UC Berkeley

The self-assembling protein shells of viruses have provided convenient scaffolds for the construction of many new materials with well-defined nanoscale architectures. Of these numerous examples, one such application is the use of viral capsids to template synthetic light harvesting structures. Through the combination of modern molecular and chemical biology techniques, the symmetry and self-assembling nature of the viral proteins can be exploited to form regular arrays of chromophores on the protein surface in a site-specific manner. Tobacco Mosaic Virus coat protein (TMVcp) was used to template organic chromophores, forming light harvesting structures reminiscent of biological systems. While many of the processes in photosynthesis are well understood, there is still much mystery surrounding the physical basis for the efficiency seen in natural systems. We set about constructing protein-templated biomimetic light harvesting systems with tunable parameters such as protein attachment chemistry, inter-chromophore distances, and inter-chromophore geometries. Through genetic manipulation of the TMVcp, protein mutants were produced with various sites of reactivity on the monomeric protein surface, manifesting as regularly spaced arrays within the assembled capsid. The spatial and geometric relationships of the reactive sites were investigated, along with the resulting protein assembly state. Next, chromophores were introduced at various locations and investigated structurally and spectroscopically. The spectral signatures observed with a range of chromophores, geometries, and pigment-protein attachments were compiled for numerous TMVcp-templated systems, and the effects of protein-templating discussed. The overall goal of this work is to gain insight into the origin of the spectral and energetic effects behind the efficiencies observed in natural systems through the use of highly tunable synthetic biomimetic systems. For a truly biomimetic system to be produced, however, there must be a charge-separation event involved in the light harvesting process. We then turned our efforts to the synthesis of water-soluble phthalocyanines capable of protein attachment. Phthalocyanines are a near infrared absorbing class of chromophores, important for their sensitization properties, and of particular interest to us for their use as singlet oxygen generation materials in photodynamic cancer therapy. The synthesis of both symmetric and asymmetric phthalocyanines was accomplished, followed by characterization. Finally, an asymmetric phthalocyanine was integrated into the interior of the bacteriophage MS2 viral capsid, and its ability to generate singlet oxygen was investigated.