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Analysis of the Relaxometric Properties of Extremely Rapidly Exchanging Gd3+ Chelates: Lessons from a Comparison of Four Isomeric Chelates.
Inorganic Chemistry ( IF 4.3 ) Pub Date : 2020-06-14 , DOI: 10.1021/acs.inorgchem.0c00905
Benjamin C Webber 1 , Katherine M Payne 1 , Lauren N Rust 1 , Claudio Cassino 2 , Fabio Carniato 2 , Theresa McCormick 1 , Mauro Botta 2 , Mark Woods 1, 3
Affiliation  

Relaxometric analyses and in particular the use of fast-field cycling techniques have become routine in the study of paramagnetic metal complexes. The field dependence of the solvent proton relaxation properties (nuclear magnetic relaxation dispersion, NMRD) can provide unparalleled insights into the chemistry of these complexes. However, analyzing NMRD data is a multiparametric problem, and some sets of variables are mutually compensatory. Specifically, when fitting NMRD profiles, the metal–proton distance and the rotational correlation time constant have a push–pull relationship in which a change to one causes a predictable compensation in the other. A relaxometric analysis of four isomeric chelates highlights the pitfalls that await when fitting the NMRD profiles of chelates for which dissociative water exchange is extremely rapid. In the absence of independently verified values for one of these parameters, NMRD profiles can be fitted to multiple parameter sets. This means that NMRD fitting can inadvertently be used to buttress a preconceived notion of how the complex should behave when a different parameter set may more accurately describe the actual behavior. These findings explain why the effect of very rapid dissociative exchange on the hydration state of Gd3+ has remained obscured until only recently.

中文翻译:

极快地交换Gd3 +螯合物的弛豫特性分析:比较四种Isomeric螯合物的经验教训。

在顺磁性金属配合物的研究中,惯性测量分析,尤其是快速场循环技术的使用已成为常规。溶剂质子弛豫特性(核磁弛豫弥散,NMRD)的场依赖性可以为这些配合物的化学性质提供无与伦比的见解。但是,分析NMRD数据是一个多参数问题,并且某些变量集是相互补偿的。具体来说,当拟合NMRD轮廓时,金属-质子距离和旋转相关时间常数具有推挽关系,其中一个变化引起另一个的可预测补偿。四种异构体螯合剂的弛豫分析表明,当拟合离解水交换速度非常快的螯合物的NMRD谱图时,等待着陷阱。在缺少这些参数之一的独立验证值的情况下,可以将NMRD曲线拟合到多个参数集。这意味着,当不同的参数集可以更准确地描述实际行为时,NMRD拟合可无意间被用来支持对复合物应如何表现的先入为主的观念。这些发现解释了为什么快速离解交换对G水化状态的影响3+直到最近才被遮盖住。
更新日期:2020-07-06
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