Desorption/ionization of biomolecules from aqueous solutions at atmospheric pressure using an infrared laser at 3 μm

A new atmospheric pressure (AP) infrared (IR) matrix-assisted laser desorption/ionization (MALDI) ion source was developed and interfaced with a Thermo Finnigan LCQ ion trap mass spectrometer. The source utilized a miniature all-solid-state optical parametric oscillator (OPO)-based IR laser system tunable in the lambda = 1.5-4 microm spectral range and a nitrogen ultraviolet (UV) laser (lambda = 337 nm) for use in comparative studies. The system demonstrated comparable performance at 3 microm and 337 nm wavelengths if UV matrices were used. However, AP IR-MALDI using a 3 microm wavelength showed good performance with a much broader choice of matrices including glycerol and liquid water. AP IR-MALDI mass spectra of peptides in the mass range up to 2000 Da were obtained directly from aqueous solutions at atmospheric conditions for the first time. A potential use of the new AP IR-MALDI ion source includes direct MS analysis of biological cells and tissues in a normal atmospheric environment as well as on-line coupling of mass spectrometers with liquid separation techniques.     

Molecular modeling study of the differential ligand–receptor interaction at the μ, δ and κ opioid receptors

3D models of the opioid receptors , and were constructed using BUNDLE, an in-house program to build de novo models of G-protein coupled receptors at the atomic level. Once the three opioid receptors were constructed and before any energy refinement, models were assessed for their compatibility with the results available from point-site mutations carried out on these receptors. In a subsequent step, three selective antagonists to each of three receptors (naltrindole, naltrexone and nor-binaltorphamine) were docked onto each of the three receptors and subsequently energy minimized. The nine resulting complexes were checked for their ability to explain known results of structure-activity studies. Once the models were validated, analysis of the distances between different residues of the receptors and the ligands were computed. This analysis permitted us to identify key residues tentatively involved in direct interaction with the ligand.     

Catalyst-free system for reductive addition of terminal alkynes via 2,2′-dithiosalicylic acid in water

Green, practical, and efficient hydrothiolation of 2,2′-dithiosalicylic acid to terminal alkynes was found to proceed smoothly in water under mild reaction conditions with moderate to good yields. The use of metal catalysts and toxic solvents was avoided, and good to excellent stereoselectivity and regioselectivity were obtained. Herein, the reaction conditions and regioselectivity are discussed, and a preliminary reaction mechanism is proposed.     

Unusual thiolate-bridged diiron clusters bearing the cis-HN═NH ligand and their reactivities with terminal alkynes

A series of well-defined thiolate-bridged diiron clusters bearing the cis-HN═NH ligand, [Cp(?)Fe(μ-SEt)(2)(μ-η(1):η(1)-HN═NH)FeCp(?)][PF(6)] (Cp(?) = η(5)-C(5)Me(4)H or η(5)-C(5)Me(5)), are successfully prepared in high yields and fully characterized by spectroscopy and X-ray crystallography. Under moderate conditions, these new Fe/S clusters exhibit high activity, not only for the catalytic cleavage of the N-N bond of hydrazines but also for the activation and coupling of terminal alkynes.     

The photochemical and thermal reactions of a triosmium cluster carrying a γ-pyrone ligand with alkynes

The reaction of the cluster Os₃(CO)₁₀(μ-H)(μ-γ-C₅H₃O₂) (1) with a number of alkynes under thermal or visible light irradiation conditions, afforded in most cases the dinuclear complexes Os₂(CO)₆(μ-γ-C₅H₃O₂)(μ-LH) (L=PhCCPh, ^tBuCCH, ^tBuCCMe or EtCCEt) (2) or the trinuclear chain complexes Os₃(CO)₉(μ-H)(μ-γ-C₅H₃O₂)(μ-RCCHC₆H₄) (R=H, Ph) (3). In the case of PhCCPh, a new isomer of Os₃(CO)₈(PhCCPh)₂, viz., Os₃(CO)₈(μ-PhCCPh)(μ-PhCCHC₆H₄) (7) has been isolated and characterised.     

Regio- and enantioselective conjugate addition of β-nitro α,β-unsaturated carbonyls to construct 3-alkenyl disubstituted oxindoles

Reversal of regioselectivity in the catalytic asymmetric conjugate additions of 3-substituted oxindoles to β-nitroenones or β-nitroacrylates was established with chiral scandium catalysts. It enabled the construction of functionalized 3,3-disubstituted oxindoles, including terminal and internal vinyl groups in excellent yields and ee values.     

Xphos ligand and platinum catalysts: A versatile catalyst for the synthesis of functionalized β-(E)-vinylsilanes from terminal alkynes

Hydrosilylation of functionalized terminal arylalkynes with a variety of silanes catalyzed by PtCl₂ or PtO₂ in the presence of the air-stable and bulky Xphos ligand was investigated. Regardless of the electronic nature (electron withdrawing or donating group) and the position (o, m, p) of the substituents on the aromatic ring, a single β-(E)-styrylsilanes was obtained in good to excellent yields. The regioselectivity of the H-Si bond addition was found to be governed by steric effects induced by the bulky Xphos ligand. A dramatic regioselectivity was also observed when functionalized terminal aliphatic alkynes were employed as a substrate and in these cases regioisomeric β-(E)-vinylsilanes were generated with excellent selectivity.     

Properties of Co-Mo coatings obtained by electrodeposition at pH 6.6

Cobalt-molybdenum coatings were prepared by electrodeposition in a sulfate-citrate bath and their morphology, structure and magnetic properties were analysed. Concentrations of 0.1 mol dm^–3 CoSO₄ and 0.005 mol dm^–3 Na₂MoO₄ at pH 6.6 led to Co-Mo deposits of 20–23% Mo that can be grown to several microns over graphite or copper substrates. At low deposition potentials or current densities, the deposits presented a close-packed hexagonal structure (hcp) that evolved to a (100)+(110) preferred orientation and acicular morphology as the deposit thickness increased. When the deposition potential or the current density was made more negative, a mixed crystalline+amorphous structure was obtained. The degree of crystallinity depended on the thickness: thin films were more amorphous than the thicker ones. Co-Mo deposits showed lower saturation magnetization (M_s) and coercivity (H_c) than the pure cobalt deposits. The crystalline+amorphous films showed the lowest H_c values (around 40 Oe).     

Enantioselective addition of terminal alkynes to N-(diphenylphosphinoyl)imines catalyzed by Zn–BINOL complexes

Chiral nonracemic N-(diphenylphosphinoyl)-protected propargylic amines have been prepared by addition of terminal alkynes to N-(diphenylphosphinoyl)aldimines in the presence of dimethylzinc and 3,3′-dibromo-BINOL as catalyst. The reaction works with a variety of aromatic and heteroaromatic aldimines and with different alkynes, providing the expected products in generally good yields and enantiomeric excesses (up to 96%).     

Magnetic properties of hexanuclear lanthanide(III) clusters incorporating a central μ6-carbonate ligand derived from atmospheric CO2 fixation

Three isostructural hexanuclear lanthanide(III) clusters are reported (Ln(III) = Gd, Tb, and Dy). The metallic core of each complex displays an unusual arrangement of ions, which is stabilized by a μ(6)-carbonate ligand. Magnetic studies show that the Ln(III) ions in each compound are weakly exchange coupled, with the Tb and Dy analogues displaying single-molecule-magnet behavior.     

Ruthenium hydride catalyzed silylvinylation of terminal alkynes under ethylene atmosphere at 80 psi

The development of methods for the stereoselective synthesis of polysubstituted 1,3-dienes is a challenge to synthetic chemistry. Herein is reported a selective approach for the synthesis of polysubstituted 1,3-dienes using the ruthenium hydride catalyzed intramolecular silylvinylation of alkynes under 80 psi of ethylene gas. This strategy affords a single diene isomer, is applicable to substrates with aryl and alkyl substitution at the propargyl and homopropargyl positions, and has been utilized in the synthesis of 5- and 6-membered oxasilacycles.     

Dissecting alkynes: full cleavage of polarized C≡C moiety via sequential bis-Michael addition/retro-Mannich cascade

The reaction of diaryl ketoalkynes with 1,2-diamino ethane leads to the full scission of the triple bond with the formation of acetophenone and imidazoline fragments. In this transformation, one of the alkyne carbons undergoes formal reduction with the formation of three C-H bonds, whereas the other carbon undergoes formal oxidation via the formation of three C-N bonds (one π and two σ). Computational analysis confirmed that the key fragmentation step proceeds via a six-membered TS in a concerted manner. Both amines are involved in the fragmentation: the N-H moiety of one amine transfers a proton to the developing negative charge at the enolate oxygen, while the other amine provides direct stereoelectronic assistance to the C-C bond cleavage via a hyperconjugative n(N) → σ*(C-C) interaction.     

Flow injection analysis at μl/min flow rates

The characteristics of knitted open tube (KOT) figure eight reactors and coil reactors at l/min flow rates were compared using plate height (H) calculations and peak height measurements. Peak broadening independent of flow rate was seen for the figure eight KOT but not the coil at flow rates of 150–300 l/min. Below 150 /min, the plate height values of both reactors were inversely proportional to flow rate. It was concluded that a 0.5-m KOT figure eight reactor is the most effective way to introduce delay time for a 1 1 injection size and tubing of 0.3 mm I.D. Enhancement of peak height response was particularly pronounced at flow rates less than 100 l/min.     

BF3·Et2O promoted conjugate addition of ethanethiol to electron-deficient alkynes

An effective method for the synthesis of vinyl thioethers through the conjugate addition of ethanethiol to electron-deficient alkynes promoted by BF₃Et₂Ohas been developed.Electron-deficient internal alkynes react with ethanethiol in this system to yield mainly Z-isomer of vinyl thioether adducts,while electron-deficient terminal alkynes afford mainly E-isomer of vinyl thioether adducts.     

Medium-wavelength infrared emission from a laser-produced oxygen plasma: Observations of OI 6h3,5H at 7.5 μm

Observations have been made of transitions in the 5 to 8 μm region of the infrared from emissions from a recombining oxygen plasma. Assignments have been made for transitions in this region using experimental and calculated energy level positions. The strongest feature occurs at 7.45 μm and is assigned as a composite line dominated by 6h^3,5H-5g^3,5G and 6g^3,5G-5f^3,5F at 7.450 and 7.426 μm respectively. This is the first experimental observation of the oxygen atom 6h^3,5H state.     

β-Halovinylsilanes in oligoyne synthesis: a fluoride-catalysed unmasking of alkynes from β-fluorovinylsilanes

A stereoselective halodestannylation of (E)-β-stannylvinylsilane 6 has been used to access a range of (E)-β-halovinylsilanes. Most notably, the β-fluorovinylsilane 14 was accessed in high yield using the Selectfluor^® reagent, and subsequently converted into a masked hexayne 22. Release of the hexayne 25 was achieved by exposing 22 to sub-stoichiometric quantities of fluoride.     

Ion beam-induced magnetic patterning at the sub-0.1 μm level

We present a method that allows magnetic patterning of a continuous magnetic film without significant modification of the surface roughness or of the film's optical indices. It involves ion irradiation of Co/Pt multilayers, using either a standard ion implantation technology combined with high resolution masking, or a focussed ion beam. We fabricated arrays of lines or dots whose magnetic properties differ on a sub-100 nm scale. We describe the ion collision physics on which the techniques are based, as well as some of the observed consequences on the micromagnetic properties of the arrays and on the ultimate resolution. Possible applications to high-density information storage are briefly discussed.     

Planar step-index waveguides obtained via sol–gel synthesis from organometallic precursors

Inorganic and hybrid sols obtained from Si, Ti, Zr and Ce organometallic precursors were used to prepare single and multilayer coatings with different thicknesses. Planar step-index waveguides with different refractive indices were thus prepared by dip-coating the above sols onto commercial soda-lime glass substrates, followed by appropriate thermal annealing. The resultant coatings were characterized by transmission electron microscopy and energy dispersive X-ray spectrometry to elucidate the interface and bonding between the sol–gel derived coatings and the glass substrates. Diffusion of alkali and alkaline earth elements from the glass into the coating layer was confirmed and proposed to play a role in the coating-substrate bonding, inducing excellent optical quality planar interfaces. Optical waveguide characterization performed on a 4.15 μm thick hybrid SiO₂:CeO₂ (95:5) step-index waveguide yielded losses of 1.50 dB/cm.     

Identification of target-specific bioisosteric fragments from ligand–protein crystallographic data

Bioisosteres are functional groups or atoms that are structurally different but that can form similar intermolecular interactions. Potential bioisosteres were identified here from analysing the X-ray crystallographic structures for sets of different ligands complexed with a fixed protein. The protein was used to align the ligands with each other, and then pairs of ligands compared to identify substructural features with high volume overlap that occurred in approximately the same region of geometric space. The resulting pairs of substructural features can suggest potential bioisosteric replacements for use in lead-optimisation studies. Experiments with 12 sets of ligand–protein complexes from the Protein Data Bank demonstrate the effectiveness of the procedure.