The Identification and Quantification of Phospholipids from Thermus and Meiothermus Bacteria

Structural identities of the major phospholipid (PL-2), minor phospholipid (PL-1) and trace phospholipid (PL-0) from representative strains of the genera Thermus and Meiothermus were established. Phospholipids were quantified using phosphorus-31 nuclear magnetic resonance (³¹P-NMR). The structures of the major phospholipid (PL-2) from Thermus filiformis MOK14.7 and Meiothermus ruber WRG6.9 were identified as 2′-O-(1,2-diacyl-sn-glycero-3-phospho)-3′-O-(α-N-acetylglucosaminyl)-N-glyceroyl alkylamine (GlcNAc-PGAA) and 2′-O-(2-acylalkyldiol-1-O-phospho)-3′-O-(α-N-acetylglucosaminyl)-N-glyceroyl alkylamine (GlcNAc-diolPGAA). Interestingly, M. ruber contained only a diacyl form of GlcNAc-PGAA (87 %), while T. filiformis contained both GlcNAc-PGAA (59 %) and GlcNAc-diolPGAA (18 %). The structures of the minor phospholipid (PL-1) were established as 2′-O-(1,2-diacyl-sn-glycero-3-phospho)-3′-O-(α-glucosaminyl)-N-glyceroyl alkylamine (GlcN-PGAA, 13 %) in T. filiformis and 2′-O-(1,2-diacyl-sn-glycero-3-phospho)-3′-O-(α-galactosaminyl)-N-glyceroyl alkylamine (GalN-PGAA, 19 %) in M. ruber. This is the first reliable discovery of phosphatidylglyceroylalkylamines modified by glucosamine or galactosamine with a free amino group. No signs of diol-based phosphatidylglyceroylalkylamines were found in PL-1 phospholipids. Similar to PL-2, trace phospholipid (PL-0) from T. filiformis contained both unsubstituted diol-based phosphatidylglyceroylalkylamine (diolPGAA) and PGAA, while M. ruber contained only free PGAA. Unlike analysis using TLC, the diol form of phosphatidylglyceroylalkylamines is clearly resolved from the diacyl form via ³¹P-NMR.     

Photostabilization of organic UV-absorbing and anti-oxidant cosmetic components in formulations containing micronized manganese-doped titanium oxide

Micronized titanium oxide (TiO2) and manganese-doped titanium oxide (TiO2:Mn) particles have been incorporated into a variety of oil-in-water (O/W) and water-in-oil-in-water (W/O/W) emulsions in conjunction with the UV-absorbing organic compounds butyl methoxydibenzoylmethane (BMDM) and octyl methoxycinnamate (OMC) and with the anti-oxidants vitamin E and vitamin C. The retention of the organics under solar exposure has been shown to be significantly enhanced by the addition of TiO2:Mn to the formulation. In the case of BMDM and OMC, the retention is increased from 20% and 24% to 63% and 83%, respectively, after 2 h of solar exposure. In this system, TiO2 particles are shown to provide only limited protection relative to BMDM and OMC. Vitamin E and vitamin C are actively degraded by the presence of TiO2 in the emulsion during solar exposure. This effect is reversed with TiO2:Mn, the use of which can protect >90% of anti-oxidants in both the oil and water phases of the formulation. The absence of reactive oxygen species (ROS) generation and surface scavenging of ROS by TiO2:Mn is responsible for a significantly reduced ROS load on the organic components and consequent photostabilization of the emulsion.     

Analytical and computational improvements in performance-index ranking algorithms for networks

Performance-index ranking algorithms, relatively recent innovations in network analysis, are distinguished by the fact that they can rank a large set of network parameter and injection change cases very rapidly. To date, their major application has been for automatic contingency selection in power systems. Here, various enhancements to the approach are given and it is shown how general ranking formulas, valid for multiple branch contingencies, can be derived easily. A ranking formula for generator contingencies, hitherto unavailable, is presented. A sparse matrix technique that permits the rapid exact evaluation of the ranking formulas is given. The speed of the performance-index ranking algorithm is estimated for several large network problems, and found to be orders of magnitude higher than that of its direct though more versatile alternative, explicit linearized contingency evaluation.     

The structure and mechanism of formation of the ‘glaze’ oxide layers produced on nickel-based alloys during wear at high temperatures

The structure and composition of the worn surfaces, and in particular of the tribologically important ‘glaze’ region, formed on Nimonic 75, Nimonic C263, Nimonic 108 and Incoloy 901 after sliding in air at elevated temperatures (150–800°C) have been determined. A typical wear scar is comprised of a number of areas, some having a thin, physically homogeneous surface ‘glaze’ layer, the rest having no ‘glaze’ surface. The ‘glaze’ layer lies on top of a region either of highly compacted oxide particles above a growing, steady-state oxide layer, or of alloy, deformed to varying degrees, depending on time of sliding, ambient temperature and the relative strength of the alloy.Electron diffraction shows the surface ‘glazes’ to consist of simple oxides after sliding at temperatures up to 400°C, viz. NiO in that on all four alloys, CoO on N108 and C263, and FeO on Incoloy 901. At the higher temperatures, NiCr₂O₄ is observed in the ‘glaze’ on all the alloys, with NiO and Cr₂O₃ on N75, Cr₂O₃ and probably CoO on C263 and N108 and α-Fe₂O₃, FeO and Fe₃O₄ on Incoloy 901. The ‘glaze’ and underlying, wear-affected, oxidized regions are shown by ion microprobe mass spectrometry, electron spectroscopy and electron probe microanalysis to consist of oxides, containing all the alloying elements, approximately in the same average proportions as in the alloys. Three possible mechanisms for the formation of the observed structure of the ‘glaze’ regions are proposed.It is concluded that high-strength properties and relatively rapid transient oxidation rates at elevated temperatures are desirable qualities in alloys employed under high temperature sliding conditions.     

The influence of aluminum additions on the oxidation of Co-Cr alloys at 1000 and 1200°C

The isothermal oxidation of Co-Cr-Al alloys, containing 10–30 % Cr and 1 or 4.5% Al in 1 atm flowing oxygen at 1000 and 1200°C has been studied by thermogravimetric methods, optical metallography, electron probe microanalysis, and scanning electron microscopy. The addition of 1 % Al to Co-10% Cr and Co-15% Cr has little effect on the over-all oxidation rate, although there is increased internal oxidation and the outer-inner scale thickness ratio is decreased. The oxidation rate is controlled largely by Co²⁺ ion diffusion out through the entire scale, with oxygen gas transport across voids, spinel blocking effects and doping in the inner layer probably playing subsidiary roles. With Co-15 %-Cr-1%Al, limited healing by Cr₂O₃ increases progressively with time at the alloy-oxide interface. An addition of 1 % Al to Co-30 %Cr assists the formation of an initially protective Cr₂O₃-rich surface layer by internally oxidizing, thereby allowing more of the chromium to diffuse to the surface and form an external scale. This Cr₂O₃ layer tends to lift and crack open, enabling CoO-rich scales to form on the exposed alloy. Co-15%Cr-4.5% Al produces a protective -Al₂O₃ layer on certain surface regions, sometimes with an overlying Cr₂O₃ layer and internal -Al₂O₃ particles in the underlying alloy. In other regions, rapidly growing CoO-rich nodules develop from the outset, or after early lifting and fracture of the -Al₂O₃ scale. Generally, the presence of 28% Cr and 4.5% Al is sufficient to ensure an external scale of -Al₂O₃, the chromium acting as an oxygen getter. If such scale fractures, healing is very rapid.     

The high-temperature internal oxidation and intergranular oxidation of nickel-chromium alloys

The development of internal oxides and intergranular oxides in dilute NiCr alloys, containing 1–5% Cr, in NiNiO packs and in 1 atm oxygen at 800–1100°C has been investigated. The internal oxide particles were relatively coarse and widely spaced and were Cr₂O₃, except for a narrow band adjacent to the surface where NiCr₂O₄ particles were also present. Several types of intergranular oxide were developed in the Ni/NiO packs, with preferential penetration being more extensive in the higher chromium-containing alloys at the lower temperatures. Discrete intergranular oxide particles were formed deep in the alloy beneath bands of Cr₂O₃ which developed over intersections of the alloy grain boundaries with the surface, or beneath continuous or discontinuous grain-boundary oxides near the surface, possibly due to the development of a relatively flat oxygen profile and a steep chromium gradient in the subjacent alloy. In the presence of a thickening NiO external scale, preferential intergranular oxidation was much less extensive than in the Ni/NiO packs as the rapid growth of the scale prevented development of Cr₂O₃-rich surface bands.     

Regions required for CD4 binding in the external glycoprotein gp120 of simian immunodeficiency virus

The external domain of the envelope glycoprotein, gp120, of simian immunodeficiency virus (SIV) has been expressed as a mature secreted product using recombinant baculoviruses and the expressed protein, which has an observed molecular mass of 110 kDa, was purified by monoclonal antibody (MAb) affinity chromatography. N-terminal sequence analysis showed a signal sequence cleavage identity similar to that of the gp120s of both human immunodeficiency virus type 1 (HIV-1) and HIV type 2. The expressed molecule bound to soluble CD4 with an affinity that was approximately 10-fold lower than that of gp120 from HIV-1. A screening of the ability of SIV envelope MAbs to inhibit CD4 binding revealed two groups of inhibitory MAbs. One group is dependent on conformation, while the second group maps to a discrete epitope near the amino terminus. The particular role of the V3 loop region of the molecule in CD4 binding was investigated by the construction of an SIV-HIV hybrid in which the V3 loop of SIV was precisely replaced with the equivalent domain from HIV-1 MN. The hybrid glycoprotein bound HIV-1 V3 loop MAbs and not SIV V3 MAbs but continued to bind conformational SIV MAbs and soluble CD4 as well as the parent molecule.     

Erosion-corrosion regimes: number, nomenclature and justification?

In studies of elevated temperature erosion by solid particles in oxidizing gaseous environments, several regimes of interaction have been identified. These regimes define whether wastage occurs predominantly due to erosion of the alloy substrate, corrosion of the substrate, or a mechanism intermediate between these processes, and various criteria for the transitions between such regimes have been identified by different investigators. In such cases, the possible number and nomenclature of regimes can sometimes be unclear.The purpose of this paper is to review all the available information on the various erosion-corrosion regimes which have been identified. The similarities and the differences between the various approaches to defining regimes are discussed. In addition, the criteria for their identification are evaluated critically. The importance of the identification of such regimes is discussed. The use of such information to establish zones of minimum wastage on erosion-corrosion maps is demonstrated. In addition, the ability of such regimes to identify variations in erosion-corrosion rate with the main erosion-corrosion variables is indicated.