Pasteur’s models

A chiral object and its mirror image are enantiomorphous, and they are each other s enantiomorphs. Louis Pasteur (Figure 2-37) was the first who suggested that molecules can be chiral. In his famous experiment in 1848, he recrystallized a salt of tartaric acid and obtained two kinds of small crystals which were mirror images of each other as seen by Pasteur s models in Figure 2-38 preserved at Institut Pasteur at Paris. Originally Pasteur may have been motivated to make these large-scale models because Jean Baptiste Biot, the discoverer of optical activity had very poor vision by the time of Pasteur s discovery [42], Pasteur demonstrated chirality to Biot, who was visibly affected... 

Figure 2-38. Pasteur s models at the Institut Pasteur (photographs by the authors).

Figure 2-49. Pasteur s models of enanliomcric crystals in the Pasteur Institute, Paris. Photographs by the authors.

Beginning with Pasteur s work in 1860 [4] the fields of stereochemistry and biology were dominated for almost nine decades by the phenomenon now called chirality. Chiral molecules are those for which a three-dimensional model of the molecule is not superimposable on the mirror image of the model. Since the operation determining the existence of chirality is reflection in a plane mirror, this... 

While it was previously believed that all enzymes were composed of protein, it appears that this view is currently undergoing some alteration, as we will see. But it can certainly be said that the vast majority of enzymes are proteins (there are over 2000 known), and each has its own specific three-dimensional structure that is the key to its functionality. In the late 1800s Emil Fischer expressed this as the lock and key model An enzyme has a particular shape so that reagent(s) for the reactions it will catalyze fit into it and are held there for reaction— as a key fits into a lock (see Fig. 16.2). John Cornforth, an Australian chemist, used this model to explain why natural molecules are formed in only one of two possible mirror images—z mystery since Pasteur s work with tartaric acid and tweezers. Cornforth saw that the enzyme acted as a three-dimensional template and only one shape would come... 

Salah, S. 2000. Weathering Processes at the Natural Nuclear Reactor of Bangombe Gabon). Identification and Geochemical Modeling of the Retention and Migration Mechanisms of Uranium and Rare Earth Elements. PhD thesis, Universite Louis Pasteur, Strasbourg, France. 

Exposure of E. coli to microwave treatments results in a reduction of the microbial population in apple juice. Canumir et al. (2002) determined the effect of pasteurization at different power levels (270-900 W) on the microbial quality of apple juice, using a domestic 2450 MHz microwave. The data obtained were compared with conventional pasteurization (83 °C for 30 s). Apple juice pasteurization at 720-900 W for 60-90 s resulted in a 2- to 4-log population reduction. Using a linear model, the D-values ranged from 0.42 0.03 minutes at 900 W to 3.88 0.26 minutes at 270 W. The value for z was 652.5 2.16 W (58.5 0.4°C). These observations indicate that inactivation of E. coli is due to heat. 

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