Agnieszka Wieckowska

Optical Analysis of Hg2+ Ions by Oligonucleotide–Gold‐Nanoparticle Hybrids and DNA‐Based Machines

Zwei verschiedene optische Methoden fur die Analyse von Hg2+-Ionen, die auf der Bildung von Thymin-Hg2+-Komplexen beruhen, werden vorgestellt. Bei diesen Methoden werden die Hg2+-Ionen mithilfe aggregierter Goldnanopartikel und einer auf der DNA-Chemie basierenden Maschine (siehe Schema) analysiert.

Amplified electrochemical detection of DNA through the aggregation of Au nanoparticles on electrodes and the incorporation of methylene blue into the DNA-crosslinked structure

The amplified electrochemical sensing of DNA is accomplished by the analyte-induced aggregation of nucleic acid-functionalized Au nanoparticles, deposition of the aggregates on a thiolated monolayer-functionalized electrode, and the voltammetric analysis of the redox-active methylene blue intercalated in the nucleic acid duplexes associated with the aggregates.

Probing Kinase Activities by Electrochemistry, Contact‐Angle Measurements, and Molecular‐Force Interactions

Three different methods to investigate the activity of a protein kinase (casein kinase, CK2) are described. The phosphorylation of the sequence-specific peptide (1) by CK2 was monitored by electrochemical impedance spectroscopy (EIS). Phosphorylation of the peptide monolayer assembled on a Au electrode yields a negatively charged surface that electrostatically repels the negatively charged redox label [Fe(CN)6]3-/4-, thus increasing the interfacial electron-transfer resistance. The phosphorylation process by CK2 is further amplified by the association of the anti-phosphorylated peptide antibody to the monolayer. Binding of the antibody insulates the electrode surface, thus increasing the interfacial electron-transfer resistance in the presence of the redox label. This method enabled the quantitative analysis of the concentration of CK2 with a detection limit of ten units. The second method employed involved contact-angle measurements. Although the peptide 1-functionalized electrode revealed a contact angle of 67.5 degrees , phosphorylation of the peptide yielded a surface with enhanced hydrophilicity, 36.8 degrees. The biocatalyzed cleavage of the phosphate units with alkaline phosphatase regenerates the hydrophobic peptide monolayer, contact angle 55.3 degrees . The third method to characterize the CK2 system involved chemical force measurements between the phosphorylated peptide monolayer associated with the Au surface and a Au tip functionalized with the anti-phosphorylated peptide antibody. Although no significant rupture forces existed between the modified tip and the 1-functionalized surface (6+/-2 pN), significant rupture forces (multiples of 120+/-20 pN) were observed between the phosphorylated monolayer-modified surface and the antibody-functionalized tip. This rupture force is attributed to the dissociation of a simple binding event between the phosphorylated peptide and the fluorescent antibody (Fab) binding region.

Electrochemical and Conformational Consequences of Copper (CuI and CuII) Binding to β-Amyloid(1–40)

Copper‐induced structural rearrangements of Aβ40 structure and its redox properties are described in this study. Electrochemical and fluorescent methods are used to characterise the behaviour of Aβ–Cu species. The data suggest that time‐dependent folding of Aβ–Cu species may cause changes in the redox potentials.

Nanostructured films of in situ deprotected thioacetyl-functionalized C60-fullerenes on a gold surface

A series of thioacetyl-functionalized fullerene-C60 derivatives were synthesized using the Prato reaction of fullerene-C60 with six different 4-(S-acetylthioalkyl)benzaldehydes. The structures of the synthesized compounds were characterized by FT-IR, 1H NMR and ESI-MS techniques. The LUMO–HOMO band gaps, derived from DFT B3LYP/6-31G* calculations, for the azomethine ylides corresponding to each 4-(S-acetylthioalkyl)benzaldehyde and fullerene-C60 were correlated with the efficiency of the Prato reaction. The compounds were deposited onto gold electrodes via self-assembly following an in situ deprotection procedure which transformed the thioacetyl-functionalized compounds into their thiolated derivatives. The redox properties of the C60 derivatives in solution were characterized using Voltammetry. The LUMO–HOMO band gaps obtained from the electrochemical data were compared with the density functional theory (DFT) values for the optimized structures. The thioacetyl-functionalized C60 derivatives were employed for the catalytic reduction of halogenated hydrocarbons. Following deprotection, they were also employed for the modification of gold substrates. The solvent dependent barrier properties of the thiolated fullerene films were investigated using Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). The topography of the C60 derivative modified electrode was investigated using X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM), which confirmed stable modification of the Au support with a three dimensional (3D) film of worm-like fullerene aggregates.

Self-assembly of a nickel(II) pseudorotaxane nanostructure on a gold surface

Tetraazamacrocyclic complexes of NiII and CuII can be used as components of catenanes or rotaxanes showing electrochemically switched intramolecular motion in solution. In our present studies, we modify these compounds with organothiol chains to attach them to the surface of the electrode using the self-assembly method and employ them next as molecular switches, which change conductivity upon applying appropriate potential. The electrochemical properties of these compounds are studied in the solution and, in the case of thiol derivative, immobilized on the electrode surface. The macrocyclic complex of NiII, immobilized on the Au surface, forms the axis of the rotaxane. This compound can be anchored to the surface by one or two thiol groups. The data obtained from scanning tunneling microscopy (STM) experiments using colloidal Au confirm that the orientation normal to the surface dominates. The electrochemical experiments reveal reversible one-electron oxidation of metal center from +2 to +3. The behavior of the electrode modified with the macrocyclic complex of NiII upon immersion in a solution containing bismacrocyclic complex of NiII points to the formation of a new rotaxane-like nanostructure on the surface of the electrode.

A novel polynuclear donor complex based on helical peptides with aligned electroactive moieties

Two newly synthesised 21-amino acid peptides substituted with ferrocene groups preserve the helical structure of the peptide and behave as multi-centre donor systems with six electroactive reversible redox centres per molecule. The formal potential of the hexaferrocene compound is slightly less positive than that of its single centre analogue.

Reticulated vitreous carbon as a scaffold for enzymatic fuel cell designing

Three - dimensional (3D) electrodes are successfully used to overcome the limitations of the low space - time yield and low normalized space velocity obtained in electrochemical processes with two - dimensional electrodes. In this study, we developed a three - dimensional reticulated vitreous carbon - gold (RVC-Au) sponge as a scaffold for enzymatic fuel cells (EFC). The structure of gold and the real electrode surface area can be controlled by the parameters of metal electrodeposition. In particular, a 3D RVC-Au sponge provides a large accessible surface area for immobilization of enzyme and electron mediators, moreover, effective mass diffusion can also take place through the uniform macro - porous scaffold. To efficiently bind the enzyme to the electrode and enhance electron transfer parameters the gold surface was modified with ultrasmall gold nanoparticles stabilized with glutathione. These quantum sized nanoparticles exhibit specific electronic properties and also expand the working surface of the electrode. Significantly, at the steady state of power generation, the EFC device with RVC-Au electrodes provided high volumetric power density of 1.18±0.14mWcm-3 (41.3±3.8µWcm-2) calculated based on the volume of electrode material with OCV 0.741±0.021V. These new 3D RVC-Au electrodes showed great promise for improving the power generation of EFC devices.

Macrocyclic Multicenter Complexes of Nickel and Copper of Increasing Complexity

Multicenter (bi-, tri-, and tetranuclear) tetraazamacrocyclic complexes were self-assembled from Ni and Cu tetraazamacrocyclic mononuclear units and α,ω-diamines as building blocks. The structures of all compounds studied were proved by spectroscopic methods (ESI MS and NMR spectroscopy). Electrochemical experiments revealed reversible one-electron electrode processes at each of the Ni(2+) and Cu(2+) centers with formation of metal cations in oxidation state +3. Long linkers allow bi- and trinuclear complexes with noninteracting metal centers to be obtained. In the case of the short linkers (e.g. ethylenediamine) higher, trinuclear species are formed as major product. The structures of the bis- and tris-macrocyclic systems were confirmed by single-crystal X-ray diffraction. The tris-macrocyclic systems form cations in the shape of triangles partially filled with counterions and solvent molecules. The cations form positively charged layers, which interact in the crystal lattice with the neighboring negatively charged layers of anions. In solution, the trinuclear complexes exhibit strong host-guest interactions with 9,10-dimethyltriptycene due to complementarity of shape and size of this guest molecule. The association constants were determined by NMR spectroscopy and voltammetry, and very good agreement was obtained. The structural flexibility of the tetranuclear complex with long linkers allows for attractive interactions between the metal-complexing macrocycles that result in folding of the molecule. On the contrary, no folding is possible in the case of short linkers consisting of two CH(2) groups.

Size Does Matter—Mediation of Electron Transfer by Gold Clusters in Bioelectrocatalysis

Metal nanostructures are often used in bioelectrocatalytic systems to increase the electrode surface area or to improve the conductivity of biofilms. We demonstrate, that decreasing the size of gold nanoparticles below 2 nm may result in a change of the mechanism of electron transfer (ET) between the enzyme active site and the electrode from direct to mediated ET. Clusters with diameters smaller than 2 nm exhibited molecule‐like behavior reflected in the appearance of oxidation and reduction peaks separated by a clearly developed HOMO—LUMO gap. The redox activity of the nanoparticles was found to contribute to the ET mechanism of fructose dehydrogenase switching it to gold cluster mediated electron transfer instead of direct ET. In the presence of gold clusters at the electrode, the overpotential of the catalyzed fructose oxidation reaction was 100 mV lower and the catalytic reaction rate constant was 2.5 times larger confirming the unique mediating role of the Au clusters.