Understanding alkali metal cation affinities of multi-layer guanine quadruplex DNA

Stabilizing solvent effects and electrostatic repulsion are responsible for the constant alkali metal cation affinity in multi-layer guanine quadruplexes.

The role of alkali metal cations in the stabilization of guanine quadruplexes: why K+ is the best

The desolvation and size of monovalent alkali metal ions are of equal importance for the cation affinity of guanine quadruplexes.

Cation affinity numbers of Lewis bases

Using selected theoretical methods the affinity of a large range of Lewis bases towards model cations has been quantified. The range of model cations includes the methyl cation as the smallest carbon-centered electrophile, the benzhydryl and trityl cations as models for electrophilic substrates encountered in Lewis base-catalyzed synthetic procedures, and the acetyl cation as a substrate model for acyl-transfer reactions. Affinities towards these cationic electrophiles are complemented by data for Lewis-base addition to Michael acceptors as prototypical neutral electrophiles.

Toward Engineering Intra-Receptor Interactions into Bis(crown ethers)

A synthetic receptor was designed in which cooperative binding of two crown ether moieties to an alkali metal ion simultaneously causes two hydrophobic substituents not involved in direct host-guest interactions to converge. Hydrophobic interactions between these substituents can be expected to contribute to the overall complex stability. Independent binding studies involving two diastereoisomers of this bis(crown ether), one in which intra-receptor interactions between the substituents are potentially possible and one in which they are not, using isothermal titration calorimetry showed that both isomers bind potassium ions in different solvent mixtures with the same overall affinity. Profound differences were observed for each isomer, however, in the enthalpies and entropies of binding, which are consistent with intra-receptor interactions in one compound. These interactions are counteracted by enthalpy-entropy compensation so that no overall improvement in cation affinity could be observed.