Lipophilicity of Peptide Anions:  An Experimental Data Set for Lipophilicity Calculations

Abstract

For the first time, the standard Gibbs energies of the transfer of peptide anions from aqueous solution to nitrobenzene were determined with the help of electrochemical measurements. These systematic studies clearly show that the lipohilicity contributions of single amino acid residues to the overall lipohilicity of a peptide anion strongly depend on the position of the amino acid in the backbone of the peptide. Therefore, additive models to calculate the overall lipophilicity of a peptide cannot provide very precise data. The present study is a plea for the experimental establishment of a data set that takes into account the individual nature of an amino acid residue and its position in a peptide.

Biphasic Electrospray Ionization for the Study of Interfacial Complexes

“…8,9 Electrochemistry has been developed over the last decades as a very efficient tool to study polarized liquid-liquid interfaces, because it is important to accurately control the potential drop across the interface between two immiscible electrolyte solutions (ITIES). 10,11 This control of the polarization can be used to drive or monitor adsorption or desorption processes 8,9,12 as well as to conduct and investigate ion 7,13 and/or electron transfer reactions across the interface. 14 Assisted ion transfer reactions are an important class of charge transfer reactions where ligands or ionophores in the organic phase can interfacially complex aqueous ions to extract them to the organic phase.…”

The determination of the standard Gibbs energies of ion transfer between water and heavy water by using the three-phase electrode approach

“…The recently developed technique to determine Gibbs energies of ion transfer using three-phase electrodes with organic solvent droplets immobilized on electrode surfaces proved to be useful for various solvent systems, e.g., water/nitrobenzene, water/dichloroethane, water/2-nitrophenyloctyl ether, water/n-octanol, water/menthol [7][8][9][10][11][12][13][14][15][16]. Since that technique provides rather low standard deviation data and offers an accuracy of the formal-potential measurement of 1 mV, we attempted to measure the small differences in Gibbs energies of ion transfer at the two interfaces H 2 Ojnitrobenzene and D 2 Ojnitrobenzene.…”

The determination of standard Gibbs energies of transfer of cations across the nitrobenzene|water interface using a three-phase electrode

“…The recent introduction of the three-phase electrode approach [12] has overcome some of the limitations of the four-electrode experiments, and led to significant progress in lipophilicity determinations of a large number of inorganic [13][14][15], and organic ions [13][14][15][16][17][18][19][20] across different liquidjliquid interfaces, such as waterjNB [12][13][14]16,17,19], waterjn-octanol [15,20], waterjmenthol [18], waterjDCE [12], and waterjnitrophenylnonyl ether [21].…”

“…When a droplet of this solution is attached to the working electrode and submerged in an aqueous electrolyte solution, the created charges in the organic liquid (due to the electrode reaction of the www.elsevier.com/locate/elecom electroactive compound) must be compensated by transfer of counter ions across the interface of the adjacent liquid phases in order to maintain the electroneutrality of the organic phase. We have shown that the standard potential of ion transfer across the liquidjliquid interface can be deduced from the formal potential of the voltammograms that portray the coupled electron transfer at the electrodejorganic solvent interface and ion transfer at the organic solventjwater solution interface [12][13][14][15][16][17][18][19][20]. A similar approach for monitoring the ion transfer across liquidjliquid interface was explored by Compton and co-workers [21][22][23][24][25], where the redox reactions of electroactive organic liquids have been studied in three-phase electrode arrangements.…”