Crystal structures and conformations of two new biisoquinoline derivatives

Crystal structural studies of two new biisoquinoline derivatives, a neutral compound C₂₀H₂₄N₂ (3) and a salt C₁₈H₂₁N₂ ⁺C₁₀H₁₄BrO₄S^– H₂O (4) are described and discussed. Compound 3 crystallizes in the monoclinic space group P2 ₁/c, with a = 11.039(2), b = 7.791(2), c = 19.001(4) Å, = 104.31(3)°, and Z = 4. Compound 4 crystallizes in the monoclinic space group P2 ₁, with a = 12.0021(3), b = 8.9189(2), c = 12.8685(4) Å, = 100.7600(10)°, and Z = 2. The absolute stereochemistry of 4 in the solid state has been determined. The biisoquinoline rings in both compounds adopt twist-boat conformations with significant deviations from ideal geometry. The two heterocyclic rings in each species are oriented so that they are not overlayed with each other and the phenyl rings are oppositely directed. The cations and the anions in 4 are linked together through an elaborate system of hydrogen bonding involving the water molecule.     

Isometric factorization of weakly compact operators and the approximation property

Using an isometric version of the Davis, Figiel, Johnson, and Pe?czyński factorization of weakly compact operators, we prove that a Banach spaceX has the approximation property if and only if, for every Banach spaceY, the finite rank operators of norm ≤1 are dense in the unit ball ofW(Y,X), the space of weakly compact operators fromY toX, in the strong operator topology. We also show that, for every finite dimensional subspaceF ofW(Y,X), there are a reflexive spaceZ, a norm one operatorJ:Y→Z, and an isometry Φ :F →W(Y,X) which preserves finite rank and compact operators so thatT=Φ(T) oJ for allT∈F. This enables us to prove thatX has the approximation property if and only if the finite rank operators form an ideal inW(Y,X) for all Banach spacesY.     

Synthesis and reactions of partially reduced biisoquinolines

An improved synthesis of the 1,1',2,2',3,3',4,4'-octahydro-1.1'-biisoquinoline ring system is described. The reactivity of this system has been investigated, including the unusually high basicity of the parent compound and its N.N'-dimethyl derivative. The resolution of the parent compound has been achieved for the first time, along with the development of a straightforward method for assaying its enantiomeric purity.     

Synthesis and electronic properties of regioisomerically pure oxochlorins

We describe a two-step conversion of C-alkylated zinc chlorins to zinc oxochlorins wherein the keto group is located in the reduced ring (17-position) of the macrocycle. The transformation proceeds by hydroxylation upon exposure to alumina followed by dehydrogenation with DDQ. The reactions are compatible with ethyne, iodo, ester, trimethylsilyl, and pentafluorophenyl groups. A route to a spirohexyl-substituted chlorin/oxochlorin has also been developed. Representative chlorins and oxochlorins were characterized by static and time-resolved absorption spectroscopy and fluorescence spectroscopy, resonance Raman spectroscopy, and electrochemistry. The fluorescence quantum yields of the zinc oxochlorins (Phi(f) = 0.030-0.047) or free base (Fb) oxochlorins (Phi(f) = 0.13-0.16) are comparable to those of zinc tetraphenylporphyrin (ZnTPP) or free base tetraphenylporphyrin (FbTPP), respectively. The excited-state lifetimes of the zinc oxochlorins (tau = 0.5-0.7 ns) are on average 4-fold lower than that of ZnTPP, and the lifetimes of the Fb oxochlorins (tau = 7.4-8.9 ns) are approximately 40% shorter than that of FbTPP. Time-resolved absorption spectroscopy of a zinc oxochlorin indicates the yield of intersystem crossing is >70%. Resonance Raman spectroscopy of copper oxochlorins show strong resonance enhancement of the keto group upon Soret excitation but not with Q(y)()-band excitation, which is attributed to the location of the keto group in the reduced ring (rather than in the isocyclic ring as occurs in chlorophylls). The one-electron oxidation potential of the zinc oxochlorins is shifted to more positive potentials by approximately 240 mV compared with that of the zinc chlorin. Collectively, the fluorescence yields, excited-state lifetimes, oxidation potentials, and various spectral characteristics of the chlorin and oxochlorin building blocks provide the foundation for studies of photochemical processes in larger architectures based on these chromophores.     

Adiabatic 1H decoupling scheme for very accurate intensity measurements in 13C NMR

Adiabatic proton decoupling has been optimized in order to obtain accurate quantitative measurements of intensities on 13C NMR spectra. For each offset, the minimum adiabaticity factor (Km) reached during the pulse was computed. This K(m) profile was used to optimize the peak value and the swept frequency range of the adiabatic pulses. With a cosinus amplitude modulation, offset-independent-adiabaticity, and the M4P5-M4P9-M4P5'-M4P9' phase cycle, an accuracy of 2 per thousand for the 13C NMR measurements was reached. An approach using bi-labeled 13C acetic acid and ethanol at 99% allowed a fine experimental determination of the uniformity of the decoupling profile. The comparison with WALTZ-16 highlights the improvements in the uniformity of the proton decoupling.     

Enantioselective oxidation of O-methyl-N-hydroxylamines using monoamine oxidase N as catalyst

Enantioselective oxidation of racemic O-methyl-N-hydroxycyclohexylethylamine, using a variant of monoamine oxidase N (MAO-N) from Aspergillus niger, yields unreacted (R)-enantiomer (e.e. = 99%) together with the oxime exclusively in the (E)-configuration.     

Modular construction of oxide structures--compositional control of transition metal coordination environments

The effects of reaction temperature and pO2 were investigated on a series of (Ba,Ca,Nd)FeO3-delta perovskite systems in order to isolate phases containing ordered arrangements of the distinct vacancy and cation ordering patterns identified in less compositionally complex iron oxide systems. Initial synthesis in air at high temperature yields cubic perovskite phases (I) with average iron oxidation states higher than 3; selected area electron diffraction together with diffuse features observed in the synchrotron X-ray diffraction (SXRD) patterns of these materials show evidence of small domains of short-range cation and vacancy order. Annealing these materials in nitrogen or in a sealed tube in the presence of an NiO/Ni buffer yielded the Fe(3+) phase Ca2Ba2Nd2Fe6O16 (II), closely related to Sr2LaFe3O8 but with partial cation order as well as anion order present the larger Ba cations are largely present in the 12-coordinate site between the octahedral iron layers, and Ca is largely present in 10-coordinate sites between octahedral and tetrahedral sites. Further reduction of Ca2Ba2Nd2Fe6O16 using a Zr getter yields the mixed-valence phase Ca2Ba2Nd2Fe6O15.6 (III). The structure of III was solved by maximum entropy analysis of XRD data coupled with analysis of high-temperature neutron diffraction data and refined against combined SXRD and high-Q ambient-temperature neutron data. This material crystallizes in a 20-fold perovskite super cell (Imma, a approximately square root(2 x a(p), b approximately 10 x a(p), c approximately square root(x 2a(p)) and can be visualized as an intergrowth between brownmillerite (Ca2Fe2O5) and the YBa2Fe3O8 structure. There are three distinct iron coordination environments, octahedral (O), square-pyramidal (Sp), and trigonal planar (Tp, formed by distorting the tetrahedral site in brownmillerite), which form a Sp-O-Tp-O-Sp repeat. Bond valence calculations indicate that Tp is an Fe(2+) site, while the O and Sp sites are Fe(3+). The A-site cations are also partially ordered over three distinct sites: 8-coordinate between the Sp layers, 10-coordinate between Tp and O layers, and 12-coordinate between Sp and O layers. Mossbauer spectroscopy, magnetometry, and variable-temperature neutron diffraction show that the material undergoes two magnetic transitions at approximately 700 and 255 K.     

-ideals of compact operators are separably determined

We prove that the space of compact operators on a Banach space is an -ideal in the space of bounded operators if and only if has the metric compact approximation property (MCAP), and is an -ideal in for all separable subspaces of having the MCAP. It follows that the Kalton-Werner theorem characterizing -ideals of compact operators on separable Banach spaces is also valid for non-separable spaces: for a Banach space is an -ideal in if and only if has the MCAP, contains no subspace isomorphic to and has property It also follows that is an -ideal in for all Banach spaces if and only if has the MCAP, and is an -ideal in .