Efficient One-Pot Synthesis of Ethyl [2-(2H-Chromene-3yl)-4-oxo-L,3-thiazolidin-3-yl]acetates

Ethyl [2-(2H-chromene-3yl)-4-oxo-1,3-thiazolidin-3yl]acetates (6a–e) were synthesized in a single pot by the reaction of 2H-3-chromenecarbaldehydes (3a–e), glycine ethyl ester hydrochloride (4), and mercaptoacetic acid (5) in diisopropylethylamine/benzene under refluxing conditions in a Dean–Stark trap.     

RCM‐Based Approach to (±)‐Cuparene

An efficient approach to the aromatic sesquiterpene cuparene has been described starting from the readily available β‐ionone and employing a combination of epoxide rearrangement‐based ring‐contraction and ring‐closing metathesis reactions as key steps.     

Spectrophotometric determination of linezolid in pharmaceuticals on the basis of coupled redox-complexation reactions

The present study describes three simple and sensitive spectrophotometric methods developed for the determination of linezolid (LZD) in pure and tablet forms. These methods are based on the oxidation of LZD by ferric chloride in the presence of 1,10-phenanthroline (method A), or 2,2′-bipyridyl (method B), or potassium ferricyanide (method C). The colored complexes were measured at 510, 522 and 758 nm for methods A, B and C, respectively. In all the methods, the absorbance is found to increase linearly with increasing LZD concentration. Beer’s law is obeyed over the concentration ranges of 0.5–6.0, 0.5–9.0 and 1.0–9.0 μg/mL for methods A, B and C, respectively. The calculated molar absorptivity values are 5.8 × 10⁴, 3.6 × 10⁴ and 4.8 × 10⁴ L/mol cm for methods A, B and C, respectively, and the corresponding Sandell’s sensitivities are 5.8 × 10^?3, 9.8 × 10^?3 and 7 × 10^?3 μg/cm², respectively. The developed methods are applied successfully to the determination of LZD in the pharmaceutical formulations and the results tallied well with label claims.     

Statistical methods in nonlinear dynamics

Sensitivity to initial conditions in nonlinear dynamical systems leads to exponential divergence of trajectories that are initially arbitrarily close, and hence to unpredictability. Statistical methods have been found to be helpful in extracting useful information about such systems. In this paper, we review briefly some statistical methods employed in the study of deterministic and stochastic dynamical systems. These include power spectral analysis and aliasing, extreme value statistics and order statistics, recurrence time statistics, the characterization of intermittency in the Sinai disorder problem, random walk analysis of diffusion in the chaotic pendulum, and long-range correlations in stochastic sequences of symbols.     

Influence of disorder on superconductivity in non-magnetic rare-earth nickel borocarbides

The effect of substitutional disorder on the superconducting properties of YNi₂B₂C was studied by partially replacing yttrium and nickel by Lu and Pt, respectively. For the two series of (Y, Lu)Ni₂B₂C and Y(Ni, Pt)₂B₂C compounds, the upper critical field H _c2(T) and the specific heat c _p(T, H) in the superconducting mixed state have been investigated. Disorder is found to reduce several relevant quantities such as T _c, the upper critical field H _c2(0) at T=0 and a characteristic positive curvature of H _c2(T) observed for these compounds near T _c. The H _c2(T) data point to the clean limit for (Y, Lu) substitutions and to a transition to the quasi-dirty limit for (Ni, Pt) substitutions. The electronic specific heat contribution γ(H) exhibits significant deviations from the usual linear γ(H) law. These deviations reduce with growing substitutional disorder but remain even in the quasidirty limit which is reached in the Y(Ni_1−x , Pt _x )₂B₂C samples for x=0.1.     

Ultrasonic Assisted Synthesis of Naphthalene Substituted Schiff Base Derivatives and Their Antioxidant Activity Studies

New Schiff base derivatives, 2,2′‐[naphthalene‐2,7‐diylbis(oxy)]bis[N′‐substituted acetohydrazide] ( 4a‐m ) were synthesized by the acid catalyzed condensation of aryl/hetero aromatic aldehydes with 2,2′‐ [naphthalene‐2,7‐diylbis(oxy)]diacetohydrazide ( 3 ) under reflux temperature and ultrasonic irradiation. These Schiff base derivatives were confirmed through spectral characterization using IR, ¹H NMR, ¹³C NMR and mass spectra. All the synthesized compounds were screened for their antioxidant activity using DPPH free radical scavenging method.     

Novel dimeric amide alkaloids from Piper chaba Hunter: isolation, cytotoxic activity, and their biomimetic synthesis

Chromatographic fractionation of methanol extract from roots of the Piper chaba Hunter resulted in the isolation of four new dimeric alkaloids, chabamide H (1), I (2), J (3), K (4) together with 11 known compounds (5-15). Their chemical structures and relative stereochemistry were determined on the basis of the comprehensive spectroscopic techniques (IR, Mass, and NMR) and further confirmed by comparison of the data with those reported in literature. In addition, cytotoxic activities of all the dimeric amides (1-7) along with their monomers (8-10) were evaluated against cervical (HELA), breast (MCF-7), liver (HEPG2), colon (HT-29), and colon (COLO-205) cancer cell lines. Among the tested isolates, 5 and 7 exhibited potent cytotoxic activity against COLO-205 cell line with IC₅₀ value of 3.10 μg/mL and 0.018 μg/mL, respectively. To prove biogenesis of the newly isolated compounds, biomimetic synthesis has also been carried out via Diels-Alder reaction by using copper(II) salts in aqueous medium.     

Formal total synthesis of cyanolide A

Formal total synthesis of cyanolide A, aglycosidic dimeric macrolide is accomplished. The key reactions involved are asymmetric acetate aldol reaction, CBS reduction, and Shiina's lactonization.     

Influence of moieties for the phase stability, spontaneous polarization and dielectric relaxations in an achiral ferroelectric bent liquid crystal, PBUOB

The occurrence of ferroelelectric phases and influence of chemical moieties in the area of supra-molecular achiral Bent core Liquid Crystals (BLCs) are reviewed. Synthesis of an intermediate/higher homolog of PBnOB series (for n=11), PBUOB, viz. 1,3−Phenyline-Bis(4−UndecylOxy Benzoate), is presented. Smectic LC phases exhibited by PBUOB are characterized by Polarized Optical Microscopy (POM), Differential Scanning Calorimetry (DSC) and Spontaneous Polarization (P_S) techniques. Observations infer a bi-variant FE LC smectic phase occurrence, viz., isotropic→B₂(FE)→B₅(FE)→solid phases in cooling and solid→B₅→isotropic phases in heating scans. Occurrence of B₂ phase is monotropic (in cooling), while B₅ phase is enantiotropic. I-B₂ and B₂-B₅ phase transitions are found to be of first order nature. The FE phases possess a moderate P_S value of ∼40 nC cm⁻². Transition temperatures from dielectric studies agree with those from TM and DSC. Two modes of relaxations are observed, viz., a slow scissor mode at ∼1 kHz and a fast mode at ∼1 MHz. Anisotropic Dipolar Model is proposed to explain the reorientation mechanism. Arrhenius shifts of Relaxation Frequency (f_R) show differing activation energies for two modes, i.e., 0.11 and 0.98 eV; 0.25 and 1.18 eV in B₂ and B₅ phases, respectively. Temperature variation of dielectric increment Δε and α-parameter LC phases reveals the relative fixture of dipole moment in polar smectic layers. An analytical study for the thermal stability, P_S and f_R in the FE phases is presented with respect to the constitution and configuration of moieties in BLCs.     

Identifying the mechanisms of polymer friction through molecular dynamics simulation

Mechanisms governing the tribological behavior of polymer-on-polymer sliding were investigated by molecular dynamics simulations. Three main mechanisms governing frictional behavior were identified. Interfacial "brushing" of molecular chain ends over one another was observed as the key contribution to frictional forces. With an increase of the sliding speed, fluctuations in frictional forces reduced in both magnitude and periodicity, leading to dynamic frictional behavior. While "brushing" remained prevalent, two additional irreversible mechanisms, "combing" and "chain scission", of molecular chains were observed when the interfaces were significantly diffused.