Addition of relaxation agents

One of the main advantages of 13C-detected INADEQUATE is that, unlike 1H-detected INADEQUATE, it provides information about connectivity of quaternary carbons. However, quaternary carbons are handicapped by slow spin-lattice relaxation. In order to improve their sensitivity, the addition of relaxation agents has been proposed.9 It should be noted, however, that this procedure should be carried out with caution, as it may degrade signal strength by quenching the nuclear Overhauser effect.10 One study showed that a moderate 

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The C-1 carbons of the nitrobenzenes tend to have an abnormally long relaxation time requiring short pulse widths and/or the addition of relaxation agents. 

Nonselective antimuscarinic drugs have been employed in the therapy of peptic ulcers (see Chapter 40) because they can reduce gastric acid secretion they also have been used as adjunctive therapy in the treatment of irritable bowel syndrome. Antimuscarinic drugs can decrease the pain associated with postprandial spasm of intestinal smooth muscle by blocking contractile responses to ACh. Some of the agents used for this disorder have only antimuscarinic activity (e.g., propantheline), while other drugs have additional properties that contribute to their antispasmodic action. Dicyclomine (Bentyl) and oxybutynin (Ditropan) at therapeutic concentrations primarily have a direct smooth muscle relaxant effect with little antimuscarinic action. 

Anesthetic techniques that have minimized adverse effects include the use of muscle relaxants and, more recently, nerve stimulators to assess adequacy of relaxation, the introduction of very rapid acting, short-duration barbiturates, and the use of atropinic agents to minimize the cardiovascular response to a combination of a seizure and anesthesia (93). In addition, 100% oxygenation (adequacy monitored by a pulse oximeter) with positive-pressure ventilation can minimize related cardiac events and memory disruption. 

The T relaxation agent increased the sensitivity of the NMR instrument by decreasing several of the mono- and diester phosphate relaxation times by factors of 2-5. In this way the delay time between scans was decreased (43). This change permits an increase in the number of scans observed per unit time. Although the presence of ferric ions creates the potential for precipitation of phosphorus-iron complexes, the addition of a large molar excess of ethylenediaminetetraacetate (EDTA) relative to ferric ions prevented precipitation, even over a large pH region (44). 

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