643 research outputs found
Carbohydrate-supramolecular gels: Adsorbents for chromium(VI) removal from wastewater
No full textHypothesis: To overcome the contamination of water by heavy metals the adsorption of the pollutant on
gel phases is an attractive solution since gels are inexpensive, potentially highly efficient and form a distinct
phase while allowing diffusion of the contaminated water throughout the material. This work tests
the chromium(VI) adsorbent capacity of new supramolecular gels for Chromium(VI) removal from
wastewater.
Experiments: First hydrophobic imidazolium salts of carbohydrate anions were synthesised as new gelators.
Subsequently, they were dissolved in a solvent by heating and, after cooling overnight, to give the
formation of supramolecular gels. The properties of the resulting gels, such as thermal stability, mechanical
strength, morphology, rheology, and kinetics of gel formation, were studied as a function of gelator
structure, gelation solvent and pollutant removal efficiency.
Findings: Carbohydrate-derived gels showed the best removal capacity, i.e. 97% in 24 h. Interestingly, in
one case, the reduction of chromium(VI) to chromium(III) also occurred after the adsorption process, and
this phenomenon has been analysed using 1H NMR spectroscopy, IR spectroscopy, and SEM. The most
efficient gel can reach an adsorption capacity of 598 mg/g in contrast to a value of 153 mg/g for the most
effectively best hydrogels reported to date. The new gel can be also recycled up to 4 times. These findings
suggest that these new, supramolecular hydrogels have potential applications in environmental
remediation
Diffusion Ordered NMR Spectroscopy (DOSY)
No full textDiffusion NMR spectroscopy has become an essential tool for investigating the supramolecular assembling processes that from molecular “bricks” lead to the construction of functional nanomaterials and nano-sized catalysts. This is probably due to the implementation and commercialization of new NMR instrumentations with the default capability of generating pulsed-field gradients (PFGs) along the direction of the magnetic field. Furthermore, while a robust package of analytical techniques is available to investigate molecules and extended materials or large biomolecules, which are the two-dimensional extremes, the characterization of the chemical mesoscale (several nanometers) is particularly challenging. It is just in this context, that is, the characterization of objects with an intermediate dimen-
sion ranging from dozens of angstroms to hundreds of nanometers, that diffusion NMR spectroscopy shows all its
potentialities. The aim of this chapter is not to discuss in detail the underlying NMR pulse sequences of diffusion experiments. The basic methodology is longstanding and excellent reviews have already been published.
Here, we want to discuss diffusion NMR experiments from a pragmatic point of view in order to show what
information can be obtained and how reliable it is, focusing attention on supramolecular objects of “intermediate”
dimensions. In particular, after recalling the principles underlying diffusion NMR spectroscopy and the measure-
ment of the translational self-diffusion coefficient (Dt)
(Section 2), we show how accurate hydrodynamic dimensions can be derived from Dt once the shape and size of the diffusing particles have been correctly taken into account (Section 3). Later on, the application of diffusion NMR to the study of supramolecular systems is described (Section 4) in terms of determination of the average hydrodynamic dimensions and thermodynamic parameters of the self-assembly processe
Activating [4+4] photoreactivity in the solid-state via complexation: from 9-(methylaminomethyl)anthracene to its silver(I) complexes.
No full textThe [4 + 4] photoreactivity of the anthracene derivative 9-(methylaminomethyl)anthracene (MAMA) has
been investigated in solution, gel medium and in the solid state. While quantitative formation of the
cyloaddition photoproduct was achieved upon irradiation at λ = 365 nm of ethanol solutions of MAMA,
only partial and slow conversion was detected in gels of low molecular weight gelators, and solid-state
reactivity was not observed due to the unfavourable relative orientation of the anthracene moieties in the
crystal. In hexafluorophosphate, tetrafluoroborate and nitrate silver(I) complexes, however, 9-(methylaminomethyl)
anthracene exhibits a more favourable mutual orientation for the aromatic fragments, and
[4 + 4] photoreactivity resulted. All compounds were structurally characterized via single crystal and/or
X-ray powder diffraction and by Raman spectroscopy; this last technique proved effective in detection of
the photoproduct in all solid state complexes
Structure calculation of an elastic hydrogel from sonication of rigid small molecule components
No full textMaking plans for hydrogels: Calculations successfully predict the molecular structure of a robust hydrogel. Melamine and uric acid cocrystallize with water upon sonication, and using experimental data, the minimized structure (see picture) was calculated and successfully compared with powder X-ray diffraction data of the xerogel
Minimizing polymorphic risk through cooperative computational and experimental exploration
No full textWe combine state-of-the-art computational crystal structure prediction (CSP) techniques with a wide range of experimental crystallization methods to understand and explore crystal structure in pharmaceuticals and minimize the risk of unanticipated late-appearing polymorphs. Initially, we demonstrate the power of CSP to rationalize the difficulty in obtaining polymorphs of the well-known pharmaceutical isoniazid and show that CSP provides the structure of the recently obtained, but unsolved, Form III of this drug despite there being only a single resolved form for almost 70 years. More dramatically, our blind CSP study predicts a significant risk of polymorphism for the related iproniazid. Employing a wide variety of experimental techniques, including high-pressure experiments, we experimentally obtained the first three known non-solvated crystal forms of iproniazid, all of which were successfully predicted in the CSP procedure. We demonstrate the power of CSP methods and free energy calculations to rationalize the observed elusiveness of the third form of iproniazid, the success of high-pressure experiments in obtaining it, and the ability of our synergistic computational-experimental approach to “de-risk” solid form landscapes
- …
