On the multiple crystallization behavior of PTFE in PMMA/PTFE nanocomposites from core–shell nanoparticles

The peculiar thermal behavior of four PTFE/PMMA (Polymethylmethacrylate) core–shell nanoparticle samples, marked DV2M1, DV2M2, DV2M4, and DV2M6, was studied by combined differential scanning calorimetry and thermogravimetric analysis. The melting process of the PTFE in the various samples, subjected to annealing and thermal treatments, does not change. In contrast, a complex fractionated crystallization‐type behavior for the PTFE component was observed. The nanocomposite produced by the PMMA shell fluidification features a perfect dispersion of the nanometric PTFE cores. In these conditions, only one crystallization exotherm at very high undercooling is observed, possibly deriving from the homogeneous nucleation mechanism. In contrast, when high temperature thermal treatments cause the decomposition with partial loss of the PMMA shell and allows some cores to get in contact and merge, a crystallization process structured into several components is observed. This behavior indicates that different nucleation mechanisms are active, possibly involving the participation of distinct types of active nuclei with distinct crystallization efficiencies. Finally, when the PMMA shell amount is substantially reduced by the thermal degradation, only the expected crystallization process at moderate undercooling (310 °C) is observed, corresponding to the bulk crystallization induced by the most efficient heterogeneous nuclei. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 548–554, 2010     

A multivalent HIV-1 fusion inhibitor based on small helical foldamers

The peptide sequence AcNH–TEG–Glu-Aib-Trp-AibAib-Trp-AibAib-Ile-Asp–OH (1), designed to display the WWI epitope found near the C-terminus of gp41, an envelope glycoprotein decorating the surface of the HIV-1 virus, has been synthesized and proved to have a relevant content of helical conformation because of the presence of five α-aminoisobutyric acid (Aib) units. Three copies of it have been connected to a tripodal platform based on 2,4,6-triethylbenzene-1,3,5-trimethylamine. The tripodal template 2 is even more structured than 1 thus suggesting a significant interaction between the three sequences connected to the platform. Preliminary inhibition assays of HIV-mediated cell fusion indicated that while the single peptide 1 is inactive within the concentration range of our assay, when it is conjugated to the tripodal platform, it is moderately active. These promising results suggest that our approach constitute a valid alternative to those reported so far.     

Hybrid organic–inorganic sol–gel materials for micro and nanofabrication

In this review hybrid organic–inorganic (HOI) resists as emerging materials alternative to organic polymers for micro and nanolithography are presented and discussed. In particular, results on sol–gel materials belonging to 3-glycidoxypropyltrimethoxysilane based HOI are presented and reviewed, highlighting as various lithographic techniques can be used to pattern their surface and showing examples of micro- and nano-patterned structures achieved with radiation assisted lithography (UV, X-rays and electron beam) or imprint techniques. It will be demonstrated the particular versatility shown by some of these materials, that in some case can be processed with all the lithographic methods herein considered, without any significant modification of their main composition and synthesis procedure. Moreover, results about the investigation of interaction between radiation and HOI materials and thermal treatment will be discussed, as well as possible synthesis strategies and composition modification developed in order to improve efficiency of curing, tailor HOI properties to specific needs (optical properties, resist composition, mechanical stability, etc.) and explore innovative and non conventional patterning techniques. The reported results highlight as these novel materials, thanks to their solution processability and higher performances respect to commercial polymeric resists, allow to use the above mentioned lithographic techniques in a direct patterning process, strongly simplifying conventional technique and reducing their processing time and costs.     

Traceability in Multi-ingredient Botanicals by HPTLC Fingerprint Approach

JPC – Journal of Planar Chromatography – Modern TLC - A high-performance thin-layer chromatography (HPTLC) method was developed for simple and rapid chemical analyses of...     

Synthesis of Carbocyclic Pyrimidine Nucleosides Using the Mitsunobu Reaction: O2‐ vs. N1‐Alkylation

The Mitsunobu reaction is an important tool in carbocyclic nucleoside chemistry for the direct coupling of alcohols with heterocyclic bases under mild conditions. Chemical evidences for an unusual competitive O²‐ vs. N¹‐alkylation of 3‐substituted pyrimidines is presented.     

Fate of the Oxygen Atoms in the Diol‐Dehydratase‐Catalyzed Dehydration of meso‐Butane‐2,3‐diol

¹⁸O‐Substituted propane‐1,2‐diols and meso‐butane‐1,2‐diols were synthesized and fed to growing cells of Lactobacillus brevis. Propan‐1‐ol and butan‐2‐ol, prepared from such diols through diol‐dehydratase‐catalyzed dehydration followed by intracellular reduction, were analyzed for their ¹⁸O‐content. For each propane‐1,2‐diol enantiomer, partial retention or complete loss of the isotope appeared to be related to the mode of substrate binding. Specific retention of the O‐atom linked to the (R)‐configured C‐atom of meso‐butane‐1,2‐diol indicates that the diol dehydratase handles this substrate like (R)‐propane‐1,2‐diol.