Inclusion complexation cotton effect

The inclusion modes of flurbiprofen with beta cyclodextrin and with heptakis(2,3,6-tri-0-methyl)-beta cyclodextrin have been studied by Imai and coworkers. They showed that, although the Cotton effects in the circular dichroic spectra induced by beta cyclodextrin in / (-) and 5(+) flurbiprofen are identical, those induced by heptakis(2,3,6-tri-0-methyl)-beta cyclodextrin differ from each other and from those induced by beta cyclodextrin. C.p.-m.a.s. C-n.m.r. experiments showed that the cyclodextrin ring is probably more distorted in the flurbiprofen inclusion complex with methylated beta cyclodextrin than in that with beta cyclodextrin. 

The 1 1 complexation was achieved by mixing the host and guest in the solid state, and the inclusion complexation was followed by measurement of CD spectra every 30 min in Nujol mulls (Fig. 13). For example, as the complexation between (-)-12c and 78 proceeds, the (+)- and (-)-Cotton effects appeared at about 275 and 300 nm, respectively, and these absorptions increased until the complexation was completed after 2 hr, although no absorption was present at the beginning of the mixing process [40],... 

The chiral arrangement of 80a molecules in the complex with (—)-12c is also easily detected by measurement of CD spectra as Nujol mulls. For example, the inclusion crystal of 80a with (—)-12c showed a (—)-Cotton effect, and that of 80a with (+)-12c showed a (+)-Cotton effect at around 260 and 310 nm, respec-... 

Both experimental data73,75 and theoretical calculations78 show that differences in the sign of the Cotton effects of 5-mono- and 5,5-disubstituted barbiturates are sensitive to chiral distortions within the barbituric acid ring. The induced CD spectra of barbiturates as inclusion complexes with / -cyclodextrin support the foregoing conclusion.79... 

Figure 3 shows that the i.c.d. and absorption spectra depend upon the concentration of the 3-c.d. complex with I. The i.c.d. spectra exhibit the positive peak around 22.0 kK in the case of low concentrations, while they generate the Cotton effect around 22.0 kK in the case of high concentrations. It is very interesting that the Cotton effect closely resembles that of dye-polypeptide system (refs. 9>10) Since the Cotton effect observed for dye-polypeptide system arises from dimeric dye bound to polypeptide, the i.c.d. band observed at high concentrations is attributed to a dimeric form of inclusion complexes. Examina-... 

ABSTRACT. Studies of chiroptical properties need separation or at least enrichment of enantiomers. The separation is difficult with chiral con-formers of molecules with very low barriers of internal rotation. However, in association with cyclodextrin, these labile molecules can exhibit a strong Cotton effect in solution one chiral conformer is favoured by complexation. The cyclodextrins have the advantage to yield inclusion complex in solution as well as crystalline clathrates. Therefore, the absolute configuration of the guest can be obtained by determining the structure of the cyclodextrin. In this work, the first CD spectrum of 4-helicene is recorded And crystal structures of several clathrates of labile molecules are studied. 

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