In Situ Quartz Crystal Microbalance Study of Self-Assembly and Mass Transfer Processes of a Redox-Active Osmium Complex

Abstract

The adsorption process of the redox-active self-assembling molecule [Os(bpy) 2 (pydpy)Cl] + (bpy ) 2,2′-bipyridine and (pydpy) ) trans-1,2-bis(4-pyridyl)ethylene) onto a Pt electrode has been investigated in aqueous KClO 4 , KPF 6 , and KNO 3 electrolyte solutions using the quartz crystal microbalance in conjunction with cyclic voltammetry. In all the electrolyte solutions examined, the adsorption of the Os complex appears to be accompanied by water molecules, whose number is higher in KPF 6 solution (38-41) than in KClO 4 (26-34). In KNO 3 solutions the hydration number increases with increasing surface coverage of the Os complex. The mass transfer during the redox reaction of the adsorbed Os complex monolayer is of the anion exchange type in all the electrolyte solutions examined. Further, it was determined that the anions are accompanied by water molecules, whose numbers (for surfaces at saturation coverage of the Os complex) in a KPF 6 solution (6-7) were higher than in the other electrolyte solutions. At surface coverage values below saturation, only 0-0.5 water molecules accompany the anions. Additionally, we also demonstrate that the film properties do not change during the self-assembly or redox processes of the Os complex, as determined by means of admittance measurements of the quartz crystal resonator on the basis of the electrical equivalent circuit.

Determination of solvation numbers of [RuII(bpy)3] and [RuII(tpy)2] functionalized-PAMAM dendrimers adsorbed onto platinum electrode surfaces

“…What is important, however, is that the resistance remained constant. Similar results have been reported for the self-assembly processes of aliphatic thiol molecules onto gold electrode surfaces [27], and of an osmium bipyridine derivative onto a platinum electrode [12]. Thus, these results indicate that the adsorbed dendrimer films, in a 0.10 M TBAP+AN solution, can be regarded as rigid, and that their film properties remain essentially constant with time.…”

“…We have previously reported that the stirring does not affect the frequency stability, which was maintained to within AE1.7 Hz for 10 h after the establishment of a constant temperature (25.0 AE 0.1°C) [12]. Thus, we can safely neglect any effects of changes in the viscosity and density of the solution on the frequency.…”

“…X-ray diffraction, UV-Vis, IR, measurement of solvation enthalpy and entropy) difficult. The use of the electrochemical quartz crystal microbalance (EQCM) which involves the combination of electrochemical and QCM techniques is a powerful method for determining solvation numbers of redox active species adsorbed onto the surface of an electrode [12]. The surface coverage can be obtained from the electrochemical measurement (e.g.…”

Electrochemistry, Surface Plasmon Resonance, and Quartz Crystal Microbalance: An Associative Study on Cytochrome c Adsorption on Pyridine Tail-Group Monolayers on Gold

“…This excess of mass can be due to multilayers of Cyt c or, more likely, to the adsorption of water molecules and/or ions in solution. 57,58 The CVs illustrated in Figure 2B were obtained in the QCM cell just after the frequency steady state was reached, ca. 50 min of immersion in PBS solution containing Cyt c. Then, the apparatus was washed and filled with PBS solution and the CVs illustrated in Figure 2C were acquired.…”

Thermodynamic, Kinetic, Surface pKa, and Structural Aspects of Self-Assembled Monolayers of Thio Compounds on Gold

“…In previously reported studies on the adsorption of Hpyt, 26 TNA, 25 and 1,4-dt 27 on gold, we found that the monolayers formed with these molecules present defects through which water molecules can penetrate. Also, Abrunã et al, 42 on the basis of a combination of QCM and cyclic voltammetry techniques, found that the formation of monolayers of an Os complex on Pt is accompanied by water molecules. Assuming that the mass difference between QCM and reductive desorption is due solely to water, the numbers of coadsorbed water molecules per molecule of adsorbate were calculated and are presented in Table 2.…”