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Chronocoulometry was applied to determine charge in a monolayer of nucleolipid (1,2-dipalmitoyl-sn‑glycero-3-(cytidine diphosphate)) deposited at a gold electrode surface. The immersion method was used to measure the potential of zero charge of the interface (Epzci), which is a sum of charge on the monolayer of the nucleolipid and charge on the gold surface. Photon polarization infrared reflection absorption spectroscopy (PM-IRRAS) was used to determine formation of the Watson-Crick complex between terminal cytidine moiety of the nucleolipid and guanine (its complementary base) added to the solution. The combination of electrochemical and spectroscopic studies allowed one to demonstrate that the Watson-Crick complex is formed when the interface is positively charged. The potential applied to the electrode affects not only the complex formation but also orientation of the cytosine moiety. The complex is formed when the cytosine moiety is oriented assuming a small angle with respect to the electrode surface.

A mixed monolayer of 1,2-dipalmitoyl-sn-glycero-3-(cytidine diphosphate) nucleolipid (DG-CDP) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) was transferred from the air–water interface onto an gold (1 1 1) electrode surface using the Langmuir-Schaeffer (horizontal touch) technique. Compression isotherms were recorded for the monolayer spread at the air–water interface. These measurements demonstrated that the mixture composition 7:3 of DG-CDP:DPPC displayed reduced repulsive interactions between polar heads and ideal packing of acyl chains. Chronocoulometric experiments were performed to demonstrate stability of this film at the gold–solution interface. Photon polarization modulation infrared reflection absorption spectroscopy showed that the tilt angle of the acyl chains is slightly higher, and the chains are less twisted in the mixed than in the pure nucleolipid monolayer. In the mixed film, the tilt of the cytosine moiety (the sensing element of the monolayer) assumes a large angle with respect to the surface normal, even when the monolayer becomes detached from the gold surface. The mixed monolayer has improved properties for future applications for detection of guanine, its complementary base.

The effect of the electrode potential on the orientation and conformation of the 1,2-dipalmitoyl-sn-glycero-3-cytidine monolayer deposited on a gold (111) electrode surface was described. The potential of zero free charge (Epzc) for the monolayer-covered electrode was determined to be −0.2 V vs SCE. The differential capacitance and charge density data indicated that the monolayer is stable at the electrode surface when (E – Epzc) > 0.0 V. At negative rational potentials, a progressive detachment (electrodewetting) of the monolayer occurs. The monolayer is fully detached from the electrode surface at (E – Epzc) < −0.6 V. The conformation and orientation of the acyl chains and the orientation of the cytosine moiety were determined with the help of photon polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). The IR measurements demonstrate that the acyl chains are predominantly in the gel phase in the adsorbed state and tilted at an angle of ∼30° with respect to the electrode surface normal. The tilt angle of the acyl chains increases when the film is detached from the gold surface, indicating that the monolayer becomes more disordered. At (E – Epzc) > 0.0 V, the plane of the cytosine moiety assumes a small angle of ∼20° with respect to the surface. At negative potentials, the tilt angle of the cytosine fragment increases and rotates. With the help of DFT calculations, these changes were explained by the repulsion of the positive pole of the cytosine permanent dipole moment by the positively charged gold surface and its attraction to the metal surface at negative electrode potentials. This work provides unique information for the future development of sensors based on the molecular recognition of nucleoside targets.

Monolayers of 1,2-dipalmitoyl-sn-glycero-3-cytidine were incubated with guanine in a 0.1 M NaF electrolyte at the surface of a Langmuir trough and transferred to gold (111) electrodes using the Langmuir–Schaefer technique. Chronocoulometry and photon polarization modulation infrared reflection absorption spectroscopy were employed to investigate the influence of the static electric field on the orientation and conformation of the cytidine nucleolipid molecules on the metal surface in the presence of guanine and to monitor the molecular recognition of guanine with the cytosine moiety. When the monolayer is exposed to guanine solutions, the cytosine moiety binds to the guanine residue in either a Watson–Crick complex at positively charged electrode surfaces or a noncomplexed state at negative surface charges. The positive electrostatic field causes the cytosine moiety and the cytosine–guanine complex to adopt a nearly parallel orientation with respect to the plane of the monolayer with a measured tilt angle of ∼10°. The parallel orientation is stabilized by the interactions between the permanent dipole of the cytosine moiety or the Watson–Crick complex and the static electric field. At negative charge densities, the tilt of the cytosine moiety increases by ∼15–20°, destabilizing the complex. Our results demonstrate that the static electric field has an influence on the molecular recognition reactions between nucleoside base pairs at the metal–solution interface and can be controlled by altering the surface charge at the metal.

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The description of the monolayer formed at Au(1 1 1) by 2-mercaptobenzimidazole (MBI) under potential control has been based on electrochemical data (charge measurements) and spectroscopic information from the subtractively normalized interfacial Fourier transform infrared spectroscopy method (SNIFTIRS). From the quantitative analysis of the SNIFTIR spectra, a surface coverage Γ/Γmax was extracted for each sample potential. The evolution of the coverage with potential was in full agreement with the charge density curve. The shift of the pzc in the presence of MBI indicates that the adsorbed molecules have a nonzero component of the permanent dipole moment in the direction perpendicular to the electrode surface. Thanks to the high quality of the spectra, it was possible to determine the orientation of MBI molecules at the surface in the monolayer and submonolayer range. The angle between the C2-axis of the molecule and the direction normal to the surface is close to 64 ± 4° and its small change (<15°) with potential indicates that the orientation of the molecules is chiefly controlled by the chemical interaction between the sulphur atom and the gold surface. © 2005 Elsevier Ltd. All rights reserved., info:eu-repo/semantics/published

The behaviour of a self-assembled monolayer of 2-mercaptobenzimidazole (MBI) at the Au(111) electrode has been examined using cyclic voltammetry and in situ FTIR spectroscopy. The charge associated with the reductive desorption is pH independent while the oxidative partial redeposition charge increases when the pH is lowered. This is due to differences between the nature and the solubility of the MBI desorption product. In alkaline and neutral media MBI desorbs as the thiolate. In contrast, in acidic solutions the thiol is the desorbed product. Subtractively normalized interfacial reflection Fourier transform absorption spectroscopy (SNIFTIRS) has been applied to investigate the MBI monolayer in contact with aqueous solutions of different pH. The SNIFTIRS data are in agreement with the electrochemical results. Moreover, quantitative analysis of the IR data provided evidence that adsorbed MBI molecules assume a tilted orientation with an angle of 60±5° between the C2 axis of the molecule and the direction normal to the gold surface. © 2003 Elsevier B.V. All rights reserved., info:eu-repo/semantics/published

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SCOPUS: ar.j, info:eu-repo/semantics/published

info:eu-repo/semantics/published

info:eu-repo/semantics/published

info:eu-repo/semantics/published