A series of dimeric metalloporphyrin molecules has been synthesized in which the two porphyrin rings are constrained to lie parallel to one another by two amide bridges of varying length that link the rings together. These cofacial metalloporphyrins have been applied to the surface of graphite electrodes and tested for catalytic activity toward the electroreduction of dioxygen to water in aqueous acidic electrolytes. All molecules tested exhibited some catalytic activity, but hydrogen peroxide rather than water was the chief reduction product. However, the dicobalt cofacial porphyrin linked by four-atom bridges produced a catalyzed reduction almost exclusively to water and at exceptionally positive potentials. Rotating ring-disk voltammetric measurements were employed to diagnose the electrode reaction pathway and a possible mechanism for the observed catalysis is suggested. The results seem to demonstrate the participation of two metal centers in controlling the course of a multiple-electron process.

Polymerization of the complexes [Ru(bpy)2(vinyl-py)2]2+ (I), [Ru(vinyl-bpy)3]2+ (II), [Ru(bpy)2(vinyl-bpy)]2+ (III),[Ru(bpy)2(vinyl-py)Cl]+ (IV), and [Fe(vinyl-bpy)3]2+ (V) can be initiated by electrochemical reduction in CH3CN solvent to produce stable, adherent, electrochemically active films on Pt, vitreous carbon, Sn02, and Ti02 electrodes. Randomly site-mixed copolymer (one-layer) and spatially segregated two-layer films of the pairs I and IV and II and V can be prepared by simultaneous and sequential polymerization of the appropriate monomers, respectively. The spatial features were confirmed by variable-angle X-ray photoelectron spectroscopy. Cyclic voltammetry of the copolymers is the additive response of the two redox components. In the two-layer films, however, oxidation state changes of the outer polymer films are constrained to occur via electron-transfer

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The 18S ribosomal DNA molecular phylogeny and lipid composition of over 120 marine diatoms showed that the capability to biosynthesize highly branched isoprenoid (HBI) alkenes is restricted to two specific phylogenetic clusters, which independently evolved in centric and pennate diatoms. The molecular record of C25 HBI chemical fossils in a large suite of well-dated marine sediments and petroleum revealed that the older cluster, composed of rhizosolenid diatoms, evolved 91.5 +/- 1.5 million years ago (Upper Turonian), enabling an accurate dating of the pace of diatom evolution that is unprecedented. The rapid rise of the rhizosolenid diatoms probably resulted from a major reorganization of the nutrient budget in the mid-Cretaceous oceans, triggered by plate tectonics.

Could chemistry be as easy as A+B=C? Higher diamondoids form from lower ones in experiments mimicking petroleum cracking. The yields are low but can be significantly improved by the addition of isobutane or isobutene. Rather than through superacid‐catalyzed carbocation rearrangement reactions—long assumed to be responsible for diamondoid growth—the reactions take place through free‐radical mechanisms akin to CVD growth.