DNA flexibility on short length scales probed by atomic force microscopy

Unusually high bending flexibility has been recently reported for DNA on short length scales. We use atomic force microscopy (AFM) in solution to obtain a direct estimate of DNA bending statistics for scales down to one helical turn. It appears that DNA behaves as a Gaussian chain and is well described by the worm-like chain model at length scales beyond 3 helical turns (10.5nm). Below this threshold, the AFM data exhibit growing noise because of experimental limitations. This noise may hide small deviations from the Gaussian behavior, but they can hardly be significant.Comment: 5 pages, 5 figures; to appear in PR

The loss of the referent: Identity and fragmentation in Richard Wright’s fiction

This thesis explores forms of fragmentation that characterize black male subjectivity in Richard Wright’s fiction and considers their relationship to the demise of the social anchors and referents which are supposed to allow black men to develop as coherent and whole. It argues that the physical and psychic disfigurement and political and social marginality to which these men are consigned are a direct result of a humanist worldview imposed on them by the two main entities that define them as marginal, namely, white society and black community. To address this relationship, the thesis deploys a poststructuralist approach to question the two societies’ humanist grounding of subjectivity in terms of its conformity to the social whole and its attendant stress on homogeneity and sameness. Wary of this humanist and Enlightenment positioning of the subject as a conscious and thinking individual who is at home with the social totality, the thesis illustrates that the experience of splitting and disjuncture undergone by black men is a corollary of societal modes of subjection that disavow difference and heterogeneity. Probing black male identity from this perspective reveals as much about its decentered nature as it does about the two societies’ humanist view of identity as a closure determined by the ostensibly stable categories of race and community. The formation of black male identity as fractured thus helps map out the instability and anxiety at the heart of collective identities, showing that both white and black societies deny black manhood in the name of preserving their own racial fixity and cultural purity. It exposes the mythical and ideological character of the two societies’ humanist pretentions of safeguarding the values of freedom, equality and the right to agency and shows how such high moral values are politically mobilized in order to maintain racially-sanctioned forms of identity and banish black men as different and inferior

Shape-assisted self-assembly

Self-assembly and molecular recognition are critical processes both in life and material sciences. They usually depend on strong, directional non-covalent interactions to gain specificity and to make long-range organization possible. Most supramolecular constructs are also at least partially governed by topography, whose role is hard to disentangle. This makes it nearly impossible to discern the potential of shape and motion in the creation of complexity. Here, we demonstrate that long-range order in supramolecular constructs can be assisted by the topography of the individual units even in the absence of highly directional interactions. Molecular units of remarkable simplicity self-assemble in solution to give single-molecule thin two-dimensional supramolecular polymers of defined boundaries. This dramatic example spotlights the critical function that topography can have in molecular assembly and paves the path to rationally designed systems of increasing sophistication

N-Heterocyclic Carbene-Platinum Complexes Featuring an Anthracenyl Moiety: Anti-Cancer Activity and DNA Interaction

International audienceA platinum (II) complex stabilized by a pyridine and an N-heterocyclic carbene ligand featuring an anthracenyl moiety was prepared. The compound was fully characterized and its molecular structure was determined by single-crystal X-ray diffraction. The compound demonstrated high in vitro antiproliferative activities against cancer cell lines with IC50 ranging from 10 to 80 nM. The presence of the anthracenyl moiety on the N-heterocyclic carbene (NHC) Pt complex was used as a luminescent tag to probe the metal interaction with the nucleobases of the DNA through a pyridine-nucleobase ligand exchange. Such interaction of the platinum complex with DNA was corroborated by optical tweezers techniques and liquid phase atomic force microscopy (AFM). The results revealed a two-state interaction between the platinum complex and the DNA strands. This two-state behavior was quantified from the different experiments due to contour length variations. At 24 h incubation, the stretching curves revealed multiple structural breakages, and AFM imaging revealed a highly compact and dense structure of platinum complexes bridging the DNA strands

Molluscum contagiosum palpébral: à propos d’un cas

Les Molluscums contagiosum (MC) sont des lésions cutanées bénignes causées par Molluscipoxvirus, ils affectent principalement les enfants et les adultes jeunes et intéressent surtout la peau et rarement les muqueuses. Le diagnostic clinique est facile, confirmé par l'analyse histologique de la lésion, cependant il n'existe pas de consensus concernant la prise en charge thérapeutique. La localisation palpébrale de MC est rare, elle pose un problème d'ordre diagnostic différentiel surtout lorsqu'elle est isolée et un problème thérapeutique vu la proximité du globe oculaire. Nous rapportons le cas d'une fille de 7 ans ayant présenté une lésion palpébrale isolée dont l'exérèse avec étude anatomopathologique a révélé un MC. A la lumière de cette observation nous décrivons les particularités cliniques, thérapeutiques, et évolutives de cette localisation rare du molluscum contagiosum

Dendrons consisting of two phosphonate functions and three oligo(ethylene glycol) (OEG) chains grafted on a central henoxyethylcarbamoylphenoxy group were synthesized and investigated as Langmuir monolayers at the surface of water. The OEG chain in the para position was graftedwith a t-Bu end-group, a hydrocarbon chain, or a partially fluorinated chain. These dendrons are models of structurally related OEG dendrons that were found to significantly improve the stability of aqueous dispersions of iron oxide nanoparticles when grafted on their surface. Compressionisotherms showed that all OEG dendrons formed liquid-expanded Langmuir monolayers at large molecular areas. Further compression led to a transition ascribed to the solubilization of the OEG chains in the aqueous phase. Brewster angle microscopy (BAM) provided evidence that the dendrons fitted with hydrocarbon chains formed liquid-expanded monolayers throughout compression, whilst those fitted with fluorinated end-groups formed crystalline-like domains, even at large molecular areas. Dimyristoylphosphatidylcholine and dendron molecules were partially miscible in monolayers.The deviations to idealitywere larger for the dendrons fitted with a fluorocarbon end-group chain than for those fitted with a hydrocarbon chain. Brewster angle microscopy and atomic force microscopy supported the view that the dendrons were ejected from the phospholipid monolayer during the OEG conformational transition and formed crystalline domains on the surface of the monolayer.

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