Effect of extraction method on phenolic content and antioxidant activity of mistletoe extracts from Viscum album subsp. abietis

The total content of polyphenols and flavonoids determined in the same plant and their corresponding antioxidant activities may vary widely, depending on the extraction conditions applied. This study was conducted to optimise the extraction conditions of phenolics and flavonoids from the mistletoe plant. Various extraction methods, i.e. ultrasound-assisted extraction technology, maceration, maceration with stirring, accelerated solvent extraction (ASE), and extraction under reflux were evaluated for their percentage extraction of polyphenols (TPC) and flavonoids (TFC) from Viscum album subsp. abietis. In addition, the anti-radical activity of extracts was analysed using the 2,2-diphenyl-1-picrylhydrazyl method. The effects of temperature, solvent type, and concentration on the phenolic extraction efficiency and antioxidant activity were studied using chemometric and statistical methods. The results showed that the extracts of V. album subsp. abietis contained large amounts of polyphenols and flavonoids (up to 57.673 mg g^?1 and 9.955 mg g^?1 of dry extract, respectively) and exhibited potent antioxidant activity, hence representing promising sources of powerful antioxidants. Due to its high extraction efficiency and considerable saving of time and solvent, ASE was more effective than the other extraction techniques. Extracts prepared with water-polar solvent mixtures displayed the highest TPC, TFC, and antioxidant activity, while organic polar solvents were the least efficient extractants.     

Effect of halogenless flame retardants on the thermal properties, flammability, and fire hazard of cross-linked EVM/NBR rubber blends

This paper presents the results of investigating the thermal stability, flammability, and fire hazard of cross-linked EVM/NBR blends unfilled and filled with halogenless flame-retardant compounds such as melamine cyanurate or magnesium hydroxide. The thermal analysis of the blends was carried out in the atmosphere of air. The activation energy of the composite destruction was determined by two non-isothermal methods: Flynn–Wall–Ozawa’s and Kissinger’s methods. The flammability of the composites obtained was determined by the method of oxygen index and on the basis of their combustion in air. The fire hazard of the vulcanizates investigated was determined with the use of a cone calorimeter and on the basis of toxicometric parameters W _LC50SM. The test results have shown that the flame retardants used increase the thermal stability of the cross-linked blends and decrease their flammability, and thereby allow one to obtain self-extinguishing or non-flammable polymeric materials. The cross-linked EVM/NBR blends filled with these flame-retardant compounds are characterized by good mechanical properties and reduced fire hazard.     

Pyrolysis kinetics of elephant grass pretreated biomasses

The Elephant Grass (Pennisetum purpureum Schum) was pretreated by two independent processes, through washing with hot water (W-EG) and acid solution (AW-EG) to improve its energy properties to apply it in a thermochemical process conversion into fuel. The biomasses were analyzed by proximate and ultimate analysis; and the pyrolysis kinetics, before and after pretreatments, were evaluated by the apparent activation energy (E _a) for decomposition in the temperature range of greater volatile matter through the Model-free kinetics using thermogravimetric analysis data. The kinetics of the microcrystalline cellulose Avicel PH-101 was performed to evaluate the E _a result of pure cellulose. The pretreatments were efficient in increasing the volatile matter and heating value, decreasing moisture and ash content, and improving its energetic power to the application in fast pyrolysis process for bio-oil production. The TG results have shown that the reduction in ash content facilitates the pyrolysis process, increasing the volatile matter and decreasing the apparent activation energy required to biomasses degradation, due to less diffusional resistances to heat and mass transfer of W-EG and AW-EG. The Avicel PH-101 showed the highest value of apparent activated energy (E _a = 276.2 kJ mol^?1) which could be explained by its crystallinity, suggesting that crystalline cellulose regions are less accessible to heat diffusion than amorphous regions, requiring more energy to its degradation.     

Improved Cyclopropanation Activity of Histidine‐Ligated Cytochrome P450 Enables the Enantioselective Formal Synthesis of Levomilnacipran

Engineering enzymes capable of modes of activation unprecedented in nature will increase the range of industrially important molecules that can be synthesized through biocatalysis. However, low activity for a new function is often a limitation in adopting enzymes for preparative‐scale synthesis, reaction with demanding substrates, or when a natural substrate is also present. By mutating the proximal ligand and other key active‐site residues of the cytochrome P450 enzyme from Bacillus megaterium (P450‐BM3), a highly active His‐ligated variant of P450‐BM3 that can be employed for the enantioselective synthesis of the levomilnacipran core was engineered. This enzyme, BM3‐Hstar, catalyzes the cyclopropanation of N,N‐diethyl‐2‐phenylacrylamide with an estimated initial rate of over 1000 turnovers per minute and can be used under aerobic conditions. Cyclopropanation activity is highly dependent on the electronic properties of the P450 proximal ligand, which can be used to tune this non‐natural enzyme activity.     

Diterpenoic Acids Analysis Using a Coupled TLC-Surface-Enhanced Raman Spectroscopy System

Hyphenation of thin layer chromatography (TLC) with surface-based spectral methods requires a homogeneous surface for direct and quantitative analysis on the chromatographic plate after separation. Since most chromatographic materials do not produce strong background signals in Raman spectroscopy (RS) or surface-enhanced RS (SERS), we tested the suitability of two different chromatographic substrates and one interface for coupling SERS with TLC. This was carried out by using a chromatographic thin layer, specially produced for RS measurements, and a monolithic silica thin layer. A typical TLC plate with a modified aluminium backplate foil on one side was used as an interface. Three biologically active diterpenes, namely gibberellic acid (GA), abietic acid (AA) and kaurenoic acid (KA), were used as test analytes. Stock solutions were applied directly onto the surface, followed by the addition of silver colloid and measurements were taken by SERS. The strongest signal (excitation at 514.5 nm) was obtained for GA using a Raman treated thin layer where the enhancement factor value was determined to be 10². Several fundamental Raman bands for GA were found at 1622, 1593, 1570, 1542, 1366 and 1236 cm⁻¹. When the monolithic silica layer was used, no useful SERS signals were observed. The SERS spectra on modified aluminium backplate for AA and GA were quite similar and no SERS spectrum was obtained for KA. Future research will be concerned towards the use of nanostructured surfaces for SERS analysis. An erratum to this article can be found at     

Isolation, purification and determination of 4-n-nonylphenol and 4-tert-octylphenol in aqueous and biological samples

The aim of the present study was to attempt to describe the procedure of isolation, purification, enrichment and determination of 4-n-nonylphenol (4-n-NP) and 4-tert-octylphenol (4-t-OP) in water and biological samples (fish tissue). There were five procedures of solid phase extraction (SPE) tested using different sorbents for the isolation of analytes from water samples. Moreover, we isolated these chemicals from biological matrices with the aid of various extraction methods. The purpose of it was to perform an optimisation of ultrasonic bath, accelerated solvent extraction (ASE) and solid phase extraction process of alkylphenols from biological samples, through the choice of selective sorbents (octadecyl, octadecyl end-capped and amine) and search solvents (methylene chloride, methanol, hexane). Reversed-phase HPLC with diode array detection was used for the determination of 4-n-NP and 4-t-OP in water and fish tissue samples. Sensitivity was evaluated by determining the limit of detection (LOD=0.06 and 0.04ng microL(-1)) and limit of quantification (LOQ=0.18 and 0.16ng microL(-1)) of 4-NP and 4-t-OP, respectively. A series of standard solutions for 4-n-NP and 4-t-OP provided the basis for plotting an analytical curve and obtaining a linear dependence in the range of approximately 1-25ng microL(-1). The best efficiencies obtained for 4-n-NP and 4-t-OP in water samples were 76.65% (+/-1.49) and 83.08% (+/-3.73), respectively. In the case of fish tissue, different situation was observed because the obtained values were considerably lower, being 68.32% for 4-t-OP using hexane (program 1) as solvent and 72.35% (program 2) for 4-n-NP using acetonitrile.     

Advantages of pentafluorophenylpropyl stationary phase over conventional C18 stationary phase--application to analysis of triamcinolone acetonide

A pentafluorophenylpropyl (PFPP) stationary phase was for the first time tested for the simultaneous determination of triamcinolone acetonide, its degradation product triamcinolone and two preservatives, methylparaben, and propylparaben. A new simple isocratic reversed phase HPLC method with UV detection, using estradiol hemihydrate as an internal standard, has been developed and validated. Chromatography was performed on a Discovery HS F5 column (150 mm x 4.6 mm, 5 microm) using a binary mobile phase composed of acetonitrile and water 45:55 (v:v). The flow-rate was 0.6 mL/min, the column temperature 25 degrees C and the UV detection was accomplished at 240 nm. The chromatography results using PFPP stationary phase were compared with those obtained using conventional C18 columns.     

Development and validation of an MEKC method for determination of nitrogen-containing drugs in pharmaceutical preparations

A fast and accurate micellar electrokinetic capillary chromatography method was developed for quality control of pharmaceutical preparations containing cold remedies as acetaminophen, salicylamide, caffeine, phenylephrine, pseudoephedrine, norephedrine and chlorpheniramine. The method optimization was realized on a Beckman P/ACE System MDQ instrument. The baseline separation of seven analytes was performed in an uncoated fused silica capillary internal diameter (ID)=50 microm using tris-borate (20 mM, pH=8.5) containing sodium dodecyl sulphate 30 mM BGE. On line-UV detection at 214 nm was performed and the applied voltage was 10 kV. The operating temperature was 25 degrees C. After experimental conditions optimization, the proposed method was validated. The evaluated parameters were: precision of migration time and of corrected peak area ratio, linearity range, limit of detection, limit of quantification, accuracy (recovery), ruggedness and applicability. The method was then successfully applied for the analysis of three pharmaceutical preparations containing some of the analytes listed before.     

A Ruthenium Bridge in Fullerene–Ferrocene Arrays: Synthesis of [Ru(C60Me5)R(CO)2] (R=C6H4Fc,C≡CFc) and Their Charge‐Transfer Properties

New fullerene–ferrocene arrays, [Ru(C₆₀Me₅)(C₄H₆Fc)(CO)₂] (Fc=ferrocenyl) and [Ru(C₆₀Me₅)(CCFc)(CO)₂], in which the ruthenium complex functions as a conjugative bridge, were synthesized by the reaction of [Ru(C₆₀Me₅)Cl(CO)₂] with FcC₆H₄MgBr and FcCCLi, respectively. These compounds were investigated by electrochemical measurement, single‐crystal X‐ray structural analysis, and photophysical measurement. Upon photoirradiation, the former compound was converted rapidly into the corresponding triplet state in toluene (τ_singlet=21 ps), whereas the charge‐separated state was predominant in THF (τ_singlet=10.5 ps; τ_CS=355 ps). The latter compound, on the other hand, formed the charge‐separated state in both toluene and THF (τ_singlet=3.0 ps; τ_CS=152 ps). Thus, the structural difference between the phenylene and acetylene bridges in 1 and 2 , respectively, was found to change the outcome of the photophysical processes.     

ESI-MS studies of mixed-ligand Fe(II) complexes containing 1,10-phenanthroline and 1,10-phenanthroline-5,6-dione as ligands

In order to monitor the progression of the synthesis and the separation of novel mixed-ligand iron complexes containing 1,10-phenanthroline, 1,10-phenanthroline-5,6-dione, and NCS- as ligands all products were mass analyzed by electrospray ionization ion trap MS/MS. The spectra of methanol (MeOH), acetonitrile (ACN), water, and ethanol (EtOH) solutions were collected and the results were compared. It was detected under applied electrospray ionization mass spectrometry (ESI-MS) conditions that MeOH, water, and EtOH formed solvent clusters around the free or complexed 1,10-phenanthroline-5,6-dione. Owing to the solvent-ligand hydrogen-bond formation, the solvent-ligand clusters were formed in the polar protic solvents. The number of protic solvent molecules per complex ion in cluster depended on the number of 1,10-phenanthroline-5,6-dione ligands in the complex ion. Unlike MeOH, EtOH, or water, ACN was not involved in the formation of the solvent clusters with the iron complexes containing 1,10-phenanthroline-5,6-dione as ligand. We also showed that the NCS- group under certain solvent conditions served as a bidentate ligand.