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To understand the relationships between channel size and ion selectivity, we have developed a new type of artificial ion channel based on pore-forming helical polymers consisting of phenanthroline-...

Anion transmembrane nanochannels constructed from dynamic covalent helices (DCHs) are reported. The dynamic covalent structures can be synthesized by one-pot dynamic covalent reactions and helically self-fold into nanotubes through intramolecular hydrogen bonding and π-π interactions. Such helical structures can vertically self-assemble into long nanofibers under π-π stacking and their hollow nanocavities finally form ion permeation pathways across the lipid membranes. Single-channel electrophysiology signals provide solid evidence of DCHs following the channel rather than the carrier mechanism. Owing to the pore-forming capacity of DCHs, nanochannels are able to accelerate the movement of anions across lipid membranes with high transport activity (EC50 =0.08 mol %). Moreover, DCH channels show dehydration energy dependent anion selectivity. This report highlights the importance of such DCHs as general channel scaffolds with economical synthesis and special nanocavities.

Units of ureidopyrimidinone (UPy) which dimerize via strong quadruple hydrogen bonding are widely used for the construction of supramolecular systems. This self-complementary system exists in the tautomerism equilibrium of 4[1H]-pyrimidinone dimer and pyrimidin-4-ol dimer, making generated supramolecular assembly systems essentially complicated. In this contribution, a rational but simple design concept is described for preorganizing the self-complementary quadruple hydrogen bonding of UPy via supramolecular strategy into a single-quadruple DDAA-AADD dimeric array. With this concept, the designed UPy derivatives form only 4[1H]-pyrimidinone dimer with a ketone configuration via intermolecular hydrogen-bonding interactions, both in the solid state as well as in solution, as is evident from single-crystal X-ray diffraction and 1H NMR spectroscopy. The single DDAA-AADD dimeric array provides defined noncovalent driving forces that can be used to generate constitutionally clear supramolecular structures that are vitally important in the fields of supramolecular chemistry and materials.

Rapid putative radiations of Rheum might be caused by the recent uplifts of the Qinghai–Tibetan Plateau and the quaternary climate oscillations. To better understand the molecular adaptation associated with Rheum radiation, in this study, the adaptive evolution of the chloroplast rbcL gene was analysed using the Phylogenetic Analysis Program. The results showed that two amino acid residues (75F, 203I) were under positive selection. The spatial analysis indicated that the site (75F) was located in the β-sheet of the N-terminal loops involved in subunit interactions in the L8S8 molecule, and the site (203I) was in the α/β-barrel active centre located on the C-terminal domain of the large subunit of Rubisco. These results suggest that potential positive selection in rbcL might have played an important role in the adaption of Rheum species to the extreme environments in Qinghai–Tibetan Plateau regions, and different species lineages might have been subjected to different selective pressures.

In this work, we investigated the self-assembly of helical small molecules and found that the formed micrometer-sized supramolecular structures represented macroscopic chirality. Our observation will provide useful information for exploring the factors which are able to essentially control the chiral expression from molecular details to high-level chirality occurred in nature.

An effective method is reported to synthesize aromatic helical polymer nanochannels by combining both the well-studied aromatic amide helical codons with pyridine-oxadiazole helical codons into helical structure sequences. With this strategy, a type of helical polymer nanochannel that shows structure-directed transmembrane transport functions is synthesized. Although such nanochannels show relatively weak selectivity for the transportation of alkali metal ions, accessible chemical mutation of helical structure sequences will provide a great chance for the design of desired channel property. The straightforward preparation of well-established pyridine-oxadiazole helical structure will significantly promote the synthesis of this kind of aromatic helical polymer nanochannels. With the development of aromatic amide foldamers, moreover, a number of "monomers" will be available for the preparation of helical polymer nanochannels.

A cyclodextrin-based artificial glutathione peroxidase (GPx) system, which was designed to carry single or double binding sites, has been investigated by observing the recognition features of these mimics. The GPx mimics exhibited high catalytic activities mainly due to the substrate recognition generated by hydrophobic driving force. The different recognition mechanisms led to quite different catalytic capacities. In contrast to single recognition, difunctional ones increased the substrate specificity remarkably. The recognition manners of enzyme mimics for substrates strongly depend on the comparative affinities and the concentrations of both substrates. In addition, the catalytic capacity of GPx mimic which contains a delicate binding site for product disulfide can be almost completely blocked via the self-produced inhibition. This work gives very worthful and important information on the understanding of native GPx.

A tellurium-based polymeric sufactant as a selen-enzyme model has been constructed by employing 11-acryl-oyloxyundecyltriethylammonium bromide (AUTEAB, 4) and a tellurium-containing compound (1). It demonstrates strong substrate binding ability for thiols and high glutathione peroxidase (GPx) activity about 6 orders of magnitude more efficient than the well-known GPx mimic PhSeSePh in an ArSH assay system. More importantly. a series of telhirium-based polymeric micelle catalysts with the catalytic tellurium center located at various positions in the micelle have been constructed, and the dramatic difference in activity indicates that the exact match of the catalytic center and binding site plays a key role in enzyme catalytic efficiency.

Glutathione peroxidase (GPx) is one of the most important antioxidative selenoenzymes in living organisms. The novel GPx mimic 6,6′-ditellurobis(6-deoxy-β-cyclodextrin) (6-TeCD) was prepared and evaluated for its capacity to catalyze the reduction of H2O2, tert-butyl hydroperoxide (t-BuOOH), and cumene hydroperoxide (CuOOH) by glutathione (GSH) or 3-carboxy-4-nitrobenzenethiol (ArSH). Compared the ArSH assay with the coupled reductase assay, we found that 6-TeCD exhibited strong substrate specificity for aromatic thiol substrate. The specificity led to efficient peroxidase activity almost 100,000-fold than that for a well-known GPx mimic diphenyl diselenide (PhSeSePh). Furthermore, reduction of lipophilic CuOOH was proceeded ca. 30 times faster than the more hydrophilic H2O2, which cannot bind into the hydrophobic cavity of β-cyclodextrin. Thus, it seemed that catalytic activity of cyclodextrin-derived GPx models strongly depends on the structurally different both substrates hydroperoxides (ROOH) and thiols.

For imitating the active site of antioxidant selenoenzyme glutathione peroxidase (GPx), an artificial enzyme selenosubtilisin was employed as a scaffold for reconstructing substrate glutathione (GSH) specific binding sites by a bioimprinting strategy. GSH was first covalently linked to selenosubtilisin to form a covalent complex GSH-selenosubtilisin through a Se-S bond, then the GSH molecule was used as a template to cast a complementary binding site for substrate GSH recognition. The bioimprinting procedure consists of unfolding the conformation of selenosubtilisin and fixing the new conformation of the complex GSH-selenosubtilisin. Thus a new specificity for naturally occurring GPx substrate GSH was obtained. This bioimprinting procedure facilitates the catalytic selenium moiety of the imprinted selenosubtilisin to match the reactive thiol group of GSH in the GSH binding site, which contributes to acceleration of the intramolecular catalysis. These imprinted selenium-containing proteins exhibited remarkable rate enhancement for the reduction of H2O2 by GSH. The average GPx activity was found to be 462 U/micromol, and it was approximately 100 times that for unimprinted selenosubtilisin. Compared with ebselen, a well-known GPx mimic, an activity enhancement of 500-fold was observed. Detailed steady-state kinetic studies demonstrated that the novel selenoenzyme followed a ping-pong mechanism similar to the naturally occurring GPx.

Mimicking the properties of the selenoenzyme glutathione peroxidase (GPx) has inspired great interest. In this report, a selenium-containing micellar catalyst was successfully constructed by the self-assembly of the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) with benzeneseleninic acid (PhSeO2H) through hydrophobic and electrostatic interaction in water. The selenium-containing micellar catalyst demonstrated substrate specificity for both 3-carboxy-4-nitrobenzenethiol (ArSH, 2) and cumene hydroperoxide (CUOOH), and their complexation was confirmed by UV and fluorescence spectra. More importantly, it demonstrated high GPx activity in two assay systems. It is about 126 times more effective than the well-known GPx mimic ebselen in the classical coupled reductase assay system; however, by using hydrophobic substrate ArSH (2) as an alternative of glutathione (GSH, 1), the micellar catalyst exhibited remarkable 500-fold and 94 500-fold rate enhancements compared with that of PhSeO2H and PhSeSePh.

It has long been known that tellurium compounds are rather toxic to living organisms, and tellurium has not been found in natural biomacromolecules to date. The principles of telluride toxicity in biological processes are still controversial partly because of the lack of information on the biochemical features of tellurium. In this contribution, we report our finding for the first time that telluroxides exhibit hydrolysis capacity. For instance, 6,6'-telluroxy-bis(6-deoxy-beta-cyclodextrin) acts as a hydrolase mimic and shows a significant rate acceleration of 106,000 for the hydrolysis of 4,4'-dinitrodiphenyl carbonate.

To elucidate the relationships between molecular recognition and catalytic ability, we chose three assay systems using three different thiol substrates, glutathione (GSH), 3-carboxyl-4-nitrobenzenethiol (CNBSH), and 4-nitrobenzenethiol (NBSH), to investigate the glutathione peroxidase (GPx) activities of 2,2'-ditellurobis(2-deoxy-beta-cyclodextrin) (2-TeCD) in the presence of a variety of structurally distinct hydroperoxides (ROOH), H2O2, tert-butyl peroxide (tBuOOH), and cumene peroxide (CuOOH), as the oxidative reagent. A comparative study of the three assay systems revealed that the cyclodextrin moiety of the GPx mimic 2-TeCD endows the molecule with selectivity for ROOH and thiol substrates, and hydrophobic interactions are the most important driving forces in 2-TeCD complexation. Furthermore, in the novel NBSH assay system, 2-TeCD can catalyze the reduction of ROOH about 3.4 x 10(5) times more efficiently than diphenyl diselenide (PhSeSePh), and its second-order rate constants for thiol are similar to some of those of native GPx. This comparative study confirms that efficient binding of the substrate is essential for the catalytic ability of the GPx mimic, and that NBSH is the preferred thiol substrate of 2-TeCD among the chosen thiol substrates. Importantly, the proposed mode of action of 2-TeCD imitates the role played by several possible noncovalent interactions between enzymes and substrates in influencing catalysis and binding.

Reaction of the hydroxyl group of serine-221 of subtilisin with phenylmethanesulfonylfluoride followed by nucleophilic substitution with sodium hydrogen telluride, a semisynthetic telluroprotein, tellurosubtilisin, was prepared. Tellurosubtilisin, which displays high substrate specificity for aromatic thiols, exhibits remarkable peroxidase activity and catalyzes the reduction of hydrogen peroxide by 3-carboxy-4-nitrobenzenethiol 20 000 times more efficiently than diphenyl diselenide.