Complete <Superscript>1</Superscript>H and <Superscript>13</Superscript>C NMR signal assignments and chemical shift calculations of four 1,2,4-oxadiazole-based light-emitting liquid crystals

In this article, we describe the complete ¹H and ¹³C NMR signal assignments of four 1,2,4-oxadiazoles possessing light-emitting liquid crystal properties. These results were obtained by using one- and two-dimensional NMR techniques as well as GIAO (PCM) calculations at B3LYP/6-311++G(d,p) level for compounds 1 and 2a–d. The computed values are in good agreement with the ones obtained experimentally. In addition, some previously unexplained thermotropic features of compounds 2a–d could be clarified with the help of the geometry optimization calculations carried out by us.     

Evaluation of the Cytotoxicity of Ayahuasca Beverages

Ayahuasca is a beverage consumed at shamanic ceremonies and currently has gained popularity on recreational scenarios. It contains beta-carboline alkaloids and N,N-dimethyltryptamine, which possesses hallucinogenic effects. Only a few studies have elicited the psychoactive effects and the dose of such compounds on neurological dopaminergic cells or animals. In this work, we aimed to study the cytotoxic effects of these compounds present in ayahuasca beverages and on five different teas (Banisteriopsis caapi, Psychotria viridis, Peganum harmala, Mimosa tenuiflora and Dc Ab (commercial name)) preparations on dopaminergic immortalized cell lines. Moreover, a characterization of the derivative alkaloids was also performed. All the extracts were characterized by chromatographic systems and the effect of those compounds in cell viability and total protein levels were analyzed in N27 dopaminergic neurons cell line. This is the first article where cytotoxicity of ayahuasca tea is studied on neurological dopaminergic cells. Overall, results showed that both cell viability and protein contents decreased when cells were exposed to the individual compounds, as well as to the teas and to the two mixtures based on the traditional ayahuasca beverages.     

Tris(3,5‐dimethylpyrazolyl)methane‐Based Heterobimetallic Complexes that Contain Zn and CdTransition‐Metal Bonds: Synthesis,Structures, and Quantum Chemical Calculations

Reactions of the tris(3,5‐dimethylpyrazolyl)methanide amido complexes [M′{C(3,5‐Me₂pz)₃}{N(SiMe₃)₂}] (M′=Mg ( 1 a ), Zn ( 1 b ), Cd ( 1 c ); 3,5‐Me₂pz=3,5‐dimethylpyrazolyl) with two equivalents of the acidic Group 6 cyclopentadienyl (Cp) tricarbonyl hydrides [MCp(CO)₃H] (M=Cr ( 2 a ), Mo ( 2 b )) gave different types of heterobimetallic complex. In each case, two reactions took place, namely the conversion of the tris(3,5‐dimethylpyrazolyl)methanide ligand (Tpmd*) into the ‐methane derivative (Tpm*) and the reaction of the acidic hydride M?H bond with the M′?N(SiMe₃)₂ moiety. The latter produces HN(SiMe₃)₂ as a byproduct. The Group 2 representatives [Mg(Tpm*){MCp(CO)₃}₂(thf)] ( 3 a / b ) form isocarbonyl bridges between the magnesium and chromium/molybdenum centres, whereas direct metal–metal bonds are formed in the case of the ions [Zn(Tpm*){MCp(CO)₃}]⁺ ( 4 a / b ; [MCp(CO)₃]^? as the counteranion) and [Cd(Tpm*){MCp(CO)₃}(thf)]⁺ ( 5 a / b ; [Cd{MCp(CO)₃}₃]^? as the counteranion). Complexes 4 a and 5 a / b are the first complexes that contain Zn?Cr, Cd?Cr, and Cd?Mo bonds (bond lengths 251.6, 269.8, and 278.9 pm, respectively). Quantum chemical calculations on 4 a / b* (and also on 5 a / b* ) provide evidence for an interaction between the metal atoms.     

Un analogue d'un théorème de Hardy pour la transformation de DunklAn analogue of Hardy's theorem for the Dunkl transform

In this Note we give a generalization of Hardy's theorem for the Dunkl transform $\text{F}{}_{\mathrm{D}}$ on $\text{R}{}^{\mathrm{d}}$. More precisely, for all a>0, b>0 and p,q∈[1,+∞], we determine the measurable functions f such that and , where $\text{L}{}_{\mathrm{k}}{}^{\mathrm{p}}\text{(}\text{R}{}^{\mathrm{d}}\text{)}$ are the L^p spaces associated with the Dunkl transform. To cite this article: L. Gallardo, K. Trimèche, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 849–854.     

Kinetics and mechanisms of homogeneous catalytic reactions. Part 2. Hydrogenation of cyclohexane catalysed by [RuH(CO)-(NCMe)2(PPh3)2]BF4

Summary Kinetic and mechanistic studies of the homogeneous hydrogenation of cyclohexane were carried out using the cationic complex [RuH(CO)(NCMe)₂(PPh₃)₂]BF₄ as the catalyst precursor, which was very efficient under mild reaction conditions in xylene solution. The experimental rate law was found to ber = {K ₁ K ₂ k ₃/([MeCN]+K _1–(1+K ₂)[C₆H₁₀]}[Ru][C₆H₁₀][H₂], which became {K ₂ k ₃/(1 +K ₂)}[Ru][H₂] at high cyclohexane concentrations. The activation parameters were calculated. The kinetic data are consistent with a mechanism involving the oxidative addition of hydrogen as the rate-determining step of the catalytic cycle.     

Electrostatic and electrophilic catalysis in the reductive cleavage of alkyl aryl ethers. The influence of ion pairing on the regioselectivity

Electrophilic and electrostatic catalysis have been identified as distinct contributions that affect the reactivity of radical anions in the reductive cleavage of alkyl aryl ethers. Two modes of mesolytic scission of these radical anions are possible: homolytic (dealkylation, a thermodynamically favored but kinetically forbidden process) and heterolytic (dealkoxylation). From our studies (alkali metal reductions, electrochemical studies, use of substrates with a preformed positive charge in certain positions of their structure) it can be concluded that the heterolytic scission is very much dependent on the electrophilic assistance by the counterion and it is only observed in contact ionic pairs with unsaturated cations (electrophilic catalysis). On the other hand, the homolytic scission is observed in solvent-separated ionic pairs, and it is especially efficient when the pair has a controlled topology with a tetralkylammonium cation (saturated cation) near the oxygen atom. The effect of the cation has, in this case, electrostatic origin (electrostatic catalysis), probably lowering the barrier of the intramolecular pi-sigma electron transfer process and thus reducing the kinetic control of the reaction in such a way that the thermodynamically more favorable process is produced.     

Crystalline host-guest complexes involving carboxylic acid hosts and a dimethyl sulphoxide guest. X-ray crystal structures of two inclusion species

The host compounds 2,2-binaphthyl-3,3-dicarboxylic acid (1) and 1,13–1-terphenyl-2,4,4-tricarboxylic acid (2) have been synthesized, and crystal structures of their inclusion compounds with DMSO {1a [1·DMSO(11)];2a [2·DMSO (12)]} have been determined from single crystal X-ray diffraction data. The crystals show monoclinic symmetry withZ=4 (P2₁/n for1a andP2₁/c for2a), with the unit cell dimensionsa=11.567(1),b=10.206(1),c=17.579(1) Å,=100.50(1)° for1a, anda=14.910(1),b=6.732(1),c=26.084(1) Å,=100.41(1)° for2a. The structural models were refined toR=0.032 with 3127 reflections for1a, andR=0.035 with 3175 observations for2a, collected atT=173(1) K. Both structures comprise a characteristic molecular recognition pattern for DMSO via strong (CO)O–HO(=S) hydrogen bonds and possible C–HO contacts, the latter ones from the guest methyl groups to the carbonyl oxygen of the host carboxyl groups. In the crystals H-bonded endless chains of alternating host and guest molecules are formed, which are held together by ordinary van der Waals' forces. Additionally, host2 binds a second DMSO molecule by a single (CO)O–HO(=S) bond.Supplementary Data relating to this article have been deposited with the British Library at Boston Spa, Wetherby, West Yorkshire, U.K., as Supplementary Publication No. SUP 82186 (9 pages)     

Stable spirocyclic Meisenheimer complexes

Meisenheimer complexes are important intermediates in Nucleophilic Aromatic Substitution Reactions (S(N)Ar). They are formed by the addition of electron rich species to polynitro aromatic compounds or aromatic compounds with strong electron withdrawing groups. It is possible to distinguish two types of Meisenheimer or sigma-complexes, the sigma(H)-complex or sigma(X)-complex (also named ipso), depending on the aromatic ring position attacked by the nucleophile (a non-substituted or substituted one, respectively). Special examples of sigma(X)- or ipso-complexes are formed through intermediate spiro adducts, via intramolecular SNAr. Some of these spirocyclic Meisenheimer complexes, a type of sigma(X)-complex, are exceptionally stable in solution and/or as solids. They can be isolated and characterized using X-ray, and various spectroscopic techniques such as NMR, UV-Vis, IR, and fluorescence. A few of these stable spirocyclic Meisenheimer complexes are zwitterionic and exhibit interesting photophysical and redox properties. We will review recent advances, synthesis and potential applications of these stable spirocyclic Meisenheimer complexes.     

Identification of shrimp species in raw and processed food products by means of a polymerase chain reaction-restriction fragment length polymorphism method targeted to cytochrome b mitochondrial sequences

A novel PCR-RFLP method has been developed for the identification of six commercially relevant penaeid shrimp species in raw and processed food products. The method can be completed within 8 h. To implement the method, PCR amplification with the crustF/crustR primers, targeted to the amplification of a ca. 181 bp region of the cytochrome b (cytb) mitochondrial gene in penaeid shrimps, was coupled to restriction analysis with CviJI, DdeI and NlaIV. The method was also applied successfully to the identification of shrimp species in complex processed foods, including this type of shellfish as an added-value food ingredient. The small size of this molecular target facilitates amplification from fresh, frozen, or precooked samples, where DNA fragmentation may be relevant and fragment size critical. We also report the first cytb mitochondrial sequences described to date for the species Farfantepenaeus notialis, Parapenaeus longirostris and Pleoticus muelleri, and these nearly triplicate current knowledge of reference nucleotide sequences in this mitochondrial region for this group of species. The cytb mitochondrial gene may also be considered as a molecular marker for identification and phylogenetic purposes in penaeid shrimp species.