Prediction of water relaxation time using near infrared spectroscopy

Abstract

Molecular rotational relaxation time of water is believed to be an important parameter to evaluate the deterioration rate of biomaterial. In this work, we proposed and verified a method of using Fourier‐transform near infrared spectroscopy, which has advantages of non‐invasion, low‐cost, high spatial resolution as well as being time efficient, to predict the relaxation time of water in biomaterial. The Langevin equation of rotational Brownian motion of water dipole with double‐fold cosine potential barrier, solution of which gives the relaxation time as a function of potential barrier height, was applied to water–saccharide systems. We assumed that this potential barrier height is comparable to the increase of hydrogen bond strength of water in saccharide solution. The hydrogen bond strength values of pure water and saccharide solutions were calculated from the measured NIR absorbance band of water at 4500 –5500 cm−1. The relaxation times yielded by this method are in good agreement with those measured by dielectric spectroscopy. Practical Applications Water plays important role in the investigation of long‐term preservation of biomaterials, since it is the medium of many chemical reactions which eventually lead to the deterioration. In principle, both cryopreservation and dry‐preservation involve the reduction of the mobility of water molecules to reduce chemical reaction rates. The rotational relaxation time as an indicator of molecular mobility of water was proved directly related to the protein deterioration rate. Compared with conventional methods of measuring water relaxation time such as dielectric spectroscopy or magnetic resonance, FT‐IR system has many advantages: low cost, non‐invasion, time efficient, and can provide spatial resolution up to μm level with infrared microscope. Therefore, our method may provide convenience to monitor crop growth and evaluate the quality of food in storage.

A method for measuring dielectric relaxation of water by NIR spectroscopy: Applicability and application to measurement of water diffusion coefficient

“…Lysozyme has been found having much weaker binding effect on water than the saccharides, evidenced by the shorter relaxation time and higher ν2 + ν3 peak wave numbers, equivalently weaker hydrogen bond strength in lysozyme solution at the same solute weight fraction. Binding ability difference was also found among saccharides in our previous work (Zhang et al, 2022) as both τ IR and τ DS SUM of monosaccharide solutions (glucose and galactose) are longer than disaccharide solutions (maltose, sucrose and trehalose). In general, the hydrogen bond state of water is subject to the functional groups and volume of solutes (Gabriel et al, 1998).…”

“…By definition, the τ DS SUM rather than τ DS RAW should be compared with τ IR since it corresponds to only water‐originated relaxation processes. However, τ DS SUM and τ DS RAW are numerically close especially when the solute effect is weak (Zhang et al, 2022). Also, for the samples where water molarity cannot be accurately determined, the τ DS SUM can be approximated by τ DS RAW .…”

“…In previous work (Zhang et al, 2022) we used saccharide solution as example to prove that the dielectric relaxation time of water can be calculated through the area ratio and wave numbers of S 0 , S 1 and S 2 of the NIR ν2 + ν3 combination band. The corresponding OH stretch frequency of S i peak, , can be known by solving the following equations: and where (1590 cm −1 ) and (3706 cm −1 ) are the HOH bending and OH stretching frequency of gas phase (Seki et al, 2020), and are the corresponding stretching and bending wavenumber of the S i peak, respectively.…”

“…For a proper comparison between the relaxation time measured by dielectric spectroscopy ( τ DS ) and NIR spectroscopy ( τ IR ), we quantitatively isolated the contribution of water molecules to the dielectric loss spectrum of solution by comparing water molarity of solution with pure water (Zhang et al, 2022). According to the Onsager‐Oncley expression (Raicu & Feldman, 2015), the dielectric strength is proportional to the number of the target dipoles per unit volume: where μ is the dipole moment of target molecule, k is Boltzmann constant, ε 0 is the vacuum permittivity, N p is the number of target molecules and V is the volume of the measured system.…”

“…The storage stability of biomaterial depends strongly on water molecular mobility (Buitink et al, 1998; Fundo et al, 2015; Rahman, 2009), which is subject to plural factors (solute, temperature, etc.) and can be quantified by measurable parameters, such as the waver number of infrared absorbance peak (Carpenter & Crowe, 1989; Kealley et al, 2008; Zhang et al, 2022), dielectric relaxation (Fung et al, 2018; Wei & Shirakashi, 2020a), nuclear magnetic resonance (NMR) relaxation (Choi & Kerr, 2003; Kealley et al, 2008), as well as water activity. Each of these parameters can be related with either a practical purpose or another parameter: Inoue et al used NMR relaxation time to evaluate degeneration of sweet potato and the temperature stresses of other crop plants (Funaba et al, 2006; Iwaya‐Inoue et al, 2004; Iwaya‐Inoue’ et al, 1993), and dielectric relaxation was correlated with water activity in saccharide aqueous solution (Ikeda et al, 2011) and protein deterioration (Wei & Shirakashi, 2020a).…”