Yes / The possibility of using differential pre‐heating prior to supramolecular gelation to control the balance between hydrogen‐bonding and aromatic stacking interactions in supramolecular gels and obtain consequent systematic regulation of structure and properties is demonstrated. Using a model aromatic peptide amphiphile, Fmoc‐tyrosyl‐leucine (Fmoc‐YL) and a combination of fluorescence, infrared, circular dichroism and NMR spectroscopy, it is shown that the balance of these interactions can be adjusted by temporary exposure to elevated temperatures in the range 313–365 K, followed by supramolecular locking in the gel state by cooling to room temperature. Distinct regimes can be identified regarding the balance between H‐bonding and aromatic stacking interactions, with a transition point at 333 K. Consequently, gels can be obtained with customizable properties, including supramolecular chirality and gel stiffness. The differential supramolecular structures also result in changes in proteolytic stability, highlighting the possibility of obtaining a range of supramolecular architectures from a single molecular structure by simply controlling the pre‐assembly temperature. / FP7 Ideas: European Research Council. Grant Number: 258775

No description available.

Design and synthesis of novel supramolecular architectures is an interesting area of research in the last two decades. Intermolecular interactions assisted self-assembly of molecular and macromolecular building blocks play an important role in obtaining the desired shape and function of the supramolecular architectures. A combination of the classical covalent synthesis with the self-assembly assisted formation of well-defined architectures (noncovalent synthesis) allows us to develop novel multifunctional materials. Our approach in this area is focused on the design of novel molecular and biomolecular building blocks and the optimization of structure-property relationship of the materials using self-assembly approach. This presentation will focus on our recent efforts on the design and synthesis of polymers and oligopeptides for investigation of the self-assembly and fine-tuning the structure-property relationship. Also, some highlights will be given on our initial investigation on how hard minerals are synthesized by natural molecules through the self-assembly processes. / Singapore-MIT Alliance (SMA)

Different approaches to surface modification were investigated in this work on gold, glassy carbon, multi-walled carbon nanotube paper and on single-walled carbon nanotubes adsorbed on glassy carbon. These approaches include electrochemical grafting, electropolymerisation, click chemistry, axial ligation, adsorption and self-assembled monolayers. The modified surfaces were characterised using a variety of techniques; predominantly electrochemistry, scanning electrochemical microscopy and X-ray photoelectron spectroscopy. For the formation of self-assembled monolayers on gold, four new manganese(III) phthalocyanines (1a-d), octa-substituted at the peripheral position with pentylthio, decylthio, benzylthio, and phenylthio groups were synthesized and characterised. X-ray photoelectron spectroscopy was used to show the formation of a sulphur-gold bond. A number of approaches using 4-azidoaniline (2a) combined with azide-alkyne click chemistry and electrochemistry were also used to anchor ferrocene and pyridine moieties on to the carbon surfaces, including direct in situ diazotation and grafting, electropolymerisation, and the synthesis of the diazonium salt followed by grafting. Iron phthalocyanine was linked to the pyridine-clicked surfaces through axial ligation, where the strong axial bond formed by the interaction between the central metal and the lone pair of the nitrogen in the pyridine group resulted in stable modified electrodes. The potential of these surfaces for the detection of analytes such as thiocyanate, hydrazine and sulphite are briefly shown as well. This work also describes for the first time the possibility of performing local micro-electrochemical grafting of a gold substrate by 4-azidobenzenediazonium (2b) using scanning electrochemical microscopy in a single and simple one step approach, without complications from adsorption.

Ultrasound directed self-assembly (DSA) relies on the acoustic radiation force associated with a standing ultrasound wave to organize particles dispersed in a fluid medium into specific patterns. State-of-the-art ultrasound DSA methods can only organize particles into (quasi-)periodic patterns, limited by the use of single-frequency ultrasound wave fields. Acoustic holography and acoustic waveguides provide alternatives to assembling complex patterns of particles, but generally provide low spatial accuracy and are not re-configurable because they require custom hardware for each specific pattern of particles, which is impractical. We introduce multi-frequency ultrasound wave fields to organize particles in non-periodic patterns. We theoretically derive and experimentally validate a solution methodology to determine the operating parameters (frequency, amplitude, phase) of any number and spatial arrangement of ultrasound transducers, required to assemble spherical particles dispersed in an inviscid fluid medium into any specific two-dimensional pattern. The results show that multi-frequency ultrasound DSA enables the assembly of complex, non-periodic patterns of particles with substantially fewer ultrasound transducers than single-frequency ultrasound DSA, and without incurring a penalty in terms of accuracy. The results of this work fundamentally transform the state-of-the-art knowledge of ultrasound DSA. Multi-frequency ultrasound wave fields enable a near-unlimited complexity of patterns of particles that can be assembled, increasing the relevance of the technology to practical implementation in engineering applications such as manufacturing of engineered composite materials that derive their properties from the spatial organization of the filler in the matrix material. Although this work focuses specifically on ultrasound wave fields, the theoretical model is valid for all wave phenomena. / Master of Science / Ultrasound directed self-assembly (DSA) is the process where particles dispersed in a fluid medium assemble into specific patterns due to their interactions with a sound wave and/or other particles. Current ultrasound DSA methods use a single-frequency ultrasound wave to assemble particles into specific patterns, which creates repeating patterns within the fluid medium. Other methods of assembling particles that allow for more complex, non-repeating patterns generally provide low spatial accuracy and do not allow dynamically changing the pattern as they require custom hardware for each specific pattern of particles, rendering these methods impractical. We use many ultrasound waves each with a different frequency to organize particles into complex, non-repeating patterns, which we call multi-frequency ultrasound DSA. We theoretically derive and experimentally validate a method that allows us to assemble any specific two-dimensional pattern of particles using multi-frequency ultrasound DSA. The results show that multi-frequency ultrasound DSA enables the assembly of complex, non-repeating patterns of particles with substantially resources than single-frequency ultrasound DSA, and without incurring a penalty in terms of accuracy. Multi-frequency ultrasound DSA enables a near-unlimited complexity of patterns of particles that can be assembled, increasing the relevance of the technology to practical implementation in engineering applications.

The understanding of self-assembly processes is important for fabrication of well-defined structures with new functionalities for applications in the area of biomedical sciences, material sciences and electronics. In this thesis, two types of self-assembly processes are described: (1) self-assembly of fullerene derivatives in water and (2) self-assembly on surfaces using layer-by-layer (LbL) approach. The various interactions and parameters involved in the self-assembly are detailed in the introductory chapter 1. The various internal parameters like molecular geometry, intramolecular and intermolecular forces that guides the self-assembly process of amphiphiles in water are discussed. The experimental procedures used in the present thesis for the fabrication of nanostructures via self-assembly approach are also described. In the later part of the chapter, the LbL technique for fabrication of thin films and microcapsules is reviewed where various interactions involved in the growth of LbL assembly are discussed. The effect of ionic strength and pH on the growth and property of LbL assemblies is elaborated. A brief discussion of the materials used in the thesis ‒ fullerene, bovine serum albumin (BSA) and nanocrystalline cellulose (NCC) is also provided The self-assembly behaviour of amphiphilic fullerene derivatives are described in chapter 2. Fullerene is anisotropically substituted with five polar hydroxyl groups using organo-copper reagent. The derivative can interact in water via the van der Waals and hydrophobic interactions of the fullerene moiety as well as the intermolecular hydrogen bonding among the hydroxyl groups and also with water. The penta-hydroxy fullerene derivative self-assembles in water as vesicular structures. The size of these vesicles can be varied by modifying the kinetics of self-assembly which was done by changing the rate of addition of non-solvent (water) to the solution of the fullerene derivative. In the second derivative, the hydroxyl groups are substituted with less polar methoxy groups. The penta-methoxy fullerene derivative cannot participate in inter-molecular hydrogen bonding formation unlike the penta-hydroxy derivative but there is possibility of hydrogen bond formation with water where oxygens on methoxy group can act as hydrogen bond acceptor. The penta-methoxy fullerene does not show any vesicle formation in water. The computational simulation studies were carried out on the two fullerene derivatives to understand the self-assembly behaviour of these two derivatives. Furthermore, the vesicle structures formed by the penta-hydroxy fullerene derivative are used for entrapment of hydrophobic polymer, poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and also hydrophilic dye, Rhodamine B. In both the cases, fluorescence quenching is observed due to electron transfer reaction with fullerene and hence these fullerene vesicles can be used to study the effect of confinement on electron transfer reactions and other chemical dynamics. The layer-by-layer self-assembly approach for the fabrication of biopolymeric thin films and microcapsules is discussed in the chapters 3 to 6. The biocompatible nanoparticles and nanofibers were used as the components of the assembly. In chapter 3, we have described fabrication of thin film of bovine serum albumin (BSA) nanoparticles via LbL approach using biopolymer chitosan as the complementary polymer. The driving force for the assembly growth of the assembly was the electrostatic and complementary hydrogen bond formation between the two components. The idea of incorporating nanoparticles in the thin film was that the nanoparticles can act as reservoirs for functional materials. The films were loaded with anticancer drug doxorubicin and show pH dependent release of the drug. The various interactions involved in the LbL assembly of BSA nanoparticles and polymers were investigated towards understanding the growth mechanism of the assembly in chapter 4. The understanding of the interactions involved in the assembly formation is important in order to modify the conditions of the assembly for enhancing the growth. It is inferred from the study reported in this chapter that not only the interaction of nanoparticles with polymers but also the inter-particle interactions are important factors in determining the growth of LbL assembly of nanoparticles/polymers. The growth of the assembly is enhanced on minimizing the inter-particle repulsions, which was achieved in case of BSA nanoparticles by modifying the pH of the assembly. We also utilized the LbL self-assembly approach for the delivery of lipophilic drugs. The lipophilic drugs are difficult to administer in the body due to their poor water solubility and hence show poor pharmacokinetic profile. The methods for incorporating hydrophobic drugs in LbL assembled thin films and microcapsules are described in chapters 5 and 6. In chapter 5, hydrophobic molecules binding property of albumin has been exploited for solubilisation of a water-insoluble molecule, pyrene (model drug) and hydrophobic drug, curcumin, by preparation of non-covalent conjugates with BSA. The interaction with BSA provided negative zeta potential to the previously uncharged molecules and hence they can be incorporated in the LbL assembled thin films and microcapsules using electrostatic as well as hydrogen bonding interaction with biopolymer, chitosan. The fabrication of protein encapsulated stable microcapsules with hydrophobic molecules incorporated in the shell of the microcapsules has also been demonstrated. The microcapsules were further capable of loading hydrophilic molecules like Rhodamine B. Thus, this approach can be employed for fabrication of multi-agent carrier for hydrophobic and hydrophilic drugs as well as therapeutic macromolecules. In chapter 6, we have incorporated nanocrystalline cellulose (NCC) LbL assembled thin films and microcapsules. The assembly formed was porous in nature due to the nano-fibrous morphology of NCC. The nanoassemblies can act as potential drug delivery carrier, which has been demonstrated by loading anticancer drug doxorubicin, and a lipophilic drug, curcumin. Doxorubicin hydrochloride, the salt form of the drug, doxorubicin, has good water solubility and hence can be postloaded in the assembly by diffusion from its aqueous solution. In the case of curcumin, which has limited solubility in water, a stable aqueous dispersion of the drug was prepared via noncovalent interaction with NCC prior to incorporation in the LbL assembly. The interaction of various other lipophilic drugs with NCC was analysed computationally.

The present thesis focuses on the selection of polymers and methods to fabricate stable and stimuli responsive multilayer self-assembly via layer-by-layer (LbL) approach. The polymers utilized in this study are biodegradable and biocompatible such as hyaluronic acid, chitosan and poly(vinyl alcohol) (PVA). The thesis is comprised of six chapters and a brief discussion on the contents of the individual chapters is given below. Chapter I reviews the LbL self-assembly approach in the context of drug delivery. The various interactions such as electrostatic, hydrogen bonding and covalent bonding involved in preparation of stable multilayer assemblies via LbL approach are discussed. Stimuli responsive behaviour of these multilayer assemblies can be tuned by choosing suitable depositing materials and method. Preparation of hollow microcapsules using LbL approach and its application in drug delivery has also been described in this chapter. Chapter II deals with the LbL assembly of a neutral polymer, poly(vinyl alcholol) (PVA). The negative charge on PVA backbone was induced by physical cross-linking with borax. The PVA-borate can undergo electrostatic interaction with positively charged chitosan in LbL process to form multilayer thin film. The thin film of PVA-borate complex/chitosan was found be responsive towards glucose concentration; disintegration of the multilayer assembly was observed at a high glucose concentration. This finding was rationalized on the basis of strong interaction of glucose with borate ions leading to dissociation of PVA-borate complex and subsequent collapse of the assembly. Thus, this multilayer self-assembly is potent for glucose triggered drug delivery. Chapter III reports the construction of a stable hydrogen bonded multilayer self-assembly based on complementary DNA base pairs (adenine and thymine) interaction. The natural polymer such as chitosan was modified with adenine whereas hyaluronic acid was modified with thymine. These two modified polymers were sequentially deposited on flat substrate and melamine formaldehyde (MF) particles; wherein strong interaction among the DNA base pairs led to the formation of stable assembly without utilizing any external cross-linking agent. The modified polymers are non-cytotoxic as proved from MTT assay. Further the multilayer assembly was used for pH responsive anticancer drug doxorubicin hydrochloride (DOX) release. In Chapter IV, glutaraldehyde mediated LbL self-assembly of single polymer multilayer thin films on flat and colloidal substrate by covalent bonding is described. A comparitive study between the native polymer (chitosan) and adenine modified polymer in the growth of thin film is performed. It is established from the study that the conformation of polymer and the availability of cross-linking points on the polymer play a crucial role in controlling the growth of these multilayer assemblies. Chapter V is divided into two parts (A and B). Part A describes a simple and unique protocol for fabrication of water dispersed chitosan nanoparticles (CH NPs). The method utilized in this work is based on the fast desolvation technique without using any additional stabilizer or any sophisticated instrumental setup. Furthermore, the CH NPs prepared from the mentioned protocol were proved to be cell-viable and are found to be responsive towards pH of the solution. In part B of this chapter, the LbL self-assembly of the responsive CH NPs is fabricated via electrostatic interaction with hyaluronic acid (HA). The growth of the multilayer thin film was found to be linear as function of number of bilayers. The morphology of thin film was characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The microscopic images reveal the uniform film morphology devoid of any phase separation of nanoparticles and polymers. Subsequently, the film was loaded with an anticancer therapeutic, doxorubicin hydrochloride (DOX). The release dynamics of encapsulated drug from the self-assembly are tunable and pH responsive. Chapter VI deals with the general and versatile method for the encapsulation of hydrophobic model drugs into polymeric multilayer assembly by using LbL approach. Electrical charge was induced on the surface of pyrene (uncharged organic substance) using an amphiphilic surfactant, sodium dodecyl sulfate (SDS) by micellar solubilization. The SDS micellar solution of pyrene was utilized to grow LbL multilayer thin film on a planar substrate and colloidal particles along with chitosan as a polycation. The LbL self-assembly of pyrene loaded SDS micelles/chitosan is additionally able to encapsulate hydrophobic or hydrophilic model therapeutics, thus providing an opportunity for dual-drug delivery. The desorption kinetics of the two model drugs from the thin film is found to follow a second order rate model.

Biological systems construct varieties of self-assembled architectures with incredible elegance and precession utilizing proteins as subunits to accomplish widespread functions. Inspired by natural systems, construction of artificial model systems with such sophistication and delicacy has become an intriguing field of research over the last two decades using so-called self-assembly process. Judiciously selected complementary building units encoded with specific chemical and structural information can be self-assembled into pre-programmed abiological architectures in a manner similar to biological self-assembly. In this regard, kinetically labile metal-ligand coordination has become an efficient and powerful protocol for the construction of highly intricate structures with specific topology and functionality due to its simple design principle, high bond enthalpy, and predictable directionality. Two-component self-assembly is very widely used methodology and easy to monitor. Recently, multi-component self-assembly has come up as an alternative and effective pathway to achieve complex architectures connecting more than two components in a single step. However, formation of selective single product from multicomponents is entropically unfavorable. Only a very few 3D architectures have been known, that are obtained from a mixture of ditopic and tri- or tetratopic donors with metal acceptors with or without employing templates. Development of template-free multicomponent architectures is still in its infancy. Strong tendency of Pd(II)/Pt(II) to attain square-planar geometry around the metal center and kinetically labile nature of Pd(II)/Pd(II)-N(pyridine) bonds made them chemists’ favourite to engineer desired supramolecular coordination architectures with structural resemblance to Platonic or Archimedean solids by employing symmetrical pyridyl donors due to their predictable directionality. In case of poly-imidazole donors, free rotation of C-N bond connecting imidazole and phenyl ring allows various dispositions of the donating nitrogen with respect to the aromatic backbone, and therefore, the structural topology of the architectures, made of poly-imidazole ligands becomes much more interesting as compared to symmetrical Platonic or Archimedean solids. The physico-chemical properties of self-assembled coordination cages depend on the structures of the complexes. Presence of large internal cavity surrounded by aromatic core, provides an excellent environment for the encapsulation of varieties of guest molecule or as nano-reactors for different organic transformations. Structural investigation in terms of packing interactions, solvent molecules, intermolecular channels can sometimes determine the property of such self-assembled materials as well. Presence of acidic water as well as H-bonded 3D-networks of water molecules in molecular pockets make them potential material for proton conduction. In addition, metal-ligand coordination offers opportunity to introduce new functionality through pre-synthetic modification of the building constituents to influence the property of the supramolecular systems. Incorporation of unsaturated ethynyl functionality attached to the heavy transition metal is expected to exhibit efficient luminescence due to the facile metal to ligand charge transfer (MLCT). Hence, the final assemblies can be employed as chemosensors for electron-deficient nitroaromatics, which are the chemical signature of many of the commercially available explosives. The present investigation is focused on design and construction of discrete, nanoscopic coordination cages with unusual structural topology employing mainly imidazole-based donors with Pd(II)/Pt(II) acceptors and their applications in catalysis, chemosensing, and proton conduction. CHAPTER 1 of the thesis provides a general introduction to self-assembly focusing on the importance and advantages of metal-ligand directional bonding approach towards the construction of supramolecular architectures with various structural topologies. This chapter also includes a brief review on the applications of such coordination cages in various fields especially as ‘molecular flask’ for the observation of unique chemical phenomena and unusual reactions. Part A of CHAPTER 2 describes the synthesis of a new hollow Pd6 water soluble cage [{(tmen)Pd}6(timb)4](NO3)12 (1) via two-component self-assembly of a triimidazole donor and 90° Pd(II) acceptor [tmen = N,N,N’,N’-tetramethylethylenediamine, timb = 1,3,5-tris(1-imidazolyl)benzene]. The assembly was successfully crystallized with a hydrophilic dianionic benzoquinone derivative (formed in situ by the decomposition of DDQ) as [{(tmen)Pd}6(timb)4](NO3)10()2(H2O)18 (3), and a hydrophobic sterically demanding aromatic aldehyde as [{(tmen)Pd}6(timb)4](NO3)12{()4a}2(H2O)27 (5a) [where 2H2 = 2,3-dichloro-5,6-dihydroxycyclohexa-2,5diene-1,4-dione, 4a = 1-pyrenecarboxaldehyde,  = exohedral and  = endohedral] to confirm the hydrophobic nature of the cavity. Experiments were carried out to show that the hydrophobic confined nanospace of the cage (1) catalyses the Knoevenagel condensation of a series of different aromatic monoaldehydes with active methylene compounds in ‘green’ aqueous medium. The Knoevenagel condensation reaction is basically a dehydration reaction because water is a by-product. So the presence of water should, in principle, promote the backward reaction as per Le Chatelier’s principle. In general, these reactions with organic substrates are not performed in water. However, difficulty has been overcome using hydrophobic cavity of the cage. It has also been established that the cavity of the cage also enhances the rate of Diels-Alder reaction of 9-hydroxymethylanthracene with N-phenylmaleimide/N-cyclohexylmaleimide. Figure 1. Catalytic Knoevenagel condensation and Diels-Alder reaction using hydrophobic cavity of the cage (1) in aqueous medium. Part B of CHAPTER 2 reports unique three-component self-assembly incorporating both tri- and tetra-topic donors. Until now, a very few 3D-architectures have been known that are obtained from self-assembly of ditopic and tri- or tetratopic donors with metal acceptors. Scheme 1. Three-component self-assembly of a Pd7 cage (1) from cis-blocked Pd(II) 90° acceptor (M), tri-imidazole (timb) and tetra-imidazole (tim) donors. Self-assembled multicomponent discrete architecture composed of both tri- and tetra-topic donors is yet to be reported due to difficulty in prediction of the final structure from the mixture of ligands having multiple donor sites. The first example of self-sorted Pd7 molecular boat [{(tmen)Pd}7(timb)2(tim)2](NO3)14(H2O)20 (1) [tmen = N,N,N’,N’-tetramethylethylenediamine, timb = 1,3,5-tris(1-imidazolyl)-benzene, tim = 1,2,4,5-tetrakis(1-imidazolyl)benzene] was synthesized via three-component self-assembly of cis-(tmen)Pd(NO3)2, tetra- (tim) and tri-topic donors (timb) in a 7:2:2 ratio. The cavity of this cage was also utilized as a nanoreactor for catalytic Knoevenagel condensations of a series of aromatic aldehydes with 1,3-dimethylbarbituric acid (e) and Meldrum’s acid (f) in aqueous media. CHAPTER 3 presents the results of an investigation on how simple variation of length and coordination mode of linear donors can self-discriminate into markedly different complex architectures, from Pd8 molecular swing [{(tmen)Pd}8(tim)2(bpy)4](NO3)16 (1) or [{(tmen)Pd}8(tim)2(stt)5](NO3)6 (2) to Pd6 molecular boat [{(tmen)Pd}6(tim)2(bpe/dpe/pin/dpb)2](NO3)12, (3/4/5/6). Also by enhancing denticity [bidentate to tridentate (ptp)] as well as introducing asymmetry, they self-sort into Pd7 molecular tent [{(tmen)Pd}7(tim)2(ptp)2](NO3)14 (7) by employing it in a self-assembly of cis-(tmen)Pd(NO3)2 and tetraimidazole (tim) donor [where tmen = N,N,N’,N’-tetramethylethylenediamine, bpy = 4,4’-bipyridyl, stt = sodium terephthalate, bpe = trans-1,2-bis(4-pyridyl)ethylene, dpe = 1,2-di(pyridin-4-yl)ethane, pin = N-(pyridin-4-yl)isonicotinamide, dpb = 1,4-di(pyridin-4-yl)benzene, ptp = 6'-(pyridin-4-yl)-3,4':2',4''-terpyridine, and tim = 1,2,4,5-tetrakis(1- imidazolyl)benzene]. In these cases, control of the geometrical principles and stereo-electronic preferences of the building units allowed the formation of such intricate architectures. Some of these assemblies represent first examples of such types of structures, and their formation would not be anticipated by taking into account only the geometry of the donor and acceptor building units. In addition to their direct structural confirmation using single crystal X-ray diffraction analysis, propensity of the assemblies (1 and 3) to form inclusion complexes with large guest like C60 in solution was also demonstrated by fluorescence quenching experiment. The high KSV values for both the assemblies 1 (1.0 × 10-5 M-1) and 2 (1.6 × 10-6 M-1) with C60 indicated the propensity of these assemblies to form complexes with C60 in solution. Furthermore, inspection of crystal packing of other five complexes (2 and 4 - 7) revealed the presence of water molecules H-bonded with NO3– (O-H···O=N) and 3D H-bonded networks of water in the intermolecular pockets. Interestingly, the present complexes (2 and 4 - 7) show high conductivity across low-humidity range at ambient temperature and achieve a conductivity of ~10-3 Scm-1 at 75% relative humidity and 296 K. These supra-molecular architectures represent a new generation of discrete materials that display high proton conductivity under ambient conditions with activation energy comparable to that of Nafion. Scheme 2. Exclusive formation of Pd8 molecular swings (1 and 2), Pd6 molecular boats (3-6), and Pd7 molecular tent (7) via self-sorting. CHAPTER 4 presents self-selection by synergistic effect of morphological information and coordination ability of the ligands through specific coordination interactional algorithms within dynamic supramolecular systems involving a tetratopic Pd(II) acceptor and three different pyridine- and imidazole-based donors (La - Lc) [La = 1,3-bis((E)-2-(pyridin-3-yl)vinyl)benzene, Lb = 1,3-di(1H-imidazol-1-yl)benzene, and Lc = tris(4-(1H-imidazol-1-yl)phenyl)amine]. Three different cages, ‘paddle wheel’ cluster Pd2(La)4(NO3)4 (2a), molecular barrel Pd3(Lb)6(NO3)6 (2b) and molecular sphere Pd6(Lc)8(NO3)12 (2c) were first synthesized via two-component self-assembly of a tetratopic Pd(II) acceptor (1) and individual pyridine- and imidazole-based donors (La - Lc). When all the four components were allowed to interact in a complex reaction mixture, only one out of three cages was isolated. The inherent dynamic nature of the kinetically labile coordination bond allows constitutional adaptation through component exchange in the competition experiment involving multiple constituents to self-organize into specific combination and thereby, achieve the thermodynamically most stable assembly. The preferential binding affinity towards a particular partner was also established by transforming a non-preferred cage to a preferred cage by the interaction with the appropriate ligand and thus, this represents the first examples of two-step cage-to-cage transformation through constitutional evolution of Figure 2. Cage-to-cage transformation from non-preferred cage to preferred cage upon treatment with appropriate ligand; and Nyquist plots of the complexes (2b and 2c) under 98% RH condition and ambient temparature. dynamic systems induced by both coordination ability and geometry of the ligand. Moreover, computational study further supported the fact that coordination interaction of imidazole moiety to Pd(II) is enthalpically more preferred compared to pyridine which drives the selection process. In addition, analysis of crystal packing of both the complexes (2b and 2c) indicated the presence of strong H-bonds between NO3- and water molecules; as well as H-bonded 3D-networks of water. Interestingly, both the complexes exhibit promising proton conductivity (10-5 to ca. 10-3 S cm-1) at ambient temperature under relative humidity of ~98% with low activation energy. CHAPTER 5 covers design and synthesis of new organometallic building block 1,3,5-tris(4-trans-Pt(PEt3)2I(ethynyl)phenyl)benzene (1) incorporating Pt-ethynyl functionality and [2 + 3] self-assembly of its nitrate analogue 1,3,5-tris(4-trans-Pt(PEt3)2(ONO2)(ethynyl)phenyl)benzene (2) with “clip” type bidentate donors (L1 – L3) separately afforded three trigonal prismatic architectures (3a – 3c), respectively (Scheme 3), Scheme 3. Schematic presentation of three different donors (L1 – L3) and a new planar tritopic acceptor (2) and their [3 + 2] self-assembly into trigonal prismatic architectures (3a - 3c). [L1 = N1,N3-di(pyridin-3-yl)isophthalamide; L2 = 1,3-bis((E)-2-(pyridin-3-yl)vinyl)benzene; L3 = 1,3-bis(pyridin-3-ylethynyl)benzene]. All these prisms were characterized and their shapes/sizes are predicted through geometry optimization employing molecular mechanics universal force field (MMUFF) simulation. The extended -conjugation including the presence of Pt-ethynyl functionality make them electron rich as well as luminescent in nature. As expected, cages 3b and 3c exhibit fluorescent quenching in solution upon addition of picric acid [PA], which is a common constituent of many explosives. Interestingly, the non-responsive nature of fluorescent intensity towards other electron-deficient nitro-aromatic explosives (NAEs) makes them promising selective sensors for PA with a detection limit deep down to ppb. Complexes 3b – c represent the first examples of molecular metallocages as selective sensors for picric acid. Furthermore, solid-state quenching of fluorescent intensity of the thin film of 3b upon exposure to saturated vapor of picric acid draws special attention for infield application.

Les métamatériaux électromagnétiques sont des composites artificiels, constitués de résonateurs etayant des propriétés optiques n’existant pas à l’état naturel. Cette thèse est consacrée à lafabrication et caractérisation de tels matériaux. Pour cela des particules métalliques coeur-écorce(d’or ou d’argent enrobées de silice) sont assemblées par la technique de Langmuir-Blodgett afin deformer des réseaux denses en monocouche et en multicouches. Ces nanoparticules jouent le rôle derésonateurs grâce à la présence de la résonance plasmon et l’écorce de silice permet de contrôler ladistance entre particules. Nous avons ainsi réalisé des matériaux dont la distance entre lesrésonateurs et la fraction métallique varient. Les analyses spectro-photométriques des films obtenus,notamment en réflexion normale, nous ont permis d’extraire les propriétés optiques de nosmatériaux. Pour cela nous avons proposé un modèle phénoménologique dans lequel nousdéfinissons la permittivité de la couche effective comme étant celle de la matrice à laquelle s’ajouteun oscillateur de Lorentz décrivant la présence d’une résonance plasmon. Nous avons pu ainsimontrer expérimentalement qu’il était possible d’obtenir des métamatériaux d’indice de réfractioninférieur à 1 quand la fraction de métal dans le matériau est suffisamment importante. / Electromagnetic metamaterials are artificial composites, containing resonators and exhiniting opticalproperties which do not exist in a natural state. This thesis is dedicated to the manufacturing and thecharacterization of such materials. Metallic core-shell particles (gold or silver core coated with a silicashell) are assembled by the Langmuir-Blodgett technique to form dense monolayer and multilayernetworks. These nanoparticles play the role of resonators thanks to the presence of the plasmonresonance of the core whereas the silica shell allows a fine control of the distance between themetallic particles. We realized materials whose distance between resonators and metallic fractionvary. The spectrophotometric analyses, in particular reflection at normal incidence, allowed us toextract the optical properties of the materials. We proposed a phenomenological model in which wedefine the permittivity of the effective layer as the permittivity of a homogenous matrix to which aLorentz oscillator is added to describe the presence of the plasmon resonance. We were able toshow experimentally metamaterials with refractive index lower than 1 can be obtained when thefraction of metal in the material is important enough.

La matrice extracellulaire est un réseau enchevêtré de macromolécules variées, en étroite relation avec les cellules qu'elle environne. Les interactions bidirectionnelles qui s'établissent entre les cellules et leur microenvironnement matriciel régulent mutuellement leur comportement et devenir. La diversité biochimique des constituants moléculaires de la matrice, leurs propriétés biophysiques, leur architecture tout comme leur dynamique représentent autant de signaux régulateurs. Parmi les constituants de la matrice, la fibronectine (FN) est une glycoprotéine structurale et fonctionnelle majeure intervenant dans de nombreux processus physiologiques et pathologiques. Ces fonctions diverses sont directement liées à la dynamique structurale de cette protéine et à sa capacité à interagir avec les autres molécules matricielles, dont elle-même. Retrouvée sous forme soluble dans les fluides biologiques, la FN est incorporée dans les matrices insolubles sous forme d'assemblages supramoléculaires principalement fibrillaires mais aussi sous forme d'agrégats. Ces assemblages sembleraient être impliqués dans des processus physiologiques et pathologiques distincts.Si l'étude des assemblages de FN est rendue possible par l'élaboration de modèles in vitro, les mécanismes de polymérisation et l'effet d'assemblages de structures définies sur le comportement cellulaire restent cependant à mieux élucider et constituent le cœur de ce travail.Les travaux ont donc consisté à élaborer des assemblages de FN, à caractériser les mécanismes et structures impliqués dans leur polymérisation, et à étudier leur influence sur un modèle de cellules cancéreuses ovariennes. D'autre part, des études préliminaires comparatives ont été menées avec un analogue végétal de la FN.L'irréversibilité de la dénaturation thermique de la FN entraîne la formation d'agrégats de type amyloïde. Deux populations d'agrégats coexistent en solution. Cette agrégation est corrélée à une diminution de l'accessibilité des sites de liaison à la gélatine et des sites RGD, et à une diminution de l'incorporation dans les réseaux matriciels. De plus, si la FN sous sa forme agrégée n'est pas cytotoxique pour les cellules étudiées, la modification de la conformation de la FN favorise leur migration isolée et aléatoire.Ces résultats soulèvent la question de l'implication de ces agrégats de FN dans des processus pathologiques tels que le développement tumoral. / Extracellular matrix is a complex meshwork of various macromolecules that have a tight relationship with the surrounding cells. Bidirectional interactions between cells and the microenvironment control their respective behaviors and fate. The biochemical diversity of matrix molecular components, their biophysical properties, their architecture but also their dynamic represent as many regulator signals. Among the components of the matrix, fibronectin (FN) is a major structural and functional glycoprotein involved in numerous physiological and pathological processes. These various functions are directly linked to the structural dynamic of this protein and its ability to interact with others matrix components, in particular with itself. Found as a soluble protein in biological fluids, FN is also incorporated in insoluble matrix as supramolecular assemblies, mainly fibrils but also aggregates. These assemblies could be involved in distinct physiological and pathological processes.If the study of the assembly of the FN is possible with the help of in vitro models, the mechanism of polymerization and the effects of defined assemblies on the cell behavior still have to be better defined.Therefore, this work consisted in elaborating FN assemblies, in characterizing the mechanisms and structures involved in their polymerization and in studying their influence on behaviors of a model of ovarian cancer cells. Besides, preliminary comparative studies have been performed with a plant analogous of FN.We show that irreversible thermal unfolding of FN triggers amyloid-like aggregation. Two states of aggregates could coexist in solution. FN aggregation correlates with a decrease of gelatin-binding domain and RGD sequence accessibility, and a decrease of the incorporation in the matrix network. Moreover, if aggregates are not cytotoxic for the studied cells, conformation change of FN promotes their single-cell and random migration.These results raise questions about the role of FN aggregates in pathological processes like tumor development.