TY  - THES
AB  - Antifreeze proteins (AFP) inhibit the growth of ice crystals and, thus, play an important role in the survival of many organisms at temperatures below the freezing point. But many aspects of the mechanism of action are still not understood, especially for antifreeze glycoproteins and glycopeptides (AFGP), which are present in some fish of the polar oceans. Therefore, within the present work several substances were investigated that inhibit the ice growth similar to AFP and AFGP. The efficiency of this growth inhibition was determined using a special form of Ostwald ripening, namely, the ice recrystallization of polycrystalline ice in aqueous solutions.
Experiments on the kinetics of ice recrystallization were conducted for determining the influence of factors such as temperature and ice volume fraction in addition to the inhibitory effect of the substances. Hence, aqueous sodium bromide and sucrose solutions were investigated at recrystallization temperatures of -25 to -5 °C. An extended form of LSW theory (Lifshitz-Slyozov-Wagner) was developed and employed for quantifying the kinetics of the ice recrystallization process and the influence of the different factors. This analysis allows for the determination of the efficiency of AFGP and some synthetic analogues in inhibiting recrystallization. The effects of very small structural changes became evident, allowing for the establishment of quantitative structure-activity relationships, in contrast to previous qualitative studies. The most efficient compound investigated in this work showed antifreeze activity already at a concentration of 0.23 µg/mL^-1. Hence, the method presented here is much more sensitive than other common procedures, which made it possible to detect activity for compounds previously classified as inactive.
Furthermore, a new experimental method is presented, which uses the optical anisotropy of ice to provide information on those ice facets, whose growth is inhibited by the specific adsorption of the glycopeptides.
The combined data strongly suggests that the adsorption-inhibition mechanism of antifreeze glycopeptides is based on a reversible adsorption to prism ice faces. In addition, the observed structure-activity relationships lead to the conclusion that the hydroxy groups of the carbohydrates at positions C4 or C6 are responsible for the adsorption. It is also clear, however, that the hydroxy groups, or motifs like the disaccharide groups of natural AFGP are not essential for activity, but they greatly increase their efficiency.
DA  - 2010
KW  - Rekristallisation
KW  - Ostwald-Reifung
KW  - Gefrierschutzprotein
KW  - Glykopeptide
KW  - Polyvinylalkohol
KW  - Peptoide
LA  - ger
PY  - 2010
TI  - Hemmung der Eisrekristallisation in wässrigen Lösungen durch Antigefrierglykopeptide
UR  - https://nbn-resolving.org/urn:nbn:de:hbz:361-17640
Y2  - 2024-11-22T04:17:34
ER  -