Easy-to-make tripodal tris-thiourea receptors based upon tris(2-aminoethyl)amine are capable of chloride/bicarbonate transport and as such represent a new class of bicarbonate transport agent.The key roles that anions play in a whole range of biological 10 processes has lead to much recent interest in the design of transporters and channels capable of carrying guests 1 such as chloride 2 or bicarbonate 3 across lipid bilayer membranes. Compounds based on tris(2-aminoethyl)amine (tren) have proven to be effective receptors for a variety of anionic 15 species. 4 Recently tren-based tris-ureas have been employed by Custelcean as agents to selectively crystallise strongly solvated tetrahedral oxo-anions such as sulfate. 5 In the anion transport arena, D.K. Smith and co-workers have shown that tren-based tris amides are capable of HCl co-transport through The results show that the thiourea derivatives are capable of both chloride/nitrate and more significanly of transporting the more hydrophilic bicarbonate anion via a chloride/bicarbonate antiport mechanism. 3
35Compounds 1-4 were synthesised by modifications of literature procedures (see ESI). 9 Proton NMR titration techniques were used to assess the stability of the receptor:anion complexes. Stability constants for the ligand-anion complexes were determined using the 40 EQNMR computer programme. 10 NMR titrations were conducted in DMSO-d 6 /0.5% water solutions with tetrabutylammonium anion salts (except for bicarbonate which was added as the tetraethylammonium salt). The results show that in all cases the receptors bind sulfate strongly with K a > bicarbonate. ¶ The X-ray crystal structure revealed that two equivalents of receptor 4 bind to a single carbonate anion in the solid state via twelve hydrogen bonds in the range 2.824(6)-3.070(7)Å with several other longer range NH … O interactions ( Figure 1a). We have previously observed that 60 anion receptors that form multiple hydrogen bond to oxoanions can perturb the pKa of the guest to the extent that the guest anion is deprotonated by free anion in solution. 11 This process may also occur here and account for the difficulty in fitting the bicarbonate NMR titration results to a simple 65 binding model. The structure itself shows the carbonate anion encapsulated between two receptors effectively shielded from the environent external to the complex. The sulfur atoms of the thiourea groups decorate the surface of the capsule-like complex (Figure 1b).
70In order to study the chloride transport properties of compounds 1-4 we prepared a series of unilamellar 1-palmitoyl-2-oleoylphophatidylcholine (POPC) vesicles loaded with sodium chloride (489 mM) and suspended them in an external NaNO 3 (489 mM) solution. A sample of receptor 1-4 75 or control compound trihexylamine (2% molar carrier to lipid) was added as a DMSO solution and the resultant Cl -efflux monitored using a chloride selective electrode. 12 After 300 s, the vesicles were lysed by addition of detergent and the final reading of the electrode was used to cali...
We describe the covalent post-modification of a hydrogen-bonded assembly with the subsequent formation of a potent transmembrane Na+ ion transporter. Olefin metathesis is used to cross-link all 16 guanosine subunits in a lipophilic G-quadruplex. The resulting unimolecular G-quadruplex folds in the environment of a phospholipid membrane and functions as a Na+ ion transporter as judged by fluorescence and 23Na NMR transport assays.
A new series of structurally simple compounds containing thiourea groups have been shown by a combination of ionselective electrode and 13 C NMR techniques to be potent chloride-bicarbonate exchange agents that function at low concentration in POPC and POPC/cholesterol membranes.
The sphingolipid, ceramide 1, facilitates transport of Cl(-) and HCO(3)(-) anions across lipid bilayers under conditions where large transmembrane pores are not formed. Ceramide's 1,3-diol unit is essential for both binding and transporting these anions.
The use of a bis-urea lithocholamide linker within a guanosine-sterol dimer resulted in formation of large and stable ion channels. The channels were longer-lived than those formed by the corresponding bis-carbamate.
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