scholarly journals Thrombin-Binding Aptamer Quadruplex Formation: AFM and Voltammetric Characterization

2010 ◽  
Vol 2010 ◽  
pp. 1-8 ◽  
Author(s):  
Victor Constantin Diculescu ◽  
Ana-Maria Chiorcea-Paquim ◽  
Ramon Eritja ◽  
Ana Maria Oliveira-Brett
Keyword(s):  
Electron Transfer ◽  
Surface Coverage ◽  
Pyrolytic Graphite ◽  
Oxidation Potential ◽  
Oxidation Peak ◽  
No Adsorption ◽  
Guanine Oxidation ◽  
Force Microscopy ◽  
Atomic Force ◽  
Quadruplex Formation

The adsorption and the redox behaviour of thrombin-binding aptamer (TBA) and extended TBA (eTBA) were studied using atomic force microscopy and voltammetry at highly oriented pyrolytic graphite and glassy carbon. The different adsorption patterns and degree of surface coverage were correlated with the sequence base composition, presence/absence of K+, and voltammetric behaviour of TBA and eTBA. In the presence of K+, only a few single-stranded sequences present adsorption, while the majority of the molecules forms stable and rigid quadruplexes with no adsorption. Both TBA and eTBA are oxidized and the only anodic peak corresponds to guanine oxidation. Upon addition of K+ions, TBA and eTBA fold into a quadruplex, causing the decrease of guanine oxidation peak and occurrence of a new peak at a higher potential due to the oxidation of G-quartets. The higher oxidation potential of G-quartets is due to the greater difficulty of electron transfer from the inside of the quadruplex to the electrode surface than electron transfer from the more flexible single strands.

scholarly journals Electrochemical Solvent Cointercalation into Graphite in Propylene Carbonate-Based Electrolytes: A Chronopotentiometric Characterization

2018 ◽  
Vol 2018 ◽  
pp. 1-5 ◽  
Author(s):  
Hee-Youb Song ◽  
Soon-Ki Jeong
Keyword(s):  
Propylene Carbonate ◽  
Redox Reactions ◽  
High Current Density ◽  
Coulombic Efficiency ◽  
Pyrolytic Graphite ◽  
Lithium Ion ◽  
In Situ Raman Spectroscopy ◽  
Force Microscopy ◽  
Atomic Force

Interfacial reactions strongly influence the performance of lithium-ion batteries, with the main interfacial reaction between graphite and propylene carbonate- (PC-) based electrolytes corresponding to solvent cointercalation. Herein, the redox reactions of solvated lithium ions occurring at the graphite interface in 1 M·LiClO4/PC were probed by chronopotentiometry, in situ atomic force microscopy (AFM), and in situ Raman spectroscopy. The obtained results revealed that high coulombic efficiency (97.5%) can be achieved at high current density, additionally showing the strong influence of charge capacity on the above redox reactions. Moreover, AFM imaging indicated the occurrence of solvent cointercalation during the first reduction, as reflected by the presence of hills and blisters on the basal plane of highly oriented pyrolytic graphite subjected to the above process.

scholarly journals Scale-Dependent Friction-Coverage Relations and Non-Local Dissipation in Surfactant Monolayers

2020 ◽  
Author(s):  
Hongyu Gao ◽  
James Ewen ◽  
Remco Hartkamp ◽  
Martin H. Müser ◽  
Daniele Dini
Keyword(s):  
Surface Coverage ◽  
Leading Edge ◽  
Thermal Dissipation ◽  
Nonequilibrium Molecular Dynamics ◽  
Kinetic Friction ◽  
Surfactant Monolayers ◽  
Force Microscopy ◽  
Sliding Surfaces ◽  
Atomic Force ◽  
Afm Tips

<div>Surfactant molecules, known as organic friction modifiers (OFMs), are added to lubricants to reduce friction and wear between sliding surfaces. In macroscale experiments, friction generally decreases as the coverage of OFM molecules on the sliding surfaces increases. However, recent nanoscale experiments with sharp atomic force microscopy (AFM) tips have shown increasing friction. To elucidate the origin of these opposite trends, we use nonequilibrium molecular dynamics (NEMD) simulations and study kinetic friction between OFM monolayers and an indenting nanoscale asperity. For this purpose, we study various coverages of stearamide OFMs on iron oxide surfaces and silica AFM tips with different radii of curvature. For our small tip radii, the friction coefficient and indentation depth both have a non-monotonic dependence on OFM surface coverage, with maxima occurring at intermediate coverage. This suggests that friction is dominated by plowing. We rationalise the non-monotonic relations through a competition of two effects (confinement and packing density) that varying the surface coverage has on the effective stiffness of the OFM monolayers. We also show that kinetic friction is not very sensitive to the sliding velocity in the range studied, indicating that it originates from instabilities. Indeed, while friction predominately originates from the plowing action of the monolayers by the leading edge of the tip, thermal dissipation is mostly localised in molecules towards the trailing edge of the tip.</div>

Scanning Tunneling Microscopy and Atomic Force Microscopy Investigation of Organic Tetracyanoquinodimethane Thin Films

1997 ◽  
Vol 12 (8) ◽  
pp. 1942-1945 ◽  
Author(s):  
H. J. Gao ◽  
H. X. Zhang ◽  
Z. Q. Xue ◽  
S. J. Pang
Keyword(s):  
Thin Films ◽  
Atomic Force Microscopy ◽  
Scanning Tunneling Microscopy ◽  
Pyrolytic Graphite ◽  
Film Surface ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Force Microscopy ◽  
Atomic Force ◽  
Microscopy Investigation

Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) investigation of tetracyanoquinodimethane (TCNQ) and the related C60-TCNQ thin films is presented. Periodic molecular chains of the TCNQ on highly oriented pyrolytic graphite (HOPG) substrates were imaged, which demonstrated that the crystalline (001) plane was parallel to the substrate. For the C60-TCNQ thin films, we found that there were grains on the film surface. STM images within the grain revealed that the well-ordered rows and terraces, and the parallel rows in different grains were generally not in the same orientation. Moreover, the grain boundary was also observed. In addition, AFM was employed to modify the organic TCNQ film surface for the application of this type of materials to information recording and storage at the nanometer scale. The nanometer holes were successfully created on the TCNQ thin film by the AFM.

Kinetics of the Nanohydrogel Flattening at a Hydrophobic Interface

2008 ◽  
Vol 8 (7) ◽  
pp. 3386-3391
Author(s):  
ImShik Lee ◽  
Haiying Sun ◽  
Jingxia Song ◽  
Ying Zhang
Keyword(s):  
Adsorption Mechanism ◽  
Pyrolytic Graphite ◽  
Force Microscopy ◽  
Atomic Force ◽  
Dynamic Observation ◽  
Membrane Mimetic ◽  
Aqueous Conditions ◽  
Unfolding Kinetics ◽  
Kinetics Of ◽  
Hydrophobic Interface

Hydrophobitized polysaccharides were designed to form the self-assembled nanohydrogels (hydrogel nanoparticles) in the aqueous conditions. For improving their biocompatibilities, they were decorated with the biomembrane-mimetic 2-methacryloyloxyethy1 phosphory1choline (MPC) polymers. The interfacial roles of the decorated membrane-mimetic nanohydrogels were investigated by choosing MPC branched choresteryl-bearing pullulan (CHP). Tapping-mode atomic force microscopy was used to study its adsorption mechanism on the hydrophobic highly oriented pyrolytic graphite (HOPG) surface in aqueous conditions. Dynamic observation at the interfaces revealed two distinctive patterns: the immobilized nanohydrogel particles and the flatten layers. The flattening (unfolding) kinetics with and without MPC branched nanohydrogel revealed that the flattening energy was at ∼37 kBT. The flattening rate of the MPC decorated nanohydrogels was ∼1.7 times faster than that without MPC decoration, corresponding to minor reduction of the flattening activation energy.

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