Jan Jadżyn

Bio: Jan Jadżyn is an academic researcher from Polish Academy of Sciences. The author has contributed to research in topics: Liquid crystal & Dielectric. The author has an hindex of 25, co-authored 234 publications receiving 2453 citations. Previous affiliations of Jan Jadżyn include Katholieke Universiteit Leuven.

Dielectric relaxation study of 1-n hexyl-4-(4-isothiocyanatophenyl)bicyclo [2,2,2] octane in the nematic and isotropic phases

Abstract: Dielectric relaxation investigations on the mesogen 1-n-hexyl-4-(4-isothiocyanato-phenyl)bicyclo[2,2,2]octane in the nematic and isotropic phases have been carried out in the frequency region from about 1 kHz to 1 GHz. Two relaxation processes have been observed in both the isotropic and nematic phases, when the measurements of the electric permittivity versus frequency are made parallel to the orientation axis of the liquid crystal. The possible mechanisms responsible for these two processes are discussed. The height of the potential barrier which hinders the rotation of the liquid crystal molecules around the short axis in the nematic state, and the order parameter of the liquid crystal under investigation have been estimated on the basis of the values for the relaxation times in the nematic and isotropic phases.

Biasing the ferronematic - a new way to detect weak magnetic field

Abstract: Magnetic properties of a ferronematic, i.e., nematic liquid crystal doped with magnetic nanoparticles in low volume concentration are studied, with the focus on the ac magnetic susceptibility. A weak dc bias magnetic field (units of Oe) applied to the ferronematic in its isotropic phase increases the ac magnetic susceptibility considerably. Passage of the isotropic-to-nematic phase transition resets this enhancement irreversibly (unless the dc bias field is applied again in the isotropic phase). These experimental findings pave a way to application possibilities, such as low magnetic field sensors, or basic logical elements for information storage.

Critical behavior of hydrogen bonds observed in high-pressure nuclear quadrupole resonance studies

Abstract: A summary of our NMR results is presented in Table I . Integration of the line shapes of the sample exposed at room temperature yields a total spin density of 1.3 X lozo CO’s per gram of catalyst. Using a CO/Ru ratio of 1 for linear CO and a CO/Ru ratio of 2 for the dicarbonyl, we obtain a dispersion of 30%. Chemisorption measurements yielded a dispersion of 27%. Upon high-temperature exposure, a greater number of dicarbonyls are formed, indicating that dicarbonyl adsorption is activated. A bridged species is also formed, whereas the relative proportion of linear species decreases. We cannot determine whether the bridged species derives directly from the linear species, or whether the adsorption of the bridged species precludes the presence of a linear species a t a particular site. Since no change is evident in the metal surface area after heating, this change in CO distribution cannot be attributed to a change in metal particle size. We have shown that I3C magic angle spinning NMR can be used to identify and quantify CO adsorbates. This technique holds promise for studying differential reactivity of adsorbed species. In addition, since dicarbonyl species may only bond to isolated atoms, the degree of atomic dispersion may be detected by 13C NMR.

Prenematic Self-Assembling of Mesogenic Molecules in Isotropic Liquid and Orientational Order in Nematic Phase

Abstract: (8OCPFB) was performed in the frequency range from 50 kHz to 100 MHz in the nematic and isotropic phases. The static permittivity and the relaxation process related to the rotation of molecules around their short axis was analyzed. For some of these liquid crystals anomalous temperature dependence of static permittivity in the pretransitional region of the isotropic phase was observed. Based on the Meier‐Saupe‐Martin model of molecular diusion in nematics, the orientational order parameter hP2i was determined from dielectric relaxation times and retardation factor. The values of hP2i calculated from the dielectric relaxation data were compared with the results obtained from measurements of polarized electronic absorption. Correlations between the magnitude of the dielectric pretransitional eect and the orientational order in the nematic phase were discussed.

Temperature Behavior of Electric Relaxational Effects due to Ionic Conductivity in Liquid Lactones

Abstract: This paper concerns the studies of temperature and frequency behavior of the complex impedance, electric modulus, and electric conductivity due to an ionic current in liquid γ-butyrolactone (GBL) and γ-valerolactone (GVL). The frequency of the applied electric stimulus (500 Hz to 5 MHz) corresponds to the static dielectric regime of the lactones. The studies were performed in the temperature range of 263 K to 313 K. It was shown that in the static dielectric case, the dc ionic conductivity (σDC) and the static dielectric permittivity \({(\varepsilon_{\rm s})}\) determine the relaxational behavior of the impedance (Z*) and the electric modulus (M*) of the molecular liquids and both spectra are of the Debye-type characterized by the same conductivity relaxation time (τσ). Both σDC and τσ of GBL and GVL fairly well fulfill an Arrhenius temperature dependence with very similar values of the thermal activation energy \({{\rm E}_{\sigma_{\rm DC}} \approx {\rm E}_{\tau_\sigma} \approx 25 \,{\rm kJ} \, . \, {\rm mol}^{-1}}\) . The temperature dependence of the static dielectric permittivity and its temperature derivative is analyzed and interpreted in terms of the dipolar aggregation in the studied lactones.

The restaurant at the end of the random walk: recent developments in the description of anomalous transport by fractional dynamics

Abstract: Fractional dynamics has experienced a firm upswing during the past few years, having been forged into a mature framework in the theory of stochastic processes. A large number of research papers developing fractional dynamics further, or applying it to various systems have appeared since our first review article on the fractional Fokker–Planck equation (Metzler R and Klafter J 2000a, Phys. Rep. 339 1–77). It therefore appears timely to put these new works in a cohesive perspective. In this review we cover both the theoretical modelling of sub- and superdiffusive processes, placing emphasis on superdiffusion, and the discussion of applications such as the correct formulation of boundary value problems to obtain the first passage time density function. We also discuss extensively the occurrence of anomalous dynamics in various fields ranging from nanoscale over biological to geophysical and environmental systems.

A Medicinal Chemist’s Guide to Molecular Interactions

Abstract: Molecular recognition in biological systems relies on the existence of specific attractive interactions between two partner molecules. Structure-based drug design seeks to identify and optimize such interactions between ligands and their host molecules, typically proteins, given their three-dimensional structures. This optimization process requires knowledge about interaction geometries and approximate affinity contributions of attractive interactions that can be gleaned from crystal structure and associated affinity data. Here we compile and review the literature on molecular interactions as it pertains to medicinal chemistry through a combination of careful statistical analysis of the large body of publicly available X-ray structure data and experimental and theoretical studies of specific model systems. We attempt to extract key messages of practical value and complement references with our own searches of the CSDa,(1) and PDB databases.(2) The focus is on direct contacts between ligand and protein functional groups, and we restrict ourselves to those interactions that are most frequent in medicinal chemistry applications. Examples from supramolecular chemistry and quantum mechanical or molecular mechanics calculations are cited where they illustrate a specific point. The application of automated design processes is not covered nor is design of physicochemical properties of molecules such as permeability or solubility. Throughout this article, we wish to raise the readers’ awareness that formulating rules for molecular interactions is only possible within certain boundaries. The combination of 3D structure analysis with binding free energies does not yield a complete understanding of the energetic contributions of individual interactions. The reasons for this are widely known but not always fully appreciated. While it would be desirable to associate observed interactions with energy terms, we have to accept that molecular interactions behave in a highly nonadditive fashion.3,4 The same interaction may be worth different amounts of free energy in different contexts, and it is very hard to find an objective frame of reference for an interaction, since any change of a molecular structure will have multiple effects. One can easily fall victim to confirmation bias, focusing on what one has observed before and building causal relationships on too few observations. In reality, the multiplicity of interactions present in a single protein−ligand complex is a compromise of attractive and repulsive interactions that is almost impossible to deconvolute. By focusing on observed interactions, one neglects a large part of the thermodynamic cycle represented by a binding free energy: solvation processes, long-range interactions, conformational changes. Also, crystal structure coordinates give misleadingly static views of interactions. In reality a macromolecular complex is not characterized by a single structure but by an ensemble of structures. Changes in the degrees of freedom of both partners during the binding event have a large impact on binding free energy. The text is organized in the following way. The first section treats general aspects of molecular design: enthalpic and entropic components of binding free energy, flexibility, solvation, and the treatment of individual water molecules, as well as repulsive interactions. The second half of the article is devoted to specific types of interactions, beginning with hydrogen bonds, moving on to weaker polar interactions, and ending with lipophilic interactions between aliphatic and aromatic systems. We show many examples of structure−activity relationships; these are meant as helpful illustrations but individually can never confirm a rule.

Supercooled dynamics of glass-forming liquids and polymers under hydrostatic pressure

Abstract: An intriguing problem in condensed matter physics is understanding the glass transition, in particular the dynamics in the equilibrium liquid close to vitrification Recent advances have been made by using hydrostatic pressure as an experimental variable These results are reviewed, with an emphasis in the insight provided into the mechanisms underlying the relaxation properties of glass-forming liquids and polymers

Ionic Liquid Crystals: Versatile Materials.

Abstract: This Review covers the recent developments (2005-2015) in the design, synthesis, characterization, and application of thermotropic ionic liquid crystals. It was designed to give a comprehensive overview of the "state-of-the-art" in the field. The discussion is focused on low molar mass and dendrimeric thermotropic ionic mesogens, as well as selected metal-containing compounds (metallomesogens), but some references to polymeric and/or lyotropic ionic liquid crystals and particularly to ionic liquids will also be provided. Although zwitterionic and mesoionic mesogens are also treated to some extent, emphasis will be directed toward liquid-crystalline materials consisting of organic cations and organic/inorganic anions that are not covalently bound but interact via electrostatic and other noncovalent interactions.