Cyclohepta-amylose inclusion complexes. A proton magnetic resonance study

Abstract

Sztmmary Proton magnetic resonance provides direct evidence for the inclusion nature of cycloheph-amylose complex formation with aromatic substrates.CYCLOAMYLOSBS (cyclodextrins) have been used as models for enzymes1P2 and proteins,3p4 because their structures are well defined3 s5 p6 and because they interact with many substrates in a manner similar to that of enzymes and proteins. It has been ~uggestedl-~ p7 y 8 that cycloamyloses form inclusion complexes with organic substrates in aqueous solution. Little direct evidence has yet been presented (except from X-ray investigation of several crystalline complexes9 ,lo) verifying inclusion of a molecular substrate within the cavity of cycloamylose.We present the first such evidence from proton magnetic resonance (1H n.m.r.) studies of the interaction of cyclohepta-amylose (C7A) (Figure la) with a variety of aromatic substrates in aqueous solution. Previous n.m.r.'j and X-ray5 studies have unequivocally established the C-1 chair conformation for the constituent glucose units in cycloarnyloses. Cyclohepta-amylose thus has primary and secondary hydroxy-groups crowning opposite ends of its torus, H-3 a n d H-6 directed toward its interior and H-1, H-2, and H-4 located on its exterior. It was expected? a priori, in light of the screening environment associated with aromatic rnoieties,ll that if inclusion does indeed occur, protons located within or near the cavity (e.g. H-3, H-5, or H-6) should be strongly shielded.:: Alternatively, if association takes place a t the exterior of the torus, H-1, H-2, and H-4 shoulcl be the more strongly affected.The effect on the high resolution lH n.m.r. spectrum of

Complexation of enalapril maleate with beta-cyclodextrin: NMR spectroscopic study in solution

“…The upfield shifts observed for the signals of H-3' and H-5', situated inside the β-CD cavity, and concomitant downfield shift changes for enalapril maleate protons in the 1 H NMR spectra of mixtures of enalapril maleate and β-CD are a clear indication of complexation between enalapril maleate and β-CD, in analogy to previous studies 5,6 . Furthermore, the magnitude of shift changes of these β-CD protons increased with the increase in the concentration of enalapril maleate.…”

“…A variety of techniques are used, for characterization of inclusion complexes in terms of geometry and configurational preferences, of which solid state and high resolution NMR spectroscopy are most important 5 . The formation of inclusion complex results in the shift changes in resonances of both the CDs and the guest protons 6 . The magnitude of Δδ is a critical function of position of proton in the molecule, size of CD cavity as well as host/guest ratio.…”

Recent Advances in Biomimetic Synthesis Involving Cyclodextrins

“…The formation of the inclusion complex between -ketotosylate molecule and -CD results in chemical shift changes of cyclodextrin. The inclusion of an aromatic guest into the cyclodextrin cavity results in upfield shifts of the H-3 and H-5 of cyclodextrin, due to the ring-current effect of the aromatic ring (Demarco & Thakkar, 1970). Study of 1 H NMR (DMSO) of the -CD, -CD-phenacyl tosylate complex, and freeze-dried reaction mixtures of -CDphenacyl tosylate-thiourea indicated up field shift of H-3 and H-5 protons in the complex as well as in the reaction mass after 30 min.…”

Bitterness Reduction of Naringin and Limonin byβ-Cyclodextrin

“…... clusion complexes. 16) The cyclodextrin molecule is doughnut-shaped. It has been reported that if certain "guest" compounds mig-rate into the interior of the cavity of the cyclodextrin, the H-3 and H-5 protons, located within the cavity, will be strongly shielded.…”