Biophysical Features of Bacillithiol,the Glutathione Surrogate of Bacillus subtilis and other Firmicutes

Bacillithiol (BSH) is the major low‐molecular‐weight (LMW) thiol in many low‐G+C Gram‐positive bacteria (Firmicutes). Evidence now emerging suggests that BSH functions as an important LMW thiol in redox regulation and xenobiotic detoxification, analogous to what is already known for glutathione and mycothiol in other microorganisms. The biophysical properties and cellular concentrations of such LMW thiols are important determinants of their biochemical efficiency both as biochemical nucleophiles and as redox buffers. Here, BSH has been characterised and compared with other LMW thiols in terms of its thiol pK_a, redox potential and thiol–disulfide exchange reactivity. Both the thiol pK_a and the standard thiol redox potential of BSH are shown to be significantly lower than those of glutathione whereas the reactivities of the two compounds in thiol–disulfide reactions are comparable. The cellular concentration of BSH in Bacillus subtilis varied over different growth phases and reached up to 5 mM , which is significantly greater than previously observed from single measurements taken during mid‐exponential growth. These results demonstrate that the biophysical characteristics of BSH are distinctively different from those of GSH and that its cellular concentrations can reach levels much higher than previously reported.     

The speciation of Si and other alloying elements in the oxide surface film of galvanically corroded weld fusion zone of laser welded AA6061 aluminium alloy

It has recently been proposed that on galvanic corrosion of laser weldments of AA6061 aluminium alloy the temporal increase in galvanic corrosion resulted from either the build up of intermetallic phases in the surface oxide layer and/or a significant increase in the surface area of the cathodic weld fusion zone due to the porous nature of the surface layer. This proposition has motivated a comprehensive surface analytical study of the incorporation of alloying elements into the oxide surface film, which is composed predominately of alumina. Si is found to be present as silicate and silicides. The Gibbs free energy of formation, per cation, of silicate is more negative than that for alumina and hence silicate formation is thermodynamically, relatively, favourable. In contrast the Gibbs free energy for oxide formation, per cation, for the other alloying elements is less negative and hence relatively unfavourable compared to the formation of alumina. We propose therefore that Fe, Cu and Cr are present in the metallic form, possibly as silicides, within the oxide surface layer. Magnesium is found to be depleted relative to the weld fusion zone presumably due to dissolution within the electrolyte.     

Tuning anti-microbial activity of poly(4-vinyl 2-hydroxyethyl pyridinium) chloride by anion exchange reactions

A series of new bioactive polymers with pendant choline analogous group was prepared by anion exchange reaction direct at the quaternary nitrogen of the polycation. Poly(4-vinyl 2-hydroxyethyl pyridinium) chloride was prepared in situ by simultaneous polymerization and quaternization of 4-vinyl pyridine with 2-chloroethanol that also acts as catalyst. The counter anion (Cl⁻) of the polycation was exchanged by anion exchange reaction with Br⁻, ⁻OH, ⁻SH, NO₃ ⁻, BF₄ ⁻ or CF₃COO⁻. Evidence of anion exchange was obtained by the characterization of the resultant polymers. The nature of the counter anion has profound effect on their properties including strong anion-dependent anti-microbial activity against bacteria and fungus. Polymer containing ⁻OH was observed to be the most potent anti-microbial agent with the lowest minimum inhibitory concentration against both the classes of microbes studied.     

How implementation of Quality by Design and advances in Biochemical Engineering are enabling efficient bioprocess development and manufacture

In recent years, Quality by Design (QbD) has gained significant prominence in the pharmaceutical industry as an efficient way of designing and controlling processes used to make therapeutic products. At its heart, QbD seeks to identify an operating envelope within which production consistently satisfies a target product quality profile and thereby achieves the desired level of safety and efficacy. Such an approach is assisted by a range of Biochemical Engineering techniques which increase process and product understanding. This perspective describes how the principles of Quality by Design and developments in the field of Biochemical Engineering are providing the pharmaceutical sector with a toolbox of methods that enable efficient bioprocess development and manufacture. Copyright © 2011 Society of Chemical Industry     

Evaluation and Controlled Release Characteristics of Modified Xanthan Films for Transdermal Delivery of Atenolol

ABSTRACT

The present study was performed to evaluate the possibility of using modified xanthan films as a matrix system for transdermal delivery of atenolol (ATL), which is an antihypertensive drug. Acrylamide was grafted onto xanthan gum (XG) by free radical polymerization using ceric ion as an initiator. Fourier transform infrared spectroscopy and differential scanning calorimetry indicated the formation of the graft copolymer. The obtained graft copolymer was loaded with ATL and films were fabricated by solution casting method for transdermal application. Various formulations were prepared by varying the grafting ratio, drug loading, and different penetration enhancers. The formulations prepared were characterized for weight, thickness uniformity, water vapor transmission rate, and uniformity in drug content of the matrix. All the thin films were slightly opaque, smooth, flexible, and permeable to water vapor, indicating their permeability characteristics suitable for transdermal studies. Fourier transform infrared spectroscopy and differential scanning calorimetry studies indicated no significant interactions between drug and polymer. Drug is distributed uniformly in the matrix but showed a slight amorphous nature. Drug-loaded films were analyzed by X-ray diffraction to understand the drug polymorphism inside the films. Scanning electron microscopic studies of the placebo and drug-loaded films demonstrated a remarkable change in their surface morphology. The skin irritation tests were performed in mice and these results suggested that both placebo and drug-loaded films produced negligible erythema and edema compared to formalin (0.8% v/v) as the standard irritant. The in vitro drug release studies were performed in phosphate buffer saline using a Keshary-Chien diffusion cell. Different formulations were prepared and variations in drug release profiles were observed. Release data were analyzed by using the Ritger and Peppas equation to understand the mechanism of drug release as well as the estimation of n values, which ranged between 0.41 and 0.53, suggesting a Fickian diffusion trend.     

Thermal Instability of Oldroydian Viscoelastic Fluid with Suspended Particles in Hydromagnetics in Porous Medium

The effect of suspended particles on the thermal instability of an Oldroydian viscoelastic fluid in hydromagnetics in porous medium is considered. The magnetic field, suspended particles, viscoelasticity, and porous medium effects create oscillatory modes in the system which did not exist previously. For stationary convection, the viscoelastic fluid behaves like a Newtonian fluid and the magnetic field has a stabilizing effect, whereas medium-permeability, suspended particles have destabilizing effects on the system. The sufficient conditions for the avoidance of overstability are obtained, and these also hold good for the case of a Maxwellian viscoelastic fluid.     

Studies in the photogalvanic effect in mixed reductants system for solar energy conversion and storage: Dextrose and Ethylenediaminetetraacetic acid-Azur A system

A mixture of two reductants (Dextrose and ethylenediamine tetraacetic acid) is used as a mixed reductants with Azur A as photosensitizer in the photogalvanic cell for solar energy conversion and storage with the aim to reduce the cost of construction for commercial viability. The photogeneration of photopotential and photocurrent were 778.0 mV and 55.0 μA, respectively, whereas maximum power of the cell was 42.79 μW. The observed power at power point of the cell was 10.87 μW and conversion efficiency was 0.1045%.The determined fill factor was 0.1942. The photogalvanic cell so developed can work for 115.0 min in dark where it was irradiated for 175.0 min. A mechanism for the photogeneration of electricity has also been proposed.     

Development of surface modification techniques for the covalent attachment of insulin-like growth factor-1 (IGF-1) on PECVD silica-coated titanium

Osseointegration is a complex process governed by the interaction of many cell types including blood cells (erythrocytes, platelets and leukocytes), phagocytic cells (macrophages) and bone cells (osteoblasts and osteoclasts) on or near the implant surface. The implant surface can be modified through a variety of methods in order to achieve control of some of these cellular interactions and consequently increase the degree of implant fixation with the surrounding bone tissue. In this investigation, titanium was coated with hydroxylated silica by plasma enhanced chemical vapour deposition (PECVD) to increase the surface hydrophilicity and generate reactive surface silanol groups. Subsequently, the silica-coated titanium surface was further modified through silanisation to generate surfaces bearing different reactive chemical functionalities consisting of aldehydes, epoxides and isocyanates, which can react with the amino groups of proteins and growth factors. 2,2,2-trifluoroethylamine (FEAM) was reacted on these surfaces to determine the coupling efficiency of the different surface chemical functionalities. The amino group of FEAM can react with an amino-reactive surface functional group to form a surface terminated with 3 fluorine atoms per FEAM molecule that can be detected by X-ray photoelectron spectroscopy. By analysing the techniques used for protein attachment with the FEAM model molecule, a successful method for isocyanate/amine coupling was found and later adapted for tethering IGF-1 molecules to the functionalised PECVD silica-coated titanium surface. Therefore, this simple method of preliminary testing protein reactivity may prove to be a cost effective strategy in the development of new biomaterial surfaces modified using protein bioconjugation methods.