Quinone Diazides for Olefin Functionalization

The utility of quinone diazides in materials science is vast and well‐documented, yet this potentially useful motif has languished in the annals of organic synthesis. Herein we show that modern tools of catalysis can be employed with free or suitably masked quinone diazides to unleash the power of these classic diazo compounds in the context of both inter‐ and intramolecular olefin cyclopropanation.     

Absolute quantification of NAD(P)H:quinone oxidoreductase 1 in human tumor cell lines and tissues by liquid chromatography–mass spectrometry/mass spectrometry using both isotopic and non-isotopic internal standards

NAD(P)H:quinone oxidoreductase 1 (NQO1, DT-diaphorase) is a prognostic biomarker and a potential therapeutic target for various tumors. Therefore, it is of significance to develop a robust method for the absolute quantification of NQO1. This study aimed to develop and validate a LC–MS/MS based method and to test the appropriateness of using non-isotopic analog peptide as the internal standard (IS) by comparing with a stable isotope labeled (SIL) peptide. The chromatographic performance and mass spectra between the selected signature peptide of NQO1 and the non-isotopic peptide were observed to be very similar. The use of the two internal standards was validated appropriate for the absolute quantification of NQO1, as evidenced by satisfactory validation results over a concentration range of 1.62–162 fmol μL⁻¹. This method has been successfully applied to the absolute quantification of NQO1 expression in various tumor cell lines and tissues. NQO1 expression in human tumor tissues is much higher than that in the neighboring normal tissues in both the cases of lung and colon cancer. The quantitative results obtained from the isotopic and non-isotopic methods are quite similar, further supporting that the use of non-isotopic analog peptide as internal standard is appropriate and feasible for the quantification of NQO1. By comparing with a classical isotopic IS, the present study indicates that the use of a non-isotopic peptide analog to the proteotypic peptide as the internal standard can get equal accuracy and preciseness in measuring NQO1. The universal applicability of the non-isotopic IS approach for the quantification of proteins warrants further research.     

Convenient Synthesis of 1H-Benzotriazolylalkylphenols

A simple, efficient, and environmentally benign method has been developed for the exclusive formation of synthetically significant 1H-benzotriazol-1-ylalkylphenols from hydroxybenzyl alcohols and benzotriazole.     

Improved method for the immunological detection of malondialdehyde-modified low-density lipoproteins in human serum

Oxidized low-density lipoproteins (ox-LDL) such as malondialdehyde-modified LDL (MDA-LDL) play an important role in the pathogenesis of atherosclerosis. This study is aimed to establish a standard enzyme-linked immunosorbent assay (ELISA) for measuring serum MDA-LDL, and evaluate its usefulness by analyzing serum samples of diabetes mellitus (DM) patients. Serum sample stability, analytical sensitivity, intra- and inter-assay precision, dilution linearity, supplementation and recovery, and interfering substances were examined. Normal reference levels in 86 healthy subjects (33 males and 53 females; average age 34.4±7.8 years) with normal lipid profiles were also determined. MDA-LDL levels in blood and serum were unstable and gradually increased during storage. However, it could be stabilized by the addition of a reagent, which included sucrose. The detection limit of the assay was 6.3 U/l. Intra- and inter-assay imprecisions were <5.6 and <9.4%, respectively. Excellent dilution linearity was observed, and the average recovery was 105%. None of the test substances, for example, hemoglobin, lipid and bilirubin interfered with the assay. The normal reference levels of MDA-LDL and MDA-LDL/LDL-C in the 86 subjects with normal lipid levels were calculated as 58.8±17.9 U/l and 60.4±11.9 mU/mg, respectively. The both serum levels of MDA-LDL (122±62.8 U/l) and MDA-LDL/LDL-C (96.8±48.5 mU/mg) in the DM patients were significantly higher than those of controls (P<0.0001). Moreover, DM patients with atherosclerosis complications showed significantly higher MDA-LDL and MDA-LDL/LDL-C levels than those without complications, 174±81.3 versus 101±39.2 U/l, (P<0.01) and 138±59.0 versus 80.3±32.1 mU/mg, (P<0.005), respectively. These results suggest that the ELISA method for MDA-LDL described in this study fulfilled the sensitivity, reproducibility, and accuracy requirements for routine clinical assays and might therefore be a useful tool for evaluating atherogenicity.     

A Bio‐Inspired,Heavy‐Metal‐Free,Dual‐Electrolyte Liquid Battery towards Sustainable Energy Storage

Wide‐scale exploitation of renewable energy requires low‐cost efficient energy storage devices. The use of metal‐free, inexpensive redox‐active organic materials represents a promising direction for environmental‐friendly, cost‐effective sustainable energy storage. To this end, a liquid battery is designed using hydroquinone (H₂BQ) aqueous solution as catholyte and graphite in aprotic electrolyte as anode. The working potential can reach 3.4 V, with specific capacity of 395 mA h g^?1 and stable capacity retention about 99.7 % per cycle. Such high potential and capacity is achieved using only C, H and O atoms as building blocks for redox species, and the replacement of Li metal with graphite anode can circumvent potential safety issues. As H₂BQ can be extracted from biomass directly and its redox reaction mimics the bio‐electrochemical process of quinones in nature, using such a bio‐inspired organic compound in batteries enables access to greener and more sustainable energy‐storage technology.     

Effect of oxidation state and coordination with Hg(II) on the electronic spectra of an anthraquinone–rhodamine sensor

ABSTRACT

In this study, a computational examination of the electronic transitions and through-space energy transfer processes lends insight into the experimental electronic spectra of a redox-sensitive rhodamine–anthraquinone dyad. Electronic transitions were calculated using density functional theory (DFT) and time-dependent DFT (TDDFT) based on models optimised from single-crystal X-ray diffraction (XRD) ion positions. DFT calculations were performed on gas-phase models using the Vienna Ab Initio Software Package (VASP) with the functional developed by Perdew, Burke, and Ernzerhof (PBE) on a basis set of plane waves. Using the DFT results, select transitions were evaluated based on a dipole–dipole coupling mechanism to find the Förster resonance energy transfer coupling, the square of which is approximately proportional to the rate of energy transfer between the donor and the acceptor. Electronic transitions during the relaxation of charge carriers are also investigated using nonadiabatic molecular dynamics. In order to investigate the transitions contributing to key peaks in the experimental absorbance spectra, TDDFT calculations were performed in Gaussian 09 with the B3LYP functional on the sensor in solution phase, which is simulated using a polarisable continuum model (PCM). The computed electron transfer process from the excited rhodamine to the quinone correlates better with the experimental data than does the computed Förster resonance energy transfer (FRET) process. This computed electron transfer process is faster than the radiative lifetime of the fluorescent state, which collectively suggests that the charge transfer process quenches fluorescence. These results support the observation that fluorescence is more prominent in the oxidised sensor than in the reduced sensor.     

Simultaneous determination of monomeric and oligomeric alkannins and shikonins by high-performance liquid chromatography-diode array detection-mass spectrometry

Alkannin and shikonin (A/S) derivatives have been found in the roots of several Boraginaceous species and are produced through plant tissue cultures. The chiral compounds alkannins and shikonins are potent pharmaceutical substances with a wide spectrum of pharmacological activities such as wound healing, antimicrobial, anti-inflammatory, anticancer and antioxidant. Although oligomeric A/S derivatives have been detected in root extracts and commercial samples their detection and determination through high-performance liquid chromatography has not been reported. Therefore, in the present study a rapid, simple high-performance liquid chromatography-diode array detection-mass spectrometry (HPLC-DAD-MS) method was developed to detect, separate and determine monomeric and oligomeric/polymeric derivatives of alkannin/shikonin simultaneously for the first time. An optimization of HPLC-DAD parameters was performed. Both atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) modes were applied, in order to compare detection of monomeric and oligomeric A/S. Additionally, oligomeric A/S constituents in several samples were identified and the mode of A/S polymerization was proposed.     

Electrochemical and Electrocatalytic Properties of Imidazole Analogues of the Redox Cofactor Pyrroloquinoline Quinone

The electrochemical and electrocatalytic properties of two synthetic imidazole analogues of the redox cofactor pyrroloquinoline quinone (PQQ) were evaluated. Cyclic voltammetry measurements as a function of pH indicated that both 4,5‐dihydro‐4,5‐dioxo‐1H‐imidazolo[5,4‐f]quinoline‐7,9‐dicarboxylic acid ( 1 ) and 4,5‐dihydro‐4,5‐dioxo‐2‐methyl‐1H‐imidazolo[5,4‐f]quinoline‐7,9‐dicarboxylic acid ( 2 ) undergo a reversible reduction of the o‐quinone moiety below pH 8 with potentials slightly more positive than those observed for PQQ. Upon incorporation into a polypyrrole membrane on the tip of a glassy carbon electrode, 1 and 2 exhibited electrocatalytic properties sufficient for the indirect amperometric detection of cysteine. The response for cysteine was linear up to 1 mM over a wide pH range. Detection limits (S/N=3) were in the μM range and dependent on the solution pH. Interference from redox active species such as dopamine and uric acid were minimized by the pH‐dependent redox potentials of 1 and 2 and thus the ability to tune the detection potential.     

Determination of dithiothreitol in complex protein mixtures by HPLC-MS

Dithiothreitol (DTT) and other reducing agents are typically used in refolding processes of recombinant human proteins during their purification from inclusion bodies. Due to its toxicity, it is essential to monitor the clearance of DTT throughout the analytical flow from the refolding phase to the final formulated product. Here we report a direct, simple, and fast liquid chromatography method using UV and tandem mass spectrometry (MS/MS) detection for DTT evaluation in complex protein mixtures. In aqueous solution DTT exists as an equilibrium mixture of the oxidized and the reduced form (H(2)DTT --> DTT(ox)) and the quantitation tools should therefore be applicable to both forms in a single step or in multiple steps. Oxidation of DTT with aqueous copper(II) nitrate trihydrate solution was introduced to determine a single oxidized compound, i. e. DTT(ox). Proteins and other components of high molecular masses were separated from DTT(ox) by ultrafiltration. Consequently, efficient separation of the DTT(ox )from other flow-through mixture components (sugars, polymers, salts, protein stabilizers) was achieved on an Atlantis dC(18) column. After chromatographic separation, DTT(ox) was selectively identified by UV absorbance at 285 nm or by selected reaction monitoring, measuring signal transition between m/z 151 --> 105. The method was validated in terms of specificity, accuracy, precision, linearity, and limit of quantification and detection. A reversed-phase HPLC separation method with atmospheric pressure chemical ionization and MS/MS detection in negative ion mode is highlighted as a viable alternative to currently existing quantitation methods involving DTT derivatization and HPLC fluorescence detection. The described approach offers simple, straightforward, selective, and high-throughput DTT quantitation in protein mixtures.     

Fabrication of Insoluble Elastin by Enzyme-Free Cross-Linking

Elastin is an essential extracellular matrix protein that enables tissues and organs such as arteries, lungs, and skin, which undergo continuous deformation, to stretch and recoil. Here, an approach to fabricating artificial elastin with close-to-native molecular and mechanical characteristics is described. Recombinantly produced tropoelastin are polymerized through coacervation and allysine-mediated cross-linking induced by pyrroloquinoline quinone (PQQ). A technique that allows the recovery and repeated use of PQQ for protein cross-linking by covalent attachment to magnetic Sepharose beads is developed. The produced material closely resembles natural elastin in its molecular, biochemical, and mechanical properties, enabled by the occurrence of the cross-linking amino acids desmosine, isodesmosine, and merodesmosine. It possesses elevated resistance against tryptic proteolysis, and its Young's modulus ranging between 1 and 2 MPa is similar to that of natural elastin. The approach described herein enables the engineering of mechanically resilient, elastin-like materials for biomedical applications.