[Interaction between acyclic phenol--formaldehyde oligomers and quaternary ammonium ions]

Chemiluminescence enhancement of 1,2-di[3,4,5-tri(3,4,5-trihydroxybenzoyloxy)benzoyloxy] benzene in the presence of quaternary ammonium ions

The chemiluminescence intensity of 1,2-di[3,4,5-tri(3,4,5-trihydroxybenzoyloxy)benzoyloxy] benzene increased in the presence of quaternary ammonium ions, such as acetylcholine chloride, choline chloride or benzyltrimethylammonium chloride. The complex of 1,2-di[3,4,5-tri(3,4,5-trihydroxybenzoyloxy)benzoyloxy] benzene with acetylcholine chloride, choline chloride or benzyltrimethylammonium chloride was investigated by (1)H-NMR spectroscopy. The structure of the complex formed from 1,2-di[3,4,5-tri(3,4,5-trihydroxybenzoyloxy)benzoyloxy] benzene with choline chloride was described by an ab initio quantum chemical calculation.

Anion binding by catechols—an NMR, optical and electrochemical study

The X-ray structure of the ClC chloride channel made it clear that O-H...chloride interactions play a key role in important biological membrane-bound systems, however, surprisingly this type of interaction has only been rarely exploited for the development of synthetic anion receptors. This paper therefore reports the anion binding strengths and selectivities of some simple commercially available bis-phenols. In particular, we compare catechol (1,2-dihydroxybenzene) and resorcinol (1,3-dihydroxybenzene) which show interesting and different selectivities between the halide anions in acetonitrile solution. Catechol binds tetrabutylammononium (TBA) chloride almost 30 times more strongly than TBA bromide, whilst for resorcinol, this difference drops to a factor of ca. 3.5. It is suggested that this is a consequence of the bite angle of the chelating hydrogen bonding groups of catechol being particularly appropriate for effective binding of the smaller anion. The oxidation of catechol to ortho-quinone is perturbed by the addition of chloride anions, as probed via cyclic voltammetry, and this compound can therefore be considered to act as an electrochemical sensor for chloride. Nitrocatechol is able to bind chloride anions more strongly than catechol as a consequence of its enhanced acidity and hence greater hydrogen bond donor character. Furthermore, nitrocatechol senses the bound anion via changes in its UV-visible spectrum. Notably, binding still occurs even in the presence of small amounts of competitive solvents (e.g. water). This observation has biomimetic importance as wet acetonitrile has some similarity in terms of overall polarity and hydrogen bond competition to the solvent shielded interiors of biological macromolecules and membranes--such as the environment within the ClC chloride channel itself. Finally, we report that catechol undergoes a unique colorimetric response on the addition of basic anions, such as fluoride. We can assign this response as being due to oxidative degradation of catechol catalysed by the basic anions (which bind to, and deprotonate, the catechol). This process is somewhat analogous to the well-known metal catalysed oxidation of catechol which can take place in aqueous solution. The speed of response and easily monitored and distinctive colour change induced by fluoride anions indicates this may be a useful mechanism for exploitation in the development of selective fluoride sensors.

Interaction between quaternary ammonium ions and dipeptides: positive anion allosteric effect

The binding properties of dipeptides possessing aromatic residues towards quaternary ammonium ions have been investigated by 1H-NMR spectroscopy. The intermolecular hydrogen bonding between exchangeable protons (OH and NH) of aromatic residues of dipeptides and the counter anion of ammonium ion is the primary force. After the formation of the intermolecular hydrogen bonding, two aromatic residues of dipeptides can provide pi-base cavity to interact with the quaternary ammonium moiety.

Interaction between Biphenols and Anions: Selective Receptor for Dihydrogenphosphate

Biphenol was shown to bind dihydrogenphosphate (H2PO4-) selectively over various other anions (MeCO2-, Cl-, Br-, I-, NO3-, HSO4-). The highly selectivity of biphenol toward dihydrogenphosphate is explained in terms of the basicity and shape of the guest anion.