Synthesis and characterization of hydroxo, pyrazolato and carboxylato derivatives of the PdR(PPh3)moiety (R = C6F5 or C6Cl5)

The hydroxo-complexes [{PdR(PPh₃)(μ-OH)}₂] (R = C₆F₅ or C₆Cl₅) have been obtained by reaction of the corresponding [{PdR(PPh₃)(μ-Cl)}2] complexes with NBu₄OH in acetone. In this solvent, the reaction of the hydroxo-bridged complexes with pyrazole (Hpz) and 3,5-dimethylpyrazole (Hdmpz) in 1:2 molar ratio leads to the formation of the new complexes [{Pd(C₅F₅)(PPh₃)(μ-azolate)}2] and [{Pd(C₆Cl₅)(PPh₃)}₂(μ-OH)(μ-azolate)] (azolate = pz or dmpz). The reaction of the bis(μ-hydroxo) complexes with Hpz and Hdmpz in acetone in 1:1 molar ratio has also been studied, and the resulting product depends on the organic radical (C₆F₅ or C₆Cl₅) as well as the azolate (pz or dmpz). The identity of the isomer obtained has been established in every case by NMR (¹H, ¹⁹F and ³¹P) spectroscopy. The reaction of the bis(μ-hydroxo) complexes with oxalic (H₂Ox) and acetic (HOAc) acids yields the binucle ar complexes [{PdR(PPh₃)}2(μ-Ox)] (R = C₆F₅ or C₆Cl₅) and [{Pd(C₆F₅)(PPh₃)(μ-OAc)}2], respectively. [{Pd(C₆F₅)(PPh₃)(μ-OH)}₂] reacts with PPh₃ in acetone in 1:2 ratio giving the mononuclear complex trans-[Pd(C₆F₅) (OH)(PPh₃)₂], whereas the pentachlorophenylhydroxo complex does not react with PPh₃, even under forcing conditions.     

Synthèse de spirohydantoines dérivées du diphényl-2,4-aza-3-bicyclo-[3.3.1]nonane et du diphényl-7,9-aza-8-bicyclo[4.3.1]decane par réaction de Bucherer dans la N,N-diméthylformamide: Influence de la température et cours stéréochimique. Communication préliminaire

Synthesis of Spyrohydantoines Derivatives of 2,4-Diphenyl-3-azabicyclo[3.3.1]nonane and 7,9-Diphenyl-8-azabicyclo[4.3.1]decane via Bucherer Reaction in N,N-Dimethylformamide: Influence of the Temperature and Stereochemical Path The unreactives ketones related to 2,4-diphenyl-3-azabicyclo [3.3.1]nonan-9-one to the Bucherer reaction in usuals conditions show excellent reactivity in DMF. as unique solvant. The stereochemical paths of these reactions and the synthetic utility of the temperature modification are described.     

A LOW INTENSITY PERMANENT LIQUID LIGHT STANDARD ACTIVATED BY RADIOACTIVITY

Abstract— The total radiant flux from a solution containing a radioactive compound, hexadecme-l-¹⁴C, plus an appropriate scintillator, has been determined. The procedure used involves comparison of its luminescent emission with the light scattered by glycogen illuminated with a monochromatic homogeneous light beam of known photon flux. These standards are particularly convenient for use with chemiluminescent and bioluminescent reactions, since the geometry of the emission may be duplicated exactly.     

Reversible intercalation of ammonia molecules into a layered double hydroxide structure without exchanging nitrate counter-ions

A zinc/aluminum LDH was precipitated with recycled ammonia from a chemical vapor deposition reaction. The LDH presented a crystalline phase with basal distance of 8.9 Å, typical for nitrate-containing LDHs, and another phase with a basal distance of 13.9 Å. Thermal treatment at 150 °C eliminated the phase with the bigger basal distance leaving only the anhydrous nitrate-intercalated LDH structure with 8.9 Å. Intense N-H stretching modes in the FTIR spectra suggested that the expansion was due to intercalation of ammonia in the form of [NH₄(NH₃)_n]⁺ species. When additional samples were precipitated with pure ammonia, the conventional LDH nitrate structure was obtained (8.9 Å basal distance) at pH=7, as well as a pure crystalline phase with 13.9 Å basal distance at pH=10 due to ammonia intercalation that can be removed by heating at 150 °C or by stirring in acetone, confirming a unusual sensu stricto intercalation process into a LDH without exchanging nitrate ions.     

New CE-ESI-MS analytical method for the separation, identification and quantification of seven phenolic acids including three isomer compounds in virgin olive oil

A sensitive and expeditious CE-ESI-MS analytical method for the separation, identification and determination of seven selected antioxidants (cinnamic and benzoic acids), including three isomers of coumaric acid (ortho-, meta- and para-) has been developed. In order to obtain the analytical separation, capillary electrophoresis and CE-MS interface parameters (e.g., buffer pH and composition, sheath liquid and gas flow rates, sheath liquid composition, electrospray voltage, etc.) were carefully optimized.The polar fraction containing the selected phenolic acids was obtained using a previously optimized SPE pretreatment. An MS detector in order to extract structural information about the target compounds and facilitate their qualitative analysis was used in the negative ion mode. The proposed off-line SPE CE-ESI-MS method was validated by assessing its precision, LODs and LOQs, linearity range and accuracy.The optimized and validated method was used in order to quantify the selected antioxidants in various samples of virgin olive oil and extra-virgin olive oil obtained from the main olive varieties cropped in Castilla-La Mancha, Spain. Salicylic acid was used as internal standard throughout in order to ensure reproducibility in the quantitative analysis of the oil samples.The results confirmed the presence of hydroxyphenyl acetic, p-coumaric, ferulic and vanillic acids in substantial amounts (μg g⁻¹ level) in all samples.     

A delayed biophysical system for the Earth's climate

Summary We consider further the Differential Daisyworld model of Watson and Lovelock that we have analyzed in a previous paper (De Gregorio et al., 1992). In this work we introduce a delay in the birthrate of the species. We consider three different models: the constant time lag model and the strong and the weak delay models. In the weak delay case no value of the delay changes the asymptotic stability of the stationary solutions. In the constant time lag and in the strong delay models, however, there exists a critical value of the delay, above which periodic solutions appear. These periodic solutions are numerically found to be globally attracting even for large delay when the linear approximation analysis is no longer valid. For both models, very regular behavior is obtained if the percentage coverage of the fertile ground of the Earth is much less than 1. As the percentage of the fertile ground increases, however, chaotic behavior is possible.     

Reactivity of hydroxo palladium and platinum complexes towards N-substituted salicylaldimines and β-ketoimines

The binuclear hydroxo complexes [{M(C6F5)2(OH)}2]2–(M=PdandPt)reactwithN-substituted salicylaldimines (HSal=NR) or -ketoimines (RN=CMeCH2COR) to give the corresponding N-substituted salicylaldiminato or -ketoiminato mononuclear complexes, [M(C6F5)2(Sal=NR)]– (M=Pd or Pt; R= Me, Et, Ph, o-MeC6H4, p-MeC6H4 or p-ClC6H4) or [(C6F5)2M{N(R)C(CH3)CHC(O)R}]– (M=Pd or Pt; R=o-MeC6H4 or p-MeC6H4; R=Me or Ph), respectively. The complexes have been characterized by partial elemental analyses, conductance measurements and spectroscopic (i.r. and 1H and 19F- n.m.r.) methods.