Purification of Glucose Oxidase and β‐Galactosidase by Partitioning in a PEG‐Salt Aqueous Two‐Phase System in the Presence of PEG‐Derivatives

Abstract

Purification of glucose oxidase from Aspergillus niger and that of β‐galactosidase from Kluyveromyces lactis have been attempted using poly(ethylene glycol) (PEG)‐sodium sulfate aqueous two phase system (ATPS) in the presence of PEG‐derivatives, i.e. PEG‐Coomassie brilliant blue G‐250 and PEG‐benzoate, PEG‐palmitate and PEG‐TMA, respectively. The enzymes showed poor partitioning towards the PEG phase in comparison with other proteins in ATPS containing no ligands. Selective partitioning of other proteins was observed towards the PEG phase in the presence of PEG‐benzoate and PEG‐palmitate enriching β‐galactosidase in the salt phase whereas in the case of glucose oxidase, PEG‐Coomassie brilliant blue G‐250 derivative worked as a better affinity ligand for other proteins. A 19‐fold purification was obtained with the PEG dye derivative after 5 stage cross extractions with 80% recovery of glucose oxidase and an enrichment factor upto ～7 for β‐galactosidase with the PEG‐TMA derivative. The interaction of PEG‐benzoate and PEG‐TMA ligands with the active site of β‐galactosidase has been evaluated by molecular modeling. The effect of the molecular weight of glucose oxidase on its partitioning was confirmed as the molecular simulation shows strong affinity interaction of PEG‐glucoside with the enzyme.     

Synthesis and Ion-Binding Properties of Polymeric Pseudocrown Ethers: A Molecular Dynamics Study

Abstract

A novel method for producing inexpensive polymeric pseudocrown ethers in situ during free-radical polymerizations was investigated using molecular dynamics simulations. This scheme is based upon a template ion and exploits the tendency of oligomeric ethylene glycol diacrylates to form intramolecular cycles during polymerization. In the scheme, a template ion is used to induce the poly(ethylene glycol) diacrylates (PEGDA) to assume cyclic structures before polymerization with a comonomer. Experimental studies demonstrated that certain salts that were insoluble in nonpolar solvents were solubilized upon the addition of oligomeric poly(ethylene glycol) (PEG) due to complexation. Further evidence of cation binding by oligomeric PEG was obtained by ¹H NMR studies of PEG and its complexes with metal salts. To optimize the template ion synthesis approach, molecular dynamics simulations were performed on PEGDA containing between two and ten ethylene glycol repeating units, with and without the presence of cations. Simulation results indicated that the presence of the templating cation significantly decreased the mean end-to-end distance, thereby bringing the unsaturated endgroups into close proximity. The PEGDA ligand that resulted in the most effective templatization for Na⁺ contained four ethylene glycol repeating units. Simulation times greater than 50 ps had little effect on the results for ligands containing 7 or fewer ethylene glycol repeating units.     

Extraction of Zirconium and Hafnium in Polyethylene Glycol‐Based Aqueous Biphasic System

Abstract

The behavior of zirconium and hafnium in PEG 2000‐Na₂SO₄‐HCl aqueous biphasic system has been investigated. The dependences of HCl concentration (0.185–0.55 M), extraction temperature (298–318 K), and extraction time (5–120 min) on distribution ratios have been determined. Extraction of this metals in PEG 2000‐Na₂SO₄‐H₂SO₄ and PEG 2000‐Na₃Cit‐HCl systems has been also studied. The sulfate and citrate complexes of Zr and Hf prefer salt‐rich phase in contrast to chloride complexes which pass into PEG rich phase in about 50% (w/w) to the greatest degree in room temperature and at short extraction time. The increase of distribution ratios (D*_Zr=3.75, D*_Hf=4.31) was observed after addition of water soluble organic ligand ‐ tiron (4,5‐dihydroxy‐m benzenedisulfonic acid disodium salt). The results obtained in studied conditions are not very useful for the separation of zirconium and hafnium.     

Evaluation of Mononuclear Ni(II) Complex of a Tetra-cryptanded Vic-dioxime and its Model Compound 14-Membered N2O2S2-Macrobicyclic Ligand as Pb2+, Cd2+, and Hg2+ Extractants

Abstract

A macrobicyclic ligand and its mononuclear Ni(II) complex were studied as extractants for Pb²⁺, Cd²⁺, and Hg²⁺. The metal picrates were used for extraction experiments. The solutions of the ligands in chloroform and dichloromethane were used as organic phases. The most effective transport was observed for Cd²⁺ picrate among the tested metal picrates with dichloromethane. The effect of pH on the extraction efficiency was evaluated for both organic solvents. The cations were stripped from the organic phase with 0.75 M nitric acid and the ligands were determined spectrophotometrically in the proper wavelength. The recovery% values of the ligands were calculated at pH 3.5.     

Actinide–lanthanide co-extraction by rigidified diglycolamides

Within the actinide and lanthanide co-extraction strategy, three rigidified diglycolamides, namely 2,6-bis (N-dodecyl-carboxamide)-4-oxo-4H-pyran (1), 2,6-bis-[N-(4-tert-butylphenyl)carboxamide]-4-oxo-4H-pyran (2), 2,6-?bis[(N-docecyl-N-methyl)carboxamide]-?4-methoxy-?tetrahydro-pyran (3), were synthesized. Moreover, the effect of structural rigidification on Am(III) and Eu(III) extraction under different conditions was investigated. The carboxamide extractant 3 resembles the extracting behavior of N,N,N′,N′‐tetraoctyl diglycolamide (TODGA) in terms of efficiency and affinity within the lanthanide family, together with fast kinetics and satisfactory cation back-extraction. The presence of 1-octanol in the diluent mixture strongly affects the ligand stability. Moreover, despite the low extraction efficiency showed by 1 and 2, all the three ligands exhibit a higher affinity for Am with respect to TODGA, resulting in a lower lanthanide/Americium separation factor, of around 4 for ligand 3 and close to 1 for ligands 1 and 2.     

New high-spin bis-o-semiquinonato cobalt(II) complexes with neutral donor ligands

Two novel bis-o-semiquinonato cobalt complexes Co(3,6-SQ)₂L (1, L¹ = 2,6-dimethyl-N-(pyridin-2-ylmethylene)benzenamine; 2, L² = 2,6-dimethyl-N-(thiophen-2-ylmethylene)benzenamine; 3,6-SQ is 3,6-di-tert-butyl-o-benzosemiquinonato radical-anion) were synthesized. According to X-ray analysis, complex 2 adopts square pyramidal geometry with N-coordinated neutral ligand L² in the apical site. According to magnetic susceptibility measurements and spectroscopic studies, both complexes contain high-spin cobalt(II) (d⁷, S = 3/2) and two radical-anionic o-semiquinonato ligands. There is antiferromagnetic metal–ligand and ligand–ligand coupling in 1, while complex 2 demonstrates weak antiferromagnetic ligand–ligand coupling at low temperature and ferromagnetic metal–ligand exchange at 150–300 K.     

Aqueous Two‐Phase Partitioning of Glucose Isomerase from Actinoplanes missouriensis in the Presence of PEG‐Derivatives and its Immobilization on Chitosan Beads

Abstract

Purification of glucose isomerase by its partitioning in a PEG‐salt aqueous two‐phase system (ATPS) in the presence of PEG derivatives has been studied. Selective partitioning of the proteins was observed towards the PEG phase containing PEG‐benzoate and PEG‐palmitate, enriching glucose isomerase in the salt phase. Cross‐current extraction in 4 stages in the presence of PEG‐palmitate gave an enrichment factor of ～5 for the enzyme. After initial purification with ATPS, glucose isomerase was immobilized on cross‐linked chitosan beads. The immobilized enzyme was stable over a wider pH range (5.2–9.0) and showed an optimum pH of 6.5     

Lanthanide selective adsorption by ion-imprinted polymer with chelidonic acid monoamide groups

Lanthanide selective adsorbent with chelidonic acid monoamide group was synthesized based on the ion-imprint method and its adsorption character was investigated. A polymerizable ligand 3 with chelidonic acid group was obtained by condensation of chelidonic acid and 4-aminostyrene. A Nd-complex monomer 7 was synthesized from the obtained ligand 3 and Nd(NO₃)₃. Copolymerization of the Nd-complex monomer, styrene and divinylbenzene afforded Nd-containing polymer 8. To obtain Nd-imprinted polymer 9, Nd ion was removed by hydrochloric acid. A non-imprinted polymer 6 composed by 3, styrene and divinylbenzene was also synthesized. Elemental analysis revealed that the content of chelidonic acid monoamide ligand in the 6 and 9 is 1.70 and 1.56 mmol·g^?1, respectively. BET method indicated that 6 and 9 has specific surface area of 14.7 and 1.51 m²·g^?1, respectively. Nd adsorption experiments revealed 9 exhibits imprinting factor (IF) 4.3 at initial concentration 0.4 mmol-Nd/L, despite 9 has 0.92-fold of ligands and 0.1-fold of specific surface area of 6. Mixed ion solution including Nd, Dy, Cu, Zn, and Co was used as a model solution for an adsorption experiment. 9 exhibits high lanthanide selectivity in a range of pH of 3.0–7.0 and a maximum adsorption amount at pH 3.75, despite 6 shows the maximum at pH 5.0. Density functional theory (DFT) calculation of a model system revealed that the ion-imprint effect and inhibition effect is cause of large adsorption amount of 9.     

Carbon Dioxide Solubility Enhancement through Silicone Functionalization: “CO2-philic” Oligo(dimethylsiloxane)-substituted Diphosphonates∗

Abstract

Carbon dioxide has received significant attention as a potential environmentally benign medium to replace hazardous organic compounds, but is a relatively poor solvent. The addition of siloxane substituents provides an attractive and inexpensive means to solubilize a wide variety of compounds in CO₂. By synthesizing and testing a family of gem-diphosphonate ligands that have been rendered CO₂-philic by incorporation of a number of related, discrete dimethylsiloxane oligomers, we show that small variations in substituents have a significant effect on the CO₂-philicity of the ligand. To our knowledge, this is the first systematic study of the effect of siloxane substituent size, branching, and position on the affinity of a ligand for CO₂. In addition, we present a general approach to the preparation of novel gem-diphosphonate ligands.     

Sorption of Aromatic Amines on a New Ligand Exchanger of Sporopollenin-Bound Co2+ Ion

Abstract

The mechanism of ligand-exchange sorption of aromatic amines such as p-chloroaniline, p-toluidine, and p-nitroaniline as ligands on a Co²⁺-loaded ligand exchanger has been studied. The observed rate seems to be related to the rate of ligand sorption with the mobile phase and pH in the aqueous phase. The saturation capacity and binding constant of ligand sorption on the resin increase with increasing basicity of amines. The rate of attainment of equilibrium sorption of aromatic amines is seen to be nearly similar. Coupled with the fact that different concentrations of solution were employed, these results may be interpreted as indicating that particle diffusion is the rate-controlling step. On the contrary, film diffusion was not rate-controlling step in the ligand sorption process under the conditions employed. It is shown that the kinetic parameters measured in single component experiments provide good prediction behavior. The pH dependencies and sorption isotherms of aromatic amines on the resins were also studied.     

Process Design for Purification of Muscle Lactate Dehydrogenase by Affinity Partitioning Using Free Reactive Dyes

ABSTRACT

It was shown that by using free reactive dyes as affinity ligands, lactate dehydrogen-ase (LDH) can be purified with affinity partitioning directly from rabbit muscle homogenization. The free reactive dyes not bound to polyethylene glycol (PEG) showed a strong tendency toward the top PEG-rich phase in aqueous two-phase systems, and thus enhanced the affinity partitioning effect. Wide-ranged reactive dyes were screened in terms of their partitioning abilities for LDH. The effects of various parameters on affinity partitioning behavior of LDH, such as phase composition, impurities in raw material, concentration of dyes, pH of the systems, and addition of salts, were studied. The optimized affinity extraction process has been carried out for the large-scale purification of LDH from rabbit muscle homogenization. The enzyme was recovered with a yield of 81*middot;3% and a purification factor of 7. Both PEG and dyes were recovered and reused directly without lowering the quality of the product.     

Sonichemical Synthesis of a New Ethylene Diamine Lead(II) Coordination Polymer as Precursor for Preparation of PbO Nano-Structure

A new nano-coordination polymer of lead(II) nitrate with the ethylenediamine (en) ligand, [Pb(en)(NO₃)₂] _n (1), has been synthesized by a sonochemical process and characterized by scanning electron microscopy, X-ray powder diffraction, IR spectroscopy and elemental analyses. The structure of 1 has been characterized by single crystal X-ray diffraction. In 1, Pb(II) ions are bridged by nitrate ligands forming linear chains, which are also further coordinated by neutral en ligands. This polymeric precursor has been used to prepare Pb(II)O nano-particles using two different methods. The prepared Pb(II)O nano-structure was characterized by scanning electron microscopy and X-ray powder diffraction.     

Pyridinedicarboxylic Acid Diamides as Selective Ligands for Extraction and Separation of Trivalent Lanthanides and Actinides: DFT Study

This article presents a general approach to solving the urgent practical problem of separation of 4f-(lanthanides, Ln³⁺) and 5f-elements (actinides, An³⁺) very similar in properties based on the DFT quantum-chemical supercomputer simulation of Ln³⁺ and An³⁺ complexes with polydentate nitrogen-containing heterocyclic ligands. The method allows to calculate the geometry parameters of ligands and complexes and the metal to ligand binding energies with accuracy, permitting a direct comparison of calculation results with the experimental data, and estimate selectivity factors for separation of Eu³⁺/Am³⁺ model pair cations (SF_Am/Eu) in extraction experiments on a semi-quantitative level.

The applicability of the method and the approach demonstrated by DFT-modeling (nonempirical PBE functional, extended relativistic full-electron basis set) of a large series of diamides of pyridine-2,6-dicarboxylic (dipicolinic) acid (L) with different substituents at the amide nitrogen atoms and in the pyridine cycle, as well as their complexes [LM]³⁺, (H₂O)_nM(NO₃)₃ (n = 3, 4), and LM(NO₃)₃ (M = Eu, Am).

Based on the theoretical analysis a new model is proposed that describes the mechanism of Ln³⁺ and An³⁺ extraction in two-phase system highly acidic water solution-organic solvent, according to which the formation of An³⁺ and Ln³⁺ complexes occurs at the water/organic interface as a substitution reaction of hydroxonium ion in a cavity of a protonated ligand for the metal cation.

Calculation results confirm the experimentally established higher extraction ability of dipicolinic acid diamides containing one aryl and one alkyl substituent at the amide nitrogen atoms compared to the N,N,N′,N′-tetraalkyl diamides (“effect of anomalous aryl strengthening”). Based on the simulation results the structure of the modified ligand L suggested that it should ensure maximum An³⁺/Ln³separation selectivity in the series of dipicolinic acid diamides.     

Bis(Diphenylcarbamoylmethylphosphine Oxide) Ligand Containing 4, 7, 10 – Trioxatridecane Spacer: Novel Effective Extractant for Actinides and Lanthanides

A novel polydentate neutral organophosphorus ligand 1 containing two Ph₂P(O)CH₂C(O)NH- bidentate moieties connected by a 4, 7, 10 - trioxatridecane spacer through amide nitrogen atoms was synthesized and studied as an extractant for U(VI), Th(IV), and lanthanides(III) ions from HNO₃ solutions. The influence of aqueous and organic phases on the extraction efficiency was elucidated and stoichiometry of the complexes extracted was determined. Bis-CMPO ligand 1 was found to possess a higher extraction efficiency towards U(VI), Th(IV), and lanthanides(III) ions than its mono analog diphenylphosphorylacetic acid N-nonylamide 5 and bis-CMPO ligands containing a di- and a triethylene glycol spacers. The values of D_U, D_Th, and D_Ln for compound 1 are more than two orders of magnitude higher than those for its mono-CMPO analog 5.     

In situ electrochemical impedance spectroscopy/synchrotron radiation grazing incidence X-ray diffraction—A powerful new technique for the characterization of electrochemical surfaces and interfaces

A marriage of electrochemical impedance spectroscopy (EIS) and in situ synchrotron radiation grazing incidence X-ray diffraction (SR-GIXRD) has provided a powerful new technique for the elucidation of the mechanistic chemistry of electrochemical systems. In this study, EIS/SR-GIXRD has been used to investigate the influence of metal ion buffer calibration ligands, along with natural organic ligands in seawater, on the behaviour of the iron chalcogenide glass ion-selective electrode (ISE). The SR-GIXRD data demonstrated that citrate - a previously reported poor iron calibration ligand for the analysis of seawater - induced an instantaneous and total dissolution of crystalline GeSe and Sb₂Se₃ in the modified surface layer (MSL) of the ISE, while natural organic ligands in seawater and a mixture of ligands in a mimetic seawater ligand system protected the MSL's crystalline inclusions of GeSe and Sb₂Se₃ from oxidative attack. Expectedly, the EIS data showed that citrate induced a loss in the medium frequency time constant for the MSL of the ISE, while seawater's natural organic ligands and the mimetic ligand system preserved the medium frequency EIS response characteristics of the ISE's MSL. The new EIS/SR-GIXRD technique has provided insights into the suitability of iron calibration ligands for the analysis of iron in seawater.     

A Novel Copper(II)–Hydrogen Oxalate Coordination Polymer Showing a New Coordination Mode

A novel Cu(II) coordination polymer of general empirical formula {[Cu(μ-HC₂O₄)₂(H₂O)₂][Cu(HC₂O₄)₂]∙6H₂O} _n (1) has been synthesized and characterized by single-crystal X-ray diffraction technique. The complex (1) crystallizes in the triclinic form with P-1 space group. It is quite surprising that single crystal X-ray analysis of 1 illustrates the presence of hydrogen oxalate ligand in the coordination environment of Cu(II) ion. Because oxalate is not present in the starting reaction mixture, it may be derived from the reduction of squarate ligand. In 1, Cu(II) ions exhibit two different coordination environments, forming a distorted octahedral geometry. The Cu1 is coordinated with six oxygen atoms from two bidentate HC₂O₄ ⁻ and two aqua ligands, while Cu2 is coordinated with six oxygen atoms from four HC₂O₄ ⁻ ligands. The HC₂O₄ ⁻ ligand acts in two different coordination modes, as a bidentate and an unprecedented tridentate bridging coordination mode.     

HEAVY METAL EXTRACTION WITH THIOCARBAMIC-O-ALKYLESTERS

ABSTRACT

Two types of thiocarbamic-O-alkylesters, four bidentate ligands HL and one bis-bidentate ligand H₂L, were used as extractants for heavy metal ions from aqueous solutions. Silver(I) was extracted as neutral complexes in a yield > 99 %. The underlying stoichiometry and the extraction constants are discussed. The extraction of silver&I) by the bis-bidentate ligand is significantly more effective than the extraction by the analogous bidentate compound. In a dioxane/water mixture neutral, cationic and anionic silver complexes were found by means of pAg and pH potentiometric titrations. The extraction behavior is discussed with regard to the calculated stability constants.     

Interfacial Mass Transfer in Ligand Accelerated Metal Extraction by Liquid Surfactant Membranes

Abstract

Interfacial mass transfer rates were determined for the extraction of Co(II), Ni(II), and Cu(II) by di-(2-ethyl hexyl) phosphoric acid by using a modified Lewis cell. This allowed us to elucidate the effect of ligands on liquid surfactant membrane extraction of heavy metal ions by ligand addition to the external aqueous phase. The effects of different ligands on the kinetics of extraction and the influence of surfactant on interfacial resistance to mass transfer were then examined.     

Alkoxymethyl-Substituted 18-Crown-6 and 21-Crown-7 Ligands: Synthesis,Complexation Properties,and Metal Ion Membrane Separations

Abstract

Three novel alkoxymethyl-substituted 18-crown-6 (8–10) and one new alkoxymethyl-substituted 21-crown-7 (11) ligands have been prepared. First, 1-O-tritylpropanetriol (1) and penta- or hexaethylene glycol ditosylate were cyclized in the presence of an alkali metal hydride. The resulting trityloxymethyl-substituted crowns were deprotected to give the hydroxymethyl-substituted 18-crown-6 (6) and hydroxymethyl-substituted 21-crown-7 (7). The latter compounds were alkylated using sodium hydride and the appropriate l-bromoalkane to form 8–11. Complexation properties of these new ligands with the alkali metal cations were studied by a calorimetric titration technique. Compared with the parent 18-crown-6 and 21-crown-7 ligands, the substituted 18-crown-6 ligands demonstrate superior selectivity for K⁺, while the substituted 21-crown-7 ligand demonstrated less selectivity for Cs⁺ over other alkali cations. Solvent extraction and membrane separation experiments using these new ligands were also carried out. The results demonstrated that the structural features of these new ligands have a significant influence on cation complexation selectivity and separations potential.     

A New Pyridine–Diphosphine Ligand for Self-Assembly of Coordination Polymers: Structure of a Polymeric Copper(I) Complex

A new pyridine–diphosphine ligand, N-4-pyridyl-2,2-bis(diphenylphosphinomethyl)propionamide, 1, designed to form polymeric coordination compounds with potential for further self-assembly through amide hydrogen bonding is described. The complex with copper(I) iodide is shown to exist as a polymer with bridging ligands 1. Dedicated to Professor Didier Astruc, especially for his pioneering research on organometallic dendrimers.