Dilute solution behavior of dendrimers and polysaccharides: SEC, ESI-MS, and computer modeling

Dendrimers, the most highly branched structures achievable, have found nume rous uses in the chemical, biological, and pharmaceutical fields. We have e mployed size exclusion chromatography (SEC) with universal calibration to d etermine molecular weight averages, distributions, intrinsic viscosities, a nd structural parameters of Starburst dendrimers, dextrans, and the starch degradation polysaccharides known as maltodextrins. Comparisons have been m ade in the dilute solution behavior of dendrimers and polysaccharides with equivalent weight-average molecular weights. Intrinsic viscosities decrease d in the order [eta](dextran) > [eta](dextrin) > [eta](dendrimer), While th e difference between dendrimer and polysaccharides may be attributed to the higher branching of the former, which leads to a higher chain density in s olution, the difference between dextran and dextrin is likely a result of t he variation in solution behavior of alpha-(1-->6) vs alpha-(1-->4) linked carbohydrates, The solution behavior of the maltodextrins studied indicates that debranching in their manufacture appears to have been more thorough t han in that of beta-limiting dextrins studied by other groups. Comparison o f molecular radii obtained from SEC data to radii from molecular dynamics s tudies show Starburst dendrimers behave as theta-stars with functionality b etween 1 and 4. Additionally, electrospray ionization mass spectrometry was employed to determine M-w, M-n, and PD of Astramol dendrimers.