Investigation of the chiral recognition role of cyclodextrin hydroxyl moieties via high performance liquid chromatography.

Cyclodextrin (CD) is known to afford excellent enantioselectivities due to its hydrophobic cavity and external H-bonding sites from hydroxyl moieties. However, there is still a lack of direct and comprehensive evidence clearly illustrating the origin of the important H-bonding effect. Regarding this issue, herein, four allylimidazole CD derivatives by selective substitution of the primary (6-position) and/or secondary (2,3-position) CD were synthesized and clicked onto silica surfaces to afford the corresponding chiral stationary phases (CSPs). The chiral chromatographic performances were systematically evaluated by separating 35 racemic analytes including isoxazolines, dansyl-amino acids, flavonoids and other racemates under reversed-phase HPLC. The chiral selection factors (α) and retention times (k) of the analytes on the as-prepared CSPs were comprehensively compared and it reveals that the enantioseparation ability was significantly altered due to the selective substituents of CD hydroxyl groups. The natural allylimidazole CD CSP (AICDCSP) was superior to the 6-O-tert-butyldimethylsilyl AICDCSP (6-TBDMAICDCSP) for most analytes. Dansyl amino acids and Ar-Pys were well separated on AICDCSP and 6-TBDMAICDCSP, where dansyl amino leucine gained the highest resolution up to 4.72 on AICDCSP, and flavonoids and Ar-Oprs were only separated on AICDCSP. These interesting separation results demonstrate that the secondary hydroxyl groups play a pivotal role in the separation of chiral compounds. In addition, the size of the CD cavity and the choice of solute also have an effect on the separation of substances. The mechanism involved in enantioselective discrimination of the selectively substituted CDs was further investigated by the molecular docking simulation.

Evaluation on the inclusion behavior of ß-cyclodextrins with lycorine and its hydrochloride.

Lycorine (Lyc) and its hydrochloride (Lyc∙HCl) as effective drugs can fight against many diseases including novel coronavirus (COVID-19) based on their antiviral and antitumor mechanism. Beta-cyclodextrin (ß-CD) is considered a promising carrier in improving its efficacy while minimizing cytotoxicity due to the good spatial compatibility with Lyc. However, the detailed mechanism of inclusion interaction still remains to be further evaluated. In this paper, six inclusion complexes based on ß-CDs, Lyc and Lyc∙HCl were processed through ultrasound in the mixed solvent of ethanol and water, and their inclusion behavior was characterized after lyophilization. It was found that the inclusion complexes based on sulfobutyl-beta-cyclodextrin (SBE-ß-CD) and Lyc∙HCl had the best encapsulation effect among prepared inclusion complexes, which may be attributed to the electrostatic interaction between sulfonic group of SBE-ß-CD and quaternary amino group of Lyc∙HCl. Moreover, the complexes based on SBE-ß-CD displayed pH-sensitive drug release property, good solubilization, stability and blood compatibility, indicating their potential as suitable drug carriers for Lyc and Lyc∙HCl.

Surface-up click access to allylimidazolium bridged cyclodextrin dimer phase for efficient enantioseparation.

In this work, a novel allylimidazolium-bridged bis(ß-cyclodextrin) chiral stationary phase was fabricated via a surface-up thiol-ene click chemistry reaction between 7-SH-ß-cyclodextrin and 1-allylimidazole-ß-cyclodextrin bonded on a silica surface. The structure of the allylimidazolium-bridged bis(ß-cyclodextrin) chiral stationary phase was characterized by Fourier transform infrared spectra, 13 C nuclear magnetic resonance, thermogravimetric analysis, and elemental analysis. Its chiral chromatographic performances were systematically evaluated by separating 35 racemic analytes including isoxazolines, dansyl-amino acids, and flavanones under reversed-phase high-performance liquid chromatography. Compared with the corresponding bottom and top layer of the ß-cyclodextrin stationary phase, the allylimidazolium-bridged bis(ß-cyclodextrin) chiral stationary phase afforded significantly accentuated chiral recognition ability due to its abundant hydrogen bond sites, electrostatic interactions, and synergistic inclusion. Furthermore, the allylimidazolium-bridged bis(ß-cyclodextrin) chiral stationary phase showed better enantioseparation ability compared to other reported bridged cyclodextrin stationary phases. In particular, Ar-Phs and dansyl-amino acid could be completely separated by allylimidazolium-bridged bis(ß-mono-6A -deoxy-6-allylimidazolium-ß-cyclodextrin chiral stationary phase) chiral stationary phase with high resolutions of 1.14-7.20 and 3.16-5.82, respectively. Molecular docking reveals that good enantioseparation ability arises from the different interaction modes and the synergistic effect of allylimidazolium-bridged bis(ß-cyclodextrin) chiral stationary phase.

[Recent advances in the research of chromatographic separation materials based on click chemistry].

Since Nobel Laureate K. B. Sharpless first introduced the concept of click chemistry in 2001, such reactions have become a powerful modular synthesis tool. Click chemistry reactions have rapidly expanded into many scientific fields, such as materials and life science, owing to their distinct advantages, which include mild conditions, fast reaction rates, high yields, low by-product generation, and simple separation and purification procedures. Nowadays, click chemistry reactions have become an essential means of designing and preparing separation materials; thus, interest in this synthetic technique has quickly grown. Here, the development of click chemistry and its unique advantages are briefly described firstly. The reports on click chemistry-based chromatographic separation materials published in the past five years are then systematically reviewed, focusing on two major separation fields: column chromatography and membrane chromatography. Meanwhile, recent advances in the separation materials obtained from three common types of click reactions, namely, azido-alkyne, thiol-alkene, and thiol-alkyne, are summarized. Finally, an outlook on the future of click chemistry is provided in developing efficient chromatographic separation materials.

Chiral porous organic frameworks and their application in enantioseparation.

Porous organic frameworks (POFs) are a kind of porous material with a network structure composed of repeated monomers, which have excellent physical and chemical properties, such as a high surface area, high porosity, uniform pore sizes and structural diversity, and which have aroused broad interest among researchers. With the rapid development of materials science, increasingly more porous materials have been developed and applied, especially metal organic frameworks (MOFs) and covalent organic frameworks (COFs), which have been widely applied in the fields of luminous materials, catalytic research, adsorption and drug transport. One of the most important applications for chiral porous materials is in chiral separation and these materials have become a research hotspot in the field of chromatographic separation and analysis in recent years. In this review, from the viewpoint of enantioseparation, the synthesis of chiral porous materials and their applications in high-performance liquid chromatography (HPLC), capillary electrochromatography (CEC), and gas chromatography (GC) are reviewed. The typical applications of MOFs in solid-phase microextraction (SPME) are also discussed.

Ultrafast Nonadiabatic Photoisomerization Dynamics Mechanism for the UV Photoprotection of Stilbenoids in Grape Skin.

Natural UV photoprotection plays a vital role in physiological protection. It has been reported that UVC radiation can make resveratrol (RSV) and piceatannol (PIC) accumulate in grape skin. In this work, we demonstrated that RSV and PIC could significantly absorb UVA and UVB, and confirmed their satisfactory photostability. Furthermore, we clarified the UV photoprotection mechanism of typical stilbenoids of RSV and PIC for the first time by using combined femtosecond transient absorption (FTA) spectroscopy and time-dependent density functional theory (TD-DFT) calculations. RSV and PIC can be photoexcited to the excited state after UVA and UVB absorption. Subsequently, the photoisomerized RSV and PIC quickly relax to the ground state via nonadiabatic transition from the S1 state at a conical intersection (CI) position between potential energy surfaces (PESs) of S1 and S0 states. This ultrafast trans-cis photoisomerization will take place within a few tens of picoseconds. As a result, the UV energy absorbed by RSV and PIC could be dissipated by an ultrafast nonadiabatic photoisomerization process.

Anisotropic charge carrier transport of optoelectronic functional selenium-containing organic semiconductor materials.

Organic semiconductors (OSCs) materials are currently under intense investigation because of their potential applications such as organic field-effect transistors, organic photovoltaic devices, and organic light-emitting diodes. Inspired by the selenization strategy can promote anisotropic charge carrier migration, and selenium-containing compounds have been proved to be promising materials as OSCs both for hole and electron transfer. Herein, we now explore the anisotropic transport properties of the series of selenium-containing compounds. For the compound containing SeSe bond, the SeSe bond will break when attaching an electron, thus those compounds cannot act as n-type OSCs. About the different isomer compounds with conjugated structure, the charge transfer will be affected by the stacking of the conjugated structures. The analysis of chemical structure and charge transfer property indicates that Se-containing materials are promising high-performance OSCs and might be used as p-type, n-type, or ambipolar OSCs. Furthermore, the symmetry of the selenium-containing OSCs will affect the type of OSCs. In addition, there is no direct relationship between the R groups with their performance, whether it or not as p-type OSCs or n-types. This work demonstrates the relationship between the optoelectronic function and structure of selenium-containing OSCs materials and hence paves the way to design and improve optoelectronic function of OSCs materials.

[Click preparation and application of chiral stationary phase based on intrinsic recognition ability of cyclodextrin].

Most of the studies on cyclodextrin (CD)-based chiral stationary phase (CSP) have focused on the functional derivatization of CD or the bridging arms to introduce more interaction sites and thus improve the chiral resolution ability. At present, there are only a few reports on CSP that can reflect the intrinsic recognition ability of natural CD. In this study, a mono(6-mercapto-6-deoxy)-ß-CD CSP (CSP1) with a clear and controllable structure was synthesized by the "thiol-ene" click reaction. CSP1 retained the intrinsic structure of natural CD to the maximum extent, and the bridge arm had no recognition site. The results of 13C solid-state nuclear magnetic resonance (SSNMR) and Fourier transform infrared (FTIR) analyses confirmed the successful preparation of CSP1. Elemental analysis results showed that compared with double-bond functionalized silica, the percentages of C, H, and N in CSP1 increased, and the calculated CD loading of CSP1 was 0.82 µmol/m2. Reversed-phase high performance liquid chromatography was performed for the chiral resolution of more than 50 chiral enantiomers, including isoxazoline, chiral lactide, chiral ketone, flavone, and dansyl amino acid. This fully demonstrated the intrinsic chiral recognition ability of natural CD, and the results showed that the intrinsic recognition ability of cyclodextrin was more conducive to the separation of Ph-Ph samples containing two hydrophobic benzene ring groups in the isoxazoline samples. For the Ph-Py and Ph-OPr samples, the separation effect was not satisfactory. The separation results for the Ph-Py samples were not ideal because the outer hydroxyl group of cyclodextrin could form a hydrogen bond with the pyridine nitrogen, thus hindering the inclusion and the separation effect. This eventually led to poor separation of the enantiomers. While the pyrrolidone group in the Ph-OPr sample could also form a good inclusion complex with cyclodextrin, its higher polarity weakened the inclusion effect compared to that for benzene rings, thus leading to poor chirality separation results. For chiral lactides, the intrinsic recognition ability of CD was good only for the separation of some samples. In the separation of chiral ketones, large steric hindrance effect inhibited the intrinsic recognition ability of CD, and the separation effect of such samples on CSP1 was not ideal. External functional groups were required in some cases to further regulate the chiral recognition performance. The molecular structure of dansyl amino acids played an important role in the separation effect, in addition to the intrinsic recognition ability of CD. The number of side chains in the substituent also affected the quality of separation. Lengthening the side chain or increasing the hydrophobicity could effectively improve the separation efficiency. The separation effect of flavanone samples on CSP1 was ordinary. The substituent positions also affected the separation effect. In order to further explore the intrinsic recognition ability of CD, the functional triazole-bridged CD-CSP (CSP2) and imidazole-bridged CD-CSP (CSP3) (the surface CD loadings of CSP2 and CSP3 were 0.51 µmol/m2 and 0.46 µmol/m2, respectively) prepared earlier were selected and compared under the same chromatographic conditions. The results showed that the separation of the sample was related not only to the structure of the chiral medium but also to the structure of the sample molecules. Functional modification of the bridge arm could improve the selectivity of some enantiomers, but would also cause partial loss of the intrinsic chiral recognition ability of CD. For samples with the intrinsic recognition ability of CD to facilitate separation, no functional group had to be added to the bridge arm when designing a chiral medium. This study provides a useful reference for the design of CD-based CSPs.

Excited state intramolecular proton transfer (ESIPT) luminescence mechanism for 4-N,N-diethylamino-3-hydroxyflavone in propylene carbonate, acetonitrile and the mixed solvents.

In this work, density functional theory (DFT) and time density functional theory (TDDFT) methods were employed to investigate the nature of the double fluorescence emission of DEAHF in these three solvents. We analyzed the geometric structures, vibrational frequencies, frontier molecular orbitals (MOs), molecular electrostatic potential surface (MEPS), calculated absorption and fluorescence spectra and the potential-energy curves for DEAHF. All the results show that the intramolecular hydrogen bond of DEAHF is strengthened from S0 to S1 and the electron density redistribution occurs between the proton acceptor and donor, which can facilitate ESIPT. Moreover, the geometric structures, absorption and emission spectra, MEPS and potential-energy curve of DEAHF are identical. It reveals theoretically that ACN and PC can maintain the polarity of the solvent with 1:1 mixing, which is consistent with the experimental results.

Resiliency of Mutualistic Supplier-Manufacturer Networks.

Current Supplier-Manufacturer (SM) networks are highly complex and susceptible to local and global disruptions, due to connectivity and interdependency among suppliers and manufacturers. Resiliency of supply chains is critical for organizations to remain operational in the face of disruptive events. Existing quantitative analyses oversimplify the mutualistic nature of SM networks, in which failure of individual entities affects not only the directly connected entities but also those connected indirectly. In this work we investigate resiliency of SM networks using the quantitative methods employed to study mutualistic ecological systems. Much like in ecological systems, catastrophic failures of SM networks are difficult to predict due to high dimensionality of their interactive space. To address this, first we create a bipartite representation and generate a multidimensional nonlinear model that captures the dynamics of a SM network. We transform the multidimensional model into a two-dimensional model without sacrificing the model's ability to predict the point of collapse. We extensively validate the model using real-world global automotive SM networks. We observe that the resiliency of a SM network depends on both the network structure and parameters. The current work offers a means for designing resilient supply chains that can remain robust to local and global perturbations.

The present status and future growth of maintenance in US manufacturing: results from a pilot survey.

A research study was conducted (1) to examine the practices employed by US manufacturers to achieve productivity goals and (2) to understand what level of intelligent maintenance technologies and strategies are being incorporated into these practices. This study found that the effectiveness and choice of maintenance strategy were strongly correlated to the size of the manufacturing enterprise; there were large differences in adoption of advanced maintenance practices and diagnostics and prognostics technologies between small and medium-sized enterprises (SMEs). Despite their greater adoption of maintenance practices and technologies, large manufacturing organizations have had only modest success with respect to diagnostics and prognostics and preventive maintenance projects. The varying degrees of success with respect to preventative maintenance programs highlight the opportunity for larger manufacturers to improve their maintenance practices and use of advanced prognostics and health management (PHM) technology. The future outlook for manufacturing PHM technology among the manufacturing organizations considered in this study was overwhelmingly positive; many manufacturing organizations have current and planned projects in this area. Given the current modest state of implementation and positive outlook for this technology, gaps, future trends, and roadmaps for manufacturing PHM and maintenance strategy are presented.

Present Status and Future Growth of Advanced Maintenance Technology and Strategy in US Manufacturing.

The goals of this paper are to 1) examine the current practices of diagnostics, prognostics, and maintenance employed by United States (U.S.) manufacturers to achieve productivity and quality targets and 2) to understand the present level of maintenance technologies and strategies that are being incorporated into these practices. A study is performed to contrast the impact of various industry-specific factors on the effectiveness and profitability of the implementation of prognostics and health management technologies, and maintenance strategies using both surveys and case studies on a sample of U.S. manufacturing firms ranging from small to mid-sized enterprises (SMEs) to large-sized manufacturing enterprises in various industries. The results obtained provide important insights on the different impacts of specific factors on the successful adoption of these technologies between SMEs and large manufacturing enterprises. The varying degrees of success with respect to current maintenance programs highlight the opportunity for larger manufacturers to improve maintenance practices and consider the use of advanced prognostics and health management (PHM) technology. This paper also provides the existing gaps, barriers, future trends, and roadmaps for manufacturing PHM technology and maintenance strategy.