Cyclohexa-amylose

Fig. 2. From left to right, Corey-Pauling-Koltun molecular models of cyclohexa-amylose, cycloheptaamylose, and cyclooctaamylose viewed from the secondary hydroxyl side of the torus. 

Fig. 5. Graph of the logarithm of the acceleration of the rate of phenol release due to 0.01 M cycloamylose against the Hammett substituent constant,

Values of /c2 and Kd for the reactions of the cycloamyloses with a variety of phenyl acetates are presented in Table IV. The rate constants are normalized in the fourth column of this table to show the maximum accelerations imposed by the cycloamyloses. These accelerations vary from 10% for p-f-butylphenyl acetate to 260-fold for m-f-butylphenyl acetate, again showing the clear specificity of the cycloamyloses for meta-substituted esters. Moreover, these data reveal that the rate accelerations and consequent specificity are unrelated to the strength of binding. For example, although p-nitrophenyl acetate forms a more stable complex with cyclohexa-amylose than does m-nitrophenyl acetate, the maximal rate acceleration, h/kan, is much greater for the meta isomer. 

Acetate Cyclohexa- amylose k obe/kunc Cyclohepta-amylose Cycloocta- amylose... 

The pH dependence of the reaction of m-tolyl acetate with cyclohexa-amylose implies a pAa of 12.1 for the catalytically active secondary hydroxyl group (Van Etten et al., 1967b). Although this pK at first appears low for the ionization of an aliphatic alcohol, it is consistent with the value of 12.35 determined thermodynamically for the ionization of the secondary hydroxyl groups of the ribose moiety of adenosine (Izatt et al., 1966 Christensen et al., 1966), and with the value of 12.2 reported by Lach for the... 

These water-soluble molecules are cyclic oligomers of a-D-glucose formed by the action of certain bacterial amylases on starches (Bender and Komiyama, 1978 Saenger, 1980 Szejtli, 1982). a-Cyclodextrin (cyclohexa-amylose) has six glucose units joined a(l, 4) in a torus [1], whereas /3-cyclodextrin (cycloheptaamylose) and y-cyclodextrin (cyclooctaamylose) have seven and eight units, respectively. 

Single Wavelength. Evidence for Distortion of Cyclohexa-amylose in Aqueous Solution. Optical Rotation and Amylose Conformation"... 

Figure 2.1.47 Huge channel structure (including hydrogen bonds) of cyclohexa-amylose potassiumacetate hydrate (62) (P2i2i2) [93] along [001] (slight rotation around Y to visualize three layers) with potassium acetate and water in the channels between the macrocycles.

Cycloamyloses have been separated by h.p.l.c. on a /u-Bondapak-carbohydrate column using acetonitrile-water mixtures as eluant. The molecular dynamics of the inclusion complexes formed between cyclohexa-amylose and some aromatic amino-acids and dipeptides have been studied by n.m.r. spectroscopy. The forces binding the complexes were found to be weak. The c.d. spectra of cyclohepta-amylose which had been complexed with 2-substituted naphthalenes were measured at various concentrations of cyclohepta-amylase and temperatures between 10-70 C. The complex with 2-naphthoxyacetic acid showed 1 1 stoicheiometry. The molar ellipticity and thermodynamic parameters were determined and enthalpy and entropy ranges calculated. The correlation was explained by a cyclohepta-amylose guest molecule interaction where the guest molecule was highly solvated. The induced c.d. spectra of cyclohepta-amylose complexes with substituted benzenes confirmed that an axial inclusion... 

Cycloamyloses. — The Raman spectrum of cyclohexa-amylose has been compared with those of maltotriose and maltose, and structural implications of the spectra discussed. 

Epichlorohydrin-cross-linked cyclohexa- and cyclohepta-amylose gels have been used for the chromatographic resolution of racemic mandelic acid and its derivatives. Modified cyclohepta-amylose bound the L-(- -)-isomers preferentially, and resolved D,L-methyl mandelate to give the D-(—)-isomer of 100% optical purity in the first fraction. Cross-linked cyclohexa-amylose bound D-(—)-isomers more strongly than L-(-t-)-isomers, resolving D,L-methyl mandelate to a smaller extent than cross-linked cyclohepta-amylose. Binding was studied quantitatively by the equilibrium method. 

Reductive cleavage of glycosldic bonds of permethylated methyl a- and B-D-glucopyranoside, cyclohexa-amylose and cellulose has been effected with triethylsllyl deuteride and boron trifluorlde or, better, with trlmethylsllyl trlflate as catalyst. 1-Deuter-ated 1,5-anhydro-D-glucltols were obtained with an a 6 ratio of... 

The molecular structure of a 1 1 complex of cyclohepta-amylose and 2,5-di-iodobenzoic acid has been determined by X-ray crystallography. The cyclohepta-amylose molecules form channels in the crystal by means of head-to-head and tail-to-tail stacking Details of the crystal structures of cyclohexa-amylose hexahydrate and cyclohexa-amylose-propan-l-ol hydrate have been sum-marized. ... 

Interaction of cyclohexa-amylose with optically active benzene derivatives shows a small but distinct chiral discrimination. Other kinetic studies with cydoamyloses have been reported as have details of various of their formation constants. ... 

The purification of pullulanase from Aerobacter aerogenes via affinity chromatography on an agarose-immobilized cyanogen bromide-activated cyclohexa-amylose has been reported. Elution from the affinity column was achieved using cyclohepta-amylose. Crossed immunoelectrophoresis was used to follow the various steps of the purification. 

The diffusion of cyclohexa-amylose and cyclohepta-amylose (a- and /3-cyclodextrin) has been studied in aqueous solutions of poly(methacrylic acid), sodium poly(styrene sulphonate) and co-poly(styrene-methacrylic acid). A decrease in the diffusion coefficients of the cycloamyloses in these polymer solutions was found to be dependent on the polymer concentration, degree of sulphonation, styrene content, and degree of neutralization. The results were interpreted assuming a 1 1 complex between the cycloamylose and an appropriate residue in the polymer. 

The direction of sodium benzoate and benzoic acid penetration of the cyclohexa-amylose cavity in aqueous solution has been determined by n.m.r. spectroscopy of the respective cycloamylose complexes. Results suggested that benzoic acid has a strong preference for binding in the cycloamylose cavity, while sodium benzoate binding is more random. Both compounds form 1 1 complexes with cyclohexa-amylose. 

Conductometric and n.m.r. spectrometric data have allowed calculation of formation constants (at 30 °C) of cyclohexa-amylose-4-methyl cinnamate anion complexes with 1 1 and 2 1 stoicheiometries. The data suggest direct binding of the carboxylate terminal of 4-methyl cinnamate by cyclohexa-amylose in the 1 1 complex, while the structure of the 2 1 complex involves occlusion of the anion between two cyclohexa-amylose molecules in a head-to-head orientation. 

The cyclic imidocarbonate derivative of cyclohexa-amylose has been treated with a 6-aminohexyl derivative of agarose and the support used for affinity chromatography of pullulanase. ... 

Previously [8], the authors succeeded in achieving a strong chiral induction (88-100% ee) for the chlorination of methacrylic acid in the crystalline CD complexes. Here, we report on the asymmetric addition of gaseous bromine, chlorine, hydrogen bromide and hydrogen chloride to styrene in the crystalline complexes of a-CD (cyclohexa-amylose) or fi-CD (cyclohepta-amylose). 

The stereospecificity of the interactions of several spin-labelled substrates with cyclohexa- and cyclohepta-amyloses, as models for chymotrypsin, has been studied. Complexes of the cycloamyloses with 2,2,6,6-tetramethyl-4-oxy-pyridyl-1-oxide in aqueous solution were examined by e.s.r. spectroscopy the nitroxide function moved to a relatively hydrophobic environment on binding to cyclohepta-amylose, and lost some freedom of rotation on binding to both cycloamyloses. The dissociation constant for the cyclohexa-amylose complex of the nitroxide is greater than that for the cyclohepta-amylose complex, consistent with measurements made on molecular models. In the hydrolysis of the asymmetric compound 3-carboxy-2,2,5,5-tetramethylpyrrolidyl-l-oxide 3-nitro-phenyl ester, catalysed by cyclohexa-amylose, enantiomeric specificity was observed in the acylation step but not in formation of the Michaelis complex , or on hydrolysis of the acylated cycloamylose intermediate. No differences were found in the e.s.r. spectra of solutions of the trapped acylcyclohexa-amylose intermediates derived from ( + )- and ( )-forms of the asymmetric nitroxide. The nitroxide function is less free to rotate in the acylcycloamylose intermediate than in the Michaelis complex and is not included in the cycloamylose cavity. 

The signals in the C n.m.r. spectra of two cyclodextrins have been completely assigned. The crystal structure of the complex formed between cyclohexa-amylose and 4-iodophenol has been reported. Fifteen products have been... 

Sweet-potato j3-amylase has been purified by affinity chromatography on cyclohexa-amylose bound covalently to agarose. Inhibition studies indicated that the size of the active site of the enzyme is complementary to cyclohexa-amylose. 

Macroporous agarose activated with l,4-bis-(2,3-epoxypropyloxy)butane reacted with cyclohexa-amylose to give an affinity matrix used in the purification of j3-amylase. ... 

Cyclohexa-amylose reacted with an epoxy derivative of agarose to yield an affinity-chromatography matrix that is suitable for use in the purification of j -amylase. ... 

Partial methylation of cyclohexa-amylose gave dodeca-O-methylcyclohexa-amylose in which all the primary and C-2 hydroxy-groups are etherified. O-Alkylated polymers obtained by treating cyclohexa-amylose with epichloro-hydrin under basic conditions catalysed the chlorination of anisole with hypo-chlorous acid, giving 4-chloroanisole with high (99%) regioselectivity. Dodeca-O-methylcyclohexa-amylose afforded greater selectivity than cyclohexa-amylose, and various features of the chlorination were discussed. 

Determination of the crystal and molecular structures of the cyclohexa-amylose (a-cyclodextrin, a-CD)-methanol complex has shown that cyclohexa-amylose assumes an unstrained relaxed structure, which is stabilized by a ring of hydrogen bonds between 0-2 and 0-3 of adjacent D-glucopyranosyl residues, on inclusion of methanol.The results support the general mechanism (Figure 2) proposed for the formation of inclusion complexes. 

The molecular motions in inclusion complexes formed by cyclohexa-amylose with 4-methylcinnamate, 3-methylcinnamate, and 4-t-butylphenate anions have been studied by and nuclear relaxation methods. The results showed that the time taken for the substrate to reorientate increases by a factor of ca. 4 on inclusion, whereas the increase in tumbling motion depends on the substrate. It was pointed out that, in general, a molecular complex should be described not only by its thermodynamic stability and formation and dissociation kinetics, but also by the dynamic rigidity, defined by the coupling between the molecular motions of the two (or more) entities of which it is composed. 

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