Synthesis of gold nanoparticles for in situ conjugation with structural carbohydrates

Fiber Spinning from Cellulose Solutions in Imidazolium Ionic Liquids: Effects of Natural Antioxidants on Molecular Weight, Dope Discoloration, and Yellowing Behavior

Spinning of cellulosic fibers requires the prior dissolution of cellulose. 3-Alkyl-1-methylimidazolium ionic liquids have proven to be suitable solvents for that purpose, but the degradation of cellulose in the spinning dope can be severe. Suitable stabilizers are therefore required that prevent cellulose degradation, but do not adversely affect spinnability or the long-term yellowing behavior of the fibers. A group of twelve renewables-based antioxidants was selected for stabilizing 5% cellulose solutions in the ionic liquids and their effects on cellulose integrity, dope discoloration, and aging behavior were tested by gel permeation chromatography (GPC) and ISO brightness measurements. Propyl gallate (a gallic acid derivative), hydroxytyrosol (from olives), and tocopheramines (a vitamin E derivative) performed best in the three test categories, minimizing both cellulose degradation, chromophore formation in the spinning dope, and yellowing upon accelerating aging of the spun fibers. The use of these stabilizers for cellulose solutions in the imidazolium-based solvent system can therefore be recommended from the point of view of both performance and sustainability.

Localized surface acetylation of aqueous counter collision cellulose nanofibrils using a Pickering emulsion as an interfacial reaction platform

The self-organization of nano-sized fibrous building blocks is essential for the construction of biomimetic architectonics and hierarchically constructed bio-based materials. The localization of hydrophobic moieties on the surfaces of such nanofibrils is key to hierarchical assembly in aqueous systems. In this study, unique self-assembling fibrous building blocks comprising amphiphilic cellulose nanofibrils (CNFs) were prepared by aqueous counter collision (ACC). The purpose of the study was to control the surface properties of ACC-CNFs by selectively acetylating their surfaces at the oil/water interfaces of a Pickering emulsion. Localized interfacial reactions occurred when the ACC-CNFs were adsorbed onto the surfaces of oil droplets containing the reaction reagents. Such acetylation reactions were achieved whilst maintaining the crystallinity and fibrous morphology of the original CNFs. The surfaces of films cast from the acetylated ACC-CNFs described herein had unique self-aggregation properties that contrasted markedly with those of films cast from acetylated ACC-CNFs prepared in homogenous dispersions.

RETRACTED: Optimized reducing-end labeling of cellulose nanocrystals: Implication for the structure of microfibril bundles in plant cell walls

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the senior authors of the article; Jean-Luc Putaux and Bruno Jean. There are serious concerns about the reliability of the data presented in this article, which critically affects the main conclusions. Namely, TEM Figs. 3, 6 and 7 show signs of manipulation, such as the presence of repeated fragments and the use of the clone stamp tool applied with some image editing software. The first author of the paper, Fangbo Lin, was contacted regarding this matter but did not respond. The two above mentioned authors apologize for any inconvenience to readers.

On nitrogen fixation and "residual nitrogen content" in cellulosic pulps

Cellulosic material is capable of permanently retaining nitrogen compounds (mostly having amino functions), which is reflected in a residual nitrogen content (in the low per mille range to the low percent range) of some pulps and certain lab samples. Merely adsorptively bound compounds can be removed by mild acidic washing, but part of the nitrogen seems to be resistant and very tightly bound, and thus not accessible for removal by washing. Tertiary and aromatic amines are not retained in this way, but only primary and secondary amines. There is only a weak correlation between the "firmly bound nitrogen" and the carbonyl content in cellulosics (because of oxidative damage), so that possible aminal, Schiff base and enamine structures can hardly be relevant as major nitrogen sources. However, there is a very good linear correlation between the ISO brightness (chromophore content) in aged pulps and the residual nitrogen content. In particular the concentration of the cellulosic key chromophore 2,5-dihydroxy-[1,4]-benzoquinone (DHBQ) determines the permanent N-binding capacity of the pulp. DHBQ reacts very readily with primary and secondary amines under ambient conditions to 2,5-diamino-substituted [1,4]-benzoquinones, which have very low solubility (because of zwitterionic resonance contributions) and thus remain on/in the pulp. Examples of nitrogen fixation in pulps are the binding of piperidine (a common amine catalyst in derivatization reactions), amine degradation products of the cellulose solvent NMMO, dimethylamine in materials processed from the cellulose solvent DMAc/LiCl, imidazole (a degradation product of 1-alkyl-3-methylimidazolium ionic liquids), and of amino groups in proteins after enzymatic treatment. The nature of the respective DHBQ-amine addition compound has been verified by complete structure determination.

Chemical Modification of Reducing End-Groups in Cellulose Nanocrystals

Native plant cellulose has an intrinsic supramolecular structure. Consequently, it can be isolated as nanocellulose species, which can be utilized as building blocks for renewable nanomaterials. The structure of cellulose also permits its end-wise modification, i.e., chemical reactions exclusively on one end of a cellulose chain or a nanocellulose particle. The premises for end-wise modification have been known for decades. Nevertheless, different approaches for the reactions have emerged only recently, because of formidable synthetic and analytical challenges associated with the issue, including the adverse reactivity of the cellulose reducing end and the low abundance of newly introduced functionalities. This Review gives a full account of the scientific underpinnings and challenges related to end-wise modification of cellulose nanocrystals. Furthermore, we present how the chemical modification of cellulose nanocrystal ends may be applied to directed assembly, resulting in numerous possibilities for the construction of new materials, such as responsive liquid crystal templates and composites with tailored interactions.

One-step synthesis of cellooligomer-conjugated gold nanoparticles in a water-in-oil emulsion system and their application in biological sensing

Monodisperse gold nanoparticles (GNPs) were synthesized in a water-in-oil emulsion system (reverse micelles) composed of 80% N-methylmorpholine N-oxide (NMMO)/20% H₂O and dodecane, stabilized with an anionic surfactant: bis(2-ethylhexyl)sulfosuccinate sodium salt. Cellooligomers with a degree of polymerization of 6 or 15 (βGlc6 or βGlc15, respectively), which were labeled at each reducing end group with thiosemicarbazide (TSC) and dissolved in the aqueous NMMO phase, were successfully conjugated to the surfaces of GNPs in situ during spontaneous NMMO-mediated gold reduction. As-synthesized βGlc6-GNPs and βGlc15-GNPs had average diameters of 11.3 ± 2.1 and 10.5 ± 0.7 nm, respectively, while their surface sugar densities were 0.21 and 0.51 chains nm^-2, respectively. Concanavalin A (ConA), a lectin that recognizes non-reducing end groups of glucose residues, aggregated with βGlc15-GNPs with higher sensitivity than it did with βGlc6-GNPs, possibly as a result of the sugar density on the GNP surfaces. The aggregates were rapidly re-suspended by adding methyl-β-d-glucopyranoside as a binding inhibitor. Other lectins and proteins showed no interaction with βGlc-GNPs. Therefore, clustering of glucose non-reducing ends on the GNP surfaces via strong intermolecular association of cellooligomers, possibly led to high affinity for ConA. This facile synthesis route to structural carbohydrate-decorated GNPs has potential applications in carbohydrate-nanometal conjugate nano-biosensor development.

Cellulose-gold nanoparticle hybrid materials

Cellulose and gold nanoparticles have exciting characteristics and new combinations of both materials may lead to promising functional nanocomposites with unique properties. We have reviewed current research on cellulose-gold nanoparticle composite materials, and we present an overview of the preparation methods of cellulose-gold composite materials and discuss their applications. We start with the nanocomposite fabrication methods, covering in situ gold reduction, blending, and dip-coating methods to prepare gold-cellulose nanocomposite hybrids. We then move on to a discussion of the ensuing properties where the combination of gold nanoparticles with cellulose results in functional materials with specific catalytic, antimicrobial, sensing, antioxidant and Surface Enhanced Raman Scattering (SERS) performance. Studies have also been carried out on orientationally ordered composite materials and on the chiral nematic phase behaviour of these nanocomposites. To exert even more control over the structure formation and the resultant properties of these functional materials, fundamental studies on the physico-chemical interactions of cellulose and gold are necessary to understand better the driving forces and limitations towards structuring of gold-cellulose hybrid materials.

Biosynthesis of Metal Nanoparticles: Novel Efficient Heterogeneous Nanocatalysts

This review compiles the most recent advances described in literature on the preparation of noble metal nanoparticles induced by biological entities. The use of different free or substituted carbohydrates, peptides, proteins, microorganisms or plants have been successfully applied as a new green concept in the development of innovative strategies to prepare these nanoparticles as different nanostructures with different forms and sizes. As a second part of this review, the application of their synthetic ability as new heterogonous catalysts has been described in C-C bond-forming reactions (as Suzuki, Heck, cycloaddition or multicomponent), oxidations and dynamic kinetic resolutions.

Temporal flickering of contrast agents for enhanced optical imaging

The temporal flickering of contrast agents that labels a biological sample is a unique modality for cellular imaging with single molecule sensitivity. It improves the signal-to-noise ratio statistics associated with the noisy in vivo environment and has promising applications in single particle tracking and super-resolution microscopy techniques. The flickering can be triggered either statistically through the mechanism of temporal fluctuations of the emitter or through external modulation. The enriching toolbox of contrast agents that are feasible for biomedical imaging for the flickering methods will be discussed, with emphasis on the emerging field of flickering gold nanoparticles and the lock-in detection mechanism. WIREs Nanomed Nanobiotechnol 2016, 8:439-448. doi: 10.1002/wnan.1375 For further resources related to this article, please visit the WIREs website.

Cellular superresolved imaging of multiple markers using temporally flickering nanoparticles

In this paper we present a technique aimed for simultaneous detection of multiple types of gold nanoparticles (GNPs) within a biological sample, using lock-in detection. We image the sample using a number of modulated laser beams that correspond to the number of GNP species that label a given sample. The final image where the GNPs are spatially separated is obtained computationally. The proposed method enables the simultaneous superresolved imaging of different areas of interest within biological sample and also the spatial separation of GNPs at sub-diffraction distances, making it a useful tool in the study of intracellular trafficking pathways in living cells.

Modification of Fibers with Nanostructures Using Reactive Dye Chemistry

Reactive dyes conventionally used to chemically bind chromophores to fabrics have been used to develop a platform technology that can modify commercially available fibers with nanoscale structures. To illustrate this concept, commercial nylon and cellulose fibers have been modified with gold nanoparticles of three sizes, metal organic framework (MOF) crystals, and quantum dots in five sizes. The gold modified cellulose and nylon samples have colors that vary based on the size of the gold particles, and the particles remained attached to the fibers, even after being washed with solvents, water, and soap. The MOF was grown on the fibers after applying reactive dyes to anchor the metal building unit to the fibers, and the process produced cellulose fibers with surface areas of ~980 m2/g. Both the nylon and cellulose MOF modified fabrics show preferential adsorption of ethylene over ethane and the ability to adsorb ammonia from air. Quantum dot modified nylon and cellulose fibers have fluorescent properties consistent with the unbound particles and remained attached to the fibers after washing with organic solvents, water, and soap. Applications are broad, and this work provides a first step at coupling conventional dyes and nanotechnology.

Cellular imaging using temporally flickering nanoparticles

Utilizing the surface plasmon resonance effect in gold nanoparticles enables their use as contrast agents in a variety of applications for compound cellular imaging. However, most techniques suffer from poor signal to noise ratio (SNR) statistics due to high shot noise that is associated with low photon count in addition to high background noise. We demonstrate an effective way to improve the SNR, in particular when the inspected signal is indistinguishable in the given noisy environment. We excite the temporal flickering of the scattered light from gold nanoparticle that labels a biological sample. By preforming temporal spectral analysis of the received spatial image and by inspecting the proper spectral component corresponding to the modulation frequency, we separate the signal from the wide spread spectral noise (lock-in amplification).

One-pot green synthesis of silver/iron oxide composite nanoparticles for 4-nitrophenol reduction

Silver/iron oxide composite nanoparticles have been synthesized successfully via a facile one-pot green route by the use of l-arginine, which created an aqueous solution of about pH 10 and acted as a reducing agent for the successive formation of iron oxide and Ag nanoparticles. The product was characterized to be silver-coated iron oxide and iron oxide hydroxide composite nanoparticles with a mean diameter of about 13.8 ± 3.0 nm and 8.53% of Ag in weight. It exhibited good catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol with sodium borohydride. The reduction reaction followed the pseudo-first-order kinetics. The corresponding rate constants increased with the increases of temperature and catalyst amount but decreased with the increase of initial 4-NP concentration, revealing an activation energy of 28.2 kJ/mol and a diffusion controlled mechanism. In addition, this product had quite good stability. No significant activity loss was observed after reuse for 5 cycles.

Hybrid immobilization of galactosyl lactose and cellobiose on a gold substrate to modulate biological responses

Bioactive O-β-d-galactopyranosyl-(1→4)-O-β-d-galactopyranosyl-(1→4)-d-glucopyranose (4'-galactosyl lactose) was site-selectively modified at a reducing end with thiosemicarbazide (TSC). As-synthesized 4'-galactosyl lactose-TSC was immobilized on a gold substrate with cellobiose-TSC as a spacer through spontaneous self-assembly chemisorption via SAu bonding. Quartz crystal microbalance analysis suggested the successful formation of self-assembled monolayers (SAMs) of 4'-galactosyl lactose-TSC and/or cellobiose-TSC. Galactose-binding lectin exhibited the highest affinity for hybrid SAMs with an equimolar ratio of the two oligosaccharide-TSCs, while glucose-binding lectin showed decreasing adsorption with a decrease in cellobiose-TSC ratios. Human hepatocellular carcinoma cells, which recognize galactose residues, efficiently adhered to the hybrid SAMs. Higher enzymatic deethoxylation of ethoxyresorufin via cytochrome P450 appeared on hybrid SAMs. These results suggested that clustering of the bioactive sugars was involved in the cellular responses, possibly via biological carbohydrate-protein interactions. This approach to designing carbohydrate-based scaffolds should provide a basis for the functional development of glyco-decorated biointerfaces for cell culture applications.

Spontaneous synthesis of gold nanoparticles on gum arabic-modified iron oxide nanoparticles as a magnetically recoverable nanocatalyst

A novel magnetically recoverable Au nanocatalyst was fabricated by spontaneous green synthesis of Au nanoparticles on the surface of gum arabic-modified Fe3O4 nanoparticles. A layer of Au nanoparticles with thickness of about 2 nm was deposited on the surface of gum arabic-modified Fe3O4 nanoparticles, because gum arabic acted as a reducing agent and a stabilizing agent simultaneously. The resultant magnetically recoverable Au nanocatalyst exhibited good catalytic activity for the reduction of 4-nitrophenol with sodium borohydride. The rate constants evaluated in terms of pseudo-first-order kinetic model increased with increase in the amount of Au nanocatalyst or decrease in the initial concentration of 4-nitrophenol. The kinetic data suggested that this catalytic reaction was diffusion-controlled, owing to the presence of gum arabic layer. In addition, this nanocatalyst exhibited good stability. Its activity had no significant decrease after five recycles. This work is useful for the development and application of magnetically recoverable Au nanocatalyst on the basis of green chemistry principles.

Green synthesis of gold-chitosan nanocomposites for caffeic acid sensing

In this work, colloidal gold nanoparticles (AuNPs) stabilized into a chitosan matrix were prepared using a green route. The synthesis was carried out by reducing Au(III) to Au(0) in an aqueous solution of chitosan and different organic acids (i.e., acetic, malonic, or oxalic acid). We have demonstrated that by varying the nature of the acid it is possible to tune the reduction rate of the gold precursor (HAuCl(4)) and to modify the morphology of the resulting metal nanoparticles. The use of chitosan, a biocompatible and biodegradable polymer with a large number of amino and hydroxyl functional groups, enables the simultaneous synthesis and surface modification of AuNPs in one pot. Because of the excellent film-forming capability of this polymer, AuNPs-chitosan solutions were used to obtain hybrid nanocomposite films that combine highly conductive AuNPs with a large number of organic functional groups. Herein, Au-chitosan nanocomposites are successfully proposed as sensitive and selective electrochemical sensors for the determination of caffeic acid, an antioxidant that has recently attracted much attention because of its benefits to human health. A linear response was obtained over a wide range of concentration from 5.00 × 10(-8) M to 2.00 × 10(-3) M, and the limit of detection (LOD) was estimated to be 2.50 × 10(-8) M. Moreover, further analyses have demonstrated that a high selectivity toward caffeic acid can be achieved without interference from catechin or ascorbic acid (flavonoid and nonphenolic antioxidants, respectively). This novel synthesis approach and the high performances of Au-chitosan hybrid materials in the determination of caffeic acid open up new routes in the design of highly efficient sensors, which are of great interest for the analysis of complex matrices such as wine, soft drinks, and fruit beverages.