Formation of cyclodextrins

Binding Forces Contributing to the Formation of Cyclodextrin Inclusion... 

Several intermolecular interactions have been proposed and discussed as being responsible for the formation of cyclodextrin inclusion complexes in an aqueous solution 6-10). They are... 

Isoxazolines 38 and 39 were obtained in different ratios by direct cycloaddition of 4-t-butylbenzonitrile oxide with acids 35 (R = H, path B) and by the intermediate formation of cyclodextrin derivatives 36 and 37 followed by basic hydrolysis and acidification (path A). The reversed regioselectivity as well as an increased rate of the cycloaddition step could be explained through the temporary association of the nitrile oxide with the cyclodextrin to give the inclusion complex 40 <06CEJ8571>. 

Complex Formation of Cyclodextrins with Hydrophilic Polymers. 144... 

The majority of reported studies of formation of cyclodextrin inclusion complexes in solution have been mainly concerned with determination of the stability constants by using equilibrium spectroscopic techniques, and the measurement of the enthalpy and entropy changes characterizing the complexation reaction. The aim of much of this work has been to determine the driving force of complex-formation. Despite the amount of research in this area, however, no general agreement has been reached, and... 

Experiments were also carried out at 80 and lOO C. According to our observations at these high temperatures, solid- phase chemical transformations may take place between certain flavor constituents and cyclodextrin hydroxyls/monoterpene alcohols and phenolic compounds appear as a result of a solid-phase transacetylation of terpeneaoetates and phenyl-acetates with the simultaneous formation of cyclodextrin-acetates/. Long term heat treatments of cyclpdextrin-flavor complexes should not be run above 6o°C in order to avoid such phenomena. 

Figure 4.6 shows the schematic diagrams of ciclodextrins, polyaniline with emeraldine base, and inclusion complex formation of cyclodextrins and a conducting polymer chain insulated molecular wire. 

Chirality Induced Upon Formation of Cyclodextrin Inclusion Complexes... 

Fig. 13. Schematic representation of complex formation of cyclodextrin with guest molecule...

Equations are derived which take into account the formation of cyclodextrin to substrate complexes other than simple one to one host guest associations. An equation is also derived which describes the binding of a mono-protic species in which either its ionized or unionized form could bind to one or two cyclodextrin molecules. Because multiple binding constants are difficult to evaluate graphically, a non-linear least squares computer program is utilized. The approach works equally well for the determination of binding constants in micellar media. 

Cyclodextrins are water-soluble hosts for hydrophobic guests. The formation of inclusion complexes is controlled by the dimensional compatibility of the guest and host cavity. Commercially available dextrins are, in fact, inclusion complexes of cyclodextrins with two water molecules closing the entrance to the cavity. The formation of cyclodextrin inclusion complexes is reversible and, therefore, is governed by concentration of guests competing for a place inside the cavity. 

Cyclodextrins are degradation products from starch by the bacterium Bacillus macerans. They are separated by precipitation with complexing agents and purified by recrystallization. They could probably be produced industrially by the tonne. The formation of cyclodextrins is interpreted as a trans glycosidation of amylose under enzymic control. The latter, in aqueous solution, adopts at least partially the shape of a helix with a period of six glucopyranose units. The bacterial enzyme catalyses the junction of two glucopyranose residues separated... 

Bakkour Y, Vermeersch G, Morcellet M, Boschin F, Martel B, Azaroual N. 2006. Formation of cyclodextrin inclusion complexes with doxycyclin-hyclate NMR investigation of their characterisation and stability. Journal of Inclusion Phenomena and Macrocyclic Chemistry 54(1-2) 109-114. 

The low selectivity of the formation of cyclodextrin inclusion complexes with guests of similar volume but of different shape or charge is explained by the existence of several binding types hydrophobic and van der Waals interactions as well as hydrogen bonds. 

Historically, nuclear magnetic resonance (NMR) spectroscopy was the instrumental technique that provided the first experimental evidence for inclusion complex formation of cyclodextrins (CD) and guest molecules in the liquid phase [1]. Since that time NMR spectroscopy remains one of the key techniques for studying CD complexes with their ligands [2],... 

K. Yoshida, T. Shimomura, K. Ito, R. Hayakawa, Inclusion complex formation of cyclodextrin and polyaniline, Langmuir, 1999, 15, 910-913. 

Fig. 1.25 Complex formation of cyclodextrin with cationic polymers in an aqueous solution.

Two opposing hypotheses attempted to describe the conformation of the a-l,4-linked glucopyranoside polymers in neutral aqueous solutions the random coil and the segmented helix structure hypotheses. The former one was based mainly on hydrodynamic studies of amylose solutions, the latter on many very different observations, but mainly on the formation and properties of amylose-helix complexes. The formation of cyclodextrins, catalysed by cyclizing enzymes, delivers further proof for the helical structure, and simultaneously is the source of a new technology the molecular encapsulation of different compounds by cyclodextrin complexation. The significance of the cyclodextrins and their derivatives in commercial applications will be discussed. 

Some antihistaminic and analgesic agents have become amenable to chiral analysis by H-nmr spectroscopy after formation of cyclodextrin inclusion complexes. In many cases equivalent protons of enantiomeric pairs showed different chemical shifts after inclusion. ... 

Further, complex formation of cyclodextrins with guest compounds such as drugs and insecticides introduced new physicochemical features to these compounds. This leads to interesting practical usages and reinforces the view that cyclodextrins are suitable models of enzymatic binding as well as enzymatic reactions. 

M. Komiyama and M. L. Bender (1978), Importance of apolar binding in complex formation of cyclodextrins with adamantanecarboxylate. J. Amer. Chem. Soc. 100, 2259-2260. 

Although fluorescence spectroscopy is the most sensitive method for studying the formation of cyclodextrin inclusion complexes, it does have two significant limitations, which must be taken into account when determining the best experimental technique for studying a given CD complex ... 

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