Maso Ricci

Assessing the optical changes in dissolved organic matter in humic lakes by spectral slope distributions

The impact of photodegradation and mixing processes on the optical properties of dissolved organic matter (DOM) was examined using a distribution of absorption spectral slopes and fluorescence measurements in two Argentine lakes. By examining the variability of the absorption spectral slopes throughout the ultraviolet and visible wavelengths, it was possible to determine which wavelength intervals were most sensitive to dominant loss processes. For DOM photodegradation, results show that increases in the absorption spectral slope between 265 and 305 nm were highly sensitive to increased exposure to solar ultraviolet radiation. A slightly larger wavelength range (265-340 nm) was found to be influenced when both mixing and photodegradation processes were considered, in terms DOM residence time, DOM absorption and UV diffuse attenuation coefficients. This same interval of spectral slopes (265-340 nm) was found to highly correlate with changes in fluorescence emission/excitation in wavelengths that are typically associated with terrestrial humic-like DOM. The identification of specific wavelength intervals, rather than the use of standard wavelength intervals or ratios, improved our ability to identify the dominant dissolved organic matter (humic-like) and major loss mechanisms (photodegradation) in these lakes.

In vivo 13C-NMR and modelling study of metabolic yield response to ethanol stress in a wild-type strain of Saccharomyces cerevisiae

In this paper the combined use of in vivo 13C‐nuclear magnetic resonance spectroscopy and mathematical modelling allowed the analysis of the response to ethanol stress in a wild‐type strain of Saccharomyces cerevisiae, in terms of a reduced metabolic activity. The model developed succeeded in describing and interpreting the effects of increasing concentrations of exogenous ethanol. In particular, the ratio between the kinetic constants associated with ethanol production and glucose consumption gave the estimation of the metabolic yield of the processes in perfect agreement with experimental results.

SPECTROSCOPIC INVESTIGATION OF THE CONFORMATIONAL PROPERTIES AND SELF-ASSOCIATION BEHAVIOR OF NATURAL COMPOUNDS IN SOLUTION

ABSTRACT The conformational properties and self-association behaviour of rifaximin and rifaximin OR (Open Ring) were investigated in solution by NMR and IR spectroscopy. The dependence of proton chemical shift on concentration and temperature were analysed to study the self-association process. IR spectra of rifaximin and rifaximin OR were also used at different concentrations to investigate the entity of specific inter- and intra-molecular interactions. Although similar in structure the two molecules had different chemical properties in solution. This could be of some interest in view of the biological importance of this class of antibiotic molecules.

Metabolic response to exogenous ethanol in yeast: An in vivo statistical total correlation NMR spectroscopy approach

In vivo NMR spectroscopy, together with selectively 13C-labelled substrates and ‘statistical total correlation spectroscopy’ analysis (STOCSY), are valuable tools to collect and interpret the metabolic responses of a living organism to external stimuli. In this study, we applied this approach to evaluate the effects of increasing concentration of exogenous ethanol on the Saccharomyces cerevisiae fermentative metabolism. We show that the STOCSY analysis correctly identifies the different types of correlations among the enriched metabolites involved in the fermentation, and that these correlations are quite stable even in presence of a stressing factor such as the exogenous ethanol.

In vivo NMR study of yeast fermentative metabolism in the presence of ferric irons

Mathematical modelling analysis of experimental data, obtained with in vivo NMR spectroscopy and 13C-labelled substrates, allowed us to describe how the fermentative metabolism in Saccharomyces cerevisiae, taken as eukaryotic cell model, is influenced by stress factors. Experiments on cellular cultures subject to increasing concentrations of ferric ions were conducted in order to study the effect of oxidative stress on the dynamics of the fermentative process. The developed mathematical model was able to simulate the cellular activity, the metabolic yield and the main metabolic fluxes occurring during fermentation and to describe how these are modulated by the presence of ferric ions.