Conformational Dynamics of Calixarenes. Kinetics of Conformational Interconversion in 5,11,17,23-Tetra-p-tert-butyl-25,26,27,28-tetramethoxycalix[4]arene under Entropic Control

Molecular dynamics simulations of free energy and conformational transition rates of calix[4]arene in chloroform

“…[21][22][23][24] With the calix͓4͔arene of this paper, however, comparison of the theoretical and experimental transition rates is complicated by the fact that the paco conformation is only very short-lived. Hence only the cone to inverted cone rate is experimentally accessible.…”

“…These primed rates can be calculated with the techniques described in this paper, while the unprimed rates are the experimentally accessible rates. 24 We now want to find a relation between k and k 1 Ј . Of course, this estimate should not be taken for granted, but it gives a reasonable approximation of the effect that is to be expected in exact calculations.…”

An Electron‐Rich Calix[4]arene‐Based Receptor with Unprecedented Binding Affinity for Nitric Oxide

“…Unlike 1 , where all four possible conformations are present in solution at ambient temperature, the methoxy‐rich calixarene derivative 3 exists only as the paco conformation (Figure B), with eight identical interconverting structures. The activation barrier of their interconversion is relatively small ( E a =14.6 kcal mol −1 ), and can be frozen at ≈−20 °C .…”

“…The desire to develop a more detailed understanding of the nature of NO bonding to multichromophoric cofacial assemblies led us to examine an electron-rich derivative of 1 (i.e., 3,F igure 2B), which can be prepared in as ingle-step synthesis from the acid-catalyzedr eactionb etween resorcinol methyl ether (1,3,5-trimethoxybenzene)a nd paraformaldehyde. [20,21] Unlike 1,w here all four possible conformationsa re present in solution at ambient temperature, [22,23] the methoxy-rich calixarened erivative 3 exists only as the paco conformation ( Fig-Figure 1. Four interconvertingconformations of 4-tert-butylcalix [4]arene methylethers (1)and their rigidification in the corresponding propyl ethers (2).…”

26,28-Diallyloxy-5,11,17,23-tetra-tert-butyl-25,27-bis(cyanomethoxy)calix[4]arene in the partial cone conformation

“…Tetraethers of (p-substituted)calix [4]arenes may be fixed in one of the four possible conformations (cone, partial cone, 1,2and 1,3-alternate) by alkylether residues larger than ethyl (Bo ¨hmer, 1995). Tetramethylethers, on the other hand, exist as a rapidly interconverting mixture of all four isomers, in which the partial cone conformation is usually preferred (Harada et al, 1992;Blixt & Detellier, 1994). Residues like ethyl (Groenen et al, 1991), cyanomethyl (Kang & Nam, 2000;Nam et al, 2002) or propargyl (Xu et al, 1996) are somewhat on the borderline and can (slowly) pass the annulus.…”