Multinuclear couplings

Multinuclear NMR data have been recorded for molsidomine 12 and its metabolite SIN-1 13, confirming that both are closed ring structures and that the positive charge is accommodated at the N3 position <1996CHE1358>. The c C4-C5 coupling constants for selected 1,2,3-oxadiazoles lie between 69.4 and 89 Hz, but correlation of these values with measures of bond order and aromaticity is difficult due to substituent effects <2000MRC617, 2002JST269>. 

The multinuclear tetrahedral iron clusters have the potential for additional formal oxidation states. Because not all of these states have been found in proteins or model compounds, it is possible that some oxidation states may be unstable. For a given Fe S protein only one redox couple is used the other possible states appear to be excluded by restrictions of the protein structure. This selection rule is illustrated with two 4Fe 4S low-molecular-weight electron transfer proteins ferredoxin and high-potential iron protein (HiPIP). The 4Fe 4S clusters in both proteins were shown by X-ray crystallography to be virtually identical. However, the redox potential and oxidation states for the two proteins are vastly... 

M-F coupling constants in, 4 245 Mo, molybdenum center probes, 40 16 multinuclear, tetracyano complexes containing oxo or nitrido ligands, 40 303-304... 

So-called blue multinuclear copper oxidase enzymes, such as laccase and ascorbate oxidase, catalyze the stepwise oxidation of organic substrates (most likely in successive one-electron steps) in tandem with the four-electron reduction of O2 to water, i.e. no oxygen atom(s) from O2 are incorporated into the substrate (Eq. 4) [15]. Catechol oxidase, containing a type 3 center, mediates a two-electron substrate oxidation (o-diphenols to o-chinones), and turnover of two substrate molecules is coupled to the reduction of O2 to water [34,35]. The non-blue copper oxidases, e.g. galactose oxidase and amine oxidases [27,56-59], perform similar oxidation catalysis at a mononuclear type 2 Cu site, but H2O2 is produced from O2 instead of H2O, in a two-electron reduction. 

Multinuclear NMR data for homologous senes of fluoromethylated malo-nates [72] and trimethylsilanes [97] are compiled in Table 11. In both senes, fluoromethyl attachment is to a quaternary site These compounds are readily synthesized using fluorohalomethanes to incorporate the final fluoromethyl moiety All the malonates, except diethyl methyltnfluoromethylmalonate (4) [93], are isopropyl-substituted diethyl esters [72]. The silane data, with the exception of trimethyltrifluoromethylsilane (5) [95], are from reference 97 Chemical shift data are very comparable, with the malonates having higher proton and fluorine chemical shifts but slightly lower carbon values. The magnitudes of cf and 2J jp coupling are similar for both sets of compounds. 

The magnetic state of compounds is given for the predominant coordination geometry where an element forms multinuclear complexes, the unpaired electrons may couple to produce diamagnetic species. 

Detailed multinuclear NMR studies and analysis of coupling constants in various diazaphospholes were reported in several recent publications <2007POL837, 2002HAC340, 2001SPE27>. 

A zirconium complex of tropyne has been prepared by hydride abstraction from a mixture of 231a-c (Scheme 28).87 This compound is extremely thermally unstable, decomposing to a complex mixture of products above —50°C. Identification of both 230 and 232 rests exclusively on low-tempera-ture, multinuclear NMR spectra. Attempts to couple 232 with reagents such as alkenes, alkynes, nitriles, or ketones gave only complex mixtures of products. 

Although the vast majority of published resin data consist of 11 and 13C NMR, multinuclear NMR is also possible. Different examples of the use of 19F MAS spectrometry were described in the literature [36, 80]. This nucleus was used to monitor different reactions on solid support, as coupling of fluorobenzyloxycarbonyl with aminoacids and SNAr nucleophilic displacements [80]. 

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