Substances, acidic

Nucleic acids are acidic substances present m the nuclei of cells and were known long before anyone suspected they were the primary substances involved m the storage transmission and processing of genetic information There are two kinds of nucleic acids ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) Both are complicated biopolymers based on three structural units a carbohydrate a phosphate ester linkage between carbohydrates and a heterocyclic aromatic compound The heterocyclic aro matic compounds are referred to as purine and pyrimidine bases We 11 begin with them and follow the structural thread... 

Tautomerism. Primary and secondary mononitroparaffias are acidic substances which exist ia tautomeric equiUbria with thek nitronic acids. 

Few aHyl monomers have been polymerized to useful, weH-characterized products of high molecular weight by ionic methods, eg, by Lewis acid or base catalysts. Polymerization of the 1-alkenes by Ziegler catalysts is an exception. However, addition of acidic substances, at room temperature or upon heating, often gives viscous liquid low mol wt polymers, frequently along with by-products of uncertain stmcture. 

Enhancers and Inducers. A sweetness enhancer is defined as a compound that imparts no taste per se, but when combined with a sweetener in small quantities, increases sweetness intensity. A tme sweetness enhancer has yet to be found. However, a good sweetness inducer, miraculin [143403-94-5] or [125267-18-7] (124), is known. Miraculin is a glycoprotein found in the fmit (called Miracle Fmit) of a West African shmb, chardella dulcifica. By itself, miraculin imparts no sweetness. When activated in the mouth by acidic substances, however, a sucrose-like sweetness is perceived. Thus, sour lemon, lime, grapefmit, rhubarb, and strawberry taste sweet when combined with miraculin. The taste conversion effect can last an hour or longer. 

Potassium carbonate (anhydrous). Has a moderate efficiency and capacity, forming the dihydrate. Suitable for an initial drying of alcohols, bases, esters, ketones and nitriles by shaking with them, then filtering off. Also suitable for salting out water-soluble alcohols, amines and ketones. Unsuitable for acids, phenols, thiols and other acidic substances. 

The resins are hardened in situ by mixing with an acidic substance just before application. A typical curing system would be four parts of toluene-p-sulphonic acid per 100 parts resin. The curing may take place at room temperature if the resin is in a bulk form but elevated temperature cures will often be necessary when the material is being used in thin films or coatings. 

Direct bromination readily yields the 6-bromo derivative (111), just as with uracil. Analogous chlorination and iodination requires the presence of alkalies and even then proceeds in low yield. The 6-chloro derivative (113) was also obtained by partial hydrolysis of the postulated 3,5,6-trichloro-l,2,4-triazine (e.g.. Section II,B,6). The 6-bromo derivative (5-bromo-6-azauracil) served as the starting substance for several other derivatives. It was converted to the amino derivative (114) by ammonium acetate which, by means of sodium nitrite in hydrochloric acid, yielded a mixture of 6-chloro and 6-hydroxy derivatives. A modified Schiemann reaction was not suitable for preparing the 6-fluoro derivative. The 6-hydroxy derivative (115) (an isomer of cyanuric acid and the most acidic substance of this group, pKa — 2.95) was more conveniently prepared by alkaline hydrolysis of the 6-amino derivative. Further the bromo derivative was reacted with ethanolamine to prepare the 6-(2-hydroxyethyl) derivative however, this could not be converted to the corresponding 2-chloroethyl derivative. Similarly, the dimethylamino, morpholino, and hydrazino derivatives were prepared from the 6-bromo com-pound. ... 

Industrial atmospheres usually accelerate the corrosion of zinc. When heavy mists and dews occur in these areas, they are contaminated with considerable amounts of acid substances such as sulphur dioxide, and the film of moisture covering the metal can be quite acid and can have a pH as low as 3. Under these conditions the zinc is dissolved but, as the corrosion proceeds, the pH rises, and when it has reached a sufficiently high level basic salts are once more formed and provide further protection for the metal. These are usually the basic carbonate but may sometimes be a basic sulphate. As soon as the pH of the moisture film falls again, owing to the solution of acid gases, the protective film dissolves and renewed attack on the metal occurs. Hudson and Stanners conducted tests at various locations in order to determine the effect of atmospheric pollution on the rate of corrosion of steel and zinc. Their figures for zinc are given in Table 4.34 and clearly show the effect which industrial contamination has on the corrosion rate. 

Many types of carbonyl compounds, including aldehydes, ketones, esters, thioesters, acids, and amides, can be converted into enolate ions by reaction with LDA. Table 22.1 lists the approximate pKa values of different types of carbonyl compounds and shows how these values compare to other acidic substances we ve seen. Note that nitriles, too, are acidic and can be converted into enolate-like anions. 

The resinification of 2-furaldehyde promoted by acidic substances or by heat has been known to chemists since the end of last century, and attempts to explain the mechanism leading to the formation of black, insoluble resins have been published... 

The polymerization of /3-(2-furyl) acrolein and some of its homologues by acids141 gave a similar phenomenology and thus, presumably, the mechanism is similar to that of the corresponding ketones. Their 7-radiation polymerization only proceeded in solution, probably because acidic substances were formed from the solvent142. ... 

The visual detection limits for fluorimetric detection are substance-dependent and lie between 5 ng (adrenaline, noradrenaline) and 30 ng (homovanillic acid) substance per chromatogram zone. 

The high temperatures ensure that inputs like MPW are effectively destroyed. Acidic substances such as HCl and SOx are neutralised by the alkali raw materials, which act in fact as a caustic scrubber. Metals are bound in the clinker or in the fly ash. Fly ash is captured with an electrofilter and subsequently added to the clinker. In general, no other flue gas cleaning is applied. 

Figure 1.1 The chemical structures of the main neurotransmitters. The relatively simple structure of acetylcholine, the monoamines and the amino acids contrasts with that of the peptides, the simplest of which are the enkephalins which consists of five amino acids substance P has eleven...

Acidic substances, glycols, nitriles and nitroalkanes. Amines and glycols. 

Extractive alkylation is used to derivatize acids, phenols, alcohols or amides in aqueous solution [435,441,448,502]. The pH of the aqueous phase is adjusted to ensure complete ionization of the acidic substance which is then extracted as an ion pair with a tetraalkylammonium hydroxide into a suitable immiscible organic solvent. In the poorly solvating organic medium, the substrate anion possesses high reactivity and the nucleophilic displacement reaction with an alkyl halide occurs under favorable conditions. 

The time-of-flight mass spectrometer was usually operated in the positive mode in order to detect the cationic sodium adducts of the analyte molecules. The anions of H-acidic substances were detected in the negative mode. This mode significantly enhanced the signals of acidic compounds, e.g. free fatty acids compared with ester signals in the mass spectra of beeswax and tung oil. 

The hydrogen ion concentration at which a colloidal system is electrically neutral the addition of acidic substances to, for example, rubber latex causes the pH value to move towards the isoelectric point, which is the region of minimum stability, and coagulation may take place. 

Hydrated or slaked lime Ca(OH)2 is an inorganic accelerator used in the curing of fluoroelastomers. In conventional sulphur cured polymers it counteracts the retardation of cure due to the presence of acidic substances in a rubber compound. Quicklime (CaO) dispersed in mineral oil or in wax/oil is used as a dessicant to reduce porosity in vulcanisates, particularly in fluid bed curing. 

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