Aliphatic Tricarboxylic Acids

The absolute configuration of norcaperatic acid (20) was determined as 2S,3S by CD measurements on the natural acid and optically active synthetic compounds as their molybdate complexes (2S). 

The structure of (+)-rangiformic acid has been revised from 22 (411) to 23 (31) on the basis of new NMR evidence. Kiimmerling et al. (488) 

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The cyclization of aliphatic tricarboxylic acids by P2S3, carried out by Challenger et a/.,23,26 gave again small yields (about 7% of ethylthieno-[2,3-i]thiophenes 20 and 21) [Eqs. (5) and (6)]. 

Aliphatic tricarboxylic acids such as citric acid exhibit a remarkably high affinity toward the stationary phase of an anion exchanger. Hence, low ionic strength bicarbon-ate/carbonate buffer solutions are not particularly suited as eluents. However, when a sodium hydroxide solution at a comparatively high concentration (c 0.08 mol/L) is used, citric acid may be eluted, and may even be separated from its structural isomer isocitric acid. When the detection of these compounds is carried out via electrical con-... 

Carboxylic acids. Aliphatic carboxylic acids (R—GOOH) are deprotonated at physiological pH (pH 7) and are therefore represented as R—COO. Thus, acetic acid (GHj—COOH) exists as acetate (CH3COO ) at pH 7. A variety of short chain mono-, di-and tricarboxylic acids are important intermediates in metabolism and may be present at low concentrations in all cells either as the acid or as a covalent adduct. Thus, acetate (C2) and malonate (C3) can exist as the key acyl-coenzyme A thioester intermediates acetylGoA and malonylCoA, respectively. Phosphoenolpyruvate (C3), 1,3-bisphosphoglyceric acid (C3) and 3-phosphoglyc,erate (C3) are key metabolic intermediates. 

Propionyl-CoA is an intermediary product in the metabo-hsm of four essential amino acids (isoleucine, valine, threonine, and methionine), the aliphatic side-chain of cholesterol, pyrimidines (uracd and thymine), and the final product of the [3-oxidation of odd-chain fatty acids. Under normal circumstances, propionyl-CoA first is converted by a biotin-dependent carboxylase to methylmalonyi-CoA, then to succinyl-CoA by an adenosylcobalamin-dependent mutase, leading to oxidation in the tricarboxylic acid cycle. Primary or secondary defects of these two enzymes were among the first organic acidurias to be discovered, and their natural history has been characterized perhaps better than any other inborn error of organic acid metabolism. 

Aliphatic Acids Not Members of the Tricarboxylic Acid Cycle. 67... 

The aromatic polyamide-imides are related to the aromatic polyamides described in the previous section. Aliphatic materials of this type were reported originally in 1947. They were formed by reacting tricarboxylic acids with diamines ... 

Poly(e-caprolactone) Aliphatic polyester Degraded by hydrolysis or bulk erosion Slow degrading Degradation products incorporated in the tricarboxylic acid cycle Low chemical versatility Some problems related with withstanding mechanical loads... 

Thermo Fisher Scientific offers two ion-exclusion columns Dionex lonPac ICE-ASl and AS6. The former is a moderately hydrophilic, microporous poly (styrene-co-divinylbenzene)-based cation exchanger with a particle diameter of 7.5 pm and ion-exchange capacity of 27 mequiv/column, functionalized with sulfonate groups. The lonPac ICE-ASl is primariliy used for the separation of weak inorganic acids, short-chain fatty acids, and alcohols. Difficulties are encountered, however, in the separation of aliphatic mono-, di-, and tricarboxylic acids. These acids elute from such stationary phases within the totally permeated volume. The selectivity of the separation in this retention range is usually very poor. Since the totally permeated volume is determined... 

This method allows the preparation of aromatic and aliphatic monoisocyanates in moderate yields and with very high purities. Of the di- and tricarboxylic acids evaluated, only hexamethylene diisocyanate was successfully synthesized. 

Organic acids are hydrocarbons that are characterized by their carboxylate function (COOH). Their hydrocarbon structure can vary considerably from aliphatic to aromatic, saturated to unsaturated, and straight chain to branched. Other variations in structure include varying chain lengths, multiple carboxylate groups (e.g., di- or tricarboxylic acids), and presence of hydroxyl- and ketofunctions. Organic acids with different molecular structures obviously differ in their physical and chemical properties. 

The fatty acids of lichens show some resemblance to those in non-lichen-forming fungi, but none are identical. Aliphatic acids, much rarer in lichens than in other plant groups, appear to be formed in a very different manner through the tricarboxylic acid cycle. Known higher aliphatic acids and related substances are acaranoic acid, acarenoic acid, (+)-aspicilin, (—)-caperatic acid, (—)-lichesterinic acid, linoleic acid, (—)-nephromopsinic acid, (+)-nephrosteranic acid, (+)-nephrosterinic... 

Aliphatic dicarboxylic and tricarboxylic acids are non-volatile compounds and may therefore just have a role as taste-active (acidic) food components. 

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