Cycloaddition reactions of 1,3-diazabuta-1,3-dienes with alkynyl ketenes

The cycloaddition reactions of ‘all-carbon’ 1,3-diazabuta-1,3-dienes with a few conjugated and unconjugated alkynyl ketenes are described. The reactions provide some interesting azetidinones and dihydropyrimidinones bearing an alkynyl moiety. The regiochemistry of cycloadduct is related with the degree of conjugation of the alkynyl ketene. Moreover, two alternative approaches to ‘all-carbon’ 1,3-diazabuta-1,3-dienes are reported.     

Highly reduced iron-doped lithium niobate for optoelectronic tweezers

We investigate the applicability of highly reduced lithium niobate samples doped with iron for the use as optoelectronic tweezers. Increasing the reduction degree of Fe-doped lithium niobate is well known to increase the photoconductivity and reduce the writing time of internal space-charge fields. Based on our measurements of the photorefractive properties, we determine the optimal conditions for dielectrophoretic trapping and present the application of Fe-doped lithium niobate as optoelectronic tweezers. For higher reduction degrees, an unexpected decrease in the photovoltaic current density and the saturation space-charge field is reported.     

Anti-Ramsey Numbers of Graphs with Small Connected Components

The anti-Ramsey number, AR(n, G), for a graph G and an integer \(n\ge |V(G)|\), is defined to be the minimal integer r such that in any edge-colouring of \(K_n\) by at least r colours there is a multicoloured copy of G, namely, a copy of G that each of its edges has a distinct colour. In this paper we determine, for large enough \(n,\, AR(n,L\cup tP_2)\) and \(AR(n,L\cup kP_3)\) for any large enough t and k, and a graph L satisfying some conditions. Consequently, we determine AR(n, G), for large enough n, where G is \(P_3\cup tP_2\) for any \(t\ge 3,\, P_4\cup tP_2\) and \(C_3\cup tP_2\) for any \(t\ge 2,\, kP_3\) for any \(k\ge 3,\, tP_2\cup kP_3\) for any \(t\ge 1,\, k\ge 2\), and \(P_{t+1}\cup kP_3\) for any \(t\ge 3,\, k\ge 1\). Furthermore, we obtain upper and lower bounds for AR(n, G), for large enough n, where G is \(P_{k+1}\cup tP_2\) and \(C_k\cup tP_2\) for any \(k\ge 4,\, t\ge 1\).     

Chiral Fibers Formation Upon Assembly of Tetraphenylalanine Peptide Conjugated to a PNA Dimer

Self-assembly of biomolecules such as peptides, nucleic acids or their analogues affords supramolecular objects, exhibiting structures and physical properties dependent on the amino-acid or nucleobase composition. Conjugation of the peptide diphenylalanine (FF) to peptide nucleic acids triggers formation of self-assembled structures, mainly stabilized by interactions between FF. In this work we report formation of homogeneous chiral fibers upon self-assembly of the hybrid composed of the tetraphenylalanine peptide (4F) conjugated to the PNA dimer adenine-thymine (at). In this case nucleobases seem to play a key role in determining the morphology and chirality of the fibers. When the PNA “at” is replaced by guanine-cytosine dimer “gc”, disordered structures are observed. Spectroscopic characterization of the self-assembled hybrids, along with AFM and SEM studies is reported. Finally, a structural model consistent with the experimental evidence has also been obtained, showing how the building blocks of 4Fat arrange to give helical fibers.     

The ENEA noble gas laboratory: status of implementation

The strategic value of noble gas capability has been recently recognized by ENEA for the acquisition of data about anthropogenic activities. Within the framework of institutional agreements, a laboratory for measurement of radioactive noble gases is under construction for environmental analysis and for monitoring studies in connection with issues related to the nuclear fuel cycle to distinguish the anthropogenic contributions to the environment. This research is intended to contribute also to the international effort to support the comprehensive nuclear-test-ban treaty verification capability. The present work summarizes the status of implementation of the noble gas laboratory at the ENEA Brasimone research centre that is located in the north-centre part of Italy by the Brasimone lake at about 850 m altitude. The radionuclides of interest are the following four xenon radioisotopes: ^131mXe, ^133mXe, ¹³³Xe and ¹³⁵Xe. The noble gas system under development at ENEA has three separate components: air collection (sampling and adsorption), processing (gas extraction and purification) and measurement (gamma-ray spectrometry analysis). The separation of the sampling equipment from the analysis is seen as necessary for the effectiveness of extensive sampling campaigns, as required in monitoring programs. Refurbishment is currently under way to accommodate a more sensitive acquisition system.     

Cold-field switching in PVDF-TrFE ferroelectric polymer nanomesas

Polarization reversal in ferroelectric nanomesas of polyvinylidene fluoride with trifluoroethylene has been probed by ultrahigh vacuum piezoresponse force microscopy in a wide temperature range from 89 to 326 K. In dramatic contrast to the macroscopic data, the piezoresponse force microscopy local switching was nonthermally activated and, at the same time, occurring at electric fields significantly lower than the intrinsic switching threshold. A "cold-field" defect-mediated extrinsic switching is shown to be an adequate scenario describing this peculiar switching behavior. The extrinsic character of the observed polarization reversal suggests that there is no fundamental bar for lowering the coercive field in ferroelectric polymer nanostructures, which is of importance for their applications in functional electronics.     

Functional polymers and sequential copolymers by phase transfer catalysis. 24. The influence of molecular weight on the thermotropic properties of a random copolyether based on 1,5-dibromopentane, 1,7-dibromoheptane,and 4,4′-dihydroxy-α-methylstilbene

The influence of molecular weight on thermal transitions and on their thermodynamic parameters is discussed for a random thermotropic liquid crystalline copolyether based on the reaction of a 1:1 molar mixture of 1,5-dibromopentane and 1,7-dibromoheptane with 4,4′-dihydroxy-α-methylstilbene. Optimum phase transfer catalyzed polyetherification reaction conditions were established for the synthesis of polymers containing bromoalkane chain ends only over a wide variety of molecular weights. All these copolyethers present a crystalline and an enantiotropic nematic mesophase over the entire range of molecular weights studied. Both the thermal transitions and their thermodynamic parameters are strongly molecular weight-dependent up to M _n = 10,000–12,000, after which they remain constant. The enthalpies and entropies of isotropization of the copolyethers are higher than those of melting. This is in contrast to the same thermodynamic parameters of the corresponding homopolyethers. The enthalpies and entropies of isotropization of both homopolymers and copolymers present similar values, suggesting that copolymerization does decrease the degree of order in the crystalline phase but does not significantly change the alignment degree of the mesogenic units in the nematic mesophase.