β-Cyclodextrin Functionalized Nanoporous Graphene Oxides for Efficient Resolution of Asparagine Enantiomers

Synthesis of chiral graphene structures and their comprehensive applications: a critical review

From a molecular viewpoint, chirality is a crucial factor in biological processes. Enantiomers of a molecule have identical chemical and physical properties, but chiral molecules found in species exist in one enantiomer form throughout life, growth, and evolution. Chiral graphene materials have considerable potential for application in various domains because of their unique structural framework, properties, and controlled synthesis, including chiral creation, segregation, and transmission. This review article provides an in-depth analysis of the synthesis of chiral graphene materials reported over the past decade, including chiral nanoribbons, chiral tunneling, chiral dichroism, chiral recognition, and chiral transfer. The second segment focuses on the diverse applications of chiral graphene in biological engineering, electrochemical sensors, and photodetectors. Finally, we discuss research challenges and potential future uses, along with probable outcomes.

Staals R, Schmid S. Nanopores Reveal the Stoichiometry of Single Oligoadenylates Produced by Type III CRISPR-Cas

Cyclic oligoadenylates (cOAs) are small second messenger molecules produced by the type III CRISPR-Cas system as part of the prokaryotic immune response. The role of cOAs is to allosterically activate downstream effector proteins that induce dormancy or cell death, and thus abort viral spread through the population. Interestingly, different type III systems have been reported to utilize different cOA stoichiometries (with 3 to 6 adenylate monophosphates). However, so far, their characterization has only been possible in bulk and with sophisticated equipment, while a portable assay with single-molecule resolution has been lacking. Here, we demonstrate the label-free detection of single cOA molecules using a simple protein nanopore assay. It sensitively identifies the stoichiometry of individual cOA molecules and their mixtures from synthetic and enzymatic origin. To achieve this, we trained a convolutional neural network (CNN) and validated it with a series of experiments on mono- and polydisperse cOA samples. Ultimately, we determined the stoichiometric composition of cOAs produced enzymatically by the CRISPR type III-A and III-B variants of Thermus thermophilus and confirmed the results by liquid chromatography-mass spectroscopy (LC-MS). Interestingly, both variants produce cOAs of nearly identical composition (within experimental uncertainties), and we discuss the biological implications of this finding. The presented nanopore-CNN workflow with single cOA resolution can be adapted to many other signaling molecules (including eukaryotic ones), and it may be integrated into portable handheld devices with potential point-of-care applications.

Enantioseparation/Recognition based on nano techniques/materials

Enantiomers show different behaviors in interaction with the chiral environment. Due to their identical chemical structure and their wide application in various industries, such as agriculture, medicine, pesticide, food, and so forth, their separation is of great importance. Today, the term "nano" is frequently encountered in all fields. Technology and measuring devices are moving towards miniaturization, and the usage of nanomaterials in all sectors is expanding substantially. Given that scientists have recently attempted to apply miniaturized techniques known as nano-liquid chromatography/capillary-liquid chromatography, which were originally accomplished in 1988, as well as the widespread usage of nanomaterials for chiral resolution (back in 1989), this comprehensive study was developed. Searching the terms "nano" and "enantiomer separation" on scientific websites such as Scopus, Google Scholar, and Web of Science yields articles that either use miniaturized instruments or apply nanomaterials as chiral selectors with a variety of chemical and electrochemical detection techniques, which are discussed in this article.

Recent advances in chiral discrimination on host-guest functionalized interfaces

Chiral discrimination has gained much focus in supramolecular chemistry, since it is one of the fundamental processes in biological systems, enantiomeric separation and biochemical sensors. Though most of the biochemical processes can routinely recognize biological enantiomers, enantioselective identification of chiral molecules in artificial systems is currently one of the challenging topics in the field of chiral discrimination. Inaccuracy, low separation efficiency and expensive instrumentation were considered typical problems in artificial systems. Recently, chiral recognition on the interfaces has been widely used in the fields of electrochemical detection and biochemical sensing. For the moment, a series of macrocyclic host functionalized interfaces have been developed for use as chiral catalysts or for enantiomeric separation. Here, we have briefly exposited the most recent advances in the fabrication of supramolecular functionalized interfaces and their application for chiral recognition.

Chiral Graphene Hybrid Materials: Structures, Properties, and Chiral Applications

Chirality has become an important research subject. The research areas associated with chirality are under substantial development. Meanwhile, graphene is a rapidly growing star material and has hard-wired into diverse disciplines. Rational combination of graphene and chirality undoubtedly creates unprecedented functional materials and may also lead to great findings. This hypothesis has been clearly justified by the sizable number of studies. Unfortunately, there has not been any previous review paper summarizing the scattered studies and advancements on this topic so far. This overview paper attempts to review the progress made in chiral materials developed from graphene and their derivatives, with the hope of providing a systemic knowledge about the construction of chiral graphenes and chiral applications thereof. Recently emerging directions, existing challenges, and future perspectives are also presented. It is hoped this paper will arouse more interest and promote further faster progress in these significant research areas.

Influence of Host-Guest Interaction between Chiral Selectors and Probes on the Enantioseparation Properties of Graphene Oxide Membranes

Graphene oxide (GO)-based membranes have displayed superior performances in the chiral resolution compared with conventional polymer-based and inorganic membranes. However, the effect of the host-guest interaction between chiral selectors and probes on the enantioseparation properties of GO-based membranes remains to be established. In this work, l-phenylalanine (l-Phe, as the chiral selector)-modified GO-based (l-Phe-GO) membranes were fabricated, and their enantioseparation performances toward various enantiomers, that is, d- and l-phenylalanine (d- and l-Phe), d- and l-methionine (d- and l-Met), N-acyl-d-phenylalanine (N-acyl-d-Phe) and N-acyl-l-phenylalanine (N-acyl-l-Phe), and N-acyl-d-methionine (N-acyl-d-Met) and N-acyl-l-methionine (N-acyl-l-Met), were detected. Results show that (i) l-Phe is preferential to transport d-enantiomers relative to l-enantiomers; (ii) as far as d-enantiomers are concerned, the d-Phe-like enantiomers move faster than d-Met-like ones through the l-Phe-GO membrane owing to their different host-guest interactions. The strength of interactions between chiral selectors and probes was further confirmed from both experimental and theoretical standpoints. In the former case, the enantioselective adsorption of l-Phe-GO nanosheets toward the aforementioned enantiomers demonstrates that l-Phe delivers a higher adsorption capacity to d-enantiomers relative to l-enantiomers, and meanwhile, d-Phe-like enantiomers are better than d-Met-like enantiomers in the adsorption capacity. In the latter case, the chiral separation mechanism is clarified using the periodical density functional theory (DFT) calculation, indicating that l-Phe interacts with d-enantiomers more strongly than l-enantiomers. Especially, our calculations unveil that the difference in the interaction strength is principally dominated by the nonstereoselective interactions between chiral probes and the GO surface. Therefore, our findings suggest that the nonstereoselective weak interaction can be employed to improve the enantioselectivity of GO-based membranes.

Supramolecular adsorption of cyclodextrin/polyvinyl alcohol film for purification of organic wastewater

Into purified organic wastewater, α-, β-, and γ-cyclodextrin (α-, β-, and γ-CD) were added to polyvinyl alcohol (PVA) with ammonium persulfate as the crosslinker. The CD/PVA composite film with low water solubility and supramolecular adsorption was prepared by solvent evaporation. Fourier transform infrared spectroscopy showed that when CD was successfully added to PVA, the crosslinking process had no effect on -OH, and the structure was stable after soaking in water for 120 h. Solubility experiments showed that the stability of PVA in water was significantly improved. The results of phenolphthalein adsorption showed that the composite film followed the Langmuir isothermal adsorption and the pseudo-second-order kinetics. According to the Langmuir equation, the theoretical maximum adsorption capacities of α-, β- and γ-CD/PVA composite films were 0.41, 2.05, and 2.00 mg/g, respectively. The parameters of the Freundlich equation indicate that the adsorption of the composite film is physical adsorption. The time for α-CD/PVA composite film to reach equilibrium was the shortest, while the longest was for β-CD/PVA composite film. The intraparticle diffusion model showed that the adsorption was mainly affected by the diffusion of the boundary layer, and the diffusion rate limitation of the boundary layer of the high-concentration phenolphthalein solution was more obvious.