Charakterisierung des Ladungstransfers von immobilisiertem Cytochrom c

The Aim of this work was to study the charge transfer of redoxactive proteinswith new techniques. Especially the behavior of individual proteins should be observed to obtain a clear and deep insight in the charge transfer and its influencing parameters. Since methods that integrate over a large number of proteins do not allow the measurement of single charge transfer, strategies should be developed to contact a single molecule with two conductors to measure the transient current. In this work cytochrome c (Cyt c) was chosen as redoxactive protein, because it is a relatively well characterized system. Cyt c was immobilized to goldelectrodes via a self assembled monolayer (SAM) ofa carboxylic terminated thiol. In order to contact a single molecule twoapproaches from molecular electronics were pursued. In a vertical adjustmentCyt c was contacted with the tip of a scanning tunneling microscope (STM).In a horizontal approach Cyt c should be contacted between a pair ofnanowires.The adlayer surface of mercaptopropionic acid (MPA), which was assembled at room temperature, consists of ordered domains with holes. The holes equal monoatomic steps of the Au(111) terraces. A temperature increase during self organization of the MPA molecules leads to a ripening of the holes. The kinetic inhibition to reach the thermodynamic more stable SAM without holes can be overcome with increasing temperature. Further a clear time dependence is observed for the self organization. The alkyl chains of the SAM consisting of mercaptoundecanoic acid (MUA) are unordered for a short assembly time (3 h). However after 24 h assembling the molecules form an ordered densely packed adlayer. The formation of hydrogen bonds of the carboxylic groups among each other is aggravated for a unordered SAM of MUA, a deprotonation is alleviated and thus the electrostatic interaction to the positive lysin groups of the protein advantaged. A increased protein adsorption is observed on a unordered SAM. In order to characterize the structure of the supramolecular system (Cyt c, SAM, Au-electrode) QCM, SPR and AFM measurements were carried out. These measurements clearly proof the adsorption of proteins on the SAM. Further more an influence of ionic strength on the adsorption behavior of Cyt c was observed. At higher ionic strengthes agglomerates were formed, whereas at lower ionic strengthes formation of a monolayer was observed.A single electron transfer of a immobilized proteinmonolayer is shown withcyclic voltammetry. Goldnanoparticles were immobilized to adsorbed yeast cytochrome c, which was proven with cyclic voltammetry. STM images of this system showed structure characteristics with a lateral dimension of 3 nm (diamter of Cyt c). Potential depending height profiles were observed for some of these objects. This phenomenon cab be described by changing conductanceof the protein due to a resonant tunneling process. An increased conductance isobserved, when energetic levels of the protein are in resonance with the fermienergy of the gold substrate. A local addressing with STM was possible. In order to reproduce and verify the data of the STM approach a contact was fabricated with a pair of facing goldelectrodes in molecular distance on a mikrochip. The nanocontacts were engineered by defining a gold nanowire with e-beam lithography and subsequently electrochemical etching. During etching quantum conductance tunneling behavior was observed. However the realized junctions showed very fractal structure. For the characterization of a single protein a well defined structure is indispensable. An improvement of the nanocontact structure was achieved by reducing the potential sweeping rates during the electro corrosion process.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2006

Author dc:creator

• Salomon, Oliver

Contributors dc:contributor

• Offenhäusser, Andreas

• info:eu-repo/classification/ddc/660
• Cytochrom c
• Proteine
• Selbstorganisation
• Rastertunnelmikroskopie
• Rastertunnelmikroskop
• Nanodraht
• Ladungstransfer
• Elektronentransfer
• Technische Chemie

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-122738%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:61054