title: Origin of supercharging in electrospray ionization of noncovalent complexes from aqueous solution.
abstract: The use of m-nitrobenzyl alcohol (m-NBA) to enhance charging of noncovalent complexes formed by electrospray ionization from aqueous solutions was investigated. Addition of up to 1% m-NBA can result in a significant increase in the average charging of complexes, ranging from approximately 13% for the homo-heptamer of NtrC4-RC (317 kDa; maximum charge state increases from 42+ to 44+) to approximately 49% for myoglobin (17.6 kDa; maximum charge state increases from 9+ to 16+). Charge state distributions of larger complexes obtained from heated solutions to which no m-NBA was added are remarkably similar to those containing small amounts of m-NBA. Dissociation of the complexes through identical channels both upon addition of higher concentrations of m-NBA and heating is observed. These results indicate that the enhanced charging upon addition of m-NBA to aqueous electrospray solutions is a result of droplet heating owing to the high boiling point of m-NBA, which results in a change in the higher-order structure and/or dissociation of the complexes. For monomeric proteins and small complexes, the enhancement of charging is lower for heated aqueous solutions than from solutions with m-NBA because rapid folding of proteins from heated solutions that do not contain m-NBA can occur after the electrospray droplet is formed and is evaporatively cooled.
authors.affiliation: Department of Chemistry, University of California-Berkeley, Berkeley, California 94720, USA.
authors.forename: Harry J
authors.initials: HJ
authors.lastname: Sterling
authors.forename: Evan R
authors.initials: ER
authors.lastname: Williams
mesh_terms: D000942:Antigens, Bacterial / Q000737:chemistry; D001059:Apoproteins / Q000737:chemistry; D001426:Bacterial Proteins / Q000737:chemistry; D001592:Benzyl Alcohols / Q000737:chemistry; D009211:Myoglobin / Q000737:chemistry; D011506:Proteins / Q000737:chemistry*; D051877:RNA Polymerase Sigma 54 / Q000737:chemistry; D012996:Solutions / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D013696:Temperature; D014867:Water / Q000737:chemistry*
chemical_list: D000942:Antigens, Bacterial; D001059:Apoproteins; D001426:Bacterial Proteins; D001592:Benzyl Alcohols; D009211:Myoglobin; D011506:Proteins; D012996:Solutions; C010857:apomyoglobin; D014867:Water; D051877:RNA Polymerase Sigma 54; C046886:3-nitrobenzyl alcohol
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