Immune heparin-induced thrombocytopenia (HIT) is a potentially serious complication of heparin therapy and is associated with antibodies directed against a complex of platelet factor 4 (PF4) and heparin. Early diagnosis of HIT is important to reduce morbidity and mortality. I developed an enzyme immunoassay that detects the binding of HIT IgG to PF4-heparin in the fluid phase. This required techniques to purify and biotinylate PF4. The fluid phase assay produces consistently low background and can detect low levels of anti-PF4-heparin. It is suited to testing alternative anticoagulants because, unlike in an ELISA, a clearly defined amount of antigen is available for antibody binding. I was able to detect anti-PF4-heparin IgG in 93% of HIT patients. I also investigated cross-reactivity of anti-PF4-heparin antibodies with PF4 complexed to alternative heparin-like anticoagulants. Low molecular weight heparins cross-reacted with 88% of the sera from HIT patients while half of the HIT sera weakly cross-reacted with PF4-danaparoid (Orgaran). The thrombocytopenia and thrombosis of most of these patients resolved during danaparoid therapy, indicating that detection of low affinity antibodies to PF4-danaparoid by immunoassay may not be an absolute contraindication for danaparoid administration. While HIT patients possess antibodies to PF4-heparin, I observed that HIT antibodies will also bind to PF4 alone adsorbed on polystyrene ELISA wells but not to soluble PF4 in the absence of heparin. Having developed a technique to affinity-purify anti-PF4-heparin HIT IgG, I provide the first estimates of the avidity of HIT IgG. HIT IgG displayed relatively high functional affinity for both PF4-heparin (Kd=7-30nM) and polystyrene adsorbed PF4 alone (Kd=20-70nM). Furthermore, agarose beads coated with PF4 alone were almost as effective as beads coated with PF4 plus heparin in depleting HIT plasmas of anti-PF4-heparin antibodies. I conclude that the HIT antibodies which bind to polystyrene adsorbed PF4 without heparin are largely the same IgG molecules that bind PF4-heparin and thus most HIT antibodies bind epitope(s) on PF4 and not epitope(s) formed by part of a PF4 molecule and part of a heparin molecule. Binding of PF4 to heparin (optimal) or polystyrene/agarose (sub-optimal) promotes recognition of this epitope. Under conditions that are more physiological and sensitive than previous studies, I observed that affinity-purified HIT IgG will cause platelet aggregation upon the addition of heparin. Platelets activated with HIT IgG increased their release and surface expression of PF4. I quantitated the binding of affinity-purified HIT 125I-IgG to platelets as they activate in a plasma milieu. Binding of the HIT IgG was dependent upon heparin and some degree of platelet activation. Blocking the platelet Fc??? receptor-II with the monoclonal antibody IV.3 did not prevent HIT IgG binding to activated platelets. I conclude that anti-PF4-heparin IgG is the only component specific to HIT plasma that is required to induce platelet aggregation. The Fab region of HIT IgG binds to PF4-heparin that is on the surface of activated platelets. I propose that only then does the Fc portion of the bound IgG activate other platelets via the Fc receptor. My data support a dynamic model of platelet activation where released PF4 enhances further antibody binding and more release.

Eventos como fosforilação e desfosforilação estão presentes nos processos de crescimento e diferenciação celular. As proteínas tirosina fosfatases estão envolvidas nestes processos. Estas enzimas são encontradas em animais, plantas e ocorrem em diversas formas, diferindo no peso molecular, substrato específico e sensibilidade a inibidores. As enzimas que possuem baixo peso molecular (entre 18-20 KDa), hidrolisam p-nitrofenilfosfato e são sensíveis ao p-hidroximercuribenzoato são chamadas como proteínas tirosina fosfatases de baixo peso molecular relativo (PTP-BMr) ou fosfatases ácidas. Vários dados sugerem que tipos de células de osso, como osteoblastos, podem expressar esta enzima ativa. Aqui, culturas de osteoblastos derivadas da medula removida do fêmur de rato foram investigadas para padronizar a metodologia de obtenção da PTP-BMr. A expressão e atividade catalítica desta enzima em diferentes estágios de crescimento de osteoblastos também foram verificadas. Foi observado que são necessários de 16-19 dias de cultura para obter maiores níveis de atividade da PTP-BMr em extrato citoplasmático. O nível de expressão do gene da PTP-BMr foi determinado por PCR em tempo real e uma maior quantificação de RNAm foi obtida em 16 dias de crescimento de osteoblasto. A caracterização bioquímica parcial confirma uma banda de atividade em gel de poliacrilamida com peso molecular de 17,6 KDa, e pH ótimo de 5,5. A hidrólise do p-nitrofenilfosfato demonstra uma pequena cooperatividade relativa (n=1,2) com K0,5= 0,12 e Vmax= 3,5U/mg. Esta atividade foi fortemente inibida (60 a 75%) por molibdato de amônio (10mM); fosfato de sódio (10mM); ortovanadato de sódio (10mM) e p-hidroximercuribenzoato de sódio (10mM). Estas propriedades são típicas desta classe. A interação entre osteoblastos e diferentes superfícies pode ativar ou desativar genes. Este presente projeto investigou se a interação com superfície de titânio pode modificar o perfil de atividade da PTP-BMr. Quando em presença de uma superfície de titânio há um maior aumento na atividade catalítica do que nos níveis de RNAm da PTP-BMr o que sugere uma estimulação da enzima a qual pode estar auxiliando no processo de formação óssea. / Events as phosphorilation and desphosphorilation are experienced in cell growth and differentiation processes. Tyrosine phosphatases proteins are involved in these processes. These enzymes are found in animals, plants and occur in multiple forms, differing in relative molecular weight, substrate specificity and sensitivity to inhibitors. The enzymes that have low molecular weight (between 18-20KDa), hydrolize p-nitrophenilphosphate and are sensible to p-hidroximercuribenzoate are known as low molecular weight relative tyrosine phosphatase proteins (PTP-LMWr) or acid phosphatase. Several data suggest that bone cell types, such as osteoblasts, may express this enzyme activity. Here, osteosblast cultures derived from medulla removed from rat femur were investigated to standardize the methodology of PTP-LMW obtainment. The expression and the catalytic activity of this protein in different stages of osteoblast growth were checked as well. It was observed that 16-19 culture days are necessary to obtain greater levels of activity of PTP-LMW in the cytoplasmatic extracts. The gene expression level of PTP-LMW was determined by quantitative real-time PCR, and a greater quantity of mRNA was observed within sixteen days of osteoblast growth. The partial biochemistry characterization confirms a single active band in poliacrilamide gel with molecular weight of about 17.6KDa, and a pH-optimum around 5.5. p-nitrophenilphosphate hydrolysis shows a small cooperative behavior (n=1.2) with K0.5=0.12mM and Vmax=3.5U/mg. This activity was strongly inhibited (about 60-95%) by ammonium molybdate (10mM); sodium phosphate (10mM); sodium orthovanadate (10mM) and sodium p-hydroximercuribenzoate (10mM). These properties are typical for this enzyme class.

Corantes reativos têxteis podem ser degradados por basidiomicetos, por meio de enzimas oxidativas e hidrolíticas, e compostos de baixa massa molar. Foi avaliada a descoloração de CI Reactive Blue 222 por Peniophora cinerea, Pleurotus ostreatus e Trametes villosa, selecionando condições ótimas para o processo e diferentes vias metabólicas foram observadas. A degradação foi confirmada por cromatografia de camada delgada. Foi sugerido que lacases de P. ostreatus oxidam o grupo cromóforo azo, ligado ao fenol, nas primeiras 24 horas, conjuntamente hidroxilização não enzimática. Lacases de P. cinerea oxidam Mn+2 e quinona, possibilitando a via de Fenton e hidroxilizando assim a molécula do corante, paulatinamente, a partir das ligações mais vulneráveis. T. villosa faz uso prioritariamente da via de Fenton, hidroxilizando gradativamente a molécula do corante. Dessa forma, embora a maioria de estudos associem a produção enzimática à descoloração, a participação dos compostos de baixa massa molar não pode ser negligenciada. / Reactive textile dyes can be degraded by basidiomycetes, by means of hydrolytic and oxidative enzymes, and low molecular weight compounds. Was evaluated the CI Reactive Blue 222 decolorization by Peniophora cinerea, Pleurotus ostreatus, and Trametes villosa, selecting optimal conditions for the process and different metabolic pathways were observed. The degradation was confirmed by thin layer chromatography. It was suggested that P. ostreatus laccases oxidize azo chromophore group attached to the phenol, within 24 hours, together nonenzymatic hydroxylizating. P. cinerea laccases oxidize Mn+2 and quinone, enabling via Fenton and so hidroxylizing the dye molecule, gradually, from the most vulnerable links. T. villosa uses primarily via Fenton, gradually hidroxylizing the dye molecule. Thus, although most studies have linked enzyme production with the decolorization, the share of low molecular weight compounds can not be neglected.

No description available.

The interplay of rhizosphere components such as root exudates, microbes, and minerals results in small-scale gradients of organic molecules in the soil around roots. The current methods for the direct chemical imaging of plant metabolites in the rhizosphere often lack molecular information or require labeling with fluorescent tags or isotopes. Here, we present a novel workflow using laser desorption ionization (LDI) combined with mass spectrometric imaging (MSI) to directly analyze plant metabolites in a complex soil matrix. Undisturbed samples of the roots and the surrounding soil of Zea mays L. plants from either field- or laboratory-scale experiments were embedded and cryosectioned to 100 mm thin sections. The target metabolites were detected with a spatial resolution of 25 mm in the root and the surrounding soil based on accurate masses using ultra-high mass resolution laser desorption ionization Fourier-transform ion cyclotron resonance mass spectrometry (LDI-FT-ICR-MS). Using this workflow, we could determine the rhizosphere gradients of a dihexose (e.g., sucrose) and other plant metabolites (e.g., coumaric acid, vanillic acid). The molecular gradients for the dihexose showed a high abundance of this metabolite in the root and a strong depletion of the signal intensity within 150 mm from the root surface. Analyzing several sections from the same undisturbed soil sample allowed us to follow molecular gradients along the root axis. Benefiting from the ultra-high mass resolution, isotopologues of the dihexose could be readily resolved to enable the detection of stable isotope labels on the compound level. Overall, the direct molecular imaging via LDI-FT-ICR-MS allows for the first time a nontargeted or targeted analysis of plant metabolites in undisturbed soil samples, paving the way to study the turnover of root-derived organic carbon in the rhizosphere with high chemical and spatial resolution.

La problématique de la sauvegarde de l’énergie pose un certain nombre de défis à la science, en particulier celui de son efficacité. La conception et la caractérisation de nouveaux matériaux isolants thermiques plus performants se révèlent donc fondamentales dans cette perspective. Les aérogels se présentent comme de sérieux candidats dans ce domaine, leur procédé de fabrication confère à certains d’entre eux des caractéristiques extrêmes telles qu’une grande porosité et une faible masse volumique. La caractérisation thermique de tels matériaux est délicate, leur faible sensibilité aux flux thermiques qui les traversent rend les méthodes connues difficiles à mettre en œuvre. A travers l’étude d’échantillons d’aérogels de faible poids moléculaire conçus au LCPM, une méthode de caractérisation adaptée a été développée. Cette méthode de type « tri-couche » offre les avantages d’être robuste et de s’affranchir de la connaissance de paramètres difficiles à atteindre dans de tels cas. La description et la validation de cette méthode sont l’objet principal de ce travail. Par ailleurs, les mesures de conductivité thermique sous vide ont été exploitées et ont permis une compréhension plus poussée de la structure de ces aérogels. Les résultats obtenus dans cette étude ouvrent donc des perspectives en vue de l’optimisation de nouvelles solutions pour l’isolation thermique / The issue of preserving energy raises a number of challenges to science, particularly its efficiency. The conception and characterization of new more efficient thermal insulating materials prove fundamental in this regard. Aerogels appear as serious candidates in this area, their manufacturing process provides extreme characteristics such as high porosity and low density for some of them. Thermal characterization of such materials is tricky, their low sensitivity to heat flux makes well-known methods difficult to implement. Through the study of low molecular weight aerogel samples designed by the LCPM a characterization method suitable to these samples has been developed by the LEMTA. This “three-layers” method offers the advantages of being robust and to overcome the knowledge of parameters that are difficult to reach in such cases. Describing and validating this method is the main object of this work. In addition, thermal conductivity measurements under vacuum have been processed which allowed a deeper understanding of the structure of aerogels. The results obtained this study open perspectives for the optimization of new solutions for thermal insulation

O copolímero SBS é o aditivo mais empregado mundialmente na modificação de ligantes asfálticos, por melhorar diversas de suas características. Um dos principais problemas deste tipo de formulação é a separação de fases, que pode ser minimizada com a incorporação de aditivos. Um novo polietileno de alta densidade e baixo peso molecular oxidado (com denominação comercial TITAN 9686) foi utilizado nesta pesquisa, com o objetivo de testar a hipótese de que a adição de proporções adequadas deste aditivo possa melhorar as características reológicas do asfalto+SBS. O experimento laboratorial foi delineado com base na técnica de experimentos com misturas, englobando um total de nove formulações compostas com asfalto, SBS e TITAN. O teor de SBS variou entre 0 e 5% em peso e o de polietileno variou entre 0 e 2% em peso. Foi utilizado óleo aromático no teor de 4% em peso para todas as nove misturas. As misturas foram analisadas em três condições de envelhecimento: virgem, curto prazo (na estufa RTFO) e longo prazo (na estufa PAV). Foram realizados os seguintes ensaios reológicos: (i) de cisalhamento em regime oscilatório em diferentes condições de temperatura e frequência (para medida do módulo complexo e do ângulo de fase, usados na determinação do grau de desempenho, no cálculo dos parâmetros G*/sen(δ) e G*.sen(δ) e na construção de curvas-mestre), (ii) de viscosidade Brookfield, (iii) de fluência e recuperação sob múltiplas tensões (para medida do percentual de recuperação e da compliância não-recuperável), (iv) de varredura de amplitude linear (para cálculo do parâmetro a f e para ajuste do modelo de fadiga) e (v) de estabilidade à estocagem. Acerca das características escolhidas para mensurar a melhora ou piora das propriedades das misturas asfalto+SBS com a adição de TITAN, podem ser feitas as seguintes observações: (i) a estabilidade à estocagem é melhorada com a adição de TITAN, em particular no teores entre 1 e 2%; (ii) a sensibilidade ao envelhecimento tanto a curto quanto a longo prazos diminui com a adição de TITAN; (iii) a adição de TITAN aumenta a resistência à deformação permanente, à luz dos parâmetros Jnr e R e aumenta a sensibilidade dos ligantes asfálticos modificados com SBS a mudanças bruscas nos níveis de tensão aplicados; e (iv) a adição de TITAN contribui com o aumento da resistência à fadiga, à luz dos parâmetros Nf , a baixos níveis de deformação, e af , e a prejudica reduzindo o parâmetro Nf a altos níveis de deformação e aumentando a temperatura crítica de fadiga ou o parâmetro G*.sen(δ). Tendo por base estas evidências, é possível concluir que a adição de TITAN, em linhas gerais, melhorou a estabilidade dos ligantes asfálticos modificados com até 5,0% de SBS. Com base nas análises realizadas, é possível afirmar que teores da ordem de 1 a 2% de TITAN, para teores de SBS entre 3,0 e 5,0%, são recomendáveis, à luz das propriedades, índices e parâmetros analisados neste trabalho. / The SBS copolymer is the most widely used additive in asphalt binder modification, since it enhances many of the properties of the original material. A critical problem that arises from this type of modification is phase separation, which can be minimized by adding other modifiers to the formulation. A new oxidized, high-density polyethylene with low molecular weight (commercial designation of \"TITAN 9686\") was used in the study with the purpose of verifying the hypothesis that the addition of suitable contents of this modifier can improve the rheological properties of the SBS-modified binder. The laboratory matrix of formulations was based on the experiments with mixtures, and nine types of materials were prepared with asphalt binder, SBS and TITAN. The SBS contents ranged from 0 to 5% by weight, whereas the polyethylene contents ranged from 0 to 2% by weight. These formulations also contained 4% of aromatic oil by weight. Three aging conditions were selected: unaged, short-term aged in the rolling thin-film oven (RTFO) and long-term aged in the pressurized aging vessel (PAV). The following tests were carried out: (i) dynamic oscillatory shear at different temperatures and frequencies of loading for the determination of the complex modulus, the phase angles and the master curves, as well as the performance grades and the numerical values of the parameters G*/sin(δ) and G*.sen(δ); (ii) rotational viscosity; (iii) creep and recovery at multiple stress levels for the determination and the percent recovery and the nonrecoverable compliance; (iv) linear amplitude sweep, in order to calculate the parameter a f and fit the fatigue model to the data; and (v) storage stability. With respect to the characteristics used in the evaluation of the properties of the AC+SBS mixtures after the addition of TITAN, the following observations can be made: (i) storage stability is improved when TITAN is added to the formulation, especially at contents ranging from 1 to 2%; (ii) the sensitivity to the short-term and long-term aging processes decreased with the incorporation of TITAN; (iii) the changes in the R and the Jnr values indicate that the addition of TITAN makes the asphalt binder more resistant to rutting, and also increases the sensitivity of the SBS-modified binders to sudden increases in the stress level; and (iv) the presence of TITAN in the material leads to an increase in the fatigue resistance as based on the parameters Nf and af at low strain levels and the increases in the critical fatigue temperature and the parameter G*.sen(δ). With reference to these evidences, it is possible to conclude that the addition of TITAN generally improves the storage stability of the SBS-modified binders with no more than 5% of copolymer by weight. Based on the results of the present study, it is possible to say that percentages between 1 and 2% of TITAN by weight are recommended for SBS contents between 3 and 5% by weight.

No description available.

The present thesis entitled “Design and Synthesis of Novel Soft Composites from Physical Gels and Nanomaterials” deals with soft materials derived from low molecular weight gels and nanomaterials. Chapter 1 gives a general introduction and overview of the low molecular weight gel (LMOG) which forms the basis of the work. It delves with the history of research in physical gel field, design of different types of gelator molecules, their interesting self-assembly patterns, potential applications of these gelator molecules as well as challenges to design new gelator molecules. It also encompasses the relatively recent area of two component gel system to conveniently bypass the cumbersome synthetic protocol. The aspect of liquid crystallinity in the gel phase is also discussed to throw light on the pattern of assembly and potential uses of these materials. Towards the end there is a comprehensive discussion on the smart nanocomposites derived from LMOGs and nanomaterials. The design, synthesis and numerous applications of inorganic-organic hybrid composites are discussed. Chapter 2A describes the synthesis and characterization of a variety of fatty acid amides of different naturally occurring L-amino acids whose molecular structures are shown in Chart 2A.1. Some of them were found to form gels with various hydrocarbons. The gelation properties of these compounds were studied by a number of physical methods including FT-IR spectroscopy, X-ray diffraction, scanning electron microscopy (SEM), differential scanning calorimetry, rheology and it was found that gelation was critically dependent on the fatty acid chain length and nature of the amino acid. Among them, L-alanine based gelators were found to be the most efficient and versatile as they self-assemble into a layered structure to form the gel network. Mechanisms for the assembly and formation of gels from these molecules are discussed. (Structural formula) Chart 2A.1. Molecular structures of various fatty acid amides of different amino acids. Chapter 2B describes efficient gelation of both aliphatic and aromatic hydrocarbon solvents by a fatty acid amide, n-lauroyl-L-alanine (Chapter 2B.1). In addition, this compound was found to gelate the binary solvent mixtures comprised of aromatic hydrocarbon e.g. toluene and aliphatic hydrocarbon e.g. n-heptane. SEM and AFM showed that the fiber thickness of the gel assembly increases progressively in the binary mixture of n-heptane and toluene with increasing percentage of toluene. The self- Chart 2B.1. Molecular structure of the gelator. assembly patterns of the gels in individual solvents, n-heptane and toluene are however, different. The toluene gel consists of predominantly one type of morphological species while n-heptane gel has more than one species leading to polymorphic nature of the gel. The n-heptane gel is thermally more stable than the toluene gel as evident from the measurement using differential scanning calorimetry. The thermal stability of the gels prepared in the binary mixture of n-heptane and toluene is dependent on the composition of solvent mixture. Rheology of the gels shows that they are shear-thinning material and show characteristic behavior of soft viscoelastic solids. For the gels prepared from binary solvent mixture of toluene and n-heptane, with incorporation of more toluene in the binary mixture, the gel becomes a more viscoelastic solid. The time sweep rheology experiment demonstrates that the gel made in n-heptane has faster gel formation kinetics than that prepared in toluene. Chapter 2C describes lyotropic mesophase formation by organogels of different fatty acid amides of L-alanine in aromatic solvents. The helical assembly, characteristic of the cholesteric mesophase was found to exhibit reflection bands in circular dichroism spectra. The reflection bands corresponded to the pitch of the helical arrangement of the gelator molecules in the aromatic solvent. Transmission Electron Microscopy (TEM) showed presence of twist in the gel fibres. Polarising optical microscopy of the organogel exhibited weak birefringence confirming lyotropic nature of the assembly. Chapter 3 deals with synthesis and characterization of a new class of molecules with molecular structures shown in Chart 3.1. Among a variety of amino acid based molecules only alanine and serine based molecules were found to form translucent gels in aliphatic hydrocarbons such as n-heptane. TEM showed presence of fiber like structures for alanine whereas serine based gelator produces unique network like structures. SEM of the dried gels exhibited presence of three dimensional fibrous networks to spongy globular cauliflower like structures depending on the molecular structure of the gelators. Rheological studies of the organogels showed that they behave like typical LMOG gels. The oscillatory rheological studies demonstrated that the L-serine based gelator, 5 formed more viscoelastic solid like gel than that of L-alanine based gelator, 1 in n-heptane. Chart 3.1. Molecular structures of different amino acid derivatives from 3,4,5-tri-dodecyloxybenzoic acid scaffold. Chapter 4A presents design and properties of new nanocomposites from LMOG and metal nanoparticles (Chart 4A.1). The profound influence of nanoparticle (NP) incorporation into physical gels was evident from various microscopic and bulk properties. The interaction of nanoparticles with the gelator assembly was found to depend critically on the capping agent coating the nanoparticles. TEM showed long range Chart 4A.1. Molecular structures of the gelator and various AuNPs synthesized. directional assembly of the certain AuNPs along the gel fibers. SEM of the dried gels and nanocomposites indicated that the morphological transformation in the composite microstructures depended profoundly on the capping agent of the nanoparticle. Differential Scanning Calorimetry showed that gel formation from sol postponed to lower temperature with incorporation of AuNPs having capping agents which were able to interact with the gel fibers. Rheological studies indicated that the gel-nanoparticle composites exhibit greater rigidity as compared to the naked gel only when the capping agents were able to interdigitate into the gelator assembly. Also, very low percentage of the AuNPs incorporation could switch the cholesteric mesophase of gel assembly, as evident from circular dichroism. We have been able to define a relationship between materials and molecular properties via manipulation of the molecular structures of NP capping agents. Chapter 4B discusses the design and preparation of novel organogel-carbon nanotube composites by incorporation of single-walled carbon nanotubes (SWNT) into physical gels formed by an L-alanine based Low Molecular Mass Organogelator (Chart 4B.1). The gelation process and the properties of the resulting nanocomposites were found to depend on the kind of SWNTs incorporated in the gels. With pristine SWNTs, only a limited amount could be dispersed in the organogels. Attempted incorporation of higher amounts of pristine SWNTs led to precipitation from the gel. To improve their solubility in the gel matrix, a variety of SWNTs functionalized with different aliphatic and aromatic chains were synthesized (Chart 4B.1). Scanning electron microscope images of the nanocomposites showed that the texture and organization of the gel aggregates were altered upon incorporation of SWNTs. The microstructures of nanocomposites were found to depend on the kind of SWNTs used. Incorporation of functionalized SWNTs into the organogels depressed the sol to gel transition temperature, with the n-hexadecyl chain functionalized SWNTs being more effective than the n-dodecyl chain functionalized counterpart. Rheological investigations of pristine SWNT containing gels indicated that the flow of nanocomposites became resistant to applied stress at a very low wt-% of SWNT incorporation. Again, more effective control of flow behavior was achieved with functionalized SWNTs possessing longer hydrocarbon chains. This happens presumably via effective interdigitation of the pendant chains with the fatty acid amides of L-alanine in the gel assembly. Also, the helical cholesteric mesophase formed by the toluene gel could be switched to a layer stacked assembly by doping functional SWNT. Remarkably, by using a near IR laser irradiation at 1064 nm for a short duration (1 min) at room temperature, it was possible to selectively induce a gel-to-sol phase transition of the nanocomposites, while prolonged irradiation (30 min) of the organogel under identical conditions did not cause gel melting. Chart 4B.1. Molecular structures of the gelator and different functionalized SWNT synthesized. Chapter 5A presents design of two component hydrogels and their potential utilization as a template for metal nanoparticle synthesis. Among a variety of acids and amines (Chart 5A.1) only stearic acid or eicosanoic acid when mixed with di- or oligomeric amines in specific molar ratios form stable gels in water. The formation of such hydrogels depends on the hydrophobicity of the fatty acid, and also on the type of amine used. The gelation properties of these two component systems were investigated using electron microscopy, FTIR, 1H NMR spectroscopy, differential scanning calorimetry (DSC) and both single crystal and cast film X-ray diffraction. FTIR spectral analysis suggests salt formation during gelation. 1H NMR of the gels indicates that the fatty acid chains are immobilized in the gel state and when the gel is melted, these chains regain their mobility. Analysis of DSC data indicates that increase in spacer length in the di-/oligomeric amine lowers the gel melting temperature. Two of these gelator salts developed into crystals and structural details of such systems could be secured by single-crystal X-ray diffraction analysis. The structural information of the salts thus obtained was compared with the XRD data of the self-supporting films of those gels. Such analyses provided pertinent structural insight on the supramolecular interactions that prevail within these gelator assemblies. From the crystal structure it is confirmed that the multilayered lamellar aggregates exist in the gel and it also showed that only one plane of symmetry is present in the gel state. Finally, the hydrogel was used as a medium for the synthesis of silver nanoparticles. The nanoparticles were found to position themselves on the fibers and produce a long ordered assembly of gel-nanoparticle composite (Figure 5A.1). Chart 5A.1. Structures and abbreviations of different acids and amines checked for gelation. Figure 5A.1. TEM images of gel-Ag-NP composite. (a) Ag-NP synthesized in hydrogel of SA-IBPA (1:3.5), (b) Magnified images of Ag-NP preferentially residing on gel fibers. Chapter 5B demonstrates the aptitude of supramolecular hydrogel formation using simple bile acids e.g. lithocholic acid (LCA) in aqueous solution containing di- or oligomeric amines (Chart 5B.1). By variation of the choice of the amines in such mixture the hydrogelation properties could be modulated. However, replacement of LCA by cholic acid or deoxycholic acid resulted in no hydrogelation. FT-IR studies show that the carboxylate and ammonium residues of the two components are primarily involved in salt formation. This promotes further assembly of the components reinforced by continuous Chart 5B.1. Structures and abbreviations of different bile acids and amines checked for gelation. hydrogen bonded network leading to gelation. Electron microscopy shows that the morphology of the gels of two component systems which also depends strongly on the amine part. Variation of amine component from the simple ethanediamine (EDA) to oligomeric amine with lithocholic acid changes the morphology of the assembly from long one dimensional nanotubes to three dimensional complex structures. Single crystal X-ray diffraction analysis with one of the amine-LCA complexes suggested the motif of fiber formation where the amines participate with the carboxylate and hydroxyl moiety through H-bonding and electrostatic forces. The rheological properties of this class of two component system provide clear evidence that this system is a shear-sensitive hydrogel and the flow behavior can be modulated varying the acid-amine ratio. From small angle neutron scattering study, it becomes clear that loose gel from LCA-EDA shows scattering oscillation due to the presence of non interacting nanotubules while for gels of LCA with oligomeric amine the individual fibers come together to form complex three dimensional structures of higher length scale.(For structural formula pl refer the pdf file)

It is widely known that early estimates about the binding properties of drug candidates are important in the drug discovery process. Surface plasmon resonance (SPR) biosensors have become a standard tool for characterizing interactions between a great variety of biomolecules and it offers a unique opportunity to study binding activity. The aim of this project was to develop a SPR based assay for pre-screening of low molecular weight (LMW) drug compounds, to enable filtering away disturbing compounds when interacting with drugs. The interaction between 47 LMW compounds and biological ligands were investigated using the instrument BiacoreTM, which is based on SPR-technology.