Thermal behavior of amylose-lipid complexes

Melting and crystallization phenomena of amylose-lipid complexes, crystallized either from dilute solution or concentrated amylose ‘melts’ under various conditions, were studied using differential scanning calorimetry (DSC). The melting enthalpies (complex/H₂O: 0·1–0·5 w/w) of the solution-grown crystalline complexes were 20·4±0·8 J g^?1 for amylosemonopalmitin (AM-1-C16), 26·5±1·5 J g^?1 for amylose-lysolecithin (AM-lys/in) and 26·6±1·6 J g^?1 for amylose-lauric acid (AM-C12). While melting of the AM-lys/in complex showed a single transition for all concentrations studied, the melting behavior of the AM-1-C16 and the AM-C12 was rather complex at low or intermediate water contents. At a heating rate of 10°C min^?1 two endothermic transitions with an intermediate exothermic peak were observed, indicative of non-equilibrium melting. A process of partial melting, followed by recrystallization and final melting, is suggested to explain such multiple-melting characteristics. These phenomena become less prominent with increasing water content; presumably due to the depression of the glass transition (T_g) and the melting temperatures (T_m). The annealing behavior of AM-1-C16 further suggested that the development of new structural order upon heating takes place primarily after partial melting of the initial crystalline structure. Overall, the DSC data are typical of those for semicrystalline polymers and consistent with a lamellar type of molecular organization in the crystalline regions of these materials.     

Potato phosphorylase catalyzed synthesis of amylose-lipid complexes

On-line size-exclusion chromatography monitoring of potato phosphorylase catalyzed amylose synthesis--starting from alpha-D-glucose-1-P and maltohexaose--revealed rather monodisperse amylose populations. In the presence of lipids, amylose-lipid complexes spontaneously formed and precipitated. They were recovered by centrifugation, freeze-dried, and characterized by wide-angle X-ray diffraction and differential scanning calorimetry. The presence of lipids during amylose synthesis led to lower amylose degrees of polymerization (DP). Lipid chain length defined amylose DP, which increased in the order myristic acid (C14), glyceryl monostearate (GMS), stearic acid (C18), and docosanoic acid (C22). The thermal stability of the complexes increased in the same manner, with the C22 complexes having the highest dissociation temperature. In addition, we hypothesized that these results provide additional evidence for the fringed micellar organization of (semi-enzymically synthesized) amylose-lipid complexes.     

Utilization of amylose-lipid complexes as molecular nanocapsules for conjugated linoleic Acid

Amylose-conjugated linoleic acid (CLA) complexes were produced by water/dimethyl sulfoxide (DMSO) and KOH/HCl complexation methods. The formation of amylose V form was confirmed by X-ray diffraction (XRD), and complexes formed at 30, 60, and 90 degrees C exhibit melting temperatures exceeding 88 degrees C. Atomic force microscopy (AFM) images showed distinct difference in complex organization, with complexes formed in water/DMSO showing spherical shape with typical diameter of 150 nm. Complexes formed by KOH/HCl showed elongated structure with typical width of 43-160 nm. Water/DMSO complexes exhibit superior protection to CLA against oxidation. All complexes showed high retention of CLA in simulated stomach conditions, and the digestion of complexes by amylases results in high hydrolysis and CLA release by pancreatin and alpha-amylase. Only moderate release was detected following hydrolysis by amyloglucosidase and beta-amylase. It is therefore suggested that amylose-CLA complexes can serve as molecular nanocapsules for protection and delivery of CLA.     

Regioselectivity of the insertion reactions of some aromatic diazo compound complexes with cyclomaltoheptaose

Pyrolysis of solid complexes of aromatic diazo compounds with cyclomaltoheptaose (β-cyclodextrin) yields ether derivatives via insertion of carbene into hydroxyl groups. The distribution of the 2-, 3-, and 6-O-isomers indicates that the regioselectivity is moderate. The guest geometry is not as important as its size in determining the ratios of regioisomers. The origins of the regioselectivity are discussed.     

Crystal and molecular structures of cyclomaltoheptaose inclusion complexes with HI and with methanol

β-Cyclodextrin (β-CD; cyclomaltoheptaose; cyclohepta-amylose; C₄₂H₇₀O₃₅) crystallises from aqueous solutions of HI and of MeOH in the form of stout prisms, which are isomorphous to each other with monoclinic space-group P2₁; cell constants for C₄₂H₇₀O₃₅ · 2HI · 8 H₂O: a = 21.25(3), b = 10.28(2), c = 15.30(2) Å, β = 113.25(9)°, and Z = 2; and for C₄₂H₇₀O₃₅ · MeOH · 6.5 H₂O: a = 21.03(3), b = 10.11(2), c = 15.33(2) Å, β = 111.02(9)°, and Z = 2. X-ray counter data were used to determine the structures of both crystals, which belong to the cage type, with β-CD molecules in nearly identical, “round” shapes. In the HI complex, one I^- is located inside, and one outside, the β-CD cavity; in the MeOH complex, the MeOH is within the cavity. The cavity is closed at the O-2,O-3 side by adjacent β-CD molecules, and at the O-6 side by water molecules hydrogen-bonded to the guest and to surrounding β-CD molecules. Interstices between β-CD molecules are filled by water of hydration molecules in distorted co-ordination.     

Monte Carlo docking simulations of cyclomaltoheptaose and dimethyl cyclomaltoheptaose with paclitaxel

The molecular basis for the remarkable enhancement of the solubility of paclitaxel by O-dimethylcyclomaltoheptaose (DM-beta-CD) over cyclomaltoheptaose (beta-cyclodextrin, beta-CD) was investigated with Monte Carlo docking-minimization simulation. As possible guests of inclusion complexation for the host cyclic oligosaccharides, two functional moieties of the suggested solution structure of paclitaxel were used where one is the C-3'N benzoyl moiety (B-ring) and the other is a hydrophobic (HP) cluster site among the C-3' phenyl (C-ring), C-2 benzoate (A-ring), and C-4 acetoxy moieties. The energetic preference of inclusion complexation of DM-beta-CD over beta-CD was analyzed on the basis of more efficient partitioning process of DM-beta-CD into the hydrophobic cluster site of the paclitaxel.     

The dimeric complex of cyclomaltoheptaose with 1,14-tetradecanedioic acid. Comparison with related complexes

The structure of the complex of cyclomaltoheptaose (beta-cyclodextrin, betaCD) with 1,14-tetradecanedioic acid has been determined and refined to a final R=0.0693 based on 9824 observed reflections. Each diacid molecule threads through two betaCD monomers arranged in dimers thus, forming a [3]pseudorotaxane. The end carboxylic groups of adjacent dimers, far apart and fully hydrated, are associated indirectly through water molecules. The positioning of the carboxylic groups with respect to the betaCD dimer and the H-bonds with water molecules are very similar to these of the corresponding complexes of the diacids with 12 and 13 carbon atoms. The bending in the middle of the aliphatic chain is more prominent, compared to that of the corresponding guests with less carbon atoms, thus the end carboxylic groups stay in the same height of the primary faces of the betaCD dimeric complex. As a consequence of the present structure, more close contacts are observed between calculated H-atoms of the guest and O-atoms of the host inside the cavity. This bending is allowed by the width of the betaCD dimer cavity at the secondary interface region.     

Inclusion complexes of bisphenol A with cyclomaltoheptaose (beta-cyclodextrin): solubilization and structure

The inclusion complexation behavior and the solubilization effects of Bisphenol A (BPA, an endocrine-disrupting chemical) by cyclomaltohexaose, -heptaose, and -octaose (alpha-, beta-, and gamma-cyclodextrins) were investigated by (1)H NMR spectroscopy and by elemental analysis. The results showed that beta- and gamma-cyclodextrins gave the satisfactory solubilization ability to BPA up to 7.2x10(3)mgL(-1) and 9.0x10(3)mgL(-1), respectively. X-ray crystallographic diffraction and ROESY spectroscopy were also employed to investigate the structure of the beta-CD/BPA inclusion complex in both aqueous solution and the solid state. The result showed that this complex adopted a 2:2 stoichiometry in the solid state, that is, a head-to-head beta-CD dimer accommodated two BPA molecules. The inclusion of BPA led to the desolvation of the beta-CD cavity and the destruction of the circularly closed hydrogen-bond network in the secondary side of beta-CD, which made the complex more soluble.     

Crystal structure of cyclomaltoheptaose (beta-cyclodextrin) complexes with p-aminobenzoic acid and o-aminobenzoic acid

Crystal structures of cyclomaltoheptaose (beta-cyclodextrin) complexes with p-aminobenzoic acid and o-aminobenzoic acid have been determined by single-crystal X-ray diffraction. The space group of the beta-cyclodextrin-p-aminobenzoic acid complex is P2(1) with a host:guest stoichiometry of 1:1, and that of the beta-cyclodextrin-o-aminobenzoic acid complex is P1 with a stoichiometry of 2:3. The different structures of the guest molecules lead to the different molecular packing structures of the two complexes. Intermolecular hydrogen-bond interactions are the main force that stabilize the supramolecular systems. In both crystals, there are water molecules located near the cavity rims and in interstices between molecules of beta-cyclodextrin participating in formation of intermolecular hydrogen bonds.     

Metal-heptaiodide interactions in cyclomaltoheptaose (beta-cyclodextrin) polyiodide complexes as detected via Raman spectroscopy

The Raman spectra of the cyclomaltoheptaose (beta-cyclodextrin, beta-CD) polyiodide complexes (beta-CD)(2).NaI(7).12H(2)O, (beta-CD)(2).RbI(7).18H(2)O, (beta-CD)(2).SrI(7).17H(2)O, (beta-CD)(2).BiI(7).17H(2)O and (beta-CD)(2).VI(7).14H(2)O (named beta-M, M stands for the corresponding metal) are investigated in the temperature range of 30-140 degrees C. At room temperature all systems show an initial strong band at 178 cm(-1) that reveals similar intramolecular distances of the disordered I(2) units (approximately 2.72 A). During the heating process beta-Na and beta-Rb display a gradual shift of this band to the final single frequency of 166 cm(-1). In the case of beta-Sr and beta-Bi, the band at 178 cm(-1) is shifted to the final single frequencies of 170 and 172 cm(-1), respectively. These band shifts imply a disorder-order transition of the I(2) units whose I-I distance becomes elongated via a symmetric charge-transfer interaction I(2)<--I3(-)-->I(2). The different final frequencies correspond to different bond lengthening of the disordered I(2) units during their transformation into well-ordered ones. In the Raman spectra of beta-V, the initial band at 178 cm(-1) is not shifted to a single band but to a double one of frequencies 173 and 165 cm(-1), indicating a disorder-order transition of the I(2) molecules via a non-symmetric charge-transfer interaction I(2)<--I3(-)-->I(2). The above spectral data show that the ability of I3(-) to donate electron density to the attached I(2) units is determined by the relative position of the different metal ions and their ionic potential q/r. The combination of the present results with those obtained from our previous investigations reveals that cations with an ionic potential that is lower than approximately 1.50 (Cs(+), Rb(+), Na(+), K(+) and Ba(2+)) do not affect the Lewis base character of I3(-). However, when the ionic potential of the cation is greater than approximately 1.50 (Li(+), Sr(2+), Cd(2+), Bi(3+) and V(3+)), the M(n+)...I3(-) interactions become significant. In the case of a face-on position of the metal (Sr(2+), Bi(3+)) relative to I3(-), the charge-transfer interaction is symmetric. On the contrary, when the metal (Li(+), Cd(2+), V(3+)) presents a side-on position relative to I3(-), the charge-transfer interaction is non-symmetric.     

Structure of inclusion complexes of cyclomaltoheptaose (cycloheptaamylose): crystal structure of the 1-adamantanemethanol adduct

Cyclomaltoheptaose (cycloheptaamylose) has been crystallized with 1-adamantanemethanol as the guest molecule. The complex crystallized in space group C222(1), with unit-cell dimensions a = 19.162 (13), b = 23.965 (17), and c = 32.597 (27) A. The structure was solved by rotation-translation search-methods. The cyclomaltoheptaose exists as a dimer in the crystal by means of extensive hydrogen-bonding across the secondary hydroxyl ends of two cyclomaltoheptaose molecules. The two halves of the dimer are related by a crystallographic two-fold axis. The primary hydroxyl ends of two adjacent cyclomaltoheptaose molecules are also related by a crystallographic two-fold axis, but do not directly hydrogen bond to one another. Instead, they are held in place by a strong hydrogen bond from the hydroxyl group of the 1-adamantanemethanol to a primary hydroxyl group on an adjacent cyclomaltoheptaose molecule. Other stabilizing hydrogen bonds are formed via three water molecules which are situated at the primary hydroxyl interface, and others that form parallel columns stabilizing the crystal structure. A unique feature of this complex is the presence of trapped water in the cavity at the secondary hydroxyl interface. This water is distributed over 3 disordered sites. Its presence blocks one possible site for the 1-adamantanemethanol, which, instead, binds near the primary hydroxyl end, with its hydroxyl group and part of the adamantane moiety protruding from the cyclomaltoheptaose.     

Crystal structures of heptakis(2,6-di-O-tert-butyldimethylsilyl)cyclomaltoheptaose, heptakis(2-O-methyl-3,6-di-O-tert-butyldimethylsilyl)cyclomaltoheptaose and heptakis(2-O-methyl)cyclomaltoheptaose

Crystal structures of heptakis(2,6-di-O-tert-butyldimethylsilyl)cyclomaltoheptaose, heptakis(2-O-methyl-3,6-di-O-tert-butyldimethylsilyl)cyclomaltohep taose and heptakis(2-O-methyl)cyclomaltoheptaose were determined from X-ray diffraction patterns obtained for single crystals of the title compounds grown from ethyl acetate and ethanol, respectively, as solvent. The crystal structures prove conclusively that quantitative migration of the tert-butyldimethylsilyl group from the 2-O- to the 3-O-position [D. Icheln, B. Gehrcke, Y. Piprek, P. Mischnick, W.A. Konig, M.A. Dessoy, A.F. Morel, Carbohydr. Res., 280 (1996) 237-250] was achieved during methylation of heptakis(2,6-di-O-tert-butyldimethylsilyl)cyclomaltoheptaose by iodomethane-sodium hydride.     

Hydrolysis of nonstarch carbohydrates of wheat-starch effluent for ethanol production

A (polysaccharide-rich) waste stream derived from a combined starch and ethanol factory was investigated regarding hydrolysis of the nonstarch carbohydrates for ethanol production. The material was characterized and processed to yield the maximum amount of sugars. The starch fraction was hydrolyzed with amylolytic enzymes, and the resulting fibrous material was separated by filtration. This material, denoted starch-free fibers (SFF), was subjected to heat treatment followed by enzymatic hydrolysis to recover the other major carbohydrate components, namely, cellulose and hemicellulose, in monomeric form. Heat treatment in a microwave oven efficiently solubilized a fraction of these polysaccharides and made the material more accessible to the cellulolytic and hemicellulolytic enzymes used in the subsequent enzymatic hydrolysis. The maximum sugar yield after enzymatic hydrolysis, achieved with pretreatment at 170 degrees C for 40 min, was 34.1 g per 100 g SFF, comprising 12.8 g glucose, 13.9 g xylose and 7.4 g arabinose, corresponding to 66%, 71% and 51% of the theoretical, respectively.     

Crystal structures of heptakis(2,6-di-O-ethyl)cyclomaltoheptaose

Heptakis(2,6-di-O-ethyl)-beta-cyclodextrin (DE-beta-CD) was crystallized in two forms from hexane and 95% aqueous methanol, respectively: A form I crystal with the space group P2(1)2(1)2(1) and a form II crystal with the space group P3(1). In both crystals, DE-beta-CD molecules are in a round shape with intramolecular O-3-H...O-2 hydrogen bonds. In the form I crystal, the DE-beta-CD molecules are arranged along the twofold screw axis to form a helically extended polymeric chain by including the 6-O-ethyl groups of the adjacent molecule. One hexane molecule with twofold disorder is located in the intermolecular channel along the a-axis. In contrast, the DE-beta-CD molecules in the form II crystal form a helical arrangement along the threefold screw axis. One methanol and one water molecule are included on the O-6 side of the molecular cavity. The water molecule links the methanol molecule and two ethoxy groups of the adjacent DE-beta-CD molecule with hydrogen bonds. The result suggests the important role of solvent in the formation of helical arrangement of DE-beta-CD molecules.     

Characterization of the hidden glass transition of amorphous cyclomaltoheptaose

An amorphous solid of cyclomaltoheptaose (β-cyclodextrin, β-CD) was formed by milling its crystalline form using a high-energy planetary mill at room temperature. The glass transition of this amorphous solid was found to occur above the thermal degradation point of the material preventing its direct observation and thus its full characterization. The corresponding glass transition temperature (T_g) and the ΔC_p at T_g have, however, been estimated by extrapolation of T_g and ΔC_p of closely related amorphous compounds. These compounds include methylated β-CD with different degrees of substitution and molecular alloys obtained by co-milling β-CD and methylated β-CD (DS 1.8) at different ratios. The physical characterization of the amorphous states have been performed by powder X-ray diffraction and differential scanning calorimetry, while the chemical integrity of β-CD upon milling was checked by NMR spectroscopy and mass spectrometry.     

A rheological investigation of cereal starch pastes and gels. Effect of pasting procedures

Wheat and maize starches have been pasted using four different pasting procedures by varying the heating and stirring rates. The flow behaviour of hot starch pastes was investigated over a wide range of concentrations (∼ 3 to 10·5%). For each type of starch each pasting procedure resulted in a specific flow behaviour. Flow curves were tentatively interpreted on the basis of swelling-solubility values, and it was demonstrated that the overall viscosity of starch pastes is primarily governed by a combination of the volume fraction of the disperse phase and the concentration and composition of the continuous phase. For the highest concentration, deformability of swollen particles seems to play a prevailing role. Concentrated starch gels also exhibited different elastic properties, depending upon pasting procedure and type of starch. Wheat starch gels were stiffer than maize gels and it was suggested that the main structural parameters involved are the deformability of the swollen particles and the amylose concentration of the continuous network.     

Physical investigations of surface membrane-water relationship of intact and gelatinized wheat-starch systems

Water mobility in intact and dried gelatinized starch was investigated by gravimetric water sorption, scanning electron microscopy (SEM), and solid-state nuclear magnetic resonance (NMR). A multi-component exponential model quantitatively measured different spin-spin relaxation times of two water components, namely bound water (Tsi) at 3.16 ms and mobile or free water (Tsii) at 3.23 ms, as a function of water activity (aw). The starch samples were moistened to 30% moisture content. SEM confirmed the disrupted, absorbent microstructure in dried, gelatinized starch powder and revealed starch granules in an incomplete gelatinized state, as compared to the complete membrane surface of the intact starch granule. Starch granules sorbed significantly differently at low aw, but after aw=0.44, sorption leveled similarly with increasing aw. The presence and role of a surface membrane was concluded, in support of the hypothetical "water sink" properties of intact granules, and was considered to influence in part the sorption behavior of incompletely gelatinized starch granules.     

Synthesis and silica-based immobilization of monofunctionalized cyclomaltoheptaose derivatives for enantioselective HPLC

Heptakis(6-O-tert-butyldimethylsilyl-2,3-di-O-methyl)cyclomaltohep taose (6-TBDMS-2,3-Me-beta-CD) and heptakis(2,3,6-tri-O-methyl)cyclomaltoheptaose (per-Me-beta-CD) were monofunctionalized by introduction of a 5-cyanopentyl group attached to one of the O-2, O-3 or O-6 positions and subsequent reduction with lithium aluminum hydride to give the corresponding mono-O-(omega-aminohexyl) derivatives. Alternatively, after attachment of a 7-octenyl group and further epoxidation the corresponding mono-omega-epoxyoctyl derivatives of 6-TBDMS-2,3-Me-beta-CD were obtained. The mono-O-(omega-aminohexyl) derivatives were immobilized by reaction with glycidoxypropyl and 'aldehyde' silica, whereas aminopropyl silica was used for the immobilization of the monoepoxyoctyl derivatives. The immobilized cyclodextrin derivatives were partially evaluated as chiral stationary phases in high-performance liquid chromatography (HPLC) and micro-HPLC.     

Crystal structure of the inclusion complex of the antibacterial agent triclosan with cyclomaltoheptaose and NMR study of its molecular encapsulation in positively and negatively charged cyclomaltoheptaose derivatives

The inclusion complexes of triclosan with native cyclomaltoheptaose (beta-cyclodextrin, betaCD) as well as with negatively and positively charged derivatives are studied. The structure of the inclusion complex betaCD/triclosan in the crystalline state [P1, a=15.189(5), b=15.230(6), c=16.293(6), alpha=91.07(4), beta=91.05(3) gamma=100.71(3)] comprises two crystallographically independent host macrocycles A and B. The packing results in betaCD dimers that align head-to-head and form infinite channels along the c-axis. Only one guest molecule statistically disordered over two positions, (the dichlorophenyl ring in the cavities of either A or B) corresponds to each dimer (a 2:1 host/guest complex). The enclosed dichlorophenyl ring enters the dimer through the primary side, whereas the hydrophilic chlorophenol ring extends in the space between dimers. Water molecules in five positions are also enclosed in the intradimer region, arranged on a plane perpendicular to the sevenfold axis of betaCD. The NMR spectroscopic studies in aqueous solution show the presence of both 1:1 and 2:1 betaCD/triclosan complexes. In the first case, two different 1:1 complexes are simultaneously present, each with either ring entering the narrow primary side of one betaCD molecule. In the 2:1 complex both rings of triclosan are included in two independent betaCD hosts, a precursor to the supramolecular arrangement found in the crystalline form. In the case of the negatively charged sodium heptakis[6-deoxy-6-(3-thiopropionate)]-betaCD, the NMR studies at pH 7.9 show a complete inclusion of triclosan inside the host in two orientations, one for the non-ionized (phenol) and reverse for the ionized (phenolate) form. Finally, for the positively charged heptakis(6-aminoethylamino-6-deoxy)-betaCD, inclusion of triclosan is possible only when the pH is raised to 10 and it is concluded that both aromatic rings are alternatively inside the cavity. However in that case also, inclusion of the entire guest in the elongated cavity is suggested.