University of Oulu

Håkansson, P. (2021). Relaxometry models compared with Bayesian techniques: ganglioside micelle example. Physical Chemistry Chemical Physics, 23(4), 2637-2648.

Relaxometry models compared with Bayesian techniques : ganglioside micelle example

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Author: Håkansson, Pär1
Organizations: 1NMR Research Unit, University of Oulu, P.O. Box 3000, 90014 Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 3.4 MB)
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Language: English
Published: Royal Society of Chemistry, 2021
Publish Date: 2021-01-27


In this work a methodology to perform Bayesian model-comparison is developed and exemplified in the analysis of nuclear magnetic relaxation dispersion (NMRD) experiments of water in a ganglioside micelle system. NMRD is a powerful tool to probe slow dynamics in complex liquids. There are many interesting systems that can be studied with NMRD, such as ionic and lyotropic liquids or electrolytes. However, to progress in the understanding of the studied systems, relatively detailed theoretical NMRD-models are required. To improve the models, they need to be carefully compared, in addition to physico-chemical considerations of molecular and spin dynamics. The comparison is performed by computing the Bayesian evidence in terms of a thermodynamic integral solved with Markov chain Monte Carlo. The result leads to a conclusion of two micelle water-pools, and rules out both less and more parameters, i.e., one and three pools. On the other hand, if only the quality of the fits is considered (i.e., mean square deviation or χ²) a three water-pool model is the best. The latter can be expected since with more adjustable parameters a better fit is more likely. Bayesian evidence is needed to rank the uncertainty of the models, and in order to explain the outcome a notation of Ockham-entropy is defined. The two approximate selection tools, Akaike and Baysian information criterions, may lead to wrong conclusions compared to the full integration. This methodology is expected to be one of several important tools in NMRD model development; however, it is completely general and should find awakened use in many research areas.

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Series: PCCP. Physical chemistry chemical physics
ISSN: 1463-9076
ISSN-E: 1463-9084
ISSN-L: 1463-9076
Volume: 23
Issue: 4
Pages: 2637 - 2648
DOI: 10.1039/D0CP04750C
Type of Publication: A1 Journal article – refereed
Field of Science: 114 Physical sciences
Funding: The COST Action CA15209 European Network on NMR Relaxometry; The Kvantum institute (University of Oulu, Finland).
Dataset Reference: Electronic supplementary information (ESI) available. See DOI: 10.1039/d0cp04750c
Copyright information: © 2021 The Author. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.