PGSE-NMR studies of solvent diffusion in poly(N-isopropylacrylamide) colloidal microgels

The solvent self-diffusion coefficient has been studied in thermoshrinking poly(N-isopropyl acrylamide) microgel dispersions by the pulsed-gradient spin-echo PGSE-NMR technique, as a function of temperature and mass fraction. After suitable corrections for the temperature, the H₂O/D₂O ratio and the relative volume fractions, all the self-diffusion data obtained over a temperature range of approximately 40 °C and mass fraction (2–12 % wt/wt) could be superimposed with the volume fraction as the universal factor. The observed reduction in the solvent self-diffusion coefficient with volume fraction was greater than that predicted by simple obstruction theory. After correction for-, and the subsequent removal of the obstruction effect, the diffusion of the solvent through the core of the particle is elucidated. As found for other polymer-solvent systems, there were no specific binding effects. The diffusion of the solvent in these dispersions over such temperature and mass fraction ranges could be rationalised assuming a constant solvent self-diffusion coefficient in the core of the particles.     

Experimental determination of the double ionization energies of the perhalomethanes,CF3Br,CF2Br2, CFBr3 and CF2ClBr

The double ionization energies of the perhalomethanes CF₃Br, CF₂Br₂, CFBr₃ and CF₂ClBr have been determined using the technique of double-charge-transfer spectroscopy. The values found are compared with those of other perhalomethane molecules also determined in this laboratory.     

EFFECTS OF ULTRAVIOLET LIGHT ON THYMIDINE INCORPORATION AND DNA CHAIN ELONGATION IN PHOTOREACTIVABLE INSECT CELLS

An insect cell line, IAL-PID2, was exposed to UV and analyzed for its ability to incorporate [3H]-thymidine and to elongate replicon-sized DNA fragments. After exposure to 5 or 10 J/m2 UV, the cells exhibited a rapid and prolonged depression in the rate of thymidine incorporation. Photoreactivation reduced this depression but did not entirely reverse it. For exposures of 5 J/m2 or above, full recovery did not occur until 18 h after exposure. The blockage of fork progression after UV exposure was fluence-dependent, with replication segments after exposure to 20 J/m2 being shorter than those observed after exposure to 10 J/m2. Immediately after exposure to either 10 or 20 J/m2, photoreactivation reversed blockage of fork progression, indicating that the (5-6) cyclobutyl pyrimidine dimer is responsible for blockage. This also indicates that blockage of fork progression may not be the only factor responsible for the prolonged depression seen in thymidine incorporation. Three hours after exposure to either 10 or 20 J/m2, replication segments were still significantly shorter than control segments. Photoreactivation completely reversed blockage after exposure to 10 J/m2, but did not completely reverse blockage after exposure to 20 J/m2, indicating that at such fluences, other lesions may play a role in UV-induced blockage of fork progression.     

Characterisation of variant forms of prophenin: mechanistic aspects of the fragmentation of proline-rich peptides

Prophenin 1 (PF-1) is a 79-residue polypeptide originally isolated from porcine leukocytes. Its amino acid sequence has been determined by a combination of mass spectrometry and Edman degradation (Harwig SSL. et al. FEBS Lett. 1995; 362: 65). Prophenin (PF) and variants thereof are also found in organic extracts of porcine pulmonary tissue (Wang Y. et al. FEBS Lett. 1999; 460: 257). In the present study we have characterised the variant forms of PF found in these extracts using nano-electrospray (nano-ES) high resolution and tandem mass spectrometry. The major forms of PF found in these extracts by nano-ES mass spectrometry are the 80-residue polypeptides prophenin-2-Pyr (PF-2-Pyr) and prophenin-2-Gln (PF-2-Gln). Prophenin-2-Pyr is refractory to Edman degradation due to the presence of an N-terminal pyroglutamic residue. In PF-2-Gln the N-terminal residue is glutamine and the C-terminus is amidated. In porcine pulmonary extracts PF-1 is present to only a minor extent. Other shorter polypeptides are also found in these extracts including 18- and 17-residue C-terminal fragments of PF. The primary structure of PF is highly unusual in that it shows four almost perfect decamer repeats of FPPPN(V/F)PGPR and, out of the 79/80 residues, 42 are proline and 14 are phenylalanine. Tryptic digestion of PF gives peptides containing the decamer repeat and collision-induced dissociation of these peptides provides an insight into the fragmentation mechanisms of proline-rich peptides. Facile cleavage within the Pro-Pro-Pro sequence of these peptides suggests the involvement of a cyclic peptide in the fragmentation mechanism. Fragmentation mechanisms that account for the formation of fragment ions at other cleavage sites are also discussed.     

Further studies on reactions of organic halides with disilanes catalysed by transition metal complexes

The interaction of a range of organic halides with (Cl₃Si)₂ or (Me₃Si)₂ in the presence of a variety of transition metal catalysts (very predominantly Pd⁰ or Pd^II complexes) have been examined. PhSiMe₃ was formed from PhCl[m.y., 15%] (m.y. - maximum yield), PhBr (m.y., 92%, with [PdL₂Br₂] as catalyst (L - PPh₃)), and (contrary to earlier reports) PhI (m.y. 51%, with [PdL₂I₂]). MeSiCl₃ was formed from MeBr (m.y., 78% with [PdL₄]) and MeI (m.y., 91% with [PdL₄]), and EtSiCl₃ from EtBr (m.y., 49%, with [PdL₂“Br₂]; L” - P(C₆H₄OMe-p)₃) and EtI (m.y. 45%, with [PdL₄]). Me₄Si was satisfactorily formed from MeBr (m.y. 42%, with [PdL₄]). Evidence was obtained for the formation of Me₃SiCF₃ from CF₃I. Very poor yields of XC₆H₄CH₂SiMe₃ were obtained from XC₆H₄CH2Br (X - H orp-Me) (with X - H some PhSiMe₃ was formed), butp-O₂NC₆H₄CH₂SiMe₃ was formed in 48% yield fromp-O₂NC₆H₄CH₂Cl with [PdL“₄] as catalyst. PhCOSiMe₃ was formed from PhCOCl (m.y. 52% with [PdL₂I₂]. The nickel complex [NiL₄] was moderately effective as a catalyst for reactions between (Cl₃Si)₂ and MeBr, EtBr, or PhCH₂Br. The new complex [PdL₂(SiCl₃)₂] was prepared by treatment of [PdL₄] with (Cl₃Si)₂ or Cl₃SiH, and shown to catalyse the reaction between MeBr and (Cl₃Si)₂.     

Thermometrie

Ohne Zusammenfassung     

Parametric study of liquid droplets impinging on porous surfaces

This work presents a numerical simulation of the fluid dynamics of a liquid droplet during impact/absorption onto a porous medium. The main focus of this paper is on a parametric study of the influence of the governing parameters upon the fluid flow characteristics. The problem is described in a non-dimensional form, and the influence of the main governing parameters is investigated, including their variation along the range of physical configurations of interest. This procedure revealed 7 main governing parameters: Reynolds number (Re), Darcy number (Da), porosity (ε), Froude number (Fr), Weber number (We), contact angle (θ) and the ratio between pore and particle diameter size in the porous substrate (α). The results indicate that the values of Da and Re are more related to the amount of momentum dissipation due to the drag of the solid matrix of the substrate, while the values of We, α and θ can be mainly related to capillary pressure.