An efficient synthesis of indane-derived bis(oxazoline) and its application to hetero Diels-Alder reactions on polymer support

Indane-derived bis(oxazolines) were synthesized in two steps and 93% overall yield starting from commercially available substrates. This ligand is as effective as tert-butyl bis(oxazoline) in hetero Diels-Alder reaction both in solution and on polymer support.     

Fiber-coupled position sensors for aerospace applications

Fiber-coupled position sensors promise advantages over their electrical counterparts for aerospace applications such as weight savings, immunity to radiated electrical interference, and improved performance, but so far, no sensor has gained widespread acceptance. This paper describes three fiber-coupled sensors presently under development at the Boeing High Technology Center including a single track analog sensor, a sensor based on weighted number system encoding, and a sensor based on FMCW laser radar techniques. Technical difficulties encountered, customer requirements, and a summary of a standardized WDM sensor interface including a broadband LED source and a compact spectograph are also discussed.     

Unusual oxidation behaviour of a propargylic alcohol

Attempts to convert a propargylic alcohol bearing an imidazolone substituent to the corresponding aldehyde under Parikh-Doering conditions gave an α,β-unsaturated-β-methylsulfanyl aldehyde, which cyclised under mildly acidic conditions.     

Investigation of the iodine–poly(vinylpyrrolidone) interaction employed in the determination of biocidal iodine by colorimetric solid-phase extraction

Colorimetric solid-phase extraction (C-SPE) has been previously explored as a means to monitor the iodine-based disinfectant used in the water systems on board the space shuttle. This same disinfectant is baselined for eventual deployment in the US water recovery system planned for node 3 of the International Space Station (ISS). With C-SPE, the I₂ concentration is determined from the diffuse reflectance spectrum (DRS) of the yellow iodine–poly(vinylpyrrolidone) (PVP) complex using the Kubelka–Munk function. However, the solution chemistry of iodine is very complex and results in a variety of inorganic species (e.g., I⁻, I₂, I₃⁻, HOI) that have very different biocidal capabilities. Thus, the nature of the interaction of iodine with PVP, and more specifically, the identity of the iodine species involved in the interaction, requires more elucidation. This paper reports the findings from a series of detailed experiments conducted to elicit a more complete understanding of the iodine–PVP system employed in C-SPE. The results indicate that I₂, one of the two dominant biocidal forms of iodine, is the species responsible for the analytical signal in our C-SPE platform. These findings lay the ground work for the planned development of a multiplexed iodine determination and speciation platform for in-flight analysis of spacecraft water samples.     

DFT-assisted design and evaluation of bifunctional copper(I) catalysts for the direct intermolecular addition of aldehydes and ketones to alkynes

Bifunctional catalysts containing discrete metal pi-acid and amine sites were designed and investigated for the direct intermolecular addition of aldehydes and ketones to unactivated alkynes. Copper(I)-based catalysts were prioritized based on intramolecular (Conia-ene type) reactions, and complexes were designed with tridentate ligands and potentially hemilabile heterocyclic spacers. The structures of the designed catalysts were computed using density functional theory (DFT), and the relative energies of putative catalytic intermediates were estimated and used to prioritize catalyst designs. Novel bifunctional precatalysts containing a thiazole spacer were synthesized via a 9-step sequence and combined with transition metals before screening for the direct addition of aldehydes and ketones to several internal and terminal alkynes. Despite the lack of desired intermolecular reactions, DFT calculations of putative catalyst intermediates appears to be a promising strategy for the design and prioritization of bifunctional catalysts for CC bond formation.     

A study of CARS nitrogen thermometry at high pressure

The accuracy of CARS N₂ thermometry has been assessed using carefully measured experimental data at high pressures for the temperature range 295 to 870 K and pressure range 1–20 bar. Excellent agreement between calculated and experimental spectra was achieved using statistically based fitting laws to model rotational relaxation. Temperature errors of within ±60 K were achieved using the MEG fitting law, and within ±30 K using an extension to the model (XMEG). Results of separate ab initio IOS calculations with ECS corrections for rotational relaxation gave good overall agreement but did not model the structure of the motionally narrowed spectra as well as the empirical models. The various models were also compared with some complementary data measured by DLR, Stuttgart in their high pressure burner for pressures up to 40 bar. This study also investigated the sensitivity of CARS thermometry to pressure; in certain regions a significant reduction in sensitivity was found. Other key factors investigated include nonlinearities in the intensified diode array detector.Work supported by the CEC Project Turbulent Combustion and Diagnostics and by AEA Technology Underlying Programme     

Formation of isoprostane bicyclic endoperoxides from the autoxidation of cholesteryl arachidonate

Autoxidation of polyunsaturated fatty acids and esters leads to a complex mixture containing hydroperoxides and cyclic peroxides. Prostaglandin bicyclic endoperoxides have been detected from the autoxidation of cholesteryl arachidonate by LC-MS and GC-MS techniques. All four possible types (I-IV) of bicyclic endoperoxides have been found starting from different regioisomeric hydroperoxides of cholesteryl arachidonate. Furthermore, the stereochemistry of Type IV bicyclic endoperoxides has been determined by conversion to pentafluorobenzyl (PFB) ester, trimethylsilyl (TMS) derivatives, and comparison with synthetic standards by the use of GC-MS. All eight possible diastereomers of the derivatized isoprostanes were observed and were separated by gas chromatography. The bicyclic endoperoxides with the two alkyl chains syn on the cyclopentane ring were formed preferentially to those with anti configuration, a result anticipated from earlier work. Substantial amounts of the anti-substituted isoprostanes, including PGF(2)(alpha), were, however, observed in the product mixture.     

Dinuclear Copper(II) Complexes Incorporating a New Septadentate Polyimidazole Ligand

The dinuclear copper(II) complexes [Cu(2)(tmihpn)(prz)](ClO(4))(2).2CH(3)CN (6) and [Cu(2)(tmihpn)(O(2)CCH(3))](ClO(4))(2).CH(3)CN (7) were prepared, where tmihpn is the deprotonated form of N,N,N',N'-tetrakis[(1-methylimidazol-2-yl)methyl]-1,3-diaminopropan-2-ol and prz is the pyrazolate anion. The crystal structures of 6 and 7 were determined and revealed that both complexes contain bridging alkoxide ligands as well as bridging pyrazolate and acetate ions, respectively. Crystal data: compound 6, triclinic, P&onemacr;, a = 18.089(2) ?, b = 22.948(3) ?, c = 9.597(2) ?, alpha = 93.37(2) degrees, beta = 94.49(2) degrees, gamma = 81.69(2) degrees, V = 3925.1 ?(3), Z = 4; compound 7, triclinic, P&onemacr;, a = 12.417(2) ?, b = 15.012(3) ?, c = 10.699(2) ?, alpha = 104.76(2) degrees, beta = 102.63(2) degrees, gamma = 99.44(2) degrees, V = 1830.1 ?(3), Z = 2. In compound 6, the coordination geometry around both copper centers resembles a distorted square pyramid, while the stereochemistry around the copper centers in 7 is best described as trigonal bipyramidal. Both complexes display well-resolved isotropically shifted (1)H NMR spectra. Selective substitution studies and integration data have been used to definitively assign several signals to specific ligand protons. Results from the solution (1)H NMR studies suggest that the basal and apical imidazole groups do not exchange rapidly on the NMR time scale and the solid state structures of the complexes are retained in solution. In addition, the magnetochemical characteristics of 6 and 7 were determined and provide evidence for "magnetic orbital switching". Antiferromagnetic coupling in 6 (J = -130 cm(-)(1)) is strong, while the copper centers in compound 7 are ferromagnetically coupled (J = +16.4 cm(-1)). Differences in the magnetic behavior of the two copper centers have been rationalized using the "ligand orbital complementary" concept. The ground state magnetic orbitals involved in spin coupling in 6 (d(x)()()2(-)(y)()()2) are different from those in 7 (d(z)()()2).     

Synthesis and characterization of a highly reducing neutral "extended viologen" and the isostructural hydrocarbon 4,4''''-di-n-octyl-p-quaterphenyl

The molecule 4,4'-di-n-octyl-p-quaterphenyl was synthesized in one step by a nickel-catalyzed cross-coupling reaction. Powder X-ray diffraction shows that it crystallizes in a layered structure with the long axis of the molecule nearly perpendicular to the layer plane. Differential scanning calorimetry indicates a transition to a liquid-crystalline phase at 81 degrees C. Reaction of 4,4'-bis(4-pyridyl)biphenyl with 1-bromooctane yields the dication 2(2+) 2Br-, an "extended viologen" isostructural with 4,4'-di-n-octyl-p-quaterphenyl. Reduction of 2(2+) 2Br- with sodium amalgam in DMF yields 2, the first neutral extended viologen to be isolated. The molecule 2 is, to the best of our knowledge, the most reducing neutral organic molecule that has been synthesized. Single-crystal X-ray diffraction shows that a diradical form, either singlet or triplet, makes an important contribution to the electronic structure of 2. The broadened 1H NMR spectrum of 2 indicates the presence of a triplet, but it has not been possible to observe the triplet by ESR spectroscopy. The electronic structure of 2 appears to be closely related to that of a classic molecule, Chichibabin's hydrocarbon.