Antonella Maccotta

Dissolution Mechanism of Crystalline Cellulose in H3PO4 As Assessed by High-Field NMR Spectroscopy and Fast Field Cycling NMR Relaxometry

Many processes have been proposed to produce glucose as a substrate for bacterial fermentation to obtain bioethanol. Among others, cellulose degradation appears as the most convenient way to achieve reliable amounts of glucose units. In fact, cellulose is the most widespread biopolymer, and it is considered also as a renewable resource. Due to extended intra- and interchain hydrogen bonds that provide a very efficient packing structure, however, cellulose is also a very stable polymer, the degradation of which is not easily achievable. In the past decade, researchers enhanced cellulose reactivity by increasing its solubility in many solvents, among which concentrated phosphoric acid (H(3)PO(4)) played the major role because of its low volatility and nontoxicity. In the present study, the solubilization mechanism of crystalline cellulose in H(3)PO(4) has been elucidated by using high- and low-field NMR spectroscopy. In particular, high-field NMR spectra showed formation of direct bonding between phosphoric acid and dissolved cellulose. On the other hand, molecular dynamics studies by low-field NMR with a fast field cycling (FFC) setup revealed two different H(3)PO(4) relaxing components. The first component, described by the fastest longitudinal relaxation rate (R(1)), was assigned to the H(3)PO(4) molecules bound to the biopolymer. Conversely, the second component, characterized by the slowest R(1), was attributed to the bulk solvent. The understanding of cellulose dissolution in H(3)PO(4) represents a very important issue because comprehension of chemical mechanisms is fundamental for process ameliorations to produce bioenergy from biomasses.

Dynamics of pistachio oils by proton nuclear magnetic resonance relaxation dispersion.

A number of pistachio oils were selected in order to test the efficacy of nuclear magnetic resonance relaxation dispersion (NMRD) technique in the evaluation of differences among oils (1) obtained from seeds subjected to different thermal desiccation processes, (2) retrieved from seeds belonging to the same cultivar grown in different geographical areas and (3) produced by using seed cultivars sampled in the same geographical region. NMRD measures relaxation rate values which are related to the dynamics of the chemical components of complex food systems. Results not only allowed to relate kinematic viscosity to relaxometry parameters but also were successful in the differentiation among the aforementioned oils. In fact, from the one hand, the larger the kinematic viscosity, the faster the rotational motions appeared as compared to the translational ones. On the other hand, relaxation rate curves (NMRD) varied according to the oxidative stresses and chemical composition of each sample. The present study showed for the first time that NMRD is a very promising technique for quick evaluations of pistachio oil quality without the need for time-consuming chemical manipulations.

Solid-liquid nuclear magnetic resonance relaxation and signal amplitude relationships with ranking of seasoned softwoods and hardwoods

In H1 NMR (nuclear magnetic resonance) relaxation measurements for a set of eight hardwood and softwood samples, each free induction decay (FID) is fitted by the sum of a “solid” signal of the form Aexp[−c(t∕TS)2][1−g(t∕TS)2+h(t∕TS)4] plus a “liquid” signal Bexp(−t∕T2-FID). Distributions of longitudinal (T1) relaxation times were computed separately for the solid and liquid components, giving also the solid/liquid H1 ratio α. From measurements on the samples dried, seasoned, and hydrated, the moisture content (liquid/solid weight ratio) was found to be approximately 0.50∕α. For each of the “seasoned” samples (10%–13% moisture content) a single T1 peak was found for the solid and two for the liquid, with the longer liquid T1 close to that of the solid, but with some differences exceeding perceived experimental uncertainties. None of the solid or liquid-long T1’s is much less than 20ms, even though liquid-short times go as low as 0.35ms, appearing to negate simple solid-to-liquid exchange on a millisecond t...

DETERMINATION OF INTRAMOLECULAR HYDROGEN BONDS IN AMIKACIN IN WATER SOLUTION BY NMR SPECTROSCOPY

Abstract An NMR investigation has been carried out on amikacin in water solution in the physiological pH range. Two-dimenstional heterocorrelated maps provide 1 H NMR chemical shifts from the unambiguous assignment of the 13 C NMR spectrum. Reorientational dynamics at the molecular level are interpreted in terms of a pseudoisotropic motion with a correlation time of 0.17 ns at 300 K. The pH and temperature dependences of 13 C NMR chemical shifts are interpreted to delineate protonation equilibria (all p K s are determined) and to assess the occurrence of two intermolecular hydrogen bonds, which are confirmed by molecular modelling.

Electronic paramagnetic resonance power saturation of wooden samples

The deterioration of wood used for artifacts of artistic interest involves the production of different free radicals from the macromolecules of the wooden matrix (cellulose, lignin, and hemicellulose). Among the techniques able to provide information about these free radicals, the contribution of electronic paramagnetic resonance (EPR) can be very valuable. In this paper, the study of EPR signals (with g≈2) of both modern and ancient wooden taxa was undertaken in order to analyze some features of the free radicals in natural wood. In particular, we have studied the microwave power saturation behaviors of seasoned wooden samples from ten species, and we have found remarkable differences between softwoods and hardwoods. These differences can be correlated to dissimilarities in the relaxation times T1 and T2 attributable to the different microscopic structures of the two trees’ categories. The method has been also applied to ancient woods belonging to works of art in order to assess the conservation state of...

Delineation of conformational and structural features of the amikacin–Cu(II) complex in water solution by 13C-NMR spectroscopy

The copper (II) complex of amikacin in water solution at pH 5.5 was investigated by 13C-NMR. The temperature dependence of spin-lattice relaxation rates was measured and fast exchange conditions were shown to apply. The motional correlation time of the complex was approximated by the pseudo-isotropic rotational correlation time of free amikacin in water solution (tau c = 0.17 ns at 300 K). Formation of a pseudo-tetrahedral 1:1 complex was demonstrated by relaxation rates analysis and also by UV-Vis spectrophotometry. Two amino nitrogens of amikacin, together with the amide nitrogen and the hydroxyl in the hydroxyl-aminopropyl carbonyl side chain, were assigned as the copper-binding sites and a model of the complex was built by using copper-carbon distances obtained by NMR analysis as input parameters.

Assessing the effect of mercury pollution on cultured benthic foraminifera community using morphological and eDNA metabarcoding approaches

Mercury (Hg) is a highly toxic element for living organisms and is known to bioaccumulate and biomagnify. Here, we analyze the response of benthic foraminifera communities cultured in mesocosm and exposed to different concentrations of Hg. Standard morphological analyses and environmental DNA metabarcoding show evidence that Hg pollution has detrimental effects on benthic foraminifera. The molecular analysis provides a more complete view of foraminiferal communities including the soft-walled single-chambered monothalamiids and small-sized hard-shelled rotaliids and textulariids than the morphological one. Among these taxa that are typically overlooked in morphological studies we found potential bioindicators of Hg pollution. The mesocosm approach proves to be an effective method to study benthic foraminiferal responses to various types and concentrations of pollutants over time. This study further supports foraminiferal metabarcoding as a complementary and/or alternative method to standard biomonitoring program based on the morphological identification of species communities.

The conformation of cytochalasin D in DMSO solution from 1H and 13C NMR relaxation rates

The conformation of cytochalasin D in solution has been delineated by measuring 13C and 1H NMR spin–lattice relaxation rates and NOESY spectra. The motional correlation time was evaluated at 0.26 ns at 300 K. A comparison with the structure of cytochalasin B in the same solvent discloses several similarities, except for a small distortion of the five-membered ring. The difference in activity is therefore ascribed to the different hydrophobicity of substituents within the macrocycle.

The response of cultured meiofaunal and benthic foraminiferal communities to lead exposure: Results from mesocosm experiments

Lead (Pb) is regarded as a highly toxic element that poses a serious threat to biota. A mesocosm experiment was performed to assess the influence of Pb on meiofaunal (metazoans within 45-500 μm) and benthic foraminiferal (protozoan) communities. To this end, sediments bearing such communities were incubated in mesocosms, exposed to different levels of Pb in seawater, and monitored for up to 8 wk. Concentrations of Pb <1 ppm in water did not promote a significant increase of this metal in sediments. Relatively high concentrations of Pb seemed to affect meiofaunal and benthic foraminiferal communities by reducing their richness or diversity, and the abundance of the most sensitive taxa. The mesocosm approach can be considered an effective method to document the responses of meiofaunal and benthic foraminiferal communities to various kinds and concentrations of pollutants over time. This approach allows the evaluation of dose-response relationships, validates the outcomes of field studies, and possibly confirms the sediment quality guidelines and thresholds. Environ Toxicol Chem 2018;37:2439-2447.

Nuclear magnetic resonance investigations of calcium-antagonist drugs. Part 4. Conformational and dynamic features of nicardipine {methyl 2-[methyl(phenylmethyl)amino]ethyl 1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)pyridine-3,5-dicarboxylate } in deuterium oxide

Conformation and dynamics of nicardipine in deuterium oxide were investigated by 1H and 13C NMR spectroscopy. Molecular motions were characterised by effective correlation times calculated by 13C spin–lattice relaxation rates and verified by the frequency dependence of 1H spin–lattice relaxation rates or by double-selective proton relaxation rates. 1H–1H dipole–dipole connectivities were observed in 2D NOE spectra and quantified by measuring absolute values of cross-relaxation rates or by fitting the experimental 1H spin–lattice relaxation rates to a model of a sum of independent pairwise interactions. A molecular model was built showing extensive folding of the (phenylmethyl)-amino-ethyl chair and a chair conformation of the dihydropyridine moiety.