Self-Assembly with Degenerate Prototropy

Abstract

This work describes a rational approach for addressing the prototropy-related problems in heterocycle-based self-assembling systems by the use of degenerate prototropy. As a proof of principle, the utility of degenerate prototropy is demonstrated herein by developing heterocycle-based AADD-type self-assembling modules that exist as "single set of protameric pair (duplex)" in both solution and solid states. These self-assembling modules are quickly accessible in good yield by reacting 2-amino-5,5-disubstituted-1H-pyrimidine-4,6-diones, available in one step by the condensation of alpha,alpha-dialkyl malonates and free guanidine, with isocyanates. Evidence from NMR spectroscopy, ESI mass spectrometry, and single-crystal X-ray diffraction studies confirmed the formation of molecular duplexes. The effect of electronic repulsion in duplex formation is also investigated. Their ready synthetic accessibility, remarkably high propensity to crystal formation, and the novel property of degenerate prototropy would make these novel self-assembling molecules promising candidates for many proposed applications.

Molecular Conductance through a Quadruple‐Hydrogen‐Bond‐Bridged Supramolecular Junction

“…[12] However,when the protic solvent ethanol (C 2 D 5 OD) is introduced, the intensity as well as the position of these NH signals changes signifi-cantly.T hese low-field NH proton signals completely disappear when the volume ratio of [D 6 ]ethanol is 20 %o rm ore (Figure 2b,c), implying that the intermolecular hydrogen bonds have been largely disassembled. [14] This was supported by the 1 HNMR and X-ray diffraction data. [12,13] However,t he ADAD tautomer and ADAD-DADAd imeric structure are effectively inhibited by the degenerate prototropy effect in the modified molecule.…”

Electron Transfer Across Multiple Hydrogen Bonds: The Case of Ureapyrimidinedione-Substituted Vinyl Ruthenium and Osmium Complexes

“…12,18 Symmetrically substituted 5,5-dialkyl-4,6dioxo-1,4,5,6-tetrahydro-pyrimidin-2-yl-urea derivatives have finally resolved the problem of nondegenerate tautomerism (Chart 1). 19 Ureido-s-triazine-bridged assemblies of various oligo(phenylenevinylene) donors and the perylene bisimide acceptor 20 and noncovalently bonded dimers of amidinium-substituted metalloporphyrins 21 or tetrathiofulvalenes 22 and a fullerenesubstituted benzoate provide intriguing examples of efficient photochemically triggered electron transfer from the excited donor to the acceptor across strong hydrogen bridges. Directed energy transfer in these systems profits from the thermodynamic driving force imminent in the relaxation of an electron from a higher-energy orbital at the excited donor to the lower-lying LUMO localized at the acceptor site.…”

Molecular Conductance through a Quadruple‐Hydrogen‐Bond‐Bridged Supramolecular Junction

“…It has been reported that two kinds of hydrogen‐bonded dimer arrays, ADAD–DADA (A=acceptor, D=donor) dimers (minor) and AADD–DDAA dimers (major), can coexist in Meijer's 2‐ureido‐4[1 H ]‐pyrimidinone motif, owing to the homodimerization of tautomeric monomers . However, the ADAD tautomer and ADAD–DADA dimeric structure are effectively inhibited by the degenerate prototropy effect in the modified molecule . This was supported by the 1 H NMR and X‐ray diffraction data.…”