Coenzyme F430 from Methanogenic Bacteria: Detection of a Paramagnetic Methylnickel(II) Derivative of the Pentamethyl Ester by 2H-NMR Spectroscopy
✍ Scribed by Shu-Kun Lin; Bernhard Jaun
- Publisher
- John Wiley and Sons
- Year
- 1991
- Tongue
- German
- Weight
- 740 KB
- Volume
- 74
- Category
- Article
- ISSN
- 0018-019X
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✦ Synopsis
Abstract
A methylnickel(II) derivative of coenzyme F430 (1) was proposed as an intermediate in the enzymic process catalyzed by methyl‐CoM reductasc. Indirect evidence points to formation of CH~3~–F430M^II^ in the reaction of F30M^1^ (obtained from F430M^II^ (2)) with eleclrophilic methyl donors. The results presented here show, that such a compound does exist. A paramagnetic CD~3~–Ni^II^ derivative 5b of the pentamethyl ester 2 (F430M) of coenzyme F430 was prepared by in situ methylation with (CD~3~)~2~Mg and characterized by its isotropically shifted ^2^H‐NMR spectrum. At −40°, the very broad D‐signal of the axially coordinated CD~3~ group is found at −490 ppm. Comparison with the ^2^H‐ and ^1^H‐NMR spectra of mcthyl(tetramethylcyclam)nickel(II) derivatives 4 ([Ni^II^(CH~3~))(tmc)]CF~3~SO~3~ (4a) is the only isolated CH~3~–Ni derivative of a N~4~macrocyclic Ni^II^ complex' shows that the large isotropic shift to high field is characteristic for a Me group axially bound to the Ni center. The temperature dependence of the isotropic shift of the C__D__~3~–Ni group in both 4b and 5b follows Curie's law and yields ^2^H hyperfine coupling constants of −0.65 (4b) and −0.85 MHz (5b), respectively. The ^1^H‐NMR spectrum indicates that, in contrast to the five‐coordinate monochloro complex [Ni^II^Cl(tmc)]^+^, intermolecular exchange of the axial ligand in [Ni^II^(CH~3~)(tmc)]^+^ 4a is either slow at the NMR time scale or does not occur at all.