This account summarizes five years of research devoted to the development of the concept of synthetic multifunctional pores. The objective is to complement a comprehensive graphical summary of molecular recognition with a survey of structural studies on the same topic. The relevance of the latter for research focusing on creation and application of supramolecular functional materials is discussed briefly in a subjective manner.
Voltage-sensitive blockage by ADP, ATP and phytate (IP6) demonstrates that active-site contraction toward the middle of newly synthesized rigid-rod beta-barrels provides a general strategy to rationally create and modulate the voltage sensitivity (and to increase the efficiency) of molecular recognition by synthetic multifunctional pores.
Dedicated to Professor Ulrich Burger on the occasion of his 65th birthdayThe usefulness of computer-assisted aliasing to secure maximal resolution of signal clusters in 1 H-and 13 C-NMR spectra (which is essential for structure determination by HMBC 2D NMR spectroscopy) in minimal acquisition time is exemplified by the complete characterization of the two complementary p-octiphenyls 1 and 2 with complex substitution patterns. The need for digital resolution near 1 Hz/pt to dissect the extensive signal clusters in the NMR spectra of these refined oligomers excluded structure determination under routine conditions. High resolution was secured by exploiting the low signal density in the 13 C dimension of HMBC spectra by using computer-assisted aliasing to maximize signal density. Based on the observed shifts in DEPT and 1 H-decoupled 13 C-NMR spectra of 1 and 2, computer-assisted aliasing allowed to reduce the number of required time increments by a factor of 20 to 30 compared to full-width spectra with identical resolution. Without signal-to-noise constraints, this computer-assisted aliasing reduced the acquisition time for highresolution NMR spectra needed for complete characterization of refined oligomers 1 and 2 by the same factor (e.g., from over a day to about an hour). With resolved signal clusters in fully aliased HSQC and HMBC spectra, unproblematic structure determination of 1 and 2 is demonstrated by unambiguous assignment of all C-and Hatoms. These findings demonstrate that computer-assisted aliasing of the underexploited 13 C dimension makes extensive molecular complexity accessible by conventional multidimensional heteronuclear NMR experiments without extraordinary efforts.
The introduction of rigid‐rod molecules as privileged scaffolds has opened routes to otherwise problematic supramolecular architecture like artificial β‐barrels and functional supramolecules covering pores, hosts, sensors, and catalysts. The usefulness of p‐oligophenyls for the construction of functional barrel‐stave architecture has, however, been limited by uniform substitution along the rigid‐rod scaffold. The objective of this report is to overcome this obstacle for the synthesis of p‐octiphenyls with orthogonally protected carboxylic acid groups along the rigid‐rod scaffold. In the reported {242}‐p‐octiphenyl 1, the two peripheral arene moieties carry carboxylic acid groups protected as benzyl esters, whereas the four central carboxylic acid groups are protected orthogonally as tert‐butyl esters (Scheme 2). The complementary orthogonal protection of the three peripheral and the two central arenes is achieved in the {323}‐p‐octiphenyl 2 (Scheme 3). The realized {242}‐ and {323}‐p‐octiphenyls 1 and 2, respectively, provide a complete set for the general access to refined rigid‐rod barrel‐stave architecture with maximized functional plasticity. The need for resolution‐enhanced (aliased) HMBC 2D‐NMR spectroscopy to characterize these refined oligomers is described in the following publication in this issue of Helv. Chim. Acta.
Studies on the usefulness of rigid-rod molecules to address pertinent questions of biological relevance are summarized. Emphasis is placed on (a) the supramolecular functional plasticity of p-octiphenyl ß-barrels expressed in molecular recognition (adaptable synthetic hosts), molecular translocation (adaptable synthetic ion channels) and molecular transformation (esterases, RNases), (b) molecular recognition of polarized membranes by rigid push-pull rods, as well as (c) the synthetic organic chemistry of rigid-rod molecules
[structure: see text] The synthesis of p-octiphenyls carrying orthogonal tert-butyl esters in the peripheral positions 1(2), 2(2), 3(3), 6(2), 7(3), and 8(2) and either p-methoxybenzyl or benzyl ester substituents in the central positions 4(2) and 5(3) is described. Resolution-enhanced HSQC/HMBC two-dimensional NMR spectroscopy is implemented as an attractive method for the complete characterization of complex p-oligophenyl scaffolds.
Applying the Woodhull equation to organic chemistry, a concept to maximize remote control of chemical processes that take place within synthetic multifunctional pores is described.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.