D-glucopyranose Units Research Articles

Relationship between Fe2+ Ca2+ ions and cyclodextrin in olive trees infected with sooty mold

In this work, Energy Dispersive X-ray Fluorescence (EDXRF) was used to observe the peak areas of chemical elements present in healthy and infected samples and a Scanning Electron Microscopy (SEM) to study the damage caused by sooty mold on olive tree leaves from the Mediterranean. Leaves infected with sooty mold presented a high concentration of Fe2+ and a low concentration of Ca2+. Our results show that the infected leaves cause a metabolic imbalance in the plants due to an anomalous behavior of macronutrients and micronutrients. Infected leaves start to develop a thin layer of glucose (Cyclodextrin) on their surface. Cyclodextrin (CD) molecules are oligosaccharides consisting of α–D-glucopyranose units linked to glucosides. The most common is β-cyclodextrin (β-CD), which has seven units of α–D-glucopyranose. There are different CDs which are widely used as molecular reactors. In this work, some connections between CD molecules conformations that were obtained in order to observe the relationship of Fe2+ and Ca2+ in the olive tree infected with sooty mold were studied. The results are discussed in terms of number of ions found inside and outside the cavity formed by the CD molecules.

Mechanism research on cellulose pyrolysis by Py-GC/MS and subsequent density functional theory studies

The mechanism of fast pyrolysis of cellulose has been studied by using an analytical pyrolyzer coupled with a gas chromatography–mass spectrometry set-up (Py-GC/MS). The results showed that the main products comprised pyrans such as levoglucosan and levoglucosenone, furans such as furfural and 5-hydroxymethyl furfural, and linear small molecular chemicals such as acetaldehyde and 1-hydroxy-2-propanone. The compositions of products from fast pyrolysis of cellubiose and glucose were similar to that from cellulose, but with higher furan contents and lower pyran contents. Based on the experimental results, density functional theory (DFT) studies were carried out to deduce the pyrolysis mechanism of cellulose. The results showed the formation of 5-hydroxymethyl furfural from d-glucopyranose unit to be easier than the formation of levoglucosan, in agreement with the experimental results. The deduced mechanism of reaction pathways in cellulose pyrolysis provides insight into the pyrolysis behavior of cellulose and allows modification of previously proposed related mechanisms.

COMPARATIVE EVALUATION OF THE ANTIOXIDANT ACTIVITIES OF THYMOL AND CARVACROL AND THE CORRESPONDING β-CYCLODEXTRIN COMPLEXES

Cyclodextrins are cyclic oligosaccharides of α-(1,4)-linked D-glucopyranose units in a ring formation. They are able to form inclusion complexes with a wide variety of molecules, improving their aqueous solubility and chemical stability, the dissolution and release rates of several molecules as well as suppressing their volatility and unpleasant odours or tastes. Thymol and carvacrol are two aromatic compounds present in the essential oils of Thymus and Origanum species, which show antioxidant properties. The main goal of this work was to evaluate the antioxidant ability of thymol and carvacrol and of the corresponding β-cyclodextrin complexes. Oxygen Radical Absorbance Capacity (ORAC), Trolox Equivalent Antioxidant Capacity (TEAC) and 2,2-diphenyl-2-picryl-hydrazil (DPPH) methods were used for evaluating the thymol and carvacrol and the β-cyclodextrin complexes scavenging free radicals capacity. With ORAC method, thymol showed better antioxidant activity than carvacrol, 47 and 33 μmol Trolox equivalent/mg (TE), respectively. Thymol- and carvacrol-β-cyclodextrin complexes maintained their capacity for scavenging the free radical with 47 and 28 μmol TE/mg, respectively. With TEAC method, thymol and carvacrol showed similar antioxidant activities: 421 and 450 μmol TE/mg, respectively. In contrast, carvacrol-β-cyclodextrin complex attained 494 μmol TE/mg while thymol complex showed only 184 μmol TE/mg. This complex seems to loose the capacity for scavenging free radicals. Different results were obtained with DPPH method. IC 50 values for thymol and the corresponding complex were similar 0.03 mg, whereas carvacrol and carvacrol-β-cyclodextrin complex showed an IC 50 =0.03 and 0.02 mg, respectively.

Phosphorylase-catalyzed N-formyl-α-glucosaminylation of maltooligosaccharides

This paper describes the phosphorylase-catalyzed enzymatic N-formyl-α-glucosaminylation of maltooligosaccharides for direct incorporation of 2-deoxy-2-formamido-α- d-glucopyranose units into maltooligosaccharides. When the reaction of 2-deoxy-2-formamido-α- d-glucopyranose-1-phosphate (GlcNF-1-P) as the glycosyl donor and maltotetraose as a glycosyl acceptor was performed in the presence of phosphorylase, the N-formyl-α- d-glucosaminylated pentasaccharide was produced, as confirmed by MALDI-TOF MS. Furthermore, the glucoamylase-catalyzed reaction of the crude products supported that the 2-deoxy-2-formamido-α- d-glucopyranoside unit was positioned at the non-reducing end of the pentasaccharide. The pentasaccharide was isolated from the crude products and its structure was further determined by the 1H NMR analysis. On the other hand, when the phosphorylase-catalyzed reactions of maltotriose and maltopentaose using GlcNF-1-P were conducted, no N-formyl-α-glucosaminylation took place in the former system, whereas the latter system gave N-formyl-α- d-glucosaminylated oligosaccharides with various degrees of polymerization. These results could be explained by the recognition behavior of phosphorylase toward maltooligosaccharides.

Thermal aging micro-scale analysis of power transformer pressboard

In order to analyze the thermal aging mechanism of the insulation paper inside the power transformer, a series of accelerated thermal aging tests were performed on pressboard. Subsequently, the atomic force microscope (AFM) together with scanning electron microscope (SEM) and X-ray diffraction (X-RD) were utilized to observe the micro surface of the thermal-aged pressboard. The experiments and analysis indicate that either the links among the D-glucopyranose units or the hexagonal mesh structures of the D-glucopyranose units were broken under thermal stress; the number of D-glucopyranose units after 6 weeks of aging was 0.8-1 per nm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , only about one third of un-aged value. The wall of a cellulose cell was deteriorated and thinned by thermal stress. At the same time, the cracks expanded gradually on the surface of the cellulose, which shortened the average width of cellulose fiber from about 40 mu of un-aged sample to about 25 mu after 6 weeks of aging. Meanwhile, the relative crystallinity and the size of the crystallite in the pressboard decreased nonlinearly with the thermal aging time.

Enzymatic α-glucosaminylation of maltooligosaccharides catalyzed by phosphorylase

This paper describes phosphorylase-catalyzed enzymatic α-glucosaminylation for the direct incorporation of a 2-amino-2-deoxy-α- d-glucopyranose unit into maltooligosaccharides. When the reaction of 2-amino-2-deoxy-α- d-glucopyranosyl 1-phosphate as the glycosyl donor with maltotetraose as a glycosyl acceptor was performed in the presence of phosphorylase, glucosaminylated oligosaccharides were produced, which were characterized by MALDI-TOF MS measurement after N-acetylation of the crude products. The N-acetylated derivative of the main product in this system was isolated by using HPLC, and its structure was confirmed by MS and 1H NMR spectra. Furthermore, glucoamylase-catalyzed reaction of the isolated compound provided support that the α-glucosamine unit is positioned at the non-reducing end of the oligosaccharide.

A kinetic study of oxidation of β-cyclodextrin by permanganate in aqueous media

Kinetic data for the permanganate—β-cyclodextrin redox system are reported for the first time. Conventional spectroscopic method was used to monitor the progress of the reaction. The reaction is first order in both [MnO 4 −] and [β-cyclodextrin]. The [H +] markedly increase the oxidation rate. Formation of an intermediate (Mn(IV)) observed during the course of reaction at 420 nm. Mn(III) is also formed in a rapid step by reaction of β-cyclodextrin and Mn(IV). Increase in [F −] causes the rate to decrease. One of the primary OH group of α- d-glucopyranose unit of β-cyclodextrin is responsible for the oxidation. An autocatalytic effect has been observed due to Mn(II) ions formed as a product of the reaction. The rate of oxidation of d-glucose is higher in comparison to β-cyclodextrin for the same concentration. Reduction of mercuric chloride indicates free radical mechanism operates during the course of reaction. The energy, enthalpy and entropy of activation have been calculated and mechanism agreement with the observation is suggested.

Large Ring Cyclodextrins: Recent Progress

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A Use of Modified Cyclodextrins as a Transporter for a Radiolabeled Tracer NMR Investigation

Cyclodextrins (D. Duchene (ed.): New Trends in Cyclodextrins and Derivatives (1991)) have long been shown to be capable of modifying the water solubility of a number of hydrophobic guests through the formation of inclusion complexes. Among the three natural cyclodextrins (α, β and γ-cyclodextrins containing 6, 7 and 8 d-glucopyranose units, respectively), β-cyclodextrin is by far the most commonly used although it exhibits a weaker solubility in water (and therefore a weaker solubilization power). This specific feature has encouraged the synthesis of derivatives exhibiting an increased solubility in water. Methylated cyclodextrins are amongst the simplest derivatives, and their properties regarding the solubility and the solubilization power for hydrophobic guests are well documented especially concerning Heptakis (2,6-di-Omethyl)-cyclodextrin (DIMEB) and Heptakis (2,3,6-tri-Omethyl)-cyclodextrin (TRIMEB) K. Koizumi et al.:J. Chromatogr. 368, 329–337 (1986). In order to avoid the use of human serum albumin (HSA), this property has been applied here to the solubilization of a very sparingly water-soluble fatty acid derivative (16-iodo-3-methylhexadecanoic acid), which is known to localise in viable myocardial cells, allowing the generation of functional images reflecting the viability of the cardiac tissue through the use of radiolabeled analog (Demaison et al.: J. Nucl-Med. 29, 1230–1236 (1998)). Nuclear magnetic resonance (NMR) was used throughout this study to evidence that the observed solubilization and stabilisation (under conditions required for sterilisation) induced by cyclodextrins are due to the formation of a true inclusion complex and not to non-specific interactions; This technique further allows to derive thermodynamic as well as structural informations for this complex. On one hand, the inclusion complex prevents thermal degradation during sterilisation process compared to HSA. On the other hand, NMR displacement experiments against HSA showed that the complex likely dissociates in vivo.

Calculations on cyclopyranoses as co-solvents of single-wall carbon nanotubes

The properties of single-wall carbon nanotubes (SWNT) are classified in zigzag armchair and chiral The solubility of SWNTs is investigated in a variety of solvents, finding a class of non-hydrogen-bonding Lewis bases that provide a good solubility. The investigated solvents are grouped into three classes. Categorized solubility is semiquantitatively correlated with solvent parameters. A MOPAC-AM1 and molecular modelling study of the linear and cyclic -linked oligosaccharides containing 1–6 d-glucopyranose (d-Glcp) units provides a clear conception of their overall conformations, their contact surfaces and their cavity proportions. This gives a first estimation of their inclusion properties. An expansion of the central channel is suggested for helical d-Glcp–SWNT complexes.

Cyclic voltammetric, EQCM and impedance study of the 1-octanol-β-cyclodextrin-electrodeposited platinum system in perchloric medium

The system of 1-octanol-β-cyclodextrin in 0.5 M HClO 4 at Pt electrodeposited on an Au/quartz crystal (Pt/Au/Q) has been studied by cyclic voltammetry (CV), the electrochemical quartz crystal microbalance (EQCM) and impedance measurements. β-Cyclodextrin (β-CD), a cyclic oligomer of seven α- d-glucopyranose units, was chosen for this study because it forms an inclusion complex with primary alcohols and because of its hydrophilic exterior. Previous cycling in 1-octanol profoundly affected (“aged”) the electrodeposited Pt, as is readily seen in subsequent CVs and mass curves in 0.5 M HClO 4. Since adsorbed 1-octanol and β-CD would tend to render the Pt surface hydrophobic and hydrophilic, respectively, these opposite tendencies should be detectable by the EQCM. Effectively, in a positive potential scan, 1-octanol and β-CD added at −0.22 V produced a mass decrease and increase, respectively, of aged Pt/Au/Q, owing to a decrease and increase of the amount of adsorbed water and/or ions, which was attributed to physisorption of these compounds. With freshly deposited Pt/Au/Q, 1-octanol added at open circuit produced a mass decrease over the whole potential cycle, again evidence of adsorption of a hydrophobic compound. The potential at which the aged Pt/Au/Q electrode immersed in an 1-octanol solution was held while β-CD was added to the electrolyte crucially affected the subsequent voltammogram and mass curve. If β-CD and 1-octanol were added together at −0.22 V, the current in a subsequent positive scan was the same as in 1-octanol added at −0.22 V, but the mass was higher, both at −0.22 V and over the whole positive scan. This mass increase was probably due to physisorption (since the current was unaffected) of the inclusion complex, since β-CD alone did not affect the mass at −0.22 V. On the contrary, if β-CD was added at open circuit to an electrolyte already containing 1-octanol, also added at open circuit, both the H desorption and Pt oxidation currents were lower than in 1-octanol, indicating a strong interaction of β-CD with the Pt surface, and the mass was also lower over most of the positive scan. Most probably this strong interaction of β-CD involves adsorbed residues formed in the dissociative chemisorption of 1-octanol at open circuit.

Kinetics of ultrasonic degradation and polymerisation degree distribution of sonochemically degraded chitosans

The process of physical degradation by means of the ultrasonic action towards chitosans with mole fraction of 2-acetamido-2-deoxy-β- d-glucopyranose units (the degree of N-acetylation, F A ) in the range of 0.10≤F A≤0.28, and the weight average polymerisation degree ( x ̄ w) in the range of 2.2≤ x ̄ w×10 −3≤3.1 has been investigated. The decrease of x ̄ w as well as changes in the distribution of the degree of polymerisation ( P) has been determined as a function of time, F A , temperature, concentration of chitosan solution and concentration of acetic acid in the solution. The use of low-power ultrasound emitter allowed to establish that in the case of chitosan (binary heteropolysaccharide) the general rate parameter ( k) increased with F A . This can be explained by the relatively stronger aggregation of macromolecules with higher F A , which results in size increase of macromolecular individuals and hence in their higher susceptibility to ultrasonic action. It was also observed that k decreased with chitosan concentration and temperature. The value of limiting degree of polimerisation ( x e ) was found to be influenced by structural parameters of chitosan chains ( F A , aggregation). The increase of acetic acid concentration caused the increase in the k value, what indicated accelerating effect of ultrasound towards acidic hydrolysis of chitosan. The shape of the P curve of sonochemically degraded chitosans are in good correlation with the mid-point breakage concept of degradation accepted in sonochemical degradation of polymers.

Enzymatic synthesis of two salicin analogues by reaction of salicyl alcohol with Bacillus macerans cyclomaltodextrin glucanyltransferase and Leuconostoc mesenteroides B-742CB dextransucrase

β-Salicin is a naturally occurring glycoside found in the bark of poplar and willow trees. Ancient man used it as an analgesic and antipyretic. It has a d-glucopyranose unit attached by a β-linkage to the phenolic hydroxyl of salicyl alcohol. Two new salicin analogues have been enzymatically synthesized by transglycosylation reactions: ( a) by the reaction of Bacillus macerans cyclomaltodextrin glucanyltransferase with cyclomaltohexaose and salicyl alcohol, followed by reactions with alpha amylase and glucoamylase to give d-glucopyranose attached by an α-linkage to the phenolic hydroxyl of salicyl alcohol as the major product, α-salicin; and ( b) by the reaction of Leuconostoc mesenteroides B-742CB dextransucrase with sucrose and salicyl alcohol, followed by reactions with dextranase and glucoamylase to give α- d-glucopyranose attached to the primary alcohol hydroxyl of salicyl alcohol as the major product, α-isosalicin.

Trehalose–protein interaction in aqueous solution

A variety of sugars are known to enhance the stability of biomaterials. Trehalose, a nonreducing disaccharide composed of two alpha, alpha(1 --> 1)-linked D-glucopyranose units, appears to be one of the most effective protectants. Both in vivo and in vitro, trehalose protects biostructures such as proteins and membranes from damage due to dehydration, heat, or cold. However, despite the significant amount of experimental data on this disaccharide, no clear picture of the molecular mechanism responsible for its stabilizing properties has emerged yet. Three major hypotheses (water-trehalose hydrogen-bond replacement, coating by a trapped water layer, and mechanical inhibition of the conformational fluctuations) have been proposed to explain the stabilizing effect of trehalose on proteins. To investigate the nature of protein-trehalose-water interactions in solution at the molecular level, two molecular dynamics simulations of the protein lysozyme in solution at room temperature have been carried out, one in the presence (about 0.5 M) and one in the absence of trehalose. The results show that the trehalose molecules cluster and move toward the protein, but neither completely expel water from the protein surface nor form hydrogen bonds with the protein. Furthermore, the coating by trehalose does not significantly reduce the conformational fluctuations of the protein compared to the trehalose-free system. Based on these observations, a model is proposed for the interaction of trehalose molecules with a protein in moderately concentrated solutions, at room temperature and on the nanosecond timescale.

Efficient Regioselective Synthesis of Mono-2-O-Sulfonyl-cyclodextrins by the Combination of Sulfonyl Imidazole and Molecular Sieves

Cyclodextrins are cyclic oligosaccharides consisting of six or more α-1,4-linked D-glucopyranose units, which possess primary hydroxyl groups at the C-6 positions and secondary hydroxyl groups at the C-2 and C-3 positions. Because cyclodextrins have a hydrophobic and optically active interior, they have been utilized as transporters of hydrophobic molecules and small molecular mimics of enzymes. The chemical modification of cyclodextrins has been investigated in order to improve these characteristics. Sulfonations of the primary or secondary hydroxyl groups of cyclodextrin have been applied for further functionalization of cyclodextrin, and several methods for regioselective sulfonations have been developed. Among these strategies, selective monotosylation of the C-6 hydroxyl group is done relatively easily by reaction of α or β-cyclodextrin and p-toluenesulfonyl chloride in pyridine1,2 or in alkaline aqueous solution.3,4 However, sulfonation of the secondary hydroxyl groups is more difficult and new sulfonation methods must be developed to provide precursors for cyclodextrin analogues such as amino and sulfide analogues. Several strategies for the sulfonation of one C-2 hydroxyl group have been reported. However, because reaction conditions can require specific sulfonation reagent,5 alkaline condition,3-7 strict anhydrous conditions,8,9 or use of protected C-6 hydroxyl groups,10,11 the methodology is not convenient to employ.

Proton NMR spectroscopy assignment of d-glucose residues in highly acetylated starch

1H NMR spectroscopy assignments have been obtained for starch acetates using COSY and HOHAHA experiments by comparison with the spectra of amylose triacetate and of peracetylated malto-oligosaccharides (maltotriose, maltotetraose, maltoheptaose). These assignments are valuable for the location and evaluation of the substitution pattern in modified starches. The bulk of the 1H NMR spectra of highly acetylated starch strongly resembles the spectrum of amylose triacetate in which all protons are identified and display distinct chemical shifts. The resolving power of the HOHAHA experiment allowed the distinction of minor spin systems. Beside these strong signals pertaining to an average 2,3,6-tri- O-acetyl- α-(1 → 4) linked d-glucopyranose unit in an infinite chain, the combination of COSY and HOHAHA experiments allowed the identification of these systems to the terminal, n-1, n-2, and to partially acetylated glucopyranosyl units. As an example, two different preparations of starch acetates with degrees of substitution 2.74 and 2.63 were examined. In one case, NMR demonstrates that the defects of acetylation are random on the polymeric chain (with corresponding signals for unacylated secondary hydroxyl positions at δ 3.61 and 3.40) while in another case, these signals are not detectable, probably due to the presence of clusters of non-acetylated residue forming solid-like zones.

Isolation, Purification, and Characterization of Cyclomaltodecaose (.EPSILON.-Cyclodextrin), Cyclomaltoundecaose (.ZETA.-Cyclodextrin) and Cyclomaltotridecaose (.THETA.-Cyclodextrin).

Cyclomaltodecaose (ε-cyclodextrin, ε-CD), cyclomaltoundecaose (ζ-CD) and cyclomaltotridecaose (θ-CD) are a series of cyclomalto-oligosaccharides composed of ten, eleven and thirteen α-(1→4)-linked D-glucopyranose units, respectively. ε-CD, ζ-CD and θ-CD were purified from the commercially available CD powder mainly using the combined treatment of HPLC and column chromatographies. The molecular weights of ε-CD, ζ-CD and θ-CD were determined by FAB-MS, and their cyclic structures were identified by 1H-NMR and 13C-NMR. Furthermore, the 13C-NMR chemical shift of large-ring cyclodextrins composed of several α-(1→4)-linked D-glucopyranose units, in which numbers 9, 10, 11, 12, and 13 are named δ-, ε-, ζ-, η-, θ-CD, were elucidated and compared with those of conventional α-, β-, and γ-CD.

Review of Chitin and Chitosan as Fiber and Film Formers

Abstract Chitin is one of the most abundant polysaccharides found in nature. It is often considered a cellulose derivative although it does not occur in organisms producing cellulose. Cellulose consists of β-(1→4)-D-glucopyranose units. In contrast, chitin has the same backbone but the 2-hydroxy has been replaced by an acetamide group, resulting in mainly β-(1→4)-2-acetamido-2-deoxy-D- glucopyranose structural units (GLcNAc). Chitosan is the N-deacetylated derivative of chitin, though this N-deacetylation is almost never complete. A sharp nomenclature border has not been defined between chitin and chitosan based on the degree of N-acetylation [1, 2]. Structural examples of cellulose, chitin, and chitosan can be found in Fig. 1. The structural and chemical features will be elaborated on in a later section.

Chemical Products from Lignocellulosics

Lignocellulosics represent that mass of organic matter produced by land-growing plants in the form of trees, shrubs, and agricultural crops. Lignocellulosics are renewable, and they sustain living conditions on our planet by recycling carbon dioxide to oxygen. Lignocellulosics serve the planet as a carbon sink. Chlorophyll is the essential catalyst and sunlight the necessary energy source that drive this carbon dioxide reduction to an organic mass that varies little from the carbon-to-oxygen ratio of carbon monoxide.There is, however, no distinct “lignocellulose” molecule. Instead, nature has found it necessary to formulate a multiphase material consisting of cellulose, hemicelluloses, and lignin. The composition of this multiphase material can be likened to a fiber-reinforced organic glass where cellulose serves as lightweight fiber, lignin serves as a continuous (glassy) matrix, and hemicelluloses serve as coupling agents. The overall composition suggests that there is 35–45% cellulose, 25–35% hemicelluloses, 20–25% lignin, and various minor constituents.In chemical terms, cellulose is a linear homopolysaccharide with a high degree of crystallinity. It consists of 1,4-β-linked D-glucopyranose units connected in syndiotactic fashion (on alternating sides of the main chain). Cellulose molecules in nature occur with molecular weights exceeding 2 million. Hemicelluloses, by contrast, are branched heterosaccharides of lesser molecular weight. They rarely exceed 20,000 daltons. Hemicelluloses are either rich in glucomannan chains (softwoods), or they consist primarily of branched xylans (hardwoods and annual crops). The chemical composition of hemicelluloses is extraordinarily similar to cellulose (i.e., polyanhydro-pyranoside), but their morphological structure is vastly different.

The tetrasaccharide nystose trihydate: crystal structure analysis and hydrogen bonding

The crystal structure of nystose trihydate, O-β- d-fructofuranosyl-(2 → 1)- O-β- d-fructofuranosyl-(2 → 1)-β- d-fructofuranosyl α- d-glucopyranoside trihydate, C 24H 42O 21·3H 2O, has been determined using Cu Kα X-ray data at 121 K. The space group is P2 12 12 1, with 4 molecules in a unit cell of dimensions a = 10.155(1), b = 13,506(1), and c = 23.278(2) Å. The structure was refined to R = 0.052 and R w = 0.048 for 2734 observed structure amplitudes. The α- d-glucopyranose unit of the molecule has the normal 4C 1 chair conformation and the three fructofuranose units have twist conformations lying between E 3 and 4T 5. One of the three water molecules is distributed over two sites: W-3 with occupancy 0.80 and W-3′ with occupancy 0.20. All the hydrogen atoms were located on the difference synthesis with the exception of those attached to the low-occupancy water site. All hydroxyls, two of the three linkage oxygen atoms, and the water molecules are involved in a complex three-dimensional network which can be decomposed into a series of infinite chains intersecting at the water molecules to form homo- and hetero-dromic cycles.