Dendritic effects in functional dendrimer molecules

Chow, Hak‐Fun; Leung, Cham-Fai; Wang, Guoxin; Yang, Yuying

doi:10.1016/j.crci.2003.07.001

Cited by 31 publications

(17 citation statements)

References 33 publications

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“…Hence, the larger hydrophobic HC dendron on one hand retarded the reaction due to larger steric effect, but on the other hand promoted the formation of a more stable emulsion and hence an increase of the reaction rate. The latter effect is similar to a positive dendritic catalytic effect, that is, increasing dendrimer generation leads to higher catalyst reactivity . Strictly speaking, dendritic catalytic effect should be ascribed to the reactivity pattern of different generations of the same type of compounds, while in our case we are comparing the same generation of compounds belonging to two different dendrimer series (i.e., Di-L-Gn vs Mono-L-Gn ).…”

Section: Resultsmentioning

confidence: 78%

Structural Effects on the Catalytic, Emulsifying, and Recycling Properties of Chiral Amphiphilic Dendritic Organocatalysts

Chow

2009

J. Org. Chem.

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Three series of chiral amphiphilic G1-G3 dendritic organocatalysts containing an optically active polar proline-derived core and one or two nonpolar hydrocarbon dendrons were prepared. These dendritic organocatalysts were employed in the asymmetric aldol and nitro-Michael additions in oil-in-water emulsions to reveal the effects of dendron size and branching on the catalytic properties. The incorporation of larger hydrophobic dendrons has the advantages of promoting emulsion formation in water, improving the reaction enantioselectivity, decreasing catalyst loading (to 1 mol %), and facilitating catalyst recovery after the reactions. In general, the larger dendrons tended to lower catalyst reactivity due to their increasing steric blocking effect. However, some astonishing observations were found in some of the G1 and G2 dendritic organocatalysts, wherein an increase in the steric bulkiness and branching of the dendron resulted in better catalyst reactivity. It was also found that higher product yields and enantioselectivities were obtained in the aldol reactions when the aromatic aldehyde contains an electron-withdrawing substituent. The catalysts could be recycled and reused five times without significant drop in product yields and enantioselectivities. In addition, cross product contamination was not found when the recovered G3 catalyst was subsequently used in another reaction involving different substrates.

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Section: Resultsmentioning

confidence: 78%

Structural Effects on the Catalytic, Emulsifying, and Recycling Properties of Chiral Amphiphilic Dendritic Organocatalysts

Chow

2009

J. Org. Chem.

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“…Such results are in contradiction with the model presuming a cooperation of two or more active sites during the catalytic cycle. 44,45 Furthermore, we evaluated the effect of attached hydroxyl group on catalytic activity. Monofunctional dendrimers Dm m AMe n with trimethylammonium groups at the periphery were tested under the same conditions as bifunctional catalysts.…”

Section: ■ Materials and Methodsmentioning

confidence: 99%

Multivalent Bifunctional Carbosilane Dendrimer-Supported Ammonium and Phosphonium Organocatalysts for the Coupling of CO₂ and Epoxides

Šťastná

Krupková

Petričkovič

et al. 2020

ACS Sustainable Chem. Eng.

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Insertion of carbon dioxide into the structure of organic epoxides leads to the formation of valuable cyclic carbonates and polycarbonates. For the purpose of this process, we report here a series of recyclable organocatalysts with superior activity. Carbosilane dendrimers (first to third generation) are employed as a support to which periphery ammonium or phosphonium centers are covalently attached to form a dendritic ionic liquid (DIL). The obtained DILs were tested as homogeneous catalysts in the cycloaddition of CO 2 to epoxides with respect to their activity and recyclability. The catalytic performance of active sites is enhanced by the presence of a proximal hydroxyl group, playing the role of a hydrogen bond donor. An experimentally observed synergistic effect was confirmed by density functional theory calculations. The activity of DILs is affected more by the structure of onium salt than by the size of the support (dendrimer generation). The dendritic catalysts of all tested generations could be recovered by nanofiltration and repeatedly reused. In order to simplify the separation of the catalysts, composite materials were prepared by intercalating the more active ammonium dendrimers into the interlayer space of a natural montmorillonite. The resulting heterogeneous catalysts were easily separable by centrifugation while retaining a reasonable level of activity.

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“…The fascination of the scientific community with observed unexpected generation-dependent properties of dendrimers led to a broad range of reports on so-called “dendritic effect” [ 3 , 4 , 5 ]. After a deeper examination of its origin, Tomalia published a study relating structure parameters to prediction of dendrimer properties [ 6 , 7 ]. Then, advantageously, the concept of formation of microenvironment with locally modified characteristics was employed in drug delivery [ 8 , 9 ], catalysis [ 10 , 11 , 12 ] or material [ 13 , 14 ] and supramolecular chemistry [ 15 , 16 ].…”

Section: Introductionmentioning

confidence: 99%

Controlled Anchoring of (Phenylureido)sulfonamide-Based Receptor Moieties: An Impact of Binding Site Multiplication on Complexation Properties

et al. 2021

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The repetition of urea-based binding units within the receptor structure does not only lead to monomer properties multiplication. As confirmed by spectroscopic studies, UV-Vis and 1H-NMR in classical or competitive titration mode, the attachment to a carrier allocates the active moieties to mutual positions predetermining the function of the whole receptor molecule. Bivalent receptors form self-aggregates. Dendritic receptors with low dihydrogen phosphate loadings offer a cooperative complexation mode associated with a positive dendritic effect. In higher dihydrogen phosphate concentrations, the dendritic branches act independently and the binding mode changes to 1:1 anion: complexation site. Despite the anchoring, the dendritic receptors retain the superior efficiency and selectivity of a monomer, paving the way to recyclable receptors, desirable for economic and ecological reasons.

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Dendritic effects in functional dendrimer molecules

Cited by 31 publications

References 33 publications

Structural Effects on the Catalytic, Emulsifying, and Recycling Properties of Chiral Amphiphilic Dendritic Organocatalysts

Structural Effects on the Catalytic, Emulsifying, and Recycling Properties of Chiral Amphiphilic Dendritic Organocatalysts

Multivalent Bifunctional Carbosilane Dendrimer-Supported Ammonium and Phosphonium Organocatalysts for the Coupling of CO₂ and Epoxides

Controlled Anchoring of (Phenylureido)sulfonamide-Based Receptor Moieties: An Impact of Binding Site Multiplication on Complexation Properties

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Dendritic effects in functional dendrimer molecules

Cited by 31 publications

References 33 publications

Structural Effects on the Catalytic, Emulsifying, and Recycling Properties of Chiral Amphiphilic Dendritic Organocatalysts

Structural Effects on the Catalytic, Emulsifying, and Recycling Properties of Chiral Amphiphilic Dendritic Organocatalysts

Multivalent Bifunctional Carbosilane Dendrimer-Supported Ammonium and Phosphonium Organocatalysts for the Coupling of CO2 and Epoxides

Controlled Anchoring of (Phenylureido)sulfonamide-Based Receptor Moieties: An Impact of Binding Site Multiplication on Complexation Properties

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Multivalent Bifunctional Carbosilane Dendrimer-Supported Ammonium and Phosphonium Organocatalysts for the Coupling of CO₂ and Epoxides