THz Spectroscopy of Bound Water in Glucose: Direct Measurements from Crystalline to Dissolved State
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THz Spectroscopy of Bound Water in Glucose: Direct Measurements from Crystalline to Dissolved State O. P. Cherkasova 1,2
3
2
& M. M. Nazarov & M. Konnikova & A. P. Shkurinov
2,4
Received: 10 October 2019 / Accepted: 20 February 2020/ # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract
The main reason for the alternation of terahertz (THz) response in biological samples is the transition of a part of water from its free to bound state and back. To analyze such results, a precise spectrum of bound water within THz range should be known. The suggested wet powder spectroscopy method is optimal for this task. We measured the THz transmission of dry glucose pressed into pellets. Then, we added a small amount of water to these pellets and again measured the THz spectra. The contribution from the free water state starts to appear in resulting THz spectra after water concentration in glucose samples reaches 14– 16%. Just below is the optimal point to extract the spectral contribution from bound water. We extracted the absorption and refraction spectra of bound water and confirmed that they are an order of magnitude weaker than those of free water within 0.07–1-THz range. Keywords Terahertz time-domain spectroscopy . Transmission . Glucose . Bound water . Wet powder . Solution
1 Introduction High water content in biological tissues and liquids determines the nature of their dielectric response in the terahertz (THz) frequency range [1, 2]. Water can be classified as bulk water (it does not form strong bonds with molecules) and bound water (it surrounds molecules and
* O. P. Cherkasova [email protected]
1
Institute of Laser Physics of the Siberian Branch of the Russian Academy of Sciences, Novosibirsk 630090, Russia
2
Institute for Problems of Laser and Information Technologies of the Russian Academy of Sciences Branch of Federal Scientific Research Center “Crystallography and Photonics” of the Russian Academy of Sciences, Shatura 140700 Moscow Region, Russia
3
Kurchatov Institute National Research Center, Moscow 123182, Russia
4
Lomonosov Moscow State University, Moscow 119991, Russia
Journal of Infrared, Millimeter, and Terahertz Waves
interacts with them) [3, 4]. With a strict analysis, it is necessary to separate strongly bound and weakly bound water [5]. Strongly or weakly bound water, as well as free (unbound) water, makes valuable but different contributions to the THz response of biological objects [1, 5, 6]. Reorientation time of hydrogen-bonded water molecules changes in the vicinity of a biomolecule [7]. This encourages us to use THz spectroscopy to study different forms of water in biological media, including blood, tissues, and solutions [6, 8–11]. The transition of water from its free to a bound state and back is the reason of changes in the THz response of biological objects [12]. For an accurate interpretation of the results, we should know the spectrum of bound water. It is a challenge, since the contribution of free water to the THz spectrum of the solutio
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