Translational and Rotational Friction of Lactodendrimer Molecules in Solutionl

The samples of fir'e hybrid dendrimer (lactopolypropylene imine) generations were studied by the methods of molecular hydrod-vnamics, including the sedimentation velocity. translationa] diffusion, and intrinsic viscosity measurement s in 0.l65Vo aqueous NaCl solutions. The molecular masses (1.9 < M sDx 10-3 < 46.5) and the corresponding hydrodynamic dimensions of the dendrimer molecules were determined. and the scaling relationships between the hydrodynamic characteristics and molecular masses were established. The results are interpreted taking into account that 80Vo of the lactodendrimer mass is concentrated at the ends of the dendrimer molecules. INTRODUCTION Dendrimers, representing molecules having a regular branched structure with identical branching points contained within every repeat unit, have been extensively studied in the recent decade t1-4l.There are two main processes for the synthesis of dendrimer structures-diverging, whereby every next generation arises from the preceding one as a result of layer growth [1], and converging, when the initially grown branched dendron units are cross-linked with the core [2]. The dendrimer substances, composed of dendrimer molecules, have good prospects for a number of applications [-4] determined by their special structure, controlled architecture, and a large content of reactive terminal groups a priori assumed to be equally accessible. Note that dendrimer structures with both organic and inorganic skeletons have been reported |,4-61. Dendrimers can be also considered as unique semiproducts for numerous subsequent modifications. The possibility of grafting various compounds onto the surface of dendrimers allows us to design various structures such as monomolecular micelles, new catalytic systems, dendrite boxes, and metallodendrimers. The possible biological applications of dendrimers are related to specific interactions between different biotThis work was partly supported by the Russian Foundation tbr Basic Research, project no. 96-03-338J7a. logically active molecules, primarily between sugar ligands and protein receptors. For example. it is suggested that several sugar fragments attached to the extemal dendrimer layer are capable of forming tightly bound complexes with protein receptors which will be stabler than individual sugars. Dendrimers are also considered as potential carriers of oli-eomeric sugars for the synthesis of neoglucoconjugates to replace the carriers based on proteins and synthetic polymers [7]. Problems encountered in the srudy of dendrimers are directly related to the fundamental questions arising in the investigations of branched macromolecules. Structures of this type, initially termed the regularly branched polymers, were originally considered by Flory [8],W. KuhnandH. Kuhn [9]. andTsvetkov [10]. For example, a relationship between the radius of inertia of a uniformly branched coil ;urd the coil volume, including branches that are most distant from the coil center, was established in [9]. Analytical expressions for the radius of inertia as a function of the total number of branches in the cases of uniform triand tetrafunctional branching were derived in [0]. These results were inspired, to a definite extent, by investigations of the gel formation processes and the study of natural branched polymers such as glycan, starch, and lignin exhibiting branching predominantly of the short-chain type and statistical character [1 1].