The immobilisation and reactivity of Fe(CN)63−/4− in an intrinsically microporous polyamine (PIM-EA-TB)

Abstract

Protonation of the molecularly rigid polymer of intrinsic microporosity PIM-EA-TB can be coupled to immobilisation of Fe(CN) 6 3−/4− (as well as immobilisation of Prussian blue) into 1-2 nm diameter channels. The resulting films provide redoxactive coatings on glassy carbon electrodes. Uptake, transport, and retention of Fe(CN) 6 3−/4− in the microporous polymer are strongly pH dependent requiring protonation of the PIM-EA-TB (pK A ≈ 4). Both Fe(CN) 6 4− and Fe(CN) 6 3− can be immobilised, but Fe(CN) 6 4− appears to bind tighter to the polymer backbone presumably via bridging protons. Loss of Fe(CN) 6 3−/4− by leaching into the aqueous solution phase becomes significant only at pH > 9 and is likely to be associated with hydroxide anions directly entering the microporous structure to combine with protons. This and the interaction of Fe(CN) 6 3−/4− and protons within the molecularly rigid PIM-EA-TB host are suggested to be responsible for retention and relatively slow leaching processes. Electrocatalysis with immobilised Fe(CN) 6 3−/4− is demonstrated for the oxidation of ascorbic acid.

Catechin or quercetin guests in an intrinsically microporous polyamine (PIM-EA-TB) host: accumulation, reactivity, and release

“…The presence of the tertiary amine functional groups in the Tröger's base (TB) structural units of PIM-EA-TB provides sites for protonation, which occurs at approximately pH 4 in aqueous environments. 13 At solution pH values higher than 4, hydrogen bonding to these amine functional groups has been observed previously for Fe(CN) 6 3− and Fe(CN) 6 4− guest species 14 and for caffeic acid. 15 For many weakly acidic guest species, hydrogen bonding to the tertiary amine in the polymer backbone is likely to contribute to the strength of host–guest interactions and thereby likely to contribute to the rate of transport processes within PIM-EA-TB.…”

Ionic Diode and Molecular Pump Phenomena Associated with Caffeic Acid Accumulated into an Intrinsically Microporous Polyamine (PIM‐EA‐TB)

“…It has recently been reported that guest species such as Fe(CN) 6 4À /3À can be accumulated and bound into PIM-EA-TB pores via hydrogen bonds. [19] It is shown here that other species such as caffeic acid readily accumulate. Furthermore, the hydrogen bonding host-guest interactions modify the transport processes during ion transport.…”

Polymers of intrinsic microporosity (PIMs) in sensing and in electroanalysis

“…The permeation and transport of species in liquid-filled PIM microchannels can be employed in sensing and detection. PIM-EA-TB has tertiary amine functional groups on the polymer backbone and therefore allows interactions with hydrogen bond forming guests such as metal complexes [34] or herbal drugs such as catechin and quercetin [35]. Accumulation of these redox active species gave electrochemical oxidation signals proportional to the solution concentration with a Langmuir isotherm related response.…”