The nature of singlet exciton fission in carotenoid aggregates.

Singlet exciton fission allows the fast and efficient generation of two spin triplet states from one photoexcited singlet. It has the potential to improve organic photovoltaics, enabling efficient coupling to the blue to ultraviolet region of the solar spectrum to capture the energy generally lost as waste heat. However, many questions remain about the underlying fission mechanism. The relation between intermolecular geometry and singlet fission rate and yield is poorly understood and remains one of the most significant barriers to the design of new singlet fission sensitizers. Here we explore the structure-property relationship and examine the mechanism of singlet fission in aggregates of astaxanthin, a small polyene. We isolate five distinct supramolecular structures of astaxanthin generated through self-assembly in solution. Each is capable of undergoing intermolecular singlet fission, with rates of triplet generation and annihilation that can be correlated with intermolecular coupling strength. In contrast with the conventional model of singlet fission in linear molecules, we demonstrate that no intermediate states are involved in the triplet formation: instead, singlet fission occurs directly from the initial 1B(u) photoexcited state on ultrafast time scales. This result demands a re-evaluation of current theories of polyene photophysics and highlights the robustness of carotenoid singlet fission.This work was supported by the EPSRC (UK) (EP/G060738/ 1), the European Community (LASERLAB-EUROPE, grant agreement no. 284464, EC’s Seventh Framework Programme; and Marie-Curie ITN-SUPERIOR, PITN-GA-2009-238177), and the Winton Programme for the Physics of Sustainability. G.C. acknowledges support by the European Research Council Advanced Grant STRATUS (ERC-2011-AdG No. 291198). J.C. acknowledges support by the Royal Society Dorothy Hodgkin Fellowship and The University of Sheffield’s Vice- Chancellor’s Fellowship scheme.This is the final published version. It was first made available by ACS at http://pubs.acs.org/doi/abs/10.1021/jacs.5b01130

INHIBITION OF GROWTH AND MYCOTOXIN PRODUCTION IN A TARO-BASED FOOD PRODUCT (BINAGOL, CINNAMON, POTASSIUM-SORBATE, NATAMYCIN, AFLATOXIN)

Cinnamon did not significantly reduce mold growth nor aflatoxin production in yeast extract sucrose (YES) broth at pH 5.0 and 6.5. Sorbate alone at 2500 ug/ml and sorbate at 1250 ug/ml with 2400 ug/ml cinnamon completely inhibited growth and aflatoxin production by Aspergillus parasiticus NRRL 2999 in YES broth at pH 5.0. Subinhibitory concentrations of these inhibitors stimulated aflatoxin production. Synergism was observed when sorbate and natamycin were used together. However, this effect was reduced when cinnamon was present. Rice paste supported higher production of aflatoxin, penicillic acid and ochratoxin A, but less patulin production than binagol. Higher amounts of toxin were generally obtained at 25 C than at 15 C. The three A. parasiticus cultures usually produced the same amount of aflatoxin regardless of the substrate. A. flavus NRRL 6555 produced higher amounts of B1 than A. flavus NRRL 13003. Greater growth was observed on taro and taro + coconut milk than on rice, but the reverse was true of aflatoxin production/mg mycelia in these substrates. Modified binagol (pH 5.5) was organoleptically similar to the original (pH 6.3). The natamycin-sorbate synergism was also observed in modified binagol, extending the shelf life to \u3e21 days. Growth of A. parasiticus in glucose ammonium nitrate broth was greatest at the highest glucose concentration and the lower caseine concentrations. Aflatoxin production was highest at lower glucose concentrations in combination with casein at all concentrations. No trend was observed with various glucose:casein combinations; high glucose to low casein concentrations did not necessarily favor aflatoxin production

Mechanisms of spectral shifts in lobster carotenoproteins. The resonance Raman spectra of ovoverdin and the crustacyanins

NRC publication: Ye