Carbohydrates In Aqueous Solution Research Articles

Enantioselective Keto–Enol Tautomerism of 3-Hydroxyflavones Upon Molecular Complex Formation of Their α-Diketo Forms with Carbohydrates in Aqueous Solutions

Complementary physicochemical methods (UV, IR, ORD) found that the α-diketo tautomer of 3-hydroxyflavones formed complexes with carbohydrates in water. The contribution of the flavone α-diketone increased sharply because it was stabilized after reacting with a carbohydrate cis-diol. The newly formed chiral center of the tautomeric diketo flavones was induced asymmetrically. The complexing ability of the carbohydrates was inversely proportional to their degree of hydration (and decreased in the order maltoseglucose-galactose-arabinose).

Linear and Cyclic Carbohydrate Receptors Based on Peptides Modified with Boronic Acids

AbstractIn this article we report the synthesis of boronic acid functionalized fluorenylmethoxycarbonyl (Fmoc) protected amino acids and their use in solid phase peptide synthesis to synthesize tripeptides with the motif Cys‐X–Cys (X=boronic acid functionalized amino acid). The interaction of these peptides with a set of carbohydrates in aqueous solution was studied by using a competitive indicator displacement assay as well as by isothermal titration calorimetry. We determined carbohydrate binding constants ranging from 2 x 101 M−1 up to 3 x 103 M−1 from these measurements. Moreover, the formation of cyclic hexapeptides was accomplished by oxidation of the thiols of the Cys to disulfides and the interactions between these cyclic receptors and carbohydrates were studied by using a competitive indicator displacement assay and isothermal titration calorimetry. The binding constants observed for these cyclic receptors are similar to the linear receptors.

Osmotic properties of carbohydrate aqueous solutions

Precise systematic osmotic coefficient measurements have been carried out for aqueous solutions of different carbohydrates and polyols by using vapor pressure osmometry (VPO) method. Herein, in order to investigate the effect of structure and stereochemistry of solutes on the vapor–liquid equilibria behavior of aqueous solutions, we studied the osmotic properties of binary aqueous sugar solutions containing pentose monosaccharides (xylose, ribose and arabinose), hexose monosaccharides (glucose, fructose, galactose and mannose), disaccharides (sucrose, maltose and lactose), trisaccharide (raffinose) and polyols (sorbitol, xylitol and maltitol) at 308.15 K and in the extended concentration range. From the experimental osmotic coefficient data, the values of water activity and vapor pressure of the investigated solutions were obtained.

Glucose induced variation of water structure from temperature dependent near infrared spectra

The different effects of glucose on water species provide evidence to explain the bioprotective function of carbohydrates in aqueous solutions.

Theoretical Study of Interaction of Some Heavy Metals with Carbohydrates in Aqueous Solution

Theoretical Study of Interaction of Some Heavy Metals with Carbohydrates in Aqueous Solution

Synthesis, composition, and properties of metal complexes with organic ligands derived from glucose

Natural biologically active compounds are formed from aqueous solutions of various carbohydrates in the presence of transition metal ions as catalysts. Their composition and properties as polycoordination compounds are insufficiently understood. Metal complexes with organic ligands were synthesized from salts of various metals (Fe3+, Co2+, Cu2+, and Mn2+) and glucose. The composition and properties of the metal complexes with organic ligands were studied by quantitative 13C NMR spectroscopy and adsorption polarography.

Solvent-enabled nonenyzmatic sugar production from biomass for chemical and biological upgrading.

We recently reported a nonenzymatic biomass deconstruction process for producing carbohydrates using homogeneous mixtures of γ-valerolactone (GVL) and water as a solvent. A key step in this process is the separation of the GVL from the aqueous phase, enabling GVL recycling and the production of a concentrated aqueous carbohydrate solution. In this study, we demonstrate that phenolic solvents-sec-butylphenol, nonylphenol, and lignin-derived propyl guaiacol-are effective at separating GVL from the aqueous phase using only small amounts of solvent (0.5 g per g of the original water, GVL, and sugar hydrolysate). Furthermore, using nonylphenol, we produced a hydrolysate that supported robust growth and high yields of ethanol (0.49 g EtOH per g glucose) at an industrially relevant concentration (50.8 g L(-1) EtOH). These results suggest that using phenolic solvents could be an interesting solution for separating and/or detoxifying aqueous carbohydrate solutions produced using GVL-based biomass deconstruction processes.

Synthesis, characterization, and spectroscopic investigation of new iron(III) and copper(II) complexes of a carboxylate rich ligand and their interaction with carbohydrates in aqueous solution.

New tetra-iron(III) (K4[1]·25H2O·(CH3)2CO and K3[2]·3H2O·(OH)) and di-copper(II) (Na3[3]·5H2O) complexes as carbohydrate binding models have been synthesized and fully characterized used several techniques including single crystal X-ray crystallography. Whereas K4[1]·25H2O·(CH3)2CO and Na3[3]·5H2O are completely water-soluble, K3[2]·3H2O·(OH) is less soluble in all common solvents including water. The binding of substrates, such as d-mannose, d-glucose, d-xylose, and xylitol with the water-soluble complexes in different reaction conditions were investigated. In aqueous alkaline media, complexes K4[1]·25H2O·(CH3)2CO and Na3[3]·5H2O showed coordination ability toward the applied substrates. Even in the presence of stoichiometric excess of the substrates, the complexes form only 1:1 (complex/substrate) molar ratio species in solution. Apparent binding constants, pKapp, values between the complexes and the substrates were determined and specific mode of substrate binding is proposed. The pKapp values showed that d-mannose coordinates strongest to K4[1]·25H2O·(CH3)2CO and Na3[3]·5H2O. Syntheses, characterizations and detailed substrate binding study using spectroscopic techniques and single crystal X-ray diffraction are reported.

WEISS LECTURECarbohydrate radicals: from ethylene glycol to DNA strand breakage

Radiation-induced DNA strand breakage results from the reactions of radicals formed at the sugar moiety of DNA. In order to elucidate the mechanism of this reaction investigations were first performed on low molecular weight model systems. Results from studies on deoxygenated aqueous solutions of ethylene glycol, 2-deoxy-d-ribose and other carbohydrates and, more relevantly, of d-ribose-5-phosphate have shown that substituents can be eliminated from the β-position of the radical site either proton and base-assisted (as in the case of the OH substituent), or spontaneously (as in the case of the phosphate substituent). In DNA the C(4’) radical undergoes strand breakage via this type of reaction. In the presence of oxygen the carbon-centred radicals are rapidly converted into the corresponding peroxyl radicals. Again, low molecular weights models have been investigated to elucidate the key reactions. A typical reaction of DNA peroxyl radicals is the fragmentation of the C(4’)-C(S’) bond, a reaction not observed in the absence of oxygen. Although OH radicals may be the important direct precursors of the sugar radicals of DNA, results obtained with poly(U) indicate that base radicals may well be of even greater importance. The base radicals, formed by addition of the water radicals (H and OH) to the bases would in their turn attack the sugar moiety to produce sugar radicals which then give rise to strand breakage and base release. For a better understanding of strand break formation it is therefore necessary to investigate in more detail the reactions of the base radicals. For a start, the radiolysis of uracil in oxygenated solutions has been reinvestigated, and it has been shown that the major peroxyl radical in this system undergoes base-catalysed elimination of , a reaction that involves the proton at N(l). In the nucleic acids the pyrimidines are bound at N(l) to the sugar moiety and this type of reaction can no longer occur. Therefore, with respect to the nucleic acids, pyrimidines are good models only in acid solutions where the elimination reaction is too slow to compete with the bimolecular reactions of the peroxyl radicals. Moreover, the long lifetime of the radical sites on the nucleic acid strand may allow reactions to occur which are kinetically of first order, and which cannot be studied in model systems at ordinary dose rates. It is therefore suggested to extend model system studies to low dose rates and to oligonucleo-tides. Such studies might eventually reveal the key reactions in radical-induced DNA degradation.

ChemInform Abstract: Phthalocyanine Conjugates with Carbohydrates: Synthesis and Aggregation in Aqueous Solutions

AbstractReview: [50 refs.

The densities and viscosities of aqueous solutions of glycine and glycylglycine containing carbohydrates and structural properties of the ternary systems

Apparent molar volumes, Vϕ for glycine (Gly) and glycylglycine (Gly-Gly) in aqueous D(+)-glucose and sucrose solutions have been determined from solution density, ρ measurements at 298.15, 303.15, 308.15, and 313.15 K as a function of the concentration of solutes (Gly and Gly-Gly). The standard partial molar volume, Vϕ0, transfer volume, ΔVϕ(tr)0, for Gly and Gly-Gly from water to aqueous carbohydrate solutions, partial molar expansibility, Eϕ0, and hydration number, nH of solute have been calculated. The viscosity data have been analyzed by means of Jones-Dole equation to obtain A- and B-coefficients, free energy of activation of viscous flow per mole of solvent, Δμ10#, and solute, Δμ20#, enthalpy, ΔH0#, and entropy of activation, ΔS0# of viscous flow were evaluated. The behavior of these parameters has been interpreted in terms of solute-solute and solute-solvent interactions.

Nucleoside recognition by oligophenyl-based synthetic lectins

Synthetic lectins are molecules which bind carbohydrates in aqueous solution through preorganised arrangements of apolar and hydrogen bonding units. In principle, this approach may be used to complex other polar molecules in water, and we now report that two synthetic lectins are also effective for nucleoside substrates. The receptors consist of biphenyl- and terphenyl-based apolar surfaces linked by isophthalamide units to form tricyclic cages. Affinities of up to 2 × 104 M− 1 were measured by 1H NMR and confirmed by isothermal titration calorimetry. These systems show excellent selectivity for nucleosides versus anionic nucleotides, as well as good discrimination between different nucleobase residues.

Phthalocyanine conjugates with carbohydrates: synthesis and aggregation in aqueous solutions

The review is focused on the current state of the synthesis of glycosylated phthalocyanines and their precursors, mono-, di-, and tetraglycosyl phthalonitriles. Features of the synthesis of phthalogen conjugates with carbohydrates and the formation of related metal phthalocyanine complexes are discussed. The formation of aggregates of phthalocyanines in various media exerts a significant effect on the physicochemical and photochemical properties of phthalocyanine macrocycles, which is especially important in the practical use of phthalocyanines as photosensitizes. An aggregation of phthalocyanine conjugates in aqueous solutions strongly decreases the quantum yield of singlet oxygen, thus diminishing the biological activity of these compounds. Specific features of phthalocyanine conjugate aggregation with carbohydrates in aqueous solutions, organic solvents, and some their mixtures are analyzed.

Low-Temperature Carbonization and More Effective Degradation of Carbohydrates Induced by Ferric Trichloride

The present work is devoted to an attempt to understand the effect of an inorganic salt such as ferric trichloride (FeCl(3)) on the carbonization and degradation of carbohydrates such as β-cyclodextrin (CD), amylose, and cellulose. Our data revealed two important observations. First, the presence of FeCl(3) led to the occurrence of a low carbonization temperature of 373 K. This is a rare phenomenon, in which carbonization improvement is present even if a small amount of FeCl(3) was added. Experimental results had provided evidence for the fact that a redox process was started during the low-temperature carbonization of β-CD, causing the reduction of FeCl(3) to ferrous chloride (FeCl(2)) by carbon materials formed in the carbonization process in air. However, the reduction process of FeCl(3) produced the in situ composite nanomaterial of Fe-FeCl(2) combination in nitrogen. Second, a molecule-ion interaction emerged between FeCl(3) and the carbohydrates in aqueous solution, resulting in a more effective degradation of the carbohydrates. Moreover, our results demonstrated that FeCl(3) played the role of a catalyst during the degradation of the carbohydrates in solution. We believe that the current work not only has a significant potential application in disposal of waste carbohydrates but also could be helpful in many fields such as environmental protection, biomass energy development, and inorganic composite nanomaterials.

ChemInform Abstract: Aqueous Solutions of Facial Amphiphilic Carbohydrates as Sustainable Media for Organocatalyzed Direct Aldol Reactions.

AbstractOptimal reaction conditions are found for the diastereoselective aldol reaction of m‐nitrobenzaldehyde (I) with cyclohexanone (II) in an aqueous solution of ethyl β‐D‐fructopyranoside.

Aqueous solutions of facial amphiphilic carbohydrates as sustainable media for organocatalyzed direct aldol reactions

The organocatalyzed direct aldol reaction was efficiently performed in aqueous solutions of facial amphiphilic carbohydrates with high diastereoselectivity and yield. Such sustainable media in addition with the use of 2% catalyst loading paves the way for the development of original ecofriendly procedures through non-covalent induction.

Renewable gasoline from aqueous phase hydrodeoxygenation of aqueous sugar solutions prepared by hydrolysis of maple wood

In this paper we demonstrate an integrated process for the production of high octane gasoline from maple wood by hydrolysis of maple wood into aqueous carbohydrate solutions followed by aqueous phase hydrodeoxygenation of the sugar solutions. The aqueous carbohydrate solutions were prepared by both hydrolysis in hot water and hydrolysis with dilute acids (H2SO4, oxalic acid). The aqueous carbohydrate solutions were a mixture of xylose, water soluble hemicellulose oligomers, acetic acid, glucose, glucose oligomers, and probably some lignin polymers. Hydrolysis with hot water produced primarily hemicellulose oligomers whereas hydrolysis with acids produced mainly xylose and acetic acid. The hydrolysis co-product was a solid enriched in cellulose and lignin. The aqueous streams were hydrodeoxygenated by a two step catalytic process in which the first catalyst bed contained a Ru/C catalyst at 393 K and the second catalyst bed contained a Pt/zirconium phosphate (Pt/ZrP) catalyst at 518 K. The Ru/C catalyst was able to selectively hydrogenate xylose into xylitol but could not selectively hydrogenate the xylose oligomers. The two stage process was able to convert the aqueous carbohydrate streams derived from maple wood into gasoline range products with carbon yields of up to 57% and an estimated octane number of 96.5. No significant catalyst deactivation was observed indicating that the catalysts are very stable. The highest gasoline yield from this two stage process was obtained from the stream produced by acid hydrolysis of maple wood with 0.5 wt% oxalic acid at 433 K for 0.5 h. These results suggest that aqueous phase processing of sugars obtained by hydrolysis is a promising option for the production of fuels and chemicals from lignocellulosic biomass.

Catalytic conversion of biomass to biofuels

Biomass has received considerable attention as a sustainable feedstock that can replace diminishing fossil fuels for the production of energy, especially for the transportation sector. The overall strategy in the production of hydrocarbon fuels from biomass is (i) to reduce the substantial oxygen content of the parent feedstock to improve energy density and (ii) to create C–C bonds between biomass-derived intermediates to increase the molecular weight of the final hydrocarbon product. We begin this review with a brief overview of first-generation biofuels, specifically bioethanol and biodiesel. We consider the implications of utilizing starchy and triglyceride feedstocks from traditional food crops, and we provide an overview of second-generation technologies to process the major constituents of more abundant lignocellulosic biomass, such as thermochemical routes (gasification, pyrolysis, liquefaction) which directly process whole lignocellulose to upgradeable platforms (e.g., synthesis gas and bio-oil). The primary focus of this review is an overview of catalytic strategies to produce biofuels from aqueous solutions of carbohydrates, which are isolated through biomass pretreatment and hydrolysis. Although hydrolysis-based platforms are associated with higher upstream costs arising from pretreatment and hydrolysis, the aqueous solutions of biomass-derived compounds can be processed selectively to yield hydrocarbons with targeted molecular weights and structures. For example, sugars can be used as reforming feedstocks for the production of renewable hydrogen, or they can be dehydrated to yield furfurals or levulinic acid. For each of the platforms discussed, we have suggested relevant strategies for the formation of C–C bonds, such as aldol condensation of ketones and oligomerization of alkenes, to enable the production of gasoline, jet, and Diesel fuel range hydrocarbons. Finally, we address the importance of hydrogen in biorefining and discuss strategies for managing its consumption to ensure independence from fossil fuels.

A composite reaction engineering approach to drying of aqueous droplets containing sucrose, maltodextrin (DE6) and their mixtures

AbstractRecently, several studies have been published on the spray drying of sucrose and other low‐molecular‐weight sugars which are typically sticky materials. Sticky materials can not be processed under normal drying conditions and may require addition of high‐molecular‐weight carbohydrates such as maltodextrin. Predicting appropriate drying conditions are however difficult due to the unavailability of drying kinetics. In this article, we have formulated the drying kinetics model using the reaction engineering approach (REA) for the drying of aqueous sucrose and aqueous maltodextrin (DE6) droplets. The relative activation energy was empirically obtained based on experimental measurements. To model the drying of droplets containing both solutes (sucrose and maltodextrin), a new “composite” REA has been established and presented here for the first time. Results demonstrated that the composite REA forms a reliable framework to model the drying of aqueous solutions of pure carbohydrates and their mixtures. © 2008 American Institute of Chemical Engineers AIChE J, 2009

Glycosidic linkage conformation of methyl-α-mannopyranoside

We study the preferred conformation of the glycosidic linkage of methyl-alpha-mannopyranoside in the gas phase and in aqueous solution. Results obtained utilizing Car-Parrinello molecular dynamics (CPMD) simulations are compared to those obtained from classical molecular dynamics (MD) simulations. We describe classical simulations performed with various water potential functions to study the impact of the chosen water potential on the predicted conformational preference of the glycosidic linkage of the carbohydrate in aqueous solution. In agreement with our recent studies, we find that results obtained with CPMD simulations differ from those obtained from classical simulations. In particular, this study shows that the trans (t) orientation of the glycosidic linkage of methyl-alpha-mannopyranoside is preferred over its gauche anticlockwise (g-) orientation in aqueous solution. CPMD simulations indicate that this preference is due to intermolecular hydrogen bonding with surrounding water molecules, whereas no such information could be demonstrated by classical MD simulations. This study emphasizes the importance of ab initio MD simulations for studying the structural properties of carbohydrates in aqueous solution.