Colloidal Silica Rods: Material Properties and Fluorescent Labeling

In this paper, the characterization and fluorescent labeling of silica rods are reported. These rods are synthesized following a recently reported method. Material properties of the silica rods measured with NMR, elemental analysis, TGA, and porosimetry are compared with those of well‐established Stöber silica spheres. Additionally, silica rods are made suitable for quantitative real‐space studies by confocal microscopy. Several methods of fluorescent labeling to prepare rods with different fluorescent patterning, ranging from uniform fluorescence levels to gradients from one rod‐end to the other, and even patterns of several colors are presented and discussed.     

Reversible Transformation between Cubane and Stairstep Cu4I4 Clusters Using Heat or Solvent Vapor

The controlled self‐assembly of CuI and an asymmetric ligand with mixed N/S donors, 2‐(tert‐butylthio)‐N‐(pyridin‐3‐yl)acetamide ( L ), afforded three Cu^I coordination polymers (CPs), [Cu₄I₄ L ₂(MeCN)₂]_n ( 1 ), [Cu₄I₄ L ₂]_n ( 2 ), and {[Cu₄I₄ L ₂] ? MeOH}_n ( 3 ). X‐ray analyses showed that CPs 1 – 3 are supramolecular isomers with 1, 2, and 3D structures, respectively. CP 1 adopts a stairstep Cu₄I₄ cluster, whereas CPs 2 and 3 are composed of cubane‐like Cu₄I₄ clusters. Crystal‐to‐crystal transformations of 1 to 2 and 3 showed reversible transformations between different Cu₄I₄ clusters using heat or solvent (acetonitrile or methanol) vapor. CP 2 was reversibly transformed to 3 by the addition of methanol and heat. Therefore, the transformations between supramolecular isomers 1 , 2 , and 3 are completely reversible.     

Structural and spectroscopic studies of LaPO4:Ce/Tb@LaPO4@SiO2 nanorods: Synthesis and role of surface coating

Highly fluorescent LaPO₄:Ce/Tb@LaPO₄@SiO₂ (core/shell/Si) nanorods(NRs) were fabricated with an average length 100 nm by co-precipitation process at low temperature. X-ray diffraction (XRD), Transmission electron microscopy (TEM), energy dispersive X-ray analysis, Fourier transform infrared, optical absorption and photoluminescence spectral techniques were applied to investigate the crystal structure, phase purity, morphology, surface chemistry and optical properties of the as-prepared samples. XRD results confirmed the formation of highly crystalline with single phase, monoclinic type structure. TEM image illustrates the poly-dispersed, narrow size distributed, irregular size rod-shaped nanostructures, with mean diameters of 20 nm and average lengths up to 140 nm. FTIR spectral analysis confirmed the silica surface modification. The comparative emission spectral study shows highest luminescence intensity of core/shell NRs, due to a reduction in nonradiative transition rate. The emission intensity enhancement proves that growing of an inert LaPO₄ layer on the surface of luminescent core-NRs was an effective way to suppress surface related quenching mechanism. These well crystalline, highly aqueous soluble along with extraordinary colloidal stability core/shell/Si NRs were extremely suitable material in fluorescent bio-labeling applications.     

Coconut shell particles reinforced cardanol–formaldehyde resole resin biocomposites: Effect of treatment on thermal properties

The current work focuses on the thermal behavior of biocomposites based on cardanol formaldehyde resin (CFR) reinforced with untreated and treated coconut shell particles (CSP). CFR has been synthesized by condensing cardanol with formaldehyde in the presence of NH₄OH catalyst (ratio of 1:1.6:0.36). Fabricating biocomposites is performed by compression moulding technique. The CSP with particle size of 50?µm is used in various proportions: 30 and 40?wt%. The CSP is immersed in 5?wt% NaOH solution for 5?h. Fourier transform infrared spectroscopy is used to characterize chemical formation of the new biocomposites. Thermogravimetric analysis and differential thermal analysis are applied to measure the thermal stability of composites. The thermal stability exhibits a slight decrease with particles loading from 30 to 40?wt% against neat CFR. This work gives a path for the possibility of CSP usage in low-value products in composite manufacturing.     

Synthesis,structural analysis,spectral investigations,and DFT calculations of 1‐(3‐amino‐4‐thia‐1,2‐diazaspiro[4.11]hexadec‐2‐en‐1‐yl)ethan‐1‐one

1‐(3‐amino‐4‐thia‐1,2‐diazaspiro[4.11]hexadec‐2‐en‐1‐yl)ethan‐1‐one was synthesized and experimentally characterized by using FT‐IR, ¹H NMR, ¹³C NMR, and UV–Vis spectroscopy. The structure of the compound was confirmed by single‐crystal X‐ray diffraction. In the crystal structure, the molecules are linked by pairs of N‐H⋯N hydrogen bonds, forming centrosymmetric dimers with the graph‐set motif. The water molecule also plays an important role in the stabilization of the crystal structure, bridging the dimers to form a two‐dimensional supramolecular network. The molecular geometry, frontier molecular orbitals, vibrational frequencies, electronic properties, and molecular electrostatic potential were calculated using density functional theory (DFT) with the B3LYP/6‐311G(d,p) basis set. Geometric parameters, vibrational assignments, and electronic properties such as calculated energies, excitation energies, and oscillator strengths were compared with the experimental data, and it was seen that the theoretical results support the experimental parameters.     

Mechanism of nucleophilic fluorination promoted by bis‐tert‐alcohol‐functionalized crown‐6‐calix[4]arene

Theoretical calculations were performed to elucidate the ability of the recently reported bis‐tert‐alcohol‐functionalized crown‐6‐calix[4]arene (BACCA) molecule to promote nucleophilic fluorination of alkyl mesylates with cesium fluoride reagent. It was found that a similar structure, named BACCAt, can separate the cesium fluoride ion pair in tert‐butanol solution. This separation has a free energy cost, even considering the double hydrogen bonds with the fluoride ion. The solvent has an important effect on the stabilization of this complex, due to interaction with the high dipole moment of the separated ion pair. The observed rate acceleration effect involves a structure with double hydrogen bonds between the BACCAt and the centers of negative charges of the S_N2 transition state. The predicted free energy barrier of 27.3 kcal mol⁻¹ is in excellent agreement with the estimated experimental value of 26.2 kcal mol⁻¹.     

Formation of Supramolecular Nanotubes by Self‐assembly of a Phosphate‐linked Dimeric Anthracene in Water

The assembly of supramolecular polymers from a phosphodiester‐linked dimeric anthracene is described. AFM and TEM imaging reveals that the supramolecular polymers self‐assemble into nanotubes in water. Subsequent photodimerization experiments indicate that the supramolecular polymerization occurs via end‐to‐end stacking rather than an interdigitation arrangement of the building blocks.     

Supramolecular arrangement and photophysical properties of a dinuclear cyanophenylboronic acid ester

Boronic esters are useful building blocks for crystal engineering and the generation of supramolecular architectures, including macrocycles, cages and polymers (one‐, two‐ and three‐dimensional), with potential utility in diverse fields such as separation, storage and luminescent materials. The novel dinuclear cyanophenylboronic ester described herein, namely 4,4′‐(2,4,8,10‐tetraoxa‐3,9‐diboraspiro[5.5]undecane‐3,9‐diyl)dibenzonitrile, C₁₉H₁₆B₂N₂O₄, was prepared by condensation of 4‐cyanophenylboronic acid and pentaerythritol and fully characterized by elemental analysis, IR and NMR (¹H and ¹¹B) spectroscopy, single‐crystal X‐ray diffraction analysis and TG‐DSC (thermogravimetry–differential scanning calorimetry) studies. In addition, the photophysical properties were examined in solution and in the solid state by UV–Vis and fluorescence spectroscopies. Density functional theory (DFT) calculations with ethanol as solvent reproduced reasonably well the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) of the title compound. Hirshfeld surface and fingerprint plot analyses are presented to illustrate the supramolecular connectivity in the solid state.     

Eight Schiff bases derived from various salicylaldehydes: phenol–imine and keto–amine forms,conformational disorder,and supramolecular assembly in one and two dimensions

Structures are reported for eight Schiff bases derived from various salicylaldehydes: five are newly synthesized and re‐investigations are reported for three previously reported structures, leading, in each case, to some revision of previous conclusions. In (E)‐N‐(3,4‐dimethylisoxazol‐5‐yl)‐4‐[(2‐hydroxybenzylidene)amino]benzenesulfonamide, C₁₈H₁₇N₃O₄S, (I), and (E)‐4‐[(5‐bromo‐2‐hydroxy‐3‐methoxybenzylidene)amino]‐N‐(3,4‐dimethylisoxazol‐5‐yl)benzenesulfonamide. C₁₉H₁₈BrN₃O₅S, (II), the isoxazole rings adopt different orientations relative to the rest of the molecules, despite the additional substituents in (II) being in the aryl ring remote from the isoxazole unit. The molecules of both (E)‐4‐bromo‐2‐[(2‐hydroxyphenylimino)methyl]‐6‐methoxyphenol, C₁₄H₁₂BrNO₃, (III), and (E)‐4‐bromo‐2‐methoxy‐6‐[(2‐methoxyphenylimino)methyl]phenol, C₁₅H₁₄BrNO₃, (IV), are both effectively planar; while (III) adopts the phenol–imine constitution, (IV) adopts the keto–amine constitution. (E)‐2‐Methoxy‐6‐[(2‐methoxyphenylimino)methyl]phenol, C₁₅H₁₅NO₃, (V), which was determined previously using powder X‐ray data assuming the phenol–imine constitution, has now been refined from single‐crystal X‐ray data, confirming the phenol–imine constitution. In (E)‐3‐benzoyl‐2‐[(5‐fluoro‐2‐hydroxybenzylidene)amino]‐4,5,6,7‐tetrahydrobenzo[b]thiophene, C₂₂H₁₈FNO₂S, (VI), the fused carbocyclic ring exhibits conformational disorder; both disorder components, having populations of 0.705 (4) and 0.295 (4), adopt half‐chair conformations. The isostructural (E)‐3‐benzoyl‐2‐[(2‐hydroxybenzylidene)amino)]‐4,5,6,7‐tetrahydrobenzo[b]thiophene, C₂₂H₁₉NO₂S, (VII), which was originally reported as having a fully ordered structure [Kaur et al. (2014). Acta Cryst. E 70 , o476–o477], has been rerefined using the original data set and found to exhibit the same type of disorder as found in (VI), with disordered populations having occupancies of 0.851 (3) and 0.149 (3). The triclinic polymorph of (E)‐[(2‐hydroxyphenylimino)methyl]phenol, C₁₃H₁₁NO₂, (VIII), which crystallizes with Z′ = 2 in the space group P, has been described variously as occurring as the keto–amine tautomer [Maciejewska et al. (1999). J. Phys. Org. Chem. 12 , 875–880] and as the phenol–imine tautomer [Tunç et al. (2009). J. Chem. Crystallogr. 39 , 672–676]. Rerefinement of this structure using one of the original data sets shows that both of the independent molecules exist in the keto–amine form. In the structures of compounds (I), (VI), (VII) and (VIII), hydrogen bonds generate simple chains, while a chain of rings is formed in (V). Sheets are formed by hydrogen bonds in both (II) and (III), while in (IV), the sheet structure is built from aromatic π–π stacking interactions.     

Controlling Dual Molecular Pumps Electrochemically

Artificial molecular machines can be operated using either physical or chemical inputs. Light‐powered motors display clean and autonomous operations, whereas chemically driven machines generate waste products and are intermittent in their motions. Herein, we show that controlled changes in applied electrochemical potentials can drive the operation of artificial molecular pumps in a semi‐autonomous manner—that is, without the need for consecutive additions of chemical fuel(s). The electroanalytical approach described in this Communication promotes the assembly of cyclobis(paraquat‐p‐phenylene) rings along a positively charged oligomeric chain, providing easy access to the formation of multiple mechanical bonds by means of a controlled supply of electricity.