Mechanical model for fiber-laden membranes

An integrated mechanical model for fiber-laden membranes is presented and representative predictions of relevance to cellulose ordering and orientation in the plant cell wall are presented. The model describes nematic liquid crystalline self-assembly of rigid fibers on an arbitrarily curved fluid membrane. The mechanics of the fluid membrane is described by the Helfrich bending-torsion model, the fiber self-assembly is described by the 2D Landau-de Gennes quadrupolar Q-tensor order parameter model, and the fiber-membrane interactions (inspired by an extension of the 2D Maier-Saupe model to curved surfaces) include competing curvo-philic (curvature-seeking) and curvo-phobic (curvature-avoiding) effects. Analysis of the free energy reveals three fiber orientation regimes: (a) along the major curvature, (b) along the minor curvature, (c) away from the principal curvatures, according to the competing curvo-philic and curvo-phobic interactions. The derived shape equation (normal stress balance) now includes curvature-nematic ordering contributions, with both bending and torsion renormalizations. Integration of the shape and nematic order equations gives a complete model whose solution describes the coupled membrane shape/fiber order state. Applications to cylindrical membranes, relevant to the plant cell wall, shows how growth decreases the fiber order parameter and moves the fibers’ director from the axial direction towards the azimuthal orientation, eventually leading to a state of stress predicted by pure membranes. The ubiquitous 54.7° cellulose fibril orientation with respect to the long axis in a cylindrical plant cell wall is shown to be predicted by the preset model when the ratio of curvo-phobic and curvo-philic interactions is in the range of the cylinder radius.     

Noise spectroscopy and interlayer phase coherence in bilayer quantum Hall systems

Bilayer quantum Hall systems develop strong interlayer phase coherence when the distance between layers is comparable to the typical distance between electrons within a layer. The phase-coherent state has until now been investigated primarily via transport measurements. We argue here that interlayer current and charge-imbalance noise studies in these systems will be able to address some of the key experimental questions. We show that the characteristic frequency of current noise is that of the zero wave vector collective mode, which is sensitive to the degree of order in the system. Local electric potential noise measured in a plane above the bilayer system, on the other hand, is sensitive to finite-wave-vector collective modes and, hence, to the soft-magnetoroton picture of the order-disorder phase transition.     

A concise synthetic strategy to functionalized chromenones via [5+1] heteroannulation and facile C-N/C-S/C-O bond formation with various nucleophiles

A highly efficient strategy to 2,3-substituted chromen-4H-ones has been developed. The methodology involves unexpected intramolecular heteroannulation of readily accessible substituted 2-hydroxy-ω-nitroacetophenone with carbon disulfide in the presence K₂CO₃ followed by methylation with methyl iodide. These chromenones were further reacted with various nucleophiles such as amines, thiols, and alkoxide resulting in the facile C-N, C-S, and C-O bond formation. The scope and generality have been discussed.     

Dynamical approach to spectator fragmentation in Au+Au reactions at 35 MeV/A

The characteristics of fragment emission in peripheral ¹⁹⁷Au+¹⁹⁷Au collisions 35 MeV/A are studied using the two clusterization approaches within framework of quantum molecular dynamics model. Our model calculations using minimum spanning tree (MST) algorithm and advanced clusterization method namely simulated annealing clusterization algorithm (SACA) showed that fragment structure can be realized at an earlier time when spectators contribute significantly toward the fragment production even at such a low incident energy. Comparison of model predictions with experimental data reveals that SACA method can nicely reproduce the fragment charge yields and mean charge of the heaviest fragment. This reflects suitability of SACA method over conventional clusterization techniques to investigate spectator matter fragmentation in low energy domain.     

New flavonoid glycosides and other chemical constituents from Clerodendrum phlomidis leaves: isolation and characterisation

Phytochemical investigation of the plant Clerodendrum phlomidis Linn. F. (Lamiaceae) has now led to the isolation of two new flavonoid glycosides (1, 2) together with six known compounds identified as pectolinaringenin (3), pectolinaringenin-7-O-β-d-glucopyranoside (4), 24β-ethylcholesta-5,22E,25-triene-3β-ol (5), 24β-ethylcholesta-5,22E,25-triene-3β-O-β-D-glucopyranoside (6), (2S,3S,4R,10E)-2-[(2′R)-2′-hydroxytetracosanoylamino]-10-octadecene-1,3,4-triol (7) and andrographolide (8) mainly by spectroscopic analysis. Compounds 4 and 6–8 are reported for the first time from C. phlomidis.     

Interface-induced anisotropy and the nematic glass/gel state in jammed aqueous Laponite suspensions

Aqueous suspensions of Laponite, a system composed of disklike nanoparticles, are found to develop optical birefringence over several days, well after the suspensions solidified because of jamming. The optical anisotropy is particularly enhanced near the air-Laponite suspension interface over length scales of several millimeters, which is beyond 5 orders of magnitude larger than the particle length scale, suggestive of large-scale ordering influenced by the interface. The orientational order increases with time and is always greater for higher concentration of salt, higher concentration of Laponite, and higher temperatures of the suspension. Although weakly birefringent, Laponite suspensions covered by paraffin oil do not show any enhancement in optical anisotropy near the interface compared to that in the bulk. We suggest that the expedited structure formation near the air interface propagating progressively inside the sample is responsible for the observed behavior. We discuss the observed nematic ordering in the context of glass-like and gel-like microstructure associated with aqueous Laponite suspensions.     

Bidirectional and unidirectional PCET in a molecular model of a cobalt-based oxygen-evolving catalyst

The oxidation of water to molecular oxygen is a kinetically demanding reaction that requires efficient coupling of proton and electron transfer. The key proton-coupled electron transfer (PCET) event in water oxidation mediated by a cobalt-phosphate-based heterogeneous catalyst is the one-electron, one-proton conversion of Co(III)-OH to Co(IV)-O. We now isolate the kinetics of this PCET step in a molecular Co(4)O(4) cubane model compound. Detailed electrochemical, stopped-flow, and NMR studies of the Co(III)-OH to Co(IV)-O reaction reveal distinct mechanisms for the unidirectional PCET self-exchange reaction and the corresponding bidirectional PCET. A stepwise mechanism, with rate-limiting electron transfer is observed for the bidirectional PCET at an electrode surface and in solution, whereas a concerted proton-electron transfer displaying a moderate KIE (4.3 ± 0.2), is observed for the unidirectional self-exchange reaction.     

An IR study of poly-1,4-phenylenevinylene (PPV), the 2,5-dimethoxy derivative [(MeO)2-PPV], and their corresponding xanthate precursor polymers and monomers

A detailed comparison of the infrared (IR) spectra of poly-1,4-phenylenevinylene (PPV), its xanthate precursor polymer, and its bis-xanthate precursor monomer along with the corresponding 2,5-dimethoxy derivatives has provided a clearer basis for characterizing these species with regard to both structure and purity. All the xanthate precursor monomers and polymers exhibit characteristic intense absorptions typical of the xanthate group near 1220, 1110, and 1050 cm(-1). Upon complete conversion of the precursor polymer to the vinylene linked final product, the intense IR peaks of the xanthate group have disappeared and new bands resulting from the vinylene linkages are found. The latter include a moderately strong band near 965 cm(-1) due to the out-of-plane -CHCH- deformation of the trans-vinylene conjugated with and linking the phenyl rings into an optoelectronic polymer. Unfortunately, the corresponding C-H stretching vibration of this same group of atoms expected to appear near 3020 cm(-1) falls in the same region of the spectrum as the aromatic C-H stretches of the phenyl rings. Similarly, for the 2,5-dimethoxy polymer derivative, [(MeO)(2)-PPV], the C-H stretching vibration near 3055 cm(-1) contains contributions from both aromatic and vinylene C-H. Density functional theory (DFT) calculations on the monomers were instrumental in assigning the infrared spectra of these materials. This study provides a systemic means for verifying that the precursor monomer has been polymerized into the precursor polymer and that thermal conversion to the conjugated polymer is complete.     

Phase transitions and equations of state at multimegabar pressures

Abstract

Review of phase transitions and equations of state at multimegabar pressures (100–300 GPa) is presented. Energy dispersive x-ray diffraction techniques in conjunction with synchrotron radiation sources are used. Besides several transition metals, Pt to 282 GPa, Re to 251 GPa, W to 209 GPa, and Fe to 255 GPa, the special focus is on Group IVA elements and isoelectronic III-V compounds. At high pressure, the isoelectronic materials are isostructural and exhibit similar equation of state.     

Diethylene glycol ether-linked 3,4,5-trihydroxybenzamides as triply branched dendritic anchors to CdSe/ZnS core/shell type nanoparticles: potential hydrophilic fluorescent probes

Functionalized N-2-mercaptoethyl-gallamides bearing three or five hydroxyl units that are tethered with diethylene glycol ether(s) allow for transferring hydrophobically pyridine-capped CdSe/ZnS core/shell nanoparticles from an organic to an aqueous layer with intact fluorescent profiles.