Stability constants of D(−)-ribose complexes with calcium in diluted aqueous and methanolic solutions

The study of D(?)-ribose complexing with calcium in aqueous solutions less than 1.64 × 10^?1M by potentiometric measurements with a calcium selective electrode afforded the value of K₁ = 1.70 liters × mole^?1 (SD = 1.05 × 10^?3). Numerical analysis indicated that complex species with 1:1 and 1:2 calcium to D(-)-ribose ratios are present simultaneously: k₁ = 1.13 liters × mole^?1 and K₂ = 8.47 liters × mole^?1 (SD = 0.95 × 10^?3).In methanolic medium 1.24 × 10^?2M with regard to calcium chloride both stoichiometric proportions were evidenced. A large error accompanying the stability constant K₁ = 28 kg × mole^?1 (RSD = 82%) renders unreasonable the K₂ value obtained from the product K₁ × K₂ = 96.5 kg² × mole^?2.The results are discussed with respect to the data published for more concentrated (1.27 M) aqueous solutions obtained on the basis of ₁H-NMR spectroscopic investigations.     

One-pot synthesis,characterization, DNA binding and enzymatic studies of 4-methyl trans-cinnamate zinc(II)-mixed ligand complexes

Four new zinc(II) complexes formulated as [Zn(L)₂] (1), [Zn(L)₂(phen)] (2), [Zn(L)₂(bipy)H₂O] (3), and [Zn(en)₂(H₂O)₂](L)₂(H₂O)₂ (4), where HL = 4-methyl trans-cinnamic acid, bipy = 2,2′-bipyridine, phen = 1,10-phenanthroline, and en = ethylenediamine, have been synthesized and characterized by FT-IR and NMR spectroscopy. Single-crystal XRD revealed distorted square-pyramidal structure for 3 and octahedral for 4. The complexes were screened for DNA interaction via viscommetry and UV–visible spectroscopy. The apparent binding constants were calculated to be 1.18 × 10⁴, 1.26 × 10⁵, 4.64 × 10⁴_, and 1.89 × 10⁴ for 1–4, respectively. The binding propensity to salmon sperm DNA was in the order: K₂ > K₃ > K₄ > K₁. Furthermore, these complexes demonstrated efficient inhibition of alkaline phosphatase, which was attributed to the binding of zinc(II) to the enzyme’s active site.     

Extraction—spectrophotometric determination of traces of cadmium with 4-(2-pyridylazo)resorcinol and a long-chain quaternary ammonium salt

A simple and highly sensitive extraction—spectrophotometric determination of cadmium is described. The ion-associate formed between the cadmium-PAR anionic chelate and cetyldimethylbenzylammonium chloride (CDBA) is extracted with chloroform at pH 10. The absorption maximum of the extracted species occurs at 505 nm, the molar absorptivity being (9.82 ± 0.30) × 10⁴ l mol^-1 cm^-1. The optimal concentration range for measurements is 0.2–1.0 μg Cd ml^-1; Beer's law is obeyed. The composition of the ion-associate is estimated to be CdPAR₂-2CDBA. The conditional extraction constant is log K'_ex ≈ 8. The stability constant of the cadmium—PAR chelate in aqueous solution is log β₂ = 17.5 ± 0.3. Extraction with N-benzoyl-N-phenylhydroxylamine is used to avoid several interferences. Moderate amounts of zinc are masked with sodium hydroxide.     

Triphenyltetrazolium chloride as a new analytical reagent for molybdenum(VI): Application to plant analysis

Solvent extraction of molybdenum(VI) ion associate with triphenyltetrazolium chloride (TTC) has been studied. TTC was proposed as reagent for the spectrophotometric determination of micro amounts of molybdenum(VI) at λ_max 250 nm. The optimum conditions for extraction of molybdenum(VI) as an ionassociation complex with TTC has been determined. Beer’s law is obeyed in the range of 0.5–10 μg/mL molybdenum(VI). The molar absorptivity of the ion-pair is 1 × 10⁶ L/mol cm. The sensitivity of the method is 9.6 × 10⁻⁵ μg/cm². The characteristic values for the extraction equilibrium and the equilibrium in the aqueous phase are: distribution constant K _D = 32.64, extraction constant K _ex = 2.19 × 10¹⁰ association constant β = 6.71 × 10⁸. The interferences of different cations, anions on molybdenum(VI) determination were also investigated. A sensitive and selective method for the determination of microquantities of molybdenum(VI) has been developed. The determination was carried out without preliminary separation of molybdenum. A novel procedure of molybdenum(VI) extraction and spectrophotometric determination in different plant samples was examined.     

Mass Spectrometric Determination of Association Constants of Bovine Serum Albumin (BSA) with para-Sulphonato-Calix[n]arene Derivatives

Electrospray Ionization Mass Spectrometry (ESI/MS) has been used to determine the association constants (K_As) and binding stoichiometries for parent para-Sulphonato-calix[n]arenes and their derivatives with bovine serum albumin (BSA). K_A values were determined by titration experiments using a constant concentration of protein. K_A measurements were carried out in a methanol–formic acid solution. 5,11,17,23–tetra-Sulphonato-calix[4]arene (1a) and 25-mono-(2-aminoethoxy)-5,11,17,23-tetra-Sulphonato-calix[4]arene (1d) interact strongly with BSA showing 3 non-equivalent binding sites with K_A1 = 7.69 × 10⁵ M⁻¹, K_A2 = 3.85 × 10⁵ M⁻¹, K_A3 = 0.33 × 10⁵ M⁻¹ and K_A1 = 1.69 × 10⁵ M⁻¹, K_A2 = 2.94 × 10⁵ M⁻¹, K_A3 = 0.60 × 10⁵ M⁻¹, respectively. The strength of the interactions between the calixarene and BSA is inversely proportional to the size of macrocyclic ring: n = 4 > n=6>>n=8.     

The Determination of Manganese by Means of Tetrazolium Violet

Abstract

The optimum conditions for extraction of manganese (VII) as an ion-association complex with Tetrazolium Violet (TV) has been determined. The ratio MnO₄ ^?: TV⁺ is 1:1. Beer's law is obeyed in the range of 0.05 - 0.6 μg ml^?1 manganese (VII). The molar absorptivity of the ion-pair is (6.67 ± 0.05) × 10⁴ L mol^?1cm^?1, extraction constant K_ex = 3.1 × 10⁴, distribution constant K_D = 56.5 and association constant β = 5.59 × 10². A sensitive and selective method for determination of microquantities of manganese (VII) in soils has been developed.     

Study of the system manganese(VII)-3,7-bis(dimethylamino)-phenothiazin-5-ium chloride-water-1,2-dichloroethane Using UV-spectrophotometry

The system manganese(VII)-3,7-bis(dimethylamino)-phenothiazin-5-ium chloride (MB)-water-1,2-dichloroethane has been studied using UV-spectrophotometry. The molar absorptivity of the complex is (3.86 ± 0.06) × 10⁴ L mol^?1 cm^?1 at 290 nm and the system obeys Beer??s law in the range 0.1?C0.99 ??g mL^?1 Mn(VII). The detection limit (DL) and quantitation limit (QL) of Mn(VII) determination were found to be 0.0146 and 0.049 ??g mL^?1, respectively. The composition of the complex is established as MB: MnO ₄ ^? = 1: 1. Extraction investigations of the system discussed were carried out. The characteristic values for the extraction equilibrium and the equilibrium in the aqueous phase was determined: extraction constant K_ex = (1.12 ± 0.05) × 10⁵, distribution constant K_D = 75.61 ± 0.1 and association constant ?? = (1.48 ± 0.08) × 10³. A new method has been developed for the microdetermination of manganese(VII) in plants and steels.     

Magnesium Ion Selective Electrodes Based on β-Diketone Compounds

Abstract

The ion selectivities for poly(vinyl chloride) (PVC)-matrix membrane ion-selective electrodes based on seven lipophilic diketone compounds were examined. All the electrodes based on the tested five β-diketone cómpounds exhibited clear Mg²′-selectivity under high pH conditions (pH10). Especially, the electrode based on 2-acetyl-1-tetralone shows excellent Mg²⁺-selectivity, and the selectivity coefficients of the Mg²+ -electrode to Ca²+, K⁺ and K⁺ (log K^pot _{mg, ca} log K^pol _mg.k and log K^pot _Mg.Na) in pH 10 solution were ?2.2, ?1.9 and ?2.7, respectively. This elecrode gave a response slope of about 60 mV/pMg²⁺ ranging from 1 × 10^?2 to 2 × 10^?2, which corresponds to twice the usual Nernstian theoretical responce slope for the divalent cation. This phenomenon is advantageous for the acccurate determination of Mg²⁺.     

Solvent Extraction of Pb(II) with AGDOMD

Abstract

The distribution of Pb(II) between an aqueous phase and a toluene phase containing dehydrated fatty acids found in distilled castor oil (AGDOMD) has been studied. Using the slope technique the conditional equilibrium constant of extraction was determined (kext = 1.02 × 10^?7) and the main species present in the organic phase was identified as (PbNO₃R. 2HR)_(o), where HR represents the fatty acid used.     

Experimental study of the D + H2(ν = 1) reaction

The D + H₂(ν = 1) reaction, D + H₂(ν = 1) → K_a HD(ν = 1) + H, → K_n HD(ν = 0) + H, → K_r D + H₂(ν = 0) has been studied. The measurements were made in a flow-tube apparatus at 300 K. Vibrationally excited H₂ was generated in a furnace and D atoms in a microwave discharge. EPR and thermometric techniques were used for the detection of D and H atoms and H₂(ν = 1). The product branching rate constants (in CM³/Molecule s) were found to be K_a = (10.7 ± 4.1) × 10^?13. K_n = (5.4 ± 2.7) × 10^?13, K_r, < 2.7 × 10^?13.     

Analytical application of second-harmonic a.c. polarography

Phase-selective second-harmonic a.c. polarography can be used to distinguish two different species having similar reduction potentials. Because each species has a different phase angle depending on the electrode kinetics, a certain phase angle can be chosen to detect only one component in the mixture. In 1 M potassium chloride solution, indium-(III) at the 4 × 10^-6 M level can be determined in the presence of 50-fold amounts of cadmium(II), and zinc(II) at the 2 × 10^-5 M level in the presence of 100-fold amounts of nickel(II).     

Study of Binding of Benzyl-Thiouracil to Human Serum Albumin by Gel Filtration Chromatography

Abstract

The binding of benzyl-thiouracil to human serum albumin was studied at 37°C and pH 7.4 by Sephadex filtration chromatography based upon Hummel and Dreyer's method. As the benzyl-thiouracil (ligand) was adsorbed on to the gel matrix, the free ligand concentrations had to be corrected through the ligand distribution between the stationary and mobile phases.

A good agreement was found between binding parameters—calculated by this method and by the classical method (equilibrium dialysis). Binding is characterized by one binding site with a moderate association constant (K₁ = 5.7 × 10⁴ M^-1) and two binding sites with a low association constant (K₂ = 7.8 × 10³ M^-1).     

Cyclohexane-1, 3-Dione bis (4-Methylthiosemicarbazone) as a Spectrophotometric Reagent for the Determination of Zn (II)

Abstract

The spectrophotometric study of reddish cyclohexane-1, 3-dione bis (4-methylthiosemicarbazone)-Zn(II) was made in dimethylformamide-water solution (λ_max= 475 nm, ∑ = 3.3×10⁴ 1.mole^?1. cm^?1. Sandell sensitivity = 2×10^?2 μg Zn(II).cm^?2, stoichiometry 1:1, and apparent stability constant 6.1×10⁴). A new method for the spectrophotometric determination of Zn(II) is proposed for concentrations between 0.1 and 2.5 ppm. The relative error (95% confidence level) is 0.7% for 1.0 pprn of Zn(II).

The extraction with ethylacetate of the reddish complex was also studied spectrophotometrically (λ_max = 493 nm, ∑ in organic phase = 4.8×10⁴ 1.mole^?1.cm. Sandell sensitivity = 3.4×10^?4 μg Zn(II).cm^?2, stoichiometry 1:1, apparent extraction constant 1.4×10⁴). A new method for the extraction-spectrophotometric determination of Zn(II) is proposed for concentrations, in aqueous phase, between 0.02 and 0.30 ppm. The relative error (95% confidence level) is 1.0% for 0.15 pprn of Zn(II).     

Flexibility of Na,K-ATPase secondary structure upon drug-protein interaction

The enzyme Na⁺, K⁺-ATPase is an integral membrane protein which transports sodium and potassium cations against an electrochemical gradient. The transport of Na⁺ and K⁺ ions is connected to an oscillation of the enzyme between the two conformational states, the E₁ (Na⁺) and the E₂ (K⁺) conformations. The enzymatic activity of ATPase is largley affected by different ligands complexation. This review reports the effects of several drugs such as AZT (anti-AIDS), cis-Pt (antitumor), aspirin (anti-inflammatory) and vitamin C (antioxidant) on the stability and secondary structure of Na,K-ATPase in vitro. Drug-enzyme binding is mainly through H-bonding to the polypeptide C=O and C-N groups with two binding constants K_1(AZT) = 5.30 × 10⁵ M^?1 and K_2(AZT) = 9.80 × 10³ M^?1 for AZT and one binding constant for K_cis-Pt = 1.93 × 10⁴ M^?1, K_aspirin = 6.45 × 10³ M^?1 and K_ascorbate = 1.04 × 10⁴ M^?1 for cis-Pt, aspirin and ascorbic acid. The enzyme secondary structure was altered from that of α-helix 19.8% (free protein) to almost 22–26% and the β-sheet from 25.6% to 18–22%, upon drug complexation with the order of induced stability AZT > cis-Pt > ascorbate > aspirin.     

Oxidative DNA cleavage by Cu(II) complexes of 1,10-phenanthroline-5,6-dione

A dimeric dichloro-bridged copper(II) complex [Cu₂(pdon)₂Cl₄] · 2DMF (1) and two mononuclear copper(II) complexes [Cu(pdon)(DMSO)Cl₂] · DMSO · H₂O (2) and [Cu(pdon)₃] · (ClO₄)₂ · 2.25CH₃CN · 6H₂O (3) (pdon = 1,10-phenanthroline-5,6-dione) have been synthesized and characterized. Variable-temperature magnetic susceptibility studies indicate the existence of weak anti-ferromagnetic coupling in the binuclear complex. The interaction of these complexes with CT-DNA (calf thymus DNA) has been studied using absorption and emission spectral methods. The apparent binding constants (K _app) for 1, 2 and 3 are 5.20 × 10⁵, 2.68 × 10⁵ and 7.05 × 10⁵ M^?1, respectively, showing moderate intercalative binding modes. All of these complexes cleave plasmid DNA to nicked DNA in a sequential manner as the concentration or reaction time is increased. The cleavage mechanism between the complex and plasmid DNA is likely to involve singlet oxygen ¹O₂ and ?OH as reactive oxygen species.     

Cr2(WO4)3和Cr2(MoO4)3的负热膨胀特性研究

用液相反应-前驱物烧结法制备了Cr₂(WO₄)₃和Cr₂(MoO₄)₃粉体。298～1 073 K的原位粉末X射线衍射数据表明Cr₂(WO₄)₃和Cr₂(MoO₄)₃的晶胞体积随温度的升高而增大, 本征线热膨胀系数分别为(1.274±0.003)×10^-6 K^-1和(1.612±0.003)×10^-6 K^-1。用热膨胀仪研究了Cr₂(WO₄)₃和Cr₂(MoO₄)₃在静态空气中298～1 073 K范围内热膨胀行为，即开始表现为正热膨胀，随后在相转变点达到最大值，最后表现为负热膨胀，其负热膨胀系数分别为(-7.033±0.014)×10^-6 K^-1和(-9.282±0.019)×10^-6 K^-1。     

Determination of thiocyanate ions at nanolevel in real samples using coated graphite electrode based on synthesised macrocyclic Zn(II) complex

The electrode characteristics and selectivities of PVC-based thiocyanate selective polymeric membrane electrode (PME) incorporating the newly synthesized zinc complex of 6,7:14,15-Bzo₂-10,11-(4-methylbenzene)-[15]-6,8,12,14-tetraene-9,12-N₂-1,5-O₂ (I ₁ ) and zinc complex of 6,7:14,15-Bzo₂-10,11-(4-methylbenzene)-[15]-6,14-diene-9,12-dimethylacrylate-9,12-N₂-1,5-O₂ (I ₂ ) are reported here. The best response was observed with the membrane having a composition of I₂:PVC:o-NPOE:HTAB in the ratio of 6:33:59:2 (w/w; milligram). This electrode exhibited Nernstian slope for thiocyanate ions over working concentration range of 4.4 × 10⁻⁷ to 1.0 × 10⁻² mol L⁻¹ with detection limit of 2.2 × 10⁻⁷ mol L⁻¹. The performance of this electrode was compared with coated graphite electrode (CGE), which showed better response characteristics w.r.t Nernstian slope 59.0 ± 0.2 mV decade⁻¹ activity, wide concentration range of 8.9 × 10⁻⁸ to 1.0 × 10⁻² mol L⁻¹ and detection limit of 6.7 × 10⁻⁸ mol L⁻¹. The response time for CGE and PME was found to be 8 and 10 s, respectively. The proposed electrode (CGE) was successfully applied to direct determination of thiocyanate in biological and environmental samples and also as indicator electrode in potentiometric titration of SCN⁻ ion.     

A new quinoline-based chemosensor in ratiometric sensing of Hg2+ ions

A new quinoline-based chemosensor 1 has been designed and synthesised. Its metal ion-binding properties have been documented in organic and aqueous organic solvents. While chemosensor 1 recognises Hg²⁺ ions (K _a = 2.15 × 10⁴ M^? 1) by exhibiting ratiometric change in emission in CHCl₃/CH₃OH (1:1, v/v), under similar condition both Zn²⁺ and Cd²⁺ ions are sensed by significant non-ratiometric increase in emission with measurable red shift. In DMSO/H₂O (5:95, v/v), the sensor 1 exhibits a greater selectivity towards Hg²⁺ ions (K _a = 9.20 × 10³ M^? 1) over the other metal ions examined.     

Study of Activation and Inhibition of Certain Metal Ions to Amylase Catalyzed Reaction by Microcalorimetry

IntroductionMostcomplicatedreactionshappenedinlivingcrea tures ,amongthemenzymecatalyzedreactionisanimpor tantclass .Itissignificantinboththeoryandpracticetoinvestigateenzymecatalyzedreaction .Therearemanyex perimentalmethodssuchasspectrophotometry ,titrimetry ,isotopemethod ,microcalorimetryandsoon ,inwhichmi crocalorimetryisanewoneduetoitshighsensitivityandaccuracy .Wecanstudythewholeprocessoftheheatef fectusingamicrocalorimeter .Sincetheabsorptionorpro ductionofheatisanintrinsicpropertyofe…     

Extraction of chromium(VI) with blue tetrazolium chloride and tetranitrotetrazolium blue chloride

The optimum conditions for extraction of microquantities of chromium(VI) as an ion-association complex with blue tetrazolium chloride (BTC) and tetranitrotetrazolium blue chloride (TNBT) has been determined. The extracted species was a 1: 2 of the BTC and TNBT cation and the chlorochromate anion. Beer’s law was obeyed in the range of 0.04–0.8 μg/mL Cr(VI) for BTC and 0.1–1.6 μg/mL Cr(VI) for TNBT. The molar absorptivities were ?₂₅₅ = 7.77 × 10⁴ L/(mol cm) (for BTC) and ?₂₇₅ = 2.04 × 10⁴ L/(mol cm) (for TNBT). Sandell’s sensitivity of the systems were found to be 6.69 × 10^?4 μg/cm² (for BTC) and 2.55 × 10^?3 μg/cm² (for TNBT). Limit of detection (LOD) is 8.55 ng/mL and limit of quantitation (LOQ) is 0.028 μg/mL Cr(VI) for BTC. For TNBT, LOD is 0.031 μg/mL and LOQ is 0.103 μg/mL. The characteristic values for the extraction equilibrium and the equilibrium in the aqueous phase have been determined. A sensitive method for determination of trace of chromium(VI) in plants has been developed.