Relaxation 7=1/2 nuclei

Thus P is a structural parameter ranging between 0 and 1 that acts at the initial moments of the oxidation process of every segment the higher the degree of closure (v), the lower the probability (P) of any spontaneous conformational changes and the greater the anodic overpotential required to create a relaxation nucleus. Under these conditions both magnitudes are related by... 

Because NOE enhancements are a function of competitive relaxation processes, they are highly dependent on the internuclear distances between the relaxed nucleus in question and nonirradiated neighbors that also can participate, as competing agents, in the overall relaxation process. For this reason, the two enhancements (A B) and B A ) are seldom identical and can be quite different. The contrast is particularly apropos of CH3-H systems, for which very different results are obtained, depending on which way the NOE experiment is performed. Due to their close spatial proximity, methyl protons are highly... 

The spectroscopy of multinuclear magnetic resonance in solution is one of the most important analytical methods in structural studies of transition metal hydride complexes. Among different nuclei, the proton plays the main role because H NMR provides a direct information about spectral properties of the hydride ligands. In addition the proton, being a non-quadrupolar and long-relaxing nucleus, gives rise to well-resolved NMR spectra which are very... 

In especially bromine and iodine NMR the and T2 relaxation times of the quadrupolar nuclei are frequently too short to be directly measurable. When, however, the halogen nuclei are spin-spin coupled to a slowly relaxing nucleus, usually a spin 1=1/2 nucleus, the relaxation times of the halogen nuclei can be indirectly measured. In this case the fluctuating magnetic field at the 1=1/2 nucleus produced by the rapidly relaxing halogen nucleus (I = 3/2 or 5/2) provides an efficient relaxation mechanism known as scalar relaxation of... 

A pulse interval of 10 s is sufficient to satisfy the spin-lattice relaxation time, T of the methyl group, which is the slowest relaxing nucleus with a Tj of 2 s at 125°C. The number of transients accumulated depended upon the ethylene content and in each case, accumulations are allowed to continue until a satisfactory signal-to-noise ratio was achieved. Each 13C NMR spectrum is recorded with proton noise-decoupling to remove unwanted 13C - IH scalar couplings. No corrections are made for differential nuclear Overhauser effects since these have been shown to be constant for the major resonances in low ethylene - propylene copolymers. ... 

The orientation of the coordinate system in (1) is laboratory fixed with the z-axis along the static magnetic field Hq. The origin is chosen to coincide with the relaxing nucleus. In this coordinate system the components t) of the electric field gradient fluctuate due to the motion of the environment relative to the nucleus considered. 

The tliree-line spectrum with a 15.6 G hyperfine reflects the interaction of the TEMPO radical with tire nitrogen nucleus (/ = 1) the benzophenone triplet caimot be observed because of its short relaxation times. The spectrum shows strong net emission with weak E/A multiplet polarization. Quantitative analysis of the spectrum was shown to match a theoretical model which described the size of the polarizations and their dependence on diffrision. 

Here Ti is the spin-lattice relaxation time due to the paramagnetic ion d is the ion-nucleus distance Z) is a constant related to the magnetic moments, i is the Larmor frequency of the observed nucleus and sis the Larmor frequency of the paramagnetic elechon and s its spin relaxation time. Paramagnetic relaxation techniques have been employed in investigations of the hydrocarbon chain... 

In the search for new structures with antiinflammatory activities some 1-substituted 3-dimethylaminoalkoxy-lJ/-indazoles (704) have been synthesized and pharmacologically tested (66JMC38). Doses of 20-40 mg g i.p. produced sedation, muscle relaxation and motor incoordination, whereas doses of 80-100 mg kg produced depression. Toxicity was fairly constant in all series, varying from 120 to 150 mg kg i.p., with the exception of compounds possessing a nitro group or an amino group in the indazole nucleus, which provoked cyanosis. 

The emission of y rays follows, in the majority of cases, what is known as P decay. In the P-decay process, a radionuclide undergoes transmutation and ejects an electron from inside the nucleus (i.e., not an orbital electron). For the purpose of simplicity, positron and electron capture modes are neglected. The resulting transmutated nucleus ends up in an excited nuclear state, which prompdy relaxes by giving offy rays. This is illustrated in Figure 2. 

Consider a nucleus that can partition between two magnetically nonequivalent sites. Examples would be protons or carbon atoms involved in cis-trans isomerization, rotation about the carbon—nitrogen atom in amides, proton exchange between solute and solvent or between two conjugate acid-base pairs, or molecular complex formation. In the NMR context the nucleus is said to undergo chemical exchange between the sites. Chemical exchange is a relaxation mechanism, because it is a means by which the nucleus in one site (state) is enabled to leave that state. 

The cells of the latter three types contain only a single nucleus and are called myocytes. The cells of skeletal muscle are long and multinucleate and are referred to as muscle fibers. At the microscopic level, skeletal muscle and cardiac muscle display alternating light and dark bands, and for this reason are often referred to as striated muscles. The different types of muscle cells vary widely in structure, size, and function. In addition, the times required for contractions and relaxations by various muscle types vary considerably. The fastest responses (on the order of milliseconds) are observed for fast-twitch skeletal... 

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