Molecular dynamics and the structure of macrocycles —Solvent acetonitrile interactions

Microwave complex permittivities,* = -J, are reported in the 1–90 GHz frequency range for the macrocycles 18-crown-6 (18C6) and 15C5 added to acetonitrile in stoichiometric proportions, in the solvent CCl₄ at 25°C. Digitized infrared spectra of the CN stretch ₂ vibration of acetonitrile for the same systems are reported in the 2300–2200 cm^–1 spectral region. The macrocycle 12C4 added to CH₃CN has also been investigated in the infrared. Both the dielectric relaxation and infrared results are interpreted in terms of macrocycle-acetonitrile interactions, probably involving a methyl-hydrogen to ethereal-oxygen interaction. These interactions with CH₃CN diminish in strength according to the sequence: 18C6 > 15C5 > 12C4.This paper is dedicated to the memory of the late Dr C. J. Pedersen.     

Phosphine-free perfluoro-tagged palladium nanoparticles supported on fluorous silica gel: application to the Heck reaction

The immobilization of phosphine-free perfluoro-tagged palladium nanoparticles Pd-1 on fluorous silica gel (FSG) and their utilization in the Heck reaction have been investigated. High yields of vinylic substitution products have been obtained. Recycling studies have shown that the solid-supported palladium catalyst can be readily recovered and reused several times without significant loss of activity. Reactions and recovery of the solid-supported palladium catalyst system can be carried out in the presence of air, without any particular precaution.     

Method validation for determination of arsenic, cadmium, chromium and lead in milk by means of dynamic reaction cell inductively coupled plasma mass spectrometry

With Regulation No. 1881/2006 the European Union fixed a maximum level for lead in milk. Consequently, there is the need to determine very low concentration of elements that may be present in milk in trace and ultratrace levels.Quadrupole inductively coupled plasma mass spectrometry (Q-ICP-MS) combined with dynamic reaction cell (DRC) has been widely employed in order to reach very low concentration, requested for this product. Furthermore, the DRC technology can help in removing polyatomic and argon-based interferences.In the present study, a method for the determination of arsenic, cadmium, chromium and lead in bovine milk was validated according to the EU common standards by means of DRC-ICP-MS. The main parameters evaluated in the validation were: recovery, repeatability and within-laboratory reproducibility, detection and quantification limits, linearity range and measurement uncertainty. Additionally, stability studies of the analyte in solution and ruggedness studies were carried out.The results obtained for limit of detection (LoD) and limit of quantification (LoQ) in μg kg⁻¹ were respectively: As, 3.1 and 9.5; Cd, 0.08 and 0.24; Cr, 0.229 and 0.693; Pb, 0.5 and 1.5. While for the recovery: As, 91%; Cd 96%; Cr 99%; Pb, 95%. As for the repeatability: As, 7%; Cd, 3%; Cr, 6%; Pb, 4%.     

The Possible Presence of Triple Ions in Electrolyte Solutions of Low Dielectric Permittivity

The cause of the appearance of a minimum in the molar electrical conductivity in many electrolyte solutions with increasing electrolyte concentration, in solvents of low dielectric permittivity, is reviewed. Tentative explanations include the formation of triple ions or, alternatively, changes in the electrical polarization of the solutions due to the presence of electrolyte ion pairs. Theoretical models for linear triple ions and apolar dimers are examined. Experimental evidence favors the polarization hypothesis over triple ions; the presence of a maximum in the dielectric permittivity with increasing electrolyte concentration is consistent with the presence of an equilibrium between ion pairs, AB, and their dimers, A₂B₂, at higher concentrations.     

Full-field automatic evaluation of an isoclinic parameter in white light

In this paper, a technique for full-field evaluation of the isoclinic parameter is presented. It combines the phase-shifting method with true color imaging technology to minimize the interaction between isoclinic and isochromatic fringes. The paper also shows how the proposed technique can be suitably integrated with known methods for evaluating the retardations. Furthermore, a digital algorithm for filtering wrapped phase data obtained by general phase-shifting techniques is presented.     

A study on the interactions between coenzyme Q 0 and superoxide anion. Could ubiquinones mimic superoxide dismutase (SOD)?

An electrochemical study was carried out on 1,4-benzoquinone, duroquinone, coenzymes Q ₀ and Q ₁₀ in the absence and in the presence of molecular oxygen in aprotic (DMF) and protic (DMF/H₂O 95:5 (v/v)) media. Water was added because the investigated reactions are deeply influenced by the presence of protons. Q ₀ and Q ₁₀ exhibited a similar electrochemical behaviour. Since Q ₀ is more soluble in protic medium than the biologically more important analogue Q ₁₀ , it was chosen as a model for a more detailed investigation. Voltammetric studies of Q ₀ carried out in aprotic and protic media in the presence of oxygen showed that, besides simple O₂ ^·− dismutation, the Q ₀ promoted dismutation of O₂ ^·− should also be considered. Spectroelectrochemical experiments with the same experimental conditions support the electrochemical results, showing that in the presence of superoxide and in aprotic medium semiquinone Q ₀ ^·− gives rise to a disproportionation equilibrium, while in the presence of water it tends to be reoxidized to the starting Q ₀ by OOH^·. EPR measurements are also in agreement with these results.     

Application of Pharmacokinetic Prediction Platforms in the Design of Optimized Anti-Cancer Drugs

Cancer is the second most common cause of death in the United States, accounting for 602,350 deaths in 2020. Cancer-related death rates have declined by 27% over the past two decades, partially due to the identification of novel anti-cancer drugs. Despite improvements in cancer treatment, newly approved oncology drugs are associated with increased toxicity risk. These toxicities may be mitigated by pharmacokinetic optimization and reductions in off-target interactions. As such, there is a need for early-stage implementation of pharmacokinetic (PK) prediction tools. Several PK prediction platforms exist, including pkCSM, SuperCypsPred, Pred-hERG, Similarity Ensemble Approach (SEA), and SwissADME. These tools can be used in screening hits, allowing for the selection of compounds were reduced toxicity and/or risk of attrition. In this short commentary, we used PK prediction tools in the optimization of mitogen activated extracellular signal-related kinase kinase 1 (MEK1) inhibitors. In doing so, we identified MEK1 inhibitors with retained activity and optimized predictive PK properties, devoid of hERG inhibition. These data support the use of publicly available PK prediction platforms in early-stage drug discovery to design safer drugs.     

Blank problems in the detection of gold by electrothermal atomisation and laser-induced fluorescence

The limit of detection of gold by electrothermal atomisation and double-resonance laser-induced atomic fluorescence can reach the low femtogram level as absolute amount of gold deposited in the furnace. At these high sensitivities, even dry firings of the graphite tube may result in a signal, which is unequivocally attributed to atomic fluorescence of the gold content of the tube released during atomisation. The occurrence and the analytical relevance of such blank signals are presented and discussed in this note.     

Chemical changes induced by ultrasound in iron

The focus of this work is a careful chemical investigation of structural damage produced by the exposure of an iron bar to pressure waves generated using an ultrasound machine (called the R-1-S reactor). In addition to the emission of neutron bursts, the ultrasound treatment caused the appearance of zones of macroscopic damage (～1 mm in size) on the exterior of the bar. Reflected-light optical and environmental scanning electron microscopy (ESEM) has shown that these external damage zones are characterized by microcraters and are covered by a thin layer of cracked amorphous material. Under back scattered electron (BSE) observation, this material shows a lower brightness than the intact ferrite surface. In addition, a zone with a high density of deformed cavities (～1300 per mm²) with irregular walls and a maximum size of 10 μm was found inside the bar. These deformed microcavities are partially filled with a material composed of a chaotic assemblage of submicron-sized (most likely amorphous) particles. A careful compositional investigation of the chaotic material inside the microcavities using the semi-quantitative data obtained with the ESEM X-ray Energy Dispersive System (EDS) has shown that it is primarily composed of carbon, manganese and chromium. These elements are also found in lower amounts within the intact ferrite matrix. In contrast, the damaged surface surrounding the craters is characterized by elements not found in the ferrite at all (i.e., O, Cl, K, Cu); elements the presence of which cannot be attributed to the occurrence of non-metallic inclusions or to contamination during fabrication. These results are also difficult to explain using the generally accepted laws of physics; however, they do appear to agree with a recent theory predicting the deformation of the local spacetime and the violation of the Local Lorentz Invariance. Such a violation should occur following the collapse of micron-sized discontinuities internal to the materials (micropores) exposed to ultrasonic pressure waves resulting in an energy density to time ratio large enough to overcome the threshold predicted by the deformed spacetime theory, triggering, in this way, a new kind of nuclear reaction. Following this theory, the C-, Mn- and Cr-rich chaotic material inside the microcavities is the product of the spherically symmetrical collapse of micropores internal to the ferrite while the presence of new elements within the cratered damage zones on the ferrite surface can be attributed to the catastrophic collapse of the subsurface pore walls resulting from microexplosions.     

Towards RGB photoelasticity: Full-field automated photoelasticity in white light

In this paper a new full-field method for the automatic analysis of isochromatic fringes in white light is presented. The method, named RGB photoelasticity, eliminates the typical drawbacks of the classical approach to photoelasticity in white light which requires a subjective analysis of colors and an experienced analyst to acquire and interpret the results. The proposed method makes it possible to determine retardations uniquely in the range of 0–3 fringe orders. For this purpose the isochromatics are acquired by means of a color video camera and the colors are decomposed in the three primary colors (red, green and blue) and compared to those stored in a calibration array in the system. Furthermore, the influence of various spurious effects on the accuracy of the proposed method is experimentally evaluated.