In Vitro Corrosion of SiC-Coated Anodized Ti Nano-Tubular Surfaces.

Peri-implantitis leads to implant failure and decreases long-term survival and success rates of implant-supported prostheses. The pathogenesis of this disease is complex but implant corrosion is believed to be one of the many factors which contributes to progression of this disease. A nanostructured titanium dioxide layer was introduced using anodization to improve the functionality of dental implants. In the present study, we evaluated the corrosion performance of silicon carbide (SiC) on anodized titanium dioxide nanotubes (ATO) using plasma-enhanced chemical vapor deposition (PECVD). This was investigated through a potentiodynamic polarization test and bacterial incubation for 30 days. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to analyze surface morphologies of non-coated and SiC-coated nanotubes. Energy dispersive X-ray (EDX) was used to analyze the surface composition. In conclusion, SiC-coated ATO exhibited improved corrosion resistance and holds promise as an implant coating material.

An Electrochemical Approach to and the Physical Consequences of Preparing Nanostructures from Gold Nanorods with Smooth Ends.

We have developed a method to smooth the end sections of nanowires and nanograps generated via the On-Wire Lithography process and studied these rods with optical spectroscopies and theoretical modeling (Discrete Dipole Approximation). The first step of the smoothing process is a reductive one aimed at controlling the diffusion and migration of metal ions to the growing nanorod surface by adjusting the applied potential and concentration of the metal ions in the growth solution. A second oxidative smoothing step, based in part on the energetic differences between topologically rough and smooth surfaces, is used to further smooth the nanorod. The RMS roughness can be reduced over five fold to approximately 5 nm. The properties of these smoothed rods were investigated by empirical and theoretical methods, where it was found the smoothed rods have sharper plasmon resonances and decreased SERS intensity.

Probing surface-porphyrazine reduction potentials by molecular design.

This manuscript reports electrochemical and angle-resolved X-ray photoelectron spectroscopy measurements of surface-bound porphyrazine monolayers in which the molecule-surface distance and molecular orientation of the porphyrazine are controlled through the design of the adsorbates. This system has allowed us to probe the importance of molecule-surface interaction in determining the shift in reduction potential upon binding to a gold surface. This quantity currently is in theoretical dispute, with one computation indicating that a porphyrazine/porphyrin exhibits an extremely large covalent binding energy ( approximately 10 eV) to a gold surface, whereas a more recent one finds the binding energy to be only a fraction of an electronvolt. Our study indicates that the shift in reduction potential upon surface binding is not a discontinuous function of the molecule-surface distance, as would be the case if covalent interaction of the porphyrazine core with the gold surface were controlling, but rather varies smoothly. This, therefore, rules out the possibility that the large potential shift seen for a porphyrazine whose macrocyclic core lies approximately 3.9 A above the gold surface, relative to one that lies approximately 8.9 A above the surface, DeltaDeltaE = 340 mV, is caused by direct covalent binding of the pi-system to the metal surface.

Tuning emissive states in electrogenerated chemiluminescence.

Electrogenerated chemiluminescence (ECL) arising from the reaction of radical ions has previously be shown to arise from a variety of states including excited singlets, triplets, excimers, and exciplexes. In this work we describe two systems that form emissive states in ECL with different properties than those when formed with photoluminescence. The first system involves the reaction of the anthracene radical anion with the radical cation of 4,N,N-trimethylaniline. ECL from this system exhibited an exciplex whose energy and intensity relative to the emission from the anthracene singlet could be tuned by adjusting the solvent permittivity and ionic strength. Under conditions considered extreme for electrochemical experiments, no added electrolyte in dimethoxyethane, the relative intensity of the anthracene-related exciplex, formed from the encounter complex, was 8 times greater and red-shifted from that generated by photoluminescence in the same solution with 100-fold exciplex partner added. In the second system examined, the benzophenone radical anion reacted with the radical cation of either phenoxathiin or 4-methoxythioanisole; the ECL emission was from the benzophenone triplet state and an excimer. The excimer, a species not seen with photoluminescence, predominated as the benzophenone concentration was elevated into the low millimolar range. The results from these two simple systems clearly demonstrate that the radical ion annihilation pathway of ECL can generate different emissive states than those formed following photoexcitation.

High-performance liquid chromatographic-nuclear magnetic resonance investigation of the isomerization of alachlor-ethanesulfonic acid.

The metabolism of the acetanilide herbicide alachlor in soils leads to the formation of alachlor-ethanesulfonic acid (alachlor-ESA) as one of the major transformation products of this compound. The unique structure of alachlor and its metabolites allows the formation of two diastereomers (s-trans and s-cis) due to the hindered rotation of the amide bond connected to a rigid aromatic ring. Although these stereoisomers do interconvert by rotation about the amide bond, the rate of interconversion is slow allowing separation of the isomers on the chromatographic time scale. Once separated, the unique nuclear magnetic resonance signals of each isomer can be used to monitor the rate of isomerization. This paper reports the on-line separation and detection of the rotational diastereomers using high-performance liquid chromatography-nuclear magnetic resonance (HPLC-NMR) to efficiently measure the isomerization rate of alachlor-ESA.