Zoran Mandić

Polyaniline as an electrocatalytic material

Abstract The catalytic influence of polyaniline (PANI) film, prepared from sulphuric and perchloric acid solutions, on hydroquinone/benzoquinone ( HQ BQ ) and Fe 2+ 3+ reactions has been investigated. The effect of the PANI layer thickness on redox reactions has been established, as well as different kinetics depending on the counter-ion incorporated. The location of the reactions taking place is discussed. Evidence is given for metal-like behaviour of PANI at potentials of emeraldine existence and redox-polymer behaviour at potentials of pemigraniline existence.

Polymer-dimer distribution in the electrochemical synthesis of polyaniline

The distribution of major products associated with the process of polyaniline (PANI) synthesis is discussed. On the basis of the results obtained in the cyclovoltammetric (cv) and constant potential (cp) synthesis the dependence of that distribution upon monomer concentration, switching potential (Eλ) and potential of synthesis, Esynth, are discussed, the corresponding reaction scheme is given and terms for the reaction rates derived. The conditions governing the polymer-dimer distribution are formulated. The origin of the middle peak, appearing during the PANI synthesis, is discussed in the light of the specific experimental conditions, and species corresponding to it are identified. A reaction scheme for the hydrolysis pathway of dimer is confirmed.

Counter-ion and pH effect on the electrochemical synthesis of polyaniline

Abstract The effect of different electrolytes at various pH values on the electropolymerization of aniline from aqueous solutions has been studied. It has been found that polyaniline can be synthesized within the whole pH range investigated, provided that the proper counter-ion is present. Distinct regions of different pH effect on aniline polymerization have been identified and the corresponding reaction mechanisms suggested. It was also found that polyaniline synthesized in the solutions having high pH values, when transferred to acidic solutions, switched from a non-conductive to a conductive state, giving voltammograms and FTIR spectra characteristic of PANI synthesized in acidic media.

The influence of counter-ions on nucleation and growth of electrochemically synthesized polyaniline film

The initial stages of polyaniline (PANI) film growth are investigated by a potentiostatic technique. The obtained I-t transients exhibit current maxima which are analyzed for the nucleation type. The evidence is given on two different stages of the nucleation process. It is established that the first stage of growth is a formation of a compact PANI layer which is followed by an additional nucleation process. For that nucleation process it is found that at lower concentrations of aniline monomer 3D progressive nucleation takes place, and with the increasing monomer concentration in perchloric acid solutions 3D instantaneous nucleation prevails. At later stages 1D growth takes place resulting in chain branching. The possibility to observe current maxima, indicating the particular nucleation process, depends on monomer concentration, on the potential of synthesis, and on the counter-ion present, ie on the rate of PANI polymerization. It is shown that clusters resulting from the nucleation process form different shapes depending on the counter-ion present.

Voltammetric studies of 2-hydroxy-5-[(4-sulfophenyl)azo]benzoic acid as a novel prodrug of 5-aminosalicylic acid.

The electrochemical properties of a colon-targeted prodrug of 5-aminosalicylic acid (5-ASA), 2-hydroxy-5-[(4-sulfophenyl)azo]benzoic acid (SPSA), were investigated in aqueous solutions at glassy carbon electrodes using cyclic voltammetry and controlled potential electrolysis. The influence of the pH and experimental time domain on the reaction pathway has been studied. The electrochemical reduction of SPSA is identified as an ECE process always leading to the cleavage of azo bond. In an acidic media SPSA is reduced in a 4e(-)/4H(+) process yielding 5-ASA and sulfanilic acid. In neutral and weakly basic media SPSA is reduced in 2e(-)/2H(+) process resulting in the hydrazo intermediate that is stable enough to enable its reoxidation back to SPSA in the time scale of the cyclic voltammetry.

Acid–base and electrochemical properties of manganese meso(ortho- and meta-N-ethylpyridyl)porphyrins: voltammetric and chronocoulometric study of protolytic and redox equilibria

Growing interest in redox-active compounds as therapeutics for oxidative stress-related diseases led to the design of metalloporphyrins as some of the most potent functional SOD-mimics. Herein we report a detailed electrochemical study of the protolytic and redox equilibria of manganese ortho and meta substituted N-ethylpyridyl porphyrins (MnPs), MnTE-2-PyP(5+) and MnTE-3-PyP(5+), in aqueous solutions. The electrochemical parameters of redox processes for all experimentally available species have been determined, as well as their diffusion coefficients and estimated sizes of aqueous cavities. The results indicate that possible changes of the intracellular acidity cannot affect the antioxidant activity of MnPs in vivo, since no change in the E(Mn(III)P/Mn(II)P) values was observed below pH 10. Furthermore, the results confirm that both of these MnPs can be efficient redox scavengers of peroxynitrite (ONOO(-)), another major damaging species in vivo. This can occur by either single-electron reduction or two-electron reduction of ONOO(-), involving either the Mn(IV)P/Mn(III)P redox couple or Mn(IV)P/Mn(II)P redox couple. In addition to kred(ONOO(-)) reported previously, the thermodynamic parameters calculated herein imply a strong and identical driving force for the reaction of both ortho and meta isomeric MnPs with ONOO(-). An enlargement of both Mn(III)P complexes upon an increase of the solution pH was also observed and attributed to the reduction of positive charge on the central ion caused by deprotonation of the axial water molecules. This expansion of aqueous cavities suggests the formation of a solvent cage and the increased lipophilicity of Mn(III)P complexes caused by increased electron density on the Mn ion.

Composite layers consisting of polyaniline and poly(o-phenylenediamine): Electrochemical deposition, electrochromic and electrocatalytic properties

The composite polymer layers consisting of polyaniline (PANI) and poly(o-phenylenediamine) (poly(o-PDA)) were electrodeposited on a platinum electrode by simultaneous electrochemical oxidation of corresponding monomers from aquaeous hydrochloric solutions. The growth of PANI and poly(o-PDA) occurs separately resulting in layers with two distinct, finely distributed phases. The first deposited layers are composed mainly of poly(o-PDA) and become richer in PANI as the electropolymerization proceeds. The aniline/o-PDA copolymer was not formed during electrodeposition, as evidenced by cyclic voltammetry and Fourier-transformed IR spectroscopy. It was demonstrated that the electrochromic properties of resulting composite layers are the combination of yellow/brown-reddish and green/dark blue observable color transitions which are characteristics of poly(o-PDA) and PANI, respectively. Electrocatalytic properties of the electrosynthesized composite layers were investigated on quinone/hydroquinone (Q/H2Q) redox system and it was shown that the composite layers increase the heterogeneous electron transfer rate with a magnitudes ranging from those obtained on pure poly(o-PDA) to those obtained on pure PANI layer.

Electrochemical reduction of desmycosin, structure investigation and antibacterial evaluation of the resulting products

Electrochemical reduction of desmycosin at the mercury electrode in aqueous medium was investigated by cyclic voltammetry and preparative scale electrolysis was carried out for the isolation and identification of products. Structure analyses of the resulting products were accomplished by MS, 1D and 2D NMR spectroscopy. The results obtained show that dimerization and two electron reduction of desmycosin occur in parallel yielding a symmetric dimer at position C13 and 10,11-dihydrodesmycosin as the end products. 10,11-dihydrodesmycosin shows decreased antibacterial activity in vitro in comparison with desmycosin, while the dimer is inactive.

Anodic deposition of lead dioxide at Nafion covered gold electrode

Anodic electrodeposition of lead dioxide at the bare and Nafion® covered gold electrode was studied by cyclic voltammetry and chronoamperometry. The results showed that Nafion® layer has a favourable effect on the efficiency of the deposition process which was caused by both thermodynamic and kinetic reasons. Electrodeposition process at Nafion® covered gold electrode goes via Pb(III) intermediate species which are stabilized within Nafion® membrane. The final PbO2 deposit crystallizes in tetragonal β-PbO2 form.

Editorial, IAPC-6 Meeting

It is with our great pleasure to announce this topical issue of Pharmaceutical Research devoted to the IAPC-6 meeting held in Zagreb, Croatia, September 4–7, 2017. The meeting was organized by the International Association of Physical Chemists, nonprofit organization, with the goal to establish contacts, interactions among scientists of different profiles and to strengthen the cooperation between researchers from academia and industry. These goals go fully along with the missions of the Society which include global innovation and partnership in order to advance science and spread knowledge. The IAPC meetings started as a series of the biennial conferences on physico-chemical methods in drug discovery and development. The first conference took place in Rovinj, Croatia, 2009, but soon it acquired a widespread interest among pharmaceutical science community usually gathering more than 100 scientists from different parts of the world. However, its global importance the conference gained after ever increasing need to widen its geographical footprint. The scientific committee decided to switch the schedule of the Meetings from biennial to annual taking place in the alternating Eastern Asia/European locations. As a result IAPC-5 conference in Zhuhai, China, August 2016, IAPC-6 conference in Zagreb, Croatia, September 2017 (Fig. 1) and IAPC-7 conference, Osaka, Japan were organized. IAPC-6 conference in Zagreb achieved a great success both from the scientific and social points of view. The scientific program was well balanced consisting of six sessions: Drug Development, Solid State, Pharmaceutical Cocrystals, PhysChem and Permeability, ADMET and DMPK and Drug Discovery. The conference attended about 150 participants from more than 30 countries. Special evening session, BPharmaceutical Cocrystals – Physicochemical Properties and Formulations^, was organized and moderated by Alex Avdeef. The session highlighted issues related to the measurement of physicochemical properties, particularly dissolution and solubility as a function of pH, in support of formulation development of oral drug products with improved bioavailability. In this special issue of Pharmaceutical Research a collection of five papers were published, four of which were in the areas of preformulation study, including formulation design (Parikh & Serajuddin, Cetina-Cizmek et al...), characterization (Grassi et al) and modelling (Avdeef). The last paper reported a computational approach to model PK and biological effects of steroids in humans. * Zoran Mandić zmandic@fkit.hr