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Protein dielectrophoresis: Key dielectric parameters and evolving theory
Author(s) -
Hölzel Ralph,
Pethig Ronald
Publication year - 2021
Publication title -
electrophoresis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.666
H-Index - 158
eISSN - 1522-2683
pISSN - 0173-0835
DOI - 10.1002/elps.202000255
Subject(s) - polarizability , dielectrophoresis , dipole , dielectric , globular protein , chemical physics , condensed matter physics , moment (physics) , dispersion (optics) , dielectric response , materials science , chemistry , physics , electric field , nuclear magnetic resonance , molecule , classical mechanics , optics , quantum mechanics
Abstract Globular proteins exhibit dielectrophoresis (DEP) responses in experiments where the applied field gradient factor ∇ E 2 appears far too small, according to standard DEP theory, to overcome dispersive forces associated with the thermal energy kT of disorder. To address this a DEP force equation is proposed that replaces a previous empirical relationship between the macroscopic and microscopic forms of the Clausius–Mossotti factor. This equation relates the DEP response of a protein directly to the dielectric increment δε + and decrement δε − that characterize its β‐dispersion at radio frequencies, and also indirectly to its intrinsic dipole moment by way of providing a measure of the protein's effective volume. A parameter Γ pw , taken as a measure of cross‐correlated dipole interactions between the protein and its water molecules of hydration, is included in this equation. For 9 of the 12 proteins, for which an evaluation can presently be made, Γ pw has a value of ≈4600 ± 120. These conclusions follow an analysis of the failure of macroscopic dielectric mixture (effective medium) theories to predict the dielectric properties of solvated proteins. The implication of a polarizability greatly exceeding the intrinsic value for a protein might reflect the formation of relaxor ferroelectric nanodomains in its hydration shell.