title: The presence of fast-exchanging proton species in aqueous solutions of paraCEST agents can impact rate constants measured for slower exchanging species when fitting CEST spectra to the Bloch equations.
abstract: LnDOTA-tetraamide complexes typically exist in solution as a mixture of square-antiprismatic (SAP) and twisted square-antiprismatic (TSAP) coordination isomers. In most cases, the SAP isomer, which is preferred for CEST imaging, predominates, and the presence of the minor TSAP isomer is assumed to have little influence on quantitative measures of the water-exchange rate constant for the SAP isomer. Here, we sought to confirm the validity of this assumption by mixing two chelates with different SAP and TSAP isomer populations while measuring the water-exchange rate constant of the SAP isomer. The results show that an increase in the population of the TSAP isomer in solution results in as much as a 30% overestimation of the water-exchange rate constant for the SAP isomer when CEST spectra are fit to the Bloch equations. This effect was shown to be significant only when the TSAP isomer population exceeded 50%.
authors.affiliation: Department of Chemistry, University of Texas at Dallas , 800 West Campbell Road, Richardson, Texas 75080, United States.
authors.forename: Osasere M
authors.initials: OM
authors.lastname: Evbuomwan
authors.forename: Joohwan
authors.initials: J
authors.lastname: Lee
authors.forename: Mark
authors.initials: M
authors.lastname: Woods
authors.forename: A Dean
authors.initials: AD
authors.lastname: Sherry
mesh_terms: D000577:Amides / Q000737:chemistry*; D003287:Contrast Media / Q000737:chemistry*; D006573:Heterocyclic Compounds, 1-Ring / Q000737:chemistry*; D028581:Lanthanoid Series Elements / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry*; D011522:Protons; D012996:Solutions; D014867:Water / Q000737:chemistry
chemical_list: D000577:Amides; D003287:Contrast Media; D006573:Heterocyclic Compounds, 1-Ring; D028581:Lanthanoid Series Elements; D009942:Organometallic Compounds; D011522:Protons; D012996:Solutions; D014867:Water; C071349:1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid