Thomas W. Bell

Complexation of Creatinine by Synthetic Receptors

Abstract A series of highly preorganized, polyheterocyclic hosts for creatinine has been synthesized. Key receptors bearing intrinsic chromophores are ketones 4 and 9 . 1 H NMR and UV-visible spectroscopy were used to detect extraction of creatinine hydrochloride by 4 into CDCl 3 and 5% ethanol/chloroform, respectively. Receptor 9 , which has an additional hydrogen-bond donor, binds creatinine in 70 % aq. methanol, as shown by changes in UV-visible absorptions at constant pH ∗ (4.3). These hexagonal lattice receptors are the most effective complexing agents known to bind creatinine, which is a clinically important constituent of blood.

Urea transport through supported liquid membranes using synthetic carriers

Urea can be transported through a supported liquid membrane (Accurel/NPOE) by carriers such as metallomacrocycles and polyaza (cleft-type) receptors. The urea flux is increased by a factor 4?8 using polyaza receptors and by a factor 10?15 using metallomacrocycles containing a salophene unit in which a uranyl cation is incorporated. These carriers have a high hydrophobicity and do not significantly leak from the membrane phase into the aqueous phases. The structure of the receptors and the type and number of binding sites have a pronounced influence on the transport rate. The lower urea fluxes found for the polyaza (cleft-type) carriers are most likely caused by a weaker complexation (only H-bond interactions). No transport is observed for carriers which form intramolecular H-bonds. Although lower fluxes are obtained than with a commercial haemodialysis membrane (Cuprophan), the selectivity of transport may be much higher using carrier-mediated transport.

A new synthesis of piperidines and pyridines and pyridines: [3+3] annulation of 2-azaallyl anions

Abstract A one-pot approach to 6-membered heterocyclic rings combines two 1,3-dipole equivalents: 2-azaallyl anions (2) and iodosilane 3. The resulting cis-2,6-disubstituted 4-methylenepiperidines are converted in high yield to 2,4,6-trisubstituted pyridines (6) byoxidation with mercuric acetate in acetic acid.

Toward Columns and Channels from Torands and Molecular Coils

Self-assembled tubular structures capable of binding and conducting metal cations are of interest in the fabrication of permeation-selective membranes and the design of supramolecular devices, such as nanoscale transducers.1, 2, 3 Artificial ion-transport assemblies can also serve as models for investigating structure and function of natural transmembrane pores and channels, such as Gramicidin aggregates.4,5 Torands6, 7, 8, 9, 10, 11, 12, 13, 14 are a recently explored class of relatively rigid, planar ligands capable of coaxial stacking; molecular coils 15,16 are analogous compounds capable of multiple-helical aggregation. Figure 1 shows the key compounds of interest in this chapter, which begins by reviewing the metal complexation and aggregation behavior of torand 1. The formation of double-helical metal complexes by molecular coils 3 and 4 is then discussed. The chapter concludes with the synthesis of triaryltorands (2) in a planned approach to novel tubular mesophases.1