Preparation, characterization, and structural systematics of diphosphane and diarsane complexes of gallium(III) halides

The diphosphane o-C6H4(PMe2)2 reacts with GaX3 (X = Cl, Br, or I) in a 1:1 molar ratio in dry toluene to give trans-[GaX2{o-C6H4(PMe2)2}2][GaX4], the cations of which contain the first examples of six-coordinate gallium in a phosphane complex. The use of a 1:2 ligand/GaCl3 ratio produced [GaCl2{o-C6H4(PMe2)2}][GaCl4], containing a pseudotetrahedral cation, and similar pseudotetrahedral [GaX2{o-C6H4(PPh2)2}][GaX4] complexes are the only products isolated with the bulkier o-C6H4(PPh2)2. On the other hand, Et2P(CH2)2PEt2, which has a flexible aliphatic backbone, formed [(X3Ga)2{mu-Et2P(CH2)2PEt2}], in which the ligand bridges two pseudotetrahedral gallium centers. The diarsane, o-C6H4(AsMe2)2, formed [GaX2{o-C6H4(AsMe2)2}][GaX4], also containing pseudotetrahedral cations, and in marked contrast to the diphosphane analogue, no six-coordinate complexes form; a very rare example where these two much studied ligands behave differently towards a common metal acceptor. The complexes [(I3Ga)2{mu-Ph2As(CH2)2AsPh2}] and [GaX3(AsMe3)] are also described. The X-ray structures of trans-[GaX2{o-C6H4(PMe2)2}2][GaX4] (X = Cl, Br or I), [GaCl2{o-C6H4(PPh2)2}][GaCl4], [GaX2{o-C6H4(AsMe2)2}][GaX4] (X = Cl or I), [(I3Ga)2{mu-Ph2As(CH2)2AsPh2}], and [GaX3(AsMe3)] (X = Cl, Br or I) are reported, and the structural trends are discussed. The solution behavior of the complexes has been explored using a combination of 31P{1H} and 71Ga NMR spectroscopy.     

Differentiation of opium and poppy straw using capillary electrophoresis and pattern recognition techniques

Opium samples from four different locations and poppy straw from different plant varieties have been assayed using micellar capillary electrophoresis incorporating a sweeping technique. Individual alkaloids (morphine, codeine, papaverine, noscapine, thebaine, oripavine, reticuline and narceine) were quantitatively determined in the different samples by a validated capillary electrophoresis method. Unsupervised pattern recognition of the opium samples and the poppy straw samples using hierarchical cluster analysis (HCA) and principal component analysis (PCA), showed distinct clusters. Supervised pattern recognition using soft independent modelling of class analogy (SIMCA) was performed to show individual groupings and allow unknown samples to be classified according to the models built using the CZE assay results.     

Complete determination of the photoionization dynamics of a polyatomic molecule. I. Experimental photoelectron angular distributions from A1Au acetylene

Angle-resolved photoelectron spectra from rotationally selected A1Au state acetylene have been recorded using velocity-map imaging. Several Renner-Teller split vibrational bands have been observed and assigned, showing good agreement with previous zero kinetic energy photoelectron (ZEKE) work [S. T. Pratt, P. M. Dehmer, and J. L. Dehmer, J. Chem. Phys. 99, 6233 (1993); S.-J. Tang, Y.-C. Chou, J. J.-M. Lin, and Y.-C. Hsu, ibid. 125, 133201 (2006).] The extracted photoelectron angular distributions (PADs) corresponding to these bands show a strong dependence on the vibronic angular momentum projection quantum number K+. Subbands with odd K+ show PADs with maximum intensity along the polarization vector of the ionizing laser beam, while those with even K+ show PADs with maximum intensity perpendicular to this direction. Velocity-map images recorded at low photoelectron energies approach rotational resolution of the ion, and the evolution of the PADs with increasing rotational level prepared in the A1Au state indicates the potential of a "complete" determination of the photoionization dynamics of the A1Au state. This is further investigated in the following paper.     

Recent developments in thio‐, seleno‐, and telluro‐ether ligand chemistry

New routes developed recently to overcome the difficulties usually associated with the sequential introduction of Te centers into polytelluro‐ethers and the introduction of tellurium into macrocyclic compounds are described, including the synthesis of the first facultative telluro‐ethers, RTe(CH₂)₃Te(CH₂)₃TeR, R = Me or Ph, and the first tridentate S₂Te‐donor macrocycles and a tetradentate S₃Te‐donor macrocycle. The first systematic investigations into the preparation and characterization of coordination complexes of MX₃ (M = As, Sb, Bi; X = Cl, Br, I) involving polydentate and macrocyclic thio‐ and seleno‐ether ligands are then discussed. The structures of examples of each class of compound are described, including the first examples of seleno‐ether adducts of the group 15 acceptors. A more limited range of telluro‐ether derivatives has been identified and the structure of the first example of this type is included. These species serve to demonstrate the wide structural diversity exhibited by these systems and the factors directing the assembly of these structures are highlighted. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:550–560, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10100     

Reactions of fused dihydro-1,2,4-thiadiazoles with isoselenocyanates giving 6aλ4-thia-1,3,4,6-tetraazapentalene derivatives and 5,10-dihydro-1,2,4-thiaselenazolo[4,5-b][2,4]benzodiazepines

3-Methyl-6,7-dihydro-5H-1,2,4-thiadiazolo[4,5-a]pyrimidine (1) reacted with isoselenocyanates with elimination of acetonitrile and concomitant addition of two molecules of the isoselenocyanate to give 2,3-di-substituted-6,7-dihydro-5H-2aλ⁴-thia-2,3,4a,7a-tetraazacyclopent[cd]indene-1(2H),4(3H)-diselones (6a)–(6j). 3-Methyl-5,10-dihydrobenzo[e]-1,2,4-thiadiazolo[4,5-a][1,3]diazepine (3) likewise reacted with alkyl isoselenocyanates to give the 2,3-dialkyl-5-10-dihydro-2aλ⁴-thia-2,3,4a,10a-tetraazapentaleno[3,3a,4-gh]benzocycloheptene-1,4-diselones (9a)–(9h), but reaction of (3) with aryl isoselenocyanates took place with elimination of acetonitrile and incorporation of one molecule of the aryl isoselenocyanate in the product to give 3-arylimino-5,10-dihydro-1,2,4-thiaselenazolo[4,5-b][2,4]benzodiazepines (10a)–(10h). Structure (10) is a new heterocyclic system. The pyrimidine (1) and the diazepine (3) reacted with aryl isoselenocyanates at room temperature in solvents of low polarity to give zwitterion 1:1 addition compounds (7) and (12), respectively. NMR studies reveal that the thiaselenazoles (10) react in solution with aryl isoselenocyanates to give diaryl diselones (11) in a reversible process involving a Dimroth rearrangement. © 1996 John Wiley & Sons, Inc.     

Residual Stress Measurement in Composite Laminates Using Incremental Hole-Drilling with Power Series

Current methods for incremental hole-drilling in composite laminates have not been successfully applied in laminates of arbitrary construction or where significant variation of residual stress exists within a single ply. This work presents a method to overcome these limitations. Series expansion is applied to each ply orientation separately so that the discontinuities in the residual stresses at ply interfaces can be correctly captured. Temperature variations described by power series are used to set up eigenstrains and consequent stresses which vary in the through-thickness direction. The calibration coefficients at each incremental hole depth are calculated through the use of finite element modelling. The inverse solution employs a least-squares approach which makes the resulting solution insensitive to measurement uncertainty. Robust uncertainties in the residual stress distributions are determined using Monte Carlo simulation. The residual stress distribution is found from that combination of series orders in the different ply orientations that has the lowest RMS uncertainty, selected only from those combinations that have converged. The method is demonstrated on a GFRP laminate of [0₂/+45/?45]_s construction where it is found that transverse cracking of the plies at the inner surface of the hole may have impacted on the accuracy of the results.     

Microfluidic HPLC‐Chip devices with integral channels containing methylstyrenic‐based monolithic media

Polyimide HPLC‐Chip devices containing poly(methylstyrene‐bis‐p‐vinylphenyl)ethane (MS/BVPE) stationary phase within the device channels and with wall attachment were prepared by thermally initiated free radical polymerization. The microfluidic devices were coupled to both UV and MS detectors. The potential of the MS/BVPE monolith as an alternative separation media within chip devices was investigated by side‐by‐side comparisons to particulate media within commercial devices. The chromatographic behavior of this stationary phase was comparable to particulate media for separations of proteins as the average peak width at half‐height was equal (6.2 s) for a separation within 8 min under gradient elution conditions. The ability to control the porosity characteristics of the MS/BVPE monolith with changes in polymerization time also extended its utility into small analyte (< 500 Da) applications, although more optimization is needed to match conventional RP media for these applications. The good mechanical stability of the MS/BVPE monolith within the microdevices enabled excellent run‐to‐run repeatability (%RSD retention time (? 0.16) and chip‐to‐chip reproducibility (%RSD retention time (1.4). The use of this material within enrichment channels also shows its potential value in more complex work flows.     

Mechanisms for the selective gas-phase fragmentation reactions of methionine side chain fixed charge sulfonium ion containing peptides

To enable the development of improved tandem mass spectrometry based methods for selective proteome analysis, the mechanisms, product ion structures, and other factors influencing the gas-phase fragmentation reactions of methionine side-chain derivatized "fixed-charge" phenacylsulfonium ion containing peptide ions have been examined. Dissociation of these peptide ions results in the exclusive characteristic loss of the derivatized side chain, thereby enabling their selective identification. The resultant product ion(s) are then subjected to further dissociation to obtain sequence information for subsequent protein identification. Molecular orbital calculations (at the B3LYP/6-31 + G (d,p) level of theory) performed on a simple peptide model, together with experimental evidence obtained by multistage dissociation of a regioselectively deuterated methionine derivatized sulfonium ion containing tryptic peptide, indicate that fragmentation of the fixed charge containing peptide ions occurs via SN2 reactions involving the N- and C-terminal amide bonds adjacent to the methionine side chain, resulting in the formation of stable cyclic five- and six-membered iminohydrofuran and oxazine product ions, respectively. These studies further indicate that the rings formed via these neighboring group reactions are stable to further dissociation by MS3. As a consequence, the formation of b- or y-type sequence ions are "skipped" at the site of cyclization. Despite this, complete sequence information is still obtained because of the presence of both cyclic products.     

Laser spectroscopy of a halocarbocation in the gas phase: CH2I+

We report the first gas-phase observation of the electronic spectrum of a simple halocarbocation, CH2I+. The ion was generated rotationally cold (Trot approximately 20 K) using pulsed discharge methods and was detected via laser spectroscopy. The identity of the spectral carrier was confirmed by modeling the rotational contour observed in the excitation spectra and by comparison of ground state vibrational frequencies determined by single vibronic level emission spectroscopy with Density Functional Theory (DFT) predictions. The transition was assigned as 3A1 <-- X1A1. This initial detection of the electronic spectrum of a halocarbocation in the gas phase should open new avenues for study of the structure and reactivity of these important ions.