A Novel Sensor Based on Carbon Paste Electrode Modified with Polypyrrole/Multi-walled Carbon Nanotubes for the Electrochemical Detection of Cytostatic Drug Rapamycin

The electrocatalytic oxidation of rapamycin, one of the most studied immunosuppressant, cancer-preventing drug, is investigated for the first time on the surface of the modified carbon paste electrode prepared by incorporating multi-walled carbon nanotubes (MWCNTs) and conductive polymer pyrrole using differential pulse voltammetry (DPV). Rapamycin exhibited a well-defined oxidation peak at +1.1 V (versus Ag/AgCl) in Briton Robinson buffer solution with a pH 4.0. Effect of the most important experimental parameters was optimized and obtained signals are linear to the concentration of rapamycin in the range from 0.1 to 20 μM with 0.06 μM limit of detection. The repeatability is calculated as ±2 % and the reproducibility as ±5 %. The possible interfering compounds were tested showing negligible effect and the sensor was successfully applied for the determination of rapamycin in commercial pharmaceutical formulations with obtained recoveries in the range from 98 % to 102 %.     

Development and validation of an HPLC method for the determination of endocrine disruptors bisphenol A and benzophenone in thermochromic printing inks

The endocrine disruptors bisphenol A (BPA) and benzophenone (BFN) could be important ingredients in thermochromic printing inks in significant amounts. Due to patent protection and use of the inks, manufacturers are not obliged to state their precise chemical composition. These substances in increasingly used thermochromic printing inks present a hazard for human health and environment in the case of inappropriate application and waste disposal. In this work we enabled identification of the inks that contain these hazardous substances by developing a new method for the analysis of BPA and BFN in thermochromic printing inks. The method is based on the reversed-phase liquid chromatography (LC) with UV detection at 226 and 254?nm. Ultrasound-assisted sample extraction in methanol was proven to be the most suitable and effective among several other solvents. The method was completely validated with satisfactory results. The specificity of the method was proven by the additional LC–tandem mass spectrometry analysis. A representative group of 15 ink samples from various manufacturers, curing and printing modes was analyzed. BPA was found in three samples with mass fractions of about 2% while BFN was found in two samples with mass fractions of 0.34 and 0.66%.     

Oxidative Catalysis Using the Stoichiometric Oxidant as a Reagent: An Efficient Strategy for Single‐Electron‐Transfer‐Induced Tandem Anion–Radical Reactions

Oxidative single‐electron transfer‐catalyzed tandem reactions consisting of a conjugate addition and a radical cyclization are reported, which incorporate the mandatory terminal oxidant as a functionality into the product.     

Reverse Spin‐Crossover and High‐Pressure Kinetics of the Heme Iron Center Relevant for the Operation of Heme Proteins under Deep‐Sea Conditions

By design of a heme model complex with a binding pocket of appropriate size and flexibility, and by elucidating its kinetics and thermodynamics under elevated pressures, some of the pressure effects are demonstrated relevant for operation of heme‐proteins under deep‐sea conditions. Opposite from classical paradigms of the spin‐crossover and reaction kinetics, a pressure increase can cause deceleration of the small‐molecule binding to the vacant coordination site of the heme‐center in a confined space and stabilize a high‐spin state of its Fe center. This reverse high‐pressure behavior can be achieved only if the volume changes related to the conformational transformation of the cavity can offset the volume changes caused by the substrate binding. It is speculated that based on these criteria nature could make a selection of structures of heme pockets that assist in reducing metabolic activity and enzymatic side reactions under extreme pressure conditions.     

Zirconia—A stationary phase capable of the separation of polar markers of myocardial metabolism in hydrophilic interaction chromatography

Creatine, phosphocreatine, and adenine nucleotides are highly polar markers of myocardial metabolism that are poorly retained on RP silica sorbents. Zirconia represents an alternative material to silica with high promise to be used in hydrophilic interaction chromatography (HILIC). This study describes a first systematic investigation of the ability of ZrO₂ to separate creatine, phosphocreatine, adenosine 5′‐monophosphate, adenosine 5′‐diphosphate, and adenosine 5′‐triphosphate and compares the results with those obtained on TiO₂. All analytes showed a HILIC‐like retention pattern when mobile phases of different strengths were tested. Stronger retention and better column performance were achieved in organic‐rich mobile phases as compared to aqueous conditions, where poor retention and insufficient column performance were observed. The effect of mobile phase pH and ionic strength was evaluated as well. The analysis of myocardial tissue demonstrated that all compounds were separated in a relevant biological material and thus proved ZrO₂ as a promising phase for HILIC of biological samples that deserves further investigation.     

Quantitative determination of free and total bisphenol A in human urine using labeled BPA glucuronide and isotope dilution mass spectrometry

Bisphenol A (BPA) is a widely used industrial chemical in the manufacturing of polycarbonate plastic bottles, food and beverage can linings, thermal receipts, and dental sealants. Animal and human studies suggest that BPA may disrupt normal hormonal function and hence, potentially, have negative effects on the human health. While total BPA is frequently reported, it is recognized that free BPA is the biologically active form and is rarely reported in the literature. The objective of this study was to develop a sensitive and improved method for the measurement of free and total BPA in human urine. Use of a labeled conjugated BPA (bisphenol A-d6 β-d-glucuronide) allowed for the optimization of the enzymatic reaction and permitted an accurate determination of the conjugated BPA concentration in urine samples. In addition, a ¹³C₁₂-BPA internal standard was used to account for the analytical recoveries and performance of the isotope dilution method. Solid-phase extraction (SPE) combined with derivatization and analysis using a triple quadrupole GC-EI/MS/MS system achieved very low method detection limit of 0.027 ng/mL. BPA concentrations were measured in urine samples collected during the second and third trimesters of pregnancy in 36 Canadian women. Total maternal BPA concentrations in urine samples ranged from not detected to 9.40 ng/mL (median, 1.21 ng/mL), and free BPA concentrations ranged from not detected to 0.950 ng/mL (median, 0.185 ng/mL). Eighty-six percent of the women had detectable levels of conjugated BPA, whereas only 22 % had detectable levels of free BPA in their urine. BPA levels measured in this study agreed well with data reported internationally.     

Minimal Tags for Rapid Dual‐Color Live‐Cell Labeling and Super‐Resolution Microscopy

The growing demands of advanced fluorescence and super‐resolution microscopy benefit from the development of small and highly photostable fluorescent probes. Techniques developed to expand the genetic code permit the residue‐specific encoding of unnatural amino acids (UAAs) armed with novel clickable chemical handles into proteins in living cells. Here we present the design of new UAAs bearing strained alkene side chains that have improved biocompatibility and stability for the attachment of tetrazine‐functionalized organic dyes by the inverse‐electron‐demand Diels–Alder cycloaddition (SPIEDAC). Furthermore, we fine‐tuned the SPIEDAC click reaction to obtain an orthogonal variant for rapid protein labeling which we termed selectivity enhanced (se) SPIEDAC. seSPIEDAC and SPIEDAC were combined for the rapid labeling of live mammalian cells with two different fluorescent probes. We demonstrate the strength of our method by visualizing insulin receptors (IRs) and virus‐like particles (VLPs) with dual‐color super‐resolution microscopy.     

Highly Functionalized and Potent Antiviral Cyclopentane Derivatives Formed by a Tandem Process Consisting of Organometallic,Transition‐Metal‐Catalyzed,and Radical Reaction Steps

A simple modular tandem approach to multiply substituted cyclopentane derivatives is reported, which succeeds by joining organometallic addition, conjugate addition, radical cyclization, and oxygenation steps. The key steps enabling this tandem process are the thus far rarely used isomerization of allylic alkoxides to enolates and single‐electron transfer to merge the organometallic step with the radical and oxygenation chemistry. This controlled lineup of multiple electronically contrasting reactive intermediates provides versatile access to highly functionalized cyclopentane derivatives from very simple and readily available commodity precursors. The antiviral activity of the synthesized compounds was screened and a number of compounds showed potent activity against hepatitis C and dengue viruses.