H+-type and OH−-type biological protonic semiconductors and complementary devices

Abstract

Proton conduction is essential in biological systems. Oxidative phosphorylation in mitochondria, proton pumping in bacteriorhodopsin, and uncoupling membrane potentials by the antibiotic Gramicidin are examples. In these systems, H+ hop along chains of hydrogen bonds between water molecules and hydrophilic residues – proton wires. These wires also support the transport of OH− as proton holes. Discriminating between H+ and OH− transport has been elusive. Here, H+ and OH− transport is achieved in polysaccharide- based proton wires and devices. A H+- OH− junction with rectifying behaviour and H+-type and OH−-type complementary field effect transistors are demonstrated. We describe these devices with a model that relates H+ and OH− to electron and hole transport in semiconductors. In turn, the model developed for these devices may provide additional insights into proton conduction in biological systems.

Long‐Range Proton Conduction across Free‐Standing Serum Albumin Mats

“…Several organic semiconductors have been also shown to have the ability to conduct protons, which enables them to support parallel proton and electron conductivity 17, 18, 19, 20. In recent years several bioorganic materials have been also proposed for protonic devices, such as polysaccharide derivatives and melanin pigment 21, 22, 23, 24, 25. While a wide diversity of materials have been shown to sustain proton current, there are only few types of proton‐conductors: oxide ions, oxoacids (and their anions), and in some cases, heterocycle molecules 10.…”

“…By weighing the mats before and after hydration, we could determine the swelling ratio (water content) of the mats to be 143 ± 18% (w/w). The large amount of water within the material distinguishes itself from other bioorganic proton conductors in the literature that contain 5–20% of water 22, 23, 24, 25. Following the hydration of the mats, most of the water could be removed by heating or placing the mats in vacuum.…”

“…In this mechanism the proton hops from one water molecule to another, and it is expected to have activation energy of 2–3kcal mol −1 (≈90–130 meV), and a KIE of 1.4 7. Gorodetsky and co‐workers31 and Rolandi and co‐workers23, 25 explained the high proton conductance of dry films of the relectin protein and polysaccharides, respectively, by the Grotthuss mechanism, and also suggested that the protein film contains water channels that support proton conductivity. In the work of Gorodetsky and co‐workers',31 similar KIE (≈1.7) values as expected for the Grotthuss mechanism have been found but with a slightly larger E a value (≈0.2eV) 31…”

Protonic transistors from thin reflectin films

“…Within the broader ionic transistor class of devices, there have been several reports of protonic transistors, [10][11][12][13][14][15][16] including two notable examples from the Rolandi group. 13,14 For these devices, the application of a voltage to the gate modulates the current flow between the source and the drain, in analogy to conventional unipolar field effect transistors.…”

“…13,14 For these devices, the application of a voltage to the gate modulates the current flow between the source and the drain, in analogy to conventional unipolar field effect transistors. 13,14 The magnitude of the current is determined by the proton charge carrier density in the device channel, as given by the equation n H+ = n H+ 0 − V GS C GS /et, where n H+ is the proton concentration at an arbitrary gate voltage, n H+ 0 is the proton concentration at a gate bias of 0 V, V GS is the gate voltage, C GS is the gate capacitance, e is the charge of the proton, and t is the thickness of the active layer. 13,14 Thus, a negative gate voltage induces the injection of protons into the channel, leading to an increase in the source-drain current, and a positive gate voltage depletes the channel of protons, leading to a decrease in the source-drain current.…”