N-Oxide Zwitterion Functionalized Positively Charged Polyamide Composite Membranes for Nanofiltration

Medicinal Chemistry of Drugs with N-Oxide Functionalities

Molecules with N-oxide functionalities are omnipresent in nature and play an important role in Medicinal Chemistry. They are synthetic or biosynthetic intermediates, prodrugs, drugs, or polymers for applications in drug development and surface engineering. Typically, the N-oxide group is critical for biomedical applications of these molecules. It may provide water solubility or decrease membrane permeability or immunogenicity. In other cases, the N-oxide has a special redox reactivity which is important for drug targeting and/or cytotoxicity. Many of the underlying mechanisms have only recently been discovered, and the number of applications of N-oxides in the healthcare field is rapidly growing. This Perspective article gives a short summary of the properties of N-oxides and their synthesis. It also provides a discussion of current applications of N-oxides in the biomedical field and explains the basic molecular mechanisms responsible for their biological activity.

Advancing Lithium-Magnesium Separation: Pioneering Swelling-Embedded Cation Exchange Membranes Based on Sulfonated Poly(ether ether ketone)

With the continuous advancement of electrodialysis (ED) technology, there arises a demand for improved monovalent cation exchange membranes (CEMs). However, limitations in membrane materials and structures have resulted in the low selectivity of monovalent CEMs, posing challenges in the separation of Li+ and Mg2+. In this investigation, a designed CEM with a swelling-embedded structure was created by integrating a polyelectrolyte containing N-oxide Zwitterion into a sulfonated poly(ether ether ketone) (SPEEK) membrane, leveraging the notable solubility characteristic of SPEEK. The membranes were prepared by using N-oxide zwitterionic polyethylenimine (ZPEI) and 1,3,5-benzenetrlcarbonyl trichloride (TMC). The as-prepared membranes underwent systematic characterization and testing, evaluating their structural, physicochemical, electrochemical, and selective ED properties. During ED, the modified membranes demonstrated notable permeability selectivity for Li+ ions in binary (Li+/Mg2+) systems. Notably, at a constant current density of 2.5 mA cm-2, the modified membrane PEI-TMC/SPEEK exhibited significant permeability selectivity ( P Mg 2 + Li + = 5.63 ) in the Li+/Mg2+ system, while ZPEI-TMC/SPEEK outperformed, displaying remarkable permeability selectivity ( P Mg 2 + Li + = 12.43 ) in the Li+/Mg2+ system, surpassing commercial monovalent cation-selective membrane commercial monovalent cation-selective membrane (CIMS). Furthermore, in the Li+/Mg2+ binary system, Li+ flux reached 9.78 × 10-9 mol cm-2 s-1 for ZPEI-TMC/SPEEK, while its Mg2+ flux only reached 2.7 × 10-9 mol cm-2 s-1, showing potential for lithium-magnesium separation. In addition, ZPEI-TMC/SPEEK was tested for performance and stability at high current densities. This work offers a straightforward preparation process and an innovative structural approach, presenting methodological insights for the advancement of lithium and magnesium separation techniques.

Bioinspired N-Oxide-Based Zwitterionic Polymer Brushes for Robust Fouling-Resistant Surfaces

Fouling-resistant surfaces are needed for various environmental applications. Inspired by superhydrophilic N-oxide-based osmolytes in saltwater fish, we demonstrate the use of a trimethylamine N-oxide (TMAO) analogue for constructing fouling-resistant surfaces. The readily synthesized N-oxide monomer of methacrylamide is grafted to filtration membrane surfaces by surface-initiated atom transfer radical polymerization (SI-ATRP). Successful grafting of the amine N-oxide brush layer as confirmed by material characterization endows the surface with increased hydrophilicity, reduced charge, and decreased roughness. Notably, the introduction of the N-oxide layer does not compromise transport properties, i.e., water permeability and water-salt selectivity. Moreover, the modified membrane exhibits improved antifouling properties with a lower flux decline (32.1%) and greater fouling reversibility (18.55%) than the control sample (45.4% flux decline and 3.26% fouling reversibility). We further evaluate foulant-membrane interaction using surface plasmon resonance (SPR) to relate the reduced fouling tendency to the synergic effects of surface characteristic changes after amine N-oxide modification. Our results demonstrate the promise and potential of the N-oxide-based polymer brushes for the design of fouling resistance surfaces for a variety of emerging environmental applications.