Various studies suggest tannins act as antioxidants, anticarcinogens, cardio-protectants, anti-inflammatory agents, and antimicrobials. However, more investigation is needed to examine the bioavailability of tannins. Tannins bind to salivary peptides by hydrophilic and hydrophobic mechanisms. Electrospray Ionization Mass Spectrometry (ESI-MS) has been used to assess both hydrophilic and hydrophobic components of protein complexes. ESI-MS could potentially be an effective tool for screening the bioavailability of tannins. Weaker binding tannins are predicted to be more highly absorbed by the body, and should therefore exhibit greater bioavailability. Rannulu and Cole have used ESI-MS to measure binding affinities of procyanidin tannin stereoisomers for salivary peptides in aqueous solution. The condensed tannins procyanidin B1, B2, B3, and B4 demonstrated significantly different binding affinities (binding strengths) for the Histatin 5 salivary peptide. The procyanidin-Histatin 5 binding mechanisms in the ESI-MS experiments by Rannulu and Cole were investigated using the FRED docking program combined with molecular dynamics optimization in the AMBER software suite. The simulations suggest residual liquid-phase binding interactions in procyanidin-Histatin 5 complexes are maintained in the gas phase under conditions resembling those in ESI-MS experiments, though the gas-phase interaction energies were enhanced. Increased hydrogen bonding and decreased π-π stacking interactions were also detected in gas versus liquid-phase procyanidin-Histatin 5 complexes. In addition, simulation results suggest multiple conformations of procyanidins bind Histatin 5 at several sites and procyanidin binding does not fix the Histatin 5 peptide backbone. The simulations agree with previous studies which indicate aromatic Histatin 5 residues are responsible for procyanidin-Histatin 5 binding and tannins can bind salivary peptides in multiple conformations. The effects of Hofmeister salts on complexation of an amphiphilic guest adamantane carboxylic acid to the hydrophobic surface of a deep-cavity cavitand have been investigated by Gibb et al. Adamantane-cavitand binding was found to be largely enthalpically driven, though adamantane binding in the presence of the salting-in anions perchlorate and thiocyanate was entropically driven. Gibb et al. also found that perchlorate-cavitand binding was enthalpically favorable, though entropically unfavorable. Potential-of-mean-force (PMF) calculations for perchlorate-cavitand and thiocyanate-cavitand complexation were performed using umbrella sampling with a modified version of the sander module from the Amber 9 software suite to further investigate the thermodynamic properties of Hofmeister-anion binding to the hydrophobic cavitand. The enthalpy for salting-in anion-cavitand complexation was calculated from the potential energy difference between the bound and unbound state (the potential energy of binding) along with the entropy. The binding entropy and enthalpy were also calculated using a finite difference approximation to the entropy. The enthalpy for perchlorate-cavitand complexation calculated from the binding energy and the finite difference approximation to the entropy was favorable with an unfavorable entropy. The binding enthalpy and entropy for thiocyanate-cavitand complexation calculated from the binding energy and finite difference approximation to the entropy were unfavorable and favorable, respectively, perhaps due to a classical hydrophobic effect. The orientation of the ligand, the number of water molecules displaced from the ligand and cavitand upon complexation, and the number of nearest-neighbor atom contacts between the ligand and the cavitand were also calculated. Additionally, the energetics of various interactions involved in salting-in anion-cavitand complexation including the anion-cavitand, anion-water, cavitand-water, and water-water interactions were assessed, though the data were inconclusive.

Protein stability plays an important role in a wide variety of settings ranging from industrial processes where proteins are used as biocatalysts to medical settings where misfolded proteins are implicated in disease. Understanding protein stability will allow design of improved bioprocess and pharmaceutical formulations as well as aid in the development of therapies for protein-based diseases. The effects of dissolved salts on protein kinetic stability are studied here. We find that ion-solvent interactions, characterized by the Jones-Dole B-viscosity coefficient, are strong indicators of salt effects on protein deactivation. This finding is used to develop a model for predicting protein deactivation in salt solutions in terms of two competing processes. Since protein unfolding and aggregation can lead to a number of protein misfolding diseases, we test the applicability of our model for describing salt effects on transthyretin aggregation. As the factors contributing to protein stability become more understood, the use of enzymes as biocatalyst for industrial process will increase, and the need for enzymes active in a wide range of reaction media will increase. We have developed a process using an enzyme in combination with organic-aqueous tunable solvents (OATS) which allows for monophasic reaction of the enzyme with hypdrophobic substrates. The reaction mixture can be separated into two phases by the addition of carbon dioxide pressure. This separation allows for both convenient recovery of the hydrophobic reaction product from the organic phase as well as recycle of the enzyme in the aqueous phase. Overall reaction conversions of 80% and little enzyme activity loss are observed after six reaction cycles.

Title: Ion Specific Hofmeister Effects on Peptides and Proteins Author: Ing. Jana Hladílková Department: Physical and Macromolecular Chemistry Advisor: Prof. Pavel Jungwirth, DSc., IOCB AS CR Advisor's email address: pavel.jungwirth@uochb.cas.cz Abstract: Classical molecular dynamics simulations in combination with advanced methods of analysis were used to shed light on missing parts of our molecular understanding of the Hofmeister series. In tandem with various experimental techniques, real proteins as well as model systems were investigated in aqueous salt solutions in order to identify and quantify ion-protein interactions either leading or not leading to the canonical cationic and anionic Hofmeister ordering. The potassium cation was found to significantly enhance the BHMT enzymatic activity in contrast to the rest of the common monovalent cations. In the quest to rationalize this behavior, a key potassium binding site in the vicinity of the active site was discovered and described. Moreover, the exceptionally strong effect of K+ on the enzymatic activity was explained by hydration properties of the cations within the limited space of the active site in interplay with their attraction to the nearby negatively charged residues. By contrast, only a small and indirect influence, which follows the cationic...

Very specific protein-salt interactions are involved in a multitude of biological phenomena such as protein folding/stability, enzymatic activity, and signal transduction events. In this work, we used two very simple, protein-mimic model biopolymers to obtain a better understanding of specific cation effects operating in aqueous protein environments. The two biopolymers used were Elastin-like Polypeptides (ELPs) and poly(N-isopropylacrylamide) (PNIPAM). ELPs are an especially an ideal model system as these polypeptides can be easily genetically engineered to observe the effect of specific amino acid residues and peptide chain length on these salt interactions. Both of these biopolymers are also highly thermoresponsive as their aqueous solutions undergo a hydrophobic collapse/aggregation induced phase transition process above a lower critical solution temperature (LCST). Thermodynamic measurements of these biopolymers were carried out under various salt solution conditions. Additionally, both of these biopolymers are suitable for making surface specific spectroscopic measurements. Vibrational sum frequeny spectroscopy (VSFS), a non-linear interface sensitive spectroscopic technique, was employed here to investigate biologically relevant cation interactions which occur at peptide/protein surfaces. First, the LCST response of a non-polar ELP and a neutral biopolymer, PNIPAM, was investigated in the presence of 12 different alkali, alkaline-earth metal and transition metal chloride salts. Even though the salt interactions for uncharged proteins are dominated by anions, subtle specific cation effects were also observed. The results followed a direct Hofmeister series for cations. Most alkali cations are excluded from the polar amide regions of proteins. More polarizable cations, however, can solvate the hydrophobic moieties and somewhat counter the salting-out effect of the chloride anion. More charged and hydrated ions like lithium and divalent cations showed a weak interaction to the amide moiety through their hydration shell. The role of acidic amino acid residues in inducing cation specificities was investigated using an aspartate-rich ELP system. Both thermodynamic and spectroscopic data conclusively proved that the negative charge on protein surfaces is the main driving force for cation partitioning and specificity under physiological relevant concentration regimes. Apparent binding constants of carboxylate moieties with cations were determined. This is the first quantitative and thoroughly systematic study of such biologically relevant cation-carboxylate interactions prevalent in enzyme active sites and protein surfaces.

The overall thrust of this project is to gain an insight into a class of surface-tethered cross-linked thin films of poly(N-alkylacrylamides) that display a lower critical solution temperature (LCST).The structure of the alkyl group and the modification of the amide groups determine the LCST and resultant volume-phase transition behavior. The aim of this study involves synthesis and characterization of thin films and to correlate the volume-transition behavior to the structure of the alkyl group. For better understanding the volume-transition behavior, the polymer films are perturbed by the Hofmeister salt series to examine trends between different alkyl groups. While most of the studies have been done with bulk gels, the majority of the applications require the use of gels at surfaces and interfaces. Surface attached polymer networks provide an alternative to bulk gels showing superior response times, thus efficiency. Hence it is significant to understand the impact of confinement on the phase transition behavior of a polymer network. Anchoring a polymer network to a surface produces volume phase transition perpendicular to the substrate. The parallel swelling and collapse of the network is highly restricted due to lateral confinement, thus impacting properties such as structure, mechanical properties, dynamics and permeability of the network. Several studies have been done with poly(N-isopropylacrylamide) anchored to a substrate, which have shown significantly different behavior than unconstrained networks. Notable examples include a gradual as opposed to a sharp volume-phase transition, and significantly less swelling above and below the LCST. These studies only looked at poly(NIPAAm); therefore it remains unknown if these results are universal and will apply to other LCST polymers. Hence, we expanded upon these studies to also investigate a library of different LCST polymers belonging to the category of N-alkylacrylamides. I have synthesized the copolymers comprising of N-alkylacrylamides and methacryloxybenzophenone (MaBP). The benzophenone moiety in MaBP is photoreactive, allowing us to cross-link the copolymers by UV irradiation. Surface attached thin films were fabricated by spin coating the solution of copolymers and cross-linking by UV irradiation. The volume phase transitions of the coatings were studied under the influence of temperature and the salts of the Hofmeister series. Information concerning the state of responsive layers, the precise temperature at which the collapse occurs, and the changes in the molecular environment during the transition were investigated by ellipsometry and ATR-FTIR. In a longer perspective, understanding the transition behavior and the influence of salts governing this transition provides a better understanding of the interactions of biopolymers in natural systems.

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第20481号 / エネ博第350号 / 新制||エネ||70(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)教授 木下 正弘, 教授 森井 孝, 教授 片平 正人 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

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Les stérosomes, des vésicules artificielles composées d’amphiphiles monoalkylés et d’un grand pourcentage de stérols, sont prometteurs dans plusieurs domaines comme les industries pharmaceutiques et alimentaires. Il existe des stérosomes chargés négativement, positivement et neutres. Dans ce mémoire, nous avons approfondi nos connaissances sur les propriétés physico-chimiques des stérosomes chargés : acide palmitique (PA)/stérol et stéarylamine (SA)/cholestérol (Chol). Premièrement, afin de mesurer la diffusion latérale de PA dans les membranes PA/stérol (30/70 mol/mol) par RMN à gradients pulsés, nous avons tenté de former des bicouches liquide-ordonnées (lo) orientées magnétiquement avec ce mélange. En s'inspirant de l’idée que l’ajout de 1,2-dihexanoyl-sn-glycéro-3-phosphocholine (DHPC), un lipide à courtes chaînes, dans le système 1,2-dimyristoyl-sn-glycéro-3-phosphocholine (DMPC) mène à la formation de bicouches orientées, nous avons étudié la formulation PA perdeutéré/acide hexanoïque (HA)/Chol avec une proportion molaire de 25/18/57 à plusieurs températures; aucune formation de bicouches orientées n’a été observée. Ce résultat pourrait être expliqué par la solubilisation partielle de HA en milieu aqueux. Alors, une quantité insuffisante serait insérée dans la bicouche pour induire son orientation. La formulation PA perdeutéré/DHPC/Chol n’a pas conduit, elle non plus, à des bicouches orientées magnétiquement à des températures et concentrations lipidiques variées. En étudiant le mélange DMPC/DHPC/Chol (67/17/14), nous avons remarqué que la présence de Chol inhibait l'orientation magnétique des bicouches. Tandis que le mélange DMPC/DHPC/stigmastérol (SS) avec les proportions molaires 67/19/14 et 72/21/7 conduisait à des bicouches orientées avec leur normale (n) perpendiculaire au champ magnétique à 40 °C et 50 °C. Ces résultats suggèrent que le mélange PA/SS avec une proportion de lipide à courtes chaînes, HA et DHPC, pourrait mener à des bicouches orientées magnétiquement. Le mélange PA/Chol avec un lipide à courtes chaînes pourrait aussi être étudié en présence des lanthanides. Deuxièmement, nous avons examiné la possibilité de moduler la libération de matériel encapsulé dans des liposomes essentiellement composés de PA et d’un stérol. Il est connu que le mélange PA/Chol (30/70) à pH ≥ 7,5 forme des liposomes très peu perméables. Il est avantageux de pouvoir moduler la perméabilité pour avoir un contrôle sur le temps de libération de leur contenu, qui est un paramètre de grande importance pour les formulations liposomales de médicaments. D’abord, il a été montré que l’acide oléique (OA)/Chol (30/70) est capable de former des vésicules, ce qui n’avait jamais été prouvé auparavant. Par contre, les bicouches OA/Chol (30/70) ne sont pas plus perméables que les bicouches PA/Chol (30/70). L’ajout de 1-palmitoyl-2-oléoyl-sn-glycéro-3-phosphatidylcholine (POPC) dans le mélange PA/Chol n’augmente pas plus la perméabilité. En effet, les cinétiques de relargage de calcéine des vésicules PA/POPC/Chol (15/27.5/57.5), POPC/Chol (40/60) et POPC étaient très semblables à celle de PA/Chol (30/70). Il a été remarqué que les études littéraires se contredisent à propos de la perméabilité à la calcéine des bicouches de phosphatidylcholine (PC). L’explication de ces divergences est inconnue pour le moment. En remplaçant la moitié de la proportion molaire de Chol par le cholate de sodium (SC) dans le mélange PA/Chol (30/70), la membrane n’était pas plus apte à libérer son contenu. Il se pourrait que le SC se retrouvant dans la bicouche n’induit pas une diminution d’empilement. Il est aussi possible que le SC ne s'insère pas dans la membrane à cause de son hydrophilie considérable et il pourrait alors former seul des micelles. En remplaçant complètement le Chol par le sulfate de cholestérol (SChol), un stérol chargé négativement, et en préparant les vésicules à un bas pH, la formulation PA/SChol (30/70) mène à une très grande perméabilité à pH 7.5; le relargage est provoqué par un saut de pH. Nos travaux suggèrent qu'il serait possible de moduler la perméabilité des liposomes en les préparant avec le mélange PA/SChol/Chol en variant les proportions entre 30/63/7 à 30/70/0. Le diagramme pH-composition du mélange PA/SChol/Chol indique que ces proportions conduisent, à pH 7.4, à la coexistence de phases solide et lo en différentes proportions, ce qui pourrait moduler la perméabilité membranaire. Troisièmement, les résultats de perméabilité obtenus avec la calcéine et les difficultés survenues lors de l’extrusion des vésicules encapsulant cette sonde nous ont amené à nous demander si la calcéine interagit avec les bicouches chargées. L’impact de certains anions, dont la calcéine, a été examiné sur les bicouches chargées positivement SA/Chol (50/50). La calorimétrie différentielle à balayage (DSC, de l’anglais differential scanning calorimetry), indique qu’il n’y a aucune transition entre 25 et 90 °C pour les liposomes SA/Chol (50/50) à pH = 7.4. L’ajout de chlorure de sodim (375 mM) n’a pas mené à la formation d’agrégats et aucune transition n’a été observée sur le thermogramme. La formation d’agrégats macroscopiques instantanément après l’ajout d’hydrogénophosphate de sodium (125 mM), de sulfate de sodium (125 mM) et de calcéine (3 mM) a été observée. Une transition a été observée sur les thermogrammes en présence de ces sels. Les agrégats observés pourraient être associés à la transition de phase. L’effet des anions sur la température et l’enthalpie de transition suivent le même ordre que la série d’Hofmeister : sulfate > hydrogénophosphate > chlorure (pas de pic). La calcéine avait l’impact le plus prononcé sur l’agrégation; ceci illustre que la calcéine n’est pas une sonde fluorescente inerte avec le mélange SA/Chol. Elle pourrait être un chaotrope volumineux. De plus, les interactions SA-calcéine plus fortes, menant à l’agrégation des vésicules, que les interactions PC-calcéine pourraient s’expliquer par le fait que la SA est chargée positivement. / Sterosomes are artificial vesicles that are composed of monoalkylated amphiphiles and a large percentage of sterols. They are promising in areas such as pharmaceutical and food industries. Sterosomes can be found in anionic, cationic and neutral form. The work of this master’s thesis focuses on gaining additional knowledge on the physicochemical properties of charged sterosomes such as palmitic acid (PA)/sterol and stearlyamine (SA)/cholesterol (Chol). Our first aim was to find an approach to form liquid-ordered (lo) bilayers that can orient in a magnetic field with the PA/sterol (30/70 mol/mol) mixture. This will allow us to study the lateral diffusion of PA. It has been demonstrated that mixing 1,2-diheptanoyl-sn-glycero-3-phosphocholine (DHPC), a short chain lipid, with 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) results in bilayers that orient with their normal (n) perpendicular to the magnetic field. Therefore, perdeuterated PA/hexanoic acid (HA)/Chol (25/18/57) mixture was studied at different temperatures; however, results showed no bilayer orientation. It was suggested that this could be due to the partial solubility of HA in aqueous phase. Consequently, an insufficient quantity of HA was available to induce bilayer orientation. Furthermore, perdeuterated PA/DHPC/Chol mixture was studied at different temperatures and lipid concentrations, which also led to no bilayer orientation. While studying DMPC/DHPC/Chol (67/17/14) formulation, it was understood that Chol inhibits bilayer orientation. On the other hand, two different molar proportions of DMPC/DHPC/stigmasterol (SS) (67/19/14 and 72/21/7) led to bilayers that orient with their n perpendicular to the magnetic field at 40 °C et 50 °C. These results suggest that by adding a short chain lipid such as HA and DHPC to PA/SS mixture could lead to oriented bilayers. Another interesting track would be to work with PA/short chain lipid/Chol mixture in the presence of lanthanides. Our second aim was to find different formulations of vesicles, containing at least PA and a sterol, with distinctive permeability. It has already been established that PA/Chol (30/70) bilayers are in lo phase as long as PA is deprotonated (pH ≥ 7,5) and have a very limited permeability. The ability to modulate permeability would allow control over the release time of an encapsulated product, which is an important parameter in the development of novel liposomal drug delivery systems. It was proven that oleic acid (OA)/Chol (30/70) mixture is able to form bilayers, which has not been shown previously. However, OA/Chol (30/70) bilayers were not much more permeable than PA/Chol (30/70) bilayers. Adding 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) in PA/Chol system did not lead to higher permeability either. Results of calcein release kinetics from PA/POPC/Chol (15/27.5/57.5), POPC/Chol (40/60) and POPC vesicles were not very different from the one found for PA/Chol (30/70) vesicles. It was noted that contradictory results were found in the literature regarding calcein permeability from phosphatidylcholine (PC) membranes. For the moment, explanations related to these divergences have yet to be given. Furthermore, no increase in membrane permeability was found after substituting half of the molar proportion of Chol by sodium cholate (SC) in PA/Chol (30/70) mixture. One suggestion would be that SC insertion in the bilayer does not induce a reduction in the packing of lipids. Another suggestion would be that SC does not insert in PA/Chol bilayers due to its considerable hydrophilic character and forms micelles on its own. Highly permeable membrane was found when Chol was completely replaced by cholesterol sulfate (SChol), a negatively charged sterol, and vesicle preparation was done at low pH. The pH-triggered release method was used. Our work suggests that by varying the molar proportion of PA/SChol/Chol mixture between 30/63/7 and 30/70/0, it would be possible to obtain different vesicle formulations with distinctive permeability. In between these molar proportions, the pH-composition diagram of PA/SChol/Chol shows the coexistence of solid and lo phases in different proportions at pH 7.4, which could modulate the permeability. Some ambiguous calcein release results and struggles arising from the extrusion of calcein-encapsulated liposomes led us to wonder if this dye interacts with charged bilayers. The impact of some anions, including calcein, was examined on SA/Chol (50/50) charged bilayers. Thermodynamic studies were done by differential scanning calorimetry (DSC). SA/Chol (50/50) mixture showed no transition between 25 and 90 °C at pH 7.4. In the presence of sodium chloride (375 mM), there was no indication of aggregation or the appearance of a transition on the thermogram. Macroscopic aggregates were instantly observed after addition sodium hydrogenphosphate (125 mM), sodium sulphate (125 mM) and calcein (3 mM). Furthermore, a phase transition was also noticed on the thermograms in the presence of these salts. It is suggested that the appearance of the transition can be associated with the formation of aggregates. The effect of anions on the transition temperature and enthalpy follows the Hofmeister series: sulfate > hydrogenphosphate > chloride (no peak). Calcein had the highest impact on the formation of aggregates. This indicates that calcein is not a good candidate to be used as a fluorescent dye with SA/Chol mixture. It was suggested that calcein could be a large chaotrope anion. In contrast to PC-calcein interactions, SA-calcein interactions led to the aggregation of vesicles probably due to stronger interactions in the presence of positively charged SA.

La poly(2-isopropyl-2-oxazoline) (PIPOZ) est un polymère thermosensible qui possède une température de solution critique inférieure (LCST) autour de 40 °C en solution aqueuse. Les travaux présentés s’intéressent aux propriétés en solution aqueuse et aux interfaces, de l’homopolymère PIPOZ, d’une PIPOZ fonctionnalisée avec un groupement lipidique (lipo-PIPOZ) et de copolymères à blocs à base de poly(éthylène glycol) et de PIPOZ. Si elle est régulièrement comparée à son isomère structurel le poly(N-isopropylacrylamide) (PNIPAM), les études sur les propriétés en solution de la PIPOZ sont cependant moins complètes que celles sur le PNIPAM. Le premier objectif des travaux présentés ici est de parfaire la connaissance du comportement en solution de la PIPOZ en présence d’additifs. Les effets de sels et de solvants hydromiscibles sur la solubilité de la PIPOZ ont été investigués par turbidimétrie et microcalorimétrie sur trois homopolymères de masses moléculaires différentes. Contrairement aux solutions de PNIPAM, l’ajout de méthanol à la solution de PIPOZ ne conduit pas au phénomène de cononsolvency où la solubilité du polymère diminue pour une certaine gamme de fractions volumiques de cosolvant. L’effet a néanmoins été observé dans le cas de système PIPOZ/Eau/THF. L’effet de sels sur la solubilité de la PIPOZ suit la série Hofmeister. La présence de sels chaotropes (NaI et NaSCN) en solution ont révélé un effet bien plus important sur la solubilité de la PIPOZ que pour son isomère. Les valeurs de point troubles de la solution de PIPOZ augmentent de plus de 30 °C pour une concentration en sel supérieure à 1 M. L’autre objectif de cette thèse est de synthétiser un système à base de PIPOZ capable de s’auto-assembler à l’interface air-eau afin de former des films interfaciaux par la technique Langmuir-Blodgett. A cette fin, un amorceur contenant un groupement lipidique (2 chaînes alkyles et un groupement phosphate) a été synthétisé et utilisé pour la polymérisation cationique par ouverture de cycle (CROP) du monomère 2-isopropyl-2-oxazoline conduisant à l’obtention d’un lipo-PIPOZ (Mn = 10 kg.mol-1). L’effet de deux sels (NaSCN et NaCl) sur les films interfaciaux a été étudié. Malgré leur effet opposé sur la solubilité de la PIPOZ en solution, ils conduisent tous les deux à l’expansion de la monocouche de lipo-PIPOZ. Transférés sur des substrats de mica, ces films ont été visualisés par microscopie à force atomique (AFM). La iv présence de sels dans la sous-phase lors de la formation de monocouches conduit à la formation d’agrégats d’épaisseur ~ 10 nm dont le diamètre augmente avec la concentration en sel. Enfin, le dernier objectif est de caractériser les propriétés en solutions de copolymères à blocs PIPOZ-b-PEG-b-PIPOZ. La polymérisation par CROP de la 2-isopropyl-2-oxazoline a été amorcée à partir d’un PEG (Mn = 2 kg.mol-1) bifonctionnel, Le polymère synthétisé (TrOH, Mn = 11 kg.mol-1) a ensuite subit une fonctionnalisation des extrémités de chaînes par des groupements octadécyles conduisant à l’obtention d’un copolymère à blocs téléchélique amphiphile et thermosensible (TrC18). Les propriétés des copolymères en solution aqueuse ont été étudiées par turbidimétrie, diffusion dynamique de la lumière (DLS), microcalorimétrie (DSC), microscopie électronique à transmission et spectroscopie à sonde fluorescente, FT-IR et AFM. Les deux copolymères sont thermosensibles et présentent des valeurs de points troubles de ~ 48 °C pour le copolymère TrOH et de ~ 38 °C pour le copolymère amphiphile. Ce dernier s’auto-assemble à température ambiante et forme, en solution aqueuse, des micelles de type fleurs de rayon hydrodynamique RH ~ 8 nm. L’effet prolongé de la température sur la cristallisation des blocs de PIPOZ a aussi été examinée. Les deux polymères cristallisent en solution aqueuse conduisant à la formation de fibres insolubles dans l’eau. Mots- / Poly(2-isopropyl-2-oxazoline) (PIPOZ) is a thermosensitive polymer whose lower critical solution temperature (LCST) in water is ~ 40 °C. This thesis focuses on the properties in aqueous solution and on interfaces of new poly(2-isopropyl-2-oxazoline) systems. PIPOZ is often compared to its structural isomer, the renowned poly(N-isopropylacrylamide) (PNIPAM). If PNIPAM has been the center of thermosensitive polymer research for the last three decades, it is PIPOZ which has recently been gaining interest. The first aim of the thesis is to improve on the knowledge on PIPOZ properties in aqueous solution in the presence of water-soluble additives. Effect of salts and cosolvents were investigated by turbidimetry and microcalorimetry (DSC) on PIPOZ homopolymers of different molecular weights. Effect of salts on PIPOZ solubility follows the Hofmeister series. Chaotropic anions (SCN-, I-) induce a large increase (up to 30 °C) of the cloud point temperature of PIPOZ solution which is 10 times larger than for PNIPAM. Adding methanol into PNIPAM aqueous solution leads to a decrease in solubility of the polymer. This phenomena is called cononsolvency. Unlike PNIPAM solutions, the addition of methanol in PIPOZ solution does not lead to a cononsolvency effect. Nevertheless, cononsolvency has been observed in the case of THF addition into PIPOZ aqueous solutions. The second aim of this work was to design and synthesize an amphiphilic PIPOZ able to anchor itself at the air-water interface and to form stable monolayer via the Langmuir-Blodgett technique. For that purpose, a lipidic initiator containing two alkyl chains and a phosphate group, was synthesized and used to initiate the cationic ring opening polymerization (CROP) of 2-isopropyl-2-oxazoline. The obtained amphiphilic (lipo-PIPOZ, Mn = 10 kg.mol-1) forms stable monolayers at the air-water interface. The presence of salt (NaCl or NaSCN) in the sub-phase during the compression of the films leads to expansion of the monolayer even if the salts have opposite effect on PIPOZ solubility in solution. The interfacial films were then transferred onto mica substrates and captured by atomic force microscopy (AFM). The salts induced the formation of aggregates (height ~ 10 nm) whose diameter depends on the salt and its concentration. At last, a block copolymer, TrOH, containing a central poly(ethylene glycol) (PEG) (Mn = 2 kg.mol-1) and two PIPOZ blocks was obtained by CROP of 2-isopropyl-2-oxazoline initiated vi by a bi-functionnal PEG. The total molecular weight was Mn ~ 11 kg.mol-1. Hydrophobic chain ends modification has been performed onto TrOH to bring amphiphilicity and to get a telechelic octadecyl-end capped block copolymer TrC18. The properties of these two block copolymers in water were characterized by dynamic light scattering (DLS), microcalorimetry (DSC), electronic transmission microscopy (TEM) and fluorescence spectroscopy, FT-IR and AFM. Cloud point temperature of copolymer solutions was found to be around 48 °C for TrOH and around 38°C for the amphiphilic analogue TrC18. The latter self-assembles at room temperature into flower micelles whose hydrodynamic radius is RH ~ 8 nm. Extended heating of both copolymer solutions leads to crystallization of PIPOZ block and insoluble fibers form in solution.

The overall thrust of this dissertation is to gain a comprehensive understanding over the factors that govern the performance and behavior of ultra-thin, cross-linked polymer films. Poly(NIPAAm) was used as a model polymer to study volume phase transition in surface tethered networks. Poly(NIPAAm) undergoes a reversible phase transition at approximately 32°C between a swollen hydrophilic random coil to a collapsed hydrophobic globule state, thought to be caused by increased hydrophobic attractions between the isopropyl groups at elevated temperatures. We present a simple photochemical technique for fabricating structured polymer networks, enabling the construction of responsive surfaces with unique properties. The approach is based on the photo-cross-linking of copolymers synthesized from N-isopropylacrylamide and methacroyloxybenzophenone (MaBP). In order correlate layer swelling to the MaBP content, we have studied the swelling behavior of such layers in contact with aqueous solutions with neutron reflection. The cross-linked networks provide a three-dimensional scaffold to host a variety of functionalities. These networks serve as a platform which can be used to amplify small local perturbations induced by various stimuli like temperature, pH, solvent, ionic strength and peptide modified hydrogels to bring about a macroscopic change. Neutron reflection experiments have shown that the volume-phase transition of a surface-tethered, cross-linked poly(NIPAAm) network coincided with the two-phase region of uncross-linked poly(NIPAAm) in solution. Parallel measurements with ATR-FTIR investigating the effect of temperature, pH and salts suggest that the discontinuous transition is the result of cooperative dehydration of the isopropyl groups, with water remaining confined between amide groups in the collapsed state as weakly hydrogen bonded bridges. Hybrid polymers with specific peptide sequences have shown specific response to external cues such as pH and metal ions exhibiting unique phase behavior.