Tetraformylresorcin[4]arene is obtained in 48% yield via a chromatography-free Duff reaction. The formylated resorcinarene reacts easily with primary aliphatic and aromatic amines. The resulting imines exist exclusively in keto-enamine forms. Owing to a system of intramolecular hydrogen bonds, the reaction selectively leads to regioisomers with C4 symmetry. They possess an inherent chirality due to a propeller-like skeleton. For chiral amines, inherently chiral diastereoisomers are observed.
Directional self-assembly of uncharged molecules in water is am ajor challenge in supramolecular chemistry. Herein,i ti sdemonstrated that peptide-based cavitands wrap around ah ydrophobic core (fullerene C 60 )b yacombination of the hydrophobic effect and hydrogen-bonding interactions to form highly ordered three-componentc omplexes in water that resemblet he molten-globule stage of proteinf olding. The complexesw ere characterized by DOSY NMR spectroscopy,s mall-angleX -ray scattering, andc ircular dichroism, and their structuresw ere confirmed by X-ray crystallography.E nhancemento ft he CD signalsb yn early one order of magnitude and increased hydrolytic stability of hydrazone bonds of the complexes relative to the nonassembled species were observed.I nc ontrast, DMSO and DMSO/ waterm ixtures were found to be highly disintegrative for these complexes. Interestingly,s ome cavitands cano nly be synthesized in the presence of the hydrophobic template followed by disassemblyoft he complexes.[a] Dr.Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.
Peptide-based cavitands (resorcin[4]arenes substituted with histidine and glutamine hydrazides) exist as monomeric species in polar solvents (DMSO and methanol). Upon complexation of fullerenes, the cavitands wrap around the hydrophobic guests forming dimeric capsular shells (as evidenced by DOSY). The self-assembly of the cavitands is based on the formation of beta-sheet-like binding motifs around the hydrophobic core. In a polar environment, these hydrogen bonded structures are kinetically stable and highly ordered as manifested by a 100-fold increase of intensity of circular dichroism bands, as well as a separate set of signals and substantial differences in chemical shifts in NMR spectra. This behavior resembles a protein folding process at the molten globule stage with non-specific hydrophobic interactions creating a protective and favourable local environment for the formation of secondary structures of proteins.
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