LC-DAD-ESI-MS Characterization of Carbohydrates Using a New Labeling Reagent

A novel labeling reagent 1-(2-naphthyl)-3-methyl-5-pyrazolone (NMP) coupling to liquid chromatography with electrospray ionization mass spectrometry for the detection of carbohydrates from the derivatized rape bee pollen samples is reported. Carbohydrates are derivatized to their bis-NMP-labeled derivatives. Derivatives showed an intense protonated molecular ion at m/z [M+H]⁺ in positive-ion detection mode. The mass-to-charge ratios of characteristic fragment ions at m/z 473.0 could be used for the accurately qualitative analysis of carbohydrates. This characteristic fragment ion is from the cleavage of C2–C3 bond in carbohydrate chain giving the specific fragment ions at m/z [MH-C _m H_2m+1O _m -H₂O]⁺ for pentose, hexose and glyceraldehydes and at m/z [MH-C _m H_2m-1O _m+1-H₂O]⁺ for alduronic acids such as galacturonic acid and glucuronic acid (m = n ? 2, n is carbon number of carbohydrate). No interferences for all aliphatic and aromatic aldehydes presented in natural environmental samples were observed due to the highly specific parent mass-to-charge ratio and the characteristic fragment ions. The method, in conjunction with a gradient elution, offered a baseline resolution of carbohydrate derivatives on a reversed-phase Hypersil ODS-2 column. The carbohydrates such as mannose, galacturonic acid, glucuronic acid, rhamnose, glucose, galactose, xylose, arabinose and fucose can successfully be detected.     

超高效液相色谱法测定卷烟烟丝中7种水溶性糖含量

以ACQUITY UPLC BEH Amide柱为分析柱,乙腈－0．2％三乙胺一水作为流动相,建立了超高效液相色谱－蒸发光散射检测器测定卷烟烟丝中鼠李糖、木糖、果糖、甘露糖、葡萄糖、蔗糖、麦芽糖7种水溶性糖的分析方法。7种水溶性糖回归方程的线性相关系数均大于0．999,检出限为0．56～1．11μg／mL。7种水溶糖的回收率在90．43％106．41％之间,相对标准偏差为1．66％－4．35％仰：6）。该方法灵敏度、准确度高,稳定性好,可用于大批量卷烟烟丝中水溶性糖含量的测定。     

Synchronous Extraction,Antioxidant Activity Evaluation,and Composition Analysis of Carbohydrates and Polyphenols Present in Artichoke Bud

This study investigated the optimization of ultrasonic-assisted aqueous two-phase synchronous extraction of carbohydrates and polyphenols present in artichoke bud, evaluated their antioxidant activities in vitro, and analyzed the composition of carbohydrates and polyphenols by high-performance liquid chromatography (HPLC). The powder mass, ultrasonic time, ammonium sulfate concentration, and alcohol–water ratio were considered the influencing factors based on the single-factor experiment results, and a dual-response surface model was designed to optimize the synchronous extraction process to extract carbohydrates and polyphenols. The antioxidant activity was evaluated by measuring the scavenging capacity of ABTS⁺· and DPPH· and the reducing capacity of Fe³⁺. The optimal process conditions in this study were as follows: the powder mass of 1.4 g, ammonium sulfate concentration of 0.34 g/mL, alcohol–water ratio of 0.4, and ultrasonic time of 43 min. The polyphenol content in artichoke bud was 5.32 ± 0.13 mg/g, and the polysaccharide content was 74.78 ± 0.11 mg/g. An experiment on in vitro antioxidant activity showed that both carbohydrates and polyphenols had strong antioxidant activities, and the antioxidant activity of polyphenols was stronger than that of carbohydrates. The HPLC analysis revealed that the carbohydrates in artichoke bud were mannose, rhamnose, glucuronic acid, galacturonic acid, glucose, galactose, and arabinose, and the molar ratio was 10.77:25.22:2.37:15.74:125.39:48.62:34.70. The polyphenols comprised chlorogenic acid, 4-dicaffeoylquinic acid, caffeic acid, 1,3-dicaffeoylqunic acid, isochlorogenic acid B, isochlorogenic acid A, cynarin, and isochlorogenic acid C, and the contents were 0.503, 0.029, 0.022, 0.017, 0.008, 0.162, 1.621, 0.030 mg/g, respectively. This study also showed that the carbohydrates and polyphenols in artichoke bud could be important natural antioxidants, and the composition analysis of HPLC provided directions for their future research. Carbohydrates and polyphenols in artichoke buds can be separated and enriched using the optimized process technology, and it is an effective means of extracting ingredients from plants.     

Raman Spectra of Carbohydrates

The Raman spectra of 13 different carbohydrates are investigated by a laser Raman spectrometer. It is found the C—H stretching vibrations around 3000 cm⁻¹ is the best region for qualitative analysis of these compounds. All compounds show an O—H stretching vibration around 3370 cm⁻¹ which was not mentioned by earlier works. Excessive background noise appears in many spectra, probably due to their amorphous stuctures.     

An Aggregation‐induced Emission Probe Based on Host–Guest Inclusion Composed of the Tetraphenylethylene Motif and γ‐Cyclodextrin for the Detection of α‐Amylase

α‐Amylase, an essential biomarker in pancreas related diseases and perform a major role in carbohydrates metabolism. Hence, monitoring the dynamic changes of α‐amylase is crucial for better clinical diagnosis of diseases. However, the existing methods are suffered from low sensitivity, time consumption and indirect assay with aid of tool enzyme or inhibitor of competitive substrates, the rapid and non‐destructive sensing of α‐amylase in biological samples was highly desired. In this work, a very simple tetraphenylethylene motif and γ‐cyclodextrin based supramolecular fluometric sensing system was firstly established. This system has no emission signal in aqueous media for the freely rotation of phenyl rings in the cavity of γ‐cyclodextrin, but the AIE residues can be released in to water after the α‐amylase hydrolysing γ‐cyclodextrin, then turn on the fluorescence. In this system, the detection limit is calculated to be 0.007 U mL^?1 in MES buffer with a linear range of 0–0.35 U mL^?1, having excellent selectivity to α‐amylase compared to other proteins. At last, our probe can be applied to the quantitative analysis of α‐amylase in human serum, showing potential in point of care testing.     

Synthesis of Fluorinated Carbohydrates

The similarities in bond length and polarization between C-F and C-OH, as well as the altered hydrogen-bonding properties present in carbohydrates bearing a fluorine atom in place of an hydroxyl group can be exploited in place of an hydroxyl group can be exploited in biochemical investigations (enzyme-carbohydrate interactions, Lectin-carbohydrate affinities, antiobody-carbohydrate binding, etc.). ^1–5 In addition, the different chemistries exhibited by the flourinated carbohydrates have made them important reagents in both metabolic studies and disease diagnosis such as the use of 2-deoxy-2-[18f]-D-fluoroglucose in positron emission tomography. 6,7 Becasue of their widespread utlity, the synthesis of fluorinated carbohydrates is of importance. However, the Introduction of fluorine into a carbohydrate moiety can be an arduous task because of (1) the protection and deprotection steps required to set up the desired hydroxyl group for the introduction of fluoride, (2) the low nucleophilicity fo fluoride ion, and (3) fluoride ion catalyzed elimination reactions. 8,9 The search for Milder and more selective methods for the introduction of fluorine into Carbohydrates has continued at a rapid pace and it is appropriate to review som of the recent results.     

Electrodeposition of Copper in Presence of Carbohydrates

The rates of electrodeposition of copper plates were determined by measuring cathodic limiting current in the absence and in the presence of carbohydrates (glucose, fructose, mannose, sucrose, lactose, and maltose). It is found that the rate of electrodeposition decreases in the presence of organic additives by an amount ranging from 1.89% to 35.85%, and depending on the types of additives and its concentrations. Our investigation of adsorption isotherm indicates that the inhibition fits both the Langmuir adsorption isotherm and Flory-Huggins adsorption isotherm; we found that the rate of electrodeposition decreases by increasing height and increasing CuSO₄ concentrations. Thermodynamic parameters are given and show that electrodeposition process is diffusion controlled. The rate of deposition and its equations are represented:

• Sh = 0.099Re^0.715 Sc^0.33 for glucose with average deviation: ±0.158%

• Sh = 0.097Re^0.715 Sc^0.33 for fructose with average deviation: ±0.058%

• Sh = 0.099Re^0.715 Sc^0.33 for mannose with average deviation: ±0.108%

• Sh = 0.098Re^0.713 Sc^0.33 for sucrose with average deviation: ±0.003%

• Sh = 0.099Re^0.714 Sc^0.33 for lactose with average deviation: ±0.018%

• Sh = 0.099Re^0.713 Sc^0.33 for maltose with average deviation: ±0.097%.

     

Activity of α‐Chymotrypsin in Cationic and Nonionic Micellar Media: Ultraviolet and Fluorescence Spectroscopic Approach

α‐Chymotrypsin (α‐CT) activity was measured in aqueous buffer with the following alkyltriphenylphosphonium bromide surfactants in the series cetyl, tetradecyl, and dodecyl as a tail length. For the sake of comparison with mixed micellar investigation on activity of α‐CT, cationic cetyltriphenylphosphonium bromide (CTPB) and nonionic surfactant Triton X‐100, Brij‐56, Brij‐35, Tween 20, and Igepal Co‐210 have been used. The p‐nitrophenyl acetate (PNPA) hydrolysis rate was determined at the surfactant concentration of both cationic and mixed micellar systems by a UV–vis spectrophotometer. The catalytic reaction follows the Michaelis–Menten mechanism, and the catalytic efficiency (k_cat/K_M) was evaluated for both homogeneous and mixed‐micellar media. The maximum catalytic efficiency was observed at 5 mM concentration of CTPB, but the highest catalytic efficiency, 572 M^?1 s^?1, was measured in the presence of mixed micellar (7.5 mM CTPB + 2.5 mM Tween‐20). The fluorescence (FL) spectra showed the differences of α‐CT conformations in the presence of cationic surfactants. The FL results suggest that the influence of cationic surfactant on proteolysis arises from the interaction with the α‐CT. The binding constant, k_sv, of α‐CT with cationic aggregates was determined in the buffer using the Stern–Volmer equation by the fluorescence spectroscopic approach.     

CE Determination of Carbohydrates Using a Dipeptide as Separation Electrolyte

The influence of aminoacid and peptide type buffers as the separation electrolyte to the resolution of underivatized neutral carbohydrates in capillary electrophoresis was investigated. With the use of plain glycylglycine as the background electrolyte, a noticeable improvement in the resolution of carbohydrates was observed. Without any additive, 50 mmol L⁻¹ glycylglycine electrolyte at pH 12 provides both the fast separation and indirect detection of sugars. The electrophoretic mobilities of 16 sugars were calculated at this buffer and the combinations of 10 sugars were simultaneously detected. The method was applied to the determination of sucrose, glucose, and fructose in commercial juice samples.     

Communication: Use of an α-Haloether for the Acetonation of Carbohydrates.

Cyclic acetals are important and commonly used protective groups for polyhydroxy compounds, e.g., carbohydrates. The formation of cyclic acetals has been thoroughly investigated and much is now known about the factors that influence the outcome of these reactions. Several reviews have been written on this subject.^1,2,3     

New Method for Carbohydrates Determination in Sugarcane Bagasse by HPAEC‐RPAD Using Glassy Carbon Electrode Modified with Carbon Nanotubes and Nickel Nanoparticles

Second generation ethanol can be produced from carbohydrates released from both sugarcane bagasse cell wall and sugarcane straw. The development of new method for the analysis of carbohydrates is, in this sense, seen as extremely relevant in the area of bioenergy. Based on the above considerations, the scope of this work encompasses the identification and quantification of carbohydrates composition in sugarcane bagasse without the need of sample derivatization, developing a novel analytical method using a glassy carbon electrode modified with multi‐walled carbon nanotubes containing nickel oxyhydroxide nanoparticles (GCE/MWCNT/NiOOH) and applying the modified electrode as a detector in HPAEC (High Performance Anion‐Exchange Chromatography) with reverse pulsed amperometric detection (RPAD) towards the determination of arabinose, galactose, glucose and xylose in hydrolyzed sugarcane bagasse. The carbohydrates concentrations determined in the hydrolyzed sugarcane bagasse were 6.1×10⁻⁴ mol L⁻¹, 1.0×10⁻² mol L⁻¹ and 2.8×10⁻³ mol L⁻¹ for arabinose, glucose, and xylose respectively. Our results showed that the present method is, in essence, attractive for analysis in the course of the production process of second generation ethanol production in that it does not require sample derivatization, has rapid run time, satisfactory separation, and can be used for the detection of carbohydrates without the interference of other electroactive species.     

Novel Selectivity in Carbohydrate Reactions III. Selective Deprotection of p-Methoxybenzyl (PMBn) Ethers of Carbohydrates by Tin(IV)Chloride 1

In multi-step syntheses involving polyhydroxylated natural products such as carbohydrates that are variously derivatized at different positions, orthogonal removal of one or another type of protecting group is of vital importance. Discrimination of different classes of protecting groups, such as ethers, esters, etc., is often possible with a great degree of success, as for example, selective removal of an 0-acetyl by catalytic transesterification in the presence of an ether protecting group, or hydrogenolytic removal of a benzyl ether protection in the presence of ester groups such as acetates.³ Differentiation of different types of protecting groups within a given class of protecting groups has also been similarly achieved with great success, as for example, hydrogenolytic removal of a benzyl ether group in the presence of a methyl ether.³ However, the situation becomes more challenging when the same protecting group is used to mask more than one position in a polyfunctional molecule and their preferential partial deprotection is required. Selective unmaslung of one or more of such protecting groups has been achieved in some cases.4 Of particular interest to us was the regioselective deprotection of the 2-0-benzyl group of per- 0-benzylated 1,6-anhydromannopyranose mediated by SnC14 (1) and Tic14 (2). Considering the greater susceptibility of p-methoxybenzyl (PMBn) ethers to Lewis acid catalysts5 and the complexation of benzyl ethers with 14b and 24b16 we decided to investigate the action of 1 on PMBn ethers of some carbohydrates, We expected the methoxy substituent on the phenyl group in the PMBn moiety to enhance complexation with 1, possibly resulting in a facile reaction under mild conditions. Since 1 is a strong Lewis acid, the need to use chlorotrimethylsilane and anisole, as in the tin(I1)chloride- chlorotrimethylsilane-anisole system for deprotection of PMBn ethers, can be eliminated. Moreover, the complex formation in the case of 1 presents possibilities for unusual regioselectivity in partial de-0-p-methoxybenzylation reactions, a problem that has not been addressed in reports on the oxidative cleavage of PMBn ethers by 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ)⁷ ceric ammonium nitrate (CAN),⁸ N-bromosuccinimide (NBS)⁸ or bromine⁸.

     

Desulfation of Sulfated Carbohydrates Mediated by Silylating Reagents

Abstract

Efficient methods of desulfation are often required in carbohydrate chemistry and biochemistry. In addition to conventional desulfation methods,^1,2 we recently reported a novel desulfation method employing a silylating reagent, N,O-bis(trimethylsilyl)-acetamide.^3,4 With this reagent, the 6-O-sulfoxyl groups of the sugar moiety are regioselectively removed and newly formed hydroxyl groups are further converted by silylation into trimethylsilyloxyl groups. The desulfated carbohydrates are easily recovered after desilylation with water or aqueous methanol. Although the mechanism for this reaction remains unclear, silylating reagents can be considered as potential reagents for desulfation reaction. In the present paper, we examined various silylating reagents to find effective and new desulfation reagents for carbohydrate sulfates.     

Regioselective Substitutions of Unsymmetrical 1,2-Diols using Dioxaphospholanes: Applications to Carbohydrates

Abstract

For several years, the method employing 1,3,2λ⁵dioxaphospholanes to effect regioselective substitution of unsymmetrical 1,2-diols has been investigated.^[1] As carbohydrates are an abundant source of diols, this study has been extended to the use of 1,2-O-isopropylidene- D-ghCOfuranOSe 1. We have synthesized a single dioxaphospholane 2 and subsequently treated it with trimethylsilyltriflate to form oxyphosphonium ions 3 and 4.     

Synthesis of Methylene Tetrahydrofurane-Fused Carbohydrates

A reliable method is disclosed to introduce a fused methylene tetrahydrofuran ring into carbohydrates. The resulting bicyclic saccharides can be used as scaffolds in medicinal chemistry and drug design. In addition, the enol ether functionality serves as a handle that enables modification in biological systems via photoclick chemistry. The approach is based on the regioselective oxidation of the C-3 hydroxy group in gluco-configured pyranosides, followed by stereoselective indium-mediated allylation. The ring formation is induced by an iodocyclization reaction with a neighboring hydroxy group. Subsequent dehydrohalogenation affords the desired methylene-tetrahydrofuran-containing carbohydrates.     

Apparent Molar Volume and Viscosity Studies on Some Carbohydrates in Solutions

 The apparent molar volume (φ_v) and viscosity (η) of L(+)-arabinose, D(+)-galactose, D(−)-fructose, D(+)-glucose, sucrose, lactose, and maltose in water and in 0.1% and 0.3% water-Surf Excel solutions were measured as a function of solute concentrations at 308.15, 313.15, and 323.15 K, respectively. The apparent molar volume (φ_v) of the carbohydrates was found to be a linear function of the concentration. From a φ_v versus molality (b) plot, the apparent molar volume at infinite dilution (), which is practically equal to the partial molar volume at infinite dilutions () of these substances was determined. The viscosity coefficients B and D for the carbohydrates were calculated on the basis of the viscosity of the solutions and the solvent using the Jones-Dole equation. The activation free energy for viscous flow (ΔG ^≠) of the solutions was also calculated using the Eyring equation. The carbohydrates showed structure making behaviour both in water and in water-Surf Excel solutions. When water-Surf Excel solutions and pure water solutions containing carbohydrate molecules are compared, the former were found to be more structured. The behaviour of these solutes in water and in water-Surf Excel solution systems is discussed in the light of solute–solvent interactions.     

Energy/Hole Transfer Phenomena in Hybrid α‐Sexithiophene (α‐STH) Nanoparticle–CdTe Quantum‐Dot Nanocomposites

Considerable attention has been paid to hybrid organic–inorganic nanocomposites for designing new optical materials. Herein, we demonstrate the energy and hole transfer of hybrid hole‐transporting α‐sexithiophene (α‐STH) nanoparticle–CdTe quantum dot (QD) nanocomposites using steady‐state and time‐resolved spectroscopy. Absorption and photoluminescence studies confirm the loss of planarity of the α‐sexithiophene molecule due to the formation of polymer nanoparticles. Upon photoexcitation at 370 nm, a nonradiative energy transfer (73 %) occurs from the hole‐transporting α‐STH nanoparticles to the CdTe nanoparticles with a rate of energy transfer of 6.13×10⁹ s^?1. However, photoluminescence quenching of the CdTe QDs in the presence of the hole‐transporting α‐STH nanoparticles is observed at 490 nm excitation, which is due to both static‐quenching and hole‐transfer‐based dynamic‐quenching phenomena. The calculated hole‐transporting rate is 7.13×10⁷ s^?1 in the presence of 42×10^?8 M α‐STH nanoparticles. Our findings suggest that the interest in α‐sexithiophene (α‐STH) nanoparticle–CdTe QD hybrid nanocomposites might grow in the coming years because of various potential applications, such as solar cells, optoelectronic devices, and so on.     

Apparent Molar Volume and Viscosity Studies on Some Carbohydrates in Solutions

Summary.  The apparent molar volume (φ_v) and viscosity (η) of L(+)-arabinose, D(+)-galactose, D(−)-fructose, D(+)-glucose, sucrose, lactose, and maltose in water and in 0.1% and 0.3% water-Surf Excel solutions were measured as a function of solute concentrations at 308.15, 313.15, and 323.15 K, respectively. The apparent molar volume (φ_v) of the carbohydrates was found to be a linear function of the concentration. From a φ_v versus molality (b) plot, the apparent molar volume at infinite dilution (), which is practically equal to the partial molar volume at infinite dilutions () of these substances was determined. The viscosity coefficients B and D for the carbohydrates were calculated on the basis of the viscosity of the solutions and the solvent using the Jones-Dole equation. The activation free energy for viscous flow (ΔG ^≠) of the solutions was also calculated using the Eyring equation. The carbohydrates showed structure making behaviour both in water and in water-Surf Excel solutions. When water-Surf Excel solutions and pure water solutions containing carbohydrate molecules are compared, the former were found to be more structured. The behaviour of these solutes in water and in water-Surf Excel solution systems is discussed in the light of solute–solvent interactions. Corresponding author. E-mail: chemistry_ru@yahoo.com Received March 19, 2002; accepted (revised) July 31, 2002 Published online February 24, 2003     

Isomerization and Cleavage of Allyl Ethers of Carbohydrates by Trans- [Pd(NH3)2Cl2

Allyl ethers are widely used for the “temporary” protection of hydroxy groups in carbohydrates. The allyl group is conveniently removed by isomerization and subsequent cleavage of the labile prop-1-enyl group.² The rearrangement of allyl ethers to prop-1-enyl ethers is readily achieved by treatment with potassium t-butoxide in dimethyl sulfoxide, using tris(tripheny1phosphine)rhodium chloride, palladium on activated charcoal and by an ene reaction with diethylazodicarboxylate. acidic conditions, ozonolysis followed by alkaline hydrolysis, reaction with alkaline permanganate solution, or treatment with mercuric chloride in the presence of mercuric oxide. The isomerization of allyl ethers to prop-1-enyl ethers can also be carried out in the presence of palladium on carbon or complex bis(benzonitrile)palladium(11) chloride. Bruce and Roshan-Ali' showed that derivatives of allyl phenyl ether are smoothly cleaved by this complex. This has made it possible to remove the protecting group in a one-pot operation. We have now investigated the effect of palladium catalysts on the isomerization and cleavage of the allyl group in carbohydrate derivatives.     

Enantioselective Synthesis of α‐Hydroxy Amides and β‐Amino Alcohols from α‐Keto Amides

Synthesis of enantiomerically enriched α‐hydroxy amides and β‐amino alcohols has been accomplished by enantioselective reduction of α‐keto amides with hydrosilanes. A series of α‐keto amides were reduced in the presence of chiral Cu^II/(S)‐DTBM‐SEGPHOS catalyst to give the corresponding optically active α‐hydroxy amides with excellent enantioselectivities by using (EtO)₃SiH as a reducing agent. Furthermore, a one‐pot complete reduction of both ketone and amide groups of α‐keto amides has been achieved using the same chiral copper catalyst followed by tetra‐n‐butylammonium fluoride (TBAF) catalyst in presence of (EtO)₃SiH to afford the corresponding chiral β‐amino alcohol derivatives.