Ripening of banana fruit monitored by water relaxation and diffusion H-1-NMR measurements

Water transverse relaxation times T2 and self-diffusion coefficients D have been measured on banana samples at different ripening stages. Relaxation data have been interpreted on the basis of a chemical and diffusive exchange,model proposed by Belton and Hills [Mol. Phys. 61(4) (1987) 999] and Hills et al. [Mol. Phys. 67(4) (1989) 903]. According to that model the observed increase of T-2 values of both cytoplasmatic and vactiolar water may be mainly attributed to the decrease of starch concentration during the ripening process. On the other hand, the observed water self-diffusion coefficient decrease is related to sugar accumulation as starch hydrolysis proceeds. At the early stages of ripening, the individual self-diffusion coefficient values of cytoplasmatic and vacuolar water differ from one another and have been calculated through the analysis of relaxation time-separated pulsed field gradient nuclear magnetic resonance experiments [J. Magn. Reson. A 112 (1995a) 237]. (C) 2004 Elsevier Ltd. All rights reserved

Dynamic phase diagram and onion formation in the system C10E3/D2O

The influence of the shear on the lamellar phase, L, of the system C10E3/D2O was studied along an isoplethal path (40 wt.% C10E3) in the temperature range 25-42degreesC. A dynamic phase diagram was determined by steady-state rheometry, where by shear action the lamellar phase was transformed into multilamellar vesicles (MLVs) ("onions"). The location of "onions" in the dynamic phase diagram, depends only on the temperature and the applied shear rate, and not on the shear history. The classical lamellar phase structure is stable at rest and at low shear rates. When exposed to higher shear rates, the lamellar structure is transformed into onions. The transition from lamellae to onions is shifted to higher shear rates with increasing temperature. In a range of shear rates in between the stable lamellae and stable onion structure, the transition is incomplete. The transformation of lamellae into onions appears to be governed by the imposed strain, in agreement with earlier studies. The effect of temperature can be understood from the general property of nonionic surfactants where the monolayer spontaneous curvature decreases with increasing temperature. (C) 2003 Published by Elsevier B.V

Valutazioni chimico-fisiche sulle interazioni lacrime artificiali e lenti a contatto in idrogel

La valutazione delle interazioni tra diversi campioni di lacrime artificiali (soluzioni di ialuronato di sodio o d’idrossipropil cellulosa) e materiali per lenti a contatto (copolimeri di 2-HEMA) è stata realizzata mediante Spettroscopia di Risonanza Magnetica Nucleare (RMN) a bassa risoluzione. In particolare, sono stati analizzati i parametri di moto RMN dell’acqua: tempi di rilassamento e coefficienti d’autodiffusione. I risultati non hanno evidenziato sostanziali cambiamenti nelle possibilità di diffusione delle molecole d’acqua nelle soluzioni di lacrime artificiali, rispetto a quelle misurate nella soluzione fisiologica. Come atteso, è stata rivelata una differenza nei valori dei tempi di rilassamento nelle varie soluzioni da attribuirsi quantitativamente alle diverse caratteristiche fisico-chimiche dei campioni. Ulteriori misure sono state effettuate sui polimeri, sia a carattere non ionico che ionico, che, dopo una lunga permanenza nelle soluzioni, risultavano rigonfiarsi e formare gel ad alta concentrazione d’acqua. Utilizzando i dati relativi ai campioni rigonfiati nella soluzione fisiologica come riferimento, è stato possibile valutare l’interazione tra gli idrogel e le lacrime artificiali. Tale confronto ha rivelato un diverso comportamento dei materiali ionici rispetto a quelli non ionici nel trattenere l’acqua al proprio interno e nell’interazione con le lacrime artificiali. Per i campioni ionici con maggiore possibilità di rigonfiamento è stata evidenziata la possibilità di inglobare ioni, se presenti nelle soluzioni, che possono far variare le caratteristiche chimico-fisiche del materiale

1H NMR RELAXATION INVESTIGATION OF INHIBITORS INTERACTING WITH TORPEDO CALIFORNICA ACETYLCHOLINESTERASE

Two naphthyridines interacting with Torpedo californica acetylcholinesterase (AChE) were investigated. H-1 NMR spectra were recorded and nonselective, selective, and double-selective spin-lattice relaxation rates were measured. The enhancement of selective relaxation rates could be titrated by different ligand concentrations at constant AChE (yielding 0.22 and 1.53 mM for the dissociation constants) and was providing evidence of a diverse mode of interaction. The double-selective relaxation rates were used to evaluate the motional correlation times of bound ligands at 34.9 and 36.5 us at 300 K, Selective relaxation rates of bound inhibitors could be interpreted also in terms of dipole-dipole interactions with protons in the enzyme active sit

Interaction of disposable contact lenses with a synthetic analogue of human tears

In questo studio sono state analizzate mediante RMN a bassa risoluzione le lenti a contatto in idrogel disposable, basate su copolimeri dell’HEMA, in interazione con soluzione salina e analogo sintetico delle lacrime umane. La misura RMN dei tempi di rilassamento tra le molecole di acqua “esterna” ed “interna” delle lenti a contatto può essere dedotta dalla loro dinamica. I tempi di rilassamento dei protoni relativi all’acqua interna sono più alti nei polimeri non ionici (Polymacon) rispetto a quelli ionici (Etafilcon A, Vifilcon A), ciò suggerisce che le molecole hanno una ridotta mobilità quando interagiscono con la matrice dei polimeri non ionici. Il trattamento con analogo sintetico delle lacrime umane induce un notevole incremento dei tempi di rilassamento nella quota relativa all’acqua interna. Così come un incremento dei tempi di rilassamento più alto dipende dalla durata del trattamento (1 minuto o un giorno) per le lenti costituite da polimeri ionici, similmente risulta essere più alto per le lenti costituie da polimeri non-ionici immerse per 1 minuto. Questo fenomeno può essere razionalmente spiegato ipotizzando che anche l’interazione proteina-matrice polimerica contribuisce a ridurre il contenuto di acqua dell’idrogel quando applicato, così come la temperatura e la evaporazione sono state già ipotizzate

Low- and high-resolution nuclear magnetic resonance (NMR) characterisation of hyaluronan-based native and sulfated hydrogels

Hyaluronan-based hydrogels were synthesised using different crosslinking agents, such as 1,3 diaminopropane (1,3-DAP) and 1,6-diaminohexane (1,6-DAE). The hydrogels were sulfated to provide materials (Hyal-1,3-DAP, Hyal-1,6-DAE, HyalS-1,3-DAP and HyalS-1,6-DAE) that were characterised by both high- and low-resolution nuclear magnetic resonance (NMR) spectroscopy. The 13C NMR spectra of the materials were analysed to identify, characterise and study the crosslinking degree of the hydrogels. The crosslinking degree was also determined by potentiometric titration and the effectiveness of the two techniques was compared. Measurements of longitudinal relaxation times (spin–lattice) and of NOE enhancement were used to study the mobility of the hydrogels. Low-resolution NMR studies allowed the determination of the water transport properties in the hydrogels. In addition, the swelling degree for the various hydrogels was calculated as a function of the longitudinal and transversal relaxation times of the water molecules. Lastly, the self-diffusion coefficients of the water in interaction with the four polysaccharides were measured by the pulsed field gradient spin echo (PFGSE) sequence

"Struttura e Proprietà di nuovi inibitori di sistemi enzimatici e dei loro complessi mediante tecniche spettroscopiche"

Caratterizzazione strutturale di derivati di nuova sintesi della Tacrina, di analoghi della Tacrina, quali naftiridine, con azione inibitrice sull'acetilcolinesterasi. Studio delle loro proprietà di moto in soluzione e della tipologia della loro azione inibitrice (inibizione competitiva e non competitiva)

Low and High resolution Nuclear Magnetic Resonance (NMR) characterization of Hyaluronan-based native and sulphated hydrogels

Hyaluronan-based hydrogels were synthesised using different crosslinking agents, such as 1,3-diaminopropane (1,3-DAP) and 1,6-diaminohexane (1,6-DAE). The hydrogels were sulfated to provide materials (Hyal-1,3-DAP, Hyal-1,6-DAE, HyalS-1,3-DAP and HyalS-1,6-DAE) that were characterised by both high- and low-resolution nuclear magnetic resonance (NMR) spectroscopy. The C-13 NMR spectra of the materials were analysed to identify, characterise and study the crosslinking degree of the hydrogels. The crosslinking degree was also determined by potentiometric titration and the effectiveness of the two techniques was compared. Measurements of longitudinal relaxation times (spin-lattice) and of NOE enhancement were used to study the mobility of the hydrogels. Low-resolution NMR studies allowed the determination of the water transport properties in the hydrogels. In addition, the swelling degree for the various hydrogels was calculated as a function of the longitudinal and transversal relaxation times of the water molecules. Lastly, the self-diffusion coefficients of the water in interaction with the four polysaccharides were measured by the pulsed field gradient spin echo (PFGSE) sequence. (c) 2006 Published by Elsevier Ltd