Segregation of separate steps in chromium-catalyzed reactions for convenience and mechanistic analysis

[structure: see text] We have developed an apparatus for carrying out redox-coupled chromium-manganese or chromium-zinc reactions on solid-supported substrates which allows recycling of the stoichiometric reductant. In addition to providing a greatly simplified procedure for these reactions, we observe striking differences in the recyclability of Mn and Zn. A preliminary extension of the methodology to the catalytic coupling of allylchromium reagents with solid-supported aldehydes is also reported.     

Synthesis and structure of Ta4SI11: disorder and mixed valency in the first tantalum sulfide iodide

The new compound Ta(4)SI(11) has been prepared by direct reaction of the elements at 430 degrees C for 2 weeks in evacuated Pyrex ampules and characterized by single-crystal X-ray diffraction, X-ray photoelectron spectroscopy, magnetic susceptibility measurements, and semiempirical electronic structure calculations. Ta(4)SI(11) crystallizes with orthorhombic symmetry in space group Pmmn; a = 16.135(3) A, b = 3.813(1) A, c = 8.131(2) A, and Z = 1. The disordered structure involves two crystallographically distinct sites for Ta atoms, both of which are 50% occupied as well as a bridging anion site that is 50% S and 50% I. Magnetic susceptibility above 100 K gives micro (eff) = 1.53 micro (B) to suggest one unpaired electron per formula unit. X-ray photoelectron spectroscopy and extended Hückel calculations suggest that the structure consists of Ta(3) triangles and "isolated" Ta atoms, leading to the formulation (Ta(3))(9+)(Ta(4+))(S(2)(-))(I(-))(11) and we hypothesize that each Ta(3) is capped by a sulfur atom.     

Dynamics of protein and mixed protein/surfactant adsorption layers at the water/fluid interface

The adsorption behaviour of proteins and systems mixed with surfactants of different nature is described. In the absence of surfactants the proteins mainly adsorb in a diffusion controlled manner. Due to lack of quantitative models the experimental results are discussed partly qualitatively. There are different types of interaction between proteins and surfactant molecules. These interactions lead to protein/surfactant complexes the surface activity and conformation of which are different from those of the pure protein. Complexes formed with ionic surfactants via electrostatic interaction have usually a higher surface activity, which becomes evident from the more than additive surface pressure increase. The presence of only small amounts of ionic surfactants can significantly modify the structure of adsorbed proteins. With increasing amounts of ionic surfactants, however, an opposite effect is reached as due to hydrophobic interaction and the complexes become less surface active and can be displaced from the interface due to competitive adsorption. In the presence of non-ionic surfactants the adsorption layer is mainly formed by competitive adsorption between the compounds and the only interaction is of hydrophobic nature. Such complexes are typically less surface active than the pure protein. From a certain surfactant concentration of the interface is covered almost exclusively by the non-ionic surfactant. Mixed layers of proteins and lipids formed by penetration at the water/air or by competitive adsorption at the water/chloroform interface are formed such that at a certain pressure the components start to separate. Using Brewster angle microscopy in penetration experiments of proteins into lipid monolayers this interfacial separation can be visualised. A brief comparison of the protein adsorption at the water/air and water/n-tetradecane shows that the adsorbed amount at the water/oil interface is much stronger and the change in interfacial tension much larger than at the water/air interface. Also some experimental data on the dilational elasticity of proteins at both interfaces measured by a transient relaxation technique are discussed on the basis of the derived thermodynamic model. As a fast developing field of application the use of surface tensiometry and rheometry of mixed protein/surfactant mixed layers is demonstrated as a new tool in the diagnostics of various diseases and for monitoring the progress of therapies.     

Ternary mutual diffusion coefficients of ZnCl2−KCl−H2O at 25°C by Rayleigh interferometry

Mutual diffusion coefficients and densities were measured for aqueous ZnCl₂–KCl mixtures at 25° by using free-diffusion Rayleigh interferometry and pycnometry, respectively. The ZnCl₂ concentrations were fixed at 1.5 mol-dm^–3, whereas those of KCl were 0.5, 1.25, 2.0, or 4.0 mol-dm^–3. This corresponds to a half charged zinc-chlorine storage battery at various suporting electrolyte concentrations. The main-term coefficient of ZnCl₂ only varies by 10% with KCl concentration, whereas that of KCl varies by about 22%. The ZnCl₂ cross-term coefficient remains small and positive; in contrast the KCl cross-term coefficient goes through a maximum and is negative at high and low KCl concentrations. At KCl concentrations of 0.5 and 4.0 mol-dm^–3, solutions with the KCl c0 are statically and dynamically (diffusively) unstable at the top and bottom of the boundary. Evaluation of the parameters of the non-linear least-squares solution to the diffusion equation is difficult for the 1.25 mol-dm^–3 KCl case, since this system has nearly equal eigenvalues in its diffusion coefficient matrix.     

NON-NUCLEAR DAMAGE AND CELL LYSIS ARE INDUCED BY UVA, BUT NOT UVB OR UVC, RADIATION IN THREE STRAINS OF L5178Y CELLS

The potential to induce non-nuclear changes in mammalian cells has been examined for (1) UVA1 radiation (340–400 nm, UVASUN 2000 lamp), (2) UVA + UVB (peak at 313 nm) radiation (FS20 lamp), and (3) UVC (254 nm) radiation (GI5T8 lamp). The effects of irradiation were monitored in vitro using three strains of L5178Y (LY) mouse lymphoma cells that markedly differ in sensitivity to UV radiation. Comparisons were made for the effects of approximately equitoxic fluences that reduced cell survival to 1–15%. Depending on the cell strain, the fluences ranged from 830 to 1600 kJ/m² for the UVASUN lamp, 75 to 390 J/m² for the FS20 lamp and 3.8 to 17.2 J/m² for the G15T8 lamp. At the exposure level used in this study, irradiation with the UVASUN, but not the FS20 or G15T8, lamp induced a variety of non-nuclear changes including damage to cytoplasmic organelles and increased plasma membrane permeability and cell lysis. Cell lysis and membrane permeabilization were induced by the UVA1 emission of the UVASUN lamp, but not by its visible + IR components (>400 nm). The results show that the plasma membrane and other organelles of LY cells are highly sensitive to UVA1 but not to UVB or UVC radiation. Also UVA1, but not UVB or UVC radiation, causes rapid and extensive lysis of LY cells. In conclusion, non-nuclear damage contributes substantially to UVA cytotoxicity in all three strains of LY cells.     

Dynamic Surface Properties of Poly(vinylpyrrolidone) Solutions

The dynamic surface tension and the complex dynamic surface elasticity of poly(vinylpyrrolidone) (PVP) solutions were measured in the concentration range 10(-5) wt% up to about 1 wt%. The surface tension changed slowly with time at low (<10(-4) wt%) and high concentrations (>0.1 wt%). At low concentrations this is a consequence of the slow transport by diffusion of PVP molecules from the depth of the bulk phase to the surface. At high concentrations the time effect is unexpected and probably the result of PVP contamination of high surface activity. The dynamic surface elasticity of PVP solutions gradually decreases with increasing concentration up to the range of high concentrations (>0.1 wt%) where an abrupt increase in the elasticity caused by the adsorbed impurity is observed. At low and medium concentrations the viscoelastic behavior of PVP adsorbed films is similar to that of the previously investigated poly(ethylene oxide) and poly(ethylene glycol) films and is determined by the number of loops and tails protruding into the bulk phase.     

Heteroarylation of unactivated C–H bonds suitable for late-stage functionalization

The late-stage introduction of diverse heterocycles onto complex small molecules enables efficient access to new medicinally relevant compounds. An attractive approach to such a transformation would utilize the ubiquitous aliphatic C–H bonds of a complex substrate. Herein, we report a system that enables direct C–H heteroarylation using a stable, commercially available O-alkenylhydroxamate with heterocyclic sulfone partners. The C–H heteroarylation proceeds efficiently with a range of aliphatic substrates and common heterocycles, and is a rare example of heteroarylation of strong C–H bonds. Importantly, the present approach is amenable to late-stage functionalization as the substrate is the limiting reagent in all cases.

The late-stage introduction of diverse heterocycles onto complex small molecules enables efficient access to new medicinally relevant compounds.     

Torsionally broken symmetry assists infrared excitation of biomimetic charge-coupled nuclear motions in the electronic ground state

The concerted interplay between reactive nuclear and electronic motions in molecules actuates chemistry. Here, we demonstrate that out-of-plane torsional deformation and vibrational excitation of stretching motions in the electronic ground state modulate the charge-density distribution in a donor-bridge-acceptor molecule in solution. The vibrationally-induced change, visualised by transient absorption spectroscopy with a mid-infrared pump and a visible probe, is mechanistically resolved by ab initio molecular dynamics simulations. Mapping the potential energy landscape attributes the observed charge-coupled coherent nuclear motions to the population of the initial segment of a double-bond isomerization channel, also seen in biological molecules. Our results illustrate the pivotal role of pre-twisted molecular geometries in enhancing the transfer of vibrational energy to specific molecular modes, prior to thermal redistribution. This motivates the search for synthetic strategies towards achieving potentially new infrared-mediated chemistry.

Channelling vibrational excitation energy to achieve ground-state charge-transfer (CT)-assisted isomerization in a donor-bridge-acceptor molecule in solution.     

The Extracts of Polygonum cuspidatum Root and Rhizome Block the Entry of SARS-CoV-2 Wild-Type and Omicron Pseudotyped Viruses via Inhibition of the S-Protein and 3CL Protease

COVID-19, resulting from infection by the SARS-CoV-2 virus, caused a contagious pandemic. Even with the current vaccines, there is still an urgent need to develop effective pharmacological treatments against this deadly disease. Here, we show that the water and ethanol extracts of the root and rhizome of Polygonum cuspidatum (Polygoni Cuspidati Rhizoma et Radix), a common Chinese herbal medicine, blocked the entry of wild-type and the omicron variant of the SARS-CoV-2 pseudotyped virus into fibroblasts or zebrafish larvae, with IC₅₀ values ranging from 0.015 to 0.04 mg/mL. The extracts were shown to inhibit various aspects of the pseudovirus entry, including the interaction between the spike protein (S-protein) and the angiotensin-converting enzyme II (ACE2) receptor, and the 3CL protease activity. Out of the chemical compounds tested in this report, gallic acid, a phytochemical in P. cuspidatum, was shown to have a significant anti-viral effect. Therefore, this might be responsible, at least in part, for the anti-viral efficacy of the herbal extract. Together, our data suggest that the extracts of P. cuspidatum inhibit the entry of wild-type and the omicron variant of SARS-CoV-2, and so they could be considered as potent treatments against COVID-19.     

Two-dimensional solidification of viscous flow over a semi infinite plate with constant heat removal

Two-dimensional solidification of forced viscous flow over a semi infinite flat plate is considered. The plate is initially maintained at a constant temperature above the freezing point of the liquid. At time t>0, heat is removed from the plate so that the liquid freezes. The continuity equation and the two-dimensional, nonsteady, momentum and energy equations in the liquid and solid phases are solved numerically. The growth of the solid layer as a function of time and position along the plate is determined.