Pt(II) Derivatives with Rollover-Coordinated 6-substituted 2,2′-bipyridines: Ligands with Multiple Personalities

We report here the synthesis, characterization and behavior of a series of Pt(II) cyclometalated rollover complexes with two substituted bipyridines, 6-ethyl-2,2′-bipyridine (bpy6Et) and 6-methoxy-2,2′-bipyridine (bpy6OMe), in comparison with previously studied 2,2′-bipyridine complexes. The two ligands have similar steric hindrance but different electronic properties. As a result, the reactivity of the two series of complexes follows very different routes. In particular, the new complexes behave differently towards protonation reactions, differences given by substituents and ancillary ligands, added to the presence of several nucleophilic centers. Reaction of complex [Pt(bpy6OMe-H)(PPh3)Me)] with [H3O⋅18-crown-6][BF4] results in a retro-rollover reaction whose final product is the cationic adduct [Pt(bpy6OMe)(PPh3)Me)]+. Surprisingly, only the isomer with the cis-PPh3-OMe geometry is formed; in spite of an expected instability due to steric hindrance, Density-Functional theory (DFT) calculations showed that this isomer is the most stable. This result shows that the cone angle is far from being a real “solid cone” and should lead to a different interpretation of well-known concepts concerning steric bulk of ligands, such as cone angle. Proton affinity values of ligands, neutral complexes and their protonated counterparts were analyzed by means of DFT calculations, allowing a comparison of their properties.

Use of 3-Methyl-2-Benzothiazolone Hydrazone in an Automated Colorimetric Method for Determination of Triglycerides in Plasma or Serum

A new automated colorimetric method is described for the determination of serum or plasma triglycerides. The samples are extracted with 2-propanol containing activated alumina. An AutoAnalyzer Sampler II and Proportioning Pump II are used in combination with a Gilford Model 300 N spectrophotometer and Model 3091-A debubbler flow cell. Following on-line saponification, glycerol is oxidatively cleaved with sodium metaperiodate. The resulting formaldehyde is reacted with 3-methyl-2-benzothiazolone hydrazone (MBTH) under mild conditions to produce the corresponding azine. Further reaction of MBTH with the azine in the presence of an oxidizing agent results in the formation of a blue cationic adduct. Beer's law is obeyed, at 670 nm, to a triglyceride concentration of 400 mg/100 ml. Because of the high sensitivity of the MBTH reaction, short incubation periods, high sampling rates (60/h), and low flow rates can be used. The results correlate well with those obtained by the Kessler-Lederer method and by a totally enzymatic method.