Milorad D. Cakić

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.

ALLICIN AND RELATED COMPOUNDS: BIOSYNTHESIS, SYNTHESIS AND PHARMACOLOGICAL ACTIVITY †

In this review, the biosynthesis of allicin (allyl thiosulfinate) by enzymatic transformation of alliin and various methods of its synthesis with detailed investigation of mechanisms and kinetics are summarized. A convenient method is also described for determination of allicin stability and the utility of the inclusion complexes of this pharmacologically active agent with β-cyclodextrins in increasing its stability. Allicin is the initial precursor for the production of ajoene ((E)- and (Z)-4,5,9-trithiadodeca- 1,6,11-triene 9-oxides) and vinyldithiin (2-vinyl-4H-1,3-dithiin, and 3-vinyl-4H-1,2- dithiin), which are more stable and show various pharmacological effects. The mechanisms of allicin transformations to these compounds are given in detail. Finally, the data on the pharmacological effects of allicin and its transformation products, ajoene and vinyldithiin, are presented.

Deconvoluted Fourier-transform LNT-IR study of coordination copper(II) compounds with dextran derivatives

Deconvoluted Fourier-transform IR spectra, recorded at room and liquid nitrogen temperature, of polysaccharide dextran and its coordination compounds with the copper(II) ion were analyzed in order to find the most specific spectral peculiarities. This allows one to obtain information about the structure and conformation of these polymer compounds. Different influences on the system of intra-and intermolecular interactions were exhibited by analogs recrystallized from D2O. The changes in intensity and width of the IR bands in the region 1450–1050 cm−1 were related to changes in conformation and short-range interactions of the dextran. In the synthesized copper(II)-dextran complexes, the presence of water molecules was confirmed. The results of the FTIR spectroscopy study allowed one to suggest a predominant crystalline form of the copper(II)-dextran complexes.

Inclusion complexes of amlodipine besylate and cyclodextrins

AbstractIn this paper the procedure for the preparation of inclusion complexes of amlodipine besylate with β-cyclodextrin (β-CD) and 2-hydrohypropyl-β-cyclodextrin (HPβ-CD) and their structural characterization was described. Molecular inclusion complexes of amlodipine besylate are prepared by the coprecipitation method and characterised by the application of spectroscopic methods FTIR, 1H-NMR and XRD. The photosensitivity of amlodipine besylate in the inclusion complexes was also determined with respect to uncomplexed agent. DSC curves indicate the loss of the clear peak due to melting of amlodipine besylate at about 200°C, while on XR diffractograms certain reflections are lost belonging to amlodipine besylate in complexes. This indicates its inclusion in the vacancies of the host. The inclusion of amlodipine besylate with cyclodextrins increases the stability, i.e. decreases the photosensitivity of amlodipine besylate.

The effect of hydrodistillation techniques on yield, kinetics, composition and antimicrobial activity of essential oils from flowers of Lavandula officinalis L.

The essential oils from flowers of Lavandula officinalis L. (L. officinalis L.= L. angustifolia Mill.) were obtained by two hydrodistillation techniques: standard (technique I) and modified (technique II) Clevenger hydrodistillation. The yield, hydrodistillation kinetics, composition and antimicrobial activity of essential oils were investigated. The higher yield of oil was obtained by hydrodistillation technique II. The new analytical hydrodistillation kinetics model of essential oil from Lavandulae flowers was defined. The essential oil composition was analyzed by gas chromatography–mass spectroscopy (GC–MS). There were differences in chemical compositions of the oils obtained by different techniques. Antimicrobial activity of essential oil obtained by technique I and II against Salmonella enteritidis, Klebsiella pneumoniae, Staphylococcus aureus, Enterococcus faecalis, Candida albicans and Aspergillus niger was the same, while the activity against Escherichia coli and Pseudomonas aeruginosa was slightly different.

Fourier-Transform IR spectroscopic investigations of Cobalt(II)–dextran complexes by using D2O isotopic exchange

Co(II) ion complexes with reduced low-molar dextran (RLMD) derivatives Mw= 5000 − 6000 g/mol, their FTIR spectroscopic characterization, as well as the spectra-structure correlation was investigated in this work. The samples of Co(II) ion complexes with RLMD were deuterated (D2O, Merck) for 2 h, at room temperature, in vacuum. FTIR spectra as an average of 40 scans were recorded at room temperature in the range 4000 – 400 cm−1. FTIR investigation of Co(II)–RLMD complexes by D2O isotopic exchange proved to be a very sensitive method for determining OH group coordination and is related to the hydrogen bond strength. The results of our investigation point to the dextran and their complexes with Co(II) ion are crystalline hydrate molecules. The correlation of physicochemical, spectrophotometric and spectroscopic investigations of these complexes, coordination chemistry of Co(II) ion and the structure of an exopolysaccharide chain are proposed different model structures of the synthesized Co(II) complexes.

The protection of Nifedipin from photodegradation due to complex formation with β-cyclodextrin

AbstractThe inclusion complex β-cyclodextrin:nifedipin was prepared in solid state by coprecipitation with 1:1 mol ratio. The structure of the obtained complex and nifedipin was characterized by use of X-ray diffraction (XR), infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), and differential scanning calorimetry (DSC) methods. The photodegradation of nifedipin and the β-cyclodextrin:nifedipin inclusion complex in solid state was monitored under natural daylight by infrared spectroscopy, whereby the free nifedipin degraded four to five times faster than the complexed nifedipin. The photodegradation products of both free and complexed nifedipin, formed during irradiation at 350 nm (with corresponding energy flux of 18 W m−2) were monitored by liquid chromatography during various time intervals. The speed of formation of nitroso- and nitro-phenyl derivatives by nifedipin irradiation was significantly higher than those of complexed nifedipin irradiation, which indicates its increased photostability in the inclusion complex. The effect on this property is significant because it contributes both to the improvement of the therapeutic effect of nifedipin and to the safer application thereof.

Synthesis and spectroscopic characterization of copper(H)-dextran complexes

Synthesis of stable copper(II) complexes with reduced dextran derivatives can be realized with low molar polysaccharides of an average molar mass 5000 g mol−1. A copper(II) content of 4–20% is achieved at pH 7–8 and at the boiling point. Copper(II) complex formation with dextran was analyzed by spectrophotometric VIS methods. The IR spectra of copper(II) complexes with dextran were analyzed to find the most stable conformation of the glucopyranose unit. The ESR parameters of the spectrum indicate a square-planar coordination of the Cu(II) ion with four oxygen ligand atoms in the same plane. Copper deficiency causes a number of pathological states [1]. In both human and veterinary medicine, commercial copper preparations based on dextran and its derivatives are used for such purposes [2]. According to the literature data, dextran has the ability of complex formation with various biometals (Zn, Fe, Co, Ca, and Mg) [3–6]. Iron complexes with different polysaccharides have special importance and they have been described in detail [7]. Synthetic procedures for the complex formation of Cu(II) with polysaccharides, including dextran, are described in scientific and patent literature [8]. However, literature data on the complex formation possibility of the Cu(II) ion with dextran derivatives are scarce.

The canal inclusion complex of allicin with carbamide: Preparation, characterization and microbiological investigation

The carbamide:allicin canal inclusion complex was prepared in the solid state. The structure of the complex obtained was characterized by x-ray crystallography, infrared spectroscopy and thermogravimetric analysis. The microbiological activities of the inclusion complex and allicin were investigated and compared with respect to fungi (Candida albicans ATCC 10231 and Aspergillus niger ATCC 16404) and bacteria (Staphylococcus aureus ATCC 6538, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 9027). It was found that the inclusion complex inhibited the growth of bacteria and fungi for a longer period than allicin in the free state.