Ozonolysis of a Series of Methylated Alkenes: Reaction Rate Coefficients and Gas‐Phase Products

The gas‐phase ozonolysis of three methylated alkenes, i.e., trans‐2,2‐dimethyl‐3‐hexene (22dM3H), trans‐2,5‐dimethyl‐3‐hexene (25dM3H), and 4‐methyl‐1‐pentene (4M1P), has been investigated in the presence of sufficient hydroxyl radical scavenger in a laminar flow reactor at ambient temperature (296 ± 2 K) and P = 1 atm of dry air (RH ≤ 5%). Ozone levels in the reactor were monitored by an automatic analyzer. Alkene and gas‐phase product concentrations were determined via online sampling either on three‐bed adsorbent cartridges followed by thermodesorption and GC/FID‐MS analysis or on 2,4‐dinitrophenylhydrazine (DNPH) cartridges for subsequent HPLC/UV analysis. Reaction rate coefficients of (3.38 ± 0.12) × 10^?17 for 22dM3H and (2.71 ± 0.26) × 10^?17 for 25dM3H, both in cm³ molecule^?1 s^?1 units, have been obtained under pseudo–first‐order conditions. Primary carbonyl products have been identified for the three investigated alkenes, and branching ratios are reported. In the case of 4M1P ozonolysis, the yield of a Criegee intermediate was indirectly determined. Kinetics and product study results are compared to those of literature when available. This work represents the first investigation of reaction products in the ozonolysis of 22dM3H, 25dM3H, and 4M1P in a flow reactor.     

Thermal decomposition of pentacoordinate uranium(VI) complexes

The thermal decomposition of some mixed uranyl complexes with Schiff bases and DMSO, EtOH or (Ph)₃PO as neutral ligand, were investigated and the corresponding activation energy, E*_a, and enthalpy of dissociation, ΔH_d, values were calculated.

The results obtained indicate that for the same neutral ligand, the thermal stability of the uranyl complexes is influenced by the Schiff base used; for the same Schiff base, the presence of (Ph)₃PO results in a greater thermal stability of the mixed complexes than when the other two neutral ligands are present.     

Oxidation of steroid α-diketones by thallium (III) acetate : Crystal and molecular structure of a spiro-cyclopentan-a,s-indaceno derivative obtained from 3,4-diketo steroids

Treatment of 2,3-diketo-cholestane (1) with thallium triacetate in acetic acid afforded mainly 3α-carbomethoxy-A-nor-5α-cholestan-2-one (2). Under similar conditions, the 3,4-diketo steroids (3 and 4) underwent extensive rearrangement affording spiro-lactones (9 and 10), in low yields. The structural assignment of the spiro-cholestane derivative was supported by crystallographic X-ray analysis. This product was the result of A and B-ring contractions followed by acid-catalysed cyclization of an unsaturated carboxy intermediate.     

Distribution of some major and trace elements in Danube Delta lacustrine sediments and soil

Sediment cores collected from lakes Mesteru and Furtuna (eastern part), Sontea channel and soil samples collected from Caraorman bar, all located in the Danube Delta, were analyzed for 42 elements (Ag, Al, As, Be, Na, Mg, P, S, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Se, Br, Rb, Sr, Y, Mo, Ag, Cd, In, Sn, Sb, Cs, Ce, Hf, Hg, Tl. Pb, Bi, Th. U) by instrumental neutron activation analysis (INAA), thick target proton induced X-ray emission (TT-PIXE) and inductively coupled plasma-mass spectrometry (ICP-MS). The INAA and TTPIXE yielded total concentrations whereas the ICP-MS data reflected the fractions soluble in 14M HNO₃. The ICP-MS data exhibited surface enrichment relative to the lower part of the sediment core of Cu, Zn, As, Ag, Cd, In, Sn, Sb, Hg, Tl, Pb, and Bi, most prominently by Cd and Hg. Their vertical distribution in the investigated cores generally reflected the pollution history of recent sediments in Danube delta, showing a steady increase until the end of the 1980s followed by a slow decrease after 1990. The vertical profiles of most remaining elements were characterized by a relatively uniform distribution along the cores. In some cases, the concentrations of As, Cd, Cu, Cr, Mn, Ni and Pb exceeded minimum thresholds of safety, as defined by the Romanian regulations. The elemental composition of the sediment below 20 cm depth (total concentrations) was similar to that of the upper continental crust (UCC) for most elements. Values distinctly higher than UCC were observed for As, Sb (factor ~5) and Cr, Ni, Cu (factor 2 to 3). The nitric acid soluble element concentrations in the soil samples in some cases showed increased values at the surface as compared to 30 cm depth, either due to air pollution or to the action of plants. In no case a large contribution to the topsoil from atmospheric deposition was evident, indicating that the surface contamination of the sediments was mainly by riverine transport. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and characterization of poly(amidoamine)-platinum(II) complexes. Detailed speciation by Matrix-Assisted Laser Desorption Ionization Mass Spectrometry

MALDI and ESI-MS have been applied to the characterization of the reaction products between the labile cis-[Pt(DMSO)₂Cl₂] (1) and trans-[Pt(DMSO)₂Cl(CH₃)] (2) complexes with the simplest poly(amidoamine) ligand (PAMAM, G = 0, 1,2-diaminoethane as core). The comparison of the mass spectra of the starting G₀ and those of the metallo-dendrimers formed upon mixing of the reagents in an equimolecular ratio, and the analysis of the isotopic distribution in the ESI spectra, have revealed the formation of cationic and neutral mononuclear complexes with PAMAM as ligand, e.g., cis-[Pt(DMSO)(PAMAM)Cl]Cl or trans-(C,N)[Pt(DMSO)(PAMAM)Cl(CH₃)], together with various minor components, which have been identified as derivatives from defective structures of PAMAM. The geometry of the main products has been deduced from the values of the protons coupling constants with the isotopically abundant ¹⁹⁵Pt. The metal-to-ligand bond is restricted to the peripheral amino groups of PAMAM which shows sufficient flexibility to involve either one or two branches in the coordination bonding.     

Enantiomeric resolution of anti-HIV agents on a cellulose derivative chiral stationary phase

Summary Anti-HIV enantiomeric 1H, 3H-thiazolo[3, 4-a] benzimidazoles have been stereospecifically analyzed by elution on a column of cellulose tris-(4-methyl-phenylbenzoate)ester adsorbed on macroporous silica (Chiralcel^R OJ).The enantiomeric resolution of the compounds examined is linked to a complex and competitive contribution of different factors.     

Influence of organic modifier and temperature on the enantiomeric separation of γ-lactams by HPLC

Summary A high-performance liquid chromatographic method is reported for the resolution of the enantiomers of a series of fused -lactams (2,7-diaza-3-oxo[3.3.0]octan-6-ones) with probable anti-HIV and anticancer activity. Resolution was achieved on a Chiralcel^® OD column, cellulose tris-(3,5-dimethylphenyl carbamate) adsorbed on macroporous silica gel; mixtures ofn-hexane and isopropyl alcohol in different proportions were used as the mobile phase. The analysis was studied at different temperatures.     

Phenyldimethylsilyl-Substituted Ketenes and Bisketenes

The phenyldimethylsilyl-substituted monoketene PhMe(2)SiCH=C=O (1) and bisketene (PhMe(2)SiC=C=O)(2) (3) have been prepared and compared to the corresponding Me(3)Si- and t-BuMe(2)Si-substituted species. The (13)C, (17)O, and (29)Si NMR spectra fit the pattern shown by other silylketenes and provide no evidence for transmission of a substituent effect of the Ph group through the silicon to the ketenyl group, as has been proposed for PhMe(2)Si-substituted radicals. The UV spectrum of 1 does show a longer lambda and greater epsilon than for t-BuMe(2)SiCH=C=O, and this may indicate some interaction of the phenyl group with the ketene chromophore, while the greater reactivity of 1 in hydration compared to t-BuMe(2)SiCH=C=O is ascribed to the inductive effect of the phenyl. The very similar ring-opening reactivity of the bis(phenyldimethylsilyl)cyclobutenedione (6) to form 3 compared to the bis(Me(3)Si) analogues also provides no evidence of a significant interaction of the phenyl with the ketene. A new type of stabilized 1,8-bisketene based on the arylbis(dimethylsilyl) grouping, namely, 1,4-bis(ketenyldimethylsilyl)benzene (12), has been prepared for the first time.