Kinetics and mechanism of the reduction of colloidal MnO2 by glycyl-leucine in the absence and presence of surfactants

The kinetics of the reduction of water-soluble colloidal manganese dioxide by glycyl-leucine (Gly-Leu) has been investigated in the presence of perchloric acid both in aqueous as well as micellar media at 35 °C. The study was carried out as functions of [MnO₂], [Gly-Leu] and [HClO₄]. The first-order-rate is observed with respect to [MnO₂], whereas fractional-order-rates are determined in both [Gly-Leu] and [HClO₄]. Addition of sodium pyrophosphate and sodium fluoride enhanced the rate of the reaction. Further, the use of surfactant micelles is highlighted as, in favourable cases, the micelles help the redox reactions by bringing the reactants into a close proximity due to hydrogen bonding. While the ionic surfactants SDS and CTAB have not shown any effect on the reaction rate, the nonionic surfactant TX-100 has catalytic effect which is explained in terms of the mathematical model proposed by Tuncay et al. (1999). The Arrhenius and Eyring equations are valid for the reaction over the range of temperatures used and different activation parameters (E_a, ΔH^#, ΔS^# and ΔG^#) have been evaluated. Kinetic studies show that the redox reaction between MnO₂ and Gly-Leu proceeds through a mechanism combining one- and two-electron pathways: Mn(IV) → Mn(III) → Mn(II) and Mn(IV) → Mn(II). On the basis of the observed results, a possible mechanism has been proposed and discussed.     

Primary, secondary metabolites, H2O2, malondialdehyde and photosynthetic responses of Orthosiphon stimaneus Benth. to different irradiance levels

The resource availability hypothesis predicts an increase in the allocation to secondary metabolites when carbon gain is improved relative to nutrient availability, which normally occurs during periods of low irradiance. The present work was carried out to confirm this hypothesis by investigating the effects of decreasing irradiance on the production of plant secondary metabolites (flavonoids and phenolics) in the herbal plant Orthosiphon stamineus, and to characterize this production by carbohydrate, H(2)O(2), and malondialdehyde (MDA) levels, net photosynthesis, leaf chlorophyll content and carbon to nitrogen ratio (C/N). Four levels of irradiance (225, 500, 625 and 900 μmol/m(2)/s) were imposed onto two-week old seedlings for 12 weeks in a randomized complete block design experiment. Peak production of total flavonoids, phenolics, soluble sugar, starch and total non-structural carbohydrate ocurred under low irradiance of 225 μmol/m(2)/s, and decreased with increasing irradiance. The up-regulation of secondary metabolites could be explained by the concomitant increases in H(2)O(2) and MDA activities under low irradiance. This condition also resulted in enhanced C/N ratio signifying a reduction in nitrogen levels, which had established significant negative correlations with net photosynthesis, total biomass and total chlorophyll content, indicating the possible existence of a trade-off between growth and secondary metabolism under low irradiance with reduced nitrogen content. The competition between total chlorophyll and secondary metabolites production, as exhibited by the negative correlation coefficient under low irradiance, also suggests a sign of gradual switch of investment from chlorophyll to polyphenols production.     

Anti-tumour promoting activity and antioxidant properties of girinimbine isolated from the stem bark of Murraya koenigii S

Girinimbine, a carbazole alkaloid isolated from the stem bark of Murraya koenigii was tested for the in vitro anti-tumour promoting and antioxidant activities. Anti-tumour promoting activity was determined by assaying the capability of this compound to inhibit the expression of early antigen of Epstein-Barr virus (EA-EBV) in Raji cells that was induced by the tumour promoter, phorbol 12-myristate 13-acetate. The concentration of this compound that gave an inhibition rate at fifty percent was 6.0 μg/mL and was not cytotoxic to the cells. Immunoblotting analysis of the expression of EA-EBV showed that girinimbine was able to suppress restricted early antigen (EA-R). However, diffused early antigen (EA-D) was partially suppressed when used at 32.0 μg/mL. Girinimbine exhibited a very strong antioxidant activity as compared to a-tocopherol and was able to inhibit superoxide generation in the 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced differentiated premyelocytic HL-60 cells more than 95%, when treated with the compound at 5.3 and 26.3 μg/mL, respectively. However girinimbine failed to scavenge the stable diphenyl picryl hydrazyl (DPPH)-free radical.     

Conductivity,thermal and infrared studies on plasticized polymer electrolytes with carbon nanotubes as filler

New composite polymer electrolytes (CPE) are prepared using solution-casting technique. The CPE are based on polyethylene oxide (PEO) and employ lithium hexafluorate (LiPF₆) as the doping salt, ethylene carbonate (EC) as the plasticizer and amorphous carbon nanotubes (αCNTs) as the filler. The crystallinity and ionic conductivity of the CPE are examined in this work. The conductivity increases from 10^?10 to 10^?5 S cm^?1 upon the addition of salt. The incorporation of EC and αCNTs into the salted polymer enhances the conductivity significantly to 10^?4 and 10^?3 S cm^?1. The Vogel–Tamman–Fulcher (VTF) plots suggest that the temperature dependence of conductivity is a thermally activated process. Differential Scanning Calorimetry (DSC) studies show that the melting transition temperature and crystallinity decrease upon the addition of salt, EC and αCNTs into the polymer electrolyte system. The complexation, nature and concentration of the various ionic species are examined using Fourier Transform Infrared Spectroscopy (FTIR). Scanning electron microscopy (SEM) images show the changes in morphologies of the composite polymer electrolytes. The application of CPE especially in batteries and the advantages of this composite are highly conductive and stable at elevated temperature.     

Effect of accelerators on thoria based nuclear fuels for rapid and quantitative pyrohydrolytic extraction of F? and Cl? and their simultaneous determination by ion chromatography

Pyrohydrolysis is a fast, reliable and convenient method for the decomposition of solid refractory samples. Thoria based mixed oxide nuclear fuels requires more than 1,200?°C reaction temperature to lose its structural integrity so as to release the halides. In the present paper, we report WO₃ accelerated pyrohydrolytic extraction technique for the separation of F^? and Cl^? from thoria based fuels along with the feasibility of using MoO₃ and V₂O₅. The mechanism of extraction has been investigated in detail using X-ray diffraction and recovery studies. ThO₂ along with its halides undergo high temperature solid state reaction with WO₃ forming Th(WO₄)₂ and releasing the halides for their subsequent hydrolysis. The quantification was carried out by ion chromatography with suppressed ion conductivity detection. The average recoveries of the spiked samples for F^? and Cl^? were 93?C99%. The method was successfully applied for simultaneous determination of F^? and Cl^? in thorium based nuclear fuel samples at 950?°C.     

Profile of Parkia speciosa Hassk Metabolites Extracted with SFE using FTIR‐PCA Method

A rapid identification, classification and discrimination tool, using Fourier Transform Infrared (FTIR) spectroscopy combined with Principal Component Analysis (PCA), was developed and applied to determine the profile of the Supercritical Fluid Extraction (SFE) of Parkia speciosa seeds under various temperature and pressure conditions (313, 323, 333, 343, 353 and 363 K and 20.68, 27.58, 34.47, 41.37, 48.26, and 55.16 MPa). The separation and identification of the compounds was carried out by Gas Chromatography coupled with Time of Flight Mass Spectrometry (GC/TOF‐MS). This technique has made it possible to detect the variability obtained under different SFE conditions and the separation of different chemical compounds in P. speciosa seeds. The FTIR‐PCA results were verified by GC/TOF‐MS, and the FTIR‐PCA method successfully identified the unsaturated carboxylic acids with the highest percentage area under the different conditions.     

Fish Oil Recovery from Viscera of Indian Mackerel (Rastrelliger kanagurta) by Supercritical Fluid: An Optimization Approach

Fish viscera, a waste of fish processing industry, can be exploited as a source of PUFA‐rich fish oil for use in food or pharmaceutical industry and at the same time the environment can be protected from pollution by fish wastes. Fish oil was recovered from viscera of Indian Mackerel (Rastrelliger kanagurta), by different supercritical fluid extraction (SFE) e.g. continuous, co‐solvent, soaking, and pressure swing techniques and the yields were compared with that of the solvent extraction method. The SFE parameters such as pressure, temperature, and CO₂ flow rate were optimised by employing Response Surface Methodology (RSM) with a view to maximize the oil yield and minimize CO₂ consumption. The central composite rotatable design (CCRD) consisting of three variables provided 20 experimental settings. Multiple regressions determined the coefficients of the second‐order polynomial equation. The optimum parameters for all 4 techniques applied were found to be 35 MPa, 60 °C, and 2 mL min^?1 with an Oil recovery ranging from 93 to 99%. The study demonstrated a lower CO₂ consumption by the soaking and pressure swing techniques at the optimized conditions. Thus, the soaking and pressure swing techniques were most effective for extracting oil from fish viscera.     

A Crystallographic Study of S-Methyl 2-(5-Chloro-2-Oxoindolin-3-ylidene)Hydrazinecarbodithioate

Abstract  

S-methyl 2-(5-chloro-2-oxoindolin-3-ylidene)hydrazinecarbodithioate (SM5ClISA) has been prepared from S-methyldithiocarbazate and 5-chloroisatin. The compound crystallized in monoclinic crystal system with space group P 2₁/n, Z = 4, V = 1201.85(7) ?³ and unit cell parameters a = 6.5466(2) ?, b = 7.5056(3) ?, c = 24.6509(8) ?, α = γ = 90° and β = 97.1434(18)°. The crystal structure reveals that the compound exists in the thione form with the chlorine occupies the fifth position in the isatin ring with the bond length of 1.739(2) ?. The 5-chloroisatin moiety is trans with respect to the C3–N2 and C3–S4 bonds whereas the methyl group of the dithiocarbazate moiety is cis with respect to the C3–N2 and C3–S5 bonds.     

The Crystal Structure and Cytotoxicity of Centrosymmetric Copper(II) Complex Derived from S-methyldithiocarbazate with Isatin

Abstract  

Copper(II) complex of S-methyldithiocarbazate with isatin has been prepared and screened for their cytotoxic activities against MCF-7 (Human non-metastatic mammary gland adenocarcinoma cell line) and MDA-MB-231 (Human metastatic mammary gland adenocarcinoma cell line). The compound crystallized in an orthorhombic crystal system with a space group C 2cb and was found to be selectively active against MCF-7 cell line (Human non-metastatic mammary gland adenocarcinoma cell line with an IC₅₀ value 0.45 μg/mL. The crystal structure of this centrosymmetric Cu(SMISA)₂ complex (SMISA = Schiff base formed by condensation reaction of S-methyldithiocarbazate with isatin) showed that the copper atom has a distorted square-planar geometry with the Schiff base coordinated to the metal ion as a uninegatively charged bidentate ligand through the azomethine nitrogen and thiolate sulfur.