Diffusion NMR in Supramolecular Chemistry

Cohen, Yoram; Avram, Liat; Evan-Salem, Tamar; Frish, Limor

doi:10.1002/9783527610273.ch6

Cited by 23 publications

(27 citation statements)

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“…[13] Centrifugation of the aqueous colloidal dispersion (see Experimental Section) allowed the facile isolation of the Pd nanoparticles. Representative transmission electron microscopy (TEM) images of the isolat-ed palladium nanoparticles (see Figure 1, bottom), obtained as depicted in the Experimental Section, show spherical nanoparticles (in the size range of 2 to 7 nm) which corroborated the use of the EinsteinStokes equation [14] to obtain the particle size from diffusion coefficients in DLS measurements. X-ray photoelectron spectroscopy (XPS) analysis of the Pd 3d region (Pd 3d 5/2 and Pd 3d 3/2 ) [15] revealed that among the palladium species detected, Pd(II) and Pd(0), the latter one was formed as a major phase (Figure 2).…”

Section: Synthesis and Characterizationmentioning

confidence: 69%

Hydroxypropyl‐α‐Cyclodextrin‐Capped Palladium Nanoparticles: Active Scaffolds for Efficient Carbon‐Carbon Bond Forming Cross‐Couplings in Water

et al. 2009

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A new approach for the preparation of palladium nanoparticles in water from a renewable source, 2-hydroxypropyl-a-cyclodextrin (a-HPCD), which acts both as a reductant and capping agent, is presented. The palladium nanoparticles were characterized by using dynamic light scattering (DLS), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), which revealed the formation of spherical particles in the size range of 2-7 nm. Further analysis by Fourier-transform infrared spectroscopy (FT-IR) and 1 H NMR did not show covalent bonds between cyclodextrins and palladium nanoparticles, suggesting that a-HPCD is only physically adsorbed on the nanoparticle surface, presumably through hydrophobic interactions which limit the mutual coalescence of nanoclusters. The catalytic activity was tested in Suzuki, Heck and Sonogashira reactions in neat water, providing good yields and selectivities of coupling products under very low Pd loadings (0.5-0.01 mol%). Remarkably, the nanocatalyst showed significant stability hence the aqueous phase remained active for four subsequent runs. The combination of a binding site for substrates (the HPCD cavity) and a reactive centre (Pd core) provides a potential to explore functional catalysis in aqueous medium.

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Section: Synthesis and Characterizationmentioning

confidence: 69%

Hydroxypropyl‐α‐Cyclodextrin‐Capped Palladium Nanoparticles: Active Scaffolds for Efficient Carbon‐Carbon Bond Forming Cross‐Couplings in Water

et al. 2009

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“…The spontaneous self-assembly of molecules 10d, 22c, 56a,b and 57a,b into hexameric capsules in organic solvents has been demonstrated with the aid of diffusion NMR systems. 187 …”

Section: Cavitands and Capsulesmentioning

confidence: 99%

Chemistry of calix[4]resorcinarenes

Jain¹,

Kanaiya

2011

Russ. Chem. Rev.

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The review demonstrates the progress in the The review demonstrates the progress in the chemistry of calix[4]resorcinarenes over the last decade. chemistry of calix[4]resorcinarenes over the last decade. Special attention is paid to their synthesis, conformational Special attention is paid to their synthesis, conformational behaviour, functionalization and ability to serve as cavi-behaviour, functionalization and ability to serve as cavitands and capsules, to form monolayers and host ± guest tands and capsules, to form monolayers and host ± guest complexes. Practical applications of calix[4]resorcinarenes complexes. Practical applications of calix[4]resorcinarenes and their derivatives in various fields are surveyed. The and their derivatives in various fields are surveyed. The bibliography includes 296 references bibliography includes 296 references.

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“…Several NMR techniques are available to monitor diffusion and have recently been reviewed. [7][8][9] Pulsed gradient spin-echo (PGSE) NMR methods have attracted increasing interest, since they allow diffusion coefficients to be measured with high accuracy; they have been successfully used with observation of 7 Li and 31 P nuclei as well as with 1 H NMR. 10,11 We report here the direct measurement of diffusion coefficients to observe ion-association interactions by counter cations with a highly-charged supramolecular assembly.…”

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confidence: 99%

Diffusion of a Highly Charged Supramolecular Assembly: Direct Observation of Ion Association in Water¹

et al. 2008

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Understanding the solution behavior of supramolecular assemblies is essential for a full understanding of the formation and chemistry of synthetic host-guest systems. [2][3][4][5][6] While the interaction between host and guest molecules is generally the focus of mechanistic studies of host-guest complexes, the interaction of the host-guest complex with other species in solution remains largely unknown, although in principle accessible by diffusion studies. Several NMR techniques are available to monitor diffusion and have recently been reviewed. [7][8][9] Pulsed gradient spin-echo (PGSE) NMR methods have attracted increasing interest, since they allow diffusion coefficients to be measured with high accuracy; they have been successfully used with observation of 7 Li and 31 P nuclei as well as with 1 H NMR. 10,11 We report here the direct measurement of diffusion coefficients to observe ion-association interactions by counter cations with a highly-charged supramolecular assembly.Raymond and coworkers have described the design and chemistry of a class of metal-ligand supramolecular assemblies over the past decade.12-15 The [Ga 4 L 6 ] 12-(L = 1,5-bis(2,3-dihydroxybenzamido)naphthalene) (1) (Figure 1) assembly has garnered the most attention, with the exploration of the dynamics and mechanism of guest exchange as well as the ability of 1 to achieve either stoichiometric or catalytic reactions inside its interior cavity. [16][17][18][19] Recent studies have revealed the importance of counter cations in solution on the chemistry of 1. During the mechanistic study of the C-H bond activation of aldehydes by [Cp * Ir(PMe 3 )(olefin)11-a stepwise guest dissociation mechanism with an ion-paired intermediate was proposed.19 Similarly, in the mechanism for the hydrolysis of iminium cations generated from the 3-aza Cope rearrangement of enammonium cations in 1, the presence of an exterior ion association was part of the kinetic model. 17 To further substantiate the indirect kinetic evidence for such ion-paired species, we sought to explore the solution behavior of 1 by studying the diffusion of 1 with varying alkali and tetraalkyl ammonium cations. For large molecules in solution, such as synthetic supramolecular assemblies, the diffusion behavior of host and guest molecules can provide valuable information on host-guest interaction. One characteristic feature of a stable host-guest complex is that the host and guest molecules diffuse at the same rate in solution; this has been observed in a number of supramolecular systems. [20][21][22][23][24][25][26] In order to confirm that this system was suitable for study by diffusion NMR spectroscopy, a PGSE-DOSY spectrum was acquired of [NEt 4 ⊂ 1] 11- (Figure 2), which shows that the host and guest molecules diffuse at the same rate. Quantitative analysis of the data, from monitoring the integral of host and guest resonances as a function of applied gradient strength, gave identical diffusion coefficients, confirming that the host and guest molecules diffuse together.

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Diffusion NMR in Supramolecular Chemistry

Cited by 23 publications

References 0 publications

Hydroxypropyl‐α‐Cyclodextrin‐Capped Palladium Nanoparticles: Active Scaffolds for Efficient Carbon‐Carbon Bond Forming Cross‐Couplings in Water

Hydroxypropyl‐α‐Cyclodextrin‐Capped Palladium Nanoparticles: Active Scaffolds for Efficient Carbon‐Carbon Bond Forming Cross‐Couplings in Water

Chemistry of calix[4]resorcinarenes

Diffusion of a Highly Charged Supramolecular Assembly: Direct Observation of Ion Association in Water¹

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Diffusion NMR in Supramolecular Chemistry

Cited by 23 publications

References 0 publications

Hydroxypropyl‐α‐Cyclodextrin‐Capped Palladium Nanoparticles: Active Scaffolds for Efficient Carbon‐Carbon Bond Forming Cross‐Couplings in Water

Hydroxypropyl‐α‐Cyclodextrin‐Capped Palladium Nanoparticles: Active Scaffolds for Efficient Carbon‐Carbon Bond Forming Cross‐Couplings in Water

Chemistry of calix[4]resorcinarenes

Diffusion of a Highly Charged Supramolecular Assembly: Direct Observation of Ion Association in Water1

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Diffusion of a Highly Charged Supramolecular Assembly: Direct Observation of Ion Association in Water¹