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M Jeremić

Publications and source records attributed to M Jeremić.

16 recordsLinked to original sources
PubMed2001

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.

Fractals↗
PubMed2000

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.

Cell Wall↗
PubMed1999

Temperature dependence of delayed fluorescence induction curve transients.

The temperature dependence of delayed millisecond fluorescence (DF) induction curve transients was investigated. The transients were obtained by keeping intact maize leaf segments in the dark for 30 to 300 s before illumination. The temperature dependence of DF induction revealed abrupt changes in activation energy of the recombination process. Those changes highly overcome the lowest energy barriers for certain types of chemical reactions, implying significant possible alterations in the DF mechanism itself. On the other hand, the particular transients responses expressed some specificities. Both the electrochemical gradient controlled changes, and the temperature induced changes contribute to it.

Darkness↗
PubMed1998

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.

Kinetics↗
PubMed1995

[Prevention of thromboembolic disease in gynecologic surgery].

We presented two groups of patients gynecologically operated and examined in a five year period; the first group of 11536 patients was under thromboembolic protection, whereas the second group of 8532 patients was without thromboembolic protection. Protective measures concerning thromboembolic disease were carried out by applying elastic stockings 24 hours before operation and by early post-operative getting up from bed. Low-molecular dextran was applied before operation as well as during the operation in the amount of 500-1000 ml. In risky patients with varicosities, recidive thrombophlebitis and cardiovascular diseases, we applied small doses of heparin subcutaneously two hours before the operation and after the operation every eight hours five days long. With such prevention of thromboembolic disease in gynecologic surgery, we achieved very favorable effects in reducing mortality to 0.05% concerning the operated, while it amounts to 0.3% in those who were without this kind of protection.

Female↗
PubMed1994

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.

Hydrogen-Ion Concentration↗
PubMed1993

Irreversible structural changes in thylakoid membranes at high temperatures. Detection by luminescence and EPR.

The character of structural changes in thylakoid membranes caused by temperature variation was investigated. Experiments were performed on maize leaf segments in vivo and in a closed temperature cycle 24-50-24 degrees C. Two biophysical methods were used for detection: luminescence and EPR. Arrhenius plots of delayed fluorescence (DF) versus reciprocal temperature revealed two break points, T1 and T2. The MeFASL (10.3) spin probe monitoring properties close to membrane surface detected only T2 transition temperature. The results were interpreted in terms of a fluidity change which starts in a membrane centre at T1 and gradually displaces toward the surface at T2. The T1 and T2 transition temperatures are sensitive to pretreatment history of plants indicating that high temperature and drought-induced membrane alterations are irreversible. Activation energies E1, E2 and E3 were determined for temperature regions below T1 between T1 and T2, and above T2, respectively. The E1 and E3 activation energies showed greater sensitivity to stress than did E2. There are some indications that the DF method could be used to screen temperature sensitive and temperature resistant genotypes.

Biophysical Phenomena↗
PubMed1981

[Partial resection of the liver in the treatment of echinococcosis].

On the basis of reports' reviewed and authors' experience, in 118 patients with hydatid disease of the liver, 15 of whom (12%) have been treated by partial resection of the liver, it can be concluded that: - Partial resections of the liver represents a radical surgical procedure in the treatment of liver hydatidosis, - A surgical treatment of the liver hydatid disease requires a total extirpations of echinococcus cysts, as well as irreversibly damaged liver tissue itself, - These resections' methods should be carried out in definite indications, - In comparison with other, especially more conservative (surgical) procedures, resections reduce complications and shorten a hospitalization, - Because of technical difficulties concerning respective surgical procedures (in particular left or right lobectomy), one should always have in mind the relative benignity of the hydatid disease, operative risk, and that other less aggressive surgical methods exist. - Surgical departments applying these methods have to employ sufficient quantity of adequate blood, well trained and experienced surgeons and equipment.

Adolescent↗
PubMedDate not supplied

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.

Ascorbic Acid↗