title: Mechanisms of Gadographene-Mediated Proton Spin Relaxation.
abstract: Gd(III) associated with carbon nanomaterials relaxes water proton spins at an effectiveness that approaches or exceeds the theoretical limit for a single bound water molecule. These Gd(III)-labeled materials represent a potential breakthrough in sensitivity for Gd(III)-based contrast agents used for magnetic resonance imaging (MRI). However, their mechanism of action remains unclear. A gadographene library encompassing GdCl3, two different Gd(III)-complexes, graphene oxide (GO), and graphene suspended by two different surfactants and subjected to varying degrees of sonication was prepared and characterized for their relaxometric properties. Gadographene was found to perform comparably to other Gd(III)-carbon nanomaterials; its longitudinal (r1) and transverse (r2) relaxivity is modulated between 12-85 mM-1s-1and 24-115 mM-1s-1, respectively, depending on the Gd(III)-carbon backbone combination. The unusually large relaxivity and its variance can be understood under the modified Florence model incorporating the Lipari-Szabo approach. Changes in hydration number (q), water residence time (τM), molecular tumbling rate (τR), and local motion (τfast) sufficiently explain most of the measured relaxivities. Furthermore, results implicated the coupling between graphene and Gd(III) as a minor contributor to proton spin relaxation.
authors.affiliation: Department of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, and Radiology, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States.
authors.forename: Andy H
authors.initials: AH
authors.lastname: Hung
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Duch
authors.forename: Giacomo
authors.initials: G
authors.lastname: Parigi
authors.forename: Matthew W
authors.initials: MW
authors.lastname: Rotz
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Manus
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Mastarone
authors.forename: Kevin T
authors.initials: KT
authors.lastname: Dam
authors.forename: Colton C
authors.initials: CC
authors.lastname: Gits
authors.forename: Keith W
authors.initials: KW
authors.lastname: Macrenaris
authors.forename: Claudio
authors.initials: C
authors.lastname: Luchinat
authors.forename: Mark C
authors.initials: MC
authors.lastname: Hersam
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Meade
keywords: gadolinium; graphene; graphene oxide; modified Florence NMRD program; relaxivity