Non-viral gene delivery agents, such as cationic polyelectrolytes, are attractive replacements to viruses due to the absence of potential immunogenic risk and the ability to tune their macromolecular structure. Although non-viral vectors possess numerous design advantages, several investigators have shown that transfer efficiencies are considerably lower when compared to viral vectors. The work reported in this dissertation aims to fundamentally understand the underlying structure-transfection relationships involved in polycation-mediated gene delivery. Efforts focused on the influence of molecular weight, macromolecular topology, carbohydrate modifications, and charge density on the overall transfection activity in vitro. Several families of polycations were synthesized in order to correlate chemo-physical characterization with transfection results. Results revealed that seemingly small changes in the structure of cationic polyelectrolytes can have profound consequences on their transfection activity. / Ph. D.

The focus of this dissertation research involves surface charge manipulation of functionalized monolayers. Application of potential to acid or base terminated organic films immobilized on electrodes results in the ionization of the terminal groups. The ionization of these groups using applied potential provides conditions favorable the control of polyelectrolyte deposition to the monolayer surface. Research is presented that asserts that the interfacial pH of acid or base terminated monolayers responds to applied potential as a result of the accumulation of phosphate counterions to the monolayer-solution interface. Results obtained from applied potential modulation of surface charge endeavors strongly suggest that manipulation of terminal group ionization with applied potential “turns on“ or “turns off“ the charge of the monolayer. Switching on the surface charge of functionalized monolayers using applied potential yields conditions that make it possible for the promotion or inhibition of electrostatic attachment of polyelectrolyte to the monolayer surface. Electrostatic interactions between immobilized polyelectrolytes and redox probes result in changes in electron transfer that can be monitored with electrochemical impedance measurements. Impedance measurements provide a qualitative assessment of the degree of potential-driven polyelectrolyte self assembly. The electrostatic interactions between the redox probe in solution and the terminal region of monolayers directly affects the extent of charge-transfer between the electrode and the redox probe in solution. For this reason, impedance measurements are able to provide an indication of whether or not potential drives to electrostatic deposition to the terminal region of a functionalized monolayer. Unlike impedance measurements, quartz crystal microbalance measurements provide quantitative mass assessments that confirm polyelectrolyte deposition of inhibition under the direction of applied potential. Application of appropriate potentials is shown to induce variations in the electrostatic interactions between redox probes in solution and terminal groups of monolayers. Variations in the electrostatic interactions between the modified electrode and the redox probe modulate electron transfer that produces varying current. Since scanning electrochemical microscopy (SECM) relies on modulation of feedback current underneath a ten-micrometer platinum tip, SECM provides a means for monitoring of potential-driven surface charge modulation. Experiments presented in this dissertation will show that in addition to monitoring the effect of applied potential on the charge of ionizable surface groups, SECM can also be used to selectively deposit a polyelectrolyte to the surface of a carboxylic acid terminated monolayer. The SECM tip was rastered over the surface of a functionalized monolayer in the form of a simple pattern while the electrode was immersed in a dilute polyelectrolyte solution. As the SECM tip was moved and potential stepped more positive than the PZC, ionization was confined ionization to one spot encouraging localized ionic self assembly. / Ph. D.

Le travail présenté dans ce manuscrit s’intéresse au mode d’action des résines thermodurcissables utilisées pour conférer au matériau papier des propriétés spécifiques. En effet, certains papiers sont destinés, au cours de leur usage, à être en contact avec des liquides et en particulier de l’eau. C’est le cas, par exemple, des papiers absorbants, de certains papiers filtres, mais aussi de papiers pour étiquettes ou pour billets de banque. En présence d’eau, les papiers perdent rapidement leur résistance mécanique, essentiellement due à la présence en grand nombre de liaisons hydrogène, d’où la nécessité d’un traitement : l’objectif est de maintenir un certain niveau de résistance des papiers saturés en eau. Ces traitements consistent à introduire dans la suspension fibreuse, en cours d’élaboration, des pré-polymères cationiques s’adsorbant à la surface des fibres. Après la formation de la feuille de papier, la feuille humide est séchée et c’est au cours de cette étape que s’amorce la réticulation de ces polymères. Elle conduit à la formation d’un réseau tridimensionnel de polymère dans le matelas fibreux. Ce réseau permet au papier de conserver ses propriétés mécaniques lorsqu’il est en contact avec de l’eau. Il présente ce que l’on appelle communément une résistance à l’état humide (REH). Un des inconvénients de ce type de traitement est lié aux difficultés de recyclage des papiers obtenus. Il nécessite un traitement particulièrement intensif et coûteux qui couple une action mécanique (désintégration, dépastillage) à une action chimique (utilisation d’hydroxyde de sodium, par exemple). Même si ces produits sont largement utilisés, les mécanismes mis en jeu que ce soit pour le développement des propriétés de REH ou pour le recyclage ne sont pas totalement compris. Dans ce contexte, ce travail a pour objectif d’étudier le mode d’action de pré-polymères de polyamideamine épichlorhydrine (PAE), couramment utilisés en papeterie pour conférer au matériau papier une résistance à l’état humide (REH). Il s’intéresse à la caractérisation de solutions commerciales de PAE et à l’étude des mécanismes réactionnels de ces pré-polymères. Il traite également de l’effet de certains paramètres de production du papier sur l’efficacité des traitements. Enfin, il apporte de éléments nouveaux sur la compréhension de l’étape de recyclage. / Polyamideamine epichlorohydrin (PAE) resin is a water soluble additive and the most used permanent wet strength additive in alkaline conditions for preparing wet strengthened papers. In this thesis, we studied some properties of PAE resins and wet strengthened papers prepared from them. In order to elucidate PAE structure, liquid state, 1H and 13C NMR was performed and permitted signals assignment of PAE structure. PAE films were prepared to study cross-linking reactions and then thermal and ageing treatments were performed. According to our results, the main PAE cross-linking reaction occurs by a nucleophilic attack of N atoms in the PAE and/or polyamideamine structures forming 2-propanol bridges between PAE macromolecules. A secondary contribution of ester linkages to the PAE cross-linking was also observed. However, this reaction, which is thermally induced, only occurs under anhydrous conditions. The mechanism related to wet strength development of PAE-based papers was studied by using CMC as a model compound for cellulosic fibres and PAE-CMC interactions as a model for PAE-fibres interactions. Based on results from NMR and FTIR, we clearly showed that PAE react with CMC that is when carboxylic groups are present in great amounts. Consequently, as the number of carboxylic groups present in lignocellulosic fibres is considerably less important and the resulting formed ester bonds are hydrolysable, we postulate that ester bond formation has a negligible impact on the wet strength of PAE-based papers. In the second part of this work, a 100% Eucalyptus pulp suspension was used to prepare PAE-based papers. PAE was added at different dosages (0.4, 0.6 and 1%) into the pulp suspension and its adsorption was indirectly followed by measuring the zeta potential. Results indicate that the adsorption, reconformation and/or penetration phenomena reach an apparent equilibrium between 10 and 30 min. Moreover, we showed that the paper dry strength was not significantly affected by the conductivity level (from 100 to 3000 µS/cm) of the pulp suspension. However, the conductivity has an impact on the wet strength and this effect seems to be enhanced for the highest PAE dosage (1%). We also demonstrated that storing the treated paper under controlled conditions or boosting the PAE cross-linking with a thermal post-treatment does not necessarily lead to the same wet strength. Degrading studies of cross-linked PAE films showed that PAE degradation in a persulfate solution at alkaline medium was more effective. A preliminary study of industrial PAE-based papers (coated and uncoated papers) was also performed. For uncoated paper, persulfate treatment was the most efficient. For coated papers, all treatments were inefficient in the used conditions, although a decrease of the wet tensile force of degraded samples was observed. The main responsible of the decrease of persulfate efficiency for coated papers was probably related to side reactions of free radicals with the coating constituents.

The electrostatic layer-by-layer (LbL) self-assembly of polyelectrolyte’s has shown applications in thin film coatings, micro patterning, nano-bioreactors and capsules for drug delivery. The film architecture can be precisely designed and controlled to nanometer scale precision with a range from 5 nm to a few microns. Both in vitro and in vivo studies indicate potential applications in biology, pharmaceutics, medicine, and other biomedical areas. This thesis work focused on the design and development of protocols to fabricate polyelectrolyte multi-layer patterns on a variety of substrates such as glass, metals and plastics such as acrylic and polycarbonate. The micro-scale polyelectrolyte patterns have applications in the creation of DNA, protein or cell based microarrays. This work also demonstrated the use of polyelectrolyte multi-layers in the enhancement of fluorescence signals from fluorophore-tagged molecules captured within the multi-layers. In-situ measurements using Fiber Bragg Gratings were carried out to study the kinetics of adsorption and desorption of polyelectrolytes participating in the layer buildup process under different process environmental conditions.

Σκοπός της εργασίας είναι η μελέτη της συμπεριφοράς προσροφημένων πολυηλεκτρολυτών. Συγκεκριμένα έγιναν μετρήσεις των δυνάμεων αλληλεπίδρασης μεταξύ των πολυμερικών αλυσίδων. Από τις μετρήσεις αυτές είναι δυνατή η εξαγωγή συμπερασμάτων για το πάχος του προσροφημένου πολυμερικού στρώματος, όπως και για το ποσοστό προσρόφησης των πολυμερών. Τα πολυμερή που μετρήθηκαν είναι αμφίφυλα δυσυσταδικά συμπολυμερή, αποτελούνται από ένα υδρόφοβο τμήμα που προσροφάται σε επιφάνειες και από ένα υδρόφιλο τμήμα. Κατά μήκος της αλυσίδας τους τα πολυμερή μας φέρουν φορτία (είναι σουλφονομένα) και για αυτό τον λόγο αποκαλούνται πολυηλεκτρολύτες. Εξετάζουμε τέσσερα διαφορετικά Μ.Β. (90Κ. 120Κ, 150Κ, 400Κ).Τα δείγματα υπό εξέταση είναι αραιά υδατικά διαλύματα (1/10000) των πολυμερών με την παρουσία ηλεκτρολύτη (άλατος) σε διάφορες συγκεντρώσεις. Τα αιωρήματα αυτά διοχετεύονται εντός κελίου στο οποίο βρίσκονται εμβαπτισμένες οι επιφάνειες προσρόφησης (μίκα). Αυτές με την σειρά τους είναι προσαρμοσμένες σε ημικυλινδρικούς φακούς που βρίσκονται σε διάταξη σταυρού. Δια μέσου των φακών διέρχεται εστιασμένη δέσμη φωτός, που οδηγείται σε φασματοσκόπιο. Εκεί αναλύεται και παρατηρούνται κροσσοί συμβολής. Με την βοήθεια της συμβολομετρίας μπορούμε να παρατηρήσουμε την μετακίνηση που υφίστανται οι φακοί , αλλά και την παρεμπόδιση που εμφανίζεται όταν αναπτύσσονται οι δυνάμεις. Οι δυνάμεις γίνονται μετρήσιμες από την κάμψη ενός ελάσματος που φέρει πάνω του προσαρμοσμένο τον ένα φακό. Τα αποτελέσματα των μετρήσεων μας δίνουν πολύτιμες πληροφορίες για την συμπεριφορά των πολυμερών. Στα κυριότερα αποτελέσματα, που μπορεί κανείς να αναφερθεί είναι η παρατηρούμενη εξάρτηση του πάχους του πολυμερικού στρώματος από το Μ.Β. των πολυμερών.(αύξηση του πάχους με ελάττωση του Μ.Β.) Επίσης παρατηρείται μία εξάρτηση του πάχους του πολυμερικού στρώματος από την μεταβολή της συγκέντρωσης του ηλεκτρολύτη στα διαλύματά μας. Για μεγάλα μοριακά βάρη παρατηρούμε ελάττωση του πάχους με την ελάττωση της συγκέντρωσης του άλατος. Ένα αξιοσημείωτο συμπέρασμα είναι το γεγονός ότι από την επεξεργασία των μετρήσεών μας φαίνεται να σχηματίζεται ένα πυκνό στρώμα κοντά στην επιφάνεια προσρόφησης από το οποίο προεξέχουν με μορφή ακροτενών πολυμερών οι αλυσίδες με μορφολογία βούρτσας. Η έλλειψη υστέρησης από τις μετρήσεις μας, επιβεβαιώνει το συμπέρασμα ότι έχουμε ακροτενή πολυμερή (πολυμερικές βούρτσες). Τέλος παρατηρούμε μονότονα απωστικές δυνάμεις μεταξύ των πολυηλεκτρολυτικών αλυσίδων. / The forces between adsorbed charged diblock copolymers were measured, by the use of the Surface Force Apparatus. Diblock copolymers forming a polymer brush structure were investigated in order to measure the adsorbed layer thickness and their behavior in salt solutions with different concentrations. As we investigate there is an interesting conformation related with the adsorbed layer. It seems to consist by two sections, an anchoring layer and a solvated brush in solution. The anchoring layer is formed from the hydrophobic blocks of the diblock polyelectrolytes. The hydrophilic blocks form a brush in solution. Positive counter ions that are found in conjunction with the negative charges on the polyelectrolyte disassociate in solution. There are as many counter ions as charges on the chain. The presence of salt in the solution means more disassociated ions in the solution. Changes to the salt concentration leads to changes to the forces as well as to the adsorbed layer. We investigate four different molecular weights of the sulfonated polyelectrolyte PtBS-NaPSS (90K, 120K, 150K, 400K) by changing the salt concentration. We find out that the adsorbed layer thickness decreases while the molecular weight increases. We also detect reduce to the layer thickness with salt concentration reduction. The adsorbed amount seems to reduce by increasing the molecular weight and increases by salt concentration reduction. Although the most important conclusion is the anchoring layer which forms a stiff layer very close to the substrate. Finally these polymeric systems can be used in numerous industrial applications as colloid stabilization, biocompatibilization, adhesion, and water treatment e.t.c.

Στην παρούσα διδακτορική διατριβή έγινε μελέτη πολυμερικών βουρτσών που διαμορφώνονται από συμπολυμερή πολυστυρενίου-πολυβουταδιενίου που φέρουν στην άκρη τους ομάδες ικανές να προσροφηθούν (PS-PB-Zw) Η μελέτη έγινε κυρίως με την τεχνικής της μέτρησης δυνάμεων (SFA) και της ανάκλασης νετρονίων. Ιδιαίτερο ενδιαφέρον παρουσιάζουν οι γραμμικές πολυμερικές αλυσίδες όπου ένα μεγάλου μοριακού βάρους πολυμερές φέρει στην άκρη του μια μόνο ακραία ομάδα. Τα γραμμικά αυτά συμπολυμερή είχαν μελετηθεί και στο παρελθόν. Το ζητούμενο όμως ήταν να μεταβάλλουμε την αρχιτεκτονική αυτή και να παρατηρήσουμε τις πιθανές μεταβολές στα ποιοτικά χαρακτηριστικά των προσροφημένων πολυμερικών στρωμάτων που διαμορφώνουν. Ως μέτρο σύγκρισης μελετήσαμε αρχικά τις ήδη μελετημένες γραμμικές αλυσίδες και στη συνέχεια προχωρήσαμε στη μελέτη των νέων δειγμάτων. Προσθέσαμε δύο και τρεις ακραίες ομάδες στο άκρο της πολυμερικής αλυσίδας μεγάλου μοριακού βάρους και αναμέναμε σύμφωνα με θεωρητικές προβλέψεις αύξηση στο προσροφημένο ποσό. Η αύξηση αυτή θα ήταν εμφανής μέσω της αύξησης του πάχους του πολυμερικού στρώματος που εύκολα μπορεί να μετρηθεί με την τεχνική της μέτρησης των δυνάμεων αλληλεπίδρασης. Επίσης μετρήσαμε άμεσα το προσροφημένο ποσό και με την τεχνική της ανάκλασης νετρονίων για πολυμερή τριών διαφορετικών μοριακών βαρών (25000, 70000 και 150000). Το σημαντικότερο αποτέλεσμά μας είναι ότι δεν παρατηρήσαμε αύξηση στο προσροφημένο ποσό σε σχέση με τις γραμμικές αλυσίδες και σε χρόνους ενός τυπικού πειράματος. Υπήρχε ωστόσο η υποψία ότι σε βάθος χρόνου μπορεί να αυξάνεται το προσροφημένο ποσό. Για το λόγο αυτό διεξαγάγαμε μια σειρά από μετρήσεις «κινητικής» με την τεχνική της ανάκλασης νετρονίων, αλλά και με συμπληρωματικές τεχνικές (διέγερση επιφανειακών πλασμονίων). Καμία μεταβολή δεν παρατηρήσαμε στο προσροφημένο ποσό, ούτε σε βάθος χρόνου αλλά ούτε και με την προσθήκη επιπλέον ακραίων ομάδων ικανών να προσροφώνται σε επιφάνειες. Στη συνέχεια επεκτείναμε τη μελέτη μας στην «αντίστροφη» αρχιτεκτονική. Διατηρήσαμε μια ακραία ομάδα και προσθέσαμε δύο και τρεις πολυμερικές αλυσίδες μεγάλου μοριακού βάρους (Μr=70000). Η αρχιτεκτονική που διαμορφώσαμε με τον τρόπο αυτό ήταν ουσιαστικά αρχιτεκτονική αστεροειδών πολυμερών με μικρό αριθμό πλοκαμιών. Στη περίπτωση αυτή παρατηρήσαμε μια σταδιακή μείωση του προσροφημένου ποσού με την προσθήκη επιπλέον βραχιόνων στο αστέρι. Η μείωση αύτη έχει παρατηρηθεί τόσο από μετρήσεις δυνάμεων, όσο και από μετρήσεις με ανάκλαση νετρονίων. Στα προφίλ δυνάμεων παρατηρούμε διαφοροποιήσεις σε σχέση με την γενική εικόνα που εμφανίζουν οι πολυμερικές βούρτσες. Αυτές οι διαφοροποιήσεις μπορούν να ερμηνευτούν με τη βοήθεια θεωρητικών προβλέψεων για τη συμπεριφορά των αστεροειδών πολυμερών. Η μείωση του προσροφημένου ποσού με αύξηση του αριθμού των πλοκαμιών μπορεί να αποδοθεί είτε σε λόγους κινητικής, είτε σε λόγους αλληλεπίδρασης μεταξύ των πολυμερικών αλυσίδων και μεταξύ των πλοκαμιών ενός μακρομορίου. Επίσης στη παρούσα διδακτορική διατριβή μελετήσαμε τη συμπεριφορά προσροφημένων ασθενών πολυ-ηλεκτρολυτών. Οι πολυ-ηλεκτρολύτες συγκεντρώνουν σταδιακά την προσοχή όλο και περισσότερων ερευνητών καθώς εμφανίζουν αρκετές σημαντικές εφαρμογές και είναι συμβατοί με βιολογικά συστήματα. Μέχρι πριν λίγο καιρό οι ασθενείς πολυ-ηλεκτρολύτες, όπως είναι το πολυακρυλικό οξύ που μελετούμε στη παρούσα εργασία, δεν είχαν μελετηθεί εκτενώς. Η μελέτη τους παρουσιάζει δυσκολίες, λόγω της πολυπλοκότητας στη συμπεριφορά τους. Αυτή εξαρτάται τόσο από τη συγκέντρωση άλατος του διαλύματος, όσο και από το pH. Μεταβάλλαμε τόσο τη συγκέντρωση άλατος του διαλύματος, όσο και το pH του διαλύματος εξετάζοντας πως αυτά επηρεάζουν το πάχος του προσροφημένου στρώματος και τα ποιοτικά χαρακτηριστικά των πολυ-ηλεκτρολυτικών προσροφημένων στρωμάτων. Παρατηρήσαμε λοιπόν μείωση του πάχους της πολυ-ηλεκτρολυτικής βούρτσας με αύξηση της συγκέντρωσης άλατος. Το αποτέλεσμα αυτό είναι πλήρως συμβατό με θεωρητικές προβλέψεις. Στη συνέχεια εξετάσαμε τη συμπεριφορά των ασθενών πολυ-ηλεκτρολυτών μεταβάλλοντας το pH του διαλύματος. Παρατηρήσαμε ότι με αύξηση του pH οι πολυμερικές αλυσίδες εκτείνονταν αυξάνοντας το πάχος της πολυμερικής βούρτσας. Αυτή η συμπεριφορά είναι άμεσο αποτέλεσμα της αύξησης του βαθμού διάστασης των πολυμερικών αλυσίδων. Αυξάνοντας το pH περισσότερα φορτία αποσπώνται από την πολυμερική αλυσίδα φορτίζοντάς την έτσι ισχυρότερα. Οι απωστικές ηλεκτροστατικές αλληλεπιδράσεις μεταξύ των φορτίων εξαναγκάζουν την αλυσίδα σε έκταση επιμηκύνοντας την πολυμερική βούρτσα. Τα αποτελέσματα αυτά είναι επίσης σε πλήρη συμφωνία με θεωρητικές προβλέψεις. / Flexible polymer chains end-tethered to a surface in good solvent tend to extend away from the surface due to excluded volume interactions. At sufficiently high grafting densities the chains become elongated normal to the surface, this extension being opposed by an elastic restoring force of entropic origin to form a layer of stretched chains referred to as a “polymer brush”. These systems have been studied extensively in recent years by numerous experimental techniques and theoretical methods. In the present investigation we have studied asymmetric star-shaped polymers whereby the different arms are either non-adsorbing PS chains or short PB chains terminating in a zwitterionic end-group known to adsorb strongly on surfaces such as mica or quartz. In this manner, it is possible on the one hand to form brushes with a single PS chain, but multiple zwitterionic stickers, and on the other to study the reverse case of multiple non-adsorbing arms attached to a surface via a single zwitterions. We have used the surface force balance technique to determine the interaction between such brush-layers formed on mica and neutron scattering to determine the absorbed amount and interanchor distance. Interactions between polymer brushes formed by highly asymmetric star-like polymers with a long PS arm and one, two or three short PB arms each terminating in a zwitterionic end-group were studied in order to explore the effect of the sticking energy on the brush structure. Polystyrene stars with two and three tails bearing a single end group were also studied to investigate how the height of the adsorbed layer and the grafting density are affected. Our measurements show no significant differences between PS with 1, 2 and 3 end groups. This may be due to kinetic reasons since additional polymer chains are hindered from attaching to a brush-bearing surface. The behavior of two PS chains with one end-group ((PS)2-PB-X) seems not to differ appreciably from that of PS-PB-X copolymer. On the other hand three PS chains with one end-group ((PS)3-PB-X) appeared to form layers with smaller brush height and greater interanchoring distance, relative to PS-PB-X layers. We can attribute this to the extra stretching that the three-chain architecture imposes on the adsorbed brush. In the present investigation we have also studied weak polyelectrolytes. Polyelectrolytes (charged polymer chains) remain among the least understood materials despite their importance in biology (proteins, DNA) and materials science. Their behavior and characteristics are not yet fully understood because of complicated correlations due to their charged nature that gives rise to long-range interactions. The counterplay of their properties as polymers and electrolytes with counterions around polyelectrolyte chains imposes additional difficulties on explaining their behavior. The association of counterions around polyelectrolytes and the pH of the solution are two parameters than can affect the properties of such systems. Especially weak polyelectrolytes (like poly-acrylic acid) are even sensitive to pH changes because of the alterable degree of dissociation. We measured forces between two charged polymer layers of Poly (isoprene-acrylic acid) diblock copolymers adsorbed on mica surfaces. Poly (isoprene-acrylic acid) diblock copolymers can be adsorbed from one end (poly-isoprene) which is sorter than the poly-(acrylic acid) part. The properties of the polymer layer at various salt concentrations and different pH of the solutions were measured by Surface Forces Apparatus. Information about the height of the polymer layer, and the adsorbed amount were extrapolated. The extracted results were compared with theoretical predictions showing well fit.

[pt] Atualmente a crescente demanda do uso de repelentes de insetos tem promovido a pesquisa de produtos mais eficazes e com uma maior durabilidade da ação repelente. O objetivo deste trabalho foi a obtenção de novas nanopartículas com propriedades interfaciais modificadas superficialmente com grupos funcionais catiônicos e polímeros aniônicos, com o intuito de melhorar a estabilidade de emulsões Pickering contendo um princípio ativo, N,N -dimetil-m-toluamida (DEET), comumente utilizado nos repelentes comerciais. A obtenção das nanopartículas incluiu a funcionalização inicial da superfície de nanopartículas de sílica comerciais com grupos amino secundários (R-NH2), seguido da introdução de grupos catiônicos de amônio quaternário (R-NR4 positivo) e posterior complexação eletrostática com polímeros aniônicos (poli(ácido acrílico), PAA, e poli(4-estireno sulfonato de sódio), PSS). As nanopartículas modificadas mostraram boa dispersabilidade em meio aquoso, favorecendo a estabilização de emulsões de tipo óleo em água (O/A). Os melhores resultados dos estudos de estabilidade no tempo das emulsões foram obtidos usando as nanopartículas catiônicas (SiNP-A,G) recobertas com PAA e com a mistura de polímeros (PAA mais PSS). As emulsões Pickering obtidas com as nanopartículas de sílica recobertas com PAA mostraram os melhores resultados na retardação da evaporação do DEET, com potencial uso para liberação lenta deste composto. / [en] Currently the increasing demand for insect repellent use has promoted research into more effective products and a longer repellent action. The objective of this work was to obtain new nanoparticles by surface modification with cationic functional groups and anionic polymers, with the aim of improving the stability of Pickering emulsions containing an active ingredient, N,N -diethyl-m-toluamide (DEET) commonly used in commercial repellents. The preparation of the nanoparticles included initial surface functionalization of commercial silica nanoparticles with secondary amino groups (R-NH2), followed by the introduction of cationic quaternary ammonium groups (R-NR4 positive) and subsequent electrostatic complexation with anionic polymers (poly (acrylic acid), PAA, and poly(sodium 4-styrenesulfonate), PSS). The modified nanoparticles showed good dispersibility in aqueous medium, favoring the stabilization of emulsions oil-in-water (O/W). The best results of the emulsion time stability studies were obtained using cationic silica nanoparticles (SiNP-A,G) covered with PAA and with the polymer mixture (PA plus PSS). The Pickering emulsions obtained with the cationic silica nanoparticles coated with PAA showed the best results in retarding DEET evaporation, with potential use for slow release of this compound.

Pesquisa em novas moléculas e estratégias antimicrobianas é crucial devido ao aumento de resistência a antibióticos pelos microrganismos. Polímeros antimicrobianos tem várias vantagens quando comparados a outros biocidas pequenos: maiores tempo de vida, potência, especificidade e baixa toxicidade residual. Logo, outras aplicações tecnológicas como recobrimentos, embalagens ou produtos têxteis antimicrobianos poderem ser exploradas. Em particular, derivados hidrossolúveis de quitosana, como os oligômeros de quitosana (OQ), são biopolímeros catiônicos extraídos de fontes renováveis que são candidatos promissores a serem agentes antimicrobianos de amplo espectro (fungos, bactérias gram-positivas e bactérias gram-negativas). Diferentemente da quitosana, que é sobretudo bioativa em pHs ácidos, OQ permanece catiônico – e portanto ativo – em pH fisiológico. Não obstante, o mecanismo exato pelo qual o polímero age nas membranas celulares permanece desconhecido em nível molecular. Este trabalho visa investigar o mecanismo de interação entre os OQ e modelos de membrana biomiméticos (Filmes de Langmuir). Para comparação, outro polieletrólito catiônico sintético com propriedades antibacterianas, o PAH – poli(hidrocloreto de alilamina) – foi investigado. Nós realizamos a Espectroscopia por Geração de Soma de Frequência (SFG) em Filmes de Langmuir de fosfolipídeos em água pura e em subfases contendo antimicrobianos. A Espectroscopia SFG nos permite obter o espectro vibracional de moléculas interfaciais (filme lipídico e moléculas que estão interagindo com ele: água e antimicrobianos) sem nenhuma contribuição de moléculas do interior do volume e é muito sensível às conformações lipídicas da membrana. Um fosfolipídeo zwitteriônico (DPPC) foi usado para modelar membranas tipo-humana, enquanto outro carregado negativamente (DPPG) modelava a tipo-bacteriana. Isotermas em subfases contendo antimicrobianos mostraram que ambos PAH e OQ causam uma pequena expansão das monocamadas de DPPC. Entretanto, para as monocamadas de DPPG ambos os polieletrólitos geraram uma expansão significativa. Entre eles, os OQ causaram um efeito mais drástico. Espectros SFG dos estiramentos CH mostraram que a conformação lipídica permaneceu bem empacotada em todos os casos (ligeiramente menos ordenada com PAH) apesar das expansões da membrana. Isto indica que os OQ foram inseridos formaram ilhas de OQ dentro do filme lipídico. Mudanças na forma de linha dos estiramentos da água interfacial indicaram que a adsorção de PAH em ambos os filmes foram capazes de compensar as cargas negativas, gerando uma inversão de cargas na superfície. Os espectros SFG dos grupos fosfato também indicaram que, em água pura, as cabeças polares de DPPC estão com uma orientação mais ordenada do que no caso do DPPG. Contudo, quando interagindo com os polieletrólitos catiônicos, as cabeças dos DPPGs se ordenam, ficando preferencialmente perpendicular à interface. Experimentos com antimicrobianos injetados na subfase enquanto os filmes de Langmuir já estavam condensados indicaram que os OQ foram capazes de penetrar na monocamada, embora causando uma expansão no filme menor. Esta comparação evidencia que a escolha da metodologia experimental afeta o resultado, mas ambas podem ser complementares, visto que podem representar diferentes fases do ciclo celular das biomembranas. A visão detalhada provida aqui para as interações moleculares desses polieletrólitos com filmes lipídicos podem os elucidar mecanismos de atividade biocida deles e auxiliar no planejamento racional de novos polímeros antimicrobianos. / Research on new antimicrobial molecules and strategies is crucial due to the increasing microorganism resistance to antibiotics. Antimicrobial Polymers have many advantages when compared to other small biocides: increased lifetimes, potency, specificity and lower residual toxicity. Therefore, they have great potential for technological applications, such as antimicrobial coatings, packages, or textile products. In particular, water-soluble derivatives of chitosan, such as chitosan oligomers (CO), are cationic biopolymers obtained from renewable sources that are promising candidates to a wide-spectrum antimicrobial agent (fungi, gram positive and gram negative bacteria). Unlike chitosan, which is mainly bioactive at acidic pH, CO remain cationic - and therefore active - at physiological pH. Nevertheless, the exact mechanism by which this polymer acts on the cell membranes remains unknown at the molecular level. This work aims at investigating the molecular interaction between CO and a biomimetic cell membrane model (Langmuir Film). For comparison, another synthetic cationic polylelectrolyte with antibacterial properties, PAH – poly(alylamine hydrochloride), has been investigated. We have carried out Sum-Frequency Generation (SFG) Spectroscopy on Langmuir Films of phospholipids on pure water and on antimicrobial containing subphases. SFG Spectroscopy allows obtaining the vibrational spectrum of interfacial molecules (lipid Langmuir Film and molecules interacting with it – water and antimicrobials), without any contribution from the bulk molecules, and is quite sensitive to the conformation of membrane lipids. A zwitterionic phospholipid (DPPC) was used to model human-like membranes, while a negatively charged phospholipid (DPPG) modeled bacterial-like membranes. Surface pressure-area isotherms on antimicrobial-containing subphases showed that both PAH and CO led to a small expansion of DPPC monolayers. However, for DPPG monolayers both polyelectrolytes led to significant expansion, with CO causing a more dramatic effect. SFG spectra in the CH stretch range showed that the lipid chain conformation remained always well ordered in all cases (slightly less ordered upon interacting with PAH), despite membrane expansion. This indicates that CO were inserted in the monolayer, forming islands of CO within the lipid film. Changes in the SFG spectral lineshape of OH stretches for the interfacial water molecules indicated that PAH adsorption on both DPPC and DPPG films was able to overcompensate the lipid negative charge and led to an overall surface charge reversal. The SFG spectra of the phosphate groups also indicated that in pure water the DPPC headgroups had a more ordered orientation than in the case of DPPG. Nevertheless, upon interaction with the cationic polyelectrolytes, the DPPG headgroups also become ordered, with a preferential orientation towards the subphase. Experiments with the antimicrobials injected in the subphase under a condensed Langmuir film indicated that CO were also capable of monolayer penetration, albeit causing a reduced film expansion. This comparison indicates that the choice of experimental methodology affects the outcome, but both may be complementary, as they may represent different phases of a biomembrane lifecycle. The detailed view provided here for the molecular interaction of these polyelectrolytes with lipid films may shed light on the mechanism of their biocidal activity and aid on a rational design of new antimicrobial polymers.

Neste trabalho foi utilizada Espectroscopia Vibracional por Geração de Soma de Freqüências, uma técnica óptica não-linear que é sensível à conformação molecular em interfaces e superfícies, para caracterizar o ordenamento molecular de filmes poliméricos automontados de polieletrólitos durante todos os passos do processo de fabricação, tendo como modelo o par de polieletrólitos PAH (poli(cloreto de alilamina)) / PSS (poli(estireno sulfonato de sódio)). Os espectros SFG permitiram verificar que durante o mergulho (in situ) do substrato na solução de polieletrólitos, estes adsorvem, mas se encontram numa configuração desordenada. Observou-se também que a secagem dos filmes pela ação de jato de nitrogênio produz filmes menos homogêneos do que por secagem espontânea, e às vezes até destruindo completamente o ordenamento molecular. Além disso, verificou-se também que camadas de polieletrólitos adsorvidas influenciam o ordenamento das camadas previamente adsorvidas. Com base nos resultados, modelos para a representação das estruturas desses filmes de polieletrólitos in situ e ex situ foram propostos. / In this work, Sum-Frequency Vibrational Spectroscopy, a nonlinear optical technique that is sensitive to molecular conformation at interfaces and surfaces, was used to characterize the molecular ordering of self-assembled films during all steps of self-assembly, having as model poly(allylamine hydrochloride) (PAH) / poly(styrene sulfonate) (PSS) polyelectrolyte assemble. SFG spectra showed that during immersion (in situ) of substrate in polyelectrolytes solutions, adsorption occurs but the molecules are in a disordered configuration. It was observed that the films drying by nitrogen flow are more inhomogeneous than those dried by spontaneous water evaporation. In some cases, dried films by nitrogen flow are quite disordered. Furthermore, it was observed that polyelectrolytes layers affect the ordering of the previously adsorbed layers. Based on our results, models were proposed to represent the structure of polyelectrolytes films in both: in situ and ex situ.

Partículas e filmes híbridos de polímeros e compostos de amônio quaternário (CAQ) foram caracterizados quanto a propriedades físicas e atividade contra cepas de Pseudomonas aeruginosa ATCC 27853 e Staphylococcus aureus ATCC 25923. Partículas híbridas foram obtidas a partir de fragmentos de bicamada (BF) de brometo de dioctadecildimetilamônio (DODAB), adicionados consecutivamente de soluções de carboximetilcelulose (CMC) e cloreto de poli (dialildimetilamônio) (PDDA) e, a seguir, caracterizadas por espalhamento de luz dinâmico para determinação de distribuições de tamanho, diâmetro médio (Dz) e potencial-zeta (ζ). Filmes híbridos foram obtidos por revestimento rotacional de lamínulas de vidro a partir de uma solução clorofórmica de poli (metil metacrilato) (PMMA) e CAQ onde [PMMA] = 10 mg/mL e [CAQs] = 0,03 4 mM de DODAB, brometo de cetiltrimetilamônio (CTAB) ou brometo de tetrapropilamônio (TPAB). Molhabilidade dos filmes e difusibilidade dos CAQs nos filmes imersos em água foram avaliadas por determinação de ângulo de contato e de tensão superficial na interface ar-água, respectivamente. Atividade antimicrobiana foi avaliada por plaqueamento e contagem de viáveis, tanto para os filmes quanto para as partículas. Para os filmes, também foram determinados halos de inibição. Partículas de DODAB BF/ CMC/ PDDA exibiram Dz e ζ dependentes da concentração dos componentes. A 0,1 mM de DODAB, 0,1 mg/mL de CMC e 0,1 mg/mL de PDDA, foram obtidas partículas pequenas (Dz = 100 nm; ζ = 30 mV). Com 0,5 mM de DODAB, 0,5 mg/mL de CMC e 0,5 mg/mL de PDDA foram obtidas partículas grandes (Dz = 470 nm; ζ = 50 mV). Contra 107 UFC/mL, 1 - 2 µg/mL de PDDA, sozinho em solução ou em forma de partículas, matou 99 % das células de P. aeruginosa. O mesmo ocorreu contra S. aureus (107 UFC/mL) em 10 µg/mL de PDDA. A ação antimicrobiana mostrou-se dependente da quantidade de cargas positivas nas partículas e independente do tamanho da partícula. Filmes de PMMA/ CAQ apresentaram maior molhabilidade do que aqueles de PMMA puro. Filmes de PMMA/ DODAB e PMMA/ TPAB submersos em água não causaram alterações de tensão superficial na interface ar-água, indicando baixa difusibilidade destes CAQs a partir dos filmes. Filmes de PMMA/ CTAB submersos em água reduziram a tensão superficial até aproximadamente 60 mN/m, mostrando a difusibilidade do CTAB no filme e sua organização na interface ar-água. O efeito antimicrobiano dos filmes PMMA/ DODAB e PMMA/ CTAB foi dependente da concentração do CAQ utilizada no preparo do filme. Viabilidade celular de 0% contra 107 UFC/mL de ambas as bactérias ocorreu com 4 mM de DODAB ou, com 2 ou 0,2 mM de CTAB contra P. aeruginosa ou S. aureus, respectivamente. Filmes de PMMA/ TPAB não apresentaram atividade antimicrobiana. Com a emergência de micro-organismos resistentes aos antibióticos, os novos nanomateriais antimicrobianos híbridos de polímeros e compostos de amônio quaternário podem representar uma alternativa de fácil obtenção e baixo custo. / Hybrid particles and films from polymers and quaternary ammonium compounds (QAC) were characterized regarding its physical properties and antimicrobial activity against strains of Pseudomonas aeruginosa ATCC 27853 or Staphylococcus aureus ATCC 25923. Hybrid particles were obtained from dioctadecyldimethylammonium bromide (DODAB) bilayer fragments (BF), consecutively added of carboximethylcellulose (CMC) and poly (diallyldimethylammonium) chloride (PDDA) solutions, and then, characterized by dynamic light-scattering for determination of size distributions, z-average diameter (Dz) and zeta-potential (ζ). Hybrid films were obtained by spin-coating of a chloroformic solution of poly (methylmethacrylate) (PMMA) and QAC on glass coverslips at [PMMA] = 10 mg/mL and [QACs] = 0.03 -4 mM where QACs were DODAB, cetyltrimethylammonium bromide (CTAB) or tetrapropylammonium bromide (TPAB). Films wettability and QACs diffusibility in the films immersed in water were evaluated by determinations of contact angle and surface tension at air-water interface, respectively. Antimicrobial activity was evaluated by plating and CFU counting both for particles and films. For the hybrid films, width of inhibition zone was also determined. DODAB BF/ CMC/ PDDA particles exhibited Dz and ζ dependent on the concentrations of the components. At 0.1 mM DODAB, 0.1 mg/mL CMC, and 0.1 mg/mL PDDA, small cationic particles were obtained (Dz = 100 nm; ζ = 30 mV). At 0.5 mM DODAB, 0.5 mg/mL CMC and 0.5 mg/mL PDDA, large cationic particles were obtained (Dz = 470 nm; ζ = 50 mV). At 107 CFU/mL, cell viability of 1 % for P. aeruginosa was obtained for PDDA in solution or covering particles at 1 or 2 µg/mL PDDA, respectively. Against S. aureus (107 CFU/mL) at 10 µg/mL PDDA, a similar result was obtained. The antimicrobial effect was dependent on the amount of positive charge on particles and independent on particle size. The hybrid films of PMMA/ QAC showed higher wettability than those of pure PMMA. PMMA/ DODAB and PMMA/ TPAB hybrid films, submerged in water, did not cause changes in surface tension at the air-water interface, indicating low diffusibility for both DODAB and TPAB in hybrid films. Films of PMMA/ CTAB, submerged in water, reduced the surface tension to about 60 mN/m, showing that CTAB could diffuse from the film to the air-water interface and change its surface tension. The antimicrobial effect of PMMA/ DODAB and PMMA/ CTAB hybrid films was clearly dependent on the QAC concentration used to prepare the films. Cell viability of 0% for P. aeruginosa and S. aureus (107 CFU/mL) occurred at 4 mM DODAB, or 2 and 0.2 mM CTAB, respectively. Films of PMMA/ TPAB showed no antimicrobial activity. With the emergence of microorganisms resistant to antibiotics, the novel hybrid antimicrobial nanomaterials may become important since they are inexpensive and easy to obtain.