Binding equilibrium study of phosphotungstic acid and HSA or BSA with UV spectrum, fluorescence spectrum and equilibrium dialysis

The binding equilibrium between phosphotungstic acid (H7[P(W2O7)6] · XH2O;PTA) and human serum albumin (HSA) or bovine serum albumin (BSA) has been studied by UV-Vis, fluorescence spectroscopies and equilibrium dialysis. It has been observed that UV absorption enhanced and the fluorescence quenched as the PTA binding to HSA or BSA at physiological pH 7.43(?.02). The Scatchard analysis indicated that there exists a strong binding site of PTA in both HSA and BSA, and the successive stability constants of these two systems are obtained by nonlinear least-squares methods fitting Bjerrum formula.     

Stöber silica’s microporosity

Substantial knowledge gap still exists in understanding Stöber silica’s confusing microporosity. In this work, we utilized simultaneous thermal analysis coupled with Fourier transform infrared spectroscopy to characterize Stöber silica samples prepared with various post-treatments including water or ethanol washing and drying at different temperatures. The results suggest that ammonia-catalyzed ethoxylation between ethanol and silanol groups can take place during drying, and the resulting ethoxyl groups along with Si-containing oligomers may contribute to serious micropore blocking. On the other hand, water washing is effective to hydrolyze and remove these pore-blocking materials and thus enable cleared micropores. Several interesting findings including the very sharp DSC peaks, high evolving temperature of ethanol, and pyrolysis of organic matters are linked to Stöber silica’s micropores. Our work has undoubtedly improved the mechanistic understanding of Stöber silica’s microporosity and will thus facilitate the practical optimization and application of this material.

     

Synthesis and characterization of silica xerogels obtained via fast sol–gel process

The synthesis and physical properties of high surface area silica xerogels obtained by a two-step sol–gel process in the absence of supercritical conditions are reported. The hydrolysis and condensation reactions were followed by infrared spectroscopy. The increment in the bands corresponding to silanol and hydroxyl groups suggests that the hydrolysis reaction was complete during the first 30 min. The effect on surface area and global reaction time under various reaction conditions, such as type of alkaline catalyst and solvents, water–monomer and solvent–monomer molar ratios, was also studied. The obtained results suggest that surface area was increased using 3-aminopropyltriethoxysilane as catalyst. The use of isopropyl alcohol as solvent promotes the reduction of the capillary stress, giving a well-structured xerogel. As a conclusion, with H₂O/i-PrOH/TEOS in a molar ratio of 10:4:1, it was possible to obtain silica xerogels with surface areas about 1,240 m²/g. Such surface areas are comparable with those obtained under supercritical conditions (aerogels), and higher than those xerogels conventionally obtained under normal condition (500–800 m²/g).     

Optimization of the assay of naphthodianthrones in dry St John’s wort extract by reversed-phase liquid chromatography

An optimization procedure for the reversed-phase liquid chromatography (RPLC) assay of naphthodianthrones in St John’s wort extract from the European Pharmacopoeia project is described. The results obtained from two screening designs showed that light exposure, recommended in the monograph as sample pretreatment, does not permit one to obtain a reproducible quantification of the main ingredients. Improvement of the method robustness implies the need to overcome the problem of light exposure, to subsequently quantify protonaphthodianthrones and to perform the separation on octadecyl (ODS)-bonded phase at optimized flow rate. The method robustness was checked by using a bifurcation sequential approach investigating the influence of 13 factors. The eluent recommended in the monograph is a ternary mixture of methanol, phosphate buffer and ethyl acetate. For the sake of simplicity, the phosphate buffer was substituted by an acetate buffer. The best composition of the ternary mixture was determined by a combined design including three mixture variables and the temperature as an independent variable. Chromatographic parameters were modelled in terms of analysis time, resolution and asymmetry. Desirability functions permit one to cope with these parameters and to determine the best compromise. The naphthodianthrones were separated on a conventional endcapped octadecyl silica gel column eluted by a ternary mobile phase at 40 °C in 10 min. Electronic Supplementary Material Supplementary material is available for this article at     

Discrete version of Wiener-Khinchin theorem for Chebyshev’s spectrum of electrochemical noise

A discrete version of Wiener-Khinchin theorem for Chebyshev’s spectrum of electrochemical noise is developed. Based on the discrete version of Wiener-Khinchin theorem, the theoretical discrete Chebyshev spectrum for the Markov random process is calculated. It is characterized by two parameters: the dispersion and the relaxation frequency (or relaxation time). The noise of corrosion process and the noise of recording equipment are measured. Using the theoretical Chebyshev spectrum, the Markov parameters were found both for the noise of the corrosion process and for the noise of the measuring equipment.     

Effect of gold nanoparticles on the fluorescence excitation spectrum of α-fetoprotein: local environment dependent fluorescence quenching

The effect of colloid gold nanoparticles (AuNPs) on the fluorescence excitation spectrum of α-fetoprotein (AFP) has been investigated experimentally. The excitation spectral peaks of AFP with low concentration from 0.01 ng ml(-1) to 12 ng ml(-1) increase monotonically with increasing of AFP concentration. When some gold colloids were added to the AFP solution, the excitation peak at 285 nm decreases distinctly. By comparing the excitation peak intensity of AFP solution with gold colloids and without gold colloids at different AFP concentrations, the quenching effect from gold nanoparticle was more effective at lower AFP concentration. So the range of concentration from 0.01 ng ml(-1) to 0.09 ng ml(-1) will be the potential range of applications because of the higher sensitivity. The physical origin based on local field effect was investigated to illuminate this local environment dependent fluorescence quenching. The changing extent of quenching with different AFP concentrations can be attributed to the nonlinear decreasing of the local field factor of gold nanoparticles as a function of environmental dielectric constant.     

Reaction of levoglucosenone with Dane’s diene

Cycloaddition of levoglucosenone to 7-methoxy-4-vinyl-1,2-dihydronaphthalene has been studied under different conditions, including heating under atmospheric pressure, in a sealed ampule, and under high pressure, as well as under microwave irradiation and in the presence of various catalysts. The chiral Diels–Alder adduct thus obtained can be used in the synthesis of estrone and its analogs.     

Inhibitive effect by extract of Mentha rotundifolia leaves on the corrosion of steel in 1 M HCl solution

An extract of Mentha rotundifolia leaves (EMRL) was tested as a corrosion inhibitor of steel in 1 M HCl using electrochemical impedance spectroscopy, Tafel polarization methods, and weight loss measurements. The inhibition efficiency of the extract of Mentha rotundifolia leaves was calculated and compared. We note good agreement between these methods. The results obtained revealed that the inhibitor tested differently reduced the kinetics of the corrosion process of steel. Its efficiency increases with the concentration and attained 92.87 % at 35 %. The effect of temperature on the corrosion behavior of steel in 1 M HCl was also studied in the range 298 and 338 K. The thermodynamic data of activation were determined. Mentha rotundifolia extract is adsorbed on the steel surface according to a Langmuir adsorption model.     

The Relationship of Freeze Tolerance with Intracellular Compounds in Baker’s Yeasts

Freeze-tolerant baker’s yeasts are required for the processing of frozen doughs. The present study was carried out to investigate the cell survival rate after frozen storage and the change of fermentability in dough due to frozen storage, and to discuss quantitatively the relationship of freeze tolerance with intracellular trehalose, amino acids, and glycerol, using six types of baker’s yeasts as the test materials. The experimental results showed that the fermentability of yeast cells in frozen dough was strongly correlated with the cell survival rate. The baker’s yeast with a higher level of cell survival rate had a larger increase in the total intracellular compound content after frozen storage, and the cell survival rate increased linearly with increasing total intracellular compound content in frozen yeast cells. Trehalose was a primary compound affecting freeze tolerance, followed by glutamic acid, arginine, proline, asparagic acid, and glycerol. The basic information provided by the present study is useful for exploring the freeze-tolerance mechanisms of baker’s yeast cells, breeding better freeze-tolerant baker’s yeast strains, and developing more effective cryoprotectants.     

Preparation of polystyrene/silica nanocomposites by radical copolymerization of styrene with silica macromonomer

A two-stage process has been developed to generate the silica-based macromonomer through surface-modification of silica with polymerizable vinyl groups. The silica surfaces were treated with excess 2,4-toluene diisocynate (TDI), after which the residual isocyanate groups were converted into polymerizable vinyl groups by reaction with hydroxypropylacrylate (HPA). Thus, polystyrene/silica nanocomposites were prepared by conventional radical copolymerization of styrene with silica macromonomer. The main effecting factors, such as ratios of styrene to the macromonomer, together with polymerization time on the copolymerization were studied in detail. FTIR, DSC and TGA were utilized to characterize the nanocomposites. Experimental results revealed that the silica nanoparticles act as cross-linking points in the polystytene/silica nanocomposites, and the glass transition temperatures of the nanocomposites are higher than that of the corresponding pure polystyrene. The glass transition temperatures of nanocomposites increased with the increasing of silica contents, which were further ascertained by DSC.     

Paneth’s epistemology of chemical elements in light of Kant’s Opus postumum

Friedrich Paneth’s conception of “chemical element” has functioned as the official definition adopted by the International Union of Pure and Applied Chemistry since 1923. Paneth maintains a distinction between empirical and “transcendental” concepts of element; furthermore, chemical science requires fluctuation between the two. The origin of the empirical-transcendental split is found in Immanuel Kant’s classic Critique of Pure Reason (1781/1787). The present paper examines Paneth’s foundational concept of element in light of Kant’s attempt, late in life, to revoke key distinctions made in his Critique, including that of regulative and constitutive functions of reason. In a section of his Opus postumum devoted to the “Transition from the Metaphysical Foundations of Natural Science to Physics,” Kant bends his philosophical system to address the newly emerging sciences of matter of his time. Specifically, he tried, without success, to develop the transcendental ground for microscale motions of bodies encountered in physical, electrical and chemical processes. Paneth’s discussion of chemical element does not take the Opus postumum into account, which is why it begins with a rejection of Kant’s rejection (in his earlier writings) of chemistry’s status as science. I make the case that Paneth’s definition of element effectively maintains something very like Kant’s critical separation of regulative and constitutive principles, while a advancing the concept of chemical science.     

Acylation of Fischer’s Base with Methyl Aroylpyruvates

Methyl (Z)-4-aryl-2-hydroxy-4-oxobut-2-enoates (methyl aroylpyruvates) reacted with 1,3,3-trimethyl- 2-methylidene-2,3-dihydro-1H-indole (Fischer’s base) to give (2Z,5E)-1-aryl-3-hydroxy-5-(1,3,3-trimethyl-2,3-dihydro-1H-indol-2-ylidene)pent-2-ene-1,4-diones.     

Aromaticity of pentafulvene’s complexes with alkaline metal atoms

Geometry of pentafulvene’s complexes with the atoms of the first group of Periodic Table (Li, Na, K, Rb, and Cs) are optimized at the B3LYP/6-311 ++G(d, p) level of theory. Two kinds of complexes are considered: (1) those which are in equilibrium geometry, and (2) complexes which are formed by gradual change in the distance between the metal atom and penta-fulvene ring. Aromaticities of the considered complexes in their equilibrium geometries are investigated using different indices included geometry-based (HOMA), magnetism-based (NICS, NICS(1), and NICS(1)zz), π-electron count-based (pEDA), and electronic-based (Shannon Aromaticity; (SA)) indices. All indices are well correlated to each other and to some local (atomic charges) and global (binding-energy) properties, with one exception—HOMA. The same regularity is observed for non-equilibrium complexes.     

Quantum-chemical modeling of possible reactions of Roussin’s red esters with aryl ligands in DMSO solution

Possible reactions of Roussin’s red esters [Fe₂(μ-SC₆H₄R)₂(NO)₄], where R = H, o-NH₂, m-NO₂, m-OH, or m-NH₂, in DMSO solution were investigated by quantum chemical modeling. It was shown that in these systems, numerous reactions can occur, including NO donation, ligand substitution, and decomposition into mononuclear iron nitrosyl complexes. The resulting compounds are also NO donors.     

Reactions of Zincke’s salts with 2,3-dimethylbenzothiazolium iodide

Reactions of 1-(2,4-dinitrophenyl)pyridinium chloride and 2-(2,4-dinitrophenyl)isoquinolinium chloride with 2,3-dimethylbenzothiazolium iodide in hot pyridine allows introduction of an aryl residue into the thiazole ring via intermolecular transformation of the pyridine ring of Zincke’s salts with participation of the methyl group in position 2 of the benzothiazolium salt.     

Oxidation of bicyclic monoterpene ketones with Caro’s acid

Previously unknown seven-membered lactones, (1R,1??R,5S,5??S)-5,5??-oxybis(1,8,8-trimethyl-2-oxabicyclo[3.2.1]octan-3-one), 2,2-dimethyl-1,6-dioxaspiro[2.6]nonan-7-one, 4-(1-hydroxy-1-methylethyl)-7-methyloxepan-2-one, and (4R,4??R,7S,7??S)-4,4??-[oxybis(propane-2,2-diyl)]bis(7-methyloxepan-2-one), were synthesized by the Baeyer-Villiger reaction using Caro??s acid as a result of oxidative and skeletal transformations of bicyclic monoterpene ketones, (+)-camphor, (+)-nopinone, and (?)-isocaranone.     

Synthesis of aromatic polyamidines in Eaton’s reagent

Aromatic polyamidines are prepared via the polycondensation of dicarboxamides and diamines in Eaton’s reagent. The polymers are investigated by elemental analysis and IR and NMR spectroscopy. Polyamidines are well soluble in concentrated sulfuric acid and concentrated formic acid and in polar organic solvents, and temperatures corresponding to their 10% weight losses are in the range 245–280°C.     

Properties of metastable linkage NO isomers in Na2[Fe(CN)5NO]·2H2O incorporated in mesopores of silica xerogels

We study the properties of photoinduced metal-nitrosyl linkage isomers in sodium nitroprusside (SNP) as a function of particle size. By embedding the molecular complex at various concentrations into mesopores of silica xerogels the size of the particles can be adjusted. The ground state is characterized by X-ray diffraction, absorption and infrared spectroscopy. The physical properties of the photoswitched molecules were analysed by steady-state low-temperature absorption, infrared spectroscopy and by nanosecond transient absorption spectroscopy. The electronic structure as well as the activation energies of the metastable linkage isomers are independent of the particle size down to single isolated molecules, indicating that the SNP complexes are quasi-free inside the pores of the gel.