Goran S. Nikolić

Fast Fourier Transform IR Characterization of Epoxy GY Systems Crosslinked with Aliphatic and Cycloaliphatic EH Polyamine Adducts

The use of fast FT-IR spectroscopy as a sensitive method to estimate a change of the crosslinking kinetics of epoxy resin with polyamine adducts is described in this study. A new epoxy formulation based on the use of polyamine adducts as the hardeners was analyzed. Crosslinking reactions of the different stoichiometric mixtures of the unmodified GY250 epoxy resin with the aliphatic EH606 and the cycloaliphatic EH637 polyamine adducts were studied using mid FT-IR spectroscopic techniques. As the crosslinking proceeded, the primary amine groups in polyamine adduct are converted to secondary and the tertiary amines. The decrease in the IR band intensity of epoxy groups at about 915 cm−1, as well as at about 3,056 cm−1, was observed due to process. Mid IR spectral analysis was used to calculate the content of the epoxy groups as a function of crosslinking time and the crosslinking degree of resin. The amount of all the epoxy species was estimated from IR spectra to changes during the crosslinking kinetics of epichlorhydrin.

Synthesis, physicochemical and spectroscopic characterization of copper(II)-polysaccharide pullulan complexes by UV–vis, ATR-FTIR, and EPR

Bioactive copper(II) complexes with polysaccharides, like pullulan and dextran, are important in both veterinary and human medicine for the treatment of hypochromic microcitary anemia and hypocupremia. In aqueous alkaline solutions, Cu(II) ion forms complexes with the exopolysaccharide pullulan and its reduced low-molecular derivative. The metal content and the solution composition depend on pH, temperature, and time of the reaction. The complexing process begins in a weak alkali solution (pH >7) and involves OH groups of pullulan monomer (glucopyranose) units. Complexes of Cu(II) ion with reduced low-molecular pullulan (RLMP, M(w) 6000 g mol(-1)) were synthesized in water solutions, at the boiling temperature and at different pH values ranging from 7.5 to 12. The Cu(II) complex formation with RLMP was analyzed by UV-vis spectrophotometry and other physicochemical methods. Spectroscopic characterizations (ATR-FTIR, FT-IRIS, and EPR) and spectra-structure correlation of Cu(II)-RLMP complexes were also carried out.

Thermal stability of the asphaltene/kerogen vanadyl porphyrins

Abstract Thermal stability of vanadyl porphyrins incorporated into the asphaltene/kerogen structures of the Dead Sea asphalt “float”, the La Luna Mara limestone and the Serpiano marl was studied by electron spin resonance (ESR). Comparative studies were also made on alkyl vanadyl porphyrins such as deoxophylloerythroetioporphyrins and (extracted and commercial) etioporphyrins and tetraphenylporphyrin. According to these studies, alkyl vanadyl porphyrins predominate in the asphaltene/kerogen framework. These porphyrins are stable up to 400°C during laboratory heating, but at and above this temperature their content sharply decreases. At 500°C and 600°C, the asphaltene/kerogen vanadyl porphyrins content follows a similar pattern to that at 400°C, except that at 600°C it was reduced to traces in less than 12 h. In addition, it is implied that a high proportion of the asphaltene/kerogen vanadyl porphyrins ( The asphaltene/kerogen vanadyl porphyrins kinetics during laboratory thermolysis are characterized by a step-wise pattern. This is attributed to thermolytic decomposition/demetallation of the asphaltene/kerogen alkyl vanadyl porphyrins with various energy barriers mediated by free radical intermediates. A rough extrapolation of pyrolytic data to longer times, based on both the Arrhenius equation and the often-quoted assumptions for the reaction rate decrease, infer that static laboratory pyrolysis of kerogen is irrelevant to natural geological processes characteristic of petroleum genesis.

The Thermal Degradation of Waterborne Polyurethanes with Catalysts of Different Selectivity

The thermal stability of waterborne polyurethanes was measured by use of the thermogravimetric analysis. Waterborne polyurethanes (wbPUR) with catalysts of different selectivity were characterized using dynamic heating. In the dynamic method, heating rates with increments of 0.5, 1, 2, 5, and 10°C min−1 were used in the range of 30–500°C, to achieve degradations of 0.025, 0.05, and 0.10, respectively. By using more selective catalysts, the resulting total time of decomposition was increased in all cases of degradation degrees for given initial temperature of waterborne polyurethanes. This paper shows how the dynamic method based on thermogravimetric analysis can be used to calculate the thermal stabilities of waterborne polyurethanes, using catalysts of different selectivity.

Attenuated total reflectance-fourier transform infrared microspectroscopy of copper(II) complexes with reduced dextran derivatives

Dextran is a water-soluble, extracellular neutral polysaccharide with a linear flexible chain of α-(1 → 6)-linked α-D-glucopyranose units, in a single compounds. In alkali solutions Cu(II) ion forms complexes with reduced low-molar dextran (RLMD). The metal content and the solution composition depended on pH. The complexing process begins in weak alkali solution (pH > 7), and involves OH groups in C2 and C3 dextran monomer units. Synthesized copper(II) complexes with RLMD, of average molar mass Mw = 5000 g/mol were investigated by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and FTIR imaging microscopy. ATR-FTIR microspectroscopic data of synthesized complexes are rare in literature. The changes in intensity and width of the IR bands in region 1500-1000 cm−1 were related to changes in conformation and short-range interactions of the ligand dextran. FTIR microscopy images shows more and less ordered structures of the Cu(II)-RLMD complexes. ATR-FTIR microspectroscopic data shows homogeneity of the Cu(II)-RLMD samples and green color of the samples confirm existence of Cu(II) ions.

Treatment of venous ulcers with the herbal-based ointment Herbadermal®: a prospective non-randomized pilot study.

Background: Venous ulcers (ulcus cruris venosum) are a common chronic disease that requires continuing treatment and significantly influences a patient‘s way of life. The therapeutic effects of the ointment Herbadermal on epithelialization and microbial flora of venous ulcers in 25 patients (10 men and 15 women) were tested over a 7-week period. The major components of the ointment are extracts of garlic, St. John’s wort, and calendula. Material and Methods: The patients were over 18 years of age, with ulceration of the lower leg no longer than 2 months or recurrent ulceration during the last 6 months. The involved patients did not use any other phytomedicines or supportive therapies. Parameters were evaluated before the treatment and every 2 weeks during the period of 7 weeks. The total treatment response was evaluated on the basis of epithelialization, granulation, fibrin deposits, exudation, and edema. Results: The percentage of epithelialization was 99.1% after 7 weeks, without significant effects on the microbial flora. Conclusion: This combination of extracts can be recommended as topical treatment for wound healing because of its epithelizing, anti-erythematous, and anti-edematous properties.

Conductometric studies on the stability of copper complexes with different oligosaccharides

AbstractBioactive copper complexes with pullulan or dextran oligosaccharides are the subject of intensive research mainly because of their possible application in veterinary and human medicine. The thermal stability and stability under oxidative conditions of the Cu(II) complexes with reduced low-molar pullulan or dextran were investigated in this paper, using a conductometric method. The influence of ligand constitutions on the stability of the complexes was examined on the basis of ligand property. Forced degradation studies were performed on bulk sample of complexes by using heat (25, 40 and 60°C) and an oxidation agent (0.1, 0.5, 1.0 and 10.0% v/v hydrogen peroxide). It can be concluded, according to the results obtained (by examining conductivity during the forced degradation studies), that Cu(II) complexes show a large pharmaceutical stability for both tests.

A Spectroscopic Study of Polynuclear Complex of Iron(III) with Inuline Oligomers

Abstract The infrared spectra of the hydrates of inuline oligomers and the complex of iron(III) with inuline oligomers and their partial deuterated analogs were studied. From the appearance and frequencies of the bands in the range of OH and OD vibrations it was concluded that these crystalohydrates have one type of H2O molecule, and relatively weak hydrogen bond (estimated Ow…O distances are 280 and 283 pm for inuline and its complex, respectively). From the FTIR spectra of the complex the β2-form for iron(III) oxihydroxide (FeOOH) was determined. On the basis of the electron spin resonance spectra it was concluded that Fe+3 ions of octahedral configuration (g-value 2.03 ± 0.01) were present in the complex. From the measured ESR line width (ΔH = 100 ± 5 mT) the approximate Fe inter atomic distance of 0.21 nm was calculated, indicating a dense packing of Fe atoms in the cluster.

Application of mathematical modeling for the development and optimization formulation with bioactive copper complex.

New formulation for treatment a copper deficiency in human organism was developed and optimized by application of mathematical modeling. This formulation contained copper (II) complex with polysaccharide pullulan, as active substance. The binder concentration [polyvinyl pyrrolidone (PVP %)], the disintegrant concentration (corn starch %) and the resistance to crushing (hardness) were taken as independent variables. In vitro measured drug release characteristics of the tablets at pH 1.20 and 7.56 were studied as response variables. Initially, the created full factorial 23 model showed that the resistance to crushing has the most significant effect on copper (II) complex release from the formulation. Optimal tablet formulation F2, with lower Hardness (50 N), lower Starch (20.0%) and higher PVP (2.7%) concentrations, is selected using the partial least squares (PLS) regression modeling. The selected formulation F2 has expressed the best drug release profile at both pH (98.66% pH = 1.20; 93.35% pH = 7.56), and the lowest variation of tablets weight. The presented theoretical approach and created PLS model can be readily applied in future copper complexes studies and formulation design.

Quantitative analysis of Loperamide hydrochloride in the presence its acid degradation products

The aim of this work was to develop a new RP-HPLC method for the determination of loperamide hydrochloride in the presence of its acid degradation products. Separation of loperamide from degradation products was performed using ZORBAX Eclipse XDB C-18, column with a mobile phase consisting of 0.1% sodium-octansulphonate, 0.05% triethylamine, 0.1% ammonium hydroxide in water:acetonitrile (45:55 v/v). The mobile phase was adjusted to pH 3.2 with phosphoric acid. The method showed high sensitivity with good linearity over the concentration range of 10 to 100 μg cm-3. The method was successfully applied to the analysis of a pharmaceutical formulation (Loperamide, Zdravlje-Actavis, Serbia) containing loperamide hydrochloride with excellent recovery. The loperamide hydrochloride degradation during acid hydrolysis and kinetics investigation was carried out in hydrochloric acid solutions of 0.1, 1.0 and 1.5 mol dm-3, at different temperatures (25 and 40°C), by monitoring the parent compound itself. The first order reaction of loperamide degradation in acid solution was determined. The activation energy was estimated from the Arrhenius plot and it was found to be 38.81 kJ mol-1 at 40°C. The developed procedure was successfully applied for the rapid determination of loperamide hydrochloride in pharmaceutical formulation (Loperamide, Zdravlje-Actavis, Serbia) and in the presence of its acid degradation products.