Thermodynamic properties of myo-inositol (original) (raw)
Highlights
- •
Temperature dependence of heat capacity of myo-inositol has been measured by precision adiabatic vacuum calorimetry. - •
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The character of heterodynamics of structure was detected. - •
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The Quartz Crystal Micrabalance technique was used for recording of the temperature dependence of the sublimation rate.
Abstract
In the present work, the temperature dependence of heat capacity of vitamin B8 (myo-inositol) has been measured for the first time over the range from 8
K to 340
K by precision adiabatic vacuum calorimetry. Based on the experimental data, the thermodynamic functions of the vitamin B8, namely, the heat capacity, enthalpy _H_°(T)–_H_°(0), entropy _S_°(T)–_S_°(0) and Gibbs function _G_°(T)–_H_°(0) have been determined for the range from T
→
0
K to 340
K. The value of the fractal dimension D in the function of multifractal generalization of Debye’s theory of the heat capacity of solids was estimated and the character of heterodynamics of structure was detected. The enthalpy of combustion (−2747.0
±
2.1)
kJ·mol−1 of the vitamin B8 was measured for the first time using high-precision combustion calorimeter. The standard molar enthalpy of formation in the crystalline state (−1329.3
±
2.3)
kJ·mol−1 of B8 at 298.15
K was derived from the combustion experiments. Using combination of the adiabatic and combustion calorimetry results the thermodynamic functions of formation of the myo-inositol at T
=
298.15
K and p
=
0.1
MPa have been calculated. The low-temperature X-ray diffraction was used for the determination of coefficients of thermal expansion.
Introduction
Myo-inositol (CAS: 87-89-8) is a sugar alcohol (isomer of glucose) widely distributed in plant and animal tissues. It is found in food, for example cereals with high bran content (buckwheat), nuts, beans, and fruit [1]. It plays an important role as the structural basis for a number of secondary messengers in eukaryotic cells, including inositol phosphates (phytic acid), phosphatidylinositol and phosphatidylinositol phosphate lipids. Inositol itself is not considered as
a vitamin because it can be synthesized by the human body. On the other hand, myo-inositol was classified as a member of the vitamin B-complex (often called vitamin B8). Patients suffering from clinical depression generally have decreased levels of inositol in their cerebrospinal fluid [2].
This work is a continuation of systematic studies of vitamins B. Earlier in the articles [3], [4], [5], [6], we have investigated the thermodynamic properties of vitamins Bn (n
=
2, 3, 9, 12). The goals of this work include calorimetric determination of the standard thermodynamic functions of the myo-inositol with the purpose of describing biochemical and industrial processes with its participation.
Section snippets
Sample
Myo-inositol was purchased from NutriVitaShop. For phase identification, an X-ray diffraction pattern of the vitamin B8 sample was recorded on a Shimadzu X-ray diffractometer XRD-6000 (CuKα radiation, geometry θ–2θ) in the 2θ range from 5° to 60° with scan increment of 0.02°. The water content in myo-inositol was determined by Karl Fischer titration. The water content of the compound is below the detection limit (0.05
wt%), so there is no crystallization and sorption water in the compound. The
Heat capacity
The Cpo measurements were carried out between 8
K and 340
K (see Table 1). The mass of the sample loaded in the calorimetric ampoules of the BKT-3.0 device was 0.5418
g. A total of 183 experimental Cpo values was obtained in two series of experiments (Fig. 1). The heat capacity of the sample varied from 20% to 50% of the total heat capacity of calorimetric (ampoule
substance) over the range between 8
K and 340
K. The experimental points of Cpo within the temperature interval (8.5–340)
K were fitted
Conclusions
The general aim of these investigations was to report the results of the thermodynamic study of the myo-inositol. The heat capacity of this vitamin B8 was measured over the temperature range from (8 to 340) K, the thermodynamic functions were calculated and the fractal dimension D evaluated. Thermochemical parameters of formation are determined by combining the data obtained by using combustion calorimetry and heat capacity measurements.
Acknowledgements
The work was performed with the financial support of the Russian Foundation of Basic Research (Project Number 16-03-00288). This work has been partly supported by the Russian Government Program of Competitive Growth of Kazan Federal University.
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2020, Journal of Chemical Thermodynamics
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