Terpenoids—LXX Structure of dehydrocostus lactone

The structure III assigned to dehydrocostus lactone by Sorm et al. has been supported by converting it into (i) guaiane, C₁₅H₂₈ (I) and (ii) s-guaiazulene and chamazulene in fairly high yield from sone of its derivatives. The lactol XII, obtainable from III gives four different products (XIII, XIV, XVIII and XXIV) when subjected to Huang-Minlon reduction at 135° and 170° respectively. The dienic monol (XVIII) the structure of which is supported by UV and NMR spectra, furnished a hydrocarbon C₁₅H₂₆ XXVIII, when subjected to metal amine reduction indicating the presence of an allylic hydroxyl in it, which proves that the lactone attachment in III is at C₆–C₇.     

FT-Raman and infrared spectra and vibrational assignments for 3-chloro-4-methoxybenzaldehyde, as supported by ab initio, hybrid density functional theory and normal coordinate calculations

Fourier-transform laser Raman (3500-50 cm(-1)) and infrared (4000-400 cm(-1)) spectral measurements have been made for the solid 3-chloro-4-methoxybenzaldehyde. The electronic structure calculations -ab initio (RHF) and hybrid density functional methods (B3LYP and B3PW91) -- have been performed with 6-31G* and 6-311G* basis sets. Molecular electronic energies, equilibrium geometries, IR and Raman spectra have been computed. Potential energy distribution (PEDs) and normal mode analysis have also been performed. A complete assignment of the observed spectra has been proposed. Investigation of the relative orientation of the aldehydic oxygen and chlorine atom with respect to the methoxy group has shown that two forms, O-cis and O-trans exist, with O-trans form being more stable. The energy difference between O-cis and O-trans forms is 0.057 kcal/mol (21 cm(-1)) with B3LYP/6-31G*, which is less than the calculated torsional vibrational frequencies of the aldehyde and methoxy group. In the CH (O) aldehydic stretching region five observed bands are probably due to multiplet Fermi resonance. An infrared doublet near 1700 cm(-1) with nearly equal intensities has been ascribed to the Fermi resonance: the two bands at 1696 and 1679 cm(-1) arise due to the interaction between the CO stretching fundamental and a combination of O-CH(3) and CC stretching vibrations.     

Light-Emitting Chiral Nematic Dimers with Anomalous Odd-Even Effect

In this report, based on the results derived from the extensive study into the thermal and photophysical properties, an anomalous mesomorphic behavior of photoluminescent, chiral nematic (N*) liquid crystalline dimers, belonging to two different series has been revealed. They comprise cholesterol and fluorescent three-ring Schiff base or salicylaldimine core interlinked via an ω-oxyalkanoyloxy spacer of varying length and parity. The effect of molecular structure on the liquid crystal (LC) behavior and photophysical properties of both the series has been probed by varying the length of the terminal n-alkoxy tails for a fixed (odd or even) parity of the spacer. The detailed investigations using complementary techniques not only evidenced the existence of the N* phase in all the dimers synthesized but also the occurrence of an intriguing odd-even effect; blue phases (BPs) exist in all the dimers comprising even-membered spacer, which surprisingly remains totally absent in their odd-membered counterparts. While the results reported hitherto are exactly opposite to the aforesaid findings, this atypical behavior has been interpreted in terms of the over-all shape of the dimers rendered by the orientation of terminal tails. Photophysical studies carried out clearly revealed the intrinsic light emitting feature of the dimers not only in their dilute solutions but also in their three condensed states viz., solid, N* phase, and isotropic liquid state; the emission intensities of the N* phase varies with the change in temperature, as expected. CD spectra of the N* phase recorded as a function of temperature show bisignate CD band characteristically, signifying large chiral correlations in the molecular self-assembly, while the origin of bands from positive to negative region suggests a right-handed twist of the N* helix.     

A Bayesian approach for the alignment of high-resolution NMR spectra

Metabolic analysis with high-resolution nuclear magnetic resonance (NMR) enables simultaneous investigation of numerous chemical species in response to biochemical changes in subjects. When the analysis involves comparing two or more NMR spectra, it is essential to properly align them because small variations across different spectra influence the alignment and thus, interfere with direct comparisons between samples. We propose a new alignment method within the Bayesian modeling framework. The proposed method allows us to estimate the amplitude and phase shifts simultaneously and to obtain robust results in the existence of noise. Effectiveness of our proposed method is demonstrated through real NMR spectra in human plasma and a comparison study with dynamic time warping and correlated optimized warping, two widely used alignment methods in spectral data.     

Electrical conductivity and dielectric constant measurements of liquid crystal–gold nanoparticle composites

The behaviour of the anisotropic electrical conductivity of liquid crystal–gold nanoparticle (LC‐GNP) composites consisting of a commercially available room temperature nematic compound doped with alkylthiol‐capped GNPs has been investigated. The nematic–isotropic transition of the composite decreases nearly linearly with increasing X, the concentration of GNP (in weight %) at a rate of about 1°C /weight %. The inclusion of GNPs increases the electrical conductivity of the system with the value increasing by more than two orders of magnitude for X = 5%. However, the anisotropy in conductivity, defined as the ratio of the conductivity along (σ_∥) and orthogonal (σ_⊥) to the director shows a much smaller but definite decrease as X increases.     

Constitutional bis(N-salicylideneaniline)s as new class of mesogens: synthesis and thermal properties

Twelve new constitutional bis(N-salicylideneaniline)s (BSANs) belonging to three different series have been prepared and characterised by the two-fold reaction of alkoxyanilines with 2,3-dihydroxyterephthalaldehyde, 4,6-dihydroxyisophthalaldehyde and 2,5-dihydroxyterephthalaldehyde. Their thermal behaviour and liquid crystallinity has been established with the help of polarising optical microscope, differential scanning calorimeter (DSC) and powder X-ray diffraction (XRD). Our study reveals this behaviour as determined by the nature of central core and the number of alkoxy tails. For example, the three series of compounds prepared are either non-mesomorphic or stabilised calamitic and discotic mesophases, such as nematic/smectic C and columnar (Col) phases. These materials represent the first examples of mesogenic BSANs exhibiting mesomorphism.     

Effect of pressure on liquid crystal dimers

We report high pressure investigations on a homologous series of liquid crystalline dimeric molecules in which the terminal chain length is kept constant but the length of the methylene spacer connecting the two mesogenic units is varied. We find that unlike the nematic-isotropic transition temperature and associated entropy change, there is no alternation in the slope of the nematic-isotropic phase boundary in the pressure-temperature plane as a function of the length of the spacer group in the molecule. By applying the Clausius-Clapeyron equation we conclude that the volume change at the transition should exhibit a strong odd-even effect. Measurements on the shortest homologue of the series, which is non-mesomorphic, show the expected result that the application of pressure induces mesomorphism in non-mesomorphic compounds.     

Measurement of L subshell fluorescence yield ratios of some high Z elements by selective excitation method

The L₁, L₂ and L₃ subshells of Hf, Ta and Re atoms have been excited selectively by using microprobe XRF beam line, Indus‐2, RRCAT, India. The consequent characteristic L X‐ray photons, emitted from the targets due to creations of vacancies in L subshells, are measured using silicon drift detector (X‐123) spectrometer. As the energy of synchrotron radiation increases, the contribution of characteristic L X‐ray intensity increases. The advantage of the increase in the intensity of the characteristic L X‐ray photons with an increase in the energy of synchrotron radiation has been used to determine the L subshell fluorescence yield ratios of Hf, Ta and Re atoms by adopting the selective excitation method. The measured ratios of L subshell fluorescence yield have been compared with theoretical and other experimental values.     

Surface roughness effects in a short porous journal bearing with a couple stress fluid

In this paper, a theoretical study of the effect of surface roughness in hydrodynamic lubrication of a porous journal bearing with couplestress fluid as lubricant is made. The modified Reynolds equations accounting for the couple stresses and randomized surface roughness structure are mathematically derived. The Christensen stochastic theory of hydrodynamic lubrication of rough surfaces is used to study the effects of surface roughness on the static characteristics of a short porous journal bearing with couplestress fluid as lubricant. Further, it is assumed that, the roughness asperity heights are small compared to the film thickness. It is observed that, the effects of surface roughness on the bearing characteristics are more pronounced for couplestress fluids as compared to the Newtonian fluids.     

Impulsive motion of a non-Newtonian fluid between two oscillating parallel plates

An exact solution for the flow of an incompressible viscoelastic fluid between two infinitely extended parallel plates, due to the harmonic oscillations of the upper plate and the impulsively started harmonic oscillations of the lower plate from rest, in the respective planes of the plates, has been obtained. The momentum transfer towards the central region and the skin friction of the lower plate are found to be greater for the viscoelastic fluid than that for viscous fluid. The effect of out-of-phase oscillations of the plates with different amplitudes on the flow characteristics has also been investigated.