Modulation of aluminum species in mordenite zeolite for enhanced dimethyl ether carbonylation

Dimethyl ether (DME) carbonylation is an important intermediate step in the synthesis of methyl acetate (MA) and ethanol. H-form mordenite (MOR) can efficiently catalyze the reaction, in which Brønsted acid sites (BASs) associated with framework Al function as active sites. But the role of other Al species such as exteraframework Al (EFAl) and framework-associated Al still remains unknown. In this study, we have proposed two convenient approaches for controlling the two Al species and investigating their influence on the DME carbonylation reaction. NH3-TPD and Py-IR analyses revealed that the number of BASs increased after the removal of EFAl and the inhibition the formation of framework-associated Al. The reactivity results showed that the elimination of EFAl promoted the DME conversion from 28% to 46%. Additionally, through the implementation of in-situ calcination to impede the presence of framework-associated Al, the DME conversion increased from 28% to 50%. With the understanding that both EFAl and framework-associated Al have a detrimental effect on the reaction, the highest conversion is achieved with these two treatments, leading to 73% DME conversion with 99% selectivity to MA. Our findings provide a systematical strategy to effectively regulate the presence of Al species in zeolite, offering insights of rational design to optimize zeolite catalysts for important industrialized process

Electrospun membranes of diselenide-containing poly(ester urethane)urea for <i>in situ</i> catalytic generation of nitric oxide

Nitric oxide (NO) plays an important role as a signalling molecule in the biological system. Organoselenium-coated or grafted biomaterials have the potential to achieve controlled NO release as they can catalyse decomposition of endogenous S-nitrosothiols to NO. However, such biomaterials are often challenged by the loss of the catalytic sites, which can affect the stability in tissue repair applications. In this work, we prepare a diselenide-containing poly(ester urethane)urea (SePEUU) polymer with Se–Se in the backbone, which is further electrospun into fibrous membranes by blending with poly(ester urethane)urea (PEUU) without diselenide bonds. The presence of catalytic sites in the main chain demonstrates stable and long-lasting NO catalytic activity, while the porous structure of the fibrous membranes ensures uniform distribution of the catalytic sites and better contact with the donor-containing solution. PEUU/SePEUU50 in 50/50 mass ratio has a physiologically adapted rate of NO release, with a sustained generation of NO after exposure to PBS at 37 °C for 30 d. PEUU/SePEUU50 has a low hemolysis and protein adsorption, with mechanical properties in the wet state matching those of natural vascular tissues. It can promote the adhesion and proliferation of human umbilical vein endothelial cells in vitro and control the proliferation of vascular smooth muscle cells in the presence of NO generation. This study exhibits the electrospun fibrous membranes have potential for utilizing as hemocompatible biomaterials for regeneration of blood-contacting tissues. Electrospun membranes of diselenide-containing poly(ester urethane)urea exhibit stable catalytic activity of NO generation, which promotes human umbilical vein endothelial cell proliferation and control the proliferation of vascular smooth muscle cells for potential applications as blood-contacting biomaterials.</p

Activation of Upper Critical Solution Temperature Behaviors of Zwitterionic Poly(l‑methionine‑<i>g</i>‑poly(sulfobetaine methacrylate)_<i>m</i>) with a Bottlebrush Structure

Aqueous poly­(sulfobetaine methacrylate) (PSBMA) solutions exhibit upper critical solution temperature (UCST) behaviors, which are influenced by the topological structure and relative molar mass of the polymer chain. In this study, a series of well-defined PSBMA-based zwitterionic bottlebrush poly­(l-methionine) derivatives, namely, poly­(l-methionine-g-(PSBMA)m) (MS-m), were synthesized via ring-opening polymerization of l-methionine N-carboxyanhydride, followed by bromo-alkylation and atom transfer radical polymerization. The aqueous MS-70 (m = 70) solution showed UCST-type thermoresponsive properties with a cloud point (Tcp) at around 38.6 °C. The variable temperature nuclear magnetic resonance results of 1H and 2D 1H–1H correlated spectroscopy and nuclear Overhauser effect spectroscopy (NOESY) demonstrated correlated peaks and coupling interactions between protons in the sulfobetaine units. When the temperature increased up to or beyond Tcp, the NOESY spectra showed that the zwitterionic bottlebrush MS-70 polypeptides transformed from the aggregated state to the monodisperse state owing to the weakened inter/intramolecular interactions between the positively and negatively charged groups. In contrast, the observed UCST transition near the physiological temperatures could be negligible in linear PSBMA or the linear-like SBMA polymer of MS-70 degraded by papain. Results indicated that the bottlebrush structure activated the solution properties of zwitterions. In brief, this study presents a precise strategy for synthesizing zwitterionic bottlebrush polypeptides with an elucidated mechanism of thermal responsiveness in aqueous solution. It provides valuable insights into expanding applications of zwitterions in biology, such as protein stabilization or zwitterionic hydrogels