Enhanced electrochemical response of carbon quantum dot modified electrodes.

A glassy carbon electrode (GCE) was surface-modified with carbon quantum dots (CQDs) and applied for the effective enhancement of the electrochemical signal for dopamine and uric acid determination. CQDs were prepared from graphite by a green modification of the Hummers method. They were characterized by FTIR-ATR, XPS, solid-state NMR, fluorescence and Raman spectroscopies. TPD-MS analysis was applied to characterize the functionalization of the surface. The CQDs were assembled on the glassy carbon electrode by adsorption because of the large number of carboxy groups on their surface warrants effective adsorption. The modified GCE exhibits a sensitivity that is almost 10 times better than of the bare GCE. The lower limits of detection are 1.3µM for uric acid and 2.7µM for dopamine.

Xylem parenchyma cell walls lack a gravitropic response in conifer compression wood.

MAIN CONCLUSION: Cell wall fluorescence and immunocytochemistry demonstrate that xylem parenchyma cell walls do not show changes in structure and composition related to gravitropic response comparable to those of tracheids, even when they have lignified secondary cell walls. Tracheid cell walls in compression wood have altered composition and structure which generates the strain responsible for correction of stem lean as part of the gravitropic response of woody plants. Xylem parenchyma cell walls vary among conifer species and can be lignified secondary walls (spruce) or unlignified primary walls (pine). It can be expected that xylem parenchyma with lignified secondary cell walls might show features of compression wood comparable to those of tracheids that have a similar type of cell wall. A comparison of xylem parenchyma cell walls in normal and compression wood in species with lignified and non-lignified parenchyma cell walls provides a unique opportunity to understand the process of reaction wood formation in conifers. Using both UV/visible fluorescence microscopy of cell wall fluorophores and immunocytochemistry of galactan and mannan epitopes, we demonstrate that xylem parenchyma cell walls do not show the changes in composition and structure typical of compression wood tracheids. Adjacent cells of different types but with similar cell wall structure can undergo cell wall developmental changes related to support or defence functions independent of their neighbours. Tracheids are sensitive to gravitropic signals while xylem parenchyma cells are not.

Further in vitro evaluation of antiradical and antimicrobial activities of phytol.

The antiradical activity of phytol was evaluated by electron paramagnetic resonance towards hydroxyl radical (·OH), superoxide anion radical (·O2(-)), methoxy radical (·CH2OH), carbon-dioxide anion radical (·CO2(-)), as well as towards nitric-oxide radical (·NO) and 2,2-diphenyl-1-picrylhydrazyl (·DPPH) radical. It reduced the production of all tested radicals showing more promising activity against ·CO2(-), ·CH2OH and ·DPPH radicals (56%, 50% and 48%, respectively) in comparison with ·NO, ·O2(-) and ·OH radicals (38%, 23% and 15%, respectively). The antimicrobial activity of phytol was evaluated by the microdilution method against eight bacterial and eight fungal strains. To varying degrees, it was proven to be active against all tested bacteria and fungi (MIC 0.003-0.038 mg/mL and MBC 0.013-0.052 mg/mL, MIC 0.008-0.016 mg/mL and MFC 0.090-0.520 mg/mL, respectively). According to the obtained results, medical foods containing phytol may support development of new therapies for heart disease.

Fluorescence lifetime imaging of lignin autofluorescence in normal and compression wood.

Wood cell walls fluoresce as a result of UV and visible light excitation due to the presence of lignin. Fluorescence spectroscopy has revealed characteristic spectral differences in various wood types, notably normal and compression wood. In order to extend this method of characterising cell walls we examined the fluorescence lifetime of wood cell walls using TCSPC (Time-Correlated Single Photon Counting) as a method of potentially detecting differences in lignin composition and measuring the molecular environment within cell walls. The fluorescence decay curves of both normal and compression wood from pine contain three exponential decay components with a mean lifetime of τm = 473 ps in normal wood and 418 ps in compression wood. Lifetimes are spatially resolved to different cell wall layers or cell types where individual lifetimes are shown to have a log-normal distribution. The differences in fluorescence lifetime observed in pine compression wood compared to normal wood, are associated with known differences in cell wall composition such as increased p-hydroxyphenyl content in lignin as well as novel deposition of ß(1,4)-Galactan. Our results indicate increased deposition of lignin fluorophores with shorter lifetimes in the outer secondary wall of compression wood. We have demonstrated the usefulness of fluorescence lifetime imaging for characterising wood cell walls, offering some advantages over conventional fluorescence imaging/spectroscopy. For example, we have measured significant changes in fluorescence lifetime resulting from changes to lignin composition as a result of compression wood formation that complement similar changes in fluorescence intensity.

Component analysis of fluorescence spectra of thiol DAB dendrimer/ZnSe-PEA nanoparticles.

The fluorescence spectroscopy technique is an accurate method and has great utility in the interpretation of complex systems based on several emission bands. An interpretation of the system requires determination of the number, positions and intensities of the spectral components. In this work, the emission spectra of the synthesized ZnSe complex coated with O-phosphorylethanolamine (ZnSe-PEA), both with and without thiol DAB dendrimer generation 5 (S-DAB G5), were analyzed using a combination of asymmetric (log-normal) and symmetric (Gaussian) models. The method applied for the deconvolution of fluorescence spectra has proven to be very sensitive for observing the stability of the ZnSe-PEA complex after binding with S-DAB. The ZnSe-PEA emission spectrum contains two components. The positions of the emission maxima of these two components are not significantly affected by the presence of S-DAB G5 in the complex, which revealed the presence of a stable complex at a pH of 7. By applying the spectral deconvolution method, strong evidence was obtained that suggested that the ZnSe-PEA complex is stable after complexation with S-DAB G5.

Levels of plant cell wall structural organization revealed by atomic force microscopy.

We used an atomic force microscope to image cell wall isolated from needles of Serbian spruce tree and that synthesized from cell wall components. We also observed the structure of lignin model polymer (DHP), as a best substitute for the natural lignin. A tendency of aggregate formation was observed in all samples. Cell wall was revealed as a laminated fibrous structure. General organization is similar in both isolated and synthesized cell wall samples, with dominating globular motifs arranged regularly as rods and forming cavities. The synthesized cell wall has a more regular structural organization than isolated cell wall. The dimensions of individual globular aggregates and pores differed between the two samples. DHP showed a similar, regular organization, with globular aggregates and holes. Globules and pores are smaller in size than the corresponding structures in both the isolated and synthesized cell walls. Such modular organization of cell walls may have a physiological role in response to the external mechanical stress caused to plant cells.

Antiproliferative effect of synthetic lignin against human breast cancer and normal fetal lung cell lines. Potency of low molecular weight fractions.

PURPOSE: Due to a lack of chemotherapeutics to efficiently control neoplastic processes, there is a need for discovering new, more efficient anticancer drugs that would distinguish malignant from normal cells. MATERIALS AND METHODS: We studied the effect of short (4 h) and long (72 h) treatment with different concentrations of the enzymatically synthesized lignin model compound (DHP) on the proliferation of two human cell lines grown in tissue culture: breast adenocarcinoma (MCF7) and normal fetal lung fibroblast (MRC5) cell lines. RESULTS: The growth of both MRC5 and MCF7 cell lines was inhibited by DHP after 4 h-treatment, while the carcinoma cell line was also sensitive to the long-term treatment with lower dose of DHP in comparison with the fetal cells. The low molecular weight DHP fractions inhibited growth of the MRC5 cells at lower concentrations compared to the treatment with all DHP fractions. CONCLUSION: The higher sensitivity to DHP of the human malignant cells compared to the normal transformed ones gives the possibility to further study DHP as a therapeutic agent.

Fractal analysis of STM images of photochemical polymer of coniferyl alcohol.

Fractal analysis was applied to images of photochemical lignin polymer obtained using scanning tunneling microscope. We studied the polymer obtained in vitro by ionic mechanism through UV radiation--induced polymerization. The analysis showed the regularity of the lignin-like polymer at different levels of organization. At the 95% confidence level, there was no significant difference in the fractal dimension between images representing different organizational levels of photochemical lignin. That means that lignin produced in in vitro conditions by photochemical mechanism of synthesis, has a fractal structural organization. The obtained values of the fractal dimension are in good agreement with the theoretically predicted value for the polyaddition and polycondensation mechanism of polymerization, known as the bulk model.

Topographical characterization and surface force spectroscopy of the photochemical lignin model compound.

By combining the results from atomic force microscopy (AFM) and environmental scanning electron microscopy (ESEM), herein we investigate properties of photochemical lignin model compounds. We provide evidence that photochemical lignin forms random, probably non-functional structures. The topography of such structures is explored using ESEM. Non-functionality of such structures is proved by AFM and atomic force spectroscopy experiments wherein the photochemical lignin functionalized tip is approached to the substrate covered with photochemical lignin. There was no evidence of existence of any kind of host-guest interaction during the approach/retraction experiments. These results provide evidence for our previously stated hypothesis that photochemical lignin polymerization may be one of the degrading effects of UV radiation to the plant cell.

A Comparative Study of Enzymatically and Photochemically Polymerized Artificial Lignin Supramolecular Structures Using Environmental Scanning Electron Microscopy.

Environmental scanning electron microscopy images of the self-assembled structures of enzymatically (DHP) and photochemically polymerized (PCP) artificial lignin are herein presented. Differences in the structural organization between DHP and PCP polymer at the supramolecular level were reported. Based on topological information, we proposed a hypothesis about possible new physiological roles of lignin in live plant cells and the ecological significance of possible in-vivo photochemical lignin polymerization. Copyright 2000 Academic Press.

Visualization of artificial lignin supramolecular structures

In this paper we are presenting the results of our environmental scanning electron microscopy (ESEM) investigation of the lignin model compound--enzymatically polymerized coniferyl alcohol, also known as dehydrogenate polymer (DHP). The goals of this study were to visualize the supramolecular organization of DHP polymer on various substrates, namely graphite, mica, and glass, and to explore the influence of substrate surface properties and associated collective phenomena on the lignin self-assembled supramolecular structure. Based on results obtained with ESEM, combined with previously published results based on scanning tunneling microscopy (STM) and electron spin resonance (ESR) technique, we looked at lignin structure ranging from a monomer on a fraction of nanometer scale to a large aggregate on a fraction of millimeter scale, therefore using six orders of magnitude range of size. Herein, we are presenting evidence that there are at least four different levels of the supramolecular structure of lignin, and that its supramolecular organization is well dependent on the substrate surface characteristics, such as hydrophobicity, delocalized orbitals, and surface-free energy.

Changes in peroxidase activity and isoenzymes in spruce needles after exposure to different concentrations of cadmium.

We studied the guaiacol peroxidase activity, isoenzyme pattern and metal content in the needles of 2-year-old spruce grown on soils supplemented with cadmium concentrations from 1 to 21 mg kg(-1). Following exposure to cadmium, an initial increase and subsequent decrease in the activity of the soluble fraction was observed. A parallel change of their isoenzyme pattern occurred. An increase of the cell wall-bound peroxidase activity under prolonged metal treatment was evident. The results obtained show that peroxidase activity and isoenzyme pattern could be used to evaluate the capacity of one part of the defense system in spruce seedlings to withstand metal stress.

Fractal analysis of STM images of lignin polymer obtained by in vitro synthesis.

Lignin, the structural polymer of the plant cell walls, is produced by free radical polymerization of phenolic alcohols, catalyzed by different peroxidases. The mechanism and the structural organization of lignin in the cell have not been completely understood. In this study we applied fractal analysis to images of lignin polymer obtained using scanning tunneling microscope. The analysis showed the regularity of the polymer at different levels of organization. According to the results obtained, at the 95% confidence level, there is no significant difference in the fractal dimension between images representing different organizational levels of lignin. In other words, lignin produced in in vitro conditions has fractal structural organization and, consequently the polymer can be expected to be regular in in vivo conditions. The value of the fractal dimension 1.929 +/- 0.021 is in good agreement with the theoretically predicted value for polyaddition and polycondensation mechanism of polymerization. The mechanism of in vivo lignin synthesis is discussed in terms of various experimental and theoretical evidences. In this paper, we could show that fractal analysis of the lignin polymer is a useful complementary approach to the experimental data collection in structural and phenomenological studies.

[Adhesion molecules in kidney diseases (part I)]. / Adhezioni molekuli u bolestima bubrega (I deo).

Adhesive molecules are (glyco)proteins of the cellular membranes. All of them have their extramembranous, transmembranous and intracytoplasmatic parts. As receptor molecules, their extracellular parts bind the specific ligand. The ligand can be found on the surface of the other cell or in the extracellular matrix (basal membranes). The following families of adhesion molecules are: cadherins, selectins, integrins and members of immunoglobuline supergene family. Different members of the same family could have different times (in ontogenesis, in adult form) and space distribution (in different tissues, different tissue structures). The contact between the cells and basal membranes with these molecules is important for cell division, maintaining the tissue architecture, polarization and function of cells, migration of cells, endo- and exo-cytosis as well as for maintaining the structure and function of basal membranes. As above stated all this is important in the occurrence morphogenesis, haemostasis, inflammation, malignant cell transformation and metastasis. This knowledge is important for the better understanding of renal diseases.

[Adhesion molecules in kidney diseases (part II)]. / Adhesioni molekuli u bolestima bubrega (II deo)]

Different adhesion molecules are involved in the maintenance of tissue architecture, morphogenesis, immunosurveillance, inflammation, tumour growth, etc. Thus, this review will be directed to the role of cadherins, selectins, integrins and members of the immunoglobuline supergene family in the pathogenesis of glomerulonephritis, acute renal failure, reaction of renal rejection, development of renal tumours, their invasion and metastases. A better understanding of the role of adhesion molecules in nephropathology may provide new aspects of treatment of different forms of renal diseases including tumours.

Spontaneous ultraweak bioluminescence in plants: origin, mechanisms and properties.

An analysis of theoretical knowledge and experimental results of ultraweak luminescence (UWL) is provided. The role of excited state of molecules and free radicals, formed in various biochemical reactions, in UWL is discussed. UWL of model reactions and in vivo systems are compared. The hypothesis of coherent electromagnetic field as a source of UWL is also discussed. Spectral, kinetic and temporal properties of UWL are summarised, as well as their connection with its origin and role in the organism. Attention is paid to recent progress in experimental methods of low-light detection. The possible use of UWL in environmental studies, selection and other applications is discussed.

[Ultrastructural changes in transplantation glomerulopathy]. / Ultrastrukturne promene transplantacione glomerulpatije.

Twenty-eight biopsy specimens were obtained from patients 3-95 months after kidney transplantation and studied by light, electron and in some cases also by immunofluorescence microscopy. Electron microscopic studies showed that the most frequent glomerular lesion was widening of lamina rata interna which is accompanied with subendothelial accumulation of finely granular material, formation of new subendothelial basement membrane and deposition of microfibrils and fine filaments. The mesangial changes were mainly those of mesangiolysis and mesangial sclerosis with deposition of mesangial matrix and microfibrils, but little cellular proliferation. Fragmented red blood cells were seen in nearly half of the patients. Arterial intimal thickening and occasionally also thrombosis produced ischaemic changes in the kidney and in the glomeruli and contributed to the process of transplant rejection.

[Electron microscopic analysis of eosinophilic renal cell carcinoma]. / Elektronosko-mikrospopska analiza eosinofilnog karcinoma celija bubrega.

Renal cell carcinoma with cytoplasmic eosinophilic globules visualized on routine histologic preparations was analyzed. Eosinophilic globules in cytoplasm of the cells in renal cell carcinoma are very rate and till today we have not heard or found in the literature an attempt to analyze and describe them and that was the aim of our study. By electron microscopy, the globules most closely resembled non-membrane bound filamentous material that normally constitutes the cytoskeleton of normal and neoplastic renal epithelium.

A study of lignin formation at the molecular level by scanning tunneling microscopy.

A scanning tunneling microscope (STM) was used to observe the temporal formation and organization of dehydrogenative polymer (DHP) synthesized from coniferyl alcohol. The images obtained elucidate this structure for the first time. The structure of DHP, as seen from STM images, shows long-range order. It appears that DHP consists of building units or modules assembled into larger assemblies called supermodules. Supermodules are interconnected into the overall lattice-like polymer structure with or without spherical regions. One module consists of about 20 monomers, while the supermodule contains about 500 monomers. Calculated molecular weights for modules and supermodules agree with DHP molecular weight distribution peaks. Samples prepared at two different pH values, 6.4 and 7.6, have the same characteristics. The results presented demonstrate that the process of lignification, even in in vitro conditions, is highly ordered, and as such contribute to our understanding of the structure of lignin, a significant constitutive and functional element of cell walls.

Effect of propagators and inhibitors on the ultraweak luminescence from maize roots.

This study has investigated the kinetics and mechanism of ultraweak luminescence in maize roots. Mannitol induced the second maximum and enhanced the main maximum of the relative intensity of luminescence from the roots. Hydroquinone and quinone enhanced the relative intensity of the luminescence. Catalase enhanced the maximum of the luminescence and changed the kinetics of the light emission. The effect of catalase on the kinetics was abolished by superoxide dismutase. Ascorbate in the presence of catalase on the kinetics was abolished by superoxide dismutase. Ascorbate in the presence of catalase reduced the luminescence maximum, but did not alter the kinetics. In the presence of catalase only, or in the combination with superoxide dismutase, or ascorbate, the luminescence intensity in the stationary phase was significantly lower compared to the control. The results support the participation of superoxide-radical, singlet oxygen, electron transfer and the role of peroxidase in the reactions generating ultraweak luminescence in the roots. Ascorbate, catalase and superoxide dismutase have a protective role in the luminescent reactions.