Die Herzinsuffizienz ist trotz zahlreicher Therapiemöglichkeiten immer noch eine der häufigsten chronischen Erkrankung und Todesursachen in westlichen Industrienationen. Eine zentrale Rolle in der Regulation der effizienten Herzkontraktion nimmt die zyklisches Adenosin-3’,5’-monophophat(cAMP)-Signalkaskade ein, wobei Veränderungen in der Kompartimentierung des sekundären Botenstoffes bisher nicht vollständig verstanden sind. Ziel dieser Studie war es deshalb Regulationsmechanismen des lokalen cAMP-Pools der Mikrodomäne der ATP-abhängigen Calciumpumpe 2a des sarkoplasmatischen und endoplasmatischen Retikulums (SERCA2a) in kardialen Mausmyozyten unter den pathologischen Rahmenbedingungen der Herzinsuffizienz zu untersuchen. Hierfür wurde ein post-Myokardinfarkt Mausmodell an einer transgene Mauslinie verwendet, die einen cAMP-abhängigen auf Förster-Resonanz-Energietransfer(FRET)-basierenden Biosensor, lokalisiert in der SERCA2a-Mikrodomäne, in vivo exprimiert. Mit Hilfe von Echtzeit-FRET-Messungen an frisch isolierten, lebenden Kardiomyozyten wurden die Beiträge der am Herzen relevanten Phosphodiesterase(PDE)-Familien zur Begrenzung des lokalen cAMP-Pools in der SERCA2a-Domäne 12 Wochen nach Myokardinfarkt gemessen und mit einer Kontrollgruppe (Sham) verglichen. Hierbei zeigte sich, dass in der Mikrodomäne sowohl unter Ruhebedingungen, als auch nach β-adrenerger Vorstimulation, eine signifikante Aktivitätsminderung der PDE4, verglichen mit der Sham-Gruppe, nachweisbar ist. Da dies mit Veränderungen im lokalen cAMP-Pool der die SERCA2a reguliert einhergeht, bietet diese Studie also eine interessante Grundlage für die weitere Untersuchung der im Krankheitsfall auftretenden Funktionsabweichungen.

Thèse réalisée en cotutelle avec l'université Montpellier2 dans le laboratoire de pharmacologie moléculaire de Jean-Philippe Pin à l'institut de génomique fonctionnelle (IGF), Montpellier, France. / Les récepteurs couplés aux protéines G (RCPG) sont une famille très diversifiée de protéines membranaires capables de répondre à un grand nombre de signaux chimiques tels que des photons, des molécules odorantes, ou des hormones. En plus de cette diversité, l’étude des RCPG montre que des associations protéiques spécifiques multiplient les possibilités de signalisation de chacun de ces récepteurs. En permettant d’atténuer, de potentialiser, ou de générer une nouvelle voie de signalisation, l’association des RCPG en oligomères s’avère une importante source de diversité. L’utilisation du transfert d’énergie de résonance de bioluminescence (BRET) qui permet de détecter les interactions protéiques a révélé de nombreuses associations de RCPG. Durant cette thèse, des outils ont été développés pour combiner efficacement le BRET à des essais de complémentation de protéines (PCA) dans le but de savoir si l’oligomérisation des RCPG pouvait impliquer plus de deux récepteurs. Les résultats présentés montrent que les récepteurs de chimiokines CXCR4 et CCR2 forment des homo et hétéro tétramères, et que l’activation d’un dimère CCR2 peut moduler la conformation d’un dimère CXCR4 par un changement conformationnel trans-récepteur. La coopérativité négative de liaison de ligand qui a été démontrée auparavant entre CXCR4 et CCR2 dans des lymphocytes T CD4+ exprimant les récepteurs de manière endogène confirme la validité biologique de cette interaction. Les données présentées suggèrent également que ces complexes peuvent engager les effecteurs Gαi et β-arrestine2, indiquant qu’ils représentent la forme fonctionnelle de ces récepteurs. Enfin, nous avons pu confirmer que chaque récepteur de l’hétérodimère CXCR4-CCR2 est impliqué dans l’engagement des effecteurs lors de l’activation de CCR2. Un autre niveau de complexité dans la signalisation des RCPG est atteint par leur capacité à coupler de multiples protéines G. La liaison du facteur dérivé des cellules stromales (SDF-1) au récepteur CXCR4 permet la migration des lymphocytes T par une voie de signalisation dépendante de la protéine Gαi. Nous avons pu démontrer en revanche que la migration des cellules de cancer du sein était initiée par un couplage de CXCR4 à la voie Gα13-Rho pour former des métastases dans des organes distants. Enfin, un dernier niveau de régulation des RCPG a été abordé par l’étude de la phosphorylation de CXCR4 suite à son activation, qui permet la désensibilisation du récepteur et l’engagement de voies de signalisation dépendantes de la β-arrestine. Il apparaît que la désensibilisation de la voie du calcium serait médiée par la phosphorylation de CXCR4 par les kinases des RCPG (GRK) GRK2 et GRK6 et le recrutement de β- arrestine2, alors GRK3, GRK6 et la β-arrestine1 potentialiseraient l’activation des kinases régulées par les signaux extracellulaires (ERK1/2). Nous suggérons également que c’est la phosphorylation de l’extrémité C-terminale de CXCR4 qui permettrait son association avec la β-arrestine. / G protein-coupled receptors (GPCRs) are a diverse family of membrane proteins capable of responding to a large number of extracellular stimuli including photons, odorant molecules and hormones. In addition to this diversity, it has been shown that GPCRs form specific protein:protein interactions, multiplying the signalling possibilities of each of these receptors. With the ability to diminish, to potentiate or even generate new signalling pathways, the oligomeric association of GPCRs plays an important role in generating this diversity. The use of bioluminescence resonance energy transfer (BRET), which allows the detection of interactions among proteins, has revealed numerous associations between GPCRs. During this thesis, tools have been developed that effectively combine BRET with protein complementation assays (PCA) with the goal of determining if interactions between GPCRs could involve more than two receptors. The results show that the chemokine receptors CXCR4 and CCR2 form both homo and hetero tetramers, and that the activation of a dimer of CCR2 can modulate the conformation of a CXCR4 dimer through a transreceptor conformational change. Negative cooperativity of ligand binding has previously been demonstrated between CXCR4 and CCR2 in CD4+ T lymphocytes endogenously expressing the receptors, confirming the biological validity of this interaction. The data presented also suggests that these complexes can engage the effector proteins Gαi and β- arrestin 2, indicating that they represent a functional form of the receptors. Furthermore, we have confirmed that each receptor of the CXCR4-CCR2 heterodimer is implicated in the engagement of effectors during the activation of CCR2. An additional level of complexity in GPCR-promoted signaling exists in their capacity to couple of multiple G proteins. Binding of stromal cell-derived factor-1 (SDF-1) to CXCR4 is known to promote T lymphocyte migration through a Gαi-dependent signalling pathway. In addition to this mechanism, we have demonstrated that breast cancer cell migration can initiated by a coupling of CXCR4 to the Gα13-Rho pathway, leading to the formation of metastases in distant organs. Finally, a novel level of GPCR regulation was revealed through the study of CXCR4 phosphorylation following its activation, which leads to the desensitization of the receptor and the engagement of β-arrestin-dependent signalling pathways. It appears that the desensitization of calcium signalling is mediated through the phosphorylation of CXCR4 by the GPCR kinases (GRKs) GRK2 and GRK6 and the recruitment of β-arrestin 2, whereas GRK3, GRK6 and β-arrestin 1 potentiate the activation of extracellular regulated kinase (ERK1/2). We also propose that the phosphorylation of the far C-terminal tail of CXCR4 is required for the interaction between the receptor and β-arrestin.

No description available.

A kinetic model of electronic energy migration within pairs of photophysically non-identical fluorophores has been developed. The model applies to fluorescent groups that exhibit different photophysical and spectral properties when attached to different positions in a macromolecule. The energy migration within such asymmetric pairs is partially reversible, which leads to the case of partial donor-donor energy migration (PDDEM). The model of PDDEM is an extension of the recently developed donor-donor energy migration model (DDEM, F. Bergström et al, PNAS 96 (1999) 12477), and applies to quantitative measurements of energy migration rates and distances within macromolecules. One important distinction from the DDEM model is that the distances can be obtained from fluorescence lifetime measurements. A model of fluorescence depolarisation in the presence of PDDEM is also presented. To experimentally test the PDDEM approach, different model systems were studied. The model was applied to measure distances between rhodamine and fluorescein groups within on-purpose synthesised molecules that were solubilised in lipid bilayers. Moreover, distances were measured between BODIPY groups in mutant forms of the plasminogen activator inhibitor of type 2 (PAI-2). Measurements of both the fluorescence intensity decays and the time-resolved depolarisation were performed. The obtained distances were in good agreement with independent determinations. Finally, the PDDEM within pairs of donors is considered, for which both donors exhibit a nonexponential fluorescence decay. In this case it turns out that the fluorescence relaxation of a coupled system contains distance information even if the photophysics of the donors is identical. It is also demonstrated that the choice of relaxation model has a negligible effect on the obtained distances. The latter conclusion holds also for the case of donor-acceptor energy transfer.

The global lighting source energy consumption accounts for about 22% of the total electricity generated. New high-efficiency solid-state light sources are needed to reduce the ever increasing demand for energy. Single-phased emitter-based composed of transparent conducting oxides (TCOs) nanocrystals and fluorescent dyes can potentially revolutionize the typical composition of phosphors, the processing technology founded on the binding of dye acceptors on the surface of nanocrystals, and the configurations of the light-emitting diodes (LEDs) and electroluminescence devices. The hybrid white-light-emitting nanomaterial is based on the expanded spectral range of the donor-acceptor pair (DAP) emission originated from the γ-gallium oxide nanocrystals via Förster resonance energy transfer (FRET) to the surface-anchored fluorescent dyes. The emission of the nanocrystals and the sensitized emission of the chromophore act in sync as an internal relaxation upon the excitation of the γ–gallium oxide nanocrystals. It extends the lifetime of the secondary fluorescent dye chromophore and the internal relaxation within this hybrid complex act as a sign for a quasi single chromophore. The model system of white-light-emitting nanostructure system developed based on this technology is the γ–gallium oxide nanocrystals-Rhodamine B lactone (RBL) hybrid complex. The sufficient energy transfer efficiency of 31.51% within this system allowed for the generation of white-light emission with the CIE coordinates of (0.3328, 0.3380) at 5483 K. The relative electronic energy differences of the individual components within the hybrid systems based on theoretical computation suggested that the luminance of the nanocomposite comprised of RBL is dominantly mediated by FRET. The production of white-light-emitting diode (WLED) based on this technology have been demonstrated by solution deposition of the hybrid nanomaterials to the commercially available ultraviolet (UV) LED due to the versatility and chemical compatibility of the developed phosphors.

This study focuses on preparing surface enhanced fluorescence (SEF) substrates for use in the enhancement of the emission signal of rhodamine B and fluorescein dyes. Fluorescence spectroscopy has been widely utilized owing to its high sensitivity. SEF is a process where the interactions of fluorophores with the localized surface plasmons of metal nanoparticles results in fluorescence enhancement, increased photostability and rates of system radiative decay which leads to a decreased lifetime. One of the most important factors of SEF studies is to provide a uniform distance between fluorophore and metal nanoparticle in a controlled manner / otherwise, F&ouml / rster resonance energy transfer takes place from fluorophore to metal nanoparticle and emission intensity of fluorophore is quenched. The spherical gold and silver nanoparticles were prepared using the well known and straightforward chemical reduction method, in which sodium citrate acted both as a reducing agent and a stabilizer around the formed nanoparticles. Silver and gold were chosen because of their high plasmon field enhancement. Since plasmon field strongly depends on the shape and size of the nanoparticles, the prepared nanoparticles were characterized using absorption spectroscopy and field emission scanning electron microscopy (FE-SEM). Prior to deposition of silver or gold nanoparticles on glass slides, the slides were derivatized by immersing them into an aqueous solution of 3-Aminopropylethoxysilane (APTES). Following derivatization, silver or gold nanoparticles were deposited by immersing the slides into the colloid mixture. Metal nanoparticle coated slides were characterized using absorption spectroscopy and field emission scanning electron microscopy (FE-SEM). Surface enhanced Raman scattering (SERS) measurements were carried out to observe the plasmon efficiency of the deposited nanoparticles. The SERS measurements were repeated for the duration of two weeks in order to check the stability of the plasmon efficiency. In this study, different types of materials (silica, zinc oxide, gold, stearic acid.) were employed as spacers to observe their effects on fluorescence enhancement. Physical vapor deposition (PVD) and Langmuir-Blodgett (LB) film deposition techniques were used for the formation of the spacer within the substrate. Fluorescence enhancement of rhodamine B and fluorescein was observed on the prepared SEF substrates. Obtained enhancement factors indicate that SEF substrates have the potential for sensitivity improvements of fluorescence sensing in many fields.

Les récepteurs couplés aux protéines G (RCPG) sont une famille très diversifiée de protéines membranaires capables de répondre à un grand nombre de signaux chimiques tels que des photons, des molécules odorantes, ou des hormones. En plus de cette diversité, l’étude des RCPG montre que des associations protéiques spécifiques multiplient les possibilités de signalisation de chacun de ces récepteurs. En permettant d’atténuer, de potentialiser, ou de générer une nouvelle voie de signalisation, l’association des RCPG en oligomères s’avère une importante source de diversité. L’utilisation du transfert d’énergie de résonance de bioluminescence (BRET) qui permet de détecter les interactions protéiques a révélé de nombreuses associations de RCPG. Durant cette thèse, des outils ont été développés pour combiner efficacement le BRET à des essais de complémentation de protéines (PCA) dans le but de savoir si l’oligomérisation des RCPG pouvait impliquer plus de deux récepteurs. Les résultats présentés montrent que les récepteurs de chimiokines CXCR4 et CCR2 forment des homo et hétéro tétramères, et que l’activation d’un dimère CCR2 peut moduler la conformation d’un dimère CXCR4 par un changement conformationnel trans-récepteur. La coopérativité négative de liaison de ligand qui a été démontrée auparavant entre CXCR4 et CCR2 dans des lymphocytes T CD4+ exprimant les récepteurs de manière endogène confirme la validité biologique de cette interaction. Les données présentées suggèrent également que ces complexes peuvent engager les effecteurs Gαi et β-arrestine2, indiquant qu’ils représentent la forme fonctionnelle de ces récepteurs. Enfin, nous avons pu confirmer que chaque récepteur de l’hétérodimère CXCR4-CCR2 est impliqué dans l’engagement des effecteurs lors de l’activation de CCR2. Un autre niveau de complexité dans la signalisation des RCPG est atteint par leur capacité à coupler de multiples protéines G. La liaison du facteur dérivé des cellules stromales (SDF-1) au récepteur CXCR4 permet la migration des lymphocytes T par une voie de signalisation dépendante de la protéine Gαi. Nous avons pu démontrer en revanche que la migration des cellules de cancer du sein était initiée par un couplage de CXCR4 à la voie Gα13-Rho pour former des métastases dans des organes distants. Enfin, un dernier niveau de régulation des RCPG a été abordé par l’étude de la phosphorylation de CXCR4 suite à son activation, qui permet la désensibilisation du récepteur et l’engagement de voies de signalisation dépendantes de la β-arrestine. Il apparaît que la désensibilisation de la voie du calcium serait médiée par la phosphorylation de CXCR4 par les kinases des RCPG (GRK) GRK2 et GRK6 et le recrutement de β- arrestine2, alors GRK3, GRK6 et la β-arrestine1 potentialiseraient l’activation des kinases régulées par les signaux extracellulaires (ERK1/2). Nous suggérons également que c’est la phosphorylation de l’extrémité C-terminale de CXCR4 qui permettrait son association avec la β-arrestine. / G protein-coupled receptors (GPCRs) are a diverse family of membrane proteins capable of responding to a large number of extracellular stimuli including photons, odorant molecules and hormones. In addition to this diversity, it has been shown that GPCRs form specific protein:protein interactions, multiplying the signalling possibilities of each of these receptors. With the ability to diminish, to potentiate or even generate new signalling pathways, the oligomeric association of GPCRs plays an important role in generating this diversity. The use of bioluminescence resonance energy transfer (BRET), which allows the detection of interactions among proteins, has revealed numerous associations between GPCRs. During this thesis, tools have been developed that effectively combine BRET with protein complementation assays (PCA) with the goal of determining if interactions between GPCRs could involve more than two receptors. The results show that the chemokine receptors CXCR4 and CCR2 form both homo and hetero tetramers, and that the activation of a dimer of CCR2 can modulate the conformation of a CXCR4 dimer through a transreceptor conformational change. Negative cooperativity of ligand binding has previously been demonstrated between CXCR4 and CCR2 in CD4+ T lymphocytes endogenously expressing the receptors, confirming the biological validity of this interaction. The data presented also suggests that these complexes can engage the effector proteins Gαi and β- arrestin 2, indicating that they represent a functional form of the receptors. Furthermore, we have confirmed that each receptor of the CXCR4-CCR2 heterodimer is implicated in the engagement of effectors during the activation of CCR2. An additional level of complexity in GPCR-promoted signaling exists in their capacity to couple of multiple G proteins. Binding of stromal cell-derived factor-1 (SDF-1) to CXCR4 is known to promote T lymphocyte migration through a Gαi-dependent signalling pathway. In addition to this mechanism, we have demonstrated that breast cancer cell migration can initiated by a coupling of CXCR4 to the Gα13-Rho pathway, leading to the formation of metastases in distant organs. Finally, a novel level of GPCR regulation was revealed through the study of CXCR4 phosphorylation following its activation, which leads to the desensitization of the receptor and the engagement of β-arrestin-dependent signalling pathways. It appears that the desensitization of calcium signalling is mediated through the phosphorylation of CXCR4 by the GPCR kinases (GRKs) GRK2 and GRK6 and the recruitment of β-arrestin 2, whereas GRK3, GRK6 and β-arrestin 1 potentiate the activation of extracellular regulated kinase (ERK1/2). We also propose that the phosphorylation of the far C-terminal tail of CXCR4 is required for the interaction between the receptor and β-arrestin. / Thèse réalisée en cotutelle avec l'université Montpellier2 dans le laboratoire de pharmacologie moléculaire de Jean-Philippe Pin à l'institut de génomique fonctionnelle (IGF), Montpellier, France.

The global lighting source energy consumption accounts for about 22% of the total electricity generated. New high-efficiency solid-state light sources are needed to reduce the ever increasing demand for energy. Single-phased emitter-based composed of transparent conducting oxides (TCOs) nanocrystals and fluorescent dyes can potentially revolutionize the typical composition of phosphors, the processing technology founded on the binding of dye acceptors on the surface of nanocrystals, and the configurations of the light-emitting diodes (LEDs) and electroluminescence devices. The hybrid white-light-emitting nanomaterial is based on the expanded spectral range of the donor-acceptor pair (DAP) emission originated from the γ-gallium oxide nanocrystals via Förster resonance energy transfer (FRET) to the surface-anchored fluorescent dyes. The emission of the nanocrystals and the sensitized emission of the chromophore act in sync as an internal relaxation upon the excitation of the γ–gallium oxide nanocrystals. It extends the lifetime of the secondary fluorescent dye chromophore and the internal relaxation within this hybrid complex act as a sign for a quasi single chromophore. The model system of white-light-emitting nanostructure system developed based on this technology is the γ–gallium oxide nanocrystals-Rhodamine B lactone (RBL) hybrid complex. The sufficient energy transfer efficiency of 31.51% within this system allowed for the generation of white-light emission with the CIE coordinates of (0.3328, 0.3380) at 5483 K. The relative electronic energy differences of the individual components within the hybrid systems based on theoretical computation suggested that the luminance of the nanocomposite comprised of RBL is dominantly mediated by FRET. The production of white-light-emitting diode (WLED) based on this technology have been demonstrated by solution deposition of the hybrid nanomaterials to the commercially available ultraviolet (UV) LED due to the versatility and chemical compatibility of the developed phosphors.

Chapter 1: Luminescence property of lanthanide and its applications Lanthanides are well-known for their unique luminescence property and have found widespread applications in sensing, bioimaging, lasers, optoelectronic devices, etc. Due to Laporte forbidden f-f transitions, lanthanides have very low intrinsic emission. The problem can be overcome by use of an ‘antenna’, which is an organic chromophore with excited state energy higher than the lanthanides’ emitting levels. Thereby it is possible to get highly emitting lanthanide complexes through energy transfer from the ‘antenna’. Due to long lifetime of lanthanides’ excited states, it's possible to perform time delayed measurement which is useful in bioassays and bioimaging since the short-lived background emission is effectively filtered. Research in supramolecular metallogels has grown rapidly in recent years, and already proven to have potential for designing advanced materials for a variety of applications, such as sensing, optoelectronics, catalysis, nanoparticle synthesis, biomedicine etc. A supramolecular gel where a lanthanide is an integrated part of it can combine the advantages of the supramolecular gel along with the unique property of lanthanide luminescence and thus such materials can be explored for potential applications. This chapter discusses the background information on the unique luminescence of lanthanides, and some examples of the applications of lanthanide complexes and lanthanide based gels. Chapter 2: Lanthanide luminescence based enzyme sensing in hydrogels This chapter describes the use of Tb/Eu luminescence in the sensing of biologically important enzymes. We discovered the sensitization of Eu(III) in Eu-cholate gel by 1-hydroxypyrene, and of Tb(III) in Tb-cholate gel by 2,3-dihydroxynaphthalene. These two sensitizers were covalently modified and sensitizer-appended hybrid (artificial) enzyme substrates were prepared for a few biologically important hydrolases. The covalently modified sensitizer termed as “pro-sensitizers”, didn't sensitize Tb(III)/Eu(III) in the hydrogel and no photoluminescence was observed. In the presence of the appropriate enzyme in the hydrogel, the pro-sensitizer was cleaved to liberate the sensitizer, which led to an enhancement of luminescence with time. Alkaline phosphatase and β-lactamase were assayed using pyrene phosphate and pyrene-oxo-cephalosporanic acid derivatives, respectively, in Eu-cholate hydrogel (Figure 1). β-Galactosidase was assayed using Tb(III) luminescence in Tb-cholate gel. The enzyme detection was based on red/green luminescence response from the gel. To understand the behaviour of the enzymes in the hydrogel, kinetic parameters were determined. The detection of different enzymes was also demonstrated in natural/biological samples like blood serum, milk and almond extract. Figure 1. Three different pro-sensitizers used for alkaline phosphatase, β-lactamase and β-galactosidase assays Chapter 3: Enzyme sensing on paper discs using lanthanide luminescence Developing a user-friendly biosensor is of considerable importance in clinical and analytical chemistry. Paper based biosensor design is an emerging field of research and paper based point of care (PoC) testing devices have already found applications in clinical, veterinary, environmental, food safety, security etc. Paper is made out of natural cellulose fibres, and has advantages of low cost, biodegradability, biocompatibility, and user friendliness. Paper based sensors have been used for the detection of ions, glucose, proteins, nucleic acids, antigens etc., with mostly colorimetric, fluorescent, electrochemical, chemiluminescence and Electrochemiluminescence readouts. In this work, the non luminescent Tb(III) and Eu(III) were embedded on paper as their cholate hydrogels and were used for detecting different hydrolases. Pro-sensitizers, as reported in Chapter 2, were immobilized on paper for the detection of a specific enzyme. The “pro-sensitizer” released the sensitizer upon enzyme action and led to luminescence enhancement from the gel coated paper disc. By this way, four different hydrolase enzymes detection were carried out using Tb(III)/Eu(III) luminescence as the readout (Figure 2) and the practical utility was demonstrated by the detection of specific enzymes in natural/biological samples. This paper disc based enzyme sensing provides a simpler and user friendly approach over the contemporary approach of enzyme sensing typically carried out in solution. Figure 2. Paper based biosensors for hydrolase enzymes Chapter 4: Luminescence resonance energy transfer in self-assembled supramolecular hydrogels Luminescence resonance energy transfer is a phenomenon of energy transfer between a FRET (Förster resonance energy transfer) pair, where a lanthanide is the donor. Lanthanides have attracted attention for the last several decades for their unique luminescence properties. LRET is a FRET process along with added advantages of Lanthanides, i.e. long lifetime of the lanthanides and characteristics emission spectra. LRET has been used for studying interaction of biomacromolecues, immunoassay, bioassays, etc. LRET in either a supramolecular organogel or a hydrogel is still an unexplored field. In this work we showed the energy transfer from Tb(III) to two different red emitting dyes in Tb-cholate hydrogel (Figure 3). The self assembly processes during hydrogelation assisted the energy transfer process without any need for laborious synthesis. The energy transfer was confirmed by time delayed emission, excitation spectra and lifetime measurement in the hydrogels. Energy transfer was observed both in the gel and the xerogel states. These luminescent materials may find applications in optoelectronics. Figure 3. Energy transfer from DHN to Tb3+ and then to red emitting dyes (Rhodamine B & Sulforhodamine 101) in the Tb-Cholate hydrogel Chapter 5: Room temperature synthesis of Lanthanide phosphate nanoparticle using a gel as a soft template Lanthanide orthophosphates are an important class of rare earth compounds, and have widespread applications in laser materials, optical sensors, heat resistance materials, solar cell etc. There are several methods in the literature for the synthesis of rare earth phosphate nanoparticles. Most of these are based on hydrothermal, microwave assisted, micro emulsion, arrested precipitation etc., which invariably dependent on stringent conditions such as (i) high temperatures and pressures, (ii) inert atmosphere and (iii) the use of external capping agents as stabilizers. Synthesis of such nanoparticles under milder conditions would always be preferable. In this context, the preparation of nanoparticles using hydrogel as template can be a possible alternative approach. The LnPO4 nanoparticle synthesis was done by diffusion of Na3PO4 in Ln-cholate hydrogels. The particles were characterized by transmission electron microscopy (TEM) and powder XRD analysis. TEM showed the formation of 3-4 nm size particles with an ordered arrangement on the gel fibre. This work demonstrated that the lanthanide cholate gels have high potential for the synthesis, and immobilization of lanthanide phosphate nanoparticles at room temperature to produce new types of composite materials. (For structural formula pl see the abstract pdf file)

No description available.