Addition and reaction products of triethyl thiophosphate and metal perchlorates at just over ambient and elevated temperatures

Triethyl thiophosphate (tetp) invariably forms adducts with various metal perchlorates (M=Mg²⁺, Al³⁺, Cr³⁺, Mn²⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺) at 35–40°C in ethanol-triethyl orthoformate (teof). Only certain of these adducts, which involve S-bonded tetp in the thione form for soft or borderline metal ions and O-bonded tetp in the thiol tautomeric form for hard metal ions, could be isolated in solid form, owing to their tendency to decompose yielding diethylthiophosphato (detp) metal complexes and ethyl perchlorate, at temperatures ranging between ambient and 80–90°C, depending on the metal ion. Several well-defined detp and detpperchlorato metal complexes were obtained by heating solutions of mixtures of tetp and metal perchlorates in ethanol-teof at 80–90°C, and characterized. In most cases, linear polymeric or dimeric complexes involving double or triple bridges of O,S-bonded bidentate detp between adjacent metal ions were isolated. However, in a number of occasions, heavily hydrated monomeric species, containing terminal S-bonded detp were obtained.     

Probing the coordination properties of glutathione with transition metal ions (Cr2+,Mn2+,Fe2+,Co2+, Ni2+,Cu2+,Zn2+,Cd2+,Hg2+) by density functional theory

Complexes formed by reduced glutathione (GSH) with metal cations (Cr²⁺, Mn²⁺,Fe²⁺,Co²⁺,Ni²⁺,Cu²⁺,Zn²⁺,Cd²⁺,Hg²⁺) were systematically investigated by the density functional theory (DFT). The results showed that the interactions of the metal cations with GSH resulted in nine different stable complexes and many factors had an effect on the binding energy. Generally, for the same period of metal ions, the binding energies ranked in the order of Cu²⁺>Ni²⁺>Co²⁺>Fe²⁺>Cr²⁺>Zn²⁺>Mn²⁺; and for the same group of metal ions, the general trend of binding energies was Zn²⁺>Hg²⁺>Cd²⁺. Moreover, the amounts of charge transferred from S or N to transition metal cations are greater than that of O atoms. For Fe²⁺,Co²⁺,Ni²⁺,Cu²⁺,Zn²⁺,Cd²⁺ and Hg²⁺ complexes, the values of the Wiberg bond indices (WBIs) of M-S (M denotes metal cations) were larger than that of M-N and M-O; for Cr²⁺ complexes, most of the WBIs of M-O in complexes were higher than that of M-S and M-N. Furthermore, the changes in the electron configuration of the metal cations before and after chelate reaction revealed that Cu²⁺, Ni²⁺,Co²⁺ and Hg²⁺ had obvious tendencies to be reduced to Cu⁺,Ni⁺,Co⁺ and Hg⁺ during the coordination process.     

Influence of metal ions on bioremediation activity of protocatechuate 3,4-dioxygenase from Stenotrophomonas maltophilia KB2

The aim of this paper was to describe the effect of various metal ions on the activity of protocatechuate 3,4-dioxygenase from Stenotrophomonas maltophilia KB2. We also compared activity of different dioxygenases isolated from this strain, in the presence of metal ions, after induction by various aromatic compounds. S. maltophilia KB2 degraded 13 mM 3,4-dihydroxybenzoate, 10 mM benzoic acid and 12 mM phenol within 24 h of incubation. In the presence of dihydroxybenzoate and benzoate, the activity of protocatechuate 3,4-dioxygenase and catechol 1,2-dioxygenase was observed. Although Fe³⁺, Cu²⁺, Zn²⁺, Co²⁺, Al³⁺, Cd²⁺, Ni²⁺ and Mn²⁺ ions caused 20–80 % inhibition of protocatechuate 3,4-dioxygenase activity, the above-mentioned metal ions (with the exception of Ni²⁺) inhibited catechol 1,2-dioxygenase to a lesser extent or even activate the enzyme. Retaining activity of at least one of three dioxygenases from strain KB2 in the presence of metal ions makes it an ideal bacterium for bioremediation of contaminated areas.     

Interactions of DNA with divalent metal ions. I. 31P-nmr studies

³¹P-nmr has been used to investigate the specific interaction of three divalent metal ions, Mg²⁺, Mn²⁺, and Co⁺², with the phosphate groups of DNA. Mg²⁺ is found to have no significant effect on any of the ³¹P-nmr parameters (chemical shift, line-width, T₁, T₂, and NOE) over a concentration range extending from 20 to 160 mM. The two paramagnetic ions, Mn²⁺ and Co²⁺, on the other hand, significantly change the ³¹P relaxation rates even at very low levels. From an analysis of the paramagnetic contributions to the spin–lattice and spin–spin relaxation rates, the effective internuclear metal–phosphorus distances are found to be 4.5 ± 0.5 and 4.1 ± 0.5 Å for Mn²⁺ and Co²⁺, respectively, corresponding to only 15 ± 5% of the total bound Mn²⁺ and Co²⁺ being directly coordinated to the phosphate groups (inner-sphere complexes). This result is independent of any assumptions regarding the location of the remaining metal ions which may be bound either as outer-sphere complexes relative to the phosphate groups or elsewhere on the DNA, possibly to the bases. Studies of the temperature effects on the ³¹P relaxation rates of DNA in the absence and presence of Mn²⁺ and Co²⁺ yielded kinetic and thermodynamic parameters which characterize the association and dissociation of the metal ions from the phosphate groups. A two-step model was used in the analysis of the kinetic data. The lifetimes of the inner-sphere complexes are 3 × 10^?7 and 1.4 × 10^?5 s for Mn²⁺ and Co²⁺, respectively. The rates of formation of the inner-sphere complexes with the phosphate are found to be about two orders of magnitude slower than the rate of the exchange of the water of hydration of the metal ions, suggesting that expulsion of water is not the rate-determining step in the formation of the inner-sphere complexes. Competition experiments demonstrate that the binding of Mg²⁺ ions is 3–4 times weaker than the binding of either Mn²⁺ or Co²⁺. Since the contribution from direct phosphate coordination to the total binding strength of these metal ion complexes is small (～15%), the higher binding strength of Mn²⁺ and Co²⁺ may be attributed either to base binding or to formation of stronger outer-sphere metal–phosphate complexes. At high levels of divalent metal ions, and when the metal ion concentration exceeds the DNA–phosphate concentration, the fraction of inner-sphere phosphate binding increases. In the presence of very high levels of Mg²⁺ (e.g., 3.1M), the inner-sphere ? outer-sphere equilibrium is shifted toward ～100% inner-sphere binding. A comparison of our DNA results and previous results obtained with tRNA indicates that tRNA and DNA have very similar divalent metal ion binding properties. A comparison of the present results with the predictions of polyelectrolyte theories is presented.     

Study of complex formation with 2-hydroxyiminocarboxylates: specific metal binding ability of 2-(4-methylthiazol-2-yl)-2-(hydroxyimino)acetic acid

Complex formation properties of a novel water soluble thiazolyloxime 2-(4-methylthiazol-2-yl)-2-(hydroxyimino)acetic acid (H₃L¹) with Cu²⁺ and Ni²⁺ were investigated in solution by potentiometrical and spectral (UV-Vis, EPR, NMR) methods. All Cu²⁺ and most of Ni²⁺ complex species detected in solution were found to have square-planar MN₄ core with oxime and heterocyclic nitrogen atoms which was rationalized in terms of destabilizing effect of repulsive interaction between oxygen atom of carboxylic group and nitrogen atom of thiazole ring in N,O-coordinated ligand conformation. It has been found that stability of metal complexes in a series of oxime ligands is dependent upon basicity of nitrogen atom of oxime group. The thiazolyloxime forms less stable complexes with Cu²⁺ but stronger ones with Ni²⁺ ions when compared to parent 2-(hydroxyimino)propanoic acid. The lower stability obtained for Cu²⁺ complexes was elucidated in terms of negative inductive effect of the thiazole and nitrile substituents as well as an effect of intramolecular attractive interaction between thiazolyl sulfur and oxime oxygen atoms in thiazolyloxime. In the case of Ni²⁺ the complexes formed are square-planar and it is why thiazolyl ligand is more effective in metal ion binding than simple 2-(hydroxyimino)propanoic acid forming only octahedral species. The solid state structure of the Co³⁺ complex K₃[Co(HL¹)₃]·5.5H₂O (1) was studied by X-ray analysis. The thiazolyloxime ligand is coordinated to Co³⁺ via oxime nitrogen and carboxylate oxygen atoms forming five-membered chelate rings.     

Biosorption of Heavy Metals (Cd2+, Cu2+, Co2+, and Mn2+) by Thermophilic Bacteria,Geobacillus thermantarcticus and Anoxybacillus amylolyticus: Equilibrium and Kinetic Studies

ABSTRACT

Two strains of thermophilic bacteria, Geobacillus thermantarcticus and Anoxybacillus amylolyticus, were employed to investigate the biosorption of heavy metals including Cd²⁺, Cu²⁺, Co²⁺, and Mn²⁺ ions. The effects of different biosorption parameters such as pH (2.0–10.0), initial metal concentrations (10.0–300.0 mg L^?1), amount of biomass (0.25–10 g L^?1), temperature (30–80°C), and contact time (15–120 min) were investigated. Concentrations of metal ions were determined by using an inductively coupled plasma optical emission spectrometry (ICP-OES). Optimum pHs for Cd²⁺, Cu²⁺, Co²⁺, and Mn²⁺ biosorption by Geobacillus thermantarcticus were found to be 4.0, 4.0, 5.0, and 6.0, respectively. For Anoxybacillus amylolyticus, the optimum pHs for Cd²⁺, Cu²⁺, Co²⁺, and Mn²⁺ biosorption were found to be 5.0, 4.0, 5.0, and 6.0, respectively. The Cd²⁺, Cu²⁺, Co²⁺, and Mn²⁺ removals at 50 mg L^?1 in 60 min by 50 mg dried cells of Geobacillus thermantarcticus were 85.4%, 46.3%, 43.6%, and 65.1%, respectively, whereas 74.1%, 39.8%, 35.1%, and 36.6%, respectively, for Anoxybacillus amylolyticus. The optimum temperatures for heavy metal biosorption were near the optimum growth temperatures for both strains. Scatchard plot analysis was employed to obtain more compact information about the interaction between metal ions and biosorbents. The plot results were further studied to determine if they fit Langmuir and Freundlich models.     

Separation of hexahistidine fusion proteins with immobilized metal ion affinity chromatographic (IMAC) sorbents derived from MN+‐tacn and its derivatives

The capabilities of a new class of immobilized (im) metal ion chelate complexes (IMCCs), derived from 1,4,7‐triazacyclononane (tacn), bis(1,4,7‐triazacyclononyl) ethane (dtne) and bis(1,4,7‐triazacyclononyl)propane (dtnp) complexed with the borderline metal ions Cu²⁺, Ni²⁺, Zn²⁺, Mn²⁺, Co²⁺, and Cr³⁺, for the purification of proteins have been investigated. In particular, the binding behavior of a model protein, the C‐terminal hexahistidine tagged recombinant fusion protein Schistosoma japonicum glutathione S‐transferase‐Saccharomyces cerevisiae mitochondrial ATP synthase δ‐subunit (GST‐δATPase‐His₆), with these new immobilized metal ion affinity chromatographic (IMAC) sorbents was compared to the properties of a conventional sorbent, derived from immobilized Ni(II)‐nitrilotriacetic acid (im‐Ni²⁺‐NTA). Investigations using the recombinant GST‐δATPase‐His₆ and recombinant S. japonicum glutathione S‐transferase (GST) lacking a hexahistidine tag have confirmed that the C‐terminal tag hexahistidine residues were required for the binding process to occur with these IMAC systems. The results also confirm that recombinant fusion proteins such as GST‐δATPase‐His₆ can be isolated in high purity with these IMAC systems. Moreover, these new macrocyclic systems manifest different selectivity features as a function of pH or ionic strength when compared to the conventional, unconstrained iminodiacetic acid (IDA) or NTA chelating ligands, complexed with borderline metal ions such as Cu²⁺ or Ni²⁺, as IMAC systems. Biotechnol. Bioeng. 2009;103: 747–756. © 2009 Wiley Periodicals, Inc.     

Effects of Ni(2+), Co(2+), and Mn(2+) on desensitized butyrylcholinesterase prepared from human serum

Human serum butyrylcholinesterase (BChE) has been converted into a stable but less active desensitized form when heated at 45°C for 24 h. The desensitized BChE follows Michaelis-Menten kinetics, whereas native enzyme exhibits slightly negative cooperativity with respect to butyrylthiocholine binding. In this study, we investigated the effects of Ni²⁺, Co²⁺, and Mn²⁺ on the desensitized BChE. It is found that all three ions were noncompetitive inhibitors of the desensitized BChE, and K _i values have been determined as 7.816±1.060 mM, 48.722±4.635 mM, and 84.795±5.249 mM for Ni²⁺, Co²⁺, and Mn²⁺, respectively. In our previous study, these ions were linear mixed-type inhibitors of the native BChE. This finding confirms that desensitized BChE changes to a different conformation than native BChE. From the comparison of K _i values of the trace elements, it can be said that Ni²⁺ is a more effective inhibitor of the desensitized BChE than Co²⁺ and Mn²⁺.     

Coordination contributions to protein stability in metal-substituted carbonic anhydrase

Contributions of the active site metal to the stability of carbonic anhydrase (CA) were quantified by differential scanning calorimetry and complementary unfolding measurements of CA substituted with Co²⁺, Cd²⁺, Cu²⁺, Ni²⁺ and Mn²⁺. The metal ions stabilize the protein to different extent, with the highest stability provided by the native Zn²⁺. This additional stability does not correlate with the enthalpy of the three metal-imidazole (His) bonds at the active site or other properties of the metal ions (charge density, hydration enthalpy). However, DFT calculations reveal an energetic penalty associated with metal coordination at the active site, and the magnitude of this penalty correlates inversely with metal contributions to the stability of the protein. While the affinity of CA for metal ions generally reflects the Irving–Williams series, the additional thermal stability provided by metal ions is modulated by the rigid His₃ coordination that is imposed at the protein site.     

Thermostable alkaline protease from newly isolated <Emphasis Type="Italic">Vibrio</Emphasis> sp.: extraction,purification and characterisation

An extracellular alkaline protease-producing Vibrio sp. was isolated from mangrove sediments of Vellar estuary. A 9.36-fold purification was achieved by a three-step purification procedure and the molecular weight of the enzyme was determined as 33 kDa by SDS-PAGE. The enzyme was active in a broad range of pH (6.0–11.0) and temperature (30–70°C), the optimum being at pH 9.0 and temperature 55°C. The enzyme was stable at alkaline pH range of 9–11 and up to a temperature of 60°C, after incubation for 1 h. Metals like Co²⁺, Hg²⁺, Ni²⁺ and Cu²⁺ inhibited the enzyme activity, whereas Fe²⁺, Ca²⁺ and Mn²⁺ were found to enhance the activity. The protease was found to be highly stable in the presence of oxidizing agents like H₂O₂, detergents such as SDS and Triton-X-100 and also some of the commonly used commercial detergents. The organic solvents like xylene, isopropanol, hexane and benzene were found to enhance as well as stabilize the enzyme activity. The extracellular production of the enzyme, the pH and thermal stability, and the stability in presence of oxidants, surfactants, commercial detergents and organic solvents, altogether suggest that it can be used as a laundry additive.     

Degradation of DNA into 5′-Monodeoxyribonucleotides in the Presence of Mn2+ Ions

DNA is known to be aggregated by metal ions including Mn²⁺ ions, but analysis of the aggregation process from a chemical viewpoint, which means identification of the product yielded during the process, has not been performed yet. On examination of the kinds of degraded materials that were in the supernatant obtained on centrifugation of a DNA mixture aggregated under conditions of 10 mM Mn²⁺ ions ([Mn]/[P] = 46.3) at 70 °C for 1 h, the degradation products were found to be dAMP, dCMP, dGMP, and TMP. These dNMPs were purified by HPLC on TSKgel ODS-80Ts and identified by LC-TOF/MS. The degradation activity was lost on pretreatment of the DNA with a phenol–chloroform mixture, and the activity was recovered by pretreatment with a mixture of DMSO and a buffer containing surfactants. Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, and Cd²⁺, as transition element metal ions, were effective as to the degradation into dNMP. Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺, as alkali earth element metal ions, were not effective as to the degradation. Monovalent anions such as Cl^?, CH₃OO^?, and NO₃ ^? were found to increase the degradation rate. Sixty μg of the 120 μg of the starting DNA in 450 μl was degraded into dNMP on reaction for 1 h in the presence of 100 mM NaCl and 10 mM Mn²⁺ ions. In this process, aggregation did not occur, and thus was not considered to be necessary for degradation. The degradation was found not to occur at pH 7.0, and to be very sensitive to pH. The OH^? ion should have a critical role in cleavage of the phosphodiester linkages in this case. The dNMP obtained in the degradation process was found to be only 5′-NMP, based on the H¹NMR spectra. This prosess should prove to be a new process for the production of 5′-dNMP in addtion to the exonuclease.     

Structural and biochemical properties of lichenase from <Emphasis Type="Italic">Clostridium thermocellum</Emphasis>

The recombinant enzyme lichenase of size 30 kDa was over-expressed using E. coli cells and purified by immobilized metal ion affinity chromatography (IMAC) and size exclusion chromatography. The enzyme displayed high activity towards lichenan and β-glucan. The enzyme showed no activity towards carboxymethyl cellulose, laminarin, galactomannan or glucomannan. Surprisingly, affinity-gel electrophoresis on native-PAGE showed that the enzyme binds only glucomannan and not lichenan or β-glucan or other manno-configured substrates. The enzyme was thermally stable between the temperatures 60°C and 70°C. Presence of Cu²⁺ ions at a concentration of 5 mM enhanced enzyme activity by 10% but higher concentrations of Cu²⁺ (>25 mM) showed a sharp fall in the enzyme activity. Heavy metal ions Ni²⁺, Co²⁺ and Zn²⁺ did not affect the activity of the enzyme at low concentrations (0–10 mM) but at higher concentrations (>10 mM), caused a decrease in the enzyme activity. The crystals of lichenase were produced and the 3-dimensional structure of native form of enzyme was previously solved at 1.50 Å. Lichenase displayed (β/α)₈-fold a common fold among many glycoside hydrolase families. A cleft was identified that represented the probable location of active site.     

Metal–bipyridine complexes in DNA backbones and effects on thermal stability

Modified oligonucleotides are showing potential for multiple applications, including drug design, nanoscale building blocks, and biosensors. In an effort to expand the functionality available to DNA, we have placed chelating ligands directly into the backbone of DNA. Between one and three nucleosides were replaced with 2,2′-bipyridine phosphates in 23-mer duplexes of DNA. An array of metal ions were added (Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, and Pt²⁺) and the influences on duplex stability were examined by melting temperature studies. Titrations and UV–vis absorption spectroscopy were used to provide insights into the nature of the metal complexes formed. We found that Ni²⁺ binding to 2,2′-bipyridine typically provided the greatest increase in duplex stability relative to the other metal ions examined. For example, addition of Ni²⁺ to one 2,2′-bipyridine–DNA duplex increased the melting temperature by 13 °C, from 65.0 ± 0.3 to 78.4 ± 0.9 °C. These studies show that metal ions and backbone ligands can be used to regulate DNA structure and stability.     

An aromatic schiff base stabilised as a coordinated enol iminium zwitterion by complex formation with a series of divalent metal ions

The Schiff base N-(2-hydroxy-3-carboxy-1-naphthylidine)-4-methyl-2-sulphonic acid aniline (bonsaH₃) has been found to react with a range of divalent metal ions (Mg²⁺, Mn²⁺, Co²⁺, Ni²⁺ and Zn²⁺ and UO₂²⁺ to give red-yellow insoluble complexes (bonsaH)_m(H₂O)_n. The solid state diffuse reflectance spectra of all the complexes have an intense visible band at ca. 470 nm. This fact, together with evidence from infrared spectra and room-temperature magnetic-moment measurements, suggests that in all cases the ligand is coordinated to the metal ion in the solid state in the enol-iminium zwitterionic form. The ¹H NMR spectra of the Mg²⁺ and Zn²⁺ complexes in DMSO-d₆ indicate that a different structure is adopted in this solvent. Comparisons with the spectra of bonsa-H₃ and (bonsa-H₂)K·H₂O suggest that the solution structure is that of an enol-imine.     

Interaction of metal ions with polynucleotides and related compounds. XXII. Effect of divalent metal ions on the conformational changes of polyribonucleotides

Changes in the conformation of poly(G), poly(C), poly(U), and poly(I) in the presence of divalent metal ions Mg²⁺, Ca²⁺, Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Cd²⁺, and Zn²⁺ have been measured by means of ORD and u.v. spectra. Mg²⁺ and Ca²⁺ ions stabilize helical structures of all the polynucleotides very effectively at concentrations several orders of magnitude lower than the effective concentration of Na⁺ion. Cu²⁺ and Cd²⁺ destabilize the helical structure of polynucleotides to form random coils. Zn²⁺, Ni²⁺, Co²⁺, and Mn²⁺ions do not behave in such a clear-cut manner: they selectively stabilize some ordered structures, while destabilizing others, depending on the ligand strength of the nucleotide base as well as the preferred conformation of that polynucleotide.     

Expression, purification and characterization of flavin reductase from Citrobacter freundii A1

Flavin reductase plays an important biological role in catalyzing the reduction of flavin by NAD(P)H oxidation. The gene that codes for flavin reductase from Citrobacter freundii A1 was cloned and expressed in Escherichia coli BL21(DE3)pLysS. In this study, we aimed to characterize the purified recombinant flavin reductase of C. freundii A1. The recombinant enzyme was purified to homogeneity and the biochemical profiles, including the effect of pH, temperature, metal ions and anions on flavin reductase activity and stability, were determined. This enzyme exhibited optimum activity at 45 °C in a 10-min reaction at pH 7.5 and was stable at temperatures up to 30 °C. At 0.1 mM concentration of metal ions, flavin reductase activity was stimulated by divalent cations including Mn²⁺, Sr²⁺, Ni²⁺, Sn²⁺, Ba²⁺, Co²⁺, Mg²⁺, Ca²⁺ and Pb²⁺. Ag⁺ was noticeably the strongest inhibitor of recombinant flavin reductase of C. freundii A1. This enzyme should not be defined as a standard flavoprotein. This is the first attempt to characterize flavin reductase of C. freundii origin.     

Chemical and functional characterization of metal-binding pseudotripeptides with different functionalized N-alkyl residues Dedicated to Professor Dr. Ernst-Gottfried Jaeger on occasion of his 65th birthday

Pseudotripeptide ligands with 4 different N-functionalized glycine residues were qualitatively, semiquantitatively and quantitatively tested for their complexation of the bivalent transition metal ions Zn²⁺, Cu²⁺, Co²⁺, Ni²⁺ and Mn²⁺. The functional side chains have different length and different groups available for complexation. MALDI-MS and ESI-MS were used for more qualitative or semiquantitative estimation of the complex formation tendencies. The found ranking differs by these two methods only for Zn²⁺ and Ni²⁺. For one of the pseudotripeptide ligands, the ligand L1, complex formation with certain transition metal was estimated quantitatively by potentiometric titration. The Zn-complex of that ligand polarizes bound water strongly, resulting in a low pK_a-value. Complexes of pseudotripeptide ligand L1 with certain metal ions were tested for their hydrolytic activity. The pseudo first order rate constants of the hydrolysis of the substrates 4-nitrophenyl acetate and bis(4-nitrophenyl)phosphate were compared to complexes with the same metal ions formed with a very well studied ligand from the literature, the 1,4,7,10-tetraaza cyclododecane (cyclen). The hydrolysis of the phosphate ester occurs very slowly compared to the acetate ester. No correlation exists between the estimated pK_a values of complexes formed from ligand L1 with different metal ions and the phosphate ester hydrolysis. The Ni ions give totally different hydrolytic activities for pseudotripeptide ligand L1 and cyclen. With one exception, the Ni-cyclen complex, all other complexes have only a low or moderate catalytic activity.     

4,5-Bis(diphenylphosphinoyl)-1,2,3-triazole ligand: Studies on metal complex formations in liquid-liquid distribution systems

The formation reactions of hydrophobic metal complexes of divalent typical element and transition metal ions with a novel chelating ligand containing N and O donor atoms, 4,5-bis(diphenylphosphinoyl)-1,2,3-triazole (L^TH), were investigated by the liquid-liquid distribution method carried out on metal ions between chloroform and aqueous solutions. The liquid-liquid distribution reaction formulae of metal ions via the formation of hydrophobic metal complexes were revealed, along with their equilibrium constants. Three types of hydrophobic mononuclear and binuclear metal complexes distributed into chloroform solutions were found, namely, ML₂ (M = Mg²⁺, Zn²⁺, Pb²⁺; L = L^T−), ML₂(HL) (M = Cd²⁺, Mn²⁺), and M₂L₃(OH) (M = Co²⁺, Ni²⁺, Cu²⁺). Linear free energy relationships were found between the equilibrium constants of the liquid-liquid distribution reactions and the stability constants of 1:1 complexes consisting of a divalent metal ion and a glycinate. These relationships suggest the chelate formation of N,O-coordination with a heterocyclic five-membered ring in the metal complexes with L^TH.     

Effect of metal ions (Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+ and Zn2+) and water coordination on the structure and properties of l-histidine and zwitterionic l-histidine

Interactions between metal ions and amino acids are common both in solution and in the gas phase. The effect of metal ions and water on the structure of l-histidine is examined. The effect of metal ions (Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Ni²⁺, Cu²⁺ and Zn²⁺) and water on structures of His·M(H₂O)m, m = 0.1 complexes have been determined theoretically employing density functional theories using extended basis sets. Of the five stable complexes investigated the relative stability of the gas-phase complexes computed with DFT methods (with one exception of K⁺ systems) suggest metallic complexes of the neutral l-histidine to be the most stable species. The calculations of monohydrated systems show that even one water molecule has a profound effect on the relative stability of individual complexes. Proton dissociation enthalpies and Gibbs energies of l-histidine in the presence of the metal cations Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Ni²⁺, Cu²⁺ and Zn²⁺ were also computed. Its gas-phase acidity considerably increases upon chelation. Of the Lewis acids investigated, the strongest affinity to l-histidine is exhibited by the Cu²⁺ cation. The computed Gibbs energies ΔG are negative, span a rather broad energy interval (from ?130 to ?1,300 kJ/mol), and upon hydration are appreciably lowered.     

Catalytic properties of d-xylose isomerase from Streptomyces violaceoruber

The catalytic properties and stability of d-xylose isomerase from Streptomyces violaceoruber have been studied. The enzyme was activated by Mg²⁺, Co²⁺ and Mn²⁺ but Ni²⁺, Ca²⁺, Zn²⁺, Cu²⁺ and Hg were ineffective. Optimum catalytic conditions were obtained at 80°C in the pH range 7.5–9.5 and in the presence of 10 mm Mg²⁺. The specific activity of the enzyme increased after treatment with 10 mm EDTA (factor 2.4). A further increase of activity (factor 2.0–2.8) was observed after preincubation of the enzyme with Mg²⁺ or Co²⁺, the preincubation time depending on the incubation temperature. The thermal stability of the enzyme is very high. At 60°C the enzyme retained optimum activity following 30 days of storage in the presence of 1 mm Co²⁺ or 10 mm Mg²⁺. At 80°C, Co²⁺ is superior as a protector against thermal denaturation. At saturating concentrations of Mg²⁺ (35°C) the K_m-values of the EDTA-treated enzyme with respect to d-xylose and d-glucose were 2.8 and 149 mm and the dissociation constants of the enzyme-Mg²⁺ complex for xylitol and d-sorbitol were 0.455 and 4.47 mm, respectively.