title: Hofmeister effect in confined spaces: halogen ions and single molecule detection.
abstract: Despite extensive research in the nanopore-sensing field, there is a paucity of experimental studies that investigate specific ion effects in confined spaces, such as in nanopores. Here, the effect of halogen anions on a simple bimolecular complexation reaction between monodisperse poly(ethylene glycol) (PEG) and α-hemolysin nanoscale pores have been investigated at the single-molecule level. The anions track the Hofmeister ranking according to their influence upon the on-rate constant. An inverse relationship was demonstrated for the off-rate and the solubility of PEG. The difference among anions spans several hundredfold. Halogen anions play a very significant role in the interaction of PEG with nanopores although, unlike K(+), they do not bind to PEG. The specific effect appears dominated by a hydration-dehydration process where ions and PEG compete for water. Our findings provide what we believe to be novel insights into physicochemical mechanisms involved in single-molecule interactions with nanopores and are clearly relevant to more complicated chemical and biological processes involving a transient association of two or more molecules (e.g., reception, signal transduction, enzyme catalysis). It is anticipated that these findings will advance the development of devices with nanopore-based sensors for chemical and biological applications.
authors.affiliation: Department of Biophysics and Radiobiology, Federal University of Pernambuco, Recife, Pernambuco, Brazil.
authors.forename: Claudio G
authors.initials: CG
authors.lastname: Rodrigues
authors.forename: Dijanah C
authors.initials: DC
authors.lastname: Machado
authors.forename: Annielle M B
authors.initials: AM
authors.lastname: da Silva
authors.forename: Janilson J S
authors.initials: JJ
authors.lastname: Júnior
authors.forename: Oleg V
authors.initials: OV
authors.lastname: Krasilnikov
mesh_terms: D000838:Anions; D001427:Bacterial Toxins / Q000378:metabolism; D001703:Biophysics / Q000379:methods*; D004553:Electric Conductivity; D053841:Electroosmosis; D006219:Halogens / Q000737:chemistry*; D006460:Hemolysin Proteins / Q000378:metabolism; D007700:Kinetics; D057230:Limit of Detection; D008956:Models, Chemical; D011092:Polyethylene Glycols / Q000737:chemistry; D012995:Solubility; D012996:Solutions; D014867:Water / Q000737:chemistry
chemical_list: D000838:Anions; D001427:Bacterial Toxins; D006219:Halogens; D006460:Hemolysin Proteins; D012996:Solutions; C021091:staphylococcal alpha-toxin; D014867:Water; D011092:Polyethylene Glycols