Proton affinities and photoelectron spectra of phenylalanine and N-methyl- and N,N-dimethylphenylalanine. Correlation of lone pair ionization energies with proton affinities and implications for N-methylation as a method to effect site specific protonation of peptides

Sherrie Campbell, Elaine M. Marzluff, M. T. Rodgers, J. L. Beauchamp, Margaret E. Rempe, Kimberly F. Schwinck, Dennis L Lichtenberger

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Abstract

A Fourier transform ion cyclotron resonance (FT-ICR) technique for measuring gas-phase proton affinities is presented which utilizes collisional dissociation of proton-bound clusters by off-resonance translational excitation. A simplified RRKM analysis relates unimolecular dissociation rates to proton affinities. This technique is used to measure values for the proton affinities of phenylalanine and N-methyl- and N,N-dimethylphenylalanine of 220.3, 223.6, and 224.5 kcal/mol, respectively (relative to the proton affinity of NH3 = 204.0 kcal/mol). The proton affinity measured for phenylalanine is in excellent agreement with reported literature values. The photoelectron spectra of these three molecules are also presented and analyzed. Assignments of bands to specific ionization processes are aided by comparison with model compounds such as methyl-substituted amines and 2-phenylethylamines. These data are employed to examine the correlation of adiabatic nitrogen lone pair ionization energies with gas-phase proton affinities for phenylalanine, N-methylphenylalanine, and N,N-dimethylphenylalanine in comparison to correlations for other amino acids and selected aliphatic amines. Although amine nitrogen methylation increases the potential for localizing charge at the amine terminus of protonated peptides by increasing the gas-phase proton affinity, the present study establishes that the increase is not sufficient to compete with protonation of some of the more basic side chains in peptides.

Original languageEnglish (US)
Pages (from-to)5257-5264
Number of pages8
JournalJournal of the American Chemical Society
Volume116
Issue number12
StatePublished - Jun 15 1994

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Methylation
Ionization potential
Protonation
Photoelectrons
Phenylalanine
Peptides
Protons
Amines
Gases
Nitrogen
Cyclotrons
Cyclotron resonance
phenylalanine methyl ester
Fourier Analysis
Ionization
Amino acids
Fourier transforms
Ions
Amino Acids
Molecules

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

@article{75d15564b9b346a68c56e159d58bdb82,
title = "Proton affinities and photoelectron spectra of phenylalanine and N-methyl- and N,N-dimethylphenylalanine. Correlation of lone pair ionization energies with proton affinities and implications for N-methylation as a method to effect site specific protonation of peptides",
abstract = "A Fourier transform ion cyclotron resonance (FT-ICR) technique for measuring gas-phase proton affinities is presented which utilizes collisional dissociation of proton-bound clusters by off-resonance translational excitation. A simplified RRKM analysis relates unimolecular dissociation rates to proton affinities. This technique is used to measure values for the proton affinities of phenylalanine and N-methyl- and N,N-dimethylphenylalanine of 220.3, 223.6, and 224.5 kcal/mol, respectively (relative to the proton affinity of NH3 = 204.0 kcal/mol). The proton affinity measured for phenylalanine is in excellent agreement with reported literature values. The photoelectron spectra of these three molecules are also presented and analyzed. Assignments of bands to specific ionization processes are aided by comparison with model compounds such as methyl-substituted amines and 2-phenylethylamines. These data are employed to examine the correlation of adiabatic nitrogen lone pair ionization energies with gas-phase proton affinities for phenylalanine, N-methylphenylalanine, and N,N-dimethylphenylalanine in comparison to correlations for other amino acids and selected aliphatic amines. Although amine nitrogen methylation increases the potential for localizing charge at the amine terminus of protonated peptides by increasing the gas-phase proton affinity, the present study establishes that the increase is not sufficient to compete with protonation of some of the more basic side chains in peptides.",
author = "Sherrie Campbell and Marzluff, {Elaine M.} and Rodgers, {M. T.} and Beauchamp, {J. L.} and Rempe, {Margaret E.} and Schwinck, {Kimberly F.} and Lichtenberger, {Dennis L}",
year = "1994",
month = "6",
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language = "English (US)",
volume = "116",
pages = "5257--5264",
journal = "Journal of the American Chemical Society",
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TY - JOUR

T1 - Proton affinities and photoelectron spectra of phenylalanine and N-methyl- and N,N-dimethylphenylalanine. Correlation of lone pair ionization energies with proton affinities and implications for N-methylation as a method to effect site specific protonation of peptides

AU - Campbell, Sherrie

AU - Marzluff, Elaine M.

AU - Rodgers, M. T.

AU - Beauchamp, J. L.

AU - Rempe, Margaret E.

AU - Schwinck, Kimberly F.

AU - Lichtenberger, Dennis L

PY - 1994/6/15

Y1 - 1994/6/15

N2 - A Fourier transform ion cyclotron resonance (FT-ICR) technique for measuring gas-phase proton affinities is presented which utilizes collisional dissociation of proton-bound clusters by off-resonance translational excitation. A simplified RRKM analysis relates unimolecular dissociation rates to proton affinities. This technique is used to measure values for the proton affinities of phenylalanine and N-methyl- and N,N-dimethylphenylalanine of 220.3, 223.6, and 224.5 kcal/mol, respectively (relative to the proton affinity of NH3 = 204.0 kcal/mol). The proton affinity measured for phenylalanine is in excellent agreement with reported literature values. The photoelectron spectra of these three molecules are also presented and analyzed. Assignments of bands to specific ionization processes are aided by comparison with model compounds such as methyl-substituted amines and 2-phenylethylamines. These data are employed to examine the correlation of adiabatic nitrogen lone pair ionization energies with gas-phase proton affinities for phenylalanine, N-methylphenylalanine, and N,N-dimethylphenylalanine in comparison to correlations for other amino acids and selected aliphatic amines. Although amine nitrogen methylation increases the potential for localizing charge at the amine terminus of protonated peptides by increasing the gas-phase proton affinity, the present study establishes that the increase is not sufficient to compete with protonation of some of the more basic side chains in peptides.

AB - A Fourier transform ion cyclotron resonance (FT-ICR) technique for measuring gas-phase proton affinities is presented which utilizes collisional dissociation of proton-bound clusters by off-resonance translational excitation. A simplified RRKM analysis relates unimolecular dissociation rates to proton affinities. This technique is used to measure values for the proton affinities of phenylalanine and N-methyl- and N,N-dimethylphenylalanine of 220.3, 223.6, and 224.5 kcal/mol, respectively (relative to the proton affinity of NH3 = 204.0 kcal/mol). The proton affinity measured for phenylalanine is in excellent agreement with reported literature values. The photoelectron spectra of these three molecules are also presented and analyzed. Assignments of bands to specific ionization processes are aided by comparison with model compounds such as methyl-substituted amines and 2-phenylethylamines. These data are employed to examine the correlation of adiabatic nitrogen lone pair ionization energies with gas-phase proton affinities for phenylalanine, N-methylphenylalanine, and N,N-dimethylphenylalanine in comparison to correlations for other amino acids and selected aliphatic amines. Although amine nitrogen methylation increases the potential for localizing charge at the amine terminus of protonated peptides by increasing the gas-phase proton affinity, the present study establishes that the increase is not sufficient to compete with protonation of some of the more basic side chains in peptides.

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