An AT-barrier mechanically controls DNA reannealing under tension

Regulation of genomic activity occurs through the manipulation of DNA by competent mechanoenzymes. Force-clamp optical tweezers that allow the structural dynamics of the DNA molecule to be measured were used here to investigate the kinetics of mechanically-driven strand reannealing. When the force on the torsionally unconstrained lambda-phage DNA is decreased stepwise from above to below the overstretching transition, reannealing occurs via discrete shortening steps separated by exponentially distributed time intervals. Kinetic analysis reveals a transition barrier 0.58 nm along the reaction coordinate and an average reannealing-step size of approximately 750 bp, consistent with the average bp interval separating segments of more than 10 consecutive AT bases. In an AT-rich DNA construct, in which the distance between segments of more than 10 consecutive AT is reduced to approximately 210 bps, the reannealing step reduces accordingly without changes in the position of the transition barrier. Thus, the transition barrier for reannealing is determined by the presence of segments of more than 10 consecutive AT bps independent of changes in sequence composition, while the length of the reannealing strand changes according to the distance between poly-AT segments at least 10 bps long

COMPOSITE CUSTOM-MADE BONE GRAFTS (SMARTBONE® ON DEMAND™) FOR A LARGE SPHENO-ORBITAL RECONSTRUCTION

The treatment of anterior and lateral skull base tumors has always constituted a complex surgical challenge: extensive bony demolitions produce aesthetic deformities that need accurate reconstructions. Indeed, highly destructive procedures increased the need to introduce new reconstructive techniques. Wide defects, e.g. those involving more than a single orbital wall, have to be reconstructed with solid tissues such as autologus grafts or alloplastic materials. Surgical visual limits may reduce the possibility to properly repair the three-dimensional bony architecture of the craniofacial skeleton: because of the nonlinear nature of the bone in the craniofacial skeleton, even small degrees of error can lead to poor outcomes. Here we investigated the innovative application of custom-made bone grafts in a case of skull base reconstructive surgery, a technique that is not previously reported. Innovations applied to this case were multiple: basing on high resolution patient’s CT scans, virtual surgery and computer-aided design were used to plan resection; contralateral disease-free skull base was used as a reference and mirroring technique was used to create the ideal grafts, which were then manufactured accordingly using the new composite custom-made bone grafts (SmartBone® on Demand™). SmartBone® is shaping resistant and offers high tenacity to screws and surgical fixation manoeuvres, because it is produced by combining bovine mineral bone structures with biopolymers and cell nutrients (polysaccharides). The patient underwent resection of a meningioma in the spheno-orbital-temporal region. The neurosurgeon resected the meningeal involved district, which was then reconstructed with a collagenous membrane. SmartBone® on Demand™ were then very precisely grafted into destination site. During follow-up, nor cerebrospinal fluid leakage nor intracranial infection were registered. Postoperative CT scans showed excellent stability and integration of all bone grafts; postoperative morphological results are satisfactory. Outcomes confirm the high reliability and accuracy of virtual surgical planning and grafts design, which, together with SmartBone® high performances, allow producing very precise and stable custom-made grafts and, finally, addressing the previously unmet needs in skull base reconstructive surgery

Palladium nanoparticles supported on polyvinylpyridine: catalytic activity in Heck-type reactions and XPS structural studies

Palladium nanoparticles, obtained by metal vapour synthesis (MVS), were deposited on cross-linked polyvinylpyridine. The Pd/PVPy system showed high catalytic activity in the Heck C-C coupling reaction of iodo- and bromo-arenes (iodobenzene, bromobenzene, p-nitrobromobenzene, p-bromoacetophenone, p-(methoxy)bromobenzene) with alkyl acrylates (methyl acrylate, n-butyl acrylate, ethylhexyl trans-3-(4-methoxyphenyl)acrylate) at 100 degrees C-175 degrees C working under nitrogen atmosphere as well as in air. The catalyst is stable and the leaching of metal in solution is very low. When reused, the recovered Pd/PVPy maintains the catalytic activity of the pristine material. XPS structural studies performed on the starting catalyst as well as on the recovered one indicate the presence of a interaction between the basic nitrogen of the pyridine present in the polymer and the metal. (C) 2009 Elsevier Inc. All rights reserved