Bestimmung von Kohlenstoff, Wasserstoff und Schwefel in organischen Substanzen

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Independent edges in bipartite graphs obtained from orientations of graphs

Given a digraph D on vertices v₁, v₂, ?, v_n, we can associate a bipartite graph B(D) on vertices s₁, s₂, ?, s_n, t₁, t₂, ?, t_n, where s_it_j is an edge of B(D) if (v_i, v_j) is an arc in D. Let O_G denote the set of all orientations on the (undirected) graph G. In this paper we will discuss properties of the set S(G) := {β₁ (B(D))) | D ? O_G}, where β₁ is the edge independence number. In the first section we present some background and related concepts. We show that sets of the form S(G) are convex and that max S(G) ≦ 2 min S(G). Furthermore, this completely characterizes such sets. In the second section we discuss some bounds on elements of S(G) in terms of more familiar graphical parameters. The third section deals with extremal problems. We discuss bounds on elements of S(G) if the order and size of G are known, particularly when G is bipartite. In this section we exhibit a relation between max S(G) and the concept of graphical closure. In the fourth and final section we discuss the computational complexity of computing min S(G) and max S(G). We show that the first problem is NP-complete and that the latter is polynomial.     

Coherent synthesis using carrier-envelope phase-controlled pulses from a dual-color femtosecond optical parametric oscillator

By using a dual-color femtosecond optical parametric oscillator (OPO), a coherent waveform was synthesized from two coresonant near-infrared signal pulses whose center wavelengths had a separation of 100 nm. Immediately after the OPO cavity the pulses had independent carrier-envelope phase-slip frequencies, and synthesis was achieved by shifting these frequencies using an acousto-optic modulator driven by an internally generated difference frequency. Soliton self-frequency shifted pulses from a photonic crystal fiber and a cross-correlation frequency-resolved optical gating (XFROG) measurement were used to analyze the result of the synthesis experiment and revealed that the synthesized waveform was a train of high-contrast 30 fs pulses.     

Radiofluorination of a Pre‐formed Gallium(III) Aza‐macrocyclic Complex: Towards Next‐Generation Positron Emission Tomography (PET) Imaging Agents

As part of a study to investigate the factors influencing the development of new, more effective metal‐complex‐based positron emission tomography (PET) imaging agents, the distorted octahedral complex, [GaCl(L)]?2 H₂O has been prepared by reaction of 1‐benzyl‐1,4,7‐triazacyclononane‐4,7‐dicarboxylic acid hydrochloride (H₂L?HCl) with Ga(NO₃)₃?9 H₂O, which is a convenient source of Ga^III for reactions in water. Spectroscopic and crystallographic data for [GaCl(L)]?2 H₂O are described, together with the crystal structure of [GaCl(L)]?MeCN. Fluorination of this complex by Cl^?/F^? exchange was achieved in high yield by treatment with KF in water at room temperature over 90 minutes, although the reaction was complete in approximately 30 minutes if heated to 80 °C, giving [GaF(L)]?2 H₂O in good yield. The same complex was obtained by hydrothermal synthesis from GaF₃?3 H₂O and Li₂L, and has been characterised by single‐crystal X‐ray analysis, IR, ¹H and ¹⁹F{¹H} NMR spectroscopy and ESI⁺ MS. Radiofluorination of the pre‐formed [GaCl(L)]?2 H₂O has been demonstrated on a 210 nanomolar scale in aqueous NaOAc at pH 4 by using carrier‐free ¹⁸F^?, leading to 60–70 % ¹⁸F‐incorporation after heating to 80 °C for 30 minutes. The resulting radioproduct was purified easily by using a solid‐phase extraction (SPE) cartridge, leading to 98–99 % radiochemical purity. The [Ga¹⁸F(L)] is stable for at least 90 minutes in 10 % EtOH/NaOAc solution at pH 6, but defluorinates over this time scale at pH of approximately 7.5 in phosphate buffered saline (PBS) or human serum albumin (HSA). The subtle role of the Group 13 metal ion and co‐ligand donor set in influencing the pH dependence of this system is discussed in the context of developing potential new imaging agents for PET.     

Detailed Structural Characterization of Sphingolipids via 193 nm Ultraviolet Photodissociation and Ultra High Resolution Tandem Mass Spectrometry

Sphingolipids serve not only as components of cellular membranes but also as bioactive mediators of numerous cellular functions. As the biological activities of these lipids are dependent on their structures, and due to the limitations of conventional ion activation methods employed during tandem mass spectrometry (MS/MS), there is a recognized need for the development of improved structure-specific methods for their comprehensive identification and characterization. Here, positive-ionization mode 193 nm ultraviolet photodissociation (UVPD)-MS/MS has been implemented for the detailed structural characterization of lipid species from a range of sphingolipid classes introduced to the mass spectrometer via electrospray ionization as their lithiated or protonated adducts. These include sphingosine d18:1(4E), dihydrosphingosine (sphinganine) d18:0, sphingadiene d18:2(4E,11Z), the isomeric sphingolipids ceramide d18:1(4E)/18:0 and dihydroceramide d18:0/18:1(9Z), ceramide-1-phosphate d18:1(4Z)/16:0, sphingomyelin d18:1(4E)/18:1(9Z) the glycosphingolipids galactosyl ceramide d18:1(4E)/24:1(15Z) and lactosyl ceramide d18:1(4E)/24:0, and several endogenous lipids present within a porcine brain total lipid extract. In addition to the product ions formed by higher energy collision dissociation (HCD), UVPD is shown to yield a series of novel structurally diagnostic product ions resulting from cleavage of both sphingosine carbon–carbon and acyl chain carbon–carbon double bonds for direct localization of site(s) of unsaturation, as well as via diagnostic cleavages of the sphingosine backbone and N–C amide bond linkages. With activation timescales and dissociation efficiencies similar to those found in conventional MS/MS strategies, this approach is therefore a promising new tool in the arsenal of ion activation techniques toward providing complete structural elucidation in automated, high-throughput lipid analysis workflows.

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Unusual neutral ligand coordination to arsenic and antimony trifluoride

The preparations and spectroscopic characterisation of the hydrolytically unstable As(III) complexes, [AsF(3)(OPR(3))(2)] (R = Me or Ph) and [AsF(3){Me(2)P(O)CH(2)P(O)Me(2)}] are described and represent the first examples of complexes of AsF(3) with neutral ligands. The crystal structure of [AsF(3){Me(2)P(O)CH(2)P(O)Me(2)}] contains dimers with bridging diphosphine dioxide, but there are also long contacts between the dimers to neighbouring phosphine oxide groups, completing a very distorted six-coordination at arsenic and producing a weakly associated polymer structure. The reaction of AsF(3) with OAsPh(3) affords Ph(3)AsF(2), and no arsine oxide complex was formed. Reaction of SbF(3) with OER(3) (R = Me or Ph, E = P or As), Me(2)P(O)CH(2)P(O)Me(2) and Ph(2)P(O)(CH(2))(n)P(O)Ph(2) (n = 1 or 2) in MeOH produces [SbF(3)(OER(3))(2)], [SbF(3){Me(2)P(O)CH(2)P(O)Me(2)}] and [SbF(3){Ph(2)P(O)(CH(2))(n)P(O)Ph(2)}] respectively. The X-ray structures reveal that the complexes contain square pyramidal SbF(3)O(2) cores with apical F and cis disposed pnictogen oxides. However, whilst [SbF(3)(OER(3))(2)] (R = Ph: E = P or As; R = Me: E = As) and [SbF(3){Ph(2)P(O)CH(2)P(O)Ph(2)}] are monomeric, [SbF(3){Me(2)P(O)CH(2)P(O)Me(2)}] is a dimer with bridging diphosphine dioxides producing a twelve-membered ring, and [SbF(3){Ph(2)P(O)(CH(2))(2)P(O)Ph(2)}] is a chain polymer with diphosphine dioxide bridges. In the OAsR(3) reactions with SbF(3), R(3)AsF(2) are also formed. Notably the Sb-O(P) bonds are shorter than As-O(P), despite the covalent radii (As < Sb), consistent with very weak coordination of the AsF(3). IR and multinuclear ((1)H, (19)F and (31)P) NMR data are reported and discussed. BiF(3) does not react with pnictogen oxide ligands under similar conditions and halide exchange of bismuth chloro complexes with Me(3)SnF gave BiF(3).     

Coordination complexes of silicon and germanium halides with neutral ligands

The coordination chemistry of silicon(IV) and (II) and germanium(IV) and (II) halides with neutral donor ligands from groups 15 (N, P or As) and 16 (O, S or Se) is reviewed; N-heterocyclic carbene complexes are also included. The focus is mainly on results published after 1990 and illustrates that significant recent developments have been made in the coordination chemistry of low-valent silicon and germanium halide complexes in particular; this is expected to pave the way for much new reaction chemistry both from a fundamental and application-driven perspective.     

Intramolecular vibrational dynamics in S1 p-fluorotoluene. I. Direct observation of doorway states

Picosecond time-resolved photoelectron spectroscopy is used to investigate intramolecular vibrational redistribution (IVR) following excitation of S(1) 18a(1) in p-fluorotoluene (pFT) at an internal energy of 845 cm(-1), where ν(18a) is a ring bending vibrational mode. Characteristic oscillations with periods of 8 ps and 5 ps are observed in the photoelectron signal and attributed to coupling between the initially excited zero-order bright state and two doorway states. Values for the coupling coefficients connecting these three vibrational states have been determined. In addition, an exponential change in photoelectron signal with a lifetime of 17 ps is attributed to weaker couplings with a bath of dark states that play a more significant role during the latter stages of IVR. A tier model has been used to assign the most strongly coupled doorway state to S(1) 17a(1) 6a(2)('), where ν(17a) is a CH out-of-plane vibrational mode and 6a(2)(') is a methyl torsional level. This assignment signifies that a torsion-vibration coupling mechanism mediates the observed dynamics, thus demonstrating the important role played by the methyl torsional mode in accelerating IVR.     

Pulsed jet discharge matrix isolation and computational study of bromine atom complexes: Br···BrXCH(2) (X = H, Cl, Br)

Halogen atoms are important reactive radicals in the atmosphere. In this work, pulsed jet discharge matrix isolation spectroscopy and computational methods were used to characterize prereactive complexes of halogen atoms with simple halons. Our experiments combined matrix isolation techniques with a pulsed DC discharge nozzle, where a dilute CH(2)XBr (X = H, Cl, Br)/rare gas sample was gently discharged and the products were deposited onto a cold KBr window. The Br···BrCH(2)X (X = H, Cl, Br) complexes were characterized by infrared and electronic spectroscopy, supported by ab initio and density functional theory (DFT) calculations, which shed light on the structure of, bonding in, and binding energy of the complexes. The correlation of charge-transfer energy with donor ionization potential (Mulliken correlation) was examined, and the charge-transfer photochemistry of the complexes was explored.