STUDIA CHEMIA - Issue no.1 / 2017 - Table of contents

The present paper presents the freeze-drying kinetics of soluble coffee in order to determine the mass transfer parameters. Several semi-theoretical and empirical models were used to find the best fit to the experimental data. The applied models were compared using the coefficient of determination (R2), the mean relative percent error (P), the root mean square error (RMSE) and the reduced chi-square (2). The Midilli model was found to fit better to the experimental freeze-drying data comparative to other models. The Fick’s second law was employed to determine the effective diffusion coefficient (Deff).

Keywords: coffee, freeze-drying, moisture ration, drying rate, Fick’s diffusion model, effective diffusion coefficient

The behaviour towards simultaneous oxidation by Cr(VI) in acidic environment of mixtures consisting of two structurally closely related thioethers (S-methylcysteine and DL-methionine) was tested, at 0.085 mol·l-1 H+ and 298  0.1 K. The kinetic and mechanistic patterns of the two substrates when oxidized separately were already known and very similar. Based on that knowledge, the individual kinetic parameters (rate and equilibrium constants) were first computed. Theoretical predictive models for the value of the observed rate constant of a mixture, based on the kinetic data from non-mixtures, are compared with experimental findings and subsequently an empirical calibration surface obtained from all experiments is discussed. Due to differences in the kinetic parameters of the two reactions, in all models the obtained surfaces are asymmetrical, and this opens the possibility to univocally determine the concentrations of both the thioethers without separation.

Keywords: chromium VI oxidation, DL-methionine, S-methylcysteine, combined kinetic response, kinetic modeling

The adsorption behavior of some lowcost adsorbents such as bentonite, meal thistle and carbonized walnut husk with respect to Cd2+ ions in aqueous solutions has been studied. The several process parameters (contact time, initial metal concentration, sorption capacity, extraction degree, rate constants, sorption rates and sorption energy) were found. For the Cd2+ ions adsorption the equilibrium time onto bentonite, meal thistle and carbonized walnut husk were found to be 2 h, 25 and 10 min, respectively. Adsorption parameters were determined using both Langmuir and Freundlich isotherms. Sorption isotherms of cadmium ions onto MBT (modified bentonite) and MTM (modified thistle meal) were the best of all described by the equation of Freundlich sorption (correlation coefficients are closest to unit). In contrast the sorption of Cd2+ ions onto MCWH (modified carbonized walnut husk) was described by the Langmuir isothermic model where the adsorption occurs on homogeneous surface by monolayer sorption without interaction between sorbed ions. The obtained results demonstrate that bentonite, meal thistle and carbonized walnut husk can remove Cd2+ ions from aqueous solutions. It means that cheap and available raw materials can be efficient adsorbents and capable to remove cationic heavy metal species from waste water. The ion-exchange mechanism of adsorption of cadmium ions by the MBT, MTM, MCWH was proposed.

Keywords: sorption, Cd, bentonite, meal thistle, carbonized walnut husk, kinetics.

Biogas production by anaerobic digestion of residual waters from different sources (a treatment plant and a beer factory) was investigated in laboratory small scale batch reactors. Both wastewaters represent efficient biogas substrates. As concern the methane composition, the value is slightly higher in the case of biogas produced by anaerobic digestion of wastewater from beer factory. In the second part of this study, anaerobic co-digestion of wastewater and cow whey was performed. Addition of cow whey to wastewater from beer factory increase the biogas yield, while the addition of cow whey to wastewater from treatment plant decrease the biogas yield. In both cases of co-digestion, the methane content in biogas was higher than in the single digestion processes.

Keywords: wastewater, anaerobic digestion, biogas, methane yield

The objective of our study was to test the bleaching effect of two whitening gels, on stained hybrid ceramic material used for Computer Aided Design/ Computer Aided Manufacturing technology. 40 rectangular specimens 12/14/1mm were prepared form Vita Enamic blocks. All specimens were accelerated stained, and distributed in two groups. Group 1 was bleached using Opalescence PF 15% (Ultradent, USA), group 2 was bleached using an experimental gel containing natural products. ΔE* (used to asses the color changes) was above the perceptibility threshold of 1.2 in 40%; and the WID (used to asses the bleaching process in dentistry) showed high units for both bleaching gels. Hybrid ceramics staining showed moderate results, while the bleaching effect was present, with no statistical difference between the discolorations produced by the two bleaching gels (p<0.05). SEM images showed that the bleaching gels did not affect the surface structure of the material.

Keywords: CAD/CAM, hybrid ceramics, polymer, bleaching, color, SEM

Microscopic properties like network dynamics and phase compositions were studied for a series of commercially available cosmetics emulsions like hair shampoo, anti-UV shielding creams and hand and body creams. Proton longitudinal and transverse nuclear magnetic relaxations were measured by recording the 1D CPMG and 2D saturation recovery–CPMG echoes decays. The one and bi-dimensional inverse Laplace transformations reveals subtitle features which characterize the microscopic dynamic behaviour associated with the in vitro natural degradation of cosmetics. The IR and UV–VIS spectra were recorded and correlated with the NMR measurement.

Keywords: commercial cosmetics; NMR; T2 relaxation; T1-T2 correlation; NMR-MOUSE®, IR and UV-VIS spectroscopy

Resveratrol is a polyphenol with important antioxidant and antiinflammatory roles. Loratadine, as a selective inverse-agonist of peripheral receptor H1, is described as an anti-allergic substance with potential antiinflammatory effects. We aimed to assess the protective capacity of loratadine against oxidative stress produced by inflammation with carrageenan in comparison with a well-known antioxidant compound, resveratrol. Our results showed that resveratrol and loratadine had no protective anti-inflammatory effects in inflamed skin. As expected, resveratrol had antioxidant effects in serum and in liver. Loratadine developed oxidative stress in tegument and serum. In this experimental model, our results do not sustain the initial hypothesis that loratadine could have a protective effect in inflammation, and, in the contrary, is capable of increasing it, by producing an oxidative stress.

Keywords: antioxidants, inflammation, loratadine, oxidative stress, resveratrol

The current study presents the analytical validation method and performance characteristics of visible molecular adsorption spectrophotometry in determining the nitrogen concentration in water samples after the catalytic oxidation under controlled temperature and pressure conditions, using potassium peroxodisulfate, according to Romanian standard SR EN ISO 11905-1:2003. The quality of the calibration range (the determination coefficient of the calibration curve, the linearity and homogenity tests), the limit of detection, the limit of quantification, selectivity, robustness, recovery tests and the uncertainty calculation of the method allow the successful use of the method, using the specific conditions imposed by the analytical standard method.

Keywords: total nitrogen, potassium peroxodisulfate, validation

The article presents the AMS (accelerator mass spectrometry) radiocarbon dating results of the baobab of Warang, Senegal. The investigation of the baobab revealed that it consists of 18 partially fused stems, which represents the largest number of stems reported for an African baobab. Three stems build the ring that closes a false cavity, while 15 stems grow outside the ring. Seven wood samples were collected from the false cavity and from the outer part of other stems. The dating results evinced that the stems belong to four different generations, out of which the first generation is around 500 years old. We also documented the presence of false stems, which emerge from a large adjacent stem, are triangular in horizontal section and act as an anchor. The baobab of Warang possesses 12 ordinary stems and 6 false stems.

Keywords: AMS radiocarbon dating, Adansonia digitata, tropical trees, multiple stems, age determination, inner cavity.

In this paper the calculation of intermolecular interaction energy based on Gavezzotti–Filippini semi-empirical method was performed for the series of substituted prolines. The initial structural data were mined from Cambridge Structural Database. The topology of each structure was analyzed with respect to a minimal generator set of the space group. It was shown that the least number of strong symmetrically independent interactions required to generate a crystal structure is likely to exceed the cardinality of a minimal generator set.

Keywords: intermolecular interaction, lattice energy, space group generator, minimal generator set

In this paper, we present graph theoretical methods to compute several vertex-eccentricity-based molecular descriptors such as the eccentric connectivity index, total eccentricity, average eccentricity and first and second Zagreb eccentricity indices for the generalized and ordinary Bethe trees and some dendrimer graphs. Also, we study the behavior of these descriptors under the rooted product of graphs and apply our results to compute these indices for some classes of molecular graphs, designed by attaching copies of ordinary Bethe trees to paths and cycles.

Keywords: Vertex eccentricity, Molecular descriptor, Molecular graph, Bethe tree, Dendrimer, Rooted product of graphs.

Relationship between the boiling points of a series of alkanes and some topological indices and geometrical descriptors is investigated using the multi linear regression MLR method. The results revealed that Wiener, Randić and volume descriptors play a more important role in the description of boiling points of alkanes, in comparison to the other molecular descriptors.

Keywords: Graph theory, MLR method, Alkane Derivatives

The aim of this study is to embed the active ingredients of the hydroalcoholic extract from the aristolochia (Aristolochia clematitis) into a new semisolid preparation and a viscoelastic methylcellulose based hydrogel in order to broaden the topical applicability of the palette’s range. The methylcellulose based hydroalcoholic gel formulation, preparation and quality evaluation was realized by continuously measuring the product’s physico-chemical parameters. The evaluated physico-chemical parameters: the swelling degree, the equilibrium swelling degree, the swelling rate and the swelling fraction, the swelling rate parameter, the swelling kinetics order, the speed constant.

Keywords: Aristolochia clematitis, hydrogel, methylcellulose, pH, swelling parameters

Chlorsulfuron (1-(2-chlorophenyl) sulfonyl-3-(4-methoxy-6-methyl- 1, 3, 5- triazin-2-yl)), a Sulfonyl herbicide was investigated for its sorption behaviour in soils from various geographical locations. The results, fitting Freundlich and Linear equations, depicted a C type curve. Linear distribution coefficient value (Kd) spanned in a range of 8.2-23.0 μg/ml while Freundlich distribution coefficient value (Kf) was found to be 7.06 -17.41 μg/ml. Low Gibbs free energy values (-14.9 to -16.0 kJ/mol) are indicative of physisorption process. The regression and correlation analysis depicted pH to be negatively correlated (r=-0.936) while organic matter and organic carbon to be positively correlated with Kd (r=0.989 and r=0.988 respectively). However the soil texture rendered positive correlation with clay (r=0.897) and negative correlation with sand and silt (r=-0.990 and r=-0.820 respectively). Desorption hysteresis coefficient (H), in all four soil was found to be less than 1 (0.44 to 0.62). Results have been statistically evaluated by ANOVA and the accuracy of fit has been calculated by plotting residual graphs in Minitab. This study is a milestone for further investigation based on Chlorsulfuron degradation and mobility patterns.

Keywords: Chlorsulfuron methyl, Soil, Adsorption, Correlation, Regression

Considering the particularities of rock salt solution mining, the current paper aims to determine the mass transfer parameters for rock salt dissolution in a plug flow system. The influence of crucial operating parameters such as flow rate and channel depth on the mean driving force, volumetric mass transfer coefficient and extraction yield was evaluated. It was found that flow rate increase intensifies the dissolution process leading to a more rapid dissolution of the rock salt deposit. Similar effect was noticed in the case of flow channel depth increase which leads to higher mass transfer area, increasing the amount of dissolved salt from the rock salt deposit.

Keywords: dissolution, mass transfer, salt mining, plug flow

Three new glucose-based asymmetric bifunctional organocatalysts containing a 6-aminopyridyl or a 6-methylpyridyl or a cinchona unit were synthesized. Asymmetric Michael addition of pentane-2,4-dione to β-nitrostyrene was catalyzed successfully by these catalysts. In case of the cinchona based glucose-thiourea derivate the S enantiomer of the corresponding Michael adduct was formed with moderate enantiomeric excess in three different solvents.

Keywords: organocatalyst, carbohydrates, cinchona alkaloids, Michael addition, asymmetric syntheses

Different unmodified and modified semiconductor photocatalysts were used for the complete decolorization of an unbuffered crystal violet solution. The decolorization efficiency of commercially available ZnO and TiO2 (anatase nanopowder) was compared with those of newly prepared goldmodified ZnOs (Au/ZnOs). Two Au/ZnOs were prepared from pure ZnO powder through deposition of gold by direct current (DC) sputtering. The morphological characterization of the Au/ZnOs was done with the aid of scanning electron microscopy. ZnO-based catalysts show significantly higher decolorization power in comparison with TiO2. Au/ZnOs show slightly higher activity than unmodified ZnO.

Keywords: semiconductor oxides, modification with gold, sputter coating, photodegradation, crystal violet

In this investigation, α-Fe2O3/SAPO-34 nano-structure were synthesized and characterized by XRD, SEM and FT-IR techniques. Morphologically, the shape of α-Fe2O3/SAPO-34 nanoparticles is close to spherical nanoparticles with an average particle size of 93 nm determined by Debye-Scherrer equation. The photocatalytic activity of α-Fe2O3/SAPO- 34 nano-structure was investigated through the degradation of doxorubicin, an anti-cancer drug using a batch reactor under UV-C irradiation and H2O2 as oxidant. The effect of various factors including drug concentration, catalyst dosage, pH and H2O2 concentration on the degradation yield were investigated. The results showed that optimum conditions were: Initial concentration of DOX = 20 ppm, pH = 8, amount of α-Fe2O3/SAPO-34 = 150 mg/L, and H2O2 concentration 4 mol/L.

Keywords: Doxorubicin, Photocatalytic degradation, α-Fe2O3/SAPO-34, Nanocatalyst

The paper follows the spatial variability and seasonal evolution of the heavy metal content of the Firiza-Strîmtori Reservoir that is the main source of drinking water for Baia Mare city located in the northwestern part of Romania. Water samples were collected from 10 sampling points located along the median line of the lake at different depths (at surface, at 5 m, 10 m, 15 m and 20 m). The experiments were carried out in the winter, spring, summer and autumn of 2015. We determined the concentration – depth profiles, both for the heavy metals iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), cadmium (Cd), lead (Pb) and also for sodium (Na), potassium (K), calcium (Ca) and magnesium (Mg). We determined the concentrations of heavy metals by atomic absorption spectrometry. We found that concentrations of heavy metals increase with depth. Generally, the concentrations of heavy metals are within the legal limits for the water used as drinking water sources. Mathematical models with high correlation coefficients were obtained in the case of heavy metal concentrations depending on depth and also for the seasonality of heavy metals upload.

Keywords: heavy metals, water quality, water reservoir, seasonality, mathematical models

It is well known that long term administration of high dose loop diuretics in patients with heart failure, may in some cases aggravate the cardiac failure symptoms. Part of this effect may be due to thiamine depletion secondary to diuretics use. The aim of our present study was to assess whether administration of benfothiamine in patients with advanced congestive cardiac failure treated on long term with high dose loop diuretics, can prevent the alteration of heart failure.

Keywords: benfothiamine, cardiovascular diseases, cardiomyopathy, diuretic treatment, heart failure, thiamine.

The main objective of a product quality study for drying agricultural products without causing distortion is to reduce the product moisture value to a final moisture value while expending the least energy and time. In the first stage of this study, nectarine slices were dried in a microwave and cabinet dryer under different drying conditions. Experiments in the microwave dryer were done at four different power levels: 90, 180, 360, and 600 W. Hot air drying was done at two temperatures, 50 and 70 °C, with a constant air velocity (2.0 m/s). In the second stage, after those experiments, the hybrid drying method were constructed based on the color parameter, and moisture ratio. In the hybrid drying method, hot air drying was carried out with microwave pretreatment. The most effective hybrid drying method in terms of optimal drying time, energy consumption, and color parameters was found to be at 180 W microwave power and 70 °C.

Keywords: Nectarine, hybrid drying, color, energy consumption

In this study, synthesized TiO2 nanorods and commercial Aeroxide P25 TiO2 nanoparticles were deposited on polyethersulfone (PES) membrane surfaces to compare their photocatalytic activity and effects on membrane surface and filtration properties. The catalysts were deposited on the membrane surface by physical deposition. The effect of the TiO2 amount on the stability of the catalyst layer and its effect on membrane resistance in presence and absence of UV irradiation were investigated. 1.2 mg/cm2 catalyst coverage proved to be a minimal appropriate coverage to prevent membrane damage during UV irradiation. The catalysts formed hydrophilic layers on the surface, and in case of both catalyst the surface free energy increased compared to the neat membrane. The photocatalytic activity and retention of the modified membranes were tested spectrophotometrically by using Acid Red1, azo dye.

Keywords: membrane filtration, TiO2 coated membranes, photocatalysis, azo dye, Acid Red 1

This paper focuses on the synthesis and analysis of some spinelstructured, ceramic pigment nanopowders (Mg(1-x)NixAl2O4) using a modified sol – gel method. This study emphasizes the influence of the Ni/Mg ratio and that of the thermal treatment on the properties of the obtained powders. The behavior of the dried gels during calcination was studied by differential thermal analysis. The formation of the spinel structure after calcination was analyzed using x-ray diffraction. The colour of the powders was characterized by UV – VIS spectroscopy, determining the absorption spectra. In addition, the trichromatic coordinates were determined, and the corresponding pigment positions were fixed on the chromaticity diagram.

Keywords: ceramic pigment nanopowders, nickel spinels, sol – gel method, sucrose, pectine.