Investigation of the Influence of Wound-Treatment-Relevant Buffer Systems on the Colloidal and Optical Properties of Gold Nanoparticles.

Biocompatible gold nanoparticles (AuNPs) are used in wound healing due to their radical scavenging activity. They shorten wound healing time by, for example, improving re-epithelialization and promoting the formation of new connective tissue. Another approach that promotes wound healing through cell proliferation while inhibiting bacterial growth is an acidic microenvironment, which can be achieved with acid-forming buffers. Accordingly, a combination of these two approaches appears promising and is the focus of the present study. Here, 18 nm and 56 nm gold NP (Au) were prepared with Turkevich reduction synthesis using design-of-experiments methodology, and the influence of pH and ionic strength on their behaviour was investigated. The citrate buffer had a pronounced effect on the stability of AuNPs due to the more complex intermolecular interactions, which was also confirmed by the changes in optical properties. In contrast, AuNPs dispersed in lactate and phosphate buffer were stable at therapeutically relevant ionic strength, regardless of their size. Simulation of the local pH distribution near the particle surface also showed a steep pH gradient for particles smaller than 100 nm. This suggests that the healing potential is further enhanced by a more acidic environment at the particle surface, making this strategy a promising approach.

Hydrogen transport in non-ideal crystalline materials.

Hydrogen-transport behaviour under (non-)isothermal conditions is discussed. An extended modelling approach based on the effective diffusion coefficient is outlined for arbitrary temperature programmes, defect properties and hydrogen-loading pressures. The influence of mathematical terms, such as the trap equilibrium reaction or microstructural changes, is critically discussed and examples of thermal desorption spectra and isothermal diffusion behaviour are given.

Dissolution of platinum: limits for the deployment of electrochemical energy conversion?

Platinum stability: Dissolution of Pt, which is one major degradation mechanism in, for example, hydrogen/air fuel cells, was monitored under potentiodynamic and potentiostatic conditions. The highly sensitive and time-resolving dissolution monitoring enables the distinction between anodic and cathodic dissolution processes during potential transient and chronoamperometric experiments, and the precise quantification of the amount of dissolved Pt.

Near-surface ion distribution and buffer effects during electrochemical reactions.

The near-surface ion distribution at the solid-liquid interface during the Hydrogen Oxidation Reaction (HOR)/Hydrogen Evolution Reaction (HER) on a rotating platinum disc electrode is demonstrated in this work. The relation between reaction rate, mass transport and the resulting surface pH-value is used to theoretically predict cyclic voltammetry behaviour using only thermodynamic and diffusion data obtained from the literature, which were confirmed by experimental measurements. The effect of buffer addition on the current signal, the surface pH and the ion distribution is quantitatively described by analytical solutions and the fragility of the surface pH during reactions that form or consume H(+) in near-neutral unbuffered solutions or poorly buffered media is highlighted. While the ideal conditions utilized in this fundamental study cannot be directly applied to real scenarios, they do provide a basic understanding of the surface pH concept for more complex heterogeneous reactions.

Electrodeposition of zinc-silica composite coatings: challenges in incorporating functionalized silica particles into a zinc matrix.

Zinc is a well-known sacrificial coating material for iron and co-deposition of suitable particles is of interest for further improving its corrosion protection performance. However, incorporation of particles that are well dispersible in aqueous electrolytes, such as silica particles, is extremely difficult. Here, we report a detailed study of Zn-SiO2 nanocomposite coatings deposited from a zinc sulfate solution at pH 3. The effect of functionalization of the silica particles on the electro-codeposition was investigated. The best incorporation was achieved for particles modified with SiO2-SH, dithiooxamide or cysteamine; these particles have functional groups that can strongly interact with zinc and therefore incorporate well into the metal matrix. Other modifications (SiO2-NH3+, SiO2-Cl and N,N-dimethyldodecylamine) of the silica particles lead to adsorption and entrapment only.

Controlling the conformational changes in donor-acceptor [4]-dendralenes through intramolecular charge-transfer processes.

The synthesis of two [4]-dendralene compounds incorporating thiophene-(p-nitrophenyl) donor-acceptor units is presented. The dendralenes adopt two different conformers in solution and solid state and the transformation between the structures can be controlled by light and heat. The electron-donating components of the dendralenes are represented by bromothienyl (in 13) and ethylenedioxythiophene(EDOT)-thienyl (in 15) end-groups. The most facile transformation involves the isomerisation of donor-acceptor conjugated systems (a conformers) into structures in which only the thiophenes are conjugated (b conformers), and this process is driven by ambient light. The structures of the two conformers of compound 13 are confirmed by single-crystal X-ray diffraction studies and the structural changes in both compounds have been monitored by 1H NMR spectroscopy and absorption studies. The transformations were found to be first-order processes with rate constants of k=0.0027 s(-1) and k=0.00022 s(-1) for 13 and 15, respectively. Density functional theory calculations at the B3LYP/6-31G* level give credence to the proposed mechanism for the a-->b conversion, which involves photoinduced intramolecular charge transfer (ICT) as the key step. The EDOT derivative (15) can be polymerised by electrochemical oxidation and a combination of cyclic voltammetry and UV/Vis spectroelectrochemical experiments indicate that the a conformer can be trapped and stabilised in the solid state.