Infrared Spectroscopy of Cationized Lysine and ε-<i>N</i>-methyllysine in the Gas Phase:  Effects of Alkali-Metal Ion Size and Proton Affinity on Zwitterion Stability

Bush, Matthew F.; Forbes, Matthew W.; Jockusch, Rebecca A.; Oomens, Jos; Polfer, Nick C.; Saykally, Richard J.; Williams, Evan R.

doi:10.1021/jp071902q

Cited by 109 publications

(248 citation statements)

References 44 publications

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“…The current spectrum is very similar to that reported before. [39] However, in the previous study, the authors did not discuss the structures of protonated lysine in detail. Our conclusions are also consistent with the IRMPD spectrum at higher frequencies (i.e.…”

mentioning

confidence: 98%

An Investigation of Protonation Sites and Conformations of Protonated Amino Acids by IRMPD Spectroscopy

McMahon

2008

ChemPhysChem

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The protonation sites and structures of a series of protonated amino acids (Gly, Ala, Pro, Phe, Lys and Ser) are investigated by means of infrared multiple-photon dissociation (IRMPD) spectroscopy and electronic-structure calculations. The IRMPD spectra of the protonated species are recorded using the combination of a free-electron laser (FEL) and an electrospray-ion-trap mass spectrometer. The structures of different possible isomers of these protonated species are optimized at the B3LYP/6-311+G(d, p) level of theory and the IR spectra calculated using the same computational method. For every amino acid studied herein, the current results indicate that a proton is bound to the alpha-amino nitrogen, except for lysine, in which the protonation site is the amino nitrogen in the side chain. According to the calculated and experimental IRMPD results, the structures of the protonated amino acids may be assigned unambiguously. For Gly, Ala, and Pro, in each of the most stable isomers the protonated amino group forms an intramolecular hydrogen bond with the adjacent carbonyl oxygen. In the case of Gly, the isomer containing a proton bound to the carbonyl oxygen is theoretically possible. However, it does not exist under the experimental conditions because it has a significantly higher energy (i.e. 26.6 kcal mol(-1)) relative to the most stable isomer. For Ser and Phe, the protonated amino group forms two intramolecular hydrogen bonds with both the adjacent carbonyl oxygen and the side-chain group in each of the most stable isomers. In protonated lysine, the protonated amino group in the side chain forms two hydrogen bonds with the alpha-amino nitrogen and the carbonyl oxygen, which is a cyclic structure. Interestingly, for protonated lysine the zwitterionic structure is a local minimum energy isomer, but the experimental spectrum indicates that it does not exist under the experimental conditions. This is consistent with the fact that the zwitterionic isomer is 9.2 kcal mol(-1) higher in free energy at 298 K than the most stable isomer. The carbonyl stretching vibration in the range of 1760-1800 cm(-1) is especially sensitive to the structural change. In addition, IRMPD mechanisms for the protonated amino acids are also investigated.

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mentioning

confidence: 98%

An Investigation of Protonation Sites and Conformations of Protonated Amino Acids by IRMPD Spectroscopy

McMahon

2008

ChemPhysChem

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“…Metal ion size-charge [6,34,[40][41][42] or amount of water molecules [31,[35][36][37][38][39] are also an important issue in zwitterion stability. Glutamic acid has two carboxylic groups of which one is on C α and the other one is on C γ .…”

Section: Conformers Of Glutamic Acid Zwitterion1mentioning

confidence: 99%

“…It is known that in solid state or in solution, amine group of amino acids get protonated, carboxyl group gets deprotonated, and the amino acid becomes zwitterionic [1,[30][31][32]. In an isolated system, all natural amino acids are canonical [33,34] and zwitterionic form can be stabilized by water molecules and metal ions [6,[30][31][32][33][34][35][36][37][38][39][40][41].…”

Section: Conformers Of Glutamic Acid Zwitterion1mentioning

confidence: 99%

Conformational analysis of glutamic acid: a density functional approach using implicit continuum solvent model

Turan

Selçuki

2014

J Mol Model

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Amino acids are constituents of proteins and enzymes which take part almost in all metabolic reactions. Glutamic acid, with an ability to form a negatively charged side chain, plays a major role in intra and intermolecular interactions of proteins, peptides, and enzymes. An exhaustive conformational analysis has been performed for all eight possible forms at B3LYP/cc-pVTZ level. All possible neutral, zwitterionic, protonated, and deprotonated forms of glutamic acid structures have been investigated in solution by using polarizable continuum model mimicking water as the solvent. Nine families based on the dihedral angles have been classified for eight glutamic acid forms. The electrostatic effects included in the solvent model usually stabilize the charged forms more. However, the stability of the zwitterionic form has been underestimated due to the lack of hydrogen bonding between the solute and solvent; therefore, it is observed that compact neutral glutamic acid structures are more stable in solution than they are in vacuum. Our calculations have shown that among all eight possible forms, some are not stable in solution and are immediately converted to other more stable forms. Comparison of isoelectronic glutamic acid forms indicated that one of the structures among possible zwitterionic and anionic forms may dominate over the other possible forms. Additional investigations using explicit solvent models are necessary to determine the stability of charged forms of glutamic acid in solution as our results clearly indicate that hydrogen bonding and its type have a major role in the structure and energy of conformers.

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“…According to the above trend, lysine would be predicted to form a zwitterionic structure relatively easily. The stabilization of the zwitterionic structure of lysine by different metal ions has also been investigated in the literature [22,23]. The IRMPD experimental results indicated that lysine is non-zwitterionic in complexes with either Li + , Na + or K + [22].…”

Section: Introductionmentioning

confidence: 99%

“…The stabilization of the zwitterionic structure of lysine by different metal ions has also been investigated in the literature [22,23]. The IRMPD experimental results indicated that lysine is non-zwitterionic in complexes with either Li + , Na + or K + [22]. The lowest-energy structure of lithiated lysine without a water molecule is non-zwitterionic and the metal ion interacts with both nitrogen atoms and the carbonyl oxygen.…”

Section: Introductionmentioning

confidence: 99%

Experimental and Theoretical Investigation of the Proton-Bound Dimer of Lysine

Marta

Martens

et al. 2011

J. Am. Soc. Mass Spectrom.

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The structure of the proton-bound lysine dimer has been investigated by infrared multiple photon dissociation (IRMPD) spectroscopy and electronic structure calculations. The structures of different possible isomers of the proton-bound lysine dimer have been optimized at the B3LYP/ 6-31+G(d) level of theory and IR spectra calculated using the same computational method. Based on relative Gibbs free energies (298 K) calculated at the MP2/aug-cc-pVTZ//B3LYP/6-31 +G(d) level of theory, LL-CS01, and followed closely (1.1 kJ mol -1 ) by LL-CS02 are the most stable non-zwitterionic isomers. At the MP2/aug-cc-pVTZ//6-31+G(d) and MP2/aug-cc-pVTZ//6-31+(d,p) levels of theory, isomer LL-CS02 is favored by 3.0 and 2.3 kJ mol -1 , respectively. The relative Gibbs free energies calculated by the aforementioned levels of theory for LL-CS01 and LL-CS02 are very close and strongly suggest that diagnostic vibrational signatures found in the IRMPD spectrum of the proton-bound dimer of lysine can be attributed to the existence of both isomers. LL-ZW01 is the most stable zwitterionic isomer, in which the zwitterionic structure of the neutral lysine is well stabilized by the protonated lysine moiety via a very strong intermolecular hydrogen bond. At the MP2/aug-cc-pVTZ//B3LYP/6-31+G(d), MP2/aug-cc-pVTZ//6-31+G(d) and MP2/aug-cc-pVTZ//6-31+G(d,p) levels of theory, the most stable zwitterionic isomer (LL-ZW01) is less favored than LL-CS01 by 7.3, 4.1 and 2.3 kJ mol -1 , respectively. The experimental IRMPD spectrum also confirms that the proton-bound dimer of lysine largely exists as charge-solvated isomers. Investigation of zwitterionic and charge-solvated species of amino acids in the gas phase will aid in a further understanding of structure, property, and function of biological molecules.

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Infrared Spectroscopy of Cationized Lysine and ε-N-methyllysine in the Gas Phase: Effects of Alkali-Metal Ion Size and Proton Affinity on Zwitterion Stability

Cited by 109 publications

References 44 publications

An Investigation of Protonation Sites and Conformations of Protonated Amino Acids by IRMPD Spectroscopy

An Investigation of Protonation Sites and Conformations of Protonated Amino Acids by IRMPD Spectroscopy

Conformational analysis of glutamic acid: a density functional approach using implicit continuum solvent model

Experimental and Theoretical Investigation of the Proton-Bound Dimer of Lysine

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