Studies on the sulfation of cellulose α-lipoate and ability of the sulfated product to stabilize colloidal suspensions of gold nanoparticles

© 2015 Elsevier Ltd. A versatile method for the synthesis of cellulose α-lipoate with a low degree of substitution (DS) has been developed using N,N-dimethylacetamide (DMA)/LiCl as a solvent and N,N′-carbonyldiimidazole (CDI) as an esterification reagent. The cellulose α-lipoate with DS of α-lipoate groups of 0.26 was converted with sulfur trioxide-pyridine complex in dimethyl sulfoxide (DMSO) as solvent. The sulfation is accompanied by an unexpected partial oxidation of the disulfide moiety leading to the formation of the corresponding stereoisomers of S-oxides. The resulting mixture of water-soluble cellulose α- and β-lipoate sulfate possesses a DS of sulfuric acid half ester groups of 1.78. This cellulose-α/β-lipoate sulfate derivative can be used as an effective stabilizer and solubilizer for the formation of colloidal suspensions of gold nanoparticles formed in situ in aqueous solution

Microscopic Damage Evolution During Very High Cycle Fatigue (VHCF) of Tempered Martensitic Steel

AbstractDimensioning of high-strength steels relies on the knowledge of Wöhler-type S/N data and the assumption of a fatigue limit for applications where the number of load cycles exceeds 107. Very high cycle fatigue (VHCF) experiments applied to a 0.5C-1.25Cr-Mo tempered steel (German designation: 50CrMo4) revealed surface crack initiation at prior austenite grain boundaries in medium strength condition (37HRC) and internal crack initiation at non-metallic inclusions at high strength condition (48HRC). Despite the formation of small cracks during cycling up to 109 cycles, it seems that the medium strength condition exhibits a real fatigue limit. Application of automated electron back-scattered diffraction (EBSD) within the shallow-notched area of electro-polished fatigue specimens had shown that prior austenite grain boundaries act as effective obstacles to crack propagation. High resolution thermography during cycling of the specimens allowed the identification of local plasticity, which led to crack initiation at a later stage of the fatigue life. It was found that Cr segregation rows play a decisive role in the crack initiation process. By means of high-resolution electron microscopy in combination with focused ion beam milling (FIB), evolution of cyclic plasticity and crack initiation was correlated with the material's microstructure. The results are discussed in terms of the completely different crack initiation mechanisms of medium and high strength variants of the same steel. EBSD and crack propagation data are used to adapt numerical modeling tools to predict crack initiation and short crack propagation

Investigation of cellulose dissolution in morpholinium-based solvents: impact of solvent structural features on cellulose dissolution

A series of\ua0N-methylmorpholinium salts with varying\ua0N-alkyl chains and Cl−, OAc−\ua0and OH−\ua0as counter ions have been synthesized and investigated for their ability to dissolve cellulose, aiming at elucidating solvent structural features affecting cellulose dissolution. Synthesis procedures have been developed to, to a high extent, rely on conversions in water and microwave-assisted reactions employing a reduced number of work-up steps and ion-exchange resins that can be regenerated. Water solutions of morpholinium hydroxides proved capable of dissolving cellulose, with those of them possessing alkyl chains longer than ethyl showing surprising dissolution ability at room-temperature. Morpholinium acetates behaved as ionic liquids, and were also capable of dissolving cellulose when combined with DMSO. The obtained cellulose solutions were characterized according to their chemical and colloidal stability using\ua013C NMR spectroscopy, size exclusion chromatography and flow sweep measurements, while the ethanol coagulates were investigated in terms of crystallinity using solid state NMR. In contrast, the morpholinium chlorides obtained were hygroscopic with high melting points and low solubility in common organic solvents\ua0e.g., acetone, DMSO and DMAc, thus lacking the ability to swell or dissolve cellulose

Debenzylation of Benzyl-Protected Methylcellulose

Methyl cellulose and its derivatives are widely used in the food industry, cosmetics, and as construction materials. The properties of methyl celluloses (MC) strongly depend on their degrees and positions of substitution. In order to generate MCs with uncommon blocky substitution, we apply fully protected O -benzyl- O -methyl celluloses (BnMC). Such complex polysaccharide derivatives could not be deprotected completely and without shift of the composition by methods usually applied to mono- and oligosaccharides. Therefore, a facile debenzylation method was developed based on photo-initiated free-radical bromination in the presence of hydrobromic acid scavengers followed by alkaline treatment. The reaction proceeds under homogeneous conditions and without the aid of any catalyst. There is no need for expensive equipment, materials, anhydrous reagents, or running the reaction under anhydrous conditions. Reaction parameters were investigated and optimized for successful debenzylation of completely protected BnMC with degrees of methyl substitution (DS Me ) around 1.9 (and DS Bn around 1.1). Side-product-free and almost complete debenzylation was achieved when 1,2-epoxybutane (0.5 eq./eq. N -bromosuccinimide) and 2,6-di- tert -butylpyridine (0.5 eq./eq. N -bromosuccinimide) were used in the reaction. Furthermore, ATR-IR and 1 H NMR spectroscopy confirmed the successful removal of benzyl ether groups. The method was developed to monitor the transglycosylation reaction of the BnMC with permethylated cellulose, for which the deprotection of many small samples in parallel is required. This comprises the determination of the methyl pattern in the glucosyl units by gas-liquid chromatography (GLC), as well as oligosaccharide analysis by liquid chromatography mass spectrometry (LC-MS) after perdeuteromethylation and partial hydrolysis to determine the methyl pattern in the chains. The unavoidable partial chain degradation during debenzylation does not interfere with this analytical application, but, most importantly, the DS and the methyl pattern were almost congruent for the debenzylated product and the original MC, indicating the full success of this approach The presented method provides an unprecedented opportunity for high throughput and parallel debenzylation of complicated glucans, such as BnMC (as a model compound), for analytical purposes. For comparison, debenzylation using Na/NH 3 was applied to BnMC and resulted in a completely debenzylated product with a remarkably high recovery yield of 99 mol% and is, thus, the method of choice for synthetic applications, e.g., for the transglycosylation product prepared under the selected conditions in a preparative scale

Engineered polysaccharides: α‐1,3‐glucan acetates showing upper critical solution temperature in organic solvents

Abstract Acetates of α‐1,3‐glucan dissolved in N , N ‐dimethyl acetamide/LiCl are prepared by converting the polysaccharide with acetyl chloride, acetic acid anhydride/pyridine, or with acetic acid/ N,N ′‐carbonyl diimidazole. Values of the degree of substitution for the acetyl groups (DS Ac ) of up to 2.6 are realized. NMR spectroscopic measurements reveal a preferred conversion of the primary hydroxyl group at position 6 followed by positions 2 and 4. Depending on the DS Ac , the samples may be soluble in solvents of different polarity at room temperature or at elevated temperatures showing upper critical solution temperature at DS of about 2.5. This process is found to be reversible

Synthesis and antimicrobial effects of highly dispersed, cellulose-stabilized silver/cellulose nanocomposites

Small, spherical silver nanoclusters were synthesised on the surface of paper as a model cellulosic fibre substrate by a standard chemical reduction method. The concentration of the silver nanoclusters on the substrate surface is roughly proportional to the initial silver salt concentration. However, there is a noticeable degree of nanocluster aggregation to larger agglomerates. The addition of small amounts of α-cellulose, carboxymethyl cellulose or aminocellulose during the synthesis of the silver/cellulose nanocomposites suppresses this aggregation and significantly increases the concentration of the silver nanoclusters on the surface of the fibres of cellulose. These small, surface-stabilised silver nanoclusters, with the desired size and morphology, deposited from aqueous solutions on the surface of cellulosic cotton fibres, show enhanced antibacterial activity against MRSA compared to that of the corresponding silver/cotton nanocomposites prepared in the absence of a cellulosic surface stabiliser

Ultracentrifuge methods for the analysis of polysaccharides, glycoconjugates, and lignins

Although like proteins, polysaccharides are synthesized by enzymes, unlike proteins there is no template. This means that they are polydisperse, do not generally have compact folded structures, and are often very large with greater nonideality behavior in solution. This chapter considers the relevant analytical ultracentrifuge methodology available for characterizing these and related carbohydrate-based systems and information this methodology supplies, in terms of sizes, shapes, and interactions using a comprehensive range of examples, including glycoconjugates and lignins. The relevance and potential of recent software developments such as SEDFIT-MSTAR, the Extended Fujita algorithm, and HYDFIT are considered

Combining Cellulose and Cyclodextrins: Fascinating Designs for Materials and Pharmaceutics

Cellulose and cyclodextrins possess unique properties that can be tailored, combined, and used in a considerable number of applications, including textiles, coatings, sensors, and drug delivery systems. Successfully structuring and applying cellulose and cyclodextrins conjugates requires a deep understanding of the relation between structural, and soft matter behavior, materials, energy, and function. This review focuses on the key advances in developing materials based on these conjugates. Relevant aspects regarding structural variations, methods of synthesis, processing and functionalization, and corresponding supramolecular properties are presented. The use of cellulose/cyclodextrin conjugates as intelligent platforms for applications in materials science and pharmaceutical technology is also outlined, focusing on drug delivery, textiles, and sensors

Phason-phonon coupling in decagonal quasicrystals

Quasikristalle haben neben den von Kristallen bekannten phononischen Freiheitsgraden weitere sogenannte phasonische Freiheitsgrade. Diese basieren auf alternativen Positionen bestimmter Atome im Quasikristall. Ein Sprung eines Atoms auf eine solche alternative Position wird Flip genannt. Beschreibt man den Quasikristall eingebettet in einem höherdimensionalen Hyperraum, so können die phasonischen Freiheitsgrade wie die phononischen als Verzerrungen beschrieben werden. Eine solche phasonische Verzerrung bewirkt im ganzen Quasikristall Flips. Die räumliche Verteilung dieser Flips in Abhängigkeit von der phasonischen Verzerrung wurde konstruiert. Die phasonischen Verzerrungen liefern in einer erweiterten Elastizitätstheorie auch einen Beitrag zur elastischen Energie. Dadurch hat ein Quasikristall neben den phononischen elastischen Konstanten auch sogenannte phasonische und insbesondere auch eine Phason-Phonon-Kopplungskonstante, die eine Wechselwirkung zwischen einer phononischenSchermode und einer phasonischen Verzerrung beschreibt. Es wurde eine Simulationsreihe entwickelt, mit der sowohl alle phononischen wie die phasonischen elastischen Konstanten und die Kopplungskonstante für einen dekagonalen Quasikristall in Molekulardynamiksimulationen bestimmt werden können