G. William Orr

An intermolecular (H2O)10 cluster in a solid-state supramolecular complex

Chemical self-assembly is the process by which ‘programmed’ molecular subunits spontaneously form complex supramolecular frameworks,. This approach has been applied to many model systems, in which hydrogen bonds,, metal–ligand coordination or other non-covalent interactions typically control the self-assembly process. In biology, self-assembly is generally dynamic and depends on the cooperation of many such non-covalent interactions. Water can play an important role in these biological self-assembly processes, for example by stabilizing the native conformation of biopolymers. Hydrogen-bonded (H2O)n clusters, can play an important role in stabilizing some supramolecular species, both natural and synthetic, in aqueous solution. Here we report the preparation and crystal structure of a self-assembled, three-dimensional supramolecular complex that is stabilized by an intricate array of non-covalent interactions involving contributions from solvent water clusters, most notably a water decamer ((H2O)10) with an ice-like molecular arrangement. These findings show that the degree of structuring that can be imposed on water by its surroundings, and vice versa, can be profound.

Calixarenes as enzyme models

Abstract A review of the progress towards the use of calixarenes as enzyme models is presented. Double recognition of a substrate is illustrated with the crystal structure of (H3O+)[La(ONC5H5)2(H2O)6(p-sulfonatocalix[4]arene)]−·6.5H2O, 1. The binding of zinc to calixarenes in a second-sphere fashion is shown with the crystal structure of Na2[Zn(H2O)4(ONC5H5)2][calix[4]arene]·8.5H2O, 4. The preparation and structures of aminomethylcalix[4]arenes are demonstrated with [p-(4-(2-pyridyl)piperidinomethyl)calix[4]arene], 5, and [p-(4-phenylpiperidinomethyl)calix[4]arene], 6.

Characterization of a well resolved supramolecular ice-like (H2O)10 cluster in the solid state

The conformation of a previously observed ice-like water cluster in the solid state proves to be robust to geometric changes in its surroundings and the hydrogen bonded arrangement is finally revealed in detail.

Structure of the p-sulfonatocalix[4]arene complex with tetramethylammonium ions, [NME4]5[p-sulfonatocalix[4]arene]·4H2O

Abstract Treatment of p-calix[4]arene sulfonic acid with excess tetramethylammonium hydroxide yields [NMe4]5[p-sulfonato-calixarene]·4H2O. The compound crystallizes from aqueous solution in the triclinic space group P1 with a = 13.125(3), b = 14.881(3), c = 16.320(4) A, α = 77.19(1), β = 77.30(1), γ = 72.30(1)°, and Dc = 1.35 g cm−3 for Z = 2 (C48H87O20N5S4). Refinement based on 5044 observed reflections yielded a final R value of 0.084. The overall structure consists of bilayers of calix[4]arenes separated by regions which contain the cations and water molecules. One of the tetramethylammonium ions is bound within the hydrophobic calix[4]arene cavity.

Supramolecular assemblies of calix [4] arenes organized by feeble forces

Abstract X-ray crystallographic investigations have shown that dimeric supramolecular assemblies of water-soluble calix[4]arenes are formed by a combination of hydrophobic effects and either hydrogen bonding or secondary bonding. For Na4(pyridinium)[calix[4]arene sulfonate] · 8H2O, a dimeric arrangement based on hydrogen bonding and hydrophobic effects is found. The compound crystallizes in the monoclinic space group P21/n with a = 11.873(3), b = 24.345(6), c = 14.846(3) A, β 96.78(2)°, and Dc = 1.66 g cm−3 for Z = 4. Refinement based on 3492 observed reflections led to a final R value of 0.051. For [Cu(NC5H5)2(H2O)3](Na)3[calix[4]arene sulfonate] · 13 H2O, the dimeric association is based on a secondary bonding interaction between the copper(II) ion and a sulfonate oxygen atom combined with hydrophobic interactions. The compound crystallizes in the monoclinic space group P21/n with a = 14.672(3), b = 25.577(5), c = 15.457(3) A, β = 101.94(4)°, and Dc = 1.55 g cm−3 for Z = 4. Refinement based on 3602 obse...

Liquid-liquid extraction of transition and alkali metal cations by a new calixarene: Diphenylphosphino calix[4]arene methyl ether

The liquid-liquid extraction of various metal ions by a diphenylphosphino calix[4]arene (1) using picrate counter ion has been studied and compared with those ofp-tert-butyl-calix[4]arene methyl ether (2) and triphenylphosphine (3). The calixarene 1 shows strong binding ability to almost all metal cations examined, but calixarene 2 shows little ability to extract any of them. Based on the continuous variation method, calixarene 1 formed 1: 2 complexes with copper(II) ion.

Calixarenes as second-sphere ligands for transition metal ions. Synthesis and crystal structure of [(H2O)5 Ni(NC5H5)]2(Na)[calix[4]arene sulfonate] 3.5 H2O and [(H2O)4Cu(NC5H5)2]-(H3O)3 [calix[4]arene sulfonate] 10 H2O

AbstractThe title compounds crystallize such that bilayers of calixarenes are separated by hydrophilic layers. In each case the transition metal has, in addition to a primary sphere of ligands, a second-sphere coordination by a calixarene. [(H2O)5Ni(NC5H5)]2(Na)[calix[4]arene sulfonate]·3.5 H2O,1, crystallizes in the triclinic space groupP

First structural authentication of third-sphere coordination: [p-sulfonatocalix[4]arene]5- as a third-sphere ligand for Eu3+

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