Dependence of thermotropic mesomorphism on lateral nitro group

A novel homologous series RO-C₆H₄-COO-C₆H₃-(NO₂)-CO-CH?CH-C₆H₄OC₁₈H₃₇(n) para of chalconyl ester derivatives have been synthesized and studied with view to understanding the effect of an ortho substituted nitro group on thermotropic liquid crystal (LC) behavior. The novel homologous series consists of thirteen homologues (C₁ to C₁₈). The C₁ to C₄ homologues are nonliquid crystal (NLC) and the rest of the homologues (C₅ to C₁₈) homologues are enantiotropically nematogenic without exhibition of a smectic phase even in the monotropic condition. Transition temperatures were determined by an optical polarizing microscope (POM) equipped with a heating stage. Texture of nematic phase are threaded or Schlieren. Analytical, thermal and spectral data supported molecular structure of homologues. Thermal stability for nematic is 147.1°C whose mesophase lengths vary between 16.0 and 32.0°C the C₇ and C₁₈ homologues, respectively, and their mesogenic exhibition range between 96.0 and 166.0°C. Thus, the present novel series is middle ordered melting type, Group efficiency order is derived from comparative study of structurally similar series. The transition curves of a phase diagram behaved in normal manner except C₁₀ and C₁₆ homologues. Odd-even effect is observed for N-I transition curve. Group efficiency order derived is: -OC₁₂H₂₅ (n) > -OC₁₈H₃₇ (n) > -OC₁₈H₃₇ (n).     

Damage smoothing effects in a delocalized rate sensitivity model for metals

It has been long time established that application of damage delocalization method to softening constitutive models yields numerical results that are independent of the size of the finite element. However, the prediction of real-world large and small scale problems using the delocalization method remains in its infancy. One of the drawbacks encountered is that the predicted load versus displacement curve suddenly drops, as a result of excessive smoothing of the damage. The present paper studies this unwanted effect for a delocalized plasticity/damage model for metallic materials. We use some theoretical arguments to explain the failure of the delocalized model considered, following which a simple remedy is proposed to deal with it. Future works involve the numerical implementation of the new version of the delocalized model in order to assess its ability to reproduce real-world problems.     

On kinematic,thermodynamic, and kinetic coupling of a damage theory for polycrystalline material

The paper proposes a new consistent formulation of polycrystalline finite-strain elasto-plasticity coupling kinematics and thermodynamics with damage using an extended multiplicative decomposition of the deformation gradient that accounts for temperature effects. The macroscopic deformation gradient comprises four terms: thermal deformation associated with the thermal expansion, the deviatoric plastic deformation attributed to the history of dislocation glide/movement, the volumetric deformation gradient associated with dissipative volume change of the material, and the elastic or recoverable deformation associated with the lattice rotation/stretch. Such a macroscopic decomposition of the deformation gradient is physically motivated by the mechanisms underlying lattice deformation, plastic flow, and evolution of damage in polycrystalline materials. It is shown that prescribing plasticity and damage evolution equations in their physical intermediate configurations leads to physically justified evolution equations in the current configuration. In the past, these equations have been modified in order to represent experimentally observed behavior with regard to damage evolution, whereas in this paper, these modifications appear naturally through mappings by the multiplicative decomposition of the deformation gradient. The prescribed kinematics captures precisely the damage deformation (of any rank) and does not require introducing a fictitious undamaged configuration or mechanically equivalent of the real damaged configuration as used in the past.     

Quantification of Lupeol in Polyherbal Formulation by High-Performance Thin-Layer Chromatography Method Using Design of Experiments as a Tool to Assess Optimization of Method Development and Extraction Efficiency

JPC – Journal of Planar Chromatography – Modern TLC - A simple, specific, and quantitative high-performance thin-layer chromatographic (HPTLC) method has been developed for the...     

Photochemical studies: Chromones,bischromones and anthraquinone derivatives

Photochemical reaction is a chemical reaction initiated by the absorption of energy in the form of light resulting in different types of reaction. Chromones, bischromones and anthraquinones are the bichromophoric molecules which contain the carbonyl group and double bond in conjugation. Photochemical reactions of these compounds result in the formation of such molecules which are not obtained via conventional methods. This review article describes the photochemical transformations of chromones, bischromones and anthraquinone derivatives and here main emphasis has been laid upon the intramolecular photochemical H-abstraction reactions that provide many exotic heterocyclics as the final photoproducts.     

Selective visual detection of Pb(II) ion via gold nanoparticles coated with a dithiocarbamate-modified 4′-aminobenzo-18-crown-6

We have developed a crown ether based selective colorimetric sensing scheme for the determination of Pb(II) ion by using gold nanoparticles modified with dithiocarbamate derivative of 4′-aminobenzo-18-crown-6 that acts as a colorimetric probe. Monodisperse Au-NPs were prepared by reacting 4′-aminobenzo-18-crown-6 with carbon disulfide to generate the dithiocarbamate ligand which was then added to the Au-NPs to form a supramolecular assembly on their surface. The Au-NPs modified in this way undergo aggregation in the presence of Pb(II) ions, and this causes the color to change from red to blue. The Pb(II)-induced aggregation can be monitored by using UV-visible spectrometry and even with the bare eye. The absorbance ratio (A_650nm/A_520nm) is linearly related to the concentration of Pb(II) in the 0.1 to 75 μM range (with a correlation coefficient of 0.9957), and the detection limit is 50 nM which is lower than the allowable level (75 nM) as defined by the US EPA. The method was successfully applied to the determination of Pb(II) in spiked water samples. Figure

Schematic representation of Pb²⁺ ion-induced DTC-CE-Au NPs aggregation via sandwich complex formation.     

Higher-Order Cyclodextrin Complexes: The Naphthalene System

Naphthalene excited dimer (excimer) fluorescence is observed in the presence of β- and γ-cyclodextrin (CD) at elevated naphthalene (NAP) concentrations (100 μM) but not at low NAP concentrations (5 μM). This is attributed to formation of 2:2 CD:NAP complexes in the former situation. Complexes of NAP with hydroxypropyl β-CD are exclusively 1:1 and no excimer emission is observed. Complexes of NAP with α-CD do not show excimer emission either but the complex stoichiometry is 2:1 CD:NAP in this case. The formation constants for both the 1:1 and 2:2 β-CD:NAP complexes have been determined and they have been found to depend on the ionic strength of the salting out agent NaCl. K_1:1 = 377 ± 35 M^-1 in the absence of salt and 657 ± 60 M^-1 at 1 M NaCl. The corresponding values for K_2:2 are (1.0 ± 0.2) × 10⁴ and (4.0 ± 0.5) × 10⁴ M^-1, respectively. Stern-Volmer fluorescence quenching studies of the 1:1 and 2:2 species by water-based quenchers (NaI and CsBr) show that both types of complexes protect the fluorophore from the quencher. However, the more completely encapsulated NAP in the 2:2 complex is protected to a greater extent. This is also the case for the 2:2 γ-CD:NAP complex. This protective effect is reflected in the observed rate constants for NAP quenching. For example, k_Q = 7.1 × 10⁹ M^-1 s^-1 for NaI in the absence of CD. This is reduced to 2.1 × 10⁹ M^-1 s^-1 for the 1:1 complex and 1.2 × 10⁹ M^-1 s^-1 for the 2:2 complex when 10 mM β-CD is present. A similar pattern is observed for CsBr as quencher. The 2:2 complexes are disrupted in the presence of additives such as linear alcohols and surfactants. The implications of these results for application of CDs for drug stabilization are discussed.