Gas-phase acidities of the 20 protein amino acids

Jones, Christopher M.; Bernier, Matthew C.; Carson, E. L.; Colyer, Kathryn E.; Metz, R.; Pawlow, Anna; Wischow, Emily D.; Webb, Ian; Andriole, Erica J.; Poutsma, John C.

doi:10.1016/j.ijms.2007.02.018

Cited by 119 publications

(164 citation statements)

References 40 publications

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“…O Ϫ intramolecular hydrogen bond. Theoretical calculations [38,39] clearly show that aspartic acid forms an anion with the lowest energy and a strong hydrogen-bonded ring structure between the main chain CO Ϫ 2 and the CO 2 H side-chain groups, as illustrated above, 5. Such bonds exhibit bond energies in the range of 14 -28 kcal/mol [40].…”

Section: For the [Gln ϫ H] ϫ · (H 2 O) And [Arg ϫ H] ϫ · (H 2 O) Compmentioning

confidence: 86%

Hydration energies of deprotonated amino acids from gas phase equilibria measurements

Wincel

2008

J. Am. Soc. Mass Spectrom.

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Section: For the [Gln ϫ H] ϫ · (H 2 O) And [Arg ϫ H] ϫ · (H 2 O) Compmentioning

confidence: 86%

Hydration energies of deprotonated amino acids from gas phase equilibria measurements

Wincel

2008

J. Am. Soc. Mass Spectrom.

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“…All mass spectra and ion abundance ratios reported here are the averages of at least 200 cumulative scans. The kinetic method [43][44][45][46] was used for the determination of relative and absolute gas phase deprotonation enthalpies based on the relative ion abundances resulting from competitive dissociation of a mass-selected cluster ion. The application of this method to data from this instrument has previously been described 47 and further details of this analysis are provided in the Supplementary Information.…”

Section: Methodsmentioning

confidence: 99%

Switching radical stability by pH-induced orbital conversion

et al. 2013

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In most radicals the singly occupied molecular orbital (SOMO) is the highest-energy occupied molecular orbital (HOMO); however, in a small number of reported compounds this is not the case. In the present work we expand significantly the scope of this phenomenon, known as SOMO-HOMO energy-level conversion, by showing that it occurs in virtually any distonic radical anion that contains a sufficiently stabilized radical (aminoxyl, peroxyl, aminyl) non-π-conjugated with a negative charge (carboxylate, phosphate, sulfate). Moreover, regular orbital order is restored on protonation of the anionic fragment, and hence the orbital configuration can be switched by pH. Most importantly, our theoretical and experimental results reveal a dramatically higher radical stability and proton acidity of such distonic radical anions. Changing radical stability by 3-4 orders of magnitude using pH-induced orbital conversion opens a variety of attractive industrial applications, including pH-switchable nitroxide-mediated polymerization, and it might be exploited in nature. AbstractIn most radicals the singly-occupied molecular orbital (SOMO) is the highest-energy occupied one

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“…However, there are some examples in the literature of global minima identified with the B3LYP functional that do not match experimental structures (although many do match). Along with those from Paizs, problems have been seen with valine [2] and serine [22]. This could be related to search routines or the B3LYP functional.…”

Section: Assessment Of Theoretical Approachmentioning

confidence: 99%

“…For example, Paizs and coworkers concluded that glycine prefers a structure with an internal hydrogen bond between the carboxylic acid and amine groups. Highlevel ab initio, other B3LYP data [2], and experimental data suggest a structure with a syn carboxyl group and a weak interaction between the amine hydrogens and the carbonyl [3][4][5]. While the energetic impact of this problem is generally minor, we feel it is important to report values based on the most appropriate conformations that can be obtained within a computational method.…”

mentioning

confidence: 99%

A reevaluation of computed proton affinities for the common α-amino acids

Gronert

Simpson

Conner

2009

J. Am. Soc. Mass Spectrom.

109

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The proton affinities of the 20 common amino acids have been computed at the G3MP2 level using structures derived from broad conformational searches at a variety of levels including G3MP2. In some cases, the conformational surveys identified more stable species than had been used in previous studies of proton affinities, though the differences in energy are sometimes rather small. The present values are likely the most reliable measure of amino acid proton affinities in the gas phase. An analysis of differences between these values and those obtained experimentally via the kinetic method indicates that the extraction of proton affinities from kinetic method data can potentially lead to large errors linked to the estimation of relative protonation entropies. . As noted by these authors, there is substantial variation in the experimental values reported for these species. The origin of this variability is most likely related to the difficulties of completing thermodynamic measurements in the gas phase on materials with low volatility. As a result, many of the experimental values are from kinetic method measurements and are subject to errors associated with the kinetic method approximation (as well as cumulative errors associated with the development of ladder-type scales). Therefore, in these systems, high-level computational work offers an attractive means of resolving differences in the various experimental measurements.While working on a computational study of the conformational preferences of neutral, gaseous amino acids, we realized that it would be possible to improve on the accuracy of the proton affinities reported by Paizs and coworkers. First, their computational strategy relied on the B3LYP approach to identify global minima and, often, they identified conformations for the neutral amino acids that did not match with those reported in previous computational and experimental studies (apparently in some cases this was the result of the search strategy and in others the computational method). For example, Paizs and coworkers concluded that glycine prefers a structure with an internal hydrogen bond between the carboxylic acid and amine groups. Highlevel ab initio, other B3LYP data [2], and experimental data suggest a structure with a syn carboxyl group and a weak interaction between the amine hydrogens and the carbonyl [3][4][5]. While the energetic impact of this problem is generally minor, we feel it is important to report values based on the most appropriate conformations that can be obtained within a computational method. For the protonated amino acids, this problem is less pronounced because the hydrogen bonding interactions are much stronger; most computational methods identify similar structures as the global minimum. Second, values reported by Paizs and coworkers are at 0 K. We have added a correction for the thermal energy of a proton, which amounts to about 1.5 kcal/mol at 298 K, as well as for the neutral and protonated amino acid. Although these corrections cancel to some extent and while the ge...

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Gas-phase acidities of the 20 protein amino acids

Cited by 119 publications

References 40 publications

Hydration energies of deprotonated amino acids from gas phase equilibria measurements

Hydration energies of deprotonated amino acids from gas phase equilibria measurements

Switching radical stability by pH-induced orbital conversion

A reevaluation of computed proton affinities for the common α-amino acids

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