Double Length Research Articles

An Isolable Disilyne Anion Radical and a New Route to the Disilenide Ion upon Reduction of a Disilyne

The reaction of 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyltetrasila-2-yne 1 with tBuLi produced disilenyllithium derivative 2, the product of the formal addition of LiH across the Si⋮Si triple bond through a single electron transfer reaction. The solvent-separated ion pair of the disilenide 3 was characterized by X-ray crystallography. The bulky SiiPr[CH(SiMe3)2]2 groups are arranged in the trans fashion with a silicon−silicon double bond length of 2.2034(9) Å. The reaction of 1 with an equivalent amount of potassium graphite (KC8) in THF produced the disilyne anion radical 4, which was isolated in the form of its potassium salt as extremely air- and moisture-sensitive dark brown crystals. The molecular structure of 4 was established by X-ray crystallography, which showed a trans-bent structure (av 113.4°) with the central Si−Si bond length of 2.1728(14) Å. An electron spin resonance (ESR) study indicates delocalization of the unpaired electron between the two central silicon atoms of 4.

Speed of sound instrument for fluids with pressures up to 100 MPa

An instrument for highly accurate measurements of the speed of sound in fluids in the temperature range between 240 and 420 K with pressures up to 100 MPa is described. The measurement principle of the speed of sound sensor is based on a double path length pulse-echo technique. The achieved measurement uncertainties are 3 mK for the temperature, 0.01% for the pressure below 10 MPa and 0.005% for the pressure between 10 and 100 MPa, and 0.014% for the speed of sound. The high accuracy of the instrument is demonstrated by measurements in liquid water and compressed argon. The results for argon prove that our pulse-echo technique agrees with the highly accurate spherical resonator technique, which is commonly employed for speed of sound measurements in gases, in the pressure range where both methods overlap within our measurement uncertainty.

Trifluoperazine Causes a Disturbance in Glycerophospholipid Monolayers Containing Phosphatidylserine (PS): Effects of pH, Acyl Unsaturation, and Proportion of PS

We have studied the interaction of trifluoperazine (TFP) with monolayers of various glycerophospholipids at 37 degrees C. TFP (1-10 microM) had little effect on surface pressure/molecular area isotherms in monolayers (on pure water) of dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylethanolamine but greatly increased the mean molecular area (mma) of dipalmitoylphosphatidylserine; the increment was greatest between 0 and 1 microM, and a further increase to 10 microM TFP gave only a slight increase in mma. With phosphatidylserine (PS)-containing stearoyl and varying acyls in the sn-1 and -2 positions, respectively, TFP increased the mma in a manner that depended on the number of double bonds and chain length. In mixtures of DPPC with two of these PS species the TFP-induced mma of the monolayers (on buffer, pH 7.4) increased linearly with the proportion of PS. Both PS and TFP have ionizable groups, and the TFP-induced mma increase had optima at pH 5.0 and 7.0. We conclude that the TFP-PS interaction is mainly, but not entirely, driven by electrostatic interactions between the TFP cation and PS headgroup anion, with an insertion of the phenothiazine moiety among the acyls in the monolayer that depends on the packing of the acyls.

Carbon chains and the (5,5) single-walled nanotube: Structure and energetics versus length

Reliable thermochemistry is computed for infinite stretches of pure-carbon materials including acetylenic and cumulenic carbon chains, graphene sheet, and single-walled carbon nanotubes (SWCNTs) by connection to the properties of finite size molecules that grow into the infinitely long systems. Using ab initio G3 theory, the infinite cumulenic chain (:C[double bond]C[double bond]C[double bond]C:) is found to be 1.9+/-0.4 kcal/mol per carbon less stable in free energy at room temperature than the acetylenic chain (.C[triple bond]C-C[triple bond]C.) which is 24.0 kcal/mol less stable than graphite. The difference between carbon-carbon triple, double, and single bond lengths (1.257, 1.279, and 1.333 A, respectively) in infinite chains is evident but much less than with small hydrocarbon molecules. These results are used to evaluate the efficacy of similar calculations with the less rigorous PM3 semiempirical method on the (5,5) SWCNT, which is too large to be studied with high-level ab initio methods. The equilibrium electronic energy change for C(g)-->C[infinite (5,5) SWCNT] is -166.7 kcal/mol, while the corresponding free energy change at room temperature is -153.3 kcal/mol (6.7 kcal/mol less stable than graphite). A threefold alternation (6.866, 6.866, and 6.823 A) in the ring diameter of the equilibrium structure of infinitely long (5,5) SWCNT is apparent, although the stability of this structure over the constant diameter structure is small compared to the zero point energy of the nanotube. In general, different (n,m) SWCNTs have different infinite tube energetics, as well as very different energetic trends that vary significantly with length, diameter, and capping.

Tetrasila-1,3-butadiene and its transformation to disilenyl anions

The reaction of dilithiosilane, (tBu2MeSi)2SiLi2 (2), with 1,1,2,2-tetrachloro-1,2-dimesityldisilane produced the tetrasila-1,3-butadiene derivative, (tBu2MeSi)2Si=Si(Mes)–(Mes)Si=Si(SiMetBu2)2 (3, Mes = 2,4,6-trimethyl-phenyl), which was isolated as reddish-purple crystals. The structure of 3 was determined by both spectroscopic and crystallographic methods; the Si=Si double bond lengths are 2.2003(12) and 2.1983(12) A, and the length of the central Si−Si single bond is 2.3376(11) A. The tetrasilabutadiene moiety is highly twisted, the torsional angle of Si1=Si2−Si3=Si4 being 72°. The reaction of 3 with tBuLi or KC8 in THF gave the disilenyllithium 4 and disilenylpotassium 5, which contain an sp2-type silyl anion, by the reductive cleavage of the central Si–Si bond in 3.

Electron Deficient Carbon−Titanium Triple Bonds: Formation of Triplet XC÷TiX3 Methylidyne Complexes

Laser-ablated titanium atoms react with CX4 (X = F and Cl) to produce triplet state XC/TiX3 complexes trapped in an argon matrix. Products are identified by their infrared spectra and comparison to theoretically predicted vibrations. Density functional theory calculations converge to C(3v) symmetry structures for these lowest-energy products. The two unpaired electrons in the carbon 2p orbitals are shared with empty titanium d orbitals leading to degenerate singly occupied pi molecular orbitals and an electron-deficient triple bond between the carbon and titanium centers, on the basis of DFT bonding analysis and spin density calculations. The carbon-titanium distances are near typical C=Ti double bond lengths, and the C-X bonds in the resulting products are shorter than in the CX4 precursors. It appears that X lone-pair conjugation contributes to the C-X bond strength and somewhat to the C-Ti bond, and Cl does better in this regard than F.

Effects of aviary and box sizes on body mass and behaviour of domesticated budgerigars (Melopsittacus undulatus)

AbstractForty-eight budgerigars (Melopsittacus undulatus) were pairwise housed in small (80 × 40 × 50 cm) and large (160 × 40 × 50 cm) (length × breadth × height) boxes, as well as in 2.0 × 1.0 × 2.0 m aviaries. All boxes and aviaries had two or three (aviaries) perches and food was offered on the bottom. The body masses of female budgerigars increased significantly when they were housed in boxes instead of aviaries. The size of the box did not influence body mass. The frequency of flying was adjusted to the size of the box as both males and females flew approximately twice as often from perch to perch in a small box than in a large box of double length. Flying behaviour differed significantly between large and small boxes and aviaries. The ratio of invariantly flying from perch to perch to all flying events increased from aviaries < large boxes < small boxes. About 75% of all flying events in small boxes consisted of flying from perch to perch. Females in boxes spent more time on the bottom where the food was placed than females in aviaries. Both the significant body mass gain in female budgerigars, as well as the invariant, stereotypic flying movements, indicated reduced welfare in budgerigars housed in boxes, compared with those in aviaries. Providing a large box did not prevent body mass gain, but did increase the variation in flying patterns. Under long-term housing conditions, boxes could lead to at least two serious welfare problems; obesity and stereotypic behaviour, and should be avoided for budgerigars. Therefore, aviary housing should be chosen wherever possible.

Milk fat and primary fractions obtained by dry fractionation: 1. Chemical composition and crystallisation properties

The chemical composition and crystallisation properties of milk fat and its primary fractions, obtained by dry fractionation at 21 °C, were investigated. The solid fraction (stearin) and the liquid fraction (olein) displayed a different triacylglycerol (TG) composition. Stearin fraction was enriched in long-chain fatty acids, whereas olein fraction was enriched in short-chain and unsaturated fatty acids. Crystallisation properties of milk fat, and both the stearin and olein fractions were studied on cooling at |d T/d t| = 1 °C min −1 by differential scanning calorimetry and time-resolved synchrotron X-ray diffraction (XRD) at small and wide angles. Two main types of crystals corresponding to double chain length structures were characterised in the stearin fraction: α 2 L 1 (47.5 Å) and β′ 2 L 2 (41.7 Å). A triple chain length structure was formed in the olein fraction: α 3 L (72.1 Å). Crystallisaton of milk fat showed the formation of two 2 L (47.3 and 41.6 Å) and one 3 L (72.1 Å) lamellar structures with an hexagonal packing (α form). A schematic representation of the 3 L packing of olein fraction was proposed to explain how a wide diversity of TG can accommodate to form a lamellar structure with a thickness of 72 Å. Furthermore, the sharpness of the small-angle XRD lines associated to the α form was explained by the formation of liquid crystals of smectic type.

Organization of Nanoparticles on Hard Substrates Using Block Copolymer Films as Templates

We present a technique for the organization of pre-synthesized nanoparticles on hard substrates, using block copolymer films as sacrificial templates. A thin block copolymer film is dip-coated on the substrate of interest and the sample is exposed to a solution containing nanoparticles. Spontaneous preferential adsorption of the nanoparticles on one phase of the block copolymer film results in their lateral organization. An oxygen plasma etch is used to remove the polymer film; the nanoparticles end up organized on the substrate. We demonstrate that this is a general approach for the patterning of inorganic nanoparticles on hard substrates, showing the organization of metal and semiconductor nanoparticles having different chemistries at the particle/solvent and solvent/polymer interfaces. The nanoparticle patterns that we present have typical periodicities in the nanometer scale. In some cases, microcontact printing is used to create a double length scale of organization, on the micrometer and on the nanometer level. The characteristic periodicity of the template is studied with respect to the nanoparticle size in order to optimize the organization. Finally, we describe how to extend this technique for the production of continuous gold nanowires on hard substrates. We expect that the flexibility of this approach and the degree of control that can be obtained over nanoparticle organization should make it a powerful tool for nanoscale fabrication.

Identification of conjugated linoleic acid elongation and β-oxidation products by coupled silver-ion HPLC APPI-MS

Atmospheric pressure photoionisation (APPI) was used in combination with silver-ion (Ag(+))-HPLC for detection of (conjugated) fatty acid methyl esters (FAME) by tandem-mass spectrometry. APPI-MS of methyl esters of conjugated linoleic acid showed an increase in signal-to-noise ratio by a factor of 40 compared to atmospheric pressure chemical ionization in the positive mode. It was possible to identify double bond position, configuration and chain length of FAME based on chromatographic separation and mass detection. The developed LC-MS method is useful for the analysis of CLA elongation and beta-oxidation products, especially with trans,trans-configuration, which are difficult to analyze by conventional GC-MS techniques.

Magneto-elastic coupling and Peierls-like phase transition of one-dimensional magnetic nanoparticle chains

The fine structure of magnetic nanoparticle periodic chains is studied by considering the competition between magnetic dipolar interaction and elastic interaction. A Peierls phase with a doubled unit cell length can be formed under proper conditions and a Peierls transition can be induced by temperature and by external magnetic field. Due to the coupling between the magnetic state and the structural state, the nanoparticle chains would possess distinct properties and exhibit interesting behaviour.

Design of a mimic of nonamyloidogenic and bioactive human islet amyloid polypeptide (IAPP) as nanomolar affinity inhibitor of IAPP cytotoxic fibrillogenesis.

Protein aggregation into cytotoxic oligomers and fibrils in vivo is linked to cell degeneration and the pathogenesis of >25 uncurable diseases, whereas the high aggregation propensity and insolubility of several bioactive polypeptides and proteins in vitro prevent their therapeutic use. Aggregation of human islet amyloid polypeptide (IAPP) into pancreatic amyloid is strongly associated with the pathogenesis of type II diabetes. IAPP is a 37-residue polypeptide that acts as a neuroendocrine regulator of glucose homeostasis. However, IAPP misfolds and self-associates into cytotoxic aggregates and fibrils even at nanomolar concentrations. Because IAPP aggregation causes beta-cell death and prohibits therapeutic application of IAPP in diabetes, we pursued a minimalistic chemical design approach to generate a molecular mimic of a nonamyloidogenic and bioactive IAPP conformation that would still be able to associate with IAPP and thus inhibit its fibrillogenesis and cytotoxicity. We show that the double N-methylated full length IAPP analog [(N-Me)G24, (N-Me)I26]-IAPP (IAPP-GI) is a highly soluble, nonamyloidogenic, and noncytotoxic IAPP molecular mimic and an IAPP receptor agonist. Moreover, IAPP-GI binds IAPP with low nanomolar affinity and completely blocks IAPP cytotoxic self-assembly and fibrillogenesis with activity in the low nanomolar concentration range. Importantly, IAPP-GI dissociates cytotoxic IAPP oligomers and fibrils and is able to reverse their cytotoxicity. Bifunctional soluble IAPP mimics that combine bioactivity with the ability to block and reverse IAPP cytotoxic self-assembly are promising candidates for the treatment of diabetes. Moreover, our amyloid disease inhibitor design concept may be applicable to other protein aggregation diseases.

Thioindigo Dyes: Highly Accurate Visible Spectra with TD-DFT

The structure and visible spectra of a large panel of thioindigo dyes and derivatives have been evaluated using a TD-PBE0/6-311+G(2d,p)//PBE0/6-311G(d,p) approach explicitly taking bulk solvent effects into account by means of the polarizable continuum model. The influence of the solvent characteristics, the trans-cis isomerization, and the chemical substitution on the benzene rings have been investigated. In addition, hemi-thioindigo dyes, thiazine-indigo, chromophore-like molecules, and selenoindigo have been considered. Though the relative oscillator strengths of the two allowed visible transitions in the nonplanar cis isomers are not always correctly reproduced by theory, the agreement between theoretical and experimental results is far above expectations. For the 170 cases studied, we obtained a mean unsigned error on the predicted lambda(max) limited to 6.9 nm or 0.03 eV, with only 6 (4) cases for which the difference exceeds 20 nm (0.10 eV). These errors are 1 order of magnitude smaller than what has previously been reported for indigoids. A linear correlation between the central double bond length and the lambda(max) has been established, while the bond length and vibrational frequency of the carbonyl groups do not correlate with the thioindigo color. The higher excitation energies of the cis conformers, compared to the trans structures, result from a less stabilized LUMO in the former case. Indeed, for cis thioindigo, the two electron-rich (in the excited state) carbonyl units lie close to each other.

Organometallic modification approach to the control of push–pull architectures: Synthesis, properties and radical polymerization of chromium N-vinylcarbazole derivatives

In an effort to combine the donor character of the carbazole unit with the electron-withdrawing nature of the chromiumtricarbonyl moiety, which can be further modified by exchange of the CO ligand, a new series of vinyl-type monomers with organometallic push–pull chromophores, ( N-vinylcarbazole)Cr(CO) 2L (L = CO ( 2), PPh 3 ( 4), ( C 3 H 5 ) + BF 4 - ( 5)) and ( N-vinylcarbazole)bisCr(CO) 3 ( 3), have been synthesized and isolated, wherein 2 could be converted into 3 under appropriate conditions. All compounds were characterized spectroscopically, and X-ray crystal structure analyses were performed for 2– 4. The coordination-induced geometrical changes occur predominantly on the N-center and its attached double bond. PPh 3 replaces a CO group leading to the N-vinyl double bond length shortening from 1.274 (12) to 1.245 (9) Å. The distance of Cr from the carbazole plane, which allows estimates of the strength of the metal–ligand π-bonding, is shorter in 3 than in 2 as a result of an electronic communication between the two Cr(CO) 3 groups on each aryl ring of carbazole molecule. Electronic absorption and fluorescence spectral features of these complexes have been studied in terms of the electronic nature of the ligands. The change from 2 to 3 causes a subtle red-shift of the absorption bands due to the electronic transitions within dinuclear-carbazole ring system. The polymerization studies of these complexes under free-radical conditions lead to a better understanding of how the organometallic moiety affects the vinyl polymerization. The intriguing effect of the organometallic moiety on the intrachain excimer formation in the resultant polymers have been shown to be likely.

The dynamics of activated surface diffusion

An elementary process occurring on surfaces is diffusion. The dynamics is simplest whenthe concentration of adsorbates is sufficiently small that interaction between adsorbatescan be ignored. But even for this tracer diffusion process, much remains to beuncovered. Here, we present the interplay between experimental measurement of tracerdiffusion and its theoretical interpretation, which leads to good estimates of theinteraction of the adparticle with the surface. We show how the results fromthree different experimental techniques—field ion microscopy, scanning tunnellingmicroscopy and quasielastic helium atom scattering—can be interpreted. Usingthe generalized Langevin equation as a model for the diffusion dynamics, weshow how the turnover theory for activated diffusion may be used to describe themeasured time evolution of the adparticle distribution on the surface. The differentactivation energy measured for hopping over single or double lattice lengths is shownto come from the added energy loss to the surface, as the particle moves overthe longer path. We discuss some of the issues which are not yet clear; theseinclude quantum effects, such as the quantum suppression of diffusion, vibrationallyassisted diffusion, multidimensional effects and diffusion in the presence of externalfields.

Artificial regression testing in the GARCH‐in‐mean model

Summary The issue of finite-sample inference in Generalised Autoregressive Conditional Heteroskedasticity (GARCH)-like models has seldom been explored in the theoretical literature, although its potential relevance for practitioners is obvious. In some cases, asymptotic theory may provide a very poor approximation to the actual distribution of the estimators in finite samples. The aim of this paper is to propose the application of the so-called double length regressions (DLR) to GARCH-in-mean models for inferential purposes. As an example, we focus on the issue of Lagrange Multiplier tests on the risk premium parameter. Simulation evidence suggests that DLR-based Lagrange Multiplier (LM) test statistics provide a much better testing framework than the more commonly used LM tests based on the outer product of gradients (OPG) in terms of actual test size, especially when the GARCH process exhibits high persistence in volatility. This result is consistent with previous studies on the subject.

5.28 The role of strategic changes in plastic adaptation oflocomotor function

Patients with unilateral neglect can misperceive horizontal distances in the contralesional space as being shorter than equivalent ipsilesional ones. We evaluated the visual and motor-proprioceptive components of space misrepresentation through a distance reproduction task performed both with and without visual guidance. Four groups of right brain damaged patients (neglect with hemianopia (N+H+), neglect with inferior quandrantanopia (N+Q+), neglect without hemianopia (N+H−) and patients without neglect or hemianopia (N−H−)) and one group of healthy controls (C) performed the line bisection task and reproduced horizontal distances either by setting the endpoints or by doubling the length of a line in the contralesional or ipsilesional space. The doubling length task was administered in three different conditions: (a) visuomotor (the patient draws the line in free vision); (b) visual (by sight the patient guides the examiner drawing the line); (c) proprioceptive-motor (the patient is blindfolded and manually inspects and extends the horizontal distance subtended by the line). Compared to C and N−H− patients, only N+H+ patients exhibited a significant ipsilesional shift in line bisection. N+H+ patients showed the most severe contralesional-overextension/ipsilesional-underextension asymmetry in the endpoint, visuomotor and visual line extension task. In the proprioceptive-motor condition no asymmetry was found and N+H− showed greater overextension on both sides of space. In N+H−, brain damage was mainly centered in central–frontal cortex and basal ganglia. These findings re-emphasize the relevance of damage to visual retinotopically organized representations of space in the genesis of horizontal space misrepresentation of neglect patients and suggest the possible association of a non-lateralized defective processing of proprioceptive-motor information with unilateral neglect.

The heterocyclic ruthenium(III) complex KP1019 (FFC14A) causes DNA damage and oxidative stress in colorectal tumor cells

The Ru(III) complex salt KP1019 induced formation of H 2O 2 in colorectal tumor cells in a dose-dependent way. It also caused DNA-strand breaks if only weakly doubling tail length to 55.87±3.97 μm. Both effects were prevented by 5 mM N-acetylcysteine (NAC) which also reduced cytotoxicity (IC 50 55 vs 30 μM without NAC). Induction of apoptosis was shown by loss of mitochondrial membrane potential in 63.4±2.1% of the population and by caspase-dependent cleavage of poly-(ADP-ribose)-polymerase (PARP). Both effects were inhibited by NAC which reduced the population with depolarized mitochondrial membranes to 24.1±1.2% and prevented PARP-cleavage indicating a central role oxidative stress in KP1019-induced apoptosis.

Linearly polarized carbon k-edge x-ray absorption spectroscopic study of heavily p-doped polyacetylene film with preferred orientation

The structures of polyacetylene (PA) films with oriented chains have been intensively investigated with linearly polarized carbon K-edge near edge x-ray absorption fine structure (NEXAFS) for the first time. The angular dependence of linearly polarized peak feature has been observed from normal to glancing incidence, with respect to the stretched direction of the PA film. The polymeric chain orientation of the stretched trans-PA has been determined with the strong angular dependence of π*C–C, σ*C–H, and π*C–C resonance. Heavily doped PA films with 6% FeCl4− or ClO4− show different near-edge peak features from the undoped PA films, especially in the energy region of ∼285 eV corresponding to electronic transition of C 1s electron to unoccupied π*C–C molecular level. Upon doping, the resonance peak position for sp2 hybridization of unsaturated C–C bonding is shifted to higher energy and the peak intensity is reduced significantly, which indicates that the cleavage of conjugated π bonds by p-doping occurs in the trans polymeric chain reducing the alternating double bond chain length. Although the peak features for σ*C–H and σ*C–C have been effectively changed, no angular dependence of the NEXAFS spectra are observed in the doped PAs.

Wood Quality of Coppiced Eucalyptus Tereticornisfor Value Addition

The anatomical, physical and mechanical properties of non-coppiced and coppiced (after first felling) wood of Eucalyptus tereticornis were studied to evaluate their quality and to recommend it for various end uses. The pith to periphery variation in specific gravity, fibre length, fibre diameter, fibre lumen diameter, double wall thickness, vessel diameter and vessel element length were investigated in both types of wood. Correlation coefficients between anatomical characteristics and specific gravity and among anatomical characteristics were established. The results of physical and mechanical properties indicate that the timber from both non-coppiced and coppiced wood can be classified as very heavy, strong, tough, very hard but liable to warp and crack badly. The studies suggest that there is no significant difference in anatomical and mechanical properties of non-coppiced and coppiced wood suggesting their timbers can be utilized for similar purposes.