Paradoxical selectivity

See Davister, M. Laszlo, P. Tetrahedron Lett., 1993, 34, 533 for examples of paradoxical selectivity in Friedel-Crafts alkylation. 

Bias in the selection of experimental subjects should also be avoided. Findings in clinic populations that are not randomly selected may not be representative of (or apply to) the general population. The phenomenon known as Berkson s Paradox (selection bias) is frequently overlooked by those attempting to causally relate environmental exposures to various health problems. 

Leading Examples Electrodialysis has its greatest use in removing salts from brackish water, where feed salinity is around 0.05-0.5 percent. For producing high-purity water, ED can economically reduce solute levels to extremely low levels as a hybrid process in combination with an ion-exchange bed. ED is not economical for the produc tion of potable water from seawater. Paradoxically, it is also used for the concentration of seawater from 3.5 to 20 percent salt. The concentration of monovalent ions and selective removal of divalent ions from seawater uses special membranes. This process is unique to Japan, where by law it is used to produce essentially all of its domestic table salt. ED is very widely used for deashing whey, where the desalted product is a useful food additive, especially for baby food. 

The earliest hint that physics and information might be more than just casually related actually dates back at least as far as 1871 and the publication of James Clerk Maxwell s Theory of Heat, in which Maxwell introduced what has become known as the paradox of Maxwell s Demon. Maxwell postulated the existence of a hypothetical demon that positions himself by a hole separating two vessels, say A and B. While the vessels start out being at the same temperature, the demon selectively opens the hole only to either pass faster molecules from A to B or to pass slower molecules from B to A. Since this results in a systematic increase in B s temperature and a lowering of A s, it appears as though Maxwell s demon s actions violate the second law of thermodynamics the total entropy of any physical system can only increase, or, for totally reversible processes, remain the same it can never decrease. Maxwell was thus the first to recognize a connection between the thermodynamical properties of a gas (temperature, entropy, etc.) and the statistical properties of its constituent molecules. 

The results in Table 3 show that H-mordenite has a high selectivity and activity for dehydration of methanol to dimethylether. At 150°C, 1.66 mol/kg catal/hr or 95% of the methanol had been converted to dimethylether. This rate is consistent with that foimd by Bandiera and Naccache [10] for dehydration of methanol only over H-mordenite, 1.4 mol/kg catal/hr, when extrt lat to 150°C. At the same time, only 0.076 mol/kg catal/hr or 4% of the isobutanol present has been converted. In contrast, over the HZSM-5 zeolite, both methanol and isobutanol are converted. In fact, at 175 X, isobutanol conversion was higher than methanol conversion over HZSM-5. This presents a seemingly paradoxical case of shape selectivity. H-Mordenite, the zeolite with the larger channels, selectively dehydrates the smaller alcohol in the 1/1 methanol/ isobutanol mixture. HZSM-5, with smaller diameter pores, shows no such selectivity. In the absence of methanol, under the same conditions at 15(fC, isobutanol reacted over H-mordenite at the rate of 0.13 mol/kg catal/hr, higher than in the presence of methanol, but still far less than over H M-5 or other catalysts in this study. 

Thrombopoietin is a cytokine that selectively stimulates megakaryocytopoiesis. Thrombopoeitin is not used therapeutically. Theoretical uses include the procurement of platelets for donation and recovery of platelet counts after myelosuppressive chemotherapy. Flowever, a modified recombinant form caused paradoxical reactions, delaying the development of therapeutic thrombopoietin. 

De Jong, M. . M. and Sabelis, M. W. (1991). Limits to runaway sexual selection the wallflower paradox. Journal of Evolutionary Biology 4 637-655. 

Danguir J, Elghozi JL. Superfusion of clomipramine within the ventromedial hypothalamus selectively suppresses paradoxical sleep in freely moving rats. Brain Res Bull 1985 15 1-4. 

Danguir J. Intracerebroventricular infusion of somatostatin selectively increases paradoxical sleep in rats. Brain Res 1986 367 26-30. 

Harvey BH, Bouwer CD (2000) Neuropharmacology of paradoxic weight gain with selective serotonin reuptake inhibitors. Clin Neuropharmacol 23 90-97... 

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