Deep oxidation of rutin and quercetin during their reaction with HAuCl4 in aqueous solutions

Russian Chemical Bulletin - The processes of deep oxidation during the reaction of rutin and quercetin with HAuCl4 under anaerobic conditions at temperatures of 30, 60, and 100 °C were...     

Physicochemical properties of aqueous solutions of dimethyl- and diethylsulfones

Aqueous solutions of dimethylsulfone (DMSO2) and diethylsulfone (DESO2) are studied by means of densimetry, surface tension, and calorimetry. The solution densities are defined and the apparent and partial molar volumes of DMSO2 and DESO2 are calculated in the temperature range of 293.15–323.15 K. It is revealed that in both cases the increase of sulfone concentration leads to the reduction of the surface tension. This is more expressed in the case of DESO2 than in the extension of the sulfone hydrocarbon chain. The calorimetric studies show that the dissolution enthalpies of DMSO2 and DESO2 do not differ substantially from one another; in both cases the dissolution of crystalline sulfones makes a crucial contribution to the enthalpy of dissolution values     

Physicochemical properties of aqueous solutions of L-aspartic acid containing chitosan

Physicochemical properties of aqueous solutions of L-aspartic acid with and without addition of chitosan have been studied by conductometry, potentiometry, refractometry, tensiometry, and viscosimetry. It has been shown that aspartic acid molecules take a cyclic configuration stabilized by hydrogen bonds in aqueous solution at c > 0.04 g/dL (298 K). The interaction of chitosan with aspartic acid results in the formation of the polymeric salt that dissociates in aqueous solution to give chitosan polycation [~(NH₃)⁺] and aspartate counterions. The addition of chitosan to solutions of L-aspartic acid results in progressive increase in the surface tension, absorbance, and refractive index as well as the change in hydrodynamic properties of the macromolecules. The polymeric salt exhibits polyelectrolyte properties in dilute aqueous solutions. The increase in temperature impairs the thermodynamic quality of the solvent for chitosan leading to the shrinkage of the polymer coils and, hence, to the decrease in the intrinsic viscosity of the system.     

肝苏颗粒中芦丁和槲皮素含量的测定

肝苏颗粒系中草药扯根菜(Penthorum Chinese Pursh) 经提炼加工而成,临床用于慢性乙型肝炎的治疗,并具有清热解毒、活血调经、利水消肿以及稳定血糖等功效[1].作为肝苏颗粒主要活性组分,槲皮素和芦丁含量是衡量肝苏颗粒质量好坏的一个主要指标.毛细管电泳具有快速、高效、分离能力强、需要样品量小等优点,在中药活性组分的分离分析中展现出了巨大的潜力,已有较多文献报道毛细管电泳法分析芦丁和槲皮素[2-7].     

Modulation of drug transport properties by multicomponent diffusion in surfactant aqueous solutions

Diffusion coefficients of drug compounds are crucial parameters used for modeling transport processes. Interestingly, diffusion of a solute can be generated not only by its own concentration gradient but also by concentration gradients of other solutes. This phenomenon is known as multicomponent diffusion. A multicomponent diffusion study on drug-surfactant-water ternary mixtures is reported here. Specifically, high-precision Rayleigh interferometry was used to determine multicomponent diffusion coefficients for the hydrocortisone-tyloxapol-water system at 25 degrees C. For comparison, diffusion measurements by dynamic light scattering were also performed. In addition, drug solubility was measured as a function of tyloxapol concentration, and drug-surfactant thermodynamic interactions using the two-phase partitioning model were characterized. The diffusion results are in agreement with a proposed coupled multicomponent diffusion model for ternary mixtures relevant to nonionic drug and surfactant molecules. Theoretical examination of diffusion-based drug transport in the presence of concentration gradients of micelles shows that drug fluxes and drug concentration profiles are significantly affected by coupled multicomponent diffusion. This work provides guidance for the development of accurate models of diffusion-based controlled release in multicomponent systems and for the applications of micelle concentration gradients to the modulation of diffusion-based drug transport.     

Physicochemical properties of eutonic aqueous solutions of zinc and copper tetraammoniates in the range 293–323 K

The density, viscosity, surface tension, and conductivity of subeutonic and eutonic solutions in the CuO-ZnO-NH₃-NH₄Cl-H₂O system at ammonia concentrations in the range 1.16–13.36 mol/l are determined experimentally in the temperature range 293–323 K. The expansion coefficient, the activation energy of viscous flow, the parachor, the orthochor, the degree of dissociation, and the equilibrium constant are calculated.     

Temperature-dependent volumetric and viscometric properties of amino acids in aqueous solutions of an antibiotic drug

Volumetric and viscometric properties of glycine and methionine (amino acids) in a 0.2 vol. % amikacin sulphate (antibiotic drug) aqueous solution with the molality range of 0.025 mol kg^?1–0.25 mol kg^?1 were measured over the temperature range of 20°C–40°C at the interval of 5°C. Different parameters like apparent molar volume (? _V), apparent molar adiabatic compression (? _κ ), isentropic compression (κ _S) along with other acoustical parameters were calculated. Parameters like viscous relaxation time (τ), free volume (V _F), internal pressure (Π _I), and molar cohesive energy (MCE) were calculated from dynamic viscosity measurements. The ? _V values are positive in both cases, but with higher magnitude observed in methionine. These positive values of ? _V are indicative of strong solute-solvent interactions at all temperatures. In case of methionine there is a sharp initial increase in the ? _V values which become almost constant with further additions of the amino acid. Structural differences in the two amino acids studied are clearly reflected in the different nature of the plots of different parameters. In case of an amino acid-drug system, dynamic viscosity increase has been attributed to the increase in the hydrophilic-ionic and hydrophilic-hydrophilic interactions with the increase in the amino acid concentration which in turn may cause more frictional resistance to the flow of the solution. All other parameters are discussed in terms of solute-solvent and solvent-solvent interactions.     

Consecutive determination of rutin and quercetin by spectrophotometric measurements

The consecutive determination of rutin and quercetin without any pretreatment for separation was examined in methanol solutions by a conventional and a two-wavelength spectrophotometry. Based the tendency of quercetin to form more stable metal complexes compared to rutin, quercetin can be determined through the tin(II) complex formation without interference from rutin. The method was applied to the determination of quercetin in the concentration range of 3.0 × 10^?6 to 2.0 × 10^?5M.Quercetin is apt to be oxidized by oxygen rather than rutin, especially in the presence of copper(II), whereas rutin is not decomposed under such a condition. After removal of quercetin through copper(II)-catalyzed oxidation, rutin ranging in concentration from 2.0 × 10^?6 to 2.0 × 10^?M was determined by the absorbance measurement of rutin-copper(II) complex in slightly alkaline methanol media.Both rutin and quercetin were determined directly by two-wavelength spectrophotometry, without adding any complex forming metals; the lower limit of detection was about 1.0 × 10^?5M. The method was extended to the determination of a smaller amounts of rutin and quercetin using the absorption peaks of their zirconium(IV) complexes, and the determination of both components in the range of 5.0 × 10^?6 to 3.0 × 10^?5M was made with a relative error of within ±4%.     

Emission properties of dihydropterins in aqueous solutions

Pterins belong to a class of heterocyclic compounds present in a wide range of living systems and accumulate in the skin of patients affected by vitiligo, a depigmentation disorder. The study of the emission of 7,8-dihydropterins is difficult because these compounds are more or less unstable in the presence of O(2) and their solutions are contaminated with oxidized pterins which have much higher fluorescence quantum yields (Φ(F)). In this work, the emission properties of six compounds of the dihydropterin family (6-formyl-7,8-dihydropterin (H(2)Fop), sepiapterin (Sep), 7,8-dihydrobiopterin (H(2)Bip), 7,8-dihydroneopterin (H(2)Nep), 6-hydroxymethyl-7,8-dihydropterin (H(2)Hmp), and 6-methyl-7,8-dihydropterin (H(2)Mep)) have been studied in aqueous solution. The fluorescence characteristics (spectra, Φ(F), lifetimes (τ(F))) of the neutral form of these compounds have been investigated using the single-photon-counting technique. Φ(F) and τ(F) values obtained lie in the ranges 3-9 × 10(-3) and 0.18-0.34 ns, respectively. The results are compared to those previously reported for oxidized pterins.     

Physicochemical properties of anionic triple-chain surfactants in alkaline solutions

A series of novel gemini cationic surfactants alkanediyl-alpha,omega-bis (hydroxyethylmethylhexadecylammonium bromide) with polymethylene spacer chain length of 4, 6, 8, and 10 carbon atoms was synthesized and characterized. Critical micellar concentrations of the gemini surfactants in aqueous solutions as determined by the surface tension and conductance measurements were observed to be in the range 1.39-3.63 microM. The critical micellar concentration was observed to increase initially with spacer length up to 6 methylene groups and to decrease thereafter with the increase in spacer length. The micellar microstructure in aqueous solutions examined through small angle neutron scattering (SANS) revealed that the extent of aggregation growth and variation in shapes of micelles strongly depend on head group polarity, spacer chain length, and temperature. The propensity to micellar growth with spacer chain length 4 was found to be much higher than with the longer spacer lengths. The fractional charge on the micelle increases with increased spacer chain length and temperature.     

Effect of thermal processing on the flavonols rutin and quercetin

The current research involves the study of the thermal treatment of quercetin and rutin in an aqueous model system (cooking). These substances were heated and their degradation was followed by high-performance liquid chromatography/diode-array detection (HPLC/DAD). The influence of pH and the involvement of oxygen in the degradation were studied. HPLC/electrospray ionization multi-stage mass spectrometry (ESI-MS(n)) was used for the structural characterization of the compounds produced. The influence of the degradation of the phenolic compounds on their antioxidant properties was elucidated by a electron spin resonance (ESR) spectrometry study of the reaction samples mixed with the stabilized radical, Fremy's salt. Strong degradation of the model substances took place under weak basic and oxidative conditions. Quercetin showed the most intense degradation. Protocatechuic acid could be identified as a cleavage reaction product by analyzing its retention time and molar mass during the degradation of quercetin. The structure of a second cleavage product could be identified on the basis of ESI-MS(n) fragmentation data. Also, several structures for reaction products of oxidized quercetin are suggested. The ESR analysis showed a decrease in the antioxidant activity of the reaction samples after heat treatment in aqueous solution.     

Solid solutions in the Zn-Co-O system: Physicochemical properties

Physicochemical analysis is used to study phase equilibria and to design a concentration diagram for the Zn-Co-O system. ZnO-, CoO-, and Co₃O₄-based mixed crystals with a fixed Zn/Co ratio have different oxygen nonstoichiometry depending on the synthesis and annealing parameters. Metastable clustering is discovered in Zn_{1 ? x} Co_xO_{1 + δ} wurtzite solid solutions, which exist stably in the range 0 ≤ x ≤ 0.2. Magnetization investigation shows that an antiferromagnetic order exists in homogeneous Zn_{1 ? x} Co_xO_{1 + δ} grains; this order is conserved up to 625 ± 25 K. The substitution of praseodymium, neodymium, samarium, or europium for zinc(II) cations in Zn_0.9Co_0.1O_{1 + δ} does not spoil the compensated antiferromagnetism of the wurtzite unit cell.     

Photochemical and photophysical properties of lumazine in aqueous solutions

Lumazine (pteridine-2,4(1H,3H)-dione, LU) was investigated for its efficiency of singlet oxygen (¹O₂) production and quenching in aqueous solution. The quantum yield of ¹O₂ production (Φ_Δ) was determined by measurements of the ¹O₂ luminescence in the near-infrared upon continuous excitation of the sensitizer. Values of Φ_Δ are sensitive to the pH and were found to be 0.44 ± 0.01 and 0.080 ± 0.004 in acidic and alkaline media, respectively. The photochemical stability of LU was investigated under different pH conditions, in the presence and in the absence of O₂. The photochemical consumption of LU in aqueous solution at room temperature under irradiation at 350 nm was followed by UV–vis spectrophotometry and HPLC. Values of the quantum yields of LU disappearance are low, indicating that LU is rather photostable under physiological conditions.     

Physicochemical and electrochemical properties of sulfolane solutions of lithium salts

The physicochemical and electrochemical properties (electrical conductivity, viscosity, density, and electrochemical stability) of sulfolane solutions of various lithium salts are studied. The nature of the anion considerably affects the physicochemical and electrochemical properties of the electrolyte systems considered. Sulfolane solutions of lithium salts have moderate electrical conductivity and high electrochemical stability, and can be used as electrolytes in lithium batteries.     

Complexation properties of phosphonocarboxylic acids in aqueous solutions

The concentration formation constants of phosphonoacetic acid (PAA) complexes with the Ca²⁺ and Mg²⁺ ions were determined in aqueous solution at 25°C by potentiometric and coulometric titrations at different ionic strengths and were extrapolated to I=0 in order to obtain thermodynamic values of the formation constants. Complexes were formed by the completely deprotonated K _f (ML) and monoprotonated K _f (MHL) forms of the PAA anion. The respective values for the complexes are: log K _f (CaL)=4.68±0.03, log K _f (CaHL)=2.61±0.08; log K _f (MgL)=5.58±0.09, log K _f (MgHL)=3.0±0.3. The enthalpy and entropy of complexation for the deprotonated Ca²⁺ and Mg²⁺ PAA species, determined from the temperature dependence of the log K _f (ML), are: H⁰(Ca) =0.6±0.2 kcal-mol^–1, S⁰(Ca)=21.4±0.6 cal-mol^–1-K^–1, H⁰(Mg)=3.0±0.7 kcal-mol^–1, and S⁰(Mg)=35±2 cal-mol^–1-K^–1. It is seen there-fore, that the complexes are entropy stabilized but enthalpy destabilized. Formation constants were also determined for Ca²⁺ and Mg²⁺ complexes with PAA analogs, phosphonoformic and 3-phosphonopropionic acids and the complexation of PAA was also studied at a single ionic strength, with Na⁺, Ag⁺, Tl⁺, Sr²⁺, Ba²⁺, Cd²⁺, Cu²⁺, and Pb²⁺ ions.     

Thermodynamic properties of aqueous alcohol and polyol solutions

In this work, we present experimental results for partial molar volumes and viscosities of aqueous solutions of n-propanol, 1,2-propanediol, 1,3-propanediol and 1,2,3-propanetriol at 25.00°C and literature data for other systems. The thermodynamic behavior of aqueous alcohol and polyol solutions is discussed in terms of the relationship between polar and non-polar groups and their effect on water structure. The relationship of hydroxyl groups to the number of non-polar groups in the solute determines the balance between hydrophobic and hydrophilic interactions and as a direct consequence, the thermodynamic behavior of properties such as partial molar volumes, and viscosity. This revised version was published online in July 2006 with corrections to the Cover Date.