Propionic acid, ionization

When one of the two acids is used in excess and the pk -values of the two acids differ strongly, the salt deficit method should be used with caution. Formic add, acetic acid, propionic acid, and trifluoroacetic acid have been electrolyzed competitively in mixtures of pairs. Formic acid and trifluoroacetic acid are comparable in case of electrolysis, both are more readily electrolyzed than acetic and propionic adds. Deviations are rationalized on the basis of differences in ionization [147]. It might 1 useful in such cases to neutralize both acids completely. Sometimes one of the two acids, although being the minor component, is more favorably oxidized possibly due to preferential adsorption or its higher acidity [148]. In this case the continuous addition of the more acidic add to an excess of the weaker acid may lead to successful cross-coupling [149], The chain length of the two acids should be chosen in such a... 

The effect of the buffer on the efficiency of electrospray ionization was mentioned earlier in Section 4.7.1. This is a good example of the dramatic effect that this may have - good chromatographic separation and ionization efficiency with formic, acetic and propionic acids, and good separation, although with complete suppression of ionization, with trifluoroacetic acid (TFA), the additive used for the protein application described previously. Post-column addition of propionic acid to the mobile phase containing TFA has been shown to reduce, or even... 

Acidic modifier Trifluoroacetic acid Formic acid Propionic acid Acetic acid Ionization completely suppressed Good separation/ionization Good separation/ionization Best separation/ionization... 

Ionization may be used to counteract disregulation of pH levels (which is maintained through the concerted action of Na /H antiporters, CL/HCO3" exchangers, and other channels and/or transporters that exist within the plasma membrane of eucaryotic cells [32,100,101]). Indeed, it has been shown that iono-phores (such as nigericin [102]) can lower the intracellular pH, while weak acids (such as propionic acid) can promote acidification. Likewise, nonsteroidal anti-... 

The use of TFA as a mobile-phase additive in LC-MS can be problematical when using electrospray ionization. In negative ion detection, the high concentration of TFA anion can suppress analyte ionization. In positive ion detection, TFA forms such strong ion pairs with peptides that ejection of peptide pseudo-molecular ions into the gas phase is suppressed. This problem can be alleviated by postcolumn addition of a weaker, less volatile acid such as propionic acid.14 This TFA fix allows TFA to be used with electrospray sources interfaced with quadrupole MS systems. A more convenient solution to the TFA problem in LC-MS is to simply replace TFA with acetic or formic acid. Several reversed-phase columns are commercially available that have sufficient phase coverage and reduced levels of active silanols such that they provide satisfactory peptide peak shapes using the weaker organic acid additives.15... 

Other than water, protein is the major constituent of meat averaging nearly 21% in heef or chicken meat, with fat varying fiom 4.6 to 11.0% in beef and fiom 2.7 to 12.6% in chickoi. The principal radiolytic reactions of aqueous solutions of aliphatic amino acids are reductive deamination and decarboxylation. Alanine yields NH3, pyruvic add, acetaldehyde, propionic acid, CO2, H2, and ethylamine (6). Sulfur-containing amino adds are espedally sensitive to ionizing radiation. Cysteine can be oxidized to cystine by the hydroxyl radical or it can react with the hydrated electron and produce... 

Low Molecular Weight Acids. The method devised for analyzing free fatty acids will resolve Ci to CB acids as shown in Figure 1, except for formic and propionic acids which are poorly resolved under the conditions used. Propionic acid, however, has been shown to be absent in all mixtures of oxidation products, and thus it presents no problem in this study. Acetophenone, shown in the chromatogram, was a convenient and reliable internal standard for this technique. Detection by thermal conductivity was selected because the flame ionization detector is insensitive to formic acid and, as noted, the high volatility of methyl formate and acetate precludes their quantitative determination by reasonably simple esterification procedures. 

Brown BB, Wagner DS, Geysen HM, A single-bead decode strategy using electrospray ionization mass spectrometry and a new photolabile linker 3-amino-3 (2-nitrophenyl) propionic acid, Mol. Diversity, 1 4-12, 1995. 

Table 1. Ionization constants of substituted acetic and propionic acids...

Brown, B.B. Wagner, D.S. Geysen, H.M. A Single-bead Decode Strategy Using Electrospray Ionization Mass Spectrometry and a New Photolabile Linker 3-Amino-3-(2-Nitrophenyl)Propionic Acid, Mol. Divers. 1,4-12 (1995). 

Fig. 3.2 (a) —HOMO energy (ionization potential) and (b) —LUMO energy (electron affinity) for SiQDs in ground-state (SO) or excited-state (SI) configuration (see text) as a function of the adsorbed PA number [22]. Reprinted with permission from (Li QS, Zhang RQ, Niehaus TA, Frauenheim T, Lee ST (2007) Theoretical studies on optical and electronic properties of propionic-acid-terminated silicon quantum dots, J Chem Theory Comput 3 1518-1526). Copyright (2007), American Chemical Society... 

In the first column the normal acids are given. It is seen that formic acid is a much stronger acid than acetic acid, which is but slightly more ionized than propionic acid. The alkyl radicals do not appear to differ markedly in chemical nature. The constants of butyric and isobutyric acid, which are given in the last column, are very nearly alike. 

The chemical ionization spectra of the alkyl esters of propionic acid contain a relatively small number of ions, and almost all of the ions found in the spectra give some information concerning the identity and structure of the ester producing the spectrum. 

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