archives@tulane.edu / Enzymes are most powerful catalysts in Nature. Despite decades of research, there are still many open questions surrounding the mechanisms by which enzymes catalyze reactions. Supramolecular chemists have made lots of effort to designing a variety of host molecules to mimic enzymes over the last decade. They aim to understand the power of noncovalent forces and how local environment can be involved in enzymes’ catalytic functions. In our studies, two synthetic water-soluble deep cavity cavitands with different electrostatic potential (EP) that can provide well-defined nano-spaces and can be encapsulated with guests through hydrophobic effect were utilized to investigative the inner guests’ pKa shifts and reactions. First, pKa shifts of thiol guests in deep cavity cavitands have been examined. Here we utilize supramolecular capsules assembled via the hydrophobic effect to encapsulate guests and control their acidity. We found that the greatest impact on the acidity of the bound guests is the position of the acid group in the yotoliter space. Moreover, the nature of the electrostatic potential field (EPF) generated by charged solubilizing groups also plays an important role in acidity, as does the counter ion complexing to the outer surface of the capsule. In summary, these results suggest an electrostatic potential field (EPF) engendered by remote solubilizing groups can affect reactions inside of confined spaces. Second, macrocyclization reactions were investigated in two different electrostatic potential (EP) nano capsules. Here, we quantify these effects through acidity and cyclization rate by the size of the encapsulated guests, which confirmed primary role of Coulombic forces with a simple mathematical model approximating the capsules as Born spheres within a continuum dielectric. These results reveal the reaction rate accelerations possible under Coulombic control and highlight important design criteria for nanoreactors. / 1 / Xiaoyang Cai

Electrostatic self-assembly is a simple, yet versatile and environmentally friendly technique. This technique has been widely used in different areas and recently it has also been used to make nano-structured separating layers for composite polyelectrolyte pervaporation membranes. Non-porous substrates are usually employed for electrostatic self-assembly depositions, but porous substrates have to be used for membrane applications because the composite membranes fabricated with non-porous substrates will have low permeation fluxes. When porous substrates were used to make composite membranes for pervaporation, it was reported that 60 double-layers were needed to get a membrane with suitable separation performance. The deposition of each double-layer needed about one hour, and the fabrication of reported self-assembled membranes with porous substrates was time-consuming and, from an industrial point of view, not practical. <br /><br /> The aim of this work was to make self-assembled composite membranes in a more practical way. The methodology used here is to find appropriate materials and suitable preparation conditions to make self-assembled composite membranes that have less than 10 self-assembled double layers but still have good performance for the dehydration of isopropyl alcohol (IPA)/ water mixtures by pervaporation. <br /><br /> A hydrolyzed polyacrylonitrile (PAN) ultrafiltration membrane is a permanently charged porous material. In this work, this porous material was, for the first time, used as a substrate for the fabrication of a composite self-assembled membrane. It was found that the hydrolyzed porous PAN membranes were good substrates for making self-assembled membranes for pervaporation. <br /><br /> In order to reduce the number of the depositions required for making composite membranes with suitable separation performance, a new deposition technique, concentration-changing deposition technique, has been developed. To obtain more extended conformations of polyelectrolytes to prevent them from going into the pores on a porous substrate, dilute deposition solutions were used for the first several depositions. After these first depositions, the pore size of the porous substrate had been reduced and more concentrated solutions (but still dilute solutions) could be used for the subsequent depositions. By using more concentrated deposition solutions, the number of the polyelectrolyte coils adsorbed by the charged substrate was increased and the thickness of each deposited layer was increased. In this way, the total number of deposition layers needed for a good membrane would be decreased. It has been proved in this work that the number of deposition layers in a composite membrane can be reduced by using the concentration-changing deposition technique. <br /><br /> By selecting appropriate materials and by selecting proper preparation conditions, composite polyelectrolyte membranes with less than 10 self-assembled double layers have been successfully fabricated. The obtained membranes had good performance for the dehydration of IPA/water mixtures by pervaporation. The lowest number of double layers in a composite membrane was 2 and this composite membrane had both a high flux and a high selectivity. It was also found that using polyelectrolytes with high molecular weights and a porous substrate with fine pores were the prerequisites for making composite polyelectrolyte membranes with less than 10 self-assembled double layers, while using a polyelectrolyte pair with high charge densities was the prerequisite for making composite membranes with a high selectivity. The successful fabrication of polyelectrolyte membranes with less than 10 double layers makes self-assembled membranes more practical because self-assembled composite membranes can be easily fabricated. <br /><br /> The data reproducibility and the stability of self-assembled composite membranes with less than 10 double layers have been discussed in this work. Random defects in the self-assembled separating layer and low repeatability of thickness in the first several deposition layers are believed to be the major reasons for the relatively low data reproducibility of single composite membranes, while the conformation change of adsorbed polyelectrolytes is one of the reasons for the flux reduction of composite membranes with less than 10 self-assembled double layers. Though the flux reproducibility of single membranes is barely acceptable (relative error about 25%), the average fluxes of several membranes made under the same conditions show good reproducibility. All composite membranes with less than 10 self-assembled double layers, from a structure point of view, were stable because the fluxes of polyelectrolyte membranes didn?t increase as time passed. <br /><br /> The separation performance of the self-assembled composite membranes developed in this work is not as good as it was originally expected, but it is still better than that of commercial poly(vinyl alcohol) (PVA) membranes for the dehydration of IPA/water mixtures, which indicates that new self-assembled composite membranes could be used for practical dehydration of IPA. The flux of the self-assembled composite membrane with 2 double layers was two times higher than that of reported self-assembled membrane in the literature when an IPA/water feed mixture with 10. 0 wt% of water was used at 60&deg;C. The composite membrane with 2 self-assembled double layers is a high performance membrane for IPA dehydration. <br /><br /> The formation of a single self-assembled layer on a non-porous substrate has been studied, but nothing has been reported about the formation of a self-assembled multilayer on a porous substrate. Based on the separation performance of different self-assembled composite membranes made from different materials and at different fabrication conditions, a two-stage process is proposed to explain the formation of a self-assembled multilayer on a porous substrate. Polyelectrolyte molecules, in the first stage, will deposit on the non-porous portion of the surface of a porous substrate while polyelectrolyte molecules will go into and fill the pores on the surface of a porous substrate to change a porous substrate into a "non-porous" substrate. In the second stage, polyelectrolyte molecules will deposit on a "non-porous substrate" to form a multilayer. This process can also be used to explain the formation of a multilayer on a non-porous substrate.

Electrostatic self-assembly is a simple, yet versatile and environmentally friendly technique. This technique has been widely used in different areas and recently it has also been used to make nano-structured separating layers for composite polyelectrolyte pervaporation membranes. Non-porous substrates are usually employed for electrostatic self-assembly depositions, but porous substrates have to be used for membrane applications because the composite membranes fabricated with non-porous substrates will have low permeation fluxes. When porous substrates were used to make composite membranes for pervaporation, it was reported that 60 double-layers were needed to get a membrane with suitable separation performance. The deposition of each double-layer needed about one hour, and the fabrication of reported self-assembled membranes with porous substrates was time-consuming and, from an industrial point of view, not practical. <br /><br /> The aim of this work was to make self-assembled composite membranes in a more practical way. The methodology used here is to find appropriate materials and suitable preparation conditions to make self-assembled composite membranes that have less than 10 self-assembled double layers but still have good performance for the dehydration of isopropyl alcohol (IPA)/ water mixtures by pervaporation. <br /><br /> A hydrolyzed polyacrylonitrile (PAN) ultrafiltration membrane is a permanently charged porous material. In this work, this porous material was, for the first time, used as a substrate for the fabrication of a composite self-assembled membrane. It was found that the hydrolyzed porous PAN membranes were good substrates for making self-assembled membranes for pervaporation. <br /><br /> In order to reduce the number of the depositions required for making composite membranes with suitable separation performance, a new deposition technique, concentration-changing deposition technique, has been developed. To obtain more extended conformations of polyelectrolytes to prevent them from going into the pores on a porous substrate, dilute deposition solutions were used for the first several depositions. After these first depositions, the pore size of the porous substrate had been reduced and more concentrated solutions (but still dilute solutions) could be used for the subsequent depositions. By using more concentrated deposition solutions, the number of the polyelectrolyte coils adsorbed by the charged substrate was increased and the thickness of each deposited layer was increased. In this way, the total number of deposition layers needed for a good membrane would be decreased. It has been proved in this work that the number of deposition layers in a composite membrane can be reduced by using the concentration-changing deposition technique. <br /><br /> By selecting appropriate materials and by selecting proper preparation conditions, composite polyelectrolyte membranes with less than 10 self-assembled double layers have been successfully fabricated. The obtained membranes had good performance for the dehydration of IPA/water mixtures by pervaporation. The lowest number of double layers in a composite membrane was 2 and this composite membrane had both a high flux and a high selectivity. It was also found that using polyelectrolytes with high molecular weights and a porous substrate with fine pores were the prerequisites for making composite polyelectrolyte membranes with less than 10 self-assembled double layers, while using a polyelectrolyte pair with high charge densities was the prerequisite for making composite membranes with a high selectivity. The successful fabrication of polyelectrolyte membranes with less than 10 double layers makes self-assembled membranes more practical because self-assembled composite membranes can be easily fabricated. <br /><br /> The data reproducibility and the stability of self-assembled composite membranes with less than 10 double layers have been discussed in this work. Random defects in the self-assembled separating layer and low repeatability of thickness in the first several deposition layers are believed to be the major reasons for the relatively low data reproducibility of single composite membranes, while the conformation change of adsorbed polyelectrolytes is one of the reasons for the flux reduction of composite membranes with less than 10 self-assembled double layers. Though the flux reproducibility of single membranes is barely acceptable (relative error about 25%), the average fluxes of several membranes made under the same conditions show good reproducibility. All composite membranes with less than 10 self-assembled double layers, from a structure point of view, were stable because the fluxes of polyelectrolyte membranes didn?t increase as time passed. <br /><br /> The separation performance of the self-assembled composite membranes developed in this work is not as good as it was originally expected, but it is still better than that of commercial poly(vinyl alcohol) (PVA) membranes for the dehydration of IPA/water mixtures, which indicates that new self-assembled composite membranes could be used for practical dehydration of IPA. The flux of the self-assembled composite membrane with 2 double layers was two times higher than that of reported self-assembled membrane in the literature when an IPA/water feed mixture with 10. 0 wt% of water was used at 60&deg;C. The composite membrane with 2 self-assembled double layers is a high performance membrane for IPA dehydration. <br /><br /> The formation of a single self-assembled layer on a non-porous substrate has been studied, but nothing has been reported about the formation of a self-assembled multilayer on a porous substrate. Based on the separation performance of different self-assembled composite membranes made from different materials and at different fabrication conditions, a two-stage process is proposed to explain the formation of a self-assembled multilayer on a porous substrate. Polyelectrolyte molecules, in the first stage, will deposit on the non-porous portion of the surface of a porous substrate while polyelectrolyte molecules will go into and fill the pores on the surface of a porous substrate to change a porous substrate into a "non-porous" substrate. In the second stage, polyelectrolyte molecules will deposit on a "non-porous substrate" to form a multilayer. This process can also be used to explain the formation of a multilayer on a non-porous substrate.

No description available.

<p>The microphase segregation behavior, which exhibits periodic patterns on a mesoscale, has been found in many systems where it has demonstrated its extreme industrial usefulness in the diblock copolymer system. When studying more general isotropic colloidal systems, periodic microphases should ubiquitously emerge in systems for which short-range inter-particle attraction is frustrated by long-range repulsion~(SALR). The morphological richness of these phases makes them desirable material targets, but our relatively coarse understanding of even simple models hinders controlling their assembly both from thermodynamic and dynamic points of view. The thermodynamic question is what should be the appropriate potential to stabilize microphases, such as cluster crystal, cylindrical, double gyroid and lamellar, while the dynamic question is whether the current experiments are long enough for these phases to appear. This dissertation will focus on solving these two parts of problems and hopefully guide the experiments to discover a simple material that can have microphase segregation behavior. In order to answer the thermodynamic problem of the stability of the microphases, we use a novel thermodynamic integration method as well as density functional methods in comparing the free energy of the microphases with uniform liquids. With the thermodynamic integration, we locate FCC-cluster, cylindrical, double gyroid and lamellar phases as well as nontrivial interplay between cluster, gel and microphase formation for a model microphase former. We also extended the methods to the model with a shorter and longer repulsion region where we found that the shorter region of the system may be in the Wigner glass of clusters of different sizes rather than the microphases. We also compare our simulation results with that from the density functional theory where we demonstrate that the classical density functional theory is qualitatively right but the simple improvement of the radial distribution functional by assuming the system is the same as Percus-Yevick hard sphere does not make a quantitatively difference. Our finding confirms that if the colloidal system has proper SALR potential as well as the right regime of area fraction and temperature, the microphase will be found in these systems. We then answer the second question which is whether the slow dynamics hinders the formation of microphases. We study the modeled microphase former and track the change of the first peak in the structure factor as well as the structural correlation time. We found that the system has a very complex dynamical regimes, including homogeneous fluid, void micelle, liquid gel and solid gel. The system becomes extreme slow in the solid gel regime but if in the regime that density and temperature are near the order-disorder transition, the lamellar self-assembly is much faster than the relaxation time of the solid gel which may explain why in the experimental system, the colloids seem stuck forever. We have collaborated with an experimental group to realize the SALR self-assemble behavior in a well controlled system. We have calibrated the system using a high precision thermodynamic integration by determining and matching the critical point and triple point of the experiments when the system is set up in the purely attractive regime. The system, however, becomes unpredictable when it goes into the SALR system where both higher body and other interactions become dominant. Finally, we try to extend our system to a spherocylinder model, which is an anisotropic particles with SALR. We have developed a novel cell list method here to accelerate the simulation. By determining the percolation transition and the order parameter, we find that the simple anisotropic interaction will introduce a much complex phase behavior of the system even in the disordered regime. We have identified several disordered phases, including homogeneous liquid, micellar liquid, free rotator gel, nematic gel and smectic gel.</p> / Dissertation

Amphiphilic polymers are a subset of macromolecules that exhibit both hydrophobic and hydrophilic moieties within their covalently bonded structures. Because of the differing solubilities of the contrasting regions of the amphiphilic polymers, they exhibit an inherent ability to self-assemble in the solution phase where one block exhibits poor compatibility with the solvent. And by tuning the composition, size and shape of the polymers, a variety of morphologies of the assembly in solution were observed, like spherical micelle, vesicle, rod-like and lamellar. The propensity to self-assemble to complex structures makes them promising candidates in wide varieties of applications, for example, drug delivery, gene transfection, catalyst, and sensing. Nowadays, most of the researches of amphiphilic polymers have been focused on simple linear di-block copolymers. Amphiphilic non-linear architectures, like dendrimers, star polymers, hyperbranched polymers, brush polymers and cyclic polymers, have been proved to exhibit unique properties compare to their linear analogs, such as lower critical micelle concentrations and better-assembled strengths because the structures are covalently tethered together. These unique properties make them a particularly attractive vehicle in drug/gene delivery. However, investigations of the amphiphilic homopolymers are limited and the majority of work have been done is focused on charged polymers, anionic or cationic. The amphiphilic ionic homopolymers largely relied on the pH of the solution to assemble into complex morphologies, perturbation of pH could result in deformation of assemblies and pro-release of encapsulate. Also, extremely severe pH environment prohibit the usages of the amphiphilic polymers in biological systems. Well defined non-ionic amphiphilic linear homopolymers bearing hydrophobic decyl groups and hydrophilic tri(ethylene glycol) monomethyl ether groups was synthesized by atom transfer radical polymerization technique and the structures were confirmed by NMR and GPC. The low polyedispersity polymers, were found to readily self-assembled to form micelles in non-polar organic phase and reverse micelles in polar aqueous phase. The assemblies were studied with UV-vis spectroscopy, fluorescence spectroscopy, dynamic light scattering, and transmission electron microscopy to determine the critical micelle concentrations and assembly size in both conditions. The synthesis towards more complex architectures of the homopolymers was also investigated. / acase@tulane.edu

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第16883号 / 工博第3604号 / 新制||工||1544(附属図書館) / 29558 / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 長谷川 博一, 教授 吉﨑 武尚, 教授 金谷 利治 / 学位規則第4条第1項該当

No description available.

Aplicações de nanomateriais em biossensores têm recebido muito interesse nos últimos anos. Entre os vários tipos de biossensores estudados, sensores de glicose têm recebido destaque devido a sua importância em diagnósticos clínicos. Apesar do grande avanço no monitoramento de glicose nas últimas décadas, ainda há muitos desafios para alcançar um monitoramento de glicemia continuo, clinicamente preciso, em conexão a um sistema fechado otimizado para a entrega de insulina no corpo. Esta dissertação descreve a fabricação de filmes layer-by-layer (LbL) obtidos a partir da enzima glicose oxidase (GOx) e dos polieletrólitos poli(amidoamina) de geração 4 (PG4) e o hibrido PG4 com as nanopartículas de ouro (PG4AuNp). As nanopartículas de ouro foram sintetizadas em meio aquoso usando o dendrímero PG4, o ácido cloroáurico (HAuCl&#8324;4) e ácido fórmico. As medidas de espectroscopia UV-Vis dos filmes automontados em substratos de quartzo mostraram um crescimento linear em função do número de bicamadas depositados apenas para o filme PG4-GOx. No filme PG4AuNp-GOx o crescimento não é linear. Em adição às caracterizações ópticas, estrutural e eletroquímica, os filmes LbL, depositados sobre substratos de vidro recoberto com óxido de índio (ITO) foram testados para a atuação em biossensores de peróxido de hidrogênio e de glicose. A biofuncionalidade da GOx e a viabilidade do método como biossensor foi demonstrada pelo aumento da corrente em função das sucessivas adições de alíquotas de glicose à solução. Os filmes sem nanopartículas não foram sensíveis a glicose. O biossensor com melhor desempenho foi o ITO-(PG4AuNp-GOx) com 5 bicamadas, que mostrou-se linear na faixa de 0 a 4,8 mM de glicose com sensibilidade 0,013 &mu;A/mM e limite de detecção 0,44 mmolL &sup1;. / Applications of nanomaterials for biosensors have been target of substantial research in the last years. Among a large number of biosensors, glucose biosensors have attracted attention due to their applications in clinical diagnostics. Despite the remarkable progress in glucose biosensors in the last decades, there are still many challenges in achieving clinically accurate continuous glycemic monitoring in connection to closed-loop systems aimed at optimal insulin delivery. This dissertation describes the fabrication of layer-by-layer (LbL) films obtained from the enzyme glucose oxidase (GOx) and the polyelectrolytes poli(amidoamine) generation 4 (PG4) and PG4 containing gold nanoparticles (PG4AuNp). Gold nanoparticles were synthesized in aqueous solution using formic acid, PG4 and HAuCl &#8324;. UV-vis spectroscopy showed a linear growth on quartz substrate only in the system PG4-GOx. In addition to the optical, structural and electrochemistry investigation, these LbL films deposited on ITO-coated glass were employed as electrochemical glucose biosensors. The biofunctionality of GOx and feasibility of the method as biosensor are demonstrated by the increase of reduction current upon additions of successive aliquots of glucose. The biosensor ITO-(PG4AuNp-GOx) &#8325; with the optimum performance had a detection limit of 0.44 mmolL&sup1; with a linear response in the range from 0 to 4.8 mmolL&sup1; and sensibility 0.013&mu;A/mmolL &sup1;.

ABA type tri-block amphiphilic polyelectrolyte consisting of poly(methyl methacrylate-block-methacrylic acid-block-methyl methacrylate) (P(MMA-b-MAA-b-MMA)) was synthesized by atom transfer radical polymerization technique (ATRP) and the self-assembly behavior of the polymers in aqueous solution was studied over the course of neutralization. Combination of potentiometric and conductometric titrations along with dynamic light scattering (DLS) techniques were used to investigate the size and shape of aggregates at various degrees of neutralization. The effect of hydrophobic-hydrophilic (MMA-MAA) ratio and polymer chain length on the aggregation behavior during neutralization was studied. P(MMA-b-MAA-b-MMA) with longer MMA segment self-assembles via the close association mechanism through stronger self-entanglement of MMA chains, whereas P(MMA-b-MAA-b-MMA) with shorter MMA chain self-assembles via the open association mechanism, as confirmed by transmission electron microscopy (TEM). Conductometric titration was used to determine the counterion condensation during the course of neutralization. When the charge density of micelle approaches a critical value as neutralization progresses, counterion condensation of Na+ ions on the polymer chains occurs. The effect of counterion condensation on the aggregation behavior during neutralization was elucidated. / Singapore-MIT Alliance (SMA)