Single-crystal voltammetry and in situ scanning tunnelling microscopy of redox metalloproteins: Bioelectrochemistry towards the single-molecule level

External electric fields (EEFs) have proven to be very efficient in catalysing chemical reactions, even those inaccessible via wet-chemical synthesis. At the single-molecule level, oriented EEFs have been successfully used to promote in situ single-molecule reactions in the absence of chemical catalysts. Here, we elucidate the effect of an EEFs on the structure and conductance of a molecular junction. Employing scanning tunnelling microscopy break junction (STM-BJ) experiments, we form and electrically characterize single-molecule junctions of two tetramethyl carotene isomers. Two discrete conductance signatures show up more prominently at low and high applied voltages which are univocally ascribed to the trans and cis isomers of the carotenoid, respectively. The difference in conductance between both cis-/trans- isomers is in concordance with previous predictions considering π-quantum interference due to the presence of a single gauche defect in the trans isomer. Electronic structure calculations suggest that the electric field polarizes the molecule and mixes the excited states. The mixed states have a (spectroscopically) allowed transition and, therefore, can both promote the cis-isomerization of the molecule and participate in electron transport. Our work opens new routes for the in situ control of isomerisation reactions in single-molecule contacts.

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In situ electrochemical scanning tunnelling microscopy investigation of structure for horseradish peroxidase and its electricatalytic property

Bioelectrochemistry and Bioenergetics ◽

10.1016/0302-4598(95)01893-x ◽

1996 ◽

Vol 39 (2) ◽

pp. 267-274 ◽

Cited By ~ 54

Author(s):

Jingdong Zhang ◽

Qijin Chi ◽

Shaojun Dong ◽

Erkang Wang

Keyword(s):

Horseradish Peroxidase ◽

Scanning Tunnelling Microscopy ◽

Microscopy Investigation ◽

Scanning Tunnelling ◽

Tunnelling Microscopy

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Mechanisms of in Situ Scanning Tunnelling Microscopy of Organized Redox Molecular Assemblies.

The Journal of Physical Chemistry A ◽

10.1021/jp011838r ◽

2001 ◽

Vol 105 (31) ◽

pp. 7494-7494 ◽

Cited By ~ 11

Author(s):

Alexander M. Kuznetsov ◽

Jens Ulstrup

Keyword(s):

Scanning Tunnelling Microscopy ◽

Molecular Assemblies ◽

Scanning Tunnelling ◽

Tunnelling Microscopy

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Voltammetry and molecular assembly of G-quadruplex DNAzyme on single-crystal Au(111)-electrode surfaces – hemin as an electrochemical intercalator

Faraday Discussions ◽

10.1039/c6fd00091f ◽

2016 ◽

Vol 193 ◽

pp. 99-112 ◽

Cited By ~ 6

Author(s):

Ling Zhang ◽

Jens Ulstrup ◽

Jingdong Zhang

Keyword(s):

Single Crystal ◽

Single Molecule ◽

Electrode Surface ◽

Molecular Assembly ◽

Electrode Surfaces ◽

Potential Control ◽

G Quadruplex ◽

Tunnelling Microscopy ◽

Dna Quadruplexes

DNA quadruplexes (qs) are a class of “non-canonical” oligonucleotides (OGNs) composed of stacked guanine (G) quartets stabilized by specific cations. Metal porphyrins selectively bind to G-qs complexes to form what is known as DNAzyme, which can exhibit peroxidase and other catalytic activity similar to heme group metalloenzymes. In the present study we investigate the electrochemical properties and the structure of DNAzyme monolayers on single-crystal Au(111)-electrode surfaces using cyclic voltammetry and scanning tunnelling microscopy under electrochemical potential control (in situ STM). The target DNAzyme is formed from a single-strand OGN with 12 guanines and iron(iii) porphyrin IX (hemin), and assembles on Au(111) through a mercapto alkyl linker. The DNAzyme monolayers exhibit a strong pair of redox peaks at 0.0 V (NHE) at pH 7 in acetate buffer, shifted positively by about 50 mV compared to free hemin weakly physisorbed on the Au(111)-electrode surface. The voltammetric hemin signal of DNAzyme is enhanced 15 times compared with that of hemin adsorbed directly on the Au(111)-electrode surface. This is indicative of both the formation of a close to dense DNAzyme monolayer and that hemin is strongly bound to the immobilized 12G-qs in well-defined orientation favorable for interfacial ET with a rate constant of 6.0 ± 0.4 s−1. This is supported by in situ STM which discloses single-molecule G-quartet structures with a size of 1.6 ± 0.2 nm.

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