On the cardinality of blocking sets in PG(2,q)

Denote by PG(2,q) the finite desarguesian projective plane of order q, where q=p^h, p a prime, q>2. We define the function m(q) as follows: m(q)=q, if q is a square; m(q)=(q+1)/2, if q is a prime; m(q)=p^h–d, if q=p^h with h an odd integer, where d denotes the greatest divisor of h different from h. The following theorem is proved: For any integer k with q+m(q)+1 k q²–m(q), there exists a blocking set in PG(2,q) having exactly k elements.To Professor Adriano Barlotti on his 60th birthday.Research partially supported by G.N.S.A.G.A. (CNR)     

Biocompatible channels for field-flow fractionation of biological samples: correlation between surface composition and operating performance

Biocompatible methods capable of rapid purification and fractionation of analytes from complex natural matrices are increasingly in demand, particularly at the forefront of biotechnological applications. Field-flow fractionation is a separation technique suitable for nano-sized and micro-sized analytes among which bioanalytes are an important family. The objective of this preliminary study is to start a more general approach to field-flow fractionation for bio-samples by investigation of the correlation between channel surface composition and biosample adhesion. For the first time we report on the use of X-ray photoelectron spectroscopy (XPS) to study the surface properties of channels of known performance. By XPS, a polar hydrophobic environment was found on PVC material commonly used as accumulation wall in gravitational field-flow fractionation (GrFFF), which explains the low recovery obtained when GrFFF was used to fractionate a biological sample such as Staphylococcus aureus. An increase in separation performance was obtained first by conditioning the accumulation wall with bovine serum albumin and then by using the ion-beam sputtering technique to cover the GrFFF channel surface with a controlled inert film. XPS analysis was also employed to determine the composition of membranes used in hollow-fiber flow field-flow fractionation (HF FlFFF). The results obtained revealed homogeneous composition along the HF FlFFF channel both before and after its use for fractionation of an intact protein such as ferritin.     

Electroanalytical and spectroscopic characterization of poly(o-phenylenediamine) grown on highly oriented pyrolytic graphite

The polymerization of ortho-phenylenediamine (o-PD) on Highly Oriented Pyrolytic Graphite (HOPG) at different pH (1,3,5,7) was investigated by electroanalytical and spectroscopic methods. Cyclic voltammetry was used both to polymerize o-PD and to study the electroactivity of the resulting poly(ortho-phenylenediamine) (PPD) film. A redox couple associated to the PPD electroactivity, deeply influenced by the pH adopted during polymerization, was recorded. A correlation between this feature and the electrochemistry shown by the oligomers of o-PD, generated in solution during the polymer synthesis, was also found. A comparison between the absorption spectra, in the visible region, of the soluble oligomers and of the PPD films was also performed, suggesting that changes in both the polymer and the oligomer structure occur and are highly related to the polymerization pH. In particular, a higher degree of conjugation is exhibited by the PPD films electrosynthesised at lower pH and this likely explains the higher conductivity as well as the higher electroactivity shown by the material obtained in these conditions.     

Surface Segregation Assessment In Poly(ε‐caprolactone)‐poly(ethylene glycol) Multiblock Copolymer Films

The ability to predict the in vivo performance of multiblock‐copolymer‐based biomaterials is crucial for their applicability in the biomedical field. In this work, XPS analysis of PCL‐PEG copolymers was carried out, as well as morphological and wettability evaluations by SEM and CA measurements, respectively. XPS analysis on films equilibrated in PBS demonstrated a further enrichment in the PEG component on the surface. Copolymer films obtained by casting using different solvents showed a dependence in segregation according to the solvent employed. Cell adhesion tests demonstrated the importance of copolymer segregation and rearrangement in a wet environment, with a dependence of these phenomena on the copolymer molecular weight.

     

π-Electron manipulation of the 5,6-dihydroxyindole/quinone system by 3-alkynylation: mild acid-mediated entry to (cross)-conjugated scaffolds and paradigms for medium-tunable chromophores

5,6-Dihydroxyindole-based systems engender increasing interest for the design and implementation of new functional aromatic scaffolds and eumelanin-like materials with tailored absorption and electronic properties. However, studies aimed at elucidating the influence of external π-conjugating groups on the redox properties and acid-induced reactivity of these highly oxidizable indolic platforms are lacking. We report herein the synthesis (as acetyl derivatives) and chemical/quantum chemical characterization of the first π-extended 5,6-dihydroxyindole derivatives, 3-ethynyl-5,6-dihydroxyindole (1) and 3,3'-(1,2-ethynediyl)bis-5,6-dihydroxyindole (2), in order to understand whether and how β extension of the enamine-like pyrrole sector affects the absorption properties, redox behavior, and protonation equilibria at both the o-diphenol and quinone levels. Oxidation of 1 and 2 proceeded smoothly to generate dark insoluble materials with eumelanin-like UV properties. On exposure to phosphate buffer at pH 3, 1 was rapidly converted to 3-acetyl-5,6-dihydroxyindole (5) and, in the presence of 5,6-dihydroxyindole, to the cross-conjugated 3,3'-ethenylidenebis-5,6-dihydroxyindole (6). DFT calculations on 1 and 2 and their quinones in their pristine states and after protonation provided a mechanistic frame to rationalize the unusual acid-mediated chemistry of 1 and disclosed 2-quinone as the prototype of a novel class of medium-dependent chromophores. The ethynyl(ene) structural motif is thus proposed as the key to new tunable π-electron extended 5,6-dihydroxyindole/5,6-indolequinone paradigms for the rational design of alkyne-containing hybrid eumelanin-type polymers.     

Cardanol Based Matrix for Jute Reinforced Pipes

The aim of this work is the development of composite pipes using renewable resources. The pipes, manufactured by filament winding technology, were obtained using an epoxy resin crosslinked with a cardanol based novolac as matrix and jute fibres as reinforcement. Cardanol is a natural oil extracted from the shell of the cashew (Anacardium occidentale L.) nut. An amount of natural materials higher than 50% by weight was achieved in the final composites. Tensile and parallel plate compression tests were carried out on the composite pipes.