CPMAS

Lyerla J R, Yannoni C S and Fyfe C A 1982 Chemioal applioations of variable-temperature CPMAS NMR speotrosoopy in solids Accounts Chem. Res. 15 208-16... 

Although not a heteroaromatic compound, the case of citrinin studied by Destro and Luz ([97JPC(A)5097] and references therein) is so significant that it deserves mention here. Citrinin exists in the crystal as a mixture of the p-quinone 5a and o-quinone 5b tautomers (Scheme 3). The equilibrium ii temperature dependent and by using CPMAS NMR (Section VI,F) and, more remarkably. X-ray crystallography, the authors were able to determine the AH and AS values (the rate is extremely fast on the NMR time scale, >10 s ). 

Some reviews relevant for this section concern N CPMAS [86AG(E)383] of pyrazoles, including CPMAS results (93MRC107) and proton transfer in solid heterocycles (94JHC695). The most relevant studies reported in Table X are (1) the use of C CPMAS NMR to identify... 

Different solid-state NMR techniques CPMAS NMR, the second moment of the signal, the spin-lattice relaxation time in the rotating frame T p) were combined to reach the conclusion that in the case of por-phine H2P the double-proton transfer is followed by a 90° rotation within the crystal (see Scheme 2). 

In the same paper, Limbach et al. (87AGE934) reported the study of the compound related to porphyrins, porphycene 79. Porphycene behaves very differently from FI2P in CPMAS DNMR experiments. Its behavior was explained assuming that the four porphycene tautomers (two cis and two trails) are present in the crystal and interconverting very rapidly due to short N-H...N distances in the seven-membered pseudorings. 

As a consequence of restricted internal mobility in molecules in the crystalline state, nuclei in different conformation environments, but identical in other respects, can produce different signals in 13C cross polarization, magic angle spinning (CPMAS) solid-state NMR. This analysis is not necessarily limited to crystalline regions, since signals of different conformations are resolved if the exchange is slow with respect to the time scale of the NMR experiment. 

Sometimes decomposition reactions can be avoided by carrying out diazotizations in concentrated sulfuric acid. By this method Law et al. (1991) obtained the 1,5-bisdiazonium salt (incorrectly called tetrazonium salt) of l,5-diamino-4,8-dihy-droxy-anthraquinone, which is deprotonated to 2.28. The structure was verified by cross-polarization magic angle spinning (CPMAS) 13C NMR spectroscopy. 

A-(6-Chloro-3-pyridylmethyl)-A-ethyl]amino-2-methyliminoacetic acid (CPMA) and N-(6-chloro-3-pyiidylmethyl)-A-ethyl-A -methylformamidme (CPMF), iV-(6-chloro-3-pyridymethyl)-A-ethylformamide (CPF). 

Nitenpyram and its metabolites. The metabolites of nitenpyram, CPMA and CPMF, are determined by HPLC under the same conditions as for the parent nitenpyram. The retention times of nitenpyram, CPMA, and CPMF are 9.2,7.9 and 5.3 min, respectively. However, these compounds are unstable and need to be derivatized to a more stable compound, CPF, prior to analysis. It is necessary to remove acetone from the extract before derivatization, because a by-product can be formed in the presence of acetone thus impacting the recovery of CPF. Nitenpyram is more effectively determined using HPLC, whereas CPF, as the analyte of nitenpyram and its metabolites, is more effective by gas chromatography/flame thermionic detection (GC/FTD). 

The residue analysis of CPMA and CPMF in vegetables and fruits is carried out as follows. A 20-g amount of the sample is homogenized for 3 min with 100 mL of acetone and filtered. The extraction procedure is repeated once with 50 mL of acetone and filtered. The combined filtrate is concentrated to 10 mL at 50 °C and, after addition of 0.2 mL of triethylamine to the concentrate, the reaction mixture is allowed to stand for 30 min at 50 °C. The mixture is applied to an Extrelut column (Extrelut 14-g). CPF from CPMA via CPMF is eluted with 50 ml of diethyl ether after washing the... 

The polar character of neonicotinoids makes them, in general, potentially mobile in soil. Acetamiprid and nitenpyram have short soil persistence. Imidacloprid and thi-amethoxam, however, are sufficiently persistent in soil to be used for soil treatment. The definition of soil residues for the various neonicotinoid compounds except for imidacloprid are the parent compound and it metabolites. The metabolites of acetamiprid are lM-1-2, lM-1-4 and lC-0 (Figure 6). The metabolites of nitenpyram are 2-[N-(6-chloro-3-pyridyl-methyl)-A-ethyl]amino-2-methyliminoacetic acid (CPMA) and A-(6-chloro-3-pyridylmethyl)-Ai-ethyl-A -methylformamidine] (CPMF). 

Solid state 13C CPMAS NMR spectra of Wheat High Molecular Weight (W.HMW) subunits show well resolved resonances identical with spectra of dry protein and peptide samples [24], Most of the amino acids side-chain resonances are found in the 0-35 ppm region followed by the alpha resonances of the most abundant amino acids glycine, glutamine and proline at chemical shifts of 42, 52 and 60 ppm, respectively, and the carbonyl carbons show a broad peak in 172-177 ppm region. The CPMAS spectra of hydrated whole HMW provides important information on the structural characteristics. 

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