Evaluation of nuclear magnetic relaxation dispersion (NMRD) curves obtained by the fast field cycling nuclear magnetic resonance (FFC-NMR) relaxometry technique is a valuable tool for analyzing the ...microscopic dynamics of condensed matter systems. However, quantitative data analysis involves several conceptual and practical issues. Moving forward from previous literature approaches, we propose a new analysis method, relying on the elaboration of the inverse integral transform of the NMRD curve. Our approach results in a true heuristic method, able to unambiguously individuate the dynamic domains in the system, thereby avoiding the possible introduction of any element of discretion. The analysis of some data sets relevant to real samples suggests the possibility that the results obtained with the heuristic method may be actually led back to some distinct physical/chemical features of the systems.
Some composite materials have been prepared, constituted by a cyclodextrin-
-urethane-based nanosponge matrix in which a reduced graphene oxide/silver nanoparticles photocatalyst has been dispersed. ...Different chain extenders were employed for designing the nanosponge supports, in such a way as to decorate their hyper-cross-linked structure with diverse functionalities. Moreover, two different strategies were explored to accomplish the silver loading. The obtained systems were successfully tested as catalysts for the photodegradation of emerging pollutants such as model dyes and drugs. Enhancement of the photoactive species performance (up to nine times), due to the synergistic local concentration effect exerted by the nanosponge, could be assessed. Overall, the best performances were shown by polyamine-decorated materials, which were able to promote the degradation of some particularly resistant drugs. Some methodological issues pertaining to data collection are also addressed.
Nuclear magnetic resonance (NMR) techniques are largely employed in several fields. As an example, NMR spectroscopy is used to provide structural and conformational information on pure systems, while ...affording quantitative evaluation on the number of nuclei in a given chemical environment. When dealing with relaxation, NMR allows understanding of molecular dynamics, i.e., the time evolution of molecular motions. The analysis of relaxation times conducted on complex liquid–liquid and solid–liquid mixtures is directly related to the nature of the interactions among the components of the mixture. In the present review paper, the peculiarities of low resolution fast field-cycling (FFC) NMR relaxometry in soil science are reported. In particular, the general aspects of the typical FFC NMR relaxometry experiment are firstly provided. Afterwards, a discussion on the main mathematical models to be used to “read” and interpret experimental data on soils is given. Following this, an overview on the main results in soil science is supplied. Finally, new FFC NMR-based hypotheses on nutrient dynamics in soils are described
Polarimetry was used to investigate the binding abilities of a chiral calix4resorcinarene derivative, bearing L-proline subunits, towards a set of suitably selected organic guests. The simultaneous ...formation of 1:1 and 2:1 host-guest inclusion complexes was observed in several cases, depending on both the charge status of the host and the structure of the guest. Thus, the use of the polarimetric method was thoroughly revisited, in order to keep into account the occurrence of multiple equilibria. Our data indicate that the stability of the host-guest complexes is affected by an interplay between Coulomb interactions, π-π interactions, desolvation effects and entropy-unfavorable conformational dynamic restraints. Polarimetry is confirmed as a very useful and versatile tool for the investigation of supramolecular interactions with chiral hosts, even in complex systems involving multiple equilibria.
New 4‐substituted acyloxyproline derivatives with different hydrophobic properties of the acyl group were easily synthesized and used as catalysts in the direct asymmetric aldol reaction between ...cyclic ketones (cyclohexanone and cyclopentanone) and several substituted benzaldehydes. Reactions were carried out using water, this being the best reaction medium examined. Screening of these catalysts showed that compounds bearing the most hydrophobic acyl chains 4‐phenylbutanoate and 4‐(pyren‐1‐yl)butanoate provided better results. The latter catalysts were successfully used in only 2 mol% at room temperature without additives to give aldol products in excellent stereoselectivities. These results demonstrate that derivatization of the proline moiety with the proper simple hydrophobic substituent in the 4‐position can furnish highly active and stereoselective catalysts without the need of additional chiral backbones in the molecule. Finally, an explanation of the observed stereoselectivities in the presence of water is provided.
Needing to extend the shelf-life of packaged food and the evolving consumer demands led researchers to seek innovative, eco-friendly, and biocompatible packaging solutions. Starch is among the most ...promising natural and renewable alternatives to non-degradable plastics. Here, we deeply study the structural features of starch films modified by adding citric acid (CA) or sodium citrate (SC) as a cross-linker and polyethylene glycol 200 (PEG200) as a plasticizer and obtained through solvent casting. The substances' influence on starch films was evaluated through Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) and Solid-state Nuclear Magnetic Resonance (ss-NMR) spectroscopies. Films' macroscopic properties, such as swelling index, solubility, thermo-mechanical features, and moisture absorption, were also assessed to foresee potential applications. Proper amounts of CA, CS, and PEG200 improve film properties and inhibit starch chains' retrogradation and recrystallization. Besides, the chemical neighbourhood of nuclei observed through ss-NMR significantly changed alongside the polymer chains' mobility. The latter result indicates a different polymer chain structural organization that could justify the film's higher resistance to thermal degradation and elongation at the break. This methodological approach is effective in predicting the macroscopic behaviour of a polymeric material and could be helpful for the application of such products in food preservation.
Starch-based films incorporating cross-linkers and plasticizers were obtained by solvent-casting of aqueous dispersions and examined to determine various micro and macroscopic features. Cross-linkers and plasticizers impart distinctive microscopic characteristics to the films, enabling a correlation and explanation of their different macroscopic properties. Display omitted
Nowadays, water pollution represents a serious problem both for agriculture and human health. Find innovative strategy for a large-scale removal of pollutants from wastewaters is thus a challenge. In ...this context, both cyclodextrin derivatives and clay minerals have been used as low-cost nanomaterials for the sorption of pollutants because of their features. Cyclodextrin derivatives are particularly recognized for the removal of organic chemicals, drugs, and pesticides from wastewater. Hectorite (Ht), a clay mineral of smectite group, shows high cation exchange capacity and negatively charged basal surfaces that could allow the removal both of heavy metal ions and organic pollutants. Herein, the synthesis of a hybrid organic/inorganic nanomaterial based on the chemical modification of Ht by grafting modified β-cyclodextrin units is reported. In this way systems with complementary and synergistic adsorption ability for removal of both organic pollutants and heavy metal ions were developed. Two different synthetic approaches were investigated, and the obtained nanomaterials were subjected to thorough structural characterization by FT-IR and 13C solid state NMR spectroscopies, dynamic light scattering, and ζ-potential measurements and the loading of organic moieties was verified by thermogravimetric analysis. In addition, the morphology was investigated by high angle annular dark field transmission electron microscopy (HAADF/STEM) coupled with energy dispersive X-ray spectroscopy (EDX).
The synthetized nanomaterial was tested as a sorbent for the removal of antibiotics, organic dyes and heavy metal ions. Finally, the simultaneous filtration of ciprofloxacin and Pb(II) ions, chosen as models, from simulated wastewater by a column filtration laboratory prototype was investigated, too.
Display omitted
•The synthesis of organic/inorganic nanomaterial based on hectorite and β-cyclodextrin is reported.•The nanomaterial was tested as a sorbent for the removal of different pollutant•Thanks to cyclodextrins the nanomaterial showed better adsorption performance than hectorite•Recycling tests showed that the nanomaterial can be reused for at least 4 cycles.•A laboratory column filtration system was set up to simultaneously remove different pollutants
Display omitted
•Ag-polyaminocyclodextrin nanocomposites show a layer-organized structure.•These systems were used as catalysts for nitroarene reduction with NaBH4.•The reduction reaction showed ...peculiar kinetic features.•Kinetics were rationalized on the by a modified Langmuir–Hinshelwood model.•Results brought us to reconsider some literature mechanistic ideas.
Silver nanoparticles stabilized by means of poly-(6-N,N-dimethyl-propylenediamino)-(6-deoxy)-β-cyclodextrin were synthesized, characterized by different techniques (UV–vis spectroscopy, Dynamic Light Scattering, High Resolution Transmission Electron Microscopy, Fourier-transform IR Spectroscopy) and used as catalysts for the reduction of various nitrobenzene derivatives with sodium borohydride. The nanocomposites obtained appear to have an organized structure, with a metal core surrounded by a layer-structured coating shell. Kinetic data, rationalized in terms of a modified Langmuir–Hinshelwood model, evidenced a non-linear dependence of the reaction rate on the concentration of the catalyst. This was explained on the grounds of the catalytic activity of differently covered catalyst areas. Careful analysis of kinetic data, in particular the effect of the para substituent on the nitroarene structure and the trends of the induction period observed at the beginning of the reaction, provided with interesting insights on the reaction course, and brought us to critically reconsider several mechanistic ideas reported in previous literature.
PDF
