In supramolecular assembly
Ļ systems are important building blocks inĀ supramolecular assemblyĀ because of their versatile noncovalent interactions with various functional groups. A notable example of applying ĻāĻ interactions in supramolecular assembly is the synthesis ofĀ catenane. The major challenge for the synthesis
Addition in pharmacological active compounds
Several variants of pi coordinated phenyls have even been tested using transition metals for stackingĀ Ī·6-phenyltropanes, using cyclopentadienyl and tricarbonyl in place of a benzene. Which in the case of the tricarbonyl doubled the compound’s affinity for its intended ligand site (posited as
Pi stacking is prevalent in protein crystal structures and also contributes to the interactions between small molecules and proteins
As a result, piāpi and cationāpi interactions are important factors in rational drug design. One example is the FDA-approvedĀ acetylcholinesteraseĀ (AChE) inhibitorĀ tacrineĀ which is used in the treatment ofĀ Alzheimer’s disease. Tacrine is proposed to have a pi stacking interaction with
Requirement of aromaticity
The conventional understanding of pi stacking involves quadrupole interactions between delocalized electrons in p-orbitals. In other words, aromaticity should be required for this interaction to occur. However, several groups have provided contrary evidence, calling into question whether pi stacking
Direct interaction model (substituent effects)
The HunterāSanders model has been criticized by numerous research groups offering contradictory experimental and computational evidence of pi stacking interactions that are not governed primarily by electrostatic effects. The clearest experimental evidence against electrostatic substituent effects
Electrostatic model (substituent effects)
An early model for the role of substituents in pi stacking interactions was proposed by Hunter and Sanders. They used a simple mathematical model based on sigma and pi atomic charges, relative orientations, and van der Waals interactions to qualitatively determine thatĀ electrostaticsĀ are dominant
Substituent effects
The ability to fine-tune pi stacking interactions would be useful in numerous synthetic efforts. One example would be to increase the binding affinity of a small-molecule inhibitor to an enzyme pocket containing aromatic residues. The effects of heteroatomsĀ and substituents on pi stacking interacti
Geometric configurations
The preferred geometries of the benzene dimer have been modeled at a high level of theory with MP2-R12/A computations and very large counterpoise-corrected aug-cc-PVTZ basis sets. The two most stable conformations are the parallel displaced and T-shaped, which are essentially isoenergetic. In contra
Evidence against pi stacking
TheĀ benzeneĀ dimer is the prototypical system for the study of pi stacking, and is experimentally bound by 8ā12 kJ/mol (2ā3 kcal/mol) in the gas phase with a separation of 4.96 Ć between the centers of mass for the T-shaped dimer. The small binding energy makes the benzene dimer difficult to s
Pi stackingĀ aka ĻāĻ stacking
InĀ chemistry,Ā pi stackingĀ (also calledĀ ĻāĻ stacking) refers to the presumptive attractive,Ā noncovalentĀ pi interactionsĀ (orbitalĀ overlap) between theĀ pi bondsĀ ofĀ aromaticĀ rings. However this is a misleading description of the phenomena since direct stacking of aromatic rings (the R