ECF (Energy-Coupling Factor)-Transporter sind prokaryotische Aufnahmesysteme für Mikronährstoffe, die eine spezielle Gruppe von Transportern mit ATP-Bindekassette (ABC) darstellen. Sie beinhalten zwei asymmetrische Membranproteine, von denen eins (S) für die spezifische Bindung und Translokation des Substrates und das andere (T) für die Kopplung mit den ATPasen (A1,A2) zuständig ist. Bei ECF-Transportern der Subklasse I bilden diese Komponenten eine Einheit, während bei Vertretern der Subklasse II ein AAT-Modul mit wechselnden S-Einheiten interagiert. In der vorliegenden Arbeit wurde der Transportmechanismus, der eine Drehung der kompletten S-Einheit in der Membran beinhaltet, anhand des Biotintransporters BioMNY erstmals experimentell validiert. Durch Rekonstitution in Lipid-Nanodiscs, chemische Quervernetzung, fluoreszenz- und ESR-spektroskopische Techniken sowie einen Bindungstest mit radioaktivem Biotin wurde gezeigt, dass (i) die ATP-Bindung an die ATPasen zu einer Aufrichtung der S-Einheit (BioY) führt, (ii) diese Bewegung die Substratbeladung ermöglicht und (iii) BioY dabei ununterbrochen mit der T-Einheit (BioN) interagiert. Dies stellt einen Gegensatz zu Systemen der Subklasse II dar, für die ein ATP-abhängiger Austausch von S-Einheiten im Transportzyklus gezeigt worden war. Darüber hinaus wurde ein Escherichia coli-Stamm konstruiert, der durch Blockierung seines hochaffinen Biotintransporters und des -synthesewegs auf Spuren von Biotin nicht wachsen kann. Dieser Stamm ermöglichte einen eindeutigen Nachweis der Transportaktivität einiger solitärer BioY-Proteine. Aufgrund der einheitlichen Topologie von S-Einheiten ist ein Kippen auch für solitäre BioY-Varianten wahrscheinlich. Auch die metallspezifischen S-Einheiten CbiM und NikM besitzen ohne AAT-Modul eine basale Co2+- bzw. Ni2+-Transportaktivität. Ein ESR-spektroskopischer Kobaltnachweises zeigte, dass die aus nur zwei Membranhelices bestehende CbiN-Einheit für die Metallbeladung von CbiM essentiell ist. / ECF (Energy-Coupling Factor) transporters are a subgroup of ABC transporters that mediate uptake of micronutrients into prokaryotic cells. In contrast to canonical ABC importers, ECF transporters comprise two unrelated membrane proteins, one of which is responsible for specific and high affinity substrate binding (S) and the other one constitutes the coupling component (T) between S and the cytosolic ABC-ATPases (A1,A2). Subclass I transporters consist of four dedicated components whereas in subclass II transporters, a central AAT-module may interact with various S units. The biotin specific subclass I ECF transporter BioMNY was used to experimentally verify the hitherto hypothetic transport mechanism, which involves a rotation of the S unit within the membrane. With a series of experiments including reconstitution of BioMNY into lipid nanodiscs, site-specific cross-linking, a substrate binding assay with radioactive biotin and both fluorescence and EPR spectroscopic techniques, the ATP-dependent rotation of BioY (S) as a prerequisite for substrate binding and release was shown for the first time for an ECF transporter. Unlike subclass II transporters, for which an ATP-dependent release of the S unit was proposed, BioY interacts continuously with BioN (T) during the transport cycle. In a second focus of the work, an Escherichia coli reporter strain for biotin transporters was constructed. Due to inactivation of both biotin synthesis and the intrinsic high affinity biotin transporter, this strain was not capable of growing on trace amounts of biotin. With the use of this strain, transport activity of recombinantly produced solitary BioY proteins that naturally lack other ECF components was evidenced. Transport activity in the absence of AAT modules is also a feature of the Co2+ and Ni2+ specific S components CbiM and NikM. An EPR spectroscopic Co2+ detection assay helped underscoring the essential role of the small membrane protein CbiN for Co2+ loading of CbiM.

Há, no Brasil, uma enorme diversidade de espécies vegetais, e um conhecimento popular de várias propriedades medicinais das mesmas. Dentre os estudos realizados com extratos de plantas, há um interesse especial na atividade antioxidante. Este trabalho, focado em atividade antioxidante, é dividido em duas partes: a primeira, utiliza a técnica de RPE para estudar a ação dos antioxidantes neutralizando os radicais livres, enquanto que a segunda utiliza a TFD para, em simulação computacional, ajudar a entender os resultados obtidos na primeira parte. Foram analisados 10 extratos vegetais: Swartzia langsdorffii, Machaerium villosum, Pterogyne nitens, Maytenus ilicifolia (casca de raiz), Pera glabrata, Aegiphyla sellowiana, Copaifera langsdorffii, Chrysophyllum inornatum, Iryanthera juruensis (folhas e sementes), Didymopanax vinosum. O estudo da atividade antioxidante com RPE utiliza dois métodos diferentes: o primeiro método mede a atividade antioxidante por meio do controle da quantidade de radicais livres, TEMPOL e DPPH, em contato com o extrato vegetal, enquanto que o segundo método utiliza o spin trap DMPO em conjunto com a reação de Fenton (Fe2+ + H2O2 => Fe3+ + HO- + HO) para analisar a ação dos extratos vegetais contra o radical hidroxila (OH?). A simulação computacional dos compostos TEMPOL, DPPH e DMPO é realizada em um método de primeiros princípios na Teoria do Funcional da Densidade, com uso de pseudopotenciais. O código utilizado é o SIESTA. As conclusões indicam que o extrato de Iryanthera juruensis, tanto de folhas quanto de sementes, exibe atividades antioxidantes bastante acentuadas, em todos os métodos utilizados. A simulação computacional aponta o TEMPOL menos reativo que o DPPH, devido a menor energia liberada em sua reação de redução. Sabendo que algumas destas espécies já são usadas popularmente por propriedades medicinais, estudos futuros para a correta identificação do agente antioxidante e seu possível uso, tanto na indústria alimentícia quanto na farmacêutica, deverão ser realizados. / There is, in Brazil, a great diversity of vegetable species, and a popular knowledge of several medicinal properties of the some of them. In studies carried out with plants? extracts, there is special interest in antioxidant activities. This work, focused in antioxidant activity, is divided in two parts: the first uses EPR technique to study the antioxidant activities neutralizing free radicals, while the second one uses DFT, in computational simulation, to understand the results obtained from the first part. Ten vegetable extracts were analyzed: Swartzia langsdorffii, Machaerium villosum, Pterogyne nitens, Maytenus ilicifolia (bark root extracts), Pera glabrata, Aegiphyla sellowiana, Copaifera langsdorffii, Chrysophyllum inornatum, Iryanthera juruensis (leaves and seeds), Didymopanax vinosum. The study with EPR uses two different methods: the first method measures the antioxidant activity by monitoring the amount of free radicals, DPPH and TEMPOL, that are in contact with the plant extract, the second method uses spin trap DMPO with Fenton reaction (Fe2+ + H2O2 => Fe3+ + HO- + HO) for the study of the plant extract antioxidant activity against the hydroxyl radical (OH?). The computational simulation of TEMPOL, DPPH and DMPO is carried out using a method of first principles within the Density Functional Theory and pseudopotentials. The code is SIESTA. The conclusions indicate that the Iryanthera juruensis extract, as of leaves as of seeds, exhibits accentuated antioxidants activities, in all of the used methods. The computational simulation indicated that the TEMPOL is less reactive than the DPPH, because the lower energy in its reduction reaction. As some of these species are already used popularly by medicinal properties, future studies for correct identification of the antioxidant compounds and its possible use, as in the food industry as in the pharmaceutical industry, should be realized.

Submitted by Erika Demachki (erikademachki@gmail.com) on 2014-10-13T21:33:03Z No. of bitstreams: 2 Dissertação - Adriana Pereira Mundim Guedes - 2013.pdf: 2999561 bytes, checksum: 755cb864a8446e6ff5c334be00ea5367 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Jaqueline Silva (jtas29@gmail.com) on 2014-10-16T18:47:44Z (GMT) No. of bitstreams: 2 Dissertação - Adriana Pereira Mundim Guedes - 2013.pdf: 2999561 bytes, checksum: 755cb864a8446e6ff5c334be00ea5367 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2014-10-16T18:47:44Z (GMT). No. of bitstreams: 2 Dissertação - Adriana Pereira Mundim Guedes - 2013.pdf: 2999561 bytes, checksum: 755cb864a8446e6ff5c334be00ea5367 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2013-09-13 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Motivated by the perspective of ruthenium complexes to be used in cancer treatment, our research group has tested the hipotesis that some complexes of Ru (III) are able to interact with serum proteins, particularly albumin and transferrin. The Complex cis- [RuCl2(NH3)4]Cl (CTRu(III)) have been tested against different kind of tumor cells, obtaining good results. Starting from promising results obtained with this compound, subsequent studies are required to understanding the mechanism by which it exerts specificity for tumor cells. In this article, we report the first application of absorption UV-Vis, Fluorescence and Electron Paramagnetic Resonance (EPR) spectroscopy, to study the complex CTRu(III) interaction with human serum albumin (hsA) and bovine serum albumin (bsA). Fluorescence measurements revealed strong proteinsbound complex with Ksv of 1.32 x 105 and 3.71 x 105 for hsA and bsA, respectively. EPR spectra from mono-nuclear Ru(III) complexes in buffer, showed a significant decrease in the overall signal intensity following the first aquation step, is consistent with the formation of oxo-bridged Ru(III) dimers. EPR spectra revealed that the BSA very rapid binding to the protein via covalent binding through ligand-exchange with protein side chains, likely with histidine imidazoles. On the other hand, the complex binds non-covalently in hsA, probably as a product of the oligomerization of the complex in hemin-biding pocket. Furthermore, two species are slowly formed by covalent binding of the complex with the histidine residues, producing a species of axial symmetry and the other rhombic symmetry. These bonds seem to arise from the interaction of the complex with the histidine residue located in the binding Sudlow’s site II. / Motivado pela perspectiva de complexos de rutênio podem ser utilizados no tratamento do câncer, o nosso grupo de pesquisa testou a Hipótese que alguns complexos de Ru (III) são capazes de interagir com as proteínas do soro, particularmente albumina e transferrina. O complexo de cis-[RuCl2(NH3)4]Cl (CTRu(III)) foi testado contra diferentes tipos de células tumorais, obtendo bons resultados. A partir de resultados promissores obtidos com este composto, estudos subsequentes são necessários para a compreensão do mecanismo pelo qual ele exerce sua especificidade para células de tumor. Neste artigo, apresentamos a aplicação de espectroscopia de absorção UV-vis, fluorescência e ressonância paramagnética eletrônica (RPE), para estudar a interação do complexo CTRu(III) com albumina sérica humano (hsA) e a albumina sérica bovina (bsA). Medidas de fluorescência revelaram uma forte ligação do complexo com as proteínas com Ksv de 1,32 x 105 e 3,71 x 105 para hsA e bsA, respectivamente. Espectros de RPE de complexos de Ru (III) mono-nucleares em tampão mostraram um decréscimo significativo na intensidade do sinal global após a primeira passo de aquação, que é consistente com a formação de dímeros de oxo complexos de Ru (III). Os espectros de RPE revelaram que a ligação à bsA é muito rápida, a ligação covalente à proteína ocorre através de troca dos ligantes com cadeias laterais de proteínas, provavelmente com o imidazol da histidina. Por outro lado, o complexo se liga não covalentemente na hsA, provalente como produto da oligomerização do complexo no bolso de ligação hemin. Além disso, duas espécies são formadas lentamente por ligação covalente do complexo com os resíduos histidina, produzindo uma espécie de simetria axial e a outra de simetria rômbica. Essas ligações parecem surgir pela interação do complexo com o resíduo histidina localizado no sítio de ligação Sudlow II.

Studies on perovskite rare earth manganites of general formula R1-xAxMnO3 (where R is a trivalent rare earth ion such as La3+, Pr3+ etc. and A is a divalent alkaline earth ion such as Ca2+, Sr2+, Ba2+, have been a very active research area in the last few years in condensed matter physics. Manganites have a distorted perovskite crystal structure with R and A ions situated at the cube corners, oxygen ions at the edge centers of the cube and Mn ions at the centres of the oxygen octahedra. In these manganites the Mn ions are found to be in mixed valence state i.e., in Mn3+ and Mn4+ states. In the octahedral crystal field of oxygen ions the single ion energy levels are split into t2g and eg levels. Mn3+ being a Jahn-Teller ion, the eg level is further split due to the Jahn-Teller effect. A strong Hund’s coupling between the spins in the t2g and eg levels renders the Mn3+ ions to be in the high spin state. The interplay of competing super exchange between Mn ions which determines the antiferromagnetism, orbital ordering and insulating behavior and double exchange between Mn ions which leads to ferromagnetism and metallicity gives rise to very complex phase diagrams of manganites as a function of composition, temperature and magnetic field. The strength of these interactions is determined by various factors such as the A-site cation radius and the Jahn-Teller distortion due to the presence of Mn3+ ions. The strongly coupled charge, spin, lattice and orbital degrees of freedom in manganites gives rise to complex phenomena such as colossal magnetoresistance (CMR), charge order (CO) and orbital order (OO) and phase separation (PS) etc. The properties of these materials are sensitive functions of external stimuli such as the doping, temperature and pressure [1-5] and have been extensively studied both experimentally and theoretically in single crystal, bulk polycrystalline and thin film forms of the samples [6-9]. Charge ordering is one of the fascinating properties exhibited by manganites. Charge ordering has historically been viewed as a precursor to the complex ordering of the Mn 3d orbitals, which in turn determine the magnetic interactions and these magnetic interactions are the driving force for charge localization and orbital order. This ordering of Mn3+ / Mn4+ charges can be destabilized by many methods. An external magnetic field can destabilize the charge ordered phase and drive the phase transition to the ferromagnetic metallic state [10-11]. Other than magnetic field, charge ordering can also be ‘melted’ by a variety of perturbations like electric field [12, 13], hydrostatic and chemical pressure [14-16], irradiation by X-rays [17], substitution at the Mn -site [18 -21] and A-site [22]. Of these, A-site substitution with bigger cations like barium is particularly of great interest since it does not interrupt the conduction path in the “MnO3” frame work Recently attention has been drawn towards the properties of nanoscale manganites. The nanoscale materials are expected to behave quite differently from extended solids due to quantum confinement effects and high surface/volume ratio. Nanoscale CMR manganites have been fabricated using diverse methods in the form of particles, wires, tubes and various other forms by different groups. It has been shown that the properties of CMR manganites can be tuned by reducing the particle size down to nanometer range and by changing the morphology [23-27]. As mentioned above, charge order is an interesting phase of manganites and these CO mangnites in the form of nanowires and nanoparticles show drastic changes in their properties compared to bulk. In contrast to the studies on the CMR compounds, there are very few reports on charge ordering nano manganites except on nanowires of Pr0.5Ca0..5MnO3 [28] and nanoparticles of Nd0.5Ca0.5MnO3 [29] and Pr0.5Sr0..5MnO3 [30]. This thesis is an effort in understanding certain aspects of charge order destabilization by two different methods, namely, doping bigger size cation (barium) in A-site (external perturbation) and by reducing the particle size to nano scale ( intrinsic). For this purpose we have selected the charge ordering system Pr1-xCaxMnO3 (PCMO) with composition x = 0.43. The reason behind choosing this composition is the observation [31] that CO is particularly weak for this value of x. We have prepared bulk, nanoparticles and nanowires of Pr0.57Ca0.41Ba0.02MnO3 manganite and have carried out microstructure, magnetic, magneto transport and EMR measurements to understand the nature of CO destabilization and also to understand other aspects such as magneto transport and magnetic anisotropy . Apart from destabilization of the charge order in PCMO we have also studied the bismuth based manganite Bi0.5Ca0.5MnO3. The reason behind choosing this system is the robust charge order of Bi0.5Ca0.5MnO3 compared to rare earth based manganites. So far no attempt has been made in comparing the electron paramagnetic resonance properties of bismuth based manganites with those of the rare earth based manganites. We have studied the magnetic, transport and electron paramagnetic resonance properties of Bi0.5Ca0.5MnO3 prepared by solid state reaction method and compared the results with those of Pr0.5Ca0.5MnO3 . In the following we present a chapter wise summary of the thesis. Chapter 1 of the thesis contains a brief introduction to the general features of manganites describing various interesting phenomena exhibited by them and the underlying interactions . Chapter 2 contains a detailed review of EPR studies on manganites describing the current level of understanding in the area. In this chapter we have also described the different experimental methodology adopted in this thesis. Chapter 3 reports the effect of a small amount (2%) of barium doped in the charge ordered antiferromagnetic insulating manganite Pr0.57Ca0.43MnO3. The samples were prepared by solid state synthesis and charecterized by various techniques like XRD, EDXA. The results of magnetization, magnetotransport and EPR/EMR experiments on both Pr0.57Ca0.43MnO3 and Pr0.57Ca0.41Ba0.02MnO3 are compared. The magnetization studies show that barium doping induces ferromagnetic phase in place of the CO-antiferromagnetic phase of the pristine sample at low temperatures as reported earlier by Zhu et al.,[31]. The transport studies show insulator to metal transition. The EPR parameters viz line width, intensity and ‘g’ value of Pr0.57Ca0.43MnO3 and Pr0.57Ca0.41Ba0.02MnO3 are compared. The magnetization and EPR studies reveal that the CO transition temperature TCO has shifted to a slightly lower value accompanied by a small decrease in the strength of the charge order. Thus a small amount of barium affects the CO phase of Pr0.57Ca0.43MnO3 and it also induces a ferromagnetic metallic phase at low temperature. Another most important and unexpected result of EMR experiment is the observation of high field signals, i.e. two EMR signals are observed at low temperatures in the ferromagnetic phase of Pr0.57Ca0.41Ba0.02MnO3. The appearance of the high field signals are understood in terms of the effects of magneto crystalline anisotropy. Chapter 4, reports the microstructure, magnetization and EMR studies of Pr0.57Ca0.41Ba0.02MnO3 nanoparticles prepared by sol-gel method. We have mainly focused on the effect of size on the charge ordered phase. The samples were characterized by different techniques like XRD, EDXA and TEM. The obtained particle size of the samples are 30, 60 and 100 nm respectively. We have compared the magnetic, magneto transport and EMR results of these nano samples with the bulk properties. The 30 nm particles do not show the CO phase whereas the 60 and 100 nm particles show CO signatures in DC- magnetization measurements. The EPR intensity also shows a similar trend. These results confirm that charge ordering can also be destabilized by reducing the particle size to nano scale. But the EPR linewidth which reflects the spin dynamics shows a change in the slope near the CO temperature and there by indicates the presence of premonitory charge ordering fluctuations in smaller particles. We also observed that the EMR linewidth increases with the decrease of particle size. Another striking result is the disappearance of high field signals in all the nanosamples. This is understood in terms of a decrease in the magnetic anisotropy in nanoparticles. Part of the result of this chapter is published [32]. Chapter 5, reports the morphological, magnetic and electron paramagnetic resonance studies of Pr0.57Ca0.41Ba0.02MnO3 nanowires. Recently our group has studied the nanowires of Pr0.5Ca0..5MnO3 [28]. In the nanowire sample of Pr0.5Ca0..5MnO3 only a partial suppression of CO is observed. This raises the question about the incomplete suppression of the CO in the nanowires: is this a consequence of the material being microscopic in one dimension and is it necessary to have a 3-dimensional nano material to have full suppression of the charge order ? In the present work we attempt to provide an answer to this question. PCBM nanowires of diameter 80-90 nm and length of ∼ 3.5 μm were synthesized by a low reaction temperature hydrothermal method. We have confirmed the single phase nature of the sample by XRD experiments. Scanning electron microscopy (SEM) and trasmission electron microscopy (TEM) were used to characterize the morphology and microstructures of the nanowires. The surface of nanowires was composed of particles of different grain size and interestingly some particles were hexagonal in shape. The bulk PCBM manganite exhibits charge order at 230 K along with a ferromagnetic transition at 110 K. However, SQUID measurements on PCBM nano-wires show a complete melting of the charge ordering and a ferromagnetic transition at 115 K. The magnetization observed in the nanowires was less compared to that in the bulk. EPR intensity measurements also support this result. Characteristic differences were observed in linewidth and ‘g’ factor behaviors of nanowires when compared with those of the bulk. EPR linewidth which reflects the spin dynamics shows a slope change near the CO temperature (like in nanoparticles) possibly due to charge order fluctuations in nanowires. The high field signals were absent in nanowires as well. Part of the result of this chapter is published [33]. Chapter 6 deals with the magnetic and electron paramagnetic resonance studies on Pr0.5Ca0.5MnO3 and Bi0.5Ca0.5MnO3. These manganites are prepared by solid state reaction method and characterized by different techniques like XRD and EDXA. Further, we have compared the results of magnetization and electron paramagnetic resonance properties of Pr0.5Ca0.5MnO3 with those of Bi0.5Ca0.5MnO3 manganite in the temperature range of 10- 300 K. The two charge ordered manganites show significant differences in their behavior. The temperature dependence of the EPR parameters i.e. line width, central field and intensity of Bi0.5Ca0.5MnO3 are quite different from the rare earth based manganite i.e. Pr0.5Ca0.5MnO3. Linewidth of BCMO is large compared to PCMO manganite and interestingly the temperature dependence of the central fields (CF) of PCMO and BCMO show opposite behavior. The CF of PCMO decreases with decrease in temperature as found in a large number of other CO systems, whereas CF of BCMO increases with decrease in temperature. This unusual behavior of resonance field is attributed to the different magnetic structure of BCMO system at low temperatures. Chapter 7 sums up the results reported in the thesis. The insight gained from the present work in understanding the destabilization of charge order by chemical doping and size reduction is discussed as well as the differences in the properties of bismuth and rare earth manganites. Further, we have indicated possible future directions of research in this area.

A liquid Cooled below its normal freezing temperature is known as a supercooled liquid. On further cooling, supercooled liquids crystallize to thermodynamically stable, ordered structures. Alternatively, if the cooling rate is fast enough, the crystallization may be avoided altogether. Below a particular temperature during rapid cooling the liquid will solidify into a disordered, amorphous phase -also known as the glassy phase of matter. This particular temperature is termed the ”glass transition temperature” (Tg). Unlike a crystalline solid, a glass is neither a thermodynamically stable phase nor does it possess long range molecular ordering. Very slow structural relaxation (in the time scale of ∼ 100 s) is always present in the glassy phase. Thus, this phase is often referred to as a metastable phase of matter. Experimental and theoretical studies related to the behavior of supercooled liquids are the subject matter of many investigations for the last few decades [1]. These studies find their applications in diverse fields such as geology, cryopreservation, glaciology and atmospheric science. However, properties of supercooled liquids and the corresponding amorphous phase are not completely understood at present, particularly for hydrogen bonded (H-bonded) systems. This thesis concerns both the crystallization and the glass formation process of H-bonded systems. The systems of interest are water, the commonly accepted universal solvent, and the aqueous binary mixture of glycerol and water. The technique of molecular probing is often used to study the cooperativety and rotational diffusion of supercooled liquids and for determination of the glass transition temperature. For the present set of work, a molecular probe technique called spin probe ESR is extensively used. Electron paramagnetic resonance or electron spin resonance (EPR/ESR) measures the electronic energy level separation and is well known for the high sensitivity. All of the systems studied in the present set of work are diamagnetic. This issue is circumvented by dissolving paramagnetic spin probe molecules, which are usually organic free radicals with one N-O group, into the systems. Spin probes are added in very low concentrations (~10-3M) to minimize the effect on the host system and also to avoid mutual interactions between them. The unpaired electron delocalized in the direction of the N-O bond serves as the paramagnetic center required for an ESR experiment. The splitting of electron energy level due to the external magnetic field (Zeeman splitting) can give rise to resonance absorption of energy if exposed to a microwave of appropriate frequency. There is also a magnetic coupling (hyperfine) between the spin of the unpaired electron and nuclear spin of the nearby nitrogen atom. The hyperfine coupling splits each electron energy levels, to the first order, symmetrically into three levels. The transitions between these levels -subject to appropriate selection rules -give rise to the ESR spectrum [2]. The spectral shape in a magnetic field sweep ESR experiment appears complex if randomly oriented spin probes are dispersed in an amorphous or polycrystalline solid matrix. The high degree of mobility in probe molecules, present in a liquid solution, can average out the individual anisotropy of magnetic tensors to get a spectrum of three equally spaced liens. Experiments can be performed spanning a spin probe reorientation timescale of 10-7-10-12 s typically in the temperature range of 4.2 -300K. In chapter one we have given a brief overview of the supercooled liquids and the phase transitions related to the present work. Particular emphasis has been given to the dynamical features of the supercooled liquid close to its glass transition temperature and their classification based on the degree of ’fragility’ [3]. Brief general introductions of the systems studied in each of the following chapters are also provided. Then, the details of ESR spectroscopy and a quantum mechanical picture of the method of spin probe ESR have been discussed [4]. A separate section has been devoted to the numerical and analytical methods used to analyze the spectrum to extract information related to the spin probe dynamics [5]. The chapter concludes with a description of the ESR spectrometer. In chapter two we have studied the glass transition and dynamics of the supercooled water by the method of spin probe ESR. The vitrification has been done by direct exposure of the bulk water sample, doped with the spin probe TEMPOL, to the liquid helium flow. The vitrified matrix turns into the ultraviscous liquid above the putative glass transition temperature of ~136 K which further transforms to cubic ice (Ic) above TX ~150 K. The supercooled fraction of water, along with the spin probes which are treated as impurities by the crystallized surroundings, remain trapped inside the veins or triple junctions of the ice grains which serve as the interfacial reservoir of impurities in a polycrystalline ice matrix. The spectra for the entire temperature range have been analyzed with the help of in-depth computation by modelling the reorientation of TEMPOL in terms of the jump angle θs and the rotational correlation time τ [5]. This model, based on a homogeneous mobility scenario of the spin probe, works nicely except in the temperature range of 140-180 K. Dynamical heterogeneity (DH) is apparent in this temperature range and a more mobile (fast) component, as compared to the one corresponding to the very slow dynamics of TEMPOL at lower temperatures (slow), is observed. The relative weight of the fast and the slow component changes with temperature and above ~180 K the entire spectrum changes into the motionally narrowed triplet. The temperature dependence of the slow component of τ shows a change in slope at a temperature close to the putative glass transition temperature of water. The fast component of τ exhibits a fragile, i.e. non-Arrhenius character at high temperature with a crossover to a strong, i.e. Arrhenius behavior below ~225 K, close to the hypothesized fragile-to-strong crossover (FSC) for water at TFSC ~228 K. The breakdown of the Debye-Stokes-Einstein (DSE) law is observed when the τ values are combined with the available viscosity data of water to evaluate the DSE ratio, paralleling the SE breakdown which has recently been observed in nanoconfined water [6]. The dynamical heterogeneity is thought to be closely associated with the static structural heterogeneities of supercooled water. The existence of large scale structural fluctuations spanning a range of low-and high-density phases of liquid water have been associated with the heterogeneous dynamics sensed by TEMPOL. Motivated by the Arrhenius like behavior of the slow component, it has been identified with the low density liquid (LDL). The fragile nature of the fast component at high temperature may be identified with that of the high density liquid (HDL) which is the predominant fraction in liquid or weakly supercooled water [6]. Chapter three reports the studies on freezing and dynamics of the supercooled water trapped inside the veins of a polycrystalline ice matrix by dissolving spin probes TEMPO and TEMPOL into it. When a millimolar spin probe aqueous solution is cooled below the freezing point of water, the spin probes -driven by the mechanism described above migrate to the liquid environment inside the ice veins. Local concentration of the probe molecules inside the veins can go up to 1-10 M [7]. Bulk crystallization is evident in differential scanning calorimetry (DSC) studies whereas the liquid environment of the spin probe below the bulk freezing is confirmed by its narrow triplet ESR spectrum. A sudden collapse of this narrow triplet into a single broad line indicates the freezing of the trapped water fraction which usually happens well below the DSC freezing point for both the probes. The spin probe detected freezing point of this interstitial water is found to be largely dependent on the properties and the amount of the dissolved probe molecules. An explanation is sought in terms of the ’destructuring effect’ on the tetrahedral ordering of the water H-bond network by both the high local concentration of the spin probes and the hydrogen bond strength, formed between the water and the spin probe molecules through the polar groups of the latter [8, 9]. These two factors are thought to play important roles in determining the reorientational dynamics of the spin probe molecules, as well. The rotational correlation times of the two probes exhibit a crossover owing to the different mobility of their salvation shells in the more ordered supercooled water. The observed relaxation behavior of this confined water using the probe TEMPO, which has little effect on water H-bond network, is found in agreement with the previous experimental investigations on water confined in a nanochannel [10]. In chapter four, the glass transition, relaxation and the free volume of the glycerol-water (G-W) system are studied over the glycerol concentration range of 5 -85 mol% with TEMPO as the spin probe. G-W mixture is intrinsically inhomogeneous due to the well established phase segregation below a critical glycerol concentration of 40 mol%. In the inhomogeneous regime the water molecules tend to form cooperative domains besides the mesoscopic G-W mixture [11]. Samples are quenched by rapid cooling down to 4.2 K inside the spectrometer cryostat. Spectra were recorded on slow heating of the sample in the temperature range of 130 -305 K. The glass transition temperature is correlated to the sharp transition of the extrema separation of the ESR spectrum. The glass transition temperatures are found to follow a concentration dependence which is closely associated to the mesoscopic inhomogeneities of the G-W system. The steady enhancement in fragility of the G-W system with the addition of water is evident from the temperature dependence of the spin probe correlation time τ for the entire concentration range. In the temperature range of 283 -303 K, the DSE law is followed i.e. the spin probe reorientation process is found to be strongly coupled to the system viscosity. In this regime, the τ values have been used along with the available viscosity data to calculate the effective volume V of the spin probe for the entire concentration range. The spin probe effective volume is a measure of the available free volume of the host matrix. A drastic change in the quantity is seen in the vicinity of the 40 mol% glycerol concentration owing to a similar structural change of the matrix due to the formation of mesoscopic scale inhomogeneities below the critical concentration [12]. The thesis concludes with a discussion about the possible future directions of research.

TDO utilizes b-type heme as a cofactor to activate dioxygen and insert two oxygen atoms into free L-tryptophan. We revealed two unidentified enzymatic activities of ferric TDO from Ralstonia metallidurans, which are peroxide driven oxygenation and catalase-like activity. The stoichiometric titration suggests that two moles of H2O2 were required for the production of one mole of N-formylkynurenine. We have also observed monooxygenated-L-tryptophan. Three enzyme-based intermediates were sequentially detected in the peroxide oxidation of ferric TDO in the absence of L-Trp including compound I-type and compound ES-type Fe-oxo species. The Fe(IV) intermediates had an unusually large quadrupole splitting parameter of 1.76(2) mm/s at pH 7.4. Density functional theory calculations suggest that it results from the hydrogen bonding to the oxo group. We have also demonstrated that the oxidized TDO was activated via a homolytic cleavage of the O-O bond of ferric hydroperoxide intermediate via a substrate dependent process to generate a ferrous TDO. We proposed a peroxide activation mechanism of the oxidized TDO. The TDO has a relatively high redox potential, the protonated state of the proximal histidine upon substrate binding as well as a common feature of the formation of ferric hydroxide species upon substrate or substrate analogues binding. Putting these together, we have proposed a substrate-based activation mechanism of the oxidized TDO. Our work also probed the role of histidine 72 as an acid-base catalyst in the active site. In H72S and H72N mutants, one water molecule plays a similar role as that of His72 in wild type TDO. MauG is a c-type di-heme enzyme which catalyze the biosynthesis of the protein-derived cofactor tryptophan tryptophylquinone. Its natural substrate is a monohydroxylated tryptophan residue present in a 119-kDa precursor protein of methylamine dehydrogenase (MADH). We have trapped a novel bis-Fe(IV) intermediate from MauG, which is remarkably stable. A tryptophanyl radical intermediate of MADH has been trapped after the reaction of the substrate with the bis-Fe(IV) intermediate. Analysis by high-resolution size-exclusion chromatography shows that MauG can tightly bind to the biosynthetic precursor and form a stable complex, but the mature protein substrate does not.

In this study, the oxygen-deficient TiO2, SrTiO3 systems and transition metal ion (Cr or V) doped TiO2, SrTiO3 and SrZrO3 systems have been investigated. We prepared samples as polycrystals, single crystals and thin films for various desires. Their structural, physical and electronic properties were measured by bulk-sensitive techniques (X-Ray Diffraction, SQUID and Electro Paramagnetic Resonance) or surface-sensitive techniques (Photoemission spectroscopy and X-ray absorption spectroscopy). The measurement of SQUID and EPR showed not only their magnetic properties but also the valence state of Cr dopant. We verified the valence state of Cr ions in oxides and found the key parameters of sample synthesis which control the valence state of Cr ions. Segregated phases such as SrCrO4 were formed when the samples were synthesized under O2 rich environment. The surface properties of Cr doped SrZrO3 films are also discussed. We found the synthesis conditions which influence on not only the behavior of Cr ions but also the resistive-switching behaviors. Various resistive-switching behaviors seem to depend on the surface chemistry of films. We found that the accumulation of Cr3+ on film surface provides a clean interface without any non-stoichiometric oxides and that this sharp interface termination results in a good performance of resistive-switching.

Perovskite rare-earth manganites of the form R1-xAxMnO3 (R – rare earth ion or Bi, A – Ca,Sr) have drawn an overwhelming research interest during the last few years owing to their extraordinary physical properties. Some of the interesting phenomena exhibited by the manganites are (a) colossal magneotresistance (CMR) (b) charge, orbital and spin ordering and (c) phase separation at nano and micron scale. The manganites are strongly correlated systems in which the charge, spin and orbital degrees of freedom are coupled. The properties of these materials are sensitive functions of external stimuli such as the doping, temperature and pressure [1-5] and have been extensively studied both experimentally and theoretically on single crystal, bulk polycrystalline and thin film forms of the samples [6-9]. Recently attention has been drawn towards the properties of nanoscale manganites. The nanoscale materials are expected to behave quite differently from extended solids due to quantum confinement effects and high surface/volume ratio. Nanoscale CMR manganites have been fabricated using diverse methods in the form of particles, wires, tubes and various other forms by different groups. It has been shown that the properties of CMR manganites can be tuned by reducing the particle size down to nanometer range and by changing the morphology [10-14]. The physical properties of antiferromagnetic insulating charge ordered manganites have been well investigated by using numerous experimental techniques on bulk solids. It is known that the charge ordered (CO) phase is ‘melted’ resulting in a ferromagnetic, metallic phase on application of high magnetic fields, electric fields, impurity ion doping, high energetic ion irradiation and by pressure [15-17]. However, no attempts have been made on the fabrication and the physical property investigations on nanoscale charge ordered manganites. Hence, we have undertaken to study the properties of charge ordered manganites prepared at nanoscale using various experimental probes. In this thesis we present the results on magnetization, magnetotransport and Electron Magnetic Resonance (EMR) (electron paramagnetic resonance in the paramagnetic phase and ferromagnetic resonance in the ferromagnetic phase) studies of the following nanoscale compounds and compare the properties with those of their bulk counterparts; (a) highly robust antiferromagnetic insulating CE –type charge ordered manganite Pr0.5Ca0.5MnO3 (PCMO) (b) highly robust antiferromagnetic insulating CE- type charge ordered manganite Nd0.5Ca0.5MnO3 (NCMO) (c) moderately robust A-type charge ordered manganite Pr0.5Sr0.5MnO3 (PSMO) (d) highly robust insulating anti-ferromagnetic charge ordered manganites Bi0.5Ca0.5MnO3 (BCMO) and Bi0.5Sr0.5MnO3 (BSMO) and (e) a CMR manganite Pr0.7Pb0.3MnO3 (PPMO). Chapter 1 of the thesis contains a brief introduction to the general features of manganites describing various interesting phenomena and the interactions underlying them. Further, we have written a detailed review on the properties of nanometric CMR manganites of various sizes and shapes. In this chapter, we have also described the experimental methodology and the analysis procedure adopted in this work Chapter 2 reports the fabrication of nanowires and nanoparticles of Pr0.5Ca0.5MnO3 (PCMO) and the results obtained from magnetization, magnetotransport and electron magnetic resonance measurements performed on nanoscale PCMO along with their comparison with those of the bulk sample. Here, the nanowires of PCMO were prepared by hydrothermal method and the nanoparticles of mean sizes 10, 20 and 40 nm were prepared by polymer assisted sol-gel method. Solid state reaction method was used to prepare the micron sized PCMO bulk material. Different techniques like XRD, TEM, EDAX and ICPAES have been used to characterize the samples. The novel result of the present investigation is the weakening of charge order and switch over from the anti-ferromagnetic phase to ferromagnetic phase in PCMO nanowires [18]. In addition, the charge order is seem to have completely suppressed in 10 nm PCMO nanoparticles as observed from the magnetization measurements. These results are particularly very significant as one needs magnetic fields of ~ 27 T to melt the charge ordered phase in PCMO. Size induced insulator-metal transition TM-I is observed in nanoscale PCMO at low temperatures accompanied by ferromagnetism. CMR of 99.7% is obtained at TM-I and at a field of 11 T. EMR studies have confirmed the presence of ferromagnetic phase at low temperatures. Temperature dependent EMR line width and intensity have shown the presence of CO phase in PCMO10 though static magnetization measurements have shown the absence of CO phase. It is found that the EMR linewidth increases with the decrease of particle size. Chapter 3 reports the fabrication of nanoparticles of Nd0.5Ca0.5MnO3 (NCMO) and the results obtained from magnetization, magnetotransport and electron magnetic resonance measurements performed on nanoscale NCMO along with their comparison with those of bulk NCMO. The nanoparticles of NCMO of mean sizes 5, 20 and 40 nm were prepared by polymer assisted sol-gel method. Solid state reaction method was used to prepare the micron sized NCMO bulk material. Different techniques like XRD, TEM, EDAX and ICPAES have been used to characterize the samples. A striking result of this particular investigation is the complete suppression of charge ordered phase in 5 and 20 nm NCMO nanoparticles as observed from the magnetization measurements [19]. Size induced insulator-metal transition TM-I is observed in nanoscale NCMO at low temperatures accompanied by ferromagnetism in accordance with Zener double exchange meachanism. CMR of 99.7% is obtained at TM-I and at a field of 11 T. EMR studies have confirmed the presence of ferromagnetic phase at low temperatures. Temperature dependent EMR line width and intensity have shown the presence of residual CO fluctuations in NCMO5 though the static magnetization measurements have shown the absence of CO phase. It is found that the EMR linewidth increases with the decrease of particle size. Low temperature X-ray diffraction measurements on NCMO20 indicate the absence of CO phase. But the preliminary results obtained from the optical spectroscopy measurements indicate the evidence for the presence of CO phase. In Chapter 4, we report the investigations on the nanoscale PSMO. PSMO nanoparticles of sizes 20, 40 and 60 nm are prepared by polymer precursor sol-gel method. PSMO nanowires of diameter 50 nm and lengths of a few microns have been prepared by hydrothermal method. The bulk polycrystalline PSMO is obtained by crushing the single crystal of the same prepared by float zone method. Various techniques like XRD, TEM, VSM, transport measurements and EMR spectroscopy have been employed to characterize and to study the size dependent magnetic, transport and electron magnetic resonance properties and to compare them with those of the bulk. Our results show that there is a disappearance of anti-ferromagnetic charge ordering phase and the appearance of a ferromagnetic phase at low temperatures in all PSMO nanoparticles and nanowires. Metal like behaviour is observed in the size induced ferromagnetic phase in nanoparticles. The EMR linewidth increases with the decrease of particle size. A comparison with the properties of the bulk material shows that the ferromagnetic transition at 265 K remains unaffected but the anti-ferromagnetic transition at TN = 150 K disappears in the nanoparticles. Further, the temperature dependence of magnetic anisotropy shows a complex behaviour, being higher in the nanoparticles at high temperatures, lower at lower temperatures in comparison with the bulk [20]. In Chapter 5, we present the fabrication, characterization and the results obtained from the magnetization and EMR measurements carried out on BCMO and BSMO nanoparticles and compare the results with those of the bulk. X-ray diffraction gives evidence for single phasic nature of the materials as well as their structures. Mono-dispersed to a large extent, isolated nanoparticles are seen in the transmission electron micrographs. High resolution electron microscopy shows the crystalline nature of the nanoparticles. Superconducting quantum interferometer based magnetic measurements from 10 K to 300 K show that these nanomanganites retain the charge ordering nature unlike the Pr and Nd based nanomanganites. The CO in Bi based manganites is thus found to be very robust consistent with the observation that magnetic fields of the order of 130 T are necessary to melt the CO in these compounds. These results are supported by electron magnetic resonance measurements [21]. In Chapter 6, we present our results on the effect of particle size on the magnetic properties of Pr0.7Pb0.3MnO3 (PPMO). PPMO nanoparticles of two different sizes (~5 nm and 30 nm) were prepared by the polymeric precursor sol-gel method. The samples are characterized by different techniques like XRD, TEM, SQUID magnetometry, EMR and optical spectroscopic measurements. It is found that the nanoparticles crystallize in the cubic perovskite structure. TEM measurements show that the 5 nm particles are uniform in size. They are also crystalline as seen by HREM and XRD measurements. SQUID magnetometry measurements have shown that the Curie temperature increases (from 220 K to 235 K) with the increase of particle size. Saturation magnetization is higher for the smaller particles studied. We have observed only one EMR signal down to 4 K in both the nanoparticles (5 and 30 nm) in contrast to the two EMR signal behaviour observed in bulk PPMO [22]. It is found that the EMR linewidth increases with the decrease of particle size in the paramagnetic phase. Temperature dependent optical spectroscopy measurements performed on 5 nm PPMO nanoparticles indicate that the insulator-metal transition temperature TM-I = 230 K, is not very different from TM-I = 235 K of the bulk sample [23] The thesis concludes with a brief writeup summarizing the results and pointing out possible future directions of research in the area.

No description available.

Treatment of the diethyl ester of o-phenylenebis(oxamic acid) (opbaH2Et2, 1) with 5/6 equivalent of MeNH2 in abs. EtOH results in the exclusive formation of the ethyl ester of o-phenylene(N′-methyl oxamide)(oxamic acid) (opooH3EtMe, 2) in ca. 50% yield. Treatment of 2 with four equivalents of [Me4N]OH followed by the addition of Cu(ClO4)2·6H2O gave [Me4N]2[Cu(opooMe)]·H2O (3A) in ca. 80% yield. As 3A appears to be a hygroscopic solid, the related [nBu4N]+ salts [nBu4N]2[M(opooMe)]·H2O (M = Cu (3B), Ni (4)) have been synthesized. By addition of two equivalents of [Cu(pmdta)(NO3)2] to a MeCN solution of 3B the novel asymmetric trinuclear complex [Cu3(opooMe)(pmdta)2](NO3)2 (5) could be obtained in ca. 90% yield. Compounds 2, 3A, 3B, 4 and 5 have been characterized by elemental analysis and NMR/IR spectroscopy. Furthermore, the solid state structures of 3A in the form of [Me4N]2[Cu(opooMe)]·MeOH (3A′), 3B in the form of [nBu4N]2[Cu(opooMe)] (3B′), 4 in the form of [nBu4N]2[Ni(opooMe)]·1.25H2O (4′) and 5 in the form of [Cu3(opooMe)(pmdta)2] (NO3)2·3MeCN (5′), respectively, have been determined by single-crystal X-ray diffraction studies. By controlled cocrystallization, diamagnetically diluted 3B (1%) in the host lattice of 4 (99%) in the form of single crystals have been made available, allowing single crystal EPR studies to extract all components of the g-factor and the tensors of onsite CuA and transferred NA hyperfine interaction. Out of these studies the spin density distribution of the [Cu(opooMe)]2− complex fragment could be determined. The magnetic properties of 5 were studied by susceptibility measurements versus temperature. An intramolecular J parameter of −65 cm−1 has been obtained, unexpectedly, as 5 should possess two different J values due to its two different spacers between the adjacent CuII ions, namely an oxamate (C2NO3) and an oxamidate (C2N2O2) fragment. This unexpected result is explained by a summarizing discussion of the experimentally obtained EPR results (spin density distribution) of 3B, the geometries of the terminal [Cu(pmdta)]2+ fragments of 5 determined by X-ray crystallographic studies and accompanying quantum chemical calculations of the spin density distribution of the mononuclear [Cu(opooMe)]2− and of the magnetic exchange interactions of trinuclear [Cu3(opooMe)(pmdta)2]2+ complex fragments. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.