Lynne Katsikas

A "Double-Diamond Superlattice" Built Up of Cd17S4(SCH2CH2OH)26 Clusters

A simple preparation of Cd17S4(SCH2CH2OH)26 clusters in aqueous solution leads to the formation of colorless blocky crystals. X-ray structure determinations revealed a superlattice framework built up of covalently linked clusters. This superlattice is best described as two enlarged and interlaced diamond or zinc blende lattices. Because both the superlattice and the clusters display the same structural features, the crystal structure resembles the self-similarities known from fractal geometry. The optical spectrum of the cluster solution displays a sharp transition around 290 nanometers with a large absorption coefficient (∼84,000 per molar per centimeter).

Heavy Metals in Seafood Mussels. Risks for Human Health

Life on earth is threatened both by environmental pollution and overpopulation. Natural phenomena contributing to pollution have always existed but anthropogenic activities are increasing contamination of air, soil and water. Waters are especially polluted by metals. The main threats to life from toxic metals are associated with exposure to Pb, Cd, Hg and As, which accumulate in organisms. Overpopulation means more food is required but the amount of arable land is declining due to human requirements. One way of overcoming these consequences of overpopulation is to exploit seas and oceans. Thus, the consumption of seafood has increased in recent years, especially in coastal regions. However, as many traditional fishing grounds have been over-fished, aquaculture seems a viable solution to these problems. Marine mussels are an excellent candidate for aquaculture. However mussels accumulate a wide range of metals in their soft tissue. Thus, the determination of the concentrations of potentially toxic substances in mussels is essential because of their usage as seafood and the potential adverse effects of their consumption on human health. Moreover, as contamination by metal pollutants continues and is even increasing in some parts of the world, particularly in less developed countries, it is also important to determine the level of pollution in the marine environment, especially in regions where aquaculture is foreseen and where the local population consumes large amounts of mussels.

The photopolymerisation of methacrylic acid by colloidal semiconductors

SummaryMethacrylic acid was photopolymerised using CdS and composite, CdS/HgS and CdS/TiO2, colloidal semiconductor particles as initiators. The previously proposed photoinitiation mechanism involving the photogenerated positive hole in the valence band of the CdS colloid was confirmed by the electron scavenging action of TiO2. The effect of pH on the course of the polymerisation was investigated and is discussed.

Thermogravimetric characterisation of poly(methyl methacrylate) photopolymerised by colloidal cadmium sulphide

The thermal stability of poly(methyl methacrylate) (PMMA) photopolymerised using colloidal cadmium sulphide as the photoinitiator was studied by thermogravimetry (TG) and differential TG (DTG).The thermal stability of the CdS initiated PMMA was greater than that of conventional radically polymerised PMMA and approached that of anionically prepared PMMA. The DTG curve of the CdS initiated PMMA was a composite of four peaks, three of which correspond to the three peaks observed in the DTG curve of standard radically prepared PMMA. It is suggested that the additional peak arises from a new mode of depolymerisation initiation, that is, from chain end unsaturation introduced into the polymer chain during polymerisation initiation with the colloidal CdS.

The polymerisation kinetics of lower dialkyl itaconates

SUMMARY: The free radical polymerisation kinetics of diethyl- (DEI), dipropyl- (DnPI), dibutyl- (DnBI), and dihexyl itaconate (DHI) in the bulk were studied in the temperature range from 50 to 70 C. The concentration of the initiator, 2,2 -azoisobutyronitrile (AIBN), was varied between 0.02 and 0.085 mol/dm 3 . The rate of polymerisation (Rp), degree of polymerisation (DP), overall polymerization rate constant (K), the ratio of the propagation and termination rate constants (kp/kt 1/2 ), as well as the chain transfer constant to monomer (CM) were determined. The values of Rp, K, and kp/kt 1/2 of the investigated monomers all increase with increasing size of the alkyl group in the ester substituent, whereas CM decreases when going from the dimethyl to the dihexyl ester. The values of CM are larger than the corresponding values for the alkyl esters of methacrylic acid.

The thermal degradation of some alkali metal salts of poly(itaconic acid)

The Li-, Na- and K salts of poly(itaconic acid) (PIA) were prepared by treating the polyacid with the corresponding aqueous hydroxide.The resulting polysalts were analyzed by elemental analysis, FTIR spectroscopy and thermogravimetry. The results indicate that the polysalts are thermally more stable than the parent PIA, they all degrade in a similar manner and somewhat more complexly than the poly(methacrylic acid) salts.

Radiation-induced Strand Breakage in Poly(Riboadenylic Acid). A Pulse Radiolysis Study on the Protective Action of Cysteamine Under Anoxic Conditions

Poly(riboadenylic acid) was irradiated in N2O-saturated dilute aqueous solution at pH 7.8 with single pulses (50-200 ns) of 16 MeV electrons. With the aid of Rayleigh light scattering measurements both the extent and rate of main-chain scission were measured in the absence and the presence of cysteamine (RSH). In both cases two modes of light scattering intensity (LSI) decrease were detected. From this finding it was concluded that two chemically different radical sites, giving rise to main-chain breakage, were produced by OH attack on the macromolecules. Cysteamine reduced the extent of LSI decrease and accelerated the rate of the slow mode of LSI decrease significantly. The fast mode of the LSI decrease is due to fragment diffusion and therefore the influence of cysteamine on the rate of decay of the short-lived radical could not be studied. The assessment of the relative importance of .OH scavenging (RSH + .OH----RS. + H2O) and of repair (PA. + RSH----PAH + RS.) with respect to protection yielded the following: in the case of the long-lived radical, repair contributes significantly at low RSH concentration (less than 10(-4) M); in the case of the short-lived radical, OH scavenging dominates and repair becomes noticeable only at [RSH] greater than 10(-4)M. The following data were evaluated in this work: 100 eV-yield of main-chain scission, G(sb) = 1.1; lifetimes of radicals: less than 50 microseconds (short-lived), 0.6 s (long-lived), kPA. + RSH = 3.4 X 10(6)M-1 S-1 (for long-lived radicals).

The Thermal Degradation of Poly(dimethyl Itaconate-co-4-vinylpyridine)

Copolymers of dimethyl itaconate (DMI) and 4-vinylpyridine (4VP) were synthetized in toluene at 60°C with0.26 mol% of AIBN as initiator. Their compositions were determined by differential refractometry and by differential scanning calorimetry. The 4VP contents of the copolymer samples ranged between 7 and 75 mol%. The reactivity ratios calculated via the Fineman-Ross method were r1=0.24 (DMI) and r2=0.57 (4VP).The thermal degradations of these copolymers were studied. The results of thermogravimetric measurements indicated that the copolymers degrade at lower temperatures than those of their parent homopolymers. A possible explanation of this anomalous behaviour is the formation of thermally unstable structures during the copolymerisation.

The thermal degradation of poly(di-n-hexyl itaconate) prepared in the presence of n-dodecyl mercaptan

Abstract The preparation of poly(di- n -hexyl itaconate) (PDHI) in the presence of the chain transfer agent n -dodecyl mercaptan resulted in polymers of increased thermal stability, owing to the suppression of the number of chain terminal double bonds. The polymers were characterised by Fourier transform IR (FTIR) spectroscopy and gel permeation chromatography. The differential thermogravimetry (DTG) curves of all the PDHI samples had two peaks, showing that degradation occurred in two stages. The area of the lower-temperature DTG peak correlated with the number of terminal double bonds.

The thermal degradation kinetics of dextran and pullulan

The effect of molar mass and, in the case of dextran, of the degree of branching on the thermal degradation kinetics of dextran and pullulan was studied in the presence and absence of oxygen. Although the initial mass loss of the dextran samples occurred at higher temperatures than that of the pullulan samples, the overall thermal degradation activation energies were lower for dextran than for pullulan. In the case of dextran the thermal stability was found to decrease with molar mass and degree of branching. The molar mass of pullulan, in the range of 104 to 105 g/mol, appeared to have no significant influence on the thermal characteristics of the samples.ZusammenfassungIn und ohne Gegenwart von Sauerstoff wurde der Einfluß der Molekülmasse, im Falle von Dextran auch der Einfluß des Verzweigungsgrades auf die thermische Zersetzungskinetik von Dextran und Pullulan untersucht. Obwohl der anfängliche Masseverlust der Dextranproben bei höheren Temperaturen eintrat als bei den Pullulanproben, ist die Gesamtaktivierungsenergie der thermischen Zersetzung für Dextran niedriger als für Pullulan. Im Falle von Dextran sinkt die thermische Stabilität mit der Molekülmasse und dem Verzweigungsgrad. Die Molekülmasse von Pullulan scheint im Bereich 104 bis 105 g/mol keinen signifikanten Einfluß auf die thermischen Merkmale der Proben zu haben.