Phase transition studies in mesogenic dimers

Schiff base liquid crystal dimers, both symmetric and non‐symmetric, in which two anisotropic groups are linked by a flexible spacer, exhibit a rich variety of smectic mesomorphism. The interest in this class of mesogens stems not only from their ability to act as model compounds for semi‐flexible mainchain liquid crystal polymers but also from their quite different properties compared to conventional low molar mass liquid crystals (monomers). We report here the phase transition studies on two examples of these schiff base liquid crystal dimers using the Differential Scanning Calorimetry and density measurements as a function of temperature. The symmetric liquid crystal dimer, α,ω‐bis (4‐n‐dodecylaniline benzylidene‐4′‐oxy)decane (10.O12O.10) exhibits a very rare Isotropic to G transition. Where as, the non‐symmetric dimer, α‐(4‐cyano biphenyl‐4′‐yloxy)‐ω‐(4‐n‐decylanilinebenzylidene‐4′‐oxy)decane (CB.O10O.10) exhibits a rare nematic to intercalated smectic A phase transition. The transitions studied, isotropic to nematic and isotropic to G exhibit a large density jump at the transition confirming their first order nature. Nematic to intercalated smectic A transition is found to be a second order transition whose behavior is similar to nematic to smectic A transition. Calculated values of pressure dependence of transition temperature and thermal expansion coefficient are also reported.     

Reduced graphene oxide/iron oxide hybrid composite material as an efficient magnetically separable heterogeneous catalyst for transfer hydrogenation of ketones

Reduced graphene oxide was synthesized and functionalized with FeSO₄⋅7H₂O to form a reduced graphene oxide/iron oxide hybrid composite. The hybrid composite was extensively characterized using various techniques. Its application for transfer hydrogenation of various ketones was studied. The investigation showed that it serves as a good catalyst for transfer hydrogenation of aromatic and some aliphatic ketones resulting in excellent isolated yields (97–99%) of products. It is magnetically separable showing good reusability. The products were characterized and compared with authentic ones.     

A Rapid High-Performance Thin-Layer Chromatographic Method to Estimate Quercetin in Benincasa hispida (Thunb.) Cogn. Fruit Pulp

JPC – Journal of Planar Chromatography – Modern TLC - Ayurvedic medicines show great promise due to their holistic approach in the treatment of diseases. However, proper standardization...     

Copper–Schiff base complex catalyzed oxidation of sulfides with hydrogen peroxide

A straightforward, efficient, and selective oxidation of sulfide to sulfoxide with 30% H₂O₂ catalyzed by copper(II)–Schiff base complex is described. The reactions proceed under mild conditions in acetonitrile at room temperature to provide a variety of aryl and alkyl sulfoxides in excellent yield.     

AlCl3 · 6H2O/KI/CH3CN/H2O: An Efficient and Versatile System for Chemoselective C–O Bond Cleavage and Formation of Halides and Carbonyl Compounds from Alcohols in Hydrated Media

AlCl₃ · 6H₂O/KI/CH₃CN/H₂O, an efficient and versatile system, cleaves the C–O bonds of esters, acetals, ethers, and oxathiolanes to the corresponding acids, alcohols, and carbonyl compounds chemoselectively at 80 °C in hydrated media with good yields. This system also converts the alcohols (primary/secondary) to halides and oxidizes the alcohols (primary/secondary) to the corresponding carbonyl compounds in the presence of DMSO.     

Design of a fused triazolyl 2-quinolinone unnatural nucleoside via tandem CuAAC-Ullmann coupling reaction and study of photophysical property

This report presents the design and synthesis of a novel fused triazolyl 2-quinolinone (FTQuon) nucleoside as a new generation of angularly widened unnatural nucleobase surrogate with two possible H-bonding faces-one H-bond acceptor and another donor. The synthesis via a tandem CuAAC-Ullmann coupling, the study of photophysical properties and theoretical calculation in the context of DNA are the main contents of this report. The newly designed nucleoside shows interesting photphysical property with slight blue shifted solvatochromicity. It also shows pH sensitive emission. All the theoretical DNA duplexes containing the FTQuon show right?handed B-form helicity as revealed from a molecular dynamics simulation using Schrodinger Macromodel. A theoretical (DFT) study indicates a good stabilizing property of FTQuon via pairing with natural pyrimidine bases. It also shows good interaction property with BSA protein signalled via a switch on fluorescence response.     

On the dipole–dipole correlation and dielectric anisotropy of some N(4-N-alkyloxy benzylidene)4′-N-alkylaniline compounds doped with silver nanoparticles

Dielectric study of the compounds N(4-n-heptyloxy benzylidene)4′-n-butylaniline and N(4-n-heptyloxy benzylidene)4′-n-hexylaniline at low frequency region (1 kHz–1 MHz) is performed using LCR meter (Agilent 4284 A). A qualitative interpretation in terms of dipole–dipole correlation for both the parallel and the perpendicular components of the dipole moment is given. Further study on the change in the dielectric permittivity and the dielectric anisotropy is made by doping the two compounds separately with dodecanethiol capped silver nanoparticles (0.25% by weight). The molecular positional ordering and relative smectic layer distance influences the change of degree (or type) of dipole–dipole pairing.     

Tracing the Route to Ammonia: A Theoretical Study on the Possible Pathways for Dinitrogen Reduction with Tripodal Iron Complexes

The chemistry of nitrogen fixation has been the subject of considerable research with a view to gaining a proper understanding of the mechanistic details. In this article, density functional calculations are performed on all the mechanistic possibilities for dinitrogen reduction mediated by the tripodal iron complexes [(SiP^Me₃)Fe^I] ( [Fe_Si] ) and [(BP^Me₃)Fe⁰] ( [Fe_B] ). Dinitrogen addition to the neutral bare complex is found to be thermodynamically more favorable than that to the anionic one. Both symmetric and asymmetric pathways, along with the possible intermediates and transition states, are considered in this study. For both systems, the symmetric path is found to be more likely, although the prospect of the asymmetric path cannot be ignored. Moreover, interconversions between these two pathways are found to be less likely. This study corroborates most experimental observations and provides theoretical insight into the possible existence of some hitherto unknown intermediates such as multiple‐bonded Fe? N species in a trigonal bipyramidal geometry. Furthermore, in agreement with experimental observations, this study also highlights the possibility of hydrogen and hydrazine evolution during the complete reduction of dinitrogen.     

Laser Raman studies on compounds 7.O4O.7 and 7.O5O.7

Laser Raman studies on two compounds of the α,ω-bis(4-alkylanilinebenzylidene -4′-oxy)alkane series were carried out in the spectral regions 1140–1220 and 1550–1650 cm^-1 as a function of temperature. Compounds 7.O4O.7 and 7.O5O.7, exhibit SmA and SmF phases. The structural differences between these liquid crystal dimers, having either an odd or an even number of carbon atoms in the spacer, are remarkably existent in the room temperature Raman spectra. The results are rationalized on the basis of the tendency of these compounds to exhibit bent shapes, and how this manifests in the odd-even effect at the molecular level assuming a semi-rigid core region of the dimeric molecule. It is found that the behaviour of the odd spacer dimer (7.O5O.7) agrees with the molecular model, whereas the even spacer dimer (7.O4O.7) behaves in a similar fashion to monomeric compounds such as the nO.m. compounds. In both cases, dynamic changes around the C=N bond have a profound effect both on the molecular shape in the different phases and on phase behaviour.     

Experimental investigation of phase transitions exhibited by symmetric liquid crystal dimers

As a part of our systematic study of phase transitions in liquid crystal dimers we report here the variation of density across the phase transitions Isotropic – Smectic A and Smectic A – Smectic F exhibited by the Schiff base liquid crystal dimeric compounds of α,ω‐bis(4‐alkylanilinebenzylidene‐4′‐oxy)alkane (m.OnO.m) homologous series. The compounds studied are 6.O5O.6 and 6.O6O.6. The compound 6.O5O.6 exhibits only Smectic A phase, whereas the compound 6.O6O.6 exhibits Smectic A and Smectic F phases. The density jumps and peak in thermal expansion coefficient at the transitions confirm the first order nature of the transitions with a smaller density jumps compared to the monomeric liquid crystals. The calculated pressure dependance of the transition temperatures using Clauasius‐ Clapeyron equation is also reported. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)