Dielectric and electro-optical response of a room temperature tri-component antiferroelectric mixture

Frequency- and temperature-dependent dielectric and switching parameters of a room temperature tri-component antiferroelectric liquid crystal mixture W-287 have been determined. Dielectric, optical texture and thermodynamic studies show wide room temperature range antiferroelectric SmC*_a (?91.1°C to <–25°C) phase in addition to high temperature paraelectric SmA* (?2.6°C) and ferroelectric SmC* (?4.4°C) phases. The dielectric studies carried out in the frequency range of 1–35 MHz under planar anchoring condition of the molecules show five different relaxation modes appearing in the SmA*, SmC* and SmC*_a phases. Using Curie–Weiss law fit, ferroelectric SmC* to paraelectric SmA* transition temperature has been found to be 91.8°C. The dielectric response of SmC*_a phase exhibits unusually three relaxation modes due to collective as well as individual molecular processes in addition to phason mode in the SmC* phase and amplitudon mode in the SmA* phase. Spontaneous polarisation, switching time and rotational viscosity have also been determined. The maximum value of P_S is ?300 nC/cm², whereas viscosity is moderate. Switching time is of the order of few milli seconds.     

Tunable two-component saccharide-based gels: The effect of the co-operation of two glucofuranose-based compounds having different gelating abilities

Addition of 1,2-O-(ethane-1,2-diyl)-α-d-glucofuranose, which is originally a poor organogelator, can support the gelating abilities of good glucofuranose-based organogelators. The properties of such two-component gels can be tuned by changing the proportion of the saccharides. The saccharide's ability to form two-component gels can be explained on the basis of its crystal structure, particularly, the way in which sugar molecules stack (or not) into hydrogen bond-based chains and the architecture of these chains. The thermal stability of the obtained two-component gels was characterised by measuring its T _gel temperature. SEM and XRD techniques were used to characterise the xerogels.

Addition of poor gelator increases the thermal stability of the gel formed by good gelator     

Supramolecular synthons and pattern recognition in adenine amides – synthesis,structures and thermal properties

An effective method for the synthesis of novel adenine amides was developed and successfully implemented, leading to 4-propyloxy-N-(9H-purin-6-yl)benzamide (1) and 4-dodecyloxy-N-(9H-purin-6-yl)benzamide (2). The compounds were fully characterised by means of spectroscopic (¹H NMR, ¹³C NMR, FT-IR) and thermal (TG, DSC) analysis. The crystallographic analysis revealed that the formation of supramolecular chains relies on hydrogen bonding between amide functionalities. All supramolecular synthons found in the crystal structure of 1 were confirmed with the temperature-dependent IR method. The temperature-dependent IR method is useful in determining supramolecular interactions for compound 2, for which the crystal structure could not be obtained. A detailed analysis of temperature-dependent FT-IR spectra was used for the first time to identify the hydrogen bonds that exist in the solid state of our compounds; it can therefore be considered a promising method for the pattern recognition of hydrogen bonding in supramolecular chemistry.     

β-( N -Acylamino)vinylphosphonium Salts--Synthesis and Properties

A reaction of g -carbonyl phosphorus ylides with imidoyl halides gives hitherto unknown g -( N -acylamino)vinylphosphonium salts. The same product can be obtained using the N-monosubtituted amide/Ph 3 PBr 2 /Et 3 N system instead of imidoyl halide. The key step of the reaction probably involves an intramolecular [1,3] O-to-N migration of the vinyl group, converting the primary O -imidoylation product into g -( N -acylamino)vinylphosphonium salt.     

REACTION OF DIPHOSPHORYL DISELENIDES WITH DIALKYLTRIMETHYLSILYL PHOSPHITES. A NEW ROUTE TO SYMMETRICAL MONOSELENOPYROPHOSPHATES

Abstract

A novel efficient synthesis of sym-monoselenopyrophosphates 3 based on the reaction of diphosphoryl diselenides 1 with dialkyltrimethylsilyl phosphites 2 is described.     

Applicability of Fraser–Suzuki function in kinetic analysis of complex crystallization processes

A modified peak-deconvolution procedure for complex crystallization processes was introduced. The method is based on the constrained curve-fitting technique using the Fraser–Suzuki (FS) function, where the FS asymmetry parameter a ₃ correlates with the value of the Johnson–Mehl–Avrami (JMA) kinetic parameter m. The correlation was verified for an extensive number of theoretically simulated JMA curves; in addition, the dependencies of the a ₃ parameter on other kinetic variables (E, A, q ⁺) were quantified. The suggested deconvolution procedure was tested on two glassy systems with different overlay degree of the involved overlapping surface and bulk crystallization processes. In both cases, the kinetic analysis of deconvoluted data provided reasonable, consistent and accurate results. However, certain level of knowledge and experience was needed in order to correctly recognize and consequently account for all deviations from the theoretical behavior caused by thermal gradients or imperfections of the data acquisition process. As the input data for the fitting procedure can be in any form equivalent to the dα/dT temperature dependence, the method seems to be highly universal and may be applied to data obtained by various TA techniques.     

Charge‐Assisted Halogen Bonding: Donor–Acceptor Complexes with Variable Ionicity

Charge‐assisted halogen bonding is unambiguously revealed from structural and electronic investigations of a series of isostructural charge‐transfer complexes derived from iodinated tetrathiafulvalene and tetracyanoquinodimethane derivatives, (EDT‐TTFI₂)₂(TCNQF_n), n=0–2, which exhibit variable degrees of ionicity. The iodinated tetrathiafulvalene derivative, EDT‐TTFI₂, associates with tetracyanoquinodimethane (TCNQ) and its derivatives of increasing reduction potential (TCNQF, TCNQF₂) through highly directional C? I???N≡C halogen‐bond interactions. With the less oxidizing TCNQ acceptor, a neutral and insulating charge‐transfer complex is isolated whereas with the more oxidizing TCNQF₂ acceptor, an ionic, highly conducting charge‐transfer salt is found, both of 2:1 stoichiometry and isostructural with the intermediate TCNQF complex, in which a neutral–ionic conversion takes place upon cooling. A correlation between the degree of charge transfer and the C? I???N≡C halogen‐bond strength is established from the comparison of the structures of the three isostructural complexes at temperatures from 300 to 20 K, thus demonstrating the importance of electrostatics in the halogen‐bonding interaction. The neutral–ionic conversion in (EDT‐TTFI₂)₂(TCNQF) is further investigated through the temperature dependence of its magnetic susceptibility and the stretching modes of the C≡N groups.     

Effect of hydrothermal treatment on the structure of an aluminosilicate polymer

The effect of hydrothermal treatment on the structure of an aluminosilicate polymer prepared by a polycondensation reaction between silicate and hydroxoaluminate in alkaline aqueous solution was studied. The structural changes were investigated using X-ray diffraction analysis, Fourier-transform infrared spectroscopy, scanning electron microscopy imaging and thermogravimetric analysis. The results indicated that the amorphous aluminosilicate polymer transformed into a crystalline product during the hydrothermal treatment at 145°C. The crystalline phase was identified as a mineral of the zeolite group, most likely phillipsite. This transformation required an alkaline environment during the hydrothermal treatment.      

Magnetic bead-based hybridization assay for electrochemical detection of microRNA

Aberrant expression of microRNAs (miRNAs), short non-coding RNA molecules regulating gene expression, is often found in tumor cells, making the miRNAs suitable candidates as cancer biomarkers. Electrochemistry is an interesting alternative to current standard methods of miRNA detection by offering cheaper instrumentation and faster assays times. In this paper, we labeled miRNA in a quick, simple, two-step procedure with electroactive complex of osmium(VI) and 2,2′-bipyridine, Os(VI)bipy, which specifically binds to the ribose at the 3′-end of the miRNA, and hybridized such labeled miRNA with biotinylated capture probe attached to the streptavidin magnetic beads. Labeled miRNA was then detected at hanging mercury drop electrode at femtomole level due to an electrocatalytic nature of the peak from the Os(VI)bipy label. We obtained good selectivity of the assay using elevated hybridization temperatures for better discrimination of perfect duplex from single and double mismatches. After optimization of the protocol, we demonstrated feasibility of our assay by detecting target miRNA in real total RNA samples isolated from human cancer cells.     

Determination of Acrylamide and Acrolein in Smoke from Tobacco and E-Cigarettes

Acrylamide and acrolein are two short-chained hazardous compounds with neurotoxic, carcinogenic, and mutagenic effects. The aim of this paper is to describe a fast and simple procedure for simultaneous determination of both acrylamide and acrolein under standard conditions, suggest a suitable calibration protocol for custom analysis, and demonstrate its applicability to the analysis of gaseous products from, e.g., cigarettes, cigars, or electronic cigarettes. A gas chromatography–mass spectrometry (GC–MS) method was developed to quantify acrylamide and acrolein in smoke vapor from electronic cigarettes, tobacco cigarettes, and cigars. Nonionic and highly polar molecules with a low boiling point and molecular mass need a suitable derivatization method to achieve appropriate retention and selectivity on commonly used relatively nonpolar stationary phases and to enhance the molecular mass for easy MS detection. The derivatization of acrylamide and acrolein was carried out by a bromination method with elemental bromine. The dibromo derivatives were extracted into an organic solvent and following a dehydrobromination procedure the samples were injected into the GC–MS system. Important experimental parameters were varied, after which the bromination time was defined as 30 min, and the injector temperature and the starting temperature of gradient were set at 280 and 50 °C respectively. Acrolein was found in all tested samples, while acrylamide was detected only in smoke from normal tobacco. Possible mechanisms for the formation of these unsaturated compounds in the samples are discussed. After its validation the newly developed method was successfully and reliably applied to the analysis of both compounds. This short method provides an easy way to determine acrylamide and acrolein in gaseous samples.