17O-NMR of Sol-Gel Processes of TEOS and TMOS

Water consumption and formation in the acid catalyzed sol-gel processing of TEOS and TMOS can be followed using 17O-NMR. By using 17O-enriched water, insight into the hydrolysis and condensation in the acid step of the sol-gel process can be obtained. It is found that, after initially strong consumption of water due to hydrolysis, a steady state water concentration results. This amount of water increases upon dilution of the reaction mixture with alcohol. For a hydrolyzed TMOS-methanol-water system lower water contents are found than in a comparable TEOS-ethanol system. Addition of ethanol to a hydrolyzed TMOS methanol system enhances the condensation and a higher water concentration is found.     

Orthogonalized hybrid orbitals in the theoretical study of polyatomic systems

Ab initio calculations on simple saturated hydrocarbons have been carried out using a basis set of orthogonalized hybrid orbitals. We propose a simple parametric procedure based on the observed transferability of Fock matrix elements calculated in this basis set. Some applications are performed in order to test this simplified non empirical method.     

Photoinduced electron transfer in a mesogenic donor-acceptor-donor system

A novel donor-acceptor-donor molecule consisting of two oligo(p-phenylene vinylene) (OPV4) units attached to a central perylene bisimide (PERY) core is described. This OPV4-PERY-OPV4 is the first mesogenic molecule that incorporates both p- and n-type semiconducting properties and possesses a liquid-crystalline mesophase, in which donor and acceptor functionalities self-assemble into an ordered material. Upon photoexcitation of the donor, a subpicosecond electron-transfer reaction occurs in OPV4-PERY-OPV4, both in solution and in (ordered) thin solid films. The lifetime of the charge-separated state is significantly longer in (ordered) thin films than in solution as a result of a reduction of geminate recombination by migration and spatial separation of charges in the film.     

Increasing the stability of DNA-functionalized gold nanoparticles using mercaptoalkanes

In this work, the stability of DNA functionalized gold nanoparticles was examined in relation to their size, temperature, as well as the presence of mono- and bivalent ions. Furthermore, we report on the stabilizing effect of an additional post-functionalization with mercaptoalkanes, optionally bearing triethylene glycol (TEG) units. Although such so-called backfilling molecules are commonly used for planar gold surfaces, they have rarely been reported in combination with DNA-functionalized nanoparticles. Our results show that, conform the DLVO theory, smaller citrate-capped gold nanoparticles were more stable towards higher concentrations of salt. Citrate nanoparticles of 30 nm in size were only stable in sodium chloride concentrations up to ~0.05 M and up to 45 °C. The stability of these uncoated nanoparticles was even lower when bivalent salts were used (i.e. <2 × 10⁻⁴ M). Immobilization of DNA on these nanoparticles, on the other hand, improved the stability in salt solutions with at least one order of magnitude. The additional use of backfilling molecules stabilized the gold nanoparticles even further, without negatively affecting the DNA hybridization efficiency. DNA functionalization also had a positive impact on the thermal stability of the nanoparticles. Unfortunately, this beneficial effect was not observed after a subsequent backfilling step.