Synthesis of fluorinated trithioether compounds: X-ray structures of 1,3,5-(CH2SRf)3-2,4,6-(CH3)3C6, Rf = C6F5, 4-HC6F4, or 2-FC6H4

A series of three new trithioether compounds containing fluorinated phenyl moieties, 1,3,5-(CH₂SR_f)₃-2,4,6-(CH₃)₃C₆, R_f = C₆F₅ (1), 4-HC₆F₄ (2), or 2-FC₆H₄ (3), were prepared by treatment of 1,3,5-(CH₂Br)₃-2,4,6-(CH₃)₃C₆ with the corresponding Pb(SC₆F₅)₂ or NaSR_f. The new structures were verified by elemental analyses, IR, ¹H NMR, ¹⁹F NMR spectroscopies, and mass spectra. The single crystal X-ray diffraction studies of 1-3 show a similar cis,trans,trans-conformation for the three fluorophenylthiomethyl groups attached to the central benzene ring with all dihedral angles between planes of central ring and external rings close to 0°, giving flat molecules. Comparing, 1-3 with closely related tripodal molecules built-up on 2,4,6-trimethylbenzene, arrangement of one SR group respect to others seems to be defined by the nature of the R substituent. Then in the case of 1-3, a parallel arrangement of rings is favored over an orthogonal one, which would bring the ortho-F atoms close to H atoms of the methylene groups.     

Recoil spectrometry: Ion accelerator based elemental characterisation of surface layers

Recoil Spectrometry covers a group of techniques that are very similar to the well known Rutherford backscattering Spectrometry technique, but with the important difference that one measures the recoiling target atom rather than the projectile ion. This makes it possible to determine both the identity of the recoil and its depth of origin from its energy and velocity, using a suitable detector system. The incident ion is typically high-energy (30–100MeV)³⁵C1,⁸¹Br or¹²⁷I. Low concentrations of light elements such as C, O and N can be profiled in a heavy matrix such as Fe or GaAs. Here we present an overview of mass and energy dispersive recoil Spectrometry and illustrate its successful use in some typical applications.     

Effective Assignment of α2,3/α2,6‐Sialic Acid Isomers by LC‐MS/MS‐Based Glycoproteomics

Distinct structural changes of the α2,3/α2,6‐sialic acid glycosidic linkages on glycoproteins are of importance in cancer biology, inflammatory diseases, and virus tropism. Current glycoproteomic methodologies are, however, not amenable toward high‐throughput characterization of sialic acid isomers. To enable such assignments, a mass spectrometry method utilizing synthetic model glycopeptides for the analysis of oxonium ion intensity ratios was developed. This method was successfully applied in large‐scale glycoproteomics, thus allowing the site‐specific structural characterization of sialic acid isomers.     

Carbohydrate carbocyclization by a zinc-mediated tandem reaction and ring-closing enyne metathesis

Methyl 5-deoxy-5-iodo-pentofuranosides are reductively ring-opened and propargylated in a tandem fashion in the presence of zinc. The 1,7-enynes thus obtained are subjected to ring-closing enyne metathesis with catalyst B to produce functionalized 1-vinyl cyclohexenes. By adding BnNH(2) to the tandem reaction, an amino group can be introduced in the 1,7-enyne products. Addition of 2-TMS-ethynylcerium(III) chloride after the reductive ring-opening produces the corresponding 1,6-enynes. Further annulation of the product 1,3-dienes can be achieved through a Diels-Alder reaction with good control of stereochemistry. These procedures constitute efficient methods for rapid carbocyclization and annulation of carbohydrates to produce a variety of functionalized five- and six-membered ring systems.     

Modelling of Pb-(TAPS)x-(OH)y system and refinement of stability constants in the region of lead hydrolysis and lead hydroxide precipitation

The influence of [(2-hydroxy-1,1-bis(hydroxymethyl)ethyl)amino]-1-propanesulfonic acid (TAPS) on solutions containing lead(II) was studied by direct current polarography (DCP) and glass electrode potentiometry (GEP). The readings were taken at fixed total TAPS to total lead(II) concentration ratios and various pH values, at 25.0 ± 0.1 °C and ionic strength 0.1 M KNO₃.Due to the basic pK_a of the ligand, which occurs in the pH range where large amount of lead polynuclear species are formed, and the occurrence of ligand adsorption, that disabled the use of high concentrations of TAPS on DCP experiments, GEP and DCP experimental conditions were put to the limit in order to provide the correct Pb-TAPS-OH model and reliable stability constants.The proposed final model is: PbL, PbL₂, PbL₂(OH) and PbL₂(OH)₂ with overall stability constants values, as log β, 3.27 ± 0.06, 6.5 ± 0.1, 12.7 ± 0.1 and 17.27 ± 0.06, respectively.A comparative analysis of the strength of complexation of TAPS and a structural related buffer, 2-hydroxy-3-[tris(hydroxymethyl)methylamino]-1-propanesulfonic acid (TAPSO), with lead is also discussed.     

Formation of dihydrouracils via cyclization of N-substituted 3-thioureidopropanoic acids and facile desulfurization

Cyclization of N-3 substituted 3-thioureidopropanoic acids in isobutyric anhydride at high temperature resulted in the unexpected formation of N-3,N-1-substituted dihydrouracils, as confirmed by thorough spectroscopic characterization. A mechanism based on the identification of intermediates observed at lower reaction temperatures is proposed.     

Structural Mimics of Acetylene Hydratase: Tungsten Complexes Capable of Intramolecular Nucleophilic Attack on Acetylene

Bioinspired complexes employing the ligands 6-tert-butylpyridazine-3-thione (SPn) and pyridine-2-thione (SPy) were synthesized and fully characterized to mimic the tungstoenzyme acetylene hydratase (AH). The complexes [W(CO)(C₂H₂)(CHCH-SPy)(SPy)] ( 4 ) and [W(CO)(C₂H₂)(CHCH-SPn)(SPn)] ( 5 ) were formed by intramolecular nucleophilic attack of the nitrogen donors of the ligand on the coordinated C₂H₂ molecule. Labelling experiments using C₂D₂ with the SPy system revealed the insertion reaction proceeding via a bis-acetylene intermediate. The starting complex [W(CO)(C₂H₂)(SPy)₂] ( 6 ) for these studies was accessed by the new acetylene precursor mixture [W(CO)(C₂H₂)_n(MeCN)_3−nBr₂] (n=1 and 2; 7 ). All complexes represent rare examples in the field of W−C₂H₂ chemistry with 4 and 5 being the first of their kind. In the ongoing debate on the enzymatic mechanism, the findings support activation of acetylene by the tungsten center.     

Boranediyl- and Diborane(4)-1,2-diyl-Bridged Platinum A-Frame Complexes

Diplatinum A-frame complexes with a bridging (di)boron unit in the apex position were synthesized in a single step by the double oxidative addition of dihalo(di)borane precursors at a bis(diphosphine)-bridged Pt⁰₂ complex. While structurally analogous to well-known μ-borylene complexes, in which delocalized dative three-center-two-electron M-B-M bonding prevails, theoretical investigations into the nature of Pt−B bonding in these A-frame complexes show them to be rare dimetalla(di)boranes displaying two electron-sharing Pt−B σ-bonds. This is experimentally reflected in the low kinetic stability of these compounds, which are prone to loss of the (di)boron bridgehead unit.