Asymmetric banana-shaped liquid crystals with two different terminal alkoxy chains

Two series of asymmetric banana-shaped compounds have been synthesized and studied. In the 1,3-phenylene bis[4-(4'-alkoxybenzoyloxy)]benzoate series the lack of symmetry was derived solely from the difference in length of the two terminal alkoxy chains. In the 3,4'-biphenylene bis[4-(4'-alkoxybenzoyloxy)]benzoate series the asymmetric nature originates from the 3,4'-substitution of the central biphenyl group and from the difference in length of the two terminal chains. All the melting points of the asymmetrical compounds in the series with the central phenyl unit are lower than those of the symmetrical compounds. The liquid crystalline B₁ or B₂ phase was retained in all cases. In the series with the central biphenyl unit the compounds with the shortest chain attached to the para-position of the central biphenyl unit have the lowest melting points. A significant lowering of the melting points in comparison with the symmetrically substituted compounds, however, could not be achieved. All the compounds of both series show a layer spacing which is comparable to those of the symmetrically substituted parent compounds. The observed switching behaviour of both the symmetric and asymmetric compounds with a B₂ phase was antiferroelectric.     

A new six-coordinate organotin(IV) complex of OP[NC5H10]3: A comparison with an analogous five-coordinate complex by means of X-ray crystallography,Hirshfeld surface analysis and DFT calculations

A new six-coordinate organotin(IV)-phosphoric triamide complex of OP[NC₅H₁₀]₃ = OP was synthesized ([Cl₂Sn(CH₃)₂(OP)₂], 1) and characterized by X-ray crystallography and spectroscopic methods (FT-IR, UV–Vis, and ¹H/¹³C/³¹P-NMR). The crystal structures of 1 and the analogous previously reported five-coordinate complex [Cl₂Sn(CH₃)₂(OP)] (IZOVIE) were compared on a structural level and by computational means using Hirshfeld surface analysis, density functional theory calculations and the atom in molecule method. The investigation of intermolecular interactions in the crystal structures of the two complexes by the Hirshfeld surface method indicates that in the absence of normal hydrogen bonds, the chlorine-based interactions H?Cl/Cl?H (for 1 and IZOVIE) and Cl?Sn/Sn?Cl (for IZOVIE) play a determinant role in the molecular assemblies. However, the prominent contacts are of H?H type. From calculated electronic parameters such as bond order, Mulliken charge and electron delocalization energy, it was found that the Sn-OP contact has a lower strength in IZOVIE than in 1, suggesting more ionic character of the metal-oxygen contact in five-coordinate complex IZOVIE. Furthermore, we discuss the similarities and differences of the two complexes 1 and IZOVIE derived from the same ligand OP by density functional theory calculations to present an insight into the organotin(IV)-phosphoric triamide coordination chemistry affected by different geometries and coordination numbers.     

Minimal 2-Fold Coverings of E d

Let N(k, d) be the smallest positive integer such that given any finite collection of open halfspaces which k-fold coversE ^d , there exists a subcollection of cardinality less than or equal toN(k,d) which k-fold coversE ^d . A well-known corollary to Helly's theorem proves N(1,d) =d+1. This provides an inductive base from which we show N(k; d) exists for all positive integers k.Our main result is .     

Probing the interaction of HTI-286 with tubulin using a stilbene analogue

HTI-286 is a synthetic analogue of the natural product hemiasterlin. HTI-286 is a potent antitumor agent that induces tubulin oligomerization. To investigate the binding stoichiometry and the binding site during this ligand-induced tubulin association, we synthesized an analogue of HTI-286 containing the chromophore stilbene. Using the distinct absorbance of the stilbene analogue, we determined the amounts of inhibitors bound to different tubulin oligomers by analytical ultracentrifugation. Herein we describe our findings based on these experiments. At the ratio of inhibitor to protein equal to or greater than 1, the stilbene analogue induces oligomerization of tubulin to a ring structure. The binding stoichiometry in the ring is one inhibitor per tubulin monomer (defined as an alpha/beta-heterodimer). At the ratio of inhibitor to protein less than 1, tubulin forms multiple intermediates, with the binding stoichiometry less than one inhibitor per tubulin monomer for all intermediates. The stable complex between the inhibitor and tubulin monomer was not detected under our experimental conditions. The binding site of the stilbene analogue does not overlap with the classic tubulin-binding agent, colchicine.     

Ion-driven ATP pump by self-organized hybrid membrane materials

We report new hybrid organic-inorganic materials, based on macrocyclic receptors 1-3 self-organized in tubular superstructures prepared by sol-gel process. Fourier transform infrared (FTIR) and NMR spectroscopic analyses demonstrate that the self-organization by hydrogen bonding of organogel superstructures of 2 and 3 were preserved in the hybrid materials throughout the sol-gel process. The molecular arrangement of heteroditopic receptors defines a particularly attractive functional transport device for both cation (tubular macrocycles) and anion (sandwich-urea) directional-diffusion transport mechanism in the hybrid membrane material. This system has been employed successfully to design a solid dense membrane, functioning as an ion-powered adenosine triphosphate (ATP(2)(-)) pump, and illustrates how a self-organized hybrid material performs interesting and potentially useful functions.     

A mild,rapid and convenient esterification of half esters of malonic acid

A new method for the esterification of half esters of malonic acid with chloroformates is described. The reaction proceeds $\text{via}$ the mixed anhydride followed by spontaneous decarboxylation.     

Experimental and Theoretical Study of the Reactivity of Gold Nanoparticles Towards Benzimidazole‐2‐ylidene Ligands

The reactivity of benzimidazol‐2‐ylidenes with respect to gold nanoparticles (AuNPs) has been investigated using a combined experimental and computational approach. First, the grafting of benzimidazol‐2‐ylidenes bearing benzyl groups on the nitrogen atoms is described, and comparisons are made with structurally similar N‐heterocyclic carbenes (NHCs) bearing other N‐groups. Similar reactivity was observed for all NHCs, with 1) the erosion of the AuNPs under the effect of the NHC and 2) the formation of bis(NHC) gold complexes. DFT calculations were performed to investigate the modes of grafting of such ligands, to determine adsorption energies, and to rationalize the spectroscopic data. Two types of computational models were developed to describe the grafting onto large or small AuNPs, with either periodic or cluster‐type DFT calculations. Calculations of NMR parameters were performed on some of these models, and discussed in light of the experimental data.     

Complexation and Sensing Behavior of Dansyl-appended Cyclodextrins and Cyclodextrin Dimers with Bile Salts

The dansyl-modified cyclodextrin derivatives 2 and 3 form complexes with the steroidal bile salts. The selectivity of the monomeric derivative 3 is similar to that of native g -cyclodextrin. All binding constants with 3 are lowered compared to g -cyclodextrin because of the competition for the cavity between the steroids and the dansyl moiety. Cholate ( 4a ) and deoxycholate ( 4b ) form weak complexes, the other bile salts ( 4c - e ) are complexed far more strongly. The difference is attributed to the absence of a 12-hydroxy group in the latter steroids. Data for dimer 2 reveal strongly enhanced binding of 4a and 4b and only slightly stronger complexes with the other steroids. Due to the low binding affinity of 3 for 4a and 4b , this receptor could not be used for their detection by fluorescence spectroscopy. Steroids 4c - e showed a decrease in fluorescence intensity. The detection of all steroids 4a - e was possible using 2 . The fluorescence intensity of the dimer increased or decreased, depending on which steroid was added.     

Statistical analysis of data from accelerated ageing tests of PES UF membranes

In this research, membrane life-time was evaluated by means of accelerated ageing experiments. A pressure pulse unit was used to perform the ageing experiments in an accelerated way. An experimental design has been set up and four ageing factors were varied at two levels. The four ageing factors studied were: fouling status of the membrane, cleaning agent concentration, magnitude of the back pulse and number of applied back pulses. The integrity of the membrane modules was evaluated by means of permeability testing, pressure decay tests and bubble tests. Also tensile tests were performed to investigate the mechanical properties of the membrane modules. The collected data was used for an analysis of variance to determine which ageing factors and which combination of ageing factors influence membrane life time. The analysis showed that the fouling status in combination with the number of applied pressure pulses were significant ageing factors. Additional tensile tests confirmed these results.