The study consists of a detailed investigation of the degradability of the emerging water contaminant-caffeine by homogeneous and heterogeneous Advanced Oxidation Processes (AOP’s), estimation of a synergy index for each hybrid operation thereof, and proposing the most plausible reaction mechanisms that are consistent with the experimental data. It also encompasses evaluation of the effect of the water matrix represented by carbonate species and humic acids, as strong scavengers of hydroxyl radicals. The results showed that single AOP’s such as sonolysis (577 kHz) and photolysis with H
2
O
2
provided complete caffeine elimination, but they were insufficient for the mineralization of the compound. Hybrid AOP’s were considerably more effective, particularly when operated at a heterogeneous mode using commercial TiO
2
. The most effective hybrid process was UV-H
2
O
2
/TiO
2
, which provided more than 75% TOC decay at the minimum test doses of the reagent and catalyst. While the addition of ultrasound to the process significantly increased the rate of caffeine decomposition, it reduced the overall degradation of the compound to 64% in terms of TOC decay. The antagonistic effect was attributed to the formation of excess H
2
O
2
, and the presence of cavity clouds and/or high density layers that inhibited the transmission of UV light. The effect of natural water ingredients was found to reduce the reaction rates, signifying the major contribution of hydroxyl radicals to the destruction of caffeine. The proposed reaction mechanisms based on OH radical attack and the calculated energy barriers were in good agreement with the experimentally detected reaction byproducts.
As weak acids or bases, in solution, drug molecules are
in either
their ionized or nonionized states. A high degree of ionization is
essential for good water solubility of a drug molecule and is required
for drug–receptor interactions, whereas the nonionized form
improves a drug’s lipophilicity, allowing the ligand to cross
the cell membrane. The penetration of a drug ligand through cell membranes
is mainly governed by the pK
a of the drug
molecule and the membrane environment. In this study, with the aim
of predicting the acetonitrile pK
a’s
(pK
a(MeCN)) of eight drug-like thiazol-2-imine
derivatives, we propose a very accurate and computationally affordable
protocol by using several quantum mechanical approaches. Benchmark
studies were conducted on a set of training molecules, which were
selected from the literature with known pK
a(water) and pK
a(MeCN). Highly well-correlated
pK
a values were obtained when the calculations
were performed with the isodesmic method at the M062X/6-31G** level
of theory in conjunction with SMD solvation model for nitrogen-containing
heterocycles. Finally, experimentally unknown pK
a(MeCN) values of eight thiazol-2-imine structures, which were
previously synthesized by some of us, are proposed.
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