Molecular distribution of some commercial nonylphenol ethoxylates using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Nonylphenol ethoxylates (NPEs) belong to a group of nonionic surfactants that are collectively referred to as alkylphenol ethoxylates (APEs). APEs find widespread use in heavy-duty commercial and household cleaning formulations, shampoos, and industrial processing, i.e. textile manufacture. Their environmental impact depends on the molecular distribution and the extent of their biodegradation in municipal sewage systems, waterways and rivers. We have established two sample preparation methods that have enabled the determination of the molecular distributions of six commercial nonylphenol ethoxylates using matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS). In both methods, alpha-cyano-4-hydroxycinnamic acid, dissolved in acetonitrile/tetrahydrofuran, was used as the matrix. In one set of experiments, the NPEs were dissolved in an acetonitrile/tetrahydrofuran solvent system prior to mixing with the matrix solution, and the resulting MALDI-TOF mass spectra produced mostly sodiated molecules [M + Na](+). The NPEs, all having the formula 4-(C(9)H(19))-C(6)H(4)-(OCH(2)CH(2))(n)-OH, are Surfonic (R)N-95, N-100, N-102, N-120, N-150 and N-300. Surfonic N-95 and N-100 gave n values of 5-20; Surfonic N-102, N-120, N-150, and N-300 gave n values of 5-21, 5-22, 8-25 and 15-40, respectively. In order to develop a sample preparation method that could be used with less polar NPEs, we dissolved the NPEs (except N-300) in pentane prior to mixing with the matrix solution, and found that the MALDI spectral quality was unaffected by the solvent systems. Copyright 1999 John Wiley & Sons, Ltd.     

Nonlinear vibration and dynamics of ceramic on ceramic artificial hip joints: a spatial multibody modelling

The present study investigates nonlinear vibration and dynamic behaviour of a ceramic-on-ceramic hip implant. The aim of this research is to firstly gain a better understanding of hip squeaking and vibration and secondly to investigate the effect of friction on contact point path during normal gait. For this purpose, a spatial multibody dynamic hip model was developed, using a friction-velocity constitutive law combined with a Hertzian contact model. Furthermore, the physiological three-dimensional rotation angles and forces are taken into account to calculate tangential and normal contact forces, respectively. Comparing the outcomes with that available in the literature allowed for the validation of our approach. It was shown that the cause of hip squeaking is friction-induced vibration owing to different phenomena such as stick–slip friction, negative-sloping friction and contact force changes. Moreover, friction-induced vibration does significantly change contact point path during the gait when compared to non-friction analysis.     

Photo-stabilising action of metal chelates in polypropylene—Part III: Thermal antioxidant action and its relationship to photo-stabilisation

The thermal antioxidative behaviour of three metal chelates in polypropylene film has been examined using hydroperoxide analysis and infra-red spectroscopy. All three chelates inhibit both hydroperoxide and carbonyl group formation during oxidation. Their thermal antioxidant efficiencies follow closely their photo-stabilising effects, suggesting that similar mechanisms of protection are involved. The rates of photo-decomposition of the metal chelates measured by second order derivative absorption spectroscopy were found to be independent of initial hydroperoxide concentration, indicating that they are ineffective macroalkoxy and hydroxy radical traps. The results suggest that metal chelates compete effectively with oxygen for macroalkyl radicals thermally and photochemically.     

Octopamine increases the excitability of neurons in the snail feeding system by modulation of inward sodium current but not outward potassium currents

Background  

Although octopamine has long been known to have major roles as both transmitter and modulator in arthropods, it has only recently been shown to be functionally important in molluscs, playing a role as a neurotransmitter in the feeding network of the snail Lymnaea stagnalis. The synaptic potentials cannot explain all the effects of octopamine-containing neurons on the feeding network, and here we test the hypothesis that octopamine is also a neuromodulator.     

Flux vortex pinning in a simple model system

Results of numerical calculations of flux vortex pinning by random one and two dimensional arrays of identical pinning centres are reported. Three different methods for determining the critical state flux gradient are described and the critical state concept is shown to break down for samples smaller than a certain size.     

Photo-stabilising action of metal chelate stabilisers in polypropylene: Part VIII—Pigment interactions

The interaction of four metal chelates—Cyasorb UV 1084, Irganox 1425, Irgastab 2002 and Sanduvor NPU—with five commercial pigments, anatase and rutile titanium dioxide, cadmium yellow, Vynamon Blue B and Monolite Yellow G, is examined using infra-red spectroscopy. Individually, four pigments offer some stabilisation to processed polypropylene. Their order of stabilisation is Monolite Yellow G > Vynamon Blue B > cadmium yellow ～ rutile titanium dioxide. Anatase titanium dioxide showed mild sensitising action. When mixed with the metal chelates their order of stabilisation is variable. The effect of a commercial antioxidant, Irganox 1010, is also examined. It is found that the antioxidant tends to suppress any synergistic effects that may be present between the chelate and the pigment.     

Photo-stabilising action of metal chelate stabilisers in polypropylene: Part V—Light stability as a function of concentration and further studies in metal stearate-stabiliser systems

The effect of concentration on the light stabilising efficiency of three metal chelates in polypropylene film has been examined. Both the calcium and nickel complexes of bis(ethyl-3,5-di-tert-butyl-4-hydroxybenzyl) phosphonate (Irganox 1425 and Irgastab 2002, respectively) exhibit the same behaviour and have a limiting concentration above which no significant further photo-protection occurs. However, in the case of the nickel complex of 2,2′-thiobis(4-tert-octyl-phenolato) n-butylamine (Cyasorb UV 1084), there is a linear relationship between light stability and concentration up to 0·1% w/w of additive. Deviations from this linearity appear at higher concentration levels. The results confirm earlier conclusions that the photo-oxidation products of the first two chelates are photo-active, whereas those of the latter are themselves photo-stabilisers.Further studies on the effects of metal stearates on the stabilising action of the two nickel complexes have been carried out. In the case of Cyasorb UV 1084, synergism was observed with strontium stearate whereas antagonism was present with all the other stearates, their order of stability being Zn > Na > Mg > Co. On the other hand, all the stearates were antagonistic with Irgastab 2002, their order of stability being Na > Co ≈ Zn > Sr > Mg. The effects are accounted for on the basis of metal exchange, supporting our earlier findings.