Cation-TT interaction

Gallivan, J.P. and Dougherty, D.A. (1999) Cation-Tt interactions in structural biology. Proceedings of the National Academy of Sciences of the United States of America, 96, 9459-9464. 

Noncovalent interactions in metal complexes of biomolecules may play an important role in the creation of supramolecular structures around the metal center. For instance, extensive three-dimensional hydrogen-bonded stmcmres grow around metal complexes of barbiturates, recognized as the most widely used drugs for the treatment of epilepsy.Electrostatic interactions between a cation and the Trring of an aromatic molecule (cation-tt interactions) are common motifs in protein structures. Little is known about alkali and alkali-earth cation-tt inter-... 

Cation-TT interactions play a crucial role in molecular recognition. For example, Na /K cation interactions with aromatic rings of some amino acids are implicated in the biological functions of specific enzymes and in the selectivity of Na" /K channels. " The same factors are responsible of the relative stability of the charge-solvated vs. zwitterionic structure of amino acids. " ... 

Cation-TT interactions are another important motif, dominated by electrostatic interactions [47] within mainly hydrophobic subsites. Such a stabilizing interaction takes place between cations like ammonium ions and electron-rich jt-systems of neighboring aromatic rings. Both interactions are often not explicitly contained in common force fields or scoring functions. 

The cation-7t interactions were evidenced by Prodi, who studied the photophysical properties of calix[4]arene-crown and their complexes with alkali metal ions. The presence of these cation ions usually caused weak effects on the absorption spectra, but sometimes caused marked changes in the intensity and wavelength maxima of the fluorescence bands of the calixarenes. The fluorescence quantum yields of complexes with alkali metal follows a precise trend for both MC46 and MC7, decreasing from potassium to cesium. These changes were explained by cation-Tt interactions between the metal ion and the two aromatic rings pointing toward it.30... 

Stratakis, M., Raptis, C., Sofikiti, N., Tsangarakis, C., Kosmas, G., Zaravinos, I.-P., Kalaitzakis, D., Stavroulakis, D., Baskakis, C. and Stathoulopoulou, A. (2006) Intrazeolite photooxygenation of chiral alkenes. Control of facial selectivity by confinement and cation-Tt interactions. Tetrahedron, 62 (46), 10623-10632. 

Crown ether 4 has been shown to be a source of unusual dinuclear silver(l) complexes <2002ICA(332)18>. In the crystal, the silver ions interact with the crown ether ligand at both the hard donor ethereal oxygens and soft benzene ring carbon atoms via intermolecular cation-Tt-interaction in -fashion, as depicted in Figure 6. The dimeric structure is further stabilized by the occurrence of intermolecular Tt-Tt-intcractions between facing benzo groups. 

Study of Cation-Tt Interactions vs. Salt Bridges in Aqueous Media Implications for Protein Engineering. 

Cation-TT interactions, which are frequently encountered in calixarenes complexes, are observed in three related potassium complexes of calix[6]arenes, [K2(MeOH)5] /)-H-calix[6]arene-2H, [K2(MeOH)4] / -t-butylcalix[6]arene-2H and [K2(H20)5] p-H-calix[6]arene-2H. The crystal... 

Plate 13 (see Plate section) shows the CPC A pseudo-difference field plot for the cationic NM3 probe. One large favourable cyan contour for the NM3 probe is located in the hydrophobic box, pointing to the possible cation-tt interaction in factor Xa. Therefore, the introduction of positively charged or polarized groups at either position will increase selectivity for factor Xa over thrombin or trypsin. Indeed, a number of highly active and specific factor Xa... 

R. Arnecke, V. Bohmer, R. Cacciapaglia, A. DaUa Cort, L. Mandolini, cation-TT Interactions between neutral calix[5]arene hosts and cationic organic guests. Tetrahedron, 1997, 53, 4901 908. 

Meadows. E.S. De Wall. S.L. Barbour. L.J. Gokel. G.W. Alkali metal cation-Tt interactions observed by using a lariat ether model system. J. Am. Chem. Soc. 2001. 123,... 

An atomic level comprehension of condensed phase structure warrants a clear understanding of the role, strength and relevance of noncovalent interactions and how they mutually influence each other. In the following discussions we present a detailed view on three prominent classes of nonbonded interactions namely cation-TT interactions, tt-tt stacking and hydrogen bonding while emphasizing... 

The cation-TT interaction involves binding of a cation to Ji-electrons (e.g., benzene, acetylene). Early mass spectrometry and ion cyclotron resonance studies have established that alkali-metal cations (e.g., Na+) bind strongly to simple aromatics. Later, Deakyne, and Meolner showed that organic ions (e.g., alkylammoniums) display affinities for aromatics. Moreover, extensive work by Dougherty and CO workers has established models of the cation- n- interaction that have been successfully demonstrated in a variety of synthetic receptors. ... 

Binding of hard anions occurs strongly at the hard Lewis acidic uranyl center, whereas cation- tt interactions are established between the aromatic side arms and the cation counterpart of the ion pair. Thus, complexation of alkali metal salts (MX) such as CsCl and RbCl with 15 resulted in the formation of isomorphous supramolecular assemblies in the solid state. In the dimeric [15-CsCl], each cation is coordinated to six oxygens, three from each receptor, thus creating a pseudo-crown-ether-Uke environment for the cation. Additionally, each metal ion in the dimeric unit is coordinated to both halide ions and, most importantly, to two aromatic side arms, one from each of the receptors giving decacoordination for the cation. The closest metal ion-aromatic carbon distances of 3.44(1) A for CsCl, 3.34-3.38(1) A for RbCl, and 3.58(1) A for CsF are observed in the respective alkali halide complexes [15 MX] indicating the conformational flexibility of the side arms and adaptability of the receptors 15 and 16 to form multiple cation- rt interactions with the hosted cations. 

Figure 13 Different ways in which calixarenes interact with cations (a) metallation at the lower rim (b) -cavity (jr-metallation) (c) endo-c Yity (d) at the lower rim with participation of additional binding sites (e) at the upper rim by coordinating groups (f) at the lower rim with participation of cation-TT interactions. O atoms at the lower rim may be 0 , OH or OR.

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