The jellyfish Aequorea victoria possesses in the margin of its umbrella a green f luorescent protein (GFP, 27 kDa) that serves as the ultimate light emitter in the bioluminescence reaction of the animal. The protein is made up of 238 amino acid residues in a single polypeptide chain and produces a greenish f luorescence ( max ؍ 508 nm) when irradiated with long ultraviolet light. The f luorescence is due to the presence of a chromophore consisting of an imidazolone ring, formed by a post-translational modification of the tripeptide -Ser 65 -Tyr 66 -Gly 67 -. GFP has been used extensively as a reporter protein for monitoring gene expression in eukaryotic and prokaryotic cells, but relatively little is known about the chemical mechanism by which f luorescence is produced. To obtain a better understanding of this problem, we studied a peptide fragment of GFP bearing the chromophore and a synthetic model compound of the chromophore. The results indicate that the GFP chromophore consists of an imidazolone ring structure and that the light emitter is the singlet excited state of the phenolate anion of the chromophore. Further, the light emission is highly dependent on the microenvironment around the chromophore and that inhibition of isomerization of the exo-methylene double bond of the chromophore accounts for its efficient light emission.
The cycloadducts of CG0 and typical dienes have been isolated by HPLC, and the anthracene and cyclopentadiene adducts characterized by FAB mass and NMR spectroscopy.Studies on fullerenesl have been extensive since the macroscopic synthesis of fullerenes was discovered in 1990.2 It is important to study the chemical reactivity of fullerenes,3.4 in order to gain fundamental knowledge for the development of fullerene derivatives with interesting physical and chemical properties. This paper reports the syntheses, isolation and characterization of several cycloadducts of C a with anthracene, cyclopentadiene, 1,3-diphenylisobenzofuran and 2,3-dimethylbutadiene. Although Diels-Alder reactions of c 6 0 have been reported recently by some groups,S-7 they mentioned that mass spectral characterization of the adducts was hampered by fragmentation into component molecules. Rubin et al. also reported that the reaction products between anthracene and C a could not be isolated and characterized. 6 We have now found that the Diels-Alder adducts of c 6 0 with anthracene or cyclopentadiene can be characterized unequivocally by means of negative ion FAB mass and 1H and 13C NMR spectroscopy.The addition reaction of c 6 0 with anthracene is typical. A mixture of C60 (18 mg), anthracene (5.4 mg) and benzene (5 ml) was refluxed for 12 h under nitrogen. After evaporation under reduced pressure below 50°C, the products were separated by HPLC (LC 908, Japan Analytical Industry, Co., Ltd.) by using gel permeation columns (Jaigel 1H + 1H) and toluene as eluent, to give 5.6 mg (25%) of the mono-adduct Cm(Cl4HI0) and 6.4 mg (24%) of di-adducts C60(C14H10)2.
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