Hydrodynamic Behavior of Dendrigraft Polylysines in Water and Dimethylformamide (original) (raw)
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Article Hydrodynamic Behavior of Dendrigraft Polylysines in Water
2012
The four first generations of dendrigraft poly-L-lysine have been studied in dimethylformamide (aprotic solvent) and in 0.2 M NaCl aqueous solutions by isothermal translation diffusion, 1 H NMR and viscometry methods. The relationships between diffusion coefficient, intrinsic viscosity and molar mass have been determined for dendrigraft poly-L-lysines, and the scaling index values have been compared to classical trifunctional dendrimers. Dendrimers and dendrigraft poly-L-lysines exhibited similitudes in their hydrodynamic behaviors. Nevertheless, dendrigraft poly-L-lysines displayed a specific behavior in solution. In contrast to dendrimers, a significant change of hydrodynamic dimension of dendrigraft poly-L-lysines according to the nature of the solvent has been observed. In aprotic solvent, the dendrigraft poly-L-lysine dimensions are about two times lower than in aqueous media (i.e., the hydrodynamic volume is contracted by a factor 8 in dimethylformamide), revealing the softness of dendrigraft poly-L-lysine compared to classical trifunctional dendrimers.
Hydrodynamic properties of carbohydrate-coated dendrimers
Carbohydrate Polymers, 1999
The hydrodynamic properties of poly(propylene imine) dendrimers, modified with outer-surface b-thiolactosyl residues (''lactodendrimers'') of generation number 1-5, have been investigated by velocity sedimentation, translational diffusion, and viscosity measurements in 0.165% NaCl aqueous solution. It has been demonstrated that apparent molecular weights (from the Svedberg equation) M sD of synthetic lactodendrimers, determined by sedimentation and diffusion experiments, are consistent with complete functionalization of initial poly-(propylene imine) dendrimers with sugar residues. The values of M sD range from 1900 to 45000 Da for generation numbers 1-5. Corresponding hydrodynamic (''equivalent Stokes'') radii range from ϳ10 to ϳ37 Å. Scaling relations of the conformation-dependent sedimentation coefficient, translational diffusion coefficient and intrinsic viscosity with molecular weight have been considered in detail and are all indicative of a spherical molecule with an inhomogeneous distribution of density (Mark-Houwink-Kuhn-Sakurada a, b and , coefficients of ϳ0.24, ϳ0.69 and ϳ0.31, respectively).
Determination of Dendrigraft Poly l Lysine Diffusion Coefficients by Taylor Dispersion Analysis
Biomacromolecules, 2007
This work focuses on the physicochemical characterization of dendrigraft poly-L-lysines (DGLs) obtained by polymerization of N-carboxyanhydride in buffered water (pH 6.5). Diffusion coefficients (D) and hydrodynamic radii (R h ) of five successive DGL generations were determined by Taylor dispersion analysis (TDA). To our knowledge, this is the first experimental work using TDA for the characterization of dendrimer-like structures. Experimental R h values obtained by TDA were compared to those derived from dynamic light scattering and size exclusion chromatography coupled to a triple detection (refractive index, viscosimetry, and static light scattering). Significant differences were obtained, especially for the highest generations, as a result of the inherent contribution of aggregates to the light scattering intensity. For that reason, TDA was found to be the most appropriate technique for determining the D values of these hyperbranched macromolecules. Regarding their physicochemical behavior, the experimental results confirm that DGLs are very similar to trifunctional dendrimers (exponential growth of the molar mass, almost linear variation of the hydrodynamic radius, high branching density, and maximum of the intrinsic viscosity or of the free volume fraction for generation 4).
Macromolecules, 1998
Steady shear flow properties of an extensive family of dendrimers were examined for the first time in medium to high concentration solutions. For this, the first seven generations of ethylenediamine (EDA) core-polyamidoamine (PAMAM) dendrimers, having molecular weights from about 500 to almost 60 000 in 30 to 75 wt % solutions in ethylenediamine (EDA) were used. It was found that these dendrimer solutions exhibited typical Newtonian flow behavior as manifested by direct proportionality of the shear stress to the shear rate (i.e., constant viscosity with respect to both shear stress and shear rate) over the entire range of shear stress and shear rate studied. In addition to this, there was no abrupt change in the slope of the shear viscosity vs molecular weight relationship, indicating that these dendrimers do not interpenetrate to form transient quasi-networks of the "entanglement"type typically found for long-chain linear or randomly branched macromolecules, nor do they engage in "sticking" interactions characteristic for the suspensions of idealized spherical particles. This rheological behavior is without precedence among high molecular weight synthetic polymers, and it is proposed that it is solely driven by the unique dendrimer macromolecular architecture which above a certain critical generation results in globular, nanoscopic spheroids whose outer surfaces close upon themselves and become impenetrable for other dendrimers or large molecules. The shear viscosity vs volume fraction dependencies showed that these dendrimers are draining to solvent molecules, but to a lesser extent than the corresponding random-coil type linear macromolecules of comparable molecular weights. These findings are consistent with a "dense-shell" model of dendrimer intramolecular morphology which can also explain their ability to encapsulate small molecular weight species in their "soft and spongy" interiors. From a typical Arrhenius-type temperature dependence of these dendrimer solutions viscosities and from the dependencies of their flow activation energy on molecular weight, it seems that the smallest kinetic unit involved in the dendrimer flow is the dendrimer molecule itself. Strong dependence of the dendrimer solution viscosity on concentration and temperature, as well as its independence on repeated loading, indicates substantial dendrimer flexibility and ability to deform. On the basis of these results and the supporting computer modeling calculations, it is proposed that the Newtonian flow behavior and the lack of an abrupt change of slope in the zero-shear viscosity vs molecular weight relationships represent characteristic "fingerprint" properties for dendrimers in general and that these properties distinguish these unique macromolecules from all other traditional classes of macromolecular architecture. It is also proposed that the critical degree of branching may be used as a defining structural criterion for distinguishing true dendrimers from their low molecular weight simple branched precursors.
Colloid & Polymer Science, 2002
The generation of dendrimers based on poly(propylene imine) with CN end groups [DAB-dend-(CN) x ] and with palmitoyl end groups [DAB-dend-(C15) x ] was studied by methods of translational diffusion and viscometry. The volumes of the DAB-dend-(CN) x and DAB-dend-(C15) x dendrimers and the previously studied DABdend-(lacto) x dendrimer were compared to evaluate the volumes of the end groups in hybrid dendrimers. The volume of the hybrid dendrimers compared to that of the initial dendrimers increases proportionally to the number of end groups: this means that the end groups are predominantly located on the periphery of each molecule, thus ensuring this volume will increase. It is shown that the volume of the end groups for DAB-dend-(C15) x is 3.5 times greater, and for DABdend-(lacto) x it is 5.0 times greater than that occupied by free molecules corresponding to the end groups. The values of the intrinsic viscosity were compared with the values of the diffusion coefficient and the chemical formula molecular weight.
Molecular Dynamics of Lysine Dendrigrafts in Methanol–Water Mixtures
International Journal of Molecular Sciences
The molecular dynamics method was used to study the structure and properties of dendrigrafts of the first and second generations in methanol–water mixtures with various volume fractions of methanol. At a small volume fraction of methanol, the size and other properties of both dendrigrafts are very similar to those in pure water. A decrease in the dielectric constant of the mixed solvent with an increase in the methanol fraction leads to the penetration of counterions into the dendrigrafts and a reduction of the effective charge. This leads to a gradual collapse of dendrigrafts: a decrease in their size, and an increase in the internal density and the number of intramolecular hydrogen bonds inside them. At the same time, the number of solvent molecules inside the dendrigraft and the number of hydrogen bonds between the dendrigraft and the solvent decrease. At small fractions of methanol in the mixture, the dominant secondary structure in both dendrigrafts is an elongated polyproline ...
The Viscosity of Solutions of Poly(propylene imine) Dendrimers in Methanol
Journal of Colloid and Interface Science, 2001
The viscosity of solutions of poly(propylene imine) dendrimers in methanol has been determined. An Ubbelohde and a low-shear rotational viscometer have been used. The viscosity was Newtonian for every concentration and shear rate used. The value of the Huggins coefficient indicates soft sphere behavior. The viscosity of the lower generations as a function of the volume fraction can be described with a single exponent, where the exponent is comparable to the intrinsic viscosity. The viscosity of the 4th and 5th generation dendrimers shows a stronger increase from a volume fraction of about 0.15 to 0.30. This increase is much smaller than that expected, using the Krieger-Dougherty formula for hard spheres with the hydrodynamic radius determined from the intrinsic viscosity. This smaller increase and the small value of the Huggins coefficient are interpreted in terms of a breakdown of the solvation layer. At a volume fraction of 0.3 the dendrimers, using the radius of gyration as the radius, start to touch each other. From the dependence of the viscosity on the concentration and the dependence of the viscosity on the molar weight, it can be concluded that dendrimers do not interpenetrate. It is concluded that they deform (collapse). C 2001 Academic Press
Macromolecules, 2002
Self-diffusion of three high generations (the fifth, sixth, and seventh) of poly(allylcarbosilane) dendrimer in solutions with deuterated chloroform has been studied over a wide range of macromolecular concentrations (). Diffusivity has been measured by NMR with a pulsed gradient of the magnetic field. It is shown that concentration dependences of the dendrimer self-diffusion coefficients (D) can be reduced to the generalized concentration dependence. Over the range of volume concentrations from 0.01 up to 0.55, the curve of the generalized dependence of D for dendrimers coincides with the analogous dependence for globular protein in aqueous solutions. Analogous to the universal concentration dependence of D for linear polymers in solvent, the generalized concentration dependence of dendrimers tends to the asymptote D′()/D 0 ∝ 0) 1 in the limit of extremely dilute solutions and to the asymptote D′()/D0 ∝-3 in the range of concentrated solutions 0.3 < < 0.55. Here, D0) lim f0 D() and D() are the self-diffusion coefficients of dendrimer in an extremely dilute solution and in a solution with macromolecular concentration , respectively. D′()) D()/L(), where L() is a normalizing function, taking into account the change of the local mobility of dendritic branches as the macromolecular concentration increases; the L() functions have been experimentally extracted from the concentration dependence of the longitudinal relaxation times for the dendrimers in solutions studied.
Colligative and Viscosity Properties of Poly(propylene imine) Dendrimers in Methanol
Macromolecules, 1999
The colligative properties of poly(propylene imine) dendrimers in methanol have been investigated with low-angle laser light scattering and vapor pressure osmometry. The molecular weights and second virial coefficients of the first five generations have been determined. The molecular weights have been found to agree with the theoretically expected values. Effective radii have been obtained from the second virial coefficient, viscosity, and the partial specific volume. Both pair interaction and viscous state of the particles are considered in terms of effective volumes. The fifth generation shows the most pronounced hard-sphere interaction probably reinforced by Coulombic repulsion. The viscosity behavior of these dendrimers is like nondraining spheres. All radii grow almost linearly with the generation number. Together with the exponential growth of their molecular weights, this excludes a power law dependence of molecular weight and radius; i.e., these dendrimers are not self-similar. This also explains the maximum in the viscosity.