Byron W. Purse

Interaction Energies and Dynamics of Acid–Base Pairs Isolated in Cavitands

The use of capsules and cavitands in physical organic chemistry is briefly reviewed, and their application to the study of salt bridges is introduced. Carboxylate/ammonium ion pairs are generated within an environment that more or less surrounds the functional groups within a synthetic fixed introverted solvent sphere. This is provided by cavitands that fold around amines and present them with a carboxylic acid function. Both organic and water-soluble versions were prepared, and their equilibrium affinities with quinuclidine bases were determined by NMR methods. The association constants range from approximately 10(3) M(-1) in water to more than 10(5) M(-1) in organic solvents. Studies of nitrogen inversion and tumbling of [2.2.2]-diazabicyclooctane within the introverted acids also illustrate the strength of the acid-base interactions. The barriers to in-out exchange of several amine guests were determined to be in the range from 15 to 24 kcal mol(-1). Some parallels with enzymes are drawn: the receptor folds around the guest species; presents them with inwardly directed functionality; and provides a generally hydrophobic environment and a periphery of secondary amide bonds.

Fluorescence Turn-On Sensing of DNA Duplex Formation by a Tricyclic Cytidine Analogue

Most fluorescent nucleoside analogues are quenched when base stacked and some maintain their brightness, but there has been little progress toward developing nucleoside analogues that markedly increase their fluorescence upon duplex formation. Here, we report on the design and synthesis of a new tricyclic cytidine analogue, 8-diethylamino-tC (8-DEA-tC), that responds to DNA duplex formation with up to a 20-fold increase in fluorescent quantum yield as compared with the free nucleoside, depending on neighboring bases. This turn-on response to duplex formation is the greatest of any reported nucleoside analogue that can participate in Watson-Crick base pairing. Measurements of the quantum yield of 8-DEA-tC mispaired with adenosine and, separately, opposite an abasic site show that there is almost no fluorescence increase without the formation of correct Watson-Crick hydrogen bonds. Kinetic isotope effects from the use of deuterated buffer show that the duplex protects 8-DEA-tC against quenching by excited state proton transfer. These results, supported by DFT calculations, suggest a rationale for the observed photophysical properties that is dependent on duplex integrity and the electronic structure of the analogue.

Encapsulation of oligoethylene glycols and perfluoro-n-alkanes in a cylindrical host molecule

Oligoethylene glycols and perfluoro-n-alkanes are suitable guests for the synthetic cylindrical host molecule 1(2); an investigation of these host-guest systems is reported.

Resorcin[6]arene as a building block for tubular crystalline state architectures

A resorcin[6]arene with an r-trans-cis-trans-cis-trans configuration of the pendant ethyl groups forms tubular crystal structures.