Spectroelectrochemical Characterization of 1,2-Dipalmitoyl-sn-glycero-3-cytidine Diphosphate Nucleolipid Monolayer Supported on Gold (111) Electrode

Abstract

The effect of the electrode potential on the orientation and conformation of the 1,2-dipalmitoyl-sn-glycero-3cytidine monolayer deposited on a gold (111) electrode surface was described. The potential of zero free charge (E pzc ) 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 − E pzc ) > 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 − E pzc ) < −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 − E pzc ) > 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.

Mixed monolayer of a nucleolipid and a phospholipid has improved properties for spectroelectrochemical sensing of complementary nucleobases

“…Several studies with nucleolipid monolayers formed at the air water interphase demonstrated molecular recognition capabilities of these monolayers to the complementary DNA bases [10][11][12][13][14][15][16][17]. Our work with 16:0 DG-CDP monolayers on gold electrodes, previously incubated with guanine in 0.1 M NaF solutions, showed the existence of specific Watson-Crick interactions between the cytosine moiety of the nucleolipid and guanine at positive electrode charge densities and non-specific interactions at negatively charged surfaces [18]. This knowledge could be used for the preparation of functionalized liposomes for drug delivery.…”

“…Electrochemical and PM-IIRAS instrumentation and measurements has been described thoughtfully in a previous work. [9]. A detailed description is also included in the supplementary information file.…”

“…The surface charge densities at the gold (111) electrode were measured by integrating current transient registered when potential was stepped from a value at which the monolayer was present at the gold surface to the potential -0.8 V vs SCE at which it was desorbed (detached) from the surface [19,20]. The procedure of these measurements was described in a previous paper [9]. At potential -0.8 V vs SCE, the charge density of gold (111) electrode initially covered by the monolayer of nucleolipid become equal to the charge of the monolayer free gold electrode.…”

“…To overcome this problems, we deposited monolayers of 1,2-dipalmitoyl-snglycero-3-(cytidine diphosphate) nucleolipid (16:0 DG-CDP) (Figure 1) on bare gold electrodes, by transferring Langmuir monolayers prepared at the air/water interface to the electrode surface by the Langmuir-Shaefer method (horizontal touch). The molecules forming the monolayer were then oriented with the hydrophobic tails towards the electrode surface, while the polar head containing the nucleobase derivative towards the electrolyte, preventing their interaction with the electrode surface [9]. The characterization of these modified electrodes by differential capacity and charge density measurements allowed us to determine the stability of the system as a function of the electrode potential.…”

In Situ and Operando Techniques for Investigating Electron Transfer in Biological Systems

“…For instance, PM‐IRRAS allows the investigation of how water cushion formation separates a phospholipid bilayer from the electrode surface influencing the membrane orientation and ET processes [110,111] . Capacitance and chronocoulometric measurements coupled with PM‐IRRAS are effective for probing the stability of the lipid monolayer on electrodes and determining the conformation and orientation of acyl chains as a function of applied potentials [112–114] as well as for studying ion channel properties, lipid‐peptide interactions, and transmembrane ion transport mechanisms [115–117] . Recently, Su et al [115] .…”