Systems formed by the supramolecular assemblages of organic molecules known as organogelators and hydrogelators are currently, and only recently, a subject of great attention and promise. In this context, low molecular weight gelators (LMWGs) are of particular interest because they provide a bottom-up approach to the formation of supramolecular architectures through self-assembly. Gelator molecules do so via the initial formation of a one-dimensional array of individual molecules bound non-covalently through forces such as: hydrogen bonds, electrostatic forces, Van der Waals interactions, and other weak forces such as π-π interactions. These interactions then lead to secondary structure formation through a similar assembly mechanism. Understanding the gelation process through characterization techniques is critical to the development of a design rationale for gelator molecules. Past and current research performed by the Wang group indicates that analogues of various 4,6-benzylidene acetals form stable gels in organic, aqueous, and organic/aqueous solvents at varying concentrations. The basis of varying the 4,6-protecting groups on glucose and glucosamine derivatives is to discern the relative structure activity relationships of these systems, and as well to fabricate functional systems which respond to external stimulus. Stimuli responsive or trigger release gel systems formed by sugar based low molecular weight gelators (LMWGs) have applications as smart biocompatible materials, and such responsiveness in various media was explored and developed to determine the feasibility of such applications using monosaccharide derivatives.

Low molecular weight gelators (LMWGs) have gained great attention over the past two decades. These compounds form self-assembled fibrous networks like micelles, cylindrical, sheets, fibers, layers and so on. The fibrous network entraps the solvent and form gel. LMWGs are interesting compounds with many potential applications in material and biomedical sciences. Many different structures have been found to be good LMWGs. Our interests focus on the carbohydrate based LMWGs. Previously, we have found that several ester derivatives of methyl 4, 6-O-benzylidene-α-D-glucopyranoside are good gelators for organic solvents and aqueous solutions. In this study, in order to understand the structure requirement, we systematically investigated the influence of sugar head groups and the attached hydrophobic tails towards gelation. The design, synthesis and gel properties of esters, amides, ureas, carbamates which derived from sugar head groups show above will be discussed in chapter II, III, IV.

Orientador: Paulo Cesar Muniz de Lacerda Miranda / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-21T09:25:32Z (GMT). No. of bitstreams: 1 Abreu_MarlondeFreitas_D.pdf: 21101958 bytes, checksum: 66d47016a4102485845b17df067519a7 (MD5) Previous issue date: 2012 / 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 / Made available in DSpace on 2018-08-27T01:55:14Z (GMT). No. of bitstreams: 1 Simoes_ThiagoAugusto_M.pdf: 2543594 bytes, checksum: 7e559c17b32f95f43db82455a855492b (MD5) Previous issue date: 2014 / 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

Low molecular weight gelators (LMWGs) are small molecules that are capable of entrapping solvents to form a gel in organic solvents or aqueous solution. These compounds rely solely on noncovalent forces to form the fibrous networks necessary to entrap a variety of solvents. The organogels and hydrogels thus formed could have applications in a variety of fields from environmental to biological to medicinal. Carbohydrates are ideal starting materials to synthesize LMWGs, because of their natural abundance, dense chirality, and biocompatibility. D-Glucose is the most common monosaccharide and D-glucosamine is isolated from natural sources, such as crab shells. Several series of compounds were synthesized using compounds 1-3 as the starting materials. These include esters, carbamates, amides, and ureas. The structure and gelation relationship was analyzed to obtain guidelines for designing new LMWGs. Compound 1 is a simple derivative of D-glucose and its terminal alkynyl esters and saturated carbamates are effective gelators. Compound 2 is a simple derivative of D-glucosamine and its amide and urea derivatives are also effective gelators. Compound 3 is formed from the deoxygenation of D-glucose. 1OOHOOCH3OHOPh2OOHOOCH3NH2OPh3OOHOOHOPh The design, synthesis and gelation properties of several classes of sugar based low molecular organo/hydrogelators will be discussed in this thesis in chapters 2, 3, and 4. After obtaining highly effective organo/hydrogelators, potential applications of these novel molecular systems can be explored. Some preliminary study on using one of the gelator in enzyme assay has shown that it is possible to utilize the hydrogels to immobilize enzymes. However, future research can explore further on the applications of these gelators.

The present thesis titled “Molecular Modulation of Material Properties: Stud- ies on Nanoparticles, Nanoassemblies and Low Molecular Mass Gelator” deals with the preparation, characterization, and investigations into the properties of gold nanoparticles coated with novel thiols. The coverage of nanoparticle surfaces with these thiols renders them with special characteristics that will be of interest in biological and sensor applications. Also, a novel low molecular mass tetrameric sugar-based hydrogelator was synthesized and its gelation properties were studied in detail. Chapter 1 gives a general introduction and an overview about Nanomaterials, with emphasis towards nanoparticles of gold, which form the basis of this work. It delves with the history of research in noble metal nanoparticles, their interesting electronic and optical properties, the present methods of synthesis of high quality nanoparticles of noble metals, numerous potential applications of these novel materials, as well as the challenges in their real-life applications, and ends with the future outlook of this field of research. Chapter 2 describes the synthesis and characterization of three cationic lipid-like disulfides whose molecular structures are shown in Fig. 2.1. Gold nanoparticles capped with these molecules were then synthesized in small size dispersion by a simple one-phase protocol. These particles exhibited remarkably different solubility properties that were dictated by the molecular structure of the capping agent. The nanoparticles were characterized by a variety of techniques like UV-visible spec- troscopy, Transmission Electron Microscopy (TEM), proton Nuclear Magnetic Resonance (1H NMR), Fourier Transform Infra-red (FTIR) spectroscopy, and Zeta Potential measurements. These nanoparticles were then examined for their interactions (structural formula) Figure 1: Chemical Structures of the cationic lipid-like thiols used for nanoparticle preparation with dipalmitoyl phosphatidyl choline (DPPC) vesicles as model biological membranes. TEM, UV-vis, and Differential Scanning Calorimetry (DSC) were employed to probe the interactions. It was found that the capping agent of the nanoparticle had a strong bearing upon the interactions of the nanoparticles with DPPC vesicles. Chapter 3 describes the assembly of hydrophilic cationic nanoparticles upon elec- trostatic interaction with a variety of anionic surfactants. The chemical structures of some of the anions employed in the study, as well as a schematic of cationic nanopar- ticle are shown in Fig. 2. Upon ion pairing with long-chain anionic surfactants, the hydrophilic cationic nanoparticles were completely hydrophobized. They could then be phase-transferred to organic layer. TEM showed that nanoparticles assemble in to a variety of mesostructures upon ion-pairing with anions. The aggregate formation was found to depend critically upon length of the hydrophobic alkyl chain as well as the head-group of the anion. Isothermal Titration Calorimetry (ITC) was employed to probe the interactions of these nanoparticles with anions. It was found that the anions that resulted in nanoparticle precipitation displayed exothermic interactions with the nanoparticle. Chapter 4 deals with the synthesis of -thiolated metal chelator derivatives whose structures are shown in Fig. 3. The molecules are based on well-known chelators viz. iminodiacetic acid and bis-(2-pyridylmethyl)amine. While the first one is carboxylic acid-based chelator, the second one is pyridine-based. Nanoparticles coated with these chelators were synthesized in a size-controlled manner. These nanoparticles exhibited pH-controlled reversible assembly. However, while S-IDA based nanoparticles aggregated at low pH values, the S-BPA based nanoparticles aggregated in high pH regimes. Mixed monolayer protected gold nanoparticles were synthesized by employing S-BPA and C12H25SH as capping agents. It resulted in the formation of nanoparticles in low size-dispersion. These nanoparticles were characterized by 1H NMR spectroscopy to infer the ratio of the two capping agents on the nanoparticle surface. These nanoparticles demonstrated metal-ion induced aggregation. It was found that the nanoparticles could differentiate Cu2+ ions from other ions, and immediately formed aggregates in presence of Cu2+ ions. Chapter 5 describes the synthesis of novel mono-thiolated “Gemini” surfactants for nanoparticle synthesis. Gemini surfactants with different spacers were prepared. These surfactants had a 12-n-12 kind of molecular structure as shown in the Fig. 4. Upon preparation of nanoparticles with these thiols, the resulting material was soluble in water in the case of rigid thiols like D2S and DBPS Chapter 6 deals with the synthesis and hydrogelation properties of a low molecular mass hydrogelator based on an azobenzene based tetrameric sugar derivative (Fig. 5). The pKa of carboxylic acids in the molecule were determined using 13C NMR. The trans-to-cis isomerization of the compound was probed by time-dependent UV-vis studies. The sugar derivative exhibited pronounced hydrogelation capacity, gelling water at micromolar concentration. The gel formed was characterized extensively (structural formula) Figure 2: Schematic of cationic nanoparticles and molecular structures of the anions employed for nanoparticle assembly (structural formula) Figure 3: Chemical structures of metal-chelator containing thiols employed for the pH-controlled and metal-ion mediated nanoparticle assembly (structural formula) Figure 4: Schematic of cationic nanoparticles and molecular structures of the anions employed for nanoparticle assembly (structural formula) Figure 5: Chemical Structure of azobenzene-based tetrameric sugar derivative exhibit- ing pronounced hydrogelation using melting temperature analysis, UV-vis, FT-IR, circular dichroism spectroscopy and scanning electron microscopy. The resultant gel exhibited impressive tolerance to the pH variation of the aqueous phase and gelated water in the pH range of 4 to 10. While UV-vis and CD spectroscopy indicated that pronounced aggregation of the azobenzene chromophores in the gelator was responsible for gelation, FT-IR studies showed that hydrogen bonding is also a contributing factor in the gelation process. The melting of gel was found to depend upon the pH of the aqueous medium in which gel was formed. The gel showed considerable photostability to UV irradiation indicating tight intermolecular packing inside gelated state that render azobenzene groups in the resultant aggregate refractory to photoisomerization. The electron micrographs of the aqueous gels thus formed showed the existence of spongy globular aggregates in such gelated materials. Addition of salts to the aqueous medium led to a delay in the gelation process and also caused remarkable morphological changes in the microstructure of the gel. Appendix A describes the employment of ligand-free palladium nanoparticles towards efficient catalysis of Heck and Suzuki reactions in aqueous medium. Hexadecyl trimethylammonium bromide was employed as the surfactant to achieve solubilization of organic compounds in aqueous medium. UV-vis and TEM investigations into the formation of nanoparticles in the reaction media were undertaken. These studies indicate that the nanoparticles were formed by reduction of potassium tetrachloropalladinate by methyl acrylate used as one of the reactants. TEM investigation indicated the formation of nanoparticle assemblies upon solvent drying. Efficient and catalytic synthesis of a number of organic compounds could be achieved in high yield.

Semiconducting polymers with a conjugated backbone are important for energy storage, conversion, and biomedical field applications. The self-assembly process of these polymers in solutions depends on the polymer concentration and quality of the solvent. The electrical properties of thin films obtained from the solution phase depend on the self-assembled process. Thin films of conjugated polymer gels with percolating networks of self-assembled structures display improved electrical conductivities. In this dissertation, we studied the impact of the secondary gel matrix formed by a low molecular weight gelator, on the self-assembly of conjugated polymers, the preservation of assembled structures in dried gel films and their electrical properties. The study utilized di-Fmoc-l-Lysine gelator, to form a hybrid gel with poly(3-hexylthiophene) in chloroform. The aggregation of P3HT with the progression of gelation was captured using spectroscopic analysis. The aggregates remain in the interstitial spaces of the fibrillar microstructure of gelator. With restricted mobility and due to higher local concentration, the aggregates formed nanofibriliar structures. Microstructural data indicated the nanostructures formed a percolating network in the dried films with good bulk conductivity, despite conductive polymer content of only 20%. Conjugated polymers require a high boiling point and toxic halogenated solvents to develop gels limiting their applications. By utilizing the amphiphilic nature of the gelator, a thermoreversible gel was obtained in 1-propanol, by combining it with an isoindigo-based DA polymer, engineered with galactose side chains to improve its solubility in eco-friendly solvents. Uniform distribution of aggregated polymer increased the shear moduli of the gels. The electrical conductivity of the dried gels confirmed the existence of percolated aggregates. Additional solvent systems were explored, such as 1-propanol mixed with chloroform. Although P3HT is insoluble in 1-propanol, by adjusting chloroform and 1-propanol ratio, a stable gel was obtained. The poor solvent, 1-propanol, assists the self-assembly of P3HT, improving the electrical performance of dried hybrid gels. The findings from this study contribute to a better understanding of the self-assembly of conjugated polymers utilizing molecular gels as templates. It provides a framework for obtaining semiconducting gels for applications in the biomedical field, and for large-scale fabrication of optoelectronic devices. Semiconducting polymers with a conjugated backbone are important for energy storage, conversion, and biomedical field applications. The self-assembly process of these polymers in solutions depends on the polymer concentration and quality of the solvent. The electrical properties of thin films obtained from the solution phase depend on the self-assembled process. Thin films of conjugated polymer gels with percolating networks of self-assembled structures display improved electrical conductivities. In this dissertation, we studied the impact of the secondary gel matrix formed by a low molecular weight gelator, on the self-assembly of conjugated polymers, the preservation of assembled structures in dried gel films and their electrical properties. The study utilized di-Fmoc-l-Lysine gelator, to form a hybrid gel with poly(3-hexylthiophene) in chloroform. The aggregation of P3HT with the progression of gelation was captured using spectroscopic analysis. The aggregates remain in the interstitial spaces of the fibrillar microstructure of gelator. With restricted mobility and due to higher local concentration, the aggregates formed nanofibriliar structures. Microstructural data indicated the nanostructures formed a percolating network in the dried films with good bulk conductivity, despite conductive polymer content of only 20%. Conjugated polymers require a high boiling point and toxic halogenated solvents to develop gels limiting their applications. By utilizing the amphiphilic nature of the gelator, a thermoreversible gel was obtained in 1-propanol, by combining it with an isoindigo-based DA polymer, engineered with galactose side chains to improve its solubility in eco-friendly solvents. Uniform distribution of aggregated polymer increased the shear moduli of the gels. The electrical conductivity of the dried gels confirmed the existence of percolated aggregates. Additional solvent systems were explored, such as 1-propanol mixed with chloroform. Although P3HT is insoluble in 1-propanol, by adjusting chloroform and 1-propanol ratio, a stable gel was obtained. The poor solvent, 1-propanol, assists the self-assembly of P3HT, improving the electrical performance of dried hybrid gels. The findings from this study contribute to a better understanding of the self-assembly of conjugated polymers utilizing molecular gels as templates. It provides a framework for obtaining semiconducting gels for applications in the biomedical field, and for large-scale fabrication of optoelectronic devices.