Dehydrated Biomimetic Membranes with Skinlike Structure and Function.

Novel vapor-permeable materials are sought after for applications in protective wear, energy generation, and water treatment. Current impermeable protective materials effectively block harmful agents but trap heat due to poor water vapor transfer. Here we present a new class of materials, vapor permeable dehydrated nanoporous biomimetic membranes (DBMs), based on channel proteins. This application for biomimetic membranes is unexpected as channel proteins and biomimetic membranes were assumed to be unstable under dry conditions. DBMs mimic human skin's structure to offer both high vapor transport and small molecule exclusion under dry conditions. DBMs feature highly organized pores resembling sweat pores in human skin, but at super high densities (>1012 pores/cm2). These DBMs achieved exceptional water vapor transport rates, surpassing commercial breathable fabrics by up to 6.2 times, despite containing >2 orders of magnitude smaller pores (1 nm vs >700 nm). These DBMs effectively excluded model biological agents and harmful chemicals both in liquid and vapor phases, again in contrast with the commercial breathable fabrics. Remarkably, while hydrated biomimetic membranes were highly permeable to liquid water, they exhibited higher water resistances after dehydration at values >38 times that of commercial breathable fabrics. Molecular dynamics simulations support our hypothesis that dehydration induced protein hydrophobicity increases which enhanced DBM performance. DBMs hold promise for various applications, including membrane distillation, dehumidification, and protective barriers for atmospheric water harvesting materials.

Sulfur-Containing Foldamer-Based Artificial Lithium Channels.

Unlike many other biologically relevant ions (Na+ , K+ , Ca2+ , Cl- , etc) and protons, whose cellular concentrations are closely regulated by highly selective channel proteins, Li+ ion is unusual in that its concentration is well tolerated over many orders of magnitude and that no lithium-specific channel proteins have so far been identified. While one naturally evolved primary pathway for Li+ ions to traverse across the cell membrane is through sodium channels by competing with Na+ ions, highly sought-after artificial lithium-transporting channels remain a major challenge to develop. Here we show that sulfur-containing organic nanotubes derived from intramolecularly H-bonded helically folded aromatic foldamers of 3.6 Šin hollow cavity diameter could facilitate highly selective and efficient transmembrane transport of Li+ ions, with high transport selectivity factors of 15.3 and 19.9 over Na+ and K+ ions, respectively.

Protein engineering of pores for separation, sensing, and sequencing.

Proteins are critical to cellular function and survival. They are complex molecules with precise structures and chemistries, which allow them to serve diverse functions for maintaining overall cell homeostasis. Since the discovery of the first enzyme in 1833, a gamut of advanced experimental and computational tools has been developed and deployed for understanding protein structure and function. Recent studies have demonstrated the ability to redesign/alter natural proteins for applications in industrial processes of interest and to make customized, novel synthetic proteins in the laboratory through protein engineering. We comprehensively review the successes in engineering pore-forming proteins and correlate the amino acid-level biochemistry of different pore modification strategies to the intended applications limited to nucleotide/peptide sequencing, single-molecule sensing, and precise molecular separations.

Anion-Selective Cholesterol Decorated Macrocyclic Transmembrane Ion Carriers.

Anion transporters play a vital role in cellular processes and their dysregulation leads to a range of diseases such as cystic fibrosis, Bartter's syndrome and epilepsy. Synthetic chloride transporters are known to induce apoptosis in cancer cell lines. Herein, we report triamide macrocycles that are easily synthesized and externally functionalized by pendant membrane-permeable groups. Among a variety of chains appended onto the macrocycle scaffold, cholesterol is found to be the best with an EC50 value of 0.44 µM. The macrocycle is highly anion-selective and transports ions via an OH-/X- antiport mechanism. The macrocycle is an interesting scaffold for ion-transport as it is able to discriminate between various anions and shows a preference for SCN- and Cl-. Such anion-selective transporters are highly attractive model systems to study ion-transport mechanisms and could potentially be of high therapeutic value.

Correction: Triamide macrocyclic chloride receptors via a one-pot tandem reduction-condensation-cyclization reaction.

Correction for 'Triamide macrocyclic chloride receptors via a one-pot tandem reduction-condensation-cyclization reaction' by Harekrushna Behera, et al., Org. Biomol. Chem., 2017, DOI: .

Triamide macrocyclic chloride receptors via a one-pot tandem reduction-condensation-cyclization reaction.

A pyridine containing triamide macrocycle and its substituted analog have been synthesized in one pot from the corresponding monomer without the use of coupling reagents. The macrocycle can selectively bind chloride ions. The ease of synthesis and chloride-binding properties of the macrocycle make it a highly attractive scaffold for ion-encapsulation, ion-transport and water purification.

Cation-Transporting Peptides: Scaffolds for Functionalized Pores?

Protein pores that selectively transport ions across membranes are among nature's most efficient machines. The selectivity of these pores can be exploited for ion sensing and water purification. Since it is difficult to reconstitute membrane proteins in their active form for practical applications it is desirable to develop robust synthetic compounds that selectively transport ions across cell membranes. One can envision tuning the selectivity of pores by incorporating functional groups inside the pore. Readily accessible octapeptides containing (aminomethyl)benzoic acid and alanine are reported here that preferentially transport cations over halides across the lipid bilayer. Ion transport is hypothesized through pores formed by stable assemblies of the peptides. The aromatic ring(s) appear to be proximal to the pore and could be potentially utilized for functionalizing the pore interior.