Puddle Is the Sea? Adsorption of Organic Guests on Hydrated MCM-41 Silica

Shenderovich, Ilya G.

doi:10.1021/acs.langmuir.0c02327

Cited by 20 publications

(19 citation statements)

References 111 publications

(162 reference statements)

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“…Even when some couplings are not available or averaged to zero by rapid molecular exchange, the 1 J( 13 C 15 N) coupling can still provide important information about the qualitative structure of such complexes. In solids, the anisotropy of the chemical shielding is much more sensitive to external influences [61,62] and molecular dynamics [63,64] than the isotropic value. Consequently, ( 13 C≡ 15 N) − is an ideal hydrogen bond acceptor for NMR studies both in solutions and in solids, because several independent parameters can be measured for the same sample under the same experimental conditions.…”

Section: Introductionmentioning

confidence: 99%

NMR Properties of the Cyanide Anion, a Quasisymmetric Two-Faced Hydrogen Bonding Acceptor

Shenderovich

Denisov

2021

Symmetry

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The isotopically enriched cyanide anion, (13C≡15N)−, has a great potential as the NMR probe of non-covalent interactions. However, hydrogen cyanide is highly toxic and can decompose explosively. It is therefore desirable to be able to theoretically estimate any valuable results of certain experiments in advance in order to carry out experimental studies only for the most suitable molecular systems. We report the effect of hydrogen bonding on NMR properties of 15N≡13CH···X and 13C≡15NH···X hydrogen bonding complexes in solution, where X = 19F, 15N, and O=31P, calculated at the ωB97XD/def2tzvp and the polarizable continuum model (PCM) approximations. In many cases, the isotropic 13C and 15N chemical shieldings of the cyanide anion are not the most informative NMR properties of such complexes. Instead, the anisotropy of these chemical shieldings and the values of scalar coupling constants, including those across hydrogen bonds, can be used to characterize the geometry of such complexes in solids and solutions. 1J(15N13C) strongly correlates with the length of the N≡C bond.

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Section: Introductionmentioning

confidence: 99%

NMR Properties of the Cyanide Anion, a Quasisymmetric Two-Faced Hydrogen Bonding Acceptor

Shenderovich

Denisov

2021

Symmetry

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“…The importance of coadsorbed water to determine the properties of organic molecules on silica has been noted in other works …”

Section: Discussionmentioning

confidence: 94%

“…The importance of coadsorbed water to determine the properties of organic molecules on silica has been noted in other works. 105 A second conclusion regarding leucine speciation is that, in samples dried without thermal activation, it is a zwitterion (as in aqueous solution) rather than the canonical formin other words, it possesses a negative carboxylate as well as a positive ammonium group. This is strongly supported by IR data, as well as by the comparison of experimental and calculated chemical shiftsall of the models giving a good fit, even the anhydrous ones, have zwitterionic Leu.…”

Section: ■ Discussionmentioning

confidence: 99%

Leucine on Silica: A Combined Experimental and Modeling Study of a System Relevant for Origins of Life, and the Role of Water Coadsorption

et al. 2022

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Leucine on silica constitutes an interesting system from the point of view of origins of life studies since leucine coadsorbed on SiO 2 together with glutamic acid can give rise to rather long linear polypeptides upon activation. It is also an ideal system to test methods of molecular characterization of biomolecules deposited on mineral surfaces since it combines a small-scale model of peptides and proteins, which are among the most important components of biodevices, with one of the most widely used inorganic materials. We have deposited L-leucine on a high surface fumed silica in the submonolayer range and characterized it by a multipronged approach including macroscopic information (thermogravimetry, X-ray diffraction), in situ spectroscopic methods (IR, multinuclear solid-state NMR including single-pulse and CP-MAS, 2-D HETCOR), and molecular modeling by density functional theory (DFT), including calculation of NMR parameters. Specific information can be obtained on the adsorption and interaction mechanism. Leucine is rather strongly adsorbed without any covalent bonds, through the formation of a specific lattice of H-bonds that often involve coadsorbed water molecules. Its state is indeed strongly dependent on the drying procedure: insufficient drying results in liquid-like surroundings for the leucine functional groups, while vacuum drying only retains a limited number of waters (of the order of 5 per leucine molecule). The most stable models have zwitterionic leucine interacting directly with surface silanols through their ammonium group, while the carboxylate interacts through bridging waters. Experimental NMR chemical shifts are satisfactorily predicted for these models, and leucine can be viewed as a probe for specific groups of surface sites known as silanol nests.

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“…In both cases, the resonance at −243 ppm, accompanied by spinning sidebands with lower intensities, belongs to more mobile molecules of 1 . The general observation that at a higher loading two phases are formed, a mobile surface phase and a stationary bulk phase, is most common when there are no particularly strong interactions between the guest molecules . It is interesting that the ratio of less mobile to more mobile molecules is determined to be 1.3 to 1 and 3.5 to 1 for 1 - 140 and 1 - 200 , respectively.…”

Section: Resultsmentioning

confidence: 99%

Molecular Dynamics and Surface Interactions of Nickelocene Adsorbed on Silica: A Paramagnetic Solid-State NMR Study

et al. 2022

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When grinding nickelocene with silica in the absence of a solvent at room temperature, it adsorbs on the surface within the pores. This has also been demonstrated visually by adsorbing green nickelocene in the pores of a large colorless silica gel specimen. While this dry adsorption and translational mobility of nickelocene within the pores is proven visually, the site-to-site mobility of the nickelocene molecules and their orientation toward the surface are not yet understood. In this contribution, mesoporous silica is used as the support material for a systematic solid-state NMR study of these issues. Paramagnetic 1 H VT solid-state NMR and T 1 relaxation times have been powerful tools for studying the dynamics of nickelocene on the silica surface. Herewith, the mobility of the surface-adsorbed nickelocene molecules in the pores could be quantified on the molecular scale. According to the obtained data, the nickelocene molecules move like a liquid on the surface. Isotropically moving molecules exchange places rapidly with surface-attached molecular states of nickelocene in a sample with submonolayer surface coverage. This finding is corroborated by a macroscopic visualization experiment. The states of the surface-attached horizontally oriented nickelocene molecules that are prevalent at temperatures below 200 K have been quantified. The temperature dependencies of the rate k in coordinates of ln(k) versus 1/T and ln(k/T) versus 1/T form ideal straight lines that allow the determination of the kinetic parameters E act = 5.5 kcal/mol, A = 1.1 × 10 10 , ΔH ‡ = 5.0 kcal/mol, and ΔS ‡ = −15 eu. Investigating a sample with equal amounts of nickelocene and ferrocene in a submonolayer amount of 80% overall surface coverage shows that the different metallocenes mix on the molecular level on the silica surface.

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For Whom a Puddle Is the Sea? Adsorption of Organic Guests on Hydrated MCM-41 Silica

Cited by 20 publications

References 111 publications

NMR Properties of the Cyanide Anion, a Quasisymmetric Two-Faced Hydrogen Bonding Acceptor

NMR Properties of the Cyanide Anion, a Quasisymmetric Two-Faced Hydrogen Bonding Acceptor

Leucine on Silica: A Combined Experimental and Modeling Study of a System Relevant for Origins of Life, and the Role of Water Coadsorption

Molecular Dynamics and Surface Interactions of Nickelocene Adsorbed on Silica: A Paramagnetic Solid-State NMR Study

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