Thiolated dextran

More recently, thiolated dextran was synthesised by modification of dextran with 4-nitrophenyl chloroformate in DMSO/pyridine in the presence of DMAP at 0 °C yielding a carbonate (content 6%), which can be substituted with cystamine. Subsequent reduction yields the thiolated dextran containing between 1 and 4% thiol moieties (Fig. 57) [370]. 

Fig. 57 Synthesis of thiolated dextran via formation of a nitrophenyl carbonate [370]...

The self-assembly and inhibition of protein adsorption by thiolated dextran monolayers at hydrophobic metal surfaces. In Ratner BD, Castner DG (eds) Surface modification of polymeric biomaterials. Plenum, New York, p 117... 

Fig. 10 A series of images depicting thiolated dextran on a gold siu-face before (a) and after (b-f) the addition of water. Initial surface changes, showing spheroidal particles, are seen after 5 minutes incubation in water (b). These swell on the siu-face until 70 minutes (d), when a continuous film is formed. Reproduced with permission from [164]. Copyright (1997) American Chemical Society...

Fig. 55 Direct thiolation of the dextran backbone accessible via Sn reaction starting from tosylates of dextran [368]...

Besides the direct thiolation of the polysaccharide backbone accessible via Sn reaction starting from tosylates of dextran, as discussed above, a number of paths for the introduction of spacer-bound thiol functions are described. Early attempts towards thiolation of dextran applied acetylthiosuccinic anhydride yielding the mercaptosuccinyl derivative of dextran (Fig. 56). The reaction was carried out by addition of acetylthiosuccinic anhydride to a solution of the macromolecule while the pH was maintained at 8 by addition of NaOH and subsequent treatment of the product with Amberlite [369]. 

The binding of proteins such as tetanus toxoid (TTd) onto dextran can also be achieved via thiolation. Therefore, dextran is converted selectively at the terminal reducing ends. This is possible either after amination and modification of the terminal amino function with 2-iminothiolan hydrochlo-... 

Probes specific for P35S were immobilized on 10 MHz quartz crystals coated with gold, employing both the mentioned immobilization procedures streptavidin/dextran-modified surfaces using a biotinylated probe and direct thiol coupling with 5 thiolated probes. 

Efficient immobilization of aptamers on surfaces is necessary for the construction of tongh, stable sensors and assay systems as one necessary step to overcome limitations for practical applications (Bini et al., 2007). Bini et al. (2007) have compared thrombin aptamers immobilized on a gold snrface by chemisorption (thiolated aptamer) and by biotin-streptavidin interaction (biotinylated aptamer carrying a linker) on a gold surface modified by a thiol-dextran-streptavidin layer. The linker-modified aptamer immobilized via streptavidin-biotin showed better reproducibility and sensitivity results for the quartz crystal sensor. Aptamers can be used for the functionalization of titanium-alloy surfaces (e.g., implant material, scaffolds) to enhance cell adhesion. The aptamers directed to osteoblasts are fixed electrochemically on the snrface of the alloy and promote cell adhesion (Gno et al., 2005, 2007). 

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