Development of new coarse-grained models for chromonic liquid crystals: insights from top-down approaches

ABSTRACT

Two top-down coarse-grained molecular simulation models for a chromonic liquid crystal, 3,6,7,10,11-hexa-(1,4,7-trioxa-octyl)-triphenylene, are tested. We use an extension of the well-known MARTINI model and develop a new coarse-grained model based on statistical associating fluid theory (SAFT)-γ perturbation theory. For both models, we demonstrate self-assembly in the isotropic phase of the chromonic and we test the effectiveness of both models in terms of the structures of the chromonic aggregates that are produced in solution and the thermodynamics of association. The latter is tested by calculations of the potential of mean force for dimers in solution, which measures the strength of molecular association. SAFT-γ provides valuable insights into the thermodynamics of assembly. Exploration of a range of interactions between unlike sites demonstrates that chromonic self-assembly only occurs in a small parameter space where the hydrophilic–lipophilic balance between aromatic core and ethylene oxide chains is optimal. Outside of this balance, chromonic self-assembly is replaced by the formation of conglomerates of molecules or short stacks.     

Inclusions and metal composition of ancient copper‐based artefacts: a diachronic view by micro‐EDXRF and SEM‐EDS

A diachronic view of the metallurgy in the Portuguese territory during the first three millennia after its appearance in the Iberian Peninsula is presented based on the current state of the art. Results of micro‐energy dispersive X‐ray fluorescence (micro‐EDXRF) analyses made on metal artefacts to determine their composition and scanning electron microscopy with energy dispersive analysis (SEM‐EDS) analyses to study microstructural features as inclusions are shown to illustrate trends and specificities of each chronological period. Generally, in early periods, namely during the Copper Age and first stages of the Bronze Age, unalloyed copper and arsenical copper were at use, and only by the Late Bronze Age (LBA) did tin bronze substitute almost completely the previous role of copper. In the Early Iron Age, during the Orientalising period, a general decrease in the average tin content in bronzes seems to happen. Regarding the inclusions observed in the metal matrix, these seem to suffer a diversification with the appearance of tin bronzes. By the Copper Age, only Cu? O and Cu? As? O inclusions are observed, while by the LBA Cu? S inclusions become regular, besides others less frequent, as Sn? O, Cu? S? Fe and Pb globules. Overall, with the present analytical study, the complementary character of micro‐EDXRF and SEM‐EDS in the study of ancient metals is demonstrated, providing a first general overview of the ancient metallurgy at the Portuguese territory which is of key importance to specific investigations of the future. Copyright © 2011 John Wiley & Sons, Ltd.     

In situ measurements of the formation and morphology of intracellular β-amyloid fibrils by super-resolution fluorescence imaging

Misfolding and aggregation of peptides and proteins is a characteristic of many neurodegenerative disorders, including Alzheimer's disease (AD). In AD the β-amyloid peptide (Aβ) aggregates to form characteristic fibrillar structures, which are the deposits found as plaques in the brains of patients. We have used direct stochastic optical reconstruction microscopy, dSTORM, to probe the process of in situ Aβ aggregation and the morphology of the ensuing aggregates with a resolution better than 20 nm. We are able to distinguish different types of structures, including oligomeric assemblies and mature fibrils, and observe a number of morphological differences between the species formed in vitro and in vivo, which may be significant in the context of disease. Our data support the recent view that intracellular Aβ could be associated with Aβ pathogenicity in AD, although the major deposits are extracellular, and suggest that this approach will be widely applicable to studies of the molecular mechanisms of protein deposition diseases.     

Metal‐Free One‐Pot Synthesis of Benzofurans

Ethyl acetohydroxamate was efficiently arylated with diaryliodonium salts at room temperature under transition‐metal‐free conditions. The obtained O‐arylated products were reacted in situ with ketones under acidic conditions to yield substituted benzo[b]furans through oxime formation, [3,3]‐rearrangement, and cyclization in a fast and operationally simple one‐pot fashion without using excess reagents. Alternatively, the O‐arylated products could be isolated or transformed in situ to aryloxyamines or O‐arylaldoximes. The methodology was applied to the synthesis of Stemofuran A and the formal syntheses of Coumestan, Eupomatenoid 6, and (+)‐machaeriol B.     

Laux‐type Oxidation of In0 Nanoparticles to In2O3 Retaining Particle Size and Colloidal Stability

As a conceptual study, In⁰ nanoparticles are obtained by NaBH₄‐driven reduction of InCl₃ · 4H₂O and transferred from a polar/hydrophilic diethylene glycol phase to a non‐polar hydrophobic dodecane phase for purification and stabilization. Finally, the In⁰ nanoparticles are oxidized via a Laux‐like reaction with nitrobenzene to In₂O₃ nanoparticles. The challenge of the reaction is to perform the final oxidation to In₂O₃ under mild conditions with the colloidal stability, particle size and particle size distribution of the initial In⁰ nanoparticles retained. To this concern, the mean diameter of the initial In⁰ nanoparticles changed from 11(1) to 14(2) nm of the oxidized In₂O₃ nanoparticles. Such multi‐step reaction, including reduction, nucleation, phase transfer, exchange of surface capping and oxidation are of increasing importance for nanoparticles. Especially, Laux‐type conditions with nitrobenzene as a molecular oxidizing agent of nanoparticles have not been used till now. Particle size, size distribution and chemical composition of the In⁰ and In₂O₃ nanoparticles are analyzed by DLS, SEM, XRD, FT‐IR and HRTEM.     

A reinterpretation of C5-BTBP extraction data, performed in various alcohols

The separation of trivalent actinides from trivalent lanthanides present in used nuclear fuel can be achieved by using solvent extraction and the BTBP class of ligands. This separation is relevant for the advanced reprocessing of the used fuel. The choice of diluents in such BTBP based systems has shown to affect the extraction as well as the separation. Long chained alcohols have previously been investigated as such diluents, showing that the americium extraction is higher into alcohols having shorter chains (hexanol, and heptanol) than in longer chained ones (nonanol and decanol). In this work it is shown that not only the distribution ratio, but also the contact time needed before reaching extraction equilibrium is shorter when using shorter chain length of the alcohol diluent. It is also shown that the rate of extraction can be correlated to the interfacial tension between the diluent and the aqueous phase. A low interfacial tension gives a fast extraction while an extraction system with higher interfacial tension needs a longer time of phase contact in order to reach extraction equilibrium.     

Separation of boundary singularities for holomorphic generators

We prove a theorem on separation of boundary null points for generators of continuous semigroups of holomorphic self-mappings of the unit disk in the complex plane. Our construction demonstrates rather strikingly the particular role of the binary operation ? given by 1/ f ? g = 1/f + 1/g on generators.     

A systematic study of the solid state and solution phase conformational preferences of β-peptides derived from transpentacin

The solid state and solution phase conformational preferences of a homologous series of β-peptides derived from (S,S)-2-aminocyclopentanecarboxylic acid (transpentacin) have been investigated using a variety of spectroscopic and crystallographic techniques. These studies indicate that the hexamer and pentamer persist as a 12-helix in both the solid state and solution phase. Although the conformational traits of a 12-helix are exhibited by oligomers with as few as three residues in the solid state, in solution the trimer exists as an equilibrium of many alternative conformers whilst the tetramer has been shown to predominantly exist in either a 12-helix or a turn-type conformation.     

Conformational Flexibility and Dynamics of Two (1→6)‐Linked Disaccharides Related to an Oligosaccharide Epitope Expressed on Malignant Tumour Cells

The conformational flexibility and dynamics of two (1→6)‐linked disaccharides that are related to the action of the glycosyl transferase GnT‐V have been investigated. NMR NOE and T‐ROE spectroscopy experiments, conformation‐dependent coupling constants and molecular dynamics (MD) simulations were used in the analyses. To facilitate these studies, the compounds were synthesised as α‐d‐ [6‐¹³C]‐Manp‐OMe derivatives, which reduced the ¹H NMR spectral overlap and facilitated the determination of two‐ and three‐bond ¹H,¹H, ¹H,¹³C and ¹³C,¹³C‐coupling constants. The population distribution for the glycosidic ω torsion angle in α‐d‐ Manp‐(1→6)‐α‐d‐ Manp‐OMe for gt/gg/tg was equal to 45:50:5, whereas in α‐d‐ Manp‐OMe it was determined to be 56:36:8. The dynamic model that was generated for β‐d‐ GlcpNAc‐(1→6)‐α‐d‐ Manp‐OMe by MD simulations employing the PARM22/SU01 CHARMM‐based force field was in very good agreement with experimental observations. β‐d‐ GlcpNAc‐(1→6)‐α‐d‐ Manp‐OMe is described by an equilibrium of populated states in which the ? torsion angle has the exo‐anomeric conformation, the ψ torsion angle an extended antiperiplanar conformation and the ω torsion angle a distribution of populations predominantly between the gauche–trans and the gauche–gauche conformational states (i.e., gt/gg/tg) is equal to 60:35:5, respectively. The use of site‐specific ¹³C labelling in these disaccharides leads to increased spectral dispersion, thereby making NMR spectroscopy based conformational analysis possible that otherwise might be difficult to attain.     

Heterylimidazoles

The condensation of heterocyclic aldehydes with aromatic -diketones in the presence of ammonium acetate in acetic acid has given 4,5-diaryl-2-quinolinylimidazoles and 4,5-diaryl-2-(acridin-9-yl) imidazoles. The oxidation of the latter with K₃Fe(CN)₆ in an alkaline medium has given the corresponding biimidazolyls, which possess photochromic and thermochromic properties.For Communication I, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1105–1108, August, 1973.