The repression of the E. coli lac operon seems to be more efficient than the current theoretical model allows for. Specifically, it is more quiet than expected during the replication of the chromosome. I have induced cells during short periods and counted the number of protein products from the operon to determine if there is a delay in activation of transcription that could account for the discrepancy. The results are compatible with a delay of 10-20 s, but the delay could not be conclusively proven. Furthermore, it has been investigated if the mechanism behind the delay might be differential localization of the lac operon with and without induction. It is shown that the lac operon is more often located in the periphery of the cell and in the internucleoid region when induced. These might be regions where genes are higher expressed, giving a delay in expression after de-repression before the gene is transported there.

The binding between the 45 kDa N-terminal domain of the a subunit of the GPIb-IX-V complex (GPIbαN) on the platelet membrane and the A1 domain of von Willebrand factor (VWF-A1), a multimeric protein circulating in the plasma, plays a key role in platelet adhesion and thrombus initiation at sites of cut-injury and atherosclerotic plaque rupture where blood vessels are subjected to high haemodynamic shear. A fundamental yet unresolved issue is how haemodynamic force upregulates this interaction (binding kinetics) and how a mechanical stimulus is translated into a biochemical signal (mechanotransduction). In order to address above issues, we setup a new biomembrane force probe (BFP) with the drifting reduction, temperature control and concurrent fluorescence imaging. My research findings are summarized into three aims: 1. VWF regions surrounding A1 hinder A1-GPIbα interaction at zero force, which is relieved by increasing force that stabilizes the interaction, giving rise to a VWF-GPIbα catch bond. 2. Three transport-related physical factors: receptor-ligand separation distance, Brownian motion and diffusivity govern the VWF-GPIbα association. 3. Mechanical force and structural variation regulate platelet signaling via the engagement duration of GPIbα mechanosensor. My thesis study advances our understanding of the biophysical and structural basis of how the VWF activation, its interaction with GPIbα and signal transduction are regulated by force when platelets' haemostatic functions are most needed.

This thesis will present the synthesis, characterization and magnetic measurements of lanthanide complexes with varying nuclearities (Ln, Ln2, Ln3 and Ln4). EuIII, GdIII, TbIII, DyIII, HoIII and YbIII have been selected as the metal centers. Eight polydentate Schiff-base ligands have been synthesized with N- and mostly O-based coordination environments which chelate 7-, 8- or 9-coordinate lanthanide ions. The molecular structures were characterized by single crystal X-ray crystallography and the magnetic properties were measured using a SQUID magnetometer. Each chapter consists of crystal structures and magnetic measurements for complexes with the same nuclearity. There are eight DyIII SMMs in this thesis which are discrete molecules that act as magnets below a certain temperature called their blocking temperature. This phenomenon results from an appreciable spin ground state (S) as well as negative uni-axial anisotropy (D), both present in lanthanide ions owing to their f electron shell, generating an effective energy barrier for the reversal of the magnetization (Ueff). The ab initio calculations are also included for the SMMs with high anisotropic energy barriers to understand the mechanisms of slow magnetic relaxation in these systems.

This dissertation describes the single-molecule magnet (SMM) behaviour of f-block cyclooctatetraenyl sandwich complexes. Chapter one introduces the concepts that dictate SMM behavior particularly in f-elements. The emphasis is to understand the origin of magnetic behaviour and the properties that make lanthanide elements particularly interesting to explore. Current strategies used to predict such behaviour are discussed and a literature review on the subject is provided. Chapter Two describes the magnetic properties of eight isostructural lanthanide sandwich complexes utilizing 1,4-bis(trimethylsilyl)cyclooctatetraenyl dianion as the ligand, [Li(DME)3][LnIII(COT”)2] (Ln = Ce, Nd, Gd, Tb, Dy, Ho, Er, Tb, COT” = 1,4-bis(trimethylsilyl)cyclooctatetraenyl dianion, DME = dimethoxyethane). The complexes display a wide range of magnetic behaviour. The best performing SMM was the erbium complex, which had a blocking temperature of 8 K. Investigating different lanthanide ions with the same ligand enabled us to evaluate our findings in relation to current models used to predict SMM behaviour in lanthanide complexes. Chapter three extends the discussion of lanthanide sandwich complexes to include higher symmetry cyclooctatetraenyl complexes of ErIII and DyIII, [K(18-C-6)][LnIII(COT)2] (18-C-6 = 1,4,7,10,13,16-hexaoxacyclooctadecane, COT = cyclooctatetraene).The change in symmetry evoked by removing the trimethylsyl- (TMS) groups on the ligand greatly influenced the magnetic properties of both complexes. Ab initio calculations revealed that the magnetic relaxation in the ErIII complex occurs via the second excited state which contributes to the very high blocking temperature of 10 K in this complex. Chapter four presents an organometallic building block approach to create triple decker lanthanide COT” complexes of GdIII, DyIII and ErIII with a molecular formula of LnIII2(COT”)3. Synthetically, we couple together the sandwich complexes discussed in Chapter 2 by oxidatively removing one ligand to produce linear complexes where the two metals are bridged by an aromatic COT” ligand. The magnetic properties of all complexes are compared to their respective mononuclear analogs. Most interesting is the unprecedented 4 K increase in blocking temperature of the triple decker ErIII analog compared to the ErIII mononuclear sandwich complex discussed in Chapter 2. This increase is due to a ferromagnetic dipole-dipole interaction between the ErIII ions through the COT” ring. The aromatic bridging ligand provides a GdIII - GdIII interaction of J = -0.448(1) cm-1. Chapter five extends the discussion of magnetic exchange coupling to include linear K2(THF)4[LnIII2(COT)4] (Ln = Gd, Dy, Er, COT = cyclooctatetraenyl dianion, THF = tetrahydrofuran) complexes of GdIII, DyIII and ErIII. Each complex is composed of two LnCOT2 units bridged linearly by a potassium ion. The magnetic interaction between metal ions is much weaker than in the triple decker complexes discussed in Chapter 4, with a GdIII-GdIII interaction of J = − 0.007(4) cm–1. The magnetic properties of the quadruple decker complexes were compared to their mononuclear equivalents (Chapter 3). Surprisingly, the ErIII complex showed an increase in magnetic blocking temperature over its mononuclear analog despite the large ErIII-ErIII separation of 8.819 Å. Ab initio calculations revealed that this increase is due to single ion effects, most likely an increase in symmetry. Chapter six deviates from lanthanide magnetism to study the magnetic properties of uranium sandwich complexes with multiple ligand systems and oxidation states. Prior to this study the SMM behaviour of uranium sandwich complexes was unknown. We report the synthesis, structure and magnetic properties of both uranium-COT” sandwich complexes and uranium-cycloheptatrienyl complexes with oxidation states spanning (III)-(V). None of the complexes showed zero-field SMM behaviour, indicating a sandwichtype ligand is not appropriate for harnessing the SMM character in uranium. We compared the slow magnetic relaxation of isostructural and valence isoelectronic uranium and neodymium complexes. The improved energy barrier in the uranium complex further motivates the use of uranium in SMM design due to its large spin-orbit coupling.

京都大学 / 0048 / 新制・論文博士 / 博士(医学) / 乙第13214号 / 論医博第2164号 / 京都大学大学院医学研究科医学専攻 / (主査)教授 渡邊 直樹, 教授 安達 泰治, 教授 江藤 浩之 / 学位規則第4条第2項該当 / Doctor of Medical Science / Kyoto University / DFAM

No description available.

My research has demonstrated the feasibility of the experimental methodologies for proton-sensitive molecular probes of proton transport at the single-molecule level where a single molecule fluorescence spectral shift was observed in poly acrylamide gel (PAAG) matrix after the addition of HCl with a grating spectrometer. Proton-sensitive molecular probes are employed for observing variations of photophysical properties as protons from acid sources transport and react with the reporter molecules such as Coumarin 6 where it has two different protonated states and then shows distinguished emission spectrum. As well, in order to understand the fluorescence properties of neutral and protonated Coumarin 6 in each emission spectrum region, dual-channel detection experiment was built where those fluorescence emission spectrum are allowed to be separated into each optical detection channel. The two-color detection will provide us with the understanding of the heterogeneities indicative of the interaction of pH-responsive probe with its environment. Based on those methodologies and results, this research will lead to investigate how proton transfer kinetics and dynamics are influenced by the geometric arrangements such as inter-functional group spacing, alignment, and flexibility in single macromolecular scaffolds which will suggest the development for future fuel cell and better understanding of biological process.

Single-molecule magnets (SMMs) have been lauded for their application in next generation devices for their enhanced information storage capabilities, increased processing speeds, and increased storage densities compared to bulk magnets. However, the success of SMMs in such applications and their technological readiness is hindered by their operation temperatures and memory lifetimes. SMMs are molecular species that possess a bistable ground state and magnetic anisotropy, which together result in an energy barrier to the reorientation of the magnetic moment. The magnetic memory response relies on its ability to retain magnetization in the absence of an external field. To this end, lanthanide ions with their large inherent magnetic anisotropy combined with well-defined crystal field microstates are attractive candidates for eliciting higher operation temperatures and lifetimes. This dissertation focuses on the use of lanthanide ions in the development of high barrier SMMs with a close emphasis on the magnetic anisotropy and crystal field manipulation through geometry, design, and modification. In the pursuit of lanthanide (Ln)-based SMMs, two cyclooctatetraenyl (COT2-) complexes of the non-Kramers ion, TmIII, [TmIII(η8-COT)I(THF)2] and [K(18-C-6)(THF)2][TmIII(η8-COT)2], were isolated. As an ion that possess an integer angular momentum projection (J = 6), it was vital that a highly symmetric local environment was utilized to observe field-induced slow magnetic relaxation. The static and dynamic properties of TmIII(η8-COT)I(THF)2] and [K(18-C-6)(THF)2][TmIII(η8-COT)2] were characterized revealing Ueff of 7.93 K and 53.3 K, respectively. More importantly, the effect of increased symmetry was observed on the rate of quantum tunneling of the magnetization (QTM), where the rate was two orders of magnitude faster in the heteroleptic complex. This emphasized the importance of local symmetry for non-Kramers ions and contributed to the rare class of TmIII SMMs. Due to the prevalent role of QTM in Ln-based SMMs, a common strategy is to induce magnetic communication between Ln ions to overcome its detrimental effects. To this end, bridging units should be sufficiently small enough to bring the Ln ions close in proximity, yet the surrounding environment of the metal center should still promote uniaxial magnetic anisotropy. We compared the effect of ancillary ligands on the magnetic properties of two dinuclear DyIII compounds with the same {μ-Cl}2 core bridge. The complexes [DyIII{N(SiMe3)2}2(μ-Cl)(THF)]2 and [DyIII(η8-COT)(μ-Cl)(THF)]2 were characterized with static and dynamic magnetic measurements. The well-matched ligand field of the silyl amide ligands with the DyIII ion, precluded the observation of zero field tunneling. While both complexes are characterized by antiferromagnetic coupling, it is evident that peripheral ligands also play a vital role in determining the performance of multinuclear SMMs. Magnetic coupling between 4f centers is classically weak; however, the use of ligands with diffuse electron clouds may penetrate the shielded 4f orbitals to effectively promote communication. One such ligand that had not previously been investigated for its ability to couple the magnetic moment of Ln ions was the trianionic cycloheptatrienyl. Utilizing Ln silyl amides, in situ deprotonation afforded the dinuclear complexes [KLnIII2(η7-C7H7){N(SiMe3)2}4] (Ln = GdIII, DyIII, ErIII). The static and dynamic magnetic characterization revealed rare and highly sought-after ferromagnetic coupling in a Ln-based system. The ancillary silyl amide ligands were a necessity for the isolation of these dinuclear species yet did not provide a synergistic ligand field for the Ln ions when combined with the cycloheptatrienyl bridge, ultimately preventing the observation of slow relaxation in some of the variants studied. Pseudo-linear complexes, those molecules with strong axial donors have shown immense promise in the design of highly efficient SMMs. Our work has shown that amides are effective in directing the anisotropy of the Ln ions, thus the removal of the central organometallic bridge from the previous compounds would effectively create a highly anisotropic complex. This was achieved in our study of a formally five-coordinate complex of a ferrocene diamide ligated DyIII ion, [(NNTBS)DyIIII(THF)2]. The static and dynamic magnetic properties were characterized, yielding Ueff = 771 K with open magnetization hysteresis loops at zero-field, due in part to the axial disposition of the nitrogen atoms of the diamide ligand. Computational analysis of the parent compound and its fragments was completed. Our results indicated that the presence of equatorially coordinated solvent molecules such as THF, influence the axiality in the crystal field microstates more significantly than the coordinated halide. The removal of coordinated solvent such as THF, is imperative to improve the performance of DyIII SMMs. By way of a bulky bisanilide ligand that precludes the approach of solvent to the metal center, combined with a large bite angle, [K(DME)n][LArDyIII(X)2], a formally four coordinate complex, was investigated. In contrast to the complex of the ferrocene diamide ligand, retention of the magnetic moment was not observed at zero-field, despite the fact that the slow relaxation dynamics occurred over a greater temperature range for which Ueff = 1278-1334 K. In addition, variants of the bound halide (X = Cl, I) were examined for their effect on the static and dynamic magnetic properties, revealing zero field relaxation times that were on average 5.6x longer for the heavier congener. The collective results of the findings presented herein are being utilized to synthesize new low-coordinate Ln-based SMMs. Combining divalent and redox chemistries with bulky amido ligands will ideally elicit even larger energy barriers to spin reversal and higher blocking temperatures, supporting the push towards Ln-based SMMs with increased technological readiness.

No description available.

Single molecule studies on CdSe quantum dots functionalized with oligo-phenylene vinylene ligands (CdSe-OPV) provide evidence of strong electronic communication that facilitate charge and energy transport between the OPV ligands and the CdSe quantum dot core. This electronic interaction greatly modify, the photoluminescence properties of both bulk and single CdSe-OPV nanostructure thin film samples. Size-correlated wide-field fluorescence imaging show that blinking suppression in single CdSe-OPV is linked to the degree of OPV coverage (inferred from AFM height scans) on the quantum dot surface. The effect of the complex electronic environment presented by photoexcited OPV ligands on the excited state property of CdSe-OPV is measured with single photon counting and photon-pair correlation spectroscopy techniques. Time-tagged-time-resolved (TTTR) single photon counting measurements from individual CdSe-OPV nanostructures, show excited state lifetimes an order of magnitude shorter relative to conventional ZnS/CdSe quantum dots. Second-order intensity correlation measurements g(2)(τ) from individual CdSe-OPV nanostructures point to a weak multi-excitonic character with a strong wavelength dependent modulation depth. By tuning in and out of the absorption of the OPV ligands we observe changes in modulation depth from g(2)(0) ≈ 0.2 to 0.05 under 405 and 514 nm excitation respectively. Defocused images and polarization anisotropy measurements also reveal a well-defined linear dipole emission pattern in single CdSe-OPV nanostructures. These results provide new insights into to the mechanism behind the electronic interactions in composite quantum dot/conjugated organic composite systems at the single molecule level. The observed intensity flickering, blinking suppression and associated lifetime/count rate and antibunching behaviour is well explained by a Stark interaction model. Charge transfer from photo-excitation of the OPV ligands to the surface of the CdSe quantum dot core, mixes electron/holes states and lifts the degeneracy in the band edge bright exciton state, which induces a well define linear dipole behaviour in single CdSe-OPV nanostructures. The shift in the electron energies also affects Auger assisted hole trapping rates, suppress access to dark states and reduce the excited state lifetime.