Gary W. Dirks

ENERGY TRANSFER FROM CAROTENOID POLYENES TO PORPHYRINS: A LIGHT-HARVESTING ANTENNA

Carotenoid to porphyrin singlet‐singlet energy transfer has been observed in a new covalently linked carotenoid‐porphyrin ester. Nuclear magnetic resonance studies reveal that the relatively high energy transfer efficiency (˜ 25%) is a result of a stacked conformation in which the 26 π electron carotenoid chromophore resides ˜4–5 Å above the mean porphyrin plane. Substantial quenching of porphyrin fluorescence was also observed. Implications for the mechanism of energy transfer and possible applications to synthetic solar energy conversions systems are discussed.

LIGHT ABSORPTION AND ENERGY TRANSFER IN POLYENE‐PORPHYRIN ESTERS

Two examples of a new class of compounds, polyenes covalently linked to meso‐tetraarylporphyrins, have been prepared. Optical studies revealed that energy transfer from a 26 π electron polyene moiety to the porphyrin was zero, whereas energy transfer efficiency from a polyene containing 18 π electrons was ˜80%. The results demonstrate that the polyene moiety can function as an efficient light gathering antenna for possible application to porphyrin‐based solar energy conversion schemes. In addition, such polyene‐porphyrin esters may serve as probes of the structural requisites for light harvesting by carotenoids in the photosynthetic membranes of green plants.

Studies Directed Towards a Practical Synthesis of Brevicomin (III) Cyclization Routes to 6, 8-Dioxabicyclo[3.2.1]octane

Abstract Bicyclic ketals have been noted as an important structural unit in sugars1, an alkaloid2, a terpene3 and in pheromones. It is with regard to this last group that we have been recently directing our attention. Frontalin (1)4 and the brevicomins (2 and 3)5 are sex aggregating pheromones of Dendroctonus frontalisand D. brevicomis, respectively. Because of their potential utility in controlling populations of pine bark beetles, considerable activity has been directed towards their syntheses. 6–10 Particularly in syntheses of brevicomin, where the exo-isomer (2) is the biologically useful isomer for insect control, does the methodology become quite important.

Stereochemistry of oligomeric proteins

Abstract The subunits of many oligomeric proteins are organized into stable arrays with high symmetry. When these proteins interact with small molecules such as enzyme substrates or inhibitors, a variety of non-equivalent forms of the protein may be produced. Some of these forms have the same atomic composition, but differ in the spatial arrangement of the subunits. These species differ in all of their properties (conformation, affinity for substrate, etc.), and the relationships among them and among their subunits may be defined using stereochemical nomenclature which has been developed for small molecules. In many cases, the number of such forms is quite large. Rigorous, group-theoretical methods for enumerating all possible species are described and illustrated for the enzyme aspartate transcarbamoylase.