| Transmembrane transport of ions plays an important role in maintaining normal physiological activities of living organisms.The transmembrane ion transport is mainly carried out through transmembrane ion channels and transporters.For transmembrane channels,they are mainly composed of pore forming proteins.However,the complexity and fragility of these proteins make them prone to lose their activities due to site mutations and structural defects,leading to ion channel diseases.Natural ion channels often have high selectivity toward specific ions and gating behaviors.Therefore,exploration of structures and operating mechanism of natural transmembrane ion transport systems would help us further understand the relationship between their structures and functions.Developing artificial transmembrane ion transport systems which are easy to synthesize and preserve with simple structure and various functions can not only simulate the construction of alternate of channel proteins and novel transporters,but also have the potential to solve channel-related medical problems.Also,it is of great importance for some potential applications in other fields such as analysis,detection,separation and so on.For transmembrane ion transport systems,dehydration of ions directly affects the selectivity and transport activity.The introduction of ion recognition site into subnanometer cavity is beneficial for ion dehydration and multi-sites synergistic binding of ions,which could enhance the interactions between inner sites and ions and play an important role in constructing artificial transmembrane ion transport systems with ion selectivity.Given this consideration,pore-containing helical structure and designable macrocyclic compound possessing inner cavity are introduced for the construction of artificial transmembrane ion transport system via organic synthesis.We hope to study the relationship between their structures and functions and further explore their biological activity.1.Hybrid pyridone-oxadiazole-pyridine helical oligomer as selective potassium channelBenefiting from designability and predictability of their structures,helices have been proved to be an effective strategy for the construction of transmembrane channels.Inspired by the superhigh selectivity of natural potassium ion channels and cyclic peptide valinomycin toward potassium,the carbonyl group is introduced for the construction of helical structures with pyridone-oxadiazole-pyridine as the helical codon.The appearance of chiral signals by circular dichroism confirms the helical conformations of these oligomers based on pyridone-oxazole-pyridine.The helical oligomers constructed via the hybridization of pyridone and phenanthroline exhibit highly efficient potassium selectivity,with an effective concentration required to obtain 50% activity(EC50)to be about 30 n M.And the helical oligomer could function through channel mechanism according to planar lipid bilayer membrane experiment.Through the introduction of carbonyl groups into the helical structure,a selective potassium ion channel is constructed to simulate natural transport systems.2.semiaza-bambusurils are transmembrane anion transporterBenefiting from the convergent positive polarized C-H bonds inside the central cavity,the macrocycle molecule of bambusurils exhibit excellent affinity for anions through interactions of hydrogen bonding.Given the high reactivity characteristics,the thiocarbonyl group of the semithio-bambusurils could be converted into amidine group via chemical modification,thereby producing the semiaza-bambusurils.The semiazabambusurils preserve high binding ability for chloride ion.The compound possessing the optimal lipophilicity,is the most efficient transporter by adjusting the composition and flexibility of the side chains.This compound shows anion selectivity through carrier mechanism and it exhibits highly efficient chloride transport across membranes,with a very low EC50(effective concentration required to obtain 50% activity)value of 20 n M.The richness of organic amines allows for various modifications for semiazabambusurils,endowing bambusurils a great platform for the construction of transmembrane ion transport systems.3.Selenide-containing Bambusurils: A Redox-Responsive Anion ChannelIn addition to high efficiency and selectivity,natural ion channels also exhibit switchable transmembrane benaviour,which is also called gated behavior.From the perspectives of drug therapy and biochemistry,developing transmembrane ion transport systems responsive to cellular endogenous substance may be promising for drug therapy.The selenoxide group is generally more hydrophilic than hydrophobic selenide by forming hydrogen bonds with water molecule.Attached with Se-substituted alkyl amine,the selenide-containing semiaza-bambusurils is constructed.Selenide-containing semiaza-bambusurils have highly efficient chloride transport activity,with EC50(effective concentration required to obtain 50% activity)values below 20 n M for the most effective compounds and can selectively transport anions across membranes through channel mechanism.The oxidized form of Selenoxide-containing semiazabambusurils lose their ion transport activity which could be recovered through activation by GSH in a concentration-dependent manner.The transmembrane transport behavior of Se-containing semiaza-bambusurils could be ON-OFF controlled in-situ manner via reversible redox reaction,achieving the construction of redox-responsive anion channel based on selenide-containing bambusurils.4.The anticancer-effect of semiaza-bambusurils transmembrane ion transport systemsThe transmembrane ion transport can disrupt the intracellular homeostasis environment,causing cancer cells death by inhibiting autophagy or inducing apoptosis.By virtue of their transmembrane performance,semiaza-bambusurils show notable anti-tumor activities and the half effective inhibitory concentrations IC50 are below 10 μM for human malignant glioblastoma cells(U87MG).Confirmed by flow cytometry,bambusurils can cause cell apoptosis and over 50% of cell apoptosis are observed for the most effective compounds within 1 hour at the concentration of 10 μM,exhibiting rapid induction of cell apoptosis.The chloride-sensitive probe of MQAE reveals that semiaza-bambusurils can facilitate the enhancement of interior chloride level via influx of chloride from the exterior of cells.The mitochondrial damage,monitored by mitochondrial membrane potential probe,could change the permeability of mitochondrial inner membrane,releasing the cytochrome c into the cytoplasm which could initiate cell apoptosis.Also,lysosomal experiments have shown that semiazabambusurils can destory the acidity of lysosomes,which enhances anti-tumor activity by inhibiting cell autophagy.With the inhibition of intracellular GSH levels by BSO,a glutathione synthase inhibitor,the activity of selenoxide-substituted semiaza-bambusurils is inhibited,showing a GSH-dependent manner.This endows selenoxide-substituted semiazabambusurils lower cytotoxicity towards normal cells of human umbilical vein endothelial cells(HUVEC)than selenide-containing semiaza-bambusurils,suggesting potential selective anti-cancer activity. |
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