Jerzy K. Zak

Radical Cation of Helical, Cross-Conjugated β-Oligothiophene

The radical cation of carbon-sulfur [7]helicene is configurationally stable in solution at room temperature. In contrast to the radical cations of alpha-oligothiophenes, which form diamagnetic pi-dimers at low temperature, the radical cation of this helical, cross-conjugated beta-oligothiophene shows a low propensity toward dimerization.

Biomaterial-based regional chemotherapy: Local anticancer drug delivery to enhance chemotherapy and minimize its side-effects

Since the majority of anticancer pharmacological agents affect not only cancer tissue but also normal cells, chemotherapy is usually accompanied with severe side effects. Regional chemotherapy, as the alternative version of conventional treatment, leads to the enhancement of the therapeutic efficiency of anticancer drugs and, simultaneously, reduction of toxic effects to healthy tissues. This paper provides an insight into different approaches of local delivery of chemotherapeutics, such as the injection of anticancer agents directly into tumor tissue, the use of injectable in situ forming drug carriers or injectable platforms in a form of implants. The wide range of biomaterials used as reservoirs of anticancer drugs is described, i.e. poly(ethylene glycol) and its copolymers, polyurethanes, poly(lactic acid) and its copolymers, poly(ɛ-caprolactone), polyanhydrides, chitosan, cellulose, cyclodextrins, silk, conducting polymers, modified titanium surfaces, calcium phosphate based biomaterials, silicone and silica implants, as well as carbon nanotubes and graphene. To emphasize the applicability of regional chemotherapy in cancer treatment, the commercially available products approved by the relevant health agencies are presented.

Advancing the delivery of anticancer drugs: Conjugated polymer/triterpenoid composite.

Exemplifying the synergy of anticancer properties of triterpenoids and ion retention qualities of conjugated polymers, we propose a conducting matrix to be a reservoir of anticancer compounds. In this study, poly(3,4-ethylenedioxythiophene), PEDOT, based matrix for electrically triggered and local delivery of the ionic form of anticancer drug, oleanolic acid (HOL), has been investigated. An initial, one-step fabrication procedure has been proposed, providing layers exhibiting good drug release properties and biological activity. Investigation of obtained systems and implementation of modifications revealed another route of fabrication. This procedure was found to yield layers possessing a significantly greater storage capacity of OL(-), as evidenced by the 52% increase in the drug concentrations attainable through electro-assisted release. Examination of the biological activity of immobilised and released OL(-) molecules proved that electrochemical treatment has negligible impact on the anticancer properties of OL(-), particularly when employing the three-step procedure, in which the range of applied potentials is limited. PEDOT/OL(-) composite has been demonstrated to be a robust and cost-effective material for controlled drug delivery.

Comparison of the surface structure of carbon films deposited by different methods

Abstract Atomic force microscopy is used to estimate and compare surface morphology of the carbon coatings, prepared using radio frequency plasma chemical vapor deposition, pulsed cathodic are discharge, ion-beam deposition and hot-filament chemical vapor deposition. The difference in the surface structure was mentioned for each method of deposition. The influence of the surface morphology on the film properties is discussed.

AFM imaging of copper stripping/deposition processes in selected electrolytes on boron-doped diamond thin-film electrodes

Abstract Electrochemical atomic force microscopy (EC AFM) studies of copper stripping/deposition processes under potentiostatic control were carried out on boron doped diamond thin-film electrodes in solutions of different ability to form copper complexes. Careful analysis of the electrode surface profiles taken at the potentials switched between oxidative and reductive values reveals the nucleation state and the early stages of complex formation when cations are released from the deposited metal. An unusual increase of the deposit-layer thickness is observed in sulfate- and phosphate-solutions at the positive potentials in contrast to an expected decrease of the surface adlayer thickness accompanying its stripping. The last effect takes place in the case of copper stripping in the presence of nitrates when no complex is formed. Similar behavior is observed on the HOPG electrode used in these studies as a reference surface.

An electrically controlled drug delivery system based on conducting poly(3,4-ethylenedioxypyrrole) matrix.

As numerous therapeutic agents are not well tolerated when administrated systemically, localized and controlled delivery can help to decrease their toxicity by applying an optimized drug concentration at extended exposure time. Among different types of drug delivery systems, conjugated polymers are considered as promising materials due to their biocompatibility, electrical conductivity and ability to undergo controllable redox reactions. In this work poly(3,4-ethylenedioxypyrrole), PEDOP, matrix is described for the first time as a reservoir of a model drug, ibuprofen (IBU). Drug immobilization process is performed in situ, during the electrochemical polymerization of 10 mM EDOP in the presence of 5-50 mM IBU. The loading efficiency of polymer matrix is dependent on IBU concentration and reaches 25.0±1.3 μg/cm2. The analysis of PEDOP-IBU chemical structure based on Raman spectroscopy, energy dispersive spectroscopy and surface morphology data provided by scanning electron microscopy shows that IBU is accumulated in the structure of matrix and evidently influences its morphology. IBU is then released in a controlled way under the influence of applied potential (-0.7 V vs. Ag/AgCl). It is demonstrated that the judicious choice of the synthesis conditions leads to a tailored loading efficiency of PEDOP matrix and to a tunable drug release.

Surface morphology of as grown and annealed bulk GaN crystals

GaN single crystals have been grown from Ga solution. The crystals grow in the form of platelets with their basal plane perpendicular to the c-axis. The two opposite crystal surfaces are not equivalent since one is N- and the other Ga-terminated. Atomic force microscopy has been applied to study surface morphology on both surfaces. It was found that one side is atomically flat. The other side consists of pyramid-like structures about 25 nm in size. The influence of annealing in an NH 3 +H 2 atmosphere in the temperature range from 600°C to 900°C was investigated. Depending on crystal face the results were drastically different. It was found that on the rough side, annealing yields an atomically flat surface with terraces of monolayer height. The size of the terraces depends on the temperature of the annealing. On the originally flat side the surface becomes rougher after annealing. The transformation of surface morphology begins at temperatures below 700°C. Preliminary results of annealing in a hydrogen atmosphere are also reported. These findings are crucial for the understanding and development of GaN homoepitaxy.

Electrooxidative catalysis using dispersed alumina on glassy carbon surfaces

Wahrend nach der Polierung mit Al2O3 nochmals gereinigte Elektroden eine Unterscheidung von Catechinen in Gegenwart von Ascorbinsaure (ein bioanalytisches Problem) nicht erlauben, ermoglichen Elektroden, die nach der Reinigung erneut mit 1.0 μm-α-Al2O3 poliert wurden, eine cyclovoltammetrische Unterscheidung von z.B. 1,2-, 1,4-Dihydroxy-benzol und Ascorbinsaure.

In situ AFM and conductivity measurements of regioregular oligoalkylthiophenes during electrochemical doping

Electrochemical properties of regioregular oligomers of 3-octylthiophene deposited as a film covering gold or platinum electrode are presented. In situ measurements of conductivity were carried out during oxidation process. These measurements revealed that tetramer is subject of consecutive dimerization reactions whereas hexamer produces a stable cation-radical. AFM in situ observations demonstrate a life of the oligomer film driven by phase transitions due to conformational changes of molecules stimulated by applied potential.

Two approaches to the model drug immobilization into conjugated polymer matrix

The purpose of this study is to develop biocompatible and conducting coating being carrier of biologically active compounds with the potential use in neuroprosthetics. Conducting polypyrrole matrix has been used to immobilize and release model drugs, quercetin and ciprofloxacin. Two routes of immobilization are described: drugs have been incorporated in the polymer matrix in the course of the electropolymerization process or after polymerization, in the course of polymer oxidation. Using UV/Vis spectroscopic detection we demonstrate that both immobilization approaches display different drug-loading efficiencies. In the case of ciprofloxacin, drug incorporation following synthesis is a more efficient immobilization approach (final drug concentration: 43.3 (±9.5) μM/cm(2)), while for quercetin the highest loading is accomplished by drug incorporation during synthesis (final drug concentration: 29.1 (±5.9) μM/cm(2)). The process of drug incorporation results in the variation of surface morphology with respect to the method of immobilization as well as the choice of drug. The results prove that electrochemical methods are efficient procedures for making multifunctional polymer matrices which might be perspective bioactive coatings for implantable neuroprosthetic devices.