Electrical properties of hydrated collagen. II. Semiconductor properties

Abstract

SynopsisThe dc conductivity of hydrated bovine Achilles' tendon collagen has been determined as a function of hydration over a limited temperature range. At ambient temperature the conductivity changes from 10-l6 (Q cm)-l in the dry state to about lo-* (Q cm)-l at -24% water content by weight. For all temperatures the conductivity increases exponentially with hydration obeying s(h) = A exp(Oh), where h is a measure of the hydration, A is independent of temperature, and the parameter b -T-1. It is shown that the data may be described by an impurity-type mechanism in which the effective activation energy for the process is dependent on temperature and hydration. Conduction is assumed to be electronic with the impurity (water) acting as a donor. In the solid state the effect of water on the conductivity is reversible indicating the absence of chemical alteration of the hydrated collagen.* 1 eV = 23.05 kcal/mol. 2423

Thermal and Photochemical Effects on the Fluorescence Properties of Type I Calf Skin Collagen Solutions at Physiological pH

“…The photochemical formation of dityrosine uses the absorbed photonic energy to accomplish tyrosyl radical formation. Ground state oxidation of tyrosine residues in collagen is most likely to involve water of hydration [15]. Our collagen samples, no doubt, were hydrated even in the solid state.…”

“…Tomaselli et al [15] found that the adsorption of water onto solid bovine Achille's tendon (BAT) caused a dramatic increase on the values of dc conductivity σ that is both temperature-and hydration parameter (h)-dependent (as much as 8 orders of magnitude at h = 0.24). Increasing hydration decreases the activation energy, and moderate hydration levels, confer semiconductor-like properties on the collagen, with water possibly acting as an impurity [15]. Although the exact mechanism of tyrosyl formation is unclear, we can speculate that moderate hydration lowers the activation energy sufficiently to allow tyrosine oxidation via electron transfer (ET), proton transfer (PT), or proton-coupled electron transfer (PCET) (for review of PCET, see [16]).…”

“…Our collagen samples, no doubt, were hydrated even in the solid state. The electrical properties of hydrated collagen have been studied by several workers (for quick review, see [15] and references therein). Tomaselli et al [15] found that the adsorption of water onto solid bovine Achille's tendon (BAT) caused a dramatic increase on the values of dc conductivity σ that is both temperature-and hydration parameter (h)-dependent (as much as 8 orders of magnitude at h = 0.24).…”

“…The electrical properties of hydrated collagen have been studied by several workers (for quick review, see [15] and references therein). Tomaselli et al [15] found that the adsorption of water onto solid bovine Achille's tendon (BAT) caused a dramatic increase on the values of dc conductivity σ that is both temperature-and hydration parameter (h)-dependent (as much as 8 orders of magnitude at h = 0.24). Increasing hydration decreases the activation energy, and moderate hydration levels, confer semiconductor-like properties on the collagen, with water possibly acting as an impurity [15].…”

DC Electrical Conductivity in Studies on Solid-State Proteins

“…It is well described fact that hydration level influences electric conductivity of collagen. The increase in water content increases electric conductivity whereas the activation energy of charge conduction process is reduced [17,[30][31][32][33][34].…”