Local quantum chemistry: The local space approximation for Møller–Plesset perturbation theory

The local space approximation is an accurate technique for describing a relatively small cluster embedded within an extended system. It has previously been developed for the Hartree-Fock, local density functional, configuration interaction, and coupled cluster electronic structure methods. Here it is extended to Møller-Plesset perturbation theory. © 1995 John Wiley & Sons, Inc.     

Transition metalcarbon bonds XXXVII. platinum acetylide complexes formed from ethynyl alcohols or ethers

Several new platinum(II) acetylide complexes, trans-{Pt[CCCR₁R₂(OR₃)]₂-L₂} (R₁, R₂  H, Me, Et; CR₁R₂  cyclohexylidene; R₃  H, Me or Ph), trans-[Pt(CCCH₂CH₂OH)₂L₂], trans-[Pt(p-tolylacetylide)₂L₂] and trans-[PtX(p-tolylacetylide)L₂] (L  PMe₂Ph or in one case, AsMe₂Ph) have been prepared. Platinum(II) acetylide complexes with tertiary hydroxyl groups are easily dehydrated by acetic anhydride/pyridine to give platinum-enyne complexes. Analogous compounds with primary hydroxyl groups do not dehydrate but give acetates. ¹H and ¹³C NMR data are given and the shift reagent Eu(fod)₃ was used to analyse the ¹H NMR spectrum of trans-[Pt(CCCH₂CH₂OH)₂(PMe₂Ph)₂].     

New polyphenylquinoxalines linked by m-terphenyl flexibilizing groups

Three new monomers with phenylglyoxyloyl groups fixed on the 4,4′-, 4,6′-, and 4,4″-positions of m-terphenyl were synthesized by different pathways. They were used to prepare a series of polyphenylquinoxalines by solution polycondensation with 3,3′-diaminobenzidine and 3,3′,4,4′-tetraaminodiphenyl ether. These polymers exhibited excellent oxidative and thermal stability as shown by thermogravimetric analysis and isothermal aging in circulating air between 300 and 450°C. Clear yellow films, cast from m-cresol solution, were used to measure their softening temperature by thermomechanical analysis (TMA). Numerical data thus obtained, indicated a thermoplastic behavior in the temperature range 300 ± 15°C. Crosslinking of the linear polymers by isothermal heat exposure under argon between 300 and 500°C was investigated by means of TMA. Molded materials were fabricated under constant pressure (996 psi) at 500–525°C with an Instron testing machine. These polymers were also used for preliminary evaluation as matrices for 181-E glass reinforced composites. Flexural values obtained after isothermal aging in air up to 400°C indicated a potential use varying from 150 hr at 350°C to 24 hr at 400°C.     

P-Nitrosophosphate compounds: new N-O heterodienophiles and nitroxyl delivery agents

P-Nitrosophosphates, such as 9, react as N-O heterodienophiles with 1,3-dienes to form highly functionalized cycloadducts that can be directly transformed into allylic phosphoramidates. The in situ periodate oxidation of the unstable N-hydroxyphosphoramidate precursors provides an efficient preparation of these new reactive intermediates. P-Nitrosophosphate (9) regioselectively reacts with 1-methoxy-1,3-butadiene to provide cycloadduct 16. P-Nitrosophosphate (9) also reacts with 9,10-dimethylanthracene to give cycloadduct 17, which undergoes retro Diels-Alder dissociation to re-form 9. In the absence of a 1,3-diene, the decomposition of 17 produces nitrous oxide, evidence for nitroxyl, the one-electron-reduced form of nitric oxide. An asymmetric P-nitrosophosphate reacted with 1,3-cyclohexadiene to form a mixture of diastereomeric cycloadducts (19 and 20) in a 1.6:1 ratio. These results identify P-nitrosophosphates as new species that react similarly to acyl nitroso compounds, making them useful synthetic intermediates and potential nitroxyl delivery agents.     

FLUORESCENCE PROPERTIES OF PORPHYRIN-GLOBIN FROM HUMAN HEMOGLOBIN

Fluorescence excitation and emission spectra, decays, and quantum yields are reported for the porphyrin-globin of hemoglobin (Hb^desFe) in aqueous solution of pH 8, at 4°C. A very weak fluorescence was observed in the UV (maximum at 334 nm), due to tryptophan and tyrosine residues, in addition to the strong porphyrin emission in the visible (maxima at 624 and 692 nm) reported previously. The absorption and fluorescence properties of the porphyrins of Hb^desFe were compared to those for free porphyrin in organic solvents and in aqueous solution. The close similarity of the fluorescence decays and quantum yields in Hb^desFe and in solution indicate the absence of stronger, specific porphyrin-protein interactions; however, slight spectral shifts point to the existence of water molecules in the Hb^desFe porphyrin environment. The fluorescence study also demonstrates the existence of efficient Trp-porphyrin energy transfer of Förster type. The extent of transfer is in satisfactory agreement with the value expected from crystallographic data for hemoglobin. The results are discussed and compared to previous fluorescence studies of hemoglobin and apohemoglobin. An improved method for the preparation of Hb^desFe is reported.     

Conditional solubility versus pO2− of cerium(III) oxide in molten equimolar NaCl+KCl at 727°C

Reactions between cerium trichloride and oxide ions were studied in NaCl+KCl (1/1) at 1000°K, by potentiometry with a calcia-stabilized zirconia membrane electrode. Titration curves clearly demonstrated the existence of soluble cerium oxychloride (CeO⁺) and precipitated cerium oxide (Ce₂O₃), with respective dissociation constants 10^?11 and 10^?30 (molality scale). The corresponding conditional solubility diagram {log S (Ce^III)=f(pO^2?)} is presented and discussed.     

Nucleophilic Substitution in Dipolar Aprotic Solvents: Hexamethylphosphoric triamide

The rate of the reaction between ethyl tosylate and chloride as well as bromide ion has been measured in hexamethylphosphoric triamide in the presence of several counterions. Rate constants for the free ions at 25.0° are 14.4 mole^?1 for chloride and 2.0 mole^?1min^?1 for bromide, both independent of the cation used. The equilibrium constants for ion pair dissociation of lithium-, ammonium- and tetra-n-butylammonium chloride are 3.97 × 10^?2, 1.52 × 10^?3 and 6.36 × 10^?3 mole, and for the corresponding bromides 3.30 × 10^?2, 9.65 × 10^?3, and 9.62 × 10^?3 mole.     

Renormalized perturbation theory of the Van der Pol oscillator

The renormalized perturbation expansion for the linewidth of the Van der Pol oscillator is extended to fifth order. The results of the previously obtained fourth order are thereby improved for pump strengthsa5. No indication of a breakdown of the expansion, even for strong pumping, is found.