Radosław Pankiewicz

Complexes of Schiff base of gossypol with n-butylamine and some monovalent or bivalent cations studied by ESI MS, NMR, FT-IR as well as PM5 semiempirical methods

Abstract A Schiff base of gossypol with n-butylamine [GSBN] was shown to be capable of complexation of 2H + , Li + , Ca 2+ and Ba 2+ cations. This process of complex formation was studied by ESI mass spectrometry, 1 H and 13 C NMR and FT-IR spectroscopy as well as by PM5 semiempirical method. It was found that gossypol Schiff base can form a 1:2 complex with H + and 1:1 complexes with Li + , Ca 2+ and Ba 2+ cations. In all complexes the Schiff base of gossypol with metal cations exists in enamine-enamine tautomer, whereas in the 1:2 complex with H + the imine–imine tautomer was found. The metal cations are coordinated through oxygen atoms of the O 1 H(O 1 ,H) hydroxyl groups and a lone pair of an N-atom. The structures of these complexes were calculated by PM5 semiempirical method and discussed.

Studies of lithium and sodium complexation by silicon podand solvents

Abstract The complex formation of lithium and sodium ions with silicon podand solvents: phenyl-tris(1,4-dioxapentyl) silane (PhSi23) and ethyl-tris(1,4-dioxapentyl) silane (EtSi23) has been studied by FTIR, 1 H-, 13 C-, 7 Li- and 23 Na NMR. The far FTIR spectra show that the Li + cations fluctuate very fast whereas Na + cations are still localised between the oxygen atoms of the oxaalkyl chains. The 7 Li NMR spectra prove that one Li + cation can be coordinated not only by one but also two silicon podand molecules. The concentration dependence of the molar conductivity of LiClO 4 in the podand solvents indicates charge transfer between ion clusters.

FTIR and NMR studies of bis(oxaalkyl) sulphates(IV) and their complexes with proton and some metal cations

Abstract The complexation of Li + and Na + cations by three bis(oxaalkyl) sulphates(IV) was studied by FTIR and NMR on 1 H, 13 C, 7 Li and 23 Na nuclei. The NMR results have proved the formation of complexes and the fluctuation of Li + and Na + cations in respective circular arrangements. In the FTIR spectra of protonated sulphates intense continuous absorptions were observed indicating fast fluctuation of the protons in the respective multiminima potentials. The continuous absorptions in the far infrared region of the FTIR spectra of Li + or Na + complexes with three bis(oxaalkyl) sulphates(IV) indicate fast fluctuations of Li + or Na + cations between O-atoms of the oxaalkyl chains. The independence of the shape of the continua on the length of the oxaalkyl chains, i. e. the number of minima in the multiminima potential, demonstrates that the fluctuation of cations occurs in the respective circular arrangements.

Potentiometric and AM1d studies of a new class of Tr-podands–silver(I) complexes

Formation of complexes of structurally comparable six silicon, boron and phosphorous Triton X podands (Tr-podands) and silver(I) cations in propylene carbonate has been studied by the potentiometric and AM1d semi-empirical methods. Three types of these podands (2–7) form stable complexes with Ag+ cations. The stability constants of the complexes including different number of silver(I) cations are determined. It has been shown that the number of Ag+ cations complexed by the podands depends strongly on the number of oxaalkyl chains and on the type of central podands atom (Si, B or P). The (7) podand (with six polyoxaalkyl chains) can complex as many as six silver(I) cations. The structures of these complexes are visualised by the AM1d semi-empirical method.

17O NMR studies of substituted 1,3,4-oxadiazoles.

Three series of substituted 1,3,4‐oxadiazoles were studied by 17O NMR spectroscopy. Chemical shifts values were correlated with empirical Hammett parameters as well as calculated bond lengths and chemical shielding values. Copyright

Magnetic properties of BiFeO3 micro-cubes synthesized by microwave agitation

In this article, we present results of field cooled (FC) and zero field cooled (ZFC) magnetization measurements and investigation of aging and memory effect in bismuth ferrite (BFO) multiferroic micro-cubes obtained by means of simple microwave synthesis procedure. It is found that difference between FC and ZFC magnetizations appear at the temperature of freezing of ferromagnetic domain walls. The decay of the magnetic moment versus time described by power-law relation and the absence of memory effect are caused by domain growth mechanism rather than by the spin-glass phase. The negligible value of remnant magnetic moment indicates that BFO compound exhibits low concentration of ferromagnetic domains and can be close to ferromagnetic to spin-glass transition.

FT-IR study of the nature of K+, Rb+ and Cs+ cation motions in gramicidin A

Abstract Hydrated complexes of gramicidin A (gA) with K + , Rb + and Cs + cations were studied by FT-IR spectroscopy. The water bands observed in the FT-IR spectrum are identical as those obtained for the hydrated gA–Li + and gA–Na + complexes studied previously. In the far infrared spectrum of the gA–K + and gA–Rb + complexes an intense continuum and a strongly broadened band were found indicating large K + and Rb + polarizability in the gA channels. These K + and Rb + polarizabilities appear, similarly as in the case of the Li + and Na + complexes, as a result of the fast fluctuation of the K + and Rb + ions between two water molecules and four CO groups of the gA backbone. The much smaller barriers in the six minima Na + potential explain the much larger mobility of Na + when compared with the Li + and other cations.

Magnetic field effects in dye-sensitized solar cells controlled by different cell architecture.

The charge recombination and exciton dissociation are generally recognized as the basic electronic processes limiting the efficiency of photovoltaic devices. In this work, we propose a detailed mechanism of photocurrent generation in dye-sensitized solar cells (DSSCs) examined by magnetic field effect (MFE) technique. Here we demonstrate that the magnitude of the MFE on photocurrent in DSSCs can be controlled by the radius and spin coherence time of electron-hole (e-h) pairs which are experimentally modified by the photoanode morphology (TiO2 nanoparticles or nanotubes) and the electronic orbital structure of various dye molecules (ruthenium N719, dinuclear ruthenium B1 and fully organic squaraine SQ2 dyes). The observed MFE is attributed to magnetic-field-induced spin-mixing of (e-h) pairs according to the Δg mechanism.

Magnetic Relaxation in Bismuth Ferrite Micro-Cubes

The process of magnetic relaxation was studied in bismuth ferrite BiFeO3 multiferroic micro-cubes obtained by means of microwave assisted Pechini process. Two different mechanisms of relaxation were found. The first one is a rapid magnetic relaxation driven by the domain reorientations and/or pinning and motion of domain walls. This mechanism is also responsible for the irreversible properties at low temperatures. The power-law decay of the magnetic moment confirms that this relaxation takes place in the system of weakly interacting ferromagnetic or superferromagnetic domains. The second mechanism is a long-term weak magnetic relaxation due to spin glass-phase.

FT-IR Study of the nature of proton and cation motions in gramicidin S

Abstract Complexes of gramicidin S (gS) with proton and monovalent cations were studied by FT-IR spectroscopy, and their structures were calculated by the PM5 semiempirical method. The far infrared spectra of the gS complexes with metal cations revealed intense continua indicating large polarizabilities of Li + , Na + , K + , Rb + and Cs + in the gS circular arrangement. These cation polarizabilities appear, similarly as in the case of the cation complexes of gramicidin A, as a result of the fast fluctuation of the cations between four or six CO groups of the gS backbone.