Journal ArticleDOI
Reversing a rotaxane recognition motif: threading oligoethylene glycol derivatives through a dicationic cyclophane.
TLDR
The new recognition motif for the template-directed synthesis of rotaxanes can now be exploited at both the molecular and macromolecular levels of structure with numerous potential applications in sight.Abstract:
An already well-established recognition motif-namely one in which the NH2+ centers in the rod sections of the dumbbell components of rotaxanes are encircled by macrocyclic polyether components-has been turned simultaneously outside-in and inside-out, a fact that has been proved beyond any doubt by the stoppering of both ends of a [2]pseudorotaxane to give a stable [2]rotaxane. The [2]pseudorotaxane is formed in nitromethane when a benzylic dibromide, obtained after reacting an excess of 1,4-bis(bromomethyl)benzene with hexaethylene glycol, is added to an equimolar amount of a dicationic cyclophane in which two -CH2OCH2- chains link a pair of dibenzylammonium ions through the para positions on their phenyl rings. When the [2]pseudorotaxane is reacted in nitromethane with triphenylphosphine, a [2]rotaxane and the corresponding free dumbbell compound are isolated in 58 and 31% yields, respectively. The structure of the [2]rotaxane is established by using mass spectrometry (FABMS and ESMS) and NMR (1H and 13C) spectroscopy in nitromethane-d3. The [2]rotaxane exhibits quite dramatic changes in the 1H chemical shifts of the signals for its CH2N+ and CH2O protons compared with those in the free dumbbell compound. The 1H NMR spectrum of the [2]pseudorotaxane shows many similar features. Titration experiments with three of the six different CH2O probes give an average Ka value of 2900 +/- 750 M-1 in nitromethane-d3. The new recognition motif for the template-directed synthesis of rotaxanes can now be exploited at both the molecular and macromolecular levels of structure with numerous potential applications in sight.read more
Citations
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Journal ArticleDOI
Stability of Self-Assembled Monolayers on Titanium and Gold
Gopinath Mani,Dave M. Johnson,Denes Marton,Victoria L. Dougherty,Marc D. Feldman,Devang N. Patel,Arturo A. Ayon,C. Mauli Agrawal +7 more
TL;DR: The stability of SAMs on Ti was investigated in Tris-buffered saline (TBS) at 37 degrees C using X-ray photoelectron spectroscopy, contact angle goniometry, and atomic force microscopy, and in ambient air and ultraviolet (UV) light.
Journal ArticleDOI
Big and little Meccano
TL;DR: The emergence of the mechanical bond during the past 25 years is giving chemistry a fillip in more ways than one as discussed by the authors, and it is providing a new lease of life to chemical synthesis where mechanical bond formation occurs as a consequence of the all-important templation orchestrated by molecular recognition and self-assembly.
Journal ArticleDOI
Systematic Investigation of Ligand Substitution Effects in Cyclophane-Based Nickel(II) and Palladium(II) Olefin Polymerization Catalysts(1)
TL;DR: In this paper, the synthesis of Ni(II) and Pd(II)-cyclophane-based α-diimine olefin polymerization catalysts bearing a range of electron-donating or -withdrawing groups is described.
Journal ArticleDOI
Preparation of beta-cyclodextrin polyrotaxane: photodimerization of pseudo-polyrotaxane with 2-anthryl and triphenylmethyl groups at the ends of poly(propylene glycol).
Miyuko Okada,Akira Harada +1 more
TL;DR: A polyrotaxane containing beta-cyclodextrins has been prepared by photoreactions of a precursor complex between beta- cyclodextrin with poly(propylene glycol) having a triphenylmethyl group at one end and a 2-anthryl group at the other end.
Journal ArticleDOI
Entropy- and hydrolytic-driven positional switching of macrocycle between imine- and hydrogen-bonding stations in rotaxane-based molecular shuttles.
TL;DR: An examination of thermodynamic parameters showed that imine-bond hydrolyses and the formation of hydrogen bonds between the macrocycle and the station are thermodynamically matched processes, because both processes are enthalpically favored and accompanied by a loss of entropy.
References
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