Zwitterionic salt

From these equations, it is possible to predid the effective lipophilicity (log D) of an acidic or basic compound at any p H value. The data required to use the relationship in this way are the intrinsic lipophilicity (log P), the dissociation constant (piCa), and the pH of the aqueous phase. The overall outcome of these relationships is the effective lipophilicity of a compound, at physiological pH, which is approximately the logP value minus one unit of lipophilicity for every unit of pH, the pit, value is below (for acids) and above (for bases) pH 7.4. Obviously, for compounds with multifunctional ionizable groups, the relationship between log P and log D, as well as log D as a function ofpH, becomes more complex [62, 65, 67]. For diprotic molecules, there are already 12 different possible shapes of log D-pH plots. Ion pairs (salts), zwitterions, and ampholytes are special cases and both measurement of log P/D and their interpretation need special attention [44, 49]. 

An a-amino acid, (a) Unionized form and (b) internal salt (zwitterion) form. 

Lin, J.C.Y., Huang, C.-J., Lee, Y.-T., Lee, K.-M. and Lin, I.J.B., Carboxylic acid functionalized imidazolium salts Sequential formation of ionic, zwitterionic, acid-zwitterionic and lithium salt-zwitterionic liquid crystals, J. Mater. Chem. 21 (22), 8110-8121 (2011). 

As with amino acids, peptides dissociate in aqueous solutions and form internal salts (zwitterions). The values of the dissociation constants pK values) and isoelectric points (pf) of some simple peptides are shown in Table 2.6. It is clear (by comparing the values for Gly, Gly-Gly and Gly-Gly-Gly) that the increase in the molecular weight of a peptide reduces the acidity and basicity of the functional groups. The pi values of peptides are lower than those of the corresponding amino acids. The pK and p/ values of peptides containing the same amino acids are different depending on the order of the amino acids (in Gly-Asp and Asp-Gly). 

Properties. Thienamycin is isolated as a colorless, hygroscopic, zwitterionic soHd, although the majority of carbapenems have been obtained as sodium salts and, in the case of the sulfated olivanic acids, as disodium salts (12). Concentrated aqueous solutions of the carbapenems are generally unstable, particularly at low pH. AH the substituted natural products have characteristic uv absorption properties that are often used in assay procedures. The ir frequency of the P-lactam carbonyl is in the range 1760 1790 cm . ... 

The methods for naming cations and anions may be combined to name zwitterions the cationic center is cited before the anionic center, both in the replacement prefixes and in the suffixes, e.g. (204). One should be aware, however, that Chemical Abstracts names zwitterions by an extraordinary circumlocution, in which water is hypothetically added and then hypothetically taken away, to give names consisting of four separate words ending in inner salt, e.g. (205). 

Because of their zwitterionic nature, amino acids are generally soluble in water. Their solubility in organic solvents rises as the fat-soluble portion of the molecule increases. The likeliest impurities are traces of salts, heavy metal ions, proteins and other amino acids. Purification of these is usually easy, by recrystallisation from water or ethanol/water mixtures. The amino acid is dissolved in the boiling solvent, decolorised if necessary by boiling with Ig of acid-washed charcoal/lOOg amino acid, then filtered hot, chilled, and set aside for several hours to crystallise. The crystals are filtered off, washed with ethanol, then ether, and dried. 

Thus the reactions of cyclic or acyclic enamines with acrylic esters or acrylonitrile can be directed to the exclusive formation of monoalkylated ketones (3,294-301). The corresponding enolate anion alkylations lead preferentially to di- or higher-alkylation products. However, by proper choice of reaction conditions, enamines can also be used for the preferential formation of higher alkylation products, if these are desired. Such reactions are valuable in the a substitution of aldehydes, which undergo self-condensation in base-catalyzed reactions (117,118). Monoalkylation products are favored in nonhydroxylic solvents such as benzene or dioxane, whereas dialkylation products can be obtained in hydroxylic solvents such as methanol. The difference in products can be ascribed to the differing fates of an initially formed zwitterionic intermediate. Collapse to a cyclobutane takes place in a nonprotonic solvent, whereas protonation on the newly introduced substitutent and deprotonation of the imonium salt, in alcohol, leads to a new enamine available for further substitution. 

Of derivatives of compound 3, the zwitterions 245 react with DMAD if magnesium bromide is added to give aminopyridine derivatives (00H(53)265). Compounds such as 102 are opened by acid to give quaternary pyridinium salts (92LA885). There are various interconversions of 2-substituted triazolopyridin-3-ones into 1-substituted zwitterions. An example is the reaction of 246 (83BCSJ2969) the reverse conversion is also reported. 

As shown in Scheme 26, Papaverine hydrochloride yields a separable mixture of Protopapaverine (67) and the salt norpapaverinium chloride (68) when heated slightly beyond its melting point for several minutes. Molecule 67 can exist as conjugated mesomeric betaine 67A (7-hydroxy form) or as 2-substituted-2//-isoquinolin-6-one 67B (6-hydroxy form) (66TL1177). Similar structures were described as zwitterionic pentacyclic... 

The papaver alkaloid Narcotoline (265) can be converted into the yellow colored Cotarnoline (267) on hydrolysis which adopts a zwitterionic ground state (56MI1, 57MI1) (Scheme 87). The corresponding dihydro derivative was also identified in nature. The UV spectrum of the zwitterionic Tarkonine (268), which forms red crystals from acetone, is shifted bathochromically in comparison to the chloride. Tarkonine is a very weak base (pA b = 9.58), which is well in accord with the formation of an inner salt, and Cotarnoline (267) is a stronger base than Tarkonine (268) (pA b = 9.15). The pK values are larger than 13 (66MI3). The methylated derivative of Narcotoline is Narcotine (266). 

In an initial step triphenylphosphine adds to diethyl azodicarboxylate 5 to give the zwitterionic adduct 6, which is protonated by the carboxylic acid 2 to give intermediate salt 7. The alcohol reacts with 7 to the alkoxyphosphonium salt 8 and the hydrazine derivative 9, and is thus activated for a SN2-reaction ... 

Amino acid zwitterions are internal salts and therefore have many of the physical properties associated with salts. They have large dipole moments, are soluble in water but insoluble in hydrocarbons, and are crystalline substances with relatively high melting points. In addition, amino acids are amphiprotic they can react either as acids or as bases, depending on the circumstances. In aqueous acid solution, an amino acid zwitterion is a base that accepts a proton to yield a cation in aqueous base solution, the zwitterion is an add that loses a proton to form an anion. Note that it is the carboxylate, -C02-, that acts as the basic site and accepts a proton in acid solution, and it is the ammonium cation, -NH3+, that acts as the acidic site and donates a proton in base solution. 

Compounds containing the neutral (formally zwitterionic) group =N2 attached by one atom to carbon are named by adding the prefix diazo- to the name of the parent compound (Rule 931.4), e.g., diazomethane, ethyl diazoacetate. Diazo is a so-called characteristic group appearing only as a prefix in substitutive nomenclature. Chemical Abstracts and Beilstein indexing of diazo compounds is analogous to that mentioned above for diazonium ions and salts, but Diazo compounds is not... 

The formation of arynes (8.26) as metastable intermediates in aromatic dediazo-niations was postulated by Stiles and Miller (1960) for the case of the 2-carboxy-benzenediazonium zwitterion (8.25) and by Cadogan and Hibbert (1964) for unsubstituted benzenediazonium salts. ... 

Diazoalkanes and related compounds are not suitable guests for the types of hosts discussed above. Very weak complexation was found with diazodicyanoimidazole (2.53 Sheppard et al., 1979) in which the mesomeric zwitterionic structure with a formal diazonio group (see Secs. 2.6 and 6.2) is dominant. However, no complexation was found for another compound with a formal diazonio group, the ben-zothiazol-azidinium salt 2.50 (Szele and Zollinger, 1982). 

The development of monoalkyl phosphate as a low skin irritating anionic surfactant is accented in a review with 30 references on monoalkyl phosphate salts, including surface-active properties, cutaneous effects, and applications to paste and liquid-type skin cleansers, and also phosphorylation reactions from the viewpoint of industrial production [26]. Amine salts of acrylate ester polymers, which are physiologically acceptable and useful as surfactants, are prepared by transesterification of alkyl acrylate polymers with 4-morpholinethanol or the alkanolamines and fatty alcohols or alkoxylated alkylphenols, and neutralizing with carboxylic or phosphoric acid. The polymer salt was used as an emulsifying agent for oils and waxes [70]. Preparation of pharmaceutical liposomes with surfactants derived from phosphoric acid is described in [279]. Lipid bilayer vesicles comprise an anionic or zwitterionic surfactant which when dispersed in H20 at a temperature above the phase transition temperature is in a micellar phase and a second lipid which is a single-chain fatty acid, fatty acid ester, or fatty alcohol which is in an emulsion phase, and cholesterol or a derivative. 

Quinoxaline (see Section 2.1.3) and many of its derivatives may be converted into A-alkylquimoxalinium or even A,A -dialkylquinoxalinediium salts by treatment with alkyl halides or the like. Occasionally, when the molecule bears a suitable acidic grouping, it may be possible to deprive the quaternary salt of its gegenion by treatment with a base to form an ylide (in which a carbon atom of the molecule bears the negative charge) or other zwitterionic entity, such as a quinoxaliniumolate. 

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