Ion permeability of SAMs on nanoparticle surfaces

This article reports on the ion permeability of self-assembled monolayers (SAMs) formed on the surface of charged alkanethiol-protected gold nanoparticles, so-called monolayer-protected clusters (MPCs). The capacitance and thus the charging energy required to add/remove an electron from the metal core are extremely sensitive to ions entering the monolayer, and the extent of ion penetration can be tuned by the charge and size of the ions and the permittivity of the solvent. Experimentally, this effect is comparable to ion association with conventional redox molecules, indicating that MPCs despite their large size and the fundamentally differing nature of the electron transfer process can be treated analogously to redox molecules.     

Apoptosis induction and mitochondria alteration in human HeLa tumour cells by photoproducts of Rose Bengal acetate

The aim of this work was to investigate the apoptosis induction and mitochondria alteration after photodamage exerted by incubation of HeLa cells with Rose Bengal acetate-derivative (RBAc) followed by irradiation for a total dose of 1.6 J/cm2. This treatment was previously demonstrated to reduce cell viability under mild treatment conditions, suggesting the restoration of the photoactive molecule in particularly sensitive cell sites. Indeed, Rose Bengal (RB) is a very efficient photosensitizer, whose photophysical properties are inactivated by addition of the quencher group acetate. The RBAc behaves as a fluorogenic substrate by entering easily the cells where the original, photoactive molecule is restored by specific esterases. Different intracellular sites of photodamage of RB are present. In particular, fluorescence imaging of Rodamine 123 and JC-1 labelled cells showed altered morphology and loss of potential membrane of mitochondria. MTT and NR assays gave indications of alteration of mitochondrial and lysosomal enzyme activities. These damaged sites were likely responsible for triggering apoptosis. Significant amount of apoptotic cell death (about 40%) was induced after light irradiation followed RBAc incubation as revealed by morphological (modification of cell shape and blebs formation), cytochemical (FITC-Annexin-V positive cells) and nuclear fragmentation assays.     

Resolving electron transfer kinetics at the nanocrystal/solution interface

The kinetics of electron transfer between individual gold nanocrystals and a solution redox species is quantified. The observed rate is dependent on the extent of electronic coupling between nanocrystals in the monolayer indicating the effect of Coulomb blockade on electrochemical kinetics.     

Chemical imaging of protein adsorption and crystallization on a wettability gradient surface

The use of self-assembled monolayers is an established method to study the effect of surface properties on proteins and other biological materials. The generation of a monolayer with a gradient of chemical properties allows for the study of multiple surface properties simultaneously in a high throughput manner. Typically, in order to detect the presence of proteins or biological material on a surface, the use of additional dyes or tags is required. Here we present a novel method of studying the effect of gradient surface properties on protein adsorption and crystallization in situ through the use of ATR-FTIR spectroscopic imaging, which removes the need for additional labeling. We describe the successful application of this technique to the measurement of the growth of a gradient monolayer of octyltrichlorosilane across the surface of a silicon ATR element. ATR-FTIR imaging was also used to study the adsorption of lysozyme, as a model protein, onto the modified surface. The sensitivity of measurements obtained with a focal plane array (FPA) detector were improved though the use of pixel averaging which allowed small absorption bands to be detected with minimal effect on the spatial resolution along the gradient. Study of the effect of surface hydrophobicity on both adsorption of lysozyme to the element and lysozyme crystallization revealed that more lysozyme adsorbed to the hydrophobic side of the ATR element and more lysozyme crystals formed in the same region. These findings strongly suggest a correlation exists between surface protein adsorption and protein crystallization. This method could be applied to the study of other proteins and whole cells.     

Preussianone, a new flavanone-chromone biflavonoid from Garcinia preussii Engl

A new flavanone-chromone biflavonoid, preussianone (1), has been isolated from the leaves of Garcinia preussii, along with four known biflavonoids. The absolute stereostructures were elucidated by chemical, spectroscopic, and chiroptical methods. The biological properties of the new biflavonoid against several bacterial strains were evaluated.     

Zéros triviaux des fonctions L p-adiques, un cas particulier

In this paper we study the trivial zero of the p-adic L function of the symmetric square of an elliptic curve and generalize a conjecture of Greenberg. For that, we use the new approach to p-adic L functions introduced in a previous work.     

Synthèse d'analogues furannique et nitro-2 furannique du benzo[e]pyrène

Pyreno[4,5-b]furan, a heterocyclic analogue of benzo[e]pyrene, and its 10-nitro derivative were prepared in six steps staring from 5-formyl-4-hydroxypyrene. These isomers of the previously described pyreno[1,2-b]-furan, pyreno[2,1-b]furan, 10-nitopyreno[1,2-b]furan and 10-nitropyreno-[2,1-b]furan are of particular interest due to their mutagenic activities.     

{4(S)‐(Piperidin‐1‐ylcarbonyl)‐4‐[3‐(trifluoro­methyl)phenylsulfon­amido]butyl}guanidinium chloride: a model of a graftable thrombin inhibitor

In the title compound, C₁₈H₂₇F₃N₅O₃S⁺·Cl⁻, the guanidine group forms N—H⋯Cl hydrogen bonds, with four N⋯Cl distances in the range 3.164 (3)–3.337 (4) Å. In the crystal packing, the cations are further linked by N—H⋯O and C—H⋯O inter­actions. The structure is compared with that of argatroban complexed with thrombin and is the subject of docking studies in the active site of thrombin.