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. 相似文献
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. 相似文献
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. 相似文献
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. 相似文献
Nonlinear Dynamics - The fluctuation of ions concentration across the cell membrane of neuron can generate a time varying electromagnetic field. Thus, memristors are used to realize the coupling... 相似文献
Structures of Ionic Di(arenesulfonyl)amides. 6. Limits to the Formation of Lamellar Metal Di(arenesulfonyl)amides: Three Lithium Complexes and One Cadmium Complex According to low‐temperature X‐ray studies, the new compounds LiN(SO2C6H4‐4‐X)2 · 2 H2O, where X = COOH ( 1 ) or COOMe ( 2 ), LiN(SO2C6H4‐4‐CONH2)2 · 4 H2O ( 3 ), and Cd[N(SO2C6H4‐4‐COOH)2]2 · 8 H2O ( 4 ) crystallize in the triclinic space group P1 ( 1 – 3 : Z′ = 1; 4 : Z′ = 1/2, Cd2+ on an inversion centre) and display almost perfectly folded anions approximating to mirror symmetry. The lithium ions in 1 – 3 have distorted tetrahedral environments respectively set up by two O=S groups drawn from different anions and two water molecules, two O=S groups of a chelating anion and two water molecules, or one O=C group and three water ligands, whereas the cation of 4 is fully hydrated to form an octahedral [Cd(H2O)6]2+ complex. The structure refinements for 3 and 4 were marred by positional disorder of the non‐coordinating N(SO2)2 moieties. Compounds 1 and 4 extend a previously described series of lamellar metal di(arenesulfonyl)amides where the two‐dimensional inorganic component is comprised of cations, N(SO2)2 groups and water molecules and the outer regions are formed by the 4‐substituted phenyl rings. Both crystal packings are governed by self‐assembly of parallel layers through exhaustive hydrogen bonding between carboxylic groups, and there is good evidence that the labile inorganic networks, generated via Li–O and hydrogen bonds in 1 or solely hydrogen bonds in 4 , are efficiently stabilized by the strong cyclic (COOH)2 motifs within the interlayer regions. In the absence of these, the lamellar architecture is seen to collapse in 2 and 3 , where the carboxyl groups are replaced by methoxycarbonyl or carbamoyl functions and the inorganic components are segregated in parallel tunnels pervading the anion lattices. 相似文献
Metal Salts of Benzene‐1,2‐di(sulfonyl)amine. 4. Hydrophobically Wrapped Two‐Dimensional Polymers: Crystal Structures of the Isostructural Metal Complexes [M{C6H4(SO2)2N}(H2O)] (M = K, Rb) and of the Structurally Related Ammonium Salt [(NH4){C6H4(SO2)2N}(H2O)] The previously unreported compounds KZ · H2O ( 1 ), RbZ · H2O ( 2 ) and NH4Z · H2O ( 3 ), where Z– is Ndeprotonated ortho‐benzenedisulfonimide, are examples of layered inorgano‐organic solids, in which the inorganic component is comprised of metal or ammonium cations, N(SO2)2 groups and water molecules and the outer regions are formed by the planar benzo rings of the anions. The metal complexes 1 and 2 were found to be strictly isostructural, whereas 3 is structurally related to them by a non‐crystallographic mirror plane ( 1 – 3 : monoclinic, space group P21/c, Z = 4; single crystal X‐ray diffraction at low temperatures). In each structure, the five‐membered 1,3,2‐dithiazolide heterocycle possesses an envelope conformation, the N atom lying about 40 pm outside the mean plane of the S–C–C–S moiety. The metal complexes feature two‐dimensional coordination networks interwoven with O–H…O hydrogen bonds originating from the water molecules. The metal centres adopt an irregular nonacoordination formed by five sulfonyl O atoms, two N atoms and two μ2‐bridging water molecules; each M+ is connected to four different anions. When NH4+ is substituted for M+, the metal–ligand bonds are replaced by N+–H…O hydrogen bonds, but the general topology of the lamella is not affected. In the three structures, the lipophilic benzo groups protrude obliquely from the surfaces of the polar lamellae and display marked interlocking between adjacent layers. 相似文献
The title complex, obtained by treating ortho‐benzenedisulfonimide (HZ) with LiOH in aqueous solution, has been characterized by low‐temperature X‐ray diffraction (triclinic, space group P&1macr;, Z' = 1). The lithium cation is bonded to one sulfonyl oxygen atom and three water molecules in a distorted tetrahedral configuration [Li‐O 189.3(3)‐201.2(3) pm, O‐Li‐O 98.5(2)‐123.2(2)?]. The zero‐dimensional [Li(Z)(H2O)3] complexes, which display an intramolecular O(W)‐H···O hydrogen bond, are cross‐linked via five O(W)‐H···O/N/O(W) interactions and a remarkably short C‐H···O bond (H···O 217 pm, C‐H···O 170?) to form a two‐dimensional assembly comprising an internal polar lamella of metal cations, (SO2)2N groups and water molecules, and hydrophobic peripheral regions consisting of protruding benzo groups. In the packing, alternate carbocycles drawn from adjacent layers set up a π‐stacking array of parallel aromatic rings (intercentroid distances 349 and 369 pm, cycle spacings 331 and 336 pm). In a short survey, the currently known crystal packings of seven MIZ · n H2O (n ≥ 0) complexes are examined and compared. 相似文献