Silver Ion Binding Energies of Amino Acids:  Use of Theory to Assess the Validity of Experimental Silver Ion Basicities Obtained from the Kinetic Method

Shoeib, Tamer; Siu, Kin Wai Michael; Hopkinson, Alan C.

doi:10.1021/jp013662z

Cited by 141 publications

(170 citation statements)

References 63 publications

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“…[1][2][3][4][5][6][7][8][9][10][11] Gas-phase study of complexes involving much larger peptide substrates has become experimentally accessible with the emergence of electrospray ionization, and also computationally accessible with advancing computational tools.…”

Section: Introductionmentioning

confidence: 99%

Alkali Metal Complexes of the Dipeptides PheAla and AlaPhe: IRMPD Spectroscopy

2008

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Complexes of PheAla and AlaPhe with alkali metal ions Na + and K + were generated by electrospray ionization, isolated in the Fourier-transform ion cyclotron resonance (FT-ICR) ion trapping mass spectrometer, and investigated spectroscopically by infrared multiple-photon dissociation (IRMPD) using light from the FELIX free electron laser over the mid-infrared range from 500 to 1900 cm -1 . Conclusions about structural features of the complexes were drawn by comparison with predicted spectra and relative free energies calculated by DFT for a number of candidate conformers.Combining spectroscopic and energetic results, it is established that the metal ion is always chelated by the amide carbonyl oxygen, and that the C-terminal hydroxyl does not complex the metal ion and is in the endo conformation. It is also likely that the aromatic ring of Phe always chelates the metal ion in a cation-π binding configuration. Along with the amide CO and ring chelation sites, a third Lewis-basic group almost certainly chelates the metal ion, giving a threefold chelation geometry. This third site may be either the Cterminal carbonyl oxygen, or the N-terminal amino nitrogen. From the spectroscopic and computational evidence, a slight preference was given to the carbonyl group, in an RO a O t chelation pattern, but the amino group is almost equally likely (particularly for 2

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Section: Introductionmentioning

confidence: 99%

Alkali Metal Complexes of the Dipeptides PheAla and AlaPhe: IRMPD Spectroscopy

2008

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“…Protonated octamers of serine are unusually stable in the gas phase [39 -41] and a structure in which all the serine molecules are zwitterionic has been proposed [39,40]. For proline, attachment of an alkali metal or Ag ϩ cation can make the zwitterion or salt-bridge form more stable than the nonzwitterion or charge-solvated form by 2-7 kcal/mol [30,42,43], but for Cu ϩ , the chargesolvated form is 3.4 kcal/mol more stable [32,44]. The higher propensity for arginine and proline to form zwitterion or salt-bridge structures is due in part to the higher gas-phase proton affinity of the proton acceptor and the poor charge-solvating ability in the case of proline.…”

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confidence: 99%

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

Lemoff

Williams

2004

J. Am. Soc. Mass Spectrom.

100

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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...

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“…As written in eq 7, a negative ΔΔH rxn favors formation of [M + H] + , whereas a positive ΔΔH rxn favors formation of [M + Me] + . The relationship in eq 7 can be rewritten as (8) Given that proton affinities are consistently higher than other cation affinities for a given molecule, [51][52][53][54] The results obtained for the reactions of doubly protonated bradykinin ions with anions derived from silver triflate and silver hexafluorophosphate are shown in Figure 4a,b, respectively. Attachment of the complete silver containing anion to doubly charged bradykinin was the dominant product for both silver triflate and silver hexafluorophosphate anions.…”

Section: Effect Of the Anionic Ligand On Cation-switching Reaction Prmentioning

confidence: 99%

Gas-Phase Ion/Ion Reactions of Multiply Protonated Polypeptides with Metal Containing Anions

2005

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Gas-phase reactions of multiply protonated polypeptides and metal containing anions represent a new methodology for manipulating the cationizing agent composition of polypeptides. This approach affords greater flexibility in forming metal containing ions than commonly used methods, such as electrospray ionization of a metal salt/peptide mixture and matrix-assisted laser desorption. Here, the effects of properties of the polypeptide and anionic reactant on the nature of the reaction products are investigated. For a given metal, the identity of the ligand in the metal containing anion is the dominant factor in determining product distributions. For a given polypeptide ion, the difference between the metal ion affinity and the proton affinity of the negatively charged ligand in the anionic reactant is of predictive value in anticipating the relative contributions of proton transfer and metal ion transfer. Furthermore, the binding strength of the ligand anion to charge sites in the polypeptide correlates with the extent of observed cluster ion formation. Polypeptide composition, sequence, and charge state can also play a notable role in determining the distribution of products. In addition to their usefulness in gas-phase ion synthesis strategies, the reactions of protonated polypeptides and metal containing anions represent an example of a gas-phase ion/ion reaction that is sensitive to polypeptide structure. These observations are noteworthy in that they allude to the possibility of obtaining information, without requiring fragmentation of the peptide backbone, about ion structure as well as the relative ion affinities associated with the reactants.

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Silver Ion Binding Energies of Amino Acids: Use of Theory to Assess the Validity of Experimental Silver Ion Basicities Obtained from the Kinetic Method

Cited by 141 publications

References 63 publications

Alkali Metal Complexes of the Dipeptides PheAla and AlaPhe: IRMPD Spectroscopy

Alkali Metal Complexes of the Dipeptides PheAla and AlaPhe: IRMPD Spectroscopy

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

Gas-Phase Ion/Ion Reactions of Multiply Protonated Polypeptides with Metal Containing Anions

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