Twist-Bend Nematic Glasses: The Synthesis and Characterisation of Pyrene-based Nonsymmetric Dimers

A selection of pyrene-based liquid crystal dimers have been prepared, containing either methylene-ether or diether linked spacers of varying length and parity. All the diether linked materials, CBOnO.Py (n=5, 6, 11, 12), exhibit conventional nematic and smectic A phases, with the exception of CBO11O.Py which is exclusively nematic. The methylene-ether linked dimer, CBnO.Py, with an even-membered spacer (n=5) was solely nematogenic, but odd-members (n=6, 8, 10) exhibited both nematic and twist-bend nematic phases. Replacement of the cyanobiphenyl fragment by cyanoterphenyl giving CT6O.Py, gave elevated melting and nematic-isotropic transition temperatures, and SmA and SmC_A phases were observed on cooling the nematic phase. Intermolecular face-to-face associations of the pyrene moieties drive glass formation, and all these materials have a glass transition temperature at or above room temperature. The stability of the glassy twist-bend nematic phase allowed for its study using AFM, and the helical pitch length, P_TB, was measured as 6.3 and 6.7 nm for CB6O.Py and CB8O.Py, respectively. These values are comparable to the shortest pitch of a twist-bend nematic phase measured to date.     

Transamidation of Amides and Amidation of Esters by Selective N–C(O)/O–C(O) Cleavage Mediated by Air- and Moisture-Stable Half-Sandwich Nickel(II)–NHC Complexes

The formation of amide bonds represents one of the most fundamental processes in organic synthesis. Transition-metal-catalyzed activation of acyclic twisted amides has emerged as an increasingly powerful platform in synthesis. Herein, we report the transamidation of N-activated twisted amides by selective N–C(O) cleavage mediated by air- and moisture-stable half-sandwich Ni(II)–NHC (NHC = N-heterocyclic carbenes) complexes. We demonstrate that the readily available cyclopentadienyl complex, [CpNi(IPr)Cl] (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), promotes highly selective transamidation of the N–C(O) bond in twisted N-Boc amides with non-nucleophilic anilines. The reaction provides access to secondary anilides via the non-conventional amide bond-forming pathway. Furthermore, the amidation of activated phenolic and unactivated methyl esters mediated by [CpNi(IPr)Cl] is reported. This study sets the stage for the broad utilization of well-defined, air- and moisture-stable Ni(II)–NHC complexes in catalytic amide bond-forming protocols by unconventional C(acyl)–N and C(acyl)–O bond cleavage reactions.     

Kinetic Behavior of Quaternary Ammonium Hydroxides in Mixed Methane and Carbon Dioxide Hydrates

This study evaluates the kinetic hydrate inhibition (KHI) performance of four quaternary ammonium hydroxides (QAH) on mixed CH₄ + CO₂ hydrate systems. The studied QAHs are; tetraethylammonium hydroxide (TEAOH), tetrabutylammonium hydroxide (TBAOH), tetramethylammonium hydroxide (TMAOH), and tetrapropylammonium hydroxide (TPrAOH). The test was performed in a high-pressure hydrate reactor at temperatures of 274.0 K and 277.0 K, and a concentration of 1 wt.% using the isochoric cooling method. The kinetics results suggest that all the QAHs potentially delayed mixed CH₄ + CO₂ hydrates formation due to their steric hindrance abilities. The presence of QAHs reduced hydrate formation risk than the conventional hydrate inhibitor, PVP, at higher subcooling conditions. The findings indicate that increasing QAHs alkyl chain lengths increase their kinetic hydrate inhibition efficacies due to better surface adsorption abilities. QAHs with longer chain lengths have lesser amounts of solute particles to prevent hydrate formation. The outcomes of this study contribute significantly to current efforts to control gas hydrate formation in offshore petroleum pipelines.     

Effect of organic dye on the performance of dye-sensitized solar cell utilizing TiO2 nanostructure films synthesized via CTAB-assisted liquid phase deposition technique

This work is concerned with the growth of TiO₂ nanostructures as photovoltaic materials of dyesensitized solar cell (DSSC) via phase liquid deposition technique treated with CTAB surfactant. This work investigates the influence of organic dyes, N719, N3 and Z907 as photosensitizer on the photovoltaic parameters of TiO₂ nanostructures dye-sensitized solar cells (DSSCs). It also highlights the effect of the concentration of the best dye, N719 on the performance of the cell. The platinum films as counter electrode of the DSSC were prepared by sputtering platinum pellet on ITO substrate. The redox couple of the electrolyte utilized in the DSSC was iodide/triiodide. The cell sensitized with N719 dye demonstrated the best performance compared with the cell sensitized with another two dyes, N3 and Z907. This is due to N719 dye possess the highest optical absorption in visible region. The cell sensitized with 0.8 mM N719 dye performs the highest short-circuit current density, J _sc and power conversion efficiency, η since it posses the highest absorption in visible region. The DSSC utilizing 0.8 mM N719 dye demonstrated the highest J _sc and η of 6.48 mA cm^?2 and 1.69%, respectively.     

Synthesis and complexation of a ‘mixed’-pyridine-naphthalene homooxacalixarene

A deep-cavity ‘mixed’ octahomotetraoxacalix[2]naphthalene[2]pyridine macrocycle has been synthesised and its single-crystal X-ray structure has been determined. Molecular modeling studies suggested that this macrocycle could be an effective host for guest aromatic diol(s) similar to Wang's methylazacalixpyridines. Binding constants were determined using ¹H NMR chemical shifts changes and comparisons were made between the diols which were tested.     

High Pressure Super-Heated Electrospray Ionization Mass Spectrometry for Sub-Critical Aqueous Solution

The heating of electrospray ion source under atmospheric pressure is limited to the normal boiling point of the solution. The boiling takes place when the vapor pressure of the liquid at a given temperature equals the ambient pressure. By using a high pressure ESI source, which has been developed previously in our laboratory, a stable electrospray ionization of super-heated aqueous solution is performed up to a solution temperature of 180°C. The ion source is pressurized with pure nitrogen to a maximum pressure of 11 atm, and it is coupled to a commercial mass spectrometer via a custom-made ion transport capillary. A booster pump with variable pumping speed is added to the pumping system to regulate the pressure in the first pumping stage at 1?~?1.3 Torr. High pressure mass spectrometry is performed on several peptides and proteins to demonstrate its application in the temperature-controlled thermally induced denaturation and dissociation. Graphical Abstract

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Halide ion effect on the chloroform chemical shift in supramolecular complexation studies with tetra-n-butylammonium salts: a 1H NMR and X-ray study

A ¹H NMR spectroscopic study of tetra-n-butylammonium halides (TBAX: X = Cl^? , Br^?  or I^? ) in CDCl₃ solutions was conducted. Complexation studies of TBAX salts with different host molecules using ¹H NMR in CDCl₃ have previously revealed that the reference residual CHCl₃ proton signal had been shifted downfield. The aim of the study was to quantify the extent of these chemical shift changes with TBAX salts. Linear concentration–chemical shift relationships in each case were obtained from the resulting titration plots obtained from the addition of the TBAX salts alone to CDCl₃. Interactions in the solid state as determined by X-ray crystallography support the solution-state investigations indicating halide ion–chloroform proton interactions.     

Enhanced Optical Properties of FeS2 Using Ni@Cu Doping and Characterization of the Structural and Chemical Compositions for Solar Cell Applications

Crystallography Reports - Transition metals doped FeS2 thin films are promising materials for optoelectronics, energy saving and storage applications. This is a first time report on the...     

Identification of Stingless Bee Honey Adulteration Using Visible-Near Infrared Spectroscopy Combined with Aquaphotomics

Honey is a natural product that is considered globally one of the most widely important foods. Various studies on authenticity detection of honey have been fulfilled using visible and near-infrared (Vis-NIR) spectroscopy techniques. However, there are limited studies on stingless bee honey (SBH) despite the increase of market demand for this food product. The objective of this work was to present the potential of Vis-NIR absorbance spectroscopy for profiling, classifying, and quantifying the adulterated SBH. The SBH sample was mixed with various percentages (10–90%) of adulterants, including distilled water, apple cider vinegar, and high fructose syrup. The results showed that the region at 400–1100 nm that is related to the color and water properties of the samples was effective to discriminate and quantify the adulterated SBH. By applying the principal component analysis (PCA) on adulterants and honey samples, the PCA score plot revealed the classification of the adulterants and adulterated SBHs. A partial least squares regression (PLSR) model was developed to quantify the contamination level in the SBH samples. The general PLSR model with the highest coefficient of determination and lowest root means square error of cross-validation (RCV2=0.96 and RMSECV=5.88 %) was acquired. The aquaphotomics analysis of adulteration in SBH with the three adulterants utilizing the short-wavelength NIR region (800–1100 nm) was presented. The structural changes of SBH due to adulteration were described in terms of the changes in the water molecular matrix, and the aquagrams were used to visualize the results. It was revealed that the integration of NIR spectroscopy with aquaphotomics could be used to detect the water molecular structures in the adulterated SBH.