SYNOPSISChain stiffness is often difficult to distinguish from molecular polydisperity. Both effects cause a downturn of the angular dependence at large q 2 ( q = (4?r/X)sin 612) in a Zimm plot. A quick estimation of polydisperity becomes possible from a bending rod ( B R ) plot in which lim(c + O)qRe/Kc is plotted against q ( (.?)>.) "* = u. Flexible and semiflexible chains show a maximum whose position is shifted from u,,, = 1.41 for monodisperse chains toward larger values as polydispersity is increased, while simultaneously, the maximum height is lowered. Stiff chains display a constant plateau at large q , its value is ?rML where ML is the linear mass density. Using Koyama's theory, the number of Kuhn segments can be determined from the ratio of the maximum height to the plateau height, if the polydispersity index z = (M,/M, -1 I-' is known. Thus, if the weight-average molecular weight M,, is known, the contour length L,, the number of Kuhn segments (Nk),, the Kuhn segment length and the polydispersity of the stiff chains can be determined. The influence of excluded volume is shown to have no effect on this set of data. The reliability of this set can be cross-checked with the mean-square radius of gyration ( s ' ) , which can be calculated from the Benoit-Doty equation for polydisperse chains. Rigid and slightly bending rods exhibit no maximum in the BR plot, and the effect of polydispersity can no longer be distinguished from a slight flexibility if only static scattering techniques are applied.

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Sugar-lipid hybrids of the type CnCm were prepared by coupling an alkane chain (Cn) with a maltooligosaccharide (Gin) over an amide linkage. Coupling was performed with maltobionolactone (G2) and n-alkylamine chains Cn with n = 8,10,12,14,16, i.e. variation of the hydrophobic part of the molecule, and with hexadecylamine (CI6) and different maltooligosaccharides (Gm, m = 2,3,4,6). The solution properties of the various products were studied by means of static and dynamic light scattering (LS) and by electron-microscopy (EM). The results may be summarized as follows: If the alkane chain is shorter than n = 14, small spherical micelles with a radius of about 3 nm are observed. In time these micelles aggregate further to form increasingly larger spherical clusters which eventually precipitate. Long rod-like micelles form when n > 14. Contour length and chain stiffness were determined by applying theories of semiflexible chains. A qualitative confirmation of the light scattering results, i.e., micelle size and shape, was obtained from electron microscopy.

Employing cationic, covalently crosslinked polyallylamine-based highly swollen microgels and anionic latices obtained by copolymerization of methacrylic acid and epoxypropyl methacrylate, the interaction of these polymer colloids with oppositely charged linear macroions is investigated by potentiometry, conductometry and turbidimetry. The microgels behave similar to linear macroions in symplex formation, if the components are reacted in the neutralized state, while in a "free acidfree base" titration only the easily accessible sites of the microgels are primarily involved in the interaction. With the more compact polymer latices a stable dispersion is formed, while with the microgels flocculation occurs. The results are discussed with regard to the influence of physical structure of the polymer colloids on stoichiometry and state of dispersion of the symplexes formed. Zur Bildung van Polyanion-Polykation-Komplexen aus geladenen Mikrogelen und Latices mit entgegengesetzt geladenen Polyelektrolyten in LosungUnter Verwendung kationischer covalent vernetzter hoch gequollener Mikrogele auf Polyallylaminbasis und anionischer Latices aus Methacrylsaure-Epoxypropylmethacrylat-Copolymeren wird die Wechselwirkung dieser Polymerkolloide mit entgegengesetzt geladenen Makroionen mittels Potentiometrie, Konduktometrie und Turbidimetrie untersucht. Die Mikrogele verhalten sich bei der Symplexbildung ahnlich wie geloste lineare Polyelektrolyte, wenn beide Titrationskomponenten in neutralisierter Form vorliegen, wahrend bei einer Umsetzung zwischen freier Polysaure und freier Polybase primar nur die leicht zuganglichen Ladungszentren der Mikrogele an der Umsetzung mitwirken. Bei den Latises bildet sich bei der Titration eine stabile "Symplex-Dispersion", wahrend im Falle der Mikrogele Flockung erfolgt. Die Ergebnisse werden hinsichtlich des Einflusses der Zuganglichkeit der Polymerkolloide auf Stochiometrie und Dispersitatszustand der gebildeten Symplexe diskutiert.

Recently, in our laboratory we started work on intra-and intermolecular crosslinked mircrogels of different molecular weights which contain free. amino groups and are soluble in water. The amino groups of the microgels react at anhydrous conditions with aldonolactones (mono-, di-or oligo-saccharides with a lactone group). The resulting sugar-surrounded microgels may be used as models of a living cell and should be suitable to investigate interactions among polysaccharides.Poly(al1ylamine) (PAlA) was found to be a suitable polymer for this purpose. It is soluble only in water and ethylene glycol. For this reason a crosslinking agent was required which reacts selectively with amino groups in aqueous solutions under mild conditions and which does not change the net charge of the polymer when crosslinking is performed.A wide variety of reagents has been studied to crosslink proteins intra-and intermolecularly in aqueous Each crosslinking agent has its own set of advantages and disadvantages in terms of specificity, reactivity, solubility and stability. Hunter and Ludwig4) showed that water-soluble imidic esters react specifically under mild conditions with amino groups of proteins. By the appropriate choice of the pH even the ratio of the reaction rates of aand &-amino groups can be varied5). The resulting amidines can be cleaved again by treatment with ammonium hydroxide to yield the original amino groups4). Since the pKa of amidines is higher than that of amino groups, an amidinated molecule has the same net charge in the acid or neutral pH range as does the unmodified amino group; thus the solubility of the crosslinked protein or polymer should not be affected by this reaction.The synthesis of a number of diimidic ester dihydrochlorides 2 (Eq. (1)) has been described6).OR' I C=N C=NH. HCI