Polyhydroxylated indolizidine alkaloids—synthesis of dideoxycastanospermine

The key transformation developed in this work is the anti-Kishi selective dihydroxylation, which proceeds by way of intramolecular participation of the nitrogen protecting group to furnish the desired stereochemistry required for castanospermine like structures. In this paper, we completed a first synthesis of a novel dideoxycastanospermine 6.     

Designed Topology and Site‐Selective Metal Composition in Tetranuclear [MM′⋅⋅⋅M′M] Linear Complexes

The ligand 1,3‐bis[3‐oxo‐3‐(2‐hydroxyphenyl)propionyl]benzene (H₄L), designed to align transition metals into tetranuclear linear molecules, reacts with M^II salts (M=Ni, Co, Cu) to yield complexes with the expected [MM???MM] topology. The novel complexes [Co₄L₂(py)₆] ( 2 ; py=pyridine) and [Na(py)₂][Cu₄L₂(py)₄](ClO₄) ( 3 ) have been crystallographically characterised. The metal sites in complexes 2 and 3 , together with previously characterised [Ni₄L₂(py)₆] ( 1 ), favour different coordination geometries. These have been exploited for the deliberate synthesis of the heterometallic complex [Cu₂Ni₂L₂(py)₆] ( 4 ). Complexes 1 , 2 , 3 and 4 exhibit antiferromagnetic interactions between pairs of metals within each cluster, leading to S=0 spin ground states, except for the latter cluster, which features two quasi‐independent S=1/2 moieties within the molecule. Complex 4 gathers the structural and physical conditions, thus allowing it to be considered as prototype of a two‐qbit quantum gate.     

Photodissociation of Mg+-XCH3 (X=F, Cl, Br, and I) complexes. II. Fragment angular and energy distributions

Angular and energy distributions of photofragments from Mg+-XCH3 (X=F, Cl, Br, and I) were deduced from time-of-flight (TOF) profiles measured by rotating the polarization direction of the dissociation laser with respect to ion beam direction. The TOF profiles of ICH3+ and MgI+ fragment ions produced from Mg+-ICH3 complex with 266 and 355 nm photons showed clear but opposite recoil anisotropy to each other. In addition, BrCH3+ formed by a dissociation of the Mg+-BrCH3 complex at a photolysis wavelength of 266 nm also showed an anisotropic distribution in the TOF profile which had the same behavior as the profile of ICH3+. For Mg+-FCH3 complex, CH3+ and MgF+ formed with a 266 nm photon had also spatial anisotropy, in which the TOF profile of MgF+ was almost opposite to that of MgI+. These anisotropic distributions were explained by (1) local excitation on the Mg+ ion, (2) rapid dissociation compared with a rotational period of the parent complex, and (3) geometrical structures of the parent complexes. Anisotropy beta parameter values were determined to be +1.30(ICH3+), -0.50(MgI+), +0.74(BrCH3+), and +0.75(CH3+ and MgF+). This dependence on the halogen atom observed in beta values was qualitatively explained by both the geometrical parameters and classical rotational periods of parent complexes. In the product energy distribution, 46%, 40%, 21%, 16%, and 16% of available energies were found to be transferred into translational energies of ICH3+, MgI+, BrCH3 +, CH3+, and MgF+, respectively. These values were compared with energy distributions estimated by a statistical prior distribution and a nonstatistical impulsive model. For ICH3+ and MgI+, the translational energies determined from the measurement had values between those estimated from statistical and nonstatistical models. On the other hand, the energy partitioning for the product ions of BrCH3+, CH3+, and MgF+ was found to be almost statistical. From these considerations, we concluded that nonstatistical processes were more important in the dissociation of Mg+-ICH3 than in other systems.     

Photodissociation of Mg+-XCH3 (X=F, Cl, Br, and I) complexes. I. Electronic spectra and dissociation pathways

Photodissociation spectra of Mg+-XCH3 (X=F, Cl, Br, and I) complexes have been measured in the ultraviolet region (225-415 nm). Several fragment ions with and without charge transfer (CT), Mg+, XCH3+, MgX+, MgCH3+, CH3+, and X+, were formed by evaporation (intermolecular bond dissociation) and intracluster reaction (intramolecular bond dissociation) via excited electronic states. Branching ratios of these ions were found to depend both on absorption bands and on halogen atoms. The ground states of the complexes were calculated to have geometries in which the Mg atom lies next to X atom of methyl halide molecules. Positive charges of the complexes are confirmed to be almost localized on Mg. Observed absorption bands were assigned to the transitions of the Mg+2P-2S atomic line perturbed by interactions with methyl halide molecules. Branching ratios of fragment ions can be partly explained by the stability of fragment ions and neutral counterparts. From the excited state potential energy curves along the Mg-X bond distance, dissociation reaction after CT was concluded to proceed predissociatively; potential curve crossings between the initially excited states and repulsive CT states may have a crucial role in the formation of CH3+, XCH3+, and X+. In particular, XCH3+ ions were formed via repulsive CT states having a character of electron excitation from Xnp to Mg+3s.     

Design and fabrication of integrated solid-phase extraction-zone electrophoresis microchip

Integrated solid-phase extraction-zone electrophoresis (SPE-ZE) device has been designed and fabricated on microchip. The structures were fabricated by using multiple layers of SU-8 polymer with a novel technique that enables easy alignment and high yield of the chips. SU-8 adhesive bonding has two major advantages: it enables bonding of high aspect ratio pillars and it results in fully SU-8 microchannels with uniform electrokinetic flow properties. The SPE-ZE device has a fluidic reservoir with 15:1 high aspect ratio pillars for bead filters that act as a SPE part in the chip structure. The separation unit is a 25 mm long electrophoresis channel starting from the outlet of SPE reservoir. Argon laser-induced fluorescence (LIF) detector was used to monitor simultaneously the SPE reservoir and the detection site at the end of the electrophoresis channel. Flow characteristics and electric field distributions were simulated with Femlab software. Fluorescein was used as the analyte for detecting the operational performance of the chip. Adsorption, bead rinsing, elution and detection were tested to verify functioning of the chip design.     

Removal of ghost images by using tilted element optical systems with polynomial surfaces for aberration compensation

A novel solution to problematic ghost images is implemented by using tilted lens elements with polynomial surfaces. Tilting the lens surfaces sends reflections out of the imaging path. The nonrotationally symmetric polynomial surfaces correct aberrations caused by tilts. The complex lens surfaces are fabricated by using gray-scale lithographic patterning of hybrid solgel glass.     

Microwave backscattering by nonspherical ice particles at 5.6 GHz using second-order perturbation series

Scattering of microwaves by an ensemble of nonspherical ice particles is studied using a scattering model based on a second-order perturbation series at 5.6 GHz (C-band). Particle shapes are defined using a Gaussian random sphere geometry. Particle inhomogeneity is taken into account using three different effective-medium approximations: Maxwell–Garnett, Bruggeman, and Coherent Potential mixing rules. By systematically varying particle size, liquid water content, Gaussian shape parameters, and internal structure, it is found that liquid water content is the most important factor for the co-polarized backscattering; the shape is relatively unimportant. For depolarized backscattering, the shape is of fundamental importance, although the other factors are significant too. Surprisingly, the type of nonsphericity is found to be important for depolarization even for scatterers that are in the Rayleigh region: elongated targets depolarize clearly stronger than more irregular shapes. This finding seems not to be strongly size dependent, at least for size parameters from 0.0059 to 0.47, and indicates that the accurate modeling of shape is important for polarization quantities even in the Rayleigh region.     

Radiometry and Radiation Efficiency of Twisted Gaussian Schell-Model Sources

Wavefields endowed with the coherence-induced property of optical twist have recently attracted a good deal of theoretical and experimental attention. We present the generalized radiometric theory of fields generated by twisted Gaussian Schell-model sources. The effects introduced by the novel, rotationally symmetric, twist phenomenon in the radiant intensity, generalized radiance, radiant emittance (irradiance), and the radiation efficiency are assessed. The radiance becomes directionally skewed as a result of the twist, whereas the radiant intensity remains axially symmetric. The twist reduces the radiation efficiency and broadens the radiation distribution, in agreement with the notion that the twist decreases the effective coherence. Several special cases, such as quasihomogeneous sources, are analyzed in detail. The radiometric results, which are physically consistent with the superposition models of twisted sources, are demonstrated by illustrative examples.     

A wrap error attack against NTRUEncrypt

We present a chosen plaintext attack on the NTRU encryption system. We assume that the attacker can detect wrap errors, that the blinding polynomial is generated from three parts (as specified in the standards) and that the attacker has a large database of carefully selected plaintexts. The attack is based on the fact that wrap errors occur more frequently if blinding polynomials with larger coefficients are used.