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Long-Range Proton Conduction across Free-Standing Serum Albumin Mats.

Amdursky N, Wang X, Meredith P, Bradley DD, Stevens MM - Adv. Mater. Weinheim (2016)

Bottom Line: Free-standing serum-albumin mats can transport protons over millimetre length-scales.The results of photoinduced proton transfer and voltage-driven proton-conductivity measurements, together with temperature-dependent and isotope-effect studies, suggest that oxo-amino-acids of the protein serum albumin play a major role in the translocation of protons via an "over-the-barrier" hopping mechanism.The use of proton-conducting protein mats opens new possibilities for bioelectronic interfaces.

View Article: PubMed Central - PubMed

Affiliation: Departments of Materials, Bioengineering and Institute of Biomedical Engineering, Imperial College London, London, SW7 2AZ, UK.

No MeSH data available.


Related in: MedlinePlus

KIE and temperature dependence studies. a) KIE of EIS where water (filled black squares) was replaced with deuterium (open blue squares). b) Temperature dependence of EIS across the X = 0.75 mm junction. c) The activation energy of the process in (b) by fitting to an Arrhenius equation (G∝ exp (−Ea/kBT)). The graphs in (a) and (b) are displayed on an isometric scale.
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adma201505337-fig-0004: KIE and temperature dependence studies. a) KIE of EIS where water (filled black squares) was replaced with deuterium (open blue squares). b) Temperature dependence of EIS across the X = 0.75 mm junction. c) The activation energy of the process in (b) by fitting to an Arrhenius equation (G∝ exp (−Ea/kBT)). The graphs in (a) and (b) are displayed on an isometric scale.

Mentions: In order to examine the in‐plane proton conductance mechanism across the BSA mat we measured the KIE and the temperature‐dependence of the conduction process. Similar to the ESPT results (Figure S5, Supporting Information), we found no KIE for the proton conductance for both EIS (Figure [qv: 4]a) and I–V (Figure S9, Supporting Information) measurements (the KIE of the EIS was slightly inverse (i.e., lower than 1) but within the error range). The EIS temperature dependence studies for two of the measured distances (l = 0.75 and 1.5 mm, Figure 4b and Figure S10, Supporting Information, respectively) showed (via an Arrhenius fit) that the proton conductance was thermally activated with Ea = 0.29 ± 0.02 eV. The temperature dependence of the I–V measurements showed a similar trend with consistent activation energies for the measured distances (Figure S11, Supporting Information). We note, however, that conductivity measurements (AC and/or DC) on hygroscopic conductors, where the electrical response is strongly affected by the state of hydration, are notoriously unreliable—the temperature dependence can be perturbed or even masked by attendant changes in the hydration state. The fact that in our experiments the water content of the mats was high (≈150% w/w, yielding reduced sensitivity to thermal changes), and further, that we conducted the measurements in a fairly narrow range around room temperature, we consider that the results are moderately robust. In addition, we note that we see an increase in conductance with increasing temperature, whereas were the measurements dominated by dehydration, the opposite would have been expected. Moreover, a simple Arrhenius fit to the temperature dependent I–V data over this limited range and under circumstances where there will be some change in the state of hydration does not allow us to draw any independent mechanistic conclusions about the underlying transport physics. It does however provide an internally self‐consistent check of the AC data and conclusions.


Long-Range Proton Conduction across Free-Standing Serum Albumin Mats.

Amdursky N, Wang X, Meredith P, Bradley DD, Stevens MM - Adv. Mater. Weinheim (2016)

KIE and temperature dependence studies. a) KIE of EIS where water (filled black squares) was replaced with deuterium (open blue squares). b) Temperature dependence of EIS across the X = 0.75 mm junction. c) The activation energy of the process in (b) by fitting to an Arrhenius equation (G∝ exp (−Ea/kBT)). The graphs in (a) and (b) are displayed on an isometric scale.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4862025&req=5

adma201505337-fig-0004: KIE and temperature dependence studies. a) KIE of EIS where water (filled black squares) was replaced with deuterium (open blue squares). b) Temperature dependence of EIS across the X = 0.75 mm junction. c) The activation energy of the process in (b) by fitting to an Arrhenius equation (G∝ exp (−Ea/kBT)). The graphs in (a) and (b) are displayed on an isometric scale.
Mentions: In order to examine the in‐plane proton conductance mechanism across the BSA mat we measured the KIE and the temperature‐dependence of the conduction process. Similar to the ESPT results (Figure S5, Supporting Information), we found no KIE for the proton conductance for both EIS (Figure [qv: 4]a) and I–V (Figure S9, Supporting Information) measurements (the KIE of the EIS was slightly inverse (i.e., lower than 1) but within the error range). The EIS temperature dependence studies for two of the measured distances (l = 0.75 and 1.5 mm, Figure 4b and Figure S10, Supporting Information, respectively) showed (via an Arrhenius fit) that the proton conductance was thermally activated with Ea = 0.29 ± 0.02 eV. The temperature dependence of the I–V measurements showed a similar trend with consistent activation energies for the measured distances (Figure S11, Supporting Information). We note, however, that conductivity measurements (AC and/or DC) on hygroscopic conductors, where the electrical response is strongly affected by the state of hydration, are notoriously unreliable—the temperature dependence can be perturbed or even masked by attendant changes in the hydration state. The fact that in our experiments the water content of the mats was high (≈150% w/w, yielding reduced sensitivity to thermal changes), and further, that we conducted the measurements in a fairly narrow range around room temperature, we consider that the results are moderately robust. In addition, we note that we see an increase in conductance with increasing temperature, whereas were the measurements dominated by dehydration, the opposite would have been expected. Moreover, a simple Arrhenius fit to the temperature dependent I–V data over this limited range and under circumstances where there will be some change in the state of hydration does not allow us to draw any independent mechanistic conclusions about the underlying transport physics. It does however provide an internally self‐consistent check of the AC data and conclusions.

Bottom Line: Free-standing serum-albumin mats can transport protons over millimetre length-scales.The results of photoinduced proton transfer and voltage-driven proton-conductivity measurements, together with temperature-dependent and isotope-effect studies, suggest that oxo-amino-acids of the protein serum albumin play a major role in the translocation of protons via an "over-the-barrier" hopping mechanism.The use of proton-conducting protein mats opens new possibilities for bioelectronic interfaces.

View Article: PubMed Central - PubMed

Affiliation: Departments of Materials, Bioengineering and Institute of Biomedical Engineering, Imperial College London, London, SW7 2AZ, UK.

No MeSH data available.


Related in: MedlinePlus