Linear-Dendritic Supramolecular Complexes as Nanoscale Reaction Vessels for “Green” Chemistry. Diels−Alder Reactions between Fullerene C₆₀ and Polycyclic Aromatic Hydrocarbons in Aqueous Medium

Abstract

This study describes the first Diels-Alder (DA) reaction performed in aqueous medium with highly hydrophobic compounds-fullerene (C 60) as the dienophile and anthracene (An) or tetracene (Tet) as the dienes, respectively. The reactions are performed in nanocontainers, constructed by self-assembly of linear-dendritic amphiphilic copolymers with poly(ethylene glycol), PEG or poly(ethylene oxide), PEO as the hydrophilic blocks and poly(benzyl ether) monodendrons as the hydrophobic fragments: G3PEO13k, dG3 and dG2. Comparative studies under identical conditions are carried out with an amphiphilic linear-linear copolymer, poly(styrene)1800- block-PEO2100, PSt-PEO, and the nonionic surfactant Igepal CO-720, IP720. The binding affinity of supermolecules built of these amphiphiles toward the DA reagents decreases in the following order: G3PEO13k > dG3 > PSt-PEO > dG2 > IP720. The kinetic constant of binding is evaluated for tetracene and decreases in a similar fashion: 5 x 10 (-7) M/min (G3PEO13k), through 4 x 10 (-7) M/min (PSt-PEO) down to 1.5 x 10 (-7) M/min for IP720. The mobility of substrates encapsulated in the micellar core, estimated by pyrene fluorescence decay, is 95-121 ns for the micelles of the linear-dendritic copolymers and notably higher for PSt-PEO (152 ns), revealing the much denser interior of the linear analogue. The apparent kinetic constant for the DA reaction of C 60 and Tet within the G3PEO13k supermolecule in aqueous medium is markedly higher than in organic solvent (toluene), 208 vs 1.82 M /min. With G3PEO13k the conversions reach 49% for the DA reaction between C 60 and An, and 55% for C 60 and Tet. Besides the monoadduct (26.5% yield) the reaction with An produces exclusively increasing amounts of D 2 h -symmetric antipodal bis-adduct, whose yield reaches up to 22.5% after 48 h. In addition to the environmentally friendly conditions notable advantages of the synthetic strategy described are the extended stability of the linear-dendritic nanovessels, the easy collection of the products formed, and the recovery and reuse of unreacted reagents and linear-dendritic copolymers.

Supramolecular Self‐Assembly of Nonlinear Amphiphilic and Double Hydrophilic Block Copolymers in Aqueous Solutions

“…It has been well established that amphiphilic block copolymers can self‐assemble in aqueous solution into a variety of morphological structures including spheres, rods, lamellae, vesicles and large compound micelles or vesicles 1–6. Over the past few decades, this field has received ever‐increasing interest due to the fact that block copolymer assemblies possess important biological or technological applications in drug delivery,7–9 imaging,10–13 sensing14, 15 and catalysis 16–20. Notably, double hydrophilic block copolymers (DHBCs) represent a special type of amphiphilic block copolymer, which can reversibly switch between micellar and unimer states depending on external conditions such as pH, temperature, ionic strength and light irradiation 21–25.…”

Chemistry in Self‐Assembled Nanoreactors

“…65 Micelles built -up in part from amphiphilic dendrons have been exploited as vessels for the aqueous -phase Diels -Alder addition reaction between C 60 and polycyclic hydrocarbons. 66 Inverted block -copolymeric micelles, featuring a poly(4 -vinylbenzoic acid) interior and a polystyrene corona in toluene, were utilized as hosts for Fe -bis(imino)pyridine based single -site alkene polymerization catalysis of ethene. 67 Rodcoil based amphiphiles, wherein the rod -fragment consisted of linear polyphenylene moieties and the coil -tail was represented by poly(ethylene glycol) chains, were shown to aggregate into micellar structures in water.…”

Hybrid Nanomaterials Containing Pamam, Polyrotaxane and Quantum Dot Blocks

“…For example attachment of dendritic moieties to linear macromolecules provides a possibility to improve their functionality and three-dimensional structures. [1][2][3][4][5][6][7][8][9][10][11] Dendrimers are interesting class of highly branched macromolecules that comprise a central core, branches expanded from the core and many surface or terminal groups, and three-dimensional features that resemble the architecture of a tree. These radial polymers have specific and systematically variable size, shape and chemical structures.…”