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

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

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

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.

International audienc

Early neonatal respiratory distress revealing meningitis caused by Streptococcus pneumoniae serotype 17F: a case report

Background: Streptococcus pneumoniae (S. pneumoniae) is the first leading cause of invasive diseases such as meningitis, bacteremia and pneumoniae in children. In this case we report an early neonatal respiratory distress revealing meningitis caused byS. pneumoniae Serotype 17F through vertical transmission, in the newborn of 3 hours of live. Case description: A male late preterm newborn was born by vaginal delivery at a gestational age of 34 weeks. At 3 hours of life, he was admitted for early moderate neonatal respiratory distress in the Neonatal Medicine and Resuscitation Service.Cerebrospinal fluid culture yielded S. pneumoniae belonging to serotype 17F while the blood culture was negative. The same pneumococcal serotype was recovered from the high vaginal swab of the mother. Both isolates were found susceptible to all tested antibiotics except tetracycline and chloramphenicol to which the strain was resistant. Antibiotherapy management of the child included ceftriaxone at 150mg/kg/day for 21 days, in combination with gentamycin at 5 mg/kg/day for 5 days. ciprofloxacin was added at 40mg/kg/day in two doses for a period of three weeks as the baby presented a hydrocephalus. Conclusion: This finding shows that clinical manifestations of neonatal pneumococcal meningitis may be atypical and/or misleading. Keywords: Streptococcus pneumoniae; neonatal meningitis; respiratory distress

Self-assembly of supramolecular triarylamine nanowires in mesoporous silica and biocompatible electrodes thereof

Biocompatible silica-based mesoporous materials, which present high surface areas combined with uniform distribution of nanopores, can be organized in functional nanopatterns for a number of applications. However, silica is by essence an electrically insulating material which precludes applications for electro-chemical devices. The formation of hybrid electroactive silica nanostructures is thus expected to be of great interest for the design of biocompatible conducting materials such as bioelectrodes. Here we show that we can grow supramolecular stacks of triarylamine molecules in the confined space of oriented mesopores of a silica nanolayer covering a gold electrode. This addressable bottom-up construction is triggered from solution simply by light irradiation. The resulting self-assembled nanowires act as highly conducting electronic pathways crossing the silica layer. They allow very efficient charge transfer from the redox species in solution to the gold surface. We demonstrate the potential of these hybrid constitutional materials by implementing them as biocathodes and by measuring laccase activity that reduces dioxygen to produce water

Interactions intra et intermoléculaires, conformation des polymères adsorbés, transitions de phases sous étirement (Que peut-on apprendre des mesures de force ?)

Le microscope à force atomique (AFM) est un outil privilégié pour sonder la matière à l'échelle nanométrique. Dans cette thèse, nous l'utilisons comme instrument de mesure de force. Nous montrons que la mesure des fluctuations thermiques des ressorts permet de déterminer précisément leur raideur à condition d'utiliser un modèle qui prend en compte la forme des modes et la méthode de détection. A l'aide de nouvelle méthodes d'analyse des courbes de rétraction, nous étudions la conformation de polymères et de copolymères adsorbés, ainsi que l'interaction spécifique entre un complexe du nickel (Ni-NTA) et l'acide aminé histidine. Nous mettons en évidence des comportements inattendus en présence de liens multiples et nous en proposons une interprétation basée sur un équilibre entre formations et ruptures des liaisons. Nous présentons des premiers résultats expérimentaux concernant la transition conformationnelle de la polylysine sous étirement.Atomic force microscopy has been shown to be a good means of investigating matter at the nanometer scale. In this thesis, we use it as a force probe. We demonstrate that the study of the cantilever's thermal fluctuations allow the precise measurement of it's spring constant. Using new way to analyze the AFM force measurements, we study the conformation of adsorbed polymers and copolymers and the specific interaction between the nickel nitrilotriacetate (Ni-NTA) and the histidine amino acid. We observed unexpected behaviours in the presence of multiple bridges between the tip and the surface and we propose an interpretation based on the equilibrium between formation and rupture of bonds. We present first experimental force profiles of polylysine around the helix-coil transition.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF