Irradiation magnetization

Remember from Section 2.3 that to tip M off the z axis, so it has a component in the x,y plane, we need an irradiating magnetic field (B[) that oscillates at exactly the precessional frequency of the nuclei of interest and is oriented perpendicular to B0. How are we going to generate such a precessing magnetic field ... 

In another example of integrated sample processing, Lee et al. accomplished cell lysis, DNA purification, and PCR amplification for pathogen detection using a single-chamber device. In this work, the authors developed a Laser-Irradiated Magnetic Bead System (LIMBS) for cell lysis and... 

In the CSCM ID technique (ref. 4) a carbon satellite either upfield or downfield of the proton is irradiated, magnetization is transfered to the attached carbon and a signal, either positive (upfield irradiation) or negative (downfield irradiation), is then observed. This might therefore be interpreted as a one dimensional technique corresponding to a H- C hetcor experiment. The technique offers two principal advantages for the natural product chemist sensitivity and selectivity, in part, because vast amounts of unwanted data are not acquired and because the digital resolution is the same as in the decoupled spectrum. The major limitation to the technique is that it is not useful in the instance of substantial proton overlap. 

In this equation, 01 is the ifeqiieney of the RF irradiation, oiq is the Lannor ifeqiieney of the spin, is the spm-spm relaxation time andM is the z magnetization of the spin system. The notation ean be simplified somewhat by defining a eomplex magnetization, AY, as in equation (B2.4.3). 

Figure B2.4.6. Results of an offset-saturation expermient for measuring the spin-spin relaxation time, T. In this experiment, the signal is irradiated at some offset from resonance until a steady state is achieved. The partially saturated z magnetization is then measured with a kH pulse. This figure shows a plot of the z magnetization as a fiinction of the offset of the saturating field from resonance. Circles represent measured data the line is a non-linear least-squares fit. The signal is nonnal when the saturation is far away, and dips to a minimum on resonance. The width of this dip gives T, independent of magnetic field inliomogeneity.

For pipelines in service in chemical plants, it is not usually convenient to place a radiation source inside the pipe and position it to irradiate each welded joint. The radioisotope source container maybe placed on the outer surface of the pipe. The radiation beams then pass through two pipe wall thicknesses to expose films placed diametrically opposite the radiation source, also on the outside of the pipe wall. Other methods, such as magnetic particle inspection of welds in steel pipe, or ultrasonic inspection of welds in pipes of all materials, supplement x-rays in many critical appHcations. The ultrasonic tests can often detect the thin, laminar discontinuities parallel to the pipe surface or the incomplete fusion discontinuities along the weld... 

External Control. The use of external control to govern the release of dmgs from dehvery systems has largely been experimental. A number of mechanisms have been explored, and include external sources such as electrical currents, magnetism, ultrasound, temperature changes, and irradiation. 

B. 3-Chlorothietane 1,1-dioxide. Thietane 1,1-dioxide (14.0 g, 0.132 mol) is placed in a three-necked, 500-mL, round-bottomed flask fitted with a magnetic stirrer, reflux condenser and a chlorine bubbler, caution sinae ahtovine is poisonous, the reaation involving it should be done in a good hood.) Carbon tetrachloride (300 mL) is added to the flask (Note 4) and the suspension is irradiated by a 250-watt sunlamp positioned as close as possible to the reaction flask without touching it (Note 5) while chlorine is bubbled through the solution for 15 min at a moderate rate (Note 6). A copious white precipitate forms and irradiation and addition of chlorine must be stopped at... 

D. 3,3-Diahlarothietane 1,1-dioxide. Thietane 1,1-dioxide (5.0 g, 0.047 mol) Is placed In a 500-mL, three-necked, round-bottomed flask equipped with a reflux condenser, magnetic stirrer, and chlorine gas bubbler. Carbon tetrachloride (350 mL) Is added and the solution Is irradiated with a 250-watt sunlamp (Note 5) while chlorine Is bubbled through the stirred mixture for 1 hr (Note 9). Irradiation and chlorine addition are stopped and the reaction mixture is allowed to cool to room temperature. The product Is collected by filtration as a white solid (4.0-4.4 g, 49-53%), mp 156-158°C (Note 10). The product can be used without further purification or It can be recrystallized from chloroform. 

A solution of 500 mg 3 -acetoxypregn-5-en-20-one-[17a,16a-c]-A -pyrazoline in 100 ml of anhydrous dioxane is stirred with a magnetic stirrer and irradiated in a water-cooled quartz reactor with a high pressure Biosol Philips 250 W quartz lamp for 1 hr. The solvent is removed at reduced pressure and the residue is chromatographed on alumina (activity III). Elution with petroleum ether-benzene (3 1) gives 0.2 g (42%) of 3 -acetoxy-16a,17a-methylene-pregn-5-en-20-one mp 193-193.5° after two recrystallizations from methylene dichloride-ethyl acetate. 

A solution of 0.17 g (51) in 160 ml benzene is stirred magnetically and irradiated for 6 hr with a Hanau NK 6/20 low-pressure mercury lamp (main emission at 2537 A) placed in a central water-cooled quartz tube. Cyrstalliza-tion of the crude product gives 0.15 g (52) (88%). 

If the oriented nuclei are now irradiated with electromagnetic radiation of the proper frequency, energy absorption occurs and the lower-energy state "spin-flips" to the higher-energy state. When this spin-flip occurs, the magnetic nuclei are said to be in resonance with the applied radiation—hence the name nuclear magnetic resonance. 

A thin glass tube containing the sample solution is placed between the poles of a strong magnet and irradiated with rf energy. 

Nuclear magnetic resonance, NMR (Chapter 13 introduction) A spectroscopic technique that provides information about the carbon-hydrogen framework of a molecule. NMR works by detecting the energy absorptions accompanying the transitions between nuclear spin states that occur when a molecule is placed in a strong magnetic field and irradiated with radiofrequency waves. 

When exposed to daylight, the sulfide and selenide halides HgsY2X2 are blackened within a few minutes. This black color reversibly disappears when the sample is heated to 90 to 120°C, or stored in the dark for several days 204, 375-377). The nature of this phototropic behavior has now been widely investigated by analytical, spectroscopic, structural, magnetic, EPR, and radiotracer investigations 205, 233, 375-377, 379, 380, 382). During irradiation of the compounds, electrons belonging to or I ions are excited to upper states. The result-... 

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