Bone tissue incorporates in vitro gallium with a local structure similar to gallium-doped brushite

During mineral growth in rat bone-marrow stromal cell cultures, gallium follows calcium pathways. The dominant phase of the cell culture mineral constitutes the poorly crystalline hydroxyapatite (HAP). This model system mimics bone mineralization in vivo. The structural characterization of the Ga environment was performed by X-ray absorption spectroscopy at the Ga K-edge. These data were compared with Ga-doped synthetic compounds (poorly crystalline hydroxyapatite, amorphous calcium phosphate and brushite) and with strontium-treated bone tissue, obtained from the same culture model. It was found that Sr²⁺ substitutes for Ca²⁺ in the HAP crystal lattice. In contrast, the replacement by Ga³⁺ yielded a much more disordered local environment of the probe atom in all investigated cell culture samples. The coordination of Ga ions in the cell culture minerals was similar to that of Ga³⁺, substituted for Ca²⁺, in the Ga-doped synthetic brushite (Ga-DCPD). The Ga atoms in the Ga-DCPD were coordinated by four oxygen atoms (1.90 Å) of the four phosphate groups and two oxygen atoms at 2.02 Å. Interestingly, the local environment of Ga in the cell culture minerals was not dependent on the onset of Ga treatment, the Ga concentration in the medium or the age of the mineral. Thus, it was concluded that Ga ions were incorporated into the precursor phase to the HAP mineral. Substitution for Ca²⁺ with Ga³⁺ distorted locally this brushite-like environment, which prevented the transformation of the initially deposited phase into the poorly crystalline HAP.Electronic Supplementary Material Supplementary material is available in the online version of this article at Abbreviations ACP amorphous calcium phosphate - DCPD dicalcium phosphate dihydrate (brushite) - HAP hydroxyapatite - ED-XRF energy dispersive X-ray fluorescence - EXAFS extended X-ray absorption fine structure - Ga-ACP gallium-doped amorphous calcium phosphate - Ga-DCPD gallium-doped brushite - Ga-HAP gallium-doped hydroxyapatite - XANES X-ray absorption near edge structure - XAS X-ray absorption spectroscopy - XRD X-ray diffraction     

Composition and ultrastructure of calcium phosphate-citrate complexes in bovine milk systems

The present studies show that the colloidal calcium phosphate of cow's milk has a (Ca + Mg)/P_i ratio of 1.67 (± 0.10; n = 22) and contains citrate, Mg and Zn at molar ratios to Ca averaging 0.05, 0.03 and 0.003, respectively. The composition of the natural colloidal phosphate of milk is similar to the precipitates formed by neutralization of ultrafiltrates obtained from acidified milks, and to that of the calcium phosphate-enriched fraction produced by extensive enzymic hydrolysis of the casein micelles in milk. Examination by electron microscopy of these artificial preparations of milk calcium phosphate revealed in both a very fine and uniform substructure which consisted of granules having an average, true diameter of approx. 2.5 nm. The size and shape of these tiny granules closely resemble the morphologies reported for the colloidal phosphate particles in native casein micelles, as well as for the subunits of amorphous calcium phosphate observed during calcification in other biological systems such as mitochondria and bone.     

Ex vivo detection of calcium phosphate and calcium carbonate in rat blood serum

The total calcium (tCa) in blood serum comprises free Ca²⁺ ions (fCa), protein-bound calcium (prCa), and complexed calcium by small anions (cCa). The cCa fraction, in addition to fCa, has been indicated to have some physiological activity. However, there is little evidence for the structure of its constituents. Here we report an ex vivo detection of the cCa constituents by synchrotron X-ray absorption near-edge structure spectroscopy. We collected the data directly on rat blood serum and, by making use of the reference samples, derived a spectrum that exhibits the features of cCa constituents. Among the features are those of the complexes of calcium phosphate and calcium carbonate. The detected complexes in the cCa fraction are mainly Ca(η²-HPO₄)(H₂O)₄ and Ca(η¹-HCO₃)(H₂O)₅⁺, in which HPO₄^2? and HCO₃^? serve as bidentate and unidentate ligands, respectively. The remained H₂O molecules on the coordination sphere of Ca²⁺ enable these complexes to behave partially like aquated Ca²⁺ ions in protein-binding. Besides, as the dominant part of prCa, albumin-bound calcium (albCa) exhibits a spectrum that closely resembles that of fCa, indicating weak interactions between the protein carboxyl groups and calcium. The weak-bound cCa and albCa, along with fCa and the relevant anions, compose a local chemical system that could play a role in maintaining the calcium level in blood.     

Colloidal Calcium Phosphate in the Reconstituted Milk Micelle May Direct Wild-type Recombinant Human β-Casein to Fold Like the Native Protein

Native human β-casein (CN) at all phosphorylation levels exhibits reproducible behavior and appears to have a unique, stable folding pattern. In contrast, the recombinant non-phosphorylated form of human β-CN (β-CN-0P) with the exact amino acid sequence (wild-type), expressed and purified from Escherichia coli, differs greatly in its behavior from the native protein and the complexes formed are unstable to thermal cycling. However, when it was incorporated into reconstituted milk micelles, using bovine κ-CN at a κ/β molar ratio of 1/3 with added Ca²⁺ ions and inorganic phosphate (P_i) at levels that would ordinarily precipitate, its association behavior vs. temperature as monitored by turbidity (OD_{400 nm}) approximated that of native β-CN-0P. This suggests that the milk micelle system, and particularly the colloidal calcium phosphate, may act as a ‘molecular chaperon’ to direct the folding of the molecule into the highly stable conformation found in the purified native human β-CN molecule.     

Effect of hydrochlorothiazide on urine saturation with brushite,in vitro collagen calcification by urine,and urinary inhibitors of collagen calcification

To clarify further the beneficial effect of thiazide diuretics on recurrent calcium nephrolithiasis, the effect of short-term hydrochlorothiazide therapy on urine saturation with brushite (CaHPO₄·2H₂O), in vitro collagen calcification by urine, and urinary inhibitors of calcification was studied.In 22 patients with idiopathic calcium oxalate/phosphate stones the urine calcium excretion decreased, the urine magnesium excretion increased and the urine magnesium/calcium ratio increased significantly (P < 0.001) during hydrochlorothiazide therapy. Supersaturation of the urine with brushite, which was present in 19 of the 22 patients, was reduced significantly (P < 0.001) in all during thiazide therapy, and to the undersaturated range in 16. The ability of urine to calcify collagen in vitro also decreased significantly (P < 0.001) during thiazide therapy, a change that correlated significantly (r = 0.4513, P < 0.05) with the decrease in brushite saturation. The concentration of urinary inhibitors of calcification, as determined with an in vitro collagen calcification system, was decreased significantly (P < 0.01) by thiazide therapy.It was concluded that, in addition to decreasing urine calcium excretion and increasing urine magnesium excretion, thiazide diuretics decrease the urinary brushite saturation and thus may prevent spontaneous nucleation or crystal growth, or both, of calcium phosphate. The ability of thiazides to decrease collagen calcification in vitro suggests that they may also prevent crystal growth on a nidus of organic matrix. Thiazides do not appear to act by increasing the excretion of urinary inhibitors of calcification.     

Dihydroxyacetone phosphate, DHAP, in the crystalline state: monomeric and dimeric forms

It was shown that dihydroxyacetone phosphate may exist in both monomeric DHAP (C₃H₇O₆P) and dimeric DHAP-dimer (C₆H₁₄O₁₂P₂) form. Monomeric DHAP was obtained in the form of four crystalline salts: CaCl(DHAP)·2.9H₂O (7a), Ca₂Cl₃(DHAP)·5H₂O (7b), CaCl(DHAP)·2H₂O (7c), and CaBr(DHAP)·5H₂O (7d) by crystallization from aqueous solutions containing DHAP acid and CaCl₂ or CaBr₂, or by direct crystallization from a solution containing DHAP precursor and CaCl₂. At least one of the salts is stable and may be stored in the crystalline state at room temperature for several months. The dimeric form was obtained by slow saturation of free DHAP syrup with ammonia at −18 °C and isolated in the form of its hydrated diammonium salt (NH₄)₂(DHAP-dimer)·4H₂O (8). The synthesis of the compounds, their crystallization, and crystal structures determined by X-ray crystallography are described. In all 7a-d monomeric DHAP exists in the monoanionic form in an extended (in-plane) cisoid conformation, with both hydroxyl and ester oxygen atoms being synperiplanar to the carbonyl O atom. The crucial structural feature is the coordination manner, in which the terminal phosphate oxygen atoms act as chelating as well as bridging atoms for the calcium cations. Additionally, the DHAP monoanions chelate another Ca²⁺ by the α-hydroxycarbonyl moiety, in a manner observed previously in dihydroxyacetone (DHA) calcium chloride complexes. In dimeric 8 the anion is a trans isomer with the dioxane ring in a chair conformation with the hydroxyl groups in axial positions and the phosphomethyl group in an equatorial position.     

Electronic structural investigations of ruthenium compounds and anticancer prodrugs

Several Ru^III compounds are propitious anticancer agents although the precise mechanisms of action remain unknown. With this paper we start to establish an experimental library of X-ray absorption spectroscopy (XAS) data for ten Ru compounds wherein the ligands [Cl⁻, dimethyl sulfoxide, imidazole, and indazole] were varied systematically to provide electronic structural information for future use in correlating spectroscopic signatures with chemical properties. Despite the considerable difference in the coordination environments of the complexes studied, the overall differences in spectral features and electronic structures calculated using density functional theory are unexpectedly small. However, the differences in the electronic structure of the Ru^III prodrugs KP1019 ([IndH][trans-RuCl₄(Ind)₂], Ind is indazole) and ICR ([ImH][trans-RuCl₄(Im)₂], Im is imidazole) observed in the XAS data show correlation with known chemical and biological activities in addition to the donor abilities of imidazole compared with indazole and reduction potentials of the complexes. These semiquantitative results lay the groundwork for future biochemical studies into the structure–function relationships of Ru-based anticancer drugs. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Calcium hydroxyapatite fractionation as a second ion exchange step in protein purification: improvement of flow rate and resolution

The use of washed brushite, CaHPO₄, as a filter aid permitted the flow rates of calcium hydroxyapatite (HAP) columns to be made reliable and high. Regeneration of the column contents yielded pure, crystalline HAP, which could be mixed with fresh brushite and reused. Column fractionation over HAP-brushite with a phosphate gradient was used as a second ion exchange step in protein purification, the first step being fractionation over DEAE-cellulose. In two examples discussed, HAP-brushite fractionation in the presence of an effector molecule, a molecule for which the enzyme of interest had a specific affinity, gave marked improvement of resolution.     

Solid-state phosphorus-31 nuclear magnetic resonance studies of synthetic solid phases of calcium phosphate: potential models of bone mineral

Phosphorus-31 NMR spectra have been obtained from a variety of synthetic, solid calcium phosphate mineral phases by magic angle sample spinning. The samples include crystalline hydroxyapatite, two type B carbonatoapatites containing 3.2 and 14.5% CO3(2-), respectively, a hydroxyapatite in which approximately 12% of the phosphate groups are present as HPO4(2-), an amorphous calcium phosphate, monetite, brushite, and octacalcium phosphate. Spectra were observed by the standard Bloch decay and cross-polarization techniques, as well as by a dipolar suppression sequence, in order to distinguish between protonated and unprotonated phosphate moieties. The spectra of the synthetic calcium phosphates provide basic information that is essential for interpreting similar spectra obtained from bone and other calcified tissues.     

Preparation and characterization of milk calcium salts by using casein phosphopeptide

Milk calcium salt solution was prepared by the following procedures using casein phosphopeptides (CPP). To CPP solution, 1 M citric acid, 1 M CaCl2 and 1 M K2HPO4 were added with stirring, while adjusting the pH to 6.7. The prepared solution was left for 12 hr at 25 degrees C and then used for subsequent experiments, or lyophilized. The concentrations of organic phosphate of CPP, calcium, inorganic phosphate, and citrate in the typical milk salt solution were 7, 30, 22, and 10 mM, respectively, which were close to those in bovine milk. The lyophilized sample was easily dissolved in water. No crystal structure of hydroxyapatite was shown in the lyophilized milk calcium salts by X-ray diffraction analysis, although the pattern of KCl crystal was observed. The X-ray diffraction pattern of commercial whey mineral, which was prepared by precipitation at alkaline pH from rennet whey, was similar to that of hydroxyapatite. It was confirmed by high-performance gel chromatographic analysis that the form of calcium phosphate in the milk calcium salts was similar to that of casein micelles.     

Composition and size distribution of bovine casein micelles

Chromatography of glutaraldehyde-fixed skim-milk on controlled-pore glass (CPG-10, 300 nm) gave three micellar fractions whose averaged diameters, measured by electron microscopy, decreased progressively with increasing elution volume. Casein micelles with diameters up to 680 nm were detected. The casein composition of the same fractions from unfixed skim-milk was determined. As the fraction elution volume increased, κ-casein varied from 7.7 to 11.4% of total casein, giving α_s/κ ratios of 6.1, 4.7 and 3.3.A plot of κ-casein content versus micelle surface-to-volume ratio for skim-milk and the column fractions approximated to a straight line. Re-calculation of the published results from two other studies also gave linear relationships between κ-casein content and surface area for artificial micelles. The three regression lines thus obtained had small intercepts. It was concluded that the data indicated the same fundamental structure for casein micelles, with a pre-dominant surface location for κ-casein, whether the micelles are natural or artificial and whether they are aggregated or by Ca²⁺ alone oy Ca²⁺ together with calcium phosphate-citrate complex.     

Determinants of Brushite Stone Formation: A Case-Control Study

Purpose

The occurrence of brushite stones has increased during recent years. However, the pathogenic factors driving the development of brushite stones remain unclear.

Methods

Twenty-eight brushite stone formers and 28 age-, sex- and BMI-matched healthy individuals were enrolled in this case-control study. Anthropometric, clinical, 24 h urinary parameters and dietary intake from 7-day weighed food records were assessed.

Results

Pure brushite stones were present in 46% of patients, while calcium oxalate was the major secondary stone component. Urinary pH and oxalate excretion were significantly higher, whereas urinary citrate was lower in patients as compared to healthy controls. Despite lower dietary intake, urinary calcium excretion was significantly higher in brushite stone patients. Binary logistic regression analysis revealed pH>6.50 (OR 7.296; p = 0.035), calcium>6.40 mmol/24 h (OR 25.213; p = 0.001) and citrate excretion <2.600 mmol/24 h (OR 15.352; p = 0.005) as urinary risk factors for brushite stone formation. A total of 56% of patients exhibited distal renal tubular acidosis (dRTA). Urinary pH, calcium and citrate excretion did not significantly differ between patients with or without dRTA.

Conclusions

Hypercalciuria, a diminished citrate excretion and an elevated pH turned out to be the major urinary determinants of brushite stone formation. Interestingly, urinary phosphate was not associated with urolithiasis. The increased urinary oxalate excretion, possibly due to decreased calcium intake, promotes the risk of mixed stone formation with calcium oxalate. Neither dietary factors nor dRTA can account as cause for hypercalciuria, higher urinary pH and diminished citrate excretion. Further research is needed to define the role of dRTA in brushite stone formation and to evaluate the hypothesis of an acquired acidification defect.     

Interactions between metal ions and carbohydrates. Syntheses and spectroscopic studies of several lanthanide nitrate–d-galactitol complexes

Two complexes of neutral d-galactitol (C₆H₁₄O₆, G) with terbium nitrate, TbGN(I) and TbGN(II), and one complex with samarium nitrate SmGN were synthesized and characterized. From IR, FIR, THz and luminescence spectra the possible coordinations were suggested, and the single-crystal X-ray diffraction results confirm the spectroscopic conclusions. In TbGN(I) (Tb(NO₃)₃·C₆H₁₄O₆·3H₂O), the Tb³⁺ is 9-coordinated with three water molecules and six OH groups from two d-galactitol molecules. Nitrate ions do not coordinate to metal ions, which is different from other reported lanthanide nitrate–d-galactitol complexes. In TbGN(II) and SmGN (Ln(NO₃)₃·C₆H₁₄O₆), Ln³⁺ is 10-coordinated with six OH groups from two d-galactitol molecules and four oxygen from two bidentate nitrate ions, and one nitrate ion is hydrogen bonded. No water exists in the structures. d-Galactitol molecules provide their 1-, 2- and 3-hydroxyl groups to coordinate with one metal ion and their 4-, 5- and 6-hydroxyl groups to coordinate with another metal ion in the three structures. There is still a new topological structure that can be observed for lanthanide–d-galactitol complexes, which indicates that the coordinations between hydroxyl groups and metal ions are complicated.     

Idiopathic calcium nephrolithiasis. 1. Differences in urine crystalloids,urine saturation with brushite and urine inhibitors of calcification between persons with and persons without recurrent kidney stone formation.

The propensity of urine to promote calcium stone formation was compared in 64 patients with recurrent idiopathic calcium nephrolithiasis and 30 healthy individuals without such a history. The rates of excretion of urine crystalloids, the urine saturation with brushite (CaHPO4-2H2O), the ability of the urine to calcify collagen in vitro, and the concentration of urine inhibitors of collagen calcification were measured. The patients had a reduced urine citrate excretion rate in addition to an increased urine calcium excretion rate, while the rates for urine magnesium, phosphate, uric acid and oxalate were not significantly different in the two groups of subjects. The urine concentration of magnesium, phosphate and uric acid was decreased in the patients because of the higher urine volume. The urine creatinine excretion rate correlated with the rates of excretion of urine calcium, magnesium, phosphate, uric acid and oxalate in both groups, which suggested that increased lean body mass, possibly associated with greater food intake, may be an important determinant of crystalloid excretion. The urine of the patients was significantly more saturated with brushite than the urine of the control subjects and resulted in greater collagen calcification when incubated in vitro. The urine concentration of inhibitors of collagen calcification, however, was not significantly different in the two groups. Thus, the urine of patients with recurrent idiopathic calcium nephrolithiasis is more highly saturated with brushite, largely as a result of an increased urine calcium excretion rate, and contains a lower concentration of magnesium and citrate, substances that tend to prevent the precipitation and growth of crystals in urine.     

The Tryptophan Synthase α2β2 Complex: A Model for Substrate Channeling,Allosteric Communication,and Pyridoxal Phosphate Catalysis

I reflect on my research on pyridoxal phosphate (PLP) enzymes over fifty-five years and on how I combined research with marriage and family. My Ph.D. research with Esmond E. Snell established one aspect of PLP enzyme mechanism. My postdoctoral work first with Hans L. Kornberg and then with Alton Meister characterized the structure and function of another PLP enzyme, l-aspartate β-decarboxylase. My independent research at the National Institutes of Health (NIH) since 1966 has focused on the bacterial tryptophan synthase α₂β₂ complex. The β subunit catalyzes a number of PLP-dependent reactions. We have characterized these reactions and the allosteric effects of the α subunit. We also used chemical modification to probe enzyme structure and function. Our crystallization of the tryptophan synthase α₂β₂ complex from Salmonella typhimurium led to the determination of the three-dimensional structure with Craig Hyde and David Davies at NIH in 1988. This landmark structure was the first structure of a multienzyme complex and the first structure revealing an intramolecular tunnel. The structure has provided a basis for exploring mechanisms of catalysis, channeling, and allosteric communication in the tryptophan synthase α₂β₂ complex. The structure serves as a model for many other multiprotein complexes that are important for biological processes in prokaryotes and eukaryotes.     

Maltobionic acid enhances intestinal absorption of calcium and magnesium in rats

ABSTRACT

In Experiment 1, the effects of calcium maltobionate (MBCa) on calcium and magnesium absorption were examined using male rats. Four diets were designed in which 25%, 50%, and 100% of calcium carbonate (CaCO₃, Control) were substituted with MBCa and were designated as MBCa-25, MBCa-50, and MBCa-100, respectively. The cecal concentration of short-chain fatty acids was significantly higher in groups MBCa-50 and MBCa-100; however, pH of cecal contents did not significantly differ among the groups. Retention rates of calcium and magnesium were significantly higher in all MBCa groups as compared to the Control. In Experiment 2, the efficiency of calcium absorption was compared using everted sacs of jejunum and ileum with CaCO₃ and MBCa as calcium sources. More calcium from MBCa was absorbed as the concentration of calcium increased in comparison to CaCO₃. It was concluded that MBCa is a better calcium source than CaCO₃ in terms of both calcium retention and absorption.

Abbreviations: ANOVA: analysis of variance; Ca: Calcium; CaCO_3: calcium carbonate; ICP-OES: Inductivity coupled plasma optical emission spectrometer; Mg: magnesium; MBCa: calcium maltobionate; OCPC: o-cresolphthalein complexone; SCFAs: short-chain fatty acids; SE: standard error; TRPM6: transient receptor potential melastatin 6.     

Crystal structure of Escherichia coli inorganic pyrophosphatase complexed with SO4: Ligand-induced molecular asymmetry

The three-dimensional structure of inorganic pyrophosphatase from Escherichia coli complexed with sulfate was determined at 2.2 Å resolution using Patterson's search technique and refined to an R-factor of 19.2%. Sulfate may be regarded as a structural analog of phosphate, the product of the enzyme reaction, and as a structural analog of methyl phosphate, the irreversible inhibitor. Sulfate binds to the pyrophosphatase active site cavity as does phosphate and this diminishes molecular symmetry, converting the homohexamer structure form (α₃)₂ into α₃′α₃″. The asymmetry of the molecule is manifested in displacements of protein functional groups and some parts of the polypeptide chain and reflects the interaction of subunits and their cooperation. The significance of re-arrangements for pyrophosphatase function is discussed.     

X-ray Absorption Spectroscopy and Magnetism of Synthetic Greigite and Greigite Magnetosomes in Magnetotactic Bacteria

Scanning transmission X-ray microscopy at the Fe 2p (L_2,3), O1s, C1s, and S2p edges was used to study greigite magnetosomes and other cellular content of a magnetotactic bacterium known as a multicellular magnetotactic prokaryote (MMP). X-ray absorption spectrum (XAS) and X-ray magnetic circular dichroism (XMCD) spectra of greigite (Fe₃S₄) nanoparticles, synthesized via a hydrothermal method, were measured. Although XAS of the synthetic greigite nanoparticles and biotic magnetosome crystals in MMPs are slightly different due to partial oxidation of the MMP greigite, the XMCD spectra of the two materials are in good agreement. The Fe 2p XAS and XMCD spectra of Fe₃S₄ are quite different from those of its oxygen analog, magnetite (Fe₃O₄), suggesting Fe₃S₄ has a different electronic and magnetic structure than Fe₃O₄ despite having the same crystal structure. Sulfate and sulfide species were also identified in MMPs, both of which are likely involved in sulfur metabolism.     

Physicochemical characterization of casein phosphopeptide-amorphous calcium phosphate nanocomplexes

Milk caseins stabilize calcium and phosphate ions and make them available to the neonate. Tryptic digestion of the caseins yields phosphopeptides from their polar N-terminal regions that contain clusters of phosphorylated seryl residues. These phosphoseryl clusters have been hypothesized to be responsible for the interaction between the caseins and calcium phosphate that lead to the formation of casein micelles. The casein phosphopeptides stabilize calcium and phosphate ions through the formation of complexes. The calcium phosphate in these complexes is biologically available for intestinal absorption and remineralization of subsurface lesions in tooth enamel. We have studied the structure of the complexes formed by the casein phosphopeptides with calcium phosphate using a range of physicochemical techniques including x-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and equilibrium binding analyses. The amorphous nature of the calcium phosphate phase was confirmed by two independent methods: x-ray powder diffraction and selected area diffraction. In solution, the ion activity product of a basic amorphous calcium phosphate phase was the only ion product that was a function of bound phosphate independent of pH, consistent with basic amorphous calcium phosphate being the phase stabilized by the casein phosphopeptides. Detailed investigations of calcium and calcium phosphate binding using a library of synthetic homologues and analogues of the casein phosphopeptides have revealed that although the fully phosphorylated seryl-cluster motif is pivotal for the interaction with calcium and phosphate, other factors are also important. In particular, calcium binding and calcium phosphate stabilization by the peptides was influenced by peptide net charge, length, and sequence.     

Copper phosphates and phosphinates with pyridine/pyrazole alcohol co-ligands: Synthesis and structure

Copper phosphates, [Cu(dtbp)₂(pzet)₂]·H₂O (1) and [Cu(dtbp)₂(pyme)₂] (2), as well as copper phosphinate, [Cu(dppi)₂(pyet)₂] (3) have been synthesized by the reaction of copper acetate with di-tert-butyl phosphate (dtbp) or diphenyl phosphinate (dppi) in the presence of pyridine base having hydroxyl group, namely, 3,5-dimethylpyrazole-2-ethanol (pzet) or 2-(hydroxymethyl)pyridine (pyme) or 2-(2-hydroxyethyl)pyridine (pyet). Single crystal X-ray diffraction studies reveal that copper ion in all the three complexes is bonded to two phosphoryl ions (P(O)O⁻) and two pyridine co-ligands. The crystal structure of 1 reveals that the hydroxyl group of the CH₂CH₂OH moiety of pzet ligand exhibits a positional disorder between the non-bonding position and the bonding position with respect to the central copper ion along the Jahn-Teller axis. Hence, the structure of 1 can be considered to exhibit both ‘square-planar’ and ‘octahedral’ coordination geometries simultaneously for the copper ion in the same complex. A similar situation for the -OH groups has not been observed in the complexes 2 and 3 and hence the coordination geometry around the copper ion is axially elongated octahedron.