The refractive indices, n D , and relative permittivities, , have been measured for the binary liquid mixtures of γ-butyrolactone, γ-valerolactone, δ-valerolactone, or -caprolactone + benzene, + toluene, or + ethylbenzene over the whole composition range at 293.15 K and 313.15 K and atmospheric pressure. For the pure lactones the dipole moments, µ, the molar polarizability, P M , and the molar refractivity, R M , were determined. From the values of and n D of the lactone + benzene mixtures, the Kirkwood correlation factor, g, was calculated indicative of the structures of the mixtures.
Molar excess enthalpies of binary liquid mixtures of γ-butyrolactone + benzene, + toluene, + ethylbenzene, and + carbon tetrachloride were measured by means of a flow microcalorimeter of Picker type at 293.15 K. For the γ-butyrolactone + carbon tetrachloride mixture the molar excess volume was determined from density measurements at 293.15 K and 313.15 K. All measurements were performed at atmospheric pressure.
The binding of CHjHg11 with tryptophan (HTrp), tryptamine (HTam+), and benzimidazole (HBIm) has been observed and formation constants (X» are reported. Xf for binding at the amine site of HTrp and HTam+ is about 60 and 10 times, respectively, that predicted from the observed correlation of log Xf with the aminium pXa for a series of simple primary amines. The enhancement is attributed to a specific interaction between CHjHg11 and the indole ring. NMR chemical shifts point to a location of the methyl group above the indole plane, and model building confirms the possibility of an unstrained geometry with CHjHg11 located parallel to and in close contact with the aromatic plane. In the complex with HBIm, CH3HgHBIm+, the NMR chemical shift of CH3 is downfield, consistent with bonding of CHjHg11 at N3 of HBIm. CHjHg11 binding quenches the fluorescence of each compound, and enhances the radiative quantum yield of phosphorescence, that of CHjHgTrp becoming 0.9 ±0.1. Phosphorescence lifetime measurements at 77 K yield reduction factors of 6000 (HTrp), 8000 (HTam+), and 40 (HBIm) relative to the unperturbed compound. Differences in the magnitude of the heavy atom effect as measured by phosphorescence lifetime reduction are attributed to differences in the position of CHjHg11 relative to the affected chromophore. Optically detected magnetic resonance measurements, and pulsed laser-excited phosphorescence decay measurements at 1.1-1.2 K show that the heavy atom effect differs for individual triplet sublevels. Complexing of HBIm with CHjHg11 has the same effect on the triplet state zero-field splittings as does protonation, suggesting that spin-orbit coupling and electron delocalization effects are not important.
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