Thermotropic ionic liquid crystals via self-assembly of cationic hyperbranched polypeptides and anionic surfactants

This work describes the dilute solution and solid-state structure of polyelectrolyte complexes generated from hyperbranched polylysine (HBPL) and various anionic, sodium alkyl sulfate surfactants. In dilute solution, the radius of gyration (Rg) of the HBPL and HBPL-surfactant complexes was determined in the Guinier regime in good solvent conditions by means of small-angle X-ray scattering (SAXS). With increasing molecular weight of the HBPL, an increase in Rg up to a maximum of 3.7 and 4.2 nm was observed for the HBPLs and HBPL-surfactant complexes, respectively. In the solid state, HBPL-surfactant complexes were found to form liquid crystalline (LC) phases, whose thermal stability and structure depended both on the molecular weight of the HBPL as well as on the nature of the anionic surfactant. Depending on the surfactant alkyl chain length, liquid crystalline phases with short range liquid-like order, columnar hexagonal packing or lamellar ordering were observed. By combination of small-angle X-ray scattering, differential scanning calorimetry (DSC), and cross-polarized light optical microscopy (CPOM), the exact structure of the LC phases, as well as their region of thermal stability, could be identified. HBPL-sodium dodecyl sulfate LC phases showed thermotropic behavior and underwent two transitions with increasing temperature. First, at lower temperatures, an order-nematic transition was observed. Upon further temperature increase, a second transition from a nematic to an isotropic phase was observed. Structural models for these different LC phases are proposed. © 2007 American Chemical Society.

Synthesis, structural characterization and applications of hyperbranched polymers based on L-lysine

Markus Scholl

L-lysine is an essential a-amino acid and a necessary building block for all proteins in the body. As an essential amino acid, L-lysine is not synthesized by humans or animals. Industrially produced L-lysine has therefore a big market as food additive, e.g. in pig food. In the body, L-lysine plays a major role in calcium absorption, building muscle proteins, recovering from surgery or sports injuries, and the body's production of hormones, enzymes, and antibodies.1 From a chemical point of view, L-lysine is an AB2 building block that contains two amino groups and one carboxylic acid group, which makes it an interesting monomer for the synthesis of dendrimers and hyperbranched polymers. L-lysine indeed has been extensively used to synthesize dendrimers2-4 or conjugates of dendrimers and linear polymers.5,6 These dendrimers and linear-dendritic hybrid architectures have attracted interest for various medical applications, including gene delivery,3,6-8 as drug carriers,9 for the development of multiple antigen peptide systems,10,11 and as magnetic resonance imaging agents.12 The drawback of these dendrimers and linear-dendritic hybrid architectures is their time consuming synthesis and their expensive large scale production. This thesis evaluates the feasibility of L-lysine as a monomer to synthesize hyperbranched polymers and investigates the potential of these materials as encapsulation agents and for various biomedical applications. As the hyperbranched polylysines are prepared in a single step and can be produced conveniently at a large scale, they may offer an interesting alternative to their widely used dendritic analogues. Including this introduction, this thesis consists of 8 chapters, which are briefly described below. Chapter 2 gives a general overview of dendritic and hyperbranched polymers build up of amide bonds. Their synthesis and applications in medicine and catalysis as well as their self-assembling and encapsulation properties will be discussed. Chapter 3 reports on the synthesis of hyperbranched polylysines via the thermal polymerization of L-lysine hydrochloride.13 Different catalysts were investigated to improve the reaction kinetics. The structure of the polymers was determined by 1H-NMR spectroscopy, and the degree of branching and the average number of branches were calculated. Chapter 4 will discuss the feasibility of different approaches to control polymer architecture during the thermal hyperbranched polymerization of L-lysine hydrochloride.14 The reactivity of the more reactive ε-NH2 group was modulated by introducing temporary protective groups. The distribution of structural units was analyzed by 1H-NMR spectroscopy and the degree of branching and the average number of branches were calculated. Chapter 5 will describe the dilute solution and solid state structure of hyperbranched polylysines and polyelectrolyte complexes generated from hyperbranched polylysine and various anionic, sodium alkyl sulfate surfactants.15 Structural models for the obtained liquid crystalline phases will be proposed. Chapter 6 will show some preliminary results of the end group modification of hyperbranched polylysine with different hydrophilic and hydrophobic agents. The feasibility of these hydrophobically modified hyperbranched polylysines to encapsulate hydrophilic dyes and transfer them from aqueous to organic media has been investigated. Chapter 7 provides a first insight into the biological properties of hyperbranched polylysine. In this chapter the results from preliminary cytotoxicity and cellular uptake experiments will be discussed. Chapter 8 will give a short summary of the work done in this thesis and an outlook. References Nelson, D. L.; Cox, M. M. "Lehninger, Principles of Biochemistry" 3rd Ed. Worth Publishing: New York, 2000. ISBN 1-57259-153-6. Denkewalter, R. G.; Kolc, J. F.; Lukasavage, W. J. In U.S. Pat. 4289872; Allied Corporation, 1981; Chem. Abstr. 1981, 102, 79324. Ohsaki, M.; Okuda, T.; Wada, A.; Hirayama, T.; Niidome, T.; Aoyagi, H. Bioconjugate Chem. 2002, 13, 510-517. Driffield, M.; Goodall, D. M.; Smith, D. K. Org. Biomol. Chem. 2003, 1, 2612-2620. Lübbert, A.; Nguyen, T. Q.; Sun, F.; Sheiko, S. S.; Klok, H.-A. Macromolecules 2005, 38, 2064-2071. Choi, J. S.; Joo, D. K.; Kim, C. H.; Kim, K.; Park, J. S. J. Am. Chem. Soc. 2000, 122, 474-480. Vlasov, G. P.; Korol'kov, V. I.; Pankova, G. A.; Tarasenko, I. I.; Baranov, A. N.; Glazkov, P. B.; Kiselev, A. V.; Ostapenko, O. V.; Lesina, E. A.; Baranov, V. S. Russ. J. Bioorg. Chem. 2004, 30, 12-20. Choi, J. S.; Lee, E. J.; Choi, Y. H.; Jeong, Y. J.; Park, J. S. Bioconjugate Chem. 1999, 10, 62-65. Sakthivel, T.; Toth, I.; Florence, A. T. Pharm. Res. 1998, 15, 776-782. Tam, J. P. Proc. Natl. Acad. Sci. U. S. A. 1988, 85, 5409-5413. Pessi, A.; Bianchi, E.; Bonelli, F.; Chiappinelli, L. J. Chem. Soc., Chem. Commun. 1990, 8-9. Nicolle, G. M.; Tóth, E.; Schmitt-Willich, H.; Radüchel, B.; Merbach, A. E. Chem. Eur. J. 2002, 8, 1040-1048. Scholl, M.; Nguyen T. Q.; Bruchmann, B.; Klok, H.-A. J. Polym. Sci. Part A Polym. Chem. 2007, 45, 5494-5508. Scholl, M.; Nguyen T. Q.; Bruchmann, B.; Klok, H.-A. Macromolecules 2007, 40, 5726-5734. Canilho, N.; Scholl, M.; Mezzenga, R.; Klok, H.-A. Macromolecules 2007, 40, 8374-8383.

EPFL2007

Molecular insights in aqueous systems

Yixing Chen

The unique structure and dynamics of the water hydrogen (H)-bond network enable a multitude of structures and chemical reactions in both bulk solutions and at interfaces. The underlying molecular interactions between water and dissolved electrolytes, organic molecules, and nanoscale interfaces are difficult to study and hence not fully understood, especially when it involves interactions of length scales larger than one nanometer. In this thesis, we perform second order nonlinear light scattering experiments to investigate extended hydration shells (over one nanometer) and interfacial structures of buried aqueous interfaces that surround nanodroplets. We investigate the spatial range of ion-water interactions by probing the molecular structure of the water network in dilute electrolyte solutions. We find that electrolytes induce long-range, non-ion-specific orientational order in the H-bond network of water (over distances up to 70 hydration shells or 20 nm). These modifications in the water network start at electrolyte concentrations as low as 10 micromolar. The amount of induced orientational order and the concentration at which it occurs is different between light and heavy water. We link the observed ion induced changes in the bulk H-bond network of water to ion induced surface tension anomalies that occur in the same concentration range. We also study the same interactions in solutions with higher electrolyte concentrations focusing on cations. We observe specific ion effects in both the local charge distribution and water ordering in extended hydration shells of ions. Cations with larger charge densities induce larger changes in these two observables that follow a direct Hofmeister trend. The ion-induced structural changes in the water network are strongly correlated with the viscosity B-coefficient and hydration free energy of cations. These correlations facilitate constructing a better molecular model for specific ion effects in aqueous solutions. Next, we study the nanoscale hydrophobe/water interface and related interactions by probing the molecular structure of the interface formed with amphiphilic alkanols. We find that alkanols form a fluid film at the oil nanodroplet surface. Long chain alkanols show similar molecular structures and number densities at the interface. With increasing alkanol density, interfacial water loses its initial orientational alignment. The structure of interfacial oil molecules is more distorted for shorter alkanols. This interfacial structure differs significantly from those of macroscopic planar alkanol/water and alkanol/air interfaces and charged surfactant/oil/water interface, which can be explained by the balance between dispersive and H-bonding interactions. Finally, we develop a new membrane model system: 3D-lipid monolayers with tunable molecular structure on oil nanodroplets in water. This in-situ prepared system mimics the structure of lipid droplets in cells. The interfacial structure of lipids can be tuned from a tightly packed monolayer (liquid condensed phase) to a dilute one (liquid condensed/liquid expanded coexistence phase) by varying the lipid/oil/water ratio. The tunability of the chemical structure, the high surface-to-volume ratio, and the small sample volume make this system ideal for studies of molecular interactions of lipids in membranes.

EPFL2017

Etude de l'effet du brassage électromagnétique sur les microstructures d'alliages cuivreux

Thomas Campanella

In order to eliminate internal and surface defects, which appear in the ingots during continuous casting of metallic alloys, homogeneous and fine structures are often required. Therefore, when the adjunction of inoculant substances is not possible, the electromagnetic stirring (EMS) process is used during solidification. It consists to create convective mouvements in the liquid part of the casting, by the action of an electromagnetic field. A fine equiaxed grain structure can then be observed. The main goal of this research is to study the effect of the EMS process on grain structures for two industrial copper-base alloys : C97 (Cu-1%Ni-1%Pb-0.2%P) and BZ4 (Cu-4%Zn- 4%Sn-4%Pb). In particular, it included the determination of the optimal experimental parameters to obtain a grain refinement, the characterization of their effect on the solidification and the understanding of the physical mechanisms driving grain refinement. For that purpose, a Bridgman type furnace was modified in order to add an electromagnetic stirring device. Indeed, as the industrial continuous casting process is rigid and complex, the investigations were easier to carry out on the Bridgman installation, enabling us to define the influence of each experimental parameter : power of the induction, casting speed, coil position, temperature of the liquid and composition of the alloy. This experimental study was completed by the numerical simulation of the experimental conditions. The analysis of the structures, refined or not, showed that the dominant factors concerning the capacity of EMS to refine the structure, are the position of the inductor with respect to the liquidus, and the permeability of the mushy zone of the alloy. The more permeable the alloy is near the liquidus the more effective is the grain refinement. Concerning the position of the inductor, in-situ temperature measurements clearly revealed the local reheating of the liquid induced by convection. To correctly refine the low concentration alloy (C97), this local reheating must be brought on the position close to the dendrite position. During EMS-induced grain refinement, fragmentation of the dendrite arms by remelting and their survival in the melt are prevalent. Remelting can occur only if the "hot" liquid penetrates the mushy zone. Thus, the concept of permeability according to the model of Karman-Cozeny was used in simulation in order to characterize the penetration of the liquid in the mushy zone. From these results, a criterion of remelting, based on Flemings model of macrosegregation, was adapted and applied to our case. This criterion shows that remelting takes place if the velocity of the interdendritic liquid is lager than the speed of the isotherms. The velocity of the interdendritic liquid was calculated by numerical simulation for both alloys, under various experimental conditions. These results confirmed the importance to bring the inductor closer to the position of the liquidus to remelt dendrites, in particular in the case of the C97 alloy, which proves to be much more difficult to refine than the BZ4 alloy. Lastly, survival of the fragments was also studied. It depends on the casting conditions (casting speed and thermal gradient) and on the composition of the alloy. From the differences in composition of both alloys, it could be shown that the survival of dendrites fragments is improved during the solidification of the BZ4 alloy, compared with the C97 alloy.

EPFL2003