Trichloroacetic acid, basicity

The basic material in seeds that is extractable with trichloroacetic acid solutions is ascribed to nonprotein nitrogen when the acid is in the 0.4-1.0 M concentration range. Gel electrophoresis on a sodium dodecylsulfate polyacrylamide medium pointed to the presence of 12 kDa polypeptides in soybean meal and 7, 10, 12 and 28 kDa in almond meal332. 

Current efforts favor tumor cell line tests, conducted by the National Cancer Institute (NCI) drug development program [62]. In the current NCI anticancer screen, each compound is tested against 60 human tumor cell lines derived from several cancer types (lung, colon, melanoma, kidney, breast, ovary, brain, leukemia). The tumor cells are seeded on 96-well microtiter plates and pre-incubated for 24 h. The test agents are then added to the wells (five 10-fold dilutions 0.01 -100 pmol/1) and are incubated for 48 h with the tumor cell lines. At the termination of the assay, the cells are fixed in situ with trichloroacetic acid (TCA), washed and dried. Sulforhodamine B (SRB), a dye that binds to the basic amino... 

The furosemide extraction procedure was later examined for potential application in the analysis of thiazide diuretics in milk. Since this procedure could not provide sufficiently clean extracts for thiazides, additional acidic and basic extraction procedures were evaluated (557). Thus, milk was deproteinized with trichloroacetic acid, phosphoric acid, or potassium dihydrogen phosphate and centrifuged. The supernatants were extracted with ethyl acetate, evaporated to dryness, reconstituted in mobile phase, and analyzed by liquid chromatography. The recoveries in most cases were low and widely variable. Basic extraction, on the other hand, with sodium bicarbonate/potassium carbonate mixture or potassium monohydrogen phosphate followed by extraction with ethyl acetate also gave poor recoveries in most cases. It appears that a significant degradation of chlorothiazide occurred under the basic conditions. 

This method describes the quantitative determination of carbonyl compounds in fats and oils. It is based upon the formation of 2,4-dinitrophenylhydrazones of carbonyl compounds in the presence of a trichloroacetic acid (TCA) catalyst, followed by colorimetric determination of the hydrazone compounds (i.e., as quinoidal ions) in an alkanolic basic solution. 

Trichloroacetic acid decomposes in water, alcohol and aniline and other basic solvents but it does not decompose in non-basic solvents such as benzene, carbon tetrachloride, sulfuric and acetic acid. Furthermore, the ethyl ester of trichloroacetic acid dissolves in alcohol but it does not decompose. It is known that this ester does not ionize in alcohol. Trichloroacetic acid, the sodium salt, the barium salt, and the anilinium salt all decompose in water at the same rate and all give beautiful first order constants throughout the whole course of the reaction. It is known that all these salts... 

However, reaction of acyclic dienamines with hydrazoic acid gives a mixture of products derived by 1,2-, 1,4- and 3,4 + 1,2-addition of HN3 to the diene system. In this case C-protonation is followed immediately by addition of the strongly nucleophilic azide anion, so that equilibrium of the C-protonated enamines cannot occur3c. Treatment of the morpholine dienamine of isophorone with trichloroacetic acid in boiling benzene resulted in decarboxylation and the 1,4-addition of a proton and the trichloromethyl anion. Basic hydrolysis of the adduct gave dienoic acid 54 (Scheme 4). 

There are a number of factors that determine whether a protonic acid can initiate polymerization of alkenes. Their acidity (pKa), and therefore the basicity of the resulting counteranion, determines the efficiency of initiation. Although reliable pKa values of acids stronger than sulfuric or hy-droiodic (pKa < -9) are difficult to obtain in aqueous solutions due to their nearly complete dissociation, the pKa values of acetic acid (4.75) and trichloroacetic acid (0.7) in water provide useful references. Conductometric and potentiometric estimates of the pK values of selected protonic acids in various organic solvents are summarized in Table 11 in descending acid strength. These values are not very precise, however, because the amount of moisture in each system was not monitored precisely. 

Table 59 presents activation parameters for the decarboxylation of trichloroacetic acid in various basic solvents. Presumably the acid is in the form of its anion in these solvents. The activation parameters fall into a fairly narrow range and the differences presumably represent specific solvation effects. In an acidic solvent, decanoic acid, the activation parameters for the decomposition of potassium trichloroacetate are increased considerably. The values are A/f = 41.4 kcal.mole" and A5 = 27.7 eu . The activation parameters presumably reflect a composite of a prior equilibrium between decanoic acid and the trichloroacetate anion along with decarboxylation of the latter anion. The rate of decarboxylation of sodium nitroacetate is about five times faster in methanol than in water . This effect was attributed to dispersion of the negative charge at the transition state , a process which is more favorable in the less polar methanol solvent. Similarly, the decar-... 

The catalytic activity of hydrogen chloride was found by Tarbell and Kincaid 34g). Continuing this work, Tarbell et al. 36) showed that certain acids and bases affect the yields of urethanes obtained from a-naphthyl isocyanate and phenols. Thus, catalytic effects were observed with sodium carbonate and acetate, pyridine, triethylamine, acetic acid, trichloroacetic acid, zinc chloride, hydrogen chloride, and boron fluoride etherate. The latter catalyst and triethylamine were found to be the most effective acidic and basic catalysts, respectively. 

Bakshi and Gavalas investigated a number of aluminas, silica-aluminas, and clays for ethanol dehydration, for which they determined acidity and basicity distributions via n-butylamine and trichloroacetic acid titrations, respectively. Catalyst activity was presumed to be given by the sum of the various group contributions, so that overall rate of reaction was given by equation 1 ... 

Acid-base properties of oxide surfaces are employed in many fields and their relationship with PZC has been often invoked. Adsorption and displacement of different organic molecules from gas phase was proposed as a tool to characterize acid-base properties of dry ZnO and MgO [341]. Hammet acidity functions were used as a measure of acid-base strength of oxides and some salts [342]. Acidity and basicity were determined by titration with 1-butylamine and trichloroacetic acid in benzene using indicators of different pAg. There is no simple correlation between these results and the PZC. Acid-base properties of surfaces have been derived from IR spectra of vapors of probe acids or bases, e.g. pyridine [343] adsorbed on these surfaces. The correlation between Gibbs energy of adsorption of organic solvents on oxides calculated from results obtained by means of inverse gas chromatography and the acceptor and donor ability of these solvents was too poor to use this method to characterize the donor-acceptor properties of the solids [344],... 

When cells are lysed, proteases (enzymes that break peptide bonds in proteins) are often activated. Degradation of proteins through protease action greatly complicates the analysis by 2D electrophoresis, so action should be taken to avoid this problem. If possible, it is advisable to inhibit proteases by disrupting the sample directly into strong denaturants such as 8 M urea, 10% trichloroacetic acid (TCA), or 2% SDS [45 7]. Proteases are less active at lower temperatures, so sample preparation at low temperature is recommended. In addition, proteolysis can often be inhibited by preparing the sample in the presence of Tris base, sodium carbonate or basic carrier ampholyte mixtures [48, 49]. 

Trichloroacetic acid is stable in toluene, carbon disulfide, or 6N-sulfuric acid, i.e., in solvents having little or no proton-acceptor properties. The situation is different in basic solvents, e.g., in water in aqueous solution trichloroacetic acid decomposes to chloroform and carbon dioxide when warmed to 70°. Thus the undissociated acid is moderately stable, but the anion is not. Cor-... 

Deactivation of 2-naphthylamine singlet state by pyridines in enhanced by dipole moment and the ability to form hydrogen bonds. Picosecond laser spectroscopy shows charge transfer from the excited amine. The fluorescence of 2-iV,A -dimethylaminopyridine induced by p-nitroaniline is also caused by exciplex formation. The latter enhances triplet population of p-nitroaniline. The quenching of the fluoresence of carbazole and some derivatives by trichloroacetic acid and related compounds in fluid solutions has been studied by Johnson.A charge-transfer interaction is involved and the basicity of carbazole and derivatives determined. Charge transfer is also involved by quenching of carbazole by halocarbons. The A -isopropylcarbazole-dimethylterephthalate exciplex has been observed in PMMA films.Photoinduced electron-transfer in the p-phenylenediamine-paraquat complex yields the paraquat cation. ... 

Figure 2.5 Solid Phase DNA Synthesis. 5 -dimethoxytrityl (DMT)-deprotection of resin bound 3 -terminal deoxynucLeoside residue is effected with trichloroacetic acid (TCA) (mechanism shown) Thereafter the first coupling reaction is enabled by phosphoamidite activation with tetrazole (mechanism shown) followed by oxidation of the newly formed diester linkage to a phosphodiester link. The process of 5 -DMTr deprotection, phosphoramidite coupling and then diester oxidation, continues for as many times as required (n-times), prior to global deprotection and resin removal under basic conditions.

In aprotic solvents. The mechanism of protonation is basically the same as that discussed above. The second order term observed by Bronsted (1928, see above) is due to an equilibrium of the acid catalyst forming dimeric aggregates. Therefore, fastest rates are measured in dipolar aprotic solvents, e.g., dimethyl sulfoxide (Blues et al., 1974). All these kinetic measurements verify a prediction made by Staudinger and Gaule at a very early date (1916), namely, that with acetic acid or trichloroacetic acid in inert solvents the reactivity of substituted diazoalkanes and a-diazo-carbonyl and a,a -dicarbonyl diazo compounds increases as the protonation equilibrium is shifted towards the corresponding alkanediazo-nium ion. This prediction includes the compounds listed in sequence 4-23 ... 

Basic proteins with low MW often cannot be fixed either with acetic acid or trichloroacetic acid/ethanol/water mixtures, and their bands diffund over time. Fixing the proteins with formaldehyde, as in Steck et al. (1980), helps. If you want to stain the gel with silver afterward, you first have to completely wash out the formaldehyde. 

Cytochrome c. The one cytochrome that is well studied is cytochrome c. It is a remarkably stable protein, surviving extraction by dilute trichloroacetic acid. The pigment in the extract has been purified by ammonium sulfate and acid precipitation, ammoniacal ammonium sulfate fractionation, electrophoresis, and ion exchange chromatography. The purest material contains 0.46 per cent iron, corresponding to a molecular weight of a little over 12,000 with one atom of iron per molecule. Cytochrome c from ox heart contains a large number of lysine residues, which make the protein very basic, with an isoelectric point over pH 10."... 

A low pH will cause the acidic moieties to be uncharged and the basic moieties to be positively charged. Some adds, such as trichloroacetic acid (TCA), will be able to form neutral ion pairs with the basic amino adds resulting in uncharged proteins that can interad, aggregate, and predpitate. 

Plasma lipids may also be co-precipitated with proteins and extracted from the precipitate. Care should be taken not to use precipitating agents, which may alter the lipids, e.g. strongly acidic or basic materials. Suitable agents are colloidal iron (Folch and van Slyke 1939), 5% trichloroacetic acid (Zilveesmit and Davis 1950), and zinc hydroxide (van Slyke and Plazin 1965). 

Subsequently, Schneider (94) suggested the addition of the hot trichloroacetic acid extraction step to the acid-soluble fraction remaining at the end of the ST procedure, thus permitting more direct isolation of the DNA fraction. This procedure (the Schmidt-Thannhauser-Schneider, or STS, procedure), which permits the use of either phosphorus or sugar assays as the measure of nucleic acid, has become a standard rapid tissue assay. Certain refinements necessary for conversion of a tissue assay method to an isotope assay method, involving more precise segregation of cellular constituents, can be regarded as- extensions or adaptations of the basic procedure. For these reasons, the procedure is described in detail. 

FIGURE 34.2 Regression curves for total volatile basic nitrogen (TVB-N) using trichloroacetic acid (TCA) (7.5%) and perchloric acid (PCA) (6%). (Adapted from Ruiz-Capillas, C. and W. F. A. Horner. 1999. /. Sci. Food Agric. 79 1982-1986.)... 

Non-basic water-soluble substances will be extracted by the trichloroacetic acid process. Barbitone was shown to be extracted, but it is not adsorbed on kaolin. In admixture with strychnine, after filtration from the kaolin the barbitone was easily adsorbed on animal charcoal. This is eluted by ether (but not by chloroform) after moistening with acetic acid. 

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