Biomedical subjects

Stefan Jurga

Publications and source records attributed to Stefan Jurga.

9 recordsLinked to original sources

PubMed2006

A comparative study of water distribution, free radical production and activation of antioxidative metabolism in germinating pea seeds.

The aim of this study was to investigate whether there is a relationship between hydration of the embryo axes and cotyledons and the resumption of the oxidative metabolism in both organs of germinating seeds of pea (Pisum sativum L. cv. Piast). Nuclear magnetic resonance ((1)H-NMR) spectroscopy and imaging were used to study temporal and spatial water uptake and distribution in pea seeds. The observations revealed that water penetrates into the seed through the hilum, micropyle and embryo axes, and cotyledons hydrate to different extents. Thus, inhomogeneous water distribution may influence the resumption of oxidative metabolism. Electron paramagnetic resonance (EPR) measurements showed that seed germination was accompanied by the generation of free radicals with g(1) and g(2) values of 2.0032 and 2.0052, respectively. The values of spectroscopic splitting coefficients suggest that they are quinone radicals. The highest content of free radicals was observed in embryo axes immediately after emergence of the radicle. Glutathione content decreased during the entire germination period in both embryo axes and cotyledons. A different profile was observed for ascorbate, with significant increases in embryo axes, coinciding with radicle protrusion. Electrophoretic analysis showed that superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11), dehydroascorbate reductase (DHAR, EC 1.8.5.1) and glutathione reductase (GR, EC 1.6.4.2) were present in dry seeds and were activated later during germination, especially in embryo axes. The presence of all antioxidative enzymes as well as low molecular antioxidants in dry seeds allowed the antioxidative machinery to be active as soon as the enzymes were reactivated by seed imbibition. The observed changes in free radical levels, antioxidant contents and enzymatic activities in embryo axes and cotyledons appear to be more closely related to metabolic and developmental processes associated with preparation for germination, and do not correspond directly to the hydration of the tissues.

Antioxidants↗

PubMed2005

Molecular dynamics of poly(L-lactide) biopolymer studied by wide-line solid-state 1H and 2H NMR spectroscopy.

The molecular dynamics of poly(L-lactide) (PLLA) biopolymer was characterized through analyses of 1H and 2H NMR line-shapes and spin-lattice relaxation times at different temperatures. At low temperatures (e.g. 90 K), the methyl group rotation is dominant leading to a significant reduction in the proton second moment. Fast methyl group reorientation occurs at ca. 130 K. In additional to the fast methyl group rotation, hydroxyl groups start to reorient as the temperature increases further, eventually leading to the breakdown of the segments of the biopolymer chains above its glass transition temperature Tg of 323 K. The analyses of the 2H NMR line-shapes indicate that both the methyl and hydroxyl reorientations can be described by the so-called cone model, in which the former has three equilibrium positions with theta(C-D) = 70.5 degrees and phi = 120 degrees while the latter one exhibits two equilibrium positions with theta(O-D) = 78 degrees and phi = 180 degrees .

Biopolymers↗

PubMed2004

Collective and local molecular dynamics in the lyotropic mesophases of decylammonium chloride: 1H and 2H NMR study.

The collective and individual dynamics of decylammonium chloride (DACl) molecules in water environment were investigated as a function of surfactant concentration and temperature. In the presence of water the DACl forms a variety of self-assembled structures, ranging from isotropic micellar systems to lyotropic liquid crystalline phases of hexagonal, nematic, and lamellar types. In order to characterize the complex molecular dynamics that occur in the DACl-water system, we applied 1H and 2H NMR techniques that cover the whole frequency range between 1 kHz and 30 MHz. The slow molecular dynamics were studied by 1H NMR fast-field-cycling T1 measurements and pulse-frequency dependence of 2H NMR transverse relaxation time, performed by means of the Carr-Purcell-Meiboom-Gill sequence. We detected a well-expressed contribution of order director fluctuations, i.e., layer undulations, with characteristic omega(-1)(L) frequency dependence of T(-1)(1) in the lamellar phase. Its presence indicates a relatively weak impact of interactions between neighboring DACl layers. The frequency dependence of proton T(-1)(1) in the hexagonal phase exhibits a different type of frequency dispersion, T(-1)(1) approximately omega(-1.32)(L). The increase in the exponent is explained with the quasi-one-dimensional character of fluctuations in elongated cylinders. Further, the T1 and T2 relaxation times of deuterons selectively attached to the C2 and C7 segments of the hydrocarbon chains of DACl were measured at a Larmor frequency of 30.7 MHz, providing quantitative information about local molecular dynamics.

Journal Article↗

PubMed2004

Studies of gelation process investigated by fast field cycling relaxometry and dynamical rheology: the case of aqueous low methoxyl pectin solution.

The Fast Field Cycling Relaxometry and the dynamical rheology were applied to study the gelation process in aqueous low methoxyl pectin solution in the presence of divalent cations from the calcium chloride. The model-free approach to the analysis of 1H NMRD data was used to separate the information on the static and dynamic behaviour of the system provided by the dispersion profiles of the systems tested. Mechanical spectroscopy was applied as a complementary method to probe the network formation. The structural changes were most pronounced for the concentration of calcium chloride between 10 and 15 mM (the static parameter beta was found to vary from 0.936 x 10(7) to 1.27 x 10(7) 1/s2) revealing the sol-gel transition on visual inspection. The presence of the gel network was confirmed by the rheological measurements. All mechanical spectra exhibited the gel like character, and the solid like response was more evident at higher concentrations of calcium cations. The mean correlation time increased with increasing salt concentration, but remained unchanged for the concentrations above 15 mM. The dynamical changes were most significant at the phase transition from the sol to the gel state.

Calcium Chloride↗

PubMed2004

Molecular dynamics of tert-butyl chloride confined in CPG studied by NMR.

The molecular dynamics of tert-butyl chloride (TBC) confined to Controlled Pore Glass matrices of 25 and 7.5 nm were investigated by measuring NMR linewidths, lineshapes, and 1H and 2H spin--lattice relaxation times. The behaviour of confined TBC can be explained assuming that the guest molecules form two distinct phases; the surface-affected phase, composed of molecules located at the pore surface, and the bulk-like phase located at the centre of the pores. The bulk-like component of confined TBC, at the temperatures corresponding to the phase III, is characterized by two dynamically different subphases.

Journal Article↗

PubMed2002

1H and 13C NMR studies of molecular dynamics in the biocopolymer of glycolide and epsilon-caprolactone.

Copolymers of glycolide and epsilon-caprolactone were studied using differential scanning calorimetry and solid-state NMR. The variation of the T1 relaxation time with temperature reflects local disorder and can be quantified in terms of the distribution of correlation times predicted by the Davidson-Cole model. T, relaxation is dominated by trans-gauche isomerisation, with an activation energy of 34-35 kJ mol(-1).

Biocompatible Materials↗

PubMed2002

A comparison between the crystal and solution structures of Escherichia coli asparaginase II.

The small angle X-ray scattering (SAXS) pattern of the homotetrameric asparaginase II from Escherichia coli was measured in solution in conditions resembling those in which its crystal form was obtained and compared with that calculated from the crystallographic model. The radius of gyration measured by SAXS is about 5% larger and the maximum dimension in the distance distribution function about 12% larger than the corresponding value calculated from the crystal structure. A comparison of the experimental and calculated distance distribution functions suggests that the overall quaternary structure in the crystal and in solution are similar but that the homotetramer is less compact in solution than in the crystal.

Asparaginase↗

PubMedDate not supplied

High-resolution solid-state 13C NMR studies of poly[(R)-3-hydroxybutyric] acid.

Solid poly[(R)-3-hydroxybutyric] acid was examined by high-resolution 13C MAS NMR, differential scanning calorimetry and infrared spectroscopy. The 13C methyl group resonance consists of three components: the rigid amorphous phase, the crystalline phase and the mobile amorphous phase. Spectral deconvolution, using the Lorentz function, reveals the relative amounts as 62% crystalline and 38% amorphous at 333 K, and 42% crystalline, 40% pure amorphous and 18% beta-orthorhombic at 413 K. NMR indicates a large difference in molecular mobility between the crystalline and amorphous regions of the sample. Infrared spectroscopy shows that the stretching at 1725 cm(-1) (characteristic of the alpha-form) comes from the crystalline region, and the bands at 1744 cm(-1) (characteristic of the beta-form) and 1800 cm(-1) come from the amorphous region.

Calorimetry, Differential Scanning↗

PubMedDate not supplied

NMR studies of restricted diffusion in lyotropic systems.

Tortuosity, 1/alpha, and surface-to-volume ratio, S/V, were determined in aqueous solutions of decylammonium, dodecylammonium and tetradecylammonium chlorides of various concentrations by measuring the apparent diffusion coefficient of water, D(app)(delta). This was found to be much smaller than in the bulk state. Such restricted diffusion is interpreted in terms of the Mitra model, where D(delta) depends on diffusion time and is controlled primarily by S/V. The samples exhibit lamellar (L), hexagonal (H) and isotropic (I) liquid crystalline phases. We observed changes in S/V upon phase transition. In the lamellar and hexagonal phases, the system is ordered, resulting in relatively small S/V ratios, compared to the micellar-isotropic phase. We did not observe a dependence on the diffusion time, delta, in the isotropic phase, because the duration of the experiment was not sufficiently short to observe the change from D(app)(delta) to D(eff). We observed the effective diffusion coefficient of water, which directly probes the tortuosity of the system. The S/V ratios were obtained by fitting the Mitra model, using known values of the bulk water diffusion coefficients, and the assumption that D(app) --> D0 for delta --> 0. S/V is correlated with the type of structure, increasing on transition to the isotropic phase and decreasing on transition to other phases. The change in tortuosity is small, but slightly larger for the isotropic phase.

Amines↗