First Synthesis of Continuous Mesoporous Copper Films with Uniformly Sized Pores by Electrochemical Soft Templating

Although mesoporous metals have been synthesized by electrochemical methods, the possible compositions have been limited to noble metals (e.g., palladium, platinum, gold) and their alloys. Herein we describe the first fabrication of continuously mesoporous Cu films using polymeric micelles as soft templates to control the growth of Cu under sophisticated electrochemical conditions. Uniformly sized mesopores are evenly distributed over the entire film, and the pore walls are composed of highly crystalized Cu.     

Molecular structures and dynamics of the stepwise activation mechanism of a matrix metalloproteinase zymogen: challenging the cysteine switch dogma

Activation of matrix metalloproteinase zymogen (pro-MMP) is a vital homeostatic process, yet its molecular basis remains unresolved. Using stopped-flow X-ray spectroscopy of the active site zinc ion, we determined the temporal sequence of pro-MMP-9 activation catalyzed by tissue kallikrein protease in milliseconds to several minutes. The identity of three intermediates seen by X-ray spectroscopy was corroborated by molecular dynamics simulations and quantum mechanics/molecular mechanics calculations. The cysteine-zinc interaction that maintains enzyme latency is disrupted via active-site proton transfers that mediate transient metal-protein coordination events and eventual binding of water. Unexpectedly, these events ensue as a direct result of complexation of pro-MMP-9 and kallikrein and occur before proteolysis and eventual dissociation of the pro-peptide from the catalytic site. Here we demonstrate the synergism among long-range protein conformational transitions, local structural rearrangements, and fine atomic events in the process of zymogen activation.     

Analysis of particle formation under monomer-starved conditions in emulsion polymerization reactors

An important characteristic of monomer-starved nucleation in semibatch reactors is that the rate of growth of particles is controlled by the rate of monomer addition. The reduced rate of growth of particles prolongs the nucleation interval by slowing down the rate of emulsifier micelle depletion and forms a larger number of particles (N_p). Model calculations show how N_p varies with the formulation parameters as the monomer-flooded nucleation shifts into monomer-starved one. Particle formation in the intermediate conversion of interval III of the styrene batch emulsion polymerization also showed an enhancement because of a low rate of growth of newly formed particles. However, at a higher conversion, the rate of particle formation decreased significantly. Modeling results show that the reduction in the rate of particle formation at high conversions could not be simply explained by existing theories which rely on the decrease in monomer concentration in the aqueous phase as a means to explain the decrease in the rate of radical capture.     

Scaling behavior of earthquakes’ inter-events time series

In this paper, we investigate the statistical and scaling properties of the California earthquakes’ inter-events over a period of the recent 40 years. To detect long-term correlations behavior, we apply detrended fluctuation analysis (DFA), which can systematically detect and overcome nonstationarities in the data set at all time scales. We calculate for various earthquakes with magnitudes larger than a given M. The results indicate that the Hurst exponent decreases with increasing M; characterized by a Hurst exponent, which is given by, H = 0:34 + 1:53/M, indicating that for events with very large magnitudes M, the Hurst exponent decreases to 0:50, which is for independent events.      

HPTLC Analysis of Tamoxifen Citrate in Drug-Release Media During Development of an In-Situ-Cross-Linking Delivery System

JPC – Journal of Planar Chromatography – Modern TLC - High-performance liquid chromatography (HPLC) has been the most popular choice for analysis of tamoxifen citrate. In this study,...     

Thermodynamics of interactions of vancomycin and synthetic surrogates of bacterial cell wall

Glycopeptide antibiotics, including vancomycin, form complexes via a set of five hydrogen bonds with the acyl-l-Lys-d-Ala-d-Ala portion of the peptidyl stems of the bacterial cell wall peptidoglycan. This complexation deprives the organism from the ability to cross-link peptidyl stems of the peptidoglycan, leading to bacterial cell death. Four synthetic fragments as surrogates of the components of the bacterial cell wall have been prepared in our lab in multistep syntheses. These synthetic samples were used in investigations of the thermodynamics properties (DeltaG degrees , DeltaH degrees , and TDeltaS degrees ) for the complexation with vancomycin by isothermal titration calorimetry (ITC). Complexation with the glycopeptide analogues is largely enthalpy-driven (formation of five hydrogen bonds), and in the analogues with a single peptidyl stem, the complexation is 1:1. The complexation is more complicated with an approximately 2 kDa cell wall surrogate (compound 4), which possesses two peptidyl stems. The data were suggestive of interactions between the two vancomycin molecules, with an entropic penalty attributable to restriction of molecular movements within the complex due to restriction of motion of the highly mobile acyl-d-Ala-d-Ala moiety of the peptidyl stems. These data were reconciled with the recently determined NMR solution structure for the peptidoglycan fragment 4 and its implications for the larger cell wall.     

Removal of heavy metals from aqueous solutions using Fe3O4, ZnO, and CuO nanoparticles

This study investigated the removal of Cd²⁺, Cu²⁺, Ni²⁺, and Pb²⁺ from aqueous solutions with novel nanoparticle sorbents (Fe₃O₄, ZnO, and CuO) using a range of experimental approaches, including, pH, competing ions, sorbent masses, contact time, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The images showed that Fe₃O₄, ZnO, and CuO particles had mean diameters of about 50?nm (spheroid), 25?nm (rod shape), and 75?nm (spheroid), respectively. Tests were performed under batch conditions to determine the adsorption rate and uptake at equilibrium from single and multiple component solutions. The maximum uptake values (sum of four metals) in multiple component solutions were 360.6, 114.5, and 73.0?mg?g^?1, for ZnO, CuO, and Fe₃O₄, respectively. Based on the average metal removal by the three nanoparticles, the following order was determined for single component solutions: Cd²⁺?>?Pb²⁺?>?Cu²⁺?>?Ni²⁺, while the following order was determined in multiple component solutions: Pb²⁺?>?Cu²⁺?>?Cd²⁺?>?Ni²⁺. Sorption equilibrium isotherms could be described using the Freundlich model in some cases, whereas other isotherms did not follow this model. Furthermore, a pseudo-second order kinetic model was found to correctly describe the experimental data for all nanoparticles. Scanning electron microscopy, energy dispersive X-ray before and after metal sorption, and soil solution saturation indices showed that the main mechanism of sorption for Cd²⁺ and Pb²⁺ was adsorption, whereas both Cu²⁺ and Ni²⁺ sorption were due to adsorption and precipitation. These nanoparticles have potential for use as efficient sorbents for the removal of heavy metals from aqueous solutions and ZnO nanoparticles were identified as the most promising sorbent due to their high metal uptake.     

Microfluidic synthesis of chitosan-based nanoparticles for fuel cell applications

A microfluidic platform is developed for the synthesis of monodisperse, 100 nm, chitosan based nanoparticles using nanogelation with ATP. The resulting nanoparticles tuned and enhanced transport and electrochemical properties of Nafion based nanocomposite membranes, which is highly favorable for fuel cell applications.