Esca applied to polymers. XXIII. RF glow discharge modification of polymers in pure oxygen and helium–oxygen mixtures

The oxidation of polyethylene, polypropylene, and polystyrene by exposure to plasmas excited in pure oxygen and helium–oxygen mixtures at low power levels has been studied. A detailed curve resolution procedure is outlined, and the rate of oxidation is shown to be a strong function of the polymer structure for pure oxygen plasmas, as is the composition of the oxidized layer; this is not the case, however, for oxidation effected by helium–oxygen mixtures. It seems likely, from a consideration of the available data, that the oxidation is confined to the outermost monolayer and is initiated by a crosslinking mechanism that involves oxygen-containing functionalities.     

Direct observation of insertion events at rac-(C2H4(1-indenyl)2)Zr(MeB(C6F5)3)-polymeryl intermediates: distinction between continuous and intermittent propagation modes

The propagating species for 1-hexene, propene, and ethene polymerization as catalyzed by [rac-(C2H4(1-indenyl)2)Zr(CH3)][CH3B(C6F5)3] has been intercepted at T < -40 degrees C and characterized by NMR methods. Observation of the propagating species permits direct monitoring of initiation, propagation, and termination processes by NMR. Detailed examination of alkene incorporation into Zr-polymeryl species using 13C-labeled 1-alkenes supports a continuous insertion mechanism whereby the anion re-coordinates after each alkene insertion.     

Macrocycles in the construction of acyclic stereochemistry

The conformations of macrocyclic intermediates provide a useful medium through which distant chiral centers may control chemical reactions. In this paper, we show that macrocycles made by cyclization of simple acyclic starting materials with an auxiliary spacer may be used to prepare stereochemically complex acyclic products.     

Chemistry of metal hydrides : XXI. Insertion of acetylenes into palladium hydrides

trans-Pd(NO₃)H(PCy₃)₂ (I) when treated with Et₄NCl forms the hydride trans-PdClH(PCy₃)₂ which in turn reacts with AgPF₆ in acetonitrile to give trans-[PdH(CH₃CN)(PCy₃)₂]PF₆ (III). Both I and III react smoothly with acetylenes containing one electron-withdrawing group to give alkenyl products. The geometry of the resulting alkenyl ligand implies that cis addition has occurred and that the hydridic hydrogen adds to the acetylenic carbon containing the electron-withdrawing group.Acetylenes containing two electron-withdrawing groups give mixtures from which both alkenyl and zerovalent acetylene compounds can sometimes be isolated. In the presence of proton sponge, monosubstituted acetylenes still give alkenyl products while those substituted with two electron-withdrawing groups give the zerovalent products in good yield. The relevance of these results to an understanding of the nature of the migratory insertion reaction is discussed.     

The preparation and characterization of a platinum ether complex

The reaction of [Pt((F₃C)CCH(CF₃))(P(C₂H₅)₃)₂CH₃OH]PF₆ with allene in methanol affords a novel metallocyclic ethereal complex [$\text{Pt((F}{}_3\text{C)CHC(CF}{}_3\text{)C(CH}{}_3\text{)CH}{}_2\text{O}$CH₃)(P(C₂H₅)₃)₂]PF₆, which has been characterized by ¹H, ²H, ¹⁹F and ³¹P NMR spectroscopy. Its structure has also been determined by a single crystal X-ray analysis. The crystal are monoclinic, space group P2₁/n, with cell dimensions a 20.012(5), b 17.222(5), c 8.902(3) Å and β 91.54(5)°. The structure was refined by full matrix least-squares methods on F, using 3097 unique observations collected by automated four circle diffractometer. Refinement converged at R  0.066. The Pt atom has a distorted square-planar coordination geometry, with cis P atoms, and PtP distances of 2.219(4) Å (trans to O) and 2.324(4) Å (trans to C). These results show the ethereal group is a weak ligand to platinum(II) but because of the chelating effect, its displacement by other ligands is thermodynamically not favorable. The mechanism of formation of the ethereal complex is also discussed.     

Therapeutic Monitoring of Isoniazid, Pyrazinamide and Rifampicin in Tuberculosis Patients Using LC

The objective of this study was to measure plasma concentration of isoniazide (INH), pyrazinamide (PZA) and rifampisin (RIF) in tuberculosis patients by using HPLC. 100 μL of plasma was deproteinized by adding trichloroacetic acid and acetonitrile to yield INH, PZA and RIF respectively. They were analysed by HPLC using a reversed phase C₁₈ pre-column linked to a 4 μm C₁₈ analytical column with a gradient solvent programme, which delivered 3% to 40% (v/v) acetonitrile in phosphate buffer in 20 min at rate of 0.8 mL min^?1. Signals were monitored by diode-array detector. Acetanilide was used as internal standard. The method is reproducible and accurate with lower limits of quantification of 0.6 mg L^?1 for INH, 1.5 mg L^?1 for PZA and 0.7 mg L^?1 for RIF. The plasma of 25 patients receiving daily standard therapy were assayed for INH, PZA and RIF 3 h after administration. Plasma concentration were found between 0.98 and 6.27 mg L^?1 for INH, 11.05 and 47.26 mg L^?1 for PZA, 5.09 and 33.20 mg L^?1 for RIF respectively. Many of the plasma levels were found to be sub therapeutic. This practical method may be used for monitoring drug plasma levels of patients who fail to respond to treatment.     

Transition metal complexes of 2-Carbethoxypyridine (Ethyl picolinate)

Summary A variety of metal(II) complexes of 2-carbethoxypyridine (L) have been prepared and characterised. With metal(II) chlorides the bis complexes can be formulated [ML₂Cl₂]^o (M=Cu^II, Ni^II, Co^II, Fe^II or Mn^II). The complexes are six-coordinate with 2-carbethoxypyridine acting as a bidentate ligandvia the pyridine nitrogen and the carbonyl group of the ester. The chloro complexes are nonelectrolytes in nitroethane; magnetic susceptibility measurements, i.r. and d-d electronic spectra are reported. With metal(II) perchlorate salts the complexes can be formulated as six-coordinate [ML₂ (OH₂)₂] [ClO₄]₂ species containing ionic perchlorate. The ester exchanges of some of these complexes with a variety of primary alcohols have been investigated.     

An unbounded systematic search of conformational space

A new method for searching internal coordinate conformational space systematically via a continuous-process procedure is described. Unlike previous systematic search methods, the new scheme generates torsionally remote conformers early in the search. It is also unbounded in that the extent of the search need not be specified at the outset. The search begins at low resolution (120° in torsion angle space) and then goes to higher and higher resolution as all points in space at a given resolution have been searched. The search may run without end or be terminated when new conformers cease to be found or when all space at some maximum allowable resolution has been explored. Conformational searches on several medium- and large-ring molecules using the new method are described and the results are compared with those from certain previously described search methods. It is found that the new method is significantly more efficient than previous procedures at finding all low energy conformers of organic molecules.