Liquid‐Crystalline Mesogens Based on Cyclo[6]aramides: Distinctive Phase Transitions in Response to Macrocyclic Host–Guest Interactions

Producing macrocyclic mesogens that are responsive to guest encapsulation presents a significant challenge. Cyclo[6]aramides, a type of macrocycle with a hydrogen‐bond‐constrained backbone, exhibit thermotropic lamellar, discotic nematic, hexagonal, and rectangular columnar mesophases over a considerably wide temperature range, including at room temperature. Additionally, cyclo[6]aramides show unusual mesophase transitions from lamellar to hexagonal columnar phase mediated by macrocyclic host–guest (H–G) interactions between the macrocycles and alkylammonium salts. The phase transition, triggered by an organic guest engaging in H–G interactions with a macrocyclic cavity, provides a novel strategy for manipulating the properties of liquid‐crystalline materials. The crystal structure of a homologous cyclo[6]aramide reveals a disk‐shaped, near‐planar molecular backbone that facilitates intermolecular π–π stacking and leads to columnar assembly.     

Rhodium(I)‐Catalyzed Regiospecific Dimerization of Aromatic Acids: Two Direct CH Bond Activations in Water

2,2′‐Diaryl acids are key building blocks for some of the most important and high‐performance polymers such as polyesters and polyamides (imides), as well as structural motifs of MOFs (metal–organic frameworks) and biological compounds. In this study, a direct, regiospecific and practical dimerization of simple aromatic acids to generate 2,2′‐diaryl acids has been discovered, which proceeds through two rhodium‐catalyzed C? H activations in water. This reaction can be easily scaled up to gram level by using only 0.4–0.6 mol % of the rhodium catalyst. As a proof‐of‐concept, the natural product ellagic acid was synthesized in two steps by this method.     

Strand displacement amplification for ultrasensitive detection of human pluripotent stem cells

Human pluripotent stem cells (hPSCs), such as embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), provide a powerful model system for studies of cellular identity and early mammalian development, which hold great promise for regenerative medicine. It is necessary to develop a convenient method to discriminate hPSCs from other cells in clinics and basic research. Herein, a simple and reliable biosensor for stem cell detection was established. In this biosensor system, stage-specific embryonic antigen-3 (SSEA-3) and stage-specific embryonic antigen-4 (SSEA-4) were used to mark human pluripotent stem cells (hPSCs). Antibody specific for SSEA-3 was coated onto magnetic beads for hPSCs enrichment, and antibody specific for SSEA-4 was conjugated with carboxyl-modified tDNA sequence which was used as template for strand displacement amplification (SDA). The amplified single strand DNA (ssDNA) was detected with a lateral flow biosensor (LFB). This biosensor is capable of detecting a minimum of 19 human embryonic stem cells by a strip reader and 100 human embryonic stem cells by the naked eye within 80 min. This approach has also shown excellent specificity to distinguish hPSCs from other types of cells, showing that it is promising for specific and handy detection of human pluripotent stem cells.     

From Anilines to Isatins: Oxidative Palladium‐Catalyzed Double Carbonylation of C?H Bonds

A novel palladium‐catalyzed C H double carbonylation introduces two adjacent carbonyl groups for the synthesis of isatins from readily available anilines. The reaction proceeds under atmospheric pressure of CO with high regioselectivity and without any additives. Density functional theory investigations indicate that the palladium‐catalyzed double carbonylation catalytic cycle is plausible.     

Glassy carbon electrode modified with gold nanoparticles and hemoglobin in a chitosan matrix for improved pH-switchable sensing of hydrogen peroxide

Hemoglobin (Hb) has been demonstrated to endow electrochemical sensors with pH-switchable response because of the presence of carboxyl and amino groups. Hb was deposited in a chitosan matrix on a glassy carbon electrode (GCE) that was previously coated with clustered gold nanoparticles (Au-NPs) by electrodeposition. The switching behavior is active (“on”) to the negatively charged probe [Fe(CN)₆ ³⁻] at pH 4.0, but inactive (“off”) to the probe at pH 8.0. This switch is fully reversible by simply changing the pH value of the solution and can be applied for pH-controlled reversible electrochemical reduction of H₂O₂ catalyzed by Hb. The modified electrode was tested for its response to the different electroactive probes. The response to these species strongly depends on pH which was cycled between 4 and 8. The effect is also attributed to the presence of pH dependent charges on the surface of the electrode which resulted in either electrostatic attraction or repulsion of the electroactive probes. The presence of Hb, in turn, enhances the pH-controllable response, and the electrodeposited Au-NPs improve the capability of switching. This study reveals the potential of protein based pH-switchable materials and also provides a simple and effective strategy for fabrication of switchable chemical sensors as exemplified in a pH-controllable electrode for hydrogen peroxide.

A pH “on-off” switchable nanobiosensor was fabricated by casting a chitosan-hemoglobin biocomposite onto nano-gold electrode. This composite film exhibits not only excellent pH-responsive on (pH 4.0)-off (pH 8.0) behavior but also excellent pH-tunable on-off bioelectrocatalysis of H₂O₂.

     

Screening of drugs of abuse and toxic compounds in human whole blood using online solid‐phase extraction and high‐performance liquid chromatography with time‐of‐flight mass spectrometry

A novel method for the screening of 151 drugs of abuse and toxic compounds in human whole blood has been developed and validated by online solid‐phase extraction with liquid chromatography coupled to time‐of‐flight mass spectrometry. Analytes were extracted and separated by using a fully automated online solid‐phase extraction liquid chromatography system with total chromatographic run time of 26 min. Time‐of‐flight mass spectrometry screening of 151 drugs of abuse and toxic compounds was performed in a full‐scan (m/z 50–800) mode using an MS^E acquisition of molecular ions and fragment ions data at two collision energies (one was 6 eV and another one was in the range of 5–45 eV). The compounds were identified based on retention times and exact mass of molecular ions and fragment ions. The limit of detection ranged from 1 to 100 ng/mL and the recovery of the method ranged from 6.3 to 163.5%. This method is proved to be a valuable screening method allowing fast and specific identification of drugs in human whole blood.     

Separation of five compounds from leaves of Andrographis paniculata (Burm. f.) Nees by off‐line two‐dimensional high‐speed counter‐current chromatography combined with gradient and recycling elution

An off‐line two‐dimensional high‐speed counter‐current chromatography method combined with gradient and recycling elution mode was established to isolate terpenoids and flavones from the leaves of Andrographis paniculata (Burm. f.) Nees. By using the solvent systems composed of n‐hexane/ethyl acetate/methanol/water with different volume ratios, five compounds including roseooside, 5,4′‐dihydroxyflavonoid‐7‐O‐β‐d ‐pyranglucuronatebutylester, 7,8‐dimethoxy‐2′‐hydroxy‐5‐O‐β‐d ‐glucopyranosyloxyflavon, 14‐deoxyandrographiside, and andrographolide were successfully isolated. Purities of these isolated compounds were all over 95% as determined by high‐performance liquid chromatography. Their structures were identified by UV, mass spectrometry, and ¹H NMR spectroscopy. It has been demonstrated that the combination of off‐line two‐dimensional high‐speed counter‐current chromatography with different elution modes is an efficient technique to isolate compounds from complex natural product extracts.     

Development of an enzyme‐linked immunosorbent assay and immunoaffinity chromatography for glycyrrhizic acid using an anti‐glycyrrhizic acid monoclonal antibody

In this work, a new monoclonal antibody specific for glycyrrhizic acid was prepared and characterized. A hybridoma secreting an anti‐glycyrrhizic acid monoclonal antibody was produced by fusing splenocytes from a mouse immunized against a glycyrrhizic acid–bovine serum albumin conjugate with the hypoxanthine–aminopterin–thymidine‐sensitive mouse myeloma cell line (Sp2/0‐Ag14). Subsequently, an indirect, competitive enzyme‐linked immunosorbent assay for glycyrrhizic acid was developed using the monoclonal antibody. In this assay, we detected an effective measuring range of 78.12–2500 ng/mL. Both intra‐assay and inter‐assay repeatability and precision were achieved, with relative standard deviations lower than 10%. In addition, glycyrrhizic acid levels in both formulated Chinese medicines and biological samples were determined with high sensitivity and efficiency. We then successfully developed a reliable immunoaffinity chromatography to separate glycyrrhizic acid completely from its parent medicine. These methods will contribute to further research investigations to better understand the interactions of glycyrrhizic acid with other drugs in the complex system of traditional Chinese medicine.