Cation-7r interactions

Recentiy published crystal structures of antibody 4C6, an antibody that catalyzes another cationic cyclization reaction (Figure 6), revealed that this antibody has exquisite shape complementarity to its eliciting hapten 5. The active site contains multiple aromatic residues which shield the high-energy intermediate from solvent and stabilize the carbocation intermediates through cation-7r interactions. 

It has already been mentioned (Section III) that the study of the diastereoselection in the electrophilic addition of singlet oxygen to the n face of chiral alkenes is of primary interest for the achievement of a selective oxyfunctionalization reaction. Zeolite confinement and cation- 7r interactions might be expected to affect significantly the diastereoselectivity in the photooxygenation of chiral alkenes. 

Figure 1 The structure of [Cs (PhCH2)3GaF ]2, illustrating the cation-7r interactions.

A resorcinarene-based receptor functionalized with a Zn-salen complex was tested for the hydrolysis of para-nitrophenyl choline carbonate (Figure 27). The presence of the cavity yielded a fivefold increase of the reaction rate (compared to the corresponding free Zn-salen complex), ascribed to the recognition of the quaternary ammonium knob inside the host by cation-7r interactions. ... 

The strong attraction between a cation and a n system is denoted as a cation/TT interaction. The size of the interaction energy for a cation/zr interaction is considerably larger than that for interactions between aromatic molecules and neutral molecules (tt/tt, OH/tt, NH/tt and CH/n interactions), as shown in Table 7. The experimental interaction energies of benzene complexes with Li, Na and K" " shown in Fig. 18 are -38.5, - 22.1 and - 17.5kcal/mol, respectively [24]. The importance of the cation/ 7r interaction in biological structures and molecular recognition processes has been... 

Regression coefficients of expression 6.26 show that the lithium cation/7r interaction is affected almost equally by the field and resonance effect of the ring substituent and that the polarizability effect is smaller, although significant. 

Ruan, C., Yang, Z. and Rodgers, M.T. (2007) Influence of the d orbital occupation on the nature and strength of copper cation- 7r interactions threshold coUision-induced dissociation and theoretical studies. Phys. Chem. Chem. Phys., 9, 5902-5918. 

Stoeckigt, D. (1997) Cation-7r Interaction in A1(L)+ complexes (L = CgHg, C5H5N, CsHg, C4H4NH, C4H4O). J. Phys. Chem. A, 101, 3800-3807. 

Amunugama, R. and Rodgers, M.T. (2003) Cation/7r interactions with a model for an extended jT network. Absolute binding energies of alkali metal cation-naphthalene complexes determined by threshold collision-induced dissociation and theoretical stndies. Int. J. Mass Spectrom. Ion Processes, 227, 1-20. 

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