Rozprawy doktorskie na temat „Supramolecular Gelator”

Orientador: Paulo Cesar Muniz de Lacerda Miranda
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química
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Resumo: O trabalho versa sobre a síntese de doze gelificantes (LMOGs) e um estudo sobre automontagem supramolecular dos LMOGs na construção de nanofibras. Foram sintetizadas duas séries de compostos derivados do metil 4,6-O-benzilideno-a-D-glicopiranosideo substituído na posição 4 do anel aromático com grupos (G) modificadores de densidade eletrônica, série A (G = n-alcoxil) e série B (G = n-alcoxicarbonil); e dois agentes de reticulação supramolecular (C e D). Fez-se um estudo da supramolecularidade usando várias técnicas. O ensaio de gelificação revelou que os LMOGs da série B enrijecem maior numero de solventes em maior faixa de concentração do que os da série A. A habilidade de gelificação foi destacada nos LMOGs de maior cadeia carbônica. Identificou-se por IV-TF que os LMOGs da série A se agregam por apenas um dos grupos OH, enquanto os LMOGs da série B pelos dois. A MEV mostrou estruturas fibrosas com morfologias cilíndricas e/ou fitas, com o menor diâmetro de 40 nm. Os termogramas no DSC indicaram que a Tgel aumentou com a concentração, porém ela diminuiu com o tamanho da cadeia carbônica em ambas as séries. O UV/vis mostrou que os grupos aromáticos estão arranjados obliquamente e próximos a um empilhamento p. As fibras de ambas as séries apresentaram helicidade P no DC. Observou-se com SAXS que a habilidade de gelificação está relacionada com o crescimento 1D. Os espectros de NOESY confirmam o que foi evidenciado no IV/térmico, sugerindo que as duas séries de LMOGs sofram automontagens diferentes. A mistura de LMOGs e de agente de reticulação não aumentou a habilidade de gelificação nem a estabilidade térmica. Com a técnica de ESI-MS verificou-se que mistura das séries, A + B, leva à agregação randômica. A análise do monocristal permitiu observar o "arranjo 1D", que ajudou a propor com outras técnicas a automontagem dos gelificantes dentro da fibra. Propõe-se que os LMOGs da serie A sofram uma torção angular maior, em relação ao cristal, durante o empacotamento helicoidal do que os LMOGs da serie B, embora as duas apresentem a mesma helicidade (P). Os agentes de reticulação C e D não contribuíram para a ramificação das fibras, mas o D apresentou boa estabilidade térmica e habilidade para enrijecer solventes polares. Por fim, fez-se um breve estudo focando a aplicação em célula solar. Os resultados mostraram que a gelificação pode minimizar a evaporação e o vazamento deste dispositivo, sem afetar muito suas propriedades
Abstract: The work presented in this thesis reports the synthesis of twelve gelators (LMOGs) and the study of the supramolecular self-assembly process in the formation of nanofibers. Two series of 4,6-O-benzylidene-a-D-glucopyranoside derivative compounds with different groups (G) at position 4 of the aromatic ring, series A (G = n-alkoxyl) and B (n-alkoxycarbonyl) and two compounds titled supramolecular crosslinking agents (C e D) were designed to study the effect of substituents (A and B) and effect the mixture of the LMOGs on self-assembly properties. The gelation test revealed that the LMOGs of the series B presented better gelation properties over the wide concentration range than the series A. The presence of long alkyl chains in both series enhanced the ability to gelate various organic solvents. The organogelators were characterized by different techniques. The FT-IR analysis of the gels indicated that the series A undergo a self-assembly process through hydrogen-bonding involving only one of the OH group, while the LMOGs of the series B aggregated with two OH group. Microscopic images (SEM) of the xerogel showed cylindrical or tape-like organized aggregates with small diameters (~40 nm). The DSC studies revealed that the Tgel increases with the molar concentration and decreases with alkyl chain size in both series of the gelators. UV/vis spectroscopy shows that the aromatic groups are obliquely orientated and approximately parallel. The helicity of the fiber of both series found to be P in CD. SAXS studies point that the gelation ability can be related to the uni-dimensional fiber growth. NOESY confirmed the different self-assembly mode between the series A and B observed in FT-IR. Both the gelation ability and Tgel were not increased with the mixtures of LMOGs (A + B or A/B + D). When analyzed in ESI-MS, the mixture of A + B resulted in a random aggregation of LMOGs. X-ray crystallographic analysis allowed creating a model of self-assembly of fiber together with other techniques. Based on these results, was proposed that the fiber of series A undergo a greater torsional deformation than the B, during helical molecular packing when compared to crystal, although the two exhibit the same helicity (P). The compounds C and D behaved not as a crosslinking agents of fiber. However, the compound D acted as gelling agent with high thermal stability in polar solvents. Finally, the gelation test with electrolyte solution revealed that LMOG does not compromise the solar cell performance, showing that the gelation can be applied to avoid the leakage or evaporation of the organic solvent
Doutorado
Quimica Organica
Doutor em Ciências

Orientador: Edvaldo Sabadini
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química
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Resumo: Materiais nanoestruturados apresentam-se em muitas formas diferentes. Um grupo de compostos ainda pouco investigado é o grupo dos organogéis, especialmente aqueles cuja estrutura tridimensional de rede é baseada na auto-organização de compostos orgânicos de baixa massa molecular, capazes de promover a gelificação no meio em que se encontram. São os chamados "Low Molecular Organic Gelators ¿ LMOG". Esses materiais termorreversíveis consistem de uma pequena quantidade de LMOG e um líquido orgânico. O presente trabalho visa esclarecer os mecanismos de auto-organização dos LMOG na escala supramolecular. Os LMOG estudados são derivados em moléculas que podem ser divididas em três partes. A parte central é constituída por um anel fenílico. Em uma das partes está ligado um grupo glicosídeo, e em outro ponto do anel uma cadeia alquílica. Procurou-se estudar as características estruturais e cinéticas de géis formados em um solvente aromático (para-xileno) e em um solvente formador de ligações de hidrogênio (n-propanol). Avaliaram-se, então, os efeitos relacionados com o balanço polar-apolar da molécula de LMOG, analisando os géis com 8, 4 e 3 unidades metilênicas da cadeia alquílica, bem como os efeitos de solvatação. A investigação dos fenômenos foi realizada utilizando a reologia rotatória e oscilatória nos regimes diluído e concentrado, aliada às técnicas de microscopia eletrônica de varredura (MEV), difratografia de raios-X e difusão dinâmica da luz (DDL)
Abstract: Nanostructured materials exist in many different ways. A group of compounds which has not been much investigated is the group of organogels, especially those whose three-dimensional network structure is based on the self-assembly of low molecular weight organic compounds. They promote gelation in the medium in which they are. These compounds are titled as "Low Molecular Mass Organic Gelator - LMOG" and they form thermoreversible materials constituted by a small amount of a LMOG and an organic liquid. The work presented in this dissertation aimed to clarify the mechanisms of self-assembly in a supramolecular scale. The LMOG molecules studied have a phenyl ring with a glycoside group bonded in one side and an alkyl chain bonded in the other part of the aromatic ring. The kinetic and structural characteristics of the gel formed in an aromatic solvent (para-xylene) and in a solvent donator of hydrogen bonding (propanol) were investigated. Therefore, the effects emerged from the polar-nonpolar balance of the LMGO molecule with 8, 4 and 4 methyl groups in the alkyl chain, as well as the solvation effect. The investigations were performed using the rotational and oscillatory rheology in dilute and concentrated regimes combined with the techniques of Scanning Electron Microscope (SEM), X-RAY diffraction and Dynamic Light Scattering (DLS)
Mestrado
Físico-Química
Mestre em Química

The aim of this thesis was to study the phenomenon of supramolecular gelation of urea-based gelators and their application as sensors for neutral organophosphorus species such as nerve agents. The work was therefore naturally divided into two major parts. The first part consisted in an investigation of the structure-gelation relationship of a series of urea gelators, in an effort to overcome the serendipitous approach that is widely applied to their discovery. Among the components of the common gelator scaffold that were optimised to deliver the best gelation performance, particular attention was given to the role of the head substituent on its benzene ring. Crystal structure prediction calculations together with liquid- and solid-state NMR were used to understand the molecular reasons behind the observed macroscopic properties of supramolecular gels formed either by nitro- or methoxy-substituted gelators. Remarkably, this approach demonstrated that, rather than electronic effects, it was the nitro substituent’s ability to interfere with the urea hydrogen bond network to cause the differences observed in the gel formation experiments, when compared to the methoxy-analogue. The second part focused on the possible application of bis/tris(urea)-based supramolecular gels as organophosphorus warfare agents’ sensors. After the development of a fast and easily interpretable in-house test, it was possible to observe the effectiveness of different candidates in responding to the presence of either the nerve agent Soman or its simulant dimethyl methyl phosphonate. It was observed that in the presence of the guest molecules gelation could be delayed or even suppressed, suggesting the formation of hydrogen bonds between guest and host that were interfering with the self-assemble of the gelator molecules. Conversely it was also found that, if present in lower amount, dimethyl methyl phosphonate could instead induce a detectable thermo-mechanical reinforcement of the gel network, as confirmed by rheology and calorimetry results, which was ascribed to solvophobic effects.

A series of amino-acid derived bis-urea gelators were synthesised, some of which show strong gelation in a wide variety of solvents. The gels were probed at the molecular, microscopic and macroscopic levels to gain insights into the gelation behaviour observed. Mixtures of different gelators also result in gels, some of which show different fibre morphologies and X-ray powder patterns to the pure gelators. The series was extended to include fluorescent 1- and 2-pyrenylalanine derived gelators and the fluorescence behaviour of the gels in solution, the gel state, in mixed gels and with the addition of anions was investigated. Tetrabutylammonium-acetate was found to disrupt urea-hydrogen bonding leading to the break-down of the gels, a process which was followed by NMR spectroscopy, rheometry and fluorescence spectroscopy. Two gelators were used to template the formation of porous polymers which SEM and gas adsorption studies show reflect the different fibre morphologies observed in the gels. The use of supramolecular gels as a medium for controlling the crystallisation of pharmaceutical compounds was developed. Proof of principle for the growth of a wide range of pharmaceutical compounds from a variety of different gels was demonstrated. The supramolecular nature of the gels was exploited by using anions to break down the gels in order to recover the crystals. Comparison of crystals grown from gels with those grown from solution highlighted a number of differences in crystal form, habit and stability. Gelators which mimic the chemical functionality of the drug compound being crystallised were synthesised. A study investigating the crystallisation of 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile (ROY) showed some differences in polymorphism when crystallised from a gel designed to mimic ROY compared to generic gels. A placement with the particle science group at GSK explored the potential of supramolecular gels for use in early stage screening of pharmaceutical compounds in an industrial setting.

This work describes the realization of physically crosslinked networks based on gelatin by the introduction of functional groups enabling specific supramolecular interactions. Molecular models were developed in order to predict the material properties and permit to establish a knowledge-based approach to material design. The effect of additional supramolecular interactions with hydroxyapaptite was then studied in composite materials. The calculated properties are compared to experimental results to validate the models. The models are then further used for the study of physically crosslinked networks. Gelatin was functionalized with desaminotyrosine (DAT) and desaminotyrosyl-tyrosine (DATT) side groups, derived from the natural amino acid tyrosine. These group can potentially undergo to π-π and hydrogen bonding interactions also under physiological conditions. Molecular dynamics (MD) simulations were performed on models with 0.8 wt.-% or 25 wt.-% water content, using the second generation forcefield CFF91. The validation of the models was obtained by the comparison with specific experimental data such as, density, peptide conformational angles and X-ray scattering spectra. The models were then used to predict the supramolecular organization of the polymer chain, analyze the formation of physical netpoints and calculate the mechanical properties. An important finding of simulation was that with the increase of aromatic groups also the number of observed physical netpoints increased. The number of relatively stable physical netpoints, on average zero 0 for natural gelatin, increased to 1 and 6 for DAT and DATT functionalized gelatins respectively. A comparison with the Flory-Rehner model suggested reduced equilibrium swelling by factor 6 of the DATT-functionalized materials in water. The functionalized gelatins could be synthesized by chemoselective coupling of the free carboxylic acid groups of DAT and DATT to the free amino groups of gelatin. At 25 wt.-% water content, the simulated and experimentally determined elastic mechanical properties (e.g. Young Modulus) were both in the order of GPa and were not influenced by the degree of aromatic modification. The experimental equilibrium degree of swelling in water decreased with increasing the number of inserted aromatic functions (from 2800 vol.-% for pure gelatin to 300 vol.-% for the DATT modified gelatin), at the same time, Young’s modulus, elongation at break, and maximum tensile strength increased. It could be show that the functionalization with DAT and DATT influences the chain organization of gelatin based materials together with a controlled drying condition. Functionalization with DAT and DATT lead to a drastic reduction of helical renaturation, that could be more finely controlled by the applied drying conditions. The properties of the materials could then be influenced by application of two independent methods. Composite materials of DAT and DATT functionalized gelatins with hydroxyapatite (HAp) show a drastic reduction of swelling degree. In tensile tests and rheological measurements, the composites equilibrated in water had increased Young’s moduli (from 200 kPa up to 2 MPa) and tensile strength (from 57 kPa up to 1.1 MPa) compared to the natural polymer matrix without affecting the elongation at break. Furthermore, an increased thermal stability from 40 °C to 85 °C of the networks could be demonstrated. The differences of the behaviour of the functionalized gelatins to pure gelatin as matrix suggested an additional stabilizing bond between the incorporated aromatic groups to the hydroxyapatite.
Diese Arbeit beschreibt die Entwicklung von durch spezifische physikalische Wechselwirkungen quervernetzten Gelatine-basierten Materialien. Dazu wurden zunächst Computermodelle entwickelt, mit denen Eigenschaften der Materialien vorhergesagt werden sollten, um so eine wissensbasierte Entwicklung zu ermöglichen, um dann die Ergebnisse mit experimentellen Daten zu vergleichen und die Materialien und Modelle als Grundlage für weitere Entwicklungen zu nutzen. Gelatine wurde mit Desaminotyrosin (DAT) und Desaminotyrosyltyrosin (DATT) funktionalisiert, die sich von der natürlichen Aminosäure Tyrosin ableiten. Diese Gruppen können potentiell π-π Wechselwirkungen und Wasserstoffbrückenbindungen auch unter physiologischen Bedingungen eingehen. Es wurden Computersimulationen der Materialien mittels Moleküldynamik durchgeführt, wobei Modelle mit 0.8 Gew.-% und 25 Gew.-% Wassergehalt betrachtet wurden. Die Validierung der Modelle erfolgte durch Vergleich der errechneten mit experimentellen Daten wie z.B. der Dichte, Bindungswinkeln sowie Röntgenstreuungsspektren. Die Modelle wurden dann zur Vorhersage der molekularen Organisation der Polymerketten, Formierung physikalischer Netzpunkte und Berechnung der mechanischen Eigenschaften eingesetzt. Die Funktionalisierung der Gelatine mit DAT bzw. DATT führten wie gewünscht zur Ausbildung physikalischer Netzpunkte durch π-π Wechselwirkungen und Wasserstoffbrücken¬bindungen. Ein Schlüsselergebnis der Simulationen war, dass mit zunehmender Zahl an aromatischen Gruppen auch eine Zunahme der physikalischen Netzpunkte beobachtet werden konnte. Die funktionalisierten Gelatinen konnten durch chemoselektive Reaktion der Aminogruppen der Gelatine mit den freien Carboxylgruppen von DAT und DATT hergestellt werden. Materialien mit 25 Gew.-% Wassergehalt hatten in der Simulation und im Experiment mechanische Eigenschaften derselben Größenordnung (z.B. E-Moduln im unteren GPa-Bereich). Der Quellungsgrad der Materialien im Experiment nahm mit zunehmender Zahl an aromatische Gruppen ab (von 2800 Vol.-% auf 300 Vol.-%), wobei der Elastizitätsmodul, die Bruchdehnung sowie die Zugfestigkeit zunahmen. Die Funktionalisierung der Gelatine ist eine chemische Methode, um die Kettenanordnung auf molekularer Ebene zu beeinflussen, während die genaue Kontrolle der Trocknungs¬bedinguungen von Gelatine-basierten Materialien eine physikalische Methode mit demselben Ziel ist. Es konnte gezeigt werden, dass die Funktionalisierung von Gelatine mit DAT oder DATT zu einer stark verminderten Helixausbildungstendenz, die jedoch durch Variation der Trocknunsgbedingungen noch fein abgestimmt werden konnte. Somit konnten die mechanischen Eigenschaften von Filmen aus funktionlisierter Gelatine mit zwei unabhängigen Methoden eingestellt werden. Komposite der mit DAT oder DATT funktionalisierten Gelatine und Hydroxyapatit (HAp) zeigten deutlich verringerter Quellung. In Zugdehnungsexperimenten und rheologischen Untersuchungen zeigten die Komposite im Gleichgewichtsquellungszustand erhöhte Elastizitätsmoduln (von 200 kPa auf bis zu 2 MPa) und Zugfestigkeit (von 57 kPa auf bis zu 1.1 MPa). Darüber hinaus konnte die Übergangstemperatur Tc deutlich gesteigert werden (von ca. 40 °C auf > 85 °C). Dieses Verhalten ließ sich auf stabilisierende Bindungen zwischen den aromatische Gruppen und dem HAp zurückführen.

Low molecular weight gelators (LMWGs) are interesting materials whose applications are as diverse and wide ranging as their molecular structures. These materials self-assemble through the formation of non-covelent intermolecular forces and interactions to form supramolecular assemblies that trap solvent within their matrices. Because of the non-covalent nature of the forces of self-assembly, the gelation process is typically thermally reversible. In addition, low molecular weight gelators can also be modified to respond to various stimuli, such as change in pH, presence of enzymes or metal cations, or exposure to light. The design of low molecular weight gelators is often difficult, and most new classes of low molecular weight gelators are discovered by serendipity. As such, it is often useful to use structural templates in the design of LMWGs. Biomolecules, such as steroids, amino acids and peptides, and carbohydrates make excellent templates due to their inherent propensity to self assemble. A review of the current literature regarding the use of biomolecules as templates for the design and synthesis of LMWGs will be presented in chapter 1. Our research group has been active in the research of carbohydrate-based LMWGs for several years, and these results are also briefly reviewed in the related chapters. The synthesis and characterization of ester derivatives of D-galactose, D-glucose, and amide derivatives of D-glucosamine will be discussed in chapters 2-4, along with their evaluation for gelation in aqueous and organic solvents, such as hexane, ethanol, water, and aqueous DMSO or ethanol mixtures.

En aquesta tesi, s’han estudiat quatre diferent sistemes supramoleculars com a receptors, gelificadors o tensioactius. S’ha analitzat la influència de diferents factors estructurals de la molècula senzilla en la seva propietat supramolecular final. S’han utilitzat diferents estratègies per a preparar els compostos estudiats. La combinació de diferents tècniques ens ha permès entendre millor aquests sistemes obtenint un resultat sinèrgic. Els resultats d’aquesta tesi estan dividits en quatre capítols: 1) Diferents receptors d’anions tripodals s’han sintetitzat i la seva complexació amb diferents anions s’ha estudiat. Fent servir RMN, les energies de Gibbs de complexació s’han calculat i la seva afinitat de cordinació s’ha estudiat. Mitjançant càlculs teòrics, l’estructura dels diferents complexes s’ha predit. També, la termodinàmica dels sistemes estudiats s’ha calculat. Els càlculs teòrics ens han permès entendre i racionalitzarels resultats experimentals. 2) Tres famílies diferents de gelificadors basats en carbocicles que contenen dos grups amida s’han estudiat per tal de determinar la influència de la mida de l’anell, les substitucions de l’anell i l’estereoquímica de la molècula en les seves habilitats gelificants. Usant el test de la inversió del tub i racionalitzant-lo amb diferents paràmetres de solubilitat, les habilitats gelificants dels diferents compostos s’han determinat. Aquest estudi s’ha acompanyat amb RMN d’alta resolució. L’agregació s’ha estudiat mitjançant càlculs teòrics, els quals estan en acord amb els espectres de dicroïsme circular obtinguts dels xerogels. Finalment, fent servir SEM, s’ha determinat la morfologia dels agregats. 3) Quatre diferents tensioactius tipus bola s’han sintetitzat i el seu caràcter com a tensioacitus s’ha estudiat per tal de determinar la influència de l’esteroquímica i la regioquímica en el seu comportament com a tensioactius. Fent servir el mètode de la gota penjatn, la variació de la tensió superficial amb la concentració s’ha analitzat. Hem desenvolupat un nou mètode per predir l’estructura dels tensioactius agregats a la superfície. Finalment, les tècniques de cryoTEM i SAXS ens han permès estudiar la morfologia i la mida dels agregats. 4) Al darrer capítol, qutre tensioactius depenents del pH s’han sintetitzat. L’estudi supramolecular de les seves propietats s’ha dut a terme usant diverses tècniques. Aquests tensioactius mostren un interessant comportament àcid-base adequat per a possibles aplicacions biològiques. És per això que s’han estudiat com a possibles nous vectors no-virals per a teràpia gènica fent servir diferents tècniques biofísiques i biològiques. Els resultats mostren que no són tòxics i que tenen propietats interessants per ser usats com a vectors.
In this thesis, four different supramolecular systems were studied as receptors, gelators or surfactants. The influence of different structural factors of the single molecule on the final supramolecular properties was analysed. Different strategies were used to prepare the studied compounds. The combination of different techniques leads us to better understand these systems obtaining synergistic results. Results of this thesis are divided in four chapters: 1) Different tripodal anion receptors were synthesised and their complexation with different anions were studied. Using NMR, complexation Gibbs energies were calculated and the binding affinity were studied. Using theoretical calculations, the structure of the complexes were predicted. Also, thermodynamics of the host-guest system were calculated and theoretical calculations lead us to rationalise the experimental results. 2) Three different families of cycloalkane diamide-based gelators were studied to determine the influence of the ring size, the substitutions of the ring and the stereochemistry on the final gelation abilities. Using the tube inversion test and rationalising it with different solubility parameters, the gelation ability was determined. This study was accompanied by high resolution NMR. Self-assembly was studied using theoretical calculations and circular dichroism. Results show that all of the studied gels are chiral despite some of the monomers are meso compounds. Then, using SEM, the morphology of the aggregates was determined. 3) Four different bolaform amphiphiles were synthesised and their behaviour as surfactants were studied to determine the influence of the stereochemistry and the regiochemistry on the final surfactant behaviour. Using the pendant drop method, the variation of the surface tension with the concentration was analysed. We developed a new method to predict the structure of the self-assembled surfactants at the surface. CryoTEM and SAXS were used to determine the morphology and size of the aggregates. 4) In the last chapter, four pH-dependent β-amino acid-based surfactants were synthesised. Supramolecular properties of these systems were studied using pendant drop method, cryoTEM, theoretical calculations, different physicochemical titrations, circular dichroism, UV-vis absorption and DLS. These surfactants show interesting acid-base behaviour suitable for biological applications. They have been studied as potential new non-viral vectors for gene therapy using different biophysical and biological techniques. Results show that these surfactants are not toxic and they have interesting features to be used as vectors.

La viscosité est une propriété fondamentale des fluides complexes et qui reste encore difficile à prédire quantitativement. Cette propriété macroscopique provient de propriétés moléculaires et mésoscopiques. La compréhension et l’estimation de l'évolution de la viscosité avec des paramètres variables est important pour plusieurs applications, entre autres pour l’extraction liquide-liquide et pour la formulation de systèmes tensioactifs aqueux.Dans ce travail, un modèle "minimal" prenant en compte les énergies libres mises en jeu a été développé pour aider à comprendre, contrôler et prédire l'évolution de la viscosité des microémulsions en présence de solutés. Le terme «minimal» signifie dans ce contexte que ce modèle est basé sur un ensemble minimal de paramètres qui sont tous mesurables ou ont une signification physique, ce qui permet d’éviter le recours à des paramètres ajustables. Ce modèle développé dans cette thèse considère les termes chimiques à l'échelle moléculaire, les termes physiques à l'échelle mésoscopique ainsi que les caractéristiques d'écoulement à l'échelle macroscopique a été appliqué sur des microémulsions pauvres en eau utilisé pour l’extraction des métaux ainsi que sur des systèmes tensioactifs anioniques aqueux
Viscosity is a fundamental property of complex fluids that is still nowadays extremely difficult to predict quantitatively. This macroscopic property originates from molecular and mesoscopic properties. The understanding and prediction of the evolution of the viscosity with changing parameters is crucial for several applications, amongst others for liquid-liquid extraction processes and for formulation of aqueous surfactant systems.In this work, a “minimal” model taking into account the relevant free energies was developed that helps to understand, control and predict the evolution of the viscosity of microemulsions in presence of solutes. The term “minimal” means in that context that this model is based on a minimal set of parameters that are all measurable and have a physical meaning, thus avoiding input of any adjustable parameter. This model that considers the chemical terms at molecular scale, the physical terms at meso-scale as well as the flow characteristics at macroscale was applied on water-poor extracting microemulsions as well as on aqueous anionic surfactant systems

The thesis entitled “Design, Synthesis and Properties of Novel Oligo-Phenylenevinylene based Supramolecular Photochromic Gels and Soft Composites with Nanomaterials” deals with soft materials derived from low molecular mass photochromic gels and nanomaterials. Chapter 1 gives a general introduction and overview of the low molecular mass gel (LMMG). It briefly delves into the history of research in physical gel field, design of different types of photochromic gelator molecules, their interesting self-assembly patterns, potential applications of these gelator molecules as well as challenges to design of new gelator molecules. A comprehensive discussion on the synthesis and numerous applications of smart nanocomposites derived from LMMGs and nanomaterials were discussed. It also encompasses the relatively recent area of two component gel system to conveniently bypass the cumbersome synthetic protocol. Interesting photophysical properties of these photochromic LMMGs were discussed towards their light-harvesting properties and aggregation induced white-light emission. Chapter 2 describes the synthesis and self-assembly properties of all-trans-tri(p-phenylenevinylene) (TPV) based molecules possessing different terminal groups, e.g. oxime, hydrazone, phenylhydrazone and semicarbazone (Chart 2A.1). Various spectroscopic and microscopic studies show the aggregation pattern of the self-assemblies promoted by hydrogen bonding, aromatic π-stacking and van der Waals interactions among the individual TPV units (Figure 2A.1). The melting temperatures of the gels and viscoelastic behaviour indicate that the presence of more hydrogen-bonding donors in the periphery of the gelator molecules makes the gel thermally and mechanically more robust. However, in the presence of more numbers of hydrogen-bonding donor/acceptors at the periphery of TPVs such as with semicarbazone a precipitation as opposed to gelation was observed. Thus, the choice of the end functional groups and the number of hydrogen-bonding motifs in the TPV backbone holds the key and modulates the effective length of the chromophore, resulting in interesting optical properties Chapter 3A demonstrates successful incorporation of pristine and long-chain functionalized single-walled carbon nanotubes (SWNTs) in supramolecular organogels of 1 (Chart 2A.1) to give rise to new nanocomposites with interesting mechanical, thermal and electrical properties (Figure 3A.1). The SWNT promoted aggregation of 1 leads to quenching of the absorption and emission intensity of 1, increases the sol-to-gel transition temperature and increases the viscoelasticity of the composite gels. The composites were semiconducting in nature and showed enhanced electrical conductivity compared to that of 1 alone. Upon irradiation with a near IR laser at 1064 nm for 5 min, it was possible to selectively induce a gel-to-sol phase transition of the nanocomposites, while irradiation for even 30 min of the native organogel under identical conditions did not cause any gel-to-sol conversion Chapter 3B describes incorporation of multi-walled boron nitride nanotubes (BNNTs) and various functionalized BNNTs by Lewis bases such as trioctylamine (TOA), tributylamine (TBA), and triphenylphosphine (TPP) in the toluene gel of 1 (Chart 2A.1). Functionalized BNNTs were synthesized first and incorporation into the gel showed evidence of wrapping of the gelator molecules on to the BNNT surface presumably brought about by π-π stacking and van der Waals interactions (Figure 3B.1). This leads to the formation of densely packed and directionally aligned fibrous networks. Such “reinforced” aggregation of the gelator molecules in presence of doped BNNTs led to an increase in the sol-to-gel transition temperature and the solidification temperature of the gel-nanocomposites as revealed from differential scanning calorimetry. Rheological investigations of the gel-nanocomposites indicate that the flow properties of the resulting materials become resistant to applied stress upon incorporation of even a very low wt% of BNNTs. Finally, the increase in thermal conductivity of the nanocomposite compared to the gelator alone was observed for the temperature range of 0-60 oC which may make these composites potentially useful in various applications depending on the choice and the amount of BNNT loading in the composite. Chapter 3C presents first successful incorporation of graphene, and long aliphatic chain (n-dodecyl, n-hexadecyl) functionalized graphene in physical organogels formed by the aromatic oligo-phenylenevinylene (OPV) based gelator 1 (Chart 2A.1) and (non-aromatic) amino acid derived gelator. The large aromatic surfaces of gelator 1 serve as a host matrix for the incorporation of graphene and other nanocarbons (fullerene, SWNT). Such carbon nanomaterials (CNMs) exerted variable effects on the gelator through non-covalent interactions, due to their differences in shapes. Various microscopic images confirm the formation of densely wrapped fibrous networks for the resulting nanocomposites upon incorporation of CNMs. Variable temperature UV-vis and fluorescence spectra reveal CNMs mediated aggregation of the gelator molecules in solution and the presence of supramolecular interaction was evident from Raman spectroscopy. This ‘reinforced’ aggregation of the gelator molecules on doped CNMs was reflected in significantly enhanced thermal, mechanical and electrical properties of the nanocomposites. Rheological investigations of gels containing small amount of CNMs indicated that the flow of nanocomposites became resistant to applied stress at a very low wt-% of CNM incorporation (0.83 wt-%). An interesting synergistic behaviour was observed in case of the composite gel of OPV based LMOG containing a mixture of EG and SWNT when compared with other mixtures of CNMs in all combinations with EG. These studies are therefore of great contemporary interest as they provide molecular level control into the preparation of novel nanocomposites of LMOG and nanocarbons. Chapter 4 describes the synthesis of two low molecular mass organogelators based on tri-p-phenylenevinylene derivatives one of which could be designated as “acceptor” while the other one as “donor” (Figure 4.1). These were prepared specifically to show the inter-gelator interactions at the molecular level between each other through the donor-acceptor type of assembly to achieve control over their macroscopic properties. Intermolecular H-bonding, π-stacking and van der Waals forces are operational for both the individual and the mixture leading them to the gel formation in chosen organic solvents. Due to the photochromic nature of this class of molecules, they exhibited interesting photophysical properties. An efficient energy transfer was demonstrated from the mixture of donor-acceptor assemblies in solution. An array of four chromophores was built up by including two known dyes i.e. anthracene and rhodamine 6G for the energy transfer studies. Interestingly a cascade energy transfer was observed in the assembly of four chromophores in the series. This allowed building up of a wide range of light harvesting process, excitation at one end of which produces an emission at the other end of the assembly. Chapter 5A discusses the synthesis of new dicationic chromophoric phenylenedivinylene bis-N-alkyl pyridinium salts to study their hydrogelation behaviour through π-stacking and van der Waals interactions (Figure 5A.1). A crucial hydrophilic-hydrophobic balance in aqueous medium controls the gelation when a specific length of the aliphatic chain (n-octyl, 2) is appended on the both ends of the central aromatic core. The hydrogels showed considerably high gel-melting temperature and more viscoelastic solid-like properties with increasing concentrations of the gelator 2. Microscopic studies exhibited concentration dependent mixed fiber-coil morphology above its gelation concentration and only fibrillar networks below the gelation concentration (Figure 5A.1). Variable temperature, UV-visible and fluorescence spectroscopy showed aggregation induced emission switches for the self-assemblies promoted by addition of various salts (either cations or anions) in diluted solutions. Aggregation induced white-light emission could be achieved in aqueous medium either by tuning the concentration of the added salt or by varying the temperature of the mixture. Cyclic-voltametric studies indicate a reversible one-electron redox behavior for the chromophore which is also diffusion-controlled in nature. Lamellar type arrangement in the self-assembly was evident from the X-ray diffraction analysis. Gradual downfield shift in the proton signals of the 1H-NMR spectra upon heating suggest aromatic π-stacking and van der Waals interactions are operational among the gelator molecules and a balance with the electrostatic interactions lead to the physical gelation in water Chapter 5B presents supramolecular π-gel formation by phenylenedivinylene bis-N-alkyl pyridinium salts appended with terminal aliphatic hydrocarbon chains of different lengths (Chart 5A.1) in specific ratios of aliphatic alcohols and water mixture. The temperature- and the ratio-variation in the ethanol/water mixture showed the aggregation pattern of the self-assemblies promoted by electrostatic, aromatic π-stacking and van der Waals interactions among the individual gelators as observed under UV-visible and fluorescence spectroscopy. With increase in the number of carbon atoms in the aliphatic chain, greater gel-melting temperature, increased viscoelastic solid-like behavior and decreased fiber diameter was observed among the gelators. However, presence of excess hydrophobic moiety at the periphery, a precipitation as opposed to gelation was observed. Cyclic-voltametric studies show a one-electron reversible redox behavior for the chromophore and the redox potential decreases with increasing the aliphatic chain length. A diffusion-controlled redox behavior was observed for shorter aliphatic chains but the longer chains make the process diffusion-limited. The electrical conductivity studies show semiconducting behavior for individual compounds and the magnitude of current increases with increasing fiber diameter (with decreasing aliphatic chain length). Chapter 6A demonstrates the synthesis of new oligo-phenylenevinylene (OPV) analogues with pyridine end-functionality (Chart 6A.1) to show efficient supramolecular organogel formation through molecular complexation with tartaric acids (TA). The salt formation between the end-pyridine and TA exhibited a significant decrease in the IR stretching frequency of the carboxylic acid. Microscopic studies showed a nucleation induced growth of the fibers that essentially led to larger aggregate formation. A circular dichroism study demonstrated an opposite sense of chirality in the complexes for two optically active TA (L and D). The expression of chiral transcription in the achiral OPVs was manifested under atomic force microscopy which showed a specific handedness in the fibers for the complex with particular optically active TA. Fluorescence spectroscopic studies exhibited a remarkable red-shift of the emission maxima due to the J-type aggregation leading to the gel formation. In a particular condition, energy transfer from aggregated donor to aggregated acceptor was observed in the gel phase. A liquid crystalline behavior was observed under polarized optical microscopy as well. Chapter 6B describes selective Hg2+ sensors which have been achieved separately under ‘naked eye’ and fluorimetric method for two-coordination assisted conjugated pyridine-end oligo-phenylenevinylene moieties (Chart 6A.1, 1 and 2). A drastic visual color change was exhibited based on the conjugation length of such chromophores. The visual color change was more prominent in the chromophore containing five aromatic rings in a conjugation compared to only three aromatic rings. However, breakdown of the conjugation length in the chromophore unit through incorporation of semicarbazide moiety (isoniazid) (Chart 6B.1) leads to a lesser degree of change either visually or spectroscopically. Coincidently, the isoniazid moiety provides an extra motif for their anion sensing properties through the deprotonation of ‘N-H’ group. Thus a selective CN- sensor was achieved. The presence of H-bonding donor (-NH-) and acceptor (-CO-) group in the semicarbazone segment and the long n-hexadecyl chains induced a physical gel formation. Addition of Hg2+ or CN- to the gel leads to the gel-to-sol transition and further addition in a reverse order could induce a reversible gel formation. Effect of addition of Hg2+ and CN- to the gel was probed by UV-vis and 1H-NMR spectroscopy which showed significant spectral shifts in favor of their interactions.

碩士
中原大學
化學研究所
101
We conduct our research in order to realize the natures of supramolecular gelators, and the conditions of releasing in vitro when we make supramolecular gelators become the carriers of drugs. GPS-1and GPO-1 gelators are synthesized in laboratory. We test it in H2O, 15 kind of organic solvents, 5different ratio of solvent- H2O mixed MeOH and H2O mixed EtOH. The result shows that the gel will turn up only when we put GPS-1into CH2Cl2, EtOAc, H2O/MeOH(2：3(v/v), 3：2(v/v), 4：1(v/v)) and H2O/EtOH(3：7(v/v), 2：3(v/v), 3：2(v/v), 4： 1(v/v)). In the experiment of pH-stimuli responsive, GPS-1 does not conform to the response, but the constructure of gel won’t be effect even when the concentration of drug achieves 600 mM. The experiment of drug releasing in vitro shows that drugs releasing mechanism conforms to the diffusion model III and adjust gelators or drugs concentration will be control primary and ultimate drug release rate .

碩士
國立成功大學
化學工程學系碩博士班
101
By controlling the length of alkyl chain, we have successfully synthesized a series of fluorescent low-molecular-weight gelators (LMWGs) of N-(pyrene-1-yl)alkyleneamide (PA) and N-(pyrene-1-yl)- N-(pyren-3-yl)alkylenedipamide (DPA) based on pyrene groups and amide moieties. Dependence of gelation properties on molecular chain length was studied. In addition, effect of pyrene group on fluorescence at different temperature under both liquid and gel states were investigated. The results show that the symmetric DPA reveals higher thermo stability but weaker gelation behavior as compared with asymmetric PA. From the results of SEM and TEM analysis, self-assembly of LMWGs forms nan-fiber and then 3D network constructions. Interestingly, both left-handed and right handed helical structures were observed under TEM. Theoretically, both racemic structures should be induced under achiral environment. From the results of temperature dependent 1H-NMR, a reasonable molecular arrangement of the self-assembled constructions via secondary forces were proposed. Furthermore, from the results of fluorescence spectra, the pyrene group of PA17 was found to change from monomer to excimer before and after gelation under UV-exposure. Oppositely, for symmetric compound DPA10, the pyrene group shows excimer behavior either in gel state or solution state. From the results of XRD and molecular simulation, both reasonable helical structure and bi-layer self-assembled model for PA17 and DPA10 were proposed.

Six series of cunitic amphiphiles based on benzene sulfonates were synthesized. The molecular characterization was performed by IR and NMR spectroscopy and the purity was determined by elemental analysis and thin layer chromatography. The thermotropic properties of these cunitic sulfonate amphiphiles were subsequently investigated by means of a combination of DSC, polarized microscopy and X-ray scattering. Most of the synthesized sulfonates were found to exhibit hexagonal columnar mesophases, some of them exhibited a complex polymorphism. The polymorphism depended upon variation of the molecular structure. The Six series of cunitic amphiphiles based on benzene sulfonates were synthesized. The molecular characterization was performed by IR and NMR spectroscopy and the purity was determined by elemental analysis and thin layer chromatography. The thermotropic properties of these cunitic sulfonate amphiphiles were subsequently investigated by means of a combination of DSC, polarized microscopy and X-ray scattering. Most of the synthesized sulfonates were found to exhibit hexagonal columnar mesophases, some of them exhibited a complex polymorphism. The polymorphism depended upon variation of the molecular structure. The phase behavior was determined by the nature of headgroup cation Mn+ (n=1, 2), and for the same Mn+ by the carbon number at the hydrophobic tail and by temperature as well. The lyotropic properties of these cunitic sulfonate amphiphiles were also studied by investigating their gelation behavior and gelling capability. A number of the amphiphiles were found to be favorable organogelators that gel various organic solvents of either high or low polarity upon self-aggregation driven by the Coulomb interaction. The morphological results by means of SEM and TEM demonstrate that the organogelators are able to form fibrous network microstructures by self-organization and self-aggregation. The cylindrical aggregates with sulfonated headgroup in the center as well embody the potential to construct ion-selective transport membranes. The cunitic amphiphiles containing polar sulfonate units at their focal point and polymerizable olefin group on their periphery were exploited to prepare functional membranes that contain ion-active transport channels. The ion-selectivity of the formed membranes was investigated by means of ion transport experiments with LiCl, NaCl, KCl solutions of different concentration. By comparison of the ion transport rates across the membranes the ionic permselectivity was demonstrated.

Research activities towards the self-assembly of small organic molecules building blocks which lead to form supramolecular gel has increased extensively during the past two decades. The fundamental investigations of the morphological properties and the mechanical properties of these supramolecular gels are crucial for understanding gelation processes. Most supramolecular gelators were discovered by serendipity, but nowadays ratiional design of new gelators has become somewh at feasible. As a consequence, an increasing number of multi stimuli-responsive and functional molecular gels are reported, offering great prospects with myriads of applications includ ing drug delivery and smart materials as shown in scheme 1. Scheme 1 Part 2: Synthesis of semiconductor nanocrystals In the last two decades, the synthetic development of semiconductor col loidal nanocrystals has been extended from the adjustment of their size, shape, and composition of the particles at the molecular level. Such adjustments of nanocrystals at the molecula r level might open different fields of applications in materials and biological sciences. I n this chapter, the concept of the shape contr ol synthesis of colloidal nanocrystals with a narrow size distribution, and the synthesis of composition dependent alloy type mat erials are described (Scheme 2). Scheme 2 Chapter 2: Synthesis of luminescent semiconductor nanocrystals Part 1: Cadmium deoxycholate: a new and efficient precursor for high ly luminescent CdSe nanocrystals This part demonstrates the sy nthesis of Cadmium deoxycholate (CdDCh2), an efficient Cd-precursor for the synthesis of high quality, monodisperse, multi color emittting CdSe Scheme 3 nanocrystals, while maintaining their high photoluminescent quantum efficiency (Scheme 3). The high thermal stability of CdDCh2 (decomposition temperature: 332 °C) was utilized to achieve high injection and growth temperatures (∼300 °C) for the syntheesis of red emitting nanocrystals with a sharp f ull width at half maximum (FWHM) and multiple excitonic absorption features. We believe that CdDCh2 can be useful for the prreparation of other nanomaterials such as CdS, CdTe and CdSe@CdS core-shell QDs. Part 2: Ligand mediated exccited state carrier relaxation dynamics of Cd1-xZnxSe1-ySy NCs derived from bile salts Bile salts of Cadmium and Zinc provide a convenient and inexpensive single step synthetic route for highly photoluminescent and stable semiconductor nanocrystals (NCs). The high thermal stabilities of Cadmium and Zinc deoxycholates (CdDCh2 and ZnDCh2) allowed us to fine-tune the synthesis of the NCs at high temperatures while maintaining the monodispersity, crystallinity and reproducibility (Scheme 4). Organic capping agent induced lattice strain affects the excited Scheme 4 state relaxation processes of the NCs. The analysis of photoluminescence decay profiles revealed that the average lifettime decreased with the increasing lattice strain of the NCs. A kinetic stochastic model of photoexcited carrier relaxation dynamics of NCs was employed to estimate the values of the radiative recombination rates, the photoluminescence quenching rates and the non-radiative recombination rates of the NCs. These data showed that the non-radiative relaxation rates and the numbeer of surface trap states increased with the incrreasing lattice strain of the NCs. Such types of NCs can have great potential in nonlinear optics, photocatalysis and solar cells. Chapter 3: Synthesis of organic-inorganic hybrid materials Part 1: Hierarchical self-assembly of photoluminescent CdS nanoparticles into bile acid derived organogel: morphological and photophysical properties In this part a strategy towards integrating photoluminescent semiconductor nanoparticles into a bio-surfactant derived organoggel has been reported. A facially amphiphilic bile thiol was used for capping CdS nanoparticless (NPs) which were embedded in a gel derived from a new bile acid organogelator in order to furnish a soft hybrid material (Scheme 5). The presence of CdS NPs in a well-ordered 1D array on the organogel network was confirmed using microscopic Scheme 5 techniques. Photophysical stuudies of the gel–NP hybrid revealed resolved excitation and emission characteristics. Time resolved spectroscopic studies showed that the average lifetime value of the CdS NPs increased in the gel state compared to the sol phase. A kinetic model was utilized to obtain quantitative information about the different decay pathways of the photoexcited NPs in the sol and gel states. Part 2: A novel strategy towards designing a CdSe quantum dot–metallohydrogel composite material This section describes an efficiient method to disperse hydrophobic CdSe quaantum dots (QDs) in an aqueous phase using cetyltriimethylammonium bromide (CTAB) micelles without any surface ligand exchange. The water soluble QDs were then embedded in the 3D self-assembled fibrillar networks (SAFINs) of a hydrogel showing homogeneous dispersibility as eviidenced by Scheme 6 optical and electron microscopico techniques (Scheme 6). The photophyssical studies of the hydrogel–QD from composite are reported for the first time. These composite materials may have potential applications in biology, optoelectronics, sensors, non-linear optics and materials science. Part 3: Photophysical aspectts of self-assembled CdSe QD-organogel hyybrid and its thermoresponsive properties A luminescent hybrid gel was constructed by incorporating CdSe quantuum dots (QDs) in a facially amphiphilic bile acid derived dimeric urea organogel throough non-covalent interaction between ligands capped on QDs surface and hydrophobic pockets of the gel (Scheme 7). The optical transparency of the hybrid materials and the dirrectionalities of the QDs in the gel medium were confirmed by photophysical and microscopic studies. The detailed excited state dynamics of the QD–organogel hybrid has been reported for the first time with the help of lifetime analysis and a kinetic decay model, and thee data revealed that the average lifetime of the QDs decreased in the gel medium. The reversible thermoresponsive behavior of the QD doped organogel was investigated by steady-state fluorescence spectroscopy. W e believe that the results obtained herein provides a route to develop a thermoresponsive system for practical application, especially because of the spatial assembly between soft organic scaffolds and colloidal QDs. Scheme 7 Part 4: In-situ formation of luminescent CdSe QDs in a metallohydrogel: a strategy towards synthesis, isolation, storage and re-dispersion of the QDs A one step, in-situ, room temperature synthesis of yellow luminesce nt CdSe QD was achieved in a metallohydrog el derived from a facially amphiphilic bile salt, resulting in a QD-gel hybrid (Scheme 8). T he ordered self-assembly and homogeneous distribution of the CdSe QDs in the hydrogel network was observed from optical and electro n micrographs. The different excited state behav iors of the hybrid were revealed for the fir st time using time resolved spectroscopy. Ad ditionally, we described the successful isolation of the photoluminescent CdSe QDs from the gel followed by their re-dispersion in an organic solvent using suitable capping ligands. Scheme 8 Chapter 4: Facially a mphiphilic bile acid derived meta llohydrogel: an efficient template for th e enantioselective Diels-Alder reactio n An enantioselective Diels-Ald er reaction mediated by a facially amphiphilic bile acid derived metallogel scaffold has been a chieved (Scheme 9). Different hydrophobic domains present in Scheme 9 the gel appear to facilitate the enantioselective reaction. Various spectro scopic and electron microscopic techniques were employed to understand the possible reasons for the stereoselectivity in the gel. Subsequently, different counter anion s dependent rate accelerations and induced enantioselectivity in the ZnCh2 gel were studied in detail. These preliminary results of the non-covalent based supramolecular heterogeneous catalysis offer new possibilities for using metallogels as nanoreactors for different stereoselective reactions.

Research activities towards the self-assembly of small organic molecules building blocks which lead to form supramolecular gel has increased extensively during the past two decades. The fundamental investigations of the morphological properties and the mechanical properties of these supramolecular gels are crucial for understanding gelation processes. Most supramolecular gelators were discovered by serendipity, but nowadays ratiional design of new gelators has become somewh at feasible. As a consequence, an increasing number of multi stimuli-responsive and functional molecular gels are reported, offering great prospects with myriads of applications includ ing drug delivery and smart materials as shown in scheme 1. Scheme 1 Part 2: Synthesis of semiconductor nanocrystals In the last two decades, the synthetic development of semiconductor col loidal nanocrystals has been extended from the adjustment of their size, shape, and composition of the particles at the molecular level. Such adjustments of nanocrystals at the molecula r level might open different fields of applications in materials and biological sciences. I n this chapter, the concept of the shape contr ol synthesis of colloidal nanocrystals with a narrow size distribution, and the synthesis of composition dependent alloy type mat erials are described (Scheme 2). Scheme 2 Chapter 2: Synthesis of luminescent semiconductor nanocrystals Part 1: Cadmium deoxycholate: a new and efficient precursor for high ly luminescent CdSe nanocrystals This part demonstrates the sy nthesis of Cadmium deoxycholate (CdDCh2), an efficient Cd-precursor for the synthesis of high quality, monodisperse, multi color emittting CdSe Scheme 3 nanocrystals, while maintaining their high photoluminescent quantum efficiency (Scheme 3). The high thermal stability of CdDCh2 (decomposition temperature: 332 °C) was utilized to achieve high injection and growth temperatures (∼300 °C) for the syntheesis of red emitting nanocrystals with a sharp f ull width at half maximum (FWHM) and multiple excitonic absorption features. We believe that CdDCh2 can be useful for the prreparation of other nanomaterials such as CdS, CdTe and CdSe@CdS core-shell QDs. Part 2: Ligand mediated exccited state carrier relaxation dynamics of Cd1-xZnxSe1-ySy NCs derived from bile salts Bile salts of Cadmium and Zinc provide a convenient and inexpensive single step synthetic route for highly photoluminescent and stable semiconductor nanocrystals (NCs). The high thermal stabilities of Cadmium and Zinc deoxycholates (CdDCh2 and ZnDCh2) allowed us to fine-tune the synthesis of the NCs at high temperatures while maintaining the monodispersity, crystallinity and reproducibility (Scheme 4). Organic capping agent induced lattice strain affects the excited Scheme 4 state relaxation processes of the NCs. The analysis of photoluminescence decay profiles revealed that the average lifettime decreased with the increasing lattice strain of the NCs. A kinetic stochastic model of photoexcited carrier relaxation dynamics of NCs was employed to estimate the values of the radiative recombination rates, the photoluminescence quenching rates and the non-radiative recombination rates of the NCs. These data showed that the non-radiative relaxation rates and the numbeer of surface trap states increased with the incrreasing lattice strain of the NCs. Such types of NCs can have great potential in nonlinear optics, photocatalysis and solar cells. Chapter 3: Synthesis of organic-inorganic hybrid materials Part 1: Hierarchical self-assembly of photoluminescent CdS nanoparticles into bile acid derived organogel: morphological and photophysical properties In this part a strategy towards integrating photoluminescent semiconductor nanoparticles into a bio-surfactant derived organoggel has been reported. A facially amphiphilic bile thiol was used for capping CdS nanoparticless (NPs) which were embedded in a gel derived from a new bile acid organogelator in order to furnish a soft hybrid material (Scheme 5). The presence of CdS NPs in a well-ordered 1D array on the organogel network was confirmed using microscopic Scheme 5 techniques. Photophysical stuudies of the gel–NP hybrid revealed resolved excitation and emission characteristics. Time resolved spectroscopic studies showed that the average lifetime value of the CdS NPs increased in the gel state compared to the sol phase. A kinetic model was utilized to obtain quantitative information about the different decay pathways of the photoexcited NPs in the sol and gel states. Part 2: A novel strategy towards designing a CdSe quantum dot–metallohydrogel composite material This section describes an efficiient method to disperse hydrophobic CdSe quaantum dots (QDs) in an aqueous phase using cetyltriimethylammonium bromide (CTAB) micelles without any surface ligand exchange. The water soluble QDs were then embedded in the 3D self-assembled fibrillar networks (SAFINs) of a hydrogel showing homogeneous dispersibility as eviidenced by Scheme 6 optical and electron microscopico techniques (Scheme 6). The photophyssical studies of the hydrogel–QD from composite are reported for the first time. These composite materials may have potential applications in biology, optoelectronics, sensors, non-linear optics and materials science. Part 3: Photophysical aspectts of self-assembled CdSe QD-organogel hyybrid and its thermoresponsive properties A luminescent hybrid gel was constructed by incorporating CdSe quantuum dots (QDs) in a facially amphiphilic bile acid derived dimeric urea organogel throough non-covalent interaction between ligands capped on QDs surface and hydrophobic pockets of the gel (Scheme 7). The optical transparency of the hybrid materials and the dirrectionalities of the QDs in the gel medium were confirmed by photophysical and microscopic studies. The detailed excited state dynamics of the QD–organogel hybrid has been reported for the first time with the help of lifetime analysis and a kinetic decay model, and thee data revealed that the average lifetime of the QDs decreased in the gel medium. The reversible thermoresponsive behavior of the QD doped organogel was investigated by steady-state fluorescence spectroscopy. W e believe that the results obtained herein provides a route to develop a thermoresponsive system for practical application, especially because of the spatial assembly between soft organic scaffolds and colloidal QDs. Scheme 7 Part 4: In-situ formation of luminescent CdSe QDs in a metallohydrogel: a strategy towards synthesis, isolation, storage and re-dispersion of the QDs A one step, in-situ, room temperature synthesis of yellow luminesce nt CdSe QD was achieved in a metallohydrog el derived from a facially amphiphilic bile salt, resulting in a QD-gel hybrid (Scheme 8). T he ordered self-assembly and homogeneous distribution of the CdSe QDs in the hydrogel network was observed from optical and electro n micrographs. The different excited state behav iors of the hybrid were revealed for the fir st time using time resolved spectroscopy. Ad ditionally, we described the successful isolation of the photoluminescent CdSe QDs from the gel followed by their re-dispersion in an organic solvent using suitable capping ligands. Scheme 8 Chapter 4: Facially a mphiphilic bile acid derived meta llohydrogel: an efficient template for th e enantioselective Diels-Alder reactio n An enantioselective Diels-Ald er reaction mediated by a facially amphiphilic bile acid derived metallogel scaffold has been a chieved (Scheme 9). Different hydrophobic domains present in Scheme 9 the gel appear to facilitate the enantioselective reaction. Various spectro scopic and electron microscopic techniques were employed to understand the possible reasons for the stereoselectivity in the gel. Subsequently, different counter anion s dependent rate accelerations and induced enantioselectivity in the ZnCh2 gel were studied in detail. These preliminary results of the non-covalent based supramolecular heterogeneous catalysis offer new possibilities for using metallogels as nanoreactors for different stereoselective reactions.

Chapter 1. Supramolecular Gels and their Applications Supramolecular gels are viscoelastic materials composed of a solid like three dimensional fibrillary network that is embedded in a liquid. Supramolecular gels are derived from low molecular weight compounds (typically MW < 3000). In the 1990s, the investigations on gels were mainly focused on designing new gelator molecules. However, during the last decade, research focus shifted towards designing functional gels and their applications. As a result of extensive work in this area, gels have been found to have varied applications in the templated synthesis of inorganic nanomaterials, hybrid materials, light harvesting systems, as responsive system and sensors, and also in drug delivery, tissue engineering etc. This chapter gives an introduction to supramolecular hydrogels/organogels and relevant bile acid chemistry touching upon the gelation properties of the bile acid derivatives. Diverse applications of the supramolecular gels are also illustrated with several examples. Scheme 1. Various applications of functional supramolecular gels Chapter 2. Bile Acid derived novel Hydrogelators Part 1. Hydrogelation of Bile acid protected Amino acids and Hybrid Materials Hydrogels from low molecular weight molecules have significant importance in biomedical applications. In this chapter, we report injectable hydrogel formation from bile acid conjugates of various amino acids. Hydrogel formation was found to be dependent on multiple factors such as bile acid backbone structure, linkage between the bile acid and the amino acid, pH etc. Single crystal structures of lithocholyl phenylalanine, lithocholyl-glycine, lithocholyl-L valine and lithocholyl-L alanine were also determined. Finally, the hydrogel frameworks were utilized to produce hybrid materials with Gold and ZnO nanoparticles. Scheme 2. (a) Crystal structure of LC-LF-OH gelator molecule, (b) photograph of gel, (c) SEM and (d) AFM image of LC-LF-OH xerogel Part 2. Hydrogelation of bile acid-dipeptide conjugates and in situ synthesis of silver and gold nanoparticles in the hydrogel matrix Fabricating supramolecular hydrogels with embedded metal nanostructures are important for the design of novel hybrid nanocomposite materials for diverse applications such as bio sensing and chemo sensing platforms, catalytic and antibacterial functional materials etc. Supramolecular self-assembly of bile acid-dipeptide conjugates have led to the formation of new supramolecular hydrogels. Gelation of these molecules depends strongly on the hydrophobic character of the bile acids. Ag+ and Au3+ salts were incorporated in the hydrogels, and photo reduction and chemical reduction led to the in situ generation of Ag and Au NPs in these supramolecular hydrogels without the addition of any external stabilizing agent. The color, size and shape of silver nanoparticles formed by photo reduction depended on the amino acid residue on the side chain. Furthermore, the hydrogel-Ag nanocomposite was tested for its antimicrobial activity. Scheme 3. Bile acid based dipeptide hydrogelators and soft hybrid materials Chapter 3. Sonogels of bile salts of In(III): use in the formation of self-templated indium sulfide nanostructures In this chapter, facile hydrogel formation by Indium(III) cholate and deoxy cholate are reported. When In(III) solution was added to aqueous solutions of sodium cholate and sodium deoxy cholate and sonicated, the mixtures formed gels. The gels thus obtained were translucent/turbid and thermos irreversible. Rheological measurements showed that all of them could be classified as viscoelastic soft solids. Scanning electron microscopy and atomic force microscopy showed typical entangled three dimensional fibrous networks. The In-Ch hydrogel were further used to prepare nanostructured In2S3 in which the cholate units possibly acted as a surfactant to confine the growth of the Nano flakes. Scheme 4. In-Ch hydrogel (Photograph and SEM image of In-Ch gel) Chapter 4. Palladium-Hydrogel Nanocomposite for C-C Coupling Reactions Supported metallic nanoparticles are important composite materials owing to their enormous potential for applications in various fields. This chapter describes the in situ formation of palladium nanoparticles in a calcium-cholate (Ca-Ch) hydrogel by reduction with sodium cyan borohydride. The hydrogel matrix appeared to assist the controlled growth as well as stabilization of palladium nanoparticles. The palladium nanoparticle/Ca-Ch hydrogel hybrid was characterized by scanning and transmission electron microscopy, atomic force microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. Furthermore, PdNP/Ca-Ch hybrid xerogel was shown to act as an active catalyst for Suzuki reaction under aqueous aerobic conditions, up to 4 cycles. This PdNP/Ca-Ch xerogel retained its catalytic activities on storage for several months. Scheme 5. Palladium-hydrogel nanocomposite for C-C coupling reactions in water Chapter 5. Sensitization of Terbium/Europium in self-assembled cholate hydrogel: An approach towards the detection of amine vapours "Luminescent" lanthanides have intrinsic low molar absorptivity, although this problem can be addressed by complexing the lanthanide ion with suitable chelating ligands which improve the luminescence properties drastically. However the design of such systems often involves careful planning and laborious synthetic steps. It is therefore desirable to have a simpler way to sensitize lanthanides with high efficiency. It was observed in our group that trivalent lanthanides formed hydrogels on the addition of sodium cholate. This chapter describes the discovery of the several biphenyl derivatives (such as 4-biphenylcarbaxaldehyde, 4-acetylbiphenyl) for sensitization of Tb(III) and Eu(III) in lanthanide hydrogels. Sensitization of Tb(III) and Eu(III) were observed by doping was characterized by scanning and transmission electron microscopy, atomic force microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. Furthermore, PdNP/Ca-Ch hybrid xerogel was shown to act as an active catalyst for Suzuki reaction under aqueous aerobic conditions, up to 4 cycles. This PdNP/Ca-Ch xerogel retained its catalytic activities on storage for several months. Scheme 6. Schematic representation of the sensitization process (the arrangement of themolecules in the gel fiber is arbitrary)(For figures pl refer the abstract pdf file)

Chapter 1. Supramolecular Gels and their Applications Supramolecular gels are viscoelastic materials composed of a solid like three dimensional fibrillary network that is embedded in a liquid. Supramolecular gels are derived from low molecular weight compounds (typically MW < 3000). In the 1990s, the investigations on gels were mainly focused on designing new gelator molecules. However, during the last decade, research focus shifted towards designing functional gels and their applications. As a result of extensive work in this area, gels have been found to have varied applications in the templated synthesis of inorganic nanomaterials, hybrid materials, light harvesting systems, as responsive system and sensors, and also in drug delivery, tissue engineering etc. This chapter gives an introduction to supramolecular hydrogels/organogels and relevant bile acid chemistry touching upon the gelation properties of the bile acid derivatives. Diverse applications of the supramolecular gels are also illustrated with several examples. Scheme 1. Various applications of functional supramolecular gels Chapter 2. Bile Acid derived novel Hydrogelators Part 1. Hydrogelation of Bile acid protected Amino acids and Hybrid Materials Hydrogels from low molecular weight molecules have significant importance in biomedical applications. In this chapter, we report injectable hydrogel formation from bile acid conjugates of various amino acids. Hydrogel formation was found to be dependent on multiple factors such as bile acid backbone structure, linkage between the bile acid and the amino acid, pH etc. Single crystal structures of lithocholyl phenylalanine, lithocholyl-glycine, lithocholyl-L valine and lithocholyl-L alanine were also determined. Finally, the hydrogel frameworks were utilized to produce hybrid materials with Gold and ZnO nanoparticles. Scheme 2. (a) Crystal structure of LC-LF-OH gelator molecule, (b) photograph of gel, (c) SEM and (d) AFM image of LC-LF-OH xerogel Part 2. Hydrogelation of bile acid-dipeptide conjugates and in situ synthesis of silver and gold nanoparticles in the hydrogel matrix Fabricating supramolecular hydrogels with embedded metal nanostructures are important for the design of novel hybrid nanocomposite materials for diverse applications such as bio sensing and chemo sensing platforms, catalytic and antibacterial functional materials etc. Supramolecular self-assembly of bile acid-dipeptide conjugates have led to the formation of new supramolecular hydrogels. Gelation of these molecules depends strongly on the hydrophobic character of the bile acids. Ag+ and Au3+ salts were incorporated in the hydrogels, and photo reduction and chemical reduction led to the in situ generation of Ag and Au NPs in these supramolecular hydrogels without the addition of any external stabilizing agent. The color, size and shape of silver nanoparticles formed by photo reduction depended on the amino acid residue on the side chain. Furthermore, the hydrogel-Ag nanocomposite was tested for its antimicrobial activity. Scheme 3. Bile acid based dipeptide hydrogelators and soft hybrid materials Chapter 3. Sonogels of bile salts of In(III): use in the formation of self-templated indium sulfide nanostructures In this chapter, facile hydrogel formation by Indium(III) cholate and deoxy cholate are reported. When In(III) solution was added to aqueous solutions of sodium cholate and sodium deoxy cholate and sonicated, the mixtures formed gels. The gels thus obtained were translucent/turbid and thermos irreversible. Rheological measurements showed that all of them could be classified as viscoelastic soft solids. Scanning electron microscopy and atomic force microscopy showed typical entangled three dimensional fibrous networks. The In-Ch hydrogel were further used to prepare nanostructured In2S3 in which the cholate units possibly acted as a surfactant to confine the growth of the Nano flakes. Scheme 4. In-Ch hydrogel (Photograph and SEM image of In-Ch gel) Chapter 4. Palladium-Hydrogel Nanocomposite for C-C Coupling Reactions Supported metallic nanoparticles are important composite materials owing to their enormous potential for applications in various fields. This chapter describes the in situ formation of palladium nanoparticles in a calcium-cholate (Ca-Ch) hydrogel by reduction with sodium cyan borohydride. The hydrogel matrix appeared to assist the controlled growth as well as stabilization of palladium nanoparticles. The palladium nanoparticle/Ca-Ch hydrogel hybrid was characterized by scanning and transmission electron microscopy, atomic force microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. Furthermore, PdNP/Ca-Ch hybrid xerogel was shown to act as an active catalyst for Suzuki reaction under aqueous aerobic conditions, up to 4 cycles. This PdNP/Ca-Ch xerogel retained its catalytic activities on storage for several months. Scheme 5. Palladium-hydrogel nanocomposite for C-C coupling reactions in water Chapter 5. Sensitization of Terbium/Europium in self-assembled cholate hydrogel: An approach towards the detection of amine vapours "Luminescent" lanthanides have intrinsic low molar absorptivity, although this problem can be addressed by complexing the lanthanide ion with suitable chelating ligands which improve the luminescence properties drastically. However the design of such systems often involves careful planning and laborious synthetic steps. It is therefore desirable to have a simpler way to sensitize lanthanides with high efficiency. It was observed in our group that trivalent lanthanides formed hydrogels on the addition of sodium cholate. This chapter describes the discovery of the several biphenyl derivatives (such as 4-biphenylcarbaxaldehyde, 4-acetylbiphenyl) for sensitization of Tb(III) and Eu(III) in lanthanide hydrogels. Sensitization of Tb(III) and Eu(III) were observed by doping was characterized by scanning and transmission electron microscopy, atomic force microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. Furthermore, PdNP/Ca-Ch hybrid xerogel was shown to act as an active catalyst for Suzuki reaction under aqueous aerobic conditions, up to 4 cycles. This PdNP/Ca-Ch xerogel retained its catalytic activities on storage for several months. Scheme 6. Schematic representation of the sensitization process (the arrangement of themolecules in the gel fiber is arbitrary)(For figures pl refer the abstract pdf file)