442 research outputs found
Bis-Thiourea Chiral Sensor for the NMR Enantiodiscrimination of N-Acetyl and N-Trifluoroacetyl Amino Acid Derivatives
No full text[Image: see text] A C2-symmetrical bis-thiourea chiral solvating agent (CSA), TFTDA, for NMR spectroscopy has been obtained by reacting (1R,2R)-1,2-bis(2-hydroxyphenyl)ethylenediamine and 3,5-bis(trifluoromethyl)phenyl isothiocyanate. TFTDA shows remarkable propensity to enantiodiscriminate N-trifluoroacetyl (N-TFA) and N-acetyl (N-Ac) derivatives of amino acids with free carboxyl functions, with the co-presence of 1,4-diazabicyclo[2.2.2]octane (DABCO) as the third achiral additive, which is needed for substrate solubilization. TFTDA shows enhanced enantiodiscriminating efficiency in comparison with the corresponding monomeric counterpart, TFTMA, pointing out cooperativity between its two symmetrical entities. A wide range of amino acid derivatives have been efficiently enantiodiscriminated in CDCl(3), with high enantioresolution quotients, which guarantee high quality in applications devoted to the quantification of enantiomers. High enantiodiscriminating efficiency is maintained also in diluted 5 mM conditions or in the presence of sub-stoichiometric amounts of CSA (0.3 equiv). The role of phenolic hydroxyls in the DABCO-mediated interaction mechanism between TFTDA and the two enantiomeric substrates has been pointed out by means of diffusion-ordered spectroscopy (DOSY) and rotating frame Overhauser effect spectroscopy (ROESY) experiments. A conformational model for both the CSA and its diastereomeric solvates formed with the two enantiomers of N-acetyl leucine has also been conceived on the basis of ROE data in order to give a chiral discrimination rationale
Paolo Uccello: the life and work of an Italian Renaissance artist
No full textDeposited with permission of the author. © 2005 Dr. Hugh HudsonThis thesis is a comprehensive assessment of the life and work of the Italian Renaissance artist Paolo Uccello (c. 1397- 1475). It employs an interdisciplinary methodology combining the examination of archival evidence of the artist’s personal, social and professional lives, the scientific examination of his artworks, the interpretation of his iconography based on the contexts his works were made for, and an approach to attributions based on documentary, stylistic and technical evidence rather than tradition. Unpublished documents presented here shed new light on Uccello’s family and early career, underlining the importance of his extended family as a point of contact between the artist and the networks of patronage in and around Florence. New scientific analyses of three works conducted for this study, including infrared reflectography, X-radiography and microsampling, reveal the sophistication of Uccello’s technique and help to clarify the chronology of his works. New interpretations of Uccello’s works proposed here, relating in particular to his use of perspective, address the significance of their contexts, highlighting the subtlety and specificity of Uccello’s imagery.
The catalogue raisonne is the most extensive survey of works attributed to Uccello to date, and presents unpublished documents for the provenances of two works attributed to Uccello. Contrary to the image of Uccello as an isolated and eccentric figure commonly encountered in the art historical literature since Vasari’s sixteenth-century biography of the artist, Uccello emerges from a detailed study of the documentary and physical evidence as an artist of his time, involved in Florentine society, religion and commerce, and an innovative artist, a creator of unforgettable images who was admired by his peers and subsequent generations of artists, ensuring his place as one of the protagonists in the field of early Renaissance art
BSR video. Materia e atmosfere nelle tre battaglie di Paolo Uccello. Catalogo della mostra, Galleria Embrice, Roma ottobre 2008, Aracne editrice s.r.l., Ariccia (RM), 2012, ISBN: 978-88-548-4960-0
No full textIl catalogo della mostra, a cura di Paolo Balmas, raccoglie i contributi di P. Balmas "La superficie come abisso" pp. 4-7), C. Severati (Battaglia di Federica, pp. 8-11) N. Dal Falco (Lo sguardo del tempo, pp. 13-14), F. Dal Falco (Proiezione a indizi, pp. 22-27). I testi metteno in luce da diversi punti di vista l'intervento artistico condotto dall'autrice, una sorta di "rianimazione" virtuale del trittico di Paolo Uccello operata attravesro il dinamismo e l'accompagnamento sonoro. Gli effetti video sono di Daniele Spanò, le musiche di Fabio Recchia.
Dal comunicato stampa: "Le tre opere del ciclo della Battaglia di San Romano, svoltasi il 1 giugno del 1432, furono dipinte da Paolo di Dono, conosciuto come Paolo Uccello, intorno al 1456 per essere conservate insieme a Palazzo Medici, in Via Larga a Firenze. Le tavole, che rappresentano ognuna un momento diverso dello scontro tra fiorentini e senesi, sono state giudicate per lungo tempo dalla critica, risalente al Vasari, una sorta di "teatro di automi" bloccati in complessi incastri prospettici. I tre quadri sono oggi dispersi in altrettanti musei: gli Uffizi, Il Louvre, la National Gallery. Federica Dal Falco ci propone una sorta di ricomposizione della pittura di Paolo Uccello, prima ancora che nello spazio, nel tempo. Le tre opere sono quindi proiettate contemporaneamente su tre schermi contigui con un video della durata di tre minuti. L'idea è quella di riunire il trittico in una visione simultanea e di restituirgli il dinamismo nascosto, attraverso la musica, composta per l'occasione da un giovane musicista, e la sovrapposizione di materie virtuali, dagli aghi di pino ai marmi. L'inserimento dei materiali, collezionati in centinaia di scatti fotografici, crea una stratificazione da cui sboccia il movimento come dalle spire del tempo l'attimo caduco e perfetto di un gesto. La catarsi della battaglia, il suo avvitarsi e ondeggiare simile a un mare d'uomini e cavalli in tempesta, si specchia nella presenza di tre testimoni: il tamburino del quadro con Niccolò Maurizi da Tolentino, Micheletto Attendolo da Cotignola, il cavallo impennato di Bernardino della Ciarda. Partecipi e isolati dal contesto, queste tre figure chiave spalancano allo sguardo il vuoto, l'interstizio che separa azione e reazione, decisione e atto, rendendo palpabile l'energia annidata tra un fotogramma e il successivo, tra due fermo-macchina. Forse, anzi certamente, la forza seduttiva del trittico di Paolo Uccello sta proprio in questa prefigurazione di un tema contemporaneo che prepara con incredibile anticipo gli esperimenti di Muybridge, la cronofotografia di Marey, le opere del futurismo, ma anche il Nu descendant l'escalier di Duchamp"
A Tamper-Resistant Storage Framework for Smart Grid security
No full textIn the past few years, the energy sector has been among the most targeted by cyber-criminals. Due to the strong reliance of Critical Infrastructures on energy distribution, and the strategic value of such systems, the impact of intrusions and data breaches cannot be underestimated. In this scenario, data constitutes a critical asset to protect, especially as the latest technological development has led to interconnected intelligent systems, named smart grids. The consequences of data tampering, exposure or loss can range from disruption of essential services, to serious risks for environment, economy and people safety. Data provenance, as the documentation of the origin of data and the processes and methodology that led to it, can bring support when facing the aforementioned attacks. The present work aims to address security issues in the energy domain, by proposing the Advanced Tamper-Resistant Storage (ATRS), a novel framework for data provenance based on blockchain technology. The ATRS allows for the creation and storage of provenance records, whose reliability is ensured by the tamper-resistance feature enabled through the combination of blockchain and TLS-based communication. The framework, tailored and tested for the smart grid domain, can easily be customized for different critical use cases
Improved synthesis of quaternary ammonium-chitosan conjugates (N+-Ch) for enhanced intestinal drug permeation
No full textThe pH-induced structural modifications of the reaction product between chitosan and 2-diethylaminoethyl chloride are studied with the purpose of testing and comparing the resulting chitosan derivatives on the basis of their intestinal drug permeability-enhancing properties. The reaction reproducibly yielded conjugates comprising short pendant chains of n adjacent diethyl-dimethylene-ammonium groups substituted onto the primary amino group of the chitosan repeating unit. The more significant derivatives, N+-Ch-7 (degree of substitution, DS = 41%; n = 3) and N+-Ch-8 (DS = 59%; n = 1.7) were prepared at pH 7 and 8, respectively. The apparent permeability (Papp) of excised rat intestine was determined by means of Ussing type chambers. The hydrophilic fluorescein sodium (NaFlu) and fluorescein isothiocyanate dextran (MW 4400 Da) (FD-4), and the lipophilic rhodamine 123 (Rh-123), were applied in Ringer buffer to the apical side. Apical to basolateral transport was measured in the absence or presence of 0.5% (w/v) of the polymer under test. N+-Ch-7 and N+-Ch-8 were more effective Papp enhancers than N-trimethyl-chitosan. Both N+-Ch-7 and N+-Ch-8 enhanced the Papp of NaFlu (enhancement ratio, ER = 1.84 and 1.33, respectively), while N+-Ch-8 was the more effective enhancer for FD-4 (ER = 2.14). The Papp of Rh-123 was significantly enhanced only by N+-Ch-7 (ER = 1.37). Permeant-polymer binding counteracted the enhancement effect of polymer on transmembrane permeant flux. Contact with the chitosan conjugates did not impair the mucosal epithelium integrity
Quinine as a highly responsive chiral sensor for the 1H and 19F NMR enantiodiscrimination of N-trifluoroacetyl amino acids with free carboxyl functions
No full textHydrogen-bond accepting and enantiodiscriminating abilities of quinine (Qui) have been exploited in the enantiodiscrimination of N-trifluoroacetyl (TFA) derivatives of amino acids by NMR (NMR) spectroscopy. NMR 1H and 19F resonances of derivatives of alanine, valine, leucine, norvaline, phenylalanine, phenylglycine, methionine, glutamic acid, proline, and tryptophan were well differentiated employing CDCl3 and/or C6D6 as solvent, with Qui acting in some cases not only as enantiodiscriminating agent, but also as solubility promoter. For derivatives soluble in both solvents, the best results were obtained in benzene-d6, with very high nonequivalence values, which were detectable not only starting from very low equimolar concentrations of 0.1 mM, but also in the presence of sub-stoichiometric amounts of Qui. The quality of enantiodifferentiation has been also evaluated by means of the enantioresoln. quotient E. The method has been applied to the detection and quantification of mixtures of amino acid derivatives by single point measurements
N-(n-Butylamide) of (S)-2-(Phenylcarbamoyloxy)propionic Acid: A New Chiral Solvating Agent, Derived From L-Lactic Acid, for the Enantiomeric Purity Determination of Derivatized Amino Acids
No full textA Thiourea Derivative of 2-[(1R)-1-Aminoethyl]phenol as a Chiral Sensor for the Determination of the Absolute Configuration of N-3,5-Dinitrobenzoyl Derivatives of Amino Acids
No full textIn the exploration of chiral solvating agents (CSAs) for nuclear magnetic resonance (NMR) spectroscopy designed for the chiral analysis of amino acid derivatives, notable advancements have been made with thiourea–CSAs. 1-TU, derived from 2-[(1R)-1-aminoethyl]phenol and benzoyl isothiocyanate, is effective in the enantiodifferentiation of N-3,5-dinitrobenzoyl (N-DNB) amino acids. In order to broaden the application of 1-TU for configurational assignment, enantiomerically enriched N-DNB amino acids were analyzed via NMR. A robust correlation was established between the relative position of specific 1H and 13C NMR resonances of the enantiomers in the presence of 1-TU. 1,4-Diazabicyclo[2.2.2]octane (DABCO) was selected for the complete solubilization of amino acid substrates. Notably, the para and ortho protons of the N-DNB moiety displayed higher frequency shifts for the (R)-enantiomers as opposed to the (S)-enantiomers. This trend was consistently observed in the 13C NMR spectra for quaternary carbons bonded to NO2 groups. Conversely, an inverse correlation was noted for quaternary carbon resonances of the carboxyl moiety, amide carbonyl, and methine carbon at the chiral center. This observed trend aligns with the interaction mechanism previously reported for the same chiral auxiliary. The configurational correlation can be effectively exploited under conditions of high dilution or, significantly, under sub-stoichiometric conditions
Improvement of peptide affinity and stability by complexing to cyclodextrin-grafted ammonium chitosan
No full textCyclodextrin-grafted polymers are attractive biomaterials that could bring together the host-guest complexing capability of pristine cyclodextrin and the pharmaceutical features of the polymeric backbone. The present paper is aimed at characterizing the potential application of ammonium-chitosan grafted with 2-methyl-β-cyclodextrin (N+-rCh-MCD) as the functional macromolecular complexing agent for the oral administration of the neuropeptide dalargin (DAL). Specific NMR characterization procedures, along with UV and fluorescence techniques, as well as biological in vitro assessments have been performed. The results indicate that N+-rCh-MCD forms water-soluble complexes with DAL, with a prevalent involvement of Tyr or Phe over Leu and Ala residues. The association constant of DAL with the polymeric derivative is one order of magnitude higher than that with the pristine cyclodextrin (Ka: 2600 M-1 and 120 M-1, respectively). Additionally, N+-rCh-MCD shields DAL from enzymatic degradation in gastrointestinal in vitro models with a three-fold time delay, suggesting a future pharmaceutical exploitation of the polymeric derivative. Therefore, the greater affinity of N+-rCh-MCD for DAL and its protective effect against enzymatic hydrolysis can be attributed to the synergistic cooperation between cyclodextrin and the polymer, which is realized only when the former is covalently linked to the latter
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