A generalization of Baer’s Lemma

There is a classical result known as Baer’s Lemma that states that an R-module E is injective if it is injective for R. This means that if a map from a submodule of R, that is, from a left ideal L of R to E can always be extended to R, then a map to E from a submodule A of any R-module B can be extended to B; in other words, E is injective. In this paper, we generalize this result to the category q _ω consisting of the representations of an infinite line quiver. This generalization of Baer’s Lemma is useful in proving that torsion free covers exist for q _ω.      

Improved synthesis of C4α- and C4β-methyl analogues of 2-aminobicyclo[3.1.0]hexane-2,6-dicarboxylate

An efficient and divergent synthesis of C4α- and C4β-methyl-substituted analogues of 2-aminobicyclo[3.1.0]hexane 2,6-dicarboxylate, which are important tools in the study of metabotropic glutamate receptor function, has been achieved. By taking advantage of an unanticipated facial selectivity of the bicyclo[3.1.0]hexane ring system, either the C4α- or C4β-methyl substituent was introduced in a highly stereoselective and high-yielding manner.     

Review of the use of NMR spectroscopy to investigate structure,reactivity, and dynamics of lead soap formation in paintings

Heavy metal carboxylate or soap formation is a widespread deterioration problem affecting oil paintings and other works of art bearing oil-based media. Lead soaps are prevalent in traditional oil paintings because lead white was the white pigment most frequently chosen by old masters for the paints and in some cases for the ground preparations, until the development of other white pigments from approximately the middle of the 18th century on, and because of the wide use of lead-tin yellow. In the latter part of the 19th century, lead white began to be replaced by zinc white. The factors that influence soap formation have been the focus of intense study starting in the late 1990s. Since 2014, nuclear magnetic resonance (NMR) studies have contributed a unique perspective on the issue by providing chemical, structural, and dynamic information about the species involved in the process, as well as the effects of environmental conditions such as relative humidity and temperature on the kinetics of the reaction(s). In this review, we explore recent insights into soap formation gained through solid-state NMR and single-sided NMR techniques.     

Simultaneous quantification of candesartan and irbesartan in rabbit eye tissues by liquid chromatography–tandem mass spectrometry

Diabetic retinopathy is a major cause of vision loss in adults. Novel eye-drop formulations of candesartan and irbesartan are being developed for its cure or treatment. To support a preclinical trial in rabbits, it was critical to develop and validate a new LC–MS/MS method for simultaneous quantification of candesartan and irbesartan in rabbit eye tissues (cornea, aqueous humor, vitreous body and retina/choroid). Eye tissue samples were first homogenized in H₂O-diluted rabbit plasma. The candesartan and irbesartan in the supernatants together with their respective internal standards (candesartan-d₄ and irbesartan-d₄) were extracted by solid-phase extraction. The extracted samples were injected onto a C₁₈ column for gradient separation. The MS detection was in the positive electrospray ionization mode using the multiple reaction monitoring transitions of m/z 441 → 263, 445 → 267, 429 → 207, and 433 → 211 for candesartan, candesartan-d₄, irbesartan and irbesartan-d₄, respectively. For the validated concentration ranges (2–2000 and 5–5000 ng/g for candesartan and irbesartan, respectively), the within-run and between-run accuracies (% bias) were within the range of −8.0–10.0. The percentage CV ranged from 0.6 to 7.3. There was no significant matrix interference nor matrix effect from different eye tissues and different rabbits. The validated method was successfully used in the Good Laboratory Practice (GLP) study of rabbits.     

Formyloxyacetoxyphenylmethane and 1,1-diacylals as versatile O-formylating and O-acylating reagents for alcohols

Formyloxyacetoxyphenylmethane, symmetric 1,1-diacylals and mixed 1-pivaloxy-1-acyloxy-1-phenylmethanes have been used as moisture stable O-formylating and O-acylating reagents for primary and secondary alcohols, allylic alcohols and phenols under solvent/catalyst free conditions to afford their corresponding esters in good yield.     

pH-dependent behavior of surface-immobilized artificial leucine zipper proteins

The coiled-coil protein motif occurs in over 200 proteins and has generated interest for a range of applications requiring surface immobilization of the constituent peptides. This paper describes an investigation of the environment-responsive behavior of a monolayer of surface-immobilized artificial proteins, which are known to assemble to form coiled-coil structures in bulk solution. An extended version of the quartz crystal microbalance (QCM-D) and surface plasmon resonance (SPR) are independently employed to characterize the adsorption of the proteins to a gold surface. The data suggest that the molecules arrange in a closely packed layer orientated perpendicular to the surface. QCM-D measurements are also employed to measure pH-induced changes in the resonant frequency (f) and the energy dissipation factor (D) of a gold-coated quartz crystal functionalized with the formed monolayer. Exposure of the protein monolayer to a pH 4.5 solution results in a shift of 43 Hz in f and a shift of -0.7 x 10(-6) in D as compared to pH 7.4. In contrast, increasing the pH to 11.2, results in f and D shifts of -17 Hz and 0.6 x 10(-6), respectively. The magnitude of the observed shifts suggests that the proteins form a rigid layer at low pH that can be hydrated to a fluid layer as the pH is increased. These observations correlate with spectroscopic changes that indicate a reduction in the helical content of the protein in bulk solutions of high pH.     

Cation-Coordinating Properties of Perfluoro-15-Crown-5

The coordinative properties of perfluoro-15-crown-5 with monocations were investigated using ¹⁹F NMR spectroscopy and ion-selective electrodes with perfluoro-15-crown-5 as the matrix of their sensor membranes and the fluorophilic tetrakis[3,5-bis(perfluorohexyl)phenyl]borate as ion exchanger site. The results show that perfluoro-15-crown-5 interacts weakly but significantly with Na⁺ and K⁺. Assuming 1:1 stoichiometry, the formal complexation constants were determined to be 5.5 and 1.7 M⁻¹, respectively. This weak binding is consistent with the strong electron withdrawing nature of the many fluorine atoms in the perfluorocrown ether. While perfluorinated crown ethers have been known to form host-guest complexes with the anions O₂⁻ and F⁻ in the gas-phase, this is the first study that quantitatively confirms cation binding to a perfluorocrown ether.     

Controlled synthesis of Bi- and tri-nuclear Cu-oxo nanoclusters on metal–organic frameworks and the structure–reactivity correlations

Precisely tuning the nuclearity of supported metal nanoclusters is pivotal for designing more superior catalytic systems, but it remains practically challenging. By utilising the chemical and molecular specificity of UiO-66-NH₂ (a Zr-based metal–organic framework), we report the controlled synthesis of supported bi- and trinuclear Cu-oxo nanoclusters on the Zr₆O₄ nodal centres of UiO-66-NH₂. We revealed the interplay between the surface structures of the active sites, adsorption configurations, catalytic reactivities and associated reaction energetics of structurally related Cu-based ‘single atoms’ and bi- and trinuclear species over our model photocatalytic formic acid reforming reaction. This work will offer practical insight that fills the critical knowledge gap in the design and engineering of new-generation atomic and nanocluster catalysts. The precise control of the structure and surface sensitivities is important as it can effectively lead to more reactive and selective catalytic systems. The supported bi- and trinuclear Cu-oxo nanoclusters exhibit notably different catalytic properties compared with the mononuclear ‘Cu₁’ analogue, which provides critical insight for the engineering of more superior catalytic systems.

The controlled synthesis of novel bi- and trinuclear Cu-oxo nanoclusters supported on UiO-66-NH₂ that show notably different catalytic properties in the photocatalytic formic acid decomposition reaction is reported.