Modulation of surface charge, particle size and morphological properties of chitosan-TPP nanoparticles intended for gene delivery

This work investigates the polyanion initiated gelation process in fabricating chitosan-TPP (tripolyphosphate) nanoparticles in the size range of 100-250 nm intended to be used as carriers for the delivery of gene or protein macromolecules. It demonstrates that ionic gelation of cationic chitosan molecules offers a flexible and easily controllable process for systematically and predictably manipulating particle size and surface charge which are important properties in determining gene transfection efficacy if the nanoparticles are used as non-viral vectors for gene delivery, or as delivery carriers for protein molecules. Variations in chitosan molecular weight, chitosan concentration, chitosan to TPP weight ratio and solution pH value were examined systematically for their effects on nanoparticle size, intensity of surface charge, and tendency of particle aggregation so as to enable speedy fabrication of chitosan nanoparticles with predetermined properties. The chitosan-TPP nanoparticles exhibited a high positive surface charge across a wide pH range, and the isoelectric point (IEP) of the nanoparticles was found to be at pH 9.0. Detailed imaging analysis of the particle morphology revealed that the nanoparticles possess typical shapes of polyhedrons (e.g., pentagon and hexagon), indicating a similar crystallisation mechanism during the particle formation and growth process. This study demonstrates that systematic design and modulation of the surface charge and particle size of chitosan-TPP nanoparticles can be readily achieved with the right control of critical processing parameters, especially the chitosan to TPP weight ratio. (c) 2005 Elsevier B.V. All rights reserved.

Preparation of magnetic cellulose composites using ionic liquids

Cellulose-magnetite composites have been prepared by suspension and dispersion of magnetite particles in a homogenous ionic liquid solution of cellulose, followed by regeneration into water, enabling the preparation of magnetically responsive films, flocs, fibers, or beads. The materials prepared were ferromagnetic, with a small superparamagnetic response, characteristic of the initial magnetite added. X-ray diffraction data indicated that the magnetite particles were chemically unaltered after encapsulation with an average particle size of approximately 25 nm.

SERS enhancement by aggregated Au colloids: effect of particle size

Aggregated Au colloids have been widely used as SERS enhancing media for many years but to date there has been no systematic investigation of the effect of the particle size on the enhancements given by simple aggregated Au colloid solutions. Previous systematic studies on isolated particles in solution or multiple particles deposited onto surfaces reported widely different optimum particle sizes for the same excitation wavelength and also disagreed on the extent to which surface plasmon absorption spectra were a good predictor of enhancement factors. In this work the spectroscopic properties of a range of samples of monodisperse Au colloids with diameters ranging from 21 to 146 nm have been investigated in solution. The UV/visible absorption spectra of the colloids show complex changes as a function of aggregating salt (MgSO4) concentration which diminish when the colloid is fully aggregated. Under these conditions, the relative SERS enhancements provided by the variously sized colloids vary very significantly across the size range. The largest signals in the raw data are observed for 46 nm colloids but correction for the total surface area available to generate enhancement shows that particles with 74 nm diameter give the largest enhancement per unit surface area. The observed enhancements do not correlate with absorbance at the excitation wavelength but the large differences between differently sized colloids demonstrate that even in the randomly aggregated particle assemblies studied here, inhomogeneous broadening does not mask the underlying changes due to differences in particle diameter.

The alteration of the structural properties and photocatalytic activity of TiO2 following exposure to non-linear irradiation sources

When TiO2 powder was irradiated with a laser light (>0.8 MW peak pulse power (PPP) at 355 nm) a visible change in its colour from white to dark blue was observed. The initial rate of change of the total colour difference was related to the laser light intensity and the longer the irradiation time the more substantial the colour change. The result of X-ray diffraction (XRD) studies showed that the crystal structure of the TiO2 developed a more rutile form after laser exposure. ESR studies indicated that the colour change was associated with the generation of Ti(III) species in the photocatalyst. Electron microscopic studies showed that more spherical shaped particles of TiO2 were observed after laser treatment although the average particle size remained largely unchanged. No significant changes in the band gap or the surface area of the laser modified TiO2 were observed. The laser modified photocatalyst showed no enhancement in activity for the destruction of methylene blue, rhodamine B and stearic acids, indicating that the rutile/anatase ratio is unimportant in the destruction of the test pollutants used in this work, via TiO2 photocatalysis

One-dimensional particle simulation of the filamentation instability: Electrostatic field driven by the magnetic pressure gradient force

Two counterpropagating cool and equally dense electron beams are modeled with particle-in-cell simulations. The electron beam filamentation instability is examined in one spatial dimension, which is an approximation for a quasiplanar filament boundary. It is confirmed that the force on the electrons imposed by the electrostatic field, which develops during the nonlinear stage of the instability, oscillates around a mean value that equals the magnetic pressure gradient force. The forces acting on the electrons due to the electrostatic and the magnetic field have a similar strength. The electrostatic field reduces the confining force close to the stable equilibrium of each filament and increases it farther away, limiting the peak density. The confining time-averaged total potential permits an overlap of current filaments with an opposite flow direction.

LDL particle size in habitual exercisers, lean sedentary men and abdominally obese sedentary men

Habitual exercisers enjoy considerable protection from coronary heart disease (CHD). Often, however, only modest differences in traditional CHD risk factors are apparent between habitual exercisers and their sedentary counterparts. For this reason, there is increasing interest in novel predictors of CHD, such as a preponderance of small, dense low-density lipoprotein (LDL) particles. Polyacrylamide gel electrophoresis was used to separate lipoprotein subfractions in 32 lean exercisers, 36 lean sedentary men and 21 obese sedentary men aged 30-45 years. Well-validated equations were used to determine LDL concentration and peak particle diameter. Waist girth was used to identify lean (<100 cm) and obese ( >= 100cm) individuals. LDL concentration was lower in lean exercisers than in lean sedentary men (2.64 +/- 0.44 vs. 3.76 +/- 0.79 mmol.l(-1), p <0.001), suggesting that habitual exercise influences this risk factor. In contrast, there were no significant differences in LDL peak particle diameter between lean exercisers, lean sedentary men and obese sedentary men (27.92 +/- 0.67, 28.09 +/- 0.62 and 27.77 +/- 0.77 nm, respectively). In multiple linear regression analysis, triglyceride concentration was the only significant predictor of LDL PPD. These data suggest that habitual exercise influences LDL concentration but does not influence LDL particle size in men aged 30-45 years.

THE EFFECT OF POWER ULTRASOUND ON THE OXIDATIVE DISSOLUTION OF RUO2.XH2O BY BROMATE IONS

The effects of continuous sonication and presonication on the kinetics of oxidative dissolution of ruthenium dioxide hydrate by bromate ions under acidic conditions are reported. Compared with unsonicated and presonicated dispersions the overall rate of dissolution of continuously sonicated dispersions is significantly greater due to a reduction in the average particle size and, hence, an increase in the specific surface area. Powder dispersions subjected to continuous ultrasound and presonication exhibit an initial induction period in their corrosion kinetics; the length of this induction period increases with increasing presonication. This corrosion feature is retained in the dissolution kinetics of powder samples which have been subjected to pre-ultrasound, but which are then stirred during the dissolution process. It is believed that this apparent permanent change in the nature of the powder particles is due to the ultrasound induced formation of a very thin layer of a largely unreactive form of ruthenium dioxide (possibly due to partial dehydration) on the surface of the powder particles. A kinetic scheme, based on this model, is used to account for the observed kinetics of dissolution of RuO2 . xH2O which have been subjected to both continuous sonication and presonication.

Increasing the size of a small peripheral iridotomy widens the anterior chamber angle:An ultrasound biomicroscopy study

Purpose: A peripheral iridotomy (PI) is the treatment of choice for pupillary block. In this study we investigated the effect of enlarging the size of a small PI on the anterior chamber angle in patients with angle closure using ultrasound biomicroscopy (UBM). Patients and Methods: Patients who had been treated with laser peripheral iridotomy for angle closure and were identified to have a small patent PI (<100 µm) with still appositionally closed anterior chamber angle were selected prospectively. The anterior chamber angle was assessed using UBM. The angle opening distance 500 µm from the scleral spur (AOD500) as well as the anterior and posterior chamber depth (ACD and PCD) 1000 µm from the scleral spur was measured. In addition, the ACD/PCD ratio was calculated. Afterwards, the PI was enlarged using an Nd: YAG laser and the UBM measurements were repeated as described above. Results: Six eyes of six patients were examined. After the enlargement of the PI the average AOD500 increased from 109 µm (±36) to 147 µm (±40) (p

Secular trends in reported portion size of food and beverages consumed by Irish adults

The present analysis aimed to investigate the changes in the reported portion sizes (PS) of foods and beverages commonly consumed by Irish adults (18-64 years) from the North South Ireland Food Consumption Survey (NSIFCS) (1997-2001) and the National Adult Nutrition Survey (NANS) (2008-10). Food PS, which are defined as the weight of food (g) consumed per eating occasion, were calculated for comparable foods and beverages in two nationally representative cross-sectional Irish food consumption surveys and were published in NSIFCS and NANS. Repeated measure mixed model analysis compared reported food PS at the total population level as well as subdivided by sex, age, BMI and social class. A total of thirteen commonly consumed foods were examined. The analysis demonstrated that PS significantly increased for five foods ('white sliced bread', 'brown/wholemeal breads', 'all meat, cooked', 'poultry, roasted' and 'milk'), significantly decreased for three ('potatoes', 'chips/wedges' and 'ham, sliced') and did not significantly change for five foods ('processed potato products', 'bacon/ham', 'cheese', 'yogurt' and 'butter/spreads') between the NSIFCS and the NANS. The present study demonstrates that there was considerable variation in the trends in reported food PS over this period.

Independent particle descriptions of tunneling using the many-body quantum transport approach

Currents across thin insulators are commonly taken as single electrons moving across classically forbidden regions; this independent particle picture is well-known to describe most tunneling phenomena. Examining quantum transport from a different perspective, i.e., by explicit treatment of electron-electron interactions, we evaluate different single particle approximations with specific application to tunneling in metal-molecule-metal junctions. We find maximizing the overlap of a Slater determinant composed of single-particle states to the many-body current-carrying state is more important than energy minimization for defining single-particle approximations in a system with open boundary conditions. Thus the most suitable single particle effective potential is not one commonly in use by electronic structure methods, such as the Hartree-Fock or Kohn-Sham approximations.

Estimation of the size of onset of sexual maturity in Nephrops norvegicus (L.).

Size at onset of maturity (SOM) was estimated for both male and female Nephrops from primary sexual characteristics and morphometric traits. SOM estimated from primary sexual characteristics based on histological examination of the gonad ranged from 15.1 mm carapace length (CL) in males to 22.9 mm CL in females. Nephrops morphometric maturity, or change in allometric growth of body parts, was estimated from appendix masculina and cutter claw lengths in males and abdomen width in females from two sites in the Irish Sea. Two regression techniques were used to estimate morphometric maturity. Estimated SOM from morphometric characteristics ranged from 23.2 to 27.6 mm CL in females and from 25.9 to 31.0 mm CL in males. Spatial variation in SOM was observed in Nephrops from different parts of the Irish Sea.