Imination of Microporous Chitosan Fibers—A Route to Biomaterials with “On Demand” Antimicrobial Activity and Biodegradation for Wound Dressings

Microporous chitosan nanofibers functionalized with different amounts of an antimicrobial agent via imine linkage were prepared by a three-step procedure including the electrospinning of a chitosan/PEO blend, PEO removal and acid condensation reaction in a heterogeneous system with 2-formylphenylboronic acid. The fibers’ characterization was undertaken keeping in mind their application to wound healing. Thus, by FTIR and 1H-NMR spectroscopy, it was confirmed the successful imination of the fibers and the conversion degree of the amine groups of chitosan into imine units. The fiber morphology in terms of fiber diameter, crystallinity, inter- and intra-fiber porosity and strength of intermolecular forces was investigated using scanning electron microscopy, polarized light microscopy, water vapor sorption and thermogravimetric analysis. The swelling ability was estimated in water and phosphate buffer by calculating the mass equilibrium swelling. The fiber biodegradation was explored in five media of different pH, corresponding to different stages of wound healing and the antimicrobial activity against the opportunistic pathogens inflicting wound infection was investigated according to standard tests. The biocompatibility and bioadhesivity were studied on normal human dermal fibroblast cells by direct contact procedure. The dynamic character of the imine linkage of the functionalized fibers was monitored by UV-vis spectroscopy. The results showed that the functionalization of the chitosan microporous nanofibers with antimicrobial agents via imine linkage is a great route towards bio-absorbable wound dressings with “on demand” antimicrobial properties and biodegradation rate matching the healing stages.

Bouncing dynamics of electrostatically actuated NEM switches

The aim of the present research is to understand the bouncing dynamic behavior of nano electromechanical (NEM) switches in order to improve the switch performance and reliability. It is well known that bouncing can dramatically degrade the switch performance and life; hence, in the present study, the bouncing dynamics of a cantilever-based NEM switch has been studied in detail. To this end, the repulsive van der Waals force is incorporated into a nano-switch model to capture the contact dynamics. Intermolecular forces, surface effects, and gas rarefication effects were also included in the proposed model. The Euler-Bernoulli beam theory and an approximate approach based on Galerkin’s method have been employed to predict transient dynamic responses. In the present study, performance parameters such as initial contact time, permanent contact time, major bounce height, and the number of bounces, were quantified in the presence of interactive system nonlinearities. The performance parameters were used to investigate the influence of surface effects and rarefication effects on the performance of an electrostatically actuated switch. Recommended operating conditions are suggested to avoid excessive bouncing for these types of NEM switches.

Theoretical and X-ray studies on the cyclisation of 1-phenyl-5-(3-aryltriaz-1-en-1-yl)-1Hpyrazole- 4-carbonitriles and 2-amino-3-(3-aryltriaz-1-en-1-yl)maleonitriles: A comparison study

The present work investigates attempts to cyclise 1-phenyl-5-(3-aryltriaz-1-en-1-yl)-1H-pyrazole- 4-carbonitriles to the desired pyrazolo[3,4-d][1,2,3]triazinimine derivatives. The cyclisations were unfruitful, and a density functional theory study was performed. This revealed the 1-phenyl-5-(3-aryltriaz-1-en-1-yl)-1H-pyrazole-4-carbonitriles are more stable than the targeted pyrazolo[3,4-d][1,2,3]triazinimine derivatives, indicating that their cyclisation is thermodynamically disfavoured; the reactant 8c is more stable than the predicted six-membered ring products 9c by 5 kJ/mol. The effect of isomerisation of the methoxy-phenyl group in the self-assembly of 8c and 8d in the crystalline lattice was investigated. The intermolecular forces in solid state were analysed in the two structural isomers 8c and 8d using calculated HirshFeld surface; the analysis indicates that the intermolecular forces are stronger in 8c than 8d and hence 8c is denser than 8d by 0.071g/mL.

Amyand David Buckingham. 28 January 1930—4 February 2021

David Buckingham was a chemical physicist and theoretical chemist who made fundamental contributions to the understanding of optical, electric and magnetic properties of molecules. Born in Australia, he was an undergraduate at the University of Sydney and the first PhD research student of John Pople (FRS 1961) at Cambridge, and there he made significant advances in the theory of intermolecular forces and nonlinear optics. He then moved to Oxford, where he and his group performed the first direct measurement of a molecular electric quadrupole moment. He was elected to the first chair of theoretical chemistry at the University of Bristol, where he wrote a particularly influential article on molecular moments, higher-order polarizabilities and intermolecular forces. His next appointment was at the University of Cambridge as the first holder of the 1968 Chair of Chemistry, and he was head of a distinguished department of theoretical chemistry for 28 years. With colleagues he pioneered experiment and theory on vibrational optical activity and developed a powerful model to predict the structures of weakly-bound molecules. A man of broad interests and achievements, he played first class cricket in the 1950s.

Physicochemical, Digestive, and Sensory Properties of Panax Notoginseng Saponins Encapsulated by Polymerized Whey Protein

Panax Notoginseng Saponins (PNS) may be beneficial to human health due to their bioactive function. The application of PNS in functional foods was limited due to the bitter taste and low oral bioavailability. PNS were encapsulated by polymerized whey protein (PWP) nanoparticles. The physicochemical, digestive, and sensory properties of the nanoparticles were investigated. Results showed that the nanoparticles had a particle size of 55 nm, the zeta potential of −28 mV, and high PNS encapsulation efficiency (92.94%) when the mass ratio of PNS to PWP was 1:30. Differential Scanning Calorimetry (DSC) results revealed that PNS were successfully encapsulated by PWP. The mainly intermolecular forces between PNS and PWP were hydrogen bonding and electrostatic attraction confirmed by Fourier Transform Infrared Spectroscopy (FTIR). Results of simulated gastrointestinal digestion indicated that the PNS-PWP (1:30) nanoparticles had smaller average particle size (36 nm) after treatment with gastric fluids and increased particle size (75 nm) after treatment with intestinal fluids. Transmission Electron Microscopy (TEM) micrographs reflected that the nanoparticles had irregular spherical structures. The encapsulated PNS exhibited significantly (p < 0.05) decreased bitterness compared to the non-encapsulated PNS confirmed by the electronic tongue. The results indicated that encapsulation of PNS with PWP could facilitate their application in functional foods.

Organo-Functionalization: An Effective Method in Enhancing the Separation and Antifouling Performance of Thin-Film Nanocomposite Membranes by Improving the Uniform Dispersion of Palygorskite Nanoparticles

Recently, palygorskite (Pal) has become a promising new membrane additive in flux enhancement and fouling reduction, which is an environmentally friendly nanoclay material under the 2:1 layer composition with 1D tubular structure. However, the aggregation of Pal due to the intermolecular forces is still an obstacle to be solved in improving membrane performance. Herein, Pal nanoparticles were chemically modified by KH550 to weaken the aggregation and improve the dispersibility, and then incorporated into the organic phase to prepare thin-film nanocomposite (TFN) membranes. The results showed that the organo-functionalization could effectively improve the membrane hydrophilicity and dispersion of Pal nanoparticles in the polyamide layer, which contributed to the enhanced water flux (from 25 to 38 L/m2·h), unchanged salt rejection (98.0%) and better antifouling capacity (91% flux recovery rate), which suggested that the organo-functionalization of nanoparticles was an efficient method in further enhancing membrane performance

Albumin–Hyaluronan Interactions: Influence of Ionic Composition Probed by Molecular Dynamics

The lubrication mechanism in synovial fluid and joints is not yet fully understood. Nevertheless, intermolecular interactions between various neutral and ionic species including large macromolecular systems and simple inorganic ions are the key to understanding the excellent lubrication performance. An important tool for characterizing the intermolecular forces and their structural consequences is molecular dynamics. Albumin is one of the major components in synovial fluid. Its electrostatic properties, including the ability to form molecular complexes, are closely related to pH, solvation, and the presence of ions. In the context of synovial fluid, it is relevant to describe the possible interactions between albumin and hyaluronate, taking into account solution composition effects. In this study, the influence of Na+, Mg2+, and Ca2+ ions on human serum albumin–hyaluronan interactions were examined using molecular dynamics tools. It was established that the presence of divalent cations, and especially Ca2+, contributes mostly to the increase of the affinity between hyaluronan and albumin, which is associated with charge compensation in negatively charged hyaluronan and albumin. Furthermore, the most probable binding sites were structurally and energetically characterized. The indicated moieties exhibit a locally positive charge which enables hyaluronate binding (direct and water mediated).