STUDIA CHEMIA - Issue no.3 / 2016 Tom 1 - Table of contents

This issue of our journal is dedicated to Professor Luminita (read Luminitsa) Silaghi-Dumitrescu at her 65th anniversary.

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The dithioarsianato ligands display a variety of coordination paterns in inorganic and organometallic compounds. Their structures and transformations are reviewed.

Keywords: dithioarsinate, 1,1-dithiolato ligands, self-assembly, organometallic, coordination

Heteroleptic diorganochalcogen compounds of type R[2-(Me₂NCH₂)C₆H₄]E [R = (phtz)CH₂, E = Se (1), S (2); R = (4-Cl-phtz)CH₂, E = S (3); R = (pz)CH₂CH₂, E = Se (4)] were prepared by reacting 2-(Me₂NCH₂)C₆H₄ELi with the appropriate organic halide in a 1:1 molar ratio. The new compounds were investigated in solution by ¹H, ¹³C and ⁷⁷Se NMR where appropriate. For compounds 1 and 4 the crystal and molecular structures were determined by single-crystal X-ray diffraction.

Keywords: Diorganoselenium compounds, hypercoordination, structure elucidation

Trifluorophosphine is a strong back-bonding ligand like the ubiquitous carbonyl ligand. In fact mononuclear zerovalent trifluorophosphine complexes such as M(PF₃)₆ (M = Cr, Mo, W), M(PF₃)₅ (M = Fe, Ru), and M(PF₃)₄ (M = Ni, Pt) are even more stable than their well-known carbonyl analogues. However, metal complexes with bridging trifluorophosphine ligands are virtually unknown. We review theoretical studies on the Co₂(PF₃)₈, Fe₂(PF₃)₉, and Cp₂Fe₂(PF₃)_n (Cp = h⁵-C₅H₅; n = 4, 3) systems analogous to the well-known metal carbonyls Co₂(CO)₆(µ-CO)₂, Fe₂(CO)₆(µ-CO)₃, Cp₂Fe₂(CO)₂(µ-CO)₂, and Cp₂Fe₂(µ-CO)₃ containing two or three bridging CO groups. In most cases structures having features other than bridging PF₃ groups are energetically preferred.

Keywords: Trifluorophosphine, iron, cobalt, density functional theory

Density functional calculations indicate that, the steric and packing factors seem to play a much more significant role than the electronic effects in influencing the bending of the rhodium(I) complexes of bisphosphonitocarbaborane(12)s.

Keywords: Rhodium(I) Complexes, Bisphosphonitocarbaborane(12)s, Density Functional Theory, Natural Bond Orbital Analysis

The active sites of the enzymes superoxide reductase (SOR) and cytochrome P450 feature square pyramidal FeN4S centers, with a thiolate in axial position trans to the substrate binding site but with differing equatorial nitrogenous ligands. The respective catalytic cycles also share a common intermediate – a ferric-(hydro)peroxo species. The detailed catalytic mechanisms are still a matter of debate for both enzymes, as some of their key catalytic intermediates have very short lifetimes. Inhibitors such as cyanide were therefore often employed to probe active sites of these enzymes and identify important structural features controlling reactivity; among these studies, ENDOR spectral data on ferric-cyanide complexes were previously reported. Here, density functional calculations are employed in order to more accurately correlate the experimental data with electronic structure elements. The data are shown to be in good agreement with experiment and also provide new insight.

Keywords: cytochrome P450, superoxide reductase, DFT, ENDOR

3-Bromo 10H-phenothiazines, even the 10H-unsubstituted derivative, can be efficiently coupled with several boronic acids to give 3-aryl 10H-phenothiazines with good to excellent yields. Selected electronic properties (UV/Vis spectroscopy, cyclic voltammetry, DFT calculations) are discussed and correlations of the Hammett-Taft substituent parameters are established for rationalizing the transmission of the remote electronic substituent effects.

Keywords: Cross-coupling – DFT calculations – Heterocycles – Substituent Effects – UV/Vis Spectroscopy

New 1,9-diacyl-5-(phenothiazinyl)dipyrromethane (aphdpm) obtained by diacylation of 5-phenothiazinyl-dipyrromethane were subjected to complexation reactions with dimethyl- and di-n-butyltin(IV) dichloride which afforded complexes of the type [Me₂Sn(aphdpm)] and [(n-Bu)₂Sn(aphdpm)] respectively [where aphdpm: 1,9-diformyl-5-(phenothiazinyl)dipyrromethane and 1,9-dibenzoyl-5-(phenothiazinyl) dipyrromethane]. Plausible structures of the new tin(IV) complexes were proposed based on spectroscopic FT-IR, ¹H-, ¹³C-, ¹¹⁹Sn-NMR and mass spectrometry studies.

Keywords: Dipyrromethene, Phenothiazine, Tin complexes

A new diphenylstannepinic derivative has been synthesized and completely characterized in solution and in solid state (multinuclear NMR spectroscopy, HRMS, X-ray diffraction). As a result of the reaction of the diphenylstannepinic derivative with bromine, a brominated product was evidenced by NMR spectroscopy.

Keywords: diphenylstannepine, dibromostilbene, dihalostannepine

The experimentally synthesized and structurally characterized metallaborane clusters containing highly electronegative heteroatoms namely (S, P, and Se) were studies by density functional theory in order to provide an insight into the influence of these heteroatoms on the polyhedral framework of metallaboranes.

Keywords: Metallaboranes, Density functional theory, heteroatoms, electronegativity

There is currently an increasing interest in developing functional foods and in the use of natural food antioxidants as health promoting additives. The purpose of our study was to compare the antioxidant potential and the total phenolic content of 12 commercial available fruit flavoured yogurts from three different producers present on the Romanian diary market. The free radical scavenging capacity was evaluated using the 2, 2-azino-bis(3-ethylbenzothiazoline)-6-sulphonic acid (ABTS) assay and the total phenolic content (TPC) was determined by Folin-Ciocalteu method. The TPC of the investigated samples varied between 362.3 and 926.7 mg gallic acid equivalents/mL yogurt and the antioxidant activity (AA) was in the range of 197.1÷ 653.8 mM Trolox/mL yogurt. A positive linear correlation between the antioxidant activity and the total phenolic content (R2 = 0.915; 0.912; 0.687) was established for the yogurt samples.

Keywords: fruit-flavoured yogurt, polyphenols, antioxidant activity

Two palladium(II) complexes of (1E,6E)-1,7-bis(4-(dimethilamino) phenyl)hepta-1,6-diene-3,5-dione were synthesized and structurally characterized with the aim of testing their cytotoxicity towards human colon tumor cells in vitro. Complexes A and B have the capacity to inhibit the cell growth in HT-29 and DLD-1 cell lines, the activity of A being superior as a result of a better accumulation inside the tumor cells.

Keywords: palladium complexes, curcumin derivative, cytotoxicity, colon cancer, cellular uptake

The antifungal activity of a series of thiazole, benzothiazole and benzothiazolyl-phenothiazine derivatives against Candida albicans and non-Candida albicans species causing invasive candidiasis was investigated using the diffusion method and the broth dilution procedure. Minimal inhibitory concentrations revealed antifungal activity against C. albicans, C. guillermondii, C. krusei and C. parapsilosis strains isolated from clinical materials (blood, urine and peritoneal fluids cultures). The tested hydrazine-thiazole derivatives showed promising antifungal activity against both fluconazole susceptible and resistive Candida species, while the benzothiazolyl-phenothiazine derivatives were not effective.

Keywords: Thiazole, Benzothiazole, Phenothiazine, Candida species

The present study is aiming to study the effect of sulfuric acid diamide (SAD) on corrosion of bronze CuSn8. In order to determine the optimal corrosion inhibiting effect SAD was tested at different concentrations. The inhibiting effect of the SAD was investigated by electrochemical methods, in a 0.2 g / L Na₂SO₄ 0.2 g / L NaHCO₃ (pH = 5) solution simulating acid rain. The results show that SAD exerts a good protection in case of CuSn₈.

Keywords: bronze corrosion, inhibitor, acidic solutions, electrochemical techniques

Two new glassy carbon modified electrodes were prepared by drop casting of chemically reduced graphene oxide (rGO) or graphene oxide (GO) on glassy carbon (GC) and then protected with a polymeric layer of Nafion or chitosan (Chit) (GC/Chit/rGO/Chit and GC/GO/Nafion). Their investigation by cyclic- and square-wave voltammetry for dopamine (DA) oxidation was aiming to estimate the analytical parameters that have the best values for GC/Chit/rGO/Chit electrode (i.e., the highest sensitivity of 1.002 ± 0.025 μA/ μM, a detection limit of 2.67 µM μM, for a linear domain from 4 to 18 µM DA). The modified GC/Chit/rGO/Chit electrode was also used for the detection of dopamine in injection vials using the standard addition method with a recovery of 99.42%.

Keywords: graphene oxide, reduced graphene oxide, dopamine, cyclic voltammetry, square wave voltammetry

The aim of this study was to develop an ecological method for the removal of Pb²⁺ ions from industrial wastewater. The electrocoagulation (EC) process of Pb²⁺ has been studied, using an electrolytic flow cell (flow rate of 20, 40, 60 mL/min) equipped with sacrificial Al electrodes, operated under galvanostatic mode (current density of 5, 10 and 15 mA/cm2). In all experimental conditions the concentration of Pb²⁺ was lowered below the maximum allowable concentration (0.5o ppm). The experimental results showed that the performances of the process are more strongly dependent on the applied current density than on the applied flow rate. The electrolytic flow cell has proved to be quite effective, allowing the complete removal of lead with a specific energy consumption of 3.08 kWh/kg Pb removed.

Keywords: lead contamination, sacrificial Al electrodes, lead removal, electrocoagulation

The increase of the graphite electrocatalytic activity toward hydrogen peroxide (HP) electrosynthesis (HPE) by the partial electroreduction of O2 can be achieved by in-situ electroactivation (EA). Our previous studies completed in strong alkaline media (1 M NaOH) by galvanostatic multi-sequence EA techniques (MSETs) revealed that an adequate graphite EA can improve HPE current efficiency (CE) up to 35 % compared to the unmodified graphite. In order to implement the optimised operational parameters to a micro-pilot scale electrochemical reactor, in a first step, several systems for the on-line HP concentration monitoring were designed and tested. Unfortunately, the preliminary test, even in moderate alkaline media (0.1 M NaOH) revealed that, at concentrations greater that 50 ppm, the HP decomposes intensively in contact with the setup components, disallowing the HP accumulation. As a consequence, for all further experiments, the alkaline supporting electrolyte was replaced with 0.1 M Na₂SO₄. In these new conditions, two models of HP on-line detectors (spectrophotometrical and amperometrical) were designed and tested, presenting adequate limit of detection (L.O.D. = 10 ppm and L.O.D. = 0.23 ppm, respectively). Also, the HPE process was studied in sulphate media, using a Pt/graphite wall-jet ring disk electrode system, revealed that the CE can reach a 46 % value for the unmodified electrode and increases up to 52 % when the auto-adaptive galvanostatic MSETs protocol is used.

Keywords: hydrogen peroxide electrosynthesis, graphite electroactivation, hydrogen peroxide on-line monitoring, wall-jet ring disk electrode, auto-adaptive techniques

Fir cone biomass was used as a precursor for the preparation of activated carbon by sulfuric acid treatment and activation. It is known that activated from different biomass sources it has a wide range of applications in water treatment. Therefore, fir cone activated carbon (FCAC) was prepared from raw fir cone by chemical treatment and used in various experiments to test its functions for the removal of Pb²⁺ . The influences of different parameters like contact time, initial lead concentration, initial pH, biomass quantity and temperature were studied. Adsorption isotherm and kinetic models were used to analyze the equilibrium data. It was found that the Freundlich isotherm model and pseudo-second-order model describe better the Pb²⁺ biosorption process. The changes in morphological structure after lead ions-biomass interactions were evaluated by SEM analysis. From these studies, it can be concluded that the fir cone activated carbon could be a promising and effectively employed bioadsorbent for the removal of Pb2 ions from aqueous solutions.

Keywords: Fir cone activated carbon, Lead, Biosorption, Isotherms

Adsorption of Malachite Green (MG) dye on a biomass prepared from fir (Abies nordmanniana) cones, followed by UV–Vis detection has been studied. The biomass was characterized using scanning electron microscopy (SEM). The maximum adsorption capacity of MG onto fir cones biomass was determined to be 2.197 mg/g. The influence of pH on the removal of the MG dye was investigated and the results showed that the best adsorption capacity were obtained in the most acidic environment (pH=2). The adsorption rates were evaluated by fitting the experimental data to conventional kinetic models such as pseudo- first- and pseudo-second-order models. From the Dubinin–Radushkevich isotherm model, a 5.95 kJ/mol value for the mean free energy was calculated, indicating that MG adsorption could include an important physisorption stage.

Keywords: adsorption, cones biomass, Abies nordmanniana, kinetics, dyes, malachite green

This study investigated the removal of Crystal Violet (CV) onto H3PO4-modified mango seeds kernel (H3PO4-MSK) from aqueous solution. The adsorbent was characterized using elemental analysis, thermal analysis (TGA), scanning electron microscopy (SEM), specific surface area and pore size distribution (BET) and Fourier Transformed Infrared Analysis (FTIR). X-ray diffraction (XRD) analysis showed that H3PO4-MSK is a type II Cellulose crystal structure, while SEM and BET analysis confirmed the macroporosity of the adsorbent. The removal efficiency of CV increased with an increase in adsorbent quantity and temperature. The maximum adsorption capacities of CV onto H3PO4-MSK increased from 23.94 to 87.23 mg/g from 30 to 50°C. Adsorption kinetics analysis indicated that pseudo-second-order and Elovich equations fitted very well the adsorption of CV onto H3PO4-MSK. The adsorption process followed the Temkin and Langmuir isotherm models. Isotherm modelling showed that CV is loosely bound to H3PO4-MSK. Further thermodynamic analysis revealed that the removal of CV from aqueous solution by H3PO4-MSK was a spontaneous and endothermic process. The proposed adsorption mechanism is CV complexation by –OH and –NH2 groups and ionic exchange on –COOH groups of H3PO4-MSK.

Keywords: H3PO4-modified mango seeds kernel, adsorption, Crystal Violet, kinetics, equilibrium, thermodynamics

Sour water system (SWS), as vital part of refineries, is aimed to process wastewater produced during different refining processes. Sour water contains contaminated water with H2S and NH3 and/or alkali metals or hydrocarbon traces. The main objective of SWS is to reduce the concentration of these contaminants below undesirable level and to make possible water reuse in the refinery. H2S is generally stripped from the sour water and sent to the Claus Unit. The paper reviews two possible designs for SWS. The first one corresponds to the traditional design of the SWS unit, while the second design uses an internal stream to heat up the feed flow. For analyzing the two different design configurations, dynamic simulators were developed in Aspen-Hysys using industrial and literature data. Different operating scenarios were tested, also involving the SWS control loops. Dynamic simulation results reveal incentives for the second analyzed design from the energy cost reduction perspective, as external need of heat utilities is diminished and this is associated to an improved separation of the contaminants.

Keywords: sour water system, dynamic model, design, pollution, energy consumption

One of the most important efficiency parameters for separation columns is the effective interfacial mass transfer area. In this study the effective mass transfer area in gas-solid-liquid turbulent contact absorber was determined using the chemical absorption of carbon dioxide into sodium hydroxide aqueous solution. The effective mass transfer area determined in this study was found to be from three to six times higher than the geometric area of the solid packing. Keywords: Three phase fluidized bed, gas-solid-liquid turbulent contact absorber, effective mass transfer area, chemical methods

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Forsterite (Mg2SiO4) powders were synthesized by solid state reaction from basic magnesium carbonate and silicon dioxide. The MgO/SiO2 molar ratio was established at 2:1, 2:1.05 and 2:1.10. In order to realize a complete reaction between compounds and avoiding the MgO (periclase) presence in the final product, an excess of SiO2 was added. Boric acid in small quantity was used as a mineralizer. The six mixtures were designed and prepared in the laboratory. After a good homogenization and mechanical activation, the raw mixtures were thermally treated at 800 °C, 900 °C, 1000 °C, 1200 °C, 1300 °C and 1350 °C with a heating rate of 2 °C/min and one hour plateau at maximum temperature. The grain size distribution of the powders obtained at 800 °C, 900 °C and 1000 °C, according to the particle analyzes, are in the nanometer range. Increasing the temperature the size of grains is increased at micrometer dimensions indicating the presence of agglomerates. The mineralogical compositions evidenced by X-ray powder diffraction (XRPD) showed as the main crystalline compound the forsterite beginning of 1200 °C temperature. The crystallinity index of forsterite depends on the thermal treatment conditions, being highest at 1350 °C. A small quantity of MgO at the maximum temperature in compositions without boric acid was identified. The shape and morphology of forsterite crystals were evidenced by TEM analyses.

Keywords: nano forsterite, biomaterial, synthesis

Drinking water quality in the water network supply of the Satu Mare municipality was investigated, aiming to quantify the variation of some physico-chemical parameters with the distance from the water treatment plant. Usually, water quality decreases in the drinking water distribution systems due to unwanted physical, chemical and biochemical reactions occurring in the distribution systems. The variation of the main physicochemical parameters of drinking water such as turbidity, pH, oxidability, chlorides and free residual chlorine concentration, conductivity, iron content, water hardness and nitrates concentrations was studied. The drinking water samples were collected weekly during the year 2013 from 16 fixed points of the distribution network of Satu Mare. The statistical analysis of the results was accomplished and presented. Univariate and bivariate regression models of the water quality variation with the distance from the water treatment plant were proposed. The distance from the water treatment plant to the each sampling point was established by measuring the length of pipelines crossed by water until that sampling point. The sampling points were chosen on the main routes of water distribution pipes in the main districts of the city of Satu Mare. These mathematical models attempted to capture the variation of the physico-chemical parameters of drinking water along the water network supply. An increasing trend of turbidity, water conductivity, water hardness and nitrates content of water was observed while the free chlorine content showed a decreasing trend.

Keywords: drinking water; free chlorine; supply network; oxidability; turbidity

This paper presents the results obtained through the synthesis of spinel - structured, ceramic pigment nanopowders (CoAl2O4 si NiAl2O4), using a modified sol – gel method. This study focuses on the influence of the thermal treatment, applied during gel calcination, 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 the thermal treatment, was analyzed using X-ray diffraction. The colour of the powders was characterized by UV–VIS spectroscopy, determining the absorption spectra. Additionally, the trichromatic coordinates were determined, and the corresponding pigment positions were fixed on the chromaticity diagram.

Keywords: ceramic pigment nanopowders, cobalt spinels, nickel spinels, sol–gel method, sucrose, pectin

ABSTRACT. Ceramic porous disks made of hydroxyapatite, HAP, loaded with silver ions and nitroxoline (5-nitro-8-hydroxyquinoline, NHQ) are used in vitro against pathogens, such as Staphylococcus aureus. HAP powder was synthesized by a wet chemical method, and its phase purity and nanocrystalline structure were assessed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Disk samples of HAP were prepared and impregnated with Ag ions and NHQ solutions. A strong antimicrobial activity of all samples was assessed by the diffusion assay in vitro against Staphylococcus aureus. Through the development of the optimal composition of these biomaterials, this approach might hold potential applications for antimicrobial coating, bone tissue engineering scaffolds and biomedical devices.

Keywords: ceramics, hydroxyapatite, silver ions, 5-nitro-8-hydroxyquinoline, antimicrobial effect

In the present study atomistic models of three-terminal Y junctions with D3h symmetry were built by the covalent assembly of singlewalled armchair carbon nanotubes and the energetic properties were evaluated using quantum chemical methods at the PM6 level of theory. The theoretical study follows the influence of the relative position of the heptagonal ring defects on the structure and stability of the junction. The deformation of the attached nanotube branches is discussed in terms of the evaluated geometric parameters. Results indicate that the size of the junction and the diameter of the nanotube will determine the proper position of the defects corresponding to the energetically favourable cluster.

Keywords: armchair carbon nanotubes, three-terminal junctions, PM6, POAV