Biomedical subjects

Ksenija Radotić

Publications and source records attributed to Ksenija Radotić.

4 recordsLinked to original sources

PubMed2006

Deconvolution of fluorescence spectra: contribution to the structural analysis of complex molecules.

Fluorescence spectroscopy is a sensitive analytical tool in the studies of both simple and complex molecular structures. In complex molecules, however, determining the number and position of components may give a specific insight into the structure, complementary to the other analytical techniques. We applied log-normal model to analyze fluorescence of simple monofluorophore molecule. In order to analyze spectra where both fluorophores and Raman emission bands were present, we developed a method obtained by combination of the symmetric, Gaussian, for Raman and asymmetric, log-normal model, for fluorescence, applicable to the molecules of different complexity. Technically, for each sample we varied excitation wavelength with 5 nm step and recorded the corresponding emission spectra. They were subsequently used for component analysis. Position of each component was plotted against the excitation wavelength. Applying this approach we could identify minimal number of components having stable positions, while their approximate probability density (APD) in a spectral series was correlated with the probable number of fluorophores in the molecule. The method was tested on molecules containing different number of fluorophores: monomers involved in the synthesis of plant polymer lignin-coniferyl alcohol (one fluorophore), ferulic acid (two fluorophores) and on lignin model compound produced from these monomers (many fluorophores). All investigated species belong to benzene-substituted class of compounds, and it is reasonable to assume that they have similar fluorescence band contour. We also report the results of environmental scanning electron microscopy (ESEM) studies showing multilayered dehydrogenative polymer (DHP) structure, in order to show complexity of the polymer. Our results present complementarity of these two approaches in the structural studies of the lignin model compound.

Biopolymers↗

PubMed2006

Component analysis of the fluorescence spectra of a lignin model compound.

In order to test whether lignin fluorescence originates from discrete fluorophores, fluorescence emission spectra of the lignin model dehydrogenative polymer (DHP) were analyzed by the band deconvolution method and time-resolved analysis of both the excitation and emission spectra. Two series of 22 fluorescence emission spectra of DHP in chloroform/methanol (3:1, v/v) solution, and as a solid suspension in water, were deconvoluted into three fluorescence and one Raman Gaussian components. Emission spectra were obtained by stepwise variation of the excitation wavelength from 360 to 465 nm. Deconvolution was performed by nonlinear fitting of all three Gaussian parameters: area, width and position. Position of all components in a series was treated as a random variable and its approximate probability distribution (APD) calculated from a series of histograms with increasing number of abscissa intervals. A five peak multimodal APD profile was obtained for both series of DHP emission spectra. The mean fluorescence lifetime varied with wavelength both in the emission and the excitation decay-associated spectra (DAS), where four kinetic components were resolved. The shapes of the excitation spectra of the four components were quite different and gradually shifted bathochromically. The multicomponent nature of the DHP emission spectra along with the changes in the mean fluorescence lifetime and the form of the excitation DAS of the four components give evidence of the heterogeneous origin of fluorescent species emitting in the visible.

Chloroform↗

PubMed2005

New insights into the structural organization of the plant polymer lignin.

The organizational features of lignin structure and the mechanism of its synthesis have significant implications for the response of the plant to stress. It was unknown whether the enzymic formation of lignin in the cell wall is an uncontrolled process or finely regulated in time and space. In vitro scanning tunneling microscopy (STM), atomic force microscopies (AFM), near-field scanning optical microscopy (NSOM). and the novel environmental scanning electron microscopy (ESEM) imaging studies of the lignin model compounds have directly shown its highly ordered structure and elucidated its modular and fractal organization. Direct evidence was presented for the existence of strong intermolecular forces responsible for holding lignin globules together in highly ordered structures. Fractal analysis was applied as a theoretical approach, to show regularity and modular organization of lignin. Surface chemistry studies of the lignin monolayer reveal intrinsic properties that may be a key to osmotic pressure and cell size control mechanism in the higher plant cells. The obtained data contribute to the explanation of the mechanisms of cell wall synthesis in vivo.

Cell Size↗

PubMed2005

Changes in Chenopodium rubrum seeds with aging.

We studied antioxidative system, germination, growth, and flowering in vitro in Chenopodium rubrum seeds of different ages. Peroxidase, superoxide dismutase, and catalase activity, as well as glutathione status, were determined in 2.5-h imbibed seeds. Germination was tested under controlled conditions. Growth and flowering of plants were tested in vitro. The enzyme activities and glutathione content were higher in younger seeds. Germination declines with seed age. Plants derived from older seeds were smaller, and flowering percentage was lower compared to plants derived from younger seeds. Gibberellic acid reduced the difference in growth and flowering between plants derived from seeds different in age.

Aging↗