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Detalles de la revista
Formato
Revista
eISSN
1339-3065
ISSN
1337-978X
Publicado por primera vez
10 Dec 2012
Periodo de publicación
2 veces al año
Idiomas
Inglés

Buscar

Volumen 6 (2013): Edición 1 (April 2013)

Detalles de la revista
Formato
Revista
eISSN
1339-3065
ISSN
1337-978X
Publicado por primera vez
10 Dec 2012
Periodo de publicación
2 veces al año
Idiomas
Inglés

Buscar

23 Artículos
Acceso abierto

Characterization of cordierite-mullite ceramics prepared from natural raw materials

Publicado en línea: 22 May 2013
Páginas: 1 - 7

Resumen

Abstract

Series of six cordierite-mullite ceramics were synthesized via solid state reaction at various temperatures from 1250 °C for pure cordierite to 1500 °C for pure mullite. Then the samples were submitted to the test of thermal shock resistance based on cycling heating-quenching procedure. X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Mercury intrusion porosimeter (MIP) have been used to characterize the samples before and after cycling heating-quenching method. Sample 6 was broken after 35 heating-quenching cycles, while the five other reminded stable. The refractoriness of samples is found to be higher than that of commercial ones. XRD shows that heating-quenching procedure has led to crystallization of cordierite and mullite phases. Apart from sample 6, the pore structure is stable with slight consolidation. The microstructure images confirm the results of XRD and MIP showing crack in sample 6 only, but compact and larger particles resulting from crystal growth in other samples due to the repeated action of heating.

Palabras clave

  • cordierite-mullite
  • thermal resistance
  • microstructure
  • pore structure
Acceso abierto

Preparation, characterization and in vitro bioactivity of polyvinyl alcohol-hydroxyapatite biphasique membranes

Publicado en línea: 22 May 2013
Páginas: 8 - 14

Resumen

Abstract

Six membranes of polyvinyl alcohol (PVA) with various weight percent - 0 %, 10 %, 20 %, 30 %, 40 % and 50 % of hydroxyapatite (HA) were prepared. Fourier Transform Infrared (FTIR) spectroscopy was used to identify the different functional groups in membrane composites. The surface morphology was examined through scanning electron microscope. The in vitro bioactivity tests in Simulated Blood Fluid (SBF) have been performed up to 28 days, especially for membrane containing 50 wt. % HA. SEM was used to characterize surface microstructure of biocomposite membranes before and after immersion in SBF. It was observed the formation of clusters within membranes with increasing amount of HA particles due to hydrogen bond and also the agglomeration and crystal growth of HA particles during drying of membranes. The bioactivity was found increasing with time immersion of biocomposite materials in SBF solution.

Palabras clave

  • polyvinylalcohol
  • nanohydroxyapatite
  • bioactivity
  • simulated body fluid
Acceso abierto

Preparation of potassium nitrate from potassium chloride and magnesium nitrate in a laboratory scale using industrial raw materials

Publicado en línea: 22 May 2013
Páginas: 15 - 19

Resumen

Abstract

Preparation of potassium nitrate from magnesium nitrate and potassium chloride was investigated. Prepared potassium nitrate contains less than 0.5 % chlorides and it can be applied as environmentally friendly fertilizer in hydroponic systems. After filtration out potassium nitrate crystals from the reciprocal system K+, Mg2+//Cl-, NO3- - H2O, the mother liquor still contains reasonable amount of potassium cations. By evaporation of the mother liquor, carnallite (MgCl2・KCl・6H2O) with admixture of MgCl2・6H2O crystallizes out. Decomposition of carnallite with cold water makes it possible to separate potassium chloride from this compound. When this KCl is returned back to the process of KNO3 making, utilization of potassium as high as 97 % can be achieved.

Palabras clave

  • potassium nitrate
  • magnesium nitrate
  • carnallite
Acceso abierto

The assessment of potential operation of wastewater treatment plant by dynamic simulations

Publicado en línea: 22 May 2013
Páginas: 20 - 24

Resumen

Abstract

In this study, Activated Sludge Model No. 1 (ASM1) was used for modelling of wastewater treatment plant. The operational data of municipal wastewater treatment plant (WWTP) were collected and treated. Experimental data and biological treatment technology were structured according to the mathematical model requirements. They were implemented into computer scheme of the plant. Very good agreement between the experimental and calculated MLSS and effluent concentrations of the monitored pollution indicators was obtained after calibration of the model. The calibrated model was used to analyze the influence of oxygen concentration in the reactor and the influence of the prepared substitution of anaerobic sludge stabilization by aerobic technology on effluent quality. Changes of oxygen concentration significantly influenced the effluent values of ammonium nitrogen and nitrate nitrogen. Considerable increase of MLSS resulted from dynamic simulations performed for biological treatment with aerobic sludge stabilization. In both cases the results of dynamic simulation indicate that the WWTP will comply with the effluent standard values.

Palabras clave

  • ASM1
  • dynamic simulation
  • biological processes
  • simulation program
  • wastewater
Acceso abierto

Removal of selected pesticides by adsorption

Publicado en línea: 22 May 2013
Páginas: 25 - 28

Resumen

Abstract

The paper is focused on the removal of selected priority hazardous substances. Five chlorinated pesticides, i.e. hexachlorobenzene (HCHB), hexachlorobutadiene (HCHBD), lindane (LIN), pentachlorobenzene (PCHB) and heptachlor (HCH) were selected as model pollutants. Higher volatility is characteristic for these substances. Adsorption of these pollutants on granular activated carbon (GAC), zeolite (Zeo) and activated sludge (AS) was investigated. The effect of contact time on the removal efficiency of studied substances was investigated. From results of the work it follows that the highest removal efficiency of studied substances was achieved by the adsorption on activated sludge. This was followed by adsorption efficiency on zeolite. The lowest removal efficiency was measured for adsorption on granular activated carbon.

Palabras clave

  • activated sludge
  • adsorption
  • granular activated carbon
  • zeolite
Acceso abierto

Effi ciency of dye sensitized solar cells with various compositions of TiO2 based screen printed photoactive electrodes

Publicado en línea: 22 May 2013
Páginas: 29 - 34

Resumen

Abstract

The TiO2 electrode has a key role in dye sensitized solar cell (DSSC) technology in the charge generation and charge transportation. The properties of TiO2 layer affect resulting efficiency of DSSC and can be controlled by printing process and chemical composition of printing paste. TiO2 pastes with different compositions of TiO2 nanoparticles, ethanol, ethyl cellulose, water, acetic acid, α-terpineol were prepared and screen printed onto the glass substrate with fluorine doped tin oxide (FTO). The TiO2 pastes for screen printing were characterized by rheological measurements and screen printed TiO2 electrodes by atomic force microscopy and UV-Vis spectroscopy. The photocurrent - voltage characteristics and efficiencies of DSSC were evaluated and compared. All prepared TiO2 pastes were suitable for screen printing with ideal rheological characteristics. The highest efficiency 0.68 % and current density ISC = 1.21 mA/cm2 reached by the DSSC based on TiO2 electrode with thickness 1.5 μm, with amount of absorbed dye 1.1 × 10-8 mol/cm2 and without visible cracks and particles aggregation. This TiO2 electrode was prepared from the paste containing 5.4 wt. % of TiO2, 65.3 wt. % of ethanol, 1.8 wt. % of ethyl cellulose, 23 wt. % of H2O and 4.5 wt. % of CH3COOH.

Palabras clave

  • TiO2 nanoporous electrode
  • dye sensitized solar cell
  • screen printing
Acceso abierto

Protective membranes at electrochemical biosensors

Publicado en línea: 22 May 2013
Páginas: 35 - 41

Resumen

Abstract

The primary role of the biosensor is to specifically detect an analyte using biochemical reaction or interaction mediated by isolated biomolecules, organelles, whole cells or biomimetic receptors. In terms of construction and function, the biosensor consists of biorecognition element and transducer connected to suitable measurement device. Electrochemical biosensor is an electrode or microelectrode with the surface chemically modified by the biorecognition element. The main problem of analysis with the biosensors is the presence of low and high molecular weight substances in the sample that interfere at the detection of analyte. Due to deposition of surface active compounds the biosensor response may be diminished depending on time of interaction with sample. These effects can be eliminated by using anti-interference membranes. This review deals with preparation and utilization of membranes for the biocomponent immobilization and with outer-sphere protective membranes.

Palabras clave

  • biosensor
  • interference
  • surface active compounds
  • protective membrane
  • chemically modified electrode
Acceso abierto

Secondary metabolite production of Epicoccum sp. isolated from lignite

Publicado en línea: 22 May 2013
Páginas: 42 - 48

Resumen

Abstract

We have extracted secondary metabolites from fossil fungus Epicoccum sp. isolated from lignite and characterized changes in production on various growth media. Chromatographic separation yielded more than 7 fractions that were characterized spectroscopically. One secondary metabolite showed antimicrobial activity. Peaks in the NMR spectra of isolated fractions differ from compounds described in literature that were isolated from recent strains of Epicoccum. The remaining water phase after the extraction was shown to have protein staining properties and could be also used for fluorescent viability stain of yeast cells.

Palabras clave

  • Epicoccum
  • secondary metabolites
  • pigments
  • isolation
Acceso abierto

Microbial and senzory quality of raw milk cheeses from the milk vending machines

Publicado en línea: 22 May 2013
Páginas: 49 - 54

Resumen

Abstract

Changes in microbial quality of lump cheeses manufactured from raw cows’ milk from milk vending machines were studied throughout 7 days of fermentation at 15 °C. The density of lactic acid bacteria, Staphylococcus aureus, Escherichia coli and coliforms were determined, continuously. Also the pH value dynamic was analyzed at the same time intervals. All together, 8 cheeses were prepared from two different vending machines in summer and in winter. Based on the results, growth dynamic of all microorganisms as well as the pH value decrease was slower in cheeses made in winter. No significant differences were observed in the maximal counts of microorganisms related to the season. However, the counts of S. aureus exceeded the EU limit 104 CFU g-1 in 7 out of 8 cheeses, probably due to slow pH value descent. Also the Slovak Food Codex limit for E. coli maximal density of less than 104 CFU g-1 was significantly exceeded. According to sensory evaluation, cheeses prepared in winter were less tasty and their typical odour was less distinctive. Results suggest that raw milk from milk vending machines is not suitable for direct consumption without proper thermal treatment.

Palabras clave

  • raw milk cheese
  • microbial safety
  • sensory analysis
Acceso abierto

Photocytotoxicity of [Cu(N-salicyliden-L-glutamato · 2H2O] · isoquinoline

Publicado en línea: 22 May 2013
Páginas: 55 - 59

Resumen

Abstract

The metal complexes have a significant role in photodynamic therapy (PDT). The most common metals studied for PDT of tumors are transitional metals. In this paper we have studied the copper(II) complexes of N-salicyliden-L-glutamate. The photocytostatic effect was monitored against mouse leukemic cell line L1210. Photocytostatic effect was confirmed for [Cu(N-salicyliden-L-glutamato・2H2O]・isoquinoline (CuCIQ), but it wasn’t observed for the parental molecule [Cu(N-salicyliden-L-glutamato・2H2O]・H2O. CuCIQ had photocytotoxic effect already at 10 μM concentration. Irradiated cells (1050 mJ.cm-2, λ = 365 nm) had half the viability of the cells incubated with CuCIQ in the dark (72 h). Co-incubation of the cells with CuCIQ and ascorbic acid increased this photocytotoxic effect and this effect correlated with the elevated level of lipoperoxidation.

Palabras clave

  • photodynamic therapy
  • photosensitizers
  • metal complexes
  • ascorbic acid
Acceso abierto

Solvation enthalpies of the proton in polar and non-polar solvents: Theoretical study

Publicado en línea: 22 May 2013
Páginas: 60 - 63

Resumen

Abstract

In spite of the importance of proton transfer in solution-phase processes, there is still no systematic theoretical study of proton solvation enthalpies. We have investigated the solvation enthalpies of the proton in seven solvents of various polarities (benzene, chloroform, acetone, methanol, ethanol, DMSO, water) using the Integral Equation Formalism Polarized Continuum Model (IEF-PCM). All computations were performed at the B3LYP and BHLYP levels of theory with aug-cc-pVDZ, aug-cc-pVTZ and aug-cc-pVQZ basis sets. Our calculations have shown that the B3LYP and BHLYP functionals provide similar solvation enthalpies. Finally, differences in the solvation enthalpy of the proton values stemming from the various basis sets do not exceed 6 kJ mol-1, with exception of DMSO and chloroform. Distance between H+ and the acceptor atom of the solvent molecule is the shortest in the case of water. It has been also found that the B3LYP distances are slightly longer.

Palabras clave

  • DFT
  • IEF-PCM
  • proton solvation enthalpy
  • solvent
Acceso abierto

Quantum-chemical study of C— H bond dissociation enthalpies of various small non-aromatic organic molecules

Publicado en línea: 22 May 2013
Páginas: 64 - 72

Resumen

Abstract

In this work, C-H bond dissociation enthalpies (BDE) and vertical ionization potentials (IP) for various hydrocarbons and ketones were calculated using four density functional approaches. Calculated BDEs and IPs were correlated with experimental data. The linearity of the corresponding dependences can be considered very good. Comparing two used functionals, B3LYP C-H BDE values are closer to experimental results than PBE0 values for both used basis sets. The 6-31G* basis set employed with both functionals, gives the C-H BDEs closer to the experimental values than the 6-311++G** basis set. Using the obtained linear dependences BDEexp = f (BDEcalc), the experimental values of C-H BDEs for some structurally related compounds can be estimated solely from calculations. As a descriptor of the C-H BDE, the IPs and 13C NMR chemical shifts have been investigated using data obtained from the B3LYP/6-31G* calculations. There is a slight indication of linear correlation between IPs and C-H BDEs in the sets of simple alkanes and alkenes/ cycloalkenes. However, for cycloalkanes and aliphatic carbonyl compounds, no linear correlation was found. In the case of the 13C NMR chemical shifts, the correlation with C-H BDEs can be found for the sets of alkanes and cycloalkanes, but for the other studied molecules, no trends were detected.

Palabras clave

  • BDE
  • NMR chemical shift
  • alkanes
  • alkenes
  • descriptor
  • radical scavenging
Acceso abierto

Preparation and NMR properties of derivatives of arylamino-methylidene malonic acid and pentane-2,4-dione

Publicado en línea: 22 May 2013
Páginas: 73 - 81

Resumen

Abstract

A set of 22 anilinomethylidene derivatives (13 new ones) of di(m)ethyl malonate, malononitrile and pentane-2,4-dione with various substituents in position 4- and 3-, respectively were prepared to study the characteristic influence of these substituents and solvents on chemical shifts in 13C NMR spectra and like reference compounds for kinetic measurements.

Palabras clave

  • NMR spectroscopy
  • substituent chemical shifts (SCS)
  • arylaminomethylidene derivatives
  • enamines
Acceso abierto

Current problems in the use of organic UV filters to protect skin from excessive sun exposure

Publicado en línea: 22 May 2013
Páginas: 82 - 88

Resumen

Abstract

The evidences of the harmful effects of skin exposure to excessive UltraViolet (UV) radiation, primarily on the development of skin cancer, have increased over the last decade. Therefore, national and international health authorities have encouraged the public to take protective sunscreens, and respectively also everyday cosmetics containing UV filters. In these products, a mixture of the UV filters, including both inorganic and organic nature, has been shown to be more effective than the individual UV filter. However, currently there are concerns about the safety and actual effectiveness of some UV filters; especially about certain UV-absorbing compounds (organic UV filters). Three cardinal problems are the most questionable. First, that certain UV filters are absorbed through the skin resulting in systemic exposure with unknown consequences. Second, that certain UV filters show the potential to be adversely endocrine disruptors. Third, that certain UV filters are partially degraded by UV radiation, what making them photounstable and unable to fulfil their basic protective function. The purpose of this article is to discuss these problems.

Palabras clave

  • sunscreens
  • organic UV filters
  • endocrine disruptors
  • dermal absorption
  • photostability
  • safety
Acceso abierto

Therapeutic potential of curcumin in medicinal chemistry

Publicado en línea: 22 May 2013
Páginas: 89 - 99

Resumen

Abstract

Extensive research over the past half century has shown that curcumin (diferuloylmethane), a polyphenolic compound of turmeric (Curcuma longa L.), can modulate multiple cell signaling pathways. Extensive clinical trials have addressed the pharmacokinetics, safety, and efficacy of this nutraceutical against numerous diseases in human. Curcumin, known for thousand years as a subject of Ayurvedic medicine, has undergone in recent times remarkable transformation into a drug candidate with prospective multipotent therapeutic application. Characterized by high chemical reactivity, resulting from an extended conjugated double bond system prone to nucleophilic attack, curcumin has been shown to interact with a plethora of molecular targets, in numerous experimental observations. In clinical trials, has been used either alone or in combination with other agent. However, its clinical advance has been limited by its short biological half-life, fast metabolism and poor systemic bioavailability after oral administration. To mitigate the above limitations, recently various formulation of curcumin, including nanoparticles, micelles, liposomes, phytosomes delivery system has been examined. The present review has been devoted towards better understanding of the phytonutraceutic properties of curcumin and turmeric based on their disease specific indications and enhancing their prophylactic and therapeutic nutraceutical qualities. The article deals with the biological activity, mode of action, toxicity and forthcoming application of these leads.

Palabras clave

  • curcumin
  • turmeric
  • absorption
  • bioavailability
  • metabolism
  • nanocurcumin
  • medicine
Acceso abierto

New detector tube for the detection of nitrite in water

Publicado en línea: 22 May 2013
Páginas: 100 - 105

Resumen

Abstract

A new colorimetric detector tube for the detection of trace concentrations of nitrite in water was developed. The detector tube is based on a diazo coupling reaction of nitrite with dapsone and N-(1-naphthyl) ethylenediamine dihydrochloride during the formation of red-violet azo dye. Spherical granules (pellets) made from the composite material were used as the carrier of chemical reagents. They were prepared by pelletizing the mixture of microcrystalline cellulose, lactose, kaolin and polyvinylpyrrolidone. Colouring is done on a layer of silica gel impregnated with citric acid. The detector tube is highly sensitive, selective and stable when stored. The detection limit is 0.1 μg.ml-1, i.e. 0.03 μg.ml-1 N(NO2 -). The optimal measuring range of nitrite concentration in the analyzed sample ranges from 0.5 to 80 μg.ml-1, i.e. 0.15-24.36 μg.ml-1 N(NO2 -). The detector tube can easily be structurally modified for analysis of nitrates with a detection limit of 1 μg/ml-1, i.e. 0.23 μg.ml-1 N(NO3 -).

Palabras clave

  • detector tube
  • composite carrier
  • dapsone
  • N-(1-naphthyl) ethylenediamine dihydrochloride
Acceso abierto

Bacterial cell membrane adaptation responses on stress caused with the environmental pollutants

Publicado en línea: 22 May 2013
Páginas: 106 - 114

Resumen

Abstract

The effect of polychlorinated biphenyls on biomass production, lipid accumulation, and on the fatty acid profile of the major membrane lipids of Alcaligenes xylosoxidans isolated from a soil long-term contaminated with polychlorinated biphenyls was examined. The lowest bacterial growth was observed in the presence of biphenyl and polychlorinated biphenyls. On the other hand, the highest growth stimulation was observed in the presence polychlorinated biphenyls. Higher growth ability was observed when polychlorinated biphenyls or 3-chlorobenzoic acid were added after three days of cultivation. Higher lipid accumulation corresponded with lower growth ability. The importance of time when bacterial strain meets polychlorinated biphenyls or 3-chlorobenzoic acid should be emphasized. The addition of toxic organic compound later in stationary growth phase led to better survival and evoked lower membrane adaptation. However, polychlorinated biphenyls or 3-chlorobenzoic acid amendment at the beginning of cultivation stimulated adaptation responses as membrane saturation, cis to trans isomerisation, and branched fatty acids alteration and decreased growth ability. Palmitic acid and 17-cyclopropyl fatty acid were observed as prevalent in the bacterial membrane as well as in the total lipids.

Palabras clave

  • adaptation mechanisms
  • bacteria
  • environmental stress
  • fatty acids
  • polychlorinated biphenyls
Acceso abierto

Inhibition of pathophysiological proteases with novel quercetin derivatives

Publicado en línea: 22 May 2013
Páginas: 115 - 122

Resumen

Abstract

Novel quercetin derivatives were prepared to change its physicochemical properties and effects on activity of proteolytic enzymes. For them preparation, the selective protection procedures some of the quercetin hydroxyl groups and acylation of the others with acylchlorides were used. The ability of these compounds to inhibit the activity of serine proteases e.g. trypsin, thrombin, urokinase and elastase was studied. In micromolar range, tested derivatives were the most potent inhibitors of thrombin. There was estimated better inhibition of thrombin for prenylated, acetylated, feruloyl and caffeoyl quercetin esters. Slight inhibitory effect of all quercetin derivatives on elastase was found. Among tested derivatives only diquercetin displayed better inhibiton. Trypsin and urokinase were inhibited by quercetin at comparable level. Slight improvement in inhibitory effect of trypsin and urokinase was seen for chloronaphtoquinone quercetin that revealed enhanced inhibiton of thrombin, too. However, no influence on elastase activity was determined for this compound. Obtained results indicate that certain modifications of quercetin structure could improve its biological properties.

Palabras clave

  • elastase
  • enzyme inhibition
  • quercetin derivatives
  • thrombin
  • trypsin
  • urokinase
Acceso abierto

Analysis of natural aroma and flavor of MD2 pineapple variety (Ananas comosus [L.] Merr.)

Publicado en línea: 22 May 2013
Páginas: 123 - 128

Resumen

Abstract

Aroma and flavor profile of MD2 pineapple variety was investigated. Fruits imported from different geographical regions (Costa Rica, Puerto Rico) were labeled as an organic food. Characteristic volatile and non-volatile compounds obtained by hydro-distillation and direct percolation were identified and quantified by gas chromatography-mass spectroscopy (GC/MS). At least 22 components in percolated extract (or 17 in distillate) were detected according to their mass spectra and retention time. Relative concentration of identified substances varied from 547.7 to 1110.0 μg.kg-1. Analysis showed dominance of esters and furanone-derived compounds as major aroma constituents. Most abundant volatiles identified in all samples were methyl 2-methylbutanoate and methyl hexanoate. Relationships between volatile and non-volatile compounds were also studied.

Palabras clave

  • pineapple
  • MD2 variety
  • flavor
  • natural aroma
  • GC/MS
Acceso abierto

A new pathway of preparation and refined structure of (NH4)2[FeCl5(H2O)]

Publicado en línea: 22 May 2013
Páginas: 129 - 132

Resumen

Abstract

The title compound, (NH4)2[FeCl5H2O] has been prepared by reaction between iron(III) chloride and ammonium chloride which was formed by hydrolysis of isonicotinamide or thionicotinamide in ethanol. The characterization was based on elemental analysis and infrared spectra. The crystal structure of the title compound has been refined by single crystal X-ray diffraction method at 293 K. Crystals are orthorhombic, Pnma, with unit cell parameters: a = 13.760(1) A, b = 9.960(1) A, c = 7.060(1) A, Z = 4 and R = 3.5 %. The iron(III) atom in [FeCl5(H2O)]2- ion is approximately octahedrally coordinated by five Cl atoms and one O atom of H2O molecule. This distortion is caused by the extensively hydrogen-bonded lattice. Structural parameters and IR spectra of similar compounds are compared and discussed.

Palabras clave

  • ammonium salt
  • aqua-pentachloroferrate(III)
  • crystal structure
  • iron
  • IR-spectrum
Acceso abierto

Multidimensional gas chromatography and its applications in food and environmental analysis

Publicado en línea: 22 May 2013
Páginas: 133 - 140

Resumen

Abstract

This review deals with overview of methods of multidimensional gas chromatography (MDGC), the classical meaning- conventional heart-cut MDGC, and the comprehensive two-dimensional gas chromatography (GC×GC). MDGC is widely used because it increases required separation efficiency, which cannot be achieved by one-dimensional gas chromatography. Selected applications in food quality and safety, monitoring of environment, food authentication are summarized. This review summarizes the advances and applications of MDGC that have been published over last 10 years.

Palabras clave

  • gas chromatography
  • comprehensive two-dimensional gas chromatography
  • heart-cut multidimensional gas chromatography
Acceso abierto

Synergetic effects of Cu2O photocatalyst with titania and enhanced photoactivity under visible irradiation

Publicado en línea: 22 May 2013
Páginas: 141 - 149

Resumen

Abstract

Heterogeneous TiO2/Cu2O nanocomposite was synthesized for photocatalysis through surface impregnation in conjunction with the environmentally friendly soft chemical reduction strategy. The detailed structural, compositional, optical and photoelectrochemical properties of the obtained products are analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), photoluminescence spectra (PL) and electron spin resonance (ESR) spectroscopy techniques. Moreover, methyl orange (MO) dye was chosen as the probe molecule for evaluation of the photocatalytic activities of the samples under visible light (λ > 420 nm) irradiation. The experiments demonstrated that MO in aqueous solution was more efficiently photodegraded using TiO2/Cu2O composite photocatalysts than pure Cu2O alone. This was attributed to the good crystallinity, wide visible-light absorption range, and the efficient electron-hole pair separation properties of the TiO2/Cu2O nanoheterostructures. In this photocatalyst, visiblelight- active Cu2O component was used as a medium to absorb photons and convert them into photogenerated charges, and TiO2 nanoparticles were used as charge collectors to transport the photoinduced charges. The TiO2/Cu2O hybrid material showed improved separation of photoinduced electron-hole pairs owing to the potential-energy differences between Cu2O and TiO2, and therefore exhibited enhanced photocatalytic activity.

Palabras clave

  • photodecomposition
  • coupled semiconductor
  • methyl orange
Acceso abierto

Calcium hydroxide: An efficient and mild base for one-pot synthesis of curcumin and it’s analogues

Publicado en línea: 22 May 2013
Páginas: 150 - 156

Resumen

Abstract

Calcium hydroxide was found to be an efficient mild base for the one-pot synthesis of curcumin and its analogues obtained by condensation of one equivalent of acetyl acetone with two equivalents of corresponding aromatic aldehyde. The present protocol offers various advantages such as high yields, inexpensive easily available mild base, easy workup and eco-friendly method.

Palabras clave

  • Calcium hydroxide
  • acetyl acetone
  • substituted benzaldehydes
  • DMF
  • Curcumin
23 Artículos
Acceso abierto

Characterization of cordierite-mullite ceramics prepared from natural raw materials

Publicado en línea: 22 May 2013
Páginas: 1 - 7

Resumen

Abstract

Series of six cordierite-mullite ceramics were synthesized via solid state reaction at various temperatures from 1250 °C for pure cordierite to 1500 °C for pure mullite. Then the samples were submitted to the test of thermal shock resistance based on cycling heating-quenching procedure. X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Mercury intrusion porosimeter (MIP) have been used to characterize the samples before and after cycling heating-quenching method. Sample 6 was broken after 35 heating-quenching cycles, while the five other reminded stable. The refractoriness of samples is found to be higher than that of commercial ones. XRD shows that heating-quenching procedure has led to crystallization of cordierite and mullite phases. Apart from sample 6, the pore structure is stable with slight consolidation. The microstructure images confirm the results of XRD and MIP showing crack in sample 6 only, but compact and larger particles resulting from crystal growth in other samples due to the repeated action of heating.

Palabras clave

  • cordierite-mullite
  • thermal resistance
  • microstructure
  • pore structure
Acceso abierto

Preparation, characterization and in vitro bioactivity of polyvinyl alcohol-hydroxyapatite biphasique membranes

Publicado en línea: 22 May 2013
Páginas: 8 - 14

Resumen

Abstract

Six membranes of polyvinyl alcohol (PVA) with various weight percent - 0 %, 10 %, 20 %, 30 %, 40 % and 50 % of hydroxyapatite (HA) were prepared. Fourier Transform Infrared (FTIR) spectroscopy was used to identify the different functional groups in membrane composites. The surface morphology was examined through scanning electron microscope. The in vitro bioactivity tests in Simulated Blood Fluid (SBF) have been performed up to 28 days, especially for membrane containing 50 wt. % HA. SEM was used to characterize surface microstructure of biocomposite membranes before and after immersion in SBF. It was observed the formation of clusters within membranes with increasing amount of HA particles due to hydrogen bond and also the agglomeration and crystal growth of HA particles during drying of membranes. The bioactivity was found increasing with time immersion of biocomposite materials in SBF solution.

Palabras clave

  • polyvinylalcohol
  • nanohydroxyapatite
  • bioactivity
  • simulated body fluid
Acceso abierto

Preparation of potassium nitrate from potassium chloride and magnesium nitrate in a laboratory scale using industrial raw materials

Publicado en línea: 22 May 2013
Páginas: 15 - 19

Resumen

Abstract

Preparation of potassium nitrate from magnesium nitrate and potassium chloride was investigated. Prepared potassium nitrate contains less than 0.5 % chlorides and it can be applied as environmentally friendly fertilizer in hydroponic systems. After filtration out potassium nitrate crystals from the reciprocal system K+, Mg2+//Cl-, NO3- - H2O, the mother liquor still contains reasonable amount of potassium cations. By evaporation of the mother liquor, carnallite (MgCl2・KCl・6H2O) with admixture of MgCl2・6H2O crystallizes out. Decomposition of carnallite with cold water makes it possible to separate potassium chloride from this compound. When this KCl is returned back to the process of KNO3 making, utilization of potassium as high as 97 % can be achieved.

Palabras clave

  • potassium nitrate
  • magnesium nitrate
  • carnallite
Acceso abierto

The assessment of potential operation of wastewater treatment plant by dynamic simulations

Publicado en línea: 22 May 2013
Páginas: 20 - 24

Resumen

Abstract

In this study, Activated Sludge Model No. 1 (ASM1) was used for modelling of wastewater treatment plant. The operational data of municipal wastewater treatment plant (WWTP) were collected and treated. Experimental data and biological treatment technology were structured according to the mathematical model requirements. They were implemented into computer scheme of the plant. Very good agreement between the experimental and calculated MLSS and effluent concentrations of the monitored pollution indicators was obtained after calibration of the model. The calibrated model was used to analyze the influence of oxygen concentration in the reactor and the influence of the prepared substitution of anaerobic sludge stabilization by aerobic technology on effluent quality. Changes of oxygen concentration significantly influenced the effluent values of ammonium nitrogen and nitrate nitrogen. Considerable increase of MLSS resulted from dynamic simulations performed for biological treatment with aerobic sludge stabilization. In both cases the results of dynamic simulation indicate that the WWTP will comply with the effluent standard values.

Palabras clave

  • ASM1
  • dynamic simulation
  • biological processes
  • simulation program
  • wastewater
Acceso abierto

Removal of selected pesticides by adsorption

Publicado en línea: 22 May 2013
Páginas: 25 - 28

Resumen

Abstract

The paper is focused on the removal of selected priority hazardous substances. Five chlorinated pesticides, i.e. hexachlorobenzene (HCHB), hexachlorobutadiene (HCHBD), lindane (LIN), pentachlorobenzene (PCHB) and heptachlor (HCH) were selected as model pollutants. Higher volatility is characteristic for these substances. Adsorption of these pollutants on granular activated carbon (GAC), zeolite (Zeo) and activated sludge (AS) was investigated. The effect of contact time on the removal efficiency of studied substances was investigated. From results of the work it follows that the highest removal efficiency of studied substances was achieved by the adsorption on activated sludge. This was followed by adsorption efficiency on zeolite. The lowest removal efficiency was measured for adsorption on granular activated carbon.

Palabras clave

  • activated sludge
  • adsorption
  • granular activated carbon
  • zeolite
Acceso abierto

Effi ciency of dye sensitized solar cells with various compositions of TiO2 based screen printed photoactive electrodes

Publicado en línea: 22 May 2013
Páginas: 29 - 34

Resumen

Abstract

The TiO2 electrode has a key role in dye sensitized solar cell (DSSC) technology in the charge generation and charge transportation. The properties of TiO2 layer affect resulting efficiency of DSSC and can be controlled by printing process and chemical composition of printing paste. TiO2 pastes with different compositions of TiO2 nanoparticles, ethanol, ethyl cellulose, water, acetic acid, α-terpineol were prepared and screen printed onto the glass substrate with fluorine doped tin oxide (FTO). The TiO2 pastes for screen printing were characterized by rheological measurements and screen printed TiO2 electrodes by atomic force microscopy and UV-Vis spectroscopy. The photocurrent - voltage characteristics and efficiencies of DSSC were evaluated and compared. All prepared TiO2 pastes were suitable for screen printing with ideal rheological characteristics. The highest efficiency 0.68 % and current density ISC = 1.21 mA/cm2 reached by the DSSC based on TiO2 electrode with thickness 1.5 μm, with amount of absorbed dye 1.1 × 10-8 mol/cm2 and without visible cracks and particles aggregation. This TiO2 electrode was prepared from the paste containing 5.4 wt. % of TiO2, 65.3 wt. % of ethanol, 1.8 wt. % of ethyl cellulose, 23 wt. % of H2O and 4.5 wt. % of CH3COOH.

Palabras clave

  • TiO2 nanoporous electrode
  • dye sensitized solar cell
  • screen printing
Acceso abierto

Protective membranes at electrochemical biosensors

Publicado en línea: 22 May 2013
Páginas: 35 - 41

Resumen

Abstract

The primary role of the biosensor is to specifically detect an analyte using biochemical reaction or interaction mediated by isolated biomolecules, organelles, whole cells or biomimetic receptors. In terms of construction and function, the biosensor consists of biorecognition element and transducer connected to suitable measurement device. Electrochemical biosensor is an electrode or microelectrode with the surface chemically modified by the biorecognition element. The main problem of analysis with the biosensors is the presence of low and high molecular weight substances in the sample that interfere at the detection of analyte. Due to deposition of surface active compounds the biosensor response may be diminished depending on time of interaction with sample. These effects can be eliminated by using anti-interference membranes. This review deals with preparation and utilization of membranes for the biocomponent immobilization and with outer-sphere protective membranes.

Palabras clave

  • biosensor
  • interference
  • surface active compounds
  • protective membrane
  • chemically modified electrode
Acceso abierto

Secondary metabolite production of Epicoccum sp. isolated from lignite

Publicado en línea: 22 May 2013
Páginas: 42 - 48

Resumen

Abstract

We have extracted secondary metabolites from fossil fungus Epicoccum sp. isolated from lignite and characterized changes in production on various growth media. Chromatographic separation yielded more than 7 fractions that were characterized spectroscopically. One secondary metabolite showed antimicrobial activity. Peaks in the NMR spectra of isolated fractions differ from compounds described in literature that were isolated from recent strains of Epicoccum. The remaining water phase after the extraction was shown to have protein staining properties and could be also used for fluorescent viability stain of yeast cells.

Palabras clave

  • Epicoccum
  • secondary metabolites
  • pigments
  • isolation
Acceso abierto

Microbial and senzory quality of raw milk cheeses from the milk vending machines

Publicado en línea: 22 May 2013
Páginas: 49 - 54

Resumen

Abstract

Changes in microbial quality of lump cheeses manufactured from raw cows’ milk from milk vending machines were studied throughout 7 days of fermentation at 15 °C. The density of lactic acid bacteria, Staphylococcus aureus, Escherichia coli and coliforms were determined, continuously. Also the pH value dynamic was analyzed at the same time intervals. All together, 8 cheeses were prepared from two different vending machines in summer and in winter. Based on the results, growth dynamic of all microorganisms as well as the pH value decrease was slower in cheeses made in winter. No significant differences were observed in the maximal counts of microorganisms related to the season. However, the counts of S. aureus exceeded the EU limit 104 CFU g-1 in 7 out of 8 cheeses, probably due to slow pH value descent. Also the Slovak Food Codex limit for E. coli maximal density of less than 104 CFU g-1 was significantly exceeded. According to sensory evaluation, cheeses prepared in winter were less tasty and their typical odour was less distinctive. Results suggest that raw milk from milk vending machines is not suitable for direct consumption without proper thermal treatment.

Palabras clave

  • raw milk cheese
  • microbial safety
  • sensory analysis
Acceso abierto

Photocytotoxicity of [Cu(N-salicyliden-L-glutamato · 2H2O] · isoquinoline

Publicado en línea: 22 May 2013
Páginas: 55 - 59

Resumen

Abstract

The metal complexes have a significant role in photodynamic therapy (PDT). The most common metals studied for PDT of tumors are transitional metals. In this paper we have studied the copper(II) complexes of N-salicyliden-L-glutamate. The photocytostatic effect was monitored against mouse leukemic cell line L1210. Photocytostatic effect was confirmed for [Cu(N-salicyliden-L-glutamato・2H2O]・isoquinoline (CuCIQ), but it wasn’t observed for the parental molecule [Cu(N-salicyliden-L-glutamato・2H2O]・H2O. CuCIQ had photocytotoxic effect already at 10 μM concentration. Irradiated cells (1050 mJ.cm-2, λ = 365 nm) had half the viability of the cells incubated with CuCIQ in the dark (72 h). Co-incubation of the cells with CuCIQ and ascorbic acid increased this photocytotoxic effect and this effect correlated with the elevated level of lipoperoxidation.

Palabras clave

  • photodynamic therapy
  • photosensitizers
  • metal complexes
  • ascorbic acid
Acceso abierto

Solvation enthalpies of the proton in polar and non-polar solvents: Theoretical study

Publicado en línea: 22 May 2013
Páginas: 60 - 63

Resumen

Abstract

In spite of the importance of proton transfer in solution-phase processes, there is still no systematic theoretical study of proton solvation enthalpies. We have investigated the solvation enthalpies of the proton in seven solvents of various polarities (benzene, chloroform, acetone, methanol, ethanol, DMSO, water) using the Integral Equation Formalism Polarized Continuum Model (IEF-PCM). All computations were performed at the B3LYP and BHLYP levels of theory with aug-cc-pVDZ, aug-cc-pVTZ and aug-cc-pVQZ basis sets. Our calculations have shown that the B3LYP and BHLYP functionals provide similar solvation enthalpies. Finally, differences in the solvation enthalpy of the proton values stemming from the various basis sets do not exceed 6 kJ mol-1, with exception of DMSO and chloroform. Distance between H+ and the acceptor atom of the solvent molecule is the shortest in the case of water. It has been also found that the B3LYP distances are slightly longer.

Palabras clave

  • DFT
  • IEF-PCM
  • proton solvation enthalpy
  • solvent
Acceso abierto

Quantum-chemical study of C— H bond dissociation enthalpies of various small non-aromatic organic molecules

Publicado en línea: 22 May 2013
Páginas: 64 - 72

Resumen

Abstract

In this work, C-H bond dissociation enthalpies (BDE) and vertical ionization potentials (IP) for various hydrocarbons and ketones were calculated using four density functional approaches. Calculated BDEs and IPs were correlated with experimental data. The linearity of the corresponding dependences can be considered very good. Comparing two used functionals, B3LYP C-H BDE values are closer to experimental results than PBE0 values for both used basis sets. The 6-31G* basis set employed with both functionals, gives the C-H BDEs closer to the experimental values than the 6-311++G** basis set. Using the obtained linear dependences BDEexp = f (BDEcalc), the experimental values of C-H BDEs for some structurally related compounds can be estimated solely from calculations. As a descriptor of the C-H BDE, the IPs and 13C NMR chemical shifts have been investigated using data obtained from the B3LYP/6-31G* calculations. There is a slight indication of linear correlation between IPs and C-H BDEs in the sets of simple alkanes and alkenes/ cycloalkenes. However, for cycloalkanes and aliphatic carbonyl compounds, no linear correlation was found. In the case of the 13C NMR chemical shifts, the correlation with C-H BDEs can be found for the sets of alkanes and cycloalkanes, but for the other studied molecules, no trends were detected.

Palabras clave

  • BDE
  • NMR chemical shift
  • alkanes
  • alkenes
  • descriptor
  • radical scavenging
Acceso abierto

Preparation and NMR properties of derivatives of arylamino-methylidene malonic acid and pentane-2,4-dione

Publicado en línea: 22 May 2013
Páginas: 73 - 81

Resumen

Abstract

A set of 22 anilinomethylidene derivatives (13 new ones) of di(m)ethyl malonate, malononitrile and pentane-2,4-dione with various substituents in position 4- and 3-, respectively were prepared to study the characteristic influence of these substituents and solvents on chemical shifts in 13C NMR spectra and like reference compounds for kinetic measurements.

Palabras clave

  • NMR spectroscopy
  • substituent chemical shifts (SCS)
  • arylaminomethylidene derivatives
  • enamines
Acceso abierto

Current problems in the use of organic UV filters to protect skin from excessive sun exposure

Publicado en línea: 22 May 2013
Páginas: 82 - 88

Resumen

Abstract

The evidences of the harmful effects of skin exposure to excessive UltraViolet (UV) radiation, primarily on the development of skin cancer, have increased over the last decade. Therefore, national and international health authorities have encouraged the public to take protective sunscreens, and respectively also everyday cosmetics containing UV filters. In these products, a mixture of the UV filters, including both inorganic and organic nature, has been shown to be more effective than the individual UV filter. However, currently there are concerns about the safety and actual effectiveness of some UV filters; especially about certain UV-absorbing compounds (organic UV filters). Three cardinal problems are the most questionable. First, that certain UV filters are absorbed through the skin resulting in systemic exposure with unknown consequences. Second, that certain UV filters show the potential to be adversely endocrine disruptors. Third, that certain UV filters are partially degraded by UV radiation, what making them photounstable and unable to fulfil their basic protective function. The purpose of this article is to discuss these problems.

Palabras clave

  • sunscreens
  • organic UV filters
  • endocrine disruptors
  • dermal absorption
  • photostability
  • safety
Acceso abierto

Therapeutic potential of curcumin in medicinal chemistry

Publicado en línea: 22 May 2013
Páginas: 89 - 99

Resumen

Abstract

Extensive research over the past half century has shown that curcumin (diferuloylmethane), a polyphenolic compound of turmeric (Curcuma longa L.), can modulate multiple cell signaling pathways. Extensive clinical trials have addressed the pharmacokinetics, safety, and efficacy of this nutraceutical against numerous diseases in human. Curcumin, known for thousand years as a subject of Ayurvedic medicine, has undergone in recent times remarkable transformation into a drug candidate with prospective multipotent therapeutic application. Characterized by high chemical reactivity, resulting from an extended conjugated double bond system prone to nucleophilic attack, curcumin has been shown to interact with a plethora of molecular targets, in numerous experimental observations. In clinical trials, has been used either alone or in combination with other agent. However, its clinical advance has been limited by its short biological half-life, fast metabolism and poor systemic bioavailability after oral administration. To mitigate the above limitations, recently various formulation of curcumin, including nanoparticles, micelles, liposomes, phytosomes delivery system has been examined. The present review has been devoted towards better understanding of the phytonutraceutic properties of curcumin and turmeric based on their disease specific indications and enhancing their prophylactic and therapeutic nutraceutical qualities. The article deals with the biological activity, mode of action, toxicity and forthcoming application of these leads.

Palabras clave

  • curcumin
  • turmeric
  • absorption
  • bioavailability
  • metabolism
  • nanocurcumin
  • medicine
Acceso abierto

New detector tube for the detection of nitrite in water

Publicado en línea: 22 May 2013
Páginas: 100 - 105

Resumen

Abstract

A new colorimetric detector tube for the detection of trace concentrations of nitrite in water was developed. The detector tube is based on a diazo coupling reaction of nitrite with dapsone and N-(1-naphthyl) ethylenediamine dihydrochloride during the formation of red-violet azo dye. Spherical granules (pellets) made from the composite material were used as the carrier of chemical reagents. They were prepared by pelletizing the mixture of microcrystalline cellulose, lactose, kaolin and polyvinylpyrrolidone. Colouring is done on a layer of silica gel impregnated with citric acid. The detector tube is highly sensitive, selective and stable when stored. The detection limit is 0.1 μg.ml-1, i.e. 0.03 μg.ml-1 N(NO2 -). The optimal measuring range of nitrite concentration in the analyzed sample ranges from 0.5 to 80 μg.ml-1, i.e. 0.15-24.36 μg.ml-1 N(NO2 -). The detector tube can easily be structurally modified for analysis of nitrates with a detection limit of 1 μg/ml-1, i.e. 0.23 μg.ml-1 N(NO3 -).

Palabras clave

  • detector tube
  • composite carrier
  • dapsone
  • N-(1-naphthyl) ethylenediamine dihydrochloride
Acceso abierto

Bacterial cell membrane adaptation responses on stress caused with the environmental pollutants

Publicado en línea: 22 May 2013
Páginas: 106 - 114

Resumen

Abstract

The effect of polychlorinated biphenyls on biomass production, lipid accumulation, and on the fatty acid profile of the major membrane lipids of Alcaligenes xylosoxidans isolated from a soil long-term contaminated with polychlorinated biphenyls was examined. The lowest bacterial growth was observed in the presence of biphenyl and polychlorinated biphenyls. On the other hand, the highest growth stimulation was observed in the presence polychlorinated biphenyls. Higher growth ability was observed when polychlorinated biphenyls or 3-chlorobenzoic acid were added after three days of cultivation. Higher lipid accumulation corresponded with lower growth ability. The importance of time when bacterial strain meets polychlorinated biphenyls or 3-chlorobenzoic acid should be emphasized. The addition of toxic organic compound later in stationary growth phase led to better survival and evoked lower membrane adaptation. However, polychlorinated biphenyls or 3-chlorobenzoic acid amendment at the beginning of cultivation stimulated adaptation responses as membrane saturation, cis to trans isomerisation, and branched fatty acids alteration and decreased growth ability. Palmitic acid and 17-cyclopropyl fatty acid were observed as prevalent in the bacterial membrane as well as in the total lipids.

Palabras clave

  • adaptation mechanisms
  • bacteria
  • environmental stress
  • fatty acids
  • polychlorinated biphenyls
Acceso abierto

Inhibition of pathophysiological proteases with novel quercetin derivatives

Publicado en línea: 22 May 2013
Páginas: 115 - 122

Resumen

Abstract

Novel quercetin derivatives were prepared to change its physicochemical properties and effects on activity of proteolytic enzymes. For them preparation, the selective protection procedures some of the quercetin hydroxyl groups and acylation of the others with acylchlorides were used. The ability of these compounds to inhibit the activity of serine proteases e.g. trypsin, thrombin, urokinase and elastase was studied. In micromolar range, tested derivatives were the most potent inhibitors of thrombin. There was estimated better inhibition of thrombin for prenylated, acetylated, feruloyl and caffeoyl quercetin esters. Slight inhibitory effect of all quercetin derivatives on elastase was found. Among tested derivatives only diquercetin displayed better inhibiton. Trypsin and urokinase were inhibited by quercetin at comparable level. Slight improvement in inhibitory effect of trypsin and urokinase was seen for chloronaphtoquinone quercetin that revealed enhanced inhibiton of thrombin, too. However, no influence on elastase activity was determined for this compound. Obtained results indicate that certain modifications of quercetin structure could improve its biological properties.

Palabras clave

  • elastase
  • enzyme inhibition
  • quercetin derivatives
  • thrombin
  • trypsin
  • urokinase
Acceso abierto

Analysis of natural aroma and flavor of MD2 pineapple variety (Ananas comosus [L.] Merr.)

Publicado en línea: 22 May 2013
Páginas: 123 - 128

Resumen

Abstract

Aroma and flavor profile of MD2 pineapple variety was investigated. Fruits imported from different geographical regions (Costa Rica, Puerto Rico) were labeled as an organic food. Characteristic volatile and non-volatile compounds obtained by hydro-distillation and direct percolation were identified and quantified by gas chromatography-mass spectroscopy (GC/MS). At least 22 components in percolated extract (or 17 in distillate) were detected according to their mass spectra and retention time. Relative concentration of identified substances varied from 547.7 to 1110.0 μg.kg-1. Analysis showed dominance of esters and furanone-derived compounds as major aroma constituents. Most abundant volatiles identified in all samples were methyl 2-methylbutanoate and methyl hexanoate. Relationships between volatile and non-volatile compounds were also studied.

Palabras clave

  • pineapple
  • MD2 variety
  • flavor
  • natural aroma
  • GC/MS
Acceso abierto

A new pathway of preparation and refined structure of (NH4)2[FeCl5(H2O)]

Publicado en línea: 22 May 2013
Páginas: 129 - 132

Resumen

Abstract

The title compound, (NH4)2[FeCl5H2O] has been prepared by reaction between iron(III) chloride and ammonium chloride which was formed by hydrolysis of isonicotinamide or thionicotinamide in ethanol. The characterization was based on elemental analysis and infrared spectra. The crystal structure of the title compound has been refined by single crystal X-ray diffraction method at 293 K. Crystals are orthorhombic, Pnma, with unit cell parameters: a = 13.760(1) A, b = 9.960(1) A, c = 7.060(1) A, Z = 4 and R = 3.5 %. The iron(III) atom in [FeCl5(H2O)]2- ion is approximately octahedrally coordinated by five Cl atoms and one O atom of H2O molecule. This distortion is caused by the extensively hydrogen-bonded lattice. Structural parameters and IR spectra of similar compounds are compared and discussed.

Palabras clave

  • ammonium salt
  • aqua-pentachloroferrate(III)
  • crystal structure
  • iron
  • IR-spectrum
Acceso abierto

Multidimensional gas chromatography and its applications in food and environmental analysis

Publicado en línea: 22 May 2013
Páginas: 133 - 140

Resumen

Abstract

This review deals with overview of methods of multidimensional gas chromatography (MDGC), the classical meaning- conventional heart-cut MDGC, and the comprehensive two-dimensional gas chromatography (GC×GC). MDGC is widely used because it increases required separation efficiency, which cannot be achieved by one-dimensional gas chromatography. Selected applications in food quality and safety, monitoring of environment, food authentication are summarized. This review summarizes the advances and applications of MDGC that have been published over last 10 years.

Palabras clave

  • gas chromatography
  • comprehensive two-dimensional gas chromatography
  • heart-cut multidimensional gas chromatography
Acceso abierto

Synergetic effects of Cu2O photocatalyst with titania and enhanced photoactivity under visible irradiation

Publicado en línea: 22 May 2013
Páginas: 141 - 149

Resumen

Abstract

Heterogeneous TiO2/Cu2O nanocomposite was synthesized for photocatalysis through surface impregnation in conjunction with the environmentally friendly soft chemical reduction strategy. The detailed structural, compositional, optical and photoelectrochemical properties of the obtained products are analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), photoluminescence spectra (PL) and electron spin resonance (ESR) spectroscopy techniques. Moreover, methyl orange (MO) dye was chosen as the probe molecule for evaluation of the photocatalytic activities of the samples under visible light (λ > 420 nm) irradiation. The experiments demonstrated that MO in aqueous solution was more efficiently photodegraded using TiO2/Cu2O composite photocatalysts than pure Cu2O alone. This was attributed to the good crystallinity, wide visible-light absorption range, and the efficient electron-hole pair separation properties of the TiO2/Cu2O nanoheterostructures. In this photocatalyst, visiblelight- active Cu2O component was used as a medium to absorb photons and convert them into photogenerated charges, and TiO2 nanoparticles were used as charge collectors to transport the photoinduced charges. The TiO2/Cu2O hybrid material showed improved separation of photoinduced electron-hole pairs owing to the potential-energy differences between Cu2O and TiO2, and therefore exhibited enhanced photocatalytic activity.

Palabras clave

  • photodecomposition
  • coupled semiconductor
  • methyl orange
Acceso abierto

Calcium hydroxide: An efficient and mild base for one-pot synthesis of curcumin and it’s analogues

Publicado en línea: 22 May 2013
Páginas: 150 - 156

Resumen

Abstract

Calcium hydroxide was found to be an efficient mild base for the one-pot synthesis of curcumin and its analogues obtained by condensation of one equivalent of acetyl acetone with two equivalents of corresponding aromatic aldehyde. The present protocol offers various advantages such as high yields, inexpensive easily available mild base, easy workup and eco-friendly method.

Palabras clave

  • Calcium hydroxide
  • acetyl acetone
  • substituted benzaldehydes
  • DMF
  • Curcumin

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