Acid radicals

Hdfer P, Grupp A, Nebenfuhr H and Mehring M 1986 Hyperfine sublevel correlation (HYSCORE) spectroscopy a 2D ESR investigation of the squaric acid radical Chem. Phys. Lett. 132 279-82... 

Acid Halogenides. For acid halogenides the name is formed from the corresponding acid radical if this has a special name (Sec. 3.1.2.10) for example, NOCl, nitrosyl chloride. In other cases these compounds are named as halogenide oxides with the ligands listed alphabetically for example, BiClO, bismuth chloride oxide VCI2O, vanadium(lV) dichloride oxide. 

Amides. Names for amides are derived from the names of the acid radicals (or from the names of acids by replacing acid by amide) for example, S02(NH2)2, sulfonyl diamide (or sulfuric diamide) NH2SO3H, sulfamidic acid (or amidosulfuric acid). 

Polyol Esters. Polyol esters are formed by the reaction of an alcohol having two or more hydroxyl groups, eg, a polyhydric alcohol and a monobasic acid. In contrast to the diesters, the polyol in the polyol esters forms the backbone of the stmcture and the acid radicals are attached to it. The physical properties maybe varied by using different polyols or acids. Trimethylolpropane [77-99-6] C H O, and pentaerythritol [115-77-5] are... 

Phospholipids. Phospholipids, components of every cell membrane, are active determinants of membrane permeabiUty. They are sources of energy, components of certain enzyme systems, and involved in Hpid transport in plasma. Because of their polar nature, phosphoUpids can act as emulsifying agents (42). The stmcture of most phosphoUpids resembles that of triglycerides except that one fatty acid radical has been replaced by a radical derived from phosphoric acid and a nitrogen base, eg, choline or serine. 

Nloha.tes, Niobic acid is amphoteric and can act as an acid radical in several series of compounds, which are referred to as niobates. Niobic acid is soluble in solutions of the hydroxides of alkaH metals to form niobates. Fusion of the anhydrous pentoxide with alkaH metal hydroxides or carbonates also yields niobates. Most niobates are insoluble in water with the exception of those alkaH metal niobates having a base-to-acid ratio greater than one. The most weU-known water-soluble niobates are the 4 3 ad the 7 6 salts (base acid), having empirical formulas MgNb O c, (aq) and M24Nb2202y (aq), respectively. The hexaniobate is hydrolyzed in aqueous solution according to the pH-dependent reversible equiHbria (130), when the pH is ca 9. 

Acidolysis requires the sue of an elevated temperature, the use of an acid catalyst (7), or both. Like alcoholysis, the reaction is reversible and requires the use of an excess of the replacing acid or removal of one of the products from the reaction if a high degree of replacement of the acid radical of an ester by another acid is to be obtained. This can be accompHshed by distilling one of the products from the reaction mixture during the acidolysis. 

Nonaqueous Bases Nonaqueous Nucleophiles Organometallic Catalytic Reduction Acidic Reduction Basic or Neutral Reduction Hydride Reduction Lewis Acids Soft Acids Radical Addition Oxidizing Agents... 

Acetic Anhydride.—The anhydudes may be regarded as o ides of the acid radicals, just as ethers are the o.xidcs of the alcohol radicals, and, like the ethers, both simple and mixed anhydrides may be prepared. The lattei, however, on distillation decompose, giving a mixture of the simple anhydiides. 

By the action of an acid chloiide on the amino-acid, the hydrogen of the amino-group may be replaced by an acid radical. Hippuric acid has been synthesised in this way. 

Benzoyl Chloride.—The formation of esters by ibe action of benzoyl chloride or othei acid chloride on an alcohol or ]ohcnol in presence of caustic soda is known as the Schotten- 13riumann reaction. The reaction may also be employed in the preparation of deri ati es of the aromatic amines containing i.n acid radical, like benzanilide, CjjH NH.CO... 

Demineralized water is water from which all the minerals have been removed by ion-eNchange. It is used where pure water is needed for a process and as boiler feed water. Mixed and multiple-bed ion-exehange units are used for this purpose, one resin converting the cations to hydrogen and the other removing the acid radicals. Water can be produced that has less than I ppm of dissolved solids. 

Saure-lostmg,/. solution of an acid, -maschine, /. souring machine, -menge, /. amount of acid, -messer, m. acidimeter hydrometer, -messkunst, /. acidimetry. -messtmg, /. acidimetry. -probe, /. acid test acid sample, -pumpe,/. acid pump, -radikal, n. acid radical, -regenerat, n. Rubber) acid reclaim. 

Dissolved mineral salts The principal ions found in water are calcium, magnesium, sodium, bicarbonate, sulphate, chloride and nitrate. A few parts per million of iron or manganese may sometimes be present and there may be traces of potassium salts, whose behaviour is very similar to that of sodium salts. From the corrosion point of view the small quantities of other acid radicals present, e.g. nitrite, phosphate, iodide, bromide and fluoride, have little significance. Larger concentrations of some of these ions, notably nitrite and phosphate, may act as corrosion inhibitors, but the small quantities present in natural waters will have little effect. Some of the minor constituents have other beneficial or harmful effects, e.g. there is an optimum concentration of fluoride for control of dental caries and very low iodide or high nitrate concentrations are objectionable on medical grounds. 

Conventional combinations Salts of strong acids and alkalis are, of course, almost completely ionised in dilute solutions. For some purposes, however, it is convenient to regard the ions as being in combination, and various systems of conventional combinations have been developed. In Britain, the system most used takes the metals and acid radicals in the order shown in Table 2.13 (after Thresh, Beale and Suckling). For example, if the amount... 

At higher acid concentrations, when formation of HCrOsB is also to be considered, because of the incorporation of the conjugate base the rate of oxidation will depend also on the nature of the acid radical present, viz. 

When mixed with potassium chlorate calcium dihydrogenphosphate detonates as violently as with decomposition of nitroglycerine. It is probably the result of the explosive decomposition of chlorine dioxide, which is formed because of the presence of acid radicals in the phosphate. 

De Groot, J.M.C., Garssen, G.J., Vliegenthart, J.F.G. and Boldingh, J. (1973). The detection of linoleic acid radicals in the anaerobic reaction of liproxygenase. Biochim. Biophys. Acta 326, 279-284. 

Sekiya, J. Aoshima, H., Kajiwara, T., Togo, T. and Hatanaka, A. (1977). Purification and some properties of potato tuber lipoxygenase and detection of linoleic acid radical in the enzyme reaction. Agric. Biol. Chem. 41, 827-832. 

Ions are derived from electrically neutral atoms (or groups of atoms) but differ from them in that they possess an electrical charge. This charge is positive for the hydrogen ion and for ions derived from metals (or nonmetallic groups such as NH4) and negative for ions derived from nonmetals or acidic radicals. 

The tests for metallic and acid radicals in chemical analysis are essentially tests for ions. For example, all soluble silver salts release silver ions in solution in water likewise, all... 

What importance could vinylphosphonic acid have for the synthesis of important biomolecules Its photolysis gives many oxidized products, including phosphoac-etaldehyde. This analogue of glycol aldehyde phosphate seems to be of interest its formation involves the recombination of hydroxyl radicals with vinylphosphonic acid radicals. 

Pellegrini N, Re R, Yang M and Rice-Evans C. 1999. Screening of dietary carotenoids and carotenoid-rich fruit extracts for antioxidant activities applying 2,2 -azinobis(3-ethylenebenzothiazohne-6-sulfonic acid) radical cation decolorization assay. Methods Enzymol 299 379-389. 

Stable organolead compounds are mostly derived from tetravalent lead and most fall within the four basic categories shown in Table 14, namely RPbX3, R2PbX2, RsPbX and R4Pb (where R is an alkyl or aryl group, and X is a halogen, OH or an acid radical). 

The reason for such a behaviour of arsenic acid is that arsenic is a member of the group 5A elements in the periodic table. Phosphorus and antimony are also group 5 elements and are known to be chemically similar to arsenic. On this basis [8,9], the antimonic acids were found to be poor cassiterite collectors. The alkyl phosphonic acids were not selective collectors. The ethylphenylene phosphonic acid was found to produce similar or better results compared to /7-tolyl arsonic acid. The structural formula for phosphonic acid (Figure 21.5) is similar to that of /7-tolyl arsonic acid but arsenic was replaced with phosphoms. The styrene phosphonic acid radicals are C6H5-CH-CH and p-ethylphenylene CH3-CH2-C6H4. 

The realization of the widespread occurrence of amino acid radicals in enzyme catalysis is recent and has been documented in several reviews (52-61). Among the catalytically essential redox-active amino acids glycyl [e.g., anaerobic class III ribonucleotide reductase (62) and pyruvate formate lyase (63-65)], tryptophanyl [e.g., cytochrome peroxidase (66-68)], cysteinyl [class I and II ribonucleotide reductase (60)], tyrosyl [e.g., class I ribonucleotide reductase (69-71), photosystem II (72, 73), prostaglandin H synthase (74-78)], and modified tyrosyl [e.g., cytochrome c oxidase (79, 80), galactose oxidase (81), glyoxal oxidase (82)] are the most prevalent. The redox potentials of these protein residues are well within the realm of those achievable by biological oxidants. These redox enzymes have emerged as a distinct class of proteins of considerable interest and research activity. 

Enzymes containing amino acid radicals are generally associated with transition metal ions—typically of iron, manganese, cobalt, or copper. In some instances, the metal is absent it is apparently replaced by redox-active organic cofactors such as S -adenosylmethionine or flavins. Functionally, their role is analogous to that of the metal ion in metalloproteins. 

As already mentioned, RNR is the metalloenzyme in which the first definitively characterized stable amino acid radical (1), later identified as a tyrosyl radical, was found in 1972. The RNR enzymes catalyse the reduction of ribonucleotides to their corresponding deoxyribonucleotides utilized in DNA biosynthesis. There are three unique classes of this enzyme, differing in composition and cofactor requirements all of them, however, make use of metal ions and free radical chemistry. Excellent reviews on RNRs are available (60, 61, 70, 89-97). 

Figure 11.11 The resonance structure of a generalized organic acid RCOO-, where R is any organic group and -COO- is the acid radical, (a) shows two possible equivalent forms for this structure, and (b) the resonance structure, which is a mixture of the two.

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