Evbuomwan Osasere M, Lee Joohwan, Woods Mark, Sherry A Dean
Department of Chemistry, University of Texas at Dallas , 800 West Campbell Road, Richardson, Texas 75080, United States.
Inorg Chem. 2014 Oct 6;53(19):10012-4. doi: 10.1021/ic501290q. Epub 2014 Sep 11.
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%.
LnDOTA-四酰胺配合物在溶液中通常以方形反棱柱体（SAP）和扭曲方形反棱柱体（TSAP）配位异构体的混合物形式存在。在大多数情况下，CEST成像更倾向的SAP异构体占主导，并且假定少量TSAP异构体的存在对SAP异构体水交换速率常数的定量测量影响很小。在此，我们通过混合两种具有不同SAP和TSAP异构体比例的螯合物，同时测量SAP异构体的水交换速率常数，来验证这一假设的有效性。结果表明，当CEST光谱拟合到布洛赫方程时，溶液中TSAP异构体比例的增加会导致对SAP异构体水交换速率常数的高估高达30%。仅当TSAP异构体比例超过50%时，这种效应才显著。
