Cobalt π-cations in carbocyclic ring constructions

In a combination of cobalt-mediated cationic and free radical chemistry, treatment of the allyl silane substituted β-hydroxycobaloxime 13 with pTSA led predominantly to the trans-disubstituted cyclopentane 14, which on irradiation with TEMPO produced 15. In a similar manner, the cobaloxime 18 was cyclised to 19 in the presence of pTSA which, on irradiation with a sunlamp then underwent radical mediated cyclisation to the substituted indane 20.     

Amides as precursors of imidoyl radicals in cyclisation reactions

Amides have been successfully used as precursors of imidoyl radicals for radical cyclisation. The amides have been converted to imidoyl selanides via reaction with phosgene to yield imidoyl chlorides followed by reaction with potassium phenylselanide. Imidoyl selanides were reacted with tributyltin hydride (Bu₃SnH) as the radical mediator with triethylborane or AIBN as initiators to yield imidoyl radicals for cyclisation reactions. Imidoyl radicals have been cyclised onto alkenes to yield 2,3-substituted-indoles and -quinolines and also onto pyrroles and indoles to give bi- and tricyclic heteroarenes.     

The synthesis of (−)-varitriol and (−)-3′-epi-varitriol via a Ramberg-Bäcklund route

A concise route to the anti-tumour natural product (−)-varitriol, together with its novel isomer (−)-3′-epi-varitriol, is described using a Horner-Wadsworth-Emmons (HWE)/conjugate addition/Ramberg-Bäcklund sequence as the cornerstone. The flexibility of the synthetic route has been demonstrated by the preparation of novel varitriol analogues.     

b1Σ+ Emissions from group V–VII diatomic molecules. b 0+ → X1 0+, X2 1 emissions of AsI and SbI

Chemiluminescence from the b 0⁺ → X₁ 0⁺ band system of AsI and of the b 0⁺ → X₁ 0⁺, X₂ 1 systems of SbI in the near-infrared spectral region has been observed in a discharge flow system. Analysis of the spectra led to the spectroscopic constants (in cm^?1) of AsI: ω_e(X₁, X₂) = 257 ± 2, ω_ex_e(X₁, X₂) = 0.82 ± 0.2, T_e(b 0⁺) = 11738 ± 5, ω_e(b 0⁺) = 271 ± 2, ω_ex_e(b 0⁺) = 0.66 ± 0.2, and of SbI: T_e(X₂ 1) = 965 ± 10, ω_e(X₁, X₂) = 206 ± 6, T_e(b 0⁺) = 12328 ± 10, ω_e(b 0⁺) = 211 ± 6. The intensity ratio of the two sub-systems b 0⁺ → X₂ 1 and b 0⁺→ X₁ 0⁺ was found to be ≈0.013 in the case of SbI and ? 0.01 for AsI.     

Self-assembled organic monolayers terminated in perfluoroalkyl pentafluoro-lambda(6)-sulfanyl (-SF5) chemistry on gold

Recently synthesized (Winter, R.; Nixon, P. G.; Gard, G. L.; Radford, D. H.; Holcomb, N. R.; Grainger, D. W. J. Fluorine Chem. 2001, 107, 23-30) SF5-terminated perfluoroalkyl thiols (SF5(CF2)nCH2CH2SH, where n = 2, 4, and 6) and a symmetric SF5-terminated dialkyl disulfide ([SF5-CH=CH-(CH2)8-S-]2) were assembled as thin films chemisorbed onto gold surfaces. The adsorbed monolayer films of these SF5-containing molecules on polycrystalline gold were compared using ellipsometry, contact angle, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and infrared spectroscopy (FTIR) surface analytical methods. The resulting SF5-dialkyl disulfide monolayer film shows moderate angle dependence in depth-dependent XPS analysis, suggesting a preferentially oriented film. The SF5-terminated perfluoroalkyl thiols exhibit angular-dependent XPS compositional variance depending on perfluoroalkyl chain length, consistent with improved film assembly (increasingly hydrophobic, fewer defects, and more vertical chain orientation increasing film thickness) with increasing chain length. Tof-SIMS measurements indicate that both full parent ions for these film-forming molecules and the unique SF5 terminal group are readily detectable from the thin films without substantial contamination from other adsorbates.     

Model systems for flavoenzyme activity: a tuneable intramolecularly hydrogen bonded flavin-diamidopyridine complex

We report the electrochemically tuneable intramolecular hydrogen bonding interactions between a covalently linked flavin-diamidopyridine unit.     

Separation of dixanthogen and sulphur xanthates by H.P.L.C.: Disproportionation of Sulphur Dixanthates

High-performance liquid chromatography on C₁₃ reverse-phase or silica gel columns, with methanol—water (85:15) or n-hexane, respectively, as mobile phase, is used to separate dixanthogens and sulphur xanthates with different alkyl groups. Detection limits are as low as 1 ng (0.05 ppm) with u.v. detectors. When molecular emission cavity analysis is used for the detector, detection limits are reduced to ca. 0.25 ng (0.013 ppm). In aqueous methanol, alkyl sulphur dixanthates, (ROCS₂)₂S, disproportionate to yield mixtures of the corresponding dixanthogen, (ROCS₂)₂ , alkyl sulphur monoxanthates, (ROCS₂)₂S₂ , and dixanthates.     

Delineation of RAID1, the RACK1 interaction domain located within the unique N-terminal region of the cAMP-specific phosphodiesterase, PDE4D5

Background  

The cyclic AMP specific phosphodiesterase, PDE4D5 interacts with the β-propeller protein RACK1 to form a signaling scaffold complex in cells. Two-hybrid analysis of truncation and mutant constructs of the unique N-terminal region of the cAMP-specific phosphodiesterase, PDE4D5 were used to define a domain conferring interaction with the signaling scaffold protein, RACK1.     

Ferrocene incorporating host-guest dyads with electrochemically controlled three-pole hydrogen bonding properties

We describe the electrochemically controlled hydrogen bonding interactions between the isobutyl flavin/2,6-diferrocenylamidopyridine (2·5) and 9,10-phenanthrenequinone/1-ferrocenyl-3-hexylurea (4·6) dyads. Cyclic and square wave voltammetry studies have shown that the binding efficiencies between these moieties can be electrochemically actuated in non-polar (CH₂Cl₂ for 2·5) or polar (DMF for 4·6) organic solvents between three distinct states.