Surface Of PS Research Articles

Interfacial Reactions in Confinement: Kinetics and Temperature Dependence of the Surface Hydrolysis of Polystyrene-block-poly(tert-butyl acrylate) Thin Films

The effect of confinement on the kinetics of the surface hydrolysis of polystyrene-block-poly(tert-butyl acrylate) (PS(n)-b-PtBA(m)) thin films on oxidized silicon substrates in 3 M aqueous hydrochloric acid was systematically investigated. As shown by X-ray photoelectron spectroscopy (XPS) and contact angle measurements, a skin layer of acid-sensitive PtBA is present on the surface of PS(n)-b-PtBA(m) films, consistent with the lower surface tension of PtBA compared to that of PS. The thickness of the skin layer was determined by angle-dependent XPS as approximately 8 nm for PS(690)-b-PtBA(1210). Tapping mode atomic force microscopy showed an increasing surface coverage of swollen poly(acrylic acid)-rich globules with increasing hydrolysis time. Using ex situ Fourier transform infrared spectroscopy, the reaction kinetics was determined quantitatively as a function of temperature, polymer film thickness, thermal pretreatment of the films, and block copolymer composition. The initial stages of the hydrolysis can be described as a pseudo-first-order reaction under all conditions investigated. The corresponding rate constants were found to be 2 orders of magnitude lower than those reported for the hydrolysis of tert-butyl acetate in solution and depended linearly on the fraction of PtBA exposed at the surface. However, the polymer film thickness, thermal pretreatment of the films, block copolymer composition, and local composition did not affect the rate constants. The negative value of the activation entropy (DeltaS(298)++ = -103 J/mol K), determined according to the Arrhenius equation and transition state theory, indicates that the tightness of the transition state is more pronounced in the PS(n)-b-PtBA(m) film compared to reactions in solution. Thus, the spatial constraints due to the incorporation of the reactive ester groups in thin polymer films are responsible for the observed reduced reactivity.

Reductive Deposition of Rh Nanostructures on n-Type Porous Silicon: X-ray Absorption and X-ray Excited Optical Luminescence Studies

22Porous silicon (PS) prepared from an n-type Si(100) wafer was utilized as a reducing agent and a nanosubstrate for the reduction of rhodium complex ions [RhCl6]3- from aqueous solution to metallic Rh nanostructures on the surface of the n-type PS. The morphology and the electronic properties of the PS layers as well as the rhodium nanostructures were studied by field emission scanning electron microscopy, X-ray absorption fine structures spectroscopy, and X-ray excited optical luminescence (XEOL). The average particle size of Rh nanostructures on PS was estimated to be approximately 7 nm by the X-ray diffraction pattern. The specificity ofXEOL allowed for the investigation of the effect of Rh nanostructures on the optical properties of PS.

Analysis of the Structure of the PsbO Protein and its Implications

The PsbO protein is a ubiquitous extrinsic subunit of Photosystem II (PS II), the water splitting enzyme of photosynthesis. A recently determined 3D X-ray structure of a cyanobacterial protein bound to PS II has given an opportunity to conduct complete analyses of its sequence and structural characteristics using bioinformatic methods. Multiple sequence alignments for the PsbO family are constructed and correlated with the cyanobacterial structure. We identify the most conserved regions of PsbO and the mapping of their positions within the structure indicates their functional roles especially in relation to interactions of this protein with the lumenal surface of PS II. Homologous models for eukaryotic PsbO were built in order to compare with the prokaryotic protein. We also explore structural homology between PsbO and other proteins for which 3D structures are known and determine its structural classification. These analyses contribute to the understanding of the function and evolutionary origin of the PS II manganese stabilising protein.

The Effect of Chemical Modification of Rice Husk with Glycidyl Methacrylate on the Mechanical and Physical Properties of Rice Husk-Polystyrene Composites

Rice husks (RH) were chemically modified with glycidyl methacrylate (GMA). The chemical loading of the GMA (weight percent gain, WPG) increased as the reaction time was increased. The modification of RH with GMA gave enhanced flexural, tensile and impact properties of rice husk-polystyrene (RH-PS) composites. These may be due to the increased interaction at the interfacial region between the surface of GMA-modified RH and PS. The modification improved dimensional stability and reduced water absorption of the composites.

Preparation of biodegradable, surface engineered PLGA nanospheres with enhanced lymphatic drainage and lymph node uptake.

Nanospheres can be utilised for the targeting of drugs and diagnostic agents to the regional lymph nodes. The surface modification of model polystyrene, (PS), and poly(lactide-co-glycolide),(PLGA), nanospheres by poly(lactide)-poly(ethylene glycol), (PLA:PEG), copolymers has been assessed by in vitro characterisation and in vivo biodistribution studies following subcutaneous administration of the nanospheres to the rat. Three PLA:PEG copolymers were investigated, with PEG chain lengths of 750, 2000 and 5000 Da. The PLA:PEG copolymers were either coated onto the surface of PS and PLGA nanospheres or used as a co-precipitate in the formation of PLGA-PLA:PEG nanospheres. Coating of the nanospheres was confirmed by an increase in their particle size and a corresponding decrease in the surface potential. The kinetics of injection site drainage and lymph node retention was determined over a 24 hour time course for naked, coated and co-precipitated nanosphere systems. Dependent on the surface characteristics, the distribution of the nanospheres can be significantly modified and the lymph node localisation dramatically enhanced by coating their surfaces with PLA:PEG copolymers or by producing co-precipitate nanospheres of PLGA and PLA:PEG. A fully biodegradable nanosphere system has been developed with excellent lymph node targeting characteristics.

Location of D + and distribution of surface charges in Photosystem II

Intramembrane position of D +, the unusually stable tyrosine radical in Photosystem II (PS II), has been estimated by analyzing the effect of an electron-spin relaxing agent dysprosium (Dy) on the microwave power saturation of the EPR signal of D +. It is shown that an estimation with an electrostatically neutral complex of Dy with hydroxyEDTA (HEDTA) gives more reliable information on the structural organization of PS II than that with a charged Dy 3+ ion or Dy-EDTA − complex. Distance from D + to the outer surface of PS II was estimated at 36 Å from the data with Dy-HEDTA. The distance to the inner surface was estimated at 28 Å with the three (33, 24 and 18 kDa) peripheral polypeptides associated or at 20 Å without these polypeptides. By comparison of the effect of Dy-HEDTA with those of Dy 3+ and Dy-EDTA −, the inner surface newly exposed after the removal of the 24 and 18 kDa polypeptides is shown to be negatively charged and after the removal of the 33 kDa polypeptide to be positively charged.

ORALLY-ADMINISTERED BOVINE COLOSTRAL IMMUNOGLOBULINS (BCI) PROTECT LEUKOPENIC MICE AGAINST Ps. AERUGINOSA (Ps)

We immunized pregnant cows with Ps Extract Vaccine (Wellcome, UK) to produce anti-Ps BCI. Anti-Ps BCI have agglutinating and opsonizing activity against Ps, but are not bacteriacidal or static. By adsorption with Ps, these activities can be removed from BCI. Bovine IgGl can be identified on the surface of Ps adsorbed with anti-Ps BCI. We compared the protective effect of orally-fed anti-Ps BCI, control BCI from non-immunized (NI) cows, pooled human immune globulin (HIG), and D5W on the mortality of leukopenic mice orally-inoculated with Ps. Mice (18-22g) were made leukopenic with cyclophosphamide, fed globulins or D5W daily (days 1-6) per gavage, and orally-inoculated on day 4 with 106 Ps serotype 10. WBCs on day 4 were 2331 ± 696. Survival data were evaluated by the Kruskal-Wallis statistic and nonparametric log-rank test with adjustment for multiple comparisons.Treatment group survival curves were not equal (p<0.01). Anti-Ps BCI-fed animals had less mortality than NI-BCI, HIG, or D5W-fed animals, but these differences reached statistical significance only for anti-Ps BCI vs D5W (z=3.676, p<0.05). Conclusion: Orally fed anti-Ps BCI may reduce the incidence and mortality of Ps sepsis in the transiently leukopenic host

An electron microscope study of fertilisation of the sea urchin egg Psammechinus miliaris

1. 1. An electron microscope investigation has been carried out on the changes occurring at the surface of the sea urchin egg Ps. miliaris during the first 90 seconds following insemination. 2. 2. The surface of the unfertilised egg is bounded by a membrane about twice as thick as that bounding the surface of the fertilised egg. At fertilisation, this membrane splits into two layers—the vitelline membrane and the plasma membrane. This is followed by the opening up of the cortical granules, and the vitelline membrane, together with the contents of the cortical granules gives rise to the fertilisation membrane. These observations confirm, in general, the commonly accepted view of the origin of the fertilisation membrane. 3. 3. The membrane bounding the cortical granules is probably identical with the plasma membrane. The relationship of the granules to the surface of the unfertilised egg is such that the contents of the cortical granules may lie outside the permeability barrier. The implications of this are discussed, both with regard to permeability data and the opening up of the granules. 4. 4. There is no observable change in structure at the surface before the vitelline membrane separates from the plasma membrane. 5. 5. Treatment of unfertilised eggs with trypsin, which prevents formation of the fertilisation membrane reduces the thickness of the vitelline membrane. 6. 6. The fertilisation membrane is initially structureless and later becomes a two layered membrane.