Reductive Elimination at Pb(II) Center of an (Amino)plumbylene-Substituted Phosphaketene: New Pathway for Phosphinidene Synthesis

A stable (amino)plumbylene-substituted phosphaketene 3 was synthesized by the successive reactions of PbCl₂ with two anionic reagents (lithium amidophosphine and NaPCO). Of particular interest, the thermal evolution of 3 , at 80 °C, leads to the transient formation of corresponding amino- and phosphanylidene-phosphaketenes ( 6 and 7 ), via a reductive elimination at the Pb^II center forming new N−P and P−P bonds. Further evolution of 6 gives a new cyclic (amino)phosphanylidene phosphorane 4 , which shows a unique reactivity as a phosphinidene. This result provides a new synthetic route to phosphinidenes, extending and facilitating further their access.     

Structure, dynamics, and electronic properties of lithium disilicate melt and glass

Ab initio molecular dynamics simulations within the framework of density functional theory have been performed to study the structural, dynamic, and electronic properties of lithium disilicate melt and the glass derived from quenching the melt. It is found that lithium ions have a much higher diffusion coefficient and show different diffusion mechanisms than the network forming silicon and oxygen ions in the melt. The simulated lithium disilicate glass structure has 100% four coordinated silicon, close to theoretical nonbridging oxygen to bridging oxygen ratio (2:3), and Q(n) distributions of 20.8%, 58.4%, and 20.8% for n=2,3,4, respectively. In the melt there are considerable amounts (10%-15%) of silicon coordination defects; however, the average silicon coordination number remains about 4, similar to that in the glass. The lithium ion coordination number increases from 3.7 in the glass to 4.4 in the melt mainly due to the increase of bridging oxygen in the first coordination shell. The bond length and bond angle distributions, vibrational density of states, and static structure factors of the simulated glass were determined where the latter was found to be in good agreement with experimental measurement. Atomic charges were obtained based on Bader and Hirshfeld population analyses [Atoms in Molecule: A Quantum Theory (Oxford University Press, Oxford, 1990); Theor. Chim. Acta 44, 129 (1977)]. The average Bader charges found in lithium disilicate glass were -1.729, 3.419, and 0.915 for oxygen, silicon, and lithium, respectively. The corresponding Hirshfeld charges were -0.307, 0.550, and 0.229. The electronic densities of states of the melt and glass were calculated and compared with those of crystalline lithium disilicate.     

Exploring the molecular mechanism for color distinction in humans

We examine here the role of the red, green, and blue human opsin structures in modulating the absorption properties of 11-cis-retinal bonded to the protein via a protonated Schiff base (PSB). We built the three-dimensional structures of the human red, green, and blue opsins using homology modeling techniques with the crystal structure of bovine rhodopsin as the template. We then used quantum mechanics (QM) combined with molecular mechanics (MM) (denoted as QM/MM) techniques in conjunction with molecular dynamics to determine how the room temperature molecular structures of the three human color opsin proteins modulate the absorption frequency of the same bound 11-cis-retinal chromophore to account for the differences in the observed absorption spectra. We find that the conformational twisting of the 11-cis-retinal PSB plays an important role in the green to blue opsin shift, whereas the dipolar side chains in the binding pocket play a surprising role of red-shifting the blue opsin with respect to the green opsin, as a fine adjustment to the opsin shift. The dipolar side chains play a large role in the opsin shift from red to green.     

H*(10) and neutron spectra around linacs

Neutron spectrum and ambient dose equivalent has been measured around two 10 MV linear accelerators. Measurements were carried out in Mevatron and Primus model linacs, both made by Siemens. Main differences between those models are the beam collimator and the vault room. Here, Bonner sphere spectrometer with a passive thermal neutron detector has been utilized to measure the neutron spectrum inside the vault. Using an active detector the neutron spectrum was measured at the vault’s door of both accelerators. With a neutron area monitor the dose equivalent was measured by the door at both vault doors. Neutron strength, total fluence rate and ambient dose equivalent were compared, from this was found that shielding conditions are better in the Primus model.     

The application of (Z)-3-aryl-3-haloenoic acids to the synthesis of (Z)-5-benzylidene-4-arylpyrrol-2(5H)-ones

Studies directed at the synthesis of (Z)-5-benzylidene-4-arylpyrrol-2(5H)-ones from (Z)-3-aryl-3-haloenoic acids are described. The successful strategy relies on the preparation of (Z)-3-aryl-3-haloenoic acids from acetophenones through the corresponding (Z)-3-aryl-3-haloenals and the conversion of the (Z)-3-aryl-3-haloenoic acids to (Z)-5-benzylidene-4-aryl-5H-furan-2-ones. The furanones were subsequently treated with primary amines and dehydrated to the corresponding (Z)-5-benzylidene-4-arylpyrrol-2(5H)-ones.     

Dynamic polarizability and the theory of the ion-acoustic turbulence in a plasma containing ions of two species

A damping rate of the induced scattering of fast ion-acoustic waves on ions, the explicit form of which depends on the plasma polarizability at the frequency of beats of the interacting waves, was determined for a nonisothermal plasma containing hot electrons and cold ions of two species. In the case of a plasma containing mobile light ions and slow heavy ions, a new phenomenon of significant decrease in the probability of induced scattering was established. This effect is related to the fact that a contribution to the dielectric function of slow ions, determining the scattering amplitude, depends on both spatial and frequency dispersion. It is shown that this decrease in the induced scattering probability leads to a growth of the turbulent noise level and to a change of the anomalous transport coefficients in the limit of large turbulent Knudsen numbers. The same effect is responsible for a relative decrease in the runaway electron production.     

Complexes dinucleaires pontes des metaux d8: II.preparation de deux series de composes du rhodium(I) pentacoordonne

In the course of the study of the reactivity of the dinuclear complexes [RhCl(CO)(C₂H₂)]₂ and [RhSR(CO)₂]₂ towards nucleophiles, two series of dinuclear pentacoordinated rhodium(I) complexes, [RhCl(CO)(C₂H₄)(amine)]₂ and [RhSR(CO)₂PR₃]₂, have been isolated.     

Reactivite des carbanions benzyliques : VI. Structure et reactivite du trimethylsilyl-9 dihydro-9,10 anthracene; preparation des bis(trimethylsilyl)-9,9 et trimethylsilyl-9 alkyl-9 dihydro-9,10 anthracenes

The structure of 9-trimethylsilyl-9,10-dihydroanthracene (Me₃SiDHA) has been studied by NMR; the coupling constants of the three 9,10 protons do not change at between 25 and 90°C (ABM spectrum; J_AB }- 18.2; J_AM ? 1.2; J_BM ? 0.3 Hz in toluene-d₈), indicating that the Me₃Si group prefers the quasi axial position. In the presence of BuLi in THF, Me₃SiDHA reacts with Me₃SiCl to yield three new products: 9,9-bis(trimethylsilyl)-9,10-dihydroanthracene (IId) (major), (9,10-dihydroanthracen-9-yl)dimethylsilyl(trimethylsilyl)methane (V) and (9-trimethylsilyl-9,10-dihydroanthracen-9-yl)dimethylsilyl(trimethylsilyl)-methane (VI) together with the known 9,10-bis(trimethylsilyl)-9,10-dihydroanthracene (cis and trans). The carbanion of Me₃SiDHA can also be alkylated (alkyl  Me, Et, i-Pr) to the new 9,9-disubstituted derivatives: 9-Me₃Si-9-alkyl-DHA.The formation of the carbanion of Me₃SiDHA has been investigated and reveals a competition in the abstraction by the base of H₉ and H₁₀; the latter is less crowded but the 9-carbanion is stabilized by the vicinity of the silicon atom. The carbanion obtained from Me₃SiDHA reacts exclusively at C(9) with D₂O. A study of the alkylation of 9-trimethylsilyl-9-deuterio-9,10-dihydroanthracene shows that the generation of the 10-carbanion is followed by a 1,4 hydrogen rearrangement which yields the 9-carbanion. The mechanism is discussed and the roles of Me₃Si and t-Bu are compared in the DHA series.     

PHOTODYNAMIC ACTIVITIES and SKIN PHOTOSENSITIVITY OF THE bis(DIMETHYLTHEXYLSILOXY)SILICON 2,3-NAPHTHALOCYANINE IN MICE

The photodynamic therapy (PDT) activity of the bis(dimethylthexylsiloxy)silicon 2,3-na-phthalocyanine (SiNc 8 ) was evaluated against the EMT-6 tumor implanted intradermally in BALB/c mice. The SiNc 8 was formulated in aqueous emulsions based on Cremophor EL or Solutol HS 15. The formulation was shown to affect plasma clearance and overall pharmacokinetics. Compared to Cremophor, Solutol promoted rapid plasma clearance and high liver retention of the dye, combined with a slight increase of dye tumor concentrations. The PDT action spectrum for tumor response of SiNc 8 in Cremophor (190 mW cm², 200 J cm², 24 h postinjection [p.i.] of 1 (jimol kg¹) showed a maximum at 780 nm, which corresponds to the absorption maximum of the monomelic dye as well as the in vivo maximum change in the “diffuse optical density” produced by the dye. The extent of tumor necrosis increased with augmented dye and light doses. Regardless of the formulation, at 1 h p.i. of 0.1 μmol kg^?! SiNc 8 , PDT efficiency (190 mW cm'², 400 J cm²) was high but accompanied by severe damage to normal tissues, at 24 h PDT resulted in complete tumor regression in 80% of the animals without adverse effects to adjacent tissues, while at 72 h p.i. PDT induced no tumor response with Cremophor and only a partial response with Solutol. At the latter time point, plasma dye clearance was nearly complete while tumor tissue levels remained high, suggesting that tumor response correlates with plasma rather than tumor dye levels. Skin sensitivity of SKhl mice to solar-simulated radiation was lower with SiNc 8 as compared to Photofrin®. Our data suggest the potential of SiNc 8 as a far-red absorbing photosensitizer in clinical PDT.