Examination of cyclic voltammetric responses reveals that inversion of the standard potentials of the first and second electron transfers occurs in the oxidation of beta-carotene and 15,15'-didehydro-beta-carotene (but not in their reduction) as well as in the reduction of canthaxanthin (but not in its oxidation). The factors that control potential inversion in these systems, and more generally in symmetrical molecules containing conjugated long chains, are investigated by quantum chemical calculations. Two main interconnected effects emerge. One is the localization of the charges in the di-ion toward the ends of the molecule at a large distance from one another, thus minimizing Coulombic repulsion. The same effect favors the solvation of the di-ion providing additional stabilization. In contrast, the charge in the ion radical is delocalized over the whole molecular framework, thus disfavoring its stabilization by interaction with the solvent. The combination of the two solvation effects allows potential inversion to occur as opposed to the case where the two electrophores are linked by a saturated bridge where potential inversion cannot occur. Localization of the charges in the di-ion, and thus potential inversion, is favored by the presence of electron-accepting terminal groups for reductions (as the two carbonyl groups in canthaxanthin) and of hole-accepting terminal groups for oxidations (as in beta-carotene).

Hexadecylquinolinium tricyanoquinodimethanide (1), a unimolecular rectifier of electrical current with a large ground-state dipole moment (43 ± 8 D), reveals large hypsochromic shifts of the absorption spectrum. Two fluorescent emissions were observed:  one in the visible region (quantum yield φ ≈ 0.01, not solvatochromic) and one in the near-infrared spectrum (weakly solvatochromic). Using a prolate spheroidal cavity model and the absorption maxima measured in eight solvents, the excited-state dipole moment of 1 is estimated as 8.7 D. The NMR spectral lines broaden above 330 K and lose the multiplet structure. The core-level N 1s XPS spectrum reveals the three expected N valence states. The valence-level XPS spectrum can be correlated with theory. Simultaneous cyclic voltammetry and electron spin resonance of the radical anion of 1 shows that the spin density in the LUMO of 1 is concentrated on the tricyanoquinodimethanide portion of the anion. The molecule is clearly zwitterionic in the ground state, both in LB films and in solution, and is undissociated (“neutral”) in its first excited state.

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Ultra-smooth nanostructured diamond (USND) can be applied to greatly increase the wear resistance of orthopaedic implants over conventional designs. Herein we describe surface modification techniques and cytocompatibility studies performed on this new material. We report that hydrogen (H)-terminated USND surfaces supported robust mesenchymal stem cell (MSC) adhesion and survival, while oxygen- (O) and fluorine (F)-terminated surfaces resisted cell adhesion, indicating that USND can be modified to either promote or prevent cell/biomaterial interactions. Given the favorable cell response to H-terminated USND, this material was further compared with two commonly used biocompatible metals, titanium alloy (Ti-6Al-4V) and cobalt chrome (CoCrMo). MSC adhesion and proliferation were significantly improved on USND compared with CoCrMo, although cell adhesion was greatest on Ti-6Al-4V. Comparable amounts of the pro-adhesive protein, fibronectin, were deposited from serum on the three substrates. Finally, MSCs were induced to undergo osteoblastic differentiation on the three materials, and deposition of a mineralized matrix was quantified. Similar amounts of mineral were deposited onto USND and CoCrMo, whereas mineral deposition was slightly higher on Ti-6Al-4V. When coupled with recently published wear studies, these in vitro results suggest that USND has the potential to reduce debris particle release from orthopaedic implants without compromising osseointegration.

Using ordered surface patterns at the nanometer scale, one can fabricate magnetic 1 or semiconductor 2 nanostructures for new devices by either direct deposition or replication. At these length scales, lithography has several disadvantages, e.g. the high cost of making and replicating electron beam-generated masks, the slow throughput due to the sequential nature of the process, and the high susceptibility to errors. Selfordering processes can produce highly ordered patterns, which however do not usually extend over large areas. Long-range self-ordering of nanometer-scale structures would thus be very desirable. 3 Nanoscale topographies were first obtained on Al after oxide formation during cycles of heating (400-660 °C) and cooling, with the formation of hexagonal or lamellar structures. 4,5 Highly ordered hexagonally arranged pores can also be obtained by anodizing Al in acid for several hours, with pore formation, then chemically removing this porous oxide and re-anodizing: pores with perfect hexagonal ordering and 60-200 nm pore-to-pore spacing form in domains a few micrometers in size. [6][7][8][9][10] In striking contrast with this slow pore growth is the rapid self-ordering produced by electropolishing, which is a fast anodic dissolution of the metal immersed in a suitable electrolyte. 4,[11][12][13][14] By electropolishing polycrystalline Al films 11,12 or foils 12,13 for 10-30 s, ordered topographies with uniaxial symmetry (stripes) or hexagonal symmetry (mounds) were reported within 1-2 µm domains: stripes were obtained at cell voltage E ) 30-50 V, hexagons at E ) 55-65 V, and random structures outside this potential window (E < 30 and E > 65 V). These structures were implicitly assumed to be the same for all crystal grains. 11-13 Assuming a preferential adsorption of organic molecules on surface ridges and diffusion control for the reactive species led