Marian Wolszczak

Some aspects of the radiation processing of conducting polymers

Abstract Recently, in our laboratory (IARC), complex studies have been made on conducting polymers such as polyaniline, polypyrrole and polythiophene. Our research programme has been directed toward a better molecular understanding of the structural properties controlling electronic conductivity of polymers. The most important issue of our studies within conducting polymer family includes effect of γ and electron beam irradiation on their electrical conductivity. The irradiation was performed on the samples in the form of pellets onto which aluminium electrodes had been vacuum-deposited. The relative conductivities of irradiated pellets prepared from highly conducting polyaniline, polypyrrole and polythiophene powders decreased with increase of irradiation dose under vacuum. On the other hand in the case of irradiation under dopant atmosphere conductivity of pellets was increased. The dramatic increase in conductivity was observed after irradiation of insulating polyaniline form (even under air atmosphere). The ESR studies suggest that the charge-transport in low doped conducting polymer can be explained by paramagnetic polaron migration along and between the polymer chains. At higher doping levels, in the case of polythiophene and polypyrrole the energetically favourable is a bipolaron state as charge carrier.

The synthesis of a new type of anthracene DNA intercalator

A new type of DNA intercalator based on anthracene 3 was synthesized. Preliminary binding studies show high affinity of this probe to CT-DNA. Higher binding constant of this compound (4.0 x 10(4) M-1) as compared with that known for 9-aminomethylanthracene, is caused presumably by enhanced electrostatic interaction.

Interaction of cationic protoberberine alkaloids with human serum albumin. No spectroscopic evidence on binding to Sudlow's site 1.

Physicochemical studies on drug interactions with human serum albumin (HSA) are relevant for elucidation, at the molecular level, of the processes occurring in vivo. In this work using optical spectroscopic methods (fluorescence, absorption, circular dichroism), we have investigated aqueous HSA solutions containing pharmaceutically important isoquinoline alkaloids, berberine and palmatine. The primary objective was to verify whether the two compounds are located in the subdomain IIA of the secondary HSA structure as reported in literature. We prove that the excited state of Trp214 residue is not quenched by the alkaloids; all observed changes in fluorescence spectra are due to inner filter effects. Furthermore, differential absorption spectra indicate that the ligands remain in a waterlike microenvironment. We infer that bound alkaloid molecules are located at the protein/water interface. Yet, such binding mode can induce some unfolding of the HSA molecule detectable in the far-UV circular dichroism (CD) spectra. We have also performed, for the first time, pulse radiolysis studies of hydrated electron scavenging in the HSA/alkaloid systems and have measured steady-state absorption spectra of irradiated samples. The results reveal that neither berberine nor palmatine is effectively protected by the protein against one-electron reduction, which is consistent with the aforementioned conclusion.

Effect of ionizing radiation on polyaniline solutions

Abstract This communication presents the optical studies associated with transition doped (metallic)-neutral (semiconductor or insulator) state for conducting polymers. Special attention is focused on the electronic properties of polyaniline. The interconversion of different oxidation states of polyanilines has been studied by chemical and radiolytic methods. The polyaniline system is described by three sets of chromophores of three different oxidation states: fully reduced leucoemeraldine base (LB), partially oxidized emeraldine base (EB), and fully oxidized pernigraniline (PB). Each oxidation state can exist in its protonated form by treatment with an acid. All members of polyaniline family are spectroscopically distinguishable. The radiolytic study presents evidence that the polyaniline can exist in a continuum of oxidation states. The highly conducting form of polymer, i.e. emeraldine salt can be converted by using ionizing radiation into leucoemeraldine salt. The leucoemeraldine base is the final product of radiolysis of emeraldine base solution. The fully oxidized form of polyaniline can also be obtained by the irradiation of EB in the presence of CCl4 or chlorobenzene.

Concentration dependence of pyrene excimer formation in doped polyethylene

Abstract Pyrene-doped low density polyethylene films were studied by steady state and time-resolved fluorescence emission spectroscopy at room temperature for dopant concentrations up to about 1.5×10−2 mol dm−3. The excimer fluorescence observed in these films for a high pyrene concentration (about 10−2 mol dm−3) was proposed to result either from pyrene molecular pairs close to the excimer configuration or from pyrene aggregates which satisfy the geometrical requirements for excimer formation.

QUENCHING OF PYRENE FLUORESCENCE BY AMPHIPHILIC NITROXIDE RADICALS EMBEDDED IN CATIONIC MICELLES

Abstract Steady-state and nanosecond time-resolved studies have been carried out on the fluorescence quenching of excited pyrene by n-doxylstearic methyl esters (n-DSE, n = 5, 10, 12) in an aqueous solution of cationic micelles of hexadecyltrimethylammonium chloride (HTAC, 0.1 M). The aggregation number (N = 114 ± 6) and the rate constants of intramicellar quenching (1.4 × 107, 1.3 × 107 and 1.05 × 107 s−1 for 5-, 10- and 12-DSE respectively) have been determined. The results are discussed in terms of the average location of the luminophore and the quencher molecules in the aggregates, considering previous findings of electron spin echo modulation studies of n-doxylstearic acid spin probes in micellar systems.

Optical spectroscopy of the aryl cation, the intermediate in the decomposition of arenediazonium salts

Abstract The UV—visible spectrum of the aryl cation is presented for the first time. The species originates from the decomposition of trisubstituted arenediazonium salts in an LiCl glass matrix at 77 K. The generation of the aryl cation in its triplet ground state (π) 5 (sp 2 ) 1 and the absence of the aryl radical in the system have been proved by electron spin resonance (ESR) spectroscopy.

One-electron reduction of pentacyanonitrosylferrate—II: Ion in frozen solutions

Abstract Spectra of γ-irradiated glassy matrices such as: methanol-water, ethylene glycol-water, 2-methoxyethanol, hexamethylphosphoric triamide-ethylene glycol, and aqueous solutions of lithium chloride and sodium formate, containing sodium nitroprusside as electron scavenger, were studied at low temperatures by absorption spectroscopy. It was found that the main product of nitroprusside reduction at 77 K is [Fe/CN/ 5 ṄO] -3 ion. The most effective reducing species is probably the shallow trapped electron. It was found that dry electrons do not reduce nitroprusside ion. Warming up of glassy samples irradiated at 77 K leads mainly to the formation of pentacoordinated [F≐/CN/ 4 NO] -2 ion or alkylnitroso complex, depending on the nature of the matrix radical.

Polyelectrolyte effects on electron transfer process

Abstract Pulse radiolysis and gamma radiolysis have been used to study the kinetics of electron scavenging by viologens bound to poly(styrenesulfonate)-(PSS) in the temperature range 6–298 K. The rate of radiation-induced one-electron reduction of methylviologen (MV 2+ ), diquat (DQ 2+ ), ethidium bromide (EB), ruthenium tris(2,2′-bipyridine) (Ru(bpy) 3 2+ ) is greatly inhibited by the presence of polyelectrolyte. The origin of the inhibition effect is shown to be determined by electrostatic forces (repulsion of electrons by the negative potential field of polyelectrolyte with trapped scavenger) and by geometric factor (caused by overlapping of the capture spheres of scavenger molecules on the PSS chain).

Electron trapping in methanol-ethyl ether glasses at 4.2–77 K

Abstract Spectra of glassy methanol-ethyl ether mixtures γ-irradiated at 4.2 K were studied at 4.2–77 K. Relatively low yield of trapped electrons at 4.2 K and decay of electron absorption during warm up indicate that decay of trapped electrons is more efficient at temperatures 4.2–50 K than at 77 K. Efficient shift of absorption band towards blue due to methanol and increase of e-t yield with methanol content suggest that electrons at 4.2 K are preferably localised in methanol clusters.