Supramolecular steric effect

When radicals with bulky substituents are found within the internal channels of the zeolite, their interactions may be inhibited by the narrow diameter of the channels, allowing them to persist for a long time (shown by electron spin resonance (ESR) spectroscopy). These steric constraints are known as a supramolecular steric effect. 

A supramolecular steric effect has been postulated to explain the persistence of the diphenylmethyl radical when absorbed onto an MFI zeolite. During the course of these studies this persistent radical was found to react reversibly with oxygen to give the zeolite-bound peroxyl radical. ... 

Hirano, T. Li, W. Abrams, L. Krusic, P. J. Ottaviani, M. F. Turro, N. J. Supramolecular steric effects as the means of making reactive carbon radicals persistent. Quantitative characterization of the external surface of MFl zeolites through a persistent radical probe and a langmuir adsorption isotherm. J. Org. Chem. 2000, d5, 1319-1330. 

Size and shape Certain steric effects can be achieved using characteristically wedge-shaped dendrons. Thus, self-assembling dendrons have been connected to supramolecular aggregates with defined dimeric or hexameric structures. Such aggregates can form columnar superstructures which reveal liquid-crystalline properties. Spherical superstructures arise from the self-assembly process when conical dendrons are used14 14,161 Similar... 

Steric effects of the substituents may stabilize the molecular packing of these supramolecular polyamides. 

In order to obtain information on the fluctuations in the DPM moiety, we performed molecular dynamics (MD) computations on DPM and 1,1-diphenylcyclohexane (5, DPC). often used as spacers in supramolecular chemistry, as well as on DPN 6 (Scheme 2). The aryl rings of DPN are disposed in a gable conformation forced by the steric effect of the four exo-norbomylic C-H bonds. In contrast to DPN, DPC adopts a helical conformation like... 

The validity of this approach was further demonstrated by the poor enantiose-lectivities obtained for proline-based catalytic centers that are imable to self-assemble with alkaloids, demonstrating that enantioselectivity is indeed due to the two-component supramolecular complex. As stated by the authors, these results indicate that this catalytic system is different from the reported asymmetric counteranion-directed catalysis (ACDC) [21] since in that case the stereocontrol is achieved mainly through steric effects instead of hydrogen bonding. 

In summary, the self-assembly of CX and the DAP-based axle is a complex phenomenon that involves three types of species (wheel, axle and anions) that can mutually interact. When the species come together, these interactions affect one another because of steric effects and, presumably, also for electronic reasons. The resulting supramolecular structure is determined by the set of interactions that... 

The affinity of a substrate with its biological target is first connected to its complementarity with this macromolecule target. The molecular recognition and affinity depend on all the favorable interactions that exist in the supramolecular assembly formed between the substrate and the macromolecule. If the presence of fluorine atoms enhances the strength or the number of these favorable interactions, the affinity of the fluorinated substrate will be higher than that of the parent compound. The main parameters involved are the steric and conformational effects, the dipolar/hydrophobic interactions, and the hydrogen bonds. 

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