Calcium D-gluconate Research Articles

Growth, investigation of calcium D-gluconate monohydrate-CDG crystals with shocked impact for electronic usage and the pure crystal for sensor application

Growth, investigation of calcium D-gluconate monohydrate-CDG crystals with shocked impact for electronic usage and the pure crystal for sensor application

Insights into chromium removal mechanism by Ca-based sorbents from flue gas

Chromium is a typical toxic pollution in sewage sludge incineration flue gas. Cr removal from flue gas is a challenge due to the high toxicity and valence variability of chromium. Ca-based sorbents, including CG-CaO, CA-CaO, and CCi-CaO, were developed for Cr capture by calcining calcium D-gluconate monohydrate, calcium acetate hydrate, and calcium citrate tetrahydrate, respectively. CG-CaO, CA-CaO, and CCi-CaO exhibit better Cr removal performance than traditional CaO. CA-CaO shows superior Cr adsorption ability due to the large BET surface area and pore volume. The Cr adsorption efficiency of CA-CaO is up to 94.79 % at 1000 °C. XRD and XPS results reveal that the adsorbed Cr contains Cr(III) and Cr(VI), and exists in the form of CaCr2O4 and CaCrO4. Cr adsorption on Ca-based sorbents is mainly controlled by adsorption and oxidation mechanism. The adsorption process of Cr on different Ca-based sorbents was described by four typical adsorption kinetic models. For CaO and CG-CaO, pseudo-first order model and Elovich model are suitable for the description of Cr adsorption. For CA-CaO and CCi-CaO, pseudo-second order model, Elovich model and Weber and Morris model fit well with the experimental values of Cr adsorption, suggesting that Cr adsorption on CA-CaO and CCi-CaO is controlled by a combined mechanism of chemisorption and intraparticle diffusion. The saturated adsorption capacity of CaO, CG-CaO, CA-CaO and CCi-CaO are evaluated to be 39.77, 48.98, 102.22 and 104.52 mg/g, respectively. The effects of incineration flue gas components on Cr adsorption were also explored. O2 shows no obvious influence on Cr adsorption over CA-CaO. HCl, SO2, NO and CO2 can inhibit Cr adsorption because of the competitive adsorption, and the inhibitory effect of SO2 is the strongest.

Effects of various parameters on solution-mediated phase transformation of calcium d-gluconate: an approach to obtain pure metastable monohydrate.

The high risk of solution-mediated phase transformation (SMPT) from the metastable monohydrate to stable Form I makes it difficult to produce pure metastable monohydrate of calcium d-gluconate. In this work, we explored the effect of various operating parameters on the SMPT of calcium d-gluconate in water and proposed an effective approach to obtain the desired monohydrate. First, the two forms of calcium d-gluconate were characterized and compared using powder X-ray diffraction (PXRD), thermal analysis, and Raman spectroscopy. The lower solubility of Form I in water illustrates its higher thermodynamic stability than monohydrate when the temperature is higher than 292 K. Afterward, the SMPT of calcium d-gluconate from monohydrate to Form I was investigated in water using in situ Raman spectroscopy combined with scanning electron microscopy and PXRD. Results showed that the nucleation and growth of Form I was the rate-limiting step in the SMPT from monohydrate to Form I. The phase transformation from monohydrate to Form I was delayed to produce pure monohydrate by decreasing temperature and agitation rate, reducing the amount of solid loading, and increasing the particle size of solid loading. Furthermore, the transformation kinetics were studied by the JMA model to explore how temperature influences the SMPT process. This study enriches the study of the calcium d-gluconate SMPT mechanism, and also provides guidance for obtaining high-quality injection-grade calcium gluconate monohydrate.

Scalable synthesis of strutted nitrogen doped hierarchical porous carbon nanosheets for supercapacitors with both high gravimetric and volumetric performances

Porous carbon nanosheets with high specific surface area have become the most promising electrode materials for supercapacitor, but their high pore volume leads to relatively low density and poor volumetric capacitance. In this work, strutted nitrogen doped hierarchical porous carbon nanosheets (SNPCNS), featuring three-dimensional nonaggregated architecture braced by struts have successfully been scalably synthesized via a novel calcium d-gluconate-exploding technique. The pyrolysis temperature and duration, and the mass ratio of calcium d-gluconate and urea formaldehyde resin are regulated for optimizing the specific surface area, pore volume and capacitive performance of SNPCNS. The optimized SNPCNS displays high specific surface area (539 m2 g−1), rich surface heteroatoms (8.1 at.% for N) and high density (1.11 g cm−3). Therefore, the supercapacitor assembled by SNPCNS electrodes presents very high gravimetric/volumetric capacitances of 286 F g−1/317 F cm−3 (in 6 M KOH) and 355 F g−1/394 F cm−3 (in 1 M H2SO4). Importantly, high gravimetric/volumetric energy densities of 40.5 W h kg−1/44.9 W h L−1 (in ionic liquid) are achieved, which are superior to those of previously reported carbon nanosheets based symmetric supercapacitors. This work provides a new strategy for the mass and low-cost production of high-performance porous carbon nanosheets for energy storage.

Crystal structure and thermodynamic properties of the coordination compound calcium D-gluconate Ca[D-C6H11O7]2(s)

The coordination compound calcium D-gluconate, Ca[D-C6H11O7]2(s), was synthesized and characterized by chemical analysis, elemental analysis, and X-ray crystallography. Single crystal X-ray diffraction technique revealed that the compound was formed by two D-gluconate anions and one calcium (II) cation. And the D-gluconate anion had a curved chain configuration with an intramolecular bond. The compound exhibited an outstanding chelate property of D-gluconate anions to calcium (II) cations, and the calcium (II) cation was eight-coordinated and chelated by four D-gluconate anions. The lattice potential energy and ionic volume of the anion were calculated to be 1434.05 kJ⋅mol−1 and 0.4211 nm3 from crystallographic data. In accordance with famous Hess law, a reasonable thermochemical cycle was designed and the standard molar enthalpy of formation of Ca[D-C6H11O7]2(s) was calculated as ΔsHm[Ca[D-C6H11O7]2, s] = -(3545.19 ± 1.07) kJ⋅mol−1 by use of an isoperibol solution-reaction calorimeter. Furthermore, molar heat capacities of the compound were measured using a Quantum Design Physical Properties Measurement System (PPMS) with specific heat option within the temperature range from (1.9–300) K. The heat capacities of the compound increased with the temperature and no thermal anomaly was found in the whole temperature region. The experimental data was fitted to a function of the absolute temperature T with a series of theoretical and empirical models for the proper temperature ranges. The values of standard thermodynamic function, Cp,mo/J⋅K−1⋅mol−1, Δ0THmo/kJ⋅mol−1, Δ0TSmo/J⋅K−1⋅mol−1, and ΔoTGmo/T/J⋅K−1⋅mol−1 (=Δ0TSmo-Δ0THmo/T) from T = (0–300) K was calculated based on the fitting results. The standard molar heat capacity, entropy and enthalpy of the compound at T = 298.15 K and 0.1 MPa was determined to be Cp,mo= (493.20 ± 2.70) J·K−1 mol−1, Hmo= (75934 ± 805) J·mol−1, Smo= (471.55 ± 2.78) J·K−1 mol−1, and Gmo/T = - (64658 ± 808) J·K−1⋅mol−1, respectively.

Slow lactate gluconate exchange in calcium complexes during precipitation from supersaturated aqueous solutions

Saturated solutions of calcium l-lactate in water or in deuterium oxide continuously dissolve calcium l-lactate by addition of solid sodium d-gluconate and become strongly supersaturated in calcium d-gluconate due to no or slow precipitation. The quantification of total dissolved calcium allied with the calcium complexes equilibrium constants allowed an ion speciation, which shows an initial non-thermal and spontaneous supersaturation of more than a factor of 50 at 25 °C only slowly decreasing after initiation of precipitation of calcium d-gluconate after a lag phase of several hours. A mathematical model is proposed, based on numerical solution of coupled differential equations of dynamics of l-lactate and d-gluconate exchange during the lag phase for precipitation and during precipitation. A slow exchange of l-lactate coordinated to calcium with d-gluconate is indicated with a time constant of 0.20 h−1 in water and of 0.15 h−1 in deuterium oxide and a kinetic deuterium/hydrogen isotope effect of 1.25. Such spontaneous non-thermal supersaturation and slow ligand exchange with a pseudo first order equilibration process with a half-life of 3.5 h in water for calcium hydroxycarboxylates can help to understand the higher calcium bioavailability from calcium hydroxycarboxylates compared to simple salts.

A Membrane-Bound Gluconate Dehydrogenase from 2-Keto-d-Gluconic Acid Industrial Producing Strain Pseudomonas plecoglossicida JUIM01: Purification, Characterization, and Gene Identification

The membrane-bound gluconate dehydrogenase (mGADH) is a critical enzyme for 2-keto-D-gluconic acid (2KGA) production in Pseudomonas plecoglossicida JUIM01. The purified native flavin adenine dinucleotide-dependent mGADH (FAD-mGADH) was consisted of a gamma subunit, a flavoprotein subunit, and a cytochrome c subunit with molecular mass of ~ 27, 65, and 47kDa, respectively. The specific activity of FAD-mGADH was determined as 90.71U/mg at optimum pH and temperature of 6.0 and 35°C. The Km and Vmax values of calcium D-gluconate were 0.631mM and 0.734mM/min. The metal ions Mg2+ and Mn2+ showed slight positive effects on FAD-mGADH activity. On the other hand, a 3868-bp-length gad gene cluster was amplified and expressed in Escherichia coli BL21(DE3). The recombinant protein showed the same molecular weight and enzyme activity as the native FAD-mGADH, which confirmed it as a FAD-mGADH encoding gene. The flavoprotein subunit and the cytochrome c subunit containing a putative FAD-binding motif and three possible heme-binding motifs concluded from alignment results of mGADHs. This study characterized the native and recombinant FAD-mGADH and would provide the basis for further genetic modification of Pseudomonas plecoglossicida JUIM01 with the intention of 2KGA productivity improvement.

Crystal and solution structures of calcium complexes relevant to problematic waste disposal: calcium gluconate and calcium isosaccharinate

The single-crystal structures of calcium D-gluconate and calcium α-D-isosaccharinate have been determined using X-ray diffraction at 100 K. Surprisingly, given its significance in industrial and medical applications, the structure of calcium D-gluconate has not previously been reported. Unexpectedly, the gluconate crystal structure comprises coordination polymers. Unusually, the calcium coordination number is nine. Adjacent metal centres are linked by three μ-oxo bridges, with a metal–metal separation of 3.7312 (2) Å. One of the gluconate ligands contradicts a suggestion from 1974 that a straight chain conformation is associated with an intramolecular hydrogen bond. This ligand binds to three adjacent metal centres. The use of synchrotron radiation provided an improved crystal structure with respect to that previously reported for the isosaccharinate complex, allowing the location of the hydroxy hydrogen sites to be elucidated. In contrast to the gluconate structure, there are no μ-oxo bridges in the isosaccharinate coordination polymer and the isosaccharinate bridging coordination is such that the distance between adjacent metal centres, each of which is eight-coordinate, is 6.7573 (4) Å. Complementing the crystal structure determinations, modelling studies of the geometries and coordination modes for the aqueous [CaGluc]+ and [CaIsa]+ complexes are presented and discussed.

In situ upgrading of bio-oil via CaO catalyst derived from organic precursors

The fast pyrolysis of biomass with catalysts is a promising route for producing upgraded bio-oil as an alternative energy source. A CaO catalyst prepared from organic calcium compounds (Org-CaO) was first used to upgrade the pyrolysis oil of Jatropha curcas seeds in situ. Calcium d-gluconate monohydrate, calcium citrate tetrahydrate, and calcium acetate hydrate were employed as the organic precursors in this work. The results showed that Org-CaO exhibited better deoxygenation ability to produce more hydrocarbons than conventional CaO derived from Ca(OH)2 (CHCaO). Acids accounted for 83% of the oxygenated compounds in the raw bio-oil and were almost completely removed via CaO. For bio-oil catalyzed by Org-CaO, the fraction of esters in the oxygenated compounds was only ∼9%, which was 20% less than that in CHCaO bio-oil. The relative content of ketones and alcohols in Org-CaO bio-oil increased by 16% versus that in CHCaO bio-oil. Org-CaO exhibited a remarkably larger pore size and much smaller particle sizes. Thus, Org-CaO entered into the fuel through the pore channels, and this promoted the formation of chemical crosslinking points between CaO and oxygenated groups. In addition, the basicity and the amount of basic sites for Org-CaO increased versus CHCaO. Thus, the adsorption forms of oxygen-containing groups in the bio-oil on the basic sites of CaO changed: the carboxyl groups were removed from the acids and were absorbed in a stable form of unidentate carbonate on oxygen vacancies (O2−). The stable form was bidentate carbonate on Ca2+–O2−. In addition, oxygen vacancies on Org-CaO extracted more hydroxyl groups from the acids, resulting in dehydroxylation of acids to form ketones and alcohols.

Calcium d-Saccharate: Aqueous Solubility, Complex Formation, and Stabilization of Supersaturation.

Molar conductivity of saturated aqueous solutions of calcium d-saccharate, used as a stabilizer of beverages fortified with calcium d-gluconate, increases strongly upon dilution, indicating complex formation between calcium and d-saccharate ions, for which, at 25 °C, Kassoc = 1032 ± 80, ΔHassoc° = −34 ± 6 kJ mol–1, and ΔSassoc° = −55 ± 9 J mol–1 K–1, were determined electrochemically. Calcium d-saccharate is sparingly soluble, with a solubility product, Ksp, of (6.17 ± 0.32) × 10–7 at 25 °C, only moderately increasing with the temperature: ΔHsol° = 48 ± 2 kJ mol–1, and ΔSassoc° = 42 ± 7 J mol–1 K–1. Equilibria in supersaturated solutions of calcium d-saccharate seem only to adjust slowly, as seen from calcium activity measurements in calcium d-saccharate solutions made supersaturated by cooling. Solutions formed by isothermal dissolution of calcium d-gluconate in aqueous potassium d-saccharate becomes spontaneously supersaturated with both d-gluconate and d-saccharate calcium salts, from which only calcium d-saccharate slowly precipitates. Calcium d-saccharate is suggested to act as a stabilizer of supersaturated solutions of other calcium hydroxycarboxylates with endothermic complex formation through a heat-induced shift in calcium complex distribution with slow equilibration upon cooling.

Terahertz time-domain spectroscopy and quantitative analysis of metal gluconates.

A series of metal gluconates (Na(+), K(+), Mg(2+), Ca(2+), Fe(2+), Cu(2+), and Zn(2+)) were investigated by terahertz (THz) time-domain spectroscopy. The absorption coefficients and refractive indices of the samples were obtained in the frequency range of 0.5-2.6 THz. The gluconates showed distinct THz characteristic fingerprints, and the dissimilarities reflect their different structures, hydrogen-bond networks, and molecular interactions. In addition, some common features were observed among these gluconates, and the similarities probably come from the similar carbohydrate anion group. The X-ray powder diffraction measurements of these metal gluconates were performed, and the copper(II) gluconate was found to be amorphous, corresponding to the monotonic increase feature in the THz absorption spectrum. The results suggest that THz spectroscopy is sensitive to molecular structure and physical form. Binary and ternary mixtures of different gluconates were quantitatively analyzed based on the Beer-Lambert law. A chemical map of a tablet containing calcium D-gluconate monohydrate and α-lactose in the polyethylene host was obtained by THz imaging. The study shows that THz technology is a useful tool in pharmaceutical research and quality control applications.

High-temperature CO2 capture cycles of hydrated limestone prepared with aluminum (hydr)oxides derived from kaolin

A simple and convenient process was used to improve the utilization of natural limestone and kaolin for calcium looping technology and environmental applications. The calcined natural limestone modified with the distilled water (denoted as Limestone-W), was systematically studied and compared with the other CaO sorbents (calcium acetate, calcium d-gluconate and calcined natural limestone). These CaO-based sorbents were tested for their CO2 capture behavior through 20 carbonation/calcination cycles in a thermo-gravimetric analyzer (TGA). Their morphology, pore structure and phase composition before and after carbonation/calcination cycles were determined by scanning electron microscopy, nitrogen adsorption, and X-ray diffraction. The first-cycle and multicycle sorption results revealed that the Limestone-W sorbent exhibited a relatively faster reaction rate and higher cyclic CO2 capture. The characterization data indicated that the Limestone-W was composed of a special calcium oxide structure with lower crystalline and higher porosity nanoparticles, which appeared to be the main reasons for its higher CO2 capture capability. However, the Limestone-W still suffered loss of reactivity, even though it was less pronounced than the other CaO sorbent. To avoid this unfavorable effect, a thermally stable inert material (aluminum hydroxide derived from kaolin) was incorporated into the Limestone-W structure. This new sorbent revealed higher stability because the formation of a stable framework of Ca12Al14O33 particles hindered densification and sintering of the CaO phase. It was concluded that the combination of the distilled water modified limestone with Al(OH)3 binder is a promising approach for synthesis of CaO-based sorbents with a higher reactivity.

Thermodynamics of dissolution of calcium hydroxycarboxylates in water.

Aqueous solubility of calcium l-lactate, calcium d-gluconate, and calcium d-lactobionate increases with temperature (10-30 °C investigated), most significantly for the least soluble d-gluconate, while the calcium ion activity of the saturated solutions decreases with temperature, as measured electrochemically, most significantly for the most soluble d-lactobionate. This unusual behavior is discussed in relation to dairy processing and explained by endothermic binding of calcium to hydroxycarboxylate anions determined to have ΔH°ass = (31 ± 3) kJ·mol(-1) for l-lactate, (34 ± 2) kJ·mol(-1) for d-gluconate, and (29 ± 3) kJ·mol(-1) for d-lactobionate in 1:1 complexes with thermodynamic binding constants at 25 °C of Kass = 49 (l-lactate), 88 (d-gluconate), and 140 (d-lactobionate). Quantum mechanical calculations within density functional theory (DFT) confirm the ordering of strength of binding. The complex formation is entropy driven with ΔS°ass > 0, resulting in decreasing calcium ion activity in aqueous solutions for increasing temperature, even for the saturated solutions despite increasing solubility.

Spontaneous supersaturation of calciumd-gluconate during isothermal dissolution of calciuml-lactate in aqueous sodiumd-gluconate

Continuing dissolution of solid calcium L-lactate pentahydrate in saturated aqueous solutions following addition of solid sodium D-gluconate corresponding to a gluconate/lactate ratio around three was found to result in homogeneous solutions supersaturated with calcium D-gluconate by a factor of seven, from which calcium D-gluconate monohydrate precipitated only slowly. In contrast, dissolution of calcium D-gluconate monohydrate by sodium L-lactate in aqueous solution with the reverse lactate/gluconate ratio also around three did not result in similar homogeneous solutions on the route to solid calcium L-lactate pentahydrate. This increasing supersaturation of calcium D-gluconate during dissolution of calcium L-lactate in aqueous sodium D-gluconate may enhance calcium bioavailability. The dissolution overshooting depends on competitive kinetics and is also of interest in modeling biomineralization and in designing novel food products with increased calcium bioavailability.

Aqueous Solubility of Calcium l-Lactate, Calcium d-Gluconate, and Calcium d-Lactobionate: Importance of Complex Formation for Solubility Increase by Hydroxycarboxylate Mixtures

Among the calcium hydroxycarboxylates important for cheese quality, D-lactobionate [Ksp = (7.0 ± 0.3) × 10(-3) mol(3) L(-3)] and L-lactate [Ksp = (5.8 ± 0.2) × 10(-3) mol(3) L(-3)] were found more soluble than D-gluconate [Ksp = (7.1 ± 0.2) × 10(-4) mol(3) L(-3)], as indicated by the solubility products determined electrochemically for aqueous 1.0 M NaCl at 25.0 °C. Still, solubility of calcium L-lactate increases by 45% in the presence of 0.50 M sodium D-gluconate and by 37% in the presence of 0.50 M sodium D-lactobionate, while solubility of calcium D-gluconate increases by 66 and 85% in the presence of 0.50 M sodium L-lactate and 0.50 M sodium D-lactobionate, respectively, as determined by complexometric titration. Sodium L-lactate and sodium D-gluconate have only little influence on solubility of calcium D-lactobionate. The increased solubility is described quantitatively by calcium binding to D-gluconate (K1 = 14 ± 3 mol(-1) L) in 1.0 M NaCl at 25 °C, D-lactobionate (K1 = 11 ± 2 mol(-1) L), and L-lactate (K1 = 8 ± 2 mol(-1) L), as indicated by the association constants determined electrochemically. In mixed hydroxycarboxylate solutions, calcium binding is quantitatively described by the geometric mean of the individual association constants for both aqueous 1.0 and 0.20 M NaCl, indicating a 1:1 stoichiometry for complex formation.

Amorphous calcium phosphates synthesized by precipitation from calcium D-gluconate solutions

The amorphous calcium phosphates were synthesized by the precipitation from non-toxic calcium D-gluconate precursor solutions. The low number of nanosized well-ordered calcium deficient hydroxyapatite clusters separated with amorphous calcium phosphate matrix was found at short aging times. The content of intramolecular water in aggregates decreased with an amount of well-ordered clusters and maturation time. The majority α-tricalcium phosphate phase and calcium deficient calcium phosphate were formed after annealing of samples with a high volume fraction of amorphous matrix and nanocrystalline apatite-like phase respectively. The very fine nanocrystalline calcium deficient hydroxyapatite was intermediate phase during thermal transformation to the final β-tricalcium phosphate. The rise of disaggregation of coarse particles to smaller well-ordered hydroxyapatite clusters with aging time was verified. The different amount and size of nanocrystalline clusters were responsible for the formation of various calcium phosphate phases after thermal treatment.

Removal of CO2 by CaO/MgO and CaO/Ca9Al6O18 in the Presence of SO2

Sorbents with their components CaO/MgO and CaO/Ca9Al6O18 were produced from calcium d-gluconate monohydrate, magnesium d-gluconate hydrate, and aluminum l-lactate hydrate as precursors with a simpl...

Block-copolymer-assisted synthesis of hydroxyapatite nanoparticles with high surface area and uniform size

We report the synthesis of hydroxyapatite nanoparticles (HANPs) by the coprecipitation method using calcium D-gluconate and potassium hydrogen phosphate as the sources of calcium and phosphate ions, respectively, and the triblock copolymer F127 as a stabilizer. The HANPs were characterized using scanning electron microscopy, x-ray diffraction, and nitrogen adsorption/desorption isotherms. Removal of F127 by solvent extraction or calcination alters the structure of HANPs. The solvent-extracted HANPs were single crystals with their 〈001〉 axis oriented along the rod axis of the HANP, whereas the calcined HANPs contained two crystal phases that resulted in a spherical morphology. The calcined HANPs had much higher surface area (127 m2 g−1) than the solvent-extracted HANPs (44 m2 g−1).

Calcium Precursors for the Production of CaO Sorbents for Multicycle CO2 Capture

A screening of potential calcium precursors for the production of CaO sorbents for CO(2) capture at high temperature was conducted in this work. The precursors studied include microsized calcium carbonate (CC-CaO), calcium hydroxide (CH-CaO), nanosized (<70 nm) calcium carbonate (CC70 nm-CaO), nanosized (<160 nm) calcium oxide (CaO160 nm-CaO), calcium acetate hydrate (CA-CaO), calcium l-lactate hydrate (CL-CaO), calcium formate (CF-CaO), calcium citrate tetrahydrate (CCi-CaO), and calcium d-gluconate monohydrate (CG-CaO). The capture capability of these sorbents was investigated using a thermogravimetric analyzer (TGA) for multiple capture cycles. CG-CaO exhibited the best capacity for capturing CO(2) with a 1-min conversion of 65.9% and a 30-min conversion of 83.8% at the ninth cycle. Subsequently, a further parametric study was conducted to examine the effect of reaction conditions such as reaction temperature (550-750 degrees C) and CO(2) gas concentration (1-15%) on the capture capacity of CG-CaO. The sorbent CG-CaO also showed a much lower decomposition temperature and higher predicted residual conversion after prolonged cycles, compared with CC-CaO.

The Catalysis of the Ruff Oxidative Degradation of Aldonic Acids by Copper(II)-Containing Solids

The catalysis of the Ruff oxidative degradation of calcium D-gluconate to D-arabinose by aqueous diluted hydrogen peroxide was investigated using copper(II)-containing solids: zeolites and resins. Among zeolites, copper(II)-exchanged Y faujasite has given good results, similar to homogeneous copper catalysts. Only minute amounts of soluble copper were detected at the end of the reaction and the recovered solid was recycled twice without diminution of efficiency. However, it was not true heterogeneous catalysis because the chelating gluconate anion leached copper right from the beginning of the reaction. So, the catalysis occurred in solution but the metal precipitated again at the end of the reaction, when all the gluconate was consumed. Copper (II) iminodiacetic resin, in which the metal cation is more strongly bound than in the gluconate complex, was not active. This demonstrates that copper(II) must be in solution in order to be active.