Carbohydrate–Carbohydrate Recognition between LewisX Glycoconjugates

The strong dependence of the NOE on the molecular mobility rendered the weak bond of a homotypical carbohydrate–carbohydrate recognition detectable in a simplified model system. The membrane-bound Le^X trisaccharide 1 , which functions as a receptor, transiently binds the dissolved Le^X trisaccharide 2 , thus slowing down its rotational diffusion. This kind of molecular recognition plays an important part in cell adhesion.     

The Fundamentals of Real‐Time Surface Plasmon Resonance/Electrogenerated Chemiluminescence

We report the integration of surface plasmon resonance (SPR), cyclic voltammetry and electrochemiluminescence (ECL) responses to survey the interfacial adsorption and energy transfer processes involved in ECL on a plasmonic substrate. It was observed that a Tween 80/tripropylamine nonionic layer formed on the gold electrode of the SPR sensor, while enhancing the ECL emission process, affects the electron transfer process to the luminophore, Ru(bpy)₃²⁺, which in turn has an impact on the plasmon resonance. Concomitantly, the surface plasmon modulated the ECL intensity, which decreased by about 40 %, due to an interaction between the excited state of Ru(bpy)₃²⁺ and the plasmon. This occurred only when the plasmon was excited, demonstrating that the optically excited surface plasmon leads to lower plasmon‐mediated luminescence and that the plasmon interacts with the excited state of Ru(bpy)₃²⁺ within a very thin layer.     

Synthesis of LeX and LeY Oligosaccharides with Azido-Type Spacer-Arms. Comparison of 3- and 4-Methoxybenzyl Groups as Key Temporary Protective Groups

Abstract

5-Azido-3-oxa-l-pentanol was prepared from 2-(2-chloroethoxy)ethanol and used as a spacer in the chemical synthesis of the trisaccharide β-D-Gal-(1→4)-[α-L-Fuc-(1→3)]-GlcNAc and the tetrasaccharide α-L-Fuc-α-(1→2)-β-D-Gal-(1→4)-[α-L-Fuc-(1→3)]-GlcNAc that represent the epitopes defining the human blood groups Le^x and Le^y. The classical 4-methoxybenzyl group and the remarably acid-stable 3-methoxybenzyl group were compared as temporary protective groups for position 3 at the glucosamine unit to circumvent the problems associated with the simultaneous presence of allyl and azido groups. The resulting oligosaccharides were coupled to proteins with high efficiency.

     

Inhibition binding studies of glycodendrimer/lectin interactions using surface plasmon resonance

Understanding protein/carbohydrate interactions is essential for elucidating biological pathways and cellular mechanisms but is often difficult due to the prevalence of multivalent interactions. Here, we evaluate the multivalent glycodendrimer framework as a means to describe the inhibition potency of multivalent mannose-functionalized dendrimers using surface plasmon resonance (SPR). Using highly robust, mannose-functionalized dithiol self-assembled monolayers on gold surfaces, we found that glycodendrimers were efficient inhibitors of protein/carbohydrate interactions. IC₅₀ values ranging from 260 nM to 13 nM were obtained for mannose-functionalized dendrimers with Concanavalin A.     

Selectin Receptors 4: Synthesis of Tetrasaccharides Sialyl Lewis A and Sialyl Lewis X Containing A Spacer Group1,2

ABSTRACT

Synthesis of two isomeric tetrasaccharides, namely Neu5Acα(2→3)Galβ(1→3)[Fucα(1→4)GlcNAcβ (sLe^a) and Neu5Acα(2→3)Galβ(1→4)[Fucα(1→3)]GlcNAcβ (sLe^x) as 3-aminopropyl glycosides is described. Preparation of these compounds was performed by sialylation of selectively protected trisaccharides Le^a and Le^x which contain three unsubstituted OH groups at positions 2, 3 and 4 of Gal residue. Glycosylation of Le^x trisaccharide with ethylthio sialoside under promotion by NIS and TfOH in acetonitrile was effective and regio- and stereoselective to give sLe^x derivative in 81% yield. In contrast, sialylation of the Lc^a acceptor was accompanied by a variety of undesirable by-processes, namely. N-thioethylation of the GlcNAc residue, β-sialylation, and lactonisation. In order to improve the yield of sLc^a tetrasaccharide the glycosylation of Le^a acceptor by sialyl donors of ethyl and phenyl thioglycoside (promoted by NIS-TfOH or NBS-Bu₄NBr), xanthate (promotion by NIS-TfOH mixture or MeOTf) and phosphite (promoted by TMSOTf) types was also studied. Among the reactions investigated the glycosylation by phenyl thioglycoside sialoside promoted by NIS-TfOH gives the best yield (39%) of sLe^a tetrasaccharide product.     

Study of the Interaction of Methylene Violet with Calf Thymus DNA Using an SPR-Based DNA Sensor

Electrochemical and surface plasmon resonance technologies were combined to detect binding of low-molecular-weight compounds to DNA. First, zirconia thin films were electrochemically deposited onto bare gold electrodes. Second, calf thymus DNA was attached onto the zirconia thin films. Finally, the interaction of methylene violet with the DNA-modified surface was tested. The binding isotherm gave a K_D of 2.21 × 10^?5 M. Fluorescence quenching experiments were performed to confirm the interaction. Regenerating surfaces with 1 mM NaOH provided reusable surfaces. This study provides a generic platform which can be tailored for the study of interactions of small molecules with DNA.     

Luminescence Resonance Energy Transfer Sensors Based on the Assemblies of Oppositely Charged Lanthanide/Gold Nanoparticles in Aqueous Solution

This work demonstrates luminescence resonance energy transfer (LRET) sensors based on lanthanide‐doped nanoparticles as donors (D) and gold nanoparticles as acceptors (A), combined through electrostatic interactions between the oppositely charged nanoparticles. Negatively charged lanthanide‐doped nanoparticles, YVO₄:Eu and LaPO₄:Ce,Tb, with high luminescence quantum yield and good water‐solubility, are synthesized through a polymer‐assisted hydrothermal method. Positively charged polyhedral and spherical gold nanoparticles exhibit surface plasmon resonance (SPR) bands centered at 623 and 535 nm, respectively. These bands overlap well with the emission of the Eu³⁺ and Tb³⁺ ions within the lanthanide nanoparticles. Herein, the gold nanoparticles are synthesized through a seed‐mediated cetyltrimethylammonium bromide (CTAB)‐assisted method. The assemblies of the oppositely charged donors and acceptors are developed into LRET‐based sensors exhibiting a donor quenching efficiency close to 100 %.     

Plasmon waveguide resonance for sensing glycan–lectin interactions

Carbohydrate-modified interfaces have been shown to be valuable tools for the study of protein–glycan recognition events. Label-free approache such as plasmonic based techniques are particularly attractive. This paper describes a new analytical platform for the sensitive and selective screening of carbohydrate–lectin interactions using plasmon waveguide resonance. Planar optical waveguides (POW), consisting of glass prisms coated with silver (50 nm) and silica (460 nm) layers were derivatized with mannose or lactose moieties. The specific association of the resulting interface with selected lectins was assessed by following the changes in its plasmonic response. The immobilization strategy investigated in this work is based on the formation of a covalent bond between propargyl-functionalized glycans and surface-linked azide groups via a Cu(I) “click” chemistry. Optimization of the surface architecture through the introduction of an oligo(ethylene glycol) spacer between the plasmonic surface and the glycan ligands provided an interface which allowed screening of glycan–lectin interactions in a highly selective manner. The limit of detection (LOD) of this method for this particular application was found to be in the subnanomolar range (0.5 nM), showing it to constitute a promising analytical platform for future development and use in a pharmaceutical or biomedical setting.     

Colorimetric and fluorometric chemosensors for selective signaling toward Ca and Mg by aza-crown ether acridinedione-functionalized gold nanoparticles

The aza-crown ether acridinedione-functionalized gold nanoparticles (ACEADD-GNPs) 6 have been synthesized and investigated as a fluorescent chemosensor for metal ions. A blue shift along with an intensity enhancement of emission and color change are observed in the presence of both Ca²⁺ and Mg²⁺ ions. The enhanced fluorescence intensity is attributed to the photoinduced electron transfer (PET) suppression through space and color change of the suspension from red to blue due to shifted surface plasmon resonance (SPR) with aggregation of nanoparticles by the sandwich complexation.     

Synthesis of Lewis a and Lewis X Pentasaccharides Based on N-Trichloroethoxycarbonyl Protection 1

Abstract

Thexyldimethylsilyl 4,6-O-benzylidene-2-deoxy-2-trichloroethoxycarbonylamino-β-D- glucopyranoside (4), having the 3-hydroxy group unprotected, is a versatile starting material for the synthesis of glucosamine containing oligosaccharides. Thus, reaction with galactosyl donor 5 or fucosyl donor 6 afforded the desired β(1-3)- and α(1-3)-linked disaccharides 7 and 8, respectively, in high yields. Reductive opening of the benzylidene moieties in 7 and 8 gave access to the 4-hydroxy groups in 9 and 10. Ensuing fucosylation of 9 or galactosylation of 10 led to Lewis A (Le^a) and Lewis X (Le^x) trisaccharide building blocks 13 and 14, respectively. Their transformation into glycosyl donors 19 and 20 and subsequent reaction with 3b-O-unprotected lactose derivative 23 as acceptor furnished the Le^a? and Le^x pentasaccharide precursors 24 and 25. Exchange of the N-trichloroethoxycarbonyl group for an N-acetyl group and removal of the O-benzyl and O-acetyl protective groups afforded the desired Le^a? and Le^x? pentasaccharides 1 and 2.

     

Evaluation of the abilities of ��-cyclodextrin to form complexes by surface plasmon resonance with a Biacore? system

Although phase-solubility studies have often been used to evaluate the interaction of cyclodextrins (CDs) with various drugs, hundreds of milligrams of both CD and drug are required to prepare a phase diagram. A method that would require considerably less material for evaluating complex formation between a CD and guest compound is therefore needed. We previously reported the detection of the interactions between ??-CD and various drugs using a Biacore^® system. In this study, we succeeded in immobilizing 6-monodeoxy-6-monoamino-??-CD on the gold surface of a sensor chip and in detecting the interactions between the immobilized ??-CD and various drugs. The interaction processes were kinetically analyzed using Biacore^®. The surface plasmon resonance sensorgrams indicated that the association and dissociation rates of the interactions between ??-CD and drugs were faster than those between ??-CD and drugs. Although the association constants calculated from the sensorgrams were smaller than those calculated from phase-solubility studies, good correlation was shown between these data.     

基于自组装多层膜的葡萄糖表面等离子体共振传感器

利用伴刀豆球蛋白A和糖类的特异性相互作用, 研制了葡萄糖表面等离子体共振传感器. 传感器的敏感膜是构建于金膜表面的伴刀豆球蛋白A/葡聚糖自组装多层膜. 在葡萄糖的存在下, 该自组装多层膜被分解, 引起表面等离子体共振信号的显著变化, 信号变化的大小与葡萄糖的浓度相关. 结果表明, 利用该传感器可以选择性地检测0.1～50 mmol•L^－1浓度范围内的葡萄糖, 且敏感膜可以多次再生使用.     

Enhanced plasmon resonance light scattering signals of colloidal gold resulted from its interactions with organic small molecules using captopril as an example

Gold nanoparticles are known for their plasmon resonance absorption (PRA) depending on their size. Our this investigation shows that plasma resonance light scattering (PRLS) signals in the corresponding PRA region could be measured using a common spectrofluorometer, and be enhanced when aggregation of gold nanoparticles occurs due to their interaction with organic small molecules (OSMs). Using captopril (Cap) as an example, we investigated the interactions of gold nanoparticles with OSMs in order to propose a general method of OSMs such as typical clinic organic drugs. In aqueous medium of pH 2.09, there are about 2.2 × 10³ Cap molecules covalently binding to the surface of a 10-nm diameter gold nanoparticle through the thiol functional group of Cap, and thus forms a core-shell assembly of [(Au)₃₁₀₀₀]@[(Cap)₂₂₀₀], displaying strong enhanced PRLS signals in the PRA region of gold colloid. The PRLS intensities characterized at 553.0 nm were found to be proportional to the concentration of Cap over the range of 0.1-1.7 mg L⁻¹ with the determination limit (3σ) of 32.0 μg L⁻¹. With that, Cap in pharmaceutical preparations could be determined with the recovery of 97.0-104.5% and R.S.D. of less than 2.4%.     

Surface plasmon resonance study on the interaction between the fructose and phenylboronic acid monolayer

Phenylboronic acid derivatives were synthesized and their self-assembled monolayers (SAMs) were formed on a gold surface. The interaction between fructose and phenylboronic acid monolayers was evaluated using surface plasmon resonance (SPR). These phenylboronic acid monolayers showed good sensitivity to fructose at a low concentration range and the resonance angle shifts increased in accordance with the alkyl chain length.     

Synthesis and molecular recognition studies of the HNK-1 trisaccharide and related oligosaccharides. The specificity of monoclonal anti-HNK-1 antibodies as assessed by surface plasmon resonance and STD NMR

The human natural killer cell carbohydrate, HNK-1, plays function-conducive roles in peripheral nerve regeneration and synaptic plasticity. It is also the target of autoantibodies in polyneuropathies. It is thus important to synthesize structurally related HNK-1 carbohydrates for optimizing its function-conducive roles, and for diagnosis and neutralization of autoantibodies in the fatal Guillain-Barré syndrome. As a first step toward these goals, we have synthesized several HNK-1 carbohydrate derivatives to assess the specificity of monoclonal HNK-1 antibodies from rodents: 2-aminoethyl glycosides of selectively O-sulfated trisaccharide corresponding to the HNK-1 antigen, its nonsulfated analogue, and modified structures containing 3-O-fucosyl or 6-O-sulfo substituents in the N-acetylglucosamine residues. These were converted, together with several related oligosaccharides, into biotin-tagged probes to analyze the precise carbohydrate specificity of two anti-HNK-1 antibodies by surface plasmon resonance that revealed a crucial role of the glucuronic acid in antibody binding. The contribution of the different oligosaccharide moieties in the interaction was shown by saturation transfer difference (STD) NMR of the complex consisting of the HNK-1 pentasaccharide and the HNK-1 412 antibody.     

Surface plasmon resonance imaging studies of protein-carbohydrate interactions

Carbohydrate arrays fabricated on gold films were used to study carbohydrate-protein interactions with surface plasmon resonance (SPR) imaging. An immobilization scheme consisting of the formation of a surface disulfide bond was used to attach thiol-modified carbohydrates onto gold films and to fabricate carbohydrate arrays. The carbohydrate attachment steps were characterized using polarization modulation Fourier transform infrared reflection absorption spectroscopy; and poly(dimethylsiloxane) microchannels were used to immobilize probe compounds at discrete locations on a gold film. The binding of the carbohydrate-binding proteins concanavalin A (ConA) and jacalin to arrays composed of the monosaccharides mannose and galactose was monitored with SPR imaging. SPR imaging measurements were employed to accomplish the following: (i) construct adsorption isotherms for the interactions of ConA and jacalin to the carbohydrate surfaces, (ii) monitor protein binding to surfaces presenting different compositions of the immobilized carbohydrates, and (iii) measure the solution equilibrium dissociation constants for ConA and jacalin toward mannose and galactose, respectively. Adsorption coefficients (K(ADS)) of 2.2 +/- 0.8 x 10(7) M(-)(1) and 5.6 +/- 1.7 x 10(6) M(-)(1) were obtained for jacalin adsorbing to a galactose surface and ConA adsorbing to a mannose surface, respectively. The solution equilibrium dissociation (K(D)) constant for the interaction of jacalin and galactose was found to be 16 +/- 5 microM, and for ConA and mannose was found to be 200 +/- 50 microM.     

Carbohydrate–protein interactions and their biosensing applications

Carbohydrate recognition is clearly present throughout nature, playing a major role in the initial attachment of one biological entity to another. The important question is whether these prevalent interactions could provide a real suitable alternative to the use of antibodies or nucleic acid for detection and identification. Currently, examples of carbohydrates being employed in biological detection systems are limited. The challenges of using carbohydrate recognition for detection mainly come from the weak affinity of carbohydrate–protein interactions, the lack of versatile carbohydrate scaffolds with well-defined structures, and the less developed high-information-content, real-time, and label-free assay technology. In this review, we focus on discussing the characteristics of carbohydrate–protein interactions in nature and the methods for carbohydrate immobilization based on surface coupling chemistry in terms of their general applicability for developing carbohydrate- and lectin-based label-free sensors. Furthermore, examples of innovative design of multivalent carbohydrate–protein interactions for sensor applications are given. We limit our review to show the feasibility of carbohydrate and lectin as recognition elements for label-free sensor development in several representative cases to formulate a flexible platform for their use as recognition elements for real-world biosensor applications.     

Determination of phenolic compounds using spectral and color transitions of rhodium nanoparticles

This work reports a new approach for the determination of phenolic compounds based on their interaction with citrate-capped rhodium nanoparticles. Phenolic compounds (i.e., catechins, gallates, cinnamates, and dihydroxybenzoic acids) were found to cause changes in the size and localized surface plasmon resonance of rhodium nanoparticles, and therefore, give rise to analyte-specific spectral and color transitions in the rhodium nanoparticle suspensions. Upon reaction with phenolic compounds (mainly dithydroxybenzoate derivatives, and trihydroxybenzoate derivatives), new absorbance peaks at 350 nm and 450 nm were observed. Upon reaction with trihydroxybenzoate derivatives, however, an additional absorbance peak at 580 nm was observed facilitating the speciation of phenolic compounds in the sample. Both absorbance peaks at 450 nm and 580 nm increased with increasing concentration of phenolic compounds over a linear range of 0–500 μM. Detection limits at the mid-micromolar levels were achieved, depending on the phenolic compound involved, and with satisfactory reproducibility (<7.3%). On the basis of these findings, two rhodium nanoparticles-based assays for the determination of the total phenolic content and total catechin content were developed and applied in tea samples. The obtained results correlated favorably with commonly used methods (i.e., Folin-Ciocalteu and aluminum complexation assay). Not the least, the finding that rhodium nanoparticles can react with analytes and exhibit unique localized surface plasmon resonance bands in the visible region, can open new opportunities for developing new optical and sensing analytical applications.     

Experimental and Molecular Mechanical Studies of Complexation of Some 2H- and 3H- Indole Derivatives with Aqueous β-Cyclodextrin

Phase solubility diagrams (PSDs) at 25 ^∘C and molecular mechanical (MM) modeling were used to study the aqueous complexation of some 2H- and 3H-indole derivatives with β-cyclodextrin (β-CD). Among the 3H-indole derivatives investigated in this work, indole-3H-butyric acid forms the most stable 1:1 complex of the B _s -type PSD, whereas shorter chain derivatives form soluble 1:1 complexes (A _L -type PSDs) with their stability increasing as the chain length increases. Indole-2 carboxylic acid forms highly stable 1:1 and 1:2 complexes, with the lower-order complex reaching saturation first (B _s -type PSD). MM modeling indicates that the stability of the complex is highly correlated with the flexibility of the 3H-indole hydrocarbon chain, which yields a better geometrical fit within the β-CD cavity resulting from different hydrophilic interactions. These interactions are represented in the H-bonding of the carboxyl group with the primary hydroxyl group network that is situated at the narrow rim of the cavity, and also by a favorable interaction of the aromatic ring with the hydroxyl group network at the other rim.     

Synthesis of polyoxyethylene grafting nylon 6 and the selective separation of cyclohexane/cyclohexanone/cyclohexanol mixture through its membranes

A polymer membrane having polyoxyethylene grafting nylon 6 was prepared by reacting of nylon 6 and ethylene oxide. The chemical compositions of the polyoxyethylene grafting nylon 6 were determined by ¹H NMR. Degree of substitution for amide group, x, and degree of polymerization for polyoxyethylene, n, in bulk polymerization at 80°C for 4–9.5 h were evaluated: x = 0.32 ± 0.01–0.56 ± 0.02 and n = 2.8 ± 0.1–6.0 ± 0.3. The polyoxyethylene grafting nylon 6 membrane showed a selective separation of cyclohexanol from a cyclohexane/cyclohexanone/cyclohexanol mixture by a pervaporation technique. The FTIR and flux analyses verified that the selectivity for cyclohexanol was attributed to the hydrogen-bonding interaction between hydroxyl group in cyclohexanol and the hydroxyl group in polyoxyethylene grafting chain. The pervaporation and an adsorption experiment of cyclohexanol through the present membrane showed that hydroxyl group in graft chain acted as a carrier for cyclohexanol.