Comparative study of the photodegradation of polybenzoxazoles and related model compounds. Stabilization of polybenzoxazoles

Polybenzoxazoles (PBO) are thermally stable polymers whose possible use under space conditions as a transparent coating aboard spacecraft is restricted by their photodegradability. This photodegradability, which results in a loss of optical properties, is due to the structural features of benzoxazoles as well as to the presence of residual impurities from the synthesis (ketones, esters, amides). Suitable structural changes, which were intrinsic (increase in the conjugation) or extrinsic (addition of nickel salts able to complex the benzoxazole units), allowed the PBO photochemical stability to be increased and subsequently their optical transparency to be maintained. The fluorescence inhibition observed when nickel salts were added suggests that, in this case, stabilization results from a singlet-singlet energy transfer. The effect of the various structural factors investigated on the stability of polybenzoxazoles was correlated with the photochemical behavior of the corresponding model compounds.     

Synthese et etude de l'agregation moleculaire d'amines derivees de l'adamantane

Adamantanealkanamines were prepared by a new method: the wittig reaction of aminophosphonium ylides with 2-adamantanone. Conductance measurements have been employed to examine and compare the aggregation behaviour of these compounds.     

Hétérocyclisation intramoléculaire par réaction d'oxymercuration. II. Oxymercuration intramolécuxlaire des allyl-2 cyclohexanols cis et trans

The intramolecular oxymercuration of two isomeric 2-allyl-cyelohexanols, has been realized with different mercuric salts. The reaction is always regiospecific, but not stereoselective, and leads to five membered mercurated heterocyclic. The reduction of organomercury compounds obtained from trans-2-allylcyclo-hexanol leads, in some cases, to a ring rearrangement, that permit us to obtain from the trans cyclised product, under different conditions either pyran or furan compounds.     

Polysulfonylamine. LXIX. Neuartige Pniktogendisulfonylamide: Synthese von Bismutdimesylamiden und Kristallstrukturen des zwölfgliedrigen Cyclodimers [Ph2BiN(SO2Me)2]2 und des ionischen Komplexes [H(OAsPh3)2]⊕(MeSO2)2N⊖

Polysulfonyl Amines. LXIX. Novel Pnictogen Disulfonylamides: Synthesis of Bismuth Dimesylamides and Crystal Structures of the Twelve-Membered Cyclodimer [Ph₂BiN(SO₂Me)₂]₂ and of the Ionic Complex [H(OAsPh₃)₂]^⊕(MeSO₂)₂N^? The novel bismuth(III or V) disulfonylamides Ph₂BiN(SO₂Me)₂ ( 1 ), PhBi[N(SO₂Me)₂]₂ ( 2 ), PhBi[N(SO₂Me)₂]Br ( 3 ), Bi[N(SO₂Me)₂]₂Cl ( 4 ), Bi[N(SO₂Me)₂]Cl₂ · 12-crown-4 ( 5 ) and Ph₃Bi[N(SO₂Me)₂]Cl ( 6 ) were obtained by acidolysis of Ph₃Bi with HN(SO₂Me)₂ (→ 1 ), by metathesis of AgN(SO₂Me)₂ with Ph₂BiCl (→ 1 ) or PhBiBr₂ (→ 2, 3 ), by condensation of BiCl₃ with Me₃SiN(SO₂Me)₂ (→ 4 ; in presence of 12-crown-4: → 5 ), or by oxidative addition of ClN(SO₂Me)₂ to Ph₃Bi (→ 6 ). Independently of the molar ratio employed, triphenylarsane oxide and dimesylamine form the crystalline 2/1 complex [H(OAsPh₃)₂]^⊕(MeSO₂)₂N^? ( 7 ). The crystal packing of 7 (monoclinic, space group C2/c) consists of discrete cations displaying crystallographic C_i symmetry and a strong O …? H …? O hydrogen bond (H atom located on a centre of symmetry, O …? O′ 241.2 pm, As? O …? O′ 120°, As? O 168.3 pm), and chiral anions with crystallographic C₂ symmetry (N? S 157.3 pm, S? N? S 122,9°). In the solid state, the bismuth(III) compound 1 (triclinic, space group P1 ) is a cyclodimer with crystallographic C_i symmetry, in which two Ph₂Bi^⊕ cations are connected through two (α-O, ω-O)-donating dimesylamide ligands to form a roughly twelve-membered [BiOSNSO]₂ ring (Bi? O 239.7 and 246.6, O? S 148.0 and 145.4, S? N 157.7 and 159.2 pm, Bi? O? S 126.6 and 127.5°). The bismuth atom adopts a pseudo-trigonal-bipyramidal geometry (O? Bi? O 165.4, C? Bi? C 93.0, O? Bi? C 83.8 to 86.5°). The essentially similar conformations of the discrete anion in 7 and of the bidentate bridging ligand in 1 are discussed in detail.     

Polysulfonylamine. CLXXVIII Onium‐Salze des Benzol‐1,2‐di(sulfonyl)amins (HZ): Eine zweite Kristallform des Ammonium‐Salzes NH4Z·H2O und Kristallstruktur des Bis(triphenylphosphoranyliden)ammonium‐Salzes [Ph3PNPPh3]Z

Polysulfonylamines. CLXXVIII. Onium Salts of Benzene‐1,2‐di(sulfonyl)amine (HZ): A Second Crystal Form of the Ammonium Salt NH₄Z·H₂O and Crystal Structure of the Bis(triphenylphosphoranylidene)ammonium Salt [Ph₃PNPPh₃]Z A dimorphic form of NH₄Z·H₂O, where Z^? is N‐deprotonated ortho‐benzenedisulfonimide, has been obtained and structurally characterized (previously known form 1A : monoclinic, P2₁/c, Z′ = 1; new polymorph 1B : monoclinic, P2₁/n, Z′ = 1). Both structures are dominated by an abundance of classical hydrogen bonds N⁺–H/O–H···O=S/OH₂, whereby the anionic N^? function does not act as an acceptor. The major difference between the dimorphs arises from the topology of the hydrogen bond network, which is two‐dimensional in 1A , leading to a packing of discrete lamellar layers, but three‐dimensional in 1B . Moreover, the latter network is reinforced by a set of weak C–H··O/N hydrogen bonds, whereas the layered structure of 1A displays only one independent C–H···O bond, providing a link between adjacent layers. The compound [Ph₃PNPPh₃]Z ( 2 , monoclinic, P2₁/c, Z′ = 1) is the first structurally authenticated example of an ionic Z^? derivative in which the cation contains neither metal bonding sites nor strong hydrogen bond donors. This structure exhibits columns of anions, surrounded by four parallel columns of cations, giving a square array. The large cations are associated into a three‐dimensional framework via weak C–H···C(π) interactions and an offset face‐to‐face phenyl interaction, while the anions occupy tunnels in this framework and are extensively bonded to the surrounding cations by C–H···O/N^? hydrogen bonds and C–H···C(π) interactions.     

Simultaneous determination of the camptothecin analogue CPT-11 and its active metabolite SN-38 by high-performance liquid chromatography: application to plasma pharmacokinetic studies in cancer patients.

CPT-11 (I; 7-ethyl-10-[4-(1-piperidino)-1- piperidino]carbonyloxycamptothecin) is a new anticancer agent currently under clinical development. A sensitive high-performance liquid chromatographic assay suitable for the simultaneous determination of I and its active metabolite SN-38 (II) in human plasma, and their preliminary clinical pharmacokinetics, are described. Plasma samples were processed using a solid-phase (C18) extraction step allowing mean recoveries of I, II and the internal standard camptothecin (III) of 84, 99 and 72%, respectively. The extracts were chromatographed on a C18 reversed-phase column with a mobile phase composed of acetonitrile, phosphate buffer and heptanesulphonic acid, with fluorescence detection. The calibration graphs were linear over a wide range of concentrations (1 ng/ml-10 micrograms/ml), and the lower limit of determination was 1 ng/ml for both I and II. The method showed good precision: the within-day relative standard deviation (R.S.D.) (5-1000 ng/ml) was 13.0% (range 4.9-19.4%) for I and 12.8% (6.7-19.1%) for II; the between-day R.S.D. (5-10,000 ng/ml was 7.9% (5.4-17.5%) for I and 9.7% (3.5-15.1%) for II. Using this assay, plasma pharmacokinetics of both I and II were simultaneously determined in three patients receiving 100 mg/m2 I as a 30-min intravenous infusion. The mean peak plasma concentration of I at the end of the intravenous infusion was 2400 +/- 285 ng/ml (mean +/- standard error of the mean). Plasma decay was triphasic with half-lives alpha, beta and gamma of 5.4 +/- 1.8 min, 2.5 +/- 0.5 h and 20.2 +/- 4.6 h, respectively. The volume of distribution at steady state was 105 +/- 15 l/m2, and the total body clearance was 12.5 +/- 1.9 l/h.m2. The maximum concentrations of the active metabolite II reached 36 +/- 11 ng/ml.     

Adaptation of the sheet resistance of an YBaCuO layer to the substrate impedance, applications

We have studied the Far Infrared transmission spectra of an MgO plate covered with an YBaCuO film of thickness t=200 Å, at different temperatures. By cooling from room temperature to temperatures < 140 K, the Far Infrared interference fringes are displaced by half a period. Explanation in terms of different adaptations of the YBaCuO sheet resistance to the MgO substrate impedance during cooling.     

Enhanced adsorption of arsenic onto maghemites nanoparticles: As(III) as a probe of the surface structure and heterogeneity

When normalized per unit of surface area, the quantity of arsenic adsorbed at the maghemite surface remains constant for particles between 300 and 20 nm. However, nanoparticles smaller than 20 nm exhibit enhanced adsorption capacity. The origin of this observed size-dependence for adsorption or "nano effect" is unclear. Arsenic was chosen as a probe of the surface structure to explore adsorption mechanisms occurring at the surface of maghemite nanoparticles (6 nm). Two factors contributing to the enhanced reactivity of nanoscale maghemites were determined. The first is related to a size-dependent structural modification of the surface of particles and the decrease of the occupancy of the tetrahedral site that leaves vacant, highly reactive adsorption sites. In particular, there is a site localized in a six-membered iron octahedral ring. This site is the only one for which an oxidation of As(III) occurs. The second factor relates to the thermodynamics of a decrease of the surface free energy. The high density of As adsorbed at the saturation of the surface can be related to crystal growth.     

Non-existence of certain semistable abelian varieties

We show that there is no semistable abelian variety defined over ℚ with bad reduction at exactly one prime p≤ 7. Received: 7 November 2000 / Revised version: 13 July 2001     

Lamellare Schichten auf der Grundlage von Wasserstoffbrücken und π‐Stapelung: Kristallstrukturen der Metall(II)‐Komplexe [Cd{C6H4(SO2)2N}2(H2O)4] und [Cu{C6H4(SO2)2N}2(H2O)4]·2 H2O

The title complexes, obtained by treating hot aqueous solutions of ortho‐benzenedisulfonimide with solid CdCO₃ or CuO, have been characterized by low‐temperature X‐ray diffraction (both triclinic, space group P&1macr;, Z = 1, metal ions on inversion centres). The cations have trans‐octahedral coordinations provided by two Cd‐N bonded or two Cu‐O bonded anions and four water molecules [Cd‐N 234.7(2) pm; Cu‐O(anion) 240.4(1) pm, elongated by Jahn‐Teller distortion]; the copper complex contains two further, non‐coordinating, water molecules per formula unit. In both structures, the uncharged zero‐dimensional building blocks are associated via strong hydrogen bonds O(W)‐H···A and one short C‐H···O bond to form two‐dimensional assemblies comprising an internal polar lamella of metal cations, (SO₂)₂N groups and water molecules, and hydrophobic peripheral regions consisting of vertically protruding benzo rings. Carbocycles drawn alternatingly from adjacent layers form π‐stacking arrays, in which the parallel aromatic rings display intercentroid distances in the range 365‐385 pm and vertical ring spacings in the range 345‐385 pm.