A very stable complex of a modified marine cyclopeptide with chloroform

Abstract

Noncovalent interactions play a pivotal role in molecular recognition. These interactions can be subdivided into hydrogen bonds, cation-p interactions, ion pair interactions and London dispersion forces. The latter are considered to be weak molecular interactions and increase with the size of the interacting moieties. Here we show that even the small chloroform molecule forms a very stable complex with a modified marine cyclopeptide. By means of high-level quantum chemical calculations, the size of the dispersive interactions is calculated; the dispersion energy (approximately À 40 kcal mol À 1 ) is approximately as high as if the four outer atoms of the guest form four strong hydrogen bonds with the host. This strong binding of chloroform to a modified marine cyclopeptide allows the speculation that the azolecontaining cyclopeptides-haloform interaction may play some biological role in marine organisms such as algae.

Strongly underestimated dispersion energy in cryptophanes and their complexes

“…The impressive difference in the complex formation constants depending on the solvent used shows that the solvent has to be a part of the equilibrium. One possible interpretation is-as already assumed 25 -that the solvent can also be enclosed by cryptophane-E. Larger solvent molecules like 1,2-C 6 D 4 Cl 2 are less effectively enclosed and therefore lead to higher chloroform binding constants, whereas solvents like C 2 D 2 Cl 4 show lower CHCl 3 @1 binding constants.…”

“…One explanation for this huge difference is probably the fact that chloroform perfectly fits to the shape of the trigonal bipyramidal cavity of 3, resulting in a multitude of dispersion interactions between the chloroform molecule and the atoms of the cavity. Furthermore, we speculated that a further possible reason for the high stability of CHCl 3 @3 compared with that of CHCl 3 @1 and CHCl 3 @2 may be that the cryptophanes do not completely exclude the solvent, while the container 3 shows improved size discrimination 25 .…”

“…One of these azole-containing cyclopeptides is the C 3 -symmetric cavitand 3 ( Fig. 1) which forms a very strong complex with chloroform and other trihalomethanes 25 . As the equilibrium is so strongly shifted to the side of the complex, the thermodynamic parameters of the complex CHCl 3 @3 were determined by temperature-dependent NMR spectroscopy at temperatures between 353 and 398 K in 1,1,2,2-C 2 D 2 Cl 4 .…”

Encapsulated Guests in the Smallest Spaces: Shrinking Guests by Compression and Investigations under Solvent-Free Conditions

“…In the previously reported complex CHCl 3 @4 the proton of the chloroform points towards the cup-shaped cyclopeptide, as proven by a cross signal in the NOESY spectrum of CHCl 3 @4 and by a highfield shift of 2.1 ppm. 6 In the now investigated complex CHCl 3 @5 no cross peak between the chloroform and the amide protons are found and the observed highfield shift is much larger (5.4 ppm). This suggests that the proton of the encapsulated chloroform is directly located over the center of a benzene unit which is the case for complex ↓CHCl 3 @5.…”

Sepia ink oligopeptide induces apoptosis and growth inhibition in human lung cancer cells

“…On the other hand, without a stable structure, it is difficult for oligopeptide to cross the cell membrane. Cyclopeptide is a kind of stabilized peptide, which goes through a feasible cyclization reaction to constrain a peptide into a relative stable conformation, has been proposed to solve the problems of linear natural peptide [17]. The cyclization decreases the conformation variation, while on the other hand increases the anti-proteolytic and anti-metabolization activities.…”