Arabic acid

Degraded arabic acid was then methylated and the methyl derivative subjected to hydrolysis with methyl alcoholic hydrogen chloride. Examination of the cleavage fragments showed them to consist of the glycosides of the substances given in column one of Table II. 

On the assumption that methylation of the degraded arabic acid was complete, the location of hydroxyl groups in the various cleavage fragments indicates the positions through which the monosaccharide units are involved in union with the other residues. Thus the isolation of three molecular proportions of 2,3,4-trimethyl-D-glucuronic acid (VIII) and one molecular proportion of 2,3,4,6-tetramethyl-D-galactose (XI)... 

The isolation of the four products listed in Table II column 1 shows that all the residues in the stable nucleus of degraded arabic acid have the pyranose form and that all the units are joined by either 1,3 or 1,6 linkages. The possible structures which could accommodate these experimental facts were indicated and later work limited the number of possibilities still further by the isolation of hexamethyI-(6-D-glucuronosyl-D-galactose) (XXII) from methylated degraded arabic acid by controlled hydrolysis. One possible structure advanced for degraded arabic acid is shown in XXIII. 

The identification of these products demonstrated that the gum molecule possesses a highly branched chain structure, a deduction already made from the study of degraded arabic acid, and that those labile sugar residues, i/-arabinose, n-rhamnose, and 3-n-galactopyranosyl-L-... 

Figure 7.7 Zeta potentials (calculated from electrophoretic mobility data) relating to particles of different ionogenic character plotted as a function of pH in acetate-veronal buffer at constant ionic strength of 0.05 mol dm 3, (a) Hydrocarbon oil droplets, (b) Sulphonated polystyrene latex particles, (c) Arabic acid (carboxylated polymer) adsorbed on to oil droplets, (d) Serum albumin adsorbed on to oil droplets...

In an investigation of arabic acid by these methods, it was found that the material obtained after three successive degradations was resistant to further degradation. A methylation study of the product from the first degradation showed that it was composed of arabinose and galactose residues and still had a highly branched structure. 

Comparison of the properties of fractions obtained from the cell and from the metabolism liquid indicates that they are of similar nature. It is not known what part the extracellular enzymes play in modifying the structure of the polysaccharides from the culture medium. The occurrence of D-arabinose in nature is rare, and its presence in the polysaccharides of M. tuberculosis indicates the unique metabolic activity of this organism. In other natural materials, arabinose occurs in the L-form (as for example in arabic acid). 

Gum arabic (acacia) has been used in pharmacy as an emulsifier. It is a polyelectrolyte whose solutions are highly viscous owing to the branched stmcture of the macromolecular chains its adhesive properties are also believed to be due to, or in some way related to, this branched stmcture. Molecular weights of between 200 000 and 250 000 (MJ have been determined by osmotic pressure, values between 250 000 and 3 x 10 by sedimentation and diffusion, and values of 10 by light scattering, which also points to the shape of the molecules as short stiff spirals with numerous side-chains. Arabic acid prepared from commercial gum arabic by precipitation is a moderately strong acid whose aqueous solutions have a pH of 2.2-2.7. It has a higher viscosity than its salts, but emulsions prepared with arabic acid cream are not as stable as those made with its salts. 

Gums.—The name gum is given to more or less complicated substances, most of which are mixtures, which contain carbohydrates, and make sticky liquids when mixed with water. On hydrolysis the gums yield a pentose or hexose. Arabin (arabic acid) occurs in nature as a mixture of the calcium, magnesium, and potassium salts in gum arabic. It is converted into arabinose on hydrolysis. Anar-A gar is jo]btajned-in China from... 

Titration of Arabic Acid with Acid and Bases... 

Briggs ( ) studied the osmotic pressure of arabic acid and sodium arabate derived from gum arabic. 

Electrodialyzed arabic acid was neutralized with sodium hydroxide and dried in vacuo. The salt contained 85 x 10equivalent of sodium per gram. This salt and varying proportions of sodium chloride and hydrochloric acid were dissolved together. Equal amounts of a sample were placed in each of two collodion sacs. To one sac 10 ml. of distilled water were added. The two sacs were then suspended in pure water and subjected to the same uniform pressure of such intensity that equilibrium would be reached by passage of water from one sac and entrance into... 

Sarcina ureae Not found Arabic acid, L-arginine, L-lysine, Fe + HCl acetate [193, 640]... 

Spirillum serpens Adonitol, L-alanine, D/L-arabinose, D/L-arabitol, D/L-lyxose, xylitol, D-fucose, D-mannose, D-mannitol, L-rhamnose, D-sorbitol, L-sorbose Arabic acid, L-arginine, glycine, L-lysj e Al + p > La3+ ]v j2+ acetate [193, 640]... 

Arabic acid, Al2(S04)3, CuCl, CuGl, CuCNOs), CUSO4, FeClj, Fe2(S04)3, La(N03)3, L-lysine, HCl, acetate... 

Arabic acid, isothiocyanic esters (e.g., allyl isothiocyanate and methyl isothiocyanate), thiocyanic esters (e.g., ethyl thiocyanate and methyl thiocyanate), Cu+, Fe +, La +, HCl, acetate... 

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