Electrochemical nitration of naphthalene in the presence of nitrite ion in aqueous non-ionic surfactant solutions

The nitration of naphthalene (NapH) at a Pt electrode in aqueous NaNO₂ solutions both in the absence and presence of a non-ionic surfactant, Brij®35 (polyoxyethylene (23) dodecanol), has been studied. The electrochemical behaviour of the reactants NapH and NaNO₂ and a mixture of the two was investigated by cyclic voltammetry (CV) to determine the optimal electrolysis conditions. The peak current of NapH decreases with increasing NaNO₂ concentration, indicating that the oxidation product of the NO₂⁻ ion interacts with the NapH radical cation (NapH⁺). Controlled potential electrolysis (CPE) was carried out and the products were analysed by HPLC. The main products detected in the micellar medium were 1-nitronaphthalene, 2-nitronaphthalene, 1,2-naphthoquinone, and 1,4-naphthoquinone. In the absence of Brij 35, the naphthoquinones were produced but no nitration products were obtained. In both cases, unknown products are inferred by mass balance, which are believed to be derived from the oxidation of 1,1′-binaphthyl (BinapH) formed by NapH⁺ coupling in both micellar and aqueous media. A mechanism of nitration by the attack of NO₂ to NapH⁺ is proposed. The higher selectivity for formation of 2-nitronaphthalene in comparison to non-aqueous homogeneous media is attributed to the effect of the micellar microenvironment.     

Synthesis of indazol‐4,7‐dione derivatives as potential trypanocidal agents

The synthesis of new indazol‐4,7‐dione derivatives via 1,3‐dipolar cycloaddition of diazomethane with 2,3‐dimethyl‐1,4‐benzoquinone ( 2 ) and 1,4‐naphthoquinone ( 7 ) followed by N‐alkylation of the pyrazol nitrogen atom of the corresponding quinones ( 3 ) and ( 8 ) with methyl chloroacetate is described. A series of amides from esters ( 5 ) and ( 10 ) were also obtained. These compounds were tested in vitro as potential anti‐trypanosomal agents. Compounds ( 4 ) and ( 8 ) were found to have significant activity.     

Biosynthesis of the angiogenesis inhibitor borrelidin by Streptomyces parvulus Tü4055: cluster analysis and assignment of functions

The biosynthetic gene cluster for the angiogenesis inhibitor borrelidin has been cloned from Streptomyces parvulus Tü4055. Sequence analysis indicates that the macrolide ring of borrelidin is formed by a modular polyketide synthase (PKS) (borA1-A6), a result that was confirmed by disruption of borA3. The borrelidin PKS is striking because only seven rather than the nine modules expected for a nonaketide product are encoded by borA1-A6. The starter unit of the PKS has been verified as trans-cyclopentane-1,2-dicarboxylic acid (trans-1,2-CPDA), and the genes involved in its biosynthesis identified. Other genes responsible for biosynthesis of the nitrile moiety, regulation, and self-resistance were also identified.     

A New Initiator Cholesteryl Chloroformate for Cupper-Based Atom Transfer Radical Polymerization of Methyl Methacrylate

The polymerization of metyl methacrylate (MMA) was studied in detail by use of CuCI/L as a catalyst and cholesteryl chloroformate (CC) as an initiator. It was found that the atom transfer radical polymerization of MMA could proceed when L equals to a multidentate aliphatic amine ligand, N,N,N‘,N“,N“-penta(methyl acrylate)diethylenetriamine (MA5-DETA), and no polymerization was occurred while L=2,2‘-bipyridine and 1,10phenanthroline. The linear proportionality of the molecular weights to the conversions and straight lines observed in ln[M]0/[M] versus time plots indicated that the present polymerization system had the typical controlled polymerization characteristics.     

Novel mechanism for priming aromatic polyketide synthases

In this issue of Chemistry & Biology, a novel priming mechanism is proposed for aromatic polyketide biosynthesis, with an iterative type I polyketide synthase generating a starter unit primed for a type II polyketide synthase. This novel priming system participates in hedamycin biosynthesis, a DNA alkylating agent.     

X-ray crystal structure of tetraaquabis (xanthosinato)nickel(II) hexahydrate

The complex [Ni(XsH_–1)₂(H₂O)₄]·6H₂O (XsH_–1: xanthosinate) was isolated from the reaction of nickel carbonate with xanthosine in aqueous solution. The octahedral coordination is supported by the reflectance measurements. Single-crystal X-ray diffraction studies show that the crystals belong to the triclinic P1 space group, with a = 7.152(1), b = 8.830(1),c = 13.783(1) Å, = 82.024(1)°, = 86.155(1)°, = 70.900(1)°, and D = 1.643 mg/m³, forZ = 1. Nickel is six coordinate with four water molecules, and two N7 atoms from xanthosinato ligands. A complicated hydrogen-bonding network is present, all possible donors taking part in it.     

Synthesis,spectroscopic studies,and crystal structure of theophyllinium tetrabromopalladate(II)

The theophyllinium tetrabromopalladate(II), [Thph]₂PdBr₄, has been synthesized and its molecular structure has been determined by single crystal X-ray diffraction. The salt crystallizes in the monoclinic space group C2 with two formula units in a cell of dimensionsa=11.074(1),b=8.545(2),c=11.804(2) Å;=95.22(1)°,V=1112.3(4) ų,D _c=2.353 mg m^–3,D _exp=2.352 mg m^–3,M _w=788.4, (MoK)=84.5 cm^–1,F(000)=752. The structure has been refined by full-matrix least-squares techniques to a final value of theR factor of 0.058 based on 907 independent intensities. The compound consists of theophyllinium cations protonated at N(9). The [PdBr₄]^2– anion is planar, with distances Pd-Br(1)=2.441(12) and Pd-Br(2)=2.412(6) Å, and Br(1)-Pd-Br(2) and Br(1)-Pd-Br(3) angles of 90.34(14)° and 89.66(14)°, respectively. The¹H-NMR spectrum of [Thph]₂PdBr₄ in DMSO-d₆ (300 MHz) is consistent with the observed solid-state structure, and its thermal behavior shows two steps: (i) a dehalogenation process about 327°C and (ii) a rapid pyrolitic decomposition in the 340–575°C temperature range giving PdO as final product.     

Desingularization and integralityof the automorphism scheme of a finite field extension

Let be the automorphism scheme of a finite purely inseparable field extension (in fact, we consider a wide class of finite ring extensions). Let be the splitting algebra of K (see 2.8) and the splitting field of K. It is proved that is integral if and only if . This may be formulated as a condition on the degree of and generalizes a result of Chase. Surprisingly, may be defined intrinsically, since is the scheme parametrizing the maximal smooth subgroups of . It is also proved that the desingularization of is the universal maximal smooth subgroup of and coincides with the blowing up along a closed subscheme canonically defined from the action of on . Received June 4, 1997; in final form July 22, 1998     

Electron impact mass spectra of phosphine sulphides and selenides

An electron impact mass spectral study of phosphine sulphides and selenides established the effect of the heteroatom and the role of the ortho substituent in the fragmentation pattern.     

Differences in voice quality between men and women: Use of the long-term average spectrum (LTAS)

The goal of this study was to determine if there are acoustical differences between male and female voices, and if there are, where exactly do these differences lie. Extended speech samples were used. The recorded readings of a text by 31 women and by 24 men were analyzed by means of the Long-term Spectrum (LTAS), extracting the amplitude values (in decibels) at intervals of 160 Hz over a range of 8 kHz. The results showed a significant difference between genders, as well as an interaction of gender and frequency level. The female voice showed greater levels of aspiration noise, located in the spectral regions corresponding to the third formant, which causes the female voice to have a more “breathy” quality than the male voice. The lower spectral tilt in the women's voices is another consequence of this presence of greater aspiration noise.