Compounds of nickel(II) with 5SR,7RS,12SR,14SR-5,12-dimethyl-7,14-diphenyl-1,4,8,11-tetraazacyclotetradecane, rmL: The structures of [Ni(rmL)](ClO4)2 · 0.5H2O and cis-[Ni(rmL)(acac)]ClO4

The imine functions of [Ni(mL¹)](ClO₄)₂ (mL¹ = meso-7RS,14SR-5,12-dimethyl-7,14-diphenyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene) are reduced by using NaBH₄ in acetonitrile/methanol to form the meso–meso and rac–meso isomeric cyclic tetramine complex cations [Ni(mmL²)]²⁺ and [Ni(rmL²)]²⁺ (mml² = 5RS,7RS,12SR,14SR- and rmL² = 5SR,7RS,12SR,14SR-5,12-dimethyl-7,14-diphenyl-1,4,8,11-tetraazacyclotetradecane) in ca. 8:1 proportions. [Ni(rmL²)]²⁺ is also prepared from rmL², formed in <1% yield by the reduction of mL¹ by NaBH₄ in ethanol. Square planar singlet ground state (S = 1) salts [Ni(rmL²)](ClO₄)₂ and [Ni(rmL²)][ZnCl₄] and triplet ground state (S = 3) trans-di-ligand octahedral compounds trans-[Ni(rmL²)X₂] ,μ-Y-trans-[Ni(rmL²)Y] and folded macrocycle compounds cis-[Ni(rmL²)(acac)]CIO₄ (acac⁻ = pentane-2,4-dionato), cis-[{Ni(rmL²)}₂(C₂O₄)](ClO₄)₂, cis-[Ni(rmL²)(H₂O)₂](ClO₄)₂ and cis-[Ni(rmL²)X₂], X⁻ = Cl⁻, Br⁻, are described. The S = 1 salt 1SR,4SR,5SR,7RS,8RS,11RS,12SR,14SR-[Ni(rmL²)](ClO₄)₂ · 0.5H₂O has a disordered structure with Ni(II) in square planar coordination by the nitrogen atoms of the macrocycle, in N-configuration III, with Ni–N_mean = 1.96(2) Å. The six-membered chelate rings both have chair conformations, with the phenyl substituents equatorially oriented and with the methyl substituents disordered over axial and equatorial orientations. The S = 3 compound cis-1SR,4SR,5SR,7RS,8SR,11SR,12SR,14SR-[Ni(rmL²)(acac)]ClO₄ has N-configuration V. The macrocycle is folded along N¹–Ni–N⁸, adjacent to the phenyl substituents {N1–Ni–N8 = 176.45(6), N4–Ni–N11 = 98.16(6)°}, with mean Ni–N = 2.09(2) Å and mean Ni–O = 2.121(5) Å. Both six-membered chelate rings have chair conformations with the methyl substituents equatorially oriented, while one has the phenyl substituent equatorially and the other has it axially oriented. The structures of the isomeric [M(rmL²)(acac)]ClO₄, [M(rrL²)(acac)]CIO₄ and [M(mmL²)(acac)]ClO₄ compounds are compared.     

Multiwaveguide implantable probe for light delivery to sets of distributed brain targets

Optical fibers are commonly inserted into living tissues such as the brain in order to deliver light to deep targets for neuroscientific and neuroengineering applications such as optogenetics, in which light is used to activate or silence neurons expressing specific photosensitive proteins. However, an optical fiber is limited to delivering light to a single target within the three-dimensional structure of the brain. We here demonstrate a multiwaveguide probe capable of independently delivering light to multiple targets along the probe axis, thus enabling versatile optical control of sets of distributed brain targets. The 1.45-cm-long probe is microfabricated in the form of a 360-μm-wide array of 12 parallel silicon oxynitride (SiON) multimode waveguides clad with SiO(2) and coated with aluminum; probes of custom dimensions are easily created as well. The waveguide array accepts light from a set of sources at the input end and guides the light down each waveguide to an aluminum corner mirror that efficiently deflects light away from the probe axis. Light losses at each stage are small (input coupling loss, 0.4 ± 0.3 dB; bend loss, negligible; propagation loss, 3.1 ± 1 dB/cm using the outscattering method and 3.2 ± 0.4 dB/cm using the cutback method; corner mirror loss, 1.5 ± 0.4 dB); a waveguide coupled, for example, to a 5 mW source will deliver over 1.5 mW to a target at a depth of 1 cm.     

The relative importance of transport phenomena in recycling isoelectric focusing.

The various transport phenomena involved in recycling isoelectric focusing are analyzed for their contributions to band spreading so as to find ways of improving the resolution of this liquid-phase protein purification method. A numerical model is proposed that takes into account diffusion, electroosmosis and electrophoretic migration as a function of pH. The electrohydrodynamic effects have so far been neglected in these calculations. The results of these calculations are compared with experimental measurements performed in different chamber geometries, with a variety of proteins and under different operating conditions, always chosen to avoid flow instabilities. This comparison shows that the resolution of this process is greatly impaired if the electroosmotic slip velocity at the wall is not suppressed.     

Novel reversible ionic-to-covalent transition in a highly conducting TTF derivative

TTF produces two completely different phenomena with the different isomers of chloranil; with the para isomer it produces an insulating, alternating stack, ambient temperature neutral solid. While with the ortho isomer, it produces a more interesting system consisting of interconvertible conducting ionic and covalent components.     

Synthesis and diastereoselective functionalisation of tricarbonyl[(3a,7a)-octahydro-3-substituted-2-(η-phenyl)benzoxazole]chromium(0) complexes

Two novel tricarbonyl[(3a,7a)-octahydro-3-substituted-2-(η⁶-phenyl)benzoxazole]chromium(0) complexes have been synthesised in excellent yield and characterised by X-ray crystallography. Treatment of complex 1 with butyllithium followed by electrophile quench (MeI, MeSSMe, Me₃SiCl, Me₃SnCl, Ph₂PCl, PhCH₂Br, PhCHO) gave 1,2-disubstituted (η⁶-arene)Cr(CO)₃ complexes in excellent yield, by completely diastereoselective ortho-deprotonation. The structures of the products 5 and 10 have been established by X-ray crystallographic analyses.