Binding energies of water to lithiated valine: Formation of solution-phase structure in vacuo

Abstract

Dissociation kinetics for loss of a water molecule from hydrated ions of lithiated valine, alanine ethyl ester and betaine are determined using blackbody infrared radiative dissociation at temperatures between Ϫ60 and 110°C. From master equation modeling of these data, values of the threshold dissociation energy are obtained for clusters containing one through three water molecules. By comparing the values for valine with its two isomers, one a model for the nonzwitterion structure, the other a model for the zwitterion structure, information about the structure of valine in these hydrated clusters is inferred. Structures, relative energies, and water binding energies for these ions are also calculated at the B3LYP/6-31ϩϩG** level of theory. With one water molecule, both experiment and theory indicate that valine is not a zwitterion and that the lithium ion coordinates with the amino nitrogen and the carbonyl oxygen (NO coordinated) and the water molecule interacts directly with the lithium ion. With two water molecules, the zwitterion and nonzwitterion structures are nearly isoenergetic, but the experiment clearly indicates a NO-coordinated nonzwitterion structure. With three water molecules, both the experimental data and theory indicate that the lithium ion binds to the carboxylate group of valine, i.e., valine is zwitterionic with three water molecules. The agreement between the experimentally determined and calculated binding energies is good for all the clusters, with deviations of Յ 0.12 eV. M olecular structure in solution depends on both the intrinsic properties of the molecule and on the effects of the surrounding solvent molecules. Exclusion of water from the interior of proteins influences protein folding and conformation. Similarly, lipid bilayer formation is due to differences in water interaction with the polar and hydrophobic ends of the lipid molecules. Gas-phase experiments make possible investigation of the intrinsic properties of the molecule. Differences between gas-phase and solution-phase structure can be attributed to solvent effects. Studies of gas-phase peptides indicate that ␣-helices can be stable in the absence of water and indicate that the propensity for helix formation for some amino acids differs in the gas phase and in solution [1,2]. For example, peptides with high valine content have a higher helix-forming propensity than their alanine analogues in the gas phase, but just the opposite is observed in aqueous solution [1].In the condensed phase, specific water molecules can play an important role in molecular structure. Such specific water molecules are often observed in crystal structures of proteins and other molecules. Evidence for specific water has been reported by Jarrold and coworkers for the molecule BPTI which tightly binds one water molecule in the gas phase [3,4]. Magic hydration numbers for gramicidin S at 8, 11, and 14 water molecules suggest stable solvation shells around the doubly protonated gas-phase ion [5], while a magic hydration number of 40 water molecules h...

Effect of regular hydration on gas phase structural stability of [zwitterionic alanine+M+] (M+=Li+, Na+, K+) complexes: A quantum chemical study

“…It is quite clear from Table 1 that the addition of one water molecules to -NO/-OO coordination modes of Ala-M + /ZAla-M + complexes at the metal ion end does not stabilize the -OO coordination mode of ZAla-M + complex in gas phase. The observed trend of stability by the addition of one water molecule in above discussed coordination modes is consistent with trend of stability reported in the previous studies [58][59][60]. Now, we have considered same coordination sites for dihydrates of -NO/OO/OH coordination modes as we have taken in the case of monohydrates.…”

Raman fingerprint of the interaction of K+ with the COO− group of zwitterionic alanine

“…[1][2][3][4] In living cells, free metal cations provide electrochemical gradients required for cellular function and they also serve as messengers. It is found that metal ion-amino acids interaction is responsible for the enzyme activity and stability of the protein structure.…”

“…The nature of the metal cation (Li + , Na + , and K + ) interaction has been investigated experimentally and theoretically with valine and glycine in presence and absence of water molecules. [1,4,27,[31][32][33] In their study it has been found that the metal cations are coordinated to the non-zwitterionic structure via the nitrogen as well as carbonyl oxygen (-NO coordination), whereas for the zwitterionic structures the coordination is held to the oxygen atoms (-OO coordination). Further, it is also found that the addition of a single water molecule does not significantly affect the relative energies calculated for the valine-cation complex.…”

“…In living systems, the biological process such as signal transduction, control on chemical reactions, and structure of macromolecules depends on electrostatic interactions among the polar and ionic species . In living cells, free metal cations provide electrochemical gradients required for cellular function and they also serve as messengers.…”

Monopeptide versus Monopeptoid: Insights on Structure and Hydration of Aqueous Alanine and Sarcosine via X-ray Absorption Spectroscopy

“…1,2,9 Salient characteristics of peptoids include their robust higher-order structure, folding dynamics, increased resistance to denaturation relative to proteins, and the means by which the structure and interactions can be intelligently designed by the primary sequence of the chain. 2,3,[10][11][12] Previous methods of studying peptides and peptoids have included circular dichroism of oligomers, 5,11,13 infrared spectroscopy, 12 NMR, 11 mass spectrometry, 14,15 and computational modeling; 16,17 these methods primarily focused on design and characterization of the secondary structure.…”