Gas phase acidities of aliphatic carboxylic acids, based on measurements of proton transfer equilibria

Caldwell, Gary W.; Renneboog, Richard M.; Kebarle, P.

doi:10.1139/v89-092

Cited by 143 publications

(121 citation statements)

References 11 publications

Supporting

Mentioning

109

Contrasting

Order By: Relevance

“…The gas-phase acidities of the references are in the range of 342-337 kcal/mol [7,8,30], from the least acidic (CH 3 OCH 2 CO 2 H) to the most acidic (CH 3 BrCHCO 2 H), Table 1. The proton-bound…”

Section: Resultsmentioning

confidence: 99%

“…In aqueous solution, MTA (pK a ϭ 3.7) is a slightly weaker acid than methoxyacetic acid (pK a ϭ 3.5) [6]. In the gas-phase, methoxyacetic acid has an acidity (⌬H acid ) of 341.9 kcal/mol [7,8], while the acidity of MTA is unknown. In this paper, we report on the first determination of the gas-phase acidity of MTA by using the Cooks' kinetic method [9,10] and theoretical calculations.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Determination of the gas-phase acidity of methylthioacetic acid using the Cooks’ kinetic method

Ren

Patel

2005

J. Am. Soc. Mass Spectrom.

View full text Add to dashboard Cite

We determined the gas-phase acidity of methylthioacetic acid (MTA) in a triple-quadrupole mass spectrometer using the Cooks' kinetic method with the consideration of entropy effects. The negatively charged proton-bound dimers were generated by electrospray ionization. Collisioninduced dissociation was applied to the dimer ions and the product ion ratios were measured at four different collision energies. The gas-phase acidity (⌬H acid ) of MTA was determined to be 340.0 Ϯ 1.7 kcal/mol using the extended kinetic method and 339.8 Ϯ 1.7 kcal/mol using the standard kinetic method. The entropy term is insignificant in this case and can be ignored. The standard kinetic method yielded a free energy of deprotonation of MTA (⌬G acid ) of 333.0 Ϯ 1.7 kcal/mol. The entropy of the acid dissociation, ⌬S acid , was estimated to be 22.8 cal/mol K. Theoretical prediction at the B3LYP/6-31 ϩ G* level of theory gives a similar value for ⌬H acid of 338.9 kcal/mol. In the gas-phase, MTA is a stronger acid than methoxyacetic acid, although in solution, MTA is a weaker one. , and as a model to study electron-transfer reactions in substituted alkyl sulfides [3]. A recent study of natural food flavors found that MTA is one of the biotransformation products of the cysteine-aldehyde conjugate by baker's yeast [4]. MTA has a similar structure as that of methoxyacetic acid, CH 3 OCH 2 CO 2 H. Both methoxyacetic acid and MTA have been used to study solvent and substituent effects on the acidity of substituted acetic acids [5,6]. In aqueous solution, MTA (pK a ϭ 3.7) is a slightly weaker acid than methoxyacetic acid (pK a ϭ 3.5) [6]. In the gas-phase, methoxyacetic acid has an acidity (⌬H acid ) of 341.9 kcal/mol [7,8], while the acidity of MTA is unknown. In this paper, we report on the first determination of the gas-phase acidity of MTA by using the Cooks' kinetic method [9,10] and theoretical calculations. ExperimentalThe gas-phase acidity (⌬H acid ) of MTA was determined by using the extended Cooks' kinetic method in which entropy effects were taken into consideration [11][12][13]. Selected applications of using the extended kinetic method to determine thermochemical quantities can be found in the current literature [14 -19]. Briefly, a series of proton-bound dimers ([A·H·A i ] Ϫ ) of deprotonated MTA (HA) with a set of conjugate bases of reference acids (HA i ) were generated in the mass spectrometer. The reference acids all have known gas-phase acidities. Each proton-bound dimer was activated by collisions with argon atoms and underwent competitive unimolecular dissociations to produce two ionic products, A Ϫ and A i Ϫ , with rate constants of k and k i , respectively, Scheme 1.With the assumption that there are no reverse activation barriers for both dissociation channels, the natural logarithm of the ratio of the rate constants can be expressed by eq 1, where R is the ideal gas constant, T eff is the effective temperature of the activated dimer ion, and ⌬H and ⌬H i are the gas-phase acidities of MTA and the reference acid, respective...

show abstract

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Determination of the gas-phase acidity of methylthioacetic acid using the Cooks’ kinetic method

Ren

Patel

2005

J. Am. Soc. Mass Spectrom.

View full text Add to dashboard Cite

show abstract

“…Deprotonated heterodimers, consisting of an analyte (A 0 ) and a reference compound (A i ) (Table 5), have been [71] 128 1446 Ϯ 9.2 Valeric acid [71] 102 1449 Ϯ 8.8 Butyric acid [71] 88 1450 Ϯ 9.2 Propionic acid [71] 74 1454 Ϯ 9.2 (b) Phenols para-F phenol [69] 112 1451 Ϯ 8.8 meta-OMe phenol [69] 124 1456 Ϯ 8.8 meta-CMe 3 phenol [69] 150 1459 Ϯ 8.8 meta-Me phenol [69] 108 1463 Ϯ 8.8…”

Section: Gas-phase Acidity Of the Steroidsmentioning

confidence: 99%

“…Used methods: ion/molecule reaction equilibrium [69,71], collision induced dissociation and kinetic methods [70]. *From NIST webbook [68].…”

Section: Gas-phase Acidity Of the Steroidsmentioning

confidence: 99%

“…Hence, these data indicate that in addition to the charge-dipole interaction, other structural parameters have a significant role in the modulation of the gas-phase acidity of steroids. To explain why the III ␤ is more acidic than III ␣ , a mechanism involving stereospecific proton interaction with the A ring has been proposed (Scheme 4) [71].…”

Section: Gas-phase Acidity Of the Steroidsmentioning

confidence: 99%

See 1 more Smart Citation

Stereochemical effects during [M-H]⁻ dissociations of epimeric 11-OH-17β-estradiols and distant electronic effects of substituents at C₍₁₁₎ position on gas phase acidity

Bourgoin-Voillard

Zins

Fournier

et al. 2009

J. Am. Soc. Mass Spectrom.

View full text Add to dashboard Cite

The affinity of estradiol derivatives for the estrogen receptor (ER) depends strongly on nature and stereochemistry of substituents in C (11) position of the 17␤-estradiol (I). In this work, the stereochemistry effects of the 11␣-OH-17␤-estradiol (III ␣ ) and 11␤-OH-17␤-estradiol (III ␤ ) were investigated using CID experiments and gas-phase acidity (⌬H°a cid ) determination. The CID experiments showed that the steroids decompose via different pathways involving competitive dissociations with rate constants depending upon the ␣/␤ C (11) stereochemistry. It was shown that the fragmentations of both deprotonated [III ␣ -H] Ϫ and [III ␤ -H] Ϫ epimers were initiated by the deprotonation of the most acidic site, i.e. the phenolic hydroxyl at C (3) . This view was confirmed by H/D exchange and double resonance experiments. Furthermore, the ⌬H°a cid of both epimers (III ␣ and III ␤ ), 17␤-estradiol (I), and 17-desoxyestradiol (II) was determined using the extended Cooks' kinetic method. The resulting values allowed us to classify steroids as a function of their gas-phase acidity as follows:Interestingly, the ␣/␤ C (11) stereochemistry appeared to influence strongly the gas-phase acidity. This phenomenon could be explained through stereospecific proton interaction with -orbital cloud of A ring, which was confirmed by theoretical calculation. . The E 2 /ER␣ complex is stabilized by hydrogen contacts occurring between, on the one hand, the hydroxyl group of phenolic A ring (E 2 ) and Glu-353 as well as Arg-394 of the hormone binding pocket (HBP), and on the other hand, between the 17␤-hydroxyl of D-ring and His-524 (Scheme 1a) [5][6][7]. Moreover, position around the functionalized site at the C (11) position (C ring) seems to contribute to the anchorage of the hormone within this pocket of the receptor [7][8][9][10][11][12][13], suggesting that steric effects at this position are important for binding affinity. Accordingly, we may consider that the proton donor character efficiency could be reinforced through electrostatic effects mediated by the nature and the stereochemistry of substituent in position 11 [14].Mass spectrometry is widely used to characterize diastereoisomeric compound through stereochemical effects [15,16]. Many reviews have described stereochemistry differentiation of the hydroxyl group in gas phase on rigid rings [17][18][19][20][21][22]. The stereochemical effects could provide evidence that the chemical pathways for ion-molecule reaction as well as the dissociation mechanisms promoted by negative charge from stereoisomeric ion species prepared in chemical ionization and electrospray [23]. For instance, the differentiation of alkoxides of trans and cis-cyclohexanediols has been widely described in negative chemical ionization [24 -26]. This technique turned out to be also appropriate to distinguish more complex polycyclic molecules, such as mono-or polyhydroxyl norborneols, saccharides, and steroids [27][28][29][30]. The origin of stereochemical effects in these systems has been described in terms of...

show abstract

Effects of solvents on the tautomerization ofN,N-dimethylglycine

Headley

Corona

Cheung

1997

J. Phys. Org. Chem.

View full text Add to dashboard Cite

Gas phase acidities of aliphatic carboxylic acids, based on measurements of proton transfer equilibria

Cited by 143 publications

References 11 publications

Determination of the gas-phase acidity of methylthioacetic acid using the Cooks’ kinetic method

Determination of the gas-phase acidity of methylthioacetic acid using the Cooks’ kinetic method

Stereochemical effects during [M-H]⁻ dissociations of epimeric 11-OH-17β-estradiols and distant electronic effects of substituents at C₍₁₁₎ position on gas phase acidity

Effects of solvents on the tautomerization ofN,N-dimethylglycine

Contact Info

Product

Resources

About

Gas phase acidities of aliphatic carboxylic acids, based on measurements of proton transfer equilibria

Cited by 143 publications

References 11 publications

Determination of the gas-phase acidity of methylthioacetic acid using the Cooks’ kinetic method

Determination of the gas-phase acidity of methylthioacetic acid using the Cooks’ kinetic method

Stereochemical effects during [M-H]− dissociations of epimeric 11-OH-17β-estradiols and distant electronic effects of substituents at C(11) position on gas phase acidity

Effects of solvents on the tautomerization ofN,N-dimethylglycine

Contact Info

Product

Resources

About

Stereochemical effects during [M-H]⁻ dissociations of epimeric 11-OH-17β-estradiols and distant electronic effects of substituents at C₍₁₁₎ position on gas phase acidity