Absorption and Fluorescence Studies of Acridine in Subcritical and Supercritical Water

Abstract

The isobaric acid/base equilibrium between acridine and the acridinium cation was measured from ambient temperature to 380°C (above the critical temperature of water, T c ) 374°C) using absorption spectroscopy. At 3500 psia, the isobaric protonation of acridine is shown to be exothermic up to approximately 315°C. Above 315°C, protonation becomes endothermic due to changes in the dielectric constant of water with temperature, which has a profound influence on the solvation of ions. The results are interpreted using a modified Born equation to account for the temperature-dependent changes in acridinium cation and proton solvation. The absorption and fluorescence spectra and the fluorescence lifetime of acridine are sensitive to changes in solvent-solute hydrogen bonding. Hydrogen bonding between acridine and water is observed to decrease from ambient temperature to the critical temperature. A relatively rapid change in hydrogen bonding occurs between 100 and 200°C.Acridine in Subcritical and Supercritical Water

Ionization constants of aqueous amino acids at temperatures up to 250°C using hydrothermal pH indicators and UV-visible spectroscopy: Glycine, α-alanine, and proline

“…The excellent agreement with the previous work on acetic acid by Mesmer et al (1989) confirms findings by Johnston (1994, 1997), Ryan et al (1997), and Chlistunoff et al (1999) that accurate ionization constants can be obtained with colorimetric indicators under hydrothermal conditions (see also Méndez De Leo et al, 2002). The combination of thermally stable colorimetric indicators with high-pressure flow cells and UV-visible spectrophotometry provides a fast and accurate method for determining dissociation constants for weak acids and bases at extremes of temperature and pressure.…”

“…This analysis is based on the recently reported values for the temperature-dependent ionization constants for acridine (Ryan et al, 1997) and 2-naphthol (Xiang and Johnston, 1994). The acid dissociation of acridinium ion to acridine can be represented by the expression HAcr…”

“…Recent work at the University of Texas (Austin) has identified five thermally stable colorimetric pH indicators, which have been used with success in UV-visible spectrophotometric flow cells to determine ionization constants of simple acids and bases at temperatures as high as 400°C (Ryan et al, 1997;Johnston, 1994, 1997;Chlistunoff et al, 1999). To apply this method to the amino acids, we have employed a high-temperature, high-pressure spectrophotometric flow system described in a previous paper by Trevani et al (2001).…”

The electronic spectra of protonated nitrogen-substituted polycyclic aromatic hydrocarbon molecules

“…These two protonated PANHs absorb in the visible or near UV spectral region, this absorption region being in agreement with the absorption recorded in water solution at low pH (Ryan et al 1997). This is the same absorption region as previously recorded for protonated PAHs with two to six aromatic rings, A79, page 3 of 11 A&A 577, A79 (2015) Fig.…”

“…1a. The first electronic transition shows clear vibrational progressions in the visible starting at 442.24 nm (22 612 cm −1 / 2.80 eV) and extending to ∼400 nm, this absorption region being in agreement with the absorption recorded in water solution at low pH (Ryan et al 1997). These progressions involve the 383 cm −1 vibrational mode starting from the 0−0 transition (ν 0 ), and a symmetric mode at 587 cm −1 (ν 18 ).…”