Recognition, degree

Odor Recognition—Degree of smell associated with fuel vapor. 

Appllca.tlons. The first widely appHcable Ic separation of enantiomeric metallocene compounds was demonstrated on P-CD bonded-phase columns. Thirteen enantiomeric derivatives of ferrocene, mthenocene, and osmocene were resolved (7). Retention data for several of these compounds are listed in Table 2, and Figure 2a shows the Ic separation of three metallocene enantiomeric pairs. P-Cyclodextrin bonded phases were used to resolve several racemic and diastereomeric 2,2-binaphthyldiyl crown ethers (9). These compounds do not contain a chiral carbon but stiU exist as enantiomers because of the staggered position of adjacent naphthyl rings, and a high degree of chiral recognition was attained for most of these compounds (9). 

This episode has been displayed in some detail because colloid science is a clear instance of a major field of research which has never quite succeeded in gaining recognition as a distinct discipline, in spite of determined attempts by a number of its practitioners. The one feature that most distinguishes colloid science from physical chemistry, polymer science and chemical engineering is that universities have not awarded degrees in colloid science. That is, perhaps, what counts most for fields with ambitions to become fullblown disciplines. 

A 1 1 mixture of thiols (7 and 2), on treatment with oxygen in the presence of a catalytic amount of Et3N, gives one unsymmetrical (4) and two symmetrical disulfides (3 and 5) (Eq. 4). As a measure of the degree of the recognition between 7 and 2 in the oxidation, the selectivity (r) is employed which is represented by the logarithmic ratio of the yield of 4 to twice that of 3 (Eq. 5). The r is so defined as to become zero when oxidation yields the three disulfides in a 1 2 1 ratio. In the present case, the recognition process is followed by covalent bond formation. 

Figure 39-13. A schematic representation of the three-dimensional structure of Cro protein and its binding to DNA by its helix-turn-helix motif. The Cro monomer consists of three antiparallel p sheets (P1-P3) and three a-helices (a,-a3).The helix-turn-helix motif is formed because the aj and U2 helices are held at about 90 degrees to each other by a turn offour amino acids. The helix of Cro is the DNA recognition surface (shaded). Two monomers associate through the antiparallel P3 sheets to form a dimer that has a twofold axis of symmetry (right). A Cro dimer binds to DNA through its helices, each of which contacts about 5 bp on the same surface of the major groove. The distance between comparable points on the two DNA a-helices is 34 A, which is the distance required for one complete turn of the double helix. (Courtesy of B Mathews.)...

The pharmacology and toxicology of certain economic poisons have been developed to a degree which surpasses investigations of any other class of nonmedicinal compounds. In certain instances more is known concerning the site and mechanism of action, the absorption, distribution, and excretion of these substances than is known concerning some of the more commonly used pharmaceutical compounds. This has come about as a result of the conscientious recognition of the public health hazards which are inherent in the economic poisons. 

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