Adsorption Dynamics of Electroactive Self-Assembling Molecules

Abstract

The kinetics of adsorption of redox active self-assembling molecules of the type [Os(bpy)aLCl]+ (bpy = 2,2'-bipyridine and L = 4,4'-bipyridine (pypy), trans-l,2-bis(4-pyridyl)ethylene (py=py), 1,3-bis(4-pyridy1)propane (dipy), or 1,2-bis(4-pyridyl)ethane (dipyH2)) have been investigated as a function of concentration, applied potential, and solvent. For all the complexes studied, the adsorption process appears to be under kinetic rather than diffusion control. Whereas the rate constant appears to be invariant with concentration at values below 1 pM, at high concentrations the kinetics are much faster. The electrode potential appears to affect the equilibrium coverage (likely due to electrostatic repulsions) but not the kinetics of adsorption. At low concentrations, there appears to be an induction period that we have tentatively ascribed to variations in local concentration in order to achieve a critical value after which adsorption is induced. In nonaqueous solvents, the solution concentration needed to achieve a saturation coverage is at least an order of magnitude larger than that in aqueous media pointing to the importance of adsorption strength and solubility differences. Whereas the rate of adsorption was not very sensitive to the nature of the solvent, the equilibrium value of the surface coverage was.

Analysis of Supramolecular Complexes of 3-Methylxanthine with Field Asymmetric Waveform Ion Mobility Spectrometry Combined with Mass Spectrometry

“…The base peak in the spectrum is the [(3-MX) 4 + Na] + ion at m/z 687.19, with the second most intense response corresponding to the [(3-MX) 8 + Na] + ion at m/z 1351.39. Monomer, dimer, and trimer sodiated complexes are observed with lower intensities at m/z 189.04, 355.09, and 521.14 respectively, suggesting that the tetrameric based complexes are more stable than non-tetrameric struc- Figure 1) were also observed using ESI-FAIMS-MS.…”

“…This suggests that the electric field strengths experienced by ions in the FAIMS (up to 60 kV cm (Figure 3b), but the reduction in ion intensity as the DF increases, expected due to increased field heating and scattering of ions through the FAIMS device at higher DFs, is not observed. The CF for maximum transmission of [(3-MX) 8 (Figure 4b), whilst having a symmetrical profile, is much more affected by the electric fields with the CF for maximum transmission increasing from 0.65 Td (DF 194 Td) to 2.85 Td (DF 323 Td), an increase of 2.20 Td, and the intensity starts to decrease significantly at DF 260 Td and above. The intensities of [(3-MX) 8 + Na] + and [(3-MX) 16 + 3Na -H] 2+ at DF values in the range 180-300 Td at the lowest fragmentor voltage of 50 V (Supplementary Figure 4), show the expected decrease in the intensity for the doubly charged [(3-MX) 16 + 3Na -H] 2+ ion at higher DFs as seen from Figure 4h.…”

“…S elf-assembling supramolecular complexes of simple molecules are of interest in a wide variety of fields [1], including structural biology [2], self-assembling membranes [3], therapeutic delivery systems [4], nanostructures [5][6][7], electrochemistry [8], and supramolecular technology [9]. 3-Methylxanthine (3-MX) is an example of a small molecule that can form stable noncovalently bound supramolecular complexes in the gas phase [10].…”

Luminescent acetylthiol derivative tripodal osmium(II) and iridium(III) complexes: Spectroscopy in solution and on surfaces

“…Traditionally, various organic molecules functionalized with thiols have been investigated for this purpose. However, recently there has been some interest toward employing organometallic complexes containing Ru [21][22][23][24] and Os [21,[25][26][27][28][29][30][31][32][33] metal ions and ligands derivatized with thiols and amino groups for SAM formation. High stability coupled with very good photophysical and electrochemical behavior, as well as the possibility to have multielectron processes make them appealing candidates over conventional organic molecules.…”

Hydrodynamic influence on the fractal morphology of the linoleic acid adsorbed layer at the mercury/electrolyte interface

“…In regards to adsorption kinetics, several theoretical models have been developed [1][2][3][4][5][6]. They are divided in two classes; one assumes kinetic control of the process while the other assumes fast adsorption with diffusion controlled mass transport.…”