Effect of Cholesteric Liquid Crystalline Compounds on the Radical Polymerization of Methyl Methacrylate

Polymerization of methyl methacrylate was carried out at 55 and 65°C using benzoyl peroxide as initiator in the presence of the fol-lowing additives: (a) cholesteric compounds like cholesterol, cho-lesteryl acetate, cholesteryl caprylate, cholesteryl stearate, choles-teryl chloride, cholesteryl laurate, cholesteryl oleyl carbonate, and cholesteryl 2-ethylhexyl carbonate, (b) a nematic liquid crystal, N-(p-methoxy benzylidene)-p-butyl aniline, and (c) rodlike molecules like 2-butynediol and diacetylene diol. The rates of polymerization, activation energies, molecular weights, and tacticities of the poly-mer are discussed in the light of monomer + additive interactions. It is found that monomer-additive complexes affect the polymerization rates.     

Carrier facilitated transport of thorium from HCl medium using Cyanex 923 in n-dodecane containing supported liquid membrane

Present studies deal with supported liquid membrane (SLM) technique for the separation of thorium from hydrochloric acid (HCl) medium using Cyanex 923 as a carrier. Effects of feed acidity, strippant, and membrane pore size and membrane thickness on the transport of thorium have been studied in detail. The optimized parameters were applied for separation of thorium from a radioanalytical waste. Stability of the membrane and membrane support was investigated. Transport of thorium increased from 78.3 to about 93.7 % with increase in acidity from 0.5 to 2 M using 0.3 M Cyanex 923 in n-dodecane as carrier and 2 M ammonium carbonate as stripping phase. The transport of thorium decreased above 2 M HCl. An attempt was made to model the physicochemical transport of thorium in SLM and understand the mechanism of thorium transport.     

Strategic utilization of catalytic metathesis and photo-thermal metathesis in caged polycyclic frames

Highly functionalized cage compounds have been prepared via cross-metathesis (CM) using Grubbs modified N-tolyl catalyst 7. A strategic utilization of photo-thermal metathesis and catalytic metathesis sequence for the synthesis of functionalized caged molecules has been demonstrated.     

Crystal structures and biological activity of homologated (N)-n-alkylammonium salts of 2-bromo-3-oxido-1,4-naphthoquinone

Structural Chemistry - Homologated (N)-n-alkylammonium salts of 2-bromo-3-oxido-1,4-naphthoquinone (BS-1 to BS-8) have been synthesized and characterized from the single crystal X-ray diffraction...     

Tandem allylic oxidation-condensation/esterification catalyzed by silica gel: an expeditious approach towards antimalarial diaryldienones and enones from natural methoxylated phenylpropenes

A new one-pot strategy has been developed, wherein abundantly available methoxylated phenylpropenes are directly transformed into corresponding dienones (1,5-diarylpenta-2,4-dien-1-ones) and enones (chalcones and cinnamic esters) via allylic oxidation-condensation or allylic oxidation-esterification sequences. Preliminary antimalarial activity studies of the above synthesized diaryldienones and enones against Plasmodium falciparum (Pf3D7) have shown them to be promising lead candidates for developing newer and economical antimalarial agents. In particular, two enones (12b and 13b) were found to possess comparatively better activity (IC(50) = 4.0 and 3.4 μM, respectively) than licochalcone (IC(50) = 4.1 μM), a well known natural antimalarial compound.     

Heme-artemisinin adducts are crucial mediators of the ability of artemisinin to inhibit heme polymerization

A lack of molecular understanding of the targets and mechanisms of artemisinin action has impeded the improvisation of more efficient antimalarials based on this class of endoperoxide drugs. We have synthesized a heme-artemisinin adduct designated as "hemart" to discover if it mediates the ability of artemisinin to inhibit heme polymerization. Hemart mimics heme in binding to Plasmodium falciparum histidine-rich protein II (PfHRP II) but cannot self-polymerize. Instead, it inhibits all heme polymerizations, including basal and those triggered by PfHRP II, Monooleoyl glycerol (MOG), or P. yoelii extract. Hemart has an edge over heme in displacing heme from PfHRP II, and either low pH or chloroquine dissociates heme but not hemart from PfHRP II. Our results suggest that hemart, by mimicking heme, stalls all mechanisms of heme polymerization, resulting in the death of the malaria parasite.     

Dielectric and Viscoelastic Behavior of Poly-(n-Butyl Methacrylate) Containing Cholesteric Compounds

Dielectric and dynamic mechanical behavior of poly(n-butyl methacrylate) (PBMA) containing small concentrations of cholesteryl chloride (ChCl), cholesteryl caprylate (ChCp), and cholesteryl laurate (ChL) have been studied in the temperature range -20 to 80°C. Tan αmax (dielectric and mechanical) in all systems containing an additive shifts to lower temperature compared to that in pure PBMA. In the glassy region, the dynamic storage modulus E′ for all the PBMA plus additive systems is higher than that for pure PBMA. This behavior is similar to the β-peak suppression and the increase in tensile strength of poly(vinyl chloride) on addition of a small concentration of plasticizer. Using the WLF equation with C₁ and C₂ obtained from the data on pure PBMA, the reference temperature T_o for PBMA plus additive systems are determined for the best fit of the experimental points to the WLF curve and are in agreement with measured glass-transition temperatures. With respect to T_o of pure PBMA, the T_o of PBMA plus additive systems are lowered, and the lowering due to these additives is in the order ChL < ChCp < ChCl. From spectrophotometric studies in solutions of polymer plus additives, equilibrium constants for the 1:1 and 1:2 complexes between the polymer and the additive are evaluated. The magnitude of the equilibrium constant K₁ increases in the order ChL > ChCp > ChCl, and hence it is concluded that the extent of β-peak suppression depends on the strength of polymer-additive interaction.     

Disengagement of the gas phase in bubble columns

The technique of gas disengagement is popularly used to assess the bubble size distribution in bubble columns. The technique involves the dynamic measurement of dispersion height when the gas supply is stopped. In this paper a mathematical model has been proposed for the process of dynamic gas disengagement. It has been shown that the initial faster disengagement is due to the presence of internal liquid circulation and not due to the presence of very large bubbles. Further, slower disengagement has been attributed to the transition from heterogeneous dispersion to homogeneous dispersion. The new model also explains the effects of superficial gas velocity, column diameter, column height and liquid phase physical properties on the gas disengagement.     

Role of Plasma Parameters on the Conjugated Structure Retention in Polyaniline Thin Film

The role of plasma parameters on the film characteristics is investigated on polyaniline thin film deposited by radio frequency (RF) plasma polymerization. A series of un-doped and iodine doped polyaniline thin films are prepared by RF discharge operating at 13.56?MHz with different discharge powers and pressure variation from 0.1 to 0.05?mbar and variation in deposition time from 20 to 40?min. A good thin film is found with a power ranging from 9?W (?28?V self bias) to 20?W (?65?V self bias) at 0.1?mbar pressure which is confirmed by fourier transform infra-red spectroscopy showing the retention of aromatic rings. In addition, iodine doping is carried out with 9?W power and 0.1?mbar pressure. The characterization of process plasma is done using Langmuir probe diagnostics and optical emission spectroscopy. A correlation has been established between film characteristics and plasma properties investigated using optical emission spectroscopy and Langmuir probe analysis. Emphasis has been given on the study of the influence of plasma parameters, particularly of the electron energy distribution function on the quality of conjugated plasma polymerized aniline film.     

A Convenient Synthesis of Bipyrido‐Fused Coumarins and Their Biological Evaluation

A convenient and efficient strategy has been devised for the synthesis of bipyrido‐fused coumarins employing Kröhnke's pyridine synthesis approach. In the present work, 4‐hydroxycoumarins 1a – d were reacted with appropriate chalcones 2a – c to afford desired bipyridyl‐fused coumarins 3a – l . The structures of all the newly synthesized compounds 3a – l were ascertained by IR, ¹H NMR, ¹³C NMR, mass spectral data, and elemental analyses. The compounds were further evaluated for their antimicrobial response against representative panel of pathogens, and the results thus obtained were compared with those of standard drugs. Few of the derivatives 3c , 3f , and 3i exhibited promising potency.