Inhibition of β-galactosidases with mono- and disaccharides

It was demonstrated that, in reactions of the hydrolysis of model substrate 2-nitrophenyl-β-D-galactopyranoside (2-NPGP) monosaccharides D-fructose and D-xylose with hydroxyl substituents oppositely directed at the neighboring carbon atoms in the furan ring, as in D-glucose, act as noncompetitive inhibitors of β-galactosidase from E. coli; for mushroom, β-galactosidases from P. canescens and A. oryzae D-galactose is a stronger inhibitor. It was also found that the inhibition constant is the highest in the case of the most active enzyme (E. coli) and is the lowest for the least active one (P. canescens).     

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.     

Thermochemistry of Microhydration of Sodiated and Potassiated Monosaccharides

The thermochemical properties ΔH ^o _n , ΔS ^o _n , and ΔG ^o _n for the hydration of sodiated and potassiated monosaccharides (Ara = arabinose, Xyl = xylose, Rib = ribose, Glc = glucose, and Gal = galactose) have been experimentally studied in the gas phase at 10 mbar by equilibria measurements using an electrospray high-pressure mass spectrometer equipped with a pulsed ion beam reaction chamber. The hydration enthalpies for sodiated complexes were found to be between −46.4 and −57.7 kJ/mol for the first, and −42.7 and −52.3 kJ/mol for the second water molecule. For potassiated complexes, the water binding enthalpies were similar for all studied systems and varied between −48.5 and −52.7 kJ/mol. The thermochemical values for each system correspond to a mixture of the α and β anomeric forms of monosaccharide structures involved in their cationized complexes.     

Chemiluminescence determination of chromium(III) and total chromium in water samples using the periodate-lucigenin reaction

A new chemiluminescence (CL) method combined with flow injection technique is described for the determination of Cr(III) and total Cr. It is found that a strong CL signal is generated from the reaction of Cr(III), lucigenin and KIO₄ in alkaline condition. The determination of total Cr is performed by pre-reduction of Cr(VI) to Cr(III) by using H₂SO₃. The CL intensity is linearly related to the concentration of Cr in the range 4.0 × 10⁻¹⁰–1.0 × 10⁻⁶ g mL⁻¹. The detection limit (3s _b) is 1 × 10⁻¹⁰ g mL⁻¹ Cr and the relative standard deviation is 1.9% (5.0 × 10⁻⁸ g mL⁻¹ of Cr(III) solution, n = 11). The method was applied to the determination of Cr(III) and total Cr in water samples and compared satisfactorily with the official method.     

A kinetic, spectral and theoretical investigation on the role of oxygen in the radiolytic oxidation of a sorbityl cyclic acetal

The oxidation process of the cyclic acetal sorbitylfurfural (SF) has been thoroughly examined from the kinetic, spectroscopic and theoretical point of view. Oxidation has been initiated by the radiolitically produced OH radical in the presence of variable oxygen amounts. Two competing reaction pathways are evidenced which lead to quite different products, although they do not affect the acetal ring integrity. The peroxidation of the hydroxylated furanic ring (k ₄=(6.1±0.9)×10⁸ M⁻¹ s⁻¹) maintains the ring structurevia HO₂^• elimination (k ₆=(1.9±0.4)×10⁵ s⁻¹). Unlike that, the peroxidation of the pseudo-allylic radical (k ₅=(1.9±0.9)×10⁹ M⁻¹ s⁻¹), formedvia β-cleavage, fixes the destructured intermediate, leading to a tetroxide, which slowly decomposes through a Russell mechanism (k ₈=(2.3±0.6)×10² s⁻¹). It is confirmed that the steady state concentration of the tetroxide is very low, which suggests a molar absorption coefficient for it around 1.2×10⁴ M⁻¹ cm⁻¹ at 265 nm. The end products of the latter pathway have been characterized as carboxylic and butenald-sorbitol derivatives. The kinetic and spectral data of every step of the process have been fitted by the above outlined mechanism. The energetics of the mechanism has been detailed byab initio computations as well, carrying further substantiation to it. Semi-empirical calculations were also employed to describe the spectral properties of each intermediate.     

Determination of pheniramine enantiomers in eye drop by capillary electrophoresis using hydroxypropyl-β-cyclodextrin as chiral selector

A capillary zone electrophoresis procedure has been developed for the chiral determination of pheniramine in eye drop. Native and derivative cyclodextrins (CDs) including γ-CD, β-CD, hydroxypropyl-β-CD and dimethyl-β-CD were tested as chiral selectors. Using 30 mM hydroxypropyl-β-CD in 50 mM phosphate buffer (pH 3.0), the acceptable resolution value (R = 1.55) was obtained. The assay was validated for linearity (3.3 × 10⁻⁶–5.0 × 10⁻⁴ M; R ² = 0.9996), limit of detection (3.3 × 10⁻⁶ M), limit of quantification (8.5 × 10⁻⁶ M), analytical precision by terms of intra- and inter-day variability (RSD ≤ 2.57%), and accuracy (recovery ≥ 89.3%). The content of pheniramine in eye drop obtained by the proposed method was in good agreement with the declared value. The results indicated that pheniramine in the eye drop was present as the racemate.     

Complexation of [2.2]paracyclophane with β- and γ-cyclodextrins studied by HPLC and NMR

The NMR spectra of [2.2]paracyclophane with β- or γ-cyclodextrin in DMF-d₇ at room temperature do not show significant complexation, while HPLC of the complexes in mixed H₂O:alcohol solvents demonstrate complexation with different stoichiometries. At 243 K in DMF solution the H3 and H5 NMR signals of γ-cyclodextrin (but not β) exhibit complexation-induced chemical shifts denoting complex formation. According to HPLC, at room temperature the [2.2]paracyclophane complex with β-cyclodextrin in 20% H₂O:EtOH exhibits 1:2 stoichiometry with K ₁ = 1×10² ± 2, K ₂ = 9.0×10⁴ ± 2×10³ (K = 9×10⁶) while that with γ-cyclodextrin in 50% H₂O:MeOH exhibits 1:1 stoichiometry with K ₁ = 4×10³ ± 150 M⁻¹. Thermodynamic parameters for both complexes have been estimated from the retention time temperature dependence. For the β-cyclodextrin complexation at 25°C ΔG ⁰ _CD is −39.7 kJ mol⁻¹ while ΔH ⁰ _CD and ΔS ⁰ _CD are −88.2 kJ mol⁻¹ and −0.16 kJ mol⁻¹ K⁻¹. For γ-cyclodextrin, the corresponding values are ΔG ⁰ _CD = −20.5 kJ mol⁻¹, ΔH ⁰ _CD = −33.5 kJ mol⁻¹ and ΔS ⁰ _CD = −0.04 kJ mol⁻¹ K⁻¹.      

Chiral separation of pheniramine by capillary electrophoresis partial-filling technique using hydroxypropyl-β-cyclodextrin as chiral selector

A simple capillary electrophoresis partial-filling technique for the enantioseparation of pheniramine is presented. Phosphate buffer and hydroxypropyl-β-cyclodextrin (HP-β-CD) were used as the electrolyte and chiral selector, respectively. Several experimental parameters such as HP-β-CD concentration, HP-β-CD plug length, CE temperature and applied voltage were studied. Under the selected conditions, pheniramine enantiomers can be separated within less than 14 min. The assay was validated for linearity (5.0 × 10⁻⁶–5.0 × 10⁻⁴ M; R ² = 0.9987), limit of detection (5.0 × 10⁻⁷ M), limit of quantitation (5.0 × 10⁻⁶ M), analytical precision (%RSD ≤ 9.8) and accuracy (%recovery = 101 ± 3). The proposed methodology was then applied to the analysis of a commercially available pharmaceutical eye drop preparation. The results are in good agreement with that declared by the manufacturer. The proposed methodology provides adequate results in terms of simplicity, cost, sample throughput, repeatability and accuracy for quality control of pheniramine enantiomers in pharmaceutical preparations.     

Synthesis,crystal structure,and third-order nonlinear optical properties of a copper(I) one-dimensional coordination polymer [Cu(μ-1,1,1,3-N<Subscript>3</Subscript>)]<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>

A novel copper(I) azide coordination polymer [Cu(μ-1,1,1,3-N₃)] _n has been synthesized by the low-temperature solution-state reaction. Crystal X-ray analyses reveal that compound [Cu(μ-1,1,1,3-N₃)] _n possesses a type of three-dimensional (3D) framework structure. The polymer was characterized by elemental analyses, IR spectra, and UV-Vis spectra. The third-order nonlinear optical (NLO) properties were also investigated, and they exhibit good linear absorption and self-defocusing performance with modulus of the hyperpolarizability (γ) 8.16 × 10⁻³⁰ esu for [Cu(μ-1,1,1,3-N₃)] _n in a 1.96 × 10⁻⁴ mol dm⁻³ DMF solution.     

Theoretical and experimental study of the structure and stability of multiply Na-substituted glucose and 2,4,6-trihydroxyacetophenone derivatives

The equilibrium geometric parameters and the energetic and spectroscopic characteristics of low lying conformers for series of polyhydroxyl molecules and ions in which sodium atoms are successively substituted for the hydroxyl hydrogen atoms have been calculated by the density functional theory B3LYP method with the 6−31G* and 6−311+G** basis sets. The glucose derivatives [Glu − nH + nNa] and [Glu − nH + (n + 1)Na]⁺ (n = 1−5) and the 2,4,6-trihydroxyacetophenone derivatives [THAP − nH + nNa] and [THAP − nH + (n + 1)Na]⁺ (n = 1−4) have been considered. The affinities of the neutral [Glu − nH + nNa] and [THAP − nH + nNa] molecules for adding Na⁺ cations, as well as the energies of successive substitution of Na atoms for H atoms in the Glu and THAP molecules and the Glu⁺ and THAP⁺ ions in their reaction with sodium acetate molecules, have been estimated. Computations show that the first substitution of Na for H in ions is slightly exothermic and, presumably, can spontaneously occur under common conditions. Further substitutions are endothermic, but the required energy inputs are small. Therefore, successive substitutions for two, three, or more hydroxyl H atoms in the molecules and ions under consideration are possible at relatively low energy inputs. The computation results and conclusions are compared with the MALDI TOF mass spectral data for Na-substituted glucose and 2,4,6-trihydroxyacetophenone derivatives in the [glucose + CH₃COONa + THAP] system where, in addition to common Glu · Na⁺ and THAP · Na⁺ ion-molecular complexes, multiply substituted positive ions of the [Glu − nH + (n + 1)Na]⁺ (n = 1−4) and [THAP − nH + (n + 1)Na]⁺ (n = 1−3) type have been identified.     

A facile and fast electrochemical method for the simultaneous determination of <Emphasis Type="Italic">o</Emphasis>-dihydroxybenzene and <Emphasis Type="Italic">p</Emphasis>-dihydroxybenzene using a surfactant

A fast and convenient analytical technique has been suggested to detect dihydroxybenzene (DHB) isomers directly and simultaneously. In 0.1 M HAc-NaAc buffer solution (pH 5.6), the reduction peaks of p -DHB and o -DHB were partly separated by differential pulse voltammetry at the glassy carbon electrode. By adding a surfactant (cetyl pyridinium chloride) to enhance the detection sensitivity and using a semi-derivative technique to improve the separation, p-DHB and o-DHB were detected simultaneously. The linear calibration ranges were 1.2 × 10⁻⁶ to 1.0 × 10⁻⁴ M for p -DHB and 8.2 × 10⁻⁷ to 1.0 × 10⁻⁴ M for o -DHB, with detection limits of 3.6 × 10⁻⁷ and 2.4 × 10⁻⁷ M, respectively. The proposed method has been applied to the direct determination of DHB isomers in water sample, and the results were excellent. The text was submitted by the authors in English.     

Molecularly imprinted solid-phase extraction and flow-injection chemiluminescence for trace analysis of 2,4-dichlorophenol in water samples

Highly sensitive flow-injection chemiluminescence (CL) combined with molecularly imprinted solid-phase extraction (MISPE) has been used for determination of 2,4-dichlorophenol (2,4-DCP) in water samples. The molecularly imprinted polymer (MIP) for 2,4-DCP was prepared by non-covalent molecular imprinting methods, using 4-vinylpyridine (4-VP) and ethylene glycol dimethacrylate (EGDMA) as the monomer and cross-linker, respectively. 2,4-DCP could be selectively adsorbed by the MIP and the adsorbed 2,4-DCP was determined by its enhancing effect on the weak chemiluminescence reaction between potassium permanganate and luminol. The enhanced CL intensity was linear in the range from 1 × 10⁻⁷ to 2 × 10⁻⁵g mL⁻¹. The LOD (S/N = 3) was 1.8 × 10⁻⁸g mL⁻¹, and the relative standard deviation (RSD) was 3.0% (n = 11) for 1.4 × 10⁻⁶g mL⁻¹. The proposed method had been successfully applied to the determination of 2,4-DCP in river water. Figure Effect of 4-VP content on the ultraviolet spectrum of 2,4-DCP in chloroform     

Voltammetric determination of <Emphasis Type="Italic">D</Emphasis>-penicillamine based on its homogeneous electrocatalytic oxidation with potassium iodide at the surface of glassy carbon electrode

The electrooxidation of D-penicillamine (D-PA) has been studied in the presence of potassium iodide in various buffered aqueous solutions (4.00 ≤ pH ≤ 9.00) at the surface of glassy carbon electrode using cyclic voltammetry, differential pulse voltammetry and chronoamperometry. It has been found that under optimum pH (pH 5.00) in cyclic voltammetry, the electrooxidation of D-PA in the presence of potassium iodide as a homogeneous mediator occurred at a potential about 220 mV less positive than that in absence of potassium iodide at the surface of glassy carbon electrode. The homogeneous electrocatalytic oxidation current wave of D-penicillamine was linearly dependent on the D-PA concentration and a linear calibration curve was obtained in the ranges 3.0 × 10⁻⁵−1.5 × 10⁻³ M and 9.0 × 10⁻⁶−1.2 × 10⁻⁴ M of D-PA with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods, respectively. The detection limits (2σ) were determined as 3.0 × 10⁻⁵ and 3.5 × 10⁻⁶ M with CV and DPV, respectively. This method was also used for voltammetric determination of D-PA in pharmaceutical preparation by standard addition method.     

Syntheses, Crystal Structures and Third-order Nonlinear Optical Properties of Coordination Polymers {[Et4N][Ag2I3]}n and [CuBr(C10H8N2S2)]n

Coordination polymers {[Et₄N][Ag₂I₃]}_n (1) and [CuBr(C₁₀H₈N₂S₂)]_n (2) were prepared by standard Schlenk techniques. Their X-ray measurements indicate that polymer (1) crystallizes in the orthorhombic space group Pnma, and polymer (2) crystallizes in the monoclinic space group P21/n. Complex (1) has a hanging ladder-like polymeric chain which can also be described as a helical chain bridged by Ag–Ag edges. Complex (2) exhibits a monoclinic crystal system with a slightly distorted tetrahedron. The nonlinear optical (NLO) properties of (1) and (2) were investigated by using Z-scan techniques with an 8 ns pulsed laser at 532 nm. These two coordination polymers exhibit NLO absorption and an effective self-focusing effect. The effective α₂ and n₂ values of cluster (1) are 3.04×10⁻¹¹ m W⁻¹ and 7.6×10⁻¹⁸ m² w⁻¹ and the effective α₂ and n₂ values of compound (2) are 1.08×10⁻¹¹ m W⁻¹ and 3.1×10⁻¹⁸ m² w⁻¹ when measured in CH₂Cl₂ solution.     

Molecularly imprinted on-line solid-phase extraction combined with chemiluminescence for the determination of pazufloxacin mesilate

A novel molecularly imprinted polymer solid-phase extraction (MISPE) with flow-injection chemiluminescence (CL) was developed for the determination of pazufloxacin mesilate (PZFX). The molecularly imprinted polymer (MIP) was synthesized by using PZFX as the imprinting molecule. A glass tube packed the particles of the MIP was employed as MISPE micro-column, which was connected into the sampling loop of the eight-way injection valve for on-line selective preconcentration and extraction of PZFX. The eluent of acetonitrile:acetic acid (9:1, v:v) was used as carrier for eluting the adsorbed PZFX to react with the mixture of cerium(IV) and sodium sulfite in the flow cell to produce strong CL. The relative intensity of CL was linear to PZFX concentration in the range from 2.5 × 10⁻⁹ to 2.5 × 10⁻⁷ g mL⁻¹. The limit of detection was 7 × 10⁻¹⁰ g mL⁻¹ (3 σ) and the relative standard deviation for 5 × 10⁻⁸ g mL⁻¹of PZFX solution was 3.7% (n = 7). This method has been applied to the determination of PZFX in human urine.     

Determination of vitamin B<Subscript>1</Subscript> in seawater and microalgal fermentation media by high-performance liquid chromatography with fluorescence detection

A highly sensitive high-performance liquid chromatographic method with fluorescence detection has been developed for determination of vitamin B₁. Vitamin B₁ was converted into a fluorescent compound by treatment with hydrogen peroxide–horseradish peroxidase and the derivative was subsequently analyzed by HPLC on a Waters Spherisorb ODS2 column (250 mm×4.6 mm ID, 5 μm) with 40:60 methanol–pH 8.5 acetate buffer solution as mobile phase and fluorescence detection at 440 nm (with excitation at 375 nm). The calibration graph was linear from 5.00×10⁻¹⁰ mol L⁻¹ to 5.00×10⁻⁷ mol L⁻¹ for vitamin B₁ with a correlation coefficient of 0.9991 (n=9). The detection limit was 1.0×10⁻¹⁰ mol L⁻¹. The method was successfully used for determination of vitamin B₁ at pg mL⁻¹ levels in microalgal fermentation media and seawater after solid-phase extraction. Recovery was from 89 to 110% and the relative standard deviation was in the range 1.1 to 4.3%.     

Study on the antioxidant activity and quantification of thioamides based on nitrogen five-membered heterocycles by the kinetic technique

The antioxidant activity of heterocyclic thioamides based on imidazole, triazole, tetrazole, thiazole, thiazoline, and thiadiazole is estimated by spectrophotometry using the rate constant of reaction with the chromogenic radical 2,2′-diphenyl-1-picrylhydrazyl. The rate constant of direct transfer of a hydrogen atom to the radical in carbon tetrachloride is maximal for 1-methylimidazoline-2-thione. The protective antioxidant effect of the preparations in ethanol falls down abruptly from 4-phenylthiazoline-2-thione (k = 1.06 × 10⁴ M⁻¹min⁻¹) to the thioamides based on triazole and thiazoline (k ∼ 20 M⁻¹min⁻¹). In acetonitrile, thiazole derivatives show the most substantial antioxidant activity, k = n ×10⁴ M⁻¹min⁻¹, which goes down to zero if the aromaticity of the heterocycle is broken. As established, for the pseudo first order reaction between thioamides and the chromogenic radical, the reaction rate linearly depends on the concentration of thioamides. A spectrophotometry kinetic method for the quantification of heteroaromatic thioamides is elaborated.     

Electroanalytical Method of Acid Blue 120 and its Supramolecular System with Cyclodextrins

In this paper, a simple, rapid, sensitive and accurate electroanalytical method of Acid Blue 120 (AB120) has been established by polarography. In a supporting electrolyte of 0.01 mol l⁻¹ Na₂HPO₄–KH₂PO₄ (pH 7.04) solution, a sensitive first derivative reduction peak (ip′) of AB120 was found by Linear Sweep Voltammetry (LSV). The peak potential is −820 mV (versus SCE). The peak current (ip′) is proportional to the concentration over the range 2.0 × 10⁻⁷–5.0 × 10⁻⁵ mol l⁻¹ (r=0.9961–0.9991) and the limit of detection (LOD) is 1.0 × 10⁻⁷ mol l⁻¹. The recovery of AB120 varied from 95.3 to 103.0% and the relative standard deviation (RSD) was 2.2% (n=8). The method has been expected to determination of wastewater in dye industry. In addition, the supramolecular system of AB120 with cyclodextrins has been studied. It can form 1:1 inclusion complex with six CDs. The inclusion constants were calculated and the inclusion ability of different kinds of CDs was compared. Furthermore, the inclusion mechanism was also preliminarily discussed, which provided some valuable information for further application of AB120 and CDs.     

Fluorescence-detecting cationic surfactants using luminescent CdTe quantum dots as probes

A novel fluorescence quenching method for the determination of cationic surfactants (CS), specifically cetyltrimethylammonium bromide (CTAB), dodecyltrimethylammonium bromide (DTAB), and cetylpyridinium chloride (CPC), has been developed using water-soluble luminescent CdTe quantum dots (QDs) modified with thioglycolic acid (TGA). The possible interference from heavy and transition metals (HTM) has been efficiently eliminated through simple sample treatment with mercapto cotton made in-house. Under optimum conditions, the extent of fluorescence quenching of CdTe QDs is linearly proportional to the concentration of CS from 2.0 × 10⁻⁷ to 7.0 × 10⁻⁶ mol L⁻¹ with a detection limit of 5.0 × 10⁻⁸ mol L⁻¹. The relative standard deviation for 1.0 × 10⁻⁶ mol L⁻¹ CTAB is 2.5% (n = 6). The proposed method exhibits high sensitivity and selectivity and furthermore avoided the use of toxic organic solvents and tedious solvent extraction procedures. It has been applied to the determination of trace CS in natural river water and commodity samples with satisfactory results. Potential interference from heavy and transition metals is eliminated during photoluminescence detection of CS through simple sample pre-treatment with mercapto cotton     

NADH screen-printed electrodes modified with zirconium phosphate,Meldola blue,and Reinecke salt. Application to the detection of glycerol by FIA

Bulk screen-printed electrodes (bSPEs) modified with zirconium phosphate (ZrP) and Meldola blue (MB) and by electrochemical deposition of a Reineckate film (bMBZrPRs-SPEs) have been constructed and used as NADH sensors. Cyclic voltammetric investigation of these bulk electrochemically modified screen-printed electrodes revealed stable catalytic activity in oxidation of the reduced form of the coenzyme nicotinamide adenine dinucleotide (NADH). Flow-injection analysis (FIA) coupled with amperometric detection confirmed the improved stability of the bMBZrPRs-SPEs (10⁻⁴ mol L⁻¹ NADH, %RSD = 4.2, n = 90, pH 7.0). Other conditions, for example applied working potential (+50 mV relative to Ag|AgCl), flow rate (0.30 mL min⁻¹) and pH-dependence (range 4.0–10.0) were evaluated and optimized. A glycerol biosensor, prepared by immobilizing glycerol dehydrogenase (GDH) on the working electrode area of a bMBZrPRs-SPE, was also assembled. The biosensor was most stable at pH 8.5 (%RSD = 5.6, n = 70, 0.25 mmol L⁻¹ glycerol). The detection and quantification limits were 2.8 × 10⁻⁶ and 9.4 × 10⁻⁶ mol L⁻¹, respectively, and the linear working range was between 1.0 × 10⁻⁵ and 1.0 × 10⁻⁴ mol L⁻¹. To assess the effect of interferences, and recovery by the probe we analyzed samples taken during fermentation of chemically defined grape juice medium and compared the results with those obtained by HPLC.