Ksenija Babić-Samardžija

N‐heterocyclic amines and derivatives as corrosion inhibitors for iron in perchloric acid

Purpose – Work reported in the present paper investigated the inhibiting properties of a number of N‐heterocyclic amines in 0.1 mol/l HClO4. An attempt also was made to correlate some molecular parameters of these compounds with their corrosion inhibitor efficiency.Design/methodology/approach – The test series included piperidine (pip), 2‐methylpiperidine (2mp), 3‐methylpiperidine (3mp), cis‐2,6‐dimethylpiperidine (26dp), 3,5‐dimethylpiperidine (35dp), 3‐hydroxy piperidine (3hp), 4‐hydroxypiperidine (4hp), 4‐aminopiperidine (4ap), piperazine (pz), 2‐methylpiperazine (2mpz) and cis‐2,6‐dimethylpiperazine (26dpz). The inhibiting effect was investigated in 0.1& mol/L HClO4 by potentiodynamic polarization (DC) and electrochemical impedance spectroscopy (EIS).Findings – The results show that these compounds suppressed both cathodic and anodic processes of iron corrosion in 0.1 mol/l HClO4 by adsorption on the surface, which followed a Langmuir adsorption isotherm. Experimental observations indicated that basic...

Biological Activity of Some Cobalt(II) andMolybdenum(VI) Complexes: in vitro Cytotoxicity

Cytotoxicity and cell growth inhibition studies were performed for five distinct cobalt(ll) [Co2(acac)tpmc](ClO4)3, [Co2(dibzac)tpmc](ClO4)3, [Co2(hfac)tpmc](CIO4)2, [Co2(tmhd)tpmc](CIO4)3 and [Co2(ox)tpmc](CIO4)2.3H20 and five molybdenum(Vl) complexes, [MoO2(pipdtc)2], [MoO2(morphdtc)], [MoO2(timdtc)2], [MoO2(pzdtc)2] and [MoO2(N-Mepzdtc)2]. The former were tested in two leukemia cell lines: chronic myelogenic leukemia (K562) and human promyelocytic cell line (U937). They showed to have relatively high toxicity in K562 cells and a relatively low cytotoxicity in U937 cells, as assessed by both MTT and Trypan Blue assays. The five molybdenum complexes were tested in human promyelotic U937 cell line and they showed to have high toxicity.

Electrochemical Examination of Mixed-Ligand Cobalt(III) Complexes with Tetraazamacrocyclic Ligand and Heterocyclic Dithiocarbamates

Electrochemical stability of eight complexes of the general formula [CoIIIRdtc(1–8)cyclam](ClO4)2, where cyclam=1,4,8,11-tetraazacyclotetradecane and Rdtc− (1–8)=4-morpholine (Morphdtc), 4-thiomorpholine (Timdtc), 4-piperazine (Pzdtc), N-methyl piperazine (N-Mepzdtc), piperidine (Pipdtc), 2-, 3- or 4-methylpiperidine (2-, 3- or 4-Mepipdtc) dithiocarbamates, respectively, were studied. The substances were examined in aqueous NaClO4 solution and nonaqueous LiClO4 in CH3CN solution by cyclic voltammetry. In aqueous solution, macrocyclic ligand cyclam is characterized by the anodic peak at 0.95 V. The Rdtc− ligands have two anodic peaks, one in the region 0.25–0.30 V and the other in the 0.78–0.95 V region. Absence of these anodic peaks in the case of the complexes indicates that coordination to cobalt(III) stabilizes both cyclam and Rdtc− ligands, but reversible peaks in the range −0.68 to −0.78 V support the Co(III) redox reaction. In nonaqueous solutions cyclam has one anodic peak at 1.75 V. The ligands with heteroatom in the ring (Morphdtc, Timdtc, Pzdtc, N-Mepzdtc) have two anodic peaks, while the other four ligands (Pipdtc, 2-, 3- and 4-Mepipdtc) have only one anodic peak. In nonaqueous solution again, coordination to Co(III) ion stabilizes the Rdtc− ligands and contrary to aqueous solution no Co(III) redox reaction occurs, indicating a greater stability of the complexes in this media. Finally, the electrochemical results are compared with spectroscopic data obtained previously.

Spectral Assignments of New Symmetric Cobalt(III) Complexes with Macrocyclic and β‐Diketonato Ligands

Three new cobalt(III) complexes of the general formula [Co(Rac)cyclam](ClO4)2, where cyclam and Rac − refer to 1,4,8,11‐tetraaza cyclotetradecane and β‐diketonato ligand, i.e., 1,3‐diphenyl‐1,3‐propanedionato (dibzac), 1,1,1,5,5,5‐hexafluoro‐2,4‐pentanedionato (hfac) and 2,2,6,6‐tetramethyl‐3,5‐heptanedionato (tmhd) ions, respectively, have been prepared. Elemental analysis, conductometric measurements, UV/VIS, IR, 1H and 13C NMR as well as mass spectroscopy have been used to characterize them. In the complexes, cobalt is hexa‐coordinated in an octahedral geometry of a folded macrocyclic ligand, and β‐diketonates are bound as O,O′‐bidentates. The spectroscopic data are influenced by the different R‐groups depending on their steric and electronic effects. Finally, a mechanism of mass fragmentation is proposed.

Iron corrosion inhibition with dihydrobis‐ and hydrotris‐(1‐pyrazolyl)borates

Purpose – The objective in the present paper is a better understanding of acidic corrosion inhibition by polypyrazolylborates on iron electrodes. Structural and electronic effects of these compounds are discussed in relation to the inhibiting efficiencies and absorption.Design/methodology/approach – Two polypyrazolylborates, i.e. dihydrobis(1‐pyrazolyl) borate (Bp) and hydrotris(1‐pyrazolyl)borate (Tp) were investigated as corrosion inhibitors for iron in 1 mol/l HCl and in 0.5 mol/l H2SO4 using Tafel measurements, linear polarization resistance and electrochemical impedance spectroscopy. Theoretical explanation between molecular parameters of these compounds and inhibitor efficiency (IE) was made using the MNDO SCF‐MO method. Morphological changes of the reacted surfaces were monitored via SEM.Findings – Results obtained show higher inhibition effect of Bp than Tp. Inhibitors are more efficient in HCl than in H2SO4. Corrosion current and corrosion rate (CR) decrease with inhibitor concentration, while po...

Thermal stability and kinetic studies of new dinuclear copper(II) complexes with octaazamacrocyclic and multidonor bidentate ligands

Abstract The thermal properties of four copper(II) complexes with N , N ′, N ″, N ‴-tetrakis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane (tpmc) and several bidentate ligands N,S (thiosemicarbazide and thiourea) or N,O donors (semicarbazide and urea), of the general formula [Cu 2 (X)tpmc](ClO 4 ) 4 , have been investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC). The thermal stability order can be recognized for the examined complexes, depending on coordinated bidentate bridging N,S or N,O ligand. Kinetic data demonstrated first-order thermal decomposition. A plausible mechanism has been proposed which explains the major products of the degradation.