Trace analysis of free and combined amino acids in atmospheric aerosols by gas chromatography–mass spectrometry

The analysis of amino acids by gas chromatography mass spectrometry (GC–MS) after their derivatization with N-(t-butyldimethylsilyl)-N-methyltrifluoroacetamide was investigated as an alternative approach for the determination of free (FAA) and combined amino acids (CAA) in aerosols. This technique showed excellent linearity with r² values ranging from 0.9029 to 0.9995 and instrumental limits of detection ranging from 0.3 to 46 pg for the different amino acids. The quality of water used for sample extraction was found to be of utmost importance for achieving low blank levels of FAA and CAA. The addition of isopropanol during the extraction of aerosols was also shown to minimize the coextraction of inorganic salts that interfered with the analysis of FAA, Moreover, the ascorbic acid was found to be the most effective reagent for preventing the oxidative destruction of CAA during the hydrolysis process. By the analysis of spiked aerosol samples, the average recoveries determined for FAA and CAA were higher than 60% and the associated relative standard deviation was lower than 10% for the majority of amino acids. The application of the adopted method in background aerosols of the eastern Mediterranean enabled the unambiguous identification and quantification of 20 amino acids. The total concentration of FAA and CAA in aerosols ranged from 13 to 34 ng m⁻³ and from 29 to 79 ng m⁻³, respectively. The GC–MS based method is proposed to overcome several analytical difficulties usually encountered with the conventional HPLC-fluoresence technique.     

Exploring the photoinduced electron transfer reactivity of aza[60]fullerene iminium cation

Photolysis of (C₅₉N)₂ solutions in the presence of neutral π-donors, such as arenes and electron-rich alkenes leads to a series of novel aza[60]fullerene monoadducts. The key step of the reaction involves a photoinduced electron transfer from the donor molecule to the iminium cation of aza[60]fullerene, followed by radical coupling of the resulting aza[60]fullerenyl radical with an intermediate stabilized radical derived from the substrate. This type of reactivity has been proven efficient with arenes having oxidation potential higher than about 1.5 V. Simple olefins, such as tri- and tetra-methylethylene, as well as cyclohexene, can also participate in this kind of photoinduced electron transfer-initiated reaction with C₅₉N⁺, affording the corresponding aza[60]fullerene derivatives. In the case of 2-methoxyprop-1-ene, 2,4-hexadiene, and β,β-dimethylstyrene, [2+2] cycloaddition reactions with the aza[60]fullerene carbon shell dominate, leading to a mixture of unidentified multiadducts.     

Alleno-acetyllenic scaffolding for the construction of axially chiral C60 dimers

The preparation of enantiopure dumbbell-type dimeric fullerenes consisting of two C₆₀ units connected by axially chiral alleno-acetylenic spacers is reported for the first time. As a key step, the attachment of the terminal alkyne moiety of the spacers to C₆₀ was efficiently accomplished by employing an in situ C₆₀-ethynylation methodology. In addition to spectral analyses, single-crystal X-ray crystallographic studies allowed for the unambiguous structural assignment of two C₆₀–alleno-acetylene conjugates. Circular dichroism measurements showed that the axial chirality of the allene moieties linked to the fullerene sphere is able to perturb the intrinsic symmetry of the fullerene π-system. Large characteristic Cotton effects were observed for two bisfullerenes in the 200–350 nm spectral region. UV/Vis absorption spectroscopic studies showed improved molar absorptivity of these dimeric fullerenes, but no strong evidence for a significant through-space electronic communication between the two C₆₀ spheres; electrochemical investigations further confirmed this conclusion.     

Enantiopure Laterally Functionalized Alleno–Acetylenic Macrocycles: Synthesis,Chiroptical Properties,and Self‐Assembly in Aqueous Media

A family of shape‐persistent alleno–acetylenic macrocycles (SPAAMs), peripherally decorated with structurally diverse pendant groups, has been synthesized and characterized in enantiomerically pure form. Their electronic circular dichroism (ECD) spectra feature a strong chiroptical response, which is more than two times higher than for open‐chain tetrameric analogues. A water‐soluble oligo(ethylene glycol)‐appended SPAAM undergoes self‐assembly in aqueous solution. Morphology studies by cryogenic transmission electron microscopy (cryo‐TEM) revealed the formation of aggregates with fibrous fine structures that correspond to tubular, macrocyclic stacks.     

Improved chromium-catalyzed allylic oxidation of Δ-steroids with t-butyl hydroperoxide

Various chromium^VI-catalyzed conditions have been tested to improve the oxidation of Δ⁵-steroids with t-BuOOH to their corresponding 5-en-7-ones. The use of PDC or the association of CrO₃ with an amine as the catalyst and CH₂Cl₂ or PhCF₃ as the solvent led usually to the best yields. A minor reaction pathway was the epoxidation of the double bond.     

Gold nanoparticles supported on TiO2 catalyse the cycloisomerisation/oxidative dimerisation of aryl propargyl ethers

Gold nanoparticles supported on TiO(2) (~1%) catalyse in high yields the selective cycloisomerisation of aryl propargyl ethers into the corresponding 2H-chromenes, under heterogeneous conditions. 2H,2'H-3,3'-Bichromenes resulting from a catalytic oxidative dimerization pathway are also formed as by-products.     

Synthesis of sulfur containing analogues of the soluble guanylate cyclase inhibitor 8-bromo-4H-[1,2,4]oxadiazolo[3,4-c][1,4]benzoxazin-1-one NS2028

Sulfur analogues of the soluble guanylate cyclase (sGC) inhibitor NS2028 1a are synthesized. Treating 8-bromo-2H-benzo[b][1,4]oxazin-3(4H)-one oxime (6) with 1,1′-thiocarbonyldiimidazole (1.1 equiv) gave the carbamothioate 8-bromo-4H-[1,2,4]oxadiazolo[3,4-c][1,4]benzoxazine-1-thione (3a) in 83% yield. Alternatively reacting NS2028 1a with P₂S₅ (0.5 equiv) affords the carbamothioate 3a in 80% yield. Similar treatment of 8-aryl substituted NS2028 analogues 1b-d with P₂S₅ gave the carbamothioates 3b-d in 64-91% yields. Although quite stable, the carbamothioates 3a-d could be thermally isomerized in the presence of Cu (10 mol %) to afford the thiocarbamates 4a-d in high yields. Interestingly, in the case of carbamothioate 3a Pd and In metals also facilitated the isomerization. Furthermore, treatment of the thiocarbamates 4a-d with P₂S₅ (0.5 equiv) affords the carbamodithioates 5a-d in 72-89% yields. All new compounds are fully characterized including single crystal X-ray data for carbamothioate 3a and thiocarbamate 4a. Finally, a mechanism is proposed for the carbamothioate to thiocarbamate isomerization.