Theoretical studies on fluorescence of phenol and 1-naphthol in both acid and alkali solutions

Determination and Difference Analysis of Phenolic Compounds in Smokers' Saliva and Mainstream Smoke

To study the differences in phenolic compounds between tobacco smokers' saliva and mainstream smoke, a method was developed for the analysis of 12 phenolic compounds in saliva and mainstream smoke based on ultrahigh-performance liquid chromatography with fluorescence detection (UPLC-FLD). The contents and distributions of phenolic compounds in tobacco smokers' saliva and mainstream smoke were compared. The results were as follows: (1) Phenolic compounds were quantitatively analyzed by the internal standard method using 4-fluorophenol as an internal standard. For smokers' saliva samples, the limits of quantification (LOQs) ranged from 2.2 to 19.1 μg/L, and the recoveries were from 80.2% to 119.2% at the three spiked levels. For mainstream smoke samples, the LOQs ranged from 0.03 to 0.26 μg/cig, and the recoveries ranged from 84.9% to 107.0% at the three spiked levels. (2) The contents of phenolic compounds from 14 cigarettes in mainstream smoke and smokers' saliva were determined. In mainstream smoking, the main phenolic compounds were hydroquinone, catechol, phenol, meta- and para-Cresol, and o-methylhydroquinone. In smokers' saliva, the main phenolic compounds were phenol and meta- and para-Cresol and the contents of phenolic compounds in smokers' saliva from different cigarettes were significantly different. (3) The content distribution patterns of phenolic compounds in smokers' saliva differed from those in mainstream smoke. The predominant phenolic compound in mainstream smoke was dihydroxybenzene, while monophenols predominated in smokers' saliva. (4) The contents of phenolic compounds from five kinds of cigarettes were analyzed in the saliva of different smokers using principal component analysis, which indicated that cigarettes with different sensory effects were clearly distinguished by differences in the contents of phenolic compounds in saliva.

In situ investigation of intrinsic relationship between protonation behavior and HA characteristics in sediments

Proton-binding study of humic acid (HA) is critical for describing and modeling the binding mechanism of HA with heavy metals. However, little is known about the intrinsic relationship between protonation behavior and HA characteristics, especially in sediments. In this study, HA was extracted from sediments and combination of spectrographic titration with parallel factor analysis, Gaussian fitting model and two-dimensional correlation spectroscopy analysis was developed as a novel in-situ tool. Results indicated that the intensity changes of fluorophores of sediment HA might be dependent on the structure characteristics (fused or non-fused ring) of phenolic species in the protonation process. Compared with phenolic groups (A1, 5.27 ± 0.05 eV; A3, 3.91 ± 0.02 eV), the carboxyl groups (A2, 4.65 ± 0.03 eV) exhibited greater contribution in the response of chromophores to the protonation process of sediment HA. Furthermore, proton binding to sediment HA first occurred in carboxyl groups and then in phenolic groups. The combined technique is a promising approach for the examination of the binding sites, binding capacities, and binding order in proton-HA binding process under environmental concentrations. Importantly, this method is a sensitive, effective and non-destructive technique without any need pre-concentrate.

Excited-state proton transfer to solvent from phenol and cyanophenols in water

The excited-state proton transfer (ESPT) to solvent from phenol (PhOH) and cyanophenols (CNOHs) in water was studied by means of time-resolved fluorescence and photoacoustic spectroscopy. A characteristic property of PhOH and CNOHs is that the fluorescence quantum yields of the deprotonated forms are remarkably small (< or = 10(-3)) and the lifetimes are extremely short (< or = 30 ps). Time-resolved fluorescence measurements for PhOH, CNOHs, and their methoxy analogues at 298 K indicate that o- and m-cyanophenols (o- and m-CNOH) undergo rapid ESPT to the solvent water with rate constants of 6.6 x 10(10) and 2.6 x 10(10) s(-1), respectively, whereas the fluorescence properties of PhOH and p-CNOH does not exhibit clear evidence of the ESPT reaction. Photoacoustic measurements show that photoexcitation of o- and m-CNOH in water results in negative volume changes, supporting the occurrence of ESPT to produce a geminate ion pair. In contrast, the volume contractions for the PhOH and p-CNOH solutions are negligibly small, which indicates that, in these compounds, the yields of solvent-separated ion pairs resulting from the ESPT are very small. The volume change per absorbed Einstein (DeltaV(r)) for o-CNOH is obtained to be -5.0 mL Einstein(-1), which is much smaller than the estimated volume contraction per photoconverted mole (DeltaV(R)). This suggests that the geminate recombination between the ejected proton and the cyanophenolate anion occurs after rapid deactivation of the excited ion pair. In the temperature range between 275 and 323 K, the proton dissociation rates of o- and m-CNOH in H(2)O and D(2)O are slower than the solvent relaxation rates evaluated from the Debye dielectric relaxation time, indicating that the overall rate constant is determined mainly by the proton motion along the reaction coordinate.