Transport in split-gate silicon quantum dots

We report on the transport properties of novel Si quantum dot structures with controllable electron number through both top and side gates. Quantum dots were fabricated by a split-gate technique within a standard MOSFET process. Four-terminal dc electrical measurements were performed at 4.2 K in a liquid helium cryostat. Strong oscillations in the conductance through the dot are observed as a function of both the top gate bias and of the plunger bias. An overall monotonic and quasi-periodic movement of the peak conductance is observed which is believed to be associated with the bare level structure of the electronic states in the dot coupled with the Coulomb charging energy. Crossing behavior is observed as well, suggestive of either many-body effects or symmetry breaking of the dot states by the applied bias.     

Über die Bestimmung von Hydrochinon und Brenzkatechin neben Resorzin und einigen anderen Phenolen

Ohne Zusammenfassung     

Synthesis and spectroscopic properties of 1,3,5-tris(arylalkynyl)-2,4,6-trimethoxybenzenes

A number of C₃-symetric 1,3,5-tris(arylalkynyl)-2,4,6-trimethoxybenzenes which carry electron withdrawing aryl substituents at the acetylenic periphery and donating methoxy groups on the central benzene ring are prepared via Sonogashira coupling. The utility of two different synthetic routes is evaluated as well as the effect of the nature of the aryl and ethynyl starting compounds in the coupling reaction. Finally, a correlation between the substitution pattern of the alkynyl compounds and their UV-vis and fluorescence spectroscopic properties is established.     

Carboxylate and alkyl carbonate coordination at the hydrophobic binding site of redox-active dicobalt amine thiophenolate complexes

A series of new dicobalt complexes of the permethylated macrocyclic hexaamine dithiophenolate ligand H(2)L(Me) have been prepared and investigated in the context of ligand binding and oxidation state changes. The octadentate ligand is an effective dinucleating ligand that supports the formation of bioctahedral complexes with a central N(3)Co(mu-SR)(2)(mu-X)CoN(3) core structure, leaving a free bridging position X for the coordination of the substrates. The acetato- and cinnamato-bridged complexes [(L(Me))Co(II)(2)(mu-O(2)CMe)](+) (2) and [(L(Me))Co(II)(2)(mu-O(2)CCH=CHPh)](+) (5) were prepared by reaction of the mu-Cl complex [(L(Me))Co(II)(2)(mu-Cl)](+) (1) with the corresponding sodium carboxylates in methanol. The electrochemical properties of these and of the methyl carbonate complex [(L(Me))Co(II)(2)(mu-O(2)COMe)](+) (8) were also investigated. All complexes undergo two stepwise oxidations at ca. E(1)(1/2) = +0.22 and at E(2)(1/2) = ca. +0.60 V vs SCE, affording the mixed-valent complexes [(L(Me))Co(II)Co(III)(mu-O(2)CR)](2+) (3, 6, 9) and the fully oxidized Co(III)Co(III) forms [(L(Me))Co(III)(2)(mu-O(2)CR)](3+) (4, 7, 10), respectively. Compounds 3, 6, 9 and 4, 7, 10 refer to acetato-, cinnamato-, and methylcarbonato species, respectively. The Co(II)Co(III) compounds were prepared by comproportionation of the respective Co(II)(2) and Co(III)(2) compounds. The Co(III)Co(III) species were prepared by bromine oxidation of the Co(II)Co(II) forms. The crystal structures of complexes 2.BPh(4).MeCN, 3.(I(3))(2), 5.BPh(4).2MeCN, 6.(ClO(4))(2).EtOH, 7.(ClO(4))(3).MeCN.(H(2)O)(3), and 9.(ClO(4))(2).(MeOH)(2).H(2)O were determined by single-crystal X-ray crystallography at 210 K. The oxidations occur without gross structural changes of the parent complexes. The Co(II)Co(III) complexes are composed of high-spin Co(II) (d(7)) and low-spin Co(III) (d(6)) ions. The Co(III)Co(III) complexes are diamagnetic. The oxidation reactions affect the binding mode of the substrates. In the Co(II)(2) and Co(II)Co(III) forms the carboxylates bridge the two Co(2+) ions in a symmetric mu-1,3 fashion with uniform C-O bond distances, whereas asymmetric bridging modes, with one short C=O and one long C-O distance, are adopted in the fully oxidized species. This is consistent with the observed shifts in vibrational frequencies for nu(as)(C-O) and nu(s)(C-O) across the series.     

Mechanisms and measurements of nanomaterial-induced oxidative damage to DNA

Many of the current investigations on the environmental and human health risks of engineered nanomaterials focus on their short-term acute toxicity. However, the long-term chronic effects of nanomaterials on living systems, and in particular, on the genetic components of living systems, also warrant attention. An increasing number of nanomaterial safety studies include an assessment of genotoxicity as part of the overall risk evaluation. The potential of nanomaterials to directly or indirectly promote the formation of reactive oxygen species is one of the primary steps in their genotoxic repertoire. The subsequent modification of genomic DNA by reactive oxygen species could lead to the development of mutagenesis, carcinogenesis, or other age-related diseases if the DNA damage is not repaired. This review focuses on the interactions of nanomaterials with DNA and specifically on the capacity of some nanomaterials to induce oxidative damage to DNA. A critical assessment of the analytical methodology and the potential biochemical mechanisms involved in nanomaterial induction of oxidative damage to DNA is presented, results obtained for the various studies with each nanomaterial are compared, and recommendations for future research are discussed. Researchers should consider, among other experimental recommendations, (1) the application of more chromatography-based and mass-spectrometry-based analytical techniques to the assessment of oxidative damage to DNA to facilitate an enhanced understanding of DNA damage mechanisms and (2) the verification of cellular viability before conducting genotoxicity assays to reduce the impact of fragmented DNA, formed as a consequence of cell death, on DNA damage measurements.     

EPMA Investigation of Roman Coin Silvering Techniques

Ancient Roman silver coins, especially forgeries, contain various amounts of silver on the surfaces. The state of preservation of the outer layer can vary strongly among different areas of the same coin, thus an investigation of the entire surface is indispensable. The measurement of the silver distribution is a first step towards uncovering the manufacturing techniques. Element mapping by electron probe micro-analysis (EPMA) with increasing step size allows a survey of the complete coin surface. The suitability of this approach is shown and applied to coins having a dark optical appearance and unknown minting technique.     

Solvent‐Dependent Truxene‐Based Nanostructures

Three truxene derivatives functionalized with alkyl chains, either attached directly or distanced by linking phenyl or ethynyl groups, self‐assemble in solution and induce the gelation of different solvents in spite of not being endowed with groups able to establish strong directional interactions. A ¹H NMR study points to face‐to‐face alternating π‐stacked motifs at the origin of nucleation. Solvents play an important role in modulating the aggregation of these derivatives giving rise to fibrous or spherical superstructures. Analysis of the influence of different solvents on the morphology of the aggregates provides a better understanding of the various stages of the hierarchical self‐assembly. The way in which alkyl chains are attached to the central core also strongly affects the self‐assembling properties and gelation ability of this series. Phenyl spacers present the highest association constants in solution and give rise to gelation in a broader range of solvents. This behavior has been rationalized by means of ¹H NMR spectroscopy, X‐ray powder diffraction, SEM, and photophysical measurements. Interestingly, it was found that these compounds in the gel state exhibit unusual emission properties most likely arising from the formation of excimers, which evidences that π–π interactions also occur in the excited state.