Analysis of phenolic acids and flavonoids in leaves of Lycium barbarum from different habitats by ultra‐high‐performance liquid chromatography coupled with triple quadrupole tandem mass spectrometry

The leaves of Lycium barbarum (LLB) have been utilized as crude drugs and functional tea for human health in China and Southeast Asia for thousands of years. To control its quality, a rapid and sensitive ultra‐high‐performance liquid chromatography coupled with triple quadrupole tandem mass spectrometry method was established and validated for the first time for simultaneous determination of 10 phenolic acids and flavonoids (including neochlorogenic acid , protocatechuic aldehyde, p‐hydroxybenzoic acid, chlorogenic acid, cryptochlorogenic acid, caffeic acid, p‐coumaric acid, ferulic acid, rutin and kaempferol‐3‐O‐rutinoside) in LLB. The separation was performed on an Acquity UPLC C₁₈ chromatographic column (100 × 2.1 mm internal diameter, 1.7 μm particle size) with 0.1% formic acid in water (A)–acetonitrile (B) as the mobile phase under gradient elution. Multiple reaction monitoring mode was adopted to simultaneously monitor the target components. The developed method was fully validated in terms of linearity (r² ≥ 0.9860), precision (RSD ≤ 6.58%), repeatability (RSD ≤ 6.60%), stability (RSD ≤ 6.17%), recovery (95.56–108.06%, RSD ≤ 4.64%) and limit of detection (0.021–0.664 ng/mL) and limit of quantitation (0.069–2.210 ng/mL), and then successfully applied to evaluate the quality of 64 batches of LLB collected from 41 producing areas in four different provinces of China. The results showed that the LLB, especially collected from Inner Mongolia regions, were rich in the phenolic acids and flavonoids. Rutin, kaempferol‐3‐O‐rutinoside and chlorogenic acid are the predominant compounds contained in LLB. The above findings will provide helpful information for the effective utilization of LLB.     

Probing the Binding Region of the Single-Stranded DNA-Binding Domain of Rat DNA Polymerase β Using Nanosecond-Pulse Laser-Induced Cross-Linking and Mass Spectrometry

In recent years, there has been a significant number of studies in which UV light has been used as a reagent to induce cross-links in nucleic acid-protein complexes. An area of considerable interest among those interested in structural biology is the garnering of information about the sites of cross-linking within the protein and nucleic acid members of photolinked conjugates, under the assumption that such knowledge should lead to identification of contact regions or sites within the native complexes. In this paper, we present our results from a photocross-linking study of the complex of the single-stranded DNA-binding domain of rat DNA polymerase β (pol β-ss) with the oligonucleotide d(ATATATA). In this study, we have used single nanosecond laser pulses as the cross-linking reagent and matrix-assisted laser desorp-tion/ionization-time of flight mass spectrometry as an analytical tool to identify cross-linked peptides purified from proteolytic digests of the cross-linked complex. Six cross-linked peptides have been identified in tryptic digests of the protein-oligonucleotide conjugates that result from irradiation of the pol β-ss-d(ATATATA) complex with a single laser pulse. Comparisons with NMR data in the literature for the same complex show that each of the cross-linked peptides contains amino acids that are in contact with the nucleic acid component of the complex.     

In-Solution Derivatization and Headspace Gas Chromatography–Mass Spectrometry for 56 Carbonyl Compounds in Tobacco Heating Products,Traditional Tobacco Products and Flavoring Capsules

Chromatographia - Optimal derivatization conditions were established for the simultaneous determination of 12 aliphatic saturated aldehydes, 8 aliphatic saturated ketones, 4 cyclic ketones, 3...     

Structure–property relationship in PCL/starch blend compatibilized with starch‐g‐PCL copolymer

The polycaprolactone (PCL)/starch blends were prepared by using the starch‐g‐PCL (SGCL) graft copolymers as compatibilizers, and their mechanical properties were correlated with the compatibilizing effect of the SGCL copolymers having various molecular structures. The modulus and strength of the PCL/starch blend were decreased, whereas the percent elongation and the toughness were increased remarkably with the addition of SGCL having appropriate graft structure. These property changes were analyzed in terms of the PCL crystallinity and the interfacial adhesion between the PCL matrix and starch dispersion phases, which were dominated by the compatibilizing effects of the SGCL copolymers. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2430–2438, 1999     

A Novel Route to the Fused Maleic Anhydride Moiety of CP Molecules

A seven‐step cascade reaction —in which selective mesylation, epoxide formation, epoxide lysis, cyclization, reiterative oxidation, and nitrogen–oxygen exchange occur sequentially—facilitates the construction of the maleic anhydride moiety of CP molecules 1 and 2 (>93% yield per step). Unstable intermediates of this reaction sequence were detected, providing evidence for the proposed mechanism and resulting in the discovery of a new chemical entity.     

Mechanistic Insights into the Interface‐Directed Transformation of Thiols into Disulfides and Molecular Hydrogen by Visible‐Light Irradiation of Quantum Dots

Quantum dots (QDs) offer new and versatile ways to harvest light energy. However, there are few examples involving the utilization of QDs in organic synthesis. Visible‐light irradiation of CdSe QDs was found to result in virtually quantitative coupling of a variety of thiols to give disulfides and H₂ without the need for sacrificial reagents or external oxidants. The addition of small amounts of nickel(II) salts dramatically improved the efficiency and conversion through facilitating the formation of hydrogen atoms, thereby leading to faster regeneration of the ground‐state QDs. Mechanistic studies reveal that the coupling reaction occurs on the QD surfaces rather than in solution and offer a blueprint for how these QDs may be used in other photocatalytic applications. Because no sacrificial agent or oxidant is necessary and the catalyst is reusable, this method may be useful for the formation of disulfide bonds in proteins as well as in other systems sensitive to the presence of oxidants.     

Mechanically Interlocked Single‐Wall Carbon Nanotubes

Extensive research has been devoted to the chemical manipulation of carbon nanotubes. The attachment of molecular fragments through covalent‐bond formation produces kinetically stable products, but implies the saturation of some of the C? C double bonds of the nanotubes. Supramolecular modification maintains the structure of the SWNTs but yields labile species. Herein, we present a strategy for the synthesis of mechanically interlocked derivatives of SWNTs (MINTs). In the key rotaxane‐forming step, we employed macrocycle precursors equipped with two π‐extended tetrathiafulvalene SWNT recognition units and terminated with bisalkenes that were closed around the nanotubes through ring‐closing metathesis (RCM). The mechanically interlocked nature of the derivatives was probed by analytical, spectroscopic, and microscopic techniques, as well as by appropriate control experiments. Individual macrocycles were observed by HR STEM to circumscribe the nanotubes.     

Highly Enantioselective Construction of Tricyclic Derivatives by the Desymmetrization of Cyclohexadienones

The asymmetric synthesis of tricyclic compounds by the desymmetrization of cyclohexadienones is presented. The reaction tolerated a large variety of substituents at different positions of the cyclohexadienone, and heterocyclic rings of different sizes were accessible. Density functional theory calculations showed that the reaction proceeds through an asynchronous [4+2] cycloaddition.     

Optical Control of Acetylcholinesterase with a Tacrine Switch

Photochromic ligands have been used to control a variety of biological functions, especially in neural systems. Recently, much effort has been invested in the photocontrol of ion channels and G‐protein coupled receptors found in the synapse. Herein, we describe the expansion of our photopharmacological approach toward the remote control of an enzyme. Building on hallmark studies dating from the late 1960s, we evaluated photochromic inhibitors of one of the most important enzymes in synaptic transmission, acetylcholinesterase (AChE). Using structure‐based design, we synthesized several azobenzene analogues of the well‐known AChE inhibitor tacrine (THA) and determined their effects on enzymatic activity. One of our compounds, AzoTHA, is a reversible photochromic blocker of AChE in vitro and ex vivo with high affinity and fast kinetics. As such, AzoTHA can be used to control synaptic transmission on the neuromuscular endplate based on the light‐dependent clearance of a neurotransmitter.