Dextran xanthate

Amylose and dextran have been studied in aqueous solution as the xanthate derivatives. Dextran xanthate has no observable c.d., but amylose xanthate in aqueous solution has a complex c.d. that indicates an organized structure. 

Fig. 2. ORD (top) and CD (bottom) of partially substituted potassium salts of dextran xanthate (A) and amylose xanthate (B) [10].

Chemically dextrans are similar to one another. The activation energy for acid hydrolysis is about 30-35 Kcal/mol (5j. The C-2 hydroxyls appear to be the most reactive in most Lewis base and acid-type reactions. A wide variety of esters and ethers have been described as well as carbonates and xanthates ( 7,8j. In alkaline solution, dextran forms a varying complex with a number of metal ions (9). 

A general lack of effectiveness has been noted for several MCAs in the suppression of GI-uptake of cadmium in mice. In this study the MCAs, the metal-binding capacity was 2-6.8 mM g 1, ranged from DTPA immobilized via amide bond formation to finely divided aminopropyl-silica, xanthates of polyvinylalcohol and various polysaccharides, and a dextran bearing ethylthiol moieties produced by action of ethylenesulphide on dextran209. ... 

Cereals, wheat bran, wheat gluten, maltodextrin, and dextran can also be xanthated,2143,2144 and continous processes have been described2139,2145 The distribution of the xanthation sites between primary and secondary groups appears initially to be random, however, there is a preference for the primary hydroxyl groups when the reaction time is prolonged 2141,2146,2147 Sodium amylopectin xanthate had a polydisperse random coil configuration in an aqueous solution of 1M NaOH.2148... 

Bernard, J., et al. 2008. Preparation of a xanthate-terminated dextran by click chemistry applieation to the synthesis of polysaceharide-eoated nanoparticles via surfactant-free ab initio emulsion polymerization of vinyl acetate. Journal of Polymer Science Part A Polymer Chemistry 46(8) 2845-2857. 

Marchessault, Sarko etal. [10, 11] have investigated the chiroptical properties of amylose xanthates extensively. The CD of amylose triacetate in trifluoroethanol shows, apart from the expected acetyl z -> tt transition at about 230 nm, an additional shortwave peak. This is again explained by assuming a helical conformation of the amylose chain. Dextran acetates and mycodextran acetates, on the other hand, do not show conformational effects. The considerable changes in the CD spectra of amylose triacetate films when the temperature increases from 30 to 190°C are particularly remarkable. As X-ray diffraction analysis shows, these effects are connected with crystallisation processes and transformation during annealing. 

The xanthates of dextran [10, 11] and cellulose [12] have plain ORD curves. As low concentrations the rotation can be expressed in a single-term Drude equation with a X value of 348 nm (absorption maximums occur at 302 and 370 nm). The ORD and CD... 

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