Influence of hydration on ion–biomolecule interactions: M⁺(indole)(H₂O)_n(M = Na, K; n = 3–6)

Abstract

The indole functional group can be found in many biologically relevant molecules, such as neurotransmitters, pineal hormones and medicines. Indole has been used as a tractable model to study the hydration structures of biomolecules as well as the interplay of non-covalent interactions within ion-biomolecule-water complexes, which largely determine their structure and dynamics. With three potential binding sites: above the six- or five-member ring, and the N-H group, the competition between π and hydrogen bond interactions involves multiple locations. Electrostatic interactions from monovalent cations are in direct competition with hydrogen bonding interactions, as structural configurations involving both direct cation-indole interactions and cation-water-indole bridging interactions were observed. The different charge densities of Na(+) and K(+) give rise to different structural conformers at the same level of hydration. Infrared spectra with parallel hybrid functional-based calculations and Gibbs free energy calculations revealed rich structural insights into the Na(+)/K(+)(indole)(H2O)3-6 cluster ion complexes. Isotopic (H/D) analyses were applied to decouple the spectral features originating from the OH and NH stretches. Results showed no evidence of direct interaction between water and the NH group of indole (via a σ-hydrogen bond) at current levels of hydration with the incorporation of cations. Hydrogen bonding to a π-system, however, was ubiquitous at hydration levels between two and five.

Spectroscopy and Infrared Photofragmentation Dynamics of Mixed Ligand Ion–Molecule Complexes: Au(CO)x(N2O)y+

“…Most previous studies of mixed-ligand complexes have focused on the spectroscopy rather than fragmentation branching ratios. Where fragmentation pathways are mentioned, it is clear that in most cases it is the weakest bound moiety which is lost most efficiently. ,, One possible exception is the study of Li + (CH 4 )­Ar 6 by Rodriguez and Lisy, in which dissociation pathways were shown to be exquisitely sensitive to the isomeric form . It is clear that in the systems of interest in the current study other inter-related factors, including the ratio of different ligands present, the structure of the complex, exactly where in the complex the IR energy is absorbed, and the efficiency of IVR, also play important roles.…”

“…With the notable exception of complexes studied by using the inert messenger technique (typically of the form ML n Ar +/– ), − ,− mixed-ligand complexes have received limited attention, in part, due to the complexity they represent. The most extensive infrared studies include those by Lisy and co-workers, who have studied a range of ML­(H 2 O) m + complexes, , including L = indole, , n -methylacetamide, acetonitrile, benzene, − and phenol . Beyer and co-workers have also studied complexes, such as CoCO 2 (H 2 O) n – and [MgCO 2 (H 2 O) n ] + , by infrared photodissociation within an ion cyclotron resonance spectrometer. , The latter undergoes a change in fragmentation pathway between n = 2 and 3, which is accompanied by a spectral shift in the asymmetric CO 2 stretch, indicating CO 2 activation.…”

The structure-giving role of Rb+ ions for water–ice nanoislands supported on Cu(111)

“…1 It has become a key phenomenon in physical chemistry, essential to understanding the behavior of ions in solutions, 2,3 for catalysis, 4 energy storage, 5,6 and in biological phenomena. [7][8][9] Moreover, solvation is crucial for understanding electrochemical reactions. 10,11 These reactions are controlled by the liquid/solid interface, in particular, the properties of the electric double layer.…”

Infrared spectra and fragmentation dynamics of isotopologue-selective mixed-ligand complexes

“…Infrared photodissociation (action) (IRPD) spectroscopy represents a powerful technique for such studies yielding information on non-covalent interactions, solvation and structural isomers. [1][2][3][4][5] Generating mixed-ligand complexes represents an additional level of challenge over simple ion-molecule species and, consequently, with the exception of inert tagging, [3][4][5][6][7][8][9][10][11] relatively few spectroscopic studies have been undertaken on multiple ligand systems: Lisy completed systematic IRPD studies on a range of small hydrated alkali metal complexes (M + L(H 2 O) n : M = Na, K and L = benzene, [12][13][14] phenol, 15 indole, 16,17 acetonitrile, 18 n-methylacetamide, 19 C 6 F 6 20 and tryptamine 21 ). Beyer and coworkers have similarly studied a range of hydrated transition metal-CO 2 clusters by employing IRPD within an ion cyclotron resonance mass spectrometer.…”