Multilayered nanoclusters of platinum and gold : insights on electrodeposition pathways, electrocatalysis, surface and bulk compositional properties

Electrochemical, surface and bulk compositional properties of multilayered nanoclusters of Pt and Au, electrochemically deposited on glassy carbon under conditions involving sequential surface–limited redox–replacement reactions (performed at open–circuit) and voltammetric dealloying of templating adlayers of electrodeposited Cu, have been studied in the direction of electrocatalytic applications. Variations in open–circuit potentials during redox–replacement steps indicated thermodynamically–favored formation of Pt(s) and Au(s). Unique bimetallic interfacial active sites, Pt|Au or Au|Pt, were effectively generated as evidenced by their distinct surface electrochemistry and multicomponent X–ray photoelectron spectral features. The bulk and surface–to–near surface distribution of Pt and Au appeared to be influenced by the stoichiometry of the surface redox–replacement reactions and sequential dealloying processes through which the nanoclusters were synthesized. Interactions between metal centers, carbon and oxygen containing surface functional groups on the glassy carbon appeared to have played a significant role in the overall stabilization and catalytic activity of the nanoclusters. Profound effects were also found on interfacial charge–transfer and adsorptive properties involving carbon monoxide and its subsequent electrooxidation to CO2, as well as on the electrocatalytic activity involving formic acid oxidation reaction, where the Pt–rich (Pt|Au) exhibited the highest activity.University of Pretoria and CSIR.http://jes.ecsdl.org/hb2016Chemistr

Nonequilibrium thermodynamics and energy efficiency in weight loss diets

Carbohydrate restriction as a strategy for control of obesity is based on two effects: a behavioral effect, spontaneous reduction in caloric intake and a metabolic effect, an apparent reduction in energy efficiency, greater weight loss per calorie consumed. Variable energy efficiency is established in many contexts (hormonal imbalance, weight regain and knock-out experiments in animal models), but in the area of the effect of macronutrient composition on weight loss, controversy remains. Resistance to the idea comes from a perception that variable weight loss on isocaloric diets would somehow violate the laws of thermodynamics, that is, only caloric intake is important ("a calorie is a calorie"). Previous explanations of how the phenomenon occurs, based on equilibrium thermodynamics, emphasized the inefficiencies introduced by substrate cycling and requirements for increased gluconeogenesis. Living systems, however, are maintained far from equilibrium, and metabolism is controlled by the regulation of the rates of enzymatic reactions. The principles of nonequilibrium thermodynamics which emphasize kinetic fluxes as well as thermodynamic forces should therefore also be considered

Modelling of the blood plasma species of biguanide derivatives exhibiting potential as diagnostic radiopharmaceuticals

99mTc-DMSA (DMSA=dimercaptosuccinic acid), the gold standard for static renal imaging, has a long uptake time, which is a limiting factor in diagnostic procedures and also leads to a relatively high radiation dose to patients. The ligands dimethyl biguanide (DMBG), biuret (BIU), 2-imino-4-thiobiuret (ITB) and carboxy-biguanide (CBIG) have nitrogen donor atoms, which are able to complex transition elements. The formation constants needed in order to establish a blood plasma model for these ligands were determined by potentiometry and the results are reported herein. Based on blood plasma modelling, it was shown that the ligands had selectivity for 99mTc over blood plasma metal ions at physiological pH and it was therefore hypothesized that the Tc-ligand complex would survive in blood plasma. Furthermore, no or few side effects related to the mobilization of blood plasma metal ions by these ligands are expected, once the radiopharmaceutical has been administered. It is also expected that these ligands should clear rapidly from the blood plasma

99mTc-labelled biguanide derivatives : chemical speciation modelling thereof and evaluation in vervets

99mTc-DMSA (dimercaptosuccinic acid) is known to be a safe and effective agent for static renal imaging. However, it has a long uptake time which is a limiting factor in diagnostic procedures and also leads to a relatively high radiation dose being administered to patients. There is a constant search for possible new renal imaging agents with a good resolution, kidney/liver contrast and low radiation dose to all organs. A series of biguanide derivatives (potential as non-insulin-dependent diabetes mellitus agents) labelled with 99mTc were investigated as potential alternative kidney-imaging agents on theoretical grounds (in silico) and their biodistribution (in vivo) verified in a limited number of animal experiments. Such a dual approach has the benefit that it reduces the number of animal experiments needed to evaluate a potential radiopharmaceutical. The blood plasma model shows little or no complexation of the biguanide type ligands by the metal ions in blood plasma. It was therefore expected that these ligands will clear rapidly through the kidneys and liver (increased lipophilicity). These predictions were verified by studies on single vervets comparing them with 99mTc-DMSA as gold standard. All the biguanide derivatives labelled with 99mTc show liver, kidney and gallbladder uptake in vervets. It was shown that the agent 99mTc-CBIG (carboxylbiguanide) has a very fast kidney clearance, which will reduce the dose to organs (as experienced for 99mTc-DMSA), although it’s potential as a kidney agent is limited by its gallbladder uptake

Measurements and Modeling To Determine the Reduction Potential of Uncomplexed Bi(III) in Nitrate Solutions for Application in Bi(III)-Ligand Equilibria Studies by Voltammetry

The free metal ion potential, <i>E</i>(M), is a critical parameter in the calculation of formation constants when using voltammetry. When studying complex formation of Bi­(III), however, <i>E</i>(Bi) cannot be directly measured. In this work a nitrate background electrolyte was employed to obtain reversible reduction waves. To determine <i>E</i>(Bi), measurements have to be made below pH ∼ 2 before the bismuth-oxy-nitrate species precipitates and thus corrections for the diffusion junction potential (monitored using Tl­(I) as an internal reference ion) must be made. Additionally shifts in potential due to both Bi­(III) hydrolysis and Bi­(III) nitrate formation must also be compensated for before <i>E</i>(Bi) can be evaluated. The value of <i>E</i>(Bi) was determined relative to <i>E</i>(Tl) so that in an experiments where ligand is added to determine formation constants, <i>E</i>(Bi) can be determined as accurately as possible (since <i>E</i>(Tl) can generally still be measured). The value of <i>E</i>(Bi) – <i>E</i>(Tl) was found to be 495.6 ± 1.4 mV for the conditions employed