Janus effect

By the way, NO is one of the causes of the ozone hole, and one cannot escape the recognition that chemical matter is like the Roman god Janus with the two faces It is beneficial where it is needed (e.g., in LTP), and it is harmful in higher amounts and where it is not needed (in our atmosphere). This is a general truism about chemical matter. We shall meet the Janus effect many times throughout the book. 

Diisobutyrylation of triethylcarbinol (14) in the presence of 60% hexafluorophosphoric acid affords 4-ethyl-2,6-diisopropyl-3,5-dimethyl-pyrylium hexafluorophosphate (16). Owing to a double Janus effect due to buttressing by the P-methyl groups, the a-isopropyl groups adopt a conformation that mimics the effect of tert-h x y groups, so that the corresponding pyridine is nonnucleophilic, like 2,6-di-/err-butyl-4-methylpyridine, which can be prepared from 3 with ammonia. 

FIGURE 5.37 Janus faces of the biotransfbrmation of xenobiotics. On one hand metabolism leads to inactivation and elimination of xenobiotics, but on the other hand many metabolites are reactive and may cause deleterious effects by binding to DNA, proteins, and other macromolecules. 

McLaurin J, Cecal R, Kierstead ME, Tian X, Phinney AL, Manea M, French JE, Lambermon MH, Darabie AA, Brown ME, Janus C, Chishti MA, Home R Westaway D, Fraser PE, Mount HT, Przybyl-ski M, George-Hyslop P (2002) Therapeutically effective antibodies against amyloid-beta peptide target amyloid-beta residues 4—10 and inhibit cytotoxicity and fibrillogenesis. Nat Med 8 1263-1269. 

Kirkwood s description is not wrong, but it is one-sided. His memorable simplicity conceals a can of worms. The molecular action of vitamin C is as simple and repetitive as flipping a coin, yet the effects are varied, unpredictable and utterly dependent on the milieu in which it operates. Just as flipping a coin leads to diametrically opposed outcomes, so too, vitamin C may on the one hand protect against illness and on the other kill tumours, or even people. The food chemist William Porter summed up the conundrum nicely, rising to an anguished eloquence rarely matched in scientific journals "Of all the paradoxical compounds, vitamin C probably tops the list. It is truly a two-headed Janus, a Dr Jekyll-Mr Hyde, an oxymoron of antioxidants."... 

Other phenothiazine dyes, such as methylene green (MG), brilliant cresyl blue (BCB), janus green (JG), toluidine blue (TB), and azure A (AA), can also be immobilized on Pt electrode surfaces by adsorption and the cyclic potential scan method used to prepare MB CMEs." The MG, BCB, JG, TB, and AA CMEs were all found to facilitate effectively the electrochemical reactions of redox proteins and the modified... 

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