Dioxane-water Solution Research Articles

The Effect of Degradation of Soda Lignin Using Pd/SO42-/ZrO2 as a Catalyst: Improved Reactivity and Antioxidant Activity.

To the value-added application of the soda lignin by improving its reactivity and antioxidant activity, a self-made Pd/SO42−/ZrO2 catalyst was used to catalyze the degradation reaction of soda lignin. The catalyst was loaded with the palladium of 1.47 wt.% while retaining the super acidity of SO42−/ZrO2. The reaction condition was determined as follows: the dioxane-water solution was selected as the reaction solution, the addition amount of the catalyst was 5 wt.% of the soda lignin, the system was heated at 100 °C for 4 h under a hydrogen pressure of 3 MPa. The reactivity of the catalyzed-soda lignin compared to the soda lignin before the reaction was significantly improved: the values of phenolic hydroxyl groups and total hydroxyl groups were increased by 35.3% and 97.1%, respectively, and the value of methoxy groups was decreased by 13%. Approximately 63.3% of the β-O-4 bonds were cleaved, which resulted in a reduction of the weight average molecular weight from 8200 g·mol−1 to 4900 g·mol−1. At the same time, the EC50 values of the catalyzed-soda lignin on DPPH (1,1-diphenyl-2-picrylhydrazyl) and ABTS+ (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) radicals scavenging were decreased by 20.6% and 32.6%, respectively, and the reducing power of catalyzed-soda lignin at the absorption value of 0.5 was increased by 10.5%. The Pd/SO42−/ZrO2 catalyst works by breaking the β-O-4 linkages and degrading the methoxy groups. The catalyzed-soda lignin exhibits the possibility of being used as the antioxidants, grafting precursors, adhesive additives, and raw materials for lignin/polymer composites.

Synthesis, potentiometric and antimicrobial activity studies on DL-amino acids-Schiff bases and their complexes

A relationship between antimicrobial activities and the formation constants of amino acid-Schiff bases and their Cu(II) and Ni(II) complexes was studied. For this purpose, a series of Schiff bases were prepared from DL-amino acids (DL-glycine, DL-alanine) and halo aldehydes (5-chloro-2-hydroxybenzaldehyde, 5-bromo-2-hydroxybenzaldehyde). Schiff bases and their Cu(II) and Ni(II) complexes were characterized by the elemental analysis, spectral analysis, magnetic moment (at ca. 25°C), molar conductivity, and thermal analysis data. The complexes were found to have general compositions [ML(H2O)]. The protonation constants of the Schiff bases and stability constants of the complexes were determined potentiometrically in a dioxane-water (1: 1) solution at 25°C and 0.1 M KCl ionic strength. Antimicrobial activities of the Schiff bases and their complexes were estimated for six bacteria, such as Bacillus cereus RSKK 863, Staphylococcus aureus ATCC 259231, Micrococcus luteus NRLL B-4375, Escherichia coli ATCC 11230, Aeromonas hydrophila 106, Pseudomonas aeroginosa ATCC 29212, and the yeast Candida albicans ATCC 10239. The role of halogen substitution on the ligands, effect of the metal ion, and stabilities of the complexes are discussed on antimicrobial activities.

Molecular rearrangements controlled by pH-driven Cu2+ motions

Ligands 1–3 contain two coordinatively distinct compartments: AH2, featuring a bis-amino bis-amido donor set, and B, featuring a bis amino-heterocycle donor set. Their coordinative tendencies towards Cu2+ have been studied in dioxane–water solution (4 ∶ 1 v/v) by means of potentiometric titration experiments. The complex species which form in the pH 2–12 range have been individuated and their formation constants calculated. At neutral or slightly acidic pH values, the Cu2+ cation forms a 1 ∶ 1 complex with the neutral ligands, residing in the B compartment. If the pH is then raised to distinctly basic values, the AH2 compartment loses its two amide protons and Cu2+ moves inside it, forming neutral complexes with a bis-amino bis-imide donor set. The nature of these complexes has been ascertained by means of UV/Vis spectroscopy and by comparison with results for ligand 5, which also binds Cu2+ by losing its two amide protons, but does not possess further binding groups appended to the amine nitrogens. With ligands 1–3, when Cu2+ is coordinated by the bis-amino bis-imide donor set, one of the two appended heterocycles of the B compartment is still bound to it, in one of its apical positions, so that, on changing the pH between neutral and basic values, the Cu2+ movement induces an overall molecular rearrangement, which was found to be reversible.

Equilibrium studies of the binary and ternary complexes involving tetracycline and amino acid or DNA constituents

The acid–base equilibria of tetracycline and its copper(II) complex formation equilibria are investigated in dioxane–water mixtures. The ternary complexes of copper(II) with tetracycline as primary ligand and amino acid or DNA constituent as secondary ligand are studied in 50% dioxane–water solution. The formation constants of the ternary and binary complexes with amino acids or DNA constituents are determined. The concentration distribution of the various complex species are evaluated. Probable mode of chelation with tetracycline and DNA constituents is discussed.

Metal complexes of triazine - Schiff bases: Spectroscopic and thermodynamic studies of complexation of some divalent metal ions with 3-(α-acetylethylidenehydrazino)-5,6-diphenyl-1,2,4-triazine

Metal complexes of some divalent metal ions (Co, Ni, Cu and Zn) with 3-(?- acetylethylidenehydrazino)-5,6-diphenyl-1,2,4-triazine (AHDT) as a Schiff-base have been investigated potentiometrically and spectrophotometrically and found to have the stoichiometric formulae 1:1 and 1:2 (M:L). The formation constants of the proton-ligand and metal-ligand complexes have been determined potentiometrically at different temperatures (10, 20, 30, 40 and 50?C) at an ionic strength of 0.1MKNO3 in 75%(v/v) dioxane-water solution. The standard thermodynamic parameters, viz. ?Go, ?Ho, and ?So, for the proton-ligand and the stepwise metal-ligand complexes have been evaluated.

Silica chemically modified with N-benzoyl- N-phenylhydroxylamine in chemisorption of hydrogen and metal ions

New chemically modified silicas – macroporous and pyrogenic – with covalently bonded chelating groups of N-benzoyl- N-phenylhydroxylamine (SiO 2–BPHA) were obtained in three-step surface reaction. From elemental analysis, metal chemisorption and pH titration the concentration of bonded groups was determined as 0.076 and 0.21 mmol g −1 for Silochrome and Aerosil, correspondingly. In both cases about 50% transformation of initial aminopropyl groups to BPHA was achieved. A chemisorption of hydrogen and some metal ions (Fe(III), V(V), Nb(V), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Pb(II)) from aqueous and acetonitrile media was investigated. The adequate approximation of interfacial equilibria was only possible if strong lateral interactions between bonded ligands were presumed. From the results of a quantitative physicochemical analysis it was found that dissociation constant of bonded BPHA considerably rose in comparison with the dissociation constants of analogs in solution. Bonded complexes with all studied metals were less stable. Linear correlation between stability of complexes in dioxane–water solution and on the silica surface was found as log β(surf.)=log β(sol.)−2.9. Strong fixation of counter-ions near the surface was concluded from experiments. In aqueous media SiO 2–BPHA demonstrates high selectivity towards Fe(III) and V(V). Linear correlation that was found between concentration of sorbed Fe 3+ and the Kubelka–Munk function for SiO 2–BPHA can be used for ion optical sensoring. Vanadium(V) forms several bonded complexes with different composition instead.

Inversion of stereoselectivity in the association between tris(oxalato)cobaltate(III) and bovine serum albumin by the addition of dioxane to aqueous solutions

Measuring the Pfeiffer effect of the addition of bovine serum albumin (BSA) as an optically active environment to a tris(oxalato)cobaltate(III) anion, [Co(ox) 3] 3−, we found that the Λ-enantiomer of the complex anion is enriched in 5 or 10% dioxane–water solutions but the Δ-enantiomer is concentrated in aqueous solution, where the enantiomeric excess is 72% (Λ rich) in 10% dioxane–water solution.

The local anaesthetic tetracaine as a quencher of perylene fluorescence in micelles

At neutral pH the local anaesthetic tetracaine hydrochloride quenches the fluorescence of the lipophilic dye perylene incorporated into non-ionic micelles. The process follows the Stern—Volmer equation, suggesting that quenching occurs through encounter of fluorophore and quencher. As the pH is lowered from 5 to 1, the apparent quenching constant decreases sigmoidally, the midpoint of the curve being at pH 2.3, close to the p K value characterizing the ionization of the anaesthetic aromatic butylamino group. Quenching is completely reversed below pH 1. These results show that the ability of tetracaine to quench the fluorescence of perylene incorporated into micelles depends on the absence of charge on its aromatic amine. Quenching was also studied in homogeneous dioxane—water solution. In this system the quenching constant also decreases sigmoidally as the pH is lowered. The inflection point of the curve is nearly coincident with the p K of tetracaine butylamino group in the same partially non-aqueous medium. Protonation of this group induces 60% reversal of the quenching, suggesting that the main mechanism of fluorescence extinction could be the electron transfer from unprotonated tetracaine aromatic amine to perylene in the excited state. However, an additional process which remains operative even when such an amino group is positively charged must also be involved. It can be concluded that the complete reversal of tetracaine quenching of perylene fluorescence in micelles induced by low pH is due to the inability of the anaesthetic to become partitioned into micelles upon protonation of its aromatic amine. In contrast, at neutral pH the local anaesthetic is able to reach the micelle non-polar core where perylene is located. This is consistent with the models, suggesting that the membrane-bound tetracaine assumes a rod-like configuration parallel to the surface normal with the aromatic butylamino group located into a highly hydrophobic region.

Study of complex formation equilibria of pamoate ion with copper(II) ion in a dioxane-water solution

Protonation constants of the carboxylate groups in pamoic acid and stability constants of copper(II) complexes with pamoic acid have been determined from EMF data in a 50% (v/v) dioxane-water solution at 25°C and 0.1 M KNO 3, and protonation constants for the hydroxyl groups have been determined spectrophotometrically in 1 M KCl aqueous medium. The values obtained for the constants are: protonation constants for the carboxylate groups: log β 1 = 4.352±0.001 and log β 2 = 7.706 ± 0.001; for the hydroxyl groups: log K 1 = 14.80±0.24 and log K 2 = 13.05±0.065. For the complex-forming reactions Cu 11+ nH 2pam ⇌ Cu(pamH) n + nH ( n = 1 or 2), the equilibrium constants are: log β 11-1 = −1.96± 0.02 and log β 21-2 = −5.28±0.02. An insoluble 3:2 copper(II)-pamoate complex is identified.

Protonation equilibria of 3-hydroxy-2-naphthoic acid in dioxane-water solution : effect of the solvent composition and of the ionic strength of the medium

The influence of the variation in the solvent composition and in the ionic strength of the medium on the autoprotolysis constant of the solvent and on the acid dissociation constants of 3-hydroxynaphthalene-2-carboxylic acid in dioxane-water solutions are studied at 25°C. In the full composition range studied (20-80% dioxane) the log of these constants is linearly correlated with the solvent polarity measured by the parameter E T /30) of Dimroth and Reichardt. In dioxane-water 1:1 (v/v) the constants are correlated to the ionic strength according to the model set by Davies equation.

Potentiometric study of the protonation and binary complexation equilibria between the hydrogen ion, copper(II) ion and zinc(II) ion and the picolinate ion in dioxane-water mixtures

Protonation constants of picolinic acid and stability constants of Cu(II) and Zn(II) picolinate complexes were determined potentiometrically in 50% (v/v) dioxane-water solution at 25°C and 0.2 M KNO 3. The values obtained for the constants were: protonation constants for picolinate ion: log β 1 = 5.36±0.01 and log β 2 = 6.80±0.04; stability constants for copper(II) complexes: log β 1.1 = 7.766±0.001 and log β 1.2 = 16.826±0.007; stability constants for the Zn(II) complexes: log β 1.1 = 6.10±0.05, log β 1.2 = 11.47±0.03 and log β 1.3 = 15.77±0.08. No protonated nor hydroxo-complex was detected in the metal ion-picolinate systems.

Potentiometric study of the Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes with 3-hydroxy-2-naphthalene carboxylic acid

Formation constants of Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes with 3-hydroxy-2-naphthalene carboxylic acid have been determined potentiometrically in a 50% (v/v) dioxane—water solution at 25°C and 0.2 M KNO 3. Experimental data are analysed using several computer programs. The obtained values for the log of the formation constant of the first 1 : 1 (metal : ligand) complex with the different metals are: Co 7.9, Ni 7.1, Cu 10.44, Zn 7.8 and Cd 7.3. The log of the formation constant for the 1 : 2 copper complex is 18.20. It is to be noted that Ni(II) yields a 1 : 1 complex weaker than expected from the Irving—Williams series.

Kinetics and mechanism of dehydrochlorination of N-aryl-C-ethoxycarbonylformohydrazidoyl chlorides

The kinetics of triethylamine (TEA) catalyzed deydrochlorination of a series of N-aryl-C-ethoxycarbonylformohydrazidoyl chlorides 1a–m have been studied under pseudo-first-order conditions in 4:1 (v/v) dioxane–water solution at 30 °C. For all compounds studied, the kinetics followed the rate law: kobs = k2 (TEA). The values of the overall second-order rate constants for the studied compounds were correlated by the equation: log k2 = 0.533σ−-0.218. The results are compatible with a mechanism involving a fast reversible deprotonation step leading to the anion of 1, followed by rate-determining step involving the loss of the chloride ion from the anion. The reaction constants of these two steps were estimated to be 0.845 and −0.312, respectively.

Thermodynamic stabilities of copper(II)-ethyl α-(phenyl)phenylpropioloyl-acetato complexes in dioxane-water media

The acid dissociation constant, K a , of ethyl α-(phenyl)phenylpropioloylacetate is determined potentiometrically in 75 vol % dioxane-water solution at 30°C as a function of ionic strength (μ) in the range 0·02–0·10 in a sodium perchlorate medium. A value of p K a ( μ → 0) of 11·66 is calculated with the aid of an extended form of the Debye-Hückel equation while a recalculation using reported values of γ± gives a value of 11·85. This is in agreement with the value calculated from results obtained in very dilute solution. The stoichiometric stability constants of the complexes formed with copper(II) are determined as a function of μ in the same range. Calculation of “thermodynamic” stability constants from these values using the Debye-Hückel equation or using reported values of γ ± does not give consistent results. It is concluded that it is incorrect to perform such calculations on results obtained in such a medium having an ionic strength μ ⩾ 0·02. The “thermodynamic” stability constants calculated from titration results in very dilute solution are log K 1 = 11·69 and log K 2 = 8·95.

Polarographic Studies on Substituted 2,2′-Bipyridyl N-Oxides

Abstract The polarographic behavior of 4-methoxy-2,2′-bipyridyl 1-oxide has been investigated in 20% dioxane-water solution. Two well defined reduction waves appear in the pH range 0.76–8.8, a third wave in pH 9.3–10.4, but only one wave in more alkaline solutions. The variation of E1⁄2 with pH followed the relations (E1⁄2)1=−0.37–0.10 pH and (E1⁄2)2=0.84−0.065 pH for waves 1 and 2, respectively. The diffusion current constant for the second wave decrease with increasing pH whereas for the first wave it remains constant upto pH 7.0 and decreases afterwards. Variation of diffusion current with temperature and reservoir height indicates the diffusion controlled nature. Wave 1 is produced by the 2 electron reduction of protonated N-oxide to 4-methoxy-2, 2′-bipyridyl. This intermediate is further reduced, at more negative potentials, to 1,4′-dihydro-4-methoxy-2,2′-bipyridyl by consuming two more electrons and two hydrogen ions simultaneously. The third wave is presumably due to catalytic hydrogen evolution.

Dihydroxyquinoxaline Studies. Solubility, Ionization Constant, and Chelating Behavior

Abstract The solubility, ionization constant, and chelating behavior of dihydroxyquinoxaline,. mainly 5,8-dihydroxyquinoxaline (5,8-DHQ) derivatives, have been measured and will be discussed. The introduction of a hydroxyl group into quinoxaline greatly lowers the solubility. The order of the decreasing solubility of 2,3-disubstituted 5,8-DHQ in water (at 20°C) is: O(CH2)2OC2H5<H<OH<CH3<C6H5<OC2H5<Cl<SH<SC2H5. For 5,8-DHQ the introduction of electron-repelling groups into 2,3-positions raises both the pKNH and pKoH values, while the introduction of electron-attracting groups into the same positions lowers both pKNHand pKoH. 5,8-DHQ, and its derivatives form colored precipitates with metal ions, but some derivatives which have pKNH values lower than zero fail to show any precipitation or coloration. 6,7-DHQ forms precipitate, and the precipitation colors distinctively with Cr(III) or Fe(II). The composition and stability constant (K) of copper(II) chelates of 5,8-DHQ and its derivatives in a dioxane-water (10 : 90 v/v) solution were studied spectrometrically. The copper chelate of 5,8-DHQ had a metal: ligand ratio of 1 : 1 and a logK value of 6.28 at pH 4.0. The structures of these copper chelates will be proposed.

Quantitative analysis of sugar components in steroidal saponins by gas liquid chromatography.

Gas chromatographic determination of monosaccharides such as L-arabinose, L-rhamnose, D-xylose, D-mannose, D-galactose, and D-glucose was studied. The recovery of sugars under hydrolysis condition was examined by GLC (Fig. 1) and was found to be almost quantitative when steroidal glycosides were hydrolyzed with N sulfuric acid in dioxane-water (1 : 3) solution (Table III). A simple and accurate method by GLC was thus presented for the individual determination of sugar components in the micro amounts (5-10 mg) of steroidal saponins. The molar ratios of sugar components were determined on the new convallasaponins by this method (Table V).

Organometallic chelate compounds—I: Formation constants of some dialkyl- and diaryl-thallium (III)-β-diketone compounds

The chelating tendencies of three β-diketones and two β,δ-triketones with some dialkyl- and diaryl-thallium (III) ions have been determined at 30° in a 75 per cent (v/v) dioxane-water solution. Only first formation constants were obtained, and there was no indication of the formation of a six-co-ordinate species of the type R 2Tl(RCOCHCOR′) 2 −) The effect of the nature of the organo group and the nature of the anion of R 2Tl +X − on the formation constant is considered.

Chelating tendencies of some substituted 2-(pyridyl)-1,3-indanediones with bivalent-metal ions

The acid dissociation constants of six substituted 2-(pyridyl)- and 2-(quinolyl)-1,3-indanediones and formation constants of three of these with some bivalent-metal ions have been determined at 30° in a 75 per cent (v/v) dioxane-water solution. The influence of steric, solvent, and electronic effects on the values of the formation constants is considered. Evidence is presented that suggests that solvent or electronic effects are responsible for the variations of chelating tendencies.

フェノールとホルムアルデヒドとの反応速度におよぼす溶媒組成の影響

フェノールとホルムアルデヒドとの反応速度におよぼす溶媒組成の影響