Cloning and expression of the gene for xylose isomerase fromThermus flavus AT62 inEscherichia coli

The gene encoding xylose isomerase (xylA) was cloned fromThermus flavus AT62 and the DNA sequence was determined. ThexylA gene encodes the enzyme xylose isomerase (XI orxylA) consisting of 387 amino acids (calculated Mr of 44,941). Also, there was a partial xylulose kinase gene that was 4 bp overlapped in the end of XI gene. The XI gene was stably expressed inE. coli under the control oftac promoter. XI produced inE. coli was simply purified by heat treatment at 90°C for 10 min and column chromatography of DEAE-Sephacel. The Mr of the purified enzyme was estimated to be 45 kDa on SDS-polyacrylamide gel electrophoresis. However, Mr of the cloned XI was 185 kDa on native condition, indicating that the XI consists of homomeric tetramer. The enzyme has an optimum temperature at 90°C. Thermostability tests revealed that half life at 85°C was 2 mo and 2 h at 95°C. The optimum pH is around 7.0, close to where by-product formation is minimal. The isomerization yield of the cloned XI was about 55% from glucose, indicating that the yield is higher than those of reported enzymes. The Km values for various sugar substrates were calculated as 106 mM for glucose. Divalent cations such as Mn²⁺, Co²⁺, and Mg²⁺ are required for the enzyme activity and 100 mM EDTA completely inhibited the enzyme activity.     

Purification, characterization, and structural investigation of a new moderately thermophilic and partially calcium-independent extracellular α-amylase from Bacillus sp. TM1

A new α-amylase was extracted from a recently found strain of Bacillus sp. and purified by ion-exchange chromatography. Sodium dodecyl sulfate polyacrylamide gel electrophoresis showed a single band for the purified enzyme with an apparent molecular weight of 59 kDa. The optimum temperature and pH range of the enzyme were 40–60°C and 4.5–7.5, respectively, and its activation energy was 1.974 kcal/mol. The K _m value for the enzyme activity on solubie starch was 4 mg/mL, and the T _m values obtained from the circular dichroism (CD) results of thermal unfolding were 78.7 and 80.2°C in the absence and presence of the calcium, respectively. The enzyme was almost completely inhibited by the addition of Fe³⁺, Mn²⁺, and Zn²⁺ and was activated by EDTA, Cr³⁺, and Al³⁺. Moreover, it was partially inhibited by Ca²⁺, Ba²⁺, Ni²⁺, and Co²⁺. Proteolytic digestion of the enzyme using trypsin combined with results from T _m using CD and irreversible thermoinactivation suggests that this enzyme can be considered a moderate thermophile with both mild flexibility and rigidity.     

Glycosidases of turnip leaf tissues

Four myrosinase (β-thioglucosidase EC. 3.2.3.1) and seven disaccharase (β-fructofuranosidase, EC. 3.2.1.26) isoenzymes were isolated from turnip leaves. The most active enzymes were isolated in pure form. Myrosinase and disaccharase mol wt was 62.0 × 10³ and 69.5 × 10³ dalton, respectively, on the basis of gel filtration on Sephadex G-200. Myrosinase pH profile showed high activity between pH 5 and 7 with the optimum at pH 5.5. The purified enzyme was heat-stable for 60 min at 30°C with only loss of 24% of activity. Its activity is strongly inhibited (100%) by Pb²⁺, Ba²⁺, Cu²⁺ and Ca²⁺ ions, and activated (70%) by EDTA at 0.04M. The pure enzyme failed to hydrolyze amylose, glycogen, lactose, maltose, and sucrose. TheK _m andV _max values of myrosinase using sinigrin as specific substrate was 0.045 mM and 2.5 U, respectively. The maximal activity of disaccharase enzyme was obtained at pH 4–5 and 35–37°C. The enzyme was heat-stable at 30°C for 30 min with only 10% loss of its activity. Its activity is strongly activated (70–240%) by Ca²⁺, Ba²⁺, Cu²⁺, and EDTA at 0.01M. The enzyme activity is specific to the disaccharide sucrose and failed to hydrolyze other disaccharides (maltose and lactose). TheK _m andV _max of disaccharase were 0.123 mM and 3.33 U, respectively.     

Purification, characterization, kinetic properties, and thermal behavior of extracellular polygalacturonase produced by filamentous fungus Tetracoccosporium sp

For the first time, a polygalacturonase from the culture broth of Tetracoccosporium sp. was isolated and incubated at 30°C in an orbital shaker at 160 rpm for 48h. The enzyme was purified by ammonium sulfate precipitation and two-step ion-exchange chromatography and had an apparent molecular mass of 36 kDa, as shown by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. Its optimum activity was at pH 4.3 and 40°C, and the K _m and V _max values of this enzyme (for polygalacturonic acid) were 3.23 mg/mL and 0.15 μmol/min, respectively. Ag⁺, Co²⁺, EDTA, Tween-20, Tween-80, and Triton X-100 stimulated polygalacturonase activity whereas Al³⁺, Ba²⁺, Ca²⁺, Fe²⁺, Fe³⁺, Ni²⁺, Mg²⁺, Mn²⁺, and SDS inhibited it. In addition, iodoacetamide and iodoacetic acid did not inhibit enzyme activity at a concentration of 1 mM, indicating that cysteine residues are not part of the catalytic site of polygalacturonase. We studied the kinetic properties and thermal inactivation of polygalacturonase. This enzyme exhibited a t _1/2 of 63 min at 60°C and its specific activity, turnover number, and catalytic efficiency were 6.17 U/mg, 113.64 min⁻¹, and 35.18 mL/(min·mg), respectively. The activation energy (ΔE ^#) for heat inactivation was 5.341 kJ/mol, and the thermodynamic activation parameters ΔG ^#, ΔH ^#, and ΔS ^# were also calculated, revealing a potential application for the industry.     

Highly Thermostable Xylanase of the Thermophilic Fungus Talaromyces thermophilus: Purification and Characterization

A thermostable xylanase from a newly isolated thermophilic fungus Talaromyces thermophilus was purified and characterized. The enzyme was purified to homogeneity by ammonium sulfate precipitation, diethylaminoethyl cellulose anion exchange chromatography, P-100 gel filtration, and Mono Q chromatography with a 23-fold increase in specific activity and 17.5% recovery. The molecular weight of the xylanase was estimated to be 25kDa by sodium dodecyl sulfate–polyacrylamide gel electrophoresis and gel filtration. The enzyme was highly active over a wide range of pH from 4.0 to 10.0. The relative activities at pH5.0, 9.0, and 10.0 were about 80%, 85.0%, and 60% of that at pH7.5, respectively. The optimum temperature of the purified enzyme was 75°C. The enzyme showed high thermal stability at 50°C (7days) and the half-life of the xylanase at 100°C was 60min. The enzyme was free from cellulase activity. K _m and V _max values at 50°C of the purified enzyme for birchwood xylan were 22.51mg/ml and 1.235μmol min⁻¹ mg⁻¹, respectively. The enzyme was activated by Ag⁺, Co²⁺, and Cu²⁺; on the other hand, Hg²⁺, Ba²⁺, and Mn²⁺ inhibited the enzyme. The present study is among the first works to examine and describe a secreted, cellulase-free, and highly thermostable xylanase from the T. thermophilus fungus whose application as a pre-bleaching aid is of apparent importance for pulp and paper industries.     

Purification and partial characterization ofRhizomucor miehei lipase for ester synthesis

A commercialRhizomucor miehei lipase was purified by ammonium sulfate precipitation. Phenyl Sepharose 6 Fast Row hydrophobic interaction chromatography, and DEAE Sepharose Fast Flow anion-exchange chromatography. The recovery of lipase activity was 32% with a 42-fold purification. The molecular size of the purified enzyme was 31,600 Dalton and the pI 3.8. The enzyme was stable for at least 24 h within a pH range of 7.0-10.0, and 96.8% of the enzyme activity remained when kept at 30‡C for 24 h. Further, about 10–30% of the lipase activity was inhibited by K⁺, Li⁺, Ni⁺, Co²⁺, Zn²⁺, Mg²⁺, Sn²⁺, Cu²⁺, Ba²⁺, Ca²⁺, and Fe²⁺ ions and by SDS, but EDTA had no effect. Under the experimental conditions, the optimum temperature for the hydrolysis of olive oil was 50‡C (pH 8.0), and for the synthesis of 1-butyl oleate, 37‡C. It was concluded that hydrolytic activity of lipase alone is not a sufficient criterion for its synthetic potential. The optimal molar ratio of oleic acid and 1-butanol was 2:1 for 1-butyl oleate synthesis. The 1-butyl oleate yield was unaffected by purification of the enzyme after 12 h.     

Characterization of Cyclodextrin Glucanotransferase Produced by <Emphasis Type="Italic">Bacillus megaterium</Emphasis>

Cyclodextrin glucanotransferase, produced by Bacillus megaterium, was characterized, and the biochemical properties of the purified enzyme were determined. The substrate specificity of the enzyme was tested with different α-1,4-glucans. Cyclodextrin glucanotransferase displayed maximum activity in the case of soluble starch, with a K _m value of 3.4 g/L. The optimal pH and temperature values for the cyclization reaction were 7.2 and 60 °C, respectively. The enzyme was stable at pH 6.0–10.5 and 30 °C. The enzyme activity was activated by Sr²⁺, Mg²⁺, Co²⁺, Mn²⁺, and Cu²⁺, and it was inhibited by Zn²⁺and Ag⁺. The molecular mass of cyclodextrin glucanotransferase was established to be 73,400 Da by sodium dodecyl sulfate–polyacrylamide gel electrophoresis, 68,200 Da by gel chromatography, and 75,000 Da by mass spectrometry. The monomer form of the enzyme was confirmed by the analysis of the N-terminal amino acid sequence. Cyclodextrin glucanotransferase formed all three types of cyclodextrins, but the predominant product was β-cyclodextrin.     

Purification and Characterization of Thermostable α-Galactosidase from <Emphasis Type="Italic">Aspergillus terreus</Emphasis><Subscript>GR</Subscript>

An extracellular thermostable α-galactosidase producing Aspergillus terreus _GR strain was isolated from soil sample using guar gum as sole source of carbon. It was purified to apparent homogeneity by acetone precipitation, gel filtration followed by DEAE-Sephacel chromatographic step. The purified enzyme showed a single band after sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The molecular weight of the purified enzyme after SDS-PAGE was 108 kDa. The enzyme showed optimum pH and temperature of 5.0 and 65 °C, respectively, for artificial substrate pNPαGal. α-Galactosidase from A. terreus _GR is found to be thermostable, as it was not inactivated after heating at 65 °C for 40 min. The K _m for pNPαGal, oNPαGal, raffinose, and stachyose are 0.1, 0.28, 0.42, and 0.33 mM, respectively. Inhibitors such as 1,10-phenanthroline, phenylmethylsulfonyl fluoride, ethylenediaminetetraacetic acid, mercaptoethanol, and urea have no effect, whereas N-bromosuccinamide inhibited enzyme activity by 100%. Among metal ions tested, Mg²⁺, Ni²⁺, Ca²⁺, Co²⁺, and Mn²⁺ had no effect on enzyme activity, but Ag⁺, Hg²⁺, and Cu²⁺ have inhibited complete activity.     

Biochemical and enzymatic properties of a novel marine fibrinolytic enzyme from <Emphasis Type="Italic">Urechis unicinctus</Emphasis>

A novel potent protease, Urechis unicinctus fibrinolytic enzyme (UFE), was first discovered by our laboratory. In this study, we further investigated the enzymatic properties and dynamic parameters of UFE. As a low molecular weight protein, UFE appeared to be very stable to heat and pH. When the temperature was <50°C, the remnant enzyme activity remained almost unchanged, but when the temperature was raised to 60#x00B0;C the remnant enzyme activity began to decrease rapidly. UFE was quite stable in a pH range of 3.0–12.0, especially at slightly alkaline pH values. Mn²⁺, Cu²⁺, and Fe²⁺ ions were activators of UFE, whereas Fe³⁺ and Ag⁺ ions were inhibitors. Fe²⁺ ion along with Fe³⁺ ion might regulate UFE activity in vivo. The optimum pH and temperature of UFE were about 8.0 and 50°C, respectively. When using casein as substrate and a substrate concentration <0.1% casein (w/v), the reaction velocity was increased with substrate concentration. Also when using casein as substrate, the determined K _m and V _max of UFE were 0.5298 mg/mL and 3.0845 mol of l-tyrosine equivalent, respectively. Our systematic research results are significant when UFE is applied for medical and industrial purposes.     

Isomerization ofn-butane on the SO4/ZrO2 catalyst promoted by IV Period metals

The catalytic activity of superacidic systems based on SO₄/ZrO₂ and modified by IV Period metals in isomerization ofn-butane was studied. At low temperatures of the reaction, the introduction of Fe³⁺, Sc³⁺, Co²⁺, or Zn²⁺ ions (1%) increases the yield of isobutane by 1.5 times due to the activation ofn-butane on the sites created by the promoting ions. The addition of Cr³⁺, V⁴⁺, or Mn²⁺ (1%) decreases the catalytic activity because of a decrease in the catalyst acidity, most likely, due to the reduction of surface sulfur species. The influence of the nature of the support and surface additives of SiO₂, TiO₂, and ZrO₂ on the activity and selectivity of the catalytic system inn-butane isomerization was studied. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7 pp. 1276–1280, July, 1999     

Characterization of xylitol dehydrogenase from debaryomyces hansenii

The xylitol dehydrogenase (EC 1.1.1.9) from xylose-grown cells ofDebaryomyces hansenii was partially purified in two Chromatographic steps, and characterization studies were carried out in order to inves tigate the role of the xylitol dehydrogenase-catalyzed step in the regu lation of D-xylose metabolism. The enzyme was most active at pH 9.0–9.5, and exhibited a broad polyol specificity. The Michaelis con stants for xylitol and NAD⁺ were 16.5 and 0.55 mM, respectively. Ca²⁺, Mg²⁺, and Mn²⁺ did not affect the enzyme activity. Conversely, Zn²⁺, Cd²⁺, and Co²⁺ strongly inhibited the enzyme activity. It was concluded that NAD⁺-xylitol dehydrogenase from D.hansenii has similarities with other xylose-fermenting yeasts in respect to optimal pH, substrate specificity, and K_m value for xylitol, and therefore should be named L-iditol:NAD⁺-5-oxidoreductase (EC 1.1.1.14). The reason D.hansenii is a good xylitol producer is not because of its value of K_m for xylitol, which is low enough to assure its fast oxidation by NAD⁺ xylitol dehydrogenase. However, a higher K_m value of xylitol dehydro genase for NAD⁺ compared to theK _m values of other xylose-ferment ing yeasts may be responsible for the higher xylitol yields.     

Purification and Characterization of a Hyperthermostable and High Maltogenic α-Amylase of an Extreme Thermophile <Emphasis Type="Italic">Geobacillus thermoleovorans</Emphasis>

The purified α-amylase of Geobacillus thermoleovorans had a molecular mass of 26 kDa with a pI of 5.4, and it was optimally active at 100 °C and pH 8.0. The T _1/2 of α-amylase at 100 °C increased from 3.6 to 5.6 h in the presence of cholic acid. The activation energy and temperature quotient (Q ₁₀) of the enzyme were 84.10 kJ/mol and 1.31, respectively. The activity of the enzyme was enhanced strongly by Co²⁺ and Fe²⁺; enhanced slightly by Ba²⁺, Mn²⁺, Ni²⁺, and Mg²⁺; inhibited strongly by Sn²⁺, Hg²⁺, and Pb²⁺, and inhibited slightly by EDTA, phenyl methyl sulfonyl fluoride, N-ethylmaleimide, and dithiothreitol. The enzyme activity was not affected by Ca²⁺ and ethylene glycol-bis (β-amino ethyl ether)-N,N,N,N-tetra acetic acid. Among different additives and detergents, polyethylene glycol 8000 and Tween 20, 40, and 80 stabilized the enzyme activity, whereas Triton X-100, glycerol, glycine, dextrin, and sodium dodecyl sulfate inhibited to a varied extent. α-Amylase exhibited activity on several starch substrates and their derivatives. The K _m and K _cat values (soluble starch) were 1.10 mg/ml and 5.9 × 10³ /min, respectively. The enzyme hydrolyzed raw starch of pearl millet (Pennisetum typhoides) efficiently.     

Purification and Characterization of Extracellular Inulinase from a Marine Yeast <Emphasis Type="Italic">Cryptococcus aureus</Emphasis> G7a and Inulin Hydrolysis by the Purified Inulinase

The extracellular inulinase in the supernatant of the cell culture of the marine yeast Cryptococcus aureus G7a was purified to homogeneity with a 7.2-fold increase in specific inulinase activity compared to that in the supernatant by ultrafiltration, concentration, gel filtration chromatography (Sephadex™ G-75), and anion exchange chromatography (DEAE sepharose fast flow anion exchange). The molecular mass of the purified enzyme was estimated to be 60.0 kDa. The optimal pH and temperature of the purified enzyme were 5.0 and 50 °C, respectively. The enzyme was activated by Ca²⁺, K⁺, Na⁺, Fe²⁺, and Zn²⁺. However, Mg²⁺, Hg²⁺, and Ag⁺ acted as inhibitors in decreasing the activity of the purified inulinase. The enzyme was strongly inhibited by phenylmethanesulphonyl fluoride (PMSF), iodoacetic acid, EDTA, and 1,10-phenanthroline. The K _m and V _max values of the purified enzyme for inulin were 20.06 mg/ml and 0.0085 mg/min, respectively. A large amount of monosaccharides were detected after the hydrolysis of inulin with the purified inulinase, indicating the purified inulinase had a high exoinulinase activity.     

Purification and Characterization of Cell Suspensions Peroxidase from Cotton (<Emphasis Type="Italic">Gossypium hirsutum</Emphasis> L.)

Two peroxidases, cPOD-I and rPOD-II, have been isolated and purified from cotton cell suspension and their biochemical characteristics studied. rPOD-II from R405-2000, a non-embryogenic cultivar, has higher activity than cPOD-I derived from Coker 312, which developed an embryogenic structure. The cPOD-I and rPOD-II had molecular mass of 39.1 and 64 kDa respectively, as determined by SDS-PAGE. Both enzymes showed high efficiency of interaction with the guaiacol at 25 mM. The optimal pH for cPOD-I and rPOD-II activity was 5.0 and 6.0, respectively. The enzyme had an optimum temperature of 25 °C and was relatively stable at 20–30 °C. The isoenzymes were highly inhibited by ascorbic acid, dithiothreitol, sodium metabisulfite, and β-mercaptoethanol. Their activities were highly enhanced by Al³⁺, Fe³⁺, Ca²⁺, and Ni²⁺, but they were moderately inhibited by Mn²⁺ and K⁺. The enzyme lost 50% to 62% of its activity in the presence of Zn²⁺ and Hg²⁺.     

Effect of copper and manganese ions on activities of laccase and peroxidases in three Pleurotus species grown on agricultural wastes

Copper (Cu²⁺) and manganese (Mn²⁺) ions influenced laccase (Lac) and peroxidase production in Pleurotus eryngii, Pleurotus ostreatus, and Pleurotus pulmonarius. In P. eryngii, the optimum Cu²⁺ concentration for Lac production was 1 mM and for peroxidases 10mM, and Mn²⁺ concentration of 5mM led to peaks of Lac and peroxidase activity. In P. ostreatus HAI 493, the highest level of Lac activity was at Cu²⁺ concentrations of 1 and 10 mM and Mn²⁺ concentration of 1mM, respectively. The absence of Cu²⁺ and Mn²⁺ caused the highest levels of peroxidase production. In P. ostreatus HAI 494, the highest level of Lac activity was at a Cu²⁺ concentration of 5 mM and at Mn²⁺ concentration of 1 mM, respectively. High levels of peroxidase activity were found in the medium without and with 1mM Cu²⁺, and at 1 and 5 mM Mn²⁺, respectively. In P. pulmonarius, the highest Lac activity was found in the presence of 5 mM Cu²⁺ and 5 mM Mn²⁺, respectively. The absence of Cu²⁺ and Mn²⁺ as well as their presence at a concentration of 1 mM led to the peaks of peroxidase activities.     

Formation and purification of nitrile hydratase fromCorynebacterium pseudodiphteriticum ZBB-41

A strain of nitrile hydratase-forming microorganism,Corynebacterium pseudodiphteriticum ZBB-41, was isolated from soil and the conditions for the enzyme formation have been studied. Addition of ferric or ferrous ions and the use of methacrylamide as an inducer greatly enhanced enzyme formation. When the strain was cultivated at 27°C for 64 h in an optimum medium, the specific activity of the enzyme was 83U/mg of dry cell weight. The enzyme was purified from the crude extract of methacrylamide induced cells in 6 steps with 9.5-fold purification and 8.8% recovery. The enzyme has a molecular mass of 80,000 and consists of two subunits with molecular mass of 28,000 and 25,000 respectively. The isoelectric point was 4.2. The Km value to acrylonitrile was 0.21 M. The enzyme was strongly inhibited by Hg²⁺, Cu²⁺, Ag⁺, iodoacetate, and phenyl mercuric acetate and can be protected by 2-mercaptoethanol. The enzyme was noncompetitively inhibited by sodium cyanide, the Ki value was 0.13 mM.     

The noncarbohydrate part of the polysaccharide complex ofSolidago virgaurea

The ash elements in the inflorescences and polysaccharides ofSolidago virgaurea L. have been determined qualitatively and quantitatively. Ca²⁺, K⁺, Mg²⁺, and Na⁺ have been detected.I. P. Pavlov Rayazan' Medical Institute. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 284–286, May–June, 1984.     

Biochemical Characterization and Antitumor Study of l-Glutaminase from Bacillus cereus MTCC 1305

l-Glutaminase (E.C.3.5.2.1) extracellularly produced by Bacillus cereus MTCC 1305 was purified to apparent homogeneity with a fine band. The molecular weight of native enzyme and its subunit were found to be approximately 140 and 35 kDa, respectively, which indicates its homotetrameric nature. The substrate specificity test of this enzyme showed its specificity for l-glutamine. The purified enzyme showed maximum activity at optimum pH 7.5 and temperature 35 °C. The enzyme retained stability up to 50 and 20 % even after treatment at 50 and 55 °C, respectively, for 30 min. Monovalent cations (Na⁺, K⁺) and phosphate ion activated the enzyme activity, while divalent cations (Mg²⁺, Mn²⁺, Zn²⁺, Pb²⁺, Ca²⁺, Co²⁺, Hg²⁺, Cd²⁺, Cu²⁺) inhibited its activity. Reducing agents (cysteine, glutathione, dithiothreitol, l-ascorbic acid, and β-mercaptoethanol) stimulated its activity, whereas thiol-binding agents (iodoacetamide, p-chloromercuribenzoic acid) resulted in the inhibition of this enzyme. Kinetic parameters, K _m, V _max, K _cat, of purified enzyme were found to be 6.25 mM, 100 μmol/min/mg protein and 2.22?×?10² M^?1s^?1, respectively. The gradual inhibition in growth of hepatocellular carcinoma (Hep-G2) cell lines was found with IC₅₀ value of 82.27 μg/ml in the presence of different doses of l-glutaminase (10–100 μg/ml).     

Xerophytic <Emphasis Type="Italic">Cereus pterogonus</Emphasis> xylose isomerase is a thermostable enzyme

A thermostable xylose isomerase (D-xylose ketol-isomerase; EC.5.3.1.5) was isolated from the cladodes of xerophytic Cereus pterogonus. The enzyme was purified to homogeneity. SDS-PAGE analysis estimated the molecular mass of the enzyme protein at 66 kDa. The enzyme exhibited temperature optima at 60 and 80°C. Though the enzyme activity was optimum at pH 7.0, the enzyme was found to be stable in both acidic and basic pH ranges in the presence of divalent ions Mn²⁺, Co²⁺, and Mg²⁺. This enzyme may find potential use in the food and beverage industry. Published in Khimiya Prirodnykh Soedinenii, No. 2, pp. 169–170, March–April, 2008.     

Physico-chemical studies on the chelation behaviour of biologically active 2-hydroxy-1-naphthaldehyde semicarbazone (HNAS) with some lanthanons

Summary The chelation behaviour of the complexes of La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Y³⁺, Tb³⁺, Dy³⁺, Ho³⁺ with biologically active 2-Hydroxy-1-naphthaldehyde semicarbazone (HNAS) has been studied potentiometrically in 75% (v/v) dioxane-water medium at various ionic strengths. The method of Bjerrum and Calvin, as modified by Irving and Rossotti has been used to find out the values of n andpL. The formation constants of metal chelates and the values ofS _min have been calculated. The order of formation constants of chelates was found to be: La³⁺3+3+3+3+3+3+3+3+3+3+.

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Physikochemische Untersuchungen zur Komplexierung von biologisch aktivem 2-Hydroxy-1-naphthaldehyd-Semicarbazon (HNAS) mit Lanthanoiden

Zusammenfassung Das Chelierungsverhalten von La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Y³⁺, Tb³⁺, Dy³⁺ und Ho³⁺ mit 2-Hydroxy-1-naphthaldehydsemicarbazon (HNAS) wurde potentiometrisch in 75% (v/v) Dioxan-Wasser bei verschiedenen Ionenstärken untersucht. Die Werte für n undpL wurden nach der Methode von Bjerrum und Calvin in der Modifikation von Irving und Rossotti bestimmt. Die Komplexbildungskonstanten der Metallchelate und die WerteS _min wurden ermittelt. Die Reihung der Komplexbildungskonstanten war La³⁺3+3+3+3+3+3+3+3+33+.