Influence of the alkyl chain length of some mesogenic molecules on their Langmuir film formation ability

Langmuir films of members of two homologous series, the 4‐n‐alkyl‐4′‐cyanobiphenyls (nCB) for n = 2–14 and trans‐4‐n‐alkyl(4′‐cyanophenyl)cyclohexanes (PCHn) for n = 2–12, have been studied by recording surface pressure/area isotherms and by Brewster angle microscopy. It has been found that the compounds with very short chains (n3) and very long chains (n>12 for nCB, n>10 for PCHn) are unable to form compressible monolayers at the air–water interface. Other members of both series can form stable Langmuir films, but both their rigidity and stability as well as the molecular packing vary with the alkyl chain length. The isotherms and BAM images imply that the organization of the liquid crystal molecules in the films is to some extent correlated with their ability to form corresponding mesophase in the bulk: nematogenic compounds tend to form rounded droplet‐like domains, whereas smectogenic compounds tend to form flat domains.     

Dynamics in ferro- and antiferroelectric phases of a liquid crystal with fluorinated molecules as studied by dielectric spectroscopy

For 1-[3-fluoro-4-(1-methylheptyloxycarbonyl)phenyl]-2-[4-2,2,3,3,4,4,4-heptafluorobutoxybutoxy)biphenyl-4-yl]ethane (1F7), built of chiral molecules, results of dielectric measurements of liquid-crystalline and solid phases are presented. Rich polymorphism of liquid-crystalline (SmC*, SmC*_A and SmI*_A) phases as well as of solid (Cr1 and Cr2) phases were observed down to –130°C. At a frequency range from 0.1 Hz to 3 MHz, the relaxation processes were detected in ferroelectric SmC*, antiferroelectric SmC*_A and highly ordered SmI*_A smectic phases. The mechanism of complex dynamics (moleculear and collective) was identified with the help of the bias field. Vitrification of conformationally disordered crystal phase Cr2 was found in accordance with calorimetric observations.     

Development of a High Performance Liquid Chromatography with Diode Array Detector (HPLC-DAD) Method for Determination of Biogenic Amines in Ripened Cheeses

Biogenic amines (BAs) are organic, basic nitrogenous compounds formed during the decarboxylation of amino acids. A method for the determination of eight biogenic amines (tryptamine, 2-phenyletylamine, putrescine, cadaverine, histamine, tyramine, spermidine, spermine) in ripened cheeses was developed and validated. Cheese samples with the addition of internal standards were extracted with 0.2 M perchloric acid and pre-column derivatized with dansyl chloride at 60 °C for 15 min, purified with toluene and dried under a stream of nitrogen. The samples were analyzed using high performance liquid chromatography with diode array detector (HPLC-DAD). The method was validated with the BAs at three concentration levels: 50, 100, and 200 mg/kg, respectively. The obtained values of correlation coefficient (R²) ranged at 0.9997–0.9998 for all of compounds. The limits of detection (LOD) and quantification (LOQ) were in ranges 1.53–1.88 and 5.13–6.28 mg/kg, respectively. The recovery for all of biogenic amines ranged from 70 to 120% and the precision (RSDr) value were <20%. The validated method was applied to analysis of 35 real ripened cheese samples purchased in Poland.     

Robust control of microdomain orientation in thin films of block copolymers by zone casting

Block copolymers with chemically immiscible segments exhibit a variety of microphase-separated nanostructures on the scale of 10-100 nm. Controlling the orientation of these microphase separated nanostructures is vital in many applications such as lithography, membranes, data storage, and so forth. Typical strategies involve the use of external fields or patterned substrates. Here, we report a robust zone casting technique to achieve highly ordered thin films of block copolymers on centimeter-scale substrates. The robustness of this technique is its powerful control on diverse morphologies and exceptional tolerance on versatility of block copolymer chemistry as well as allowance of a wide spectrum of substrates. We demonstrate that perpendicular orientations with respect to the surface are achieved for block copolymers with both lamellar and cylindrical morphologies by controlling solution casting rate, temperatures, and block copolymer chemical structures. Thin films of both noncrystalline and crystalline block copolymers exhibit excellent orientational order and lateral order. However, the lateral order in the thin films of crystalline block copolymers shows dependence on casting temperature and melting temperature of the crystalline segment. Remarkably, all the ordering is independent of the substrates on which the block copolymer films are cast.     

Enhanced Water Splitting at Thin Film Tungsten Trioxide Photoanodes Bearing Plasmonic Gold–Polyoxometalate Particles

Tungsten trioxide (WO₃) is one of a few stable semiconductor materials liable to produce solar fuel by photoelectrochemical water splitting. To enhance its visible light conversion efficiency, we incorporated plasmonic gold nanoparticles (Au NPs) derivatized with polyoxometalate (H₃PMo₁₂O₄₀) species into WO₃. The combined plasmonic and catalytic effect of Au NPs anchored to the WO₃ surface resulted in a large increase of water photooxidation currents. Shielding the Au NPs with polyoxometalates appears to be an effective means to avoid formation of recombination centers at the photoanode surface.     

Thio Analogs of Pyrimidine Bases: Synthesis And Spectroscopic Study of New Potentially Biologically Active Disulfides of N,O-(N,N- or O,O-)-Di- and N,N,O-Tri-(o-, m-, and p-)bromobenzyl-2-thiouracils

Nine new disulfides of N,O-(N,N- or O,O-)-di- and N,N,O-tri-(o-, m- and p-)bromobenzyl-2-thiouracils have been prepared. The structures of these compounds were confirmed by spectroscopic (FT-IR, UV-Vis, ¹H NMR) and elemental analyses. Estimation of pharmacotherapeutic potential has been made for synthesized compounds on the basis of Prediction of Activity Spectra for Substances (PASS).     

Enthalpy of fusion of poly(3‐hexylthiophene) by differential scanning calorimetry

The enthalpy of fusion for a perfect, infinite poly(3‐hexylthiophene) (P3HT) crystal () must be known to evaluate the absolute crystallinity of P3HT. This value, however, is still ambiguous as different values have been reported using various experimental techniques. Here, we extrapolate the enthalpy of fusion for extended chain crystals of oligomeric P3HT to infinite molecular weight and obtain a value of 42.9 ± 2 J/g employing differential scanning calorimetry with a correction based on grazing incidence small angle X‐ray scattering data. Also, we define the onset of chain folding within P3HT crystallites at a chain length of 5 Kuhn segments. Knowledge of allows calculation of P3HT percent crystallinity in thin films for applications such as organic field effect transistors and solar cells. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1469–1475     

Crystal and molecular structure of nitrophenyl 2,3,4-tri-O-acetyl-β-d-xylopyranosides

Comprehensive structural analyses were performed for o-, m-, and p-nitrophenyl 2,3,4-tri-O-acetyl-β-d-xylopyranosides. Single-crystal X-ray diffraction data were collected and revealed that meta isomer undergoes temperature-dependent polymorph transition (crystal structures of two polymorphs were obtained). This transition was verified by differential scanning calorimetry. The number of molecules in the independent part of the crystal unit cells of the compounds under investigation was in agreement with the number of resonances in solid-state ¹³C and ¹⁵N NMR spectra. The o- and p-nitrophenyl 2,3,4-tri-O-acetyl-β-d-xylopyranosides exist as single polymorph at room temperature, as confirmed by powder X-ray diffraction measurements.