Faraday Discussions最新文献

Non-isocyanate polyurethanes (NIPUs) can be prepared from the highly unsaturated oils or fatty acid methyl esters obtained from waste fish and algae oil. The abundant carbon–carbon double bonds can be epoxidized and reacted with CO₂ to produce cyclic carbonates. Upon reaction with a bioderived amine from waste cashew nutshells, a NIPU is obtained. Fish-oil derived NIPUs were studied for biodegradation and were found to be susceptible to degradation by bacteria and fungi. Algae oil tri- and diacylglycerides were converted to their fatty acid methyl esters (FAMEs) and used for the preparation of NIPUs in a similar fashion to fish oil. NIPUs could be obtained as thermoset films, which were characterized via infrared spectroscopy to verify urethane linkage formation and dynamic mechanical analysis for their physical properties. These processes can lead to new opportunities in waste valorization of the aquaculture industry and demonstrate the promise of algae as an abundant source of biomass.

The Lewis acidic borane tris(pentafluorophenyl)borane, B(C₆F₅)₃ or BCF, has been found to selectively depolymerize polycarbonates to their corresponding cyclic carbonates without the need of a co-catalyst. Depolymerizations of poly(propylene carbonate) (PPC) and poly(cyclohexene carbonate) (PCHC) in toluene were studied with varying catalyst loadings and temperatures. Good conversions to the respective cyclic carbonates were observed down to 2.5 mol% BCF and at temperatures down to 75 °C. No conversion was observed under solvent-free or liquid-assisted grinding conditions in a mixer mill. Kinetic studies via in situ infrared spectroscopy of the system showed an activation energy of 50.2 ± 6.7 kJ mol⁻¹ for PPC and 83.5 ± 1.7 kJ mol⁻¹ for PCHC. Entropy of activation values were found to be −190.6 ± 18.4 J K⁻¹ mol⁻¹ for PPC and −114.7 ± 3.8 J K⁻¹ mol⁻¹ for PCHC. Initial rates of conversion were significantly faster for PPC than PCHC. Aliquots were taken from reaction mixtures and analyzed via¹H NMR spectroscopy and gel permeation chromatography to understand the reaction mechanism, which was found to occur via chain-end backbiting rather than random chain scission. Depolymerization attempts were performed on systems containing various additives/impurities including poly(bisphenol A carbonate), H₂O and CO₂. H₂O was seen to inhibit the reaction. Therefore, it was not surprising that a commercial polycarbonate-diol did not depolymerize under the reaction conditions explored.

The catalytic reduction of lignin into bio-chemicals is desirable yet remains a challenge due to its heterogeneity and complexes. Herein, a copper oxide supported monoclinic ZrO₂ (CuO/m-ZrO₂) catalyst is fabricated for efficient reductive catalytic fractionation (RCF) of softwood lignin, affording a yield of monophenols up to 18.7 wt% with a high selectivity (82.3%) for 4-n-propanol guaiacol. Some key parameters, such as β-O-4′ models, solvent, mass ratio, reaction temperature and time, are systematically investigated to reveal their effects on the yields of monomers. Notably, mechanistic studies indicate the interactions between metal and acid sites enhance catalytic activity toward the effective scission of C–O bonds. Furthermore, a successful isolation of 68.3% monophenols is achieved in the gram scale amplification reaction. The monophenol formation pathway is deduced by the expansion of β-O-4′ model compounds and other substrates. The insights from this work pave a new way for the rational design of non-precious catalysts for the transformation of lignin into fine chemicals.

The fusion of lipid membranes progresses through a series of intermediate steps with two significant energy barriers: hemifusion-stalk formation and fusion-pore expansion. The cell’s ability to tune these energy barriers is crucial as they determine the rate of many biological processes involving membrane fusion. However, a mechanism that allows the cell to manipulate both barriers in the same direction remains elusive, since membrane properties that the cell could dynamically tune during its life cycle, such as the lipids’ spontaneous curvatures and membrane tension, have an opposite effect on the two barriers: tension inhibits stalk formation while promoting fusion-pore expansion. In contrast, increasing the total membrane concentration of lipids with negative intrinsic curvatures, such as cholesterol, promotes hemifusion-stalk formation while inhibiting pore expansion, and vice versa for lipids with positive intrinsic curvatures. Therefore, changes in these membrane properties increase one energy barrier at the expense of the other, resulting in a mixed effect on the fusion reaction. A possible mechanism to change both barriers in the same direction is by inducing lipid composition asymmetry, which results in tension and spontaneous curvature differences between the monolayers. To test the feasibility of this mechanism, a continuum elastic model was used to simulate the fusion intermediates and calculate the changes in the energy barriers. The calculations showed that a reasonable lipid composition asymmetry could lead to a 10–20k_BT difference in both energy barriers, depending on the direction from which fusion occurs. We further provide experimental support to the model predictions, demonstrating changes in the time to hemifusion upon asymmetry introduction. These results indicate that biological membranes, which are asymmetric, have a preferred direction for fusion.

Crystallization-driven self-assembly (CDSA) offers a powerful approach for constructing well-defined nanostructures; however, achieving precise control over two-dimensional (2D) platelet formation remains challenging, particularly for poly(L-lactide) (PLLA). In this work, we developed a seeded growth strategy using a mixture of homopolymers and diblock polymers to prepare PLLA platelets. In this system, homopolymers facilitate the formation of 2D platelets and enhance crystallization kinetics, while diblock polymers stabilize the platelets and provide functional moieties through their corona-forming block. By systematically optimizing temperature, polymer composition, and polymer length, we achieved size-controllable platelets. Furthermore, we successfully transferred the platelet preparation from batch to a continuous flow system to enable scalable production. This study contributes to the advancement of biodegradable and biocompatible nanoparticles, offering new possibilities for their application in biomedical and functional materials.

Biominerals have unique morphologies and complex hierarchical microstructures, so the study of biomineralization has benefited greatly from the development of advanced microscopy and characterization tools. In my career, I witnessed a revolutionary change in the theories relating to biomineral formation mechanisms. While much of this was due to the advancements in imaging techniques, I present an argument to suggest that in vitro model systems played an important role in steering the biomineral community toward resolving the non-classical crystallization processes that are now understood to lie at the foundation of biological calcification processes. This retrospective review will discuss two case studies that are classic examples of biominerals, mollusk nacre for the invertebrates, and bone for the vertebrates. It will therefore be biased given my group's discovery of the Polymer-Induced Liquid-Precursor (PILP) process, which serendipitously emulated the morphologies and textures of these (and other) biominerals. The goal, however, is not to repeat that body of literature, but rather to demonstrate how the use of model systems has helped decipher mineralization mechanisms, and to propose new ideas that could be explored to further advance the field.

Supramolecular hydrogels are physical hydrogels that are formed by non-covalent interactions such as hydrogen bonding, electrostatic attraction, hydrophobic interactions, and π–π stacking. Compared to typical, chemically cross-linked hydrogels, supramolecular networks commonly have stimuli-responsive behavior including reversibility and injectability, which are being widely studied for uses in drug delivery, tissue engineering, and wound healing. This review highlights recent developments in supramolecular network design and behavior focusing on the different possible molecular building blocks, including peptides, polysaccharides, synthetic polymers, and multicomponent systems. We further discuss self-assembly mechanisms of hydrogel formation, as well as recent advances in stimuli-responsive supramolecular hydrogels triggered by pH, temperature, and light. Advanced characterization techniques such as rheological analysis, spectroscopy, scattering methods, and electron microscopy are summarized to understand hydrogel structure, assembly pathways, and ultimate network properties. This review provides readers with an updated understanding of supramolecular hydrogels and highlights current research presented during the Faraday Discussions meeting on advances in supramolecular gels, promoting the rational design and development of novel materials to address complex biomedical and other technological challenges.

One of the defining properties of the eukaryotic plasma membrane is the glycocalyx, which is formed by glycosylated lipids and proteins. The glycocalyx is arranged asymmetrically, as it is exclusive to the extracellular side of the membrane. Membrane asymmetry therefore includes both lipid and carbohydrate asymmetry, whereby the latter has the most skewed trans-leaflet imbalance. The glycocalyx plays a structural role that protects cell integrity and it also participates in mechanosensing and other cellular processes. However, our understanding of glycocalyx function is hampered by the lack of suitable model systems to perform biophysical investigation. Here, we describe the engineering of lipid bilayers that are chemically conjugated at the outer surface with one of the most abundant glycocalyx components, chondroitin sulfate (CS). Membranes were doped with a reactive phospholipid, which allowed thiol–maleimide conjugation of thiol-modified CS at the lipid headgroup. Our data show that we achieved CS conjugation of large unilamellar vesicles, supported lipid bilayers, and giant unilamellar vesicles. CS conjugation of vesicles allowed electrostatic recruitment of poly-L-lysine, which could recruit other CS-coated vesicles or CS in solution. Overall, we describe a simple and robust method for polysaccharide functionalization of vesicles which can be applied to gain new mechanistic understanding of the pathophysiological role of the glycocalyx.