Large-scale Synthesis and Functional Elements for the Antimicrobial Activity of Defensins

Human neutrophil defensins, and their analogues incorporating anionic, hydrophobic or cationic residues at the N- and C-termini, were synthesized by solid-phase procedures. The synthetic defensins were examined for their microbicidal activity against Candida albicans, two Gram-negative bacteria (Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis) and two Gram-positive bacteria (Streptococcus gordonii and Streptococcus mutans). The human neutrophil peptide 1 (HNP1) and HNP2 were found to be potent candidacidal agents. HNP3, which differs by one amino acid at the N-terminus of its sequence, was totally inactive. The Gram-negative bacteria A. actinomycetemcomitans and P. gingivalis and the Gram-positive bacteria S. gordonii and S. mutans were insensitive to human defensins. However, the insertion of two basic residues, such as arginine, at both the N-terminus and the C-terminus of HNP2 significantly enhanced antifungal and antibacterial activity. The addition of anionic residues, such as aspartic acid, at the N- and C-termini rendered the molecule totally inactive. The presence of two hydrophobic amino acids, such as valine, at the N-terminus of HNP2 and of two basic arginine residues at its C-terminus resulted in molecules that were optimally active against these oral pathogens. The results suggest that the N- and C-terminal residues in defensin peptides are the crucial functional elements that determine their microbicidal potency. The three-dimensional structure of all defensins constitutes the same amphiphilic beta-sheet structure, with the polar face formed by the N- and C-terminal residues playing an important role in defining microbicidal potency and the antimicrobial spectrum. The enhanced microbicidal activity observed for defensin peptides with two basic residues at both the N- and C-termini could be due to optimization of the amphiphilicity of the structure, which could facilitate specific interactions with the microbial membranes

Investigation of corrosion behaviour of magnesium in aqueous solutions

The paper present.. the corrosion data of ma~nesium metal in different aqueous solutions such as NHl~l, Naf and NaCl04 of concentrations ran~ing from 0.1 to 2.0 M. Pola.-isation and optical methods have been used to evaluate the cOITosion paraDlt'ters and surface properties. The dependence of the open circuit potential, cOlTosion potential, corrosion currt'nt and Tafel slopes on the nature and concentmtion of the electrolytes has been examined. Corrosion current increases linearly with concentration of the electrolyte in all the media. The findinJ!;s further infer the corrosivity of the anions decrease in the ordt'r as CI-> r > no:;. The naturt' of the corrosion products formed on the surface as well as lIlorphnlogical features of the specimt'll nhtained from XRD and SEM techniques are also discussed in this communicatioII

Galvano-gasometric studies of magnesium in aqueous solutions

The difference effect (∆) behaviour of magnesium is studied in Na2SO4, NaBr, MgSO4 and MgBr2 solutions up to 2.0 M concentration using galvano-gasometry set up. Comparison of the hydrogen gas evolution rates obtained from galvano-gasometry method and from the atomic absorption spectrophotometer (AAS) shows a lower value in the former. A transition from positive difference effect to negative difference effect in sodium salt solutions and its absence in magnesium salt solutions are observed during the study. The current density at which the transition occurred is termed as transition current density denoted by the symbol ~. The relationship of iτ with the nature and concentration of the electrolytes are also discussed in this communicatio

Saltcake Dissolution Studies in Single-Shell Tank Retrieval

Results of column dissolution experiments designed to evaluate the physical and chemical processes inherent to saltcake dissolution are presented along with model chemical equilibrium calculations. Two different compositions representing saltcakes in Hanford tanks were characterized, and porosities and permeabilities for a third composition based upon the saltcake waste in Tank 41H at the Savannah River Site (SRS) were also evaluated. Whereas the surrogates are all chemically similar, the presence of high phosphate loadings for the Hanford (HNF) simulants was noted as significantly affecting draining. The permeability was higher for the SRS saltcake, and the sodium nitrate loading in this saltcake was roughly 80% by weight compared to less than 60% by weight for the HNF compositions. Average values of the permeability and porosity were reduced for the surrogates based on Hanford Tanks S-112 and S-101. Here a secondary layer formed above the saltcake bed and was found to contain a large amount of gibbsite, Al(OH)3. Experiments with 3 molal (m) NaOH as a diluent, compared to water, did not result in additional layer formation that has been attributed to a change in local pH thereby altering the solid liquid equilibrium. Chemical analysis of the two HNF saltcakes indicated solids re-precipitation as a function of diluent added. The events were signified by large decreases in the nitrate and carbonate anion concentrations and were confined to low % dilution by weight values. Solids re-precipitation is noted as arising from the mixing of the dissolved saltcake stream with pockets of saturated interstitial liquor

Investigation on die wear behaviour during compaction of aluminium matrix composite powders

The focus of the current study was to evaluate and quantify the effects of particle reinforcements and lubricants on the die wear during compaction of Al matrix composites. A new wear model was developed and combined with experiments to quantify die wear using automatic die compaction experiments. The influences of the reinforcement particle type and content, as well as the premixed lubricant content, are presented and discussed.X110sciescopu

Utilisation of silicon rubber to characterise tool surface quality during die compaction

A new methodology was developed to observe and measure tool wear and tool surface quality during the die compaction process. The newly developed method is a non-destructive test that relies on silicon rubber to transcribe the inner surface profile of the compaction die. After verification of the method, aluminium and iron alloy powders were compacted to quantify tool wear and tool surface quality with two die materials, tungsten carbide and tool steel. The tool surface quality was quantified by recording surface roughness of the die replicas on a surface profilometer.X1167sciescopu

Co3O4 microcubes with exceptionally high conductivity using a CoAl layered double hydroxide precursor via soft chemically synthesized cobalt carbonate

Cubic microparticles of Co3O4 spinel were synthesized by calcination of CoCO3 obtained using CoAl layered double hydroxide (LDH) as a unitary precursor through soft-chemical decomposition. The obtained cobalt spinel showed an exceptionally high electrical conductivity at room temperature. This is attributed to high concentrations of charge carriers (Co4+), unique morphology, high reduction temperature and low activation barrier

An electrolyte for energy efficient magnesium electrolytic cells

153-156<span style="font-size:11.0pt;line-height: 115%;font-family:Calibri;mso-fareast-font-family:" times="" new="" roman";mso-bidi-font-family:="" "times="" roman";mso-ansi-language:en-us;mso-fareast-language:en-us;="" mso-bidi-language:ar-sa"="" lang="EN-US">The new generation cells for magnesium metal extraction such as bipolar cells are energy efficient. In such cells, the electrolyte composition plays a major role in obtaining pure metal with less energy consumption. To identify such an electrolyte, a series of experiments have been carried out with alkali and alkaline earth chlorides. A ternary composition consisting of magnesium chloride, sodium chloride and potassium chloride has been found suitable.</span

Green Synthesis and Antimicrobial Activity of Monodispersed Silver Nanoparticles Synthesized Using Lemon Extract

<div><p>A simple, environmentally benign green synthesis of silver nanoparticles was achieved using lemon fruit extract (<i>Citrus lemon</i>). The synthesized silver nanoparticles were characterized using UV-Vis spectroscopy, infrared spectroscopy, powder X-ray diffraction, and transmission electron microscopy. The predominantly spherical monodispersed 2–10 nm sized silver nanoparticles were obtained for the first time using lemon extract. The antimicrobial activity of silver nanoparticles was also explored. Lemon extract–mediated synthesis is cost efficient, eco-friendly and an easy alternative to conventional methods of silver nanoparticles synthesis.</p></div