Simona Concilio

YADAMP: yet another database of antimicrobial peptides

This work presents an antimicrobial peptide database (YADAMP) based on an extensive literature search. This database is focused primarily on bacteria, with detailed information for 2133 peptides active against bacteria. YADAMP was created to facilitate access to critical information on antimicrobial peptides (AMPs). The main difference between YADAMP and other web databases of AMPs is the explicit presence of antimicrobial activity against the most common bacterial strains. YADAMP allows complex queries, easily accessible through a web interface. Peptide information can be retrieved based on peptide name, number of amino acids, net charge, hydrophobic percentage, sequence motif, structure and activity against bacteria. YADAMP is suitable for reviewing information on AMPs and for structure-function analyses of peptides. The database can be accessed via a web-based browser at http://www.yadamp.unisa.it.

Novel Extended Tetrathiafulvalenes Based on Acetylenic Spacers: Synthesis and Electronic Properties

A selection of mono- and diacetylenic dithiafulvalenes was synthesized and employed for the construction of extended tetrathiafulvalenes (TTFs) with hexa-2,4-diyne-1,6-diylidene or deca-2,4,6,8-tetrayne-1,10-diylidene spacers between the two 1,3-dithiole rings. By stepwise acetylenic scaffolding using (E)-1,2-diethynylethene (DEE) building blocks, an extended TTF containing a total of 18 C(sp) and C(sp(2)) atoms in the spacer was prepared. The versatility of the acetylenic dithiafulvene modules was also established by the efficient synthesis of a thiophene-spaced TTF, employing a palladium-catalyzed cross-coupling reaction. The developed synthetic protocols allow functionalization of the extended TTFs in three general ways: with 1) peripheral substituents on the fulvalene cores, 2) alkynyl moieties laterally appended to the spacer, and 3) cobalt clusters involving acetylenic moieties. Strong chromophoric properties of the extended TTFs were revealed by linear and nonlinear optical spectroscopies. Extensive electrochemical studies and calculations on these compounds are also reported, as well as X-ray crystallographic analyses.

Third-order nonlinear optical properties of in-backbone substituted conjugated polymers

We present an alternative approach to tune the third-order nonlinear optical properties of organic molecules by inserting a functional group into the path of the π-electron conjugation instead of at its ends. We show that this scheme has a beneficial influence on the second-order hyperpolarizability for short molecules, but that in two instances where such molecules were polymerized into longer molecules the overall hyperpolarizability is reduced.

Nonlinear optical properties of polymers containing a new azophenylbenzoxazole chromophore

The synthesis of the new highly extended chromophore 2-[4-(N,N-dihydroxyethylaminophenylazo)-phenyl]benzoxazole is described. Two polymers obtained by the polycondensation of this chromophore with propyloxyterephthalic acid and 2,4-tolylenediisocyanate and one obtained by the polycondensation of 2-[4-N,N-bis(2-hydroxyethyl)aminophenyl]-6-nitro-benzoxazole with 2,4-tolylenediisocyanate have been prepared and characterized. The polymers are amorphous and exhibit good optical clarity, satisfactory thermal stability above the glass transition temperature and are soluble in common organic solvents. Second order nonlinear optical behavior of the polymers has been studied through measurement of the electrooptic coefficient on films poled between parallel electrodes. The maximum value measured for the electrooptic coefficient (r33) is 6.5 pm/V at an incident laser wavelength of 1.552 mm. q 2001 Elsevier Science Ltd. All rights reserved.

Synthesis and characterisation of polyesters with nonlinear optical properties

Eight new homo- and copolymers have been obtained by polycondensation of terephthalic acid and propyloxyterephthalic acid with two different second order NLO-active chromophores derived from 4-[N,N-bis(2-hydroxyethyl)amino]-benzaldehyde. Polymers exhibit good optical clarity, satisfactory thermal stability above the glass transition temperature and most of them are soluble in common organic solvents. Second order nonlinear optical properties of two corona poled polymer films were evaluated by second harmonic generation (SHG) measurements with an incident radiation of 1542 nm.

Nonlinear optical properties of some side chain copolymers based on benzoxazole containing chromophores

Acrylate-methylmethacrylate copolymers have been synthesized for nonlinear optical applications. Acrylate monomer units are characterized by the presence in the side chain of phenylbenzoxazole groups containing electron donor-electron acceptor substituents. The phase behavior of all polymers has been investigated by DSC, X-ray diffraction and polarizing microscopy: two of them exhibit liquid crystalline behavior of smectic type. For four polymers, nonlinear optical properties have been examined by second harmonic generation measurements on thin films (∼ 1 μm thickness) electrically poled by corona discharge. Second order susceptibility coefficients d33 and average relaxation times 〈τ〉, relative to the time stability of the chromophore poling, have been measured.

Switching Device Based on a Thin Film of an Azo-Containing Polymer for Application in Memory Cells

Results obtained on a conductive multilevel device realized with a 100 nm azo-polymer film are reported. The capability to switch between three different conductance states makes the device versatile both for Write Once Read Many and Write Many Read Many memory cell application. The analysis of the - curves indicates that the hysteretic conductance change with the external voltage can be explained in terms of different hopping distances existing between the nearest neighbors intervening in the two conformational states of the molecular structure.

Synthesis and liquid crystalline properties of low molecular mass compounds containing the 1,4-bis(5-phenyl-1,3,4-oxadiazolyl)benzene unit

The synthesis and characterization of low molecular mass compounds containing 1,4-bis(5-phenyl-1,3,4-oxadiazolyl)benzene is reported. All compounds are fluorescent in solution. Due to the flat shape of the conjugated unit, smectic-like packing is observed at high temperatures for some of the synthesized compounds. Moreover the insertion of a lateral flexible alkoxy unit strongly destabilizes the smectic order whilst promoting the appearance of a nematic phase in the case of the shortest methoxy unit. The mesogenic character of this unit may be of interest in the synthesis of liquid crystalline polymeric systems, taking advantage of both the fluorescent properties and the peculiar molecular structure of the liquid crystalline state.

The effect of hydroxylated fatty acid-containing phospholipids in the remodeling of lipid membranes☆

The synthetic fatty acid 2-hydroxyoleic acid (2OHOA) is an antitumor drug that regulates membrane lipid composition and structure. An important effect of this drug is the restoration of sphingomyelin (SM) levels in cancer cell membranes, where the SM concentration is lower than in non-tumor cells. It is well known that free fatty acid concentration in cell membranes is lower than 5%, and that fatty acid excess is rapidly incorporated into phospholipids. In a recent work, we have considered the effect of free 2OHOA in model membranes in liquid ordered (Lo) and liquid disordered (Ld) phases, by using all-atom molecular dynamics. This study concerns membranes that are modified upon incorporation of 2OHOA into different phospholipids. 2OHOA-containing phospholipids have a permanent effect on lipid membranes, making a Ld membrane surface more compact and less hydrated, whereas the opposite effect is observed in Lo domains. Moreover, the hydroxyl group of fatty acid chains increases the propensity of Ld model membranes to form hexagonal or other non-lamellar structures. This article is part of a Special Issue entitled: Membrane Structure and Function: Relevance in the Cells Physiology, Pathology and Therapy.

Interpenetration of Natural Polymer Aerogels by Supercritical Drying

Natural polymers, such as alginate and gelatin, can be used to produce scaffolds for tissue engineering applications; but, their mechanical and biochemical performance should be improved. A possible solution to obtain this result, is the generation of multi-component scaffolds, by blending two or more polymers. One way to realize it, is the formation of an interpenetrating polymer network (IPN). In this work, the interpenetration of alginate and gelatin hydrogels has been successfully obtained and preserved by supercritical CO2 (SC-CO2) drying performed at 200 bar and 35 °C, using different blend compositions: from alginate/gelatin = 20:80 v/v to alginate/gelatin = 80:20 v/v. The process allowed modulation of morphology and mechanical properties of these blends. The overall result was made possible by the supercritical drying process that, working at zero surface tension, allows preserving the hydrogels nanostructure in the corresponding aerogels.