Helical Inclusion Complexes Research Articles

Fabrication of Nanostructured Supramolecules through Helical Inclusion of Amylose toward Hydrophobic Polyester Guests, Biomimetically through Vine-Twining Polymerization Process.

This review article presents the biomimetic helical inclusion of amylose toward hydrophobic polyesters as guests through a vine-twining polymerization process, which has been performed in the glucan phosphorylase (GP)-catalyzed enzymatic polymerization field to fabricate supramolecules and other nanostructured materials. Amylose, which is a representative abundant glucose polymer (polysaccharide) with left-handed helical conformation, is well known to include a number of hydrophobic guest molecules with suitable geometry and size in its cavity to construct helical inclusion complexes. Pure amylose is prepared through enzymatic polymerization of α-d-glucose 1-phosphate as a monomer using a maltooligosaccharide as a primer, catalyzed by GP. It is reported that the elongated amylosic chain at the nonreducing end in enzymatic polymerization twines around guest polymers with suitable structures and moderate hydrophobicity, which is dispersed in aqueous polymerization media, to form amylosic nanostructured inclusion complexes. As the image of this system is similar to how vines of a plant grow around a support rod, this polymerization has been named 'vine-twining polymerization'. In particular, the helical inclusion behavior of the enzymatically produced amylose toward hydrophobic polyesters depending on their structures, e.g., chain lengths and substituents, has been systematically investigated in the vine-twining polymerization field. Furthermore, amylosic supramolecular network materials, such as hydrogels, are fabricated through vine-twining polymerization by using copolymers, where hydrophobic polyester guests or maltooligosaccharide primers are covalently modified on hydrophilic main-chain polymers. The vine-twining polymerization using such copolymers in the appropriate systems induces the formation of amylosic nanostructured inclusion complexes among them, which act as cross-linking points, giving rise to supramolecular networks at the nanoscale. The resulting materials form supramolecular hydrogels, films, and microparticles.

Helical Inclusion Complexes of Amylose with Aromatic Compounds: Crystallographic Evidence for New V-Type Allomorphs

Helical Inclusion Complexes of Amylose with Aromatic Compounds: Crystallographic Evidence for New V-Type Allomorphs

Structure-digestibility relationship of starch inclusion complex with salicylic acid

Amylose, the linear component of starch, can complex with small molecules to form single helical inclusion complexes of 6, 7, or 8 glucosyl units per helical turn, known as V6, V7, and V8. In this study, starch-salicylic acid (SA) inclusion complexes with different amounts of residual SA were obtained. Their structural characteristics and digestibility profiles were obtained with complementary techniques and an in vitro digestion assay. Upon complexation with excess SA, V8 type starch inclusion complex was formed. When excess SA crystals were removed, the V8 polymorphic structure could remain, while further removing intra-helical SA converted the V8 conformation to V7. Furthermore, the digestion rate of the resulted V7 was lowered as indicated by increased resistant starch (RS) content, which could be due to its tight helical structure, whereas the two V8 complexes were highly digestible. Such findings could have practical implications for novel food product development and nanoencapsulation technology.

Preparation of amylose-poly(methyl methacrylate) inclusion complex as a smart nanocarrier with switchable surface hydrophilicity

Amylose, as a linear biopolymer, tends to form helical inclusion complexes with suitable guest species. This is of great importance for a variety of applications, especially in the pharmaceutical and food industry. In this study, we propose an approach for the preparation of a novel inclusion complex with switchable surface hydrophilicity. For this purpose, amylose was first conjugated to ethylene diamine hydrophilic residues. Then, the short chains of the hydrophobic poly(methyl methacrylate, PMMA) were grafted onto the cavity of amylose through atom transfer radical polymerization (ATRP). According to CD spectroscopy results, the amylose-PMMA inclusion complexes displayed solvent-directed helical chirality inversion using either DMSO or water as a solvent. Fluorescence imaging, AFM and DLS techniques revealed the solvent-dependent surface hydrophilicity of the amylose-PMMA inclusion complex. Interestingly, its morphological studies displayed a central cavity, which makes it suitable for carrying cargoes in drug delivery applications. Obtaining the amylose-polymer inclusion complexes with tailorable hydrophilicity of both the exterior surface and the interior cavity can be of paramount importance for a wide variety of bio-applications.

Pullulanase Debranching of Various Starches Upgrades the Crystalline Structure and Thermostability of Starch‐Lauric Acid Complexes

Cassava, rice, and chickpea starches with different amylose contents and amylopectin structure are used to prepare helical inclusion complexes with lauric acid (LA) and to investigate the effect of pullulanase debranching on complex formation, crystalline structure, thermostability, and morphology compared to their non‐debranched counterparts. The quantity of inclusion complexes in debranched starches increased 2–9 times compared to non‐debranched starches, due to the release of debranched, linear amylopectin chains. The amount of complexes after debranching increased with amylopectin content, and with the proportion of amylopectin short chains. Retrogradation occurred under the same conditions as and in competition with complexation; however, carefully adjusting the conditions enabled minimization of retrogradation and maximization of complex formation.

Development of new nanostructure based on poly(aspartic acid)-g-amylose for targeted curcumin delivery using helical inclusion complex

While curcumin has a broad range of beneficial properties such as anticancer, antioxidant and antibacterial activities, its poor solubility, low stability and non-selectivity toward tumor cells often limit its applications. Herein, we described the preparation and characterization of a new fully biocompatible graft copolymer from folic acid/amylose-functionalized poly(aspartic acid) (FA-PAsp-Am) as an effective nanocarrier using a simple aminolysis method. The inclusion complex formation ability of amylose (Am) with curcumin (Cur) as well as its glycotargeting ability when it grafted to the polyaspartic acid (PAsp) backbone as a side chain, could impart more selectivity to tumor cells, promote the solubility of curcumin and improve its stability against UV–Visible irradiation, as demonstrated by UV–Visible exposure test results. The obtained data from FT-IR, H-NMR, Fluorescence, SEM, DLS and UV–Visible techniques confirmed the successful synthesis of the polymer nanocarrier. The observed nanofiber like morphology (20nm width by SEM) of the nanocarrier and the host-guest interaction of curcumin with the amylose helices facilitate the high efficiency of the drug loading. The influence of pH, on the curcumin release behavior also was assessed. Furthermore, the antioxidant ability of curcumin was largely maintained after the loading in the FA-PAsp-Am system. These properties collectively make the folic acid (FA) functionalized poly(aspartic acid)-graft-amylose@curcumin of potential interest for various biomedical applications such as targeted drug delivery systems.

Structural effects of microalgae additives on the starch gelatinisation process

This work presents a detailed structural characterisation of the starch gelatinisation process and the effect of the addition of three microalgae species, Nannochloropsis gaditana sp., Scenedesmus almeriensis and Spirulina, by means of an advanced approach consisting of temperature-resolved simultaneous SAXS/WAXS experiments, combined with DSC. Furthermore, regular and high amylose corn starch were utilised to evaluate the impact of the amylose content.The presence of microalgae has been seen to limit water accessibility towards the interior of starch granules, reducing granule swelling and, thus, hindering the arrangement of amylopectin helices into highly ordered crystalline structures. As a result, more heterogeneous lamellar structures, with reduced apparent crystallinity, are attained. Despite the existence of lipidic compounds in the three microalgae species, the tough cell walls in Nannochloropsis and Scenedesmus impede their release towards the aqueous medium. In contrast, the weak cell walls in Spirulina are disrupted by stirring, allowing cell components to be released. The diffused lipids form helical inclusion complexes with the amylose chains and promote the crystallisation of V-type structures. The presence of amylose-lipid complexes counteracts the limited water swelling effect and results in the formation of more crystalline and homogeneous lamellar structures. This result is relevant for the food industry due to the potential of Spirulina to affect the processability and nutritional characteristics of starch-based products.

Synthesis and characterization of acetylated amylose and development of inclusion complexes with rifampicin

Amylose (AM) tends to form single helical inclusion complexes with suitable agents. These complexes are considered promising biomaterial carrier since the guest molecules can be released later, leading to many applications, especially in the pharmaceutical industry. Rifampicin (RIF) has long been recognized as an active drug against Mycobacterium tuberculosis, however, the administration of RIF in high dosages can originate unwanted side-effects. Due to the fact that the use of native amylose (AM) in the formation of complexes is limited by their low water solubility, it was acetylated with a medium degree of substitution (DS), allowing solubilizing (0.5gL−1) acetylated amylose (AMA) in water at neutral pH, in opposition to that observed with native amylose (trace solubility). The resulting acetylated amylose was characterized by means of Fourier Transform Infrared (FT-IR) spectroscopy and Scanning Electron Microscopy (SEM). FT-IR results indicated that the acetylation of anhydroglucose units of amylose corresponds to a low DS, whereas SEM results suggested that the smooth surfaces of amylose granules were changed into rougher surfaces after acetylation. Ultraviolet absorption spectroscopy (UV–vis) analysis confirmed the formation and allowed the quantification of both native (AM-RIF) and acetylated (AMA-RIF) amylose inclusion complexes. Their characterization in solution was performed by dynamic light scattering (DLS) and zeta potential (ZP) measurements. The average size of inclusion complexes as determined by DLS, ranged between 70 and 100nm. Besides, ZP analysis showed that both complexes are more stable in the presence of RIF. This study may lead to the development of an effective method for the preparation of amylose inclusion complexes, which is beneficial to their further application in drug delivery systems.

Formation of inclusion complexes between high amylose starch and octadecyl ferulate via steam jet cooking

Amylose-ligand inclusion complexes represent an interesting approach to deliver bioactive molecules. However, ferulic acid has been shown not to form single helical inclusion complexes with amylose from high amylose maize starch. To overcome this problem a lipophilic ferulic acid ester, octadecyl ferulate, was prepared and complexed with amylose via excess steam jet cooking. Jet-cooking octadecyl ferulate and high amylose starch gave an amylose–octadecyl ferulate inclusion complex in 51.0% isolated yield. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) confirmed that a 61 V-type inclusion complex was formed. Amylose and extraction assays showed the complex to be enriched in amylose (91.9±4.3%) and contain 70.6±5.6mgg−1 octadecyl ferulate, although, minor hydrolysis (∼4%) of the octadecyl ferulate was observed under the excess steam jet-cooking conditions utilized. This study demonstrates that steam jet cooking is a rapid and scalable process in which to prepare amylose–octadecyl ferulate inclusion complexes.

Small differences in amylopectin fine structure may explain large functional differences of starch

Four amylose-free waxy rice starches were found to give rise to gels with clearly different morphology after storage for seven days at 4°C. The thermal and rheological properties of these gels were also different. This was remarkable in light of the subtle differences in the molecular structure of the amylopectin in the samples. Addition of iodine to the amylopectin samples suggested that not only external chains, but also the internal chains of amylopectin, could form helical inclusion complexes. It is suggested that these internal helical segments participate in the retrogradation of amylopectin, thereby stabilising the gels through double helical structures with external chains of adjacent molecules. Albeit few in number, such interactions appear to have important influences on starch functional properties.

Rheological properties of wheat starch influenced by amylose–lysophosphatidylcholine complexation at different gelation phases

Amylose is able to form helical inclusion complexes with lysophosphatidylcholine (LPC). This complexation influences the functional and rheological properties of wheat starch; however it is well known that the formation of these complexes lead the starchy systems to a slower enzymatic hydrolysis. Based on this, to benefit from both the structuring properties of starch and also lower digestibility of the inclusion complexes, the objective of this study is the formation of amylose–LPC inclusion complexes while developing a firm network providing the desired functional properties in a starchy system. To investigate the influence of amylose–LPC complex formation at different stages of starch gelation on the viscosity behavior of wheat starch, 3% (w/w) LPC was added at three different points of the viscosity profile, obtained by rapid visco analyzer (RVA). LPC addition at all points affected the gelation behavior of wheat starch as compared with the reference. LPC addition at half-peak and peak of the viscosity profile resulted in a viscosity increase during cooling. Measuring the dynamic rheological properties of the freshly prepared gelatinized samples showed a decrease of storage modulus (G′) and loss modulus (G″) in the presence of LPC. During storage, in the presence of LPC, a lower elasticity was observed which indicates a lower rate of amylose retrogradation due to complexation with LPC.

Starch aerogel beads obtained from inclusion complexes prepared from high amylose starch and sodium palmitate

Starch aerogels are a class of low density, highly porous, renewable materials currently prepared exclusively from retrograded starch gels and are of interest due to their high surface area, porosity, biocompatibility, and biodegradability. Recently, we have reported the preparation and properties of amylose-fatty acid salt helical inclusion complexes prepared by steam jet-cooking amylose-containing starches and then blending the resulting dispersions with sodium palmitate. Dispersions of these amylose-sodium palmitate complexes prevent amylose from retrograding and possess polyelectrolyte properties due to the anionic charge of the sodium palmitate. Stable aqueous dispersions of these complexes form hydrogels when added to acid to lower the pH, and these hydrogels were used to prepare their corresponding xerogels, cryogels, and aerogels. Solvent exchange with ethanol and supercritical carbon dioxide (SC-CO2) drying of the starch gels preserved the structure of the gels and yielded aerogels having a macroporous nanoparticulate internal structure. Depressurization rates during SC-CO2 drying were examined to optimize aerogel properties, and starch aerogels with densities between 0.120–0.185 g cm−3 and BET surface areas ranging between 313–362 m2 g−1 were obtained. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, and scanning electron microscopy (SEM), were used to characterize the aerogels. The corresponding xerogels and cryogels had inferior properties. This method provides an alternative method for the preparation of starch aerogels and eliminates many difficulties associated with starch gelatinization and retrogradation procedures that are currently used to prepare the prerequisite starch gels.

Preparation of starch-stabilized silver nanoparticles from amylose–sodium palmitate inclusion complexes

Starch-stabilized silver nanoparticles (AgNP) were prepared from amylose–sodium palmitate helical inclusion complexes by first converting sodium palmitate within the amylose helix to silver palmitate by an ion-exchange reaction with silver nitrate, and then reducing the complexed silver palmitate salt with NaBH4. This process yielded stable aqueous solutions that could be dried and then re-dispersed in water for end-use applications. Reaction products were characterized by inductively coupled plasma-atomic emission spectroscopy (ICP-AES), UV–VIS spectroscopy, X-ray diffraction, TEM, SEM and light microscopy. Addition of acid to reduce the pH of aqueous starch-AgNP solutions produced an increase in viscosity, and nearly quantitative precipitation of starch-AgNP was observed at low pH. Smaller AgNP and higher conversions of silver nitrate to water-soluble starch-AgNP were obtained in this process, as compared with a process carried out under similar conditions using a commercial soluble starch as a stabilizer.

Jet‐Cooked High Amylose Corn Starch and Shortening Composites for Use in Cake Icings

Butter cream is an all-purpose icing that is used to both ice and decorate cakes. Cream icings contain up to 40% shortening. As consumers become aware of the need to reduce fat in their diet, the demand for healthy, flavorful, and low-fat food increases. High-amylose corn starch was cooked in an excess-steam jet cooker in the presence of oleic acid. Amylose formed helical inclusion complexes with the fatty acid. Shortening was added at different levels to jet-cooked starch. The resulting starch-lipid composites (SLC) had 0%, 8%, 16%, and 24% fat. The composites were used to substitute shortening in the preparation of cake icings with 1% to 13% fat. SLC icings were formulated by either keeping the total solids constant, or the starch and sugar to water ratio constant as the fat level was reduced. The effect of fat and formulation of shortening and SLC icings on the physical and rheological characteristics were studied. It was found that low-fat SLC icings can be prepared by optimizing the formulation. Practical Application: This study indicates potential new applications for SLC that benefit the confectionary industry by generating new products offering healthy alternatives to the consumers.

Rheological Properties of Starch‐Oil Composites with High Oil‐to‐Starch Ratios

ABSTRACTMany applications have been developed for aqueous dispersions of jet‐cooked starch‐oil composites prepared by excess steam jet cooking. Previous formulations have typically contained 20–50% oil by weight based on the weight of starch. To expand the range of potential applications, new preparation methods were investigated to increase the oil content to as high as four times the weight of starch. High‐amylose corn starch was cooked in an excess‐steam jet cooker in the presence of oleic acid, and soybean oil was added to form the starch‐oil composites. Amylose is removed from solution by forming helical inclusion complexes with the oleic acid and, if the materials are cooled sufficiently quickly, the helical inclusion complexes only form small aggregates and shells around the oil droplets. Depending on the composition and preparation method, a wide range of stable, high‐oil materials from low‐viscosity liquids to smooth pastes can be formed. The flow, textural, and structural properties of these materials are shown. The materials can be used in a wide range of applications, including spray lubricants, lotions, and for fat delivery in cake mixes.

Polymerization and characterization of self-assembled β-cyclodextrin-threaded chiral monomers

A helical inclusion complex polymer was fabricated through the polymerization of β-cyclodextrin-threaded chiral monomers. The photo induced polymerization of inclusion complex clusters caused shrinkage of the polymer and decreased the pitches, leading to the disappearance of spring-like construction under TEM. From the results of circular dichroism of the inclusion complex polymer, the helical construction was confirmed, and an entanglement of the polymer chains is proposed. After removal of the β-cyclodextrins from the pendant groups of the inclusion complex polymer, the helical structure was found to be maintained. The highly ordered molecular arrangement of β-cyclodextrins removed from the inclusion complex polymer was confirmed using POM. Here we demonstrate the fabrication of helical polymer fibers composed of entangled polymers through self-assembled β-cyclodextrin-threaded chiral monomers. The helical polymer construction was maintained by the entwisted polymer chains even after the removal of β-cyclodextrins from the pendant groups of the inclusion complex polymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2975–2981, 2010

Starch‐Soybean Oil Composites With High Oil: Starch Ratios Prepared By Steam Jet Cooking

AbstractAqueous mixtures of soybean oil and starch were jet cooked at oil: starch ratios ranging from 0.5:1 to 4:1 to yield dispersions of micron‐sized oil droplets that were coated with a thin layer of starch at the oil‐water interface. The jet cooked dispersions were then centrifuged at 2060 and 10,800×g, the buoyant, high‐oil fractions that rose to the surface were isolated, and the size distributions of the oil droplets were determined. Experiments were conducted with normal dent, waxy, and high‐amylose corn starches; and oleic acid was added during jet cooking to form helical inclusion complexes with amylose. With normal dent and waxy corn starches, nearly all of the oil was recovered in the buoyant layers, and only small amounts of oil were found in the aqueous mid layers and settled solids. Oil droplet diameters in the buoyant layers obtained with normal dent and waxy corn starch ranged from under 5 µm to over 50 µm. Centrifugation at high versus low relative centrifugal force produced only minor differences in the droplet size distributions. With high‐amylose starch, microscopy showed that most of the oil droplets were entrapped within aggregates of sub‐micron particles that were apparently formed from amylose‐oleic acid inclusion complexes when the dispersions were cooled. Droplet sizes increased with an increase in the oil: starch ratio, and decreased when oleic acid was added during jet cooking.

Rheological Properties of Dispersions of Spherulites from Jet‐Cooked High‐Amylose Corn Starch and Fatty Acids

ABSTRACTHigh‐amylose corn starch was cooked in an excess‐steam jet cooker in the presence of 5% oleic or palmitic acid, based on amylose. The cooked product was rapidly cooled in an ice bath and then freeze‐dried or drum‐dried. Amylose was removed from solution by forming helical inclusion complexes with the fatty acid, and the inclusion complexes formed submicron spherical particles upon cooling. The dried material was reconstituted to form a paste that exhibited gel‐like properties upon standing, but that flowed readily when shear was applied. The rheological properties of these pastes were measured to determine the effects on the flow properties of 1) the solids concentration in the reconstituted paste, 2) the method of sample drying and reconstitution, and 3) the fatty acid used. The materials were very spreadable, and at the highest concentrations their flow properties were similar to a commercial shortening. The pasting properties of the dried solids were also examined.

Complexation, Structure, and Superoxide Dismutase Activity of the Imidazolate-Bridged Dinuclear Copper Moiety with β-Cyclodextrin and Its Guanidinium-Containing Derivative

An imidazolate-bridged homodinuclear complex, {[Cu(L)(H2O)]2(im)}(ClO4)3 (1), assembled with beta-cyclodextrin (betaCD) and its guanidinium-containing derivative (betaGCD), and thus a helical inclusion complex, {[Cu(L)(H2O)(betaCD)]2(im)}(ClO4)3 (2), were successfully isolated and structurally characterized. Structural analysis showed that each Cu(II) ion has a distorted square pyramidal N4Ow coordination sphere and forms a chiral chain through hydrogen-bonding and hydrophobic interactions. The UV-vis data showed that such a chain can provide the imidazolate bridge additional stability and results in the dissociation equilibrium taking place at the physiological pH. The obtained IC50 value for 2 (0.23 muM) showed a high superoxide dismutase (SOD) activity, which corresponds to a highly stable imidazolate bridge. Interestingly, the guanidinium-containing 1/betaGCD system showed higher SOD activity (IC50 = 0.16 muM), which is enhanced at least by 30% in comparison with that of guanidinium-lacking 2. This result supports that the positive guanidinium plays a role in the catalytic mechanism of Cu,Zn-SOD by ensuring that superoxide enters and peroxide leaves rapidly from the coordination sphere of the copper ion.

The influence of oil on the properties of slowly-cooled jet-cooked normal corn starch dispersions

Previous work has shown that when aqueous dispersions of normal corn starch are jet-cooked under excess steam conditions, the properties of the final product depend on the manner in which the cooked dispersion is cooled. Phase separation of the component molecules of starch alters the final properties, and the extent of phase separation depends on the cooling conditions. Both irregular, amorphous particles and spherical or toroidal crystalline particles were observed in the cooled products. Stable starch-oil composites with a wide range of applications are formed if oil is jet cooked with starch, and the goal of this work was to examine the effect of the added oil on the rheological and structural properties of cooled dispersions. A Rapid Visco Analyser was used to obtain a range of cooling profiles and stirring rates. The dynamic moduli increased with the addition of oil, and the effect was greater for mineral oil than soybean oil. Light microscopy showed that the crystalline particles were not formed in the presence of oil, but samples with oil contained different types of large and small spherical particles. The change in behavior is attributed to the selective extraction of fatty acid components of native lipid by the oil droplets, or to the preferential accumulation of amylose–lipid helical inclusion complexes at the oil droplet surface.