Derivatives of 2-propionyl-6-dimethylaminonaphthalene (PRODAN) with twisted carbonyl groups were investigated as highly responsive sensors of H-bond donating ability. The PRODAN derivative bearing a pivaloyl group (4) was prepared. The torsion angle between the carbonyl and naphthalene is 26° in the crystal. It shows solvatochromism that is similar to five other PRODAN derivatives (1-3, 5-6). Twisted-carbonyl derivatives 3, 4 and 6 show strong fluorescence quenching in protic solvents. The order of magnitude of the quenching is linearly related to the H-bond donating ability of the solvent (SA), but not to other solvent properties. Binary mixtures of protic solvents show specific interaction effects with respect to quenching and solvatochromism. Aggregation in water is an issue with the pivaloyl derivatives.
Derivatives of 2-propionyl-6-dimethylaminonaphthalene (PRODAN) with twisted carbonyl groups were investigated as highly responsive sensors of H-bond donating ability. The PRODAN derivative bearing a pivaloyl group (4) was prepared. The torsion angle between the carbonyl and naphthalene is 26° in the crystal. It shows solvatochromism that is similar to five other PRODAN derivatives (1-3, 5-6). Twisted-carbonyl derivatives 3, 4 and 6 show strong fluorescence quenching in protic solvents. The order of magnitude of the quenching is linearly related to the H-bond donating ability of the solvent (SA), but not to other solvent properties. Binary mixtures of protic solvents show specific interaction effects with respect to quenching and solvatochromism. Aggregation in water is an issue with the pivaloyl derivatives.
“…This behavior is shown graphically in Figure 3 using Catalan's solvent acidity parameter to characterize the H-bond donating ability of the solvent 16. It should be noted that the effect of H-bonding solvents on the fluorescence of 1 continues to be an active area of investigation 3, 17-20…”
The synthesis and photophysical properties of 7-(dimethylamino)-3,4-dihydrophenanthren-1(2H)-one (7) and 3-(dimethylamino)-8,9,10,11-tetrahydro-7H-cyclohepta[a]naphthalen-7-one (8) are reported. These compounds possess a cycloalkanone substructure that controls the extent of twisting of the carbonyl group. The six-membered ring in 7 forces the carbonyl group to be coplanar with the naphthalene ring, whereas the seven-membered ring in 8 induces a significant twist. Both have the substructure of PRODAN (6-propionyl-2-(dimethylamino)naphthalene, 1).Comparing the photophysical behavior of these compounds with that of PRODAN and 2,2-dimethyl-1-(4-methyl-1,2,3,4-tetrahydrobenzo[f]quinolin-8-yl)propan-1-one (3) indicates that PRODAN likely emits from a PICT excited state rather than from an O-TICT excited state.
“…In addition, water molecules may also form hydrogen bonds to BADAN, and the BADAN moiety itself may undergo a conformational change from a relatively planar to a relatively twisted excited state. Both hydrogen bonding (Artukhov et al 2007; Balter et al 1988; Chapman et al 1995; Józefowicz et al 2005; Parasassi and Gratton 1995; Rowe and Neal 2006; Samanta and Fessenden 2000; Viard et al 1997) and conformational twisting (Abbyad et al 2007; Lobo and Abelt 2003; Parusel et al 1998; Vincent et al 2005) were found to contribute to the relaxation of the fluorescence of the well-known lipid probes PRODAN and LAURDAN, whose chromophore moieties are identical to that of BADAN.Fig. 2Experimental ( a , b ) and reconstructed streak camera images ( c , d ) of BADAN-labeled M13 coat protein mutants having the label in the polar (G03C, a and c ) and hydrophobic core (V29C, b and d ) region of mixed PC/PG phospholipid bilayers.…”
Profiles of lipid-water bilayer dynamics were determined from picosecond time-resolved fluorescence spectra of membrane-embedded BADAN-labeled M13 coat protein. For this purpose, the protein was labeled at seven key positions. This places the label at well-defined locations from the water phase to the center of the hydrophobic acyl chain region of a phospholipid model membrane, providing us with a nanoscale ruler to map membranes. Analysis of the time-resolved fluorescence spectroscopic data provides the characteristic time constant for the twisting motion of the BADAN label, which is sensitive to the local flexibility of the protein–lipid environment. In addition, we obtain information about the mobility of water molecules at the membrane–water interface. The results provide an unprecedented nanoscale profiling of the dynamics and distribution of water in membrane systems. This information gives clear evidence that the actual barrier of membranes for ions and aqueous solvents is located at the region of carbonyl groups of the acyl chains.
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