K. Subramanyam Reddy

Structural characterization and molecular order of rodlike mesogens with three- and four-ring core by XRD and 13C NMR spectroscopy.

Structural characterizations using XRD and (13)C NMR spectroscopy of two rodlike mesogens consisting of (i) three phenyl ring core with a polar cyano terminal and (ii) four phenyl ring core with flexible dodecyl terminal chain are presented. The three-ring-core mesogen with cyano terminal exhibits enantiotropic smectic A phase while the four-ring mesogen reveals polymesomorphism and shows enantiotropic nematic, smectic C, and tilted hexatic phases. The molecular organization in the three-ring mesogen is found to be partial bilayer smectic Ad type, and the interdigitation of the molecules in the neighboring layers is attributed to the presence of the polar terminal group. For the four-ring mesogen, the XRD results confirm the existence of the smectic C and the tilted hexatic mesophases. A thermal variation of the layer spacing across the smectic C phase followed by a discrete jump at the transition to the tilted hexatic phase is also observed. The tilt angles have been estimated to be about 45° in the smectic C phase and about 40° in tilted hexatic phase. (13)C NMR results indicate that in the mesophase the molecules are aligned parallel to the magnetic field. From the (13)C-(1)H dipolar couplings determined from the 2D experiments, the overall order parameter for the three-ring mesogen in its smectic A phase has been estimated to be 0.72 while values ranging from 0.88 to 0.44 have been obtained for the four-ring mesogen as it passes from the tilted hexatic to the nematic phase. The orientations of the different rings of the core unit with respect to each other and also with respect to the long axis of the molecule have also been obtained.

13 C–1H dipolar couplings for probing rod-like hydrogen bonded mesogens

Hydrogen bonding is the most important non-covalent interaction utilised in building supramolecular assemblies and is preferred often as a means of construction of molecular, oligomeric as well as polymeric materials that show liquid crystalline properties. In this work, a pyridine based nematogenic acceptor has been synthesized and mixed with non-mesogenic 4-methoxy benzoic acid to get a hydrogen bonded mesogen. The existence of hydrogen bonding between the pyridyl unit and the carboxylic acid was established using FT-IR spectroscopy from the observation of characteristic stretching vibrations of unionized type at 2425 and 1927 cm−1. The mesogenic acceptor and the complex have been investigated using 13C NMR in solution, solid and liquid crystalline states. Together with the 2D separated local field NMR experiments, the studies confirm the molecular structure in the mesophase and yield the local orientational order parameters. It is observed that the insertion of 4-methoxy benzoic acid not only enhances the mesophase stability but also induces a smectic phase due to an increase in the core length of the hydrogen bonded mesogen.

Synthesis and Characterization of Two Phenyl Ring Core-Based Thiophene Mesogens

Novel thiophene mesogens built with two phenyl ring core and alkoxy terminal chains are synthesized by multistep route. The phenyl ring core is connected to thiophene by ester unit at (a) 2-position and (b) 3-position to yield 2-series of mesogens. The structural characterization of them is accomplished by using spectroscopy tools and the mesophase characteristics are evaluated by HOPM and DSC. The 13C chemical shifts of representative mesogens calculated from DFT by quantum chemical calculations are compared with experimental 13C chemical shifts and further utilized for structural assignment of core unit carbons. A good agreement between calculated and experimental values is noticed. An enantiotropic nematic phase is confirmed for all the mesogens and accordingly threaded nematic texture in HOPM is observed and is supported by DSC transition enthalpy values. The mesophase as well as thermal stabilities of the mesogens are discussed with reference to terminal chain length and position of the linking unit on thiophene.

Synthesis, Structural and Mesophase Characterization of Three Ring Based Thiophene Liquid Crystals

Thiophene based calamitic mesogens are receiving paramount importance due to their applications in functional organic materials. The insertion of thiophene in the core unit favours a large change in mesophase characteristics as well as application properties in contrast to those mesogens with phenyl ring core alone. In this work, we report the structural as well as mesophase characterization of six mesogens which are built with a core of three phenyl rings and thiophene ring. The thiophene ring is placed at one end of the core and varied the other end with alkyl/alkoxy chains to investigate the mesophase characteristics. The molecular structures of representative mesogens are confirmed by means of FT-IR and Two-dimensional solution NMR techniques. An enantiotropic nematic phase is observed in all the cases as supported by HOPM and DSC techniques. The mesophase characteristics such as melting and clearing temperatures and phase stability are discussed. A dramatic increase in nematic phase stability for the synthesised mesogens is noticed in contrast to two phenyl ring based thiophene mesogens reported in literature.

PREPARATIVE ISOLATION AND UPLC-TOF MS IDENTIFICATION OF EIGHT DEGRADANTS FROM STRESSED TABLETS OF ESOMEPRAZOLE

Esomeprazole is a proton pump inhibitor, used in the treatment peptic ulcer disease (PUD). Eight degradants were found in the formulated drug under the stress conditions, (40°C/75% Relative Humidity (RH) for 6 months) with Relative Retention Times (RRTs) 0.26, 0.29, 0.32, 0.59, 0.88, 0.96, 1.12, and 1.33 by a LC-MS compatible method. A simple effective gradient preparative HPLC method was developed with the runtime of 20 min to isolate all the degradants. The degradants were stabilized and identified by UPLC-ToF MS. The method is capable and can be used to isolate further degradants. Supplemental materials are available for this article. Go to the publishers online edition of Journal of Liquid Chromatography and Related Technologies to view the free supplemental file.

Viscosities of binary mixtures containing one polar component

Viscosities of binary mixtures, benzene + benzonitrile, benzene + methylpropylketone and cyclohexane + methylpropylketone were determined at 303·15 K. The experimental results were analysed in the light of Bloomfleld and Dewan’s theory. The analysis showed that the theory correctly predicts the sign of viscosity function in the case of benzene + benzonitrile and cyclohexane + methylpropylketone.

Hansen Solubility Parameters of Cellulose Acetate Phthalate-Polycaprolactonediol Blend by Inverse Gas Chromatography

The specific retention volumes, V0g, for 21 solute probes in a cellulose acetate phthalate (CAP)–polycaprolactonediol (PCLD) blend were determined by inverse gas chromatography (IGC) in the temperature range 323.15–413.15 K. The retention diagrams drawn between lnV0g vs. revealed the presence of the glass transition temperature at about 373 K. Therefore, the Flory-Huggins interaction parameters at infinite dilution, χ∞12, were calculated using V0g values in the temperature range 373.15–413.15 K. The χ∞12 values decreased with increase of temperature for all the solutes. Further, the χ∞12 values decreased with decrease of chain length of n-alkanes whereas in 1-alcohols the trend was reversed. The Hansen solubility parameters (HSP) were determined in the temperature range 373.15–413.15 K following the Flory-Huggins solution model. The dispersive and polar components of the HSP decreased with increase of temperature whereas the hydrogen bonding component slightly increased with increase of temperature.

Viscosities of binary liquid mixtures of polar-apolar and polar-polar systems at 303·15 K

Viscosities for the binary liquid mixtures of methylethylketone with benzen, toluene, chlorobenzene, bromobenzene and nitrobenzene were determined at 303·15 K. The deviation in viscosity was calculated and its behaviour was studied as a function of mole fraction. The deviation in viscosity is negative in the system methylethylketone with benzene and is positive in the other systems. The results are discussed in terms of dipole-induced dipole and dipole-dipole interactions.