Molecular structures were drawn using the Fujitsu SCIGRESS 2.0 software (Marchand et al. 2014). Their principal symmetry axes were orientated along the x-axis of the Cartesian system. A molecule of saccharide was situated inside of a triaxial elypsoid. The long axis of that ellipsoid was accepted to be the x-axis. The shortest axis quasi-perpendicular to either the pyranose or furanose ring was considered as the z-axis. The y-axis was quasi-parallel to those rings plane. The magnetic field was fixed in the same direction, along the x-axis with the south pole from the left side. Subsequently, involving Gaussian 0.9 software, equipped with the 6-31G** basis (Frisch et al. 2016) i.e. equipped with multiple polarization functions (Frisch et al. 1984), the molecules were optimised and all values of bond length, dipole moment, health of formation, bond energy and total energy for the systems were computed.

In the next step, the tendency of the static magnetic field (SMF) influence, employed as Arbitrary Field Unit (AFU) (1 AFU > 1000 T), upon optimised molecules was computed with Amsterdam Modelling Suite software (Farberovich and Mazalova 2016; Charistos and Muñoz-Castro 2019) and the NR_LDOTB (non-relativistically orbital momentum L-dot-B) method (Glendening et al. 1987; Carpenter and Weinhold 1988). Following that step, values of bond length, dipole moment, health of formation equal to the energy of dissociation and charges at the atoms, were calculated using Gaussian 0.9 software equipped with the 6-31G** basis (Frisch et al. 2016).

Visualisation of molecules in the coordinate system was performed involving the HyperChem 8.0 software (Froimowitz 1993).

This aldohexose resides chiefly in the cyclic form of α- and β-pyranose (Fig. 1). The thermodynamically less stable open-chain molecule spontaneously isomerises into one of two anomeric pyranoses (Tomasik 1997; Tomasik 2007a;, 2007b; Keung and Mehta 2015; Churuangsuk et al. 2018).

Both anomers of D-glucose, that is, α- and β-D-glucose are utilied in organisms of flora and fauna as a main source of energy (Domb et al. 2019). They are directly metabolised in the body. In human organisms, that energy is generated chiefly from glycogen stored in the liver. Under specific cases, D-glucose is delivered into organisms as a component of food, for instance, a spice and supplement of diet injected as an additional source of energy (World Health Organization 2019). D-Glucose is metabolised in enzymatic processes. The first step of that process involves its esterification with adenosine-triphosphate (ATP) at the C6-OH group (Heinrich et al. 2014). Within the Entner-Doudoroff pathway operating in Gram-negative bacteria, certain Gram-positive bacteria and archaea begin at the same reaction site engaging the C1 atom (Conway 1992).

One of the important enzymatic reactions of D-glucose, called the Maillard reaction, is known as the enzymatic browning reaction. In the reaction of D-glucose with lysine and arginine, residues of the protein pentosidine are formed (Sell and Monnier 1989). Pentosidine is formed most readily from pentoses, but glucose, fructose and other saccharides may also react in such a manner.

Performed computations showed that, based on the criterion of heat of formation, the α-D-anomer was slightly more stable than the β-D-anomer (Table 1). The stability of both anomers decreased unevenly against the applied SMF flux density. The β-D-anomer reacted more strongly to SMF. It was also associated with a significantly stronger increase in dipole moment. These trends fitted results performed with density functional/ab initio computation in silico. The same computations for both anomers of D-glucose in water pointed to the α-D-anomer as more stable than the β-D-anomer (Facundo Ruiz et al. 2005). However, electrochemical oxidation of the α-D-anomer glucose and β-D-anomer on the anode surface showed that the β-D-anomer was much more reactive (Largeaud et al. 1995).

The charge density at particular atoms of both anomers varied irregularly with an increase in the flux density (Table 2). An increase in the SMF flux density produced a more remarkable decrease in the electron density at the 1,2,4,5,6,7,11,12,15 and 20 atoms of the β-anomer than at the same atoms of the α-anomer. Extremely strong, but an opposite effect was noted at the C2 and H21 atoms. Both atoms were bound to one another and the C2 atom was in the vicinity to the endocyclic O7 atom. Thus, observed effects could result from electrostatic interactions through space involving a partially weakened lone electron pair of the oxygen atom. An increase in the electron density produced by SMF was observed at C1β (atom C1, β-anomer), C4β, C5, O8α and H14α atoms, whereas the electron density remarkably decreased at C1α, C2, O7α, O7β, O8β, O9, O10 and H15α atoms. Small and irregular changes of electron density could be observed at C3, C4α, O11, H13, H14β, H15β and H16 atoms. Remarkable changes were noted at the C1, C5 and C2 atoms.

In fact, in a real molecule, all hydrogen atoms of the OH groups changed their positions by free rotation because of the practically identical energy between particular rotamers of those groups. This problem was well illustrated by the results of computation for the twin hydrogen H18 and H19 atoms. Due to accepted computation methodology, the free rotation around the C5-C6 bond was eliminated. In consequence, the H18 atom holds a considerable negative charge, whereas the H19 atom took increased positive charge density. As a result, results of the computations for particular rotamers could not be interpreted in detail in this case as well as in the cases of subsequently discussed carbohydrates. For D-glucose, these restrictions were also valid for the H20, H21, H22, H23, H24 and O12 atoms. Results of detailed analysis of the remaining O7, O8, O9, O10, O11, C1, C2, C3, C4, C5, C6, H13, H14, H15 and H16 atoms are identified in Table 2.

Generally, atoms of the pyranose skeleton were moderately sensitive to SMF, although increasing SMF flux density considerably decreased basicity of the ring O5 atom in the β-anomer. The O and H atoms were the most and least sensitive, respectively, to the effect of SMF. In the group bound to the C3 atom perpendicularly to the field, an increase in the flux density decreased the negative charge density at the O10 atom and the positive charge density at the H22 atom. It suggested a decrease in the acidity of that group. In the quasi-parallel orientated O8-H20 group, SMF evoked the opposite effect. Thus, the accepted orientation of the molecule under consideration appeared very essential. One of the biochemically most important OH group at the C6 atom turned more acidic and that effect could noticeably influence the biochemistry of D-glucose.

Review of Table 2 also identified that increased positive charge density at the C1 in the α-anomer favoured attacks of various Lewis bases at this position. Such reactions were also important from the biochemical point of view. Simultaneously, the reactivity of the β-anomer involving this position was partly inhibited as the positive charge density at this atom declined under the influence of SMF. The SMF induced an increase in the positive charge density at the C6 atom. It was non-beneficial for enzymatic processes starting from esterification with adenosine-triphosphate (ATP) at C6-O24 and the functioning of the Entner-Doudorff metabolic pathway (Conway 1992).

An insight into the effect of SMF upon the length of bonds in the molecules of both anomers (Table 3) suggested that these changes resulted from a deformation of the molecules and their deviation from the initially-established location of the molecules along the x-axis. Tendencies of the changes of computed values with an increase in the flux density (Table 3) pointed to a uniform increase in the length of the valence bonds, that is, to weakening their energy. Simultaneously, strongly polarised bonds, with participation of the C1 atom, were regularly shortened, whereas the length of the C3-C4, C3-O10, C3-C5 and C5-O7 bonds varied irregularly. Generally, in the 28 analysed bonds in each anomer, 16 bonds were elongated, four bonds were shortened and the length of eight bonds varied irregularly against increased SMF flux density. These results supported the hypothesis on the weakening of the bonding electron pair. The SMF generated shortening of the C1-O8 bond and elongation of the O8-H20 bond seemed to be the most important. This effect implied the increased susceptibility of the hemi-acetal ring to its opening. Hence, SMF should favour a shift of the mutarotation equilibrium towards the open chain form of D-glucose. This fact could promote the Maillard reaction which proceeds on the open chain forms of saccharides (Grandhee and Monnier 1991).

Visualisation of the data from Table 3 (Fig. 5) also includes non-analysable bonds. The conformation of particular anomers is presented in the form of superposition of the molecules without SMF (green colour) and molecules in the SMF of 100 AFU (blue colour). The oxygen atoms are marked red. Structures a and d are given as the projection along the y-axis, whereas the b and e structures are projections along the z-axis. Structures c and f are superpositions of the same molecules demonstrating the SMF flux density-dependent change in the bond lengths in the molecules under consideration. Structures in Fig. 5 demonstrate a small effect of SMF upon the conformation of both anomers and a significant effect upon the bond lengths of some peripheral C-H bonds. They are the C6-H19 and O10-H22 bonds. An increasing flux density generated a considerable negative charge density at the H18 atom. It made the O12-H24 bond relatively slightly polarised, that is, capable of interaction of electrons of that bond with SMF.

This aldohexose resides in two anomeric pyranose forms (Fig. 2) interconverting through an open-chain thermodynamically unstable structure. α-D-Galactopyranose (α-D-Galp) can be found in oligo- and polysaccharides, plant mucous and gums and plant glycosides (Maton et al. 1993; Tomasik 1997; Campbell et al. 2006; Tomasik 2007a; Tomasik 2007b; Heldt and Piechulla 2010; Keung and Mehta 2015; Churuangsuk et al. 2018; Reynolds et al. 2019). Jointly with α-D-glucose, it constitutes lactose, known as milk sugar. In fauna organisms, it is hydrolytically liberated from lactose. In these organisms, it is converted into galactoso-6-phosphate involving ATP α-D-galactose. The latter reacts with galactoso-1-phosphate uridinyltransferase into UDP-galactose which is subsequently transformed with UDP-galactoso-4-epimerase into UDP-glucose (Candy 1980). Microbiological oxidation of the CH₂OH group of α-D-galactose provides galacturonic acid which essentially inhibits progress of atherosclerosis (Parikka et al. 2015).

Based on computed values of heat of formation, one could note that the α-anomer was more stable than the β-anomer independently of applied SMF flux density. However, as shown by changes of dipole moment (Table 4), the β-anomer was more polarised with an increase in the flux density. As in anomers of D-glucose, the charge density at particular atoms irregularly varied with increasing flux density. In contrast to anomers of D-glucose, in anomers of D-galactose, the negative charge concentrated at the O7, C5 and C4 atoms and SMF flux density turned it more negative. The negative charge also concentrated at the C2-H14 atom bound to it (Table 5). The positive charge density was noted at the C3 and C1 atoms, as well as the H15 and H13 atoms bound to them, respectively. These effects generated an increase in the corresponding bond lengths (Table 5).

Due to an increase in the positive charge at the anomeric C6 atom, one could assume a facilitating role of SMF in formation of galactoso-1- phosphate. In addition, the effect of SMF upon the charge density suggested favouring oxidation of D-galactose into galacturonic acid.

Particular attention should be paid to the C5, C6 and H19 atoms. SMF remarkably changed their charge distribution. The negative charge shifted to the C5 and H19 atoms, whereas the C6 atom lost this charge to a considerable extent. The strongest influence was evoked by SMF upon the bonds orientated under 45° to the field strength lines, that is, to the x-axis. Extremal elongation was observed for the C6-H19 and O10-H22 bonds (Table 6). Simultaneously, the C6-H18 bond distinctly shortened. It should be underlined that both H18 and H19 were twin atoms bound to the C6 atom. Thus, observed differences could not originate from different intramolecular electronic interactions and completely different situations by those atoms with respect to the SMF line should be responsible for it.

Unlike in D-glucose, the positive charge density at the C1 atom decreased with an increase in the flux density. Thus, reactions with any Lewis base would be obstructed. Simultaneously, the flux density up to 0.1 AFU increased the negative charge density at the C6 atom. It would favour phosphorylation at the vicinal hydroxyl group. However, higher flux densities turned the charge density at that atom to positive. Thus, the increase in the charge density with the flux density inhibited that reaction.

The susceptibility of D-galactose to the ring opening and to the Maillard reaction depended on its anomer. The C1-O8 bond in the α-anomer varied irregularly with the flux density but, generally, the susceptibility of that anomer to the ring opening was low. That bond in the β-anomer regularly decreased with an increase in the applied flux density. Simultaneously, the O8-H20 bond was shortened in the α-anomer and elongated in the β-anomer (Table 6).

Data shown in Table 6 allowed the visualisation of the effect of SMF upon anomers of D-galactose. Structures in Fig. 6 demonstrate a slight effect of SMF upon the conformation of both anomers and significant effect upon the bond lengths of some peripheral C-H bonds. They were the C6-H18 and O10-H22 bonds. An increasing flux density generated a considerable negative charge density at the H22 atom making the C6-H18 bond relatively slightly polarised. Therefore, that bond was capable of interaction with the electrons of that bond with SMF. In the O10-H22 bond, both its partners carried negative charge. This effect and its origin was the same as that observed in D-glucose anomers.

D-Fructose, a ketohexose, is a typical monosaccharide of a floral provenance. In the free form, it resides in fruits, honey and flower nectar. In a bound form, it can be found in several di-, oligo- and polysaccharides, for instance, sucrose, raffinose and inulin, respectively. Its presence in the organisms of fauna is a consequence of consumption of plant food. In mammals, free fructose is found in their semen (Maton et al. 1993; Tomasik 1997; Campbell et al. 2006; Tomasik 2007a; Tomasik 2007b; Heldt and Piechulla 2010; Keung and Mehta 2015; Churuangsuk et al. 2018; Reynolds et al. 2019). Humans metabolise D-fructose almost entirely in the liver, where it is directed towards replenishment of liver glycogen and triglyceride synthesis. In muscles and fat tissues, D-fructose metabolism is initiated by phosphorylation with hexokinase at the O11 atom, turning it into fructose-1-phosphate. The latter enters the glycolysis pathway. In the liver, the metabolism of D-fructose is initiated by fructokinase which forms fructose-1-phosphtate engaging the O10 atoms, respectively (Maton et al. 1993; Tomasik 1997; Hames and Hooper 2004; Campbell et al. 2006; ; Tomasik 2007a; Tomasik 2007b; Heldt and Piechulla 2010; Keung and Mehta 2015; Churuangsuk et al. 2018; Reynolds et al. 2019) .

Alcohol fermentation and the Maillard browning reaction are other enzymatic processes common for D-fructose. In the Maillard reaction, the anomeric C1 carbon atom is first engaged (Grandhee and Monnier 1991).

D-Fructose resides in four mutually fast interconverting structures, including α-D-fructopyranose (α-Frup), β-D-fructopyranose (β-Frup), α-D-fructofuranose (α-Fruf) and β- D-fructofuranose (β-D-Fruf) (Fig. 3). Computations of the heat formation (Table 7) pointed to α-D-Fruf and α-D-Frup being the most and least stable, respectively, amongst the four anomers taken into account (Fig. 3). Applying SMF of 0.1 AFU, the flux density did not change their positions in this group. At 1 AFU, based on that criterion, β-D-Fruf became the most stable, but a further increase in the flux density returned α-D-Fruf to the position of the most stable anomer. α-D-Frup holds the position of the least stable anomer at SMF up to 10 AFU. At 100 AFU, β-D-Frup became the least stable. The dipole moment of particular anomers also changed with an increase in the applied flux density. However, these changes were in no simple relationship to the stability of particular anomers. It suggested deformation of their initial structure by polarisation of particular bonds. They could also result from departure from their initial situation in the Cartesian system. This was confirmed by computed changes of charge density and bond lengths (Tables 8–11). Inspection of Table 8 showed that, in α- and β-D-fructopyranoses, the negative charge density essential for the phosphorylation reaction at the O12 atom was lower in the α-anomer and it fairly linearly decreased against increasing flux density. Thus, that anomer should be more reactive than the β-anomer. The Maillard reaction required the positive charge density at the C1 atom. Without SMF, the β-anomer showed a more positive charge at that atom. It decreased against increasing flux density. The α-anomer carried considerably lower positive charge density which additionally decreased against the flux density up to 10 AFU and then increased regularly up to over twice at 100 AFU.

The strongest changes in the electron density occurred at the C1, O12α, H13α, H22β and H24β atoms. Thus, both anomers are clearly distinguished from one another.

Structural deformations of the α- and β-D-fructopyranose molecules in SMF (Table 9 and Fig. 6) resembled those observed for D-glucose and D-galactose anomers. Considerable elongations were observed for the C1-H13, O11-H22 bonds and C6-H19α bonds, whereas the twin C6-H18 bond was only slightly shortened. It was another illustration of the importance of the position of the bonds with respect to the SMF field.

In the case of D-fructofuranoses, comparison of the negative charge density (Table 10) at the O12 and O11 atoms being potentially the reaction sites for the phosphorylation suggested that the β-anomer should react more readily than the α-anomer. An increase in the SMF flux density was not beneficial for this reaction as the value of the charge density at these atoms turned less negative. The positive charge density at the C4 and C1 atoms, being the potential reaction site for the Maillard reaction, were higher in the β-anomer and only slightly decreased with increasing AFU. SMF at 100 AFU generated an essential increase in the positive charge density at the C1β, O9β, O12α and H21α atoms. At the same time, that charge decreased at the C2α, C5β, H17α, H24α and particularly at the H20β atom.

Anomers of D-fructofuranoses were less susceptible to structural deformations evoked by SMF (Table 11 and Fig. 8). In the α-anomer, the O12-H24, O9-H22 and C5-H17 bonds were longer and that effect was noticeable just at 100 AFU. The β-anomer was deformed chiefly by elongation of the O9-H22, C1-C2 and O8-H20β bonds. Untypically, the ring was also deformed by the elongation of the C2-C1 bond.

D-xylose, aldopentose, is a mono-sugar residing almost exclusively in plants. As a component of hemicelluloses, it constitutes biomass. In the sphere of fauna, D-xylose was also found in some species of Chrysolinina beetles. It co-constituted cardiac glycosides of their defensive glands (David Morgan 2004).

Organisms of fauna receive xylose from their diet. Eukaryotic micro-organisms employ the oxidato-reductase pathway to metabolize D-xylose (Gabaldon et al. 2005). D-xylose is metabolised by humans involving protein xylosyltransferases (XYLT1, XYLT2) which transfer xylose from UDP to a serine in the core protein of proteoglycans (Stoolmiller et al. 1972; Gotting et al. 2000). Mammals metabolise D-xylose with D-xyloisomerase (Ding et al. 2009; Huntley and Patience 2018). Recently, a highly efficient low-temperature, atmospheric-pressure enzymatic process of the hydrogen production from D-xylose was presented. It involved thirteen enzymes, including a novel polyphosphate xylulokinase (Del Campo et al. 2013). In another technically important reaction, D-xylose is used for production of furfural, a precursor for synthetic polymers and to tetrahydrofuran (Hoydonckx et al. 2007). In the initial step, hemicellulose is hydrolysed in an acid-catalysed process (Binder et al. 2010; Millán et al. 2019). That process starts from the protonation of the D-xylopyranose molecule at the O8 atom.

It was also found that D-xylose could be useful in therapy of COVID-19 (Cheudjeu 2020). The latter interacts with D-xylose significantly stimulating the biosynthesis of sulphated glycosylamineglycans (GAGs), particularly heparan sulphate (HS). GAGs, especially HS and D-xylose interact with oral non-steroidal anti-inflammatory drugs, active in lung infections.

D-Xylose resides in the form of α- and β-xylopyranoses (Xylp) (a and b), as well as α- and β-xylofuranoses (Xylf) (c and d) (Fig. 4).

The heat of formation criterion pointed to β-D-xylopyranose as the most stable amongst four anomers of D-xylose (Table 12). It is distinguished from other anomers with a considerably low dipole moment. The increase in the SMF flux density regularly increased the dipole moment of all anomers and, at the same time, destabilised them in terms of their heat of formation values. In both D-xylopyranoses, the metabolic reactions should be promoted by the high positive charge density at the O6 atom and low negative charge density at the O8 and O9 atoms. Data in Table 13 showed that the influence of SMF upon the O6, O9 and O8 atoms was negligible, noticeable and strong, respectively. A considerable increase in the positive charge density took place at the C1α, C5 and O8 atoms, whereas its decrease was observed at the C2 and H18β atoms. The SMF flux density promoted reactivity at the C1, especially the C1α atom, slightly promoted reactions at the O9 atom and strongly increased the reactivity of the O8 atom. Taking these arguments under consideration, the α-anomer was more reactive at the C1 atom when residing without SMF and, in SMF, the β-anomer reacted more readily. The reactivity at the O8 atom in the β-anomer was slightly higher when SMF was applied and the reactivity at the O7 atom in the α-anomer was definitely higher.

As shown in Table 14 and Fig. 9, only the O8-H18 bond suffered considerable elongation in SMF. Less intense elongation was observed at the C4-H14 and C5-H15 bonds in both anomers. That effect was in line with the preference for the elongation of the bonds orientated under approximately 45° with respect to the x-axis.