Thermal decomposition kinetics of thiophene-2-carboxaldehyde thiosemicarbazone complexes of nickel(II) and palladium(II)

The thermal analysis of Ni(II) and Pd(II) complexes with thiophene-2-carboxaldehyde thiosemicarbazone have been studied using TG technique. Their decompositions are subjected to critical evaluation using the equations of Coats-Redfern, Horowitz-Metzger and modified Horowitz-Metzger and the kinetic parameters (non-isothermal method) have been evaluated for each step of decomposition by the method of weighted least-squares.     

Thermal decomposition kinetics of polymeric complexes of copper(II) and mercury(II) with N,N′-bis(dithiocarboxy)piperazine

The thermal decomposition behaviour of polymeric complexes of Cu(II) and Hg(II) with N,N-bis(dithiocarboxy)piperazine is investigated in air by thermogravimetric (TG), derivative thermogravimetric (DTG) and differential thermal analysis (DTA) techniques. The kinetic parameters (non-isothermal method) for their decomposition have been evaluated by graphical as well as by least-squares methods. The equations of Coats-Redfern, Freeman-Carroll and Horowitz-Metzger have been applied. The results indicate that the values ofE,A and S obtained by these three different methods agree well. It was also found that the decomposition of these metal chelates follow first-order kinetics.

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Zusammenfassung Mittels TG, DTG und DTA wurde das thermische Zersetzungsverhalten von Polymerkomplexen aus Cu(II) bzw. Hg(II) mit N,N-Bis(dithiocarboxy)piperazin an Luft untersucht. Für ihre Zersetzung (nichtisotherme Methode) wurden die kinetischen Parameter sowohl graphisch als auch durch Methoden mit den kleinsten Fehlerquadraten ermittelt. Dabei wurden die Gleichungen von Coats-Redfern, Freeman-Carroll und von Horowitz-Metzger angewendet. Alle drei Verfahren zeigen übereinstimmende Resultate fürE, A undS. Es wurde weiterhin gefunden, daß diese Metallchelate einer Reaktion erster Ordnung unterliegen.

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The authors are thankful to Prof. C. G. R. Nair, Head of the Department of Chemistry, University of Kerala and Dr. M. P. Kannan, Department of Chemistry, University of Calicut for some helpful discussions.     

QUANTIS: Data quality assessment tool by clustering analysis

Automatically generated kinetic networks are ideally validated against a large set of accurate, reproducible, and easy-to-model experimental data. However, although this might seem simple, it proves to be quite challenging. QUANTIS, a publicly available Python package, is specifically developed to evaluate both the precision and accuracy of experimental data and to ensure a uniform, quick processing, and storage strategy that enables automated comparison of developed kinetic models. The precision is investigated with two clustering techniques, PCA and t-SNE, whereas the accuracy is probed with checks for the conservation laws. First, the developed tool processes, evaluates, and stores experimental yield data automatically. All data belonging to a given experiment, both unprocessed and processed, are stored in the form of an HDF5 container. The demonstration of QUANTIS on three different pyrolysis cases showed that it can help in identifying and overcoming instabilities in experimental datasets, reduce mass and molar balance closure discrepancies, and, by evaluating the visualized correlation matrices, increase understanding in the underlying reaction pathways. Inclusion of all experimental data in the HDF5 file makes it possible to automate simulating the experiment with CHEMKIN. Because of the employed InChI string identifiers for molecules, it is possible to automate the comparison experiment/simulation. QUANTIS and the concepts demonstrated therein is a potentially useful tool for data quality assessment, kinetic model validation, and refinement.     

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.     

COMPARISON OF THE EFFECTS OF UV-VISIBLE IRRADIATION OF MELANINS and MELANIN-HEMATOPORPHYRIN COMPLEXES FROM HUMAN BLACK and RED HAIR

Clinical evidence indicates that people with light skin and red hair have a higher incidence of UV radiation-induced diseases including cancer. It is not known whether this is because of the lower protection due to the smaller amounts of eumelanin present in the skin of these people or whether the presence of pheomelanin in their skin is responsible for the higher susceptibility to carcinogenesis. Irradiation of melanoproteins from red hair with UV-visible light has been reported to produce superoxide. Comparative studies on the formation of superoxide during the irradiation of the melanins isolated from human black and red hair (BHM and RHM, respectively) are reported in this paper. These showed that no superoxide formation could be detected in the case of the BHM. whereas the formation of superoxide during the irradiation of RHM could be definitely demonstrated. Irradiation of the RHM with NADH resulted in the oxidation of more NADH than the irradiation of NADH with BHM. The observation that RHM is an active photosensitizer indicates that this property of pheomelanin present in light skin may at least partly be responsible for the harmful effect of radiation on people with light skin and/or red hair. Administration of hematoporphyrin followed by visible irradiation is a currently used mode of therapy for cancer. The present studies have shown that hematoporphyrin is bound to both BHM and RHM. The binding of hematoporphyrin to the melanins increased the formation of superoxide by RHM and the oxidation of NADH by both the melanins. The binding of porphyrins to melanins may have an influence upon the photosensitivity in diseases such as porphyrias and may also affect the therapeutic efficacy of hematoporphyrin.     

Nanoclay modified silica phenolic composites: mechanical properties and thermal response under simulated atmospheric re‐entry conditions

Ablative nanocomposites based on nanoclay‐dispersed addition curable propargylated phenolic novolac (ACPR) resin, reinforced with chopped silica fiber, were investigated for their thermal response behavior under simulated heat flux conditions corresponding to typical atmospheric re‐entry conditions. Organically modified nanoclay (Cloisite 30B) was incorporated to different extents (1–10%) in the ACPR resin matrix containing silica fiber to form the composite. The composites displayed optimum mechanical properties at around 3 wt% of nanoclay loading. The resultant composites were evaluated for their ablative characteristics as well as mechanical, thermal and thermo‐physical properties. The reinforcing effect of nanoclay was established and correlated to the composition. The mechanical properties of the composites and its pyrolysed product improved at moderate nanoclay incorporation. Plasma arc jet studies revealed that front wall temperature is lowered by 20°C and that at backwall by 10–13°C for the 3 wt% nanoclay‐incorporated composites due to impedance by nanoclay for the heat conduction. Nanoclay diminished the coefficient of thermal expansion by almost 50% and also reduced the flammability of the composites. The trend in mechanical properties was correlated to the microstructural morphology of the composites. The nanomodification conferred better strength to the pyrolysed composites. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis, characterization, and antifungal studies of transition metal complexes of ω-bromoacetoacetanilide isonicotinylhydrazone

Isonicotinic acid hydrazide or isonicotinylhydrazide, commonly known as isoniazid, is an antibacterial agent that has been used to treat tuberculosis. It interacts with microbial cell walls. Schiff’s bases or anils are the compounds having >C=N−N< linkages, which have immense applications as catalysts, stabilizers, pigments, dyes, and drugs. They have good ability to form chelates with many metal ions. Isoniazid can form Schiff’s bases with diketones such as acetoacetanilide. Acetoacetanilide isonicotinylhydrazone and its metal chelates exhibit anticancer activity. Our studies on N-methyl-acetoacetanilide isonicotinylhydrazone and its metal chelates revealed that they are active against pathogenic fungal strains. Hence, it is worthwhile to synthesize new complexes of ligands having different substituents on the acetoacetanilide moiety. We synthesized five new metal chelates of ω-bromoacetoacetanilide isonicotinylhydrazone. The ligand behaved as a tridentate monoanion or as a tridentate dianion in the complexes. These compounds were characterized mainly by elemental analysis; conductivity measurements; and electronic, infrared, and nuclear magnetic resonance spectral studies. We also carried out antifungal studies of these compounds against four selected pathogenic fungal strains using a cup-plate technique. Both the ligand and its metal chelates were active against all fungal strains investigated. However, the chelates were found to be more active than the ligand.     

Synthesis,characterization and antitumour studies of metal chelates of acetoacetanilide thiosemicarbazone

Summary Complexes of transition metals with acetoacetanilide thiosemicarbazone, AatH₂, have been prepared and characterized. The complexes were found to have the following stoichiometries: [Mn(Aat)(H₂O)₂]_n; [Zn(Aat)(H₂O)₂]; [M(Aat)(H₂O)], where M = Cd^II or Hg^II; [Cu(Aat)]_n; [Ag(AatH)]; [M(AatH)₂], where M = Co^II or Ni^II, and [Fe(Aat)Cl(H₂O)]_n. The compounds have been studied for their possible antitumour activity against Ehrlich Ascites tumour cells in vitro.     

Synthesis,characterization and thermal analysis of [Fe(N2H4)2(CH3COO)2]

[Fe(N₂H₄)₂(CH₃COO)₂] was synthesised and characterized for the first time by chemical analysis, magnetic measurements, electronic and IR spectral studies. Its thermal reactivity was ascertained by thermogravimetric (TG) and derivative thermogravimetric (DTG) techniques and it has been concluded that unlike some other metal carboxylate hydrazinates, it does not show any autocatalytic behaviour. The decomposition was also subjected to kinetic analysis using the equations of Coats-Redfern and Horowitz-Metzger by the method of weighted least-squares.     

Preparation and characterization of vanillin thiosemicarbazone complexes with Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II)

Complexes of vanillin thiosemicarbazone (3-methoxy-4-hydroxybenzaldehyde thiosemicarbazone), (vtsch) with several divalent metal ions have been isolated. Structures have been assigned to these complexes based on electrical conductivity, magnetic susceptibility and spectroscopic measurements