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No / We describe a series of experiments designed to investigate the conformational transition that highly-branched polymers with ligands undergo when interacting with bacteria, a process that may provide a new sensing mechanism for bacterial detection. Fluorescent highly-branched poly(N-isopropyl acrylamide)s (HB-PNIPAM) were prepared by sequential self-condensing radical copolymerizations, using anthrylmethyl methacrylate (AMMA) and fluorescein-O-acrylate (FA) as fluorescent comonomers and 4-vinylbenzyl pyrrole carbodithioate as a branch forming monomer. Differences in reactivity necessitated to first copolymerize AMMA then react with FA in a separate sequential monomer feed step. Modifications of the chain ends produced vancomycin-functional derivatives (HB-PNIPAM-Van). The AMMA and FA labels allow probing of the conformational behaviour of the polymers in solution via Forster resonance energy transfer experiments. It was shown that interaction of this polymer's end groups with Staphylococcus aureus induced a macromolecular collapse. The data thus provide conclusive evidence for a conformational transition that is driven by binding to a bacterium.

Le récepteur de chimiokine CXCR7 a été récemment identifié comme liant la chimiokine SDF-1, anciennement considérée comme ligand exclusif du récepteur CXCR4. Ces deux récepteurs sont exprimés majoritairement dans les mêmes types cellulaires et, ainsi, la découverte de CXCR7 incite à réévaluer les effets respectifs de SDF-1 sur CXCR4. Étant donné son rôle dans le cancer, CXCR4 est une cible de choix pour le développement de molécules thérapeutiques. Également, CXCR7 semble être impliqué dans la croissance tumorale. AMD3100, un antagoniste «sélectif» pour CXCR4, est maintenant commercialisé. Cet antagoniste a été identifié comme liant lui aussi CXCR7. De plus, sur CXCR7, l’AMD3100 agit comme agoniste puisqu’il induit le recrutement de la β-arrestine, à l’opposé de son effet sur. En revanche, AMD3100 n’induit pas le recrutement de la β-arrestine à CXCR4. Basé sur ces résultats, il est nécessaire de revoir la sélectivité d’autres antagonistes synthétiques de CXCR4. À l’aide de la technique de BRET (Résonance d’un transfert d’énergie par bioluminescence), nos résultats montrent que le Tc14012, un autre antagoniste synthétique de CXCR4, et structurellement distinct de l’AMD3100, interagit avec CXCR7. Contrairement à CXCR4, les deux antagonistes de CXCR4 agissent comme agonistes sur CXCR7 en induisant le recrutement de la β-arrestine. Nos résultats suggèrent que l’organisation spatiale du corps du récepteur serait responsable de cet effet opposé. En conclusion, AMD3100 et Tc14012 ne sont pas sélectifs pour CXCR4, puisqu’ils interagissent avec CXCR7. Lors du développement de nouvelles molécules synthétiques ciblant CXCR4, il serait alors nécessaire d’en évaluer leur sélectivité, et leurs effets en les testant aussi sur CXCR7. / ASBTRACT SDF-1 was at first thought to exclusively bind CXCR4, but it was subsequently found to also bind to the chemokine receptor CXCR7. CXCR4 is a promising target for drug development due to its role in cancer. AMD3100 is newly commercialised synthetic antagonist of CXCR4. This drug leads to massive release of hematopoietic stem cell into the peripheral blood. It was found that AMD3100 also binds to CXCR7 and acts as an agonist of β-arrestin recruitment to CXCR7. An antagonist of CXCR4 acts as an agonist on CXCR7. Prompted by this observation, we tested whether this might hold true for other CXCR4 antagonist. Tc14012, a peptidomimetic of T140, has been extensively described as a potent CXCR4 antagonist. We find that TC14012 also interacts on CXCR7. Like AMD3100, TC14012 alone induces β-arrestin recruitment to CXCR7. Thus, two structurally unrelated CXCR4 antagonists, AMD3100 and TC14012, are agonists of the CXCR7-arrestin pathway. This suggests distinct activation mechanisms of the arrestin pathway by CXCR4 and CXCR7. The results we obtained using a BRET (Bioluminescence Resonance Energy Transfer)-based arrestin recruitment assay, suggest that the CXCR7 receptor core is responsible for the recruitment of beta-arrestin in response to AMD3100 and TC14012. The finding that both AMD3100 and TC14012 do not only bind CXCR4, but also CXCR7, with opposite effects on arrestin recruitment, is important for the use of the compounds as tools to dissect SDF-1-mediated effects. This may be a general feature of synthetic ligands of the two receptors, with potential consequences for drug development. Key words: Chemokine receptor, CXCR4 and CXCR7, BRET, β-arrestin recruitement, TC14012, AMD3100 and SDF-1.

Nanotechnology builds devices from the bottom up with atomic accuracy. Among the basic nano-components to fabricate such devices, semiconductor nanoparticle quantum dots (QDs), metal nanocrystals, proteins, and nucleic acids have attracted most interests due to their potential in optical, biomedical, and electronic areas. The major objective of this research was to prepare nano-components in order to fabricate functional nano-scale devices. This research consisted of three projects. In the first two projects, we incorporated two desirable characteristics of QDs, which are their abilities to serve as donors in fluorescence energy transfer (FRET) and surface energy transfer (SET) as well as to do multiplexing, to engineer QD-based nanoconjugates for optical and biomedical applications. Immobilizing luminescent semiconductor CdSe/ZnS QDs to a solid platform for QD-based biosensors offers advantages over traditional solution-based assays. In the first project, we designed highly sensitive CdSe/ZnS QD SET-based probes using gold nanoparticles (AuNPs) as FRET acceptors on polystyrene (PS) microsphere surfaces. The emission of PS-QD was significantly quenched and restored when the AuNPs were attached to and then removed from the surface. The probes were sensitive enough to analyze signals from a single bead and for use in optical applications. The new PS-QD-AuNP SET platform opens possibilities to carry out both SET and FRET assays in microparticle-based platforms and in microarrays. In the second project, we applied the QD-encoded microspheres in FRET-based analysis for bio-applications. QDs and Alexa Fluor 660 (A660) fluorophores are used as donors and acceptors respectively via a hairpin single stranded DNA. FRET between QD and A660 on the surface of polystyrene microspheres resulted in quenching of QD luminescence and increased A660 emission. QD emission on polystyrene x microspheres was restored when the targeted complementary DNA hybridized the hairpin strand and displaced A660 away from QDs. The third project involved fabrication of different nanoconjugates via self-assembly of template-based metal nanowires and metal nanoparticles using oligonucleotides as linkers. These nanoconjugates can serve as building blocks in nano-electronic circuits. The template method restricted the oligonucleotides attachment to the tip of the nanowires. Nanowires tagged with hybridizable DNA could connect to complementary DNA-modified metal crystals in a position-specific manner.

Within the emerging methods of controlled free radical polymerization, the Reversible Addition-Fragmentation chain Transfer (RAFT) process has been recently established as a powerful technique to synthesize standard polymers with controlled characteristics (narrow polydispersity and predictable molar masses). This method is now employed to synthesize well-defined, reactive precursor polymers that are subsequently converted into speciality polymers such as fluorescent-labeled polycations. Those are suitable for Electrostatic Self-Assembly (ESA). The observation of the Förster Resonance Energy Transfer (FRET) in such films is established, contributing to the understanding of the self-organization during thin film growth. The RAFT process using Benzyl Dithiobenzoate (BDTB) is shown to enable the control of the free radical polymerization of vinylbenzyl chloride (VBC). The high tolerance of the method to functional groups allows the preparation of such reactive polymers with narrow polydispersities and predictable molar masses. The well-defined precursors are easily converted, for instance, to polycations. Also they are easily functionalized by fluorophores, here derived from coumarin and perylene. The fluorophores, as pendent side chains, served as label to investigate the alternating deposition process, while the influence of molecular variations on the self-assembly can be systematized. Furthermore, when using complementary fluorophores, Fluorescence Resonance Energy Transfer (FRET) studies in organized media become possible. The alternating deposition cycles are followed by UV-Vis spectroscopy, ellipsometry, and X-Ray reflectivity. Regular growth is observed for three complementarily labeled polycations. Noteworthy, fluorescence and UV-Vis studies reveal the formation of large fluorescent dye aggregates for one coumarin and for the perylene derivative in the ESA multilayers. When these polycations are used in mixed thin films, Förster Resonance Energy Transfer (FRET) between fluorophores is observed. The non-radiative nature of the different energy transfer was confirmed by fluorescence decay time measurements/ Parmi les récentes méthodes pour contrôler la polymérisation radicalaire, le procédé RAFT (Reversible Addition-Fragmentation chain Transfer) a été récemment établi et s'impose comme une méthode performante pour la synthèse de polymères standards possédant des caractéristiques contrôlées (faibles polydispersités et masses molaires prédictibles). Cette méthode est désormais utilisée pour la synthèse de précurseurs réactifs bien définis qui sont par la suite convertis en polymères spécialisés, par exemple en polycations marqués a l'aide de sondes fluorescentes. Ces polycations peuvent être ensuite auto-assemblés électrostatiquement afin d'élaborer des films minces. Le phénomène de transfert de fluorescence (Förster Resonance Energy Transfer –FRET-) dans de tels films a été établi, contribuant par là-même à une meilleure compréhension du phénomène d'auto-organisation durant la croissance des films. Le procédé RAFT, utilisant le dithiobenzoate de benzyle (BDTB), a démontré sa capacité à contrôler la polymérisation radicalaire du chlorométhlstyrène (VBC). La tolérance de cette méthode vis à vis des groupes fonctionnels permet la synthèse de polymères réactifs possédant de faibles polydispersités et des masses molaires prédictibles. Les précurseurs ainsi définis sont facilement convertis, en polycations par exemple. Ils sont tout aussi facilement fonctionnalisés par des fluorophores dérivés de la coumarine ou du pérylène. Les fluorophores en tant que chaînes pendantes servent de marqueurs pour étudier le processus de dépôts alternés, alors que l'influence des variations au niveau moléculaire peut être systématisée. De plus, en utilisant des fluorophores complémentaires, il devient possible de mener des études sur le transfert de fluorescence (FRET) au sein de milieux organisés. Les cycles de dépôts alternés ont été suivis par spectroscopie UV-Vis, éllipsométrie et reflexion des rayons X. Une croissance régulière est observée dans le cas des trois polycations marqués. Il convient de noter que les études UV-Vis et de fluorescence révèlent la formation de larges aggrégats de fluorophores au sein des multicouches, dans le cas d'une coumarine et du dérivé de pérylène. Lorsque les polycations complémentaires sont utilisés dans des films minces mixtes, le FRET est observé. La nature radiative ou non-radiative du processus de transfert d'énergie a été confirmée par des mesures de déclin de fluorescence.

While much is known about the structure and interactions of the β-carboxysomal proteins, interactions of the proposed vertex protein CcmL with the other components have not yet been directly demonstrated. A fluorescence resonance energy transfer based method combined with other complementary spectrophotometry techniques as well as x-ray crystallography and transmission electron microscopy was used in a Thermosynechococcus elongatus BP-1 model to study these interactions. CcmL was found to interact with the various CcmK shell proteins with a clear binding preference for CcmK2; the previously proposed interaction of CcmL with CcmM was shown to not occur in vitro, and a possible CcmL-CcmL interaction was observed tentatively. In addition, analysis of a novel x-ray crystal structure of Nostoc sp. PCC7120 CcmL in a decameric form suggests a possibility of a CcmL-CcmL back-to-back interaction. This study gives the first direct experimental evidence for the biological role of CcmL as the carboxysomal vertex protein.

RÉSUMÉ Le récepteur de chimiokine CXCR7 a été récemment identifié comme liant la chimiokine SDF-1, anciennement considérée comme ligand exclusif du récepteur CXCR4. Ces deux récepteurs sont exprimés majoritairement dans les mêmes types cellulaires et, ainsi, la découverte de CXCR7 incite à réévaluer les effets respectifs de SDF-1 sur CXCR4. Étant donné son rôle dans le cancer, CXCR4 est une cible de choix pour le développement de molécules thérapeutiques. Également, CXCR7 semble être impliqué dans la croissance tumorale. AMD3100, un antagoniste «sélectif» pour CXCR4, est maintenant commercialisé. Cet antagoniste a été identifié comme liant lui aussi CXCR7. De plus, sur CXCR7, l’AMD3100 agit comme agoniste puisqu’il induit le recrutement de la β-arrestine, à l’opposé de son effet sur. En revanche, AMD3100 n’induit pas le recrutement de la β-arrestine à CXCR4. Basé sur ces résultats, il est nécessaire de revoir la sélectivité d’autres antagonistes synthétiques de CXCR4. À l’aide de la technique de BRET (Résonance d’un transfert d’énergie par bioluminescence), nos résultats montrent que le Tc14012, un autre antagoniste synthétique de CXCR4, et structurellement distinct de l’AMD3100, interagit avec CXCR7. Contrairement à CXCR4, les deux antagonistes de CXCR4 agissent comme agonistes sur CXCR7 en induisant le recrutement de la β-arrestine. Nos résultats suggèrent que l’organisation spatiale du corps du récepteur serait responsable de cet effet opposé. En conclusion, AMD3100 et Tc14012 ne sont pas sélectifs pour CXCR4, puisqu’ils interagissent avec CXCR7. Lors du développement de nouvelles molécules synthétiques ciblant CXCR4, il serait alors nécessaire d’en évaluer leur sélectivité, et leurs effets en les testant aussi sur CXCR7. Mot-clés : Récepteur de chimiokine CXCR4 et CXCR7, BRET, recrutement de la β-arrestine, AMD3100, Tc14012 et SDF-1. / ASBTRACT SDF-1 was at first thought to exclusively bind CXCR4, but it was subsequently found to also bind to the chemokine receptor CXCR7. CXCR4 is a promising target for drug development due to its role in cancer. AMD3100 is newly commercialised synthetic antagonist of CXCR4. This drug leads to massive release of hematopoietic stem cell into the peripheral blood. It was found that AMD3100 also binds to CXCR7 and acts as an agonist of β-arrestin recruitment to CXCR7. An antagonist of CXCR4 acts as an agonist on CXCR7. Prompted by this observation, we tested whether this might hold true for other CXCR4 antagonist. Tc14012, a peptidomimetic of T140, has been extensively described as a potent CXCR4 antagonist. We find that TC14012 also interacts on CXCR7. Like AMD3100, TC14012 alone induces β-arrestin recruitment to CXCR7. Thus, two structurally unrelated CXCR4 antagonists, AMD3100 and TC14012, are agonists of the CXCR7-arrestin pathway. This suggests distinct activation mechanisms of the arrestin pathway by CXCR4 and CXCR7. The results we obtained using a BRET (Bioluminescence Resonance Energy Transfer)-based arrestin recruitment assay, suggest that the CXCR7 receptor core is responsible for the recruitment of beta-arrestin in response to AMD3100 and TC14012. The finding that both AMD3100 and TC14012 do not only bind CXCR4, but also CXCR7, with opposite effects on arrestin recruitment, is important for the use of the compounds as tools to dissect SDF-1-mediated effects. This may be a general feature of synthetic ligands of the two receptors, with potential consequences for drug development. Key words: Chemokine receptor, CXCR4 and CXCR7, BRET, β-arrestin recruitement, TC14012, AMD3100 and SDF-1.

Nucleic acids and proteins, some of the building blocks of life, are not static structures but highly dynamic entities that need to interact with one another to meet cellular demands. The work presented in this thesis focuses on the application of highly sensitive fluorescence methods, both at ensemble and single-molecule level, to determine the dynamics and structure of specific biomolecular interactions with nanometer resolution and in temporal scales from nanoseconds to minutes, which includes most biologically relevant processes. The main aims of my PhD can be classified in three areas: i) exploring new fluorescent sensors with increased specificity for certain nucleic acid structures; ii) understanding how some of these nucleic acids sense the presence of small molecules in the cellular environment and trigger gene regulation by altering their structure; and iii) understanding how certain molecular machines, such as helicase proteins, are able to unwind the DNA double helix by using chemical energy in the form of ATP hydrolysis.

Alzheimer's disease (AD) is characterised by a series of biomolecular aggregation events, which include the formation of neurotoxic protein structures composed of the β-amyloid (Aβ) peptide. In this thesis, fluorescence self-quenching (FSQ) between fluorescently-labelled peptides is introduced as a strategy for detecting and characterizing Aβ aggregates in solution, and for overcoming limitations associated with conventional methods. Using a combination of steady-state, picosecond time-resolved fluorescence and transmission electron microscopy, the fluorescence response of HiLyte Fluor 555-labelled Aβ peptides is characterised to demonstrate that Aβ self-assembly organizes the covalently attached probes in close proximity to trigger the self-quenching sensing process over a broad range of conditions. Importantly, N-terminal tagging of β-amyloid peptides is shown to not alter the self-assembly kinetics or the resulting aggregated structures. When performed in Förster resonance energy transfer (FRET) format, this method becomes a ratiometric platform to gain insights into amyloid structure and for standardizing in vitro studies of amyloid self-assembly. The ability of FSQ-based methods to monitor the inhibition of Aβ aggregation by model test compounds including the small heat shock protein (Hsp), the amyloid-binding alcohol dehydrogenase protein (ABAD) and bovine serum albumin (BSA) is also demonstrated. Given that Aβ is formed within the cell membrane and is known to induce its disruption, sophisticated single-molecule fluorescence spectroscopy methods were developed to quantify membrane dynamics induced by the presence of disrupting agents, such as Aβ and detergents. The solubilisation dynamics of single liposomes induced by the non-ionic surfactant Triton-X 100 (TX-100) were studied in real-time. Using this approach, the swelling and permeabilization steps of the solubilisation process were unambiguously separated within single FRET trajectories, and their kinetic details as a function of Triton-X 100 and presence of cholesterol within the membrane structure were examined. Finally, single-molecule stepwise-photobleaching techniques were employed to study the effect of Aβ oligomers interacting with supported-lipid bilayers, establishing a platform from which to investigate how the presence of a membrane layer affects Aβ oligomerization at the level of individual molecules. Overall, the fluorescence-based strategies for amyloid- and liposome-sensing presented in this work bridges the gap between current morphology-specific techniques and highly-specialized single-molecule methods to provide a biophysical toolbox to investigate the changes in structure, size and molecular interactions accompanying the amyloid aggregation pathway and for the screening of novel therapeutic and diagnostic agents.

This thesis consists of two parts. The first part deals with the visible emission of ZnO Nanocrystals and its possible application in Resonance Energy Transfer (RET) studies. The second part of the thesis is on the magnetic properties of the layered transition metal Thiophosphates MPS3 (M = Mn, Fe), their solid solutions and intercalation compounds. Recent advances in semiconductor nanocrystals or quantum dots (QDs) as inorganic fluorophores have pioneered a new direction in the fluorescent based techniques to investigate fundamental processes in lifesciences. Their broad absorption spectra with narrow, Size-tunable emissions with high quantum e±ciency and stability under relative harsh environments have made inorganic QD's the fluorophores of choice in many applications. Among inorganic fluorophores the II-VI semiconductors based on cadmium chalcogenides are the front-runners. The cytotoxicity associated with these QDs is, however, a major drawback and has lead to the search for new nanocrystalline fluorophores that are non-toxic and possess the same favorable fluorescence properties as the Cd based QDs, viz, tunability and narrow spectral profile. ZnO Nano particles are known to exhibit two emission bands; a narrow emission band in UV around 380 nm (3.25 eV) at a wavelength just below the onset of the band gap excitation in the absorption spectra and a broad emission band in the blue-green part of the visible spectrum, with a maximum between 500 and 550 nm (2.5-2.2 eV). The UV Emission originates from the recombination of bound excitons - excited electrons in the Conduction band with holes in the valence band. The visible emission of ZnO nanocrystals is known to involve deep trap states that lie approximately midway between the Conduction and valence bands and surface defects that exist as shallow traps. In principle, visible-light-emitting ZnO nanocrystals would be ideal candidates as replacement for Cd-based fluorescent labels since they are nontoxic, less expensive, and chemically stable in air. Nanoscale ZnO, however, tends to aggregate and/or undergo Ostwald ripening be-Cause of high surface free energy resulting in an increase in crystallite size and consequent Disappearance of the visible emission. Most attempts to stabilize the ZnO nanocrystals by Capping has usually resulted in the quenching of the visible trap emission. The objective of the present study was to stabilize the visible light emission of ZnO nanocrystals, to Understand the origin and mechanism of the visible emission and to explore the possibility Of using the visible emission of ZnO in RET studies. The stabilization of visible light emission in ZnO nanocrystals was achieved by forming ZnO:MgO core-shell nanocrystals. The nanocrystals were synthesized by a sequential preparative procedure that involved formation of a ZnO core followed by an MgO shell. The Nanocrystals were characterized by using XRD, TEM, optical absorption and photoluminescence spectroscopy. These are described in Chapter 2 of the thesis. The ZnO: MgO Core-shell nanostructures exhibit stable emission in the visible for extended periods. Application of the ZnO: MgO nanocrystals either as fluorescent probes or RET studies require that they be dispersible in both polar and non-polar solvents. This as realized by appropriate choice of the capping agents (Chapter 3). ZnO: MgO nanocrystals with hydrophobic surface were obtained by capping the nanocrystals with oleic acid. The oleate capped ZnO: MgO nanocrystals are soluble in a variety of non-polar organic solvents with no change in their emission properties. Water-soluble ZnO: MgO nanocrystals were obtained by capping the ZnO:MgO nanocrystals with carboxymethyl-β-cyclodextrin (CMCD). The hydroxyl groups located at the rim of the cyclodextrin cavity renders the surface hydrophilic. The integrity of the CMCD molecules are preserved on capping and their by hydrophobic cavities available for host-guest chemistry. The visible emission of The ZnO: MgO nanocrystals are unaltered by the nature of the capping agent. The origin and mechanism of the visible emission from ZnO: MgO nanocrystals has been Investigated using time-resolved emission spectroscopy technique (Chapter 4). The time-evolution of the photoluminescence spectra show that there are, in fact, two features in the visible emission whose relative importance and efficiencies vary with time. These features originate from recombination involving trapped electrons and holes, respectively, And with efficiencies that depend on the occupancy of the trap density of states. The application of the visible emission of ZnO: MgO nanocrystals as resonance energy transfer (RET) donors in water and hydrophobic media are demonstrated. In aqueous media, the carboxymethyl β-cyclodextrin (CMCD) capped ZnO: MgO nanocrystals is able to accommodate the organic dye Nile Red by an inclusion in the anchored hydrophobic cyclodextrin cavity forming a 1:1 complex. Nile Red was chosen as the guest molecule because its absorption has appreciable overlap with ZnO: MgO visible emission, a prerequisite for RET to occur. The resonance energy transfer on the band gap excitation of The ZnO core to included Red molecules in the CMCD-ZnO: MgO-Nile Red supramolecular assembly is demonstrated in aqueous media. A similar RET process is shown to occur in the non-polar media in the oleate capped ZnO: MgO nanocrystals when Nile Red is partitioned from the solvent into hydrophobic anchored oleate chains. The wavelength dependent energy transfer in the system has been studied using time-resolved emission spectroscopic technique. The importance of trap states in giving rise to non-Forster distance dependence for the RET is highlighted. The second part of the thesis deals with magnetism in low dimensional layered transition metal thiophophates, MPS3 (M = Mn, Fe). Low dimensional magnetic systems continue to be a fertile ground for discovering new phenomena and properties. Among two-dimensional magnetic systems the insulating transition metal thiophosphates are one of the few known layered systems, in which both magnetic and crystallographic lattices are two dimensional (2D). In the metal chalcogenophosphates, the magnetic MPX3 layers are separated by a van der Waals gap that effectively rules out interlayer exchange and hence these systems are nearly perfect 2D magnetic systems, with the magnetic ions forming a honeycomb arrangement within the layer. Due to the crystallographic two-dimensional nature these materials may be intercalated by variety of molecules or ions leading to change in magnetic properties. The objective of this thesis work is to try and modify the magnetic properties of the transition metal thiophosphates either by forming solid solutions of the type, M1-xMxPS3, (M, M = Mn, Fe) or by intercalating hydrated metal ions within the layers. The structure, Bonding, reactivity and magnetic properties are briefly introduced in Chapter 7. The Scope and nature of the present work in presented towards the end of the chapter. MnPS3 and FePS3 have identical crystal structures and both order antiferromagnetically at low temperatures, TN. The in-plane magnetic structures of the antiferromagnetically ordered the Neel state in the two compounds are, however, different. In MnPS3 the spins Alternate up-down whereas in FePS3 the spins are arranged as ferromagnetic chains with Alternate chains coupled antiferromagnetically. Since the crystal structures are identical, These two compounds can form solid solutions, Mn1-xFexPS3(0≤x≥1) over the entire concentration range. The magnetic properties of the single crystals of the solid solutions was measured by using a SQUID magnetometer. This system is of interest since the contrasting Neel states of the end-members may give rise to new magnetic phenomena at intermediate composition. It is shown that the magnetic behavior falls into three distinct categories. The Mn-rich compositions behave like a dilute MnPS3 lattice, the Fe-rich compositions behave like dilute FePS3 and in the intermediate compositions a spin-glass like phase appears. The phase boundaries for these regime in Mn1-xFexPS3, 0≤x≥1 is shown to be related to the percolation threshold for a honeycomb lattice. MnPS3 is known to undergo a unusual ion-exchange intercalation reaction. Intercalation occurs by the inclusion of hydrated metal ions in the galleries of MnPS3 with charge neutrality maintained by loss of the Mn2+ ions from the layer (Equation). MnPS3 + 2xG+ (aq) → Mn1-xPS3 [G (H2O) y] 2x + xMn2+ (aq) Where G is a neutral guest species. This chemistry has been exploited to intercalate hydrated Mn2+ ions in the interlamellar space to give Mn1-xPS3[Mn(H2O)6]x. the magnetic properties of this 3D analogue of MnPS3 has been investigated in Chapter 9.