STUDIA CHEMIA - Issue no.4 / 2019 - Table of contents

This article presents the mathematical model of mass balance, the mathematical model at equilibrium for steam methane reforming process and the analysis of the equilibrium model for different operating conditions (T, P, Xfeed). The optimal operating conditions were established based on the analysis of the equilibrium model. It was also developed the mathematical model of heat balance, while the optimal size of catalyst granules was determined. The optimal working conditions were set by the equilibrium process’ analysis, the reactor feed ratio, H2O:CH4, 3:1, the temperature in the range of 780-1140 K and the pressure of about 30 atm.

Keywords: steam methane reforming, mathematical modeling, stoichiometric independent reaction, equilibrium process analysis

Hydrogen production from fossil fuels plays an important role in the global H2 demand. In general, H2 production from fossil sources implies syngas generation, typically by gasification or reforming, followed by the water gas shift process. The aim of this work is to determine the behaviour of the water gas shift process (in a packed bed reactor) through modelling and simulation using COMSOL Multiphysics software. In the developed model, diffusion is the main type of transport of the chemical substances. The challenges are to model the complex phenomena associated with a multiscale system: a macroscale level in the macropores between the dumped catalyst particles and a microscale level, inside of the pellets’ micropores.

Keywords: Hydrogen production, Water gas shift reactor, CFD modelling using COMSOL Multiphysics software.

The paper presents the rheological characterization of a bio-ester with possible lubricant properties, obtained from soybean oil fatty acids. The rheological characterization was carried out under thermostatic conditions, using a Brookfield CAP2000+L viscometer in the characteristic domain of these fluids. The variation of the apparent viscosity ηa as a function of shear rate γ and the variation of the two indices (K and n) as a function of temperature were determined, as well as the flow activation energy, Ea from Arrhenius type equations. A rheological model was proposed.

Keywords: apparent viscosity, fatty acids, non-Newtonian behavior

The adsorption of Toluidine Blue (TB) cationic dye was performed using raw and treated (thermal, chemical, thermo-chemical, ultrasonic) diatomite. Solid samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (EDX), and Fourier Transformed Infrared Spectroscopy (FTIR). Adsorption experiments were performed in batch conditions (20 ± 2°C, 100 mg TB/L, 100 mL, 0.1 g adsorbent). The best sample proved to be the one thermally treated at 250°C for 2 h with an adsorption capacity of 7.97 mg/L and 77% removal efficiency. The regeneration process of the used diatomite was also performed (calcination, HCl, water), the most efficient was the one using water. Kinetic models (pseudo-first-, pseudo-second-order, liquid film, and intra-particle diffusion) were considered to describe the experimental data. The calculated data showed that liquid film diffusion might be rate-determining step in this case.

Keywords: diatomite, adsorption, toluidine blue, regeneration, kinetics

Oil palm fruit fibre (OPFF) was investigated for its potential and probability to remove heavy metal ion and dye from the aqueous solutions. Different operational parameters were studied under batch experiment. The effective pH to attain maximum adsorption of MG and Pb(II) by OPFF was around pH 4 to 5. The adsorption process was rapid at the beginning and slowly achieved equilibrium within 180 minutes and 120 minutes for MG and Pb(II), respectively. From the experimental result, the pseudo-second-order kinetic model provided better correlation compared to pseudo-first-order kinetic model with R2 > 0.999. Various isotherm equations, such as Langmuir, Freundlich, and BET isotherm models were used to analyze the adsorption isotherm result. The experimental data fitted well into Langmuir and BET isotherm models with R2 = 0.996 and 0.984, respectively. The maximum adsorption capacity of OPFF from Langmuir equation was 41.67 and 10.10 mg/g for MG and Pb(II), respectively. Besides, characterization study of OPFF which include point of zero charge (pHzpc), chemical modification on the functional group and surface morphology was also performed in this study.

Keywords: Pb(II), Malachite Green, Oil palm fibre, Adsorption, Batch study, Characterization study

In this study we consider 25 of the most commonly used phthalates and summarize the available data that support their effects on humans. For 15 of the 25 investigated phthalates (60%) there are no human hazard assessment data, neither from experimental nor from computational studies, which underlines the necessity of their risk assessment. Consequently, we have used various computational tools to predict their ADME-Tox profiles and assess their harmful effects on humans. The outcomes of our study reveal that the investigated phthalates have good bioavailability and skin permeability which are associated with toxicity, especially when they are inhaled. They are able to interact with important molecular targets in the human organism such as membrane receptors, cytochromes, kinases, phosphatases, transcription factors, or transporters. These interactions may conduct to predicted harmful effects of phthalates, such as toxicity and irritations of the respiratory and gastrointestinal tracts, skin and eye irritations, endocrine disruption potential, or non-genotoxic carcinogenicity. The investigated phthalates are not predicted to produce genotoxic carcinogenicity, mutagenicity and cardiotoxicity. Beside the investigated phthalates, the di(2-ethylhexyl) phthalate reflects the highest number of toxic effects, and the ditridecyl phthalate and the diisotrodecyl phthalate illustrate the smallest number of possible toxicological effects, namely skin irritation, non-genotoxic carcinogenicity and endocrine disruption potential.

Keywords: phthalates, ADME-Tox, pharmacokinetics, toxicological effects

The effect of the color change of stained and then bleached composite resins blocks have been evaluated. 28 blocks, made from Admira fusion composite resin and divided in 3 groups, were included in the present study. They were stained in coffee for 3 days and then bleached with Opalescence gel (GO) and experimental bleaching gel based on green tea extract (GE). All color indices were measured in all situations (initially, after staining and after bleaching) with Vita Easy Shade spectrophotometer. It was used the CIE*L*a*b system for the color change parameters. The group bleached with Opalescence presented the most significant color changes. The bleaching effect of the experimental gel is lower that Opalescence bleaching gel.

Keywords: green tea, composite blocks, staining, bleaching, color change

The aim of this in vitro study was to assess the remineralization process of human enamel, using two commercial pastes (containing calcium, phosphates, hydroxyl-apatite and sodium fluoride) and an experimental gel (obtained from fruit extract). 40 caries free extracted human teeth were divided into 4 groups: 3 study groups (n=12), and 1 control group (n=4). For the study groups, the remineralization agent differed: GC Tooth Mousse, Recaldent, Remin Pro (Voco) and an experimental gel made by “Raluca Ripan” Chemistry Institute (Cluj Napoca, Romania). ATR-FTIR (Jasco-610, Japan) was employed to verify the protective effect of the remineralizing products on enamel. UV-Vis spectra were used to determine mineral loss and gain during demineralizationremineralization process. No significant statistic difference emerged between specimens in study groups and the specimens in control group. Under the limitations of the in vitro study, the application of the tested product proved to be effective on enamel remineralization.

Keywords: remineralization, enamel, mineral deficiency

In this paper, the simultaneous quantitative assay of Fluocortolone caproate (FCC), Fluocortolone pivalate (FCP) and Cinchocaine HCl (CIN) in suppository has been reported as a simple alternative analytical method. A partial least squares (PLS-2) regression was used for resolution of the overlapped spectrophotometric signals from mixtures of the three drugs. A calibration set containing FCC, FCP and CIN was constructed by using 33 full factorial design in the concentration range of 4.5-8.5, 5-7 and 8-12 μg/mL, respectively. Absorption spectra were recorded in the range 240-350 nm. To check the quality of the proposed method, it was applied to the determination of these compounds in synthetic mixtures and pharmaceutical formulation, suppository. The PLS-2 method yielded recoveries ranging from 91 to 106%. The results compared well with those from the reported HPLC method.

Keywords: fluocortolone caproate, fluocortolone pivalate, cinchocaine HCl, PLS

The article discloses the accelerator mass spectrometry (AMS) radiocarbon dating results of the Big Reniala of Isosa, which is a massive Grandidier baobab (Adansonia grandidieri Baill.) of Madagascar. The investigation of this baobab shows that it consists of 5 perfectly fused stems and exhibits a clttfgruster structure. The calculated wood volume of the tree is 540 m3, which makes the Big Reniala of Isosa the largest individual of all Adansonia species and also the biggest known angiosperm in terms of volume. Several samples were collected from the outer part of the stems. The oldest dated sample had a radiocarbon date of 934 ± 24 BP, which corresponds to a calibrated age of 845 ± 25 years. This value indicates an age of 1000 ± 100 years for the big Reniala of Isosa.

Keywords: AMS radiocarbon dating, Adansonia grandidieri, tropical trees, multiple stems.

Traditional home-made plum and apple brandies were analysed aiming to assess the main physico-chemical characteristics including density, ethanol content, total acidity, total extract, total sulphur dioxide (SO2) and refractive indices. The major volatile compounds, such as, methanol, linear superior alcohols (propan-1-ol, butan-1-ol, butan-2-ol), branched superior alcohols (2-methylpropan-1-ol and 3-methylbutan-1-ol) and also ethyl acetate, acetaldehyde and acetal compounds, were assessed using gas chromatography coupled with flame ionization detector (GC-FID). The technology of incorporating fruit (cherries and pears) or wood (mulberry and poplar) in the brandy was presented along with the influence of their addition on the composition of the plum and apple brandies and on their physico-chemical characteristics. The changes in the composition of plum and apple brandies throughout 4 weeks of maturation process in the presence of wood or fruit, showed an increase in density, acidity and total extract and decrease in the concentration of ethanol, total sulphur dioxide (SO2) and acetaldehydes. The addition of mulberry and poplar wood in the brandies decreased the concentration of acetaldehyde. The addition of both fruits significantly increased the concentration of ethyl acetate.

Keywords: volatile substances, gas chromatography, wood embedding, fruit embedding

The concentration of 12 metals (Mg, Ca, K, M, Fe, Co, Ni, Cr, Cu, Pb, Cd, and Zn) in 14 classes of alcoholic beverages were determined by ICP-MS after HNO3/H2O2 digestion. The mean concentration of metals (μg/mL) in these alcoholic beverages varied in the ranges 0.26-15.43, 0.94- 234.43, 0.56-278.02, 0.02-2.69, 0.18-2.64, 0.03-0.13, 0.03-0.13, 0.02-0.29, 0.04-2.51, 0.03-0.30, 0.02-0.04, and 0.13-0.88 for Mg, Ca, K, Mn, Fe, Co, Ni, Cr, Cu, Pb, Cd, and Zn respectively. The concentration of metals found in these particular alcoholic beverages was below the International Statutory Limits for metals in alcoholic beverages. The estimated daily intake of the metals based on a per capita consumption of 14.4 L per annum pure alcohol was lower than the tolerable daily intake of each metal. The individual and combined target hazard quotients of the metals were < 1, indicating no longterm health concerns from the consumption of these alcoholic beverages based on their metal content alone.

Keywords: alcoholic beverages, daily intake, target hazard quotients, Romania

Results on the obtaining and the study of a plant growth stimulator based on 1-propyl-4-(3'-amino-1’,2’,4'-triazolo-3'-thiopropinyl) piperidin-4-ol are presented in the article. 1-propylpiperidin-4-on and 3-mercaptopropinyl-5-amin- 1,2,4- triazolo were obtained with the basic parameters of the synthesis for synthesizing of 1-propyl-4-(3'-amino-1', 2', 4'-triazolo-3'-thiopropinyl) piperidin-4- ol. The structures of the obtained organic compounds were proved using IR spectroscopy and 1H and 13C NMR spectrometry. The obtained 1-propyl-4-(3’- amino-1’2’4’-triazolo-3’-thiopropynyl)-piperidine-4-ol was tested for growthstimulating activity on spring wheat grains compared with control (water) and has proved to be a domestic growth regulator «Akpinol-alpha» (KN-2).

Keywords: growth stimulators, organic compounds, IR spectroscopy, NMR spectrometry, growth stimulating activity, piperidine.

The ultraviolet-visible (UV-Vis) spectroscopy coupled with cluster analysis (CA) was evaluated for the classification of some medicinal plants of different geographical growing area. To have a deeper view, the experiment was carried out on herbs belonging to different families. The UV-Vis spectra of hydroalcoholic extracts were acquired in the range of 200-800 nm. The hierarchical clustering analysis (HCA) was applied to the data matrix provided by unprocessed, normalized and standardized spectra respectively. Different types of distance measuring of (dis)similarity between the samples as well as different kinds of linkage or amalgamation rule were taken into account. The best results for the classification of the selected medicinal plants were obtained using Ward’s method as the amalgamation rule combined with 1-Pearson r clustering distance measurement. The obtained results reveal the ability of HCA with Ward and 1-Pearson r algorithm to identify plant species even when the raw material has different provenience areas and different pedoclimatic growing conditions. In addition, this methodology revealed a direct link between herbs from different families.

Keywords: medicinal plants, classification/identification, UV-Vis spectroscopy, cluster analysis

Phytochemistry represents a large interdisciplinary research area which apply the chemical knowledge in plant biology, biochemistry and physiology. Since centuries, the technology related to the isolation and characterization of phytochemicals (plant secondary metabolites) developed gradually towards a holistic approach of omics’ technology, as part of the “systems biology” concept. This review underlines the scientific progress during the last eight decades, from “classical” phytochemistry to metabolomics, applied on plants and food and reflects not only the role of phytochemicals as key-molecules with essential roles in plants and with great benefits on animal and human health, but also their involvement in plant chemotaxonomy, food technology and authenticity. First, a selection of the major groups of phytochemicals and their main bioresources. The metabolomic technology is presented, as a high-throughput analytical platform to identify, by untargeted or targeted techniques, the fingerprint or key metabolites of a specific pathway in plants or for authentication of a food matrix. Updated literature data are presented, including a summary of eight decades of achievements of the research group related to Chemistry and Biochemistry of Natural Products at the University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca, celebrating now 150 years of existence.

Keywords: Phytochemistry, Metabolomics, Analytical platform