Intramolecular stacking

In a physicochemical study of oligo- or polynucleotides, it has been reported that Hypochromicity, depends on the degree of polymerization [61]. The value of native DNA is about 60%, which corresponds to the Hypochromicity, of the absorption of its mononucleotides [60]. The present result indicates that the purine rings may intramolecularly stack by themselves in an aqueous solution... 

The extent of intramolecular stacking interactions depends strongly on both the nature of the bases involved (i.e. purines stack better than pyrimidines) and the steric features of the nucleotides. For example, the stability of Cu + complexes of the type [Cu(phen)(AMP)] decreases in the order 2 -AMP > 5 -AMP > 3 -AMP. [Cu(5 -AMPH)(bipy)(H20)]2 and [Cu(3 -GMP)(phen)(H20)]2 are the only known Cu-purine complexes in which N-7 is not involved in coordination to Cu +. ... 

Flavonoids, physicochemical and analytical characteristics of 88MI47. Highly acylated anthocyanins, structure, stability and intramolecular stacking of 88YGK426. 

The fluorescence of the /t -benzoadenine moiety is quenched dramatically (fluorescence intensity is shown by its quantum yield in ethanol (tPf = 0.25), a denaturing solvent. The quantum yields of /tn-benzo-AMP are identical in water and ethanol 335 nm, A (HjO) 372 nm,... 

No crystals suitable for X-ray diffraction studies could be obtained for these two CT complexes. On the other hand, the structure of the donor in its neutral form is known and, as it is shown in Fig. 8-16, it displays an approximately Q symmetric conformation with the two substituents lying on top of each other, thus indicating that the intramolecular stacking can be realized. Flowever, the actual conformation of the molecule is distorted, such that the two heterocyclic substituents are not perfectly parallel, and are found to significantly diverge from coplanarity with the respective Cp ring. If such a distorted conformation is also adopted by the cationic form in the CT complex, then it will turn out to be detrimental to optimum intermolecular interactions in the solid state. Whether or not stacks of such cations significantly contribute to conductivity is at present not known. 

Newcomb and Gellman have examined aromatic stacking interactions in aqueous solution by studying intramolecular stacking interactions in the compounds shown in Figure 104 [135]. Their studies showed that neither hydrophobic nor dispersion interactions are responsible for the stacking observed under the conditions studied. 

In contrast to (Ph2Zn)2, both bis(pentafluorophenyl)zinc and bis[2,4,6-tris(trifluoromethyl)phenyl]zinc have a two-coordinate monomeric solid-state structure approaching linearity, which is certainly a result of electronic and steric (see Steric Effect) properties of the orffto substituents (Figured). In the crystal structure of both compounds, the aromatic rings are almost orthogonal to one another. This special situation alleviates intramolecular (see Intramolecular) steric interactions and allows intramolecular stacking interactions between rings on adjacent molecules. 

The stacking interaction between tryptophan and uracil was studied in the model compound (59) intramolecular stacking in... 

Table 2. Thermodynamic parameters for intramolecular stacking in m Ap1I.

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