Fluorescence Enhancement of Unconstrained GFP Chromophore Analogues Based on the Push-Pull Substituent Effect
Unlike the high fluorescence quantum yield of the naturally occurring green fluorescence protein (GFP, φf ~ 0.8), the GFP chromophore, a benzylidenedimethylimidazolinone (BDI) dye, is nearly nonfluorescent (φf a rational design of uGFPc toward an unprecedentedly high fluorescence quantum efficiency of 0.60 in hexane. This is achieved by a combined ortho-CN and meta-dimethylamino substituent electronic effect that largely suppresses the Z → E photoisomerization (the τ torsion) reaction, which is the major nonradiative decay channel of uGFPc. The structural design relied on the assumptions that the τ torsion of the meta-amino-substituted BDI systems leads to a zwitterionic twisted intermediate state (1p?) and that destabilizing the 1p? state by an electron-withdrawing CN substituent at the ortho or para position could slow down the τ torsion. The observed CN position effect conforms to the design concept. The push-pull substitution of BDI also leads to sensitive fluorescence-quenching responses to electron donors such as trimethylamine and to H-bond donors such as methanol.
A new family of halogen-chelated hoveyda-grubbs-type metathesis catalysts
Coordination, not insertion: New ruthenium benzylidenes with a chelating halogen atom were easily prepared and showed excellent stability and activity as metathesis catalysts (see figure). Structure-activity studies reveal that strength of the ruthenium-halogen interaction can be tuned across a wide range to set up a family of latent to active catalysts. Copyright
Barbasiewicz, Michal,Michalak, Michal,Grela, Karol
p. 14237 - 14241,5
(2020/09/16)
Fluorescence sensing based on cation-induced conformational switching: Copper-selective modulation of the photoinduced intramolecular charge transfer of a donor-acceptor biphenyl fluorophore
The fluorescence emission energy of donor-acceptor substituted biphenyls is highly sensitive towards conformational changes of the interannular twist angle. By integrating 4-dimethylamino-4′-cyano-biphenyl into the ligand backbone of a thioether-rich metal receptor we designed a fluorescence sensor that exhibits high selectivity towards copper. Upon metal binding the ligand undergoes a significant conformational change, which induces a strong hypsochromic shift of the photoinduced charge-transfer emission. Steady-state absorption and fluorescence spectroscopy revealed a high affinity towards Cu(I) with a well-defined 1:1 metal-ligand complex stoichiometry. The nature of the conformational changes upon Cu(I) coordination were analyzed in detail by 1H NMR and 2D NOESY experiments. The spectroscopic data provide a coherent picture, which is consistent with a Boltzmann ground-state distribution of several rotamers that are locked into a more flattened geometry upon coordination of Cu(I).
Cody, John,Fahrni, Christoph J.
p. 11099 - 11107
(2007/10/03)
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