Unexpectedly Enhanced Solubility of Aromatic Amino Acids and Peptides in an Aqueous Solution of Divalent Transition-Metal Cations

Abstract

We experimentally observed considerable solubility of tryptophan (Trp) in a CuCl_{2} aqueous solution, which could reach 2-5 times the solubility of Trp in pure water. Theoretical studies show that the strong cation-π interaction between Cu^{2+} and the aromatic ring in Trp modifies the electronic distribution of the aromatic ring to enhance significantly the water affinity of Trp. Similar solubility enhancement has also been observed for other divalent transition-metal cations (e.g., Zn^{2+} and Ni^{2+}), another aromatic amino acid (phenylalanine), and three aromatic peptides (Trp-Phe, Phe-Phe, and Trp-Ala-Phe).

Synthesis, Characterization, and Reaction Studies of Pd(II) Tripeptide Complexes

“…Calculations were performed with version 4.2.1 of the ORCA program [ 61 , 62 ]. The density functional theory based protocol consisted of the PBE0-D3BJ functional [ 63 , 64 , 65 ] (including the D3 dispersion correction by Grimme and coworkers [ 66 , 67 ]) and the triple-zeta basis set def2-TZVP [ 68 ]. The RIJCOSX [ 69 , 70 ] approximation was used to calculate Coulomb and Exchange integrals, using the def2/J auxiliary basis set by Weigend et al [ 71 ] and the GridX5 (ORCA keyword) grid was used.…”

Acidity-dependent self-rolling of graphene oxide nanoscrolls via metal cation-π interaction

“…4a and Fig. S10, the maximum absorbance of GO with CNTs in water was ~230 nm, which was assigned to the π-π* transitions from the conjugated double bonds of an aromatic structure [38, 49,50]. After adding metal cations, the intensity at the maximum absorbance decreased, suggesting that the conjugated double bonds were affected.…”

Quantitative determination of cation–π interactions between metal ions and aromatic groups in aqueous media by a hydrogel Donnan potential method

“…Studying cation–π interactions between metal ions and aromatics in aqueous media is difficult. 9–14 The majority of molecules with π-electrons are water-insoluble, which limits the choice for potential research systems. 15 Hydrophilic modifications, as reported for water-soluble aromatic systems such as tryptophan (Trp), p -sulfonatocalix[4]arene, and peptides, bring forth the complexity of structures.…”

“…The presence of diverse interactions in these systems, such as coordinate bonds and ionic bonds, makes it challenging to identify the specific associations by cation–π interactions. 10,12,13 Furthermore, the hydration effect usually weakens the cation–π interactions, which leads to weak signals when using routine spectroscopic techniques, especially for the metal ions with a large hydration radius, e.g. , Li + .…”