| Abstract: | The temperature-dependent dyeability of oligoglucanes and polyglucanes with I2/KI solution is based on the interaction between iodine and the C-atoms of glucosidic bonds (Vetter and Thorn 1, 2]). Only when the helix is compressed, the expansion of the lumen that is necessary for the attachment of iodine bands is achieved as suggested by Freudenberg et al. in 1939 3]. The development of colour starts with the maltododecaosis (just over two spirals) within a temperature range of 20 to 25°C adsorbing one pentaiodide and bringing about a pale shade of pink. The rich blue tone is achieved with pure amyloses forming a maximum of about 610 to 620 nm. Unramified polysaccharides which had been synthesised by our team from 30 glucoside residues, still showed a purple colour with a maximum of 510 nm at temperatures from 20 to 25°C. Defined polysaccharides from 40 residues are bluish-purple (just 7 spirals of a tension-free helix) with a maximum absorption of about 550 nm. According to our knowledge, the rich blue tone requires at least 50 glucoside residues linked in an unramified chain 1, 2]. Amylopectin from potatoes has a maximum of 575 to 580 nm which shifts to 555 to 560 nm after partial break-down into β-dextrin by β-amylase (EC 3.2.1.2) and does a long-wave re-shift to 570 nm after splitting off of the side-chain stumps in the basic structure by pullulanase (EC 3.2.1.41). In the case of maize, the maximum is 535 nm for amylopectin, 520 nm for β-dextrin, and 555 nm for the basic structure. This means that in amylopectin from potatoes the helical sections available for the adsorption of iodine bands are longer than those in amylopectin from maize 4]. In glycogen iodine accumulates in a diffuse manner without forming any long bands. For this reason, an absorption shoulder of merely 400 to 500 nm is found by photometry 4]. A treatment with β-amylase makes the situation even worse; only when the side-chain stumps are separated by pullulanase does the formation of iodine bands in the basic structure of the glycogen improve to a maximum of 500 nm. This maximum corresponds to unramified sections of less than 30 glucoside residues 4, 2, 6]. |
