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Alcohol and Aldehyde Adducts of Zinc Thiolates:  Structural Modeling of Alcoholdehydrogenase

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posted on 1999-04-03, 00:00 authored by Bodo Müller, Astrid Schneider, Markus Tesmer, Heinrich Vahrenkamp
Bis(pentafluorothiophenolato)zinc (1) and bis(2,4,6-triisopropylthiophenolato)zinc (2) can be combined with nitrogen-containing derivatives of benzyl alcohol and benzaldehyde to form (N,O-chelate) zinc thiolates. 2-Pyridylmethanol as well as 2-quinolylmethanol (HetMeOH) yield [(HetMeO)Zn(SR)]4 (3, 4) having a cyclo-Zn4(μ-O)4 backbone and only terminal SR. Likewise, thiolate 1 and 2-(dimethylamino)benzyl alcohol form zwitterionic [(dimethylammoniobenzylato)Zn(SR)2]2 (5) with bridging alkoxide and terminal thiolate. In contrast, 6-picolylmethanol (PicMeOH) and thiolate 1 result in [(PicMeOH)Zn(SC6F5)2] (6) containing zinc in a tetrahedral ZnNS2O, environment. Simple aromatic aldehydes form polymeric complexes [(RCHO)Zn(SC6F5)2] (7:  R = p-tolyl, 8:  R = mesityl) with a [Zn−S] backbone. Chelating aldehydes (CA) yield mononuclear complexes with tetrahedral ZnNS2O coordination [(CA)Zn(SC6F5)2] (9, CA = pyridine-2-carbaldehyde; 10, CA = 6-methylpyridine-2-carbaldehyde; 11, CA = 6-methoxypyridine-2-carbaldehyde; 12, CA = quinoline-2-carbaldehyde; 13, CA = 2-(dimethylamino)benzaldehyde). In contrast, N-methylimidazole-2-carbaldehyde (ImA) is coordinated twice in tetrahedral [(ImA)2Zn(SC6F5)2] (14) lacking any Zn−O interactions. Pyridine-2,6-dicarbaldehyde (PDA) forms trigonal bipyramidal [(PDA)Zn(SC6F5)2] (15) with ZnNO2S2 ligation. The structures of 3, 4, 6, 8, 10, 11, 13, and 14 were determined crystallographically, and the structures of 5 and 15 were deduced from those of the corresponding ZnBr2 complexes. The ZnNS2O coordination pattern observed for the enzyme has been reproduced to a very good approximation. In complexes 6 and 10, which are almost superimposable, it is realized for both the corresponding alcohol and aldehyde.

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