Browsing by Author "Kozak, Maciej"
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Item Clear distinction between CAC and CMC revealed by high-resolution NMR diffusometry for a series of bis-imidazolium gemini surfactants in aqueous solutions(RSC, 2018-11) Szutkowski, Kosma; Kołodziejska, Żaneta; Pietralik, Zuzanna; Zhukov, Igor; Skrzypczak, Andrzej; Materna, Katarzyna; Kozak, MaciejThe aggregation behavior in the transition region was studied for a series of dicationic surfactants 3,3′-[α,ω-(dioxaalkane)]bis(1-dodecylimidazolium)dichlorides with varied spacer length from two to twelve carbon atoms. We employed Nuclear Magnetic Resonance diffusometry and Bayesian DOSY analysis to obtain the aggregate size distribution in the transition region. The critical concentrations CC were independently obtained from surface tension, electric conductivity, UV-Vis and NMR methods. The micelle aggregation numbers were estimated from the self-diffusion coefficients and were independently confirmed using steady-state fluorescence quenching. The morphology of the aggregates was characterized by small-angle scattering of synchrotron radiation and molecular dynamics simulations. The obtained CC values are identified as critical aggregation concentrations CAC. A broad transition region was observed, and stable micelles were obtained at much higher concentrations than CAC. The accurate CMC values could not be identified for the systems in the study. We indicated that the distribution of aggregate size becomes small and the system becomes homogeneous at much larger concentrations than CAC (typically 15–20 mM). The existence of a slow exchange between two environments, an aggregate and aqueous environment, was confirmed by 1H NMR and 2D HSQC NMR spectroscopy.Item The effect of ionizing radiation on chloramphenicol(Springer Netherlands, 2006) Marciniec, Barbara; Stawny, Maciej; Kozak, Maciej; Naskrent, MarekThe effect of ionizing radiation on the physicochemical properties of chloramphenicol in solid state has been studied. The compound was e-beam irradiated with doses from the range 25–400 kGy and the possible changes were detected in the organoleptic methods (colour, form, odour, solubility and clarity), by SEM observations, X-ray, chromatography (TLC), spectrophotometry (UV, IR, EPR) and thermal (DSC) methods. No significant changes relative to the unirradiated sample were observed as a result of irradiation with the dose of 25 kGy – a standard dose for radiation sterilization, besides free radicals generation. Higher doses were found to produce a change in colour, increase in absorbance (UV), changes in the XRD spectra and appearance of products of radiolysis. The presence of the radiolysis products was confirmed by the TLC method, indirectly by DSC showing a decrease in the melting point from 0.2 to 4.5°C and enthalpy from 3.8 to 23.3 J g–1, respectively. A linear relationship was obtained between the irradiation dose (25–400 kGy) and the melting point of chloramphenicol, characterised by the correlation coefficient r=0.9968. The EPR signal intensity increased with increasing dose of irradiation and the lifetime of the free radicals was longer than 6 months. No changes were detected in SEM and IR spectra. As follows from our results, the DSC method is most suitable for a fast monitoring of the drugs subjected to sterilization by irradiation as it permits detection of changes occurring even on irradiation with low doses and their quantitative description.Item Thermal study of four irradiated imidazoline derivatives in solid state(Springer Netherlands, 2007) Marciniec, Barbara; Kozak, Maciej; Naskrent, Marek; Dettlaff, Katarzyna; Ogrodowczyk, Magdalena; Stawny, Maciej; Wachowski, LeszekFour imidazoline derivatives: antazoline (AN), naphazoline (NN), tymazoline (TM), xylometazoline (XM), in the form of hydrochlorides in solid phase have been subjected to high energy e-beam irradiation from an accelerator (10 MeV) at a dose varied from 25 to 200 kGy. The effects of the irradiation have been assessed by DSC, X-ray diffraction, FTIR, EPR and TLC. The standard sterilisation dose of 25 kGy has been found to produce changes in the properties of one derivative (XM), two other ones (AN and TM) have been found sensitive to doses >100 kGy, whereas NN has been resistant to irradiation in the whole range studied (25–200 kGy). EPR results indicated that the changes taking place in the therapeutic substances studied are related to radical formation. The irradiation induced changes in colour, a decrease or increase in the melting point, changes in the XRD pattern, small changes in the shape of FTIR peaks and the presence of radiolysis products. The XM compounds cannot be sterilised by irradiation because of the radiation induced changes in its physico-chemical properties.