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L'Écuyer, Tristan Simon. "Water dimer atmospheric absorption." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/mq24864.pdf.
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Hamdan, Abdullah. "Infrared spectroscopy of methane dimer." [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=978829921.
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Guhathakurta, Anjan. "Topological specificity of ColE1 dimer resolution." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321370.
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Broomhead, Nathan. "Dimer models and Calabi-Yau algebras." Thesis, University of Bath, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.500694.
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In this thesis we use techniques from algebraic geometry and homological algebra, together with ideas from string theory to construct a class of 3-dimensional Calabi-Yau algebras. The Calabi-Yau property appears throughout geometry and string theory and is increasingly being studied in algebra. Dimer models, first studied in theoretical physics, give a way of writing down a class of non-commutative algebras, as the path algebra of a quiver with relations obtained from a 'superpotential'. Some examples are Calabi-Yau and some are not. We consider two types of 'consistency' condition on dimer models, and show that a 'geometrically consistent' dimer model is 'algebraically consistent'. Finally we prove that the algebras obtained from algebraically consistent dimer models are 3-dimensional Calabi-Yau algebras.
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Qian, Yue, and 钱玥. "Electronic spectroscopy of transition metal dimer." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hub.hku.hk/bib/B50899971.
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This thesis reports laser spectroscopic studies of gas-phase transition metal dimers using laser ablation/reaction with free jet expansion and laser-induced fluorescence (LIF) spectroscopy technique. Themolecules studied in this work are palladium dimer (Pd2) and vanadium dimer (V2). Many compounds formed from these transition metals are important and functional catalysts in chemical reactions. Therefore, it is of great significance to start from the fundamental level to understand the properties and characteristics of the metal bonding and also the behavior of these metals when reacting with other chemicals.
The electronic transitions of Pd2and V2in the visible region were studied. Gas-phase Pd2and V2moleculeswereproduced by laser ablation of palladium and vanadium metal rod, respectively. For the Pd2molecule, eleven vibrational bands were recorded and analyzed, and have been assigned to the 〖[17.1]〗^3 □_g□ X^3 □_u^+ transition system. The bond length and vibrational frequency of the ground X^3 □_u^+ state were determined to be 2.47 Å and 211.38 cm-1, respectively. This is the first experimental investigation of the electronic transitions of Pd2.For the V2molecule,six vibrational bands were observed and assigned to a new 〖[19.6] 〗^3 □_u^□□ X^3 □_g^□ transition system. Molecular constants for the 〖[19.6] 〗^3 □_u^□ excited state were obtained from high-resolution LIF spectra. The electronic structure of the Pd2andV2molecules was discussed in detail using molecular orbital energy level diagrams, which is important for understanding the nature of chemical bonding in these dimers. Comparison of the transition metal dimers studied in this work with other dimers is also presented.published_or_final_version
Chemistry
Master
Master of Philosophy
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Griffiths, Hywel David. "Nucleoprotein complexes in ColE1 dimer resolution." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268532.
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Macdonald, James William. "Laser photoionisation spectroscopy of silver dimer." Thesis, University of Edinburgh, 1993. http://hdl.handle.net/1842/11074.
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A number of experimental techniques have been brought together to create a powerful investigative tool. This laser vaporisation, supersonic expansion, laser ionisation mass spectrometry amalgam has allowed the study of two distinct types of molecular species. Many heteronuclear diatomic species have been prepared and investigated for the first time. These novel molecules are of interest due to their utility as bulk phase alloys. Mass spectra are presented for many such combinations. Homonuclear diatomic species have been analysed using these techniques for some time. In particular, this work has focused on transition metal species as this is one of the few methods which permits such study. Spectroscopic investigations of the A, B and C states of the silver dimer (Ag2) molecule are presented here. The analysis of this work has provided the following rotational constants for these states; X state Be = 0.04878 cm-1 A state Be = 0.04432 cm-1 B state Be = 0.04544 cm-1 and C state B0 = 0.04851 cm-1. All values are for the 107,109Ag2 isotopomer. The first ionisation potential (I.P.) of any molecular system is an important parameter in the understanding of that species. The value of the I.P. has been evaluated for the silver dimer molecule under differing experimental conditions. It is reported here both under the influence of a potential field (I.P. = 61658.4 cm-1) and under field free conditions (I.P. = 61740.0 cm-1).
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Hossain, Mir Ashad. "Does SABP2 Exist As a Dimer?" Digital Commons @ East Tennessee State University, 2011. https://dc.etsu.edu/etd/2255.
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Salicylic acid binding protein 2 (SABP2) is one of the key enzymes in salicylic acid-dependent plant defense pathway. SABP2 is a 29 kDa protein present in extremely low abundance in plants and it catalyzes the conversion of signaling molecule methyl salicylate into salicylic acid. Although it has been shown that 6x His-tagged SABP2 over expressed in E. coli is a homodimer, its exact conformation in planta is still unknown. Therefore, we proposed to determine if SABP2 exist as a dimer and/or monomer under natural condition. To verify the exact conformation of native SABP2 protein in plant, SABP2 was purified from wild type tobacco using a 5-step purification protocol. Analysis of purified SABP2 in gel filtration and immunoblot assay suggested that SABP2 exists as a monomer in tobacco plant. Studies on SABP2 conformation will give us insight into the structure and functional relationship of this protein in salicylic acid-dependent disease resistance pathway.
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FABBRICATORE, RICCARDO. "CRITICAL PHENOMENA IN RANDOM DIMER MODELS." Doctoral thesis, Università degli Studi di Milano, 2021. http://hdl.handle.net/2434/814963.
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This thesis introduces the concept of criticality and universal behaviour for vastly different systems. The assumption of conformal invariance for systems at critical temperature is shown to yield incredible predictions with the use of Conformal Field Theory. By focusing on the properties of geometrical shapes at criticality, we introduce Schramm-Loewner Evolution (SLE), a powerful tool to extract information about conformality.
Rigorously proving that a discrete system exhibits critical behaviour and conformal invariance in the thermodynamic limit is no easy task. When the system is imbued with quenched disorder, this task becomes even harder. As of today, there is no rigorous proof that a single disordered system exhibits SLE-compatible excitations. This thesis, albeit not providing any such proof, analyses numerically and extensively shows under which conditions such behaviour can be observed in a system with quenched disorder, namely the Random Dimer Model.
The Random Dimer Model consists of a dimer cover of a weighted graph. Its ground state corresponds to the minimum-weight perfect matching. Dimers are often used in Statistical Mechanic, providing a fruitful mapping from a model to a combinatorial problem. By topological perturbations, we obtain excitations in the form of fractal curves. Observables based on these geometrical objects, such as their length, are shown to behave as power laws compatible with other well-known systems at critical point.
Moreover, the extensive analysis of winding angle and Left Passage Probability at the thermodynamic limit, strongly suggests that excitation curves in the Random Dimer Model are conformal and compatible with Schramm-Loewner Evolution. The latter casts light on the yet vastly unexplored question of conformal behaviour for disordered models at critical temperature in the thermodynamic limit.
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Attwood, Brian Christopher. "Global phase diagram for monomer/dimer mixtures." NCSU, 2001. http://www.lib.ncsu.edu/theses/available/etd-20011012-113555.
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The objective of this thesis is to calculate the global phase diagram predicted by the Generalized Flory Dimer equation of state for mixtures of square-well monomers and dimers. Towards that goal, we first extend the Generalized Flory Dimer (GFD) theory for hard sphere monomer/dimer mixtures to square-well monomer/dimer mixtures. Theoretical predictions for the compressibility factor as a function of volume fraction are compared to discontinuous molecular dynamic simulation results on monomer/dimer mixtures at well depth ratios 0.5 - 1.5 and dimer mole fractions 0.111 - 0.667 and on monomers/8-mer mixtures at well depth ratios 0.5 - 1.5. Agreement is found generally to be good and consistent with the agreement obtained when the GFD theory is applied to other square-well systems. Next we calculate the GFD predicted global phase diagram for square-well monomer/dimer mixtures using a brute force method. The locus of critical points in the direction implies that monomer/dimer systems have a greater tendency towards liquid-liquid immiscibility in our system than in monomer/monomer systems.
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Danby, Grahame. "Close coupling calculations of dimer energy levels." Thesis, Durham University, 1985. http://etheses.dur.ac.uk/7243/.
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The aim of this thesis is to calculate the bound state energies of molecular dimers. The problem is formulated for a system consisting of any two diatomic molecules, treated as rigid rotors. Simplifications which arise from symmetry considerations are fully discussed. The de Vogelaere and R-matrix propagator algorithms have been used to solve the resulting systems of coupled second order differential equations. Their numerical convergence properties are compared in test calculations on the Ar-HCl system. The above methods are used to calculate the bound state energies of H(_2)-H(_2), using four separate ab initio potentials. The CI potential of Meyer, Schaefer and Liu (designated "M80") is found to give the best agreement with spectroscopic measurements, though a small shift in the position of the repulsive wall is indicated. The M80 potential is then used in the remaining calculations; these include the evaluation of the energies of resonances and bound states lying above the dissociation limit of the dimer, corresponding to rotationally excited H (_2). The results of these calculations are used to assess the validity of approximations made in the proposed identification of H (_2)-H (_2) features in the far infrared spectra of the Jovian atmosphere. The Born-Oppenheimer approximation permits the use of the M80 potential to calculate the bound states and resonances of D (_2) -D (_2). That some of these resonances have dual Feshbach/shape character is noted. The dimer structure, accompanying the observed near infrared S (_1)(0) and Q(_1)(0) + S(_o)(0) spectra in ortho-deuterium, is modelled by treating the two D(_2) molecules as distinguishable rigid rotors. We conclude that the experiments provide evidence both for rotational splitting of the levels and for internal rotational predissociation. Alternative line assignments to those hitherto made are also suggested. We end with a general discussion in which suggestions for future work are made.
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Le, Masurier Peter John. "Magnetic resonance studies of dimer liquid crystals." Thesis, University of Southampton, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243072.
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Tapia, Amador Jesus. "Combinatorial Reid's recipe for consistent dimer models." Thesis, University of Bath, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.669022.
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The aim of this thesis is to generalise Reid's recipe as first defined by Reid for $G-\Hilb(\mathbb{C}^3)$ ($G$ a finite abelian subgroup of $\SL(3, \mathbb{C})$) to the setting of consistent dimer models. We study the $\theta$-stable representations of a quiver $Q$ with relations $\mathcal{R}$ dual to a consistent dimer model $\Gamma$ in order to introduce a well-defined recipe that marks interior lattice points and interior line segments of a cross-section of the toric fan $\Sigma$ of the moduli space $\mathcal{M}_A(\theta)$ with vertices of $Q$, where $A=\mathbb{C}Q/\langle \mathcal{R}\rangle$. After analysing the behaviour of 'meandering walks' on a consistent dimer model $\Gamma$ and assuming two technical conjectures, we introduce an algorithm - the arrow contraction algorithm - that allows us to produce new consistent dimer models from old. This algorithm could be used in the future to show that in doing combinatorial Reid's recipe, every vertex of $Q$ appears 'once' and that combinatorial Reid's recipe encodes the relations of the tautological line bundles of $\mathcal{M}_A(\theta)$ in $\Pic(\mathcal{M}_A(\theta))$.
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Pabari, Josephine Clare. "Microwave spectroscopy of near-dissociation molecular ions." Thesis, University of Southampton, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342636.
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Yoon, Kisun. "Synthesis and Applications of Non-spherical Dimer Colloids." Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10568.
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Colloids are promising building blocks in material synthesis because of their controllability of size and surface properties. The synthesis of chemically and/or geometrically anisotropic colloidal particles has received attentions with the expectation of building blocks for complex structures. However, the synthesis of anisotropic colloidal particles is by far more difficult than the synthesis of spherical colloidal particles. Lack of monodispersity and productivity of many anisotropic particles often limits their applications as a building block for complex structures. Thus, it is highly desirable to develop methods which can produce a large amount of monodisperse non-spherical particles with controllable asymmetric surface properties. This dissertation details the work for developing such a method. The major result of this dissertation is a synthetic method to produce monodisperse non-spherical colloids with anisotropic surface property in a large quantity. The anisotropic colloid, which we call it as Dimer particle, has two fused lobes like a dumbbell and each lobe’s size can be independently controlled. We present a novel method to synthesize sub-micron size Dimer particles. This method can produce a large amount of submicron-sized Dimer particles with good monodispersity and well-controlled shape. Submicron-sized Dimer particles have been highly desired since they can be used as a building block for self assembly using Brownian motion, colloidal surfactant for Pickering emulsion, and photonic materials. To fully take advantage of the anisotropy of the particles, we develop a facile method to tailor the surface property of each lobe independently by asymmetrically coating the particles with gold nanoparticles. This method doesn’t need the arrangement of particles onto any type of interfaces. Asymmetric coating of gold nanoparticles can be carried out simply by mixing Dimer particles with gold nanoparticles. The formation mechanism of the submicron-sized Dimer particles is explained with evidences. Finally, we illustrate that Dimer particles show rich phase behavior under electric fields and explain the behavior by considering various interactions involved in the system. Our investigation shows that electric field can effectively control the orientation and assembled structure of Dimer particles. In conclusion, these asymmetrically functionalized Dimer particles are promising building blocks to generate suprastructures that will be useful in photonic, electronic and diagnostic applications.Engineering and Applied Sciences
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Cartwright, Peter C. "Mass selective laser photoionisation spectroscopy of copper dimer." Thesis, University of Edinburgh, 1989. http://hdl.handle.net/1842/13333.
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Salihoglu, Omer. "AUTLER-TOWNES SPECTROSCOPY OF THE LITHIUM DIMER MOLECULE." Diss., Temple University Libraries, 2009. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/32174.
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PhysicsPh.D.
This thesis consists of two experimental applications of the Autler-Townes (AT) spectroscopy. In the first experiment, we have determined the electronic transition dipole moment for the 7Li2 A1Σu+ - X1Σg+ system experimentally by using a 4-level continuous wave extended Λ excitation scheme and compared our results with theoretical predictions. 7Li2 is a good test case for the accuracy of the AT splitting based technique to determine the transition dipole moment and its internuclear distance R dependence. The molecule has only 3 electrons per atom. The A1Σu+ - X1Σg+ potential energy curves were well known and thus, one could calculate accurate rovibrational wavefunctions for the simulations. In addition two different quantum mechanical models were available for the comparison: an all-electron valence bond self-consistent-field method and a pseudo-potential molecular orbital method. Our experimental results for the absolute magnitude of the transition dipole matrix elements for rovibronic transitions for different R-centroid values are in excellent agreement with ab initio theoretical calculations of the transition dipole moment. We believe that this technique will become an important method for accurate measurement of the absolute value and R-dependence of electronic transition dipole moments in molecules. The comparison with theory reinforces this view on the accuracy and universality of the AT method. The focus of the second part of this thesis is on experimentally controlling the singlet-triplet character of the 7Li2 molecule by using an external coupling laser field. We have demonstrated experimentally for the first time that the frequency domain quantum control scheme developed by T.Kirova and F. C. Spano (Physical Review A, 71, 063816, 2005) can be used to control the mixing coefficients of a weakly perturbed pair of singlet and triplet rovibrational levels. The coupling field, when tuned to resonance with the rovibronic transition involving the singlet component, causes it to AT split, leading to enhanced mixing of the pair of levels, as predicted by theory.
Temple University--Theses
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Yao, Jian. "NMR Study of Neurophysin Dimer Dissociation by Cosolvents." PDXScholar, 1996. https://pdxscholar.library.pdx.edu/open_access_etds/5209.
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Neurophysins (NPs) make up a relatively small, stable, and highly soluble class of proteins. They have physiological roles of storage and stabilizing' of peptide hormones oxytocin and vasopression within the posterior pituitary neurosecretory granules. At the concentration of NP found within the granules, NP would exist as a dimer in the absence or presence of bound peptide. The NP monomer-monomer interface involves B-sheet/ B-sheet contact, which can be modulated by the presence of cosolvent. This remarkable feature of NP makes it a model for Alzheimer's disease. One of the characteristics of Alzheimer's disease is the presence of plaques of B-amyloid protein that are deposited on the brain. The plaques are rich in B-structure. Being water-insoluble makes them impossible to be directly studied by solution-state NMR. The purpose of this study was to modify the solvent system to lower the NP dimerization constant and characterize the nature of solvent on dissociation of dimer. A set of cosolvents was selected to try to reduce NP dimerization at relatively high concentration of NP. The organic cosolvents included deuterated methanol, dimethyl sulfoxide, ethyl acetate, propionitrile, and acetonitrile. Also, the protein unfolding reagents, deuterated urea and guanidine monohydrochloride, were tried. The interaction between bromophenol blue and NP was also studied because this dye binds predominately to the dimer form of NP. Highresolution NMR techniques were used to sense the NP-I dimer I monomer equilibrium. Among the organic cosolvents used, only acetonitrile and propionitrile were found shift the dimer ~ monomer equilibrium significantly toward monomer. The cosolvent probably changed the character of the solvent system, penetrated the monomer-monomer interface and interacted with the interface residues, caused the break up of dimer. The unfolding reagents were found to partly unfold the NP simultaneously with dissociation of the dimer. Bromophenol blue binds to NP-I at low pH, but the solubility of NP-dye complex is too low to be studied extensively by solution-state NMR methods.
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Howlett, Alyson Cerny. "Role of molecular chaperones in G protein B5-Regulator of G protein signaling dimer assembly and G protein By dimer specificity." BYU ScholarsArchive, 2009. https://scholarsarchive.byu.edu/etd/2065.
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In order for G protein signaling to occur, the G protein heterotrimer must be assembled from its nascent polypeptides. The most difficult step in this process is the formation of the Gβγ dimer from the free subunits since both are unstable in the absence of the other. Recent studies have shown that phosducin-like protein (PhLP1) works as a co-chaperone with the cytosolic chaperonin complex (CCT) to fold Gβ and mediate its interaction with Gγ. However, these studies did not address questions concerning the scope of PhLP1 and CCT-mediated Gβγ assembly, which are important questions given that there are four Gβs that form various dimers with 12 Gγs and a 5th Gβ that dimerizes with the four regulator of G protein signaling (RGS) proteins of the R7 family. The data presented in Chapter 2 shows that PhLP1 plays a vital role in the assembly of Gγ2 with all four Gβ1-4 subunits and in the assembly of Gβ2 with all twelve Gγ subunits, without affecting the specificity of the Gβγ interactions. The results of Chapter 3 show that Gβ5-RGS7 assembly is dependent on CCT and PhLP1, but the apparent mechanism is different from that of Gβγ. PhLP1 seems to stabilize the interaction of Gβ5 with CCT until Gβ5 is folded, after which it is released to allow Gβ5 to interact with RGS7. These findings point to a general role for PhLP1 in the assembly of all Gβγ combinations, and suggest a CCT-dependent mechanism for Gβ5-RGS7 assembly that utilizes the co-chaperone activity of PhLP1 in a unique way. Chapter 4 discusses PhLP2, a recently discovered essential protein, and member of the Pdc family that does not play a role in G protein signaling. Several studies have indicated that PhLP2 acts as a co-chaperone with CCT in the folding of actin, tubulin, and several cell cycle and pro-apoptotic proteins. In a proteomics screen for PhLP2A interacting partners, α-tubulin, 14-3-3, elongation factor 1α, and ribosomal protein L3 were found. Further proteomics studies indicated that PhLP2A is a phosphoprotein that is phosphorylated by CK2 at threonines 47 and 52.
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SANLI, AYDIN. "Transition Dipole Moment and Lifetime Study of Sodium Dimer and Lithium Dimer Electronic States via Autler-Townes and Resolved Fluorescence Spectroscopy." Diss., Temple University Libraries, 2017. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/444569.
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PhysicsPh.D.
This dissertation consists of three major studies. The first study, described in Chapter 3, focuses on the experimental work we carried out; experimental study of the electronic transition dipole moment matrix elements (TDMM) for the and electronic transitions of the sodium dimer molecule. Here we obtained the electronic transition dipole moments through Autler-Townes and resolved fluorescence spectroscopy and compared them to the theory. The second study, described in Chapter 4, is on sodium dimer ion-pair states. In this work, we calculated the radiative lifetimes and electronic transition dipole moments between Na2 ion-pair states ( , , , ) and state. This study was published in 2015. The last study, described in Chapter 5, is the total lifetime (bound-bound plus bound-free) and transition dipole moment calculations of the ion-pair electronic states, , of the lithium dimer molecule.
Temple University--Theses
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Jimenez, Segura Marco Polo. "Dimer solid-liquid transition in the honeycomb-lattice ruthenate Li2-xRuO3." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/216167.
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Qu, Xinmei. "Mercury dimer spectroscopy and an Einstein-Podolsky-Rosen experiment." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-3041.
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Field, Christopher Martyn. "Mathematical and experimental approaches to the dimer catastrophe theory." Thesis, University of Cambridge, 2011. https://www.repository.cam.ac.uk/handle/1810/237378.
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Multicopy plasmids rely on random distribution for stable inheritance by daughter cells at division. Threats to plasmid copy number increase the probability of plasmid loss, which can be detrimental to both plasmid and host. Plasmid dimers emerge through homologous recombination. Dimers have two independent origins of replication and thus have a replicative advantage and reduced copy number. Models of plasmid behaviour suggest that dimers would overtake a cell population, but that this can be prevented if they impose a small metabolic load, which has been observed in vivo. Plasmid ColE1 also contains a cer site, which allows for dimer resolution by XerCD site-specific recombination. A small RNA, Rcd, is expressed from the cer site in dimers and interacts with tryptophanase to increase the concentration of indole in the cell. It is proposed that, as indole inhibits cell division, Rcd imposes a checkpoint on the cell until plasmid dimers are resolved. In this work, plasmid behaviour in a growing cell population was modelled stochastically in more detail than previous work. A plasmid replication model suggested that dimers replicate to more than half the average copy number of monomers, perhaps accounting for their increased metabolic load. A cell population model suggested that the presence of dimer-only cells decreased the average plasmid stability by less than in previous models, which used a fixed plasmid copy number. The rate of dimer resolution required to affect plasmid stability was unreasonably high, indicating the necessity of the Rcd checkpoint. The model thus suggested that the checkpoint may be an escape route for dimer-only cells rather than an immediate response to the emergence of an initial dimer. The Rcd checkpoint itself was also subject to critical analysis. It was realised that neither inhibition of cell division nor cell growth were sufficient to assist dimer resolution; inhibition of plasmid replication was required. Experiments in vivo found that indole inhibited plasmid replication at a concentration that may be achievable endogenously. DNA gyrase was investigated as a component of the mechanism of this inhibition, and indole was found to inhibit its supercoiling activity in vitro.
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Bengtsson, Jonas. "POLYMERIZATION OF δ-VALERO LACTONE BY NOVEL CYCLODEXTRIN DIMER." Thesis, KTH, Skolan för kemivetenskap (CHE), 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-156213.
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På senare tid har forskning syftat till att främja miljövänligare teknik inom alla fält. Det visar sig inom materialframställningen som en önskan att använda material som inte är beroende av olja, inte tillverkade med tungmetaller samt nedbrytbara med en minimal miljöpåverkan. Detta har bland annat gett organiska katalysatorer en större plats inom forskningen. En av dessa är cyclodextrin, en cyklisk oligosackarid som har påvisats bilda makromolekylara komplex med andra molekyler. En aspekt av detta är att den kan hydrolysera polymerer då den bildar komplex med hydrofila molekyler och kan aktivera dessa genom vätebindning. Vilket Harada et. al. visade kunde utnyttjas for att polymerisera cycliska estrar. Detta examensarbete utforskar en del av det arbetet genom att dels verifiera polymerisationstekniken som ar en lösningsmedelsfri polymerisation dels försök till att framstalla en ny dimer av cyclodextrin som ska effektivt kunna polymerisera cycliska estrar mer effektivt an tidigare. Den nya dimern bygger på en thiourea-länk. Aven om polymerisation med vanlig cyclodextrin har visats fungera sa kan den föreslagna dimern inte polymerisera lika effektivt. Syntesen ar problematisk och annars åtråvarda egenskaper hos cyclodextrin, som makromolekylär komplexbildning, kan inhibera polymerisationen och tidigare uppreningssteg.
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Cvitaš, Marko Tomislav. "Interactions and collisions of cold molecules : lithium + lithium dimer." Thesis, Durham University, 2004. http://etheses.dur.ac.uk/3667/.
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There is at present great interest in the properties of ultracold molecules. Molecules are created in traps in excited rovibrational states and any vibrational relaxation results in the trap loss. This thesis provides a theoretical study of interactions and collisions in the spin-polarized lithium -b lithium dimer system at ultralow energies. Potential energy surface of the electronic quartet ground state of lithium trimer is generated ab initio using the CCSD(T) method and represented by an IMLS/Shepard fit. Long-range nonadditive interactions are modelled using a symmetric global form with coefficients taken from a fit to the atom-molecule dispersion coefficients. The surface allows barrierless atom-exchange reactions. It has a global minimum of ≈ 4000 cm(^-1) at equilateral geometries with r(_e) = 3.1 Å. The nonadditive interactions are very strong near equilibrium. They increase the well depth by a factor of 4 and reduce the interatomic distance by ≈ 1 Å. Another surface of À symmetry in C(_s) meets the ground state surface at linear geometries at short range. Part of the seam, near D(_ooh) geometries, is in an energetically accessible region for cold collisions. Inside the seam, the lowest À surface correlates with (^4)II rather than (^4)Σ state. Inelastic and reactive collisions are investigated using a quantum mechanical coupled channel method in hyperspherical coordinates. Bosonic and fermionic systems in the spin-stretched states are considered. The inelastic rate coefficients from the rovibrationally excited states of dimer at ultralow collision energies are large, often above 10-(^-10) cm(^3)s(^-1) The elastic cross sections are ≈ 3 orders of magnitude lower at 1 nK. Atom-molecule mixtures, at the densities found in Bose-Einstein condensates of alkali metal atoms that were recently produced, would last only a fraction of a second. Classical Langevin model describes semi-quantitatively the energy dependence of inelastic cross sections above ≈ 50 mK. No systematic differences between the bosonic and fermionic systems were found. Sensitivity of the results on potential was investigated. Reactions in isotopic mixtures of lithium may be exothermic even from the molecular ground state. The reactive rate coefficients are 1 - 2 orders of magnitude smaller than those in systems involving an initially vibrationally excited dimer.
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Harte, Suzanne Marie. "Variable temperature diffraction studies of hydrogen bonded dimer systems." Thesis, University of Glasgow, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438927.
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Zhou, Ya Jun. "The effect of ageing on alkyl ketene dimer sizing." Thesis, University of Manchester, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337537.
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Lukman, Steven. "Singlet exciton fission in acene dimer and diradicaloid molecules." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/267735.
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This dissertation describes our study of a photophysical process that leads to ultrafast generation of triplet excitons following photoexcitation, singlet exciton fission, in three different acene dimers and diradicaloids. In pentacene and tetracene dimers, we investigate their mechanism of singlet fission. In a series of diradicaloids, we study the relation between molecular structure, diradical character and the suitability for singlet fission. In the first two chapters we explore singlet fission in pentacene dimer. We demonstrate fast and highly efficient intramolecular singlet fission, consisting of two covalently attached pentacene units. The singlet fission pathway is governed by the energy gap between singlet and charge-transfer states, which change dynamically with molecular geometry but are primarily set by the side group. The process exhibits a sensitivity to solvent polarity and competes with geometric relaxation in the singlet state, while subsequent triplet decay is strongly dependent on conformational freedom. The near orthogonal arrangement of the pentacene units is unlike any structure currently proposed for efficient singlet fission and points toward new molecular design rules. Furthermore, these results are the first to demonstrate the role of charge-transfer states in singlet fission and highlight the importance of solubilising groups to optimise excited-state photophysics. In the next chapter, we examine singlet fission in tetracene dimer, where singlet fission is energetically unfavourable. We demonstrate triplet yield as high as 190% can be achieved via fission from higher singlet excited states mediated by charge-transfer states. The outcomes of this study provide deeper insight into the role of hot singlet states in singlet fission and point toward less stringent molecular design rules. In the last chapter, we shift our focus on a new class of molecules, diradicaloid molecules. We explore a family of zethrene molecules, with tuneable diradical character, and demonstrate their general ability to undergo rapid singlet fission via spin-entangled and emissive triplet-pair state TT. A wide range of zethrene molecules are found to be suitable for singlet fission, with additional benefits of high absorption coefficients and photo-/chemical stability.
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Bieker, Helen [Verfasser]. "Dissociation dynamics of size-selected water dimer / Helen Bieker." Hamburg : Staats- und Universitätsbibliothek Hamburg Carl von Ossietzky, 2020. http://d-nb.info/1230561943/34.
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Bradley, Patricia Marie. "Photochemistry and photophysical properties of metal-metal dimer complexes /." The Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=osu1486461246814571.
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Dove, Chris Hays. "Models for the formation of 5.8S ribosomal RNA dimer." Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/50088.
Full textAbstract:
Ribosomal 5.85 RNA is a component of the large (605) ribosomal subunit in eucaryotes. Studies of 5.85 rRNA in solution have shown that under certain conditions, including standard isolation procedures, the molecule complexes with itself to form dimers and higher multimers. Two models have been proposed in the literature to explain the intermolecular interactions responsible for 5.85 rRNA dimer formation. The terminal interaction model of Sitz et al. (Biochem. 17, 5811-5815, 1978) proposes that the dimer forms through base-pairing of the 5' and 3' terminal sequences of two 5.85 rRNA molecules. Pavlakis et al. (Nucl. Acids Res. 7, 2213-2237, 1978) showed that 5.85 rRNA lacking the 3' terminal region was capable of forming dimer. They proposed an alternative model for 5.85 rRNA dimer formation in which an entirely different part of the molecule interacts to form a double-stranded palindrome.
In this study, enzymatic probing techniques and stability measurements (both experimental and theoretical) were used to determine which model most accurately describes the intermolecular interactions of the 5.88 rRNA dimer. The methods used for determining stability were not able to discriminate between the models for 5.88 rRNA dimer formation. Results from the structural probing studies, however, support the terminal interaction model and indicate that the palindrome interaction does not occur in 5.88 rRNA dimer formed from the intact molecule.Master of Science
incomplete_metadata
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Stucky, Eric. "An Exposition of Kasteleyn's Solution of the Dimer Model." Scholarship @ Claremont, 2015. http://scholarship.claremont.edu/hmc_theses/89.
Full textAbstract:
In 1961, P. W. Kasteleyn provided a baffling-looking solution to an apparently simple tiling problem: how many ways are there to tile a rectangular region with dominos? We examine his proof, simplifying and clarifying it into this nearly self-contained work.
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Baker, John C. III. "Application of the Fisher Dimer Model to DNA Condensation." VCU Scholars Compass, 2017. http://scholarscompass.vcu.edu/etd/4791.
Full textAbstract:
This paper considers the statistical mechanics occupation of the edge of a single helix of DNA by simple polymers. Using Fisher's exact closed form solution for dimers on a two-dimensional lattice, a one-dimensional lattice is created mathematically that is occupied by dimers, monomers, and holes. The free energy, entropy, average occupation, and total charge on the lattice are found through the usual statistical methods. The results demonstrate the charge inversion required for a DNA helix to undergo DNA condensation.
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Adriana, Gelover Santiago Carmen. "π-conjugated polymers containing dithiafulvene and thioketene dimer units." 京都大学 (Kyoto University), 2005. http://hdl.handle.net/2433/144937.
Full textAbstract:
Kyoto University (京都大学)0048
新制・課程博士
博士(工学)
甲第11593号
工博第2539号
新制||工||1345(附属図書館)
23236
UT51-2005-D342
京都大学大学院工学研究科高分子化学専攻
(主査)教授 中條 善樹, 教授 増田 俊夫, 教授 伊藤 紳三郎
学位規則第4条第1項該当
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Mingione, Emanuele <1980>. "Rigorous results in Spin Glasses and Monomer-Dimer systems." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amsdottorato.unibo.it/6963/1/TesiMingione.pdf.
Full textAbstract:
In this work I reported recent results in the field of Statistical
Mechanics of Equilibrium, and in particular in Spin Glass models and Monomer Dimer models .
We start giving the mathematical background and the general formalism
for Spin (Disordered) Models with some of their applications to physical and mathematical problems.
Next we move on general aspects of
the theory of spin glasses, in particular to the Sherrington-Kirkpatrick model which is of fundamental interest for the
work. In Chapter 3, we introduce the Multi-species Sherrington-Kirkpatrick
model (MSK), we prove the existence of the thermodynamical limit and the
Guerra's Bound for the quenched pressure together with a detailed analysis of
the annealed and the replica symmetric regime. The result is a multidimensional
generalization of the Parisi's theory. Finally we brie
y illustrate the strategy of
the Panchenko's proof of the lower bound.
In Chapter 4 we discuss the Aizenmann-Contucci and the Ghirlanda-Guerra identities for a wide class of Spin Glass models. As an example of
application, we discuss the role of these identities in the proof of the lower bound.
In Chapter 5 we introduce the basic mathematical formalism of Monomer
Dimer models. We introduce a Gaussian representation of the partition function
that will be fundamental in the rest of the work.
In Chapter 6, we introduce an interacting Monomer-Dimer model.
Its exact solution is derived and a detailed study of its analytical properties and
related physical quantities is performed.
In Chapter 7, we introduce a quenched randomness in the
Monomer Dimer model
and show that, under suitable conditions the
pressure is a self averaging quantity. The main result is that, if we consider
randomness only in the monomer activity, the model is exactly solvable.
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Mingione, Emanuele <1980>. "Rigorous results in Spin Glasses and Monomer-Dimer systems." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amsdottorato.unibo.it/6963/.
Full textAbstract:
In this work I reported recent results in the field of Statistical
Mechanics of Equilibrium, and in particular in Spin Glass models and Monomer Dimer models .
We start giving the mathematical background and the general formalism
for Spin (Disordered) Models with some of their applications to physical and mathematical problems.
Next we move on general aspects of
the theory of spin glasses, in particular to the Sherrington-Kirkpatrick model which is of fundamental interest for the
work. In Chapter 3, we introduce the Multi-species Sherrington-Kirkpatrick
model (MSK), we prove the existence of the thermodynamical limit and the
Guerra's Bound for the quenched pressure together with a detailed analysis of
the annealed and the replica symmetric regime. The result is a multidimensional
generalization of the Parisi's theory. Finally we brie
y illustrate the strategy of
the Panchenko's proof of the lower bound.
In Chapter 4 we discuss the Aizenmann-Contucci and the Ghirlanda-Guerra identities for a wide class of Spin Glass models. As an example of
application, we discuss the role of these identities in the proof of the lower bound.
In Chapter 5 we introduce the basic mathematical formalism of Monomer
Dimer models. We introduce a Gaussian representation of the partition function
that will be fundamental in the rest of the work.
In Chapter 6, we introduce an interacting Monomer-Dimer model.
Its exact solution is derived and a detailed study of its analytical properties and
related physical quantities is performed.
In Chapter 7, we introduce a quenched randomness in the
Monomer Dimer model
and show that, under suitable conditions the
pressure is a self averaging quantity. The main result is that, if we consider
randomness only in the monomer activity, the model is exactly solvable.
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SCUDIERI, PAOLO. "Intermolecular Interactions in the TMEM16A Dimer Controlling Channel Activity." Doctoral thesis, Università degli studi di Genova, 2018. http://hdl.handle.net/11567/929402.
Full textAbstract:
TMEM16A e TMEM16B sono proteine di membrana con funzione di canali
del cloruro attivati da calcio. Attraverso la generazione di canali chimerici, e in
particolare, sostituendo la regione carbossi-terminale di TMEM16A con la regione
equivalente di TMEM16B, sono stati ottenuti dei canali dotati di una maggiore
attività. Il progressivo accorciamento della regione chimerica ha permesso di
restringere il “dominio attivante” a una corta sequenza di 14 aminoacidi localizzata
vicino all’ultimo dominio transmembrana e ha generato proteine-canale TMEM16A
dotate di un’attività molto alta anche a concentrazioni basse di calcio intracellulare.
Per chiarire il meccanismo molecolare alla base di questo effetto, sono stati
eseguiti esperimenti basati sulla generazione di doppie chimere, Forster resonance
Energy transfer e cross-linking intermolecolare. Inoltre, è stato generato un
modello tridimensionale teorico di TMEM16A basato sulla struttura di una proteina
TMEM16 del fungo Nectria haematococca. I risultati ottenuti indicano che
l’aumentata attività nei canali chimerici è causata da un’alterazione dell’interazione
tra il carbossi-terminale e la prima ansa intracellulare di TMEM16A.
L’identificazione di piccole molecole farmacologiche in grado di mimare
questa perturbazione potrebbe rappresentare la base di un approccio farmacologico
volto a stimolare il trasporto ionico TMEM16A-dipendente. L’attivazione
farmacologica di TMEM16A potrebbe essere utile per stimolare la secrezione
epiteliale nelle vie aeree, un effetto potenzialmente benefico in patologie quali la
fibrosi cistica e altre malattie ostruttive croniche dell’apparato respiratorio
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Arnstein, Stephen A. "Pi-pi to full ci." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28269.
Full textAbstract:
Thesis (M. S.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2009.Committee Chair: Sherrill, C. David; Committee Member: Bredas, Jean-Luc; Committee Member: Hud, Nicholas; Committee Member: Perry, Joseph.
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Cabungcal-Buchli, Sabina Sarah. "Die Wertigkeit der D-Dimer-Diagnostik bei Patienten mit Verdacht auf akute thromboembolische Ereignisse während der Einführungsphase des D-Dimer-Tests am Inselspital Bern /." [S.l.] : [s.n.], 2008. http://opac.nebis.ch/cgi-bin/showAbstract.pl?sys=000277024.
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Chung, Teng-Te. "Functional analysis of melanocortin 2 receptor variants and dimer formation." Thesis, Queen Mary, University of London, 2010. http://qmro.qmul.ac.uk/xmlui/handle/123456789/450.
Full textAbstract:
The adrenocorticotropic hormone (ACTH) receptor, also known as the melanocortin 2 receptor (MC2R) is primarily expressed in the adrenal gland and binds to ACTH to activate a signalling cascade that leads to steroidogenesis. The characterisation of the melanocortin 2 receptor has previously been hindered by the failure of cell surface expression in heterologous cells. Unlike other melanocortin receptors, MC2R surface expression requires an accessory protein called melanocortin 2 receptor accessory protein (MRAP). MRAP has been shown to facilitate trafficking of MC2R from the endoplasmic reticulum to the plasma membrane and it also has a role in MC2R signalling. Naturally occurring MC2R mutations occur in Familial Glucocorticoid Deficiency (FGD) type 1. The functional defect remains uncertain for the majority, mainly due to the difficulties in characterisation which has been limited in Y6 cells (mouse derived adrenal cells which are free of MCRs) because of poor transfection efficiency. The first two results chapter of this thesis focus on the molecular biology of FGD mutations and the genotype-phenotype relationship of the disease. The functional defects of these mutations have been analysed in transfectable heterologuous cells stably expressing MRAP. The majority of the missense mutations are trafficking-defective, and yet all appear to interact with MRAP, but some mutations are trafficking-competent and fail to signal. Clinical details including the age of presentation; presenting plasma ACTH and cortisol; height and weight were examined in FGD type 1 and 2 (mutation of MC2R or MRAP respectively) to determine whether there is a genotype-phenotype correlation. Within FGD type 1, there was no clear clinical distinction between the functional defects in vitro and in vivo data. However, there were phenotypic differences between 3 FGD type 1 and 2, with FGD 2 appearing to be more severe with a younger age and a lower height SDS at presentation. The final part of this thesis focuses on MC2R dimerisation and signalling of the receptor. Co-immunoprecipitation studies showed that MC2R homodimerisation is constitutive. This interaction was not enhanced in the presence of MRAP or ACTH. No effect on signalling was observed. When a signalling mutant (R128C) and a ligand binding mutant (D103N) were co-transfected with MRAP and stimulated with ACTH, signalling was not restored, suggesting no cross talk between the two receptors. In the final discussion the implication of these findings are considered with respect to their relevance to disease and novel therapeutic strategies.
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Wu, Wei. "Exchange calculations between donors in silicon and metal-phthalocyanine dimer." Thesis, University College London (University of London), 2007. http://discovery.ucl.ac.uk/1445188/.
Full textAbstract:
This thesis describes the calculation of exchange interactions for systems of electrons, and their potential uses for quantum information processing. The first part treats exchange between donor impurities (including especially deep donors) in silicon, while the second describes exchange in copper and manganese phthalocyanines. Part I uses the quantum defect method and a model central-cell correction to evaluate the exchange interaction between two deep donors by a Heitler-London-type approach. This part also describes calculations of the exchange in a three-donor complex, where one donor plays the role of a 'control atom' whose optical excitation switches the coupling strengths, and the other two are qubits embodying the quantum information. Variational calculations are described which give the control electron freedom to reside on different parts of the complex it is found that the exchange between two qubits is increased when the control electron be comes delocalized, and that it is possible for the exchange to become ferromagnetic. These observations are rationalised in terms of multi-centre exchange processes using Green's function perturbation theory. In Part II, exchange interactions between copper(II) phthalocyanine (Cu(II)Pc) and manganese (II) phthalocyanine dimers (Mn(II)Pc) are described these systems have both long excited-state lifetimes and tunable magnetic properties. The theoretical studies described include both a model Green's function calculation, to understand the roles of the competing exchange processes, and ab initio density functional theory calculations. The model calculations of Cu(II)Pc show that the dominant contribution comes from so-called indirect exchange, and depends strongly on the stacking angle. The magnitude of the exchange interaction from the ab initio calculations of Cu(II)Pc roughly agrees with the experiment.
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Schleicher, David, Alexander Tronnier, Hendrik Leopold, Horst Borrmann, and Thomas Strassner. "Unusual dimer formation of cyclometalated ruthenium NHC p-cymene complexes." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-219362.
Full textAbstract:
We present the synthesis and structural characterization of novel ruthenium complexes containing C^C* cyclometalated N-heterocyclic carbene ligands, η6-arene (p-cymene) ligands and one bridging chlorine ion. Complexes of the general formula [Ru(p-cymene)(C^C*)Cl] were prepared via a one-pot synthesis using in situ transmetalation from the correspondent silver NHC complexes. These complexes react with sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaBArF4) to form dinuclear complexes of the general structure [Ru(p-cymene)(C^C*)-μ-Cl-(p-cymene)(C^C*)Ru]+[BArF4]−. Solid-state structures confirm that the pseudo-tetrahedral coordination around the metal center with the η6-ligand aligned perpendicularly to the C^C* ligand and the i-Pr group “atop” is retained in the bimetallic complexes.
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Schleicher, David, Alexander Tronnier, Hendrik Leopold, Horst Borrmann, and Thomas Strassner. "Unusual dimer formation of cyclometalated ruthenium NHC p-cymene complexes." Royal Society of Chemistry, 2016. https://tud.qucosa.de/id/qucosa%3A30175.
Full textAbstract:
We present the synthesis and structural characterization of novel ruthenium complexes containing C^C* cyclometalated N-heterocyclic carbene ligands, η6-arene (p-cymene) ligands and one bridging chlorine ion. Complexes of the general formula [Ru(p-cymene)(C^C*)Cl] were prepared via a one-pot synthesis using in situ transmetalation from the correspondent silver NHC complexes. These complexes react with sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaBArF4) to form dinuclear complexes of the general structure [Ru(p-cymene)(C^C*)-μ-Cl-(p-cymene)(C^C*)Ru]+[BArF4]−. Solid-state structures confirm that the pseudo-tetrahedral coordination around the metal center with the η6-ligand aligned perpendicularly to the C^C* ligand and the i-Pr group “atop” is retained in the bimetallic complexes.
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Lyon, Robert Patrick. "Enzymology at the dimer interface of cytosolic glutathione S-transferases /." Thesis, Connect to this title online; UW restricted, 2002. http://hdl.handle.net/1773/8165.
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Evans, Genevieve Laura. "Disrupting the quaternary structure of DHDPS as a new approach to antibiotic design." Thesis, University of Canterbury. Biological Sciences, 2010. http://hdl.handle.net/10092/4469.
Full textAbstract:
This thesis examined the enzyme dihydrodipicolinate synthase (DHDPS, E.C. 4.2.1.52) from the pathogen Mycobacterium tuberculosis. DHDPS is a validated antibiotic target for which no potent inhibitor based on substrates, intermediates or product has been found. The importance of the homotetrameric quaternary structure in E. coli DHDPS has been demonstrated by the 100-fold decrease in activity observed in a dimeric variant, DHDPS-L197Y, created by site-directed mutagenesis. This suggested a new approach for inhibitor design: targeting the dimer-dimer interface and disrupting tetramer formation.
DHDPS catalyzes the first committed step in the biosynthetic pathway of meso-diaminopimelic acid, a critical component of the mycobacterial cell wall. In this study, wild-type M. tuberculosis DHDPS was thoroughly characterized and compared with the E. coli enzyme. A coupled assay was used to obtain the kinetic parameters for M. tuberculosis DHDPS: KM(S) ASA = 0.43 (±0.02) mM, KMpyruvate = 0.17 (±0.01) mM, and kcat = 138 (±2) s 1. Biophysical techniques showed M. tuberculosis DHDPS to exist as a tetramer in solution. This is consistent with the crystal structure deposited as PDB entry 1XXX. The crystal structure of M. tuberculosis DHDPS showed active-site architecture analogous to E. coli DHDPS and a dimeric variant of M. tuberculosis DHDPS was predicted to have reduced enzyme activity.
A dimeric variant of M. tuberculosis DHDPS was engineered through a rationally designed mutation to analyze the effect of disrupting quaternary structure on enzyme function. A single point mutation resulted in a variant, DHDPS-A204R, with disrupted quaternary structure, as determined by analytical ultracentrifugation and gel-filtration chromatography. DHDPS-A204R was found to exist in a concentration-dependent monomer-dimer equilibrium, shifted towards dimer by the presence of pyruvate, the first substrate that binds to the enzyme. The secondary and tertiary structure of DHDPS-A204R was analogous to wild-type M. tuberculosis DHDPS as judged by circular dichroism spectroscopy and X ray crystallography, respectively. Surprisingly, this disrupted interface mutant had similar activity to the wild type enzyme, with a kcat of 119 (±6) s-1; although, the affinity for its substrates were decreased: KM(S) ASA = 1.1 (±0.1) mM, KMpyruvate = 0.33 (±0.03) mM. These results indicated that disruption of tetramer formation does not provide an alternative direction for drug design for DHDPS from M. tuberculosis.
Comparison with the recently discovered dimeric DHDPS from Staphylococcus aureus shed further light on the role of quaternary structure in DHDPS. In M. tuberculosis DHDPS-A204R and the naturally dimeric enzyme, the association of monomers into the dimer involves a greater buried surface area and number of residues than found in E. coli DHDPS-L197Y. This provides a framework to discriminate which DHDPS enzymes are likely to be inactive as dimers and will direct future work targeting the dimer-dimer interface of DHDPS as an approach for drug design.
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INTROINI, BIANCA. "DESIGN OF CHIMERIC ION CHANNELS TO MONITOR CAMP-INDUCED CONFORMATIONAL CHANGES AND DYNAMICS." Doctoral thesis, Università degli Studi di Milano, 2020. http://hdl.handle.net/2434/719688.
Full textAbstract:
Hyperpolarization-activated cyclic nucleotide-gated (HCN1-4) channels are the molecular correlate of Ih (or If) current, which plays a key role in the control of neuronal and cardiac rhythmicity. HCNs are activated by the hyperpolarization of the membrane potential and further regulated by the direct binding of cyclic AMP (cAMP) to the cytoplasmic Cyclic Nucleotide Binding Domain (CNBD). cAMP binding determines the removal of the autoinhibitory action exerted by the CNBD on the pore opening and causes conformational changes that propagate from the CNBD to the pore through the C-linker, increasing channel open probability and speeding activation kinetics.
cAMP modulation of HCN controls rhythmicity and excitability at cardiac and neuronal level and pain perception. Thus, in order to understand several physiological functions, as well as diseases affecting both the cardiac and neuronal system, a detailed description of the cAMP-induced conformational changes is required. Moreover, functional studies indicate that cAMP binding to the CNBD induces the transition of the C-terminal domains, from dimer of dimer to tetramer and that this transition is driven by the movements of the C-linker.
The goal of this work is to describe the propagation of the movements through the C-linker to the pore. To this end, I have applied spectroscopic techniques, such as Electron Paramagnetic Resonance (EPR) and Double Electron-Electron Resonance (DEER) to study dynamic changes in the structure of the purified and labelled protein. First, I constructed a chimeric channel by fusing the C-linker/CNBD of human HCN4 to the prokaryotic pore domain of KcsA. This protein has the advantage that can be produced and easily purified in E. coli. Isothermal Titration Calorimetry (ITC) and Differential Scanning Calorimetry (DSC) measurements demonstrated that the purified chimera is able to bind cAMP. Particularly, ITC gave a Kd value of 1.7 μM, which agrees with the one previously published for the isolated C-linker/CNBD fragment of HCN4. Moreover, the rescue of a K+-uptake deficient E. coli strain demonstrated that the chimeric channel is able to conduct a K+ ions flow.
EPR-DEER experiments performed on the chimera revealed that the binding of cAMP to the CNBD domain causes clear conformational changes in the C-terminal region, which transits from a dimer of dimers conformation to a 4-fold symmetrical gating ring. These data confirm previous biochemical and functional indication obtained on the full-length channel and give further details on the direction and the extent of subunit displacement occurring during the conformational transition. The transition of the channel from a dimer of dimer to a tetrameric configuration of the cytosolic domain might reflect a pre-conditioning state for cAMP action on channel gating and partly explains the agonist activity exerted by cAMP on channel kinetics and open probability.
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Law, Yu Kay. "Relationship Between the Kinetics of Thymine Dimer Formation and the Excited State Dynamics of DNA." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1276861431.
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Moorcroft, D. "Molecular structure studies using NMR relaxation methods." Thesis, University of Salford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.353972.
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Allard, Olivier. "Long-range interactions in the calcium dimer studied by molecular spectroscopy." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=97513440X.
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Yan, Haiyan. "Dimer-acid based polyamide and its application in textile xerographic printing." Thesis, Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/8709.
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