Advances in Biomimetics Part 9 docx

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Interaction of cationic antimicrobial peptides with model membranes. J. Biol. Chem. 276, 35814-35722, 0021-9258. 13 Biomimetic Membranes as a Tool to Study Competitive Ion-Exchange Processes on Biologically Active Sites Beata Paczosa-Bator 1 , Jan Migdalski 1 and Andrzej Lewenstam 1,2 1 Faculty of Material Science and Ceramics, AGH University of Science and Technology, PL-30059 Cracow 2 Centre for Process Analytical Chemistry and Sensor Technology ‘ProSens’, Process Chemistry Centre, Åbo Akademi University, FIN-20500 Åbo-Turku, 1 Poland 2 Finland 1. Introduction The change in membrane potential with time is of fundamental importance in cell biology. From the biological point of view we are interested in the mechanism of voltage dependent channel block and related ionic antagonism that happens on the ion-binding sites forming channel necks (Migdalski at al., 2003; Paczosa at al., 2004; Paczosa-Bator at al., 2006). We argue that by applying biomimetic approach, the processes invisible in routine membrane research could be “amplified” and exposed for further scientific exploration. In our case, this argument refers to electrical potential transients and/or local concentration redistributions provoked a competitive calcium/magnesium or potassium/sodium/lithium ions exchange on the biological sites. Voltage-activation of the N-methyl-d-aspartate (NMDA) receptor channel, allowing for calcium ion influx by relieving the block by magnesium ion (Nowak at al., 1984; McBain at al., 1994), or monovalent ion effects such as potassium-sodium/ lithium/TEA(tetraethylammonium) in the case of potassium and sodium channels (Hille, 1992) is used to illustrate the value of biomimetic methodology. From the electrochemical point of view, our strategy means an interest in the time- dependent (dynamic) characteristics of a membrane potential resulting from competitive ion-exchange processes. The membranes used in our studies are in electrochemistry known as the electroactive parts of ion-selective sensors sensitive for magnesium, calcium, potassium, sodium and lithium, which are the ions of our interest. To bridge mentioned above biological and electrochemical interests we use biomimetic membranes. The novelty of our approach is in applying conductive polymers (CPs) as with purposely dispersed bioactive sites. This allows observation of a competitive (antagonistic) ion exchange and its coupling with a membrane potential formation process on biologically active sites (BL). The sites in focus of our research, adenosinotriphosphate (ATP), adenosinodiphosphate (ADP), heparin (Hep) and two amino acids – asparagine (Asn) and glutamine (Gln), competitively bind calcium, magnesium, lithium, sodium and potassium ions and thus play an important role in ion-dependent biological membrane processes (Saris Advances in Biomimetics 278 at al., 2000). In particular, ATP takes part in active membrane potential formation, Hep in the anticoagulation process (Desai, 2004) and Asn and Gln in the voltage-ligand gated influx on calcium ions via the NMDA channels (McBain & Mayer, 1994). The following methodology is accepted for applying CPs as biomimetic membranes. In order to obtain the membranes (CP-BL-Y, where Y = K + , Na + , Li + , Ca 2+ , Mg 2+ ), first ATP, ADP, Hep, Asn or Gln are introduced into the CP matrix during electropolymerization. Next, the calcium, magnesium, lithium, sodium or potassium potentiometric sensitivity is induced by soaking in an alkaline solution of one of these ions until close-to-Nernstian sensitivity for the films is obtained. The films are then used to monitor the equilibration processes induced by the change in bulk concentration of magnesium/calcium or lithium/potassium/sodium ions or stimulation with external electrical signal (Paczosa- Bator at al., 2009). The resulting transitory potential response is recorded and characteristic potential transients observed are theoretically interpreted. 2. Conducting polymers used and their properties It is well known that conducting polymers (CPs) such as poly(pyrrole) (PPy), poly(N- methylpyrrole) (PMPy) or poly(3,4-ethylenedioxythiophene) (PEDOT) in the oxidation process during electrodeposition are easily doped with small inorganic anions and in consequence exhibit anionic open-circuit sensitivity. Cationic sensitivity can be observed if the CP films are doped with cations during reduction. This happens when the CP film is doped with bulky immobile anions, for instance naphthalenesulphonate, indigo carmine or methylene blue (Gao at al., 1994; Bobacka et al., 1994). The ionic sensitivity induced in this way is dependent on the redox status of the polymer film and is rather nonselective (Lewenstam at al., 1994). As we shown, the cationic sensitivity may be enhanced and stabilized with use of bulky, metal-complexing ligands from the group of metallochromic indicators as dopants. This happens because the bulky dopants retain in the polymer film their complexing properties known from water chemistry and the selective cationic sensitivity results from the complex formation inside CP films (Migdalski et al., 1996). This provides the unique possibility of forming CP films doped with bulky and biologically active anions such as adenosinotriphosphate (ATP), adenosinodiphosphate (ADP), heparin (Hep) or amino acids – asparagine (Asn) and glutamine (Gln). These films may be used as biomimetic membranes to inspect processes important for membrane potential formation or membrane transport (Paczosa-Bator at al., 2007). Our observations have shown that the conducting polymer designed for biomimetic membranes should have smooth surface morphology (a. Paczosa-Bator at al., 2006). It is well known that the morphology of conducting polymer films depends on many experimental parameters, such as substrate used, electrodeposition method, kind of monomer and doping anions, kind of solvent, pH and post deposition treatment of the film. Depending on the further application of conducting polymer layers, different surface morphology (rough or smooth) and different structure are required (Niu at al., 2001; Unsworth at al., 1992; Maddison & Unsworth 1989). 3. Materials and methods The electrosynthesis of conducting polymer membranes on GC and ITO electrodes was carried out using an Autolab general Purpose System (AUT20.Fra2-Autolab, Eco Chemie, Biomimetic Membranes as a Tool to Study Competitive Ion-Exchange Processes on Biologically Active Sites 279 B.V., Utrecht, The Netherlands) connected to a conventional, three-electrode cell. The working electrode was a glassy carbon (GC) disk with an area of 0.07 cm 2 or conducting glass pieces with an area of about 1 cm 2 (ITO, Lohja Electronics, Lohja, Finland, used for the FTIR, EDAX, XPS and LA-ICP-MS experiments). The reference electrode was an Ag/AgCl/3M KCl electrode connected to the cell via a bridge filled with supporting electrolyte solution, and a glassy carbon (GC) rod was used as the auxiliary electrode. The solutions used for polymerization contained selected monomer and an electrolyte that provided the doping ion. Electropolymerization was performed in solutions saturated with argon at room temperature. The potentials were measured using a 16-channel mV-meter (Lawson Labs, Inc., Malvern, PA). The reference electrode was an Ag/AgCl/3M KCl electrode. All experiments were performed at room temperature. The X-ray photoelectron spectroscopy (XPS) analysis was performed with a Physical Electronics Quantum 2000 XPS-spectrometer equipped with a monochromatized Al-X-ray source. The Energy Dispersive Analysis of X-ray (EDAX) measurements were performed using a Scanning Electron Microscope, SEM model LEO 1530 from LEO Electron Microscopy Ltd, which was connected to an Image and X-ray analysis system – model Vantage from ThermoNoran. The LA-ICP-MS measurements were performed using a model 6100 Elan DRC Plus of ICP-MS from Perkin Elmer SCIEX (Waltham, USA) and UP-213 of Laser Ablation from “New wave Research” Merchantek Products (Fremont, USA). The Fourier Transform Infrared (FTIR) spectra were recorded with a Bruker IFS 66/S instrument. The Atomic Force Microscopy (AFM) images were recorded with a NanoScope IIIa microscope (Digital Instruments Inc., Santa Barbara, CA), equipped with the extender electronics module enabling phase imaging in tapping mode. For numerical calculations Mathcad 2001 Professional by MathSoft, Inc. Canada, was used. 4. Procedures of CP-BL-Me electrode preparation 4.1 Conducting polymer films - deposition The electrodeposition of the poly(pyrrole), poly(N-methylpyrrole) or poly(3,4-ethylene- dioxytiophene) films was carried out from solution that contained dopant and selected monomer. The monomer concentration was equal to 0.1M for pyrrole and N-methylpyrrole or 0.01 M for 3,4-ethylenedioxythiophene. Dopant concentration was equal to 0.1M for ATP, ADP, Gln or Asn. PEDOT, PMPy and PPy were electrodeposited onto the working electrode potentiostatically, under constant potential or dynamically with potential cycling. In the last case the scan rate was equal to 20 mV·s -1 . Deposition time or number of cycles was selected to obtain desired charge density. CP films doped with ATP and ADP were deposited potentiostatically under +0.9 V or +1.02 V (PEDOT), +0.66, 0.68 or +0.70 V (PPy) as well as +0.8 V (PMPy) (vs. Ag/AgCl/3M KCl) or dynamically by scanning the potential in the range 0 – (+0.9) V or 0 – (+1.02) V (PEDOT films) and 0 – (+0.70) V (PPy films) (vs. Ag/AgCl/3M KCl). The charge density was equal to 510 – 750 mC·cm -2 . PPy-Asn(Gln) films were grown on the working electrode at a potential of +1.00 V (vs. Ag/AgCl/3M KCl) and charge density of 240 mC·cm -2 was used. The growth of heparin-doped poly(pyrrole) and poly(3,4-ethylenedioxythiophene) was performed using solutions containing 40 mg·ml -1 of heparin and 0.1 M pyrrole or 0.01M 3,4- ethylenedioxythiophene. Dynamic growth was performed by scanning the potential Advances in Biomimetics 280 between 0 and +0.80 V (PPy) or 0 and +0.92 V (PEDOT) (vs. Ag/AgCl/3M KCl) and potentiostatic growth was achieved by holding a potential at +0.80 V (PPy) and +0.92 V or +0.96 V (PEDOT) (vs. Ag/AgCl/3M KCl) for different times in order to obtain charge density 480 – 840 mC·cm -2 . 4.2 The process of making CP-BL membranes cation-sensitive After synthesis, the polymer membranes were washed with deionized water and then the electrodes were soaked and stored in a alkaline mixture of 0.1 M YCl n and Y(OH) n were Y was a main cation. Only conditioning in the alkaline solution was effective. The cation complexes with BL were formed after CP-BL film deprotonation in alkaline solutions (protons were substituted with other cations) as shown on Fig. 1. As a rule, a cationic response with a linear range within the K + , Na + , Li + activities from 10 -1 M to 10 -4 M and Ca 2+ , Mg 2+ activities from 10 -1 M to 10 -5 M with a close-to-Nernstian slope was observed for the CP-BL films usually after 1 week of soaking. Fig. 1. Ion-exchange processes during conditioning of CP-BL membrane in alkaline solution. 5. Results and discussion 5.1 Electrodeposition and its influence on potentiometric response The short response time of the CP-BL membranes is highly desirable to study the transient membrane potential changes during equilibration processes. As we have shown for CP-ATP membranes, the response time is strongly dependent on the film morphology. The AFM and potentiometric study conducted in parallel have exemplified the strong influence of the film preparation conditions on its further potentiometric response. Generally, CP-BL films made under dynamic conditions are close to two dimensional structures i.e. they are flat and compact, while the potentiostatic deposition leads to three- dimensionally morphology of the films. Fig. 2 presents the exemplary AFM phase contrast images of the PPy-ATP membranes taken after film deposition under different conditions: potentiostatic under +0.66 V (a), +0.68 V (b), +0.70 V (c) and dynamic (0- (+0.7) V) (d). The [...]... vibration in benzene ring 1380 1381 0.012 0.018 11 C-O stretching vibration in syringyl ring 1326 1327 0.030 0.016 12 C-O stretching vibration in guaiacyl ring 1267 1266 0.013 0.010 13 C-O stretching vibration in syringyl ring 1216 1217 0.056 0.038 14 C-H stretching vibration in syringyl ring 1121 1125 0.015 0.018 15 C-O bending vibration in secondary alcohol, ether 1085 1084 0.018 0.364 16 C-O bending vibration... 30-33, ISSN 10 09- 8666 Shi, S L & He, F W (2003) Analysis & Detection of Pulp & Paper, China Light Industry Press, ISBN 7-50 19- 392 0 -9/ TS.2332, Beijing Stenius, P & Vuorinen, T ( 199 9) Direct Characterization of Chemical Properties of Fibers, In: Analytical Methods in Wood Chemistry, Pulping and Papermaking, Sjöström, E & Alén, R., (Ed.), 1 49- 191 , Springer-Verlag, ISBN 3-540-63102-X, Berlin, Heidelberg,... syringyl-type present in residual lignin were degraded Structural linkages were cleaved including β-O-4, β-1, β-5 and β-β Molecular weight of residual lignin was decreased as reaction proceeding, oppositely that of C9-structural uint was increased due to the increase in oxygen element content according to the C9-experimental formulas obtained in this study Besides the structural changes occured in. .. conditioning in alkaline lithium solution (b) 288 Advances in Biomimetics 5.4 Influence of interfering cations on biomimetic CP-BL membranes After inducing a proper sensitivity the influence of other ions on biomimetic membranes potential was studied by adding the interfering ions to the solution of main ions As expected, in the case of membranes sensitive towards monovalent cations, strong interferences... cellulose, hemicellulose and lignin 1032 1032 0.0 29 0.026 7 C=O stretching vibration in cellulose and hemicellulose 98 7 98 8 0.022 0.012 8 C1 deformation vibration in polysaccharide 896 896 0.060 0.0 49 9 Crystallinity index (Shi & He, 2003) O’KI = A 1433cm-1/A 896 cm-1 N·O’KI = A 1375cm-1/A 2 899 cm-1 0.783 0.8 49 0 .90 3 0 .94 9 Table 6 Results of FTIR analysis of resultant bleached pulp when oxygen delignified... 2 899 290 1 0.141 0.121 2 CH2 shear vibration in cellulose 1433 1432 0.054 0.055 3 CH bending vibration in cellulose and hemicellulose 1375 1376 0.120 0.116 4 C=O stretching vibration in lignin 1237 1238 0.008 0.001 5 C=O stretching vibration in cellulose and hemicellulose 10 59 10 59 0.423 0.386 6 C=O stretching vibration in cellulose, hemicellulose and lignin 1032 1032 0.0 29 0.026 7 C=O stretching vibration... vibration in primary alcohol, ether 1051 1052 0.5 29 0.027 17 C-H bending vibration in benzene ring 898 899 0.023 0.006 Table 3 Results of FTIR analysis of isolated residual lignins before and after Co-salen biomimetic treatment 301 Mechanism of Co-salen Biomimetic Catalysis Bleaching of Bamboo Pulp reactivity of residual lignin in pulp The decrease in relative intensity of 292 4, 1462 cm-1 indicated... Co-salen Biomimetic Catalysis Bleaching of Bamboo Pulp Yan-Di Jia and Xue-Fei Zhou Kunming University of Science & Technology China 1 Introduction Biomimetics have enzymatically and chemically the catalytic performance and the advantage to reduce pollution (Xie, 199 9), and thus have been introduced into the pulping and bleaching field (Huynh, 198 6; Cui & Dolphin, 199 4) Co-salen can be easily synthesized... according to the relative intensity, which was just because of the oxidation reaction in which obvious increase in carbonyl (1640 cm-1) was observed This increase can enhance the No Assignment (Jiang, 20 09) Wavenumber /cm-1 Untreated Treated Rel intensity Untreated Treated 1 OH stretching vibration 3425 3432 0.555 0.485 2 CH asymmetrical stretching vibration in CH3, CH2, CH 292 4 292 3 0. 198 0. 191 3 CH... complexes Biochemical & Biophysical Research Communications, 1 39, 3, 1104-1110, ISSN 0006- 291 X Jiang, T D (20 09) Lignin, Chemical Industrial Press, ISBN 97 8-7-122-03 796 -1, Beijing Liu, J.; Shanguan, G Q & Li, J ( 199 1) Synthesis and oxygen-carrying effect of [Co II(salen)] complex Journal of Jining Medical University, 14, 4, 19- 20, ISSN 1000 -97 60 Liu, Z C.; Liu, F.; Lu, Y.; Xie, M X & Zhang, Y Q (2002) . conditioning in alkaline lithium solution (b). Advances in Biomimetics 288 5.4 Influence of interfering cations on biomimetic CP-BL membranes After inducing a proper sensitivity the influence. peptide-induced membrane destabilization. Biophys. J. 93 , 42 89- 4 299 , 0006-3 495 . Matsuzaki, K., Harada, M., Handa, T., Funakoshi, S., Fujii, N., Yajima, H., and Miyajima, K. ( 198 9). Magainin 1-induced. Chemical Bulletin 47, 2 490 -2 495 , Mileykovskaya, E., Zhang, M., and Dowhan, W. (2005). Cardiolipin in energy transducing membranes - Review. Biochemistry Mosc. 70, 191 - 196 , 0006- 297 9. Mubagwa,