According to the model free approach assumption four protein dynamic related parameters, the slow and fast local motion of the NH vector, the generalized order parameter, and the 15N shielding anisotropy can be estimated at each residue by the spectral density functions at the resonant frequencies of N (omega_N) and H (omega_H). In this work, we study the linear and nonlinear estimations of the aforementioned parameters of the two proteins C12A-p8^MTCPI and Pilin from strain K122-4. The principal components of the four parameters of C12A-p8^MTCPI are used to cluster the residues. The results show that the principle components provide useful information about the secondary structure of the protein. Finally, we propose a practical method to examine the model free assumption by characterizing the distribution of the transverse rate R_2 in multifield.

Thesis (doctoral)--Universität, Leipzig, 1999.

This thesis introduces a workflow to accomplish invasion-consistent Nuclear Magnetic Resonance (NMR) measurement interpretations. Magnetic resonance measurements are affected by mud-filtrate invasion because the radial depth of investigation (DOI) of NMR logging tools is very shallow (approximately 1 to 4 inches). This characteristic indicates that identification of in-situ fluid saturations from NMR measurements is uncertain. Calculation of fluid saturations from apparent electrical resistivities and nuclear logs does not guarantee a precise estimation of the fluid distributions. Free water in the reservoir displaced by oil based mud (OBM) poses more challenges in the estimation of in-situ fluid saturations. To mitigate this ambiguity, I construct layer-by-layer static and dynamic reservoir models. The common stratigraphic framework (CSF) proposed by Voss et al. (2009) was used to construct the earth model. Appraisal of static petrophysical properties is based on the iterative adjustments to minimize the discrepancy between available well logs and their numerical simulations. Evaluation of dynamic petrophysical properties can be achieved with the simulation of mud-filtrate invasion. This simulation can assess accurate fluid saturations at specific radial distances. In addition, numerically simulated apparent resistivity and nuclear logs are in agreement with measured logs. Algorithms are also developed to cross-validate NMR measurements based on the assumption of spherically shaped water-wet pores. The algorithms need all petrophysical parameters and fluid saturations yielded from the dynamic model as inputs. Various NMR parameter changes were tested to validate this algorithm. Examples of NMR responses include wettability change and kerogen contained in nano-scale pores. For the field case examples, two 15 meter-thick depth intervals in oil- and gas-bearing siliciclastic formations were selected. Two-dimensional (2D) NMR simulations were performed with petrophysical parameters provided from the numerical simulation of mud-filtrate invasion. The 2D NMR maps are more favorable in fluid typing than conventional NMR T₂ distributions because they contrast fluid diffusion coefficient. Comparisons of simulation results to inversion results confirm the validity of the workflow introduced in this thesis for the quantification of virgin reservoir fluids and mud-filtrate saturations. Finally, forward modeling and inversion processes are applied to 2D NMR data. The reconstructed echo decay sequences are more advantageous than raw measurements because of their higher signal to noise ratio (SNR). Linear inversion using these echo decay sequences provides proton density distribution functions of D-T₂ and T₁-T₂ maps. Application of inversion to the two field cases measured from two different radial depths verifies the validity of the NMR interpretations. / text

Protein synthesis is an important cellular process, and the RNA helicase eIF4A plays a vital role in unwinding messenger RNA and scanning during translation initiation. eIF4A has little activity in isolation, but is modulated by other initiation factors such as eIF4G and eIF4H. In this thesis, we explore how these proteins come together to form a functional unwinding complex. We begin with the NMR solution structure of a single domain from this complex, eIF4G HEAT2. We then map interactions involving HEAT2 and its binding partners, as well as those involving the N-terminal domain of eIF4A. We use this information first to construct a structure of the two-domain complex of HEAT2 and eIF4A-NTD, and expand this work toward the structure of the 70kDa, three-domain complex of HEAT2 with full-length eIF4A. Finally, we incorporate eIF4H and another domain of eIF4G to model the entire functional complex, and explore how interactions between domains rearrange upon binding, hydrolysis, and release of ATP. These results give us a better understanding of how eIF4G modulates eIF4A helicase activity. Moreover, the domain organization of the complex allows us to construct a more compelling model to explain how eIF4A facilitates preinitiation complex scanning along a messenger RNA.

Although extensive literature exists on NMR of water in MCM-41, the origin of a number of NMR spectral features in this material had not been understood. Specifically, the OH proton resonance observed in the dry material disappears completely as it is hydrated to 0.2 mono-layer hydration level. The purpose of this study was to gain insight into the physical basics for these spectral features and in the process broaden our understanding of behaviour/interactions of water molecules in porous material. First, measurements of MAS spectra as a function of temperature and hydration, at very low hydrations, made possible a definitive spectral peak assignment. Second, using 1D and 2D selective inversion recovery and magnetization exchange experiments, as well as MAS and non-MAS techniques, magnetization exchange between the water protons and surface OH group protons was quantified. The present results lead to the conclusion that chemical exchange is not responsible for producing the observed changes in proton spectra in MCM-41 as this material is hydrated up to the 0.2 mono-layer hydration level. This represents an important result as it is at odds with what is assumed in the literature in this connection and means that previous conclusions about hydration dynamics in this material need to be revisited. A dynamics model of water interaction with the surface OH hydration sites was introduced to explain the observed proton spectra. The model can successfully predict the observed chemical shifts and temperature dependent changes of proton spectra in the very low hydration MCM-41.

Conduction electron interactions in sodium and potassium studied by magnetic resonance techniques Christopher D. Latham Department of Physics, Stocker Road, University of Exeter, EX4 4QL, UK. Abstract Pure sodium consists of a mixture of body centred cubic (BCC) and hexagonal close packed (HCP) crystals at low temperatures and these two phases exhibit subtly di?erent many body e?ects despite their almost identical conduction electron densities. This thesis represents a ?rst attempt to unravel the di?erences in the values of the many body parameters which characterize the description of the two phases in terms of the Fermi liquid theory. Fresh theoretical estimates of several many body parameters are presented and shortcomings in earlier theoretical work are highlighted. It has been found that the cause of these e?ects can be attributed to the di?erent and anisotropic phonon spectra in the two crystal phases. This has little e?ect on the lowest order many body parameters; the cyclotron e?ective masss, m * c, the paramagnetic susceptibility, ?p and the Landau-Silin Fermi liquid theory spin coe?cient, B0; but the second spin coe?cient B1 is very di?erent in the two crystal phases; it also seems likely that it is highly anisotropic. This di?erence leads to the observation of splittings in the microwave transmission spin wave spectra and di?erent spin wave coalescence angles for the two phases. Experimental results of measurements on sodium are presented. The conduction electron spin resonance (CESR), observed by the 35 GHz microwave transmission spectometer at Exeter, is split into two distinct lines which can be identi?ed with the two crystal phases present. A continuum region between the lines indicates that there is some averaging of electron spins among crystal grains or there may be some sodium present in an intermediate, faulted crystal phase in the samples. These observations con?rm the earlier work of Myler (1982), who used re?ection methods, and demonstrate with exceptional clarity, the presence of the two crystal phases. Analysis of the microwave transmission spectra, in various ?eld orientations, of spin waves, Gantmakher-Kaner oscillations, and cyclotron wave signals shows no observable di?er¬ences between the two phases of the quantities m * c, ?p and B0. The estimated values, con?rmed by spin wave measurements, of B1 are -0.01 ± 0.01 in BCC sodium and -0.05 ± 0.01 in HCP sodium at 5 K. The strong possibility of anisotropy in B1 may result in ambiguity in the values obtained from spin wave measurements depending on the details of the methods used to solve for the various quantities. For the ?rst time the microwave frequency size e?ect (MFSE) has been properly identi?ed and measured for potassium metal. This is the microwave frequency version of the radio frequency size e?ect but with the additional complication that the time of ?ight of the conduction electrons across the sample is comparable with the period of the microwaves. The electron orbits are identi?ed as being the symmetrical “type II” orbits, in the terminology of size e?ect studies. Unusually high quality spectra obtained during the early test work on the 35 GHz spectrometer enabled this study to be made. August 1987

No description available.

No description available.

This present work investigates the NMR relaxation properties of a wide range of both healthy and leukaemic tissues to determine which tissues show the largest changes with disease development and to assess the timescale of these changes (white blood cell count was used to stage disease progression). The study makes use of a T-cell leukaemia animal model noted for its similarities to human lymphoblastic leukaemia animal studies of selected tissues assessed how well NMR changes related to pathological alterations in tissue structure and composition and identified possible causes for the observed NMR changes. Biochemical investigations were also performed to obtain a broader picture of the disease process. The sensitivity of another NMR technique known as Magnetization Transfer (MT) in the detection of leukaemic tissue changes was investigated. Various aspects of the instrumentation were developed, appropriate pulse sequences were written and suitable MT parameter settings for tissue experiments determined. Quantitative analysis of MT data was performed by fitting experimental results to a theoretical model for the MT process. Optimal MT parameter settings were established and the contribution of different processes to the MT effect were evaluated. Tissue postmortem NMR relaxation and MT properties were also investigated to determine the influence of postmortem measurement time in <I>in vitro</I> NMR results. Generally, it was found the NMR relaxation is more sensitive to disease development than MT. Liver showed the largest relaxation time changes although spleen showed the earliest significant changes. Therefore, tissues other than bone marrow show large NMR changes and would be worth investigating in a clinical environment. Also the different timescale of NMR changes between tissues may provide useful clinical information.

This thesis describes the introduction of whole body Nuclear Magnetic Resonance (NMR) Imaging into clinical practice using the 1.7 MHz NMR imager designed and built in the Department of Bio-Medical Physics and Bio-Engineering at the University of Aberdeen. At the time of its introduction in 1980, it was the only such imager in the world capable of examining the whole body. In 1983, a 3.4 MHz imager was built in the Aberdeen Royal Infirmary by the same Department and the clinical trial continued using this larger instrument. NMR imaging is unique as an imaging technique in that it does not use ionising radiation to process images, but instead utilises the response of hydrogen protons in a magnetic field to pulsed radio-frequency signals, providing information about the body's soft tissues based on their water content. Studies to assess the usefulness of this imaging method for clinical diagnosis have been performed, paying particular attention to the measurement of proton-spin-lattice relaxation time (T<SUB>1</SUB>) which is known to vary in different disease states. It is shown that whilst the specific measurement of T<SUB>1</SUB> is not an accurate method for disease diagnosis, no one T<SUB>1</SUB> value being pathognomic of one disease state, the use of images made from T<SUB>1</SUB> measurements provide diagnostically useful information at both 1.7 and 3.4 MHz. The method has been compared with all other available diagnostic techniques, including tissue histology and is found to be a superior method for the examination of the cerebellum, brainstem, cervical cord and the base of the skull. It is as diagnostically useful as other diagnostic imaging methods for the study of malignancy in the head and neck region, the pelvis and musculo-skeletal system and in certain instances for the examination of the thorax and abdomen. Being free of ionising radiation, it has been found useful in the assessment of normal and abnormal pregnancy. NMR imaging at both 1.7 and 3.4 MHz provides a new, non-invasive method for the display of normal living anatomy and for the accurate diagnosis of a wide range of diseases. It is concluded that it will become an important new diagnostic imaging method, replacing some of the established methods of diagnostic imaging in clinical practice.