# Proton Nuclear Magnetic Resonance Relaxation in Aqueous Sugar Solutions: Can Low-Field Nuclear Magnetic Resonance Relaxation Measurements Differentiate between “Bound” and “Free” Water?

## TL;DR

This paper explores how low-field NMR relaxation measurements can distinguish between different types of water in sugar solutions.

## Contribution

A new second-order reaction kinetics-based model is introduced for interpreting proton NMR relaxation data.

## Key findings

- Sucrose-water and sucrose-D2O systems show biexponential behavior in T1 and T2 relaxation times.
- Nonexchangeable and exchangeable protons contribute differently to relaxation times, consistent with their concentrations.

## Abstract

Understanding water interactions in complex systems is
crucial,
as they play a key role in fields such as biochemistry, pharmaceutical
formulations, and food science. Nuclear magnetic resonance (NMR) relaxation
measurements have become one of the widely used methods to visualize
various water characteristics owing to their noninvasive nature and
ease of use. However, unambiguous data interpretation can be challenging
and potentially misleading if not carefully analyzed. One such example
is the observation of multiple relaxation times, which is often linked
to different water types such as “bound” and “free”.
In this paper, we present a new approach for the interpretation of
proton NMR relaxation data using a second-order reaction kinetics-based
model. The case of first-order asymptotic analysis considering fast
proton exchange is shown to be of particular relevance. The presented
theory is tested using a series of sucrose–water and sucrose-D2O systems with varying sucrose content. The comparison of
these systems reveals a biexponential behavior in both T
1 and T
2 relaxation times.
These observations are interpreted by considering both nonexchangeable
and exchangeable protons in the system, with the corresponding contribution
coefficients following trends consistent with the concentrations of
these proton types.