Relationship between gas-phase proton affinities of conjugate bases B's and free energies of hydration of conjugate acid ions BH+'s for B = alkyl-substituted H2O and NH3

Hiraoka, Kenzo

doi:10.1139/v87-213

Cited by 20 publications

(16 citation statements)

References 15 publications

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“…Although other factors could be involved which determine where the ionizing protons reside (e.g. steric effects, charge solvation, and Coulombic effects), similar proton affinities between the N-terminal imidazole and the secondary ε-amino group suggest a fairly equal population of ions protonated at both sites [22,23]. We hypothesize, as illustrated in Scheme 1, that isomers protonated at the secondary ε-amino group can fragment via the CCE pathway through a charge-directed mechanism (eliminating [C 7 H 7 ] + ) while amide backbone fragmentation persists for isomers not protonated at that site.…”

Section: Resultsmentioning

confidence: 99%

“…This suggests that for simple peptides like the model GK-NHCH 3 , singly-charged precursors protonated at the secondary ε-amino group can fragment competitively either by the b n − y m or CCE pathways. However, another point to consider is that a secondary amino group typically has a higher gas-phase proton affinity [23] than primary amino groups. This implies that a greater distribution of ions could be protonated on the derivatized side chain compared to peptides containing unmodified lysyl residues and also suggests that more energy may be required to mobilize a proton from the secondary ε-amino group thus favoring the CCE pathway over the b n − y m pathway.…”

Section: Resultsmentioning

confidence: 99%

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Gas-phase fragmentation characteristics of benzyl-aminated lysyl-containing tryptic peptides

Simon

Papoulias

Andrews

2010

J. Am. Soc. Mass Spectrom.

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The fragmentation characteristics of peptides derivatized at the side-chain -amino group of lysyl residues via reductive amination with benzaldehyde have been examined using collision-induced dissociation (CID) tandem mass spectrometry. The resulting MS/MS spectra exhibit peaks representing product ions formed from two independent fragmentation pathways. One pathway results in backbone fragmentation and commonly observed sequence ion peaks. The other pathway corresponds to the unsymmetrical, heterolytic cleavage of the C -N bond that links the benzyl derivative to the side-chain lysyl residue. This results in the elimination of the derivative as a benzylic or tropylium carbocation and a (n Ϫ 1) ϩ -charged peptide product (where n is the precursor ion charge state). The frequency of occurrence of the elimination pathway increases with increasing charge of the precursor ion. For the benzylmodified tryptic peptides analyzed in this study, peaks representing products from both of these pathways are observed in the MS/MS spectra of doubly-charged precursor ions, but the carbocation elimination pathway occurs almost exclusively for triply-charged precursor ions. The experimental evidence presented herein, combined with molecular orbital calculations, suggests that the elimination pathway is a charge-directed reaction contingent upon protonation of the secondary -amino group of the benzyl-derivatized lysyl side chain. If the secondary -amine is protonated, the elimination of the carbocation is observed. If the precursor is not protonated at the secondary -amine, backbone fragmentation persists. The application of appropriately substituted benzyl analogs may allow for selective control over the relative abundance of product ions generated from the two pathways. Specifically, the inability to predict the relative intensities of sequence product ions produced reduces the confidence of peptide sequence assignments when data from MS/MS spectra are searched against immense lists of in silico peptide sequences generated from proteome databases [2][3][4]. This represents a barrier to the development of more effective computational tools for accurately assigning peptide sequences to MS/MS spectra as most database search tools are practically limited to treating the formation of all possible product ions with equal probabilities. An improved understanding of the detailed mechanisms involved in peptide fragmentation with CID will directly lead to more effective search tools. Not surprisingly, peptide fragmentation by CID has been studied extensively, and these efforts have culminated in a number of theoretical models that explain many of the observed fragmentation properties of peptides [1]. One example, the "Pathways in Competition" model [1], is associated with the mobilization of ionizing protons [5] to the amide backbone, competitive cleavages of the amide bonds, and post-cleavage proton transfer and chemical reactions. This model currently represents the most comprehensive description of the mechanism leading to the formatio...

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Gas-phase fragmentation characteristics of benzyl-aminated lysyl-containing tryptic peptides

Simon

Papoulias

Andrews

2010

J. Am. Soc. Mass Spectrom.

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“…It is also reported that the proton transfer is less likely to occur between a weaker acid and a primary amine. 50,51 Moreover, the difference between the proton affinity of HAc (342.33 kcal mol −1 ) and ethanolamine (220.87 kcal mol −1 ) is large. The larger difference in proton affinities, the lower possibility of proton transfer between acid and base.…”

Section: Reports the Cosmo-rs Predictedmentioning

confidence: 99%

Integration of acetic acid catalysis with one-pot protic ionic liquid configuration to achieve high-efficient biorefinery of poplar biomass

et al. 2021

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“…Similarly, the term microbasicity for polybasic molecules in solution can be defined. The basicity has been defined as a change in Gibbs free energy, Δ G , for protonation process, ${\rm{L}} + {\rm{H}}^ + \rightleftharpoons {\rm{HL}}^ +$ 13–15. Obviously, for a polybasic molecule when an individual site undergoes protonation, the related Δ G is a micro‐Δ G and corresponding basicity is a microbasicity for the molecule.…”

Section: Introductionmentioning

confidence: 99%

Prediction of microscopic protonation constants of polybasic molecules via computational methods: A complete microequilibrium analysis of spermine

Salehzadeh

Gholiee

Bayat

2010

Int J of Quantum Chemistry

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For the first time, a simple methodology is reported for theoretical calculation of microscopic protonation constants of polybasic molecules in solution. Density functional theory study was used for complete microequilibrium analysis of spermine, H 2 N(CH 2 ) 3 NH(CH 2 ) 4 NH(CH 2 ) 3 NH 2 , a linear tetraamine with 16 known microspecies. A general thermodynamic cycle is proposed to calculate protonation microconstants of polybasic molecules using calculated micro-DG values in aqueous solution. The microscopic protonation constants were determined with considering both the most abundant and most stable conformers for all microspecies. The results show that the microscopic protonation constants derived from the most abundant conformers (i.e., linear conformers in which the intramolecular hydrogen bonding does not exist) are in good agreement with the corresponding available experimental data.

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Relationship between gas-phase proton affinities of conjugate bases B's and free energies of hydration of conjugate acid ions BH⁺'s for B = alkyl-substituted H₂O and NH₃

Cited by 20 publications

References 15 publications

Gas-phase fragmentation characteristics of benzyl-aminated lysyl-containing tryptic peptides

Gas-phase fragmentation characteristics of benzyl-aminated lysyl-containing tryptic peptides

Integration of acetic acid catalysis with one-pot protic ionic liquid configuration to achieve high-efficient biorefinery of poplar biomass

Prediction of microscopic protonation constants of polybasic molecules via computational methods: A complete microequilibrium analysis of spermine

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