Biomedical subjects

J Cirák

Publications and source records attributed to J Cirák.

3 recordsLinked to original sources

PubMed2002

Surface modified microelectrodes for selective electroanalysis of metal ions in environmental components.

The surface modification of electrodes was achieved by the Langmuir-Blodgett technique. The monolayers of laponite clay and polythiophene were formed at the air-water interface and these films were then transferred onto carbon microelectrodes. The behaviour of both untreated and coated electrodes was tested by originally developed double-step voltcoulometry (DSVCM). The dependence of charge response on the concentration of Cu(2+) species was investigated. Straight calibration curves were obtained and enhanced sensitivity of coated electrodes was documented. It is shown that the accumulation of Cu ions into laponite clay was maintained even after transferring the electrode into a pure water. The characteristic features of the "memory effect" are discussed.

Aluminum Silicates↗

PubMed1988

The lateral order of dipalmitoylphosphatidylcholine model membranes in the presence of N-alkyl-N,N,N-trimethylammonium ions as studied by Raman spectroscopy.

Effects of N-alkyl-N,N,N-trimethylammonium ions with different alkyl substituents (hexyl, nonyl, dodecyl, and octadecyl) on the lateral packing of lipids in dipalmitoylphosphatidylcholine (DPPC) dispersions in H2O was investigated by Raman spectroscopy in a spectral region of 2800--3100 cm-1 at temperatures between 22--70 degrees C. The lateral order parameter Slat calculated by empirical equation reveals that the addition of the ions decreases the lateral ordering of lipid hydrocarbon chains in the gel phase, while in the liquid crystalline state the lateral ordering is increased. In addition, this observation is supported by decomposition of the spectra into component bands using a computer fitting program. This enabled to follow changes in individual band parameters (position, amplitude, and height) in dependence on temperature and/or additives. The results suggest that N-alkyl-N,N,N-trimethylammonium ions have a condensing effect on DPPC bilayer in the liquid crystalline state, the effect increasing with the increasing length of the alkyl substituent.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1980

Relation or Raman order parameters to spin labeling parameters.

For the quantitation of Raman and spin labeling data order parameters are commonly used. The spin label order parameter measured at any depth in the layer is a weighed sum of the segmental order since, due to fast conformational interconversions, each CH2 segment is partly in trans and partly in non-trans, e.g. gauche, kink, jog, etc. conformation during the measurement. The weighing factor, the trans finding probability, varies along the chain (cf. flexibility profile) but its mean value should be equal to the Raman trans order parameter. This correlation is illustrated with the experimental data obtained for dipalmitoyl phosphatidylcholine and n-alcohol mixtures. The rate of rotational diffusion, a dynamical parameter from spin labeling studies, is correlated with the lateral packing density as measured by the Raman lateral order parameter. For the obtained linear correlation a qualitative explanation is given. The effect of a series of long chain alcohols on the phase transition characteristics of dipalmitoyl phosphatidylcholine was investigated. The possible role of hydrogen bonding in the interfacial region is emphasized.

Alcohols↗