title: A nuclear magnetic resonance study of water in aggrecan solutions.
abstract: Aggrecan, a highly charged macromolecule found in articular cartilage, was investigated in aqueous salt solutions with proton nuclear magnetic resonance. The longitudinal and transverse relaxation rates were determined at two different field strengths, 9.4 T and 0.5 T, for a range of temperatures and aggrecan concentrations. The diffusion coefficients of the water molecules were also measured as a function of temperature and aggrecan concentration, using a pulsed field gradient technique at 9.4 T. Assuming an Arrhenius relationship, the activation energies for the various relaxation processes and the translational motion of the water molecules were determined from temperature dependencies as a function of aggrecan concentration in the range 0-5.3% w/w. The longitudinal relaxation rate and inverse diffusion coefficient were approximately equally dependent on concentration and only increased by upto 20% from that of the salt solution. The transverse relaxation rate at high field demonstrated greatest concentration dependence, changing by an order of magnitude across the concentration range examined. We attribute this primarily to chemical exchange. Activation energies appeared to be approximately independent of aggrecan concentration, except for that of the low-field transverse relaxation rate, which decreased with concentration.
authors.affiliation: School of Physics and Astronomy , University of Leeds , Leeds LS2 9JT , UK.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Foster
authors.affiliation: School of Physics and Astronomy , University of Leeds , Leeds LS2 9JT , UK.
authors.forename: Robin A
authors.initials: RA
authors.lastname: Damion
authors.affiliation: Leeds Institute of Rheumatic and Musculoskeletal Medicine , University of Leeds, St James's University Hospital , Leeds LS9 7TF , UK.
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Baboolal
authors.affiliation: Academic Division of Medical Physics, University of Leeds, Leeds LS2 9JT, UK; National Institute for Health Research, Leeds Musculoskeletal Biomedical Research Unit, Chapel Allerton Hospital, University of Leeds, Leeds LS2 9LN, UK.
authors.forename: Stephen W
authors.initials: SW
authors.lastname: Smye
authors.affiliation: School of Physics and Astronomy , University of Leeds , Leeds LS2 9JT , UK.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Ries
keywords: activation energy; aggrecan; chemical exchange; diffusion; glycosaminoglycan; relaxation