Biomedical subjects

Istvan Szalai

Publications and source records attributed to Istvan Szalai.

3 recordsLinked to original sources

PubMed2006

Pulsating pH-responsive nanogels.

A novel method is presented for the design of robust, sustained nanochemomechanical oscillators. The approach is based on the switching of chemoresponsive nanogel beads between their collapsed and swollen state by coupling them to an appropriately chosen nonlinear reaction. The presented system utilizes a proton activated oscillatory reaction and pH-sensitive nanobeads of gel that provide more than an order of magnitude volume change. A key point of our approach is the control of the colloid stability of the nanobeads of gel in a wide range of experimental parameters (pH, ionic strength, temperature) without interfering with the swelling characteristics of the nanogel particles. This was achieved by utilizing the interaction of nanogels with ionic surfactants.

Biophysics↗

PubMed2006

New experimental data and mechanistic studies on the bromate-dual substrate-dual catalyst batch oscillator.

The bromate-hypophosphite-acetone-Mn(II)-Ru(bpy)(3)(2+) batch oscillator was recently suggested for studying two-dimensional pattern formation. The system meets all major requirements that are needed for generation of good quality traveling waves in a thin solution layer. The serious drawback of using the system for studying temporal and spatial dynamical phenomena is its unknown chemical mechanism. In order to develop a mechanism that explains the observed long-lasting batch oscillations the bromate-hypophosphite-acetone-Mn(II)-Ru(bpy)(3)(2+) oscillator was revisited. We studied the dynamics both in the total system and in some composite reactions, and kinetic measurements were carried out in three subsystems. From the new experimental results we concluded that the two oscillatory sequences observed in the full system are originated from two oscillatory subsystems, the Mn(II)-catalyzed bromate-hypophosphite-acetone and the Ru(bpy)(3)(2+)-catalyzed bromate-bromoacetone reactions. Here we propose a mechanism which is capable of simulating the dynamical features that appeared in the complex system.

Journal Article↗

PubMed2005

Spatial bistability in a pH autocatalytic system: from long to short range activation.

The acid-auto-activated chlorite-tetrathionate reaction is studied in a one-side-fed spatial reactor. It was previously shown that in these conditions the unstirred reaction-diffusion system can generate oscillatory and excitable states even though under well-stirred nonequilibrium conditions only steady-state bistability is observed. Numerical simulations suggest that these temporal reaction-diffusion instabilities result from long-range activation by rapidly diffusing protons. We study here experimentally and numerically the effect of introducing into this reaction-diffusion system macromolecular carboxylate species that reduce the effective diffusivity of protons. Consistent with the original assumption, the introduction of such slow mobility proton-binding species quenches both oscillatory and excitability dynamics. Within the bistability domain the direction of the propagation of an interface between the two steady states depends on control parameter value. We elaborate on the fact that beyond a low critical concentration of macromolecular carboxylate species, the stability limit of the "thermodynamic" branch of spatial steady state does not depend on this concentration. Despite the relative simplicity of the kinetic model used in the numerical simulations, the results are in quasi-quantitative agreement with the experimental observations.

Journal Article↗