1,721,086 research outputs found
MICRO-IMMOBILIZED ENZYME REACTORS: EVALUATION OF THE APPROPIATE CHROMATOGRAPHIC SUPPORT
No full textIt is here reported the preparation and comparison of different monolithic micro-IMERs (Immobilized Enzyme Reactors) containing covalently immobilized human recombinant acetylcholinesterase (AChE). In particular, following previous studies on AChE-IMERs (1,2), object of this work was the covalent immobilisation of the target enzyme on disk-shaped columns of smaller dimensions (6 x 2 mm, Bed Volume = 56 mL) to increase the enzyme density on the matrix surface.
Since the surface chemistry of the chosen chromatographic support will influence the yield of immobilisation as well as the environment in which the target enzyme will be inserted, the choice of an appropriate support for IMERs development represents an important issue. Moreover, “aspecific” interactions between matrix and substrate and inhibitors will also depend on the chosen material. In this context, CIM disks with different chemistries were chosen for AChE immobilisation, in particular, ethylendiamino (EDA), epoxy and CDI-CIM mini disks were selected. Moreover the introduction of an appropriate spacer arm was evaluated when required.
On-line automated HPLC inhibition studies on a selected series of AChE inhibitors were performed; Aspecific interactions were evaluated and results obtained for the same compound on different CIM-based IMERs were compared.
Results showed that purposely pre-derivatized CDI-based IMER gave promising eluting profile and low aspecific interactions and may therefore represent a valid chromatographic support for the development of monolithic micro-IMERs.
(1) M. Bartolini, V. Cavrini, V. Andrisano: Monolithic micro-immobilized-enzyme reactor with human recombinant acetylcholinesterase for on-line inhibition studies. J Chromatogr A 2004, 1031: 27-34.
(2) M. Bartolini, V. Cavrini, V. Andrisano: Choosing the right chromatographic support in making a new acetylcholinesterase-micro-immobilised enzyme reactor for drug discovery. J Chromatogr A. 2005, 1065:135-44
FLUORESCENCE BASED STUDIES ON BETA-AMYLOID MISFOLDING AND AGGREGATION
No full textRecent findings about the relationship between amyloid b-peptide (Ab) accumulation and cognitive decline in Alzheimer's disease (AD) suggest a complex role for Ab in this neurodegenerative process. The transition of Ab soluble monomers to toxic small oligomers involves an initial transition from a non organized/a-helix monomer to a b-sheet rich conformer. This early step represents a suitable target to design new potent inhibitors and obtain effective therapeutics for AD. Moreover, several chaperone molecules are though to accelerate amyloid aggregation, i.e., the enzyme acetylcholinesterase (AChE). Since most of the marketed drugs for AD are AChE inhibitors, the investigation of the inhibitory potency against the AChE-induced amyloid aggregation exerted by anti-cholinesterase agents definitively represents an interesting area of investigation for drug discovery. The in vitro Ab aggregation can be evaluated by a fluorescence-based assay by using Thioflavin T (ThT) as fluorescent dye. More in details, ThT specifically binds to amyloid fibrils (in the beta-sheet conformation) giving rise to an intense specific emission band (lem = 490 nm) in its fluorescent spectrum (1-3). Therefore the increase in the specific fluorescence emission was used to monitor amyloid fibrils formation. Two fluorescence-based assays specifically developed (4,5) for the evaluation of beta-amyloid self- and AChE-induced aggregation were applied to follow the aggregation process as well as to screen for potential inhibitors. The concomitant use of circular dichroism spectroscopy was helpful to set up the optimal experimental conditions and to draw some hypotheses on the mechanism of action of known and new inhibitors.
(1) H. Naiki, K. Higuchi, K. Nakakuki, T. Takeda, Lab. Invest. 1991, 65, 104.
(2) H. LeVine, Protein Sci. 1993, 2, 404.
(3) H. LeVine 3rd, Methods Enzymol. 1999, 309, 274.
(4) M. Bartolini, C. Bertucci, M.L. Bolognesi, A. Cavalli, C. Melchiorre, V. Andrisano, Chembiochem 2007, 8, 2152.
(5) M. Bartolini, C. Bertucci, V. Cavrini, V. Andrisano, Biochem. Pharmacol. 2003, 65, 407
Synthesis and pharmacological evaluation of a novel class of multi target Huprine-based anti-Alzheimer hybrids
No full textAnalisi Volumetrica - Titolazioni Acido-Base
No full textL'analisi volumetrica o volumetria comprende vari metodi di analisi quantitativa, tutti caratterizzati dall'applicazione di un procedimento pratico definito con il termine "titolazione". Si tratta di un procedimento che permette di determinare la quantità di un analita in una soluzione (campione o titolato), basandosi sulla misura del volume di un reagente a concentrazione nota (titolante) che viene aggiunto al campione fino a che la sua reazione con l'analita arriva a completamento
Determination of triclosan in personal health care products by liquid chromatography (HPLC)
No full textAn isocratic reversed-phase liquid chromatographic (HPLC) method is proposed for the practical and reliable determination of triclosan, an antimicrobic agent incorporated into a variety of personal health care products. Chromatographic separations were performed on a C-18 column using acetonitrile-TEA phosphate (70 mM; pH 3.5) 55:45 (v/v) as mobile phase and UV detection at 230 and 280 nm. The selectivity of the method was assured by the on-line photodiode array detector. The identity of the triclosan peak was also confirmed by HPLC MS. The method was successfully applied to the determination of triclosan in commercially available health care products (deodorant stick, dentifrice gel, mouthrinse, toothpaste and handwash). All the products displayed triclosan concentrations in compliance with the EEC directive (less than or equal to 0.3%). (C) 2002 Published by Editions scientifiques et medicales Elsevier SAS
Initial characterization of stem bark extracts from Phyllanthus muellerianus as source of new natural entities with anti-cholinesterase properties
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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