The loss of a methyl radical and the retro diels—Alder reaction in the electron impact mass spectrometry of 2-cyclohexen-1-ol and related compounds

The electron impact mass spectra of 2-cyclohexen-1-ol and of several of its ²H and ¹³C labelled analogues show that the molecular ions lose a methyl radical by a completely different means from the mechanism described previously. Moreover, the retro Diels–Alder reaction also proceeds in a non-classical way; in addition to the elimination of an olefinic molecule from unrearranged molecular ions, a second more important route implies a formal 1,3 allylic rearrangement prior to the retro Diels–Alder reaction. The mass spectra of a series of alkyl substituted homologues show that the competition between the two processes is closely related to the size of the olefinic moiety that is expelled.     

Interaction between the type-3 copper protein tyrosinase and the substrate analogue p-nitrophenol studied by NMR

The interaction of the monooxygenating type-3 copper enzyme Tyrosinase (Ty) from Streptomyces antibioticus with its inhibitor p-nitrophenol (pnp) was studied by paramagnetic NMR methods. The pnp binds to oxidized Ty (Ty(met)) and its halide (F(-), Cl(-)) bound derivatives with a dissociation constant in the mM range. The Cu(2) bridging halide ion is not displaced upon the binding of pnp showing that the pnp does not occupy the Cu(2) bridging position. The binding of pnp to Ty(met) or Ty(met)Cl leads to localized changes in the type-3 (Cu-His(3))(2) coordination geometry reflecting a change in the coordination of a single His residue that, still, remains coordinated to Cu. The binding of pnp to Ty(met)Cl causes a decrease in the Cu(2) magnetic exchange parameter -2J from 200 cm(-)(1) in the absence to 150 +/- 10 cm(-)(1) in the presence of pnp. From the (1)H and (2)D NMR relaxation parameters of pnp bound to Ty(met), a structural model of pnp coordination to the Ty type-3 center could be derived. The model explains the absence of hydroxylase activity in the closely related type-3 copper protein catechol oxidase. The relevance of the experimental findings toward the Ty catalytic mechanism is discussed.     

Titanium(III) chloride and electrochemical reduction of pyrazine,quinoxaline and triazine derivatives and of their salts

The reduction of pyrazine, quinoxaline and triazine derivatives by titanium(III) chloride leads to di- or tetrahydrogenated compounds. High yields of tetrahydro compounds are also obtained through the reduction of quinoxalinium salts. These results are compared with those obtained by electrochemical reduction.     

Comparison of ferroelectric domain delineation in triglycine sulphate by the etching technique and the pyroelectric laser technique. Application to the study of polarization reversal

It is shown that the well-known etch technique and the newly developed pyroelectric laser technique can reveal similar domains. However the latter technique is so fast that it appears as the best one to study problems such as nucleation and domain wall motion.

In the case of an alanine doped TGS crystal it is shown that domain wall motions started at a given nucleation field E₁ stop at some characteristic boundary lines in the crystal. To carry on the polarization reversal, we have to increase the electric field up to some higher value E₂ which is the minimum value of the nucleation field in the next area. Then a new domain is growing very rapidly by wall motions until the characteristic boundary lines of this area are reached. These lines are probably dislocation lines. It is shown that a direct side observation of domains is possible. Conical and cylindrical domains are clearly visible.     

Analyse du titane et de ses alliages par spectrométrie d'émission dans l'ultraviolet-vide

The large ultraviolet spectrograph for analysis in vacuum (VUV spectrograph) developed by ONERA and described in a previous article, has been used for multielements quantitative analysis: in pure titanium, concentrations of oxygen, nitrogen, hydrogen and carbon have been determined as well as silicon and iron impurities; in titanium-based alloys, addition metals at high concentration, Al, V, Mo, Zr, Si, have also been determined simultaneously with the gaseous elements and impurities. The analytical lines located between 200 and 2600 Å and corresponding to highly ionized atoms (II to VI) have been selected. The stability of the equipment has been tested and the repeatability of results has been investigated. This new analytical technique allows the study of various surface phenomena such as the variations in oxygen, nitrogen and carbon concentrations with a resolution in depth of a few microns. The method allows it to envisage the quantitative analysis of surface phenomena on metal films with a thickness below one micron.     

The number of elliptic curves over ℚ with conductorNwith conductorN

We prove that the number of elliptic curves E/ℚ with conductorN isO(N ^1/2+ε). More generally, we prove that the number of elliptic curves E/ℚ with good reduction outsideS isO(M ^1/2+ε), whereM is the product of the primes inS. Assuming various standard conjectures, we show that this bound can be improved toO(M ^c/loglogM ). Research partially supported by NSF DMS-9424642.     

Stable Conversion Chemistry‐Based Lithium Metal Batteries Enabled by Hierarchical Multifunctional Polymer Electrolytes with Near‐Single Ion Conduction

The low Coulombic efficiency and serious safety issues resulting from uncontrollable dendrite growth have severely impeded the practical applications of lithium (Li) metal anodes. Herein we report a stable quasi‐solid‐state Li metal battery by employing a hierarchical multifunctional polymer electrolyte (HMPE). This hybrid electrolyte was fabricated via in situ copolymerizing lithium 1‐[3‐(methacryloyloxy)propylsulfonyl]‐1‐(trifluoromethanesulfonyl)imide (LiMTFSI) and pentaerythritol tetraacrylate (PETEA) monomers in traditional liquid electrolyte, which is absorbed in a poly(3,3‐dimethylacrylic acid lithium) (PDAALi)‐coated glass fiber membrane. The well‐designed HMPE simultaneously exhibits high ionic conductivity (2.24×10^?3 S cm^?1 at 25 °C), near‐single ion conducting behavior (Li ion transference number of 0.75), good mechanical strength and remarkable suppression for Li dendrite growth. More intriguingly, the cation permselective HMPE efficiently prevents the migration of negatively charged iodine (I) species, which provides the as‐developed Li‐I batteries with high capacity and long cycling stability.     

Suppressed Mobility of Negative Charges in Polymer Electrolytes with an Ether‐Functionalized Anion

Suppressing the mobility of anionic species in polymer electrolytes (PEs) is essential for mitigating the concentration gradient and internal cell polarization, and thereby improving the stability and cycle life of rechargeable alkali metal batteries. Now, an ether‐functionalized anion (EFA) is used as a counter‐charge in a lithium salt. As the salt component in PEs, it achieves low anionic diffusivity but sufficient Li‐ion conductivity. The ethylene oxide unit in EFA endows nanosized self‐agglomeration of anions and trapping interactions between the anions and its structurally homologous matrix, poly(ethylene oxide), thus suppressing the mobility of negative charges. In contrast to previous strategies of using anion traps or tethering anions to a polymer/inorganic backbone, this work offers a facile and elegant methodology on accessing selective and efficient Li‐ion transport in PEs and related electrolyte materials (for example, composites and hybrid electrolytes).