Martina Opietnik

Synthesis of Gold Nanoparticles for In Situ Conjugation with Structural Carbohydrates

Gold nanoparticles (GNPs) have recently attracted much attention as innovative nanomaterials with unique properties in the fields of physicochemistry and biomedicine, 2] because of their quantum-size effects. Surface modification of GNPs is essential for enhancing their functionality and versatility, hence extensive efforts have been devoted to methodological studies toward the synthesis of GNPs and modification of their surfaces with a variety of functional molecules. Of the various substances used for surface modification of GNPs, carbohydrates have become a major target because of their specific molecular characteristics and actions in living systems. Many types of carbohydrate-related molecules have been used for conjugation with GNPs. However, there have been few reports on the related uses of structural carbohydrates because of their poor solubility and the considerable difficulties in their reaction with GNPs. Cellulose, a b-1,4-linked d-glucopyranose polymer that is the major constituent of plant cell walls, is a typical structural polysaccharide. It has unique amphipathic and self-assembling properties because of the formation of regular intra and intermolecular hydrogen bonds. Such molecular features are expected to provide a high potential for gathering the functional carbohydrate moieties on GNP surfaces. However, cellulose that has a degree of polymerization (DP) greater than six is insoluble in both common aqueous and organic media because of its inherent, strong molecular interactions. 11] Consequently, it is extremely difficult to apply to the glycomodification of GNP surfaces by using conventional approaches. Herein we present the first preparation of GNPs that uses an ideal solvent for structural carbohydrates such as cellulose, namely hot 80% N-methylmorpholine-N-oxide (NMMO)/ H2O, and the in situ conjugation of the GNPs with thiolabeled cellulose through spontaneous chemisorption. We have previously reported the successful formation and resulting biofunctionality of cellulose nanolayers from cellulose thiosemicarbazones (cellulose-TSCs, Figure 1a). These nanolayers, which are formed through self-assembling S–Au chemisorption on a gold plate, have a parallel-chain alignment.

Shaped hemocompatible aerogels from cellulose phosphates: preparation and properties

Abstract Hemocompatible, shaped cellulose phosphate aerogels were obtained from phosphorylated cellulosic pulps of low degree of phosphorylation (DSP≤0.20) by dissolution in stabilized NMMO×H2O, shaping, reprecipitation with ethanol and subsequent scCO2 drying. The novel aerogels were found to be promising materials for cell scaffolding and bone grafting. Special features include their interconnected and spread porosity, highly porous surface and microstructure, good hemocompatibility, and suitable hydroxyl apatite-binding environment. Adsorption of Ca2+ ions to the phosphate groups did not invert the negative inflammatory response observed after phosphorylating cellulose, but increased platelet-dependent parameters of hemostasis.

Synthesis of redispersible spherical cellulose II nanoparticles decorated with carboxylate groups

Cellulose II gels from a product line of the Lyocell fiber process were transformed into spherical nanoparticles by carboxymethylation and subsequent homogenization. Three populations of nanoparticles were synthesized and their particle size analysis by TEM and DLS revealed a dependence of the size on the amount of introduced carboxylate groups. The higher the amount of functionalization, the smaller the particle sizes. The three synthesized nanocolloidal populations feature a mean size of 73 nm, 107 nm and 129 nm and degree of substitution of 0.15, 0.09 and 0.04, respectively. After drying, the particles can easily be redispersed in water which distinguishes them from most alternative cellulosic nanomaterials.

Side reactions of 4-acetamido-TEMPO as the catalyst in cellulose oxidation systems

Abstract TEMPO/hypochlorite oxidation of cellulosics are frequently used to obtain water-soluble polyglucuronates or nano-disperse materials. The reaction under neutral conditions offers a big advantage over hitherto applied alkaline systems as base-induce β-elimination reactions causing severe cellulose degradation are suppressed. Although 4-acetamido-TEMPO seems to offer high initial activities in cellulose oxidation, the TEMPO derivative is irreversibly converted into species with much lower reactivity. The degradation pathways and the chemical structure of the 4-acetamido-TEMPO-derived (by)products have been clarified. Degradation is strongly dependent on the pH value of the reaction mixture. In acidic conditions (pH<5), 4-oxo-TEMPO is formed by an oxidative deamination process, the 4-oxo-derivative still being capable of performing cellulose oxidation. In alkaline media, a similar process proceeds, but is immediately followed by a Favorskij rearrangement to a pyrrolidine-3-carboxylic acid (PROXYL) derivative. In both cases, the released acetamido moiety is slowly converted into methylamine by a decarboxylative rearrangement (Hofmann degradation). The results suggest that the instability and the chemical fate of 4-acetamido-TEMPO needs to be considered when cellulose oxidations and their kinetics are addressed: the recyclability of the 4-acetamido-TEMPO catalyst is rather limited.

A General Aqueous Silanization Protocol to Introduce Vinyl, Mercapto or Azido Functionalities onto Cellulose Fibers and Nanocelluloses

The effective and straight-forward modification of nanostructured celluloses under aqueous conditions or as “never-dried” materials is challenging. We report a silanization protocol in water using catalytic amounts of hydrogen chloride and then sodium hydroxide in a two-step protocol. The acidic step hydrolyzes the alkoxysilane to obtain water-soluble silanols and the subsequent addition of catalytic amounts of NaOH induces a covalent reaction between cellulose surficial hydroxyl groups and the respective silanols. The developed protocol enables the incorporation of vinyl, thiol, and azido groups onto cellulose fibers and cellulose nanofibrils. In contrast to conventional methods, no curing or solvent-exchange is necessary, thereby the functionalized celluloses remain never-dried, and no agglomeration or hornification occurs in the process. The successful modification was proven by solid state NMR, ATR-IR, and EDX spectroscopy. In addition, the covalent nature of this bonding was shown by gel permeation chromatography of polyethylene glycol grafted nanofibrils. By varying the amount of silane agents or the reaction time, the silane loading could be tuned up to an amount of 1.2 mmol/g. Multifunctional materials were obtained either by prior carboxymethylation and subsequent silanization; or by simultaneously incorporating both vinyl and azido groups. The protocol reported here is an easy, general, and straight-forward avenue for introduction of anchor groups onto the surface of never-dried celluloses, ready for click chemistry post-modification, to obtain multifunctional cellulose substrates for high-value applications.