STUDIA CHEMIA - Issue no. 2 T2 / 2019 - Table of contents

Professor Ioan Bâldea on His 80th Anniversary

Keywords:

The development of a new optical method to measure the delay time following the spark ignition in gaseous explosive mixtures, based on the measurement of the emitted radiation intensity detected with a photo diode active in visible and near infrared range is presented. Several CH4-air-inert mixtures were used to test the validity of the method. Our results are comparable with the available literature data. The influence of the different operational factors was investigated to establish the range of the optimum conditions.

Keywords: spark ignition, ignition delay, emitted radiation intensity, CH4-airinert mixtures

The aim of this study is to investigate the corrosion behavior of low carbon steel (S235) used in petrochemical industry. The corrosion process was analyzed in simulated wastewater at different values of pH and at different temperatures and also in real wastewater from the exploitation of crude oil from Transylvania, Romania. Two commercial corrosion inhibitors (Nalco 73413 (Nalco Products, USA,) and Galoryl IC20 (ArrMazz Chemicals SAS, USA) were tested at different concentrations. The corrosion behavior was investigated by electrochemical impedance spectroscopy and potentiodynamic polarization measurements. Adsorption of these inhibitors was found to obey Langmuir adsorption isotherm.

Keywords: electrochemical impedance spectroscopy, polarization curves, steel corrosion, corrosion inhibitors, petroleum industry corrosion.

Silver nanoparticles (AgNPs) were synthesized by chemical reduction method, using different reducing systems. The interaction of AgNPs and vancomycin hydrochloride (V) was investigated by UV-Vis spectroscopy, and their tendency to form AgNP@V associations or complexes was identified in colloidal solutions. Moreover their affinity to self-assembly and aggregate is also examined. This behavior is important and decisively influences the antimicrobial effect of AgNP@V complexes.

Keywords: silver nanoparticles, vancomycin, UV-VIS spectroscopy

The influence of the dolomite-brucite concentration and temperature on the global process of sulfur dioxide, SO2, absorption into dolomite-brucite suspensions was established. According to the proposed macro-kinetic model, the chemical reaction between H2SO3 and MeCO3 takes place into the adsorbed layer, at the outer surface of the granules. The low values of the activation energies obtained, Ea << 25.1 kJ/mol, confirmed for working conditions, that the global chemisorption process was limited to diffusion stage. At suspension concentrations lower than 5% and high temperatures, the chemisorption was carried out according to the shrinking core model without crust, when the diffusion of H2SO3 through the liquid phase is the limitative stage. At concentrations higher than 10% the chemisorption was carried out according to the unreacted core model with crust formation, when the diffusion of H2SO3 through the crust of products remains the limitative phenomenon.

Keywords: dolomite-brucite suspension, sulfur dioxide, chemisorption, activation energy, macro-kinetic mechanism.

Dynamic intensification of distillation columns has shown significant promise in achieving energy savings with minimal investment in new equipment. Conceptually, it entails making a desired product as a blend of two auxiliary products (one with higher purity, the other with lower purity, but both having lower energy consumption). Practically, dynamic intensification means periodically switching between two operating states corresponding to the aforementioned products. Past work has relied on ad-hoc choices of auxiliary products. In this paper, we introduce a new optimization framework for selecting auxiliary products for dynamic intensification. An extensive case study concerning the separation of a methanol/propanol mixture is then presented. We show that optimizing the choice of auxiliary products can lead to significant energy savings (more than 3.6% compared to a column operated at steady state) derived from dynamic intensification.

Keywords: process intensification; dynamic intensification; distillation; energy efficiency, optimization

The energy conversion systems based on partial oxidation processes (hydrocarbons catalytic reforming, solid fuel gasification) are very promising for integrating carbon capture technologies due to high CO2 partial pressure in syngas to be treated. In these systems, the water-gas-shift (WGS) reaction has a very important place in concentrating the syngas energy as hydrogen and to convert carbon species as CO2. This paper is evaluating various WGS process configurations to be applied in catalytic reforming and gasification designs ranging from the conventional designs (multiple catalytic shift reactors) to more innovative reactive gas-solid systems (chemical & calcium looping) for simultaneous syngas conversion and CO2 capture. As the evaluations show, the reactive gas-solid systems are more promising in reducing energy penalty for CO2 capture as well as to increase the overall energy efficiency and carbon capture rate. As illustrative examples, the coal gasification for hydrogen and power co-generation with carbon capture were assessed.

Keywords: Partial oxidation, Water-gas-shift, Carbon capture, Reactive gasliquid and gas-solid systems.

This study presents the sintering of new forsterite ceramics (FCs) using nano forsterite powder, obtained by a sol-gel method. The forsterite ceramics were sintered between 1200 and 1450 °C. The resulted forsterite ceramics, namely FC at sintering temperature, T, written as FC(T), were characterized by various methods, XRD, AFM, apparent density, porosity and shrinkage. Mechanical properties were determined for FC(1400), with a Young elastic modulus at about 43.84 GPa and nano-indentation hardness at around 3.07 GPa. Furthermore, the in vitro biocompatibility of FC(1200) was evaluated using cell staining with fluorescein diacetate, FDA, assay. The cell viability results confirmed that forsterite ceramic, FC(1200), promotes cell adhesion and proliferation in cell culture, with no significant cytotoxic effects. These findings strongly recommend the new forsterite ceramics, as potential biomaterials for biomedical applications.

Keywords: forsterite ceramics, porosity, density, biocompatibility

In clinical practice, the simultaneous use of zolpidem and phenytoin cannot always be avoided, although it can be associated with additive depressants effects on the central nervous system. Considering the common metabolic pathways involving CYP3A and CYP2C, a pharmacokinetic interaction between phenytoin and zolpidem is possible, although not previously quantified. The study was designed as a non-randomized, two-period preclinical trial. Twenty male subjects were included in a study consisting of two periods. Between these, subjects were treated for 6 days with a single daily dose of 150 mg phenytoin. For each treatment period, pharmacokinetic parameters of zolpidem were determined. The multiple-dose administration of phenytoin influenced zolpidem’s pharmacokinetics in healthy volunteers, decreasing its exposure through enzymatic induction.

Keywords: zolpidem; phenytoin; drug interaction; enzymatic induction

The blackthorn (Prunus spinosa L.) fruits are known as a valuable source of anthocyanins and for their high antioxidant capacity. The aim of the present study was to investigate the thermal stability of anthocyanins from blackthorn fruits, at different temperatures (2°C, 20°C and 75°C) and to determine the kinetic and thermodynamic parameters of their degradation reactions. Data analysis indicated a first-order reaction kinetics for the degradation of blackthorn anthocyanins at various temperatures. Kinetic parameters, such as reaction rate constant k, half-life t1/2, and activation energy Ea values were determined. The obtained results indicated that blackthorn anthocyanins stored at 2°C exhibited the highest stability, the degradation constant rate being 5.0·10-4 h-1. The activation energy of the thermal degradation was also determined and was found to be 53.96 kJ/mol. The activation enthalpy ΔH, Gibbs free energy ΔG and activation entropy ΔS for the degradation process were also determined.

Keywords: Prunus spinosa L., anthocyanins, degradation kinetics

The article reports the radiocarbon investigation results of the superlative African baobabs from Savé Valley, Zimbabwe. Several wood samples collected from these baobab were analysed by AMS (accelerator mass spectrometry) radiocarbon dating. The radiocarbon dates of the oldest samples were 1529 ± 14 BP for Matendere Big baobab, 1179 ± 19 BP for Chishakwe Big tree and 1096 ± 35 BP for Mokore Giant baobab. The corresponding calibrated ages are 1430 ± 15, 1090 ± 40 and 1020 ± 25 calendar yr. The oldest tree from Savé Valley, which we described previously, is the Humani Bedford Old baobab. The radiocarbon date of its oldest sample, 1655 ± 14 BP, corresponds to a calibrated age of 1580 ± 30 calendar yr.

Keywords: AMS radiocarbon dating, Adansonia digitata, tropical trees, dendrochronology, age determination, Zimbabwe

Reticulation/polymerization of proteins using bifunctional reagents, with glutaraldehyde as a typical example, has a wide range of applications – of which HBOC (hemoglobin/hemerythrin based oxygen carriers) are illustrative. Here, the kinetics of the derivatization reaction of hemoglobin and albumin with glutaraldehyde are revisited, in order to establish the optimal conditions such as concentration of protein and derivatization agent for which the final product can be a reasonable candidate for blood substitutes. A purpose-built mixing device is described, which allows automated mixing of up to four reagents in less than 100 milliseconds, allowing for polymers with a more reproducible molecular weight.

Keywords: hemoglobin, glutaraldehyde, bovine serum albumin, blood substitutes, mixer, polymerization

The first part of this study aims at evaluating by DFT methods the structural features and the stability of a stannylene derivative, Sn(II) being included into an extended polycyclic framework. Natural Bond Orbital (NBO) analyses are performed in order to understand bonding patterns and also the role of secondary electronic effects on the stability of this unsaturated derivative. In the second part, the coordination of NHC and THF ligands to the Sn(II) atom of the polycyclic stannylene species are investigated. The strength of these interactions and the nature of the chemical bonds formed are also discussed.

Keywords: stannylene, stilbene, DFT calculations, NBO analyses

Conventional solid-state synthesis was used to produce mixed valence manganite La0.7Ca0.3MnO3 (LCMO) from the mechanochemically activated mixture of the corresponding metal oxides. Prepared samples were characterized by XRD and SEM measurements. The results showed that it is possible to produce single phase LCMO perovskite after at least 2h of ball milling of the reaction mixture, followed by 1400 ºC sintering of the drypressed sample pellets. The prolonged milling time as well as the higher sintering temperature leads to further stabilization of crystal structure.

Keywords: perovskite manganites, LCMO, mechanochemical synthesis, XRD, SEM, microstructural characterization

The present study was focused on evaluating the manner in which heavy metals, originated from natural and anthropic sources (former mining activity in Baiut metallogenic area), in the upper basin of the Lapus River, transferred into sediments and accumulated in the riparian vegetation. Total concentrations ofPb, Ni, and Cd, classified as priority hazardous substances in the WFD, were measured in samples of water, sediments and some emergent flora species (Equisetum fluviatile, Myosotonaquaticum, Carexaquatilis, Salix fragilis, Mentha aquatica, Juncus spp.), in 4 selected sections of the Lapus River, including a reference section (a pollution free area). The heavy metal concentration in collected samples were determined by atomic adsorption spectrometry. In all the monitored sections the heavy metals concentrations were higher in plants than in sediments or water samples. The highest concentrations were recorded for Pb, then for Ni and lastly for Cd in the genus Carex and Salix in the most contaminated river section. The results of the study show that the ability to accumulate heavy metals differs between species, and affinity for a particular metal depends on its bioavailability.

Keywords: heavymetals, riparian vegetation, surface water, mining activity, Lapus River

PMMA denture base materials are used for several decades without significant improvements in their composition. The addition of different fillers has been proved to improve some of the acrylic resin’s characteristics. Recent studies focused on enhancing PMMA properties using nanoparticles. In our study we assessed the effect of adding graphene and silver nanoparticles on the solubility, ductility and resilience of a commercial denture base acrylic resin.

Keywords: solubility PMMA, ductility, resilience acrylic resin, graphene, silver nanoparticles

Characterization of five representative archaeological ceramic shards from the Tăşnad-Sere C 52 site by optical microscopy (OM), XRD, and FT-IR spectroscopy [1] was continued by the detailed analysis of the XRD and FT-IR spectroscopic data in order to obtain a deeper insight into the samples microstructure and mineral composition. The XRD investigations were also extended to several clayish soil samples collected in the archaeological site area. The fresh results permit more exact conclusions about the possible local provenance of the raw materials used by the ancient potters.

Keywords: archaeological ceramics, provenance, XRD microstructure analysis, FT-IR spectra deconvolution

Polyethyleneimines (PEIs) and polyamidoamine dendrimers (PAMAM) are widely used as non-biological transporters in modern gene therapies. In this study, several zero-generation aromatic core “ZAC” dendrimers were computationally studied for predictive toxicity assessment. The chemical synthesis of the ZAC dendrimers was carried out using three different bromomethylbenzene derivatives as aromatic core and dialkanolamines as branching units with different carbon chain length. Quantitative structureactivity relationships (QSAR) and virtual high throughput toxicity screening (vHTTS) assays were applied on the synthesized zero generation dendrimers to evaluate their toxicities.

Keywords: molecular descriptors, pharmacophore, QSAR, continuous structures, toxicity, maximum recommended daily dose, dendrimers.

2-(chlorobenzilidene)hydrazinyl-thiazole derivatives were conveniently prepared by Hantzsch reaction protocol, starting with thiosemicarbazone and ethyl 2-bromo-3-oxo-3-phenylpropanoate. Their antioxidant capacity was screened by electron transfer based assays. The results of both DPPH (1,1-Diphenyl-2-picrylhydrazyl) free radical scavenging, as well as Ferric Ion Reducing Antioxidant Power (FRAP) assay, indicated antioxidant capacity for the tested hydrazone derivatives. At the concentration of 9.5 μg/mL, the DPPH radical scavenging activity of ethyl 2-(2-(3- chlorobenzylidene)hydrazinyl)-4-phenylthiazole-5-carboxylate was found to be more than 93%.

Keywords: synthesis, thiazoles, antioxidant capacity, DPPH, FRAP

The purpose of this study was the development and validation of an LC-MS/MS method, for the determination of tadalafil from human plasma. The sample workup involved a simple protein precipitation procedure. A core/shell type analytical column (50×2,1 mm, 2.6 Å) was used with C18 stationary phase. The mobile phase consisting of 30% acetonitril and 70% water provided good peak shape, accuracy and precision (stable ionization). The mass spectrometer was operated in positive electrospray ionization mode for analyte and internal standard. The following parameters were evaluated for validation purpose: selectivity, sensitivity, matrix effect, anticoagulant effect, linearity, precision and accuracy, recovery, short and long term analyte/IS stability in solvent/matrix and carryover. The validated calibration range was 22.2-1111.3 ng/ml. The correlation coefficient R2 was at least 0.9995 in all validation batches. The validated method has been successfully used for the evaluation of bioequivalence of generic tadalafil 20 mg formulations.

Keywords: tadalafil, phosphodiesterase 5 inhibitor, method validation, bioequivalence trial, LC-MS/MS

The current study aimed to determine the chemical composition and antibacterial activity of two essential oils extracted from herbs belonging to the family Lamiaceae (mint and oregano), and their beneficial impact on the biochemical and microbiological changes occurring in fresh cheese during storage time. Based on the essential oils results three types of fresh cheese were formulated and the consumer prefer sample were sensory evaluated using the 9-point hedonic test. In order to determine the stability during storage, the selected sample and the essential oil free control sample were sampled initially, after 6 and 12 days of storage than subjected to physicochemical (protein, fat, moisture, ash, total carbohydrates, and energy) and microbiological analyses (S. aureus, E. coli).

Keywords: Antibacterial activity, Biochemical changes, essential oils, microbiologic, sensory evaluation, storage, volatile profile

By changing the buffer composition from phosphate to acetate (in both cases, the pH value was 6.0), the sensitivity of the estimation of peroxidase activity in polyacrylamide gels was improved from 4 μg/well to 0.4 μg/well. The optimized method, including electrophoretic separation and zymogram technique realized with guaiacol as substrate, can be performed in only 135 minutes. The improved method was applied to monitor the expression of recombinant peroxidase in a Gram-negative bacterium: the peroxidase activity was detected at 4 h after induction of expression.

Keywords: zymography, peroxidase, guaiacol, SDS-PAGE

The synthesis of new 2-(2-(3-formyl-10H-phenothiazin- 7yl)vinyl)-3H-indolium iodide and comparison of the UV–visible absorption/ emission spectral changes for several indolium cyanine dyes upon variation of organic solvents and aqueous solutions with pH in the range between 5–8 pH units were described.

Keywords: cyanine dyes, phenothiazine, indolium iodide, solvatochromism, pH sensitivity

Nowadays there is increasing interest in using various electrochemical methods as alternative to the energy consuming physico - mechanical, hydrometallurgical and pyrometallurgical techniques for metals recovery from waste printed circuit boards (WPCBs). Thus, cyclic voltammetry (CV) and cyclic square-wave voltammetry (CSWV) methods were used for studying the electrochemistry of some metals (Cu, Sn, Pb, Fe, Zn) on glassy carbon electrode from synthetic leaching solutions containing known concentrations of metallic ions and in real solution obtained from dissolving 10 WPCBs. A good linear correlation was obtained between the parameters evaluated by ICP-OES and cyclic voltammetry. The influence of pH and oxidation/reduction potential (ORP) on the corrosion rate of the mentioned metals was studied gravimetrically. Based on the obtained results, a complex sensors array (amperometric, pH, temperature and ORP) was proposed to assure the accurate monitoring and control of the electrochemical process for metals recovery from WPCBs.

Keywords: waste printed circuit boards, metals recovery, sensor array, potentiometric and voltammetric sensors

Different isolates of Trichoderma are able to produce metabolites which induce some morphological and physiological changes in plant such as enhanced plant growth and response to plant pathogens or reduced plant stress. The aim of the present study is to evaluate the effect of some Trichoderma isolates on plant growth promoting and physiological parameters of tomato plants. Also, the Trichoderma isolates were assessed based on IAA (indole 3-acetic acid) production and ability to solubilize phosphate, traits associated to growth. Tomato seed treatment with Trichoderma isolates led to a significant increase in plant height as well as root length and root fresh/ dry weight. However, metabolite production varied among isolates and depends on the isolate. Our data indicated that three of the Trichoderma isolates studied increase leaf pigments content and improve the photosynthetic activity of tomato plants.

Keywords: chlorophylls, carotenoids, IAA, root length, fresh weight