Refractive Index Sensitivity Analysis of Ag, Au, and Cu Nanoparticles

The localized surface plasmon resonance (LSPR) spectrum of noble metal nanoparticles is studied by quasi-static approximation. Taking the sensitivity of LSPR shape to the size and shape of nanoparticle along with surrounding refractive index, parameters like refractive index sensitivity and sensing figure of merit have been determined. In the present analysis from the sensing relevant parameters, it is concluded that Ag represents a better sensing behavior than Au and Cu over the entire visible to infrared regime of EM spectrum.     

Scattering Efficiency and LSPR Tunability of Bimetallic Ag,Au, and Cu Nanoparticles

Scattering efficiencies of Ag–Cu, Ag–Au, and Au–Cu alloy nanoparticles are studied based on Mie theory for their possible applications in solar cells. The effect of size (radius), surrounding medium, and alloy composition on the scattering efficiency at the localized surface plasmon resonance (LSPR) wavelengths has been reported. In the alloy nanoparticles of Ag_1?x Cu _x , Au_1?x Cu _x and Ag_1?x Au _x ; the scattering efficiency gets red-shifted with increase in x. Moreover, the scattering efficiency enhancement can be tuned and controlled with both the alloy composition and the surrounding medium refractive index. A linear relationship which is in good agreement to the experimental observations between the scattering efficiency and metal composition in the alloys are found. The effect of nanoparticle size and LSPR wavelength (scattering peak position) on the full width half maxima and scattering efficiency has also been studied. Comparison of Au–Ag, Au–Cu, and Ag–Cu alloy nanoparticles with 50-nm radii shows the optical response of Ag–Cu alloy nanoparticle with wide bandwidth in the visible region of the electromagnetic spectrum making them suitable for plasmonic solar cells. Further, the comparison of Ag–Cu alloy and core@shell nanoparticles of similar size and surrounding medium shows that Cu@Ag nanoparticle exhibits high scattering efficiency with nearly the same bandwidth.     

Comparative density functional theory based study of the reactivity of Cu,Ag, and Au nanoparticles and of (111) surfaces toward CO oxidation and NO2 reduction

Development of multi-target drugs is becoming increasingly attractive in the repertoire of protein kinase inhibitors discovery. In this study, we carried out molecular docking, molecular dynamics simulations, molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) binding free energy calculations, principal component analysis (PCA), and dynamical cross-correlation matrices (DCCM) to dissect the molecular mechanism for the valmerin-19 acting as a dual inhibitor for glycogen synthase kinase 3β (GSK3β) and cyclin-dependent kinase 5 (CDK5). Detailed MM-PBSA calculations revealed that the binding free energies of the valmerin-19 to GSK3β/CDK5 were calculated to be ?12.60?±?2.28 kcal mol^-1 and ?11.85?±?2.54 kcal mol^-1, respectively, indicating that valmerin-19 has the potential to act as a dual inhibitor of GSK3β/CDK5. The analyses of PCA and DCCM results unraveled that binding of the valmerin-19 reduced the conformational dynamics of GSK3β/CDK5 and the valmerin-19 bound to GSK3β/CDK5 might occur mostly through a conformational selection mechanism. This study may be helpful for the future design of novel and potent dual GSK3β/CDK5 inhibitors.     

Comparative Studies on Plastoquinone II. Analysis for Plastoquinones A, B, C, and D

Two different methods for the extraction and assay of plastoquinones A, B, C and D from chloroplasts of green plants have been described. The long procedure involves separation of aqueous and lipid phases of extract in a separatory funnel, column chromatography, purification on thin-layer plates, and spectrophotometric assays for quantitative determination of the various plastoquinones. The short procedure is based on spotting lipid extracts from chloroplasts on thin layer plates and comparing leucomethylene blue spots of unknown quinones with a series of spots produced by known amounts of the 4 standard plastoquinones on the same plate.

Reliability of the 2 procedures is shown by presenting recovery data (82% recovery for PQ A by the long method and 64-100% recovery by the short method). Various solvent systems for quinone purification are described. Separation of plastoquinones B and C into 6 components each is demonstrated for spinach and a tomato mutant, high pigment (hp). Plastoquinone C is shown to be equivalent to C₁-C₄ while D corresponds to PQ C₅ and C₆ according to Griffiths, Wallwork and Pennock's designation. The term PQ D is therefore redundant and should be abandoned in favor of specific designation of PQ C type.

     

Resolution Estimation of the Au, Ag, Cu, and Al Single- and Double-Layer Surface Plasmon Sensors in the Ultraviolet, Visible, and Infrared Regions

Figures of merit are introduced for estimation of achievable resolution of surface plasmon (SP) sensors by modulation type. The resolution of SP sensors in the Kretschmann’s geometry is estimated by numerical simulation for combinations of silver (Ag), copper (Cu), aluminum (Al), chromium, and titanium layers with a gold (Au) layer in the ultraviolet (UV), visible, and infrared (IR) regions in cases of detecting the change of the refractive index of water and the presence of an adsorption layer in water. SP biosensors with angular modulation based on Al exhibit low resolution in the UV region; Ag, Au, and Cu biosensors show best resolution in the visible region. Biosensors with intensity modulation demonstrate high performance in the near IR by Ag, Au, and Cu metals, and in the UV by Al.     

Radiotracer Studies on Waterborne Copper Uptake,Distribution, and Toxicity in Rainbow Trout and Yellow Perch: A Comparative Analysis

Rainbow trout (Oncorhynchus mykiss) are often used to estimate important biotic ligand model (BLM) parameters, such as metal-binding affinity (log K) and capacity (B_max). However, rainbow trout do not typically occupy metal-contaminated environments, whereas yellow perch (Perca flavescens) are ubiquitous throughout most of North America. This study demonstrates that dynamic processes that regulate Cu uptake at the gill differ between rainbow trout and yellow perch. Rainbow trout were more sensitive to acute aqueous Cu than yellow perch, and toxicity was exacerbated in soft water relative to similar exposures in hard water. Whole body Na loss rate could account for acute Cu toxicity in both species, as opposed to new Cu uptake rate that was not as predictive. Time course experiments using radiolabelled Cu (⁶⁴Cu) revealed that branchial Cu uptake was rather variable within the first 12 h of exposure, and appeared to be a function of Cu concentration, water hardness, and fish species. After 12 h, new branchial Cu concentrations stabilized in both species, suggesting that metal exposures used to estimate BLM parameters should be increased in duration from 3 h to 12+ h. In rainbow trout, 71% of the new Cu bound to the gill was exchangeable (i.e., able to either enter the fish or be released back to the water), as opposed to only 48% in yellow perch. This suggests that at equal exposure concentrations, proportionally more branchial Cu can be taken up by rainbow trout than yellow perch, which can then go on to confer toxicity. These qualitative differences in branchial Cu handling between the two species emphasize the need to develop BLM parameters for each species of interest, rather than the current practice of extrapolating BLM results derived from rainbow trout (or other laboratory-reared species) to other species. Data reported here indicate that a one-size-fits-all approach to predictive modeling, mostly based on rainbow trout studies, may not suffice for making predictions about metal toxicity to yellow perch—that is, a species that inhabits metal-contaminated lakes around northern Canadian industrial operations.     

Comparative Environmental Assessment in the Studies of Benthic Diatom,Macroinvertebrate, and Fish Communities

Community response to environmental gradients operating at hierarchical scales was assessed in studies of benthic diatoms, macroinvertebrates and fish from 44 stream sites in the New York City watershed. Hierarchical cluster analysis (TWINSPAN) of diatoms and fish partitioned the study sites into four groups, i.e., acid streams, reservoir outlets and wetland streams, large eutrophic streams, and small eutrophic streams; macroinvertebrate TWINSPAN distinguished an additional group of silty eutrophic streams. The correspondence among the three assemblage TWINSPAN groupings was moderate, ranging from 51 to 57%. The similarity across the four major group types was the highest among large eutrophic stream and acid stream assemblages, and the lowest among small eutrophic stream assemblages. Stepwise discriminant function analysis revealed that environmental factors discriminated most effectively the diatom grouping and least effectively the fish grouping. The best environmental predictors for diatom and macroinvertebrate grouping were conductance and percent surface water, while population density was most powerful in separating the fish groups. Carbaryl was the only pesticide that correlated with macroinvertebrate grouping. Partial redundancy analyses suggested a differential dependence of freshwater communities on the scale of the environmental factors to which they respond. The role of small‐scale habitat and habitatland cover/land use interaction steadily increased across the diatom, macroinvertebrate, and fish assemblages, whereas the effect of large‐scale land cover/land use declined.     

Studies of Zn, Mg, Cu, Ca and Fe in cadmium poisoned toads before and after treatment with EDTA

Zn, Mg, Cu, Ca and Fe were determined spectrophotometrically in liver, kidneys, muscle, spleen and blood of Bufo regularis after a single i.m. injection of 6.2 mg Cd/kg (which represents the 96 hr LD50) alone or in combination with 40 mg EDTA/kg (the minimal EDTA concentration causing 100% survival over that period). Cadmium administration caused recognizable effects on the essential metals levels in different tissues and organs. In the majority of the tissues and organs studied, zinc and copper concentrations returned to their normal ranges in animals that received both cadmium and EDTA. In contrast, magnesium, calcium and iron contents not only returned back to their control values but also exceeded them.     

General Trends in Trace Element Utilization Revealed by Comparative Genomic Analyses of Co, Cu, Mo, Ni, and Se

Trace elements are used by all organisms and provide proteins with unique coordination and catalytic and electron transfer properties. Although many trace element-containing proteins are well characterized, little is known about the general trends in trace element utilization. We carried out comparative genomic analyses of copper, molybdenum, nickel, cobalt (in the form of vitamin B₁₂), and selenium (in the form of selenocysteine) in 747 sequenced organisms at the following levels: (i) transporters and transport-related proteins, (ii) cofactor biosynthesis traits, and (iii) trace element-dependent proteins. Few organisms were found to utilize all five trace elements, whereas many symbionts, parasites, and yeasts used only one or none of these elements. Investigation of metalloproteomes and selenoproteomes revealed examples of increased utilization of proteins that use copper in land plants, cobalt in Dehalococcoides and Dictyostelium, and selenium in fish and algae, whereas nematodes were found to have great diversity of copper transporters. These analyses also characterized trace element metabolism in common model organisms and suggested new model organisms for experimental studies of individual trace elements. Mismatches in the occurrence of user proteins and corresponding transport systems revealed deficiencies in our understanding of trace element biology. Biological interactions among some trace elements were observed; however, such links were limited, and trace elements generally had unique utilization patterns. Finally, environmental factors, such as oxygen requirement and habitat, correlated with the utilization of certain trace elements. These data provide insights into the general features of utilization and evolution of trace elements in the three domains of life.     

Invertebrate Strategies in Comparative Learning Studies

Despite the overwhelming variety and abundance of invertebratespecies the contribution of invertebrate studies to our understandingof the behavioral and physiological bases of learning has beenminimal. Although anthropocentric biases may be responsiblefor the inordinate number of studies performed with the usuallaboratory animals, clearly a vigorous extension of the comparativeapproach in the behavioral sciences is demanded. Several featuresof the comparative approach are outlined and suggestions aremade which minimize any of its inherent difficulties. A multi-leveland polythetic approach is proposed which considers multiplecharacteristics supplemented by evidence obtained at other levelsto establish a meaningful behavioral taxonomy. Controlled systematicvariation may be used to analyze the functional relations ofthe performance of different species on the same behavioraltask. Another strategy compares simplified and complex versionsof the same system in order to assess the quantitative and qualitativerelationships between complexity and capacity. The structureof many invertebrate species renders them ideally suited tosuch analysis. Data on habituation obtained in Limulus polyphemusemploying such a paradigm is discussed. The relationships betweenelectrophysiological habituation and levels of neural complexityare clearly demonstrated. Future contributions from this preparationas well as from other invertebrate species are also discussed.     

Formation and characterization of aurothioneins: Au,Zn,Cd-thionein, Au,Cd-thionein, and (thiomalato-Au)chi-thionein

Three gold-containing thioneins (Au,Zn,Cd-Th, Au,Cd-Th, and (TmSAu)chi Th, where Th = thionein and TmS = thiomalate) have been prepared by the reactions of horse kidney Zn,Cd-thionein with gold thiomalate (AuSTm). When thionein was present in excess, the thiomalate ligand was displaced and the protein chelated the gold in a bidentate fashion. Primarily zinc but also some cadmium was displaced to form Au,Zn,Cd-Th or Au,Cd-Th. Excess AuSTm reacted to form (TmSAu)chi-thionein with monodentate coordination of the protein to each bound gold, retention of the thiomalate, loss of zinc and cadmium, and an increase in the Stokes radius of the product. EXAFS/XANES studies of Au,Zn,Cd-Th and (TmSAu)chi Th established that the oxidation states and coordination environments of gold were Au(I)S2 and that the gold-sulfur bond distances were 229 and 230 pm, respectively. Radioimmunoassay established that the aurothioneins retained their antigenicity to native metallothionein antibodies. Metal exchange reactions with gold were complete within 5-10 min when Zincon or 4-(2-pyridylazo) resorcinol was used to monitor Cd2+ and Zn2+ displacement.     

Molecular dynamics study on deformation and mechanics of nanoscale Au/Cu multilayers under indentation

The effects of individual layer thickness, indentation velocity, and temperature on the mechanical properties and mechanics of nanoscale Au/Cu multilayers under indentation were studied using molecular dynamics simulations based on the many-body embedded-atom potential. The simulation results show that layer interfaces act as strong barriers that resist the propagation of dislocations, even at an extremely small individual layer thickness of 3 nm. The number of dislocations increases significantly and the growth of dislocations decreases with decreasing individual layer thickness. There is no clear relationship between the magnitude of the required indentation force and the number of film layers; however, the average required indentation force increases with increasing indentation velocity and decreasing temperature. During indentation at a relatively low velocity, dislocation propagation is more significant; the number of disordered atoms significantly increases at a relatively high indentation velocity.     

Studies on the expression of Cu,Zn superoxide dismutase in human tissues during development

The developmental expression of Cu,Zn superoxide dismutase in human lung and erythrocytes has been studied using activity measurements, immunoblotting and immunohistochemistry. Enzyme activity in erythrocytes increased significantly during gestation but no developmental trend was seen in lung. Immunoblotting identified a single enzyme form that was present in a variety of tissues and immunohistochemistry showed the enzyme to have widespread distribution in lung tissue. These data indicate that Cu,Zn superoxide dismutase is consistently expressed during human development and that, unlike in other species, no late-fetal surge in expression occurs.     

Comparative effects of pitavastatin and probucol on oxidative stress, Cu/Zn superoxide dismutase, PPAR-gamma, and aortic stiffness in hypercholesterolemia

Reactive oxygen species-scavenging enzyme Cu/Zn superoxide dismutase (SOD) regulated by peroxisome proliferator-activated receptors (PPARs) plays an important role in vascular responsiveness. However, it remains unknown whether statin restores vascular dysfunction through the activation of reactive oxygen species-scavenging enzymes in vivo. We hypothesized that pitavastatin restores vascular function by modulating oxidative stress through the activation of Cu/ZnSOD and PPAR-gamma in hypercholesterolemia. New Zealand White male rabbits were fed either normal chow or a 1% cholesterol (CHO) diet for 14 wk. After the first 7 wk, the CHO-fed rabbits were further divided into three groups: those fed with CHO feed only (HC), those additionally given pitavastatin, and those additionally given an antioxidant, probucol. The extent of atherosclerosis was assessed by examining aortic stiffness. When compared with the HC group, both the pitavastatin and probucol groups showed improved aortic stiffness by reducing aortic levels of reactive oxidative stress, nitrotyrosine, and collagen, without affecting serum cholesterol or blood pressure levels. Pitavastatin restored both Cu/ZnSOD activity (P < 0.005) and PPAR-gamma expression and activity (P < 0.01) and inhibited NAD(P)H oxidase activity (P < 0.0001) in the aorta, whereas probucol inhibited NAD(P)H oxidase activity more than did pitavastatin (P < 0.0005) without affecting Cu/ZnSOD activity or PPAR-gamma expression and activity. Importantly, Cu/ZnSOD activity was positively correlated with the PPAR-gamma activity in the aorta (P < 0.005), both of which were negatively correlated with aortic stiffness (P < 0.05). Vascular Cu/ZnSOD and PPAR-gamma may play a crucial role in the antiatherogenic effects of pitavastatin in hypercholesterolemia in vivo.