Effect of lithium chloride on the palisade layer of the Triton-X-100 micelle: two sites for lithium ions as revealed by solvation and rotational dynamics studies

Dynamic Stokes' shift measurements using coumarin 153 as the fluorescence probe have been carried out to explore the effect of added electrolyte, lithium chloride (LiCl), on solvation dynamics in the Triton-X-100 (TX-100) micelle and thus to understand the changes in micellar Palisade layer, especially the entrapped water structures in the Palisade layer. At all concentrations of LiCl, the spectral shift correlation function shows biexponential decay. At lower LiCl concentrations, the longer solvation time is seen to decrease, although the shorter solvation time is not affected much. At higher LiCl concentrations, both longer and shorter solvation times increase with electrolyte concentration. The present observations have been rationalized assuming two possible modes of interaction of the Li+ ions in the micellar palisade layer. For LiCl concentrations below about 1.5 M, the Li+ ions appear to bind preferably to the ether groups of surfactant molecules, and the increased micellar hydration with the added salt effectively makes the solvation dynamics faster. At higher LiCl concentrations, available ether binding sites for the Li+ ions seem to get occupied effectively and the excess Li+ ions start remaining in the Palisade layer as strongly hydrated free ions. Because of strong hydration of the Li+ ions, the mobility of the entrapped water molecules in the micellar Palisade layer decreases significantly, causing the solvation dynamics to slow at higher LiCl concentrations. The fluorescence anisotropy results in the present systems are also in support of the above inferences drawn from solvation dynamics results. The present results with LiCl salt are found to be substantially different than those obtained in our earlier study (Kumbhakar et al. J. Phys. Chem. B 2005, 109, 14168) with salts such as NaCl, KCl, and CsCl. These differences are attributed mainly to the binding of the Li+ ions with the surfactant ether groups, which seems to be unlikely for the other alkali cations.     

Design of peptides with α,β-dehydro-residues: Synthesis and crystal structure of a tetrapeptide Boc-Ala-ΔPhe-ΔPhe-Phe-OCH<Subscript>3</Subscript>

In order to develop general rules of peptide design with α,β-dehydro-residues, a peptide, Boc-Ala-ΔPhe-ΔPhe-Phe-OCH₃, was synthesized. The peptide was crystallized from its solution in an acetone:water mixture (70:30). The crystals belong to orthorhombic space group P2₁2₁2₁ with a = 9.403(1) Å, b = 16.871(1) Å, c = 21.638(1) Å, and Z = 4. The peptide adopts a conformation with two overlapping types II′ and III β-turns having dihedral angles, φ₁ = 53.7(6)^°, ψ₁ = ?135.9(4)^°, φ₂ = ?59.2(5)^°, ψ₂ = ?17.9(5)^°, φ₃ = ?68.4(5)^°, ψ₃ = ?18.8(6)^°. The conformation was further characterized by two intramolecular 4 → 1 hydrogen bonds involving imino nitrogen atoms of ΔPhe³ and Phe⁴ as donors and carbonyl oxygen atoms of blocking group Boc and Ala¹ as acceptors. The packing of the molecules in the unit cell is stabilized by an intermolecular hydrogen bond, N₂–H₂?s O′₃ [?x, y+1/2, ?z+1/2] = 2.894 Å and van der Waals forces involving aromatic side chains.     

XPS study of glassy Pd80Ge20

An X-ray photoemission and Auger electron spectroscopy study of the electronic structure of Pd₈₀Ge₂₀ alloy in its glassy and crystalline states is reported. The glassy state shows some modifications in the valence band structure, symmetry of the Pd $\text{3}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{?3}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ spin-orbit doublet and a shift in M₄₅-V-V Auger transition of Pd. Analysis of the chemical shifts in the core-level binding energies of the constituents indicates negligible charge transfer from the metalloid atom (Ge) to d-band of the Pd.     

Bispidine as a β-strand nucleator: from a β-arch to self-assembled cages and vesicles

The development of synthetic scaffolds that nucleate well-folded secondary structures is highly challenging. Herein, we designed and synthesized a series of core-modified peptides (F1, F2, F3, and F4) that fold into β-strand structures. These bispidine-scaffolded peptides were studied by CD, IR, NMR, single crystal XRD, and Molecular Dynamics (MD) simulations to investigate their conformational preferences. Solid-state and solution studies revealed that bispidine is a versatile scaffold that could be placed either at the terminal or at the middle of the peptide strand for nucleating the β-strand structure. Scaffolds that nucleate an isolated β-strand conformation are rare. Bispidine placed at the C-terminus of the peptide chain could nucleate a β-strand conformation, while bispidine placed at the middle resulted in a β-arch conformation. This nucleation activity stems from the ability to restrict the psi torsion angle (ψ) through intramolecular C5 hydrogen bonding between the equatorial hydrogen(s) of bispidine and the carbonyl oxygen(s) of the amino acid close to the scaffold. Furthermore, the bispidine peptidomimetic with a super secondary structure, namely β-arch, assembled into single-hole submicron cages and spherical vesicles as evident from microscopic studies. The design logic defined here will be a significant strategy for the development of β-strand mimetics and super secondary structures.

Bispidine is a versatile scaffold that could be placed either at the terminal or at the middle of the peptide strand for nucleating β-strand structures. These β-strand mimetics self-assemble to single hole submicron cages and vesicles.     

Surrogate model‐based strategy for cryogenic cavitation model validation and sensitivity evaluation

The study of cavitation dynamics in cryogenic environment has critical implications for the performance and safety of liquid rocket engines, but there is no established method to estimate cavitation‐induced loads. To help develop such a computational capability, we employ a multiple‐surrogate model‐based approach to aid in the model validation and calibration process of a transport‐based, homogeneous cryogenic cavitation model. We assess the role of empirical parameters in the cavitation model and uncertainties in material properties via global sensitivity analysis coupled with multiple surrogates including polynomial response surface, radial basis neural network, kriging, and a predicted residual sum of squares‐based weighted average surrogate model. The global sensitivity analysis results indicate that the performance of cavitation model is more sensitive to the changes in model parameters than to uncertainties in material properties. Although the impact of uncertainty in temperature‐dependent vapor pressure on the predictions seems significant, uncertainty in latent heat influences only temperature field. The influence of wall heat transfer on pressure load is insignificant. We find that slower onset of vapor condensation leads to deviation of the predictions from the experiments. The recalibrated model parameters rectify the importance of evaporation source terms, resulting in significant improvements in pressure predictions. The model parameters need to be adjusted for different fluids, but for a given fluid, they help capture the essential fluid physics with different geometry and operating conditions. Copyright © 2008 John Wiley & Sons, Ltd.     

Neutron spallation source and the Dubna Cascade Code

Neutron multiplicity per incident proton,n/p, in collision of high energy proton beam with voluminous Pb and W targets has been estimated from the Dubna Cascade Code and compared with the available experimental data for the purpose of benchmarking of the code. Contributions of various atomic and nuclear processes for heat production and isotopic yield of secondary nuclei are also estimated to assess the heat and radioactivity conditions of the targets. Results obtained from the code show excellent agreement with the experimental data at beam energy,E < 12 GeV and differ maximum up to 25% at higher energy     

Crystallographic analysis of 9-(3-methylbut2-enyloxyfurano)[3,2-g] benzopyran-2-one

This structure of 9-(3-methylbut-2-enyloxyfurano)[3,2-g] benzopyran-2-one has been determined by X-ray diffraction methods. The compound crystallizes in the triclinic (space group P \(bar 1\)) with the unit cell parameters a = 11.1150(10), b = 11.8240(10), c = 11.9290(10) Å, α = 64.90(1)^°, β = 83.53(1)^°, γ = 89.25(1)^° and Z = 4. The structure has been solved by direct methods and refined to reliability index of 0.043. The unit cell contains two crystallographically independent molecules in the asymmetric unit, which exhibit different side-chain conformations. The crystal structure is stabilized by the intra molecular and intermolecular C–H?sO interactions.     

Nonnegative matrices having nonnegative Drazin pseudoinverses

Necessary and sufficient conditions for nonnegative matrices having nonnegative Drazin pseudoinverses are obtained. A decomposition theorem which characterizes the class of all nonnegative matrices with nonnegative Drazin pseudoinverses is proved, thus answering a question raised by several people. It is also shown that if a row (or column) stochastic matrix has a nonnegative Drazin pseudoinverse A(^d), then A(^d) is some power of A. These results extend known results for nonnegative group-monotone matrices.     

Evidence supporting a single electron transfer pathway in the reduction of aromatic ketones by metal alkoxides. Lithium isopropoxide,an excellent reducing agent for aromatic ketones.

Reactions of various metal alkoxides with aromatic ketones have been shown to produce radical intermediate. Lithium isopropoxide has been found to be an excellent reducing agent for aromatic ketones and reduces benzophenone at a faster rate than does aluminum isopropoxide.