High-resolution spectroscopy of SO2 using a frequency-doubled,continuous-wave dye laser

The SO₂ molecule is of considerable interest in the context of atmospheric pollution, and in many laser monitoring techniques the ultraviolet absorption band at 300 nm is used to determine SO₂ concentrations in the atmosphere. Recent laboratory experiments with a resolution of 2 × 10^-3 nm showed that variations could occur in absorption cross-section measurements made with different laser bandwidths due to unresolved fine structure. We have investigated absorption spectra with a line width of 3 × 10^-6 nm, using a frequency-doubled continuous-wave dye laser, and have confirmed the existence of fine structure in the absorption even when collisionally broadened with an atmosphere of nitrogen. These measurements provide a data base from which valid absorption cross sections may be calculated for all monitoring laser bandwidths. We estimate the pressure broadening coefficient for nitrogen in this wavelength region as 83 ± 38 kHz Pa^-1 (11 ± 5 MHz torr^-1). The temperature dependence of the absorption cross-section was also investigated.     

Multipole pairing states and the correspondence between two- and four-particle transfer reactions

Data for the ^58,60Ni(⁶Li, d) ^62,64Zn reactions, together with an analysis in terms of a simple multipole pairing model, indic that two-phonon states are extremely weakly excited. This result arises from the dominance of monopole pairing correlations in four-particle transfer reactions and explains the observed correspondence between two- and four-particle transfer reactions populating the same final nucleus.     

The first-to-zero-sound transition in non-superfluid liquid 4He

Neutron inelastic scattering from ⁴He at T = 2.3 K shows that for Q ? 2 nm^?1 “sound-wave” excitations propagate with the characteristics of ordinary or first sound while for Q ? 3 nm^?1 they propagate with the characteristics of zero sound.     

Copula‐based robust optimal block designs

Blocking is often used to reduce known variability in designed experiments by collecting together homogeneous experimental units. A common modeling assumption for such experiments is that responses from units within a block are dependent. Accounting for such dependencies in both the design of the experiment and the modeling of the resulting data when the response is not normally distributed can be challenging, particularly in terms of the computation required to find an optimal design. The application of copulas and marginal modeling provides a computationally efficient approach for estimating population‐average treatment effects. Motivated by an experiment from materials testing, we develop and demonstrate designs with blocks of size two using copula models. Such designs are also important in applications ranging from microarray experiments to experiments on human eyes or limbs with naturally occurring blocks of size two. We present a methodology for design selection, make comparisons to existing approaches in the literature, and assess the robustness of the designs to modeling assumptions.     

Embedded cluster modeling of excited chromium impurities in halide elpasolites

Abstract

Embedded cluster calculations performed on both ground (⁴A_2g) and excited (⁴T_2g) states of substitutional Cr³⁺ in halide elpasolites account successfully for the pressure dependence of photoluminescence spectra.     

Specificity of Furanoside–Protein Recognition through Antibody Engineering and Molecular Modeling

Recognition of furanosides (five‐membered ring sugars) by proteins plays important roles in host–pathogen interactions. In comparison to their six‐membered ring counterparts (pyranosides), detailed studies of the molecular motifs involved in the recognition of furanosides by proteins are scarce. Here the first in‐depth molecular characterization of a furanoside–protein interaction system, between an antibody (CS‐35) and cell wall polysaccharides of mycobacteria, including the organism responsible for tuberculosis is reported. The approach was centered on the generation of the single chain variable fragment of CS‐35 and a rational library of its mutants. Investigating the interaction from various aspects revealed the structural motifs that govern the interaction, as well as the relative contribution of molecular forces involved in the recognition. The specificity of the recognition was shown to originate mainly from multiple CH–π interactions and, to a lesser degree, hydrogen bonds formed in critical distances and geometries.     

A Traveling Wave Ion Mobility Spectrometry (TWIMS) Study of the Robo1-Heparan Sulfate Interaction

Roundabout 1 (Robo1) interacts with its receptor Slit to regulate axon guidance, axon branching, and dendritic development in the nervous system and to regulate morphogenesis and many cell functions in the nonneuronal tissues. This interaction is known to be critically regulated by heparan sulfate (HS). Previous studies suggest that HS is required to promote the binding of Robo1 to Slit to form the minimal signaling complex, but the molecular details and the structural requirements of HS for this interaction are still unclear. Here, we describe the application of traveling wave ion mobility spectrometry (TWIMS) to study the conformational details of the Robo1-HS interaction. The results suggest that Robo1 exists in two conformations that differ by their compactness and capability to interact with HS. The results also suggest that the highly flexible interdomain hinge region connecting the Ig1 and Ig2 domains of Robo1 plays an important functional role in promoting the Robo1-Slit interaction. Moreover, variations in the sulfation pattern and size of HS were found to affect its binding affinity and selectivity to interact with different conformations of Robo1. Both MS measurements and CIU experiments show that the Robo1-HS interaction requires the presence of a specific size and pattern of modification of HS. Furthermore, the effect of N-glycosylation on the conformation of Robo1 and its binding modes with HS is reported.

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Graphical Abstract ?

     

Molecular and crystal structure of Cp2Mo(mto), mto=monothiooxalate

Compoundl, Cp₂Mo(mto) is obtained by the reaction of Cp₂MoCl₂ with methanol solutions of potassium dithiooxalate in air. Red platelike crystals of Cp₂Mo(mto) were grown by the slow diffusion of pentane into a CH₂Cl₂ solution ofl and have been studied by X-ray crystallography: space group, P2₁/n,a=7.578(1),b=10.551(2),c=14.090(3) Å, =94.38(2)°,V=1123.1(4) ų,Z=4. The mto ligand chelates to the Mo atom through one oxygen atom and the sulfur atom. The two Cp rings form dihedral angles of 24° with the least-squares plane of the mto ligand. The Mo–O and Mo–S bond distances are 2.193(5) and 2.449(2) Å, respectively.     

Structural and NMR Studies of the Hexameric Copper(I) Complex with N‐n‐butyl‐N′‐ethoxycarbonyl‐thioureate

The copper sulfide mineral flotation collector, N‐n‐butyl‐N′‐ethoxycarbonyl‐thiourea (H₂bectu), and the 1:1 hexameric copper(I) thioureate complex, [Cu(Hbectu)]₆, have been characterized by single crystal X‐ray diffraction. H₂bectu crystallizes in the triclinic space group with a = 5.2754(4), b = 9.0042(7), c = 12.6030(9) Å, α = 80.528(6), β = 90.173(6), γ = 76.472(7)°. An intramolecular N‐H···O hydrogen bond between the thioamide proton and carbonyl oxygen forms a planar six‐membered ring in the central core of the molecule with C=O, C=S and C‐N bond lengths in accord with those reported for other N‐alkyl/aryl‐N′‐acyl‐thiourea compounds. [Cu(Hbectu)]₆ crystallizes in the monoclinic space group C2/c with a = 23.269(5), b = 13.243(4), c = 23.037(7) Å, β = 91.81(2)° as discrete hexameric clusters disposed about a crystallographic centre of symmetry with a Cu₆S₆ core consisting of two Cu₃S₃ chair‐shaped rings linked by coordination of the deprotonated amide nitrogen atom to a copper atom in the adjacent ring. The six ligands assemble as a paddlewheel structure with the ethoxy and n‐butyl substituents packing in an alternating head to tail arrangement. Temperature dependent solution ¹H NMR spectroscopic studies show that the hexameric structure of the complex is maintained in solution.     

On achieving experimental accuracy from molecular dynamics simulations of flexible molecules: aqueous glycerol

The rotational isomeric states (RIS) of glycerol at infinite dilution have been characterized in the aqueous phase via a 1 micros conventional molecular dynamics (MD) simulation, a 40 ns enhanced sampling replica exchange molecular dynamics (REMD) simulation, and a reevaluation of the experimental NMR data. The MD and REMD simulations employed the GLYCAM06/AMBER force field with explicit treatment of solvation. The shorter time scale of the REMD sampling method gave rise to RIS and theoretical scalar 3J(HH) coupling constants that were comparable to those from the much longer traditional MD simulation. The 3J(HH) coupling constants computed from the MD methods were in excellent agreement with those observed experimentally. Despite the agreement between the computed and the experimental J-values, there were variations between the rotamer populations computed directly from the MD data and those derived from the experimental NMR data. The experimentally derived populations were determined utilizing limiting J-values from an analysis of NMR data from substituted ethane molecules and may not be completely appropriate for application in more complex molecules, such as glycerol. Here, new limiting J-values have been derived via a combined MD and quantum mechanical approach and were used to decompose the experimental 3J(HH) coupling constants into population distributions for the glycerol RIS.