Identifying chemical sources of airborne contamination in lichen biomonitors through instrumental neutron activation analysis

Chemical elements were determined in epiphytic lichens from Terceira and Santa Maria islands (Azores, Portugal), by k ₀-standardized, instrumental neutron activation analysis. Abundance ranges were generally below those in mainland Portugal, except for Br (Terceira), Cl (Santa Maria), Na (Santa Maria), and Se (both islands). Elemental (averaged) contents of As, Br, Cl, Co, Cr, Mg, Na, Se, Hg and Zn were significantly different between the islands. Anthropogenic influence was discernible in Terceira if not in Santa Maria, where only crustal and marine sources are apparent.     

Enantioselective Access to Spirocyclic Sultams by Chiral Cpx–Rhodium(III)‐Catalyzed Annulations

Chiral spirocyclic sultams are a valuable compound class in organic and medicinal chemistry. A rapid entry to this structural motif involves a [3+2] annulation of an N‐sulfonyl ketimine and an alkyne. Although the directing‐group properties of the imino group for C?H activation have been exploited, the developments of related asymmetric variants have remained very challenging. The use of rhodium(III) complexes equipped with a suitable atropchiral cyclopentadienyl ligand, in conjunction with a carboxylic acid additive, enables an enantioselective and high yielding access to such spirocyclic sultams.     

Enhanced aqueous solubility of long wavelength voltage-sensitive dyes by covalent attachment of polyethylene glycol

Long wavelength voltage-sensitive dyes (VSDs) called Pittsburgh (PGH) dyes were recently synthesized by coupling various heterocyclic groups to a styryl-thiophene intermediate forming extended, partially rigid chromophores. Unlike most styryl VSDs, dyes with a sulfonic acid anchor directly attached to the chromophore showed no solvatochromic absorption shifts. The limited water solubility of many long wavelength VSDs requires the use of surfactants to transport the dye through physiological saline solutions and effectively label biological membranes. Here, we tested the chemical substitution of the sulfonic acid moiety with polyethyleneglycol (PEG) chains, ranging from MW 750 to 5000, to overcome the poor solubility of VSDs while retaining their properties as VSDs. The chemical synthesis of PGH dyes and their PEG derivatives are described. The PEG derivatives were soluble in aqueous solutions (>1 mM) and still reported membrane potential changes. In frog and mouse hearts, the voltage sensitivity (DeltaF/F per action potential) and spectral properties of PEG dyes were the same as the sulfonated analogues. Thus, the solubility of VSDs can be considerably improved with small polyethyleneglycol chains and can provide an effective approach to improve staining of excitable tissues and optical recordings of membrane potential.     

The Crystal Structure of Hop‐17(21)‐en‐3β‐yl acetate of Pluchea pteropoda Hemsl. from Vietnam

The title compound isolated from the roots of a Vietnamese plant and being known for its activity against fever was identified by this X‐ray analysis to be a pentacyclic triterpene of hopanoide type with a C17=C21 endocyclic double bond in the five membered ring. The presence of several axially substituted methyl groups on both the α and β side causes the so called "mid‐molecule strain" having already been reported in the literature for other hopane type ring systems.     

Ruthenocene and cyclopentadienyl pyrrolyl ruthenium as precursors for ruthenium atomic layer deposition: a comparative study of dissociation enthalpies

RuCp₂ (ruthenocene) and RuCpPy (cyclopentadienyl pyrrolyl ruthenium) complexes are used in ruthenium (Ru) atomic layer deposition (ALD) but exhibit a markedly different reactivity with respect to the substrate and co-reactant. In search of an explanation, we report here the results of a comparative study of the heterolytic and homolytic dissociation enthalpy of these two ruthenium complexes, making use of either density functional theory (DFT) or multiconfigurational perturbation theory (CASPT2). While both methods predict distinctly different absolute dissociation enthalpies, they agree on the relative values between both molecules. A reduced heterolytic dissociation enthalpy is obtained for RuCpPy compared to RuCp₂, although the difference obtained from CASPT2 (19.9?kcal/mol) is slightly larger than the one obtained with any of the DFT functionals (around 17?kcal/mol). Both methods also agree on the more pronounced stability of the Cp^? ligand in RuCpPy than in RuCp₂ (by around 9?kcal/mol with DFT and by 6?kcal/mol with CASPT2).     

Controlling the Spontaneous Precipitation of Silver Nanoparticles in Sol-Gel Materials

The mechanisms responsible for spontaneous silver precipitation in silver-doped sol-gel materials are identified. The chemistry of the solvent phase is found to be the critical factor in controlling this phenomenon. The addition of HCl as catalyst leads to the formation of AgCl and subsequent formation of silver upon light exposure. Another factor leading to silver precipitation is the reducing capability of methanol radicals. Silver precipitation is inhibited by simply washing out the pore solvents by a solvent exchange method.