Weak Interaction Effects Research Articles

High-resolution FTIR spectrum of CH2D79Br: the ground, v 5=1 and v 9=1 state constants

The first high-resolution infrared spectrum of CH2D79Br has been investigated in the range 710–1080 cm−1 by Fourier transform infrared spectroscopy employing a synchrotron radiation source at an unapodized resolution of 0.0025 cm−1. This spectral region accounts for the fundamental bands ν 5 (ν 0 = 768.809 cm−1) and ν 9 (ν 0 = 930.354 cm−1), having the structure of hybrid a/b- and c-type bands of near-prolate asymmetric tops, respectively. The rovibrational analysis was performed over a wide range of transitions with quantum numbers J ≤ 72 and Ka ≤ 16. The experimentally determined ground-state constants including four sextic coefficients were obtained for the first time by merging the ground-state combination differences of the two bands. The A-reduced Watson Hamiltonian in the Ir representation was adopted to fit the data. Only weak interaction effects ascribed to a-type Coriolis coupling influenced the Ka = 10–14 stacks of the bands. The residuals were adjusted by including one higher-order interaction term in a dyad model.

The Design of Chiral Double Hydrogen Bonding Networks and Their Applications to Catalytic Asymmetric Carbon-Carbon and Carbon-Oxygen Bond-Forming Reactions

This review focuses on the applications of multicenter organocatalysts, which can form chiral hydrogen bonded networks. The high tunabilities of these catalysts in terms of their active sites, chiral spacers, and tolerated reaction conditions have been used advantageously in applications to various classes of catalytic asymmetric carbon―carbon and carbon―oxygen bond forming reactions. The high stereoselectivities of these reactions are attributed to the chemoselective dual activation of both the nucleophile and electrophile reacting partners in asymmetric space. The key requirements for the cooperative effects of weak noncovalent-bonding interactions are discussed.

Evidence for conformational changes in the yeast deoxyhypusine hydroxylase Lia1 upon iron displacement from its active site.

The unique amino acid hypusine is formed exclusively in eIF5A by the successive action of deoxyhypusine synthase and deoxyhypusine hydroxylase (yeast Lia1, human DOHH). Although the first enzyme has been extensively studied, both Lia1 structure and the mechanism of action remain unclear. Hence, a multi-approach was used to evaluate Lia1 catalysis, metal/substrate binding, structural conformation and stability. Mutational analyses of Lia1 revealed fine differences in the mode of substrate binding between the human and yeast counterparts. Like human DOHH, recombinant Lia1 is an iron metalloenzyme. Iron is essential for enzyme activity since its loss renders the enzyme totally inactive. The separation of iron-free and iron-bound forms by gel filtration and native electrophoresis suggests differences in Lia1 tertiary structure related to the iron binding. The ability of Lia1 to undergo conformational changes prompted us to use a set of complementary spectroscopic approaches and SAXS to obtain detailed information on the processes underlying dissociation of iron from Lia1 at different levels of the protein organization. The additive effect of weak interactions, especially within the metal center, resulted in an active enzyme in a stabilized and compact three-dimensional fold. Loss of tertiary contacts upon iron displacement led to an elongated conformation of Lia1, in which the N- and C-terminal domains are no longer in close proximity to guarantee the proper orientation of the active groups within the active site pocket. Our results demonstrate an essential structural role for iron binding in addition to its contribution to the catalysis of hypusine formation in the eIF-5A precursor.

Observation of a Localization Transition in Quasiperiodic Photonic Lattices

We report the observation of the signature of a localization phase transition for light in one-dimensional quasiperiodic photonic lattices, by directly measuring wave transport inside the lattice. Below the predicted transition point an initially narrow wave packet expands as it propagates, while above the transition expansion is fully suppressed. In addition, we measure the effect of focusing nonlinear interaction on the propagation and find it increases the width of the localized wave packets.

Zinc(II) and cadmium(II) complexes with PDT: study of the effect of weak interactions on crystal packing

Two new zinc(II) and cadmium(II) complexes, [Zn(PDT)2(NCS)2] (1) and [Cd((PDT)2I1.6(H2O)0.4(OH)0.4] · 0.4H2O (2) (“PDT” is the abbreviation of 3-(2-pyridyl)-5, 6-diphenyl-1,2,4-triazine), have been synthesized and characterized by elemental analysis, IR, 1H NMR spectroscopy, and studied by X-ray crystallography. Zinc(II) in 1 is six coordinate ZnN6. 2 is a co-crystal with cadmium(II) being 60% six-coordinated with a CdN4I2 environment and 40% seven-coordinated with a CdN4O2I environment. The supramolecular features in these complexes are guided/controlled by weak directional intermolecular S ··· π, C–H ··· π, C–H ··· I, and π ··· π interactions.

Effects of Weak Intermolecular Interactions on the Molecular Isomerism of Tricobalt Metal Chains

Depending on the number of interstitial solvent molecules, n, crystals of the linear chain compound Co(3)(dipyridylamide)(4)Cl(2) x nCH(2)Cl(2) adopt either symmetrical or unsymmetrical metal chain structures. We explore here the possible reasons for such behavior using Hirshfeld surface analysis of intermolecular interactions as well as the charge density determined from 100(1) K X-ray diffraction data on the unsymmetrical complex Co(3)(dipyridylamide)(4)Cl(2) x 2.11 CH(2)Cl(2), u-1, and crystal structures of u-1 determined from single crystal synchrotron X-ray diffraction data at 20, 150, and 300 K. The new crystal structures are compared with previous structural results on a crystal with slightly different solvent content. This change in solvent content only affects the bond distances to atom Co(3), which are also strongly affected by temperature changes due to a spin crossover transition. Large differences in intermolecular interactions are revealed by the Hirshfeld surface analysis between symmetrical (s-1) and unsymmetrical (u-1) crystal solvates, suggesting that the molecular isomerism is strongly influenced by crystal packing effects. Topological analysis of the static electron density of u-1 suggests that there is direct metal-metal bonding for both the shorter Co(1)-Co(2) and the longer Co(2)-Co(3) contact. The approximate description of the system as a (Co(2))(2+)-dimer and an isolated Co(2+)-ion is reflected in the character of the metal-ligand interactions, which are more ionic for the isolated Co(3) atom, and the topological charges Co(1)(+0.50), Co(2)(+0.77), and Co(3)(+1.36). The two termini of u-1 are found to be very different, both in terms of structural surroundings as well as topology. The central Co(2) atom is similar to a cobalt atom in a tetragonally distorted octahedral environment resulting in preferred occupancy in the t(2g) orbitals. The Co(1) atom has significant deformation in the xz and yz planes (z along the chain axis, x and y toward ligands) reflecting covalent interactions with the terminal chlorine atom Cl(1). The Co(3) atom has a relatively high occupancy of the d(x(2)-y(2)) orbital and a relatively low occupancy of the d(xy) orbital confirming that these orbitals are involved in the spin crossover process and predominantly responsible for the observed variation in bond lengths with temperature.

Competition between recombination and epistasis can cause a transition from allele to genotype selection

Biochemical and regulatory interactions central to biological networks are expected to cause extensive genetic interactions or epistasis affecting the heritability of complex traits and the distribution of genotypes in populations. However, the inference of epistasis from the observed phenotype-genotype correlation is impeded by statistical difficulties, while the theoretical understanding of the effects of epistasis remains limited, in turn limiting our ability to interpret data. Of particular interest is the biologically relevant situation of numerous interacting genetic loci with small individual contributions to fitness. Here, we present a computational model of selection dynamics involving many epistatic loci in a recombining population. We demonstrate that a large number of polymorphic interacting loci can, despite frequent recombination, exhibit cooperative behavior that locks alleles into favorable genotypes leading to a population consisting of a set of competing clones. When the recombination rate exceeds a certain critical value that depends on the strength of epistasis, this "genotype selection" regime disappears in an abrupt transition, giving way to "allele selection"--the regime where different loci are only weakly correlated as expected in sexually reproducing populations. We show that large populations attain highest fitness at a recombination rate just below critical. Clustering of interacting sets of genes on a chromosome leads to the emergence of an intermediate regime, where blocks of cooperating alleles lock into genetic modules. These haplotype blocks disappear in a second transition to pure allele selection. Our results demonstrate that the collective effect of many weak epistatic interactions can have dramatic effects on the population structure.

Structural Basis of the Broad Specificity of a General Odorant-Binding Protein from Honeybee

General odorant-binding proteins (GOBPs) are believed to transport a wide range of volatile hydrophobic molecules across the aqueous sensillum lymph toward olfactory receptors in insects. GOBPs are involved in the first step of odorant recognition, which has a great impact in agriculture and in insect-mediated human disease control. We report here the first structural study of a GOBP, the honeybee ASP2, in complex with a small hydrophilic ligand. The overall fold of the NMR structure of ASP2 consists of the packing of six alpha-helices creating an internal cavity and closely resembles that of the related pheromone-binding proteins (PBPs). The predominantly hydrophobic internal cavity of ASP2 provides additional possible interactions (pi-stacking, electrostatic contact) for ligand binding. We also show that the internal cavity of ASP2 has the ability to bind ligands of different structures and properties, including a hydrophobic component of the floral scent [2-isobutyl-3-methoxypyrazine (IBMP)] and a small hydrophilic ligand. We further demonstrate that IBMP binds ASP2 with two stable alternative conformations inside the ASP2 binding pocket. The (15)N NMR relaxation study suggests that significant backbone mobility occurs at the ligand entry site at the millisecond rate, which likely plays a role in the recognition and the uptake-release mechanism of ligands by ASP2. We propose that the broad ligand specificity of GOBPs compared with PBPs is conferred by the cumulative effects of weak nonspecific protein-ligand interactions and of enhanced protein internal dynamics at the ligand entry site.

Connecting Internet Use with Gaps in Cancer Knowledge

This study applies the knowledge gap hypothesis to the specific domain of Internet use for cancer information. In particular, this study examines disparities in online information seeking by education and ethnicity, and subsequent gaps in cancer knowledge. Perceived risk of cancer and ease of connection to the Internet are concerned as contingent factors influencing knowledge gaps. A subsample of the 2003 Health Information National Trends Survey—those who have ever been online—was analyzed. Data supported the hypothesis that high education groups and White Americans were more likely to use the Internet for cancer information than were their counterparts, and online information seeking enlarged to some degree the cancer knowledge gaps between education groups. Perceived cancer risk had a weak but significant three-way interaction effect with ethnicity and online seeking on cancer knowledge, which suggests the importance of motivation in attenuating the knowledge gaps. The moderating role of ease of connection to the Internet was not supported. Discussion about the findings and further suggestions are offered.

Head-to-tail Aggregates of Sulfonatomethylated Calix[4]resorcinarene in Aqueous Solutions

Two amphiphilic water-soluble sulfonatomethylated calix[4]resorcinarene derivatives were studied by various 1H NMR techniques (1H NMR titration, 2D NOESY, NMR diffusion measurements). The derivative with methyl moieties at the lower rim (1) was found to be non-aggregated in the range 0–10 mM in aqueous solutions. Lengthening of the lower rim substituent to pentyl (2) results in self-aggregation of 2 in aqueous solutions with the aggregation number varying from 3 at 1 mM to 20 at 10 mM. The 2D NOESY 1H NMR spectroscopy data reveal an unusual head-to-tail packing mode in aqueous solutions, resulting from the cooperative effect of weak hydrophobic interactions. Binding of guests (tetramethylammonium and N-methylpyridinium) results in additional stabilization of the aggregates whilst the head-to-tail packing mode of the aggregate is retained.

Genetic association tests in the presence of epistasis or gene‐environment interaction

A genetic variant is very likely to manifest its effect on disease through its main effect as well as through its interaction with other genetic variants or environmental factors. Power to detect genetic variants can be greatly improved by modeling their main effects and their interaction effects through a common set of parameters or "generalized association parameters" (Chatterjee et al. [2006] Am. J. Hum. Genet. 79:1002-1016) because of the reduced number of degrees of freedom. Following this idea, I propose two models that extend the work by Chatterjee and colleagues. Particularly, I consider not only the case of relatively weak interaction effect compared to the main effect but also the case of relatively weak main effect. This latter case is perhaps more relevant to genetic association studies. The proposed methods are invariant to the choice of the allele for scoring genotypes or the choice of the reference genotype score. For each model, the asymptotic distribution of the likelihood ratio statistic is derived. Simulation studies suggest that the proposed methods are more powerful than existing ones under certain circumstances.

Polarization and Policy Reform: Anti-Corruption Policymaking in Sub-Saharan Africa

The ability of political systems to adopt policy reforms contributes to their internal stability. This article analyses 29 anti-corruption reforms in seven sub-Saharan countries. It seeks to explain the level of adopted reform in these countries from conflicts of interests between policy actors. Two groups of policy actors are distinguished: veto-players (endowed with an exercisable veto) and stakeholders (with an interest in policy reforms). A veto-player model is applied and extended with effects of (a) policy polarization between all policy actors and (b) institutional fractionalization between veto-players and stakeholders. The authors hypothesize a negative (interaction) effect of these variables with the win-set on the level of reform. As expected, the core variable of the veto-player model, size of the win-set of the status quo, significantly and positively affects the level of adopted reform. Unexpectedly, the number of veto-players has a significant and positive effect on the level of reform, whereas polarization among veto-players does not affect the level of reform. In contrast, fractionalization between veto-players and stakeholders has a significant negative direct effect on the level of anti-corruption reform and a weak interaction effect with size of the win-set. Thus, even when veto-players agree on the desirability of anticorruption reforms, the adoption of reforms is obstructed by a high level of fractionalization between veto-players and stakeholders.

Protein‐responsive imprinted polymers with specific shrinking and rebinding

Stimuli-responsive protein imprinted polymers were obtained via a combination of molecular imprinting and reversible stimuli-responsive polymer using lysozyme or cytochrome c as template, N-isopropylacrylamide (NIPA) as major monomer, methacrylic acid (MAA) and acrylamide (AAm) as functional co-monomers, and N,N-methylenebisacrylamide (MBAAm) as crosslinker. The molecularly imprinted polymers (MIPs) can respond not only to external stimuli such as temperature and salt concentration, but also to the corresponding template protein with significant specific volume shrinking. This specific shrinking behavior was attributed to the synergistic effect of multiple-site weak interactions (electrostatic force, hydrogen bonding and hydrophobic interaction) and the cavity effect. The MIPs showed highly selective adsorption of template proteins with specific shrinking compared with the non-imprinted polymers. The results indicated that the MIPs seemed to change shape to accommodate the conformation of the template protein leading to the formation of a shape complementary cavity.

1P-061 Effect of Weak Interaction on the Electronic Structure and Electrochemical Properties of Pseudoazurin Met16X mutants(The 46th Annual Meeting of the Biophysical Society of Japan)

1P-061 Effect of Weak Interaction on the Electronic Structure and Electrochemical Properties of Pseudoazurin Met16X mutants(The 46th Annual Meeting of the Biophysical Society of Japan)

Negative magnetoresistance effects in metallic n-type GaSb

A negative magnetoresistance at low magnetic fields and low temperatures was evidenced in n-type GaSb samples having an electron density just above the critical value for the metal-insulator transition and was interpreted in terms of quantum-interference effects. The inelastic scattering time was derived as a function of the temperature by the analysis of the data with a standard model, which includes weak localization and electron-electron interaction effects. The results of the fitting and the Isawa electron-electron scattering time were found to agree only if a nonnegligible amount of disorder is taken into account in the quantum-interference correction to the conductivity near the metal-insulator transition. These results are discussed in the light of the structural characterization of the investigated samples. The negative magnetoresistance effects were also observed in non-Ohmic measurements, with a behavior consistent with the usual electron temperature model.

Synthesis of Mixed‐ligand Complexes of Copper(II) with Lactate and 2,2′‐Dipyridylamine: Study of the Effect of Weak Interactions on their Crystal Packing

AbstractTwo new mononuclear mixed‐ligand complexes [Cu(HL)(OAc)(dipyam)] (1)·H2O and [Cu(HL)Cl(dipyam)] (2)·Solv (HL = monoanionic lactate and dipyam = 2,2′‐dipyridylamine) have been synthesized and structurally characterized by X‐ray diffraction. The supramolecular association in these complexes have also been analyzed. In both cases the copper(II) ion is in a slightly distorted square‐pyramidal environment. The two complexes are extended into 3D networks, through hydrogen bonding alone in 1 and through both hydrogen bonding and π‐π interactions in 2.

The magnetic fields of large Virgo Cluster spirals

Because of its proximity the Virgo Cluster is an excellent target for studying interactions of galaxies with the cluster environment. Both the high-velocity tidal interactions and effects of ram pressure stripping by the intracluster gas can be investigated. Optical and/or \ion{H}{i} observations do not always show effects of weak interactions between galaxies and their encounters with the cluster medium. For this reason we searched for possible anomalies in the magnetic field structure in Virgo Cluster spirals which could be attributed to perturbations in their gas distribution and kinematics. Five angularly large Virgo Cluster spiral galaxies (NGC 4501, NGC 4438, NGC 4535, NGC 4548 and NGC 4654) were the targets for a sensitive total power and polarization study using the 100-m radio telescope in Effelsberg at 4.85 GHz. For two objects polarization data at higher frequencies have been obtained allowing Faraday rotation analysis. Distorted magnetic field structures were identified in all galaxies. Interaction-induced magnetized outflows were found in NGC 4438 (due to nuclear activity) and NGC 4654 (a combination of tidal tails and ram pressure effects). Almost all objects (except the anaemic NGC 4548) exhibit distortions in polarized radio continuum attributable to influence of the ambient gas. For some galaxies they agree with observations of other species, but sometimes (NGC 4535) the magnetic field is the only tracer of the interaction with the cluster environment. The cluster environment clearly affects the evolution of the galaxies due to ram pressure and tidal effects. Magnetic fields provide a very long-lasting memory of past interactions. Therefore, they are a good tracer of weak interactions which are difficult to detect by other observations.

Weak interaction effects in top-quark pair production at hadron colliders

Top-quark physics plays an important role at hadron colliders such as the Tevatron at Fermilab or the upcoming Large Hadron Collider (LHC) at CERN. Given the planned experimental precision, detailed theoretical predictions are mandatory. In this article we present analytic results for the complete weak corrections to gluon-induced top-quark pair production – neglecting purely photonic corrections, completing our earlier results for the quark-induced reaction. As an application we discuss top-quark pair production at the Tevatron and LHC. In particular we show that, although they are small for inclusive quantities, weak corrections can be sizeable for differential distributions.

Adjacent Cell Interaction and MRAM Error Rate Prediction

Effects of weak magnetostatic interaction among adjacent cells on the array quality factor (AQF) of a conventional single particle MRAM array are analyzed by the mean-field theory. Inaccuracy of the theory at modest interaction is discussed, and attributed to the emergence of stripe pattern. A numerical method is also described, for quantifying the effect of magnetostatic interaction on a write margin test. This methods allows write margins on common test patterns and on the actual data file (which is substantially random) to be compared

Counterion, Temperature, and Time Modulation of Nanometric Chiral Ribbons from Gemini-Tartrate Amphiphiles

Amphiphile supramolecular assemblies result from the cooperative effects of multiple weak interactions between a large number of subcomponents. As a result, prediction of and control over the morphologies of such assemblies remains difficult to achieve. Here, we described the fine-tuning of the shape, size, and morphology transitions of twisted and helical membranes formed by non-chiral dicationic n-2-n gemini amphiphiles complexed with chiral tartrate anions. We have reported that such systems express the chirality of the tartrate components at a supramolecular level and that the mechanism of the chiral induction by counterions involves specific anion cation recognition and the induction of conformationally labile chirality in the cations. Here, we demonstrate that the morphologies and dimensions of twisted and helical ribbons, as well as tubules, can be controlled and that interconversion between these structures can be induced upon modifying temperature, upon introducing small amounts of additives, or slightly modifying molecular structure. Specifically, electron microscopy, IR spectroscopy, and small-angle X-ray scattering show that (i) varying the hydrophobic chain length or adding gemini having bromide counterions (1%) or the opposite enantiomer (10%) leads to an increase of the diameter of membrane tubules from 33 to 48.5 nm; (ii) further addition (1.5%) of gemini bromide or a slight increase in temperature induces a transition from tubules to twisted ribbons; (iii) the twist pitch of the ribbons can be continuously tuned by varying enantiomeric excess; and (iv) it was also observed that the morphologies of these ribbons much evolve with time. Such unprecedented observations over easy tuning of the chiral supramolecular structures are clearly related to the original feature that the induction of chirality is solely due the counterions, which are much more mobile than the amphiphiles.