Analysis of rates of tunneling across self-assembled monolayers (SAMs) of n-alkanethiolates SC n (with n = number of carbon atoms) incorporated in junctions having structure Ag TS -SAM//Ga 2 O 3 /EGaIn leads to a value for the injection tunnel current density J 0 (i.e., the current flowing through an ideal junction with n = 0) of 10 3.6±0.3 A·cm −2 (V = +0.5 V). This estimation of J 0 does not involve an extrapolation in length, because it was possible to measure current densities across SAMs over the range of lengths n = 1−18. This value of J 0 is estimated under the assumption that values of the geometrical contact area equal the values of the effective electrical contact area. Detailed experimental analysis, however, indicates that the roughness of the ). A comparison of the characteristics of conical Ga 2 O 3 / EGaIn tips with the characteristics of other top-electrodes suggests that the EGaIn-based electrodes provide a particularly attractive technology for physical-organic studies of charge transport across SAMs. ■ INTRODUCTIONMeasurements, using a number of techniques, of rates of charge transport by tunneling across self-assembled monolayers (SAMs) of n-alkanethiolates on silver and gold substrates show an interesting, puzzling, and unresolved mixture of consistency and inconsistency. Rates of tunneling across these SAMs follow the simplified Simmons equation,( 1) with the falloff in current density J(V) (A·cm ). Using mercury drops as top-electrodes, measurements of rates of tunneling across n-alkanes anchored to heavily doped silicon surfaces led to β = 0.9 ± 0.2 nC −1 , similar to the values observed for nalkanethiolates on Au and Ag substrates. , observed in large-area junctions using, as top-electrodes, conductive polymers, 13 Hg-drops supporting an insulating organic film (Hg-SAM), 14−16 and Ga 2 O 3 /EGaIn tips. 17−20 Why is there high consistency in values of β, but broad inconsistency in values of J 0 (V) within these systems?A priori, at least four factors might contribute to differences in J 0 (V) among methods of measurements:(i) In large-area junctions, assuming that the effective electrical contact area (A elec )the area through which current actually passescoincides with the geometrical contact area (A geo ) estimated by optical microscopy could result in errors in the conversions of values of current into current densities. Contact between surfaces occurs only through asperities distributed on the surfaces, which are always rough to some extent; in addition, only a fraction of the true, physical contact area is conductive.21−24 Estimations of the effective contact area from measurements of adhesion and friction between surfaces indicate that values of A elec /A geo vary in the range 10 −2 −10 −4 , depending on the hardness of the materials, the heights, widths, and number of asperities on both surfaces, and loads applied to the contacts. 22,23,25−27

Allosteric regulation of organometallic catalysts could allow for greater control over reactions. We report an allosteric supramolecular structure in which a monometallic catalytic site has been buried in the middle layer of a triple-layer complex. Small molecules and elemental anions can open and close this complex and reversibly expose and conceal the catalytic center. The ring-opening polymerization of ε-caprolactone can be turned on by the in situ opening of the triple-layer complex and then completely turned off by reforming it through the abstraction of Cl(-), the allosteric effector agent, without appreciable loss of catalytic activity. This process can regulate the molecular weights of the resulting polymers.

Because the p300/CBP-mediated hyperacetylation of RelA (p65) is critical for nuclear factor-KB (NF-KB) activation, the attenuation of p65 acetylation is a potential molecular target for the prevention of chronic inflammation. During our ongoing screening study to identify natural compounds with histone acetyltransferase inhibitor (HATi) activity, we identified epigallocatechin-3-gallate (EGCG) as a novel HATi with global specificity for the majority of HAT enzymes but with no activity toward epigenetic enzymes including HDAC, SIRT1, and HMTase. At a dose of 100 Mmol/L, EGCG abrogates p300-induced p65 acetylation in vitro and in vivo, increases the level of cytosolic IKBA, and suppresses tumor necrosis factor A (TNFA)-induced NF-KB activation. We also showed that EGCG prevents TNFA-induced p65 translocation to the nucleus, confirming that hyperacetylation is critical for NF-KB translocation as well as activity. Furthermore, EGCG treatment inhibited the acetylation of p65 and the expression of NF-KB target genes in response to diverse stimuli. Finally, EGCG reduced the binding of p300 to the promoter region of interleukin-6 gene with an increased recruitment of HDAC3, which highlights the importance of the balance between HATs and histone deacetylases in the NF-KB-mediated inflammatory signaling pathway. Importantly, EGCG at 50 Mmol/L dose completely blocks EBV infection-induced cytokine expression and subsequently the EBV-induced B lymphocyte transformation. These results show the crucial role of acetylation in the development of inflammatory-related diseases. [Cancer Res 2009;69(2):583-92]

Molecular rectification is a particularly attractive phenomenon to examine in studying structure−property relationships in charge transport across molecular junctions, since the tunneling currents across the same molecular junction are measured, with only a change in the sign of the bias, with the same electrodes, molecule(s), and contacts. This type of experiment minimizes the complexities arising from measurements of current densities at one polarity using replicate junctions. This paper describes a new organic molecular rectifier: a junction having the structure Ag TS /S(CH 2 ) 11 -4-methyl-2,2′-bipyridyl//Ga 2 O 3 /EGaIn (Ag TS : template-stripped silver substrate; EGaIn: eutectic gallium−indium alloy) which shows reproducible rectification with a mean r + = |J(+1.0 V)|/|J(−1.0 V)| = 85 ± 2. This system is important because rectification occurs at a polarity opposite to that of the analogous but much more extensively studied systems based on ferrocene. It establishes (again) that rectification is due to the SAM, and not to redox reactions involving the Ga 2 O 3 film, and confirms that rectification is not related to the polarity in the junction. Comparisons among SAM-based junctions incorporating the Ga 2 O 3 /EGaIn top electrode and a variety of heterocyclic terminal groups indicate that the metal-free bipyridyl group, not other features of the junction, is responsible for the rectification. The paper also describes a structural and mechanistic hypothesis that suggests a partial rationalization of values of rectification available in the literature.