4 research outputs found
Thiosquaramides: pH switchable anion transporters
The transport of anions across cellular membranes is an important biological function governed by specialised proteins. In recent years, many small molecules have emerged that mimick the anion transport behaviour of these proteins, but only a few of these synthetic molecules also display the gating/switching behaviour seen in biological systems. A small series of thiosquar-amides was synthesised and their pH-dependent chloride binding and anion transport behaviour was investigated using 1H NMR titrations, single crystal X-ray diffraction and a variety of vesicle-based techniques. Spectrophotometric titrations and DFT calculations revealed that the thiosquaramides are significantly more acidic than their oxosquaramide analogues, with pKa values between 4.0 and 9.0. This led to the observation that at pH 7.2 the anion transport ability of the thiosquaramides is fully switched OFF due to deprotonation of the receptor, but is completely switched ON at lower pH
Sensitive Structural Control of Macrocycle Threading by a Fluorescent Squaraine Dye Flanked by Polymer Chains
A macrocyclic tetralactam is threaded
by a complementary squaraine
dye that is flanked by two polyethylene glycol chains to produce a
pseudorotaxane complex with favorable near-infrared fluorescence properties.
The association thermodynamics and kinetics were measured for a homologous
series of squaraines with different <i>N</i>-alkyl substituents
at both ends of the dye. The results show that subtle changes in substituent
steric size have profound effects on threading kinetics without greatly
altering the very high association constant