Complexation of polysaccharide and monosaccharide with thiolate boronic acid capped on silver nanoparticle

Zwitterionic Thiolate-Protected Ag22(0/I) and Ag20(I) Clusters: Assembly, Structural Characterization, and Antibacterial Activity

Zwitterionic thiolate ligands have the potential to introduce novel assembly modes and functions for noble metal clusters. However, their utilization in the synthesis of silver clusters remains understudied, particularly for the clusters containing reductive Ag(0) species. In this article, we report the first synthesis of a mixed-valence silver(0/I) cluster protected by zwitterionic Tab as thiolate ligands (Tab = 4-(trimethylammonio)benzenethiolate), denoted as [Ag22(Tab)24](PF6)20·16CH3OH·6Et2O (Ag22·16CH3OH·6Et2O), alongside an Ag(I) cluster [Ag20(Tab)12(PhCOO)10(MeCN)2(H2O)](PF6)10·11MeCN (Ag20·11MeCN). Ag22 has a distinct hierarchical supratetrahedral structure with a central {Ag6} kernel surrounded by four [Ag4(Tab)6]4+ units. High-resolution electrospray ionization mass spectra demonstrate that Ag22 has two free electrons, indicating a superatomic core. Ag20 has a drum-like [Ag12(Tab)6(PhCOO)6(H2O)]6+ inner core capped by two tetrahedral-like [Ag4(Tab)3(PhCOO)2(MeCN)]2+ units. Ag20 can be transformed into Ag22 after its reaction with NaBH4 in solution. Antibacterial measurements reveal that Ag22 has a significantly lower minimum inhibitory concentration than that of the Ag20 cluster. This work not only extends the stabilization of silver(0/I) clusters to neutral thiol ligands but also offers new materials for the development of novel antibacterial materials.

A brief insight to the role of glyconanotechnology in modern day diagnostics and therapeutics

Carbohydrate-protein and carbohydrate-carbohydrate interactions are very important for various biological processes. Although the magnitude of these interactions is low compared to that of protein-protein interaction, the magnitude can be boosted by multivalent approach known as glycocluster effect. Nanoparticle platform is one of the best ways to present diverse glycoforms in multivalent manner and thus, the field of glyconanotechnology has emerged as an important field of research considering their potential applications in diagnostics and therapeutics. Considerable advances in the field have been achieved through development of novel techniques, use of diverse metallic and non-metallic cores for better efficacy and application of ever-increasing number of carbohydrate ligands for site-specific interaction. The present review encompasses the recent developments in the area of glyconanotechnology and their future promise as diagnostic and therapeutic tools.

Luminescent, ferromagnetic silver glyconanoparticles: synthesis to annealing-induced substrate specific transformation

Sugar cane juice has been harnessed as a green reducing agent for the synthesis of silver nanoparticles, followed by annealing of the latter into helical and rod-like structures on polymer and silicon surfaces respectively.

BSA-boronic acid conjugate as lectin mimetics

We report bovine serum albumin (BSA)-boronic acid (BA) conjugates as lectin mimetics and their glyco-capturing capacity. The BSA-BA conjugates were synthesized by amidation of carboxylic acid groups in BSA with aminophenyl boronic acid in the presence of EDC, and were characterized by Alizarin Red S (ARS) assay and SDS-PAGE gel. The BSA-BA conjugates were immobilized onto maleimide-functionalized silica beads and their sugar capturing capacity and specificity were confirmed by ARS displacement assay. Further, surface plasmon resonance (SPR) analysis of the glyco-capturing activity of the BSA-BA conjugates was conducted by immobilizing BSA-BA onto SPR gold chip. Overall, we demonstrated a BSA-BA-based lectin mimetics for glyco-capturing applications. These lectin mimetics are expected to provide an important tool for glycomics and biosensor research and applications.

Boronic acid-protected gold clusters capable of asymmetric induction: spectral deconvolution analysis of their electronic absorption and magnetic circular dichroism

Gold clusters protected by 3-mercaptophenylboronic acid (3-MPB) with a mean core diameter of 1.1 nm are successfully isolated, and their absorption, magnetic circular dichroism (MCD), and chiroptical responses in metal-based electronic transition regions, which can be induced by surface D-/L-fructose complexation, are examined. It is well-known that MCD basically corresponds to electronic transitions in the absorption spectrum, so simultaneous deconvolution analysis of electronic absorption and MCD spectra of the gold cluster compound is conducted under the constrained requirement that a single set of Gaussian components be used for their fitting. We then find that fructose-induced chiroptical response is explained in terms of the deconvoluted spectra experimentally obtained. We believe this spectral analysis is expected to benefit better understanding of the electronic states and the origin of the optical activity in chiral metal clusters.

Metal-metal-interaction-facilitated coordination polymer as a sensing ensemble: a case study for cysteine sensing

A detailed investigation of the absorption and CD signals of Ag(I)-cysteine (Cys) aqueous solutions at buffered or varying pH has allowed us to suggest that coordination polymers are formed upon mixing Ag(I) and Cys bearing a Ag(I)-Cys repeat unit. The formation of the coordination polymers are shown to be facilitated by both the Ag(I)···Ag(I) interaction and the interaction between the side chains in the polymeric backbone. The former allows for an immediate spectral sensing of Cys with enantiomeric discrimination capacity with both high sensitivity and selectivity, and the contribution of the side-chain/side-chain interaction serves to guide extended sensing applications by means of modulating this interaction. With our preliminary data on the corresponding Cu(I)-Cys and Au(I)-Cys systems that exhibited similar spectral signals, we conclude that the M(I)-SR coordination polymers (M = Cu, Ag, or Au) could in general function as spectral sensing ensembles for extended applications. This sensing ensemble involves the formation of coordination polymers with practically no spectral background, thus affording high sensing sensitivity and selectivity.

Glyconanomaterials: synthesis, characterization, and ligand presentation

Glyconanomaterials, nanomaterials carrying surface-tethered carbohydrate ligands, have emerged and demonstrated increasing potential in biomedical imaging, therapeutics, and diagnostics. These materials combine the unique properties of nanometer-scale objects with the ability to present multiple copies of carbohydrate ligands, greatly enhancing the weak affinity of individual ligands to their binding partners. Critical to the performance of glyconanomaterials is the proper display of carbohydrate ligands, taking into consideration of the coupling chemistry, the type and length of the spacer linkage, and the ligand density. This article provides an overview of the coupling chemistry for attaching carbohydrate ligands to nanomaterials, and discusses the need for thorough characterization of glyconanomaterials, especially quantitative analyses of the ligand density and binding affinities. Using glyconanoparticles synthesized by a versatile photocoupling chemistry, methods for determining the ligand density by colorimetry and the binding affinity with lectins by a fluorescence competition assay are determined. The results show that the multivalent presentation of carbohydrate ligands significantly enhances the binding affinity by several orders of magnitude in comparison to the free ligands in solution. The effect is sizeable even at low surface ligand density. The type and length of the spacer linkage also affect the binding affinity, with the longer linkage promoting the association of bound ligands with the corresponding lectins.

"Clickable" affinity ligands for effective separation of glycoproteins

In this paper, we present a new modular approach to immobilize boronic acid ligands that can offer effective separation of glycoproteins. A new "clickable" boronic acid ligand was synthesized by introducing a terminal acetylene group into commercially available 3-aminophenyl boronic acid. The clickable ligand, 3-(prop-2-ynyloxycarbonylamino)phenylboronic acid (2) could be easily coupled to azide-functionalized hydrophilic Sepharose using Cu(I)-catalyzed 1,3-dipolar cycloaddition reaction under mild condition. Compared to other boronic acid affinity gels, the new affinity gel displayed superior effectiveness in separating model glycoproteins (ovalbumin and RNase B) from closely related bovine serum albumin and RNase A in the presence of crude Escherichia coli proteins. Because of the simplicity of the immobilization through "click chemistry", the new ligand 2 is expected to not only offer improved glycoprotein separation in other formats, but also act as a useful building block to develop new chemical sensors for analysis of other glycan compounds.

Synthesis and application of novel phenylboronate affinity materials based on organic polymer particles for selective trapping of glycoproteins

We report on synthesis concepts for the fabrication of various novel phenylboronate affinity materials based on polymethacrylate epoxy beads (Fractogel EMD Epoxy (M) 40-90 microm) and the testing of these functionalized polymer particles for selective trapping of a glycoprotein from a standard mixture containing a glycosylated and a nonglycosylated protein. Two inherently different approaches for the functionalization of the bare beads with boronate groups have been elucidated. In the first, the epoxy residues of the polymer particles were converted into reactive thiol groups which were subsequently used as anchor moieties for the immobilization of 4-vinylphenylboronic acid by radical addition or radical polymerization reaction. Three different ways for the generation of sulfhydryl groups have been examined leading to materials with distinct linker chemistries. In the second and more straightforward approach, the epoxy groups were reacted with 4-mercaptophenylboronic acid. The novel materials were thoroughly characterized by (i) quantitation of the sulfur content by elemental analysis, (ii) reactive sulfhydryls were determined in a photospectrometric assay, (iii) boron content was measured by inductively coupled plasma-atomic emission spectrometry, and (iv) the amount of reactive boronate groups was evaluated in a fast binding assay employing adenosine as test compound. A maximum concentration of 1.2 mmol boronate groups per gram dry beads could be achieved by the presented synthesis routes. Employing the novel phenylboronate affinity materials in capture and release experiments in the batch mode, a standard glycoprotein, viz. transferrin (Tf) from human serum was separated from a nonglycosylated protein, BSA. A commercial boronate affinity material based on 3-aminophenylboronic acid modified agarose gel was employed as reference material and was found to perform significantly worse compared to the herein presented novel polymethacrylate particles.

Boronate affinity saccharide electrophoresis: a novel carbohydrate analysis tool

The incorporation of specialised carbohydrate affinity ligand methacrylamido phenylboronic acid in polyacrylamide gels for fluorophore-assisted carbohydrate electrophoresis greatly improved the effective separation of saccharides that show similar mobilities in standard electrophoresis. Polyacrylamide gel electrophoresis using methacrylamido phenylboronic acid in low loading (typically 0.5-1% dry weight) was unequivocally shown to alter retention of labelled saccharides depending on their boronate affinity. While conventional fluorophore-assisted carbohydrate electrophoresis of 2-aminoacridone labelled glucose oligomers showed an inverted parabolic migration, an undesired trait of small oligosaccharides labelled with this neutral fluorophore, boron affinity saccharide electrophoresis separation of these carbohydrates completely restored their predicted running order, based on their charge/mass ratio, and resulted in improved separation of the analyte saccharides. These results exemplify boron affinity saccharide electrophoresis as an important new technique for analysing carbohydrates and sugar-containing molecules.

Single molecule photophysics near metallic nanostructures

Metal-enhanced fluorescence (MEF) is useful in single molecule detection (SMD) by increasing the photostability, brightness and increase in radiative decay rates of fluorophores. We have investigated MEF from an individual fluorophore tethered to a single silver nanoparticle and also a single fluorophore between a silver dimer. The fluorescence lifetime results revealed a near-field interaction mechanism of fluorophore with the metal particle. Finite-difference time-domain (FDTD) calculations were employed to study the distribution of electric field near the metal monomer and dimer. The coupling effect of metal particles on the fluorescence enhancement was studied. We have also investigated the photophysics of FRET near metal nanoparticles and our preliminary results suggest an enhanced FRET efficiency in the presence of a metal nanoparticle. In total, our results demonstrate improved detectability at the single molecule level for a variety of fluorophores and quantum dots in proximity to the silver nanoparticles due to the near-field metal-fluorophore interactions.

Electrochemically amplified detection for lipopolysaccharide using ferrocenylboronic acid

A novel electrochemical technique for lipopolysaccharide (LPS) detection has been developed using a combination of ferrocenylboronic acid derivatives and an enzyme-modified electrode. The enzyme-modified electrode was constructed from a gold electrode modified with a bovine serum albumin membrane containing diaphorase. Ferrocenylboronic acid derivatives are oxidized on the electrode, and then regenerated by a diaphorase-catalyzed reaction in the presence of NADH. The consumption/regeneration cycle for ferrocenylboronic acid derivatives resulted in a chemically amplified current response. The current response for ferrocenylboronic acid derivatives decreased in association with its complexation with glycosyl units of LPS, and this current decrease caused by LPS was also amplified by the recycling process. On the other hand, the addition of a monosaccharide such as D-mannose or D-galactose induced no response at the same LPS concentration. The enzyme membrane immobilized on the electrode plays an important role in selectivity as well as chemical amplification. In addition, the enzyme-modified electrode exhibited a rapid response of 5 min for LPS, which is much faster than the currently used method. The detection limit of LPS from Escherichia coli O127:B8 was as low as 50 ng ml-1.

Engineering the nanoparticle-biomacromolecule interface

Monolayer-protected nanoparticles feature tunable size, surface functionality and core material, providing scaffolds for targeting biomacromolecules. This review highlights recent advances in nanoparticle-biomacromolecule interactions, focusing on two key areas: (1) The modulation of structure and function of biomacromolecules through engineered interactions with nanoparticle surfaces; (2) The use of biomacromolecules as building blocks for nanostructured materials.

A model for DNA detection by metal-enhanced fluorescence from immobilized silver nanoparticles on solid substrate

N-(2-Mercaptopropionyl)glycine (tiopronin)-coated silver nanoparticles (average diameter of metal core=5 nm) were prepared by a modified Brust method. Tiopronin ligands were partially displaced by thiolate single-stranded oligonucleotides via ligand exchange. These particles were immobilized onto a solid substrate through hybridization with target oligonucleotides in a layer-by-layer approach. The dye-labeled complementary oligonucleotides were bound to the particle layers through hybridization. Fluorescence intensity was enhanced with a simultaneous increase of plasmon absorbance from accumulated particles. A steady state was shown at the 10th particle layer and then the fluorescence enhancement showed a plateau. This result reveals that increasing the particle layer contributes to fluorescence enhancement. This novel method was used to detect DNA hybridization through both absorbance and emission spectral changes.

Glyconanoparticles: types, synthesis and applications in glycoscience, biomedicine and material science

Nanoparticles are the subject of numerous papers and reports and are full of promises for electronic, optical, magnetic and biomedical applications. Although metallic nanoparticles have been functionalized with peptides, proteins and DNA during the last 20 years, carbohydrates have not been used with this purpose until 2001. Since the first synthesis of gold nanoparticles functionalized with carbohydrates (glyconanoparticles) was reported, the number of published articles has considerably increased. This article reviews progress in the development of nanoparticles functionalized with biological relevant oligosaccharides. The glyconanoparticles constitute a good bio-mimetic model of carbohydrate presentation at the cell surface, and maybe, excellent tools for Glycobiology, Biomedicine and Material Science investigations.