A systematic evaluation of different hydrogen bonding patterns in unsymmetrical 1,n′-disubstituted ferrocenoyl peptides

Discovery of linear receptors for multiple dihydrogen phosphate ions using dynamic combinatorial chemistry

We describe the use of dynamic combinatorial chemistry to discover a new series of linear hydrazone-based receptors that bind multiple dihydrogen phosphate ions. Through the use of a template-driven, selection-based approach to receptor synthesis, dynamic combinatorial chemistry allows for the identification of unexpected host structures and binding motifs. Notably, we observed the unprecedented selection of these linear receptors in preference to competing macrocyclic hosts. Furthermore, linear receptors containing up to nine building blocks and three different building blocks were amplified in the dynamic combinatorial library. The receptors were formed using a dihydrazide building block based on an amino acid-disubstituted ferrocene scaffold. A detailed study of the linear pentamer revealed that it forms a helical ditopic receptor that employs four acylhydrazone hydrogen-bond donor motifs to cooperatively bind two dihydrogen phosphate ions.

Intra- and intermolecular charge transfer: twin themes and simultaneous competing transitions involving ferrocenes

Electronic absorption spectra of ferrocene, ferrocenecarboxylaldehyde, butylferrocene, and 1,1'-diacetylferrocene in pure organic polar and non-polar solvents, pure halocarbon solvents and in several hexane-halocarbon solvent mixtures have been recorded. The investigated ferrocenes have shown several intra-molecular electronic transitions of the types pi-pi*, n-pi*, and d-d*. On using protonic solvents (HA) each of the ferocenes (Fc) acquires a proton exported from the solvent to form a complex with the formula [FcH](+)[A](-). However, on using halocarbon solvents each of the ferrocenes has shown an intermolecular charge-transfer-to-solvent (CTTS) which is characterized by the appearance of new absorption spectral band(s) for each ferrocene-halocarbon solvent interaction. Formation constants (K(CT)) and molar absorption coefficients (epsilon(CT)) of these interactions have been determined and discussed. The study has indicated that the observed different transitions are dependent upon the number and nature of the substituents involved in the ferrocenes.