Cigarette smoke contains two very different populations of free radicals, one in the tar and one in the gas phase. The tar phase contains several relatively stable free radicals; we have identified the principal radical as a quinone/hydroquinone (Q/QH2) complex held in the tarry matrix. We suggest that this Q/QH2 polymer is an active redox system that is capable of reducing molecular oxygen to produce superoxide, eventually leading to hydrogen peroxide and hydroxyl radicals. In addition, we have shown that the principal radical in tar reacts with DNA in vitro, possibly by covalent binding. The gas phase of cigarette smoke contains small oxygen- and carbon-centered radicals that are much more reactive than are the tar-phase radicals. These gas-phase radicals do not arise in the flame, but rather are produced in a steady state by the oxidation of NO to NO2, which then reacts with reactive species in smoke such as isoprene. We suggest that these radicals and the metastable products derived from these radical reactions may be responsible for the inactivation of alpha 1-proteinase inhibitor by fresh smoke. Cigarette smoke oxidizes thiols to disulfides; we suggest the active oxidants are NO and NO2. The effects of smoke on lipid peroxidation are complex, and this is discussed. We also discuss the toxicological implications for the radicals in smoke in terms of a number of radical-mediated disease processes, including emphysema and cancer.

Free-radical chemistry of cigarette smoke and its toxicological implications.

The role of surface chemistry in catalysis with carbons

The current established catalytic processes used in chemical industries use metals, in many cases precious metals, or metal oxides as catalysts. These are often energy-consuming and not highly selective, wasting resources and producing greenhouse gases. Metal-free heterogeneous catalysis using carbon or carbon nitride is an interesting alternative to some current industrialized chemical processes. Carbon and carbon nitride combine environmental acceptability with inexhaustible resources and allow a favorable management of energy with good thermal conductivity. Owing to lower reaction temperatures and increased selectivity, these catalysts could be candidates for green chemistry with low emission and an efficient use of the chemical feedstock. This Review highlights some recent promising activities and developments in heterogeneous catalysis using only carbon and carbon nitride as catalysts. The state-of-the-art and future challenges of metal-free heterogeneous catalysis are also discussed.

Metal-Free Heterogeneous Catalysis for Sustainable Chemistry

The paramagnetism of cigarette tar is found to be associated with at least four different types of species. One of the types is responsible for over 80 percent of the total paramagnetism and has a signal intensity that is independent of temperature from 60 to 250 K. This non-Curie-Weiss temperature dependence indicates that the principal paramagnetic species in tar is not an organic monoradical (doublet) species but instead is a donor-acceptor excimer with a paramagnetic excited state and a diamagnetic ground state. Modeling experiments suggest that the excimer consists of quinone (Q) and hydroquinone (QH2) molecules held in a tar matrix. Since such Q-QH2 species are catalysts for the oxidation of hydrocarbons and are very active redox systems, this paramagnetic species may be implicated in the cocarcinogenic properties of tar. Alternatively, since semiquinone radicals are known to bind to DNA, the tar paramagnetic species may be directly involved in the carcinogenic properties of tar.

https://science.sciencemag.org/content/sci/220/4595/425.full.pdf

The Radicals in Cigarette Tar: Their Nature and Suggested Physiological Implications

Activated carbons were used as catalysts for the oxidative dehydrogenation of ethylbenzene. The type and amount of functional groups on the surface of the carbon catalysts was modified by oxidative treatments in the gas or in the liquid phase, while heat treatments at different temperatures were used to selectively remove some of the functional groups. The performance of these catalysts was evaluated in terms of conversion, styrene yield and selectivity. The results show that the gas phase treatments lead to improved performance associated with an increase in the amount of carbonyl/quinone groups on the surface, which were identified as the active sites for the reaction. A good correlation between catalytic activity and the concentration of these surface groups was obtained.

Yasuhiro Iwasawa

Papers

Reaction mechanism for styrene synthesis over polynaphthoquinone

New SiO2-attached «Mo-pair» catalysts-preparations, surface structures, and chemical nature

The nature of adsorbed sites on catalysts: II. Behavior of basic compounds on silica-alumina catalyst at elevated temperatures

Catalytic oxidation of hydrogen sulfide on polynaphthoquinone

Control of the selectivity and increase of the catalytic activity of polynaphthoquinone by various Lewis acids