1,721,032 research outputs found
Basics of NMR Spectroscopy (for Novices)
No full textThe NMR phenomenon is based on the detection of how an atomic nucleus with a non-null spin interacts with a magnetic field. Thus, NMR spectroscopy can be used to study any chemical element having a spinning nucleus. For organic chemists, this is a technique par excellence employed to retrieve the structure of “small” molecular compounds, by detecting 1H and 13C nuclei; however, with a few adaptations, it constitutes a very useful tool of general applicability for the detection of other elements and for the
characterization of complex systems such as supramolecular aggregates,
biomolecules and organic or inorganic materials. This, in turn, opens the
way to diverse applications in industrial, biomedical and environmental
contexts. NMR is a very versatile technique: indeed, it should be rather
considered as a constellation of different interrelated techniques, e.g. 1D
and 2D (correlation spectroscopy) spectroscopy in the liquid phase, NOEbased, TOCSY and solid-state techniques, relaxometry, and so on. Any
chemist is perfectly aware of the topics covered in this chapter; therefore, the following presentation aims at outlining the fundamental concepts and aspects of modern NMR for those people (engineers, biologists, environmentalists, physicians, etc.) who are not familiar with the subject. For a more detailed and exhaustive discussion, interested readers are strongly advised to consult the reference textbooks listed at the end of this presentation
The Use of NMR Techniques in Cultural Heritage
No full textAir pollution is deeply involved in the progressive degradation of Cultural Heritage. Therefore, environment technologies have to deal also with the analysis and preservation of monuments and artistic artefacts in general. Solid-state and mobile NMR techniques can be particularly helpful for monitoring the conservation state of Cultural Heritage, and for planning preservation actions in this sense. This chapter focuses on the basic principles of CP-MAS NMR and MOUSE NMR and on their applications in the context of artwork preservation. Some interesting cases of study are presented
Nuclear magnetic resonance with fast field-cycling setup: A valid tool for soil quality investigation
Full text linkNuclear 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
The Meaning of Pollution and the Powerfulness of NMR Techniques
No full textA short survey is presented herein on the use of the various Nuclear Magnetic Resonance (NMR) based techniques in the context of environmental analysis and environmental remediation. Starting from the general concept of “pollution” and its multifaceted aspects, a brief overview on the diverse use that NMR-related techniques may find in monitoring environmental problems and in providing useful tools for the implementation of smart solutions for environmental remediation is given. Future perspectives and challenges are briefly addressed
NMR Techniques for the Evaluation of Biochar Characteristics
No full textBiochar, a carbonaceous material, has emerged as a valuable tool for environmental remediation and soil fertility enhancement. Its activity - i.e., its ability to either change soil properties or affect the fate of organic and inorganic pollutants - depends on both biochar's physical and chemical characteristics. The most recent literature evidenced that conventional chemical analyses are insufficient to fully understand biochar’s functionality in environmental compartments. Therefore, new, and more sophisticated technologies are needed to unveil the mechanisms underlying biochar’s actions. In this chapter, the different NMR techniques for biochar evaluation are presented, and limits and advantages for each technique are acknowledged
Host−Guest Interactions between β-Cyclodextrin and the (Z)-Phenylhydrazone of 3-Benzoyl-5-phenyl-1,2,4-oxadiazole: The First Kinetic Study of a Ring−Ring Interconversion in a “Confined Environment”
No full textThe effect of β-cyclodextrin (β-CD) on the mononuclear heterocyclic rearrangement of the (Z)-phenylhydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole (1) in aqueous borate buffer at pH = 9.6 has been analyzed at temperatures ranging from 293.15 to 313.15 K. The trend of the absorption spectra of 1 as a function of time has been accounted for with the formation of two different 1:1 complexes between β-CD and 1, the first, “unreactive” complex being formed faster than the “reactive” one. The occurrence of negative activation enthalpy values for the studied interconversion evidences the kinetic relevance of inclusion processes. Computational models elaborated using the MM2 molecular mechanics force field give an idea of the relative importance of the different complexes, additionally helping us to formulate a suitable reaction scheme
Spectrophotometric determination of binding constants between some aminocyclodextrins and nitrobenzene derivatives at various pH values
No full textThe inclusion capacity of three modified cyclodextrins—namely mono-(6-N,N-dimethylamino-6-deoxy)- (3), mono-6-(2-aminoethyl)-amino-6-deoxy- (4) and mono-6-(2-N,N-dimethylaminoethyl)-amino-6-deoxy- (5) β-cyclodextrin, with six para-substituted nitrobenzenes (A–F) has been investigated at three different pH values. Molecular interactions in inclusion complexes have also been investigated by means of molecular mechanics (MM2/QD) models. The desolvation of the cyclodextrin is the most important factor in determining the binding ability of the various hosts. However, for a given host, electrostatic and van der Waals interactions and the formation of a hydrogen bond between the donor amino group and the oxygen atom of a secondary hydroxyl group are the most important contributions in determining the binding constant of different guests
Fast field cycling NMR relaxometry as a tool to monitor Parmigiano Reggiano cheese ripening
No full textIt is widely recognized that the longer the ageing, the more valuable Parmigiano Reggiano (PR) cheese becomes, due to the improvement of its sensorial and nutritional properties. Up to now, the evaluation of PR properties has been performed on samples mainly aged up to 40 months. For this reason, this study was aimed at collecting information about the chemical-physical characteristics of PR cheeses after ageing at 24, 48 and 84 months. The basic analyses on water amount, protein content and volatile organic compounds (VOC) revealed that PR ageing is associated to the decomposition of the organic components into smaller units. This drives water molecules closer to the aforementioned units, thereby leading to a reduction of water activity. Moreover, it appears, from VOC investigation, that either the total amount of long chain fatty acids (LCFA) or the sole 9Z-octadecenoic acid considerably increased with PR aging, thereby making these molecular systems good fingerprint to monitor PR ripening. Fast field cycling (FFC) NMR relaxometry revealed different components of the molecular dynamics in the complex PR cheese samples, which were attributed to water trapped in casein micelles, water bound to polar groups in organic components, proteins, and fats. In particular, the reduction of the correlation times associated to the organic components was explained by the molecular size decrement following degradation processes. The ageing-independent component of the motion was assigned to water molecules bound to polar groups in organic moieties. Finally, the ageing-independent contribution to the overall relaxation rate was assigned to water molecules in casein micelles. This study revealed that FFC NMR relaxometry can be a promising technique to monitor the chemical physical changes during Parmigiano Reggiano cheese ripening
C3N4/reduced graphene oxide photocatalysts loaded with Ag or Ag/Pt for H2 evolution from aqueous solution of triethanolamine
No full textComposites of C3N4/reduced graphene oxide have been used as photocatalysts for triethanolamine photo-
reforming with H2 generation in aqueous solution. The rate of H2 production over the Ag loaded best per-
forming photocatalyst reached 525 μmol⋅
Straightforward preparation of highly loaded MWCNT-polyamine hybrids and their application in catalysis
No full textMultiwalled carbon nanotubes (MWCNTs) were easily and efficiently functionalised with highly cross-linked polyamines. The radical polymerisation of two bis-vinylimidazolium salts in the presence of pristine MWCNTs and azobisisobutyronitrile (AIBN) as a radical initiator led to the formation of materials with a high functionalisation degree. The subsequent treatment with sodium borohydride gave rise to the reduction of imidazolium moieties with the concomitant formation of secondary and tertiary amino groups. The obtained materials were characterised by thermogravimetric analysis (TGA), elemental analysis, solid state 13C-NMR, Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), potentiometric titration, and temperature programmed desorption of carbon dioxide (CO2-TPD). One of the prepared materials was tested as a heterogeneous base catalyst in C-C bond forming reactions such as the Knoevenagel condensation and Henry reaction. Furthermore, two examples concerning a sequential one-pot approach involving two consecutive reactions, namely Knoevenagel and Michael reactions, were reported. This journal i
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