Asymmetric Bond Research Articles

A Possible Use of a Polymeric Amphiphile as Petroleum Pollution Collector

A polymeric amphiphile was synthesised by addition of phosphonate groups to asymmetric terminal double bonds of polybutadiene giving α, β-unsaturated phosphonic acids. The polymer was characterized by NMR and FT-IR. The synthesis produces a complex cream-like O/W emulsion containing simultaneously water and toluene. The oil droplets are interconnected by polymer chains avoiding the dispersion of the emulsion in water. When this emulsion is spread on a crude petroleum overflow on water, the oil stain shrink and is absorbed by the cream-like emulsion. The resulting product can be manipulated more easily than the original oil to extract it from the water surface.

Amphidinolide B: Asymmetric Synthesis of a C7−C20 Synthon

[reaction: see text] An asymmetric synthesis of a C(7)-C(20) synthon of amphidinolide B is described. The synthesis entails the construction of C(7)-C(13) and C(14)-C(20) fragments and makes extensive use of catalytic asymmetric bond constructions to establish the requisite stereochemical relationships. Fragment coupling proceeds by Suzuki cross-coupling and installs the trisubstituted diene unit that is among amphidinolide B's defining structural features.

Atomically sharp domain walls of Rb 2Cd 2(SO 4) 3 langbeinites: 4 d electron effects

First-principle calculations are performed for the study of Rb 2Cd 2(SO 4) 3 langbeinites. Electronic bands, joint and partial densities of states as well as charge density distribution are analyzed systematically. We find that because oxygen atomic 2 p electrons strongly hybridize with Rb or Cd 4 d and S 2 p states, there exist two-type ionic groups in the langbeinite structures. The couple strength between the cation bonds and the SO 4 tetrahedra in the monoclinic phase is stronger than that in the orthorhombic. Hybridization effects of 4 d electrons are the origin of monoclinic paraelectricity and orthorhombic ferroelectricity, relating to atomically shape domain wall rotations. As a result, the asymmetric cation bonds (Rb O and Cd O) and the subsequent rotations of the SO 4 tetrahedra can lead to the driving force of the ferroelectric behaviors. It is shown that atomically shape domain walls originate from such coupling ionic groups, arising at the cell boundaries. The predicted pyroelectric current effects were observed experimentally in the ferroelectric phase.

One or More CC Bond(s) Formed by Substitution: Substitution of Halogen

AbstractFor Abstract see ChemInform Abstract in Full Text.

Asymmetric Organocatalysis of Structurally Well‐Defined Chiral Quaternary Ammonium Fluorides

AbstractFor Abstract see ChemInform Abstract in Full Text.

Asymmetric organocatalysis of structurally well-defined chiral quaternary ammonium fluorides.

Unique organocatalysis of both naturally occurring cinchona alkaloid-derived and purely synthetic chiral quaternary ammonium fluorides in synthetically useful stereoselective bond-forming reactions is overviewed. The development of this chemistry was initiated by the in situ generation of generally hygroscopic ammonium fluorides from the corresponding easy-to-handle ammonium salts in the presence of excess metal fluorides and their direct use for subsequent enantioselective reactions. On the other hand, chiral ammonium fluorides have been prepared by using ion-exchange resins and successfully applied as catalyst to various asymmetric bond formation reactions under homogeneous conditions. In addition, utilization of chiral quaternary ammonium bifluorides as organocatalysts in asymmetric synthesis is described, featuring their characteristic reactivity and selectivity.

Error Counting in a Quantum Error-correcting Code and the Ground-State Energy of a Spin Glass

Upper and lower bounds are given for the number of equivalence classes of error patterns in the toric code for quantum memory. The results are used to derive a lower bound on the ground-state energy of the ± J Ising spin glass model on the square lattice with symmetric and asymmetric bond distributions. This is a highly non-trivial example in which insights from quantum information lead directly to an explicit result on a physical quantity in the statistical mechanics of disordered systems.

ADSORPTION SITES OF THE PRODUCTS OF GeH4 ON ASYMMETRIC Si(100)(2×1) SURFACE

The decomposition of GeH 4 on Si (100)(2×1) was investigated on different adsorption models of fragments using density functional theory method. The most probable adsorption model of fragments corresponding to the growth steps of SiGe film has been obtained by geometry optimization and single value total energy calculations. The relative adsorption energies of GeH 3, GeH 2 and GeH have been found to be -5.6, -5.1, and -4.5 eV for their most probable adsorption models respectively. It has been found that, the asymmetric dimer bond rows of Ge on Si (100) surface can be constructed by following the adsorption models corresponding to the relative adsorption energies of GeH 3, GeH 2 and GeH .

2.0 μ m wavelength InAs quantum dashes grown on a GaAs substrate using a metamorphic buffer layer

We describe optical and structure characteristics of InAs quantum dashes grown on a GaAs substrate using an AlGaAsSb metamorphic buffer. The metamorphic buffer increases the lattice constant of the growth matrix from 5.653 to 5.869 Å. The increased lattice constant of the growth matrix yields a lattice mismatch with the InAs active region of only 3.2% and accommodates a large In content to access emission wavelengths >2.0 μm. From our comparison with quantum dot structures, we conclude that the elongated quantum dash formation is due to asymmetric surface bonds in the zinc blende crystal structure that control surface migration in low strain conditions.

In situ Characterization of Supported Metal Catalysts and Model Surfaces by Time‐Resolved and Three‐Dimensional XAFS Techniques

AbstractFor Abstract see ChemInform Abstract in Full Text.

In situ characterization of supported metal catalysts and model surfaces by time-resolved and three-dimensional XAFS techniques

This paper emphasizes novel issues in in situ characterization techniques for catalysts and model surfaces, namely, energy dispersive X-ray absorption fine structure (DXAFS) for time-resolved structure analysis and polarization-dependent total-reflection fluorescence X-ray absorption fine structure (PTRF-XAFS) for 3D structure analysis, which have been developed in the past 5–10 years. DXAFS is a powerful technique for elucidating dynamic structural changes at active metal sites on catalyst surfaces that involve a sequence of formation and breaking of metal–metal, metal–adsorbate, and metal–support bonds; it opens a new area of structure kinetics, revealing kinetic parameters during catalytic reactions, catalyst preparations, and catalyst deactivation and regeneration. PTRF-XAFS is another powerful technique for elucidating 3D structures of active metal sites at single crystal model surfaces, determining structural parameters in three different directions independently with high surface sensitivity, which opens up a new area of catalytic structural chemistry, presenting information on asymmetric and anisotropic bond arrangements and transformations. The issues addressed in this paper are relevant to important key issues in understanding new catalytic structures and reaction mechanisms and to developing new concepts and strategies for novel catalytic materials, which can hardly be addressed by other techniques.

Enantioselective Synthesis of the Protein Phosphatase Inhibitor (‐)‐Motuporin.

A highly convergent asymmetric synthesis of the protein phosphatase inhibitor motuporin 1a is described. Synthesis and coupling of the individual peptide fragments [34 + 35 → 51] followed by macrocyclization afforded the fully protected motuporin precursor 33, which is converted to the natural product by dehydration and ester hydrolysis. Six of the eight stereogenic centers associated with the natural product were introduced using asymmetric crotylsilane bond construction methodology. Our approach features an efficient Pd(0)-catalyzed cross-coupling reaction between a configurationally well-defined vinyl zinc intermediate 22 and an (E)-vinyl iodide 7, which afforded compound 43, resulting in the construction of the trisubstituted (E,E)-diene system of the motuporin side chain. Improved reaction conditions for macrocyclization in the formation of 33 are also detailed.

High Frequency Electron Spin Resonance Study of Hydrogenated Microcrystalline Silicon

AbstractDangling bond defects (DB) in hydrogenated microcrystalline silicon (μc-Si:H) have been studied by X-band (9 GHz) Q-band (33 GHz) and W-band (90 GHz) electron spin resonance (ESR) spectroscopy. In X-band ESR spectra, all the samples showed asymmetric dangling bond defect signal at g = 2.005 – 2.006. The DB signal shape shows little dependence on substrate temperature in the X-band electron spin resonance (ESR) spectra. In the Q-band and W-band ESR spectra, existence of two centers in DB signals is clearly indicated by the shape of the spectra. The Q-band ESR spectra shape reviles that the peak of one center is at g = 2.0055andthe other is around at g = 2.0060. In addition, the DB signal showed dependence on substrate temperature. The dependence of the DB signals can be explained by difference of intensity ratio of the peaks by these two centers. The signal at g = 2.0060 is consistent with the asymmetric ESR signal observed in the microcrystalline silicon embedded in SiO2. W-band ESR measurement indicates that the signal observed at g = 2.0060 is due to single inhomogeneous species and does not consist of plural species.

Enantioselective synthesis of the protein phosphatase inhibitor (-)-motuporin.

A highly convergent asymmetric synthesis of the protein phosphatase inhibitor motuporin 1a is described. Synthesis and coupling of the individual peptide fragments [34 + 35 --> 51] followed by macrocyclization afforded the fully protected motuporin precursor 33, which is converted to the natural product by dehydration and ester hydrolysis. Six of the eight stereogenic centers associated with the natural product were introduced using asymmetric crotylsilane bond construction methodology. Our approach features an efficient Pd(0)-catalyzed cross-coupling reaction between a configurationally well-defined vinyl zinc intermediate 22 and an (E)-vinyl iodide 7, which afforded compound 43, resulting in the construction of the trisubstituted (E,E)-diene system of the motuporin side chain. Improved reaction conditions for macrocyclization in the formation of 33 are also detailed.

Electronic structure of SiO2: Charge redistribution contributions to the dynamic dipoles/effective charges of the infrared active normal modes

This article applies ab initio calculations at the (i) Hartree–Fock self-consistent field single determinant and (ii) configuration interaction multideterminant expansion levels to study the diagonal components of the dynamic dipoles, Δμi/Δqj with i=j, or equivalently infrared effective charges, ei*, associated with asymmetric bond stretching νy, symmetric bond stretching νz, and out-of-plane bond rocking νx, normal mode infrared active vibrations of noncrystalline SiO2. The normal mode dynamic dipoles (hereafter, Δμ/qi) are decomposed into equilibrium charge density (ionic) and orbital variation (charge redistribution) contributions. The calculations are based on small clusters in which Si–O–Si groups are connected through O atoms to embedding Si atom terminators Si* that emulate the connectivity of these Si–O–Si groups to the SiO2 continuous random network. Values of Δμ/Δqi have been determined as a function of the Si–O–Si bond angle α at the bridging O-atom sites, and agree with values obtained from analysis of infrared spectra. Finally, the ab initio calculations are extended to noncrystalline silicon–carbon alloys and silicon nitride, and values of Δμ/Δqi are determined for infrared active vibrations associated with N- and C-atom asymmetric stretching normal mode motions. The normalized equilibrium charge density or ionic contributions of the O, N, and C atoms follow trends expected on the basis of their relative Pauling electronegativities in bonds with Si.

Asymmetric C[sbnd]C bond formation by the mixed oxidative coupling of 1,1′-bi-2-naphthyl esters

Asymmetric CC bond formation was effected by the oxidative coupling of two different ester enolates using (R)-(+)-1,1′-bi(2-naphthol) as a common tether which served to link together both ester moieties in an asymmetric environment. Reduction of the corresponding succinates afforded diastereomerically pure 2,3-disubstituted-1,4-butanediols.

First-order spin-Peierls transition in S=1 antiferromagnetic Heisenberg chains

We investigate a one-dimensional S=1 antiferromagnetic Heisenberg model coupled to a lattice distortion by a quantum Monte Carlo method. The instability to a dimerized chain depends on the value of the spin–phonon coupling, unlike the case of S=1/2. We find the first-order transition between the uniform Haldane state and the dimerized state. Two non-magnetic states coexist in the chain and a domain-wall structure is observed. In the coexistent state, we find that the length of the uniform Haldane region shrinks, which causes an asymmetrical bond distortion in the dimerized region.

Antimicrobial Activity of Wool Treated with a New Thiol Cationic Surfactant

Wool can be an appropriate medium for growing and transferring microorganisms under favorable temperature and humidity conditions. These microorganisms can result in wool damage, skin irritation, or infections. A new and effective quaternary ammonium surfactant, N-dodecyl-N, N-dimethyl glycine cysteamine hydrochloride (DABM), has recently been synthesized. DABM can react with wool by means of its thiol group, either with cysteine-S-sulphonate residues (Bunte salts) of sodium bisulphite pretreated wool or with the disulfide bond of cystine wool, forming an asymmetrical disulfide bond. The antimicrobial activity of bisulphite-pretreated and untreated wool, both treated with DABM, is studied against gram-positive and gram-negative bacteria by means of the protective antibacterial AATCC, test method 100-1989 and SEM observation. Both wool samples show biocide activity against B. pumilus and bacteriostatic activity against S. aureus. The absence of gram-positive and gram-negative bacteria attached to the wool surface fibers is observed by SEM.

Hydrogen-bond geometry and its isotope effect in crystals with OHO bonds—revisited

The O–H vs O⋯O correlation in OHO hydrogen bonds is briefly reviewed based on the development during these twenty years and the geometric isotope effect ΔR is revised including the new data. It is pointed out that the following still remains to be settled: (1) whether or not the O–H distances in asymmetric bonds for the same O⋯O distance scatter in short hydrogen bonds at low temperature; (2) whether there exists or not the exceptional compounds that exhibit the extraordinarily large geometric isotope effect (∼0.1Å); (3) where the critical hydrogen-bond distance is located; and (4) the peculiar hydrogen-bond geometry and its origin in high-pressure ice.

Ultrafast structural deformation of NO2 in intense laser fields studied by mass-resolved momentum imaging

The ultrafast structural deformation of NO2 in an intense laser field (1.0 PW/cm2) is studied by mass-resolved momentum imaging (MRMI) of the Op+ and Nq+ (p,q=1–3) fragment ions produced from NO2z+ through the Coulomb explosion processes, NO2z+→Op++Nq++Or+ (z=p+q+r). The N–O distance just before the Coulomb explosion is elongated significantly from that in the electronic ground state, and it monotonically increases from 1.7 to 2.1 Å as z increases from 4 to 9. The ∠O–N–O bond angle increases toward a linear configuration as a function of z, which is interpreted in terms of the formation of the light-dressed potential energy surfaces. The two-body fragmentation pathways to produce NO+ and NO2+ are also investigated by the MRMI measurements to derive the extent of the asymmetrical bond elongation of one of the two N–O bonds.