A 3D supramolecular dimeric assembly based on thiacalix[4]arene by halogen bonding and carbonyl bonding and its dynamic NMR study of conformational preferences

The dimeric assembly of 5,11,17,23-tetrabromo-25,26,27,28-tetrahydroxy thiacalix[4]arene (2) was constructed with several interesting noncovalent interactions such as halogen bonding, sulfur···sulfur (S···S), C=O···π, and hydrogen bonding which were also supported by DFT calculations. In addition, we studied the conformational preferences of 2 using variable temperature NMR experiments. The results revealed that the compound exists in various conformations in a solution state and in a partial cone conformation in a solid state.     

A computational study of cation-π interactions in polycyclic systems: exploring the dependence on the curvature and electronic factors

Density functional theory (B3LYP) calculations with double and triple-ζ quality basis sets were performed on the Li⁺ and Na⁺ π-complexes of corannulene 2, sumanene 3CH₂, heterosumanenes 3X, triphenylene 4 and heterotrindenes 5X. The metal ions bind to both convex and concave faces of buckybowls, with a consistent preference to bind to the convex surface by about 1-4 kcal/mol. The metal ion complexation with the π-framework of the central six-membered ring span wider range compared to benzene, indicating the control of size, curvature and electronic perturbations over the strength of cation-π interactions. Computations show that the bowl-to-bowl inversion barriers are only slightly altered upon metal complexation, indicating the continuity of bowl-to-bowl inversion despite metal complexation. We have calculated the binding energies of model systems, triphenylene (4) and heterotrindenes (5X), which indicate that the interaction energies are controlled by electronic factors. While the inversion barrier is dependent mainly on the size of the heteroatom, the extent of binding is independent of the size of the atom or the bowl depth.     

Growth of Fe on Ge(1 1 1) at room temperature studied by X-ray photoelectron diffraction

The growth of ultrathin Fe films of various coverages on Ge(1 1 1) at room temperature using molecular beam epitaxy (MBE) was studied via X-ray photoelectron diffraction (XPD or XPED) together with low energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS). All experimentally observed XPD patterns suggested local order structures of the Fe layers for all thicknesses studied. The short-range order of the resulting structures was found to be enhanced for thinner layers whereas the long-range order was gradually lost with increasing Fe thicknesses. At a very low coverage of 0.8 Å Fe and Ge tend to react to the partly ordered structure in which Fe atoms were located in local environments similar to those for higher Fe coverages. Comparison of theoretical and experimental XPD patterns, along with XPS results, showed that intermixing between Fe and Ge occurred during the pseudomorphic growth with a stacking fault near the interface for all Fe coverages under study. Nevertheless, small percentage of domains without the stacking fault was also found to coexist with those with the stacking fault by performing a quantitative analysis of a reliability factor R of the Fe2p pattern for 5.4 Å. The orientation changes of the Ge2p and Ge3d XPD patterns with Fe thickness were unambiguously explained in terms of their different dependencies on the overlayer thickness due to the different inelastic mean free path lengths used in the simulations. Also, Fe got increasingly enriched in the grown layers with increased Fe coverage. The resulting structures and intermixing are discussed in detail.     

The effect of sample salt additives on capillary electrophoresis analysis of intact proteins using surface modified capillaries

The effect of adding alkali salts to protein samples for capillary electrophoretic (CE) analysis of intact proteins was studied. A high degree of peak stacking, even for large proteins, was found to occur when alkali salts were added to the sample. The addition of salt to the protein sample promotes a strong improvement in the peak efficiency of individual proteins giving up to 2.1 × 10⁶ apparent plates/m. The concentration of salt required in the sample to reach optimal peak efficiency show dependency on both the molecular weight and molar concentration of the protein. However, adding salt will, at a sufficiently high concentration, cause a mixture of proteins to co-migrate to one very sharp peak. The observed sample stacking effect was obtained with a number of different surface modified silica capillaries indicating a general phenomenon and not surface coating specific.     

Nucleophilic substitution reaction at an sp carbon of vinyl halides with an intramolecular thiol moiety: synthesis of thio-heterocycles

This article presents a full account of intramolecular vinylic substitution reactions of bromoalkenes having an acetylthio moiety, which give sulfur-containing heterocycles such as dihydrothiophene, tetrahydrothiopyran, and 2-alkylidenethietane derivatives. The reaction pathways of the substitution reactions were investigated by theoretical and experimental studies.     

New lacunar-type and pendant groups containing derivatives of β-unsubstituted dibenzotetraaza[14]annulenes—syntheses and crystal structures

Three new lacunar-type derivatives of β-unsubstituted dibenzotetraaza[14]annulene have been synthesized along with a range of their open-chain pendant group containing counterparts. The crystal structures of two representative products have been determined and the noncovalent interactions explored. A number of C-H?π and π?π interactions involving aliphatic chains and aromatic regions of the macrocycle have been evidenced. The relative ease and high yield of lacunization are suggested to be largely due to self-assembly processes, driven by favorable noncovalent interactions between reacting units.     

One-dimensional porphyrin H-aggregates induced by solvent polarity

A series of new porphyrin derivatives possessing the side arms of alkyl-substituted thiophene oligomer were synthesized. The effects of solvent polarity on the formation of supramolecular assembly have been studied by UV-vis absorption, fluorescence emission, and TEM measurement. The linear-shape porphyrin derivatives bearing two thiophene pentamers at meso-position showed the significant spectral changes in both blue-shift and band broadening of Soret bands which indicate the formation of a relatively larger porphyrin H-aggregate that occurred in nonpolar solvent such as n-hexane.     

Two compounds constructed from Strandberg-type polyoxoanions,metals and organic ligands

Two new hybrid compounds, [Cu(1)(phen)(H₂O)][Cu(2)(phen)(H₂O)]([Cu(3)]_0.25(H₂O)][P₂Mo₅O₂₃]·3.75H₂O (1) and [Cu(en)₂]_1.5[P₂Mo₅O₂₃]₂·(enH₂)₃·2H₂O (2) (phen = 1,10-phenanthroline, en = ethylenediamine), have been hydrothermally synthesized and characterized by IR, UV–Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), powder XRD analyses, TG analyses, cyclic voltammogram analyses, elemental analyses, and single crystal X-ray diffraction analyses. Single crystal X-ray diffraction analyses reveal that the two compounds have a 1-D chain structure formed by Strandberg-type POMs and TMCs with –A–B–C–B–A–B–C–B– linking mode, then further extend into a 2-D layer structure through π?π or hydrogen bond interactions.     

Damage resistance of carbon fibre reinforced epoxy laminates subjected to low velocity impact: Effects of laminate thickness and ply-stacking sequence

A major concern affecting the efficient use of composite laminates is the effect of low velocity impact damage on the structural integrity [1–3]. The aim of this study is to characterize and assess the effect of laminate thickness, ply-stacking sequence and scaling technique on the damage resistance of CFRP laminates subjected to low velocity impact. Drop-weight impact tests are carried out to determine impact response. Ultrasonic C-scanning and cross-sectional micrographs are examined to assess failure mechanisms of the different configurations.It is observed that damage resistance decreases as impact energy increases. In addition, thicker laminates show lower absorbed energy but, conversely, a more extensive delamination due to higher bending stiffness. Thinner laminates show higher failure depth. Furthermore, quasi-isotropic laminates show better performance in terms of damage resistance. Finally, the results obtained demonstrate that introducing ply clustering had a negative effect on the damage resistance and on the delamination area.     

Conformation of aromatic rings in isolable atropisomers of 2-arylindoline derivatives and kinetic evidences for π-π interaction

The equilibrium constants [K=anti/syn] of a pair of atropisomers due to restricted rotation about Csp³-Csp² bond for [2-(2-hydroxynaphthalen-1-yl)-3,3-dimethylindolin-1-yl](4-substituted phenyl)methanone were determined in some solvents. The presence of the effective π-π interaction was demonstrated by the correlation between the equilibrium constants (K) and the substituent effect of the phenyl groups (σ_p), suggesting that the ‘neutral-type’ interaction is operative.