Dalibor L. Sekulić

Nonlinear ionic pulses along microtubules

Microtubules are cylindrically shaped cytoskeletal biopolymers that are essential for cell motility, cell division and intracellular trafficking. Here, we investigate their polyelectrolyte character that plays a very important role in ionic transport throughout the intra-cellular environment. The model we propose demonstrates an essentially nonlinear behavior of ionic currents which are guided by microtubules. These features are primarily due to the dynamics of tubulin C-terminal tails which are extended out of the surface of the microtubule cylinder. We also demonstrate that the origin of nonlinearity stems from the nonlinear capacitance of each tubulin dimer. This brings about conditions required for the creation and propagation of solitonic ionic waves along the microtubule axis. We conclude that a microtubule plays the role of a biological nonlinear transmission line for ionic currents. These currents might be of particular significance in cell division and possibly also in cognitive processes taking place in nerve cells.

Symbolic computation of some new nonlinear partial differential equations of nanobiosciences using modified extended tanh-function method

Abstract By means of computerized symbolic computation and a modified extended tanh-function method the multiple travelling wave solutions of nonlinear partial differential equations is presented and implemented in a computer algebraic system. Applying this method, we consider some of nonlinear partial differential equations of special interest in nanobiosciences and biophysics namely, the transmission line models of microtubules for nano-ionic currents. The nonlinear equations elaborated here are quite original and first proposed in the context of important nanosciences problems related with cell signaling. It could be even of basic importance for explanation of cognitive processes in neurons. As results, we can successfully recover the previously known solitary wave solutions that had been found by other sophisticated methods. The method is straightforward and concise, and it can also be applied to other nonlinear equations in physics.

Study of NiFe2O4 and ZnFe2O4 Spinel Ferrites Prepared by Soft Mechanochemical Synthesis

Two types of ferrites, NiFe2O4 and ZnFe2O4 were prepared by soft mechanochemical synthesis. XRD and Raman spectroscopy were used to characterize the ferrite samples. On the basis of magnetic measurements was confirmed that the degree of inversion changes after sintering. The conduction activation energy, ΔE was determined by fitting the DC conductivity data with the Arrhenius relation. The effect of temperature on impedance parameters was studied using an impedance analyzer in a wide frequency range (100 Hz - 10 MHz). It was observed that the impedance spectra of NiFe2O4 and ZnFe2O4 ferrites include both grain and grain boundary effects.

Actin filaments as the fast pathways for calcium ions involved in auditory processes

We investigated the polyelectrolyte properties of actin filaments which are in interaction with myosin motors, basic participants in mechano-electrical transduction in the stereocilia of the inner ear. Here, we elaborated a model in which actin filaments play the role of guides or pathways for localized flow of calcium ions. It is well recognized that calcium ions are implicated in tuning of actin-myosin cross-bridge interaction, which controls the mechanical property of hair bundle. Actin filaments enable much more efficient delivery of calcium ions and faster mechanism for their distribution within the stereocilia. With this model we were able to semiquantitatively explain experimental evidences regarding the way of how calcium ions tune the mechanosensitivity of hair cells.

Protein-based nanobioelectronics transmission lines

Extensive research is underway to understand and exploit the interface between biomacromolecules and integrated systems. An ideal biological candidate for use in nanoscale electronic devices is the microtubule, an essential component of the eukaryotic cytoskeleton, which has been shown to be electrically conductive. In this paper, we theoretically analysed the possible use of microtubules as protein structure for building biomolecular nanoscale nonlinear transmission lines in the context of the polyelectrolyte character of these cytoskeletal filaments. We verify these hypotheses both analytically and computationally through a quantitative electrical model based on the atomic resolution structures of the key functional proteins. Each tubulin dimmer protein is an electric element with a capacitive, inductive, and resistive property due to the molecular structure of microtubules.

Role of nonlinear localized Ca2+ pulses along microtubules in tuning the mechano–sensitivity of hair cells

This paper aims to provide an overview of the polyelectrolyte model and the current understanding of the creation and propagation of localized pulses of positive ions flowing along cellular microtubules. In that context, Ca(2+) ions may move freely on the surface of microtubule along the protofilament axis, thus leading to signal transport. Special emphasis in this paper is placed on the possible role of this mechanism in the function of microtubule based kinocilium, a component of vestibular hair cells of the inner ear. We discuss how localized pulses of Ca(2+) ions play a crucial role in tuning the activity of dynein motors, which are involved in mechano-sensitivity of the kinocilium. A prevailing notion holds that the concentration of Ca(2+) ions around the microtubules within the kinocilium represents the control parameter for Hopf bifurcation. Therefore, a key feature of this mechanism is that the velocities of these Ca(2+) pulses be sufficiently high to exert control at acoustic frequencies.

An improved electrical model of microtubule as biomolecular nonlinear transmission line

The manner in which microtubules, the essential cellular biopolymers, handle and process electrical signals is still uncompleted puzzle. In this paper, we have elaborated some new electrodynamic properties of these protein-based nanotubes, specifically, their ability to conduct ionic currents. In that context, it has been established an improved electrical model of microtubule as biomolecular nonlinear transmission line. We described the basic nanoscale electric elements of model and estimated the corresponding parameters, stressing the particular importance of tubulin C-termini. The properties of the localized electric nanocurrent of positive ions and accompanying voltage along a microtubule are analytically and numerically analyzed here.

Soft mechanochemical synthesis and characterization of nanodimensional spinel ferrites

NiFe2O4 and ZnFe2O4 ferrites have been prepared by soft mechanochemical synthesis. The sintered samples were analyzed by XRD and Raman spectroscopy. Investigation of the magnetization as a function of magnetic field confirms an expected change of the degree of inversion in the spinel structure with the sintering. Impedance spectroscopy on the sintered pellets of ferrites was performed in the wide frequency range (100 Hz-10 MHz) at different temperatures using an Impedance/Gain-Phase Analyzer (HP-4194).

Study of Nanodimensional Spinel Ni 0.5 Zn 0.5 Fe 2 O 4 Ferrite Prepared by Mechanochemical Synthesis

The nanodimensional Ni0.5Zn0.5Fe2O4 ferrites were prepared from mixture of NiO/ZnO/α-Fe2O3 and Ni(OH)2/Zn(OH)2/Fe(OH)3 powders by (soft) mechanochemical synthesis after 5 and 10 h of milling time. The XRD of the sample obtained after 10 h milling time shows single phase cubic spinel structure. TEM analysis revealed that all samples are composed of more or less agglomerated nanosize particles. The average size of nano crystallites is ~20 nm. The degree of the cation inversion of NZF is estimated for spinel fraction in all samples by Rietveld analysis. In the Raman spectra are observed all of first-order active modes. In the spectra of the single phase “hydroxide” samples it is visible that the energy position and intensity of modes is dependent on the composition and cation distribution. It was shown that the modes in Raman spectra of nickel-zinc ferrite that originate from vibrating of different cations could be clearly distinguished. From the ratio of intensities of the A 1g-type Raman modes, it is possible to estimate the inversion of cations. The Mossbauer spectra were fitted by several subspectra and according to known subspectral areas of both iron sites the degree of inversion was calculated, also. The cation inversion is λ = 0.36(3) for ferrite sample obtained from the mixture of appropriate hydroxide for 10 h milling.

Structural, Electrical Conduction and Dielectric Studies of Mechano-synthesized Manganese Nanoferrite

In this paper, we have investigated the structural, electrical and dielectric properties of nanostructured manganese ferrite of 49 nm grain size, synthesized by mechanochemical technique. The structural studies have been made by using the X-ray diffraction, TEM and Raman spectroscopy, which confirmed the formation of spinel phase and nanostructure of prepared MnFe2O4. The electrical measurements were made in the frequency range 102–106 Hz at different temperatures between 25 and 175 °C. The temperature dependence of DC conductivity satisfies the Arrhenius relation, which indicates the semiconducting nature of sintered sample. The drift mobility was estimated from the DC conductivity measurement and it has been found that the temperature dependent. Analysis of the experimental AC electrical conductivity data shows that correlated barrier hopping mechanism is the most probable mechanism of conduction for prepared manganese ferrite. The dielectric permittivity and loss tangent of MnFe2O4 decrease with increase in frequency, while these parameters increase with increasing temperature. Such dielectric behavior is explained by using the mechanism of polarization process, which is correlated to hopping of charge between Fe2+ and Fe3+ ions as well as between Mn2+ and Mn3+ ions at octahedral sites.