On additives, morphological evolution and dielectric breakdown in low density polyethylene

A series of low density polyethylene systems has been studied with respect to structural evolution and short-term dielectric breakdown behaviour. All materials were based upon a single polymer, that is commonly used in high voltage applications, but with different additives. In all three of these systems, multiple melting transitions were observed, as a result of molecular fractionation effects during crystallization. In the virgin polymer, a space-filling banded spherulitic morphology was found to develop at low temperatures (102 °C and below) whereas, at higher temperatures, only a few isolated axialites were observed. Inclusion of the antioxidant resulted in greatly increased nucleation densities, such that, at low temperatures, no evidence of spherulitic organisation remained. At higher temperatures, sheaf-like lamellar aggregates developed, which were much smaller and much more numerous than in the case of the virgin polymer. Further addition of dicumyl peroxide (DCP) resulted in the rapid formation of a crosslinked network at 200 °C. Some crosslinking also occurred at 150 °C, but over a much longer timescale. Where extensive crosslinking occurred prior to crystallization, the resulting gel inhibited structural development, such that only a few small, isolated sheaves were able to form at 102 °C. In view of the principal application area of this material, the breakdown strength of each of the above systems was then measured and the whole data set was analysed statistically. When structural factors were considered alongside the statistics, no clear trends emerged to indicate that either the compositional or morphological variations were reflected in the short-term electrical failure processes.     

Analysis of anions by solid-state spot-tests

Trituration and capillary solid-state spot-tests for 25 anions with a number of organic and inorganic reagents have been examined. A comparative study of the corresponding reactions in solution has also been made. Incorporation of a glass-wool plug in the capillary improves the selectivity. Schemes are presented for possible use of the technique.     

PHOTOSENSITIVITY IN THE SKIN OF THE LIZARD, Anolis carolinensis

Skin of the lizard, Anolis carolinensis, is remarkably sensitive to light. Illuminated in vitro with visible light from a tungsten source (110 W (m-2)), skin changes from brilliant green to dark brown (50% reduction in reflectance) within 2-4 min as a result of dispersion of melanin from a perinuclear position within dermal melanophores into superficial dendritic processes. Reversal of the process, reaggregation of pigment, will occur within 2.0 min upon return to darkness. This photic response can be initiated with light levels as low as 5.0 W m(-2) and is maximized by light levels only 5% that of midwinter sunshine. Pigment dispersion in response to both melanocyte simulating hormone and to light is inhibited by cytochalasin-B, indicating that microfilaments may be the motor element for pigment movement in that direction. Colchicine, but not cytochalasin-B, totally blocks pigment reaggregation following melanocyte stimulating hormone exposure and partially blocks it in the dark phase of the photic response. The results of this study are consistent with a model for pigment movement in A. carolinensis that provides microfilaments for pigment dispersion and microtubule involvement in both dispersion and aggregation. Finally, because it is readily visible, easily quantified, rapid and reversible, photic response in the skin of A. carolinensis is recommended as a valuable model system for the study of saltatory movement of organelles within cells.     

Dimethyldihydropyrene-dehydrobenzoannulene hybrids: studies in aromaticity and photoisomerization

The synthesis and study of dehydrobenzoannulene (DBA)-dimethyldihydropyrene (DDP) hybrids as models for the investigation of aromaticity in weakly diatropic systems is reported. Three new monofused DBA-DDP hybrids have been synthesized, and their NMR spectra are discussed with regard to quantifying the aromaticity remaining in multibenzene-fused DBAs. Nucleus-independent chemical shifts, determined at a series of locations for each compound, bond lengths, and (1)H and (13)C NMR chemical shifts were calculated and used to probe the aromaticity of these hybrids. Systems where more than one annulene/DBA is fused to the DDP core have also been obtained, and their potential use in photoinduced isomerization applications is discussed.     

Fine structures of zeolite-Linde-L (LTL): surface structures, growth unit and defects

High-resolution electron microscopy (HREM) has been used to image the surface structure of nano- and micrometer-sized synthetic crystals of zeolite-Linde-L (LTL). Columnar holes and rotational, nano-sized, wheel-like defects were observed within the crystals, where the hole has a minimum size equal to that of the rotational defect. Predictions of surface structure from atomistic computer simulation concur with the observations from HREM and provide insight into the crystal growth mechanism of perfect and defective LTL. Analysis of the energetics of the formation of rotational defect structures reveals that the driving force for defect creation is thermodynamic and furthermore, the rotational defects could be created in high concentrations. Formation of a columnar hole is found to be slightly energetically unfavourable and therefore we speculate that the incidence of both rotational and nano-sized vacancy defects is strongly dependent on kinetic factors and reaction conditions. The morphology of nano- and microcrystalline LTL is contradistinct and we use insights from simulation to propose an explanation of the disparity in crystal shape.     

NMR and UV studies of 3'-S-phosphorothiolate modified DNA in a DNA : RNA hybrid dodecamer duplex; implications for antisense drug design

High-resolution NMR spectroscopy has been used to establish the conformational consequences of the introduction of a single 3[prime or minute]-S-phosphorothiolate link in the DNA strand of a DNA : RNA hybrid. These systems are of interest as potential antisense therapeutic agents. Previous studies on similarly modified dinucleotides have shown that the conformation of the sugar to which the sulfur is attached shifts to the north (C(3[prime or minute])-endo/C(2[prime or minute])-exo). Comparisons made between NOESY cross-peak intensities, and coupling constants from PE-COSY spectra, for both non-modified and modified duplexes confirm that this conformational shift is also present in the double helical oligonucleotide system. In addition it is noted that in both the dinucleotides and the modified duplex, the conformation of the sugar ring 3[prime or minute] to the site of modification is also shifted to the north. That this pattern is observed in the small monomeric system as well as the larger double helix is suggestive of some pre-ordering of the sequences. The conclusion is supported by consideration of the (1)H chemical shifts of the heterocyclic bases near the site of the modification. The enhanced stability that these conformational changes should bring was confirmed by UV thermal melting studies. Subsequently a series of singly and doubly 3[prime or minute]-S-phosphorothiolate-modified duplexes were investigated by UV. The results are indicative of an additive effect of the modification with thermodynamic benefit being derived from alternate spacing of two modified linkers.     

The chemical shift tensor for the hydroxyl proton: Ca(OH)2

The proton chemical shift tensor of the hydroxyl proton in calcium hydroxide has been measured using multiple pulse NMR techniques. The tensor is axially symmetric with susceptibility corrected components σ_tT = ?9.3 ± 1 ppm and

ppm relative to TMS. 792 79     

Langmuir films of (alpha-amino) phosphorus amphiphiles on various ion-containing subphases

Monolayers of amphiphilic (alpha-amino)phosphonocarboxylic and (alpha-amino)phosphonic acids have been formed by adsorption at the air/water interface. The influence of both the ionic strength and the pH of the subphase on the stability and compactness of the monolayers have been studied. The stability and the compactness of the Langmuir films are enhanced by introduction of metallic ions such as Ca(2+) or Mg(2+) in the subphases. These effects are more pronounced with Ca(2+). These metal ions can form dimeric complexes with the phosphorus moieties of the surfactant polar heads and therefore bring the amphiphiles closer. For the less hydrophobic derivative, complexation with Ca(2+) or Mg(2+) is required to ensure the formation of a stable monomolecular film. For both phosphonocarboxylic and phosphonic compounds, models have been proposed to represent the complexation phenomenon at the air/water interface.     

The theory and practice of liquid-liquid partition chromatography of phenols

An equation is given for the design of liquid-liquid partition Chromatographie columns which relates the separation factors and column, characteristics with the number of theoretical plates required for a desired separation. This equation should be applicable to the separation of acids or bases when a buffered stationary phase is used, thus permitting a more rational approach to this technique.Using this approach a complete separation of the three isomeric cresols has been achieved. Methods are given for this determination and also for the determination of phenol in tar acid mixtures.     

Synthesis of Some Novel 2‐Anilinothiophene, 2,3′‐Bithienyl and Thienylthiopyridine Derivatives Resistance to Penicillium Digitatum Effect the Fruit

Reaction of benzotriazol‐1‐yl acetone 1 with phenyl isothiocyanate followed with α‐chloroacetone or ethyl‐α‐chloroacetate afforded 2‐anilinothiophenes 3 or 4 , respectively. Treatment of 3 with malononitrile at different reaction conditions afforded 6 or 7 . Reaction of 1 with CS₂ in DMF and phenacylbromide afforded S‐alkylated thiophene 10 . Reactions of the latter compound with different active methylene nitriles afforded thienylthiopyridine derivatives 14 and 15 . Condensation of 10 with hydrazine hydrate afforded hydrazon derivative 16 . Reaction of thiophene 17 with formamide in DMF afforded 19 which converted to N‐thienylpyrimidine 20 when treated with malononitrile. The structure of the newly synthesized compounds has been established on the basis of their analytical and spectral data. The compounds were also investigated for antibacterial and antifungal activities.