Electrochemical evaluation of dsDNA—Liposomes interactions

The aim of the present work was to evaluate the interaction between double-stranded DNA (dsDNA) and liposomes by voltammetric methods. The experimental results were analyzed considering the initial studies regarding the oxidation mechanism of dsDNA purine bases by cyclic and differential pulse voltammetry at the glassy carbon electrode (GCE). The interaction between dsDNA and 1,2-Dimyristoyl-sn-glycero-3-phosphocholine (DMPC) was studied in a suspension containing both dsDNA and DMPC liposomes, prepared in pH = 7.0, 0.1 M phosphate buffer and using different incubation time periods. The formation of dsDNA-liposome complex was put in evidence by the decrease of the dsDNA oxidation peaks, dependent upon the incubation time. This behavior was explained considering the electroactive centers of dsDNA, guanosine monophosphate and adenosine monophosphate residues, part of them hidden inside the dsDNA-liposome complex structure and thus being unable to reach the GC electrode and preventing their oxidation. The electrochemical results are relevant for a better physicochemical characterisation of the dsDNA and dsDNA-liposome complex, which can be important for the development of gene therapy vectors

Three-Layered Photovoltaic Cell with an Enlarged Photoactive Region of Codeposited Dyes

Three-layered organic solar cells with an interlayer of codeposited dyes of p-type Copper Phthalocyanine (CuPc) and n-type 5,10,15,20-Tetra (4-Pyridil) 21H,23H-Porphine (TPyP) between the respective dye layers were prepared and characterised. The analysis of their dark current-voltage ($I - U$) characteristics at room temperature has been presented in order to elucidate the conduction mechanisms and to evaluate the cell parameters. The analysis of photovoltaic properties shows that the photocurrent of three-layered cells is about ten times larger than that of a double layered cell, due to the efficient carrier photogeneration in the code-posited layer. The best power conversion efficiency, at 0.35% was obtained under illumination with monochromatic light of 30 $\mu$W cm$^{-2}$, at 520 nm.Nous avons élaboré des cellules photovoltaïques avec trois couches minces de colorants organiques entre deux électrodes : ITO et Al. Les cellules ont été faites en utilisant CuPc comme semi-conducteur de type-p et TPyP comme semi-conducteur de type-n. Entre les deux couches de CuPc et TPyP, une couche mince de CuPc+TPyP a été deposée par co-évaporation thermique des deux matériaux organiques. L'analyse des caractéristiques électriques ($I - U$) des cellules dans l'obscurité est présentée pour comprendre les mécanismes mis en jeu et pour évaluer leur paramètres électriques. L'analyse des propriétés photovoltaïques a montré que le photocourant des cellules avec trois couches minces est 10 fois plus grand que celui mesuré sur les cellules à deux couches minces, grâce à une création plus efficace des photoporteurs dans la couche mince co-évaporée. Le rendement de conversion énergétique est maximal à 0,35% pour la lumière avec une longueur d'onde de 520 nm et une intensité lumineuse de 30 $\mu$W cm$^{-2}$

IMPACT OF SOLUTE MOLECULAR PROPERTIES ON THE ORGANIZATION OF NEARBY WATER: A CELLULAR AUTOMATA MODEL

The goal of this study was the creation of a model to understand how solute properties influence the structure of nearby water. To this end, we used a two-dimensional cellular automaton model of aqueous solutions. The probabilities of translocation of water and solute molecules to occupy nearby sites, and their momentary distributions (including that of vacancies), are considered indicative of solute molecular mechanics and hydrophatic character, and are reflected in water molecules packing, i.e. 'organization'. We found that in the presence of hydrophilic solutes the fraction of water molecules with fewer neighbors was dominant, and inverse-proportionally dependent on their relative concentration. Hydrophobic molecules induced water organization, but this effect was countered by their own flexibility. These results show the emergence of cooperative effects in the manner the molecular milieu affects local organization of water, and suggests a mechanism through which molecular mechanics and crowding add a defining contribution to the way the solute impacts on nearby water

Physics studies in Europe; a comparative study

What are the differences and similarities between physics studies at different universities across Europe (here the definition of Europe is broad)? How much does a student have to work to obtain a degree in physics? Questions like those prompted EUPEN (European Physics Education Network) to make a survey. During 1997 and 1998 the working groups of EUPEN sent out a number of questionnaires to a number of institutions and to individual students. In this report we focus on issues relating to the workload to obtain a degree in physics as expressed in contact hours-lectures, problem solving, laboratory work-and 'private study time. The different teaching/learning styles are also considered. Some of the results have already been presented at conferences

New strategies for early diagnosis of heart allograft rejection.

BACKGROUND: Allograft rejection is mediated by T cells that recognize allogeneic major histocompatibility complex (MHC) molecules via the direct and indirect pathway. The direct pathway involves T cells that react against MHC/peptide complexes expressed on the surface of donor antigen-presenting cells (APCs). In contrast, T cells involved in the indirect pathway recognize peptides derived from processing and presentation of allogeneic MHC molecules by self (recipient) APCs. To explore the relative contribution of these two pathways to rejection, we have evaluated the response of peripheral blood T cells from 50 heart transplant recipients against donor APCs (direct recognition) and against self APCs pulsed with synthetic peptides corresponding to the hypervariable region of the mismatched HLA-DR antigens of the donor (indirect recognition). METHODS: T cell reactivity against donor APCs was quantitated by measuring the expression of CD69 on allostimulated CD3+ LDA1+ cells. Reactivity to synthetic allopeptides was determined in limited dilution assays. RESULTS: Serial studies of the kinetics of direct and indirect recognition showed that both pathways contribute to early acute rejection episodes. Primary rejection was accompanied invariably by indirect recognition of a dominant allopeptide. Intermolecular spreading of T cell epitopes was observed during recurrent rejections. Enhanced recognition of donor alloantigens via the direct pathway was found predominantly during early rejection episodes. A single form of allorecognition was shown to occur in some rejection episodes. CONCLUSIONS: Monitoring of the direct and indirect pathway of allorecognition provides a reliable method for prediction and differential diagnosis of acute rejection of heart allografts