Electrochemical Evaluation of 4-(Dimethylamino)pyridine Adsorption on Polycrystalline Gold

Abstract

Using differential capacity and chronocoulometry, we have studied the electrosorption of 4-(dimethylamino)pyridine (DMAP) on polycrystalline gold electrode surfaces. Our results indicate that the orientation of DMAP is highly dependent on the electrode potential and electrolyte pH. At pH values at or above the primary pKa, the adsorbed species is DMAP and orients vertically on the electrode surface via the lone pair of electrons on the pyridine ring's nitrogen atom. At very low pH values (<3) the adsorbed species is the protonated ion, DMAPH+, which can be desorbed from the electrode surface when the metal's surface charge density is made appreciably positive of the potential of zero charge. At intermediate electrolyte pH, either DMAP or DMAPH+ is adsorbed on the surface depending on the electrode's potential. At negative charge densities, DMAPH+ lies nearly flat on the gold electrode and the surface coverage is correspondingly low. When the electrode is positively charged, the adsorbate undergoes a phase transition to a vertical orientation and is simultaneously deprotonated to DMAP. Our results rationalize the stability of DMAP-ligated gold nanoparticles as a function of pH and demonstrate that the ligand's surface coverage is the principal factor in determining the stability of the colloidal system.

Preparation and Characterization of 4-Dimethylaminopyridine-Stabilized Palladium Nanoparticles

“…From a comparison of these palladium nanoparticles with those produced using the phase transfer procedure reported by Gittins et al 16 In previous studies on DMAP stabilized gold nanoparticles it has been proposed that DMAP binds to the surface of gold nanoparticles in a perpendicular orientation via the lone pair of electrons on the endocyclic nitrogen atom. 16,[37][38][39] It is believed that electron delocalisation places a formal negative charge on the endocyclic nitrogen atom, which is highly favorable for bonding to the gold nanoparticle while concomitantly placing a formal positive charge on the exocyclic nitrogen atom. A similar weak non-covalent interaction would be expected for the DMAP stabilized palladium nanoparticles reported here (see Figure 3).…”

Microsecond Resolved Infrared Spectroelectrochemistry Using Dual Frequency Comb IR Lasers

“…Briefly, DMAP adsorbs on polycrystalline gold from neutral and basic solutions through the lone pair of electrons on the endocyclic nitrogen. This phase of adsorption is stable on the metal surface in the approximate potential range −0.8 V < E < 0.5 V . The pyridine derivative is totally desorbed by application of potentials more negative than −0.8 V. The broad-band ATR-SEIRAS spectrum of DMAP consists of several strong absorbance peaks corresponding to A′ ring modes, the most prominent of which is centered at approximately 1628 cm –1 , which conveniently lies within the approximately 100 cm –1 comb bandwidth.…”

“…The potential dependent adsorption of DMAP on gold surfaces has been previously studied with both electrochemical , and spectroelectrochemical techniques. Briefly, DMAP adsorbs on polycrystalline gold from neutral and basic solutions through the lone pair of electrons on the endocyclic nitrogen.…”

Surface sensitive infrared spectroelectrochemistry using palladium electrodeposited on ITO-modified internal reflection elements

“…A detailed description of the differential capacity setup is described elsewhere. 33 Electrochemical ATR-SEIRAS measurements SEIRA spectra were obtained using a Bruker Vertex 70 FTIR spectrometer equipped with a liquid-nitrogen-cooled MCT detector. The angle of incidence and the spectral resolution were set to 601 and 8 cm À1 , respectively.…”