Proton‐Driven Conformational Switch of a Cyclohexyl Skeleton Coupled with NH···O Hydrogen‐Bond Formation

Abstract

We report an unprecedented, proton‐drivenring transfor‐mation from a chair to a twist‐boat conformation in the doublyamide‐derived Kemp’s acid compounds r‐1,c‐3,c‐5‐(CH3)3‐3,5‐(Ph2CHNHCO)2C6H6‐1‐COOH (1) and (NMe4){r‐1,c‐3,c‐5‐(CH3)3‐3,5‐(Ph2CHNHCO)2C6H6‐1‐COO–} (2) with a protonated and deprotonated carboxyl group, respectively. Each conformation was determined by X‐ray analyses and 1H NMR spectroscopy. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Large Amplitude, Proton- and Cation-Activated Latch-Type Mechanical Switches: O-Protonated Amides Stabilized by Intramolecular, Low-Barrier Hydrogen Bonds within Macrocycles

“…These switches are of the mechanical type, implying movement with the eventual goal of prescribed motion involving molecular machines. Mechanical switches utilizing protons as the switching mechanism, up to now, have also included the absorption of a photon in the case of reversible ring opening and closing in benzspiropyrans and diarylethene compounds; the translocation of metal cations between adjacent binding sites upon change in pH; or changes in conformation because of solvent polarity, including chair-boat and E-Z isomerization . Mechanical proton switches have also been observed altering the host−guest chemistry of ditopic macrocycles and rotaxanes and also produce conformation changes in large DNA adducts .…”

Designed Molecular Switches: Controlling the Conformation of Benzamido-diphenylacetylenes

“…Molecules that can change conformation in a stimulus-dependent fashion are valued synthetic targets due to their potential use as logic gates, − information storage systems, , sensors, and as stepping stones toward the design of angstrom scale machines . In light of the myriad applications for switches, many structural motifs have been pursued in the past 15 years that exhibit a conformational change based upon a variety of stimuli. − …”

“…7 In light of the myriad applications for switches, many structural motifs have been pursued in the past 15 years that exhibit a conformational change based upon a variety of stimuli. [7][8][9][10][11][12][13][14][15][16][17]…”

Ion-mediated conformational switches

“…Signicant research has been carried out under this premise. [39][40][41][42][43][44] For example, Samoshin has exploited the pH-dependent conformational switching of piperidine derivative 6 (Scheme 5). 43 At neutral pH the preferred conformation places all substituents in equatorial positions, as determined by application of Eliel's equation to solution-state NMR data, 45 and by DFT analysis.…”