Design and characterisation of a thin-layered dual-band electrochemical cell

The development of a thin-layered dual-band electrochemical cell operating at flow conditions is described. Influence of experimental parameters related to the geometric design of the channel electrode as well as the flow rate on the collection efficiency were studied by using ferricyanide as a probe, results being in agreement with predictions from literature. Fiagram responses obtained by injecting thiosulphate+iodide solutions to the carrier electrolyte (1 M Ac⁻/1 M HAc) were evaluated by measuring peak current and charge values at both electrodes. Data showed the influence of the flow rate and the ratio between iodide and thiosulphate concentrations on the profile of fiagrams recorded at the first electrode and the results are discussed on the basis of both sample dispersion and thickness of the reaction layer. Analytical applications of the proposed generator-collector cell involved titrations with electrogenerated iodine, thiosulphate concentrations as low as 1 μM being measured with high precision.     

DNA tridimensional context affects the reactivity of eukaryotic DNA topoisomerase I

Cleavage sites of eukaryotic DNA topoisomerase I on curved linear DNAs are clustered, map on the same side of the curve (the external one) and their distribution has the same period as the helical repeat, as observed on curved DNA tracts of Crithidia fasciculata, of Saccharomyces cerevisiae ARS1, of pT7CAT and on synthetic DNAs. The effects of the tridimensional context on both the cleavage and the topoisomerization reactions of DNA topoisomerase I were determined using serial DNA constructs made with inserts in which synthetic curves lie in a plane and in which the orientation of the planes of curvature is shifted by 72 degrees, 144 degrees, 216 degrees, 288 degrees and 360 degrees. The insertion of a curve markedly changes the reaction properties of the surrounding sequences.     

Autologous and heterologous neutralization analyses of primary feline immunodeficiency virus isolates

Feline immunodeficiency virus (FIV) provides a model system with which the significance of neutralizing antibody (NA) in immunosuppressive lentivirus infections may be studied. To date, no detailed analysis of the neutralization properties of primary FIV isolates has been reported. In this study, we have conducted the first comprehensive study of the sensitivity to autologous and heterologous neutralization in a lymphoid cell-based assay of 15 primary FIV isolates and, for comparison, of one tissue culture-adapted strain. Primary isolates in general proved highly NA resistant, although there was considerable individual variation. Variation was also observed in the capacity of immune sera to neutralize heterologous FIV isolates. The ability of sera to neutralize isolates or for isolates to be neutralized by sera did not correlate with epidemiological and genetic relatedness or with the quasispecies complexity of the isolates. From the study of specific-pathogen-free cats experimentally infected with viral isolates associated with NA of different breadths, it appears that the development of FIV vaccines cannot rely on the existence of viral strains inherently capable of inducing especially broad NA responses.     

Commutative grammars

Commutative grammars are a formalism for generating bags, equivalent to vector addition systems and Petri nets. Known results are recalled and new one are presented on reachability and boundedness. In particular some subclasses of commutative grammars are introduced which admit a positive answer to these problems, and generate semilinear languages. Finally the equivalence, via Parikh mapping, of commutative and matrix grammars is proven.     

Modelling of HLA-DQ2 and its interaction with gluten peptides to explain molecular recognition in celiac disease

Celiac disease (CD) is sustained by abnormal intestinal mucosal T-cell response to gluten and it is strongly associated with HLA class II molecules encoded by DQA1*0501/DQB1*02 (DQ2) or DQA1*03/DQB1*0302 (DQ8). The in vitro stimulatory activity of gliadin increases after treatment with tissue transglutaminase (tTG) which catalyses the deamidation of specific residues of glutamine to glutamate that can serve as anchors for binding to DQ2 as well as to DQ8 molecules. We modelled the three-dimensional structure of the DQ2 dimer protein, the most frequent in celiac patients, by using a homology modelling strategy, and deposited the model in the Protein Data Bank (PDB). Then, we simulated the interactions of DQ2 with different gluten peptides and the deamidation of specific peptide glutamines in the known p4, p6, p7 and p9 anchor positions, as well as in p1 and p5 positions, and other substitutions for which experimental effects on binding are available by previous experimental studies. By evaluating the energy of interaction and the H-bond interactions, we were able to distinguish what substitutions improve the interaction peptide-DQ2, in agreement with previously published experimental data. By analysing the peptide-DQ2 complex at the atom level, we observed that these glutamate side chains can interact with specific positively charged amino acids of DQ2, absent in other HLA alleles not related to celiac disease. The simulation was also extended to other peptides, related to celiac disease but for which no experimental data exists about the effects of glutamine deamidation. Our results give an interpretation at the molecular level of previously reported binding experimental data and open a new window to gain further insights about peptide recognition in celiac disease.     

Equivalenza tra grammatiche,sistemi di equazioni in variabili di linguaggio e serie formali

Sommario Scopo di questo lavoro è ricercare condizioni di equivalenza di tre diversi modi per definire un lingnaggio: una grammatica non contestuale, un sistema di equazioni in variabili di linguaggio, un sistema di equazioni in variabili serie formali. Per raggiungere questo obbiettivo si introduce il ben noto concetto di serie formale; inoltre si dimostra l'esistenza e l'unicità della soluzione di un sistema di equazioni mediante il classico teorema del punto unito di Banach.

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The purpose of this paper is to investigate conditions for the equivalence of three different manners of defining a language: a context-free grammar, a system of equations whose variables are languages, a system of equations whose variables are formal sums. In order to achieve this goal, the well-known concept of formal sum is introduced; moreover the existence and uniqueness of the solution of a system of equations is proved by means of Banach's classical fixed-point theorem.

     

Structure control, coating properties, and durability of fluorinated acrylic-based polymers

Fluorinated acrylates were employed for the synthesis of conventional, side-chain fluorinated, fully acrylic random copolymers, and of more unusual hybrid copolymers with vinyl ethers. The latter can feature alternating structure and peculiar material properties associated with fluorine or fluorinated groups substitution onto the polymer backbone. Improved efficacy and durability of the resulting coating, highly desirable for the consolidation and protection of highly valued works of art, was achieved through a systematic approach involving a detailed study of their photodegradation behavior, and extensive testing of protection efficacy upon application onto micro-and macroporous stone substrates of different chemical composition and morphology. Presented on behalf of FATIPEC (AITIVA) at the 78th Annual Meeting of the FSCT in Chicago, IL on October 16–20, 2000. Dipartimento di Chimica e Chimica Industriale, Via Risorgimento 35, 56126 Pisa, Italy. Dipartimento di Chimica IFM, via Pietro Giuria 7, 10125 Torino, Italy. Piazza Leonardo da Vinci 32, 20133 Milano, Italy, Lucia.