Film-pore diffusion models—analytical and numerical solutions

The sorption of acid dyes from aqueous effluents onto activated carbon has been studied. The effects of initial dye concentration and activated carbon mass on the rate of Acid Blue 80 and Acid Yellow 117 removal have been investigated. Three mass transport models based on film and pore diffusion control have been applied to model the experimental concentration decay curves. The models are compared on the basis of the solid-phase loading capacity using various assumptions since the assignment of an appropriate solid-phase loading has been the subject of several papers on this topic and no comparisons have been provided on the effectiveness of each approach. The equilibrium solid-phase concentration is assumed: (i) incorporating a time-dependent solid-phase concentration Y_e,t, (ii) equal to the intersection point of the equilibrium isotherm and the operating line and (iii) the point on the equilibrium isotherm where the liquid-phase concentration equals the initial concentration in the film-pore diffusion model.     

Characterization of protein immobilization on nanoporous gold using atomic force microscopy and scanning electron microscopy

Nanoporous gold (NPG), made by dealloying low carat gold alloys, is a relatively new nanomaterial finding application in catalysis, sensing, and as a support for biomolecules. NPG has attracted considerable interest due to its open bicontinuous structure, high surface-to-volume ratio, tunable porosity, chemical stability and biocompatibility. NPG also has the attractive feature of being able to be modified by self-assembled monolayers. Here we use scanning electron microscopy (SEM) and atomic force microscopy (AFM) to characterize a highly efficient approach for protein immobilization on NPG using N-hydroxysuccinimide (NHS) ester functionalized self-assembled monolayers on NPG with pore sizes in the range of tens of nanometres. Comparison of coupling under static versus flow conditions suggests that BSA (Bovine Serum Albumin) and IgG (Immunoglobulin G) can only be immobilized onto the interior surfaces of free standing NPG monoliths with good coverage under flow conditions. AFM is used to examine protein coverage on both the exterior and interior of protein modified NPG. Access to the interior surface of NPG for AFM imaging is achieved using a special procedure for cleaving NPG. AFM is also used to examine BSA immobilized on rough gold surfaces as a comparative study. In principle, the general approach described should be applicable to many enzymes, proteins and protein complexes since both pore sizes and functional groups present on the NPG surfaces are controllable.     

A highly sensitive ultraviolet sensor based on a facile in situ solution-grown ZnO nanorod/graphene heterostructure

The weak photon absorption and fast carrier kinetics of graphene limit its application in photodetection. This limitation can be overcome by introducing photosensitive nanostructures to graphene. Herein we report the synthesis of a ZnO nanorod/graphene heterostructure by a facile in situ solution growth method. By combining the attributes of photosensitive ZnO nanorods and highly conductive graphene, we for the first time demonstrate a highly sensitive visible-blind ultraviolet (UV) sensor based on graphene related heterostructure. The photoresponsibility of the UV sensor can reach 22.7 A W(-1), which is over 45,000 fold higher than that of single graphene sheet based photodetectors.     

Structure-function studies of an engineered scaffold protein derived from Stefin A. II: Development and applications of the SQT variant

Constrained binding peptides (peptide aptamers) may serve as tools to explore protein conformations and disrupt protein-protein interactions. The quality of the protein scaffold, by which the binding peptide is constrained and presented, is of crucial importance. SQT (Stefin A Quadruple Mutant-Tracy) is our most recent development in the Stefin A-derived scaffold series. Stefin A naturally uses three surfaces to interact with its targets. SQT tolerates peptide insertions at all three positions. Peptide aptamers in the SQT scaffold can be expressed in bacterial, yeast and human cells, and displayed as a fusion to truncated pIII on phage. Peptides that bind to CDK2 can show improved binding in protein microarrays when presented by the SQT scaffold. Yeast two-hybrid libraries have been screened for binders to the POZ domain of BCL-6 and to a peptide derived from PBP2', specific to methicillin-resistant Staphylococcus aureus. Presentation of the Noxa BH3 helix by SQT allows specific interaction with Mcl-1 in human cells. Together, our results show that Stefin A-derived scaffolds, including SQT, can be used for a variety of applications in cellular and molecular biology. We will henceforth refer to Stefin A-derived engineered proteins as Scannins.     

Effects of selected water chemistry variables on copper pitting propagation in potable water

The pit propagation behavior of copper (UNS C11000) was investigated from an electrochemical perspective using the artificial pit method. Pit growth was studied systematically in a range of HCO₃⁻, SO₄²⁻ and Cl⁻ containing-waters at various concentrations. Pit propagation was mediated by the nature of the corrosion products formed both inside and over the pit mouth (i.e., cap). Certain water chemistry concentrations such as those high in sulfate were found to promote fast pitting that could be sustained over long times at a fixed applied potential but gradually stifled in all but the lowest concentration solutions. In contrast, Cl⁻ containing waters without sulfate ions resulted in slower pit growth and eventual repassivation. These observations were interpreted through understanding of the identity, amount and porosity of corrosion products formed inside and over pits. These factors controlled their resistive nature as characterized using electrochemical impedance spectroscopy. A finite element model (FEM) was developed which included copper oxidation kinetics, transport by migration and diffusion, Cu(I) and Cu(II) solid corrosion product formation and porosity governed by equilibrium thermodynamics and a saturation index, as well as pit current and depth of penetration. The findings of the modeling were in good agreement with artificial pit experiments. Malachite, bronchantite, cuprite, nantokite and atacamite corrosion products were both observed in experiment and predicted by the model. Stifling and/or repassivation occurred when the resistance of the corrosion product layer became high enough to lower the pit bottom potential and pit current density such as 10^-5 A/cm² could be attained with thick and dense layer. The ramifications of these findings towards pit propagation characteristics in potable waters will be discussed with improved insight into the roles of Cl⁻ and SO₄²⁻ ions.     

Systematic study of back pressure and anode stoichiometry effects on spatial PEMFC performance distribution

A segmented cell system was applied to investigate the effects of the anode and cathode back pressure and hydrogen stoichiometry on fuel cell performance in terms of overpotential distributions along the flow field. The segmented cell system was designed with closed loop Hall sensors and a data acquisition system allowing simultaneous spatial electrochemical impedance spectra (EIS) measurements. It was determined that an increase in back pressure for the tested serpentine flow field design results in an improvement of the cell performance and uneven improvement of individual segments’ performance. In general, the performance and the overpotentials become more uniform downstream with an increase in the back pressure due to a decrease in activation and mass transfer losses. Spatial EIS data for the PEMFC operated at different back pressures support the overpotential analysis. Hydrogen stoichiometry variations do not affect the performance of the cell or the individual segments at low current density because there is no significant hydrogen concentration gradient in the flow field. However, at high current densities a reduction in hydrogen stoichiometry produces a slight decrease in performance for inlet segments while outlet segments showed a noticeable performance loss. The decrease in performance is attributed to an increase in mass transfer losses due to nitrogen diffusion from the cathode to the anode. This effect becomes more pronounced for the outlet segments due to a downstream nitrogen accumulation. Under high current density conditions, the cell is locally fuel starved even with a high fuel stoichiometry creating conditions leading to cell degradation by carbon corrosion. More importantly, this local degradation is masked by the overall cell performance which remains largely unaffected.     

Antimicrobial hydrogels formed by crosslinking polyallylamine with aldaric acid derivatives

Aqueous dispersions (0.1 wt %) of hydrogels 1 and 5 —formed by crosslinking polyallylamine hydrochloride (MW 60,000) with aldaric acid derivatives, diethyl L ‐tartrate and N,N′‐bis(methoxycarbonylmethyl)‐D ‐glucaramide, respectively—exhibited complete (log 5) kill within 4 h of Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Candida albicans suspended in culture medium. This antimicrobial activity was much higher than that of uncrosslinked polyallylamine (1 wt % killed only 75% of E. coli in 24 h). When dispersed at 10 and 100 ppm, hydrogel 5 displayed complete (log 5) kill of E. coli within 30–60 and 15 min, respectively. Hydrogels 1 and 5 were active against S. aureus and Salmonella choleraesuis dried on hard stainless steel surfaces and accelerated the deaths of E. coli, P. aeruginosa, S. aureus, and C. albicans in a model skin cream formulation. A 0.8% aqueous dispersion of hydrogel 5 was also effective as a hand sanitizer, killing 99.7% of Serratia marcescens on human hands within 5 min. Hydrogels 1 and 5 caused no dermal irritation or allergic contact sensitization under the conditions of a human repeat insult patch test. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Polyampholyte acrylic latexes for tablet coating applications

Polyampholyte latexes can exist within a certain pH range as low‐viscosity aqueous dispersions, while upon a pH shift to the vicinity of the isoelectric point they undergo ionic coacervation. Three classes of coacervation latexes were synthesized and evaluated for their suitability for use in tablet coating applications. Pharmaceutical tablet coatings are commonly based on hydroxypropyl methyl cellulose, poly(vinyl alcohol), and acrylic polymers. Because of the high viscosity of their aqueous solutions, and to the consequent required low concentrations of the tablet coating polymers in the coating solutions to enable sufficiently low viscosity for effective spray application, the current commercial pharmaceutical tablet coating technology requires the removal of large amounts of water during the manufacturing process. In this work, films prepared from high‐solids, low‐viscosity coacervated acrylic latexes showed good hardness, very low tackiness, an excellent combination of optical properties, and very low water vapor permeability. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40049.     

Quantitative Analysis of PMLA Nanoconjugate Components after Backbone Cleavage

Multifunctional polymer nanoconjugates containing multiple components show great promise in cancer therapy, but in most cases complete analysis of each component is difficult. Polymalic acid (PMLA) based nanoconjugates have demonstrated successful brain and breast cancer treatment. They consist of multiple components including targeting antibodies, Morpholino antisense oligonucleotides (AONs), and endosome escape moieties. The component analysis of PMLA nanoconjugates is extremely difficult using conventional spectrometry and HPLC method. Taking advantage of the nature of polyester of PMLA, which can be cleaved by ammonium hydroxide, we describe a method to analyze the content of antibody and AON within nanoconjugates simultaneously using SEC-HPLC by selectively cleaving the PMLA backbone. The selected cleavage conditions only degrade PMLA without affecting the integrity and biological activity of the antibody. Although the amount of antibody could also be determined using the bicinchoninic acid (BCA) method, our selective cleavage method gives more reliable results and is more powerful. Our approach provides a new direction for the component analysis of polymer nanoconjugates and nanoparticles.     

Small Alterations in Cobinamide Structure Considerably Influence sGC Activation

Specially designed B‐ring‐modified cobalamin derivatives were synthesized and tested as potential activators of soluble guanylyl cyclase (sGC). Herein, we disclose the influence of substituents at the c‐ and d‐positions in hydrophilic and hydrophobic cobyrinic acid derivatives on their capacities to activate sGC. The presence of the amide group at c‐/d‐position in cobyrinic acid derivatives strongly influence the level of sGC activation. Removal of the d‐position altogether has a profound effect for hydrophobic compounds. In contrast, little differences were observed in hydrophilic ones.