A study on the interaction of cationized chitosan with cellulose surfaces

This investigation describes the interaction of trimethyl chitosans (TMCs) with surfaces of cellulose thin films. The irreversible deposition/adsorption of TMCs with different degrees of cationization was studied with regards to the salt concentration and pH. As substrates, cellulose thin films were prepared by spin coating from trimethylsilyl cellulose and subsequent regeneration to pure cellulose. The pH-dependent zeta potential of cellulose thin films and the charge of TMCs were determined by streaming potential and potentiometric charge titration methods. A quartz crystal microbalance with dissipation monitoring was further used as a nanogram sensitive balance to detect the amount of deposited TMCs and the swelling of the bound layers. The morphology of the coatings was additionally characterized by atomic force microscopy and related to the adsorption results. A lower degree of cationization leads to higher amounts of deposited TMCs at all salt concentrations. Higher amounts of salt increase the deposition of TMCs. Protonation of primary amino groups results in the immobilization of less material at lower pH values. The results from this work can further be extended to the modification of regenerated cellulosic materials to obtain surfaces, with amino- and trimethylammonium moieties.     

Reductive ring cleavage of 1-alkyl-4-benzoylamino-5-phenyl-3-pyrazolidinones with raney-nickel alloy. Synthesis of N-benzoyl-3-alkylamino-3-phenylalanine amides from rel-(4R,5R)-4-benzoylamino-5-phenyl-3-pyrazolidinone

rel-(4R,5R)-4-Benzoylamino-5-phenyl-3-pyrazolidinone ( 1 ) was alkylated at position 1 with carbonyl compounds 2a-g . The corresponding rel-(4R,5R)-4-benzoylamino-5-phenyl-3-pyrazolidinone-1-azomethine imines 3a-g , were treated with sodium borohydride to give rel-(4R,5R)-1-alkyl-4-benzoylamino-5-phenyl-3-pyrazolidinones 4a-g . Reduction of pyrazolidinones 4a-g with Raney-nickel alloy in methanolic potassium hydroxide furnished rel-(4R,5R)-N-benzoyl-3-alkylamino-3-phenylalanine amides 5a-f .     

Flame retardant activity of SiO2-coated regenerated cellulose fibres

An alternative route to lower the flammability of viscose fibres is presented. Instead of adding a flame retardant to the viscose dope chemically, we have grown a layer of silica (SiO₂) on the surface of a regenerated cellulose fibre via a sol-gel process. One set of samples was used as-received, while the other was pre-treated in an 18% NaOH solution, giving a rough, etched surface to the fibre. The different surface morphology of both fibre types triggered a different growth of silica layers. On an untreated fibre, silica formed a 300-400 nm thick surface layer containing a high density of cracks and holes. Conversely, on a NaOH pre-treated fibre, the silica layer intruded into fibre interior, adhered more tightly to the fibre structure and formed an almost defect-free, thin (100 nm) layer on the outer fibre surface. This type of silica layer increased the temperature at which the fibre started to decompose by 20 °C. It also hindered significantly the flow of oxygen to the generated volatiles during the thermal decomposition, and increased the temperature of glowing combustion of the residual char; the temperature of the corresponding exothermic peaks increased by ca. 20 °C and 40 °C. In contrast, the thermal effects of silica coatings that grew on an untreated fibre were much smaller.     

Synthesis of CDE molecular fragments related to sendanin mediated by titanocene(III)

A practical, brief, and diastereoselective synthesis of limonoid CDE fragments from a readily available starting material is described. The key step was the titanocene(III)-promoted cyclization of unsaturated epoxylactones, readily prepared from α-cyclocitral. In this way, we confirm the viability of our procedure for the synthesis of a limonoid model with different functionalization patterns. We also report the antifeedant activity of epoxylactones 18 and 19, which show significant antifeedant activity against Spodoptera littoralis and Spodoptera frugiperda, two insect species with different feeding ecologies.     

A novel synergistic formulation between a cationic surfactant from lysine and hyaluronic acid as an antimicrobial coating for advanced cellulose materials

In this investigation, a novel coating for viscose fabric surface modification was developed using a synergistic formulation between a natural antimicrobial cationic surfactant from lysine (MKM) and a biopolymer hyaluronic acid (HA). The interaction between MKM and HA in aqueous solutions, as well as the interactions between their synergistic formulation (HA-MKM) and viscose fabric (CV) were studied using pH-potentiometric titrations’, turbidity measurements, the Kjeldahl method for the determination of nitrogen amounts, attenuated total reflectance fourier transform infrared spectroscopy, and scanning electron microscopy. The hydrophilic and antimicrobial properties of the functionalised CV were examined in order to evaluate its usages for medical applications. The results of the interaction studies showed that MKM and HA interact with each other by forming a precipitate when the binding sites of HA are saturated. The precipitate has a slightly positive charge at neutral pH due to excess binding of the MKM to HA. The excess positive charge was also detected on CV coated with HA-MKM. This was proven to be very beneficial for the antimicrobial properties of the functionalised CV. The antimicrobial tests showed exceptional antimicrobial activity of the functionalised CV against Escherichia Coli, Staphylococcus Aureus, Streptococcus Agalactiae, Candida Albicans, and Candida Glabrata, making the CV fabric highly interesting for potential use in medicine.     

A brief and stereoselective synthesis of limonoid models, with antifeedant activity against Locusts migratoria

A short stereoselective preparation of havanensin-type limonoid models is reported. The synthesis is based on a radical domino reaction of an epoxyketone to a bicyclic hydroxyketone, and is achieved in six and nine steps from simple cyclohexenones. The epoxyhavanensin derivatives show significant antifeedant activity against Spodoptera littoralis and Spodoptera frugiperda, and the epoxyketone 21 shows potent antifeedant activity against Locusts migratoria.     

Controlling the Assembly of Cellulose-Based Oligosaccharides through Sequence Modifications

Peptides and nucleic acids with programmable sequences are widely explored for the production of tunable, self-assembling functional materials. Herein we demonstrate that the primary sequence of oligosaccharides can be designed to access materials with tunable shapes and properties. Synthetic cellulose-based oligomers were assembled into 2D or 3D rod-like crystallites. Sequence modifications within the oligosaccharide core influenced the molecular packing and led to the formation of square-like assemblies based on the rare cellulose IV_II allomorph. In contrast, modifications at the termini generated elongated aggregates with tunable surfaces, resulting in self-healing supramolecular hydrogels.