Cori Ester as the Ligand for Monovalent Cations

Gerty T. and Carl F. Cori discovered, during research on the metabolism of sugars in organisms, the important role of the phosphate ester of a simple sugar. Glucose molecules are released from glycogen—the glucose stored in the liver—in the presence of phosphates and enter the blood as α-D-glucose-1-phosphate (Glc-1PH2). Currently, the crystal structure of three phosphates, Glc-1PNa2·3.5·H2O, Glc-1PK2·2H2O, and Glc-1PHK, is known. Research has shown that reactions of Glc-1PH2 with carbonates produce new complexes with ammonium ions [Glc-1P(NH4)2·3H2O] and mixed complexes: potassium–sodium and ammonium–sodium [Glc-1P(X)1.5Na0.5·4H2O; X = K or NH4]. The crystallization of dicationic complexes has been carried out in aqueous systems containing equimolar amounts of cations (1:1; X–Na). It was found that the first fractions of crystalline complexes always had cations in the ratio 3/2:1/2. The second batch of crystals obtained from the remaining mother liquid consisted either of the previously studied Na+, K+ or NH4+ complexes, or it was a new sodium hydrate—Glc-1PNa2·5·H2O. The isolated ammonium–potassium complex shows an isomorphic cation substitution and a completely unique composition: Glc-1PH(NH4)xK1−x (x = 0.67). The Glc-1P2− ligand has chelating fragments and/or bridging atoms, and complexes containing one type of cation show different modes of coordinating oxygen atoms with cations. However, in the case of the potassium–sodium and ammonium–sodium structures, high structural similarities are observed. The 1D and 2D NMR spectra showed that the conformation of Glc-1P2− is rigid in solution as in the solid state, where only rotations of the phosphate group around the C-O-P bonds are observed.


Introduction
Carbohydrates are a very important class of biological molecules.Commonly called sugars, they perform various functions in living organisms, from providing energy, through storing it, to building cellular structures.They are the only compounds that can be created in the process of synthesis from water, carbon dioxide, and chemical energy during photosynthesis; most of the compounds in this group are of plant origin.In the animal world, it is possible to synthesize sugars using, among other things, amino acids and lipids [1].In the 19th century, physiologist Claude Bernard discovered glycogen, a polysaccharide composed of glucose residues connected by α-1,4-glycosidic bonds.It serves as a glucose reserve; when the body is in good condition, the liver stores excess sugar in the form of glycogen, while in states of hypoglycemia, it breaks down, and the released glucose molecules allow the normalization of sugar levels [2].
Gerty and Carl Cori studied glycogenolysis-the process of glycogen breakdown which, in the first stage, produces glucose-1-phosphate (called Cori ester) and a chain of sugar molecules shortened by one unit [3,4].They determined the structure of the compound and also identified the enzyme that catalyzes its formation, i.e., phosphorylase [3].During their research, they determined for the first time the essence of the function of carbohydrates in animal bodies, as well as the influence of insulin and adrenaline on the blood glucose level.
In the functioning of the body (with the exception of organic compounds), elements that regulate physiological functions are essential [5].Such elements include water and a group of macro-elements: sodium, potassium, magnesium, and calcium.Their deficiency or excess causes disturbance of the alkaline-acid balance, heart problems, and muscle dysfunction.At the cellular level, Na ions play important roles in biological communication to trigger responses.The rapid inflow of sodium ions into the cell triggers the activation of neurons, which allows the transmission of nerve impulses [5].The Na + K + -ATPase, also called the sodium pump, is a cell membrane protein involved in the process of monovalent cation transport.This sodium-potassium pump actively transfers potassium into the cell, maintaining the correct cationic composition on both sides of the cell membrane.All animal cells remove Na ions and retain K. Potassium cations activate various intracellular processes, while sodium cations inside cells act as inhibitory factors [1].
Moreover, the structure of any complex containing a phosphate ligand and K and Na cations has not been investigated.
Cori ester is a very important metabolite in animal organisms.Despite the significance of this ester, only a small number of structural characterizations of its complexes with monovalent cations of biological importance have been published so far.There are four papers presenting structural studies of the crystals of complexes with the α-D-glucose-1-phosphate anion.One sodium complex (Glc-1PNa 2 •3.5•H 2 O) [15,16] and two complexes containing potassium cations have been analyzed, i.e., Glc-1PK 2 •2H 2 O [17] and Glc-1PHK [18].
Considering the coexistence and competition of various molecules and ions in body fluids, we decided to expand this set of the Cori ester complexes.The synthesis and analysis of new complexes with ammonium cations and complexes containing two types of monovalent cations in the same phase were carried out.It was demonstrated over a hundred years ago that K and NH 4 cations can exhibit the isomorphic substitution [19,20].However, in the phases containing two other cations, e.g., K and Na, Na and NH 4 , the formation of complexes in which specific cations will have preferred coordination sites for the Glc-1P 2− anions can be expected.For this reason, we decided to synthesize and obtain single crystals of the ammonium salt of α-D-glucose phosphate and complexes containing two cations by utilizing Glc-1PH 2 acid and carbonates.An X-ray structural analysis of single crystals and NMR spectroscopy of aqueous solutions were selected as the research methods.

Complexes in Solid Phase
The aim of the research presented here was to determine the role of the Cori ester (Figure 1) as a ligand coordinating monovalent cations (NH 4 , K and Na); this was possible to observe through obtaining crystalline complexes and identifying their structure (Tables S2-S8).
The first step of the synthesis was to obtain the Glc-1PH 2 acid from the potassium complex through ion exchange chromatography.The acid subsequently reacted with selected carbonates to form complexes with various stoichiometries (Scheme 1).Crystals of these complexes were obtained by crystallization using the antisolvent method: propan-2-ol was added to the aqueous solution, followed by diffusion of ethanol vapors, which caused a supersaturation of the solution.The chemical composition of the obtained crystals was different and depended on the cations present in the system (Scheme 1).During the second crystallization step, the remaining mother liquor produced previously known hydrates of sodium and potassium complexes, except for the new sodium pentahydrate Glc-1P2Na-5H2O.Structural studies were performed for the resulting crystals, including previously known complexes, with detailed data presented in Table 1.The first step of the synthesis was to obtain the Glc-1PH2 acid from the potassium complex through ion exchange chromatography.The acid subsequently reacted with selected carbonates to form complexes with various stoichiometries (Scheme 1).Crystals of these complexes were obtained by crystallization using the antisolvent method: propan-2-ol was added to the aqueous solution, followed by diffusion of ethanol vapors which caused a supersaturation of the solution.The chemical composition of the obtained crystals was different and depended on the cations present in the system (Scheme 1).During the second crystallization step, the remaining mother liquor produced previously known hydrates of sodium and potassium complexes, except for the new sodium pentahydrate Glc-1P2Na-5H2O.Structural studies were performed for the resulting crystals, including previously known complexes, with detailed data presented in Table 1 Scheme 1. Crystalline products obtained after the reaction of α-D-glucose-1-phosphate ester with monovalent cations.The first step of the synthesis was to obtain the Glc-1PH2 acid from the potassium complex through ion exchange chromatography.The acid subsequently reacted with selected carbonates to form complexes with various stoichiometries (Scheme 1).Crystals of these complexes were obtained by crystallization using the antisolvent method: propan-2-ol was added to the aqueous solution, followed by diffusion of ethanol vapors, which caused a supersaturation of the solution.The chemical composition of the obtained crystals was different and depended on the cations present in the system (Scheme 1).During the second crystallization step, the remaining mother liquor produced previously known hydrates of sodium and potassium complexes, except for the new sodium pentahydrate Glc-1P2Na-5H2O.Structural studies were performed for the resulting crystals, including previously known complexes, with detailed data presented in Table 1.* redetermination of structure [16,17].
The reaction of Glc-1PH2 with ammonium carbonate gave the expected product (Table 2).However, the most interesting are the stoichiometries of complexes containing Scheme 1. Crystalline products obtained after the reaction of α-D-glucose-1-phosphate ester with monovalent cations.Table 1.Crystallographic data for potassium/sodium Glc-1P complexes.

Identification Code Glc-1P2(NH4) Glc-1P(NH4)Na Glc-1PH(NH4)K Glc-1PHK [18]
Formula Glc-1P(NH 4 ) 2 •3H 2 O Glc-1P(NH 4 ) 1.5 Na 0.5  The Glc-1PK 1.5 Na 0.5 •4H 2 O and Glc-1P(NH 4 ) 1.5 Na 0.5 •4H 2 O are isomorphic, but the ammonium-potassium complex has a completely different composition and structure (Scheme 1, Table 2).The products of a synthesis (crystallization) in the latter system are completely unpredictable, a mixture of complexes is formed, and the crystals are of poor quality and unstable.The first product formed in the crystallization process that was identified was the acidic complex with the NH 4 :K ratio of approximately 70%:30% [Glc-1PH(NH 4 ) 0.69 K 0.31 ].Both cations occupy the same position in the crystal lattice, i.e., the isomorphic substitution occurs.Only the already known potassium complex, Glc-1PK 2 •2H 2 O, was identified in the second crystallization, while the remaining products were amorphous, which was confirmed by X-ray microdiffraction patterns.
The lattice parameters, the symmetry of crystals, and the positions of the cations in the unit cell indicate that the Glc-1PKNa, Glc-1P(NH4)Na and Glc-1P2(NH4) complexes are isomorphic (Tables 1 and 2).They all crystallize in the P 2 1 2 1 2 space group, and the two (of three) positions occupied by the cations lie on the two-fold symmetry axes (Figure 2).Research on this group of complexes revealed another interesting feature.Namely, the ammonium complex Glc-1P2(NH4) crystals are hygroscopic and stable for 1-2 months.However, the co-presence of small amounts of Na or K cations in the crystal lattice stabilizes the crystals, which do not decompose even after ten years.
two cations: K+Na, NH4+Na and NH4+K.The first two products are obtained in the reaction according to the following scheme: The Glc-1PK1.5Na0.5·4H2Oand Glc-1P(NH4)1.5Na0.5·4H2Oare isomorphic, but the ammonium-potassium complex has a completely different composition and structure (Scheme 1, Table 2).The products of a synthesis (crystallization) in the latter system are completely unpredictable, a mixture of complexes is formed, and the crystals are of poor quality and unstable.The first product formed in the crystallization process that was identified was the acidic complex with the NH4:K ratio of approximately 70%:30% [Glc-1PH(NH4)0.69K0.31].Both cations occupy the same position in the crystal lattice, i.e., the isomorphic substitution occurs.Only the already known potassium complex, Glc-1PK2·2H2O, was identified in the second crystallization, while the remaining products were amorphous, which was confirmed by X-ray microdiffraction patterns.The lattice parameters, the symmetry of crystals, and the positions of the cations in the unit cell indicate that the Glc-1PKNa, Glc-1P(NH4)Na and Glc-1P2(NH4) complexes are isomorphic (Tables 1 and 2).They all crystallize in the P 21212 space group, and the two (of three) positions occupied by the cations lie on the two-fold symmetry axes (Figure 2).Research on this group of complexes revealed another interesting feature.Namely, the ammonium complex Glc-1P2(NH4) crystals are hygroscopic and stable for 1-2 months.However, the co-presence of small amounts of Na or K cations in the crystal lattice stabilizes the crystals, which do not decompose even after ten years.In the crystals of Glc-1PKNa and Glc-1P(NH4)Na, the sodium cations have coordinates ½, 0, z, while the K/NH4 cations occupy positions x, y, z and ½, ½, z (Figure 2a,b).Due to this arrangement of atomic positions, the stoichiometry of cations K/NH4-Na in the crystal is 3/2:1/2, whereas the three ammonium cations in the Glc-1P2(NH4) complex (Figure 2c) are located in the general position on the two-fold axis (the Wyckoff position b) and are disordered around the second position of the two-fold axis (the Wyckoff posi- In the crystals of Glc-1PKNa and Glc-1P(NH 4 )Na, the sodium cations have coordinates ½, 0, z, while the K/NH 4 cations occupy positions x, y, z and ½, ½, z (Figure 2a,b).Due to this arrangement of atomic positions, the stoichiometry of cations K/NH 4 -Na in the crystal is 3/2:1/2, whereas the three ammonium cations in the Glc-1P2(NH4) complex (Figure 2c Some structural similarities can also be observed in the anhydrous structures of hydrogen phosphates, Glc-1PH(NH4)K and Glc-1PHK: the symmetry of the crystal lattice, the translation along a, the volume of the unit cell, and the anion orientation are preserved (Table 2, Figure 3).However, the isomorphic substitution of the K + cations with 69% of NH 4 + cations changed the lengths of translations b and c.This is due to replacing most of the K-O coordination bonds with the N-H-O hydrogen bonds.
positions on the 2-fold axes are marked as .
In the crystals of Glc-1PKNa and Glc-1P(NH4)Na, the sodium cations have coordinates ½, 0, z, while the K/NH4 cations occupy positions x, y, z and ½, ½, z (Figure 2a,b).Due to this arrangement of atomic positions, the stoichiometry of cations K/NH4-Na in the crystal is 3/2:1/2, whereas the three ammonium cations in the Glc-1P2(NH4) complex (Figure 2c) are located in the general position on the two-fold axis (the Wyckoff position b) and are disordered around the second position of the two-fold axis (the Wyckoff position a) [21].
Some structural similarities can also be observed in the anhydrous structures of hydrogen phosphates, Glc-1PH(NH4)K and Glc-1PHK: the symmetry of the crystal lattice, the translation along a, the volume of the unit cell, and the anion orientation are preserved (Table 2, Figure 3).However, the isomorphic substitution of the K + cations with 69% of NH4 + cations changed the lengths of translations b and c.This is due to replacing most of the K-O coordination bonds with the N-H-O hydrogen bonds.

Structure of α-D-Glucopyranosyl-1-Phosphate Dianion
The Cori ester, α-D-glucopyranose-1-phosphate, is composed of a pyranose ring substituted with the phosphate group attached to its C1 position, three hydroxyl groups (the C2, C3, C4 positions), and the hydroxymethylene group (the C5 position).The ring adopts the chair conformation, which is not significantly changed by interactions with cations and water molecules present in the crystals.Fitting of the pyranose rings of all dianions observed in the studied crystals shows that the equatorial atoms directly connected to this ring (O1, O2, O3, O4, C6) have a rigid orientation of C-O/C bonds (Figure 4).A detailed comparison of dianion conformations shows that the differences in the position of the carbon atoms are <0.2Å, and the position of the P1 atom differs by a maximum of 0.5 Å (Glc-1P2Na-5H2O vs. Glc-1PKNa).

Structure of α-D-Glucopyranosyl-1-Phosphate Dianion
The Cori ester, α-D-glucopyranose-1-phosphate, is composed of a pyranose ring substituted with the phosphate group attached to its C1 position, three hydroxyl groups (the C2, C3, C4 positions), and the hydroxymethylene group (the C5 position).The ring adopts the chair conformation, which is not significantly changed by interactions with cations and water molecules present in the crystals.Fitting of the pyranose rings of all dianions observed in the studied crystals shows that the equatorial atoms directly connected to this ring (O1, O2, O3, O4, C6) have a rigid orientation of C-O/C bonds (Figure 4).A detailed comparison of dianion conformations shows that the differences in the position of the carbon atoms are <0.2Å, and the position of the P1 atom differs by a maximum of 0.5 Å (Glc-1P2Na-5H2O vs. Glc-1PKNa).
Different coordination modes of cations and hydrogen bonds formed between anions and water molecules cause variable directions of the O-H bond vectors of the O3 and O4 hydroxyl groups, while the O2-H group has a rigid orientation (as shown in Figure 4).The conformations around the C5-C6 bond are well described by the O5-C5-C6-O6 torsion angle.In all complexes containing Na and NH 4 cations, the orientation of the O6-H hydroxyl group relative to the O5 pyranose atom is -synclinal; only in the dipotassium complex does it adopt a +synclinal conformation (Figure 4).Some differences are also noticeable in the relative position of the pyranose O5 oxygen atom and P1 phosphorus.The torsion angles of the synclinal orientation in the O5-C1-O1-P1 fragment differ by approximately 10-15 • ; this angle adopts higher values (≈90 • ) in the homocationic complexes and smaller values (≈75 • ) in heterocationic ones (Figure 4).Different coordination modes of cations and hydrogen bonds formed between an ons and water molecules cause variable directions of the O-H bond vectors of the O3 an O4 hydroxyl groups, while the O2-H group has a rigid orientation (as shown in Figure 4 The conformations around the C5-C6 bond are well described by the O5-C5-C6-O6 to sion angle.In all complexes containing Na and NH4 cations, the orientation of the O6hydroxyl group relative to the O5 pyranose atom is -synclinal; only in the dipotassiu complex does it adopt a +synclinal conformation (Figure 4).Some differences are also n ticeable in the relative position of the pyranose O5 oxygen atom and P1 phosphorus.Th torsion angles of the synclinal orientation in the O5-C1-O1-P1 fragment differ by ap proximately 10-15°; this angle adopts higher values (≈90°) in the homocationic complex and smaller values (≈75°) in heterocationic ones (Figure 4).

Environment of α-D-Glucopyranosyl-1-Phosphate Dianion
The analysis of the cation coordination by the Glc-1P dianion shows significant di ferences in the mode of interactions (Figure 5).Anions are multidentate ligands; they ca potentially coordinate cations through the nine oxygen atoms present in their structure Additionally, the cation coordination spheres are completed by water molecules prese in the crystals (Tables S10-S14).The Supplementary Materials contain information abou the coordination numbers of cations, the values of the X + -O cation coordination bond and the most important hydrogen bonds.
The simplest coordination mode is observed in the structure of the Glc-1P2Na-5H2 complex (Figure 5b, Table S12).Five oxygen atoms are involved in coordination, with th O5 and O6 oxygen atoms performing chelating functions and the O1, O2, O13 oxyge atoms being the second chelating fragment.In the dipotassium dihydrate complex (Fi ure 5c, Table S9), the anion is surrounded by eight cations, seven oxygen atoms are i volved in the coordination, and two chelating fragments can be observed here.The cat on-anion interactions in Glc-1P2(NH4) occur through N-H-O hydrogen bonds (Tab

Environment of α-D-Glucopyranosyl-1-Phosphate Dianion
The analysis of the cation coordination by the Glc-1P dianion shows significant differences in the mode of interactions (Figure 5).Anions are multidentate ligands; they can potentially coordinate cations through the nine oxygen atoms present in their structures.Additionally, the cation coordination spheres are completed by water molecules present in the crystals (Tables S10-S14).The Supplementary Materials contain information about the coordination numbers of cations, the values of the X + -O cation coordination bonds, and the most important hydrogen bonds.
The simplest coordination mode is observed in the structure of the Glc-1P2Na-5H2O complex (Figure 5b, Table S12).Five oxygen atoms are involved in coordination, with the O5 and O6 oxygen atoms performing chelating functions and the O1, O2, O13 oxygen atoms being the second chelating fragment.In the dipotassium dihydrate complex (Figure 5c, Table S9), the anion is surrounded by eight cations, seven oxygen atoms are involved in the coordination, and two chelating fragments can be observed here.The cation-anion interactions in Glc-1P2(NH4) occur through N-H-O hydrogen bonds (Table S16, Figure 5f).
It seems that the difference in the ionic radii of Na (1.14-1.16Å) and K (1.52-1.65 Å) [22] favors the selective binding of sodium to the chelating fragment O5-C5-C6-O6.The intraanionic O5 to O6 distance in Na complexes is slightly smaller than in Glc-1P2K (where there is no chelation) and is equal to 2.75-2.8Å (Figure 5).The most interesting observation comes from analyzing crystal structures containing two cations, i.e., K/Na and NH 4 /Na.In addition to their isomorphic nature, which was discussed earlier, the mode in which the sodium cation interacts with the anion is identical to that in which the disodium hydrates.In each of these structures, the Na cation is chelated by the O5 and O6 atoms and, if the symmetry of the crystal allows it, these cations are positioned on the two-fold symmetry axis (Figure 5a,b,d,e and Tables S11-S14).This position of the cation and chelation by the anions creates a dimeric anion-Na-anion structure (Figure 6).It seems that the difference in the ionic radii of Na (1.14-1.16Å) and K (1.52-1.65 Å) [22] favors the selective binding of sodium to the chelating fragment O5-C5-C6-O6.The intra-anionic O5 to O6 distance in Na complexes is slightly smaller than in Glc-1P2K (where there is no chelation) and is equal to 2.75-2.8Å (Figure 5).The most interesting observation comes from analyzing crystal structures containing two cations, i.e., K/Na and NH4/Na.In addition to their isomorphic nature, which was discussed earlier, the mode in which the sodium cation interacts with the anion is identical to that in which the disodium hydrates.In each of these structures, the Na cation is chelated by the O5 and O6 atoms and, if the symmetry of the crystal allows it, these cations are positioned on the two-fold symmetry axis (Figure 5a,b,d,e and Tables S11-S14).This position of the cation and chelation by the anions creates a dimeric anion-Na-anion structure (Figure 6).It seems that the difference in the ionic radii of Na (1.14-1.16Å) and K (1.52-1.65 Å) [22] favors the selective binding of sodium to the chelating fragment O5-C5-C6-O6.The intra-anionic O5 to O6 distance in Na complexes is slightly smaller than in Glc-1P2K (where there is no chelation) and is equal to 2.75-2.8Å (Figure 5).The most interesting observation comes from analyzing crystal structures containing two cations, i.e., K/Na and NH4/Na.In addition to their isomorphic nature, which was discussed earlier, the mode in which the sodium cation interacts with the anion is identical to that in which the disodium hydrates.In each of these structures, the Na cation is chelated by the O5 and O6 atoms and, if the symmetry of the crystal allows it, these cations are positioned on the two-fold symmetry axis (Figure 5a,b,d,e and Tables S11-S14).This position of the cation and chelation by the anions creates a dimeric anion-Na-anion structure (Figure 6).

Environment of α-D-Glucopyranosyl-1-Hydrogenphosphate Anion
Previously, the similarities in the structure of the crystal network of the anhydrous hydrogen phosphate complexes, i.e., Glc-1PHK and Glc-1PH(NH4)K, were discussed.The analysis of the potassium mode of coordination and isomorphically substituted NH 4 /K ions shows even greater convergence.The surroundings of the anions are similar except for the mode of coordination to the phosphate group (Figure 7).In the ammonium-potassium complex, NH 4 /K cations are chelated by three oxygen atoms: O11 and O1 of the phosphate and O2 of the hydroxyl group.Meanwhile, in the potassium complex, only the K-O2 bond is formed.As a result, the potassium coordination number changes from 6 to 8 in Glc-1PH(NH4)K crystal (Table S15).
NH4/K ions shows even greater convergence.The surroundings of the anions are similar except for the mode of coordination to the phosphate group (Figure 7).In the ammonium-potassium complex, NH4/K cations are chelated by three oxygen atoms: O11 and O1 of the phosphate and O2 of the hydroxyl group.Meanwhile, in the potassium complex, only the K-O2 bond is formed.As a result, the potassium coordination number changes from 6 to 8 in Glc-1PH(NH4)K crystal (Table S15).

Nuclear Magnetic Resonance Studies
NMR spectroscopy in aqueous solution was used to study the structure of α-D-glucose-1-phosphate anion of the three selected complexes: Glc-1P2K, Glc-1P2Na, and Glc-1PKNa.The analysis of 1 H NMR, 13 C NMR, and 31 P NMR spectra showed that their profiles had striking similarities.They exhibited consistent shapes and identical coupling constants, which can be seen in Figures S1-S21 in the Supplementary Materials.The signal originating from the anomeric proton (H1) close to the phosphate group showed minor variations within the experimental error.However, also notable is the change in the coupling constant for H6a and H6b (Table S1), which may be caused by possible chelation to the O5, O6 atoms.The 31 P NMR experiments without proton decoupling confirmed the coupling of the anomeric proton to the phosphorus atom of the phosphate group.The singlet signal undergoes a splitting process that results in a doublet signal.The characteristic splitting from protons coupled with P in each compound can be seen in Figure 8.
The measured { 31 P}-{ 1 H} coupling constant for both homocationic complexes, Glc-1P2K and Glc-1P2Na, was 7.46 Hz.The measured coupling constant aligns with that previously observed for α-D-glucose 1-phosphate disodium (Glc-1P2Na) [23].However, the measured coupling constant was one-third lower, at 4.98 Hz, in the case of the heterocationic Glc-1PKNa.The detection of such a large change in the { 31 P}-{ 1 H} coupling constant within the mixed phosphate complex Glc-1PKNa is interesting and suggests that it is most likely the result of a change in conformation resulting from the interaction of two different metal cations with the phosphate group.

Nuclear Magnetic Resonance Studies
NMR spectroscopy in aqueous solution was used to study the structure of α-D-glucose-1-phosphate anion of the three selected complexes: Glc-1P2K, Glc-1P2Na, and Glc-1PKNa.The analysis of 1 H NMR, 13 C NMR, and 31 P NMR spectra showed that their profiles had striking similarities.They exhibited consistent shapes and identical coupling constants, which can be seen in Figures S1-S21 in the Supplementary Materials.The signal originating from the anomeric proton (H1) close to the phosphate group showed minor variations within the experimental error.However, also notable is the change in the coupling constant for H 6a and H 6b (Table S1), which may be caused by possible chelation to the O5, O6 atoms.The 31 P NMR experiments without proton decoupling confirmed the coupling of the anomeric proton to the phosphorus atom of the phosphate group.The singlet signal undergoes a splitting process that results in a doublet signal.The characteristic splitting from protons coupled with P in each compound can be seen in Figure 8.

General Information
The reagents were obtained from commercial suppliers and used without further purification.Dipotassium glucose-1-phosphate dihydrate (Glc-1PK2·2H2O 96%) was purchased from Reanal (Budapest, Hungary), Amberlit IR-120 was purchased from Aldrich (Milwaukee, WI, USA); disodium carbonate, dipotassium carbonate, diammonium carbonate, HCl 2n, ethanol 96%, and propan-2-ol were purchased from POCH S.A (Gli- The measured { 31 P}-{ 1 H} coupling constant for both homocationic complexes, Glc-1P2K and Glc-1P2Na, was 7.46 Hz.The measured coupling constant aligns with that previously observed for α-D-glucose 1-phosphate disodium (Glc-1P2Na) [23].However, the measured coupling constant was one-third lower, at 4.98 Hz, in the case of the heterocationic Glc-1PKNa.The detection of such a large change in the { 31 P}-{ 1 H} coupling constant within the mixed phosphate complex Glc-1PKNa is interesting and suggests that it is most likely the result of a change in conformation resulting from the interaction of two different metal cations with the phosphate group.
The NMR spectra were recorded using a Bruker Ascend spectrometer ( 1 H 500 MHz, 13 C NMR 126 MHz, 31 P NMR 202 MHz) with D 2 O as the solvent, with a sample molarity of 0.05 mmol/mL at room temperature.Chemical shifts (δ) are given in ppm relative to residual H 2 O ( 1 H) as a reference.Coupling constants (J) are in Hz.The following abbreviations of signal patterns are as follows: s (singlet), d (doublet), t (triplet), q (quartet), m (multiplet), br (broad).
The single crystal diffraction data were collected at room temperature with a Super-Nova diffractometer (Oxford Diffraction; Agilent, Yarnton, UK [24]) with the graphite monochromated CuKα radiation (λ = 1.54184Å), except for the unstable Glc-1P2(NH4) complex, for which the data collection was performed on a KM4 diffractometer with Mo Ka radiation (λ = 0.71069 Å).A CrysAlisPro 1.171.42.79a program system [25] or KM4 Software ver.KM4B8 (Wrocław, Poland) [26] was used for data collection, cell refinement, and data reduction.The intensities were corrected for Lorentz and polarization effects, and multi-scan absorption corrections were applied.The crystal structure was solved by direct methods using the SHELXT program and refined by the full-matrix least squares method on F 2 using the SHELXL-2018/3 program [27,28].The non-hydrogen atoms were refined with anisotropic displacement parameters, The carbon-bonded H-atoms were positioned at calculated positions and refined using the riding model.Hydrogen atoms bonded to oxygen atoms (in OH groups, water molecules) were treated depending on the quality of the crystal and the diffraction data.Some of them were located from differential electron density maps, some in calculated positions, and then the positions were refined or fixed.The experimental details and final atomic parameters for the analyzed crystals were deposited with the Cambridge Crystallographic Data Centre as a Supplementary Material (CCDC Nos 2345573-2345579).

Syntheses
Glc-1PK 2 was subjected to ion exchange chromatography to obtain acid (Glc-1PH 2 ).The potassium complex (0.194 g; 0.5 mmol) was dissolved in 25 mL of redistilled water and applied to an Amberlit IR-120 loaded column (45 cm × 2 cm).Elution with water from a column yielded 28 mL of solution with a pH of 3.25.The aqueous Glc-1PH 2 solution was rotary-evaporated to 22 mL.

Preparation of the Glc-1P2(NH 4 ) Complex
While stirring, 0.048 g (0.5 mmol) of (NH 4 ) 2 CO 3 was added to 17 mL of Glc-1PH 2 solution.The resulting mixture had a pH of 5.96.Then, 19 mL of propan-2-ol was added to the solution, obtaining an opalescent solution with a pH of 8.01.The solution was crystallized using an antisolvent vapor diffusion method.For this purpose, a vessel with the solution was placed in a chamber containing ethanol.Crystallization was carried out at a temperature of 10 • C; the first crystals appeared after 24 h.After eight days, the solution

Figure 2 . 13 Figure 2 .
Figure 2. The crystal packing of isomorphic complexes; view down the c axis.The Na/NH 4 cation positions on the 2-fold axes are marked as ) are located in the general position on the two-fold axis (the Wyckoff position b) and are disordered around the second position of the two-fold axis (the Wyckoff position a) [21].

Figure 6 .
Figure 6.View of two Glc-1P 2− dianions chelating the Na cation located on the two-fold axis.

Figure 7 .
Figure7.View of the Glc-1HP -anions and surrounding cations.In the structure of the NH4/K complex (a), the isomorphic cation substitution (NH4:K = 69%:31%) is marked only in one position.

Figure 7 .
Figure 7.View of the Glc-1HP − anions and surrounding cations.In the structure of the NH 4 /K complex (a), the isomorphic cation substitution (NH 4 :K = 69%:31%) is marked only in one position.