Enhancer constitutional isomers

Whereas peptidyl prolyl cis-trans isomerases constitute a well-characterized enzyme class comprising well over 1000 members with small sequence variations in the proteins of different species, the discovery of secondary amide peptide bond cis-trans isomerases (APIases) had to await the development of suitable enzyme assays. Fortunately, spectral differences in the UV region between cis and trans isomers of dipeptides could be exploited to identify and quantify isomerization rate-enhancing factors in biological material [149]. 

In another attempt, azobenzene-appended y-cyclodextrin 11 was prepared. Upon the irradiation with 320- to 390-nm light, 70% of the E-isomer in water isomerized to the Z-isomer, which exhibited an enhanced binding ability for (-)-borneol and (-l-)-fenchone. Benzo-18-crown-6 12 linked to a phenol was synthesized. Upon irradiation by UV light, the azo linkage isomerized to the Z-isomer. It slowly reverted to the E-form in the dark and rapidly upon irradiation with visible light. An enhanced extraction of Ca + by the Z-isomer has been observed. The Z structure constitutes a photoresponsive anion cap. ... 

The HSE values of 14 thus obtained (Table 5) constitute about 30—50% of the HSE value calculated, based on the similar type reaction 5, for the most aromatic 10 7r electron bicyclic structure of naphthalene 62.2 (MP2(full)/6-31G ) and 53.7 (B3LYP/6-31G ) kcal mol . As shown in Figure 7, compounds 14 and their isoelectronic analogues possess the closed-shell jr-electron system similar to that of the aromatic pentalene dianion. Table 5 contains also the values of A characterizing the enhanced stability of the bicyclic Czv structures 14 relative to their unstrained monocyclic isomers 14a. 

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