Top PDF Carbon-13 magnetic resonance spectroscopy

Carbon-13 magnetic resonance spectroscopy

Carbon-13 magnetic resonance spectroscopy

The field of 13 c nmr has been reviewed previously (9, 10) and the earlier work will not be discussed here in detail. Studies of 13 c nuclear magnetic resonance may be conveni[r]

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Chapter 11 Structure Determination: Nuclear Magnetic Resonance Spectroscopy. Nuclear Magnetic Resonance Spectroscopy Nuclear Magnetic Resonance

Chapter 11 Structure Determination: Nuclear Magnetic Resonance Spectroscopy. Nuclear Magnetic Resonance Spectroscopy Nuclear Magnetic Resonance

The Nature of NMR Absorptions • The two methyl groups of methyl acetate are nonequivalent • The two sets of hydrogens absorb at different positions • When the frequency of rf irradiation is held constant and the applied field strength is varied each nucleus in a molecule comes into resonance at a slightly different field strength, mapping the carbon-hydrogen framework of an organic molecule

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Nuclear Magnetic Resonance Spectroscopy

Nuclear Magnetic Resonance Spectroscopy

corresponds to 400 MHz for 1 H measurement) and usually more FIDs need to be accumulated to build up the SNR. However, some factors alleviate these difficulties. These include the broadband decoupling of all 1 H– 13 C coupling patterns using special pulse sequences, so that each carbon signal is a singlet. This also has the effect of boosting the SNR through the NOE from the 1 H spins, this being most effective for CH, CH 2 and CH 3 carbons. One disadvantage of 13 C NMR spectroscopy is that some carbons, particularly quaternary carbons (which have only at best weak NOE) also have long relaxation times and are saturated easily and thus give weak peaks. For these reasons, quantitative studies based on 13 C resonances are more prone to error than those based on 1 H resonances. The
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Nuclear Magnetic Resonance Spectroscopy

Nuclear Magnetic Resonance Spectroscopy

• In the benzene molecule all six hydrogens are equivalent since the bonding of all six to the carbon atoms is identical. Only one peak will be observed. • A substitution on one or more of the positions of the benzene ring will upset this equivalency -the extent of change depends upon the number and/or nature of the substituted group(s).

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Proton Nuclear Magnetic Resonance Spectroscopy

Proton Nuclear Magnetic Resonance Spectroscopy

Proton Nuclear Magnetic Resonance Spectroscopy Introduction: The NMR Spectrum serves as a great resource in determining the structure of an organic compound by revealing the hydrogen and carbon skeleton. Historically, NMR was initially used to study the nuclei of Hydrogen atoms; however, any atom with an odd mass or atomic number has a nuclear spin that can be studied by NMR. Without the application of an applied magnetic field, protons are spinning in a randomly oriented manner and are generating a magnetic field (called the magnetic moment) 1 . However, once an external (applied) magnetic field is present the protons either align with (parallel) or against (anti parallel) it. The parallel orientation, called the alpha spin, has a lower energy than the anti parallel (beta) spin. The stronger the applied magnetic field the greater the energy difference (∆E) between the parallel and anti parallel states (Diagram 1) 2 . Therefore, the strength of the magnetic field determines the energy required to cause a nuclear spin flip. The energy difference (∆E) between the ground and excited states is approximately 0.02 cal/mol which correlates to radio wave photons. An NMR signal is created once the radio wave photons supplied match the (∆E) of the nucleus.
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Magnetic resonance in reaction engineering: beyond spectroscopy

Magnetic resonance in reaction engineering: beyond spectroscopy

Which species dominate at the pore surface? The recent implementation of this measurement came from parallel work undertaken in characterising rock-core wettability, as required for developing oil recovery processes [20]. In this field two-dimensional MR relaxometry experiments are used to characterise the relative strength of interaction of hydrocarbon and aqueous species with the interior surface of the rock — the parallel between hydro- carbon/brine/rock and a multi-component mixture within a solid catalyst is obvious. These experiments are based on simple, robust measurements of nuclear spin relaxa- tion times; relaxation times characterise the return of the nuclear spin system to equilibrium following excitation of the nucleus of interest using radio-frequency excitation.
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Magnetic resonance spectroscopy in Alzheimer’s disease

Magnetic resonance spectroscopy in Alzheimer’s disease

According to one model of biomarkers in AD, amyloid pathology accumulates before evidence of neurodegeneration. 82 Amyloid PET imaging serves as a sur- rogate for brain amyloid load and FDG-PET and Structural MRI serve as markers of neurodegeneration. While these imaging markers are well validated measures of amyloid and neurofibrillary tangle pathology, they do not measure microglial activation. MRS mI is a potential surrogate marker for glial activity. A recent 13-carbon MRS and 1 H MRS linked glial and microglial activity to mI elevation in AD. 83
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In vivo mouse cardiac hyperpolarized magnetic resonance spectroscopy

In vivo mouse cardiac hyperpolarized magnetic resonance spectroscopy

As expected, spectra acquired in wild type mice (C57BL/6) showed similar resonances to the rat. However, carbon dioxide was only occasionally visible in the high temporal resolution spectra. Carbon dioxide was present in summed spectra, indicating that its ab- sence was due to lower SNR in the mouse compared to the rat. Pyruvate and lactate appearance mirrored that of rats, whilst alanine signals appeared to be slightly elevated compared to the time evolution in the rat and also showed significant temporal differences in appear- ance. However, the major difference between rat and mouse spectra was the relative levels of bicarbonate pro- duction, which were 7-fold lower in the mouse heart compared to the rat heart when normalized to max- imum pyruvate signal, possibly representing a species difference in PDH expression/activity due to differences in cardiac work load. This is supported by previous measurements which would suggest a lower PDH activ- ity in the mouse compared with the rat (2.4 μmol/min/g tissue (mouse) [38] vs 5.1 μmol/min/g tissue (rat) [19]).
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PROTON NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY (H-NMR)

PROTON NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY (H-NMR)

How do we determine how many equivalent protons there are? There are many ways to determine how many sets of equivalent protons there are in a molecule. For example, we can see if there is a line of symmetry. Protons that are aligned on a line of symmetry are equivalent. Another way is to replace the proton with deuterium to form two molecules, and if the two molecules are the same, then the two protons are equivalent. The third way to determine how many equivalent protons there are is to look at the atom attached to the proton (usually a carbon) and observe what that atom is bonded to, and then the atom bonded to that, all the way until a difference is observed. If there is no difference, the protons are
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MAGNETIC RESONANCE SPECTROSCOPY (MRS)

MAGNETIC RESONANCE SPECTROSCOPY (MRS)

The documented increases ranged from 23-50%. Most gain in SNR was with short echo time spectroscopy with little improvement at long echo times. Artefacts were worse and acquisitions took slightly longer at 3 T. The authors concluded that objective evidence to guide routine diagnostic use of 3 T technology is lacking. The Canadian Agency of Drugs and Technologies in Health (CADTH) published a systematic review for 1.5 tesla magnetic resonance imaging scanners compared with 3.0 tesla magnetic resonance imaging scanners. Twenty-five studies met the inclusion criteria for the systematic review. The six neurology studies, four cerebrovascular studies, three cardiac studies, one renal study, three musculoskeletal studies, and eight oncology studies were assessed. All studies were prospective and observational, assessing between 20 patients and 65 patients who received repeat testing with 1.5 T MRI and with 3.0 T MRI within one week for acute conditions and one month for chronic conditions.
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Nuclear Magnetic Resonance Spectroscopy

Nuclear Magnetic Resonance Spectroscopy

The vector sum of the magnetic moments of one type of nuclei is a measure of the number of protons of that type in the molecule. The determination of the magnetic moment for protons in each type of electronic environment forms the essence of the NMR experiment.

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Nuclear Magnetic Resonance Spectroscopy

Nuclear Magnetic Resonance Spectroscopy

• Nonequivalent protons on adjacent carbons have magnetic fields that may align with or oppose the external field.. • This magnetic coupling causes the proton to absorb slightly downf[r]

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Nuclear Magnetic Resonance Spectroscopy

Nuclear Magnetic Resonance Spectroscopy

• In a magnetic field, there are now two energy states for a proton: a lower energy state with the nucleus aligned in the same direction as B 0 , and a higher energy state in which the nucleus aligned against B 0 . • When an external energy source (h  ) that matches the energy difference (E) between these two states is applied, energy is absorbed, causing the nucleus to “spin flip” from one orientation to another.

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Nuclear Magnetic Resonance (NMR) Spectroscopy

Nuclear Magnetic Resonance (NMR) Spectroscopy

Two decay routes (non-radiative): 1. Spin-Lattice Relaxation (T 1 ) -also called: longitudinal relaxation -due to interactions between nuclear spin states and magnetic micro environments in the sample -magnetic micro environments must be at the Larmor Frequency of the absorbing nuclei in order to couple

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Magnetic Resonance Spectroscopy as applied to epilepsy

Magnetic Resonance Spectroscopy as applied to epilepsy

For this reason external referencing is frequently used to quantify the metabolite signal. The signal from water, or a metabolite of known concentration, can be measured in a separate acquisition from a phantom (test object). This overcomes the problem of the incomplete information about the water concentration. A “same time” external standard can be measured in the same sequence as the subject of interest. “Same-place” external standard measurement can also be used. This requires that the phantom is measured in the same position within the magnetic field as would be occupied by the specimen of interest, for example the centre of the brain in a volunteer undergoing a Head MRS study (thus overcoming the major problems of spatial non-uniformity). “Same place” scanning must clearly be performed at a different time point to the acquisition of the volunteer scan. It is therefore vulnerable to changes in coil sensitivity (brought about by the change from loading by a head to loading by a phantom), and to receiver instability (whether caused by explicit gain changes or unexpected drift). Corrections for RF non-uniformity across the different regions in the brain are still needed in principle, although they may be minimal in a relatively uniform coil.
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Introduction to Nuclear Magnetic Resonance Spectroscopy

Introduction to Nuclear Magnetic Resonance Spectroscopy

 A transceiver antenna, called the NMR probe, is inserted into the center bore of the magnet, and the sample is placed inside the probe..  Sample can be in a narrow tube, or.[r]

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Proton Nuclear Magnetic Resonance Spectroscopy

Proton Nuclear Magnetic Resonance Spectroscopy

Proton Nuclear Magnetic Resonance Spectroscopy In this laboratory exercise we will learn how to use the Chemistry Department's Nuclear Magnetic Resonance (NMR) spectrometer and how to interpret the spectra obtained using this spectrometer. NMR is one of the most powerful techniques available to the organic chemist for molecular structure determination. Therefore, knowing how to obtain and interpret NMR spectra is of critical importance.

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Improved Acquisition Methods for Hyperpolarized Carbon-13 Magnetic Resonance Imaging

Improved Acquisition Methods for Hyperpolarized Carbon-13 Magnetic Resonance Imaging

3.1 Abstract Acquisition timing and B 1 calibration are two key factors that affect the quality and accu- racy of hyperpolarized 13 C MRI. The goal of this project was to develop a new approach using regional bolus tracking to trigger Bloch-Siegert B 1 mapping and perform real-time B 1 calibration based on regional B 1 measurements, followed by dynamic imaging of hyperpolar- ized 13 C metabolites in vivo. The proposed approach was implemented on a system which allows real-time data processing and real-time control on the sequence. Real-time center frequency calibration upon the bolus arrival was also added. The total hyperpolarized sig- nal loss caused by the proposed bolus tracking and real-time frequency/power calibration was calculated based on applied flip angles and expected to be less than 7%. The feasibil- ity of applying the proposed framework for in vivo hyperpolarized [1- 13 C]pyruvate imaging was tested on a clinical 3T scanner on healthy rats, tumor-bearing mice and human ap- plications including brain, heart, kidney and prostate. Automatic acquisition timing based on either regional bolus peak or bolus arrival was achieved with the proposed framework.
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Metabolism of Methanol in Plant Cells. Carbon-13 Nuclear Magnetic Resonance Studies

Metabolism of Methanol in Plant Cells. Carbon-13 Nuclear Magnetic Resonance Studies

MATERIALS AND METHODS Cell Preparation Cell suspensions were chosen in preference to dense tissues to improve the homogeneity of the incubation con- ditions (particularly the extracellular pH and the oxygen supply). Sycamore (Acer pseudoplatanus L.) cells were grown at 20°C as a suspension in liquid nutrient medium according to the method of Bligny and Leguay (1987). The culture medium, well aerated and containing various con- centrations of [ 13 C]methanol (0.2–5 mm), was kept at a volume of 0.3 L and stirred continuously at 60 rpm. Under these conditions the cell number doubling time was 40 to 48 h, after a lag phase of approximately 2 d, and the maximum cell density was attained after 7 to 8 d of growth, when the stationary phase was attained. The cell suspen- sions were maintained in exponential growth by subcul- tures every 7 d. Anaerobiosis resulted in a failure of the cells to utilize methanol. The cell wet weight was measured after straining culture aliquots onto a glass-fiber filter.
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Magnetic Resonance Spectroscopy Investigations of Alzheimer Disease

Magnetic Resonance Spectroscopy Investigations of Alzheimer Disease

ii Alzheimer disease is a progressively devastating neurodegenerative disease of the brain that impairs cognition and is ultimately fatal. Cholinesterase inhibitors are the current standard treatment for Alzheimer disease and they can alleviate some of the symptoms and thus improve quality of life. Cognitive measures aid in the diagnosis and monitoring of individuals with Alzheimer disease, but they do not directly measure disease pathophysiology. The purpose of this thesis is to investigate metabolic changes measured with proton magnetic resonance spectroscopy within the hippocampus and posterior cingulate, two brain regions known to be effected in Alzheimer disease, following cholinesterase inhibitor treatment. Such treatment is aimed at increasing the deficit of acetylcholine in Alzheimer disease. Secondly, to develop a 7 Tesla proton magnetic resonance spectroscopy data acquisition and metabolite quantification protocol to be used for future studies.
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