Tt-Stacking

TT-stacking and charge-transfer interaction between aromatic residues in the receptor and delocalized regions of the substrate van der Waals attraction between hydrophobic regions on the two components... 

Figure 16-19. A Tt-stacked arrangement of Ooci-OPV5-CN" molecules in the crystal lattice (view at a slight angle with respect to the long molecular axis). B lop-view (lop) and side-view (bottom) of two nearest-neighbor Oocl-OPV5-CN" molecules in the crystal. related by a translation along the ci-axis. The distance of 3.5 A corresponds to the shortest distance between two atoms on different molecules (sec Fig. 16-18 for details).

The two macrocycles appear to be largely parallel even in the DPD and DPP series, where the stmcture of the linker would seem to favor a conformer in which the planes of the macrocycles would be at an angle to each other. The parallel arrangement of the two macrocycles is thought to result from the drive to maximize tt-tt stacking. 

These catalysts are believed to function through an acyclic TS. In addition to the normal steric effects of the open TS, the facial selectivity is probably influenced by tt stacking with the aryl ring and possibly hydrogen bonding by the formyl hydrogen.152... 

An 8-phenylmenthol ester was employed as the chiral auxiliary to achieve enantioselectivity in the synthesis of prostaglandin precursors.83 The crucial features of the TS are the anti disposition of the Lewis acid relative to the alcohol moiety and a tt stacking with the phenyl ring that provides both stabilization and steric shielding of the a-face. 

The innate sensitivity of DNA-mediated CT to perturbations in the TT-stack has prompted us to employ this chemistry as a probe of stacking structure and dynamics. We have developed a new class of DNA-based diagnostic tools that diagnose DNA mutations such as single base-pair mismatches and lesions, analyze DNA-protein interactions, and probe the sequence-depen-dent dynamics and flexibility of DNA. These applications rely on electrochemical probing of CT in DNA films self-assembled on gold electrodes. 

The structure of a non-hydrolyzed dimer, cA-[(2,2 -bipyridine)palladium(II)]2(/i-l,3-N03)2 2+ is shown in Figure 45.521 The dimerized m-( 2.2-bi pyridine) Pd11 units aggregate into a dimer-to-dimer linear conformation through direct metal—metal interaction522 and tt-tt stacking.523 Notably, the dimer was first reported to be linked by double nitrato-bridges (/x-l,3-N03)2 in a cofacial... 

Red emission chomophores having a long wavelength emission band are usually polar, such as the above DCM series. The push-pull red emitters are normally prone to aggregation in the solid state owing to dipole dipole interactions or through intermolecular tt-tt stacking, especially when the molecules are flat as is the case for DCM. As a consequence, the push-pull red... 

Figure 33. The partial encapsulation of a pair of tt-stacked C60 units in Ni[pz(Ar-Me2)g]2 C60 (lOOd).

As stated in Section 27.3.2, dispersion interactions are fundamental building blocks in intermolecular interactions. Their accurate calculation in the case of larger systems (say tt stacking of aromatic rings) remains, however even today, despite the... 

In 1990 Rebek reported an interesting self-replicating systems based on the Kemp s triacid derivative 82 (see Scheme 43) [112-114]. By a combination of hydrogen bonding and tt-tt stacking interactions, diamine 83 forms a binary complex with 82. In such a complex, the amine is ideally positioned to react with the activated ester in 82 yielding the ds-amide complex 84. 

Murray and colleagues199 developed some 2,5-diketopiperazines as new chiral auxiliaries and examined their asymmetric induction in the Diels-Alder reactions of their A-acryloyl derivatives with several dienes. Some of their results with dienophile 320 have been summarized in Table 19 (equation 89). When the benzyl group on 320 was substituted by an isopropyl or /-butyl group, the diastereofacial selectivity dropped dramatically. It was proposed that tv-tt stacking between the phenyl group and the electron-poor double bond provided a more selective shielding of one face of the double bond in this special case. 

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